Cardiovascular magnetic resonance has been utilized in the management and care of pediatric patients for nearly 40 years. It has evolved to become an invaluable tool in the assessment of the littlest of hearts for diagnosis, pre-interventional management and follow-up care. Although mentioned in a number of consensus and guidelines documents, an up-to-date, large, stand-alone guidance work for the use of cardiovascular magnetic resonance in pediatric congenital 36 and acquired 35 heart disease endorsed by numerous Societies involved in the care of these children is lacking. This guidelines document outlines the use of cardiovascular magnetic resonance in this patient population for a significant number of heart lesions in this age group and although admittedly, is not an exhaustive treatment, it does deal with an expansive list of many common clinical issues encountered in daily practice. The role of imaging and the modalities utilized in pediatric and congenital heart disease (CHD) is continually evolving. Cardiovascular magnetic resonance (CMR) is now a standard modality in imaging CHD and is considered a “one-stop-shop” with the capability of visualizing anatomy and assessing ventricular function, blood flow and tissue characterization. It is utilized in conjunction with other imaging modalities in almost all instances including echocardiography, invasive angiography, cardiac computed tomography (CT) and nuclear medicine. The spectacular improvements in diagnosis, treatment and follow-up in this patient population is in part due to the use of this multimodality imaging approach.There is significant literature supporting the use of CMR in pediatric CHD and acquired heart disease, however, there is wide practice variation among centers for which patients undergo CMR. Availability, diagnostic accuracy, economics and patient burden all play a role in which imaging modality is utilized for various diagnostic categories in the different centers. Echocardiography has been and remains the front line imaging modality for most CHD patients, however, the objectives and frequency of use of echocardiography have changed with the increased utilization, established and evolving capabilities of CMR and cardiac CT.1 pediatric CHD and acquired pediatric heart disease are unique and distinct entities which has different requirements and needs such as smaller structures, higher heart rates, complex unknown anatomy and the more pressing concern of avoiding ionizing radiation. Currently, there is only a consensus document that is available on CMR which is dedicated to pediatric CHD and pediatric acquired heart disease,2 an old CMR consensus documents with only small sections on pediatrics and CHD4 and an old appropriate use criteria (AUC) document with again, only small sections on pediatrics and CHD.5 A document describing technical protocols has been published but does not set forth guidelines or indications.6 Finally, CMR is included in the most recent AUC for multimodality imaging in the follow-up care of patients with CHD with given scenarios which is different than guidelines document for the use of CMR at all stages of care.7Although there are current guidelines in adult CHD which involve CMR,8 Where literature is sparse or non-existent, consensus opinion of the writing group is presented. The document includes both disease specific  and technique specific  sections focused on pediatric CHD and acquired heart disease. Each section includes a brief introduction followed by a review of the literature supporting use of CMR with formal recommendations for indications at the end of the section.The primary objective of this document is to present guidelines based on the existing literature supporting CMR for commonly encountered pediatric CHD and acquired pediatric heart disease. It is beyond the scope of this paper to delineate CMR physics, technical details and protocols focused on imaging children, as there are excellent guidelines for this published elsewhere.These guidelines are intended to assist providers in the decision to utilize CMR. They represent an extensive review of the available current scientific evidence. Many clinical scenarios are complex and some may not be covered exactly by the document; final judgement as to whether CMR is appropriate for a particular patient requires individualized decision making. In those situations, clinical decision making should consider the quality and availability of data in the area where care is provided. When these CMR guidelines are used as a basis for either regulatory or payer decisions, the goal should be improvement in quality of care. The writing group acknowledges that there may be some institutions that do not have access to or have expertise in CMR performance and as such, other imaging modalities such as cardiac CT may be considered.This document is not a multimodality or cross-sectional imaging guideline for all the diseases mentioned or an in depth analysis of a comparison between imaging modalities. It is primarily a work on CMR indications. Where appropriate, a few comments are made regarding other imaging modalities. As a general rule, in emergency situations  and in relative or absolute contraindications of CMR  cardiac CT or cardiac catheterization may be considered.A panel of acknowledged CMR experts was selected and rigorously reviewed by the Society for Cardiovascular Magnetic Resonance (SCMR) to develop these guidelines, to grade the level of clinical evidence and to write recommendations based on current knowledge of CMR and other imaging modalities. The writing group was composed of pediatric cardiologists and radiologists from both North America and Europe, representing different geographical regions, gender, ethnicities, races, perspectives and scopes of clinical practice. Representatives from the American Heart Association (AHA), the American Academy of Pediatrics and the Society for Pediatric Radiology were included in the writing group. Representation by an outside organization does not necessarily imply endorsement.Each member of the writing committee reported all relationships with industry and other entities relevant to pediatric CMR. Every effort was made by members to avoid actual, potential or perceived conflicts of interest.After numerous planning meetings, various sections of this document were written and developed by multiple committee members. Each section was distributed to the entire committee, reviewed, extensively discussed and edited at monthly meetings. All committee members had the opportunity to question and respond which allowed for rigorous debate. Final guideline recommendations were made by consensus agreement of the writing committee; the vast majority of recommendations were unanimous. When all sections were drafted, they were merged and sent out for review to the committee for final approval. Following peer review, the writing committee chair engaged authors to address reviewer comments and finalize the document for approval by participating organizations.The recommendations listed in this document are evidence-based whenever possible. An extensive evidence review was conducted through March 2021. The literature searches were limited to studies conducted in human subjects and published in English. The references selected for this document are representative and not all-inclusive.The final version of the document was submitted to the SCMR publications committee and the SCMR Board of Trustees for review and approval. After their comments were incorporated and the document approved, the document was circulated to those organizations who contributed representatives to the writing committee  along with the North American Society for Cardiac Imaging, the European Association of Cardiovascular Imaging and the American Society of Echocardiography to review this document and to give their approval.9 The class of recommendation (COR) is indicative of the strength of the recommendation which takes into account the estimated magnitude and certainty of benefit, in this case, medically relevant diagnostic information relative to the risk of CMR. The level of evidence (LOE) rates the quality of scientific evidence that supports the COR based on type, quantity and consistency of data from imaging studies. COR and LOE are determined independently. See Table These guidelines are classified using a standard evidence-based methodology developed by the AHA/ American College of Cardiology (ACC) Task Force.The driving force for the development of these guidelines is based on an appreciation of the increasing use of CMR and a realization that the indications for pediatric CMR lack global consensus. Given the historical predominance of catheter based angiograms which chronologically was followed by echocardiography and the emergence of cardiac CT and CMR, it is clear there is a need for guidelines to optimize use of CMR. Although the guideline committee was aware of the lack of high levels of evidence with supporting randomized trials regarding pediatric CMR for many indications which is common for imaging modalities, a guideline document based on expert consensus with supporting literature nonetheless was deemed to be clinically useful.10 varying loads and physiology are imposed on the ventricle. To further complicate matters, SVs are not one lesion but rather a collection of many different types which fall under the same diagnostic category.The patient born with single ventricle (SV), where only one pumping chamber effectively exists, is one of the most complex of all CHD. Nearly all patients require reconstructive surgery or heart transplantation. During reconstructive surgery, which ultimately leads to the Fontan procedure,11 Hypoplastic left heart syndrome (HLHS) has been noted to occur in 0.016–0.36% of all live births and in pathologic series, represents 1.4–3.8% of CHD14 Tricuspid atresia prevalence ranges from 0.3 to 0.7% of all patients with CHD and occurs in ~ 1 in 15,000 live births.15As an umbrella category for a vast array of lesions and with different terminology, it is difficult to state the exact incidence precisely. In one of the most comprehensive collections of studies on incidence, per million live births, a mean of 266 for hypoplastic left heart complexes, 222 for hypoplastic right heart complexes, 132 for pulmonary atresia, 79 for tricuspid atresia and 120 for “single ventricle” whose details were not delineated in studies was found.One of the major problems with a unified imaging strategy of SVs as a group is the variable anatomy; for example: (A) D-loop vs L-loop, (B) right (RV) vs left ventricle (LV), or (C) anatomic true SV versus a “functional” SV. As can clearly be seen, there can be a seemingly hopeless number of complex combinations, however, the underlying theme is that only one usable ventricle is present or both ventricles are connected in such a way that separating them into 2 pumping chambers is impossible.16 which includes a systemic to pulmonary artery or ventricular to pulmonary artery (Sano)21 shunt  blood into the lungs is performed to complete the Fontan operation.Another issue with a unified imaging strategy of SVs as a group is that during the various stages of surgical reconstruction, as noted above, the physiology of the cardiovascular system changes dramatically. The ultimate goal of surgery is to completely separate the systemic and pulmonary circulations and place them in a “series circuit.” In the native state, some patients, such as those with HLHS will always require surgical intervention—the Norwood Stage I procedure,Finally, a third issue with a unified imaging strategy is that surgical reconstruction can vary greatly. To perform an aortic to pulmonary anastomosis, a Norwood or Damus-Kaye-Stansel procedure can be used. For a bidirectional superior cavopulmonary connection, a hemiFontan or bidirectional Glenn (BDG) can be performed. For a Fontan, a myriad of ways have been employed as modifications such as a lateral wall tunnel, an extracardiac conduit, or an atrio-pulmonary connection (not performed anymore), all with or without a fenestration.Prior to any surgery, CMR is not used frequently in the native state; generally, echocardiography is sufficient to allow for anatomic and hemodynamic characterization. Occasionally, if certain aspects of the anatomy are not delineated by echocardiography, such as pulmonary artery (PA) or pulmonary venous anatomy, CMR will be employed at this juncture . In addition, if a “borderline” ventricle is present, CMR may be used to aid in the decision of a 1- versus 2-ventricle repair . Further, pulmonary blood flow is delineated by visualization of the systemic to pulmonary or Sano shunt (if present), pulmonary stenosis, the pulmonary arteries and aortic to pulmonary collaterals. At the BDG/hemiFontan stage, besides reassessment of the aortic arch, the superior cava connections  or Kawashima connections to the PAs) are visualized along with the pulmonary arteries, aortic to pulmonary and veno-venous collaterals Figure . Finally35 Ventricular performance parameters have been demonstrated to correlate with exercise performance34 and has been shown to correlate with transplant free survival after Fontan.36CMR should be utilized to quantify 3D function which can be followed on a routine basis throughout all stages of surgical reconstruction and beyond. This includes regional wall motion abnormalities, ventricular volumes and mass, ejection fraction and cardiac index as delineated in Table 39 Valve function is a significant issue in SV patients. For example, Mahle et al. has demonstrated that 6% of patients have moderate to severe atrioventricular valve regurgitation.40 Cohen et al. has shown that neoaortic regurgitation was present in 61% of patients up to 21 years of followup with progression in 49%.41Valve function, including atrioventricular and semilunar valve regurgitant volume and fractions, using phase contrast CMR (PC-CMR) or a combination of PC-CMR with ventricular volumes, should be assessed. PC-CMR has been used in the past to quantify valve function in CHD.43 to assess physiology and hemodynamics. Important indices in the care of the SV patient are cardiac index as this is generally decreased, pulmonic flow (Qp)/systemic flow (Qs) which generally is close to one, flows to both lungs and systemic to pulmonary collateral flow48 which has been linked to short term outcomes such as hospital stay and presence of pleural effusions .49 In the BDG stage, cardiac catheterization cannot assess Qp because of systemic to pulmonary collaterals.43 Flows to both lungs are important parameters to determining the need for branch PA dilation, especially in SV patients where a patulous aortic reconstruction can compress the central PA. As mentioned in the forgoing paragraphs, PC-CMR is also used in the measurement of valve function.PC-CMR has been used extensively in SV patients50 as well as diffuse fibrosis.51 Myocardial scarring may be an etiology for regional wall dysfunction as well as a nidus for arrhythmia. For example, diffuse fibrosis has negatively correlated with strain51 while discrete fibrosis has been linked to adverse ventricular mechanics and ventricular tachycardia.50 Myocardial scarring is commonly found around the os of the Sano shunt with accompanying regional wall motion abnormalities , higher cost  and longer preoperative stay (2 vs 1 day) relative to the CMR group. There was one major adverse event in the CMR group in a patient with a Blalock-Taussig shunt who developed shunt thrombosis and required cardiopulmonary resuscitation and extracorpeal membrane oxygenation (ECMO); 4 days later the patient underwent routine BDG and was in good clinical status at 3-month follow-up. The operative course, the number of successful BDG and the frequency of postoperative complications were similar. At 3-month follow-up, there was no differences in clinical status, oxygen saturation or frequency of reintervention.In a follow-up prospective trial, Brown et al.55 studied 99 SV patients retrospectively and listed a set of criteria to determine who might benefit from cardiac catheterization and who may be able to safely proceed to surgery without it. These criteria were clinical as well as echocardiographic based and 46 fell into the category of those who could forgo catheterization. The criteria identified all patients who died or did not proceed to Fontan as well as 9 of 11 who required intervention; it had a negative predictive value of 93% (those who can forgo catheterization) with a sensitivity of 81%. However, the positive predictive value was only 25% and the specificity only 52% and the authors thought that this may be partly due to the inability of echocardiography to adequately assess the branch PAs. They suggested the addition of CMR would substantially increase pre-operative predictive values.Prior to Fontan, Ro et al.27 ; all patients underwent