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In Vitro Atherosclerotic Plaque Characterization by Acoustic Impedance Monitoring, Part II: Experimentation and Validation

Department of Aeronautics and Astronautics, Stanford University, Stanford, CA 94305, USA, rdugnani{at}stanfordalumni.org

F.K. Chang

Department of Aeronautics and Astronautics, Stanford University, Stanford, CA 94305, USA

Although coronary atherosclerosis is the leading cause of hospitalization and death in the United States, at present no effective diagnostic technique is available to effectively characterize atherosclerotic plaque in vivo and in real-time. In `Introduction' of this article, we propose the use of an impedance-based technique to diagnose the presence of atherosclerotic plaque. Both analytical and finite element methods are developed to study the effect of a multi-layer substrate in contact with a sensor on the sensor's electro-mechanical impedance. Also a modified version of the Krimholtz, Leedom, and Matthaei (KLM) model is introduced to design the sensor dimension based on a sensor/plaque configuration. An appropriate fabrication technique for manufacturing a small-scale PZT sensor is also proposed for possible use in small arteries. In section `Analytical Model' of the article, we show that the presence of plaque can be accurately predicted by using the proposed impedance-probing technique on samples of human, atherosclerotic tissues. The presence of atherosclerotic plaque in the samples — as predicted by our technique — is confirmed by a histological examination carried out at the Stanford Histology Research Core Lab. The plaque mechanical properties are approximated based on a modified KLM model describing the sensor-artery system. The properties predicted are found to be consistent with the values reported in the literature. A brief study pertaining to the pressure necessary to achieve an acceptable contact between the PZT sensors and the probed artery is presented in the last section of the article. This work suggests that it is possible to characterize atherosclerotic plaque in real-time using the described impedance-based monitoring technique. One future possible application for this technique could be — for instance — the detection of unstable plaque in arteries prior to percutaneous transmural angioplasty (PTA).

Key Words: atherosclerotic plaque • unstable plaque • plaque diagnostic system • plaque characterization • impedance methods • impedance monitoring.

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