Lung (a-EIT, td-EIT)<unk>  is particularly useful for monitoring lung function because lung tissue resistivity is five times higher than most other soft tissues in the thorax. This results in high absolute contrast of the lungs. In addition, lung resistivity increases and decreases several-fold between inspiration and expiration which explains why monitoring ventilation is currently the most promising clinical application of<unk>  since mechanical ventilation frequently results in ventilator-associated lung injury (VALI). The feasibility of<unk>  for lung imaging was first demonstrated at Rensselaer Polytechnic Institute in 1990 using the NOSER algorithm. Time difference<unk>  can resolve the changes in the distribution of lung volumes between dependent and non-dependent lung regions and assist in adjusting ventilator settings to provide lung protective ventilation to patients during critical illness or anesthesia. Most<unk>  studies have focused on monitoring regional lung function using the information determined by time difference<unk>  (td-EIT). However absolute<unk>  (a-EIT) also has the potential to become a clinically useful tool for lung imaging, as this approach would allow one to directly distinguish between lung conditions which result from regions with lower resistivity (e.g. hemothorax, pleural effusion, atelectasis, lung edema) and those with higher resistivity (e.g. pneumothorax, emphysema). Adhesive electrodes on chest of a 10-day-old baby<unk>  reconstruction (left) and impedance change over six breaths, from. Data available on The above image shows an<unk>  study of a 10-day-old baby breathing normally with 16 adhesive electrodes applied to the chest. Image reconstruction from absolute impedance measurements requires consideration of the exact dimensions and shape of a body as well as the precise electrode location since simplified assumptions would lead to major reconstruction artifacts. While initial studies assessing aspects of absolute<unk>  have been published, this area of research has not yet reached the level of maturity which would make it suitable for clinical use. In contrast, time difference<unk>  determines relative impedance changes that may be caused by<unk> her ventilation or changes of end-expiratory lung volume. These relative changes are referred to a baseline level, which is typically defined by the intra-thoracic impedance distribution at the end of expiration. Time difference<unk>  images can be generated continuously and right at the bedside. These attributes make regional lung function monitoring particularly useful whenever there is a need to improve oxygenation or CO2 elimination and when therapy changes are intended to achieve a more homogenous gas distribution in mechanically ventilated patients.<unk>  lung imaging can resolve the changes in the regional distribution of lung volumes between e.g. dependent and non-dependent lung regions as ventilator parameters are changed. Thus,<unk>  measurements may be used to guide specific ventilator settings to maintain lung protective ventilation for each patient. Besides the applicability of<unk>  in the ICU, first studies with spontaneously breathing patients reveal further promising applications. The high temporal resolution of<unk>  allows regional assessment of common dynamic parameters used in pulmonary function testing (e.g. forced expiratory volume in 1 second). Additionally, specially developed image fusion methods overlaying functional<unk> -data with morphological patient data (e.g. CT or MRI images) may be used to get a comprehensive insight into the pathophysiology of the lungs, which might be useful for patients suffering from obstructive lung diseases (e.g. COPD, CF). After many years of lung<unk>  research with provisional<unk>  equipment or series models manufactured in very small numbers, two commercial systems for lung<unk>  have recently entered the medical technology market: Dräger's PulmoVista® 500 and Swisstom AG's Swisstom BB2. Both models are currently being installed in intensive care units and are already used as aides in decision making processes related to the treatment of patients with acute respiratory distress syndrome (ARDS). The increasing availability of commercial<unk>  systems in ICUs will show whether the promising body of evidence obtained from animal models will apply to humans as well <unk> -guided lung recruitment, selection of optimum PEEP levels, pneumothorax detection, prevention of ventilator associated lung injury (VALI), etc.). This would be highly desirable, given that recent studies suggest that 15% of mechanically ventilated patients in the ICU will develop acute lung injury (ALI) with attendant progressive lung collapse and which is associated with a reportedly high mortality of 39%. Just recently, the first prospective animal trial on<unk> -guided mechanical ventilation and outcome could demonstrate significant benefits in regard to respiratory mechanics, gas exchange, and histological signs of ventilator-associated lung injury. In addition to visual information (e.g. regional distribution