New Development of Tissue Characterization using Acoustic Microscopy with High Frequency Ultrasound

在这项研究中，我们新开发了一个声学组织定征系统，使用高频超声声学显微镜。在该系统中，我们可以测量人体组织标本的传播速度和超声衰减，以评估动脉硬化标本的硬度。此外，为了更准确地评价组织的硬度，我们开发了一种新的方法来评价组织的体积模量和密度.我们使用了反射和扫描声学显微镜，利用高频（超过450 MHz）显微镜（HSAM-500 S）与计算机控制器和分析仪耦合。将通过尸检从人冠状动脉和其他组织获得的标本切成4微米厚，并在载玻片上制备没有石蜡的标本。在C模式图像中，我们获得了与光学显微镜相似的清晰图像。此外，我们还测量了C模式图像中的超声衰减。在X-Z模式图像中，我们能够通过将通过耦合介质的传播速度（Vw）、样本厚度（ds）和干涉条纹的位移（DELTAz）的值插入到以下方程中来获得通过样本的传播速度（Vs）：Vs=Vw/（1-DELTAz/ds）。2.为了测量试样的体积模量和密度，研制了一种覆盖在试样上的声学覆盖膜。该覆盖膜由聚碳酸酯制成，并置于样品和传播介质之间。盖膜具有已知的声阻抗（3.5MKS），高于两者中的任一个。从覆盖膜反射的信号的强度表示样品的声阻抗（Zs）。因此，如果我们使用这种覆盖膜使用声学显微镜测量试样的Zs和Vs，我们可以估计试样的Ks和rhos如下：Ks=ZsVs，rhos=Zs/Vs。这样，我们可以更精确地评估试样的硬度。

In this study, we have newly developed an acoustic tissue characterization system using an acoustic microscopy with high frequency ultrasound. In this system, we can measure the propagation velocity and ultrasonic attenuation of human tissue specimen in order to evaluate the hardness of the specimen in arteriosclerosis. Furthermore, in order to evaluate the hardness of the tissue more precisely, we developed a new method to evaluate the bulk modulus and density of tissue specimen.1. We used a reflecting and scanning acoustic microscopy utilizing a highly frequency (more than 450 MHz) microscope (HSAM-500S) coupled with a computer controller and analyzer. Specimen which were obtained from human coronary arteries and other tissue by autopsy, were cut in 4 micron thickness, and prepared without paraffin on slide glass. In C mode image, we obtained clear images similar to those from optical microscopy. Furthermore we measure the ultrasonic attenuation in C mode image. In X-Z mode image, we were able to obtain propagation velocities through specimen (Vs) by inserting values for the propagation velocity through the coupling medium (Vw), the specimen thickness (ds) and the shift in the interference fringe (DELTAz) into the following equation : Vs=Vw/(1-DELTAz/ds).2. 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 cover membrane has a known acoustic impedance (3.5MKS) higher than either of the two. 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 specimen more precisely.