山本 浩¹, 後藤 雅人¹, 田部井 誠², 上田 光宏³

Hiroshi YAMAMOTO¹, Masahito GOTO¹, Makoto TABEI², Mitsuhiro UEDA³

¹東京工業大学総合理工学研究科物理情報工学, ²東京工業大学精密工学研究所, ³東京工業大学理工学国際交流センター

¹Department of Information Processing, Tokyo Institute of Technology, ²Presicion and Interigence Laboratory, Tokyo Institute of Technology, ³International Cooperation Center for Science and Technology, Tokyo Institute of Technology

キーワード : Beam pattern, Ray tracing, Equivalent lens, Simulator, Phantom

The transducers used in ultrasonic diagnosis are concave shaped or linear array types. The beam profile of the transducer is determined by the shape of the vibrating plane in the case of the concave type or by the phase difference of each array element in the linear array type. The beam profile is in the uniform sound velocity medium. Unfortunately, in the human body there are tissues which cause non-constant sound velocities. Because of this, the phase front of transmitted waves will be muddied, and the B-scan image obtained will be unclear. Some methods to compensate the distorted B-scan image have been reported recently. To evaluate the effect of these methods, we need a beam profile which is a wave transmitted through the body. Traditionally, this profile can be obtained by experiments using real tissue or phantoms. Because of the difficulty of obtaining real tissue and in making phantoms which have an arbitrary sound velocity and atenuation coefficient, it is very difficult to perform such experiments. If the beam profile can be obtained by a computer calculation, we can evaluate the effect of the compensation methods quantitatively and easily. In this paper, we describe the construction of a simulator to calculate the beam profile with arbitrary acoustic parameters. We used the acoustic ray tracing method and the equivalent lens method to derive the complex sound pressure correctly. To evaluate the reliability of the simulator, we carried out an experiment using two phantoms and compared the results of the experiments.