studies have shown that most acute coronary syndromes ( acs ) result from the rupture of unstable plaques and subsequent thrombus formation ( 1 , 2 ) . the risk of atherosclerotic plaque disruption and thrombosis is thought to be closely related to plaque composition rather than the severity of an actual luminal stenosis ( 3 - 5 ) . therefore , it is of paramount clinical importance to elucidate the composition of coronary atherosclerotic plaques . the atherosclerotic plaque imaging is the arterial wall imaging ( 6 , 7 ) . atherosclerosis is a systemic disease of the vessel wall that occurs frequently in the aorta and in the carotid , coronary and peripheral arteries . the formation and development of the atherosclerotic plaque is at the arterial intima . a number of publications ( 8 - 10 ) showed that vivo and ex vivo mr imaging can characterize the composition of great vessels , such as carotid and aortic atherosclerotic plaques . however , imaging the coronary artery wall with magnetic resonance in vivo is challenging due to the cardiac and respiratory motion artifacts , smaller size and tortuous course . currently , bright blood technique is usually used in imaging human coronary artery in vivo ( 11 ) . although the black blood technique was used in human coronary artery studies in vivo ( 12 - 14 ) , only coronary wall thickening could be delineated but the compositions of coronary atherosclerotic plaque were not identified . poor spatial resolution is another limitation for mri when identifying coronary atherosclerotic plaque composition in vivo . but the studies were minimal and the procedure was complicated , the coronary artery was dissected from heart ( 15 , 16 ) . recent study demonstrated that ex vivo mri imaging can classify the human coronary atherosclerotic plaques ( 17 ) . the general purpose of the present study is to investigate the feasibility and optimize imaging protocol for ex vivo porcine and human coronary artery wall using mri , thus , potentially directing vivo mr vessel wall imaging techniques for characterizing coronary atherosclerotic plaques . initially , to derive optimal protocol for ex vivo coronary artery wall imaging , 10 fresh porcine hearts ( weighted from 500 g to 750 g ) were prospectively studied with mri on the day of explanation . , the heart was flushed with water to clear clots within the chambers and coronary arteries , and then , a three - way tube was inserted into the left main coronary artery through the left coronary sinus and fixed in order to inject the contrast . to null the lumen and improve the contrast between the wall and lumen , 20 ml of diluted mri contrast medium containing iron - oxide particles ferucarbotran ( resovist , spio , bayer schering pharma , berlin , germany ) was injected into the lad via the three - way tube , mimicking black blood technique . the optimal proportion of mr contrast agent and saline solution was 1% vs. 99% ( 17 ) . the porcine heart was imaged by using the signa 1.5 t hd mr scanner ( ge medical systems ) . to investigate optimal coronary vessel wall delineation , three different surface coils were respectively used as described in table 1 ( temporomandibular surface coil , eight - channel head surface coil and knee coil ) . the 3-planar imaging was used for the localization and 3d steady state free precession ( ssfp ) sequence was used to delineate lad with repeat time ( tr ) 7.5 ms , echo time ( te ) 3.1 ms , field of view ( fov ) 12  12 cm , slice thickness 3.0 mm , slice space 1.5 mm , matrix 256  192 , number of excitations ( nex ) 1 ( fig . , 10 ml saline solution was injected into the left coronary artery via a three - way tube . then , 2d spin - echo t1-weighted image ( t1wi ) with fat saturation was performed respectively with temporomandibular surface coil , eight - channel head surface coil and knee coil using the same parameters ( tr 440 ms , te 21 ms , fov 12  9 cm , slice 2 mm , slice space 0.2 mm , matrix 384  256 , a resolution in - plane of 313  352 um , 3 signal averages ) . the purpose of using different coil imaging 2d spin - echo t1w1 was to select the coil with the highest snr image . next , 2d spin - echo t1wi was repeated with temporomandibular surface coil and matrix 512  512 ( same other parameters ) . the purpose of using 512  512 in matrix was to investigate if the snr and cnr of the images were acceptable on the basis of higher spatial resolution . lastly , t1wi , proton density - weighted image ( pdwi ) and fast spin echo t2-weighted image ( fse t2wi ) with fat saturation , were performed by using temporomandibular