A status report for medical impedance imaging

Biomedical impedance imaging forms images of the interior of the human body based on the passive electrical properties of the body tissues. Because the electrical properties of different tissues art different, and some tissues' properties change with their functional state, clinical monitoring for abnormal function, particularly of the heart and lungs, may be possible. This paper reviews the current state of this technology, its possible medical applications, and speculates on future directions for the field. Impedance imaging is most highly developed for two-dimensional, cylindrical applications. The ability of impedance imaging systems to show changes in conductivity is much greater than their ability to show absolute, or static conductivity values. Most present systems make a reference data set under some conditions, such as at end-expiration of a breath. They then form images of the changes that occur in later datasets, for example during inspiration. These images of changes are called dynamic images, and in this case would show areas such as the lungs, whose conductivity changed during inspiration. Image accuracy and resolution are reduced when the object studied is 3-dimensional, or is not of circular cross-section.