Quantitative Assessment of Tissue Hardness of Coronary Artery Wall Specimens by Acoustic Tissue Characterization System with a Wide Band Frequency Ultrasound.

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The aim of this study was to develop an acoustic tissue characterization system able to quantitatively measure tissue characteristics in biological specimens, and to evaluate tissue hardness, especially of the human coronary artery wall, using this system.1. We developed the quantitative measurement system for tissue characterization mainly from a scanning acoustic microscope(HSAM-500S) operating at 450MHz. To precisely measure the absolute propagation velocity of ultrasound, we made a new stage for mounting specimens to precisely regulate both specimen thickness and temperature of the objective specimen environment. We were able to judge the accuracy of the specimen thickness by reading patterns of the interference fringe shift, and also ensure that the temperature of the environment around the specimen could be controlled with an accuracy of *0.1ﾟC.2. We examined temperature-dependent changes in the propagation velocity of ultrasound using a digital voltmeter for controlling temperat … More ure. 4-micron-thick specimens of liver, myocardium and coronary artery were mounted on a stage of exactly 4 microns depth, after which we measured propagation velocities at various controlled temperatures. The rates of increase in propagation velocity with temperature in the 3 tissues between 30ﾟC and 50ﾟC were as follows : liver ; 2.68m/s/ﾟC, myocardium; 4.26m/s/ﾟC, coronary artery (intima) ; 0.60m/s/ﾟC. We confirmed that propagation velocity varied distinctly in each of the 3 tissues according to the temperature of the specimen, and that therefore each tissue had temperature-dependent acoustic characteristics.3. We measured the absolute propagation velocity of ultrasound in the intima of human coronary artery specimens obtained by autopsy from 13 patients with a variety of diseases. On the bases of findings in the intima with an optical microscope, we classified these specimens into 3 groups; normal, early stages of scleroses, and advanced stages of sclerosis. Ultrasound propagation velocity at 25ﾟC was as follows : normal; 1947.3*100.2m/s, early stage; 1694.3*64.1m/s, advanced stage; 2246.3*96.0m/s. Generally, the faster the propagation velocity, the harder the tissue. We therefore concluded that optically defined sclerotic intima tissue in early stages of disease showed an initial softening as compared with normal tissue, and this was followed by subsequent hardening with advancing calcification.4. As quantitative assessment of tissue characteristics in biological specimen by 10-100MHz ultrasound, we were getting on with the development of a new system and the experimental study to measure the attenuation due to absorption of ultrasound through the tissue, ex. blood or coronary artery, using 50MHz ultrasound system. Less