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.