음장해석과 가시화를 통한 의료용 초음파프로브의 결함요소 검출

Abstract

Ultrasound probes for medical application have many piezoelectric elements arrayed in a line or on a two-dimensional surface. Some or all of the elements are employed for electronic beamforming to get an image line, and a frame of image is obtained by electronic scanning or steering of the formed beam. If a few elements among them are electromechanically defective due to cracks, disconnecting of electric lines and so on, the image obtained by the probe might be degraded. In this study, the feasibility of detection of defective elements in a medical ultrasound probe was basically investigated by using the acoustic fields for a 3 MHz linear phased array transducer which has sixteen piezoelectric elements. The fields were simulated theoretically and measured experimentally using a visualization system based on the Schlieren method. The simulation results for steering angles of 0° and 30° show that the side-lobe patterns of the transducer including a defective element are quite different from those of the transducer with all normal elements, and those patterns are in good agreement with the results of visualization. It is shown that the defective elements in a linear array transducer can be detected by comparison of the simulated side-lobe patterns and the visualized ones in two dimensional acoustic fields. In addition, the influences of a few defective elements on imaging were analyzed by simulation for a commercial 7.5 MHz 1D linear array probe with 192 elements. The qualitative difference in images and the quantitative variation of lateral and axial resolutions according to the number of defective elements were analyzed.