Medical instrumentation and finite element analysis for the assessment of vulnerable plaque

This work elucidates the fundamentals, calibration procedure and in vitro results of an instrument for the assessment of vulnerable plaque. Heart disease is a number one killer in United States. More than 60% of all sudden deaths caused by myocardial infarction are due to plaque disruption or the rupture of a vulnerable plaque. Researchers believe vulnerable plaques that do not limit flow may be particularly dangerous because they produce no warning symptoms, but can rupture suddenly causing heart attack and death. The significance of this work is that the early detection of these unstable atherosclerotic plaques, independent of the degree of luminal diameter narrowing, is a crucial tool in the battle against heart disease.;A self-heated thermistor probe is used to deliver heat and also to measure the temperature response. A pulse-power integrated-decay technique for the measurement of thermal conductivity of biological tissues is presented. Three dimensional finite element analyses are used to design and optimize this technique. The results indicate that the thermal decay technique protocol had better accuracy than constant temperature heating techniques.;In the clinical setting, tissues removed surgically are often fixed in formalin for subsequent pathological analysis. Effect of formalin fixation on thermal conductivity of the biological tissues is presented. These results suggest that, in terms of thermal properties, it is equally appropriate to perform in vitro studies in either fresh tissue or formalin-fixed tissue.;The thermal conductivity measurements of plaques removed from human carotid arteries, femoral arteries or aortic valves, with a known atherosclerosis as determined by histology are presented. Finite element modeling was used to spatially map the varying conductivity of heterogeneous tissue into a single measurement made by the thermistor and also to determine the effective volume of measurement. The average thermal conductivity as measured using the thermal decay technique, for fiber (stable plaque) was 4.79 (sigma = 0.55) mW/cm-°C and lipid close to the lumen (vulnerable plaque) was 4.35 (sigma = 0.91) mW/cm-°C. Finite element analyses and in vitro experiments suggest the self-heated thermistor technique can be used to detect vulnerable plaque.