Electrical impedance of layered atherosclerotic plaques on human aortas.

Electrical impedance measurements were performed on 13 atherosclerotic human aortic segments at 67 measuring spots in order to determine whether or not on the basis of these data a distinction can be made between atherosclerotic lesions and normal tissue. Stenosis localization and guidance of interventional techniques could be among the applications of an impedance measuring technique implemented on a catheter system. The experimental results, obtained with a two-electrode measuring technique, show that the apparent resistivity of an atherosclerotic spot does not necessarily deviate much from the resistivity of normal tissue. This is clarified by histology which shows that the majority of lesions has a surface layer of connective, fibrous tissue having almost similar conducting properties as the normal arterial wall. For gaining a deeper understanding of the way in which the measured data come about, a physical model of an atherosclerotic lesion is presented and confronted with the data. Both experimental data and theoretical considerations lead to the conclusion that only when the superficial fibrous layer is absent or very thin in relation to the size of the measuring electrode, the measured resistivity at a lesion is much higher than at normal spots. This occurs as a consequence of the high ohmic properties of the calcified or lipid deposits in the atherosclerotic lesion.