スタント カワン, 大槻 茂雄, 奥島 基良

Kawan SOETANTO, Shigeo OHTSUKI, Motoyoshi OKUJIMA

東京工業大学精密工学研究所

Research Laboratory of Precision Machinery and Electronics，Tokyo Institute of Technology

キーワード : Relative sound velocity, Ultrasonic tomogram, Distorted image, Refraction, Massive tissue

Many researchers have dealt with the criteria of diagnosis of tissues on the basis of shape, boundary echo, internal echo, posterior echo, attenuation, velocity, and so on. Base on the ultrasonic beam refraction, the intensity of posterior echo of massive tissue was analyzed by Okujima et al. and was measured by Robinson et al., and distorted image behind a massive tissue was pointed out by Robinson et al. Furthermore, we are intended to estimate the sound velocity with these phenomena.
Experiment was conducted with a cylinder that size was larger compared with ultrasonic beam width and some reference reflectors in a water tank were used as phantom. First, the effect of sound velocity of such cylinder on its posterior image of some reflectors were analyzed by experiment and by computer simulation based on the ray theory. Second we devised some estimation methods of relative sound velocity of a cylinder to the surroundings based on above results. These methods were investigated as follows: 1) In case or a plane reflector, it could be estimated from the posterior image of plane distorted toward or away, and furthermore its value could be determined by calculating the amount of the shift of this posterior image and the size of the cylinder image in a direction longitudinal to the ultrasonic beam, 2) In case of scatters, it could be estimated from the reduction rate of the image size in a direction lateral to the ultrasonic beam, 3) In case of a point reflector, it could be estimated from the number and positions of the displayed image.
In this paper, we present above results and proposed to estimate in vivo sound velocity of a massive tissue from the posterior distorted image obtained by conventional ultrasonic equipment.