surface coil after mr contrast injection . the parameters of t1wi were tr 440 ms , te 21 ms , fov 12  9 cm , slice 2 mm , slice space 0.2 mm , matrix 512  512 , a resolution in - plane of 234  176 um , 3 signal averages . the parameters of pdw included tr 2000 ms , te 21 ms , fov 12  9 cm , slice 2 mm , slice space 0.2 mm , matrix 512  512 , 3 signal averages . the parameters of t2wi were tr 4500 ms , te 105 ms , fov 12  9 cm , slice 2 mm , slice space 0.2 mm , matrix 512  512 , 3 signal averages . the hearts from 8 consecutive autopsy subjects with known coronary artery diseases ( 8 males aged from 84 to 90 years with a mean age of 86.3  1.4 years , 4 died from malignancy , 3 from infections and 1 with myocardial infarction ) underwent the coronary mr examinations . the imaging protocols were described above , with temporomandibular surface coil and matrix 512  512 . although the snr and cnr with 512  512 images in matrix were lower than those with 384  256 in matrix ( the increase in matrix and spatial resolution will consequentially sacrifice snr ) using temporomandibular surface coil , spatial resolution was remarkably increased and image quality was better than the 384  256 in matrix with eight - channel head coil and knee coil . therefore , we imaged human coronary artery wall with temporomandibular surface coil and 512  512 in matrix . the proximal 40 mm of the lad was sectioned into 10 tissue blocks of 4 mm in thickness , and the distance from the tissue block to the bifurcation of the left main coronary artery was recorded to match with mr images . after decalcification , the tissue blocks were embedded in paraffin and prepared for histological examination in sections 4-m thick . blocks were stained with haematoxylene and eosin ( he ) . to test the optimal protocol for ex vivo coronary artery wall imaging , the proximal segment of lad in porcine heart was chosen as a target vessel . signals of the lad wall , lumen , surrounded by fatty tissues adjacent to lad , myocardium of anterior part of interventricular septum and noise were respectively measured . snr of image , cnr1 between the lad wall and lumen , cnr2 between the lad wall and surrounding fatty tissue were respectively calculated . two experienced radiologist , blinded to the histopathology results , evaluated the original two - dimensional , cross - sectional mr images independently and collectively resolved any differences in reading . each reader classified the plaque independently twice , 2 months apart , to determine the intra - observer variability . the plaques were classified according to the aha criteria and modified the histological classification by cai et al . mri can not distinguish type iv lesion from type v lesion , so they are called type iv - v ( lipid , necrosis , fibrosis ) lesion . type iv - v lesions showed high or equal signal intensity on t1wi and pdw , low or equal signal intensity on t2wi . type vi ( sub - acute hemorrhage ) lesions showed high signal intensity on t1wi and t2wi . type viii ( fibrosis without lipid core ) lesions had equal signal intensity on t1wi and high or equal signal intensity on t2wi . for each image location , there were three images ( t1wi , pdw , t2wi ) available for reviews to determine the lesion type . to decrease dependence on lesion type , mr images of proximal 40 mm of lad were selected at a 4-mm interval ( originally 14 - 20 images , selected 1 from 2 images ) . this protocol generated 7 to 10 image locations per lad that could be compared with histological sections . the histopathologic sections were analyzed by an experienced pathologist who was blinded to the mri results , and plaques were classified according to the aha criteria ( 19 , 20 ) . i.e. , type iv - v ( lipid , necrosis , fibrosis ) ; type vi ( hemorrhage ) ; type vii ( calcification ) and type viii ( fibrosis without lipid core ) . mri images and histopathologic sections were matched prospectively in the region of the proximal 40 mm of the lad . the process of matching images to histopathologic sections used landmarks such as the relative distance from the left main trunk bifurcation , and some morphological features such as vessel shapes and lumen sizes , the location of the lad branches , as well as calcifications . for the porcine hearts , comparisons of the snr , cnr1 , cnr2 of t1wi using temporomandibular surface coil , eight - channel head surface coil and knee coil were performed using analysis of variance , with p - value < 0.05 considered statistically significant . comparisons of the snr and cnr of t1wi using temporomandibular