抄録
Numerical simulations and experiments are carried out to apply ultrasonic computed tomography (CT) for a noninvasive measurement of bone density distribution. When ultrasonic rays pass through such an object as bone, it is refracted and propagates along curved paths. In such case, the reconstruction methods usually used will lead to inexact or even false results. To overcome this difficulty encountered in ultrasonic CT, the following procedure may be considered. First, an approximate distribution of sound velocities is determined with usual reconstruction method on the assumption of straight-line propagation. Then, after the corrected curved ray paths have been computed based on the result, a more exact sound velocity distribution can be reconstructed as the solutions of linear algebraic equations. This procedure is confirmed to be very effective from the present numerical simulation for a cylindrical object with high sound velocity. Through the measurements of the forefingers, the sound velocity distributions corresponding to the above first approximation could be obtained. The results show that the shape of the finger is enlarged due to the sound ray refraction. because of the complex sound velocity distribution in a bone, the solution of second approximation has not yet obtained.
