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

本研究的目的是检验是否可以通过扫描声学显微镜测量超声衰减、传播速度和体积模数来评估基于声学特性和弹性特性的心肌存活性。我们研究了缺血心肌的声学特性，如顿抑心肌。犬在LAD暂时阻断15分钟后再灌流60分钟期间进行了研究。取心肌标本(顿抑心肌)，取自缺血区的心内膜，切成4微米厚，在玻片上不做石蜡切片。光镜和电子显微镜下未见缺血心肌(顿抑心肌)与正常心肌的差异。在电子显微镜下，只有轻微的线粒体和细胞膜肿胀，在缺血心肌中有少量细胞水肿的零星证据。缺血心肌(顿抑心肌)的传播速度为1656SY·+-36M/S，正常心肌为1657SY·+-8M/S。两组间无显著差异。因此，我们认为，顿抑心肌的微小变化不会导致声学特性的显著变化。此外，为了评估缺血心肌的硬度，我们使用了一种新的方法来测量组织标本的体积弹性系数和密度。为了测量试件的体积弹性模量(Ks)和密度(Rhos)，我们研制了一种声覆盖膜覆盖试件。这种覆盖膜是由聚碳酸酯制成的，并夹在样品和繁殖介质之间。从盖膜反射的信号强度代表了样品的声阻抗(Zs)。因此，如果我们用这个盖膜用声学显微镜测量样品的Zs和Vs，我们可以估计样品的Ks和Rhos如下：Ks=Zsvs，Rhos=Zs/Vs。这样，我们就可以评价缺血心肌的硬度。

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.