surface coil with different matrix were performed using analysis of variance . for the human hearts , the sensitivity , specificity and accuracy of mri for classifying the plaques were calculated . to test for intra - observer and inter - observer agreements of mri - based plaque classification , initially , to derive optimal protocol for ex vivo coronary artery wall imaging , 10 fresh porcine hearts ( weighted from 500 g to 750 g ) were prospectively studied with mri on the day of explanation . , the heart was flushed with water to clear clots within the chambers and coronary arteries , and then , a three - way tube was inserted into the left main coronary artery through the left coronary sinus and fixed in order to inject the contrast . to null the lumen and improve the contrast between the wall and lumen , 20 ml of diluted mri contrast medium containing iron - oxide particles ferucarbotran ( resovist , spio , bayer schering pharma , berlin , germany ) was injected into the lad via the three - way tube , mimicking black blood technique . the optimal proportion of mr contrast agent and saline solution was 1% vs. 99% ( 17 ) . the porcine heart was imaged by using the signa 1.5 t hd mr scanner ( ge medical systems ) . to investigate optimal coronary vessel wall delineation , three different surface coils were respectively used as described in table 1 ( temporomandibular surface coil , eight - channel head surface coil and knee coil ) . the 3-planar imaging was used for the localization and 3d steady state free precession ( ssfp ) sequence was used to delineate lad with repeat time ( tr ) 7.5 ms , echo time ( te ) 3.1 ms , field of view ( fov ) 12  12 cm , slice thickness 3.0 mm , slice space 1.5 mm , matrix 256  192 , number of excitations ( nex ) 1 ( fig . , 10 ml saline solution was injected into the left coronary artery via a three - way tube . then , 2d spin - echo t1-weighted image ( t1wi ) with fat saturation was performed respectively with temporomandibular surface coil , eight - channel head surface coil and knee coil using the same parameters ( tr 440 ms , te 21 ms , fov 12  9 cm , slice 2 mm , slice space 0.2 mm , matrix 384  256 , a resolution in - plane of 313  352 um , 3 signal averages ) . the purpose of using different coil imaging 2d spin - echo t1w1 was to select the coil with the highest snr image . next , 2d spin - echo t1wi was repeated with temporomandibular surface coil and matrix 512  512 ( same other parameters ) . the purpose of using 512  512 in matrix was to investigate if the snr and cnr of the images were acceptable on the basis of higher spatial resolution . lastly , t1wi , proton density - weighted image ( pdwi ) and fast spin echo t2-weighted image ( fse t2wi ) with fat saturation , were performed by using temporomandibular surface coil after mr contrast injection . the parameters of t1wi were tr 440 ms , te 21 ms , fov 12  9 cm , slice 2 mm , slice space 0.2 mm , matrix 512  512 , a resolution in - plane of 234  176 um , 3 signal averages . the parameters of pdw included tr 2000 ms , te 21 ms , fov 12  9 cm , slice 2 mm , slice space 0.2 mm , matrix 512  512 , 3 signal averages . the parameters of t2wi were tr 4500 ms , te 105 ms , fov 12  9 cm , slice 2 mm , slice space 0.2 mm , matrix 512  512 , 3 signal averages . the hearts from 8 consecutive autopsy subjects with known coronary artery diseases ( 8 males aged from 84 to 90 years with a mean age of 86.3  1.4 years , 4 died from malignancy , 3 from infections and 1 with myocardial infarction ) underwent the coronary mr examinations . the imaging protocols were described above , with temporomandibular surface coil and matrix 512  512 . although the snr and cnr with 512  512 images in matrix were lower than those with 384  256 in matrix ( the increase in matrix and spatial resolution will consequentially sacrifice snr ) using temporomandibular surface coil , spatial resolution was remarkably increased and image quality was better than the 384  256 in matrix with eight - channel head coil and knee coil . therefore , we imaged human coronary artery wall with temporomandibular surface coil and 512  512 in matrix . the proximal 40 mm of the lad was sectioned into 10 tissue blocks of 4 mm in thickness , and the distance from the tissue block to the bifurcation of the left main coronary artery was recorded to match with mr images . after decalcification , the tissue blocks were embedded in paraffin and prepared for histological examination in sections 4-m thick . to test the optimal protocol for ex vivo coronary artery wall imaging , the proximal