echocardiography, however, 41 patients underwent CMR only, 41 patients underwent catheterization only and 37 patients underwent both catheterization and CMR. No clinically significant differences were noted in patient characteristics, hemodynamics or clinical status prior to or after surgery between the CMR only and the catheterization only groups with CMR adding information in 82% of patients. Parameters such as cardiopulmonary bypass time, circulatory arrest time, days in the intensive care unit, other surgical procedures, surgical complications, interventions after Fontan, the incidence of pleural effusions, length of stay in the hospital and oxygen saturation at discharge were similar in all 3 groups. Diagnostic success at surgery relative to all imaging modalities was ≥ 95%. In the group that had both CMR and catheterization, measurements of blood vessels were similar and there were no discrepant findings. Echocardiography could not delineate completely the pulmonary arterial anatomy in 46–53% of patients.Another study assessed 3 groups prior to FontanPreoperatively or prior to commitment to either a univentricular or biventricular circulation, CMR is reasonable to determine anatomy, physiology and ventricular function not elucidated by echocardiography or to aid in determining one vs. two ventricle repair .Prior to BDG, if there is no primary indication for an intervention or there is no indication of increased pressures or pulmonary vascular resistance by echocardiography, CMR is indicated to determine anatomy, physiology, hemodynamics and ventricular function for use in surgical planning in routine cases . See Table 2Prior to Fontan, if there is no primary indication for an intervention or there is no indication of increased pressures  or pulmonary vascular resistance by echocardiography, CMR is indicated for use in surgical planning in routine cases   every 2–3 years, especially when they reach the teenage years and is indicated in the symptomatic patient if there is no primary indication for an intervention or there is no indication of increased pressures (eg end-diastolic or Fontan pressures) or pulmonary vascular resistance by echocardiographyPrior to surgery or at any stage of surgical reconstruction, CMR can be useful to evaluate anatomy and ventricular function including volumes and mass and valve function . Tissue characterization such as late gadolinium enhancement (LGE) may be useful in prognostication Prior to surgery or at any stage of surgical reconstruction, CMR can be useful to evaluate hemodynamics such as flows, cardiac index, Qp/Qs, flows to both lungs, fenestration flow (if Fontan) and systemic to pulmonary collateral flow .56 is the most common cyanotic CHD and has a prevalence of ~ 6% of all CHDs57 and an average incidence of 32.6 per 100,000 live births11 (~ 1660 babies born each year with TOF in the United States58). The main pathologic basis is antero-cephalad deviation of the developing conal septum which causes a malalignement type ventricular septal defect (VSD), resulting in an “overriding aorta’’ and right ventricular (RV) outflow tract (RVOT) obstruction, ultimately leading to RV hypertrophy. Repair typically consists of VSD closure and relief of RVOT obstruction, typically by placement of a transannular patch, which in most instances results in severe pulmonary regurgitation (PR) from disruption of pulmonary valve integrity; RV volume overload typically ensues.59 Another commonly used approach is placement of an RV to pulmonary artery conduit instead of a transannular patch which may also result in PR and RV volume overload. Definitive repair is generally performed in infancy with survival rates of > 98% in multiple series.65 Because of the high success rate in childhood, the number of repaired TOF patients has been increasing over the years with adult survivors of TOF repair now outnumbering children in a number of regions.66 The 30 year survival rate is > 90%68Tetralogy of Fallot (TOF)74 consistently found diminished RV and LV performance with decreased RV ejection fraction (RVEF) and LV ejection fraction (LVEF), mostly in patients with PR. Patients with RV volume overload are at risk for sudden death, ventricular arrhythmias, increased New York Heart Association (NYHA) class and decreased exercise performance.Despite these successes, complications related to residual anatomic and hemodynamic abnormalities are nearly universal. In the vast majority of patients, as mentioned, relief of the RVOT obstruction leads to PR and RV volume overload with resultant reduced RV and LV performance and are at risk for poor clinical outcomes. Multiple studies that have investigated resting RV and LV function after TOF repair77 This exercise incompetence may result from either primary LV dysfunction or by “ventricular-ventricular” interaction, where the dilated RV impinges on LV geometry causing poor performance.88 When TOF patients were studied at rest and during exercise testing, the incremental exercise response of LVEF in TOF patients was depressed relative to controls and LVEF during exercise correlated with both RV end diastolic volume index (RVEDVI) and the severity of PR.77 When comparing exercise performance in TOF patients and controls, significant differences exist in peak workload, maximal heart rate and systolic blood pressure.76 A review of 22 exercise studies89 found that 14 showed a significant relationship between PR with abnormal RV function and decreased exercise capacity. Further implicating RV volume overload are studies that demonstrate once the RV volume overload is abolished by pulmonary valve replacement (PVR), exercise tolerance improved.88Exercise capacity is significantly decreased in TOF survivors and deserves special attention.90 A recent study suggests that TOF survivors have a higher degree of RV and LV diffuse fibrosis compared to normal, raising the possibility of an etiology for conduction disturbances or decreased exercise performance92; the degree and time course of this fibrosis has yet to be defined. Table Numerous other residua can be present. Residual or recurrent RVOT obstruction or pulmonary stenosis may be present at any age and commonly occur in the first several years after the initial repair; RV to PA conduits commonly need to be upsized as the patient grows and later on may become calcified and stenotic. Scar tissue from surgical relief of the infundibulotomy as well as the use of a patch to enlarge the RVOT results in non-contractile myocardium which may progress to aneurysm formation. Residual atrial septal defects (ASD) or VSD, branch PA stenosis, tricuspid regurgitation as well as aortic dilation and aortic valve regurgitation may all occur. Arrhythmia and conduction disturbances are commonly encountered.98 Multiple CMR techniques have been utilized for anatomical assessment of the RVOT, branch pulmonary arteries (PAs)  expansion92; in adult, TOF survivors showed a higher rate of adverse clinical events in TOF patients with ECV ≥ 30% than those with < 30%  Figure  and aort) Figure . PC-CMR9Prior to surgery in young children, echocardiography is primarily utilized for the management and care of the patient with TOF and CMR is generally not routinely indicated. There are a few exceptions such as:Lack of visualization of various structures such as the branch PAs by echocardiographyaortic arch anomaliesdiscontinuous branch PAsaorto-pulmonary collaterals Figure complex TOF or situs anomaliesinconsistent clinical data that may indicate the need for an intervention other than routine repair.After surgical repair, numerous sequelae can be present and CMR is indicated to assess nearly all of them:PR  PR is a major issue and CMR is the only technique that allows for accurate quantification of not only of regurgitant volumes but regurgitant fraction as well (using PC-CMR)99 with echocardiography only having a modest correlation with CMR.37 It has been utilized since the early to mid 90 s for this evaluation100 and has been demonstrated to positively correlate with RV end-diastolic volume (RVEDV).102 In the absence of residual intracardiac shunts and other valve insufficiency, the difference in ventricular stroke volumes would equal the PR volume by PC-CMR.RV  Cine CMR is the gold standard in determining quantitative biventricular size and mass and has been so for many decades.106 PR results in RV dilation with decreased function, risking morbidity and mortality,107 and the effects of RV dilation on LV function108 are important to follow by CMR. In a large cohort of patients spanning the gamut of ages, RV hypertrophy relative to RV volume was predictive of death and ventricular tachycardia.109 RVEF has been associated with impaired exercise performance.110 Typical values for RV dilation and hypertrophy in TOF have been published by many groups.113114 Relatively recently, both RV and LV strain from routine cine CMR has been performed using either CMR feature tracking or tissue tracking of the myocardium. Both RV global longitudinal strain (GLS) and LV global circumferential strain (GCS) by CMR have emerged as predictors of poor outcome across a wide gamut of age ranges including pediatric and adolescents and may be useful in prognostication.96It has been known for a number of years that intrinsic regional RV wall function is decreased in TOF survivors using CMR.115 and in the TOF population, has been found to be present in both the RV and the LV. This increased signal intensity also occurs at the site of patch material such as the VSD and the transannular patch  and every 3 years if the RV does not fall into these ranges for anyone 10 years of age or older; for those younger, it is ordered to address specific questions not addressed by echocardiography.120A published recommendation from the American Society of Echocardiography, developed in collaboration with SCMR and the Society for Pediatric Radiology recommends yearly CMRs based on RV performance parameters  velocity and the pressure drop across the RVOT and annulus by assessing the peak velocity by Doppler, in-plane PC-CMR may be utilized for this, although uncommon.n Figure ), the br125 It has been validated against X-ray angiography126 and is superior to echocardiography.127 Branch PA stenosis or dilation  should be noted. Physiologically, using PC-CMR, differential PA blood flow is obtained by CMR and has shown to be accurate130 even in the presence of stents,131 and may be used as a component in the decision making process to determine the need for intervention on the branch PAs.Since the mid to late 90’s CMR has been known to be a highly sensitive technique to assess the branch PAs in TOF.Left Sided Structures Aortic root and ascending aortic dilation are known phenomenon seen in TOF and not only can significantly dilate in a high proportion of patients in the late teens and adulthood132 but also may cause considerable pathology.133 In addition, right aortic arches occur in ~25% of TOF along with branching abnormalities and the occasional vascular ring. These structures are routinely and easily imaged by CMR with and without contrast. Aortic regurgitation (AR), associated with aortic root and ascending aortic dilation, occurs in TOF134 and should be quantified by CMR38 using PC-CMR.Residual Shunting Residual ASD and VSD flow can be present after surgical repair and can be diagnosed by echocardiography. CMR has utility not only visualizing these structures when inadequate echocardiography windows are present, but the strength of the modality is to quantify net shunting via PC-CMR with internal checks (see Qp/Qs section). In addition, in TOF patients with pulmonary atresia and multiple aortic to pulmonary collaterals, CMR again can visualize and quantify the shunt which has been performed since the 1990s.136Other Considerations TR occurs not uncommonly in TOF and is also generally seen by echocardiography. CMR can quantify atrioventricular valve regurgitation in 2 separate ways for internal consistency and accuracy. Spatial relationships of the cardiovascular system and the airways can be important such as in TOF with absent pulmonary valve leaflets along with the relationship of the sternum in case of reoperation and CMR is useful in defining this anatomy. Coronary artery anatomy, for years a staple of CMR, can be defined as well in case of stenting the RVOT and main PA (see Coronary Artery section).It should be noted that in certain circumstances, where the necessary airway or coronary anatomy cannot be obtained by CMR, or if visualization within a stent is needed for delineation of size, cardiac CT may be considered as an alternative.Pulmonary Valve Replacement PVR deserves special attention in that it eliminates PR, decreases RV volume overload and improves symptoms including TR and exercise intolerance138 but the threshold ventricular volumes above which a PVR should be performed is unknown.144 Indexed end-diastolic volumes have ranged in various studies from 140 to 180 cc/m2. Other parameters to consider for PVR include large RVOT aneurysms, RVOT obstruction, sustained tachyarrhythmias related to RV volume overload, left to right shunt with a Qp/Qs > 1.5, severe AR or dilation.145 CMR has played a major role in attempting to determine the optimal timing of PVR and is indicated for baseline and follow-up evaluation of the TOF patient for PVR.Prior to definitive TOF surgery, CMR can be useful to delineate various anatomic structures when there is a lack of visualization by echocardiography. In addition, it can be beneficial to delineate, aortic arch anomalies, discontinuous branch PAs, aorto-pulmonary collaterals and complex TOF anatomy or situs anomalies as an adjunct to echocardiography .After definitive TOF repair, CMR is reasonable to delineate anatomy, physiology, blood flow, ventricular function and tissue characterization. In specific, assessing biventricular performance , valve function  and flows to both lungs are crucial to quantify . RVOT, branch PA and aortic root/aortic anatomy are important to evaluate and measure . Discrete myocardial scarring is important to identify .CMR is indicated to evaluate RV volumes as a baseline, every 2–3 years if not dilated and ≥ 10 years of age or yearly if dilated and in the range to be considered for PVR .Annual CMR is useful when surgery is being considered to evaluate RVOT aneurysms or obstruction, sustained tachyarrhythmias related to RV volume overload, left to right shunt with a Qp/Qs > 1.5, severe AR or dilation if being considered for PVR .If the child requires sedation or anesthesia for CMR, this modality is reasonable to delineate anatomy, physiology, blood flow, ventricular function and tissue characterization when echocardiography suggests pathology or cannot visualize structures . This can be performed as a baseline in childhood and prior to reaching the teenage years .Myocardial strain  and diffuse fibrosis  by CMR might be considered for prognostication.13 accounting for 5–7% of all CHD.146 This section will focus on TGA with D-looped ventricles with repair using the arterial switch operation (ASO);L-looped TGA and repair with an atrial inversion operation is in the section on systemic RVs. The ASO is nowadays the surgical technique of choice for repair of TGA147 consisting of (1) transecting the aorta and the main PA at the level of the sinotubular junction, (2) removing the coronary ostia from the original aortic root and transferring them with a piece of surrounding tissue (button) to the neo aortic (pulmonary) root, (3) relocating the PA anteriorly and connecting it to the previous aortic root, and (4) relocating the aorta posteriorly and anastomosing it to the neoaortic root (native pulmonary root). With this technique, the branch PAs most commonly straddle the ascending aorta (LeCompte maneuver). Any additional intracardiac communication is closed during the surgery. This procedure allows both anatomical and functional repair restoring ventriculo-arterial concordance.Transposition of the great arteries (TGA) is anatomically defined as a ventriculo-arterial discordance and is the second most frequent cyanotic CHD with a prevalence of 0.2–0.3 / 1000 livebirths with a male predominance of 1.5–3:1,148 Nevertheless, potential postoperative complications include supravalvar and branch PA stenosis, coronary ostial occlusion/narrowing with subsequent myocardial ischemia and LV dysfunction, AR and neo-aortic root dilatation.149 Coronary artery complications after ASO have been reported in up to 10% of cases.151 Early detection of coronary artery lesions is essential for preventing ischemia and potentially life-threatening events. Notably, hearts after the ASO operation are denervated, and chest pain is not a reliable symptom of ischemia in these patients.152ASO can be performed successfully with low mortality rate.153 Even though there is one meta-analysis that concludes that coronary surveillance is not needed,154 