of tidal volume),<unk>  measurements provide raw data sets that can be used to calculate other helpful information (e.g. changes of intrathoracal gas volume during critical illness) – however, such parameters still require careful evaluation and validation. Another interesting aspect of thoracic<unk>  is its ability to record and filter pulsatile signals of perfusion. Although promising studies have been published on this topic, this technology is still at its beginnings. A breakthrough would allow simultaneous visualization of both regional blood flow and regional ventilation – enabling clinicians to locate and react upon physiological shunts caused by regional mismatches of lung ventilation and perfusion with associated hypoxemia. Breast (MF-EIT)<unk>  is being investigated in the field of breast imaging as an alternative/complementary technique to mammography and magnetic resonance imaging (MRI) for breast cancer detection. The low specificity of mammography and of MRI result in a relatively high rate of false positive screenings, with high distress for patients and cost for healthcare structures. Development of alternative imaging techniques for this indication would be desirable due to the shortcomings of the existing methods: ionizing radiation in mammography and the risk of inducing nephrogenic systemic fibrosis (NSF) in patients with decreased renal function by administering the contrast agent used in breast MRI, Gadolinium. Literature shows that the electrical properties differ between normal and malignant breast tissues, setting the stage for cancer detection through determination of electrical properties. An early commercial development of non-tomographic electrical impedance imaging was the T-Scan device which was reported to improve sensitivity and specificity when used as an adjunct to screening mammography. A report to the United States Food and Drug Administration (FDA) describes a study involving 504 subjects where the sensitivity of mammography was 82%, 62% for the T-Scan alone, and 88% for the two combined. The specificity was 39% for mammography, 47% for the T-Scan alone, and 51% for the two combined. Several research groups across the world are actively developing the technique. A frequency sweep seems to be an effective technique for detecting breast cancer using<unk> . United States Patent US 8,200,309 B2 combines electrical impedance scanning with magnetic resonance low frequency current density imaging in a clinically acceptable configuration not requiring the use of gadolinium chelate enhancement in magnetic resonance mammography. Cervix (MF-EIT) In addition to his pioneering role in the development of the first<unk>  systems in Sheffield professor Brian H. Brown is currently active in the research and development of an electrical impedance spectroscope based on MF-EIT. According to a study published by Brown in 2000, MF-EIT is able to predict Cervical intraepithelial neoplasia (CIN) grades 2 and 3 according to Pap smear with a sensitivity and specificity of 92% each. Whether cervical MF-EIT is going to be introduced as an adjunct or an alternative to the Pap smear has yet to be decided. Brown is academic founder of Zilico Limited which distributes the spectroscope (ZedScan I). The device received EC certification from its Notified Body in 2013 and is currently being introduced into a number of clinics in the UK and healthcare systems across the globe. Brain (a-EIT, td-EIT, mf-EIT)<unk>  has been suggested as a basis for brain imaging to enable detection and monitoring of cerebral ischemia, haemorrhage, and other morphological pathologies associated with impedance changes due to neuronal cell swelling, i.e. cerebral hypoxemia and hypoglycemia. While<unk> ’s maximum spatial resolution of approximately 15% of the electrode array diameter is significantly lower than that of cerebral CT or MRI (about one millimeter), temporal resolution of<unk>  is much higher than in CT or MRI (0.1 milliseconds compared to 0.1 seconds). This makes<unk>  also interesting for monitoring normal brain function and neuronal activity in intensive care units or the preoperative setting for localization of epileptic foci by telemetric recordings. Holder was able to demonstrate in 1992 that changes of intracerebral impedance can be detected noninvasively through the cranium by surface electrode measurements. Animal models of experimental stroke or seizure showed increases of impedance of up to 100% and 10%, respectively. More recent<unk>  systems offer the option to apply alternating currents from non-adjacent drive electrodes. So far, cerebral<unk>  has not yet reached the maturity to be adopted in clinical routine, yet clinical studies are currently being performed on stroke and epilepsy. In this use<unk>  depends upon applying low frequency currents above the skull that are around 2 or arterial blood pressure in sports medicine or home care.
Electrical impedance tomography
Impedance–pH monitoring
Impedance threshold device
Gastric tonometry
Sweat test
Esophageal pH monitoring
Salicylate testing
Electrical impedance myography