segment of lad in porcine heart was chosen as a target vessel . signals of the lad wall , lumen , surrounded by fatty tissues adjacent to lad , myocardium of anterior part of interventricular septum and noise were respectively measured . snr of image , cnr1 between the lad wall and lumen , cnr2 between the lad wall and surrounding fatty tissue were respectively calculated . two experienced radiologist , blinded to the histopathology results , evaluated the original two - dimensional , cross - sectional mr images independently and collectively resolved any differences in reading . each reader classified the plaque independently twice , 2 months apart , to determine the intra - observer variability . the thickness of the vessel wall and signal of plaque were recorded . the plaques were classified according to the aha criteria and modified the histological classification by cai et al . mri can not distinguish type iv lesion from type v lesion , so they are called type iv - v ( lipid , necrosis , fibrosis ) lesion . type iv - v lesions showed high or equal signal intensity on t1wi and pdw , low or equal signal intensity on t2wi . type vi ( sub - acute hemorrhage ) lesions showed high signal intensity on t1wi and t2wi . type viii ( fibrosis without lipid core ) lesions had equal signal intensity on t1wi and high or equal signal intensity on t2wi . for each image location , there were three images ( t1wi , pdw , t2wi ) available for reviews to determine the lesion type . to decrease dependence on lesion type , mr images of proximal 40 mm of lad were selected at a 4-mm interval ( originally 14 - 20 images , selected 1 from 2 images ) . this protocol generated 7 to 10 image locations per lad that could be compared with histological sections . the histopathologic sections were analyzed by an experienced pathologist who was blinded to the mri results , and plaques were classified according to the aha criteria ( 19 , 20 ) . i.e. , type iv - v ( lipid , necrosis , fibrosis ) ; type vi ( hemorrhage ) ; type vii ( calcification ) and type viii ( fibrosis without lipid core ) . mri images and histopathologic sections were matched prospectively in the region of the proximal 40 mm of the lad . the process of matching images to histopathologic sections used landmarks such as the relative distance from the left main trunk bifurcation , and some morphological features such as vessel shapes and lumen sizes , the location of the lad branches , as well as calcifications . to test the optimal protocol for ex vivo coronary artery wall imaging , the proximal segment of lad in porcine heart was chosen as a target vessel . signals of the lad wall , lumen , surrounded by fatty tissues adjacent to lad , myocardium of anterior part of interventricular septum and noise were respectively measured . snr of image , cnr1 between the lad wall and lumen , cnr2 between the lad wall and surrounding fatty tissue were respectively calculated . to test the delineation of atherosclerotic plaque , the ex vivo human hearts were evaluated . two experienced radiologist , blinded to the histopathology results , evaluated the original two - dimensional , cross - sectional mr images independently and collectively resolved any differences in reading . each reader classified the plaque independently twice , 2 months apart , to determine the intra - observer variability . the thickness of the vessel wall and signal of plaque were recorded . the plaques were classified according to the aha criteria and modified the histological classification by cai et al . mri can not distinguish type iv lesion from type v lesion , so they are called type iv - v ( lipid , necrosis , fibrosis ) lesion . type iv - v lesions showed high or equal signal intensity on t1wi and pdw , low or equal signal intensity on t2wi . type vi ( sub - acute hemorrhage ) lesions showed high signal intensity on t1wi and t2wi . type viii ( fibrosis without lipid core ) lesions had equal signal intensity on t1wi and high or equal signal intensity on t2wi . for each image location , there were three images ( t1wi , pdw , t2wi ) available for reviews to determine the lesion type . to decrease dependence on lesion type , mr images of proximal 40 mm of lad were selected at a 4-mm interval ( originally 14 - 20 images , selected 1 from 2 images ) . this protocol generated 7 to 10 image locations per lad that could be compared with histological sections . the histopathologic sections were analyzed by an experienced pathologist who was blinded to the mri results , and plaques were classified according to the aha criteria ( 19 , 20 ) . i.e. , type iv - v ( lipid , necrosis , fibrosis ) ; type vi ( hemorrhage ) ; type vii ( calcification ) and type viii ( fibrosis without lipid core ) . mri images and histopathologic sections were matched prospectively in the region of the proximal 40 mm of the lad . the process of matching images to histopathologic sections used landmarks such as the relative distance from the left main trunk bifurcation , and some morphological features such as vessel shapes and lumen sizes , the location of the lad branches , as well as calcifications . for the porcine hearts , comparisons of the snr , cnr1 , cnr2 of t1wi using temporomandibular surface coil , eight - channel head surface coil and knee coil were performed using analysis of variance , with p - value < 0.05 considered statistically significant . comparisons of the snr and cnr of t1wi using temporomandibular surface coil with different matrix were performed using analysis of variance . for the human hearts , the sensitivity , specificity and accuracy of mri for classifying the plaques were calculated . to test for intra - observer and inter - observer agreements of mri - based plaque classification , the snr , cnr1 and cnr2 of t1wi using temporomandibular surface coil , eight - channel head surface coil and knee coil were summarized in table 1 . the snr , cnr1 and cnr2 of t1wi using temporomandibular surface coil were higher than those using eight - channel head surface coil and knee coil ( p < 0.05 ) ( fig . 2 ) . the snr and cnr2 of t1wi using knee coil were higher than those using eight - channel head surface coil ( p < 0.05 ) . however , the cnr1 of t1wi using knee coil was higher than that using eight - channel head surface coil and did not reach statistical significance ( p > 0.05 ) . the snr and cnr1 and cnr2 of t1wi with 512  512 in matrix using temporomandibular surface coil were lower than those with 384  256 in matrix ( p < 0.05 ) ( fig . 3 ) , but markedly higher than those using eight - channel head coil and knee coil with 384  256 in matrix ( p < 0.05 ) . accordingly , the image quality of t1wi , pdw and t2wi with 512  512 in matrix using temporomandibular surface coil was still satisfactory due to the coronary artery wall visualized clearly , accompanying higher spatial resolution compared with 384  256 in matrix ( fig . a total of 58 mri images from the 8 hearts were matched with corresponding histopathologic sections . among the histopathologic sections , there were 18 lipid - rich plaque sections ( type iv - v ) ( 31% ) ( fig . 5 ) , 4 hemorrhage plaque sections ( type vi ) ( 7% ) ( fig . 6 ) , 33 calcified plaque sections ( type vii ) ( 57% ) ( fig . 7 ) , and 3 fibrous plaque sections ( type viii ) ( 5% ) ( fig . 8) . the accuracy of mri for classification of plaques was 93% ( 54/58 ) , and the distribution of plaques was shown in table 2 . the sensitivity and specificity of mri for identifying different types of plaques were : type iv - v , 94% and 95% ; type vi , 100% and 98% ; type vii , 91% and 100% ; and type viii , 100% and 98% , respectively . intra - observer agreement among two readers for two readings with 2 months apart was excellent ( k = 0.85 and k = 0.83 ) . agreement between two readers was also very good for plaque classification ( k = 0.8 ) . the snr , cnr1 and cnr2 of t1wi using temporomandibular surface coil , eight - channel head surface coil and knee coil were summarized in table 1 . the snr , cnr1 and cnr2 of t1wi using temporomandibular surface coil were higher than those using eight - channel head surface coil and knee coil ( p < 0.05 ) ( fig . 2 ) . the snr and cnr2 of t1wi using knee coil were higher than those using eight - channel head surface coil ( p < 0.05 ) . however , the cnr1 of t1wi using knee coil was higher than that using eight - channel head surface coil and did not reach statistical significance ( p > 0.05 ) . the snr and cnr1 and cnr2 of t1wi with 512  512 in matrix using temporomandibular surface coil were lower than those with 384  256 in matrix ( p < 0.05 ) ( fig . 3 ) , but markedly higher than those using eight - channel head coil and knee coil with 384  256 in matrix ( p < 0.05 ) . accordingly , the image quality of t1wi , pdw and t2wi with 512  512 in matrix using temporomandibular surface coil was still satisfactory due to the coronary artery wall visualized clearly , accompanying higher spatial resolution compared with 384  256 in matrix ( fig . a total of 58 mri images from the 8 hearts were matched with corresponding histopathologic sections . among the histopathologic sections , there were 18 lipid - rich plaque sections ( type iv - v ) ( 31% ) ( fig . 