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Experimental study of sidelobe reduction filters in ultrasound imaging

The experimental results of two types of sidelobe reduction filters are presented. These filters, named sidelobe filter and null filter, improve the resolution by scaling the received signal according to the ratio of the mainlobe and the sidelobe levels. In the sidelobe filter, sidelobe echoes can be obtained in the sidelobe direction of transmit beam by applying beam steering in receive focusing. Also some echoes can be obtained in null directions of the transmit field response, and this information, which can be obtained by taking Fourier transform, can also be used for purposes of sidelobe reduction. We can control each filter response by adjusting the filter order and scale factor. Computer simulation results show that the two types of filters can achieve more than 10 dB of the sidelobe level reduction, as well as the mainlobe width narrowing, which helps overcome the diffraction limited resolution of conventional focusing schemes. Experiments are also performed using a prototype system based on a modified commercial diagnostic ultrasound scanner (SA8800, Medison Co.). Experimental results with phantom and in-vivo data demonstrate that the proposed scheme is highly effective in enhancing the image resolution and contrast.