Simulating annular array probe performance by ray tracing

Abstract

The imaging performance of annular array probes has been simulated by a ray tracing method. A particular strength of the method is the ability to account for refraction and attenuation of materials between the transducer and the imaging point, including coupling fluid, probe cap, and tissue layers. Rays are traced from the surface of the transducer to the field point under consideration. The aperture function, real and imaginary parts, is reconstructed as seen from that point. Beam profiles are determined by a Fourier transform of the aperture function. Electronic functions, such as time delay focusing, apodization, errors in gain, and time delay, can be simulated by modifying the aperture function appropriately. Examples are given of nonspherical geometry and effects of subcutaneous fat layer. Apodization is shown to require extremely tight phase control, both across transducer elements and in focusing accuracy.