5 ) , 4 hemorrhage plaque sections ( type vi ) ( 7% ) ( fig . 6 ) , 33 calcified plaque sections ( type vii ) ( 57% ) ( fig . 7 ) , and 3 fibrous plaque sections ( type viii ) ( 5% ) ( fig . 8) . the accuracy of mri for classification of plaques was 93% ( 54/58 ) , and the distribution of plaques was shown in table 2 . the sensitivity and specificity of mri for identifying different types of plaques were : type iv - v , 94% and 95% ; type vi , 100% and 98% ; type vii , 91% and 100% ; and type viii , 100% and 98% , respectively . intra - observer agreement among two readers for two readings with 2 months apart was excellent ( k = 0.85 and k = 0.83 ) . agreement between two readers was also very good for plaque classification ( k = 0.8 ) . the major findings of the study were 2-folded : firstly , we found that visualizing the coronary artery wall in vitro using temporomandibular surface coil was of the highest snr and cnr ; secondly , we demonstrated that high - resolution mri closely agrees with histopathology in the detection of human coronary atherosclerotic plaques compositions and classification of plaques . the 2.5-inch temporomandibular surface coil is dramatically superior to eight - channel head surface coil and knee coil in ex vivo coronary artery wall imaging . however , knee coil was commonly used in ex vivo coronary artery imaging with magnetic resonance techniques in previous literatures ( 6 , 21 ) . the snr and cnr of small objects such as coronary arterial wall are improved as the diameter of surface coil decreases . the 2.5-inch temporomandibular surface coil is dramatically smaller than eight - channel head surface coil and knee coil , and matches very well with the coronary artery . therefore , we used the temporomandibular surface coil and the snr and cnr of coronary artery wall imaging were markedly higher than those using eight - channel head surface coil and knee coil . to our knowledge , this is the first report to image coronary artery wall ex vivo using temporomandibular surface coil . ex vivo high - resolution mri was able to distinguish human coronary atherosclerotic plaque composition and accurately classify advanced plaques . based on composition , the aha classifies coronary atherosclerotic plaques into 8 different types ( 19 , 20 ) . type i - iii plaques belong to early lesions , which can be dissipated ; and type iv - viii plaques belong to advanced lesions . type iv - v ( lipid , necrosis , fibrosis ) lesions showed high or equal signal intensity on t1wi and pdw , low or equal signal intensity on t2wi . type vi ( sub - acute hemorrhage ) lesions showed high signal intensity on t1wi and t2wi . type viii ( fibrosis without lipid core ) lesions had equal signal intensity on t1wi and high or equal signal intensity on t2wi . in this study , the sensitivity and specificity of mri for classifying advanced plaques were high ( type iv - v , 94% and 95% ; type vi , 100% and 98% ; type vii , 91% and 100% ; and type viii , 100% and 98% , respectively ) . one method is using the high - field mri scanner , in which snr and spatial resolution can be further improved ( 22 , 23 ) . secondly , the number of fibrous plaques was limited because type viii lesions are rare and may have a potential influence on the assessment of type viii lesions . thirdly , the whole coronary arteries including rca and lcx ca n't be covered because the temporomandibular surface coil is smaller than the knee joint and head coils . temporomandibular surface coil was dramatically superior to eight - channel head coil and knee coil for ex vivo coronary artery wall imaging , providing for higher spatial resolution and improved snr with 512  512 in matrix . ex vivo high - resolution mri was able to distinguish human coronary atherosclerotic plaque compositions and accurately classify advanced plaques , which may be helpful for directing the development and optimizing the vivo mr vessel wall imaging techniques for characterizing coronary atherosclerotic plaques . temporomandibular surface coil was dramatically superior to eight - channel head coil and knee coil for ex vivo coronary artery wall imaging , providing for higher spatial resolution and improved snr with 512  512 in matrix . ex vivo high - resolution mri was able to distinguish human coronary atherosclerotic plaque compositions and accurately classify advanced plaques , which may be helpful for directing the development and optimizing the vivo mr vessel wall imaging techniques for characterizing coronary atherosclerotic plaques .