multiple studies have concluded otherwise.155Advanced imaging in patients with TGA after ASO is targeted to detect all potential residual findings requiring medical or surgical treatment. These include ventricular dysfunction, supravalvar pulmonary or aortic stenosis, branch PA stenosis, coronary artery stenosis/occlusion, neo-aortic or pulmonary valve regurgitation and, neoaortic root dilation.Echocardiography is the first line imaging modality prior to ASO and in most cases, CMR is not indicated. Occasionally there may be anatomic or physiologic abnormalities not delineated by echocardiography  and for those few cases, CMR is useful to delineate this missing information prior to surgery. When it is necessary to delineate the coronary anatomy or if echocardiography fails to do so, CMR has become more utilized; however, at the current time, it is not widespread and standard of care remains cardiac catheterization with cardiac CT as a backup.CMR is indicated and can depict almost all common potential residual findings after ASO Table .157 CMR has a high accuracy and reproducibility and is therefore the ideal modality for repeated measurements during follow up.159 In ASO patients, CMR can recognize diminished ventricular function in ASO patients at times when echocardiography fails to do so .CMR is considered the modality of choice for quantification of biventricular volumes and function, especially the RV Table .6,8,156,161 In presence of ventricular dysfunction, concomitant evaluation of myocardial perfusion and scar imaging are essential for assessing coronary artery obstruction. RV dysfunction is rarer but can occur in combination with RVOT obstruction or stenosis of the branch PAs. Therefore, in presence of RV dysfunction, imaging the RVOT and the PAs is mandatory. Due to the position of the RVOT located immediately posterior to the sternum and of the branch PAs straddling the ascending aorta, visualization by transthoracic echocardiography (TTE) is rarely sufficient as patients grow and postoperative scar tissue often limit clear visualization of these structures.Mild biventricular dilation is not uncommon after the ASO operation. LV dysfunction has been observed in up to 20% of the cases and is correlated to clinical symptoms.163 Whole-heart CMR  enables accurate detection of the abnormal origin and course of the coronary arteries even in very young patients with CHD165 and patients with TGA after ASO are no exception.166 Thus, evaluation of the coronary origins and courses routinely added to the CMR protocol167 (see section on CMR for coronary arteries).After coronary artery transfer by the ASO, the origin of both coronary arteries is usually in a different position than normal, facing the anteriorly positioned neopulmonary artery Figure . Dependi168 Myocardial perfusion, typically with the vasodilator adenosine,170 can be safely and accurately performed in children.177 In 56 myocardial first-pass perfusion scans performed in children, a sensitivity of 87% and a specificity of 95% have been described when compared with coronary angiography171 . Elevated diffuse myocardial fibrosis has been observed in a cohort of pediatric ASO patients183 As the cross-section of the PAs is ellipsoid, the antero-posterior dimension is usually smaller than the supero-inferior one184 .A comprehensive CMR examination should be performed during routine follow-up of patients who received an ASO and is complimentary to echocardiography CMR is beneficial for quantification of biventricular volumes and function in TGA after the ASO .CMR is beneficial for visualization of the coronary arteries in TGA after the ASO .CMR is recommended for evaluation of the main PA and branch PA stenosis with assessment of differential pulmonary flow CMR is recommended for measure of neoaortic root enlargement and quantification of neoaortic valve regurgitation Vasodilator stress perfusion CMR imaging is useful in symptomatic patients to test for ischemia  and may be considered as an initial, non-invasive screening test for myocardial perfusion defects and therefore detection of potential coronary artery obstruction. In the case of suspected myocardial perfusion defects, CMR may be considered for visualization of coronary ostial stenosis CMR is useful in screening for myocardial scarring with LGE (viability imaging) or in confirming the diagnosis in cases of symptomatic individuals, given manipulation of the coronary arteries in this lesion .198 Partial anomalous PV connection (PAPVC) is the most frequent observed lesion and can occur in isolation but more frequently in association with an ASD   can be congenital or acquired after an intervention or during the progression of a disease. Congenital PV lesions are rare and occur with a prevalence of 0.6–1.2 / 10 000 livebirths.) Figure . In presm Figure .204 As variations of the course of the PVs are not infrequent, accurate imaging of each PV is mandatory prior to surgery. Moreover, obstruction in the PV pathway is not rare and can be caused by (a) stenosis of each PV, (b) stenosis at the site of connection, (c) extrinsic compression of the connecting channel, (d) compression of the vertical vein in between the left bronchus and the left PA (supracardiac type)  occurs in four different formations defined by the location of the connection of the PVs to the right-sided circulation. In order of prevalence, the sites of connection are: supracardiac Figure , infradi) Figure , (e) in ) Figure  or other206 This can occur with or without associated CHD, and unilateral PV stenosis can lead to flow asymmetry to the lungs . It is not uncommon to have recurrent and/or progressive PV obstruction or even death after surgical repair.207Finally, congenital stenosis of one or more PVs can occur, a progressive disease which leads to a dismal outcome Figure .206 This209 Greater than 4 PVs may be present and therefore, echocardiography delineation of only 4 PVs without searching for others in lesions associated with PAPVC is not sufficient and CMR is mandatory. In patients with limited acoustic windows, CMR is indicated to delineate other PVs even if 4 are visualized on echocardiography. Besides providing clear information on the exact location of PV connection and drainage required for proper planning of all surgical corrections such as the Warden operation,211 CMR is useful to assess size and function of the dilated right heart, assessing the contribution of the anomalous vein(s) to the left to right shunt and to measure Qp/Qs  but also flows in each PV and PA.In congenital stenosis of one or more PVs, CMR angiography provides exact depiction of the location of stenosis, number of veins affected and can be repeated during follow up Figure . PV sten218 and qualitatively.219 The normal PV flow curve consists of 2 forward waves during systole and early diastole as well as a short wave of reverse flow during late diastole at atrial contraction. This normal flow profile can be altered in several conditions or if atrial compliance is disturbed. In presence of unilateral PV stenosis, a redistribution of flow occurs within the lung and can be assessed by measuring the flow in the pulmonary arteries by CMR; this is correlated with particular changes in flow profile.221 Flow profiles are also affected directly within the PVs; proximal to a focal stenosis, flow loses its triphasic profile similarly as observed by using Doppler echocardiography.219 On the other hand, peak PV flow velocities > 100 cm/s indicate significant obstruction.217Flows in the PVs can be assessed quantitatively204 Due to anatomic complexity, echocardiography is often insufficient to describe all diagnostic features required for surgical and medical management. In these lesions, CMR has an important role for surgical planning or staged palliation223 especially in SV patients. The PV may become impinged between the dilated heart and the spine or the descending aorta  and to overcome some pitfalls associated with scintigraphy.188In general, in comparison to other modalities, cross sectional imaging is superior to echocardiography or conventional angiography due to 3D data acquisition which enables a targeted multiplane reformatting and therefore, visualization of each single PV without superimposition of other vascular structures.In patients with PV stenosis or suspected anomalous PV connection, whether PAPVC or TAPVC, CMR should be performed for anatomic evaluation whenever echocardiography is insufficient .CMR is useful to understand the hemodynamics of PV anomalies such as calculating any shunt (Qp/Qs) caused by anomalous PV connection and associated intracardiac lesions as an indication for surgical repair  as well as quantifying differential lung perfusion with flow redistribution .CMR examination should be performed for assessing PV anatomy in cases with complex CHD when there is a clinical or imaging suspicion of anomalies of PV connection or drainage, particularly heterotaxy syndrome CMR angiography should be performed for surgical planning of repair of PV anomalies It is reasonable to perform at least one CMR examination during follow up after surgical repair for PV anomalies .227 or Ross procedure.228 Clearly, many of these diseases lend themselves to potentially decrease myocardial perfusion, possibly resulting in ischemia and infarction.Categorically, pediatric coronary artery pathologies can be either congenital or acquired. Acquired lesions can also be sub-categorized as either “disease” based or “surgically” based. Congenital lesions would include those related to anomalous aortic origin of a coronary artery (AAOCA) from an inappropriate sinus , anomalous origin from a different vessel such as anomalous origin of the left coronary from the PA, and/or anomalous course of a coronary artery  or exit . “Acquired disease” based lesions would include Kawasaki disease whereas “surgically” based lesions would include alterations of the locations of the coronary ostia or their proximal courses related to corrective surgeries such as the arterial switch operation (Jatene procedure)Echocardiography, CT, and CMR are the most commonly used non-invasive imaging modalities for the evaluation of pediatric patients with coronary artery pathologies. Echocardiography is the most easily available with its inherent mobility and high temporal resolution and remains the front-line imaging modality. In many instances, echocardiography is utilized as a screening tool for progression of disease  or may suggest a pathology as an incidental finding .Cardiac CT, with state-of-the-art dual-source or volume CT scanners, compared to CMR performed on 1.5 T or 3 T CMR scanners, has slightly higher isotropic spatial resolution (0.5–0.6 mm), faster total examination and scanning time and can, at times, accommodate high heart rates (> 120 bpm) despite a modest temporal resolution for nearly all scanners of 75 ms, although the fastest scanner can obtain a resolution of 66 ms. The drawbacks are that CT requires ionizing radiation and rapid bolus intravenous injection of iodinated contrast agent along with possibly administering medication to slow the heart rate (e.g. propranolol). Cardiac CT typically is limited to morphologic imaging due to radiation exposure concern.229 in addition to assessing myocardial function , perfusion177 and infarction (ie viability imaging).172 Further, CMR adds anatomic information as well in the same patient such as those with TGA after ASO.172 CMR can obtain in-plane resolution of 0.5–0.6 mm230 at 3 T in children and can usually obtain 1–1.2 mm isotropic resolution at 1.5 T. CMR can also obtain coronary images without the need for contrast in the pediatric age range232 in multiple different formats (eg bright blood or dark blood)233 although contrast can enhance the imaging.234 Newer techniques,236 currently utilized in several pediatric centers, take advantage of the significant increase signal afforded by the iron-particle blood pool contrast agent, ferumoxytol, and have shown very promising results with sub-mm isotropic whole-heart coverage even in infants with high heart rates  were screened with CMR for cardiomyopathy and anomalous coronary artery origin from the opposite sinus with an intramural segment (ACAOS-IM). There were 23 such cases (6 left-ACAOS-IM and 17 right-ACAOS-IM)239 establishing a prevalence of 0.4%.In a prospective study of 50 patients , Hussain et al.s Figure  even in 240 In a prospective study of whole-heart coronary CMR in 100 patients , of the 58 patients who underwent surgery, all CMR coronary artery findings were confirmed including 4 cases of coronary anomalies.165 In addition, coronary anomalies of “course” such as an intraseptal or retroaortic course, are important to delineate and have been demonstrated by CMR.237 Finally, anomalies of exit such as those with pulmonary atresia with intact ventricular septum with coronary cameral fistulae or a RV dependent coronary circulation can be delineated by CMR, especially important because of the sequelae of myocardial infarction  artery with respect to RVOT, significant in patients with TOF.CMR can be used to assess for the morphology including size, shape, and location of coronary aneurysms in diseases such as Kawasaki’s disease Figure . Similar241 has shown in a prospective study of 16 patients (age range 3–8 years) that coronary CMR correlated completely with invasive cath for size and location of aneurysms. There were no cases of stenoses for comparison. Suzuki et al.242 and in related work by Takemura et al.242 showed in a retrospective study with a larger cohort of 106 Kawasaki disease patients  and a smaller cohort of 35 consecutive pediatric KD patients (under 6 years of age) that imaging of coronary arteries in pediatric patients with Kawasaki disease can routinely be performed with a 96% success rate. High sub-millimeter spatial resolution imaging that is used for AAOCA has been successful in young patients with Kawasaki disease.244 In addition, CMR should also assess for global and regional ventricular dysfunction, coronary perfusion, and myocardial scarring/LGE during the convalescence and follow up of the Kawasaki disease patients.246 Advanced imaging of characterization of the coronary vessel wall has also been shown to be possible.246Mavrogeni et al.172 In 100 patients after ASO, Rodriguez et al. studied 100 whole heart 3D CMRs and found coronary artery stenosis in nearly 11%.166CMR can be used to characterize the anatomy of the coronary arteries following surgery in which the position and/or origin of the native coronary arteries have been altered such as after the Ross procedure or TGA after ASO Figure . Taylor 247 including those in the pediatric age range248 and in other diseases such as Takayasu’s arteritis249 is an emerging application of CMR coronary imaging but should be considered experimental at this time.Imaging coronary artery walls for vasculopathy in transplant patientsFor patients with suspected AAOCA or other congenital anomalies of origin, course or exit, CMR is recommended to depict the origin and detailed anatomy of the vessels for both diagnosis and pre-operative planning .For patients with Kawasaki disease or other acquired “diseased” based coronary pathology, CMR is recommended to accurately depict the size, shape, and location of coronary aneurysms .For patients with acquired “surgically” based coronary pathology such as TGA after ASO or Ross procedure, CMR is recommended to evaluate the post-operative coronary anatomy as part of a clinically indicated comprehensive CMR examination. CMR should be utilized to assess the secondary effects of congenital coronary anomalies or acquired pathology such as effects on myocardial function , perfusion and infarction  both prior to and after repair (if surgery) or in followup.11 and a prevalence of ~ 7% of patients with CHD.198 Coarctation is a discrete or relatively discrete narrowing of the proximal descending thoracic aorta, most commonly located in the juxtaductal region, immediately distal to the left subclavian artery .Important anatomic and hemodynamic data is obtained with CMR having been utilized for many years in the assessment of coarctation of the aorta. Multiple techniques, including non-contrast and contrast CMR sequences are used to provide a complete anatomical 3D analysis Figure . Collate263 After surgical coarctation repair, CMR is the preferred imaging modality.265 Monitoring for restenosis is important and visualization of collaterals and measurement of flow volume increase from the coarctation repair site to the diaphragm aorta level is more reliable for assessment of recoarctation than arm-leg blood pressure drop.259 Aneurysms may occur at the repair site . With the advent of ferumoxytol, in stent visualization has improved for bright blood imaging but exact dimensions remains still elusive. If visualization of the interior of the stent is needed, CT and invasive angiography