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
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.