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

在这项研究中，我们新开发了一种使用高频超声声学显微镜的声学组织表征系统。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，为了更精确地评估组织的硬度，我们开发了一种新的方法来评估组织样品的体积模量和密度。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-500S）与计算机控制器和分析仪相结合。标本取材于人体冠状动脉和其他解剖组织，切成4微米厚，在玻片上不加石蜡。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，我们还测量了超声在C模图像中的衰减。在X-Z模式图像中，我们可以通过将通过耦合介质的传播速度（Vw），样品厚度（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试样的传播速度（Vs）： Vs=Vw/(1-DELTAz/ds).2。为了测量试样的体积模量（Ks）和密度（rho），我们研制了一种覆盖试样的声覆盖膜。这种覆盖膜是由聚碳酸酯制成的，并插入在试样和繁殖介质之间。覆盖膜的已知声阻抗（3.5MKS）高于两者中的任何一种。覆盖膜反射的信号强度代表试样的声阻抗（Zs）。因此，如果我们用这种覆盖膜的声学显微镜测量试样的Zs和Vs，我们可以估计出试样的Ks和rho：Ks = ZsVs,罗斯= z / Vs。这样可以更准确地评价试样的硬度。

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.