may be performed.269 There has also been recent work using 4D flow CMR to measure pressure drop in the aorta of patients with coarctation.271 Although promising, 4D flow is not yet routinely performed in clinical practice across all centers.Besides collateral flow measurements and cardiac index, 4-dimensional (4D) flow CMR imaging has been utilized to determine flow and visualize 4D flow patterns in coarctation of the aorta both prior to and after repair.272 LV mass, ventricular volumes, global and regional ventricular dysfunction should be routinely assessed. LV myocardial strain can be assessed using tissue or feature tracking and can be abnormal with LV hypertrophy and systemic hypertension.273 Diffuse fibrosis and increased ECV may be increased in hypertensive heart disease,274 although not routinely performed clinically. All of these methods for determining LV status will provide important data for making clinical decisions.Physiologic assessment of the effects of coarctation on the LV can be assessed by CMR as it is the gold standard for this evaluation.At the initial diagnosis of coarctation by echocardiography, CMR is recommended to provide conclusive anatomical and functional details needed prior to treatment or to decide if treatment is needed including anatomy of the coarctation, LV hypertrophy, cardiac index and the presence of a BAV etc. if these are not fully delineated by echocardiography .CMR is reasonable to assess collateral flow in patients with coarctation of the aorta, especially if it is unclear from other criteria that treatment is needed .After surgical repair of coarctation, CMR is indicated to monitor the status of the aorta and to visualize restenosis or aneurysm formation .After stent placement, CMR can be useful to provide anatomic and hemodynamic assessment of the aorta surrounding the stent, but not to accurately visualize in-stent stenosis .After coarctation repair, CMR is recommended to assess the aorta and LV function every 1–3 years in children and adolescents, similar to adults, if echocardiography is insufficient or pathology is suspected .CMR holds the potential to assess LV myocardial strain and diffuse fibrosis/increased ECV in patients with coarctation to assess effects on the LV and may be considered for this purpose .276 Some families demonstrate an autosomal dominant inheritance pattern.277 Unless associated with significant stenosis or regurgitation or other LV outflow tract lesions, young individuals are often asymptomatic  followed by fusion of the right and non-coronary commissures (28%); fusion of the left and non-coronary commissures is the least common. The vast majority of patients with coarctation have fusion of the right and left coronary commissures while fusion of the right and non-coronary commissures is most commonly associated with aortic regurgitation.278 Other types of morphology include partial or complete fusion of one or more of the commissures of the coronary cusps with associated cusp asymmetry and complete or incomplete raphe, as well as “true” symmetric BAV cusps without raphe. Some severely malformed valves are labeled “unicommissural” which may or may not be classified under this label , PC-CMR sequences allow for direct measurement of forward and reverse volume used to calculate a regurgitant fraction, as well as peak velocity of the jet in the prescribed plane286; checks on the data include subtracting the flow of caval return, main PA flow or the sum of branch PA flowfrom aortic forward flow making CMR more accurate. CMR also allows for assessment of myocardial blood flow with first-pass perfusion at rest and stress, as well as tissue characterization with myocardial LGE for fibrosis and viability. All this information by CMR provides assistance in determining timing for aortic valve intervention or replacement.3CMR can assess hemodynamic effects of associated stenosis and AR from aortic valve disease. This includes LV hypertrophy and dilation as well as functional volumetric analysis, changes in strain or fibrosis and ECV expansion. In those with significant aortic valve dysfunction, CMR is advantageous for serial evaluation of LV volumes and mass. The standard for determining ventricular sizes and volumes is CMR.288 Because of its strong association with coarctation of the aorta, patients diagnosed with a BAV should also undergo imaging for coarctation of the aorta.250 CMR has also been used to evaluate shear wall stress of the aorta in patients with BAV.289 See Genetic Aortopathy section and the 4D flow imaging subsection.CMR allows for evaluation of the ascending aorta Figure  as it reIf echocardiography is unable to visualize morphology of a BAV or visualize the aortic root or ascending aorta adequately, CMR is indicated to provide the needed information. CMR should be used for serial monitoring in the setting of BAV valve with associated aortic stenosis or AR and to quantify these hemodynamics .CMR is useful for serial monitoring of the size of the aortic root and ascending aorta in the setting of BAV. CMR is recommended for serial monitoring of the effects of aortic stenosis and AR on the LV   and to obtain direct measurement of AR volume, peak flow velocity and aortic valve area when determining need for aortic valve/aortic surgery .CMR is beneficial to determine lesions associated with BAV such as coarctation of the aorta, interrupted aortic arch other left sided obstructed lesions .Genetic disorders associated with aortopathy include Marfan syndrome (MFS), autosomal dominant Vascular Ehlers-Danlos (EDS), Loeys-Dietz (LDS), aneurysms-osteoarthritis syndromes, Turner syndrome, Noonan Syndrome and non-syndromic familial thoracic aortic aneurysms and dissections (FTAAD). These group of disorders are associated with altered connective tissue composition leading to a combination of cardiovascular, skeletal and often ocular manifestations.The cardiovascular features include valvular and vascular disease, in particular aortic dilatation with increased risk of dissection, aneurysm, rupture and death. The aortic dilation most often affects the aortic root and ascending aorta but can also affect the more distal aorta including the transverse arch and descending aorta. These disorders have variable effect on other cardiac structures. For example, mitral valve prolapse (MVP) is a feature of MFS and LDS, but not EDS, which in turn has a higher risk of coronary artery dissections than the other aortopathies. Turner syndrome is due to the partial absence of an X chromosome, and phenotypically has short stature and ovarian insufficiency, in addition to aortic dilatation, BAV, PAPVR and aortic coarctation. Noonan Syndrome is considered a renin-angiotensin system (RAS)opathy, a group of disorders which have mutations in the signaling proteins for RAS/mitogen activated protein kinase (MAPK) pathway and results in cardiovascular, facial and lymphatic anomalies. Inheritance and penetrance of all these conditions is variable, with many patients representing new sporadic mutations. The diagnosis of these conditions is most often in infancy, due to the combination of musculoskeletal, facial and cardiovascular anomalies. However, the progressive nature of the associated vasculopathy means that lifelong cardiovascular imaging surveillance is required. Table 290 Most of the genetic aortopathy patients have the potential for complex abnormalities that may affect the entire aorta necessitating comprehensive evaluations. Furthermore, the presence of concomitant skeletal abnormalities renders echocardiography less reliable due to poor acoustic windows. The need for accurate and reproducible aortic size measurements is of utmost importance as aortic size is considered a surrogate for aortic dissection, surveillance recommendations and surgical interventions in genetic aortopathies.291 The 2010 published guidelines for diagnosis and management of thoracic aortic diseases including genetic aortopathies with surgical repair recommendations for genetic aortopathies are purely based upon aortic size.291A small study comparing reproducibility of aortic measurements at multiple levels in both pediatric BAV and genetic aortopathy patients showed that echocardiography derived measurements were systematically smaller by 5–7% and were less reproducible than CMR measurements, particularly in dilated aortic roots and in the descending aorta.292 In patients > 15 years of age, a unique index, the aortic size index (ASI), was proposed (ASI = maximum aortic diameter/bodysurface area) and has been shown to be a better predictor of vascular complications than traditional Turner z score analysis.293 The AHA recently published a scientific statement on the management of Turner syndrome and recommends CMR at diagnosis and CMR surveillance due to the high incidence of undiagnosed vascular anomalies such as coarctation, PAPVC, systemic venous anomalies and coronary anomalies. In low risk Turner syndrome patients, imaging surveillance can be performed every 5–10 years, but with increased frequency of surveillance in patients with high ASIs (> 2.3 cm/m2).294The aortopathy in Turner syndrome is complicated by the presence of short stature necessitating a Turner specific z-score (TSZ) developed for 2D echocardiography.295 Cohort studies have shown that nearly 60% of MFS patients will have aortic root dilatation by age 35 years and that the aorta increases further with age.298The natural history of most genetic aortopathies is one of a thinned aortic wall which progressively dilates and loses distensibility thereby heightening the risks of aneurysm formation and dissection throughout its length, but particularly at the root.299 Similarly, the 2014 AHA/ACC guidelines recommend CMR for quantification of AR in patients with moderate or severe AR with suboptimal echocardiography images and evaluation of LV systolic function and volumes.300 Atrioventricular valve disease is more common in MFS compared to other genetic aortopathies with some studies demonstrating > 65% prevalence of mitral valve disorders. Infants and children with MFS present early with tricuspid and mitral valve fibroxanthomatous thickening and prolapse.302 CMR has emerged as an important noninvasive modality to diagnose and characterize MVP and help quantify mitral regurgitation.306As the root dilates, aortic leaflets fail to fully coapt and AR increases. Echocardiography is the mainstay of AR surveillance but a systematic review of 11 articles comparing quantification of AR by CMR to semiquantitative evaluation with echocardiography confirmed that direct aortic measurements using PC-CMR at the sinotubular junction/aortic valve are highly reproducible and accurate and predicts those who progress to surgery with high overall sensitivity and specificity.307 however, in a subgroup of aortopathy patients without significant valvular dysfunction or aortic dilatation, subclinical cardiac dysfunction has been described,308 attributed to a combination of increased aortic wall stiffness and extracellular matrix abnormalities. CMR is the reference standard for evaluating biventricular function as mentioned previously309 and can be used to evaluate ventricular performance.Dilated cardiomyopathy is an under-recognized clinical feature of aortopathy syndromes. Myocardial dysfunction is often considered to be the consequence of valvular insufficiency and ventricular volume overload,310 Patients with Turner syndrome have increased incidence of PAPVC, systemic venous anomalies such as left SVC/interrupted IVC, congenital portosystemic shunts and coronary artery anomalies, many of which are not appreciated on echocardiography, yet relatively easily appreciated on CMR.Although aortic aneurysms generally occur at the aortic root in many patients Figure , approxi313 Multiple CMR sequences, both contrast and non-contrast enhanced, all provide specific and unique information including exact positioning of the intimal flap and ability to distinguish slow flow from thrombus in the false lumen.Aortic dissection is a catastrophic complication of aortic wall disease associated with high mortality and morbidity. In acute symptomatic dissection, rapid imaging diagnosis is essential. CMR can be used to diagnose dissection, distinguish aortic pseudoaneurysm from dissection and assess intimal flaps and aortic branch vessel involvement.314Increased arterial tortuosity of the head and neck vessels, particularly the vertebral arteries, has been described in LDS, MFS and Turner syndrome Figure  and can 316 Less is known about genetic aortopathies, however, emerging 4D- flow CMR data suggests that similar findings are present in pediatric genetic aortopathy patients and become more pronounced over time.318Figure  HemodynaAdvantages of CMR MR has been shown to be very accurate in the diagnosis of thoracic aortic disease with sensitivities and specificities that can exceed echocardiography.321 CMR provides a multiplanar evaluation of the thoracic aorta and its branch vessels and can conceivably cover the entire systemic arterial circulation from head to toe. CMR has the additional ability to evaluate the competence of the valves and assess LV function in addition to a detailed morphological assessment of the thoracic vessels and additional musculoskeletal abnormalities that are related to aortopathies. The modality is also very accurate in the diagnosis of aortic dissection but in cases of suspected acute dissection, CT may be preferred to speed of examination in a potentially unstable patient. CMR is also preferred for VTI calculation due to the beam hardening CT artifacts related to the intraforaminal courses of these vessels. There is a plethora of CMR literature in pediatric genetic aortopathies.327CMR is the recommended imaging modality for aortic size measurement and surveillance in pediatric patients with genetic aortopathy, as well as assessment of valve regurgitation and LV function. .CMR should be utilized for complete arterial screening and surveillance in pediatric patients with genetic aortopathy .Depending upon the risk of the mutation, serial CMRs should be performed every few years  and if stenosis, dilation or aneurysm are determined to be progressing, serial CMRs should be occur more frequently (as much as every 6 months) .CMR is indicated for assessment of aortic dissection risk: In patients with Turner syndrome with additional risk factors, including BAV, coarctation of the aorta, and/or hypertension, and in patients who attempt to become pregnant or who become pregnant, it may be reasonable to perform imaging of the heart and aorta to help determine the risk of aortic dissection. .CMR may be beneficial for VTI measurement for risk stratification in patients with genetic aortopathy risk: Limited populations examined have suggested that VTI > 50 is associated with adverse clinical outcomes. .329 The vessels encircle the trachea and esophagus and can lead to varying degrees of compression and clinical symptoms involving the respiratory and/or gastrointestinal system. Some patients are asymptomatic, diagnosed incidentally when imaging is needed for other unrelated reasons and do not require treatment.329 Visualization of the entire ring or sling can be challenging due to indirect imaging of structures with chest radiography or barium esophagram and suboptimal acoustic windows with echocardiography. Due to their significant respiratory symptoms, some patients may first undergo bronchoscopy, revealing a pulsatile stenosis and tracheomalacia, again indirect evidence of a vascular anomaly.334 In addition, the vascular structures completing the ring may be atretic, or unable to be opacified with any imaging modality.336Vascular rings and slings are rare congenital anomalies involving the aortic arch and PAs, representing about 1–3% of CHD.347 CMR provides many advantages for the assessment of vascular rings and slings including imaging of the airway and allowing a conclusive diagnosis to guide in therapeutic management.There is an extensive history of the utilization of CMR to diagnose aortic arch anomalies334 Neonates may present with life-threatening complications of the airway.331 With significant tracheomalacia, symptoms may persist after surgical intervention, with some cases requiring further tracheal surgery.331 CMR has been demonstrated to successfully diagnose patent double arches and those with atretic portions and is superior to cardiac catheterization angiography in its ability to demonstrate associated compression of the airway.335The most common type of vascular ring, accounting for about 50–60% of cases, is double aortic arch, with persistence of both fourth arches. The double aortic arch may be right-dominant, left-dominant, or codominant, though right dominance occurs in the large majority Figure . Portion348 Both double aortic arch and right aortic arches constituting vascular rings have been known to occur in conjunction with CHD such as TOF.349The next most common vascular ring type involves a right aortic arch (30–35% of cases) with aberrant left subclavian artery, left ligamentum arteriosum and diverticulum of Kommerell Figure . A small342Circumflex aortic arch is more rare type of vascular ring with contralateral locations of the transverse aortic arch over the bronchus and descending aorta where there is a “retroesophageal segment” of the aortic arch; that is to say a right aortic arch with a left descending aorta or a left aortic arch with a right descending aorta Figure . Over haOther rarer vascular rings with varying location of aberrant vessels and the ligamentum arteriosum (eg right aortic arch with an aberrant left innominate vein) have all been optimally imaged with CMR Figure .340A PA sling is the anomalous origin of the left PA from the right PA which courses between the trachea and esophagus, creating a “sling “around the distal trachea or proximal right bronchus Figure . Impinge332 CT can create 3D reconstructions of the great vessels as well as the trachea and can be utilized for this in centers that do not have the expertise in CMR. Invasive angiography is not indicated for the sole diagnosis of vascular rings and slings and have been replaced by CMR,334 but may be utilized in the setting of additional intracardiac defects needing intervention.Vascular rings and slings may present with life-threatening complications of the airway in the newborn period. Upper airway obstruction and dysphagia are common presenting symptoms during this time and later in infancy or early childhood and beyond. Prolonged or recurrent respiratory symptoms or refractory asthma may necessitate workup for vascular anomalies. While chest radiography, barium esophagography, bronchoscopy and echocardiography are suggestive of a vascular ring or sling, full details of the vascular anomaly and impacted structures  must be delineated further for adequate surgical management, and these can be provided by CMR. As some surgeons prefer a 3D reconstruction of the great vessels prior to operating on arch anomalies, CMR can faithfully create a 3D model using both contrast enhanced and non-contrast techniques.After preliminary assessment and clinical suspicion for a vascular ring or pulmonary sling, CMR is indicated for definitive anatomic diagnosis in the management of these lesions prior to therapeutic intervention.  