Evaluation of Progression of Arteriosclerosis by the Quantitative Assessment of Acoustic Tissue Characteristics Using Acoustic Microscopy

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The aim of this study is to examine whether we can evaluate myocardial viability based on acoustic characteristics and elastic properties by measuring the ultrasonic attenuation, propagation velocity, and bulk modulus with a scanning acoustic microscopy. We investigated acoustic properties in ischemic myocardium such as stunned myocardium.The dogs were studied during 15 min of temporary LAD occlusion followed by 60 min of reperfusion. Myocardial specimens (stunned myocardium) which were obtained from endocardium in ischemic regin, were cut in 4 micron thickness, and prepared without paraffin on slide glass.1. We could not find any differences between iscemic myocardium (stunned myocardium) and normal using optical microscopy and electron microscopy. Using electron microscopy, only minimal swelling of the mitochondria and arcolemma was noted, with scattered evidence of mild cellular edema present in iscemic myocardium.2. Propagation velocity was 1656(]SY.+-[)36m/s in iscemic myocardium (stunned myocardium), and was 1657(]SY.+-[)8m/s in normal. There was no significant difference between them. Therefore, we considered that minimal changes in stunned myocardium produced no significant changes in acoustic properties.3. Furthermore, in order to evaluate the hardness of the ischemic myocardium, we use a new method to measure the bulk modulus and density of tissue specimen. We developed an acoustic cover membrane covering specimen in order to measure bulk modulus (Ks) and density (rhos) of specimen. This cover membrane is made of polycarbonate and is interposed between the specimen and the propagating medium. The intensity of the signal reflected from the cover membrane represents the acoustic impedance (Zs) of the specimen. So, if we measure Zs and Vs of specimen using the acoustic microscopy with this cover membrane, we can estimate Ks and rhos of specimen as follows ; Ks=ZsVs, rhos=Zs/Vs. In this way, we can evaluate the hardness of ischemic myocardium.