Flows to both lungs may be assessed in pulmonary sling.CMR is indicated for the assessment of tracheal narrowing in patients with vascular rings and slings CMR is indicated for the assessment of associated lesions of vascular rings such as TOF TGA, apart from those with a SV, may occur with a systemic RV in 2 different categories:350 There is atrioventricular and ventriculoarterial discordance which results in normal hemodynamics where systemic venous returns is directed towards the lungs and pulmonary venous return is directed towards the body. These patients most commonly have no other CHD, but if CHD occurs, they most commonly have VSD, pulmonary stenosis or may have Ebstein’s anomaly of the left sided tricuspid valve.Congenitally corrected transposition (ccTGA), also called L-looped TGA or TGA {S,L,L}, occurs when the morphologic LV is on the right side of the circulation and associated with the pulmonary valve and the morphologic RV is on the left side of the circulation and associated with the aorta.TGA after atrial inversion, also called TGA after atrial switch, occurs when patients with D-looped TGA  undergo an atrial switch operation, either a Senning or a Mustard procedure. In D-looped TGA, there is atrioventricular concordance and ventriculoarterial discordance resulting in the systemic and pulmonary venous systems in parallel circuits; the Senning and Mustard procedures baffle venous return to the correct ventricle physiologically. Most of these operations were performed in the era prior to ASO so the vast majority of these patients are adults although in some circumstances, this is performed in the "double switch" operation for TGA {S,L,L}.350 Mechanics of the systemic RV are markedly different from the single RV and from the normal systemic LV.30 Both the RVs in ccTGA and TGA after atrial inversion can be dilated, spherical and poorly functioning.351 For those with TGA after atrial inversion, after a high short term mortality rate (up to 20%), there is a longer lower mortality rate which nevertheless remains significant.352 Multiple studies have demonstrated a significant decline in RV function in adulthood, with or without symptoms.354 Both RV and LV in the systemic RV circulation demonstrate abnormal response to exercise.355Whether the RV can tolerate a lifetime of systemic vascular resistance and pressure, whether a morphologic D-loop or L-loop, has always been debated, making study of RV performance in this patient population crucial. In a multi-institutional retrospective analysis, by 45 years of age, 67% of those with ccTGA with intracardiac lesions and 25% without intracardiac lesions had heart failure and systemic ventricular dysfunction.362 including the aforementioned abnormal response to exercise. Adverse cardiac events have been associated with RV volume, RV mass index, RVEF, RV wall stress and LV volume.365 There is evidence to demonstrate that as they age, patients with a systemic RV have functional decline and no resting parameters correlate with exercise function.367 Because of the ability to quantify ventricular performance independent of geometry, CMR has been utilized in several pharmacologic trials in this patient population.369 Systolic strain by CMR has also been quantified using feature tracking methods370 and dyssynchrony, as measured by feature tracking, correlates well with major cardiac events in those with a systemic RV.363CMR is ideally suited for the study of the systemic RV in the setting of TGA due to its ability to overcome the issues of RV geometry and retrosternal location that challenge echocardiography. The issue of RV geometry is very germane in these diseases as the RV remodels and the anatomy changes when it becomes a systemic ventricle. In addition, the geometry of a D-looped RV Figure  as in TG373  with internal checks along with in-plane velocity mapping to visualize the leak. Ventricular outflow tract obstruction is assessed by CMR on a routine basis.376In patients with TGA after atrial inversion, CMR has been utilized for several decades to assess the size, patency and leaks of intra-atrial baffles3 Figure  as well 377 however, this may also be due to Ebstein’s anomaly of the left sided tricuspid valve378; either way, it presents a volume load on the ventricle. Indeed, in the presence of significant TR and if present, deteriorating RV function, a “double switch” may be performed, combining an ASO procedure with a Senning379 and CMR is utilized not only to evaluate the intra-atrial baffle but also the coronary arteries and ventricular function. CMR, as previously noted, can measure atrioventricular valve insufficiency via 2 methods utilizing PC-CMR alone or in combination with cine CMR. There is evidence to demonstrate that the systemic RVEF cannot increase in response to increasing atrioventricular valve insufficiency.380 Ultimately, though, accurate measurements of TR by CMR are important as this has been linked to ventricular function and clinical outcomes in this patient population.383Similar to the debate regarding whether the RV can tolerate a lifetime of systemic vascular resistance and pressure, the ability of the morphologic tricuspid valve to maintain systemic atrioventricular valve work is also questioned. TR is generally due to annular dilation and systemic RV dysfunction in ccTGA,Other anatomic abnormalities can be assessed by CMR including VSD repair, pulmonary stenosis and PR after repair and the size of the branch PA in patients with ccTGA Figure . PC-CMR 384 In a study of 34 patients with systemic RVs, LGE was linked not only to older age, lower RVEF and arrhythmia but also higher RV wall stress, reduced peak oxygen uptake during exercise and a worsening of clinical symptoms.365 LGE in the systemic RV is related to collagen content385 as well as ventricular dyssyncrhony.386 Diffuse fibrosis, using ECV, has also been assessed in the systemic RV in a dual chambered circulation.388 Importantly, the presence of myocardial fibrosis is prospectively related to a mix of adverse clinical outcomes in follow up.390 These types of studies have been important in understanding the role of fibrosis in the natural history of the systemic RV, and may indirectly imply a role of anti-fibrotic medical therapy.Characterization of the myocardium with CMR has demonstrated a role for the assessment of myocardial fibrosis and its link to the gradual decline of the systemic RV Figure . The preCMR is indicated for quantification of systemic RV volumes, mass, and ejection fraction  and can be useful for quantification of pulmonary LV performance parameters in patients with a dual chambered circulation CMR is recommended for the assessment of the systemic atrioventricular valve  in patients with a systemic RV CMR is useful for detecting systemic RV myocardial fibrosis, which may have important implications for a given patient’s prognosis and therapy options CMR is beneficial for the detection of stenosis and leaks of the interatrial baffle in those patients with systemic RVs who have undergone an atrial inversion procedure  as well as for detection of the presence and severity of outflow tract obstruction .CMR is useful to assess associated lesions and the sequelae of repair such as VSD, pulmonary stenosis and PR, especially in patients with ccTGA .391 On histopathology, HCM is characterized by myocyte disarray, myocardial hypertrophy and fibrosis along with abnormal small intramural arterioles with thickened walls and narrowed lumen resulting in ventricular dysfunction and ventricular arrhythmias. The presentation of HCM is heterogenous with varied symptomatology including fatigue, chest pain, palpitations and even sudden cardiac death (SCD). Treatment options include medical management, surgical myomectomy or alcohol septal ablation for relief of critical LV outflow obstruction (gradient ≥ 50 mmHg), and implantable cardioverter and defibrillators (ICD) for those patients considered to be at highest risk for SCD.Hypertrophic cardiomyopathy (HCM) is a disorder of increased LV mass and may be differentiated into syndromic (with other systemic involvement) and nonsyndromic (without other systemic involvement) types. This section describes nonsyndromic disease. This type of HCM is a common genetic cardiomyopathy resulting from autosomal dominant mutations in multiple genes encoding the cardiac sarcomere; including cardiac β-myosin heavy chain, cardiac myosin binding protein C and Troponin T. There have been over 1400 mutations described.393 Both sets of guidelines have similar requirements regarding the diagnosis of HCM, which in adults is defined as a left ventricular wall thickness (LVWT) of > 15 mm in one or more myocardial segments, not explained by loading conditions. In children, the diagnosis requires an LVWT > 2 standard deviations from the predicted mean (z score > 2).Guidelines for the diagnosis and treatment of HCM have been published by both the European society of Cardiology (ESC) and the ACC/AHA.393 The ESC guidelines differ from the ACC/AHA in that the ESC uses a risk prediction model to guide use of implanted cardiodefibrillator (ICD). In addition, the ESC guidelines are only intended for adult use while the ACC/AHA guidelines are intended for both adult and pediatric use. In the ACC/AHA guidelines, focus on the presence of at least one clinical risk factor for SCD , family SCD history or abnormal blood pressure response to exercise) as class IIa indications for the implantation of ICD as primary SCD prevention. Recently, there have been attempts at creating risk calculators solely for pediatric use.396Risk stratification for SCD in pediatric HCM has also been extrapolated from these adult based guidelines as suggested in the current ACC/AHA guidelines.397 One of the critical indications for pediatric CMR in this disease is the identification of increased LVWT not visualized by echocardiography but visualized by CMR.399 This is not a trivial occurrence particularly when the increased LVWT is focal and limited (as is not infrequently the case in pediatrics) which is present in up to 5% of children. This leads to an HCM diagnosis that would have otherwise been missed with CMR solely responsible for diagnosis.402The diagnosis of HCM is characterized by an increased diastolic LVWT in at least one segment in the presence of a nondilated LV chamber Figure  which is403 and apical HCM which may manifest clinically with arrhythmias, diastolic dysfunction and small cavity size,405 all of which can be delineated comprehensively by CMR. RV hypertrophy is additionally observed in a third of adult HCM patients, most commonly at the RV septal hinge points.406 CMR derived LVWT measurements have a primary role in risk stratification with massive LV hypertrophy (LVWT ≥ 30 mm) associated with the highest risk of SCD.408 A meta-analysis of 25 pediatric HCM studies found a similar significant association between extreme LVWT and SCD in children and young adolescents. The hazard ratio for LVWT was 1.80 . The odds ratio estimate for extreme LV hypertrophy was 1.70 . For pediatric patients, new guidelines suggest that a maximal LVWT with a Z score ≥ 20 or > 10 in conjunction with other risk factors is reasonable as a risk factor for SCD.393The most common pattern of HCM is increased LVWT in the basal anteroseptal region which is frequently associated with LVOT obstruction and mitral valve leaflet elongation. Other phenotypes include diffuse hypertrophy involving more than 50% of the myocardium, reverse septal contour, apical aneurysm309 bSSFP sequences performed in the standard planes provide accurate measurements of LVEF, chamber size and LV mass409  as well as due to septal hypertrophy is one of the leading causes of exercise intolerance in HCM patients and may necessitate invasive treatment measures such as myomectomy or septal ablation. LVOT gradients are conventionally measured using echocardiography, but CMR can identify the site of obstruction and assess whether there are contributing anomalies such as anomalous insertion of the anterior papillary muscle and elongated mitral valve leaflets  at end systole.414 LGE usually is patchy and midmyocardial in distribution. LGE has been described in 46–73% of children and adolescents with phenotypic HCM, despite preserved systolic function; it has been shown to increase annually with serial CMR surveillance, constituting on average 10.4% of LV mass.416 Those children with LGE were found to have greater LV mass and were at risk for adverse events including ventricular tachycardia,417 aborted SCD418 as well as having decreased ventricular strain  has been noted in HCM. Studies investigating myocardial perfusion in HCM patients have demonstrated abnormal perfusion metrics in both hypertrophied and non-hypertrophied segments of the LV, as well as correlation between the extent of perfusion abnormalities, LGE and degree of hypertrophy.441 As with perfusion, although promising, at present, it remains a research technique and more studies are needed.Recent interest in T2 weighted imaging and its association with SCD has developed Figure . Two stuMyocardial bridging of the LAD is more common in HCM than in other causes of LV hypertrophy and may potentially be a mechanism for SCD, although there is no evidence to support this hypothesis. Myocardial bridging may be demonstrated by specific coronary CMR sequences (see Coronary section).442 enabling a diagnosis of HCM which may be missed by TTE.402 This holds true even in children, who have better acoustic windows than adults; a small study of pediatric HCM patients demonstrated that echocardiography derived measurements had poorer inter-observer and intra-observer reproducibility compared with CMR measurements.443 This may be due to superior visualization of the LV epicardial/endocardial borders with CMR, and visualization of all hypertrophied segments without any risk of obliquity444.Although TTE assessment of patients with HCM has been traditionally performed, limited acoustic windows, an inability to reliably capture focal hypertrophy and imaging plane obliquity may result in both under and overestimation of LVWT. CMR provides high contrast between bright blood and dark myocardium, excellent spatial resolution, and full biventricular coverage. In addition, short-axis images, derived perpendicular to the true LV long axis, allows LVWT measurements by CMR to be more precise and reproducible,CMR is the only non-invasive modality that can assess tissue characteristics including the presence of macroscopic and global fibrosis, the former of which can be clinically utilized to risk stratify patients regarding potential ICD implantation. The emerging roles of parametric T1 mapping, myocardial perfusion imaging, and T2 imaging will likely increase our understanding of tissue characterization and may further stratify SCD risks.445 .This includes patients with LV hypertrophy in whom there is a suspicion of alternative diagnoses including the athlete’s heart. In children and adolescents with a diagnosis of HCM, contrast enhanced CMR surveillance should occur every 3–5 years for risk stratification, evaluation of LGE, wall thickness and ventricular performance .CMR is the recommended for confirmation of HCM diagnosis, evaluation of possible apical HCM or aneurysm and surveillance of LVWT in HCMCMR is the recommended to screen for HCM in patients with a family history of HCM when echocardiography is inconclusive 393 . CMR is also useful to monitor LVOT obstruction in pediatric HCM patients when echocardiography is inconclusive CMR is beneficial to monitor ventricular function when a more accurate measure than echocardiography is needed, when there is a concern for ventricular performance by echocardiography, or in selected patients for risk stratification for ICD placementCMR is reasonable for the evaluation of myocardial fibrosis for risk stratification in pediatric HCM, possible ICD placement and to monitor the patient more closely than those without LGE. CMR can be beneficial in pediatric patients with LV hypertrophy in whom alternative diagnoses in addition to HCM are suspected. 97 CMR strain measurements may be considered in pediatric HCM patients to monitor ventricular function as well as for risk stratification; patients should be monitored more closely if strain is below the lower limits of normal446 The United States prevalence is estimated to be 1.4 per 10,000 males.447 DMD patients also develop respiratory insufficiency. The restrictive lung disease is a result of diaphragm and secondary respiratory muscle weakness. Historically, the most common cause of death was respiratory failure. However, improved respiratory therapies have resulted in cardiomyopathy and resultant heart failure and arrhythmias becoming the most common cause of death.448Duchenne muscular dystrophy (DMD) is an X-linked genetic neuromuscular disorder resulting in dystrophin protein mutation. DMD is one of the dystrophinopathies that also include Becker muscular dystrophy (BMD), and X-linked dilated cardiomyopathy. DMD results in the more severe phenotype presenting as skeletal muscle weakness early in life and often progressing to loss of ambulation early in the second decade of life. BMD is milder with a considerably more variable phenotype. The incidence of DMD is estimated to be ~ 1 / 5000 live male births.449 Although myocardial damage is present on a cellular or histological level starting very early in life, echocardiographic abnormalities are usually delayed until the second decade of life. For DMD, risk of LV dysfunction increases significantly with age, from < 5% for boys < 10 years of age to > 75% for men > 20 years of age.450 There are patients who will have reduced ejection fraction as early as 8 years of age.451 Subtle abnormalities of deformation using strain analysis can be seen in patients as young as 5 years.452The cardiomyopathy of DMD and BMD is characterized by progressive loss of functional myocytes leading to regional dysfunction followed by global dysfunction. Although, the cardiomyopathy has been commonly described as having a dilatated phenotype, chamber dilation occurs only in the late stages of the disease. The cardiomyopathy is variable both in age of onset and severity. Histologically, the dystrophinopathies lead to alternating areas of myocyte hypertrophy, atrophy and necrosis, and finally fibrosis with replacement of cardiomyocytes by connective tissue and fat. It is estimated that ~ 30% are symptomatic, but elucidating symptoms from patients who are non-ambulatory secondary to skeletal muscle disease is very difficult.453 All recommend that cardiac care begin shortly after initial diagnosis is made. Since the risk of cardiovascular involvement is low for very young children, the initial evaluation consists of clinical evaluation, baseline ECG, and TTE. Yearly TTEs are recommended until the child is old enough to undergo CMR without sedation.There are several guidelines available addressing the cardiovascular care of DMD/BMD patients.455 As patients age, the image quality is degraded due to several factors including spinal and thoracic bony deformities, increased thoracic and abdominal adiposity that decreases ultrasound penetration and alteration of the inter-rib spaces decreasing the size of acoustic windows. A study evaluating TTE image quality for 31 DMD patients aged 11–34 years showed that none of the apical four-chamber image acquisitions were of diagnostic quality.456 In a study designed specifically to assess the ability of TTE to assess DMD patients,457 they found that by 13 years of age, 50% of the studies were classified as suboptimal with ≥ 30% of segments inadequately visualized, and by 15 years of age, 78% of studies were suboptimal. Consequently, in this population, TTE data may not always accurately reflect cardiac function. Some of these limitations can be overcome by administration of ultrasound contrast,458 however, contrast echocardiography has not been included in the standard clinical care guidelines and is used only in patients who have suboptimal acoustic windows and contraindications to CMR. Secondary to the known difficulty with accurate TTE assessment, the first CMR studies for DMD cardiomyopathy patients were performed to accurately measure the LVEF where echocardiographic windows were poor.TTE has limitations in neuromuscular diseases.460 so it is not surprising that it has been utilized for accurate measures of ventricular function in children with this diagnosis464 and to assess the efficacy of treatment.465 Although the use of CMR is very common in this patient population, there are few direct head-to-head comparisons of CMR with echocardiography. Brunklaus et al.462 studied 35 DMD boys  who underwent both TTE and CMR, and although echocardiographic shortening fraction correlated with CMR LVEF , 75% of the TTE studies had deficient ultrasound scanning windows and in 26% measurements, either significantly over- or underestimated LV systolic function compared to CMR. Buddhe et al.464 studied 35 subjects with a mean age of 13.6 years old who also had both TTE and CMR and found, similar to the previous study, weak correlation of TTE parameters with CMR EF.CMR is a proven modality for accurate and reproducible assessment of both RV and LV volumes and masses that is not affected by body habitus or lung artifacts,468 Hagenbuch et al. found that serial monitoring of cardiac dysfunction by serial strain measurements was able to predict progression of the disease in the absence of deterioration of LVEF.469CMR strain imaging has been studied in patients with DMD and has been found useful to detect occult contractile dysfunction and dyssynchrony.462 although there have been a number of other studies of LGE with ventricular function in pediatrics.467 Silva and colleagues showed the feasibility of using CMR for routine assessment of both ambulatory and non-ambulatory DMD patients and demonstrated for the first time that DMD patients have LGE in a pattern that appears to represent the known myocardial fibrofatty replacement. They showed that even patients with normal LVEF were positive for LGE down to age 8 years and that LVEF was markedly different between the groups with and without LGE, linking LGE with decreased LV performance. They noted the LGE was predominantly seen in the inferolateral and anterolateral segments, a finding that has long been known from early pathology studies.470The first large scale clinical report of CMR in DMD with both ventricular function and myocardial characterization using LGE came from Brazil in 2007,471 finding 32% with LGE primarily involving the basal inferolateral segment of the LV in a sub-epicardial distribution. Patients with LGE were older than those without (mean age 16.4 vs 12.9 years), but most importantly, they noted a similar finding to that seen by Silva et al.461 where LGE was inversely correlated with LVEF. A larger study of 314 DMD children by Hor et al. showed the overall prevalence of LGE was ~ 36%,451 increasing from 17% of patients < 10 years to 34% of those aged 10–15 years and 59% of those > 15 years-old. Ten percent (11/113) of patients who had LGE died an average of 10.8 months after CMR. Conversely, only one patient from the LGE negative group died. Patients who died had larger LV volume and greater number of positive LGE segments compared to those who remained alive.The first report of CMR in a small multi-institutional retrospective study in children with DMD showed LGE was prevalent,472 and during a mean follow-up time of 47 ± 18 months, the primary endpoint (death or transplantation) was observed in 3% and the secondary endpoint  in 24%. They found that LVEF and the presence of “transmural” LGE were independent predictors for secondary endpoints. Interestingly, in the group of patients with preserved function (LVEF > 45%), patients with “transmural” LGE had a significantly lower event-free-survival compared to those without. Similarly, in children and adolescents, Menon et al. found LGE present in 78% of the boys.473 Compared with patients without LGE, those with LGE were older with lower LVEF (46 ± 12 vs 56 ± 9% respectively) and a higher incidence of ventricular tachycardia . Interestingly, during the study period, six of the subjects (19%) died. The factors associated with mortality were increased age, advanced grade of LGE, higher LV end-systolic volume, lower LVEF, and ventricular tachycardia.CMR has been associated with outcomes for the DMD/BMD population. In young adults, Florian et al. prospectively studied 88 male DMD/BMD patients474 They determined that LVEF declined ~ 0.58% per year independent of LGE status. More interestingly, LVEF did not decline over time if LGE was absent but declined at a rate of ~ 2.2% per year when LGE was present. The number of LGE-positive LV segments increased with age as well.There are now longitudinal studies of CMR in DMD populations that help to inform the appropriate longitudinal timing for these exams. Tandon et al. reviewed 465 serial CMR DMD studies, all of whom had ≥ 4 assessments.Limitations of CMR as it Relates to DMD Patients Although CMR imaging does not suffer from the limitation of poor acoustic windows attributable to body habitus, thoracic abnormalities, or lung disease, there are factors that do limit its utility for imaging every patient with DMD. Some DMD patients cannot be comfortably positioned on the CMR table because of significant contractures, severe back pain, or immobility which is particularly true for older, non-ambulatory patients. CMR image quality is limited in patients with atrial or ventricular arrhythmias, irregular respiratory rates or motion, or inability to remain motionless in the scanner. Although some of these limitations can be overcome with sedation or anesthesia, such studies come with increased risk in this patient population secondary to compromises in respiratory or cardiac function. A thorough risk–benefit analysis is required before undertaking a sedated CMR study for a DMD patient. Finally, there is potential for artifact leading to CMR image degradation from implanted devices in DMD patients including both cardiac electrophysiologic therapeutic devices such as pacemakers and ICDs as well as skeletal devices including spinal fixation rods.CMR should be used to evaluate biventricular size and systolic function of DMD and BMD patients after the age of 8 years (or when they do not need sedation)  and may be performed every year if needed.CMR myocardial fibrosis evaluation of DMD and BMD patients is recommended for prognostication and risk stratification .CMR strain analysis of DMD and BMD patients may be considered for prognostication and risk stratification .476 Management requires differentiation of specific tumor types, an objective for which imaging plays a significant role. Echocardiography remains the primary modality for initial detection and screening of cardiac tumors though has a limited ability to further characterize the mass other than its presence with the exception of echogenic and echolucent (presumably cystic) regions. In addition, echocardiography can be limited by acoustic windows and reliable differentiation of tumor from vegetation or thrombus can be difficult. Many masses are benign but still need to be distinguished from malignancies, characterized for prognosis, assessed for impact on heart/valve function and determined whether an intervention is needed. Thus, additional imaging is generally warranted.Cardiac tumors are rare in the pediatric population, with an incidence between 0.027 and 0.3%.482:After identification of masses by echocardiography, CMR is utilized in a number of different ways Figure  and has Precise definition of anatomic location of the tumor including size, sites of myocardial attachment, and tissue layers involved.Tissue characterization and differentiation between benign and malignant tumors as well as to differentiate the mass with thrombus.483Differentiation between tumor and thrombusDetermining the extent of the tumor and relationship with surrounding structures to determine impact on heat and valve function and guide surgical resection (eg outflow tract obstruction).Imaging of fetal tumors482As certain genetic syndromes are also associated with cardiac tumors, CMR is especially useful in establishing the diagnosis when cardiac masses are noted on echocardiography in that patient population.491 Other publications498 have provided reviews and experiences of various centers of the utility and approach to CMR imaging for pediatric masses and how the findings may direct care.Given the overall low incidence of cardiac tumors and the varied types of tumors in pediatrics, relevant published CMR experience includes case reports as well as relatively small case series.2 upon which clinical decisions are often based. Various publications have described tissue characterization techniques for differentiating benign tumors such as rhabdomyomas499 most commonly or myxomas487 from others such as osteoscarcoma,490 highly vascularized tumors such as hemanginomas,491 or adipose tissue such as lipoma.489As noted in a prior consensus statement, the utility of CMR is its ability to describe location, size, hemodynamic effects, and tissue type of cardiac masses 477 97% of tumors were correctly identified compared to histologic diagnosis. Of these, a single correct diagnosis was made in 55% and a limited differential diagnosis which included the correct diagnosis was made in 42% (21% with 2 diagnoses and 23% with 3 or more diagnoses). There were only 2 cases of incorrect diagnoses, both having an atypical appearance on CMR. Generally, incorrect or incomplete diagnoses related either to atypical features of the mass, such as unusual location, or to technical imaging issues such as incomplete image acquisition or poor quality. This multicenter experience demonstrated the clinical utility of CMR in differentiating masses non-invasively, and thus its role in clinical management of affected patients CMR is indicated to distinguish between a benign and malignant cardiac tumor. CMR is indicated to distinguish cardiac tumor from thrombus. 2) for description of location, size, and any hemodynamic effect, but may be less useful for tissue characterization. Non-contrast CMR is reasonable in patients with compromised renal function  which remains the diagnostic gold standard and can help guide therapy.501 EMB, however, is prone to low sensitivity related to sampling error,502 practice variation503 or adverse events due to its invasive nature.505 Thus, the diagnosis of myocarditis in pediatrics is often made from a combination of clinical factors including the patient’s history, symptoms, ECG changes and serologic findings.506Myocarditis is a potentially life-threatening disease and a significant cause of pediatric morbidity and mortality.506 In adults, CMR has become a well-established modality for diagnosing myocarditis507 with recommendations by the International Consensus Group on CMR (ie the “Lake Louise” criteria) published in 2009508 and updated in 2018.509 Evidence suggests CMR is indicated in the diagnosis of pediatric myocarditis; as a matter of fact, one of the first publications of CMR findings and tissue characterization in myocarditis was in children in 1991 which also compared these findings to EMB.510Non-invasive imaging plays a key role in diagnosis, almost always starting with echocardiography, with the addition CMR imaging to vastly increase the diagnostic sensitivity and specificity.511 CMR is useful in the setting of suspected myocarditis for:In the clinical setting of acute chest pain and concerning diagnostic testing , a diagnosis of myocardial inflammation can significantly affect prognosis and management.Confirming the presence of myocardial inflammation and edemaDifferentiating ischemic (i.e. coronary) from non-ischemic causes of myocardial inflammation.Risk stratification and prognosticationGuiding subsequent investigations512 or dilated cardiomyopathy. Beyond these findings, however, echocardiography lacks the sensitivity and specificity to further characterize myocardial inflammation and a test with higher diagnostic accuracy is required for further clinical management.TTE is usually the 1st non-invasive imaging test in the evaluation of suspected myocarditis and allows assessment of ventricular function, size, regional wall motion abnormalities, valvular abnormalities and pericardial effusion. The common TTE findings in myocarditis are usually non-specific though TTE can help distinguish between the different myocarditis phenotypes of fulminant myocarditis (severe dysfunction), acute (non-fulminant) myocarditis508 Additional supportive criteria such as pericarditis, pericardia effusion or LV systolic dysfunction is also evaluated by CMR.509 The 2009  Lake Louise criteria consists of:The value of CMR in myocarditis is to evaluate the tissue characteristics of myocardial inflammation; edema, hyperemia and capillary leak (using T1 and T2 weighted sequences) and necrosis or scarring of ventricular myocardium Figure .500,508 514T2 weighted imaging showing the presence of myocardial edema.508 consistent with myocardial hyperemia or inflammation.T1-weighted images obtained before and early after administration of gadolinium-contrast revealing early gadolinium enhancement (EGE),515 showing LGE, characteristic of myocardial necrosis or scarring.T1-weighted segmented inversion-recovery gradient-echo sequenceIt also specified two positive findings (either T2 or T1 based) are necessary to diagnose myocarditis Figure .516 or single-center series with relatively small populations.520 There has been one retrospective multicenter study that has evaluated CMR techniques in children with myocarditis which included 13 centers and 143 subjects521 and although there was variability in tissue characterization protocols among centers, overall sensitivity for CMR positive myocarditis was high (82%).The Lake Louise criteria have been validated in pediatrics mainly from case reports523The updated recommendations included one T2 relaxation-based marker for myocardial edema (T2-mapping or T2 weighted images) and one T1 relaxation-based marker  for associated myocardial injury.510 While the inclusion of multiparametric mapping is supported by a robust evidence base in adults, the mutiparametric mapping literature in pediatrics has been limited to small single-center studies.527 There is, however, emerging data about the potential added value of multiparametric mapping in the evaluation of pediatric myocarditis.528 The authors of the 2018 Lake Louise criteria currently state that “the original Lake Louise Criteria provide a good overall diagnostic performance, and thus they should remain in use in centers that have good experience with their application.” The MYKKE consortium is one effort currently underway to establish a multicenter registry with prospective data collection in pediatric myocarditis.529The 2009 Lake Louise criteria were updated in 2018 to include parametric mapping techniques that have significantly advanced in the diagnosis of myocardial inflammation in adult patients.In the setting of myocarditis resembling an acute coronary syndrome with a young patient presenting acutely with chest pain, elevated cardiac enzymes and ECG abnormalities, CMR can be used to differentiate between myocarditis and myocardial infarction due to coronary artery disease:530In myocarditis, the pattern of LGE enhancement is characteristically subepicardal, may be transmural , and usually in a patchy distribution.The LGE pattern from coronary artery disease , is subendocardial or transmural and in a distribution of coronary perfusion territory.Establishing the diagnosis of myocarditis in a patient with low risk for coronary artery disease (i.e. most pediatric patients) is helpful and avoids unnecessary cardiac catheterization for coronary angiography.536 Similarly, CMR has been shown to be useful in evaluating outcomes in pediatrics538 including a large, multi-center study.539 Lastly, myocarditis has a known association with dilated cardiomyopathy (DCM), either as a precursor to DCM or as an acute illness that “unmasks” previously undetected DCM.540 Long-term studies in patients with acute myocarditis report the development of DCM in 21%, showing the utility of CMR for chronic management.541CMR can be useful for risk stratification with adult studies showing robust outcomes data on adverse cardiac events and arrhythmias.Following the diagnosis of myocarditis by CMR, more detailed information may be needed from EMB to direct therapy. In this situation, there is diagnostic synergy between non-invasive CMR and invasive EMB to identify and treat particular etiologies of myocarditis. Examples may include giant cell or eosinophilic myocarditis that are typically treated with immunomodulator therapy.The original Lake Louise Criteria (2009) is recommended for diagnosing myocardial inflammation for centers that have a good experience with these criteria in the pediatric age range .CMR with gadolinium-based contrast is indicated for evaluation of myocarditis to confirm the presence of myocardial inflammation in pediatric patients .CMR is beneficial in children and adolescents for differentiating ischemic from non-ischemic causes of myocardial inflammation, risk stratification/prognostication, and guiding subsequent investigations .CMR with multiparametric mapping can potentially add value in the evaluation of pediatric myocarditis, and more studies are needed in this population .The end result of many congenital and pediatric heart lesions is ventricular dysfunction which may result in much of the morbidity and mortality associated with these diseases. Therefore, quantifying ventricular function is a vital aspect of continuing assessment.At the simplest level, cardiac failure is defined as an inability to produce adequate cardiac output to supply the bodies metabolic needs. Thus, measurement of cardiac output can provide important information regarding cardiac function. The traditional reference standard method of measuring cardiac output is at cardiac catheterization using either thermodilution or the Fick method. Unfortunately, invasive assessment is associated with not insignificant risk as well as cost and is therefore not performed routinely. More importantly, most CHD patients have normal baseline cardiac output due to cardiac compensation . Many symptoms are actually related to these compensatory mechanisms as well as an inability to augment cardiac output during exercise. Assessment of many of these compensatory mechanisms requires visualization of the ventricles and therefore, cardiac imaging is vital.309The most ubiquitous cardiac imaging modality used in CHD and acquired pediatric heart disease is echocardiography which has many advantages over other imaging techniques and is considered the first line method of assessing cardiac size and function. Nevertheless, echocardiography still has some significant problems such as operator dependence, poor acoustic windows and poor blood pool to myocardial contrast. In the last 20 years, as mentioned, CMR has become the reference standard method of assessing biventricular function.Many CHD lesions are associated with volume loading due to shunts or valvular regurgitation. This is true in not only such common shunt lesions such as ASDs, VSDs and patent ductus arteriosus but in more complex and less common lesions such as anomalous pulmonary venous connections or left SVC connected to the left atrium. Similarly, valvular regurgitation in patients with BAV, cleft mitral valve or TR associated with HLHS can cause significant volume loads. The cardiac response to volume loading is dilation which can result in increased risk of arrhythmia, increased wall stress and predisposition to dysfunction. Thus, measuring ventricular volumes is an important component of evaluating CHD.544Although less common, small ventricular volumes also need to be evaluated. Varying degrees of hypoplasia are seen in diseases such as HLHS, critical aortic stenosis, double outlet RV and malaligned atrioventricular canals to name a few. There has been a number of studies which attempt to aid in management of these patients, however, many questions remain.There are other lesions which occur in pediatric and CHD where the assessment of biventricular performance is important. Patients with anomalous coronary artery origins and courses, patients with surgically manipulated coronary arteries (see section on Coronary arteries), and patients with myocarditis (see Myocarditis section) are all examples where ventricular performance are useful.545 or the malformed LV in CHD. Newer 3D echocardiographic techniques do hold promise for true volumetric assessment, however, they still suffer from operator dependence and potentially inadequate acoustic windows. CMR has some distinct advantages over echocardiography. Firstly, it is not limited by body habitus and can be acquired in any patient irrespective of size. Secondly, unrestricted 2D imaging can be performed, allowing imaging of contiguous slices covering both ventricles. The result is true 3D measurement of ventricular volumes.546 Further, although there are CMR techniques that can be real-time (ie instantaneous acquisition), cine imaging for ventricular function is built over multiple heart beats, averaging the data in the image; whereas in echocardiography or catheterization, the imager is required to average the ventricular function in their minds, CMR averages it in the image itself and the quantification is a more true reflection of typical ventricular performance in the patient. Finally, modern bSSFP CMR techniques provide high blood pool myocardial contrast, aiding segmentation and further post-processing.547Although ventricular volumes can be estimated by 2D echocardiography, most methods rely on significant geometric assumptions. These may hold true for the normal LV but are inadequate for the crescentic RV549An important benefit of accurate volume assessment is that it also enables precise measurement of ejection fraction which is a well-recognized measure of cardiac function and ventricular arterial coupling and an important prognostic marker in many forms of CHD and pediatric cardiovascular disease.Another metric that can be accurately evaluated from this sort of data is ventricular mass. Increased ventricular mass is common in patients with obstructive lesions (e.g. aortic stenosis or PA stenosis) or in for example, the RV of HLHS or TOF. As CMR allows visualization of the whole ventricular mass, especially the RV and its free wall, it enables very accurate measurement which is key to understanding the physiology and managing patients.551 For these reasons CMR is now be considered the reference standard method of measuring LV and RV volumetric data.Several studies have shown that CMR provides highly accurate and reproducible measurement of ventricular volumes, mass and ejection fraction data in CHD.549SV at different stages of the Fontan palliation  and exercise tolerance, as well as response to interventions .552Several studies have demonstrated that CMR measurements of ventricular volumes, mass and ejection fraction provide important clinical information in conditions such as repaired TOF,553 Studies have validated real-time CMR for measurement of ventricular volumes and they should be considered a possible alternative to conventional imaging. Real-time imaging can also be useful in patients with irregular cardiac rhythm, although no large-scale studies demonstrating utility have been performed. Motion correction techniques, now in common use, can be used to increase image quality and negate respiratory artifacts.There are some limitations in using CMR to measures ventricular volumes and ejection fraction. In some patients, particularly children, breath holding is difficult and free breathing approaches are required including signal averaged and real-time acquisitions. Real-time sequences are becoming increasingly used in pediatric imaging and with the advent of new accelerated techniques, are now reaching the quality of conventional breath hold cines.554 However, this should be considered a subsidiary measurement rather than the main reason to perform CMR. A better method of assessing systolic and diastolic function may be to directly measure myocardial motion in diastole and myocardial velocities have been measured by CMR and validated against echocardiography.555Diastolic dysfunction is often overlooked as a cause of symptoms in CHD. Evaluation of diastolic dysfunction requires measurement of the dynamic aspects of ventricular filling. Thus, a limitation of conventional ventricular volume and ejection fraction assessment is that it provides little information regarding diastolic function. The traditional method of assessing diastolic function is echocardiography assessment of atrioventricular valve inflow. Specifically, the ratio of peak early to late inflow velocities (E/A ratio) is an important indicator of ventricular diastolic dysfunction. The E/A ratio can also be assess using PC-CMR and some studies have demonstrated clinical utility.557 tissue phase mapping and strain/displacement encoding. These techniques have been used to better understand pathophysiology in CHD. However, significant clinical utility has not been demonstrated and a number of sequences are still at the research stage.Volumetric measurement enables evaluation of global changes to ventricular volume and function. However, assessment of volumes alone does provide the full picture of cardiac dysfunction. There is evidence that both systolic and diastolic early ventricular dysfunction is better identified by evaluating the specific aspects of local myocardial motion. Although the cardiac myocyte can only shorten, the heart has complex local motion due to the specific arrangement of myocytes. This includes longitudinal and radial contraction, twisting and wall thickening. Some or all of these metrics can be measured with echocardiography using tissue Doppler or strain imaging. However, like all echocardiographic techniques, they may suffer from inadequate windows and are always operator dependence. There are also several CMR techniques that can be used to evaluate myocardial motion such as myocardial tagging,559 processed using the same tools used for echocardiography strain imaging. The main benefit of this approach is that imaging acquired for conventional volumetric analysis can also provide local motion data. This has allowed retrospective analysis of historical cine data and demonstration of clinical utility. Several studies have now shown that strain metrics can independently predict outcome (e.g. death or major cardiac event) and exercise tolerance in patients with CHD.562 However, no large scale studies have demonstrated that CMR strain measures outperform conventional ventricular volumes or ejection fraction data. Thus, currently, strain assessment should be considered as an addition to rather than a replacement of conventional ventricular volumes.More recently, strain (and strain rate) data has been derived from conventional CMR cines using feature and tissue tracking,Regional ventricular wall motion is important in pediatric heart disease patients such as AAOCA, surgically manipulated coronary arteries, myocarditis, arrhythmogenic RV cardiomyopathy and other lesions which occur in pediatric and CHD. This may be performed qualitatively on cine imaging or using quantitative measures such as myocardial strain.Finally, tissue characterization such as LGE and diffuse fibrosis can add another dimension to the assessment of ventricular function, elucidating the etiology of regional or global myocardial dysfunction (see previous sections).CMR should be performed for the evaluation of biventricular volumes, mass and ejection fraction in patients with volume or pressure overload lesions as well as with varying degrees of RV or LV hypoplasia .CMR is useful in assessing biventricular volumes and ejection fraction in patients with non-structural pediatric heart disease  or in those patients with congenital or surgically manipulated coronary artery lesions .CMR is indicated in assessing ventricular volumes and ejection fraction in patients with SV .CMR strain analysis may be considered in assessing ventricular function in CHD and prognostication of outcome .CMR tissue characterization is reasonable in assessing ventricular function in CHD and prognostication of outcome 563 Shunts are characterized in 3 main ways: (i) location, (ii) magnitude and direction, and (iii) effect on ventricular volume and function. This section addresses evaluation of shunt magnitude and direction by calculation of the systemic and pulmonary blood flow ratio (Qp/Qs). A left-to-right shunt will result in greater blood flow to the pulmonary vasculature compared to the systemic vasculature and a Qp/Qs ratio > 1 (higher Qp/Qs indicates a larger shunt). Conversely, a right-to-left shunt will result in greater flow to the systemic vasculature and thus a Qp/Qs ratio < 1 . Quantifying Qp/Qs is vital in deciding appropriate management of patients with shunt lesions and is included in most current international guidelines.564Cardiovascular shunts between the systemic and pulmonary circulations are the commonest result of CHD, accounting for approximately 50% of all cases.565 Secondly, quantification of Qp/QS is only possible if sampling can be performed distal to the shunt which is not possible in some extracardiac lesions . Finally, in some lesions such a SV after BDG, it is impossible to obtain adequate mixed systemic venous saturation as it is separated into SVC and IVC circuits.43 For all these reasons, non-invasive assessment of Qp/QS is becoming increasingly important in the assessment of shunt lesions.The reference standard method of measuring Qp/Qs is invasive oximetry with measurement of oxygen saturations (or content) in the pulmonary and systemic arterial and venous systems. This method should be used if measurement of PA pressure and pulmonary vascular resistance are also required . However, there are some disadvantages to catheter based evaluation of Qp/Qs. The most obvious are its invasive nature which can associated be morbidity and high cost. Furthermore, there, some technical problems with invasive oximetry that should be understood. Firstly, the requirement for measurement of oxygen saturation from multiple sampling sites during steady state can result in significant error propagation and inaccurate Qp/Qs quantification.566 The main benefit of this approach is that echocardiography is already the first line method of anatomically evaluating shunt lesions. Unfortunately, echocardiographic evaluation of shunt magnitude is prone to inaccuracy due to inadequate data acquisition and invalid assumption in the calculation.567The simplest non-invasive method is Doppler echocardiography with several techniques based on vessel area and blood flow velocity being described.22 however, precise measurement of flow in these vessels remained a challenge up until the past 10 years. Their clinical impact has been debated in the past568 in part due to the challenge of quantification, although it is clear now that there is an effect on patient care and management571; it has also been demonstrated by pilot data that these collaterals can be mostly obliterated in the catheterization lab with a measured decrease in the collateral flow.44 Similarly, veno-venous collaterals are found not uncommonly in SV patients, from 20 to 33%,573 and interventions have some time been needed. Finally, known since the 1930s and 1940s,574 aortic collaterals develop from existing vessels such as intercostal and mammary arteries to bypass aortic obstructions such as coarctation of the aorta which clearly has clinical implications for the diagnosis and treatment of the disease.Collateral flow in CHD comes in 4 broad categories: (1) systemic to pulmonary Figure , (2) ven576 and invasive oximetry in patient studies.579 A further benefit of PC-CMR over invasive oximetry is that measurement Qp and Qs is not limited to assessment of flow in the pulmonary trunk and aorta respectively. For instance, Qp and Qs can be quantified by measuring flow in the PV and vena cavae respectively. These alternative calculations are particularly useful in situations where: (i) it is not possible to measure blood flow in one of the great arteries  and (ii) invasive oximetry fails, such as patients with systemic-to-pulmonary arterial collaterals. Finally, and maybe more importantly for the accuracy of the technique, these multiple methods of evaluating Qp and Qs can be performed in the same patient, providing key internal quality assurances.Recently, CMR has become the non-invasive reference standard method of measuring Qp/Qs using PC-CMR which has been shown to allow highly accurate and reproducible quantification of Qp/Qs. In PC-CMR, through plane flow is directly measured without assumptions—which has been borne out by the significant number of studies that have demonstrated good agreement between PC-CMR and both direct measurement of flow in phantom studiesAn important additional benefit of CMR is the ability to accurately measure ventricular volumes (see Ventricular function section). It is possible to measure Qp/Qs directly using ventricular stroke volumes. However, shunt location must be taken into consideration. An ASD and VSD may both have a Qp/Qs of 2:1, but RV stroke volume will be twice the LV stroke volume in the ASD, while LV stroke volume will be twice the RV stroke volume in the VSD. Thus, without knowledge of shunt location, ventricular stroke volume should be used with caution. Furthermore, accurate assessment of Qp/Qs using ventricular stroke volume relies on competence of the atrioventricular and semilunar valves. Consequently, measurement of ventricular volumes is not the first line method of calculating Qp/QS. Nevertheless, ventricular stroke volumes do provide a way of performing internal quality assurance of the PC-CMR calculation. More importantly, evaluation of ventricular size and function allows accurate evaluation of the physiological sequelae of a shunt lesion .581 This is relevant as these lesions are difficult to image with echocardiography, particularly in older patients. Several studies have also shown that CMR provides comprehensive evaluation of secundum ASDs and can determine candidacy for transcatheter or surgical closure.584 Patients with VSDs are generally diagnosed and managed using echocardiography, however, CMR with 3D imaging may useful for delineation of complex or multiple defects.585 Finally, CMR can be useful in delineating the anatomy of patent ductus arteriosus and aorto-pulmonary windows in older patients, where echocardiography can be insufficient.Another important advantage of CMR is the ability to anatomically delineate shunts. Studies have shown that CMR can provide definitive diagnosis and evaluation, for example, of sinus venosus defects and anomalous PV connections (see PV section).With all the possible shunt lesions in CHD other than the ones listed above such a truncus arteriosus, double outlet RV, TOF, it is not feasible to list them all in this guidance. Suffice it to say that when clinically important shunt lesions are present, imaging with CMR is useful.45 CMR is the only methodology that can accurately quantify this flow.43 The use of CMR to quantify this flow has demonstrated that these collaterals do have a measurable effect on outcome571 and act to steal blood from key organs such as the brain.47 CMR has been able to quantify the short term decrease in systemic-to-pulmonary collateral flow after embolization in the catheterization lab.44Systemic-to-pulmonary collateral vessels can be visualized by CMR most notably by administering contrast Figure  and flow260 An increased flow volume at the diaphragm indicates significant collateral flow into the aorta, bypassing the narrowing (see Coarctation of the aorta section).258 Venovenous collaterals are also imaged by CMR588 and their presence needs to be taken under consideration prior to intervention.CMR has also been extensively used to quantify collateral flow around a coarctation site Figure  which isCMR should be used for the evaluation of the magnitude and direction of intracardiac shunts in children and adults such as with ASDs and VSDs as examples .CMR is indicated for the evaluation of the magnitude and direction of extracardiac shunts in children and adults such as with patent ductus arteriosus and systemic-to-pulmonary collaterals as in Fontan patients .CMR is beneficial for the anatomic and quantitative flow assessment of systemic-to-pulmonary collaterals, aortic and venovenous collaterals .115 The principle of this technique is that gadolinium-based contrast agents have increased volume of distribution in abnormal myocardium. The difference between normal and abnormal tissue distribution volume (Vd) results in a CMR signal difference. The mechanism of increased Vd is variable. In inflammatory disease such as acute myocarditis or acute ischemia, the increased volume of distribution results from myocardial cell injury or death. In chronic myocardial infarction or fibrosis in cardiomyopathies, the extracellular space is expanded.CMR is an integral part of the non-invasive imaging of both acquired and CHD lesions in children for the evaluation of complex cardiac anatomy, quantification of ventricular and valvular function, and myocardial characterization. A primary mode of myocardial characterization is with post-contrast LGE imaging.589The standard LGE imaging is performed ~10 min following intravenous administration of 0.1–0.2 mmol/kg of gadolinium-based contrast agent (GBCA). Because of increased cardiac output, LGE imaging in pediatrics can start as early as 6 min after infusion. It should be noted that due to the risk of nephrogenic systemic fibrosis, the use of GBCA should be used with caution in acute or chronic renal disease. Multiple versions of the sequence have been developed since it was first introduced.Masses (see Tumor section) CMR with LGE imaging is very useful in the evaluation of pediatric cardiac masses because of its tissue characterization capabilities, allowing a narrowing of differential diagnoses. Cardiac mass evaluation includes standard cine, T1-weighted, and T2-weighted, perfusion and LGE sequences. Using LGE in a comprehensive study of cardiac masses adds significantly to the differentiation of common tumor types.477 This is particularly true for fibroma that shows marked enhancement. In addition, CMR using LGE and a TI scout following gadolinium administration is highly accurate in discerning tumor versus chronic thrombus.483Myocarditis and Other Inflammatory Diseases (See Myocarditis Section) LGE is a primary component of the CMR myocarditis evaluation..509 The presence of LGE in patients with suspected myocarditis has a high specificity with the signal thought to represent areas of necrosis or fibrosis. The LGE lesions are typically patchy, subepicardial, located in the basal or mid-ventricular segments, and are not in a coronary distribution. The median area under the ROC curve for LGE alone in myocarditis is 83% but that is much improved when other criteria are taken into account. It is sensitive for acute myocarditis with large severely affected areas. It is not sensitive for mild cases and does not yield information regarding acute edema or active inflammation.CHD In a variety of both unrepaired and repaired CHD, LGE imaging has been investigated . Scarring can be an iatrogenic complication when a coronary is injured or there is a problem with cardiopulmonary bypass or myocardial protection. The following lists some of the applications in CHD but is certainly not comprehensive. Figures , 42, 43 117 A greater degree of RV LGE has been shown to be associated with arrhythmias and lower exercise capacity, all of which imply poor prognosis.118In TOF (see TOF section), LGE is normally detected in the RVOT , particularly following transannular patch repair, but occasionally extends beyond the site.365 LGE can be seen because of myocardial fibrosis from either preoperative hypoxemia or from demand–supply mismatch caused by increased myocardial mass or decreased myocardial flow reserve. The extent of LGE correlates with age, RV dysfunction, QRS duration, QT dispersion and clinical events (arrhythmia and sudden cardiac death).LGE is seen in patients following both the ASO and atrial switch procedure for TGA (see TGA section).50 and can be seen in the LV of patients with HLHS as endocardial fibroelastosis (see SV section). Presence and extent of LGE correlate with lower ejection fraction, dilated and hypertrophied systemic ventricle, regional wall motion abnormalities and NSVT; however, positive LGE is shown not to be associated with clinical endpoints (i.e. death or listing for cardiac transplant).LGE has been seen in 28% of patients who had the Fontan operation592 Subendocardial LGE in adolescents who underwent balloon valvuloplasty in infancy corresponds to fibroelastosis on pathology and is associated with diastolic dysfunction.Congenital aortic valvular stenosis in children is caused by developmentally abnormal dysplastic aortic valve. Severe aortic stenosis can result in myocardial fibrosis manifested as LGE in a diffuse subendocardial pattern.Ischemic Lesions (See Coronary Section) Although rare in children and adolescents, myocardial infarctions occur as a result of cardiac surgery, thrombotic events, inflammatory heart disease (including Kawasaki disease) and hypercoagulable states.594 This becomes even more important with patients who have congenital coronary abnormalities  or who have had coronary manipulation due to CHD . CMR has an important role in the evaluation of myocardial infarction and LGE is useful in establishing the diagnosis and extent of ischemic myocardial injury. LGE in a myocardial infarct is always subendocardial extending toward the epicardium and becoming transmural in severe infarctions. LGE can be used to quantify the scar either in a qualitative or quantitative manner. There is an inverse correlation between the extent of scar and recovery of contractile function.Pericardial Disease CMR is used in the diagnosis and management of both acute and chronic pericarditis. Acute pericarditis manifests with pericardial thickening (> 4 mm) and pericardial effusion. Most standard acute pericarditis does not require CMR. LGE imaging shows focal or diffuse pericardial enhancement.517 More complicated cases of recurrent or chronic pericarditis often require advanced imaging and studies have shown the correlation between pericardial enhancement and systemic inflammation. Chronic pericarditis results in restriction from non-compliant and thickened pericardium. In patients with constrictive pericarditis who have LGE as evidence of pericardial inflammation, aggressive anti-inflammatory therapy may result in resolution without the need for surgery.Hypertrophic Cardiomyopathy (See Hypertrophic Cardiomyopathy Section) LGE is seen in 40–80% of adults with HCM. Recent studies in children have shown LGE in 28–73% of patients in a similar pattern as in adults. LGE has been shown to have diagnostic importance for both diagnosis and management. It is correlated with adverse clinical outcomes including arrhythmia and SCD in both children and adults.419 There is a significant relationship between the extent of LGE and the presence of NSVT.Dilated Cardiomyopathy CMR demonstrates linear mid-myocardial LGE in a non-vascular distribution in patients with idiopathic DCM. The presence of LGE, regardless of its extent or distribution, is associated with adverse prognosis such as SCD. In children, a study performed on a group with DCM showed the presence of LGE in only 16%.595Neuromuscular Disease CMR is the standard for longitudinal evaluation of neuromuscular disease patients as they age and echocardiography becomes more difficult. LGE is an important part of these exams as increase in signal likely represents fibrofatty replacement of myocardium and portends onset of declining function.474CMR with LGE is recommended for evaluation of cardiac tumors or masses. CMR with LGE is indicated for assessment of suspected myocarditis CMR with LGE is reasonable for assessment of post-operative CHD CMR with LGE is indicated for assessment of pediatric HCM, dilated cardiomyopathy and neuromuscular disease patients CMR with LGE should be used for myocardial viability assessment in pediatric patients with decreased ventricular function, suspicion of a CHD, acquired, or iatrogenic coronary lesions .CMR with LGE can be beneficial for assessment of chronic pericarditis when the diagnosis or therapeutic strategy is unclear Not applicable.All authors contributed substantially to the research, writing and editing of these guidelines. All recommendations were voted on by the writing committee. All authors read and approved the final manuscript.There was no funding for this guidelines manuscript.Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.Not applicable.Not applicable.The authors declare that they have no competing interests.