A Fast Contrast Improved Zero-Phase Filtered Delay Multiply and Sum in Ultrasound Computed Tomography

In linear array B-mode imaging, the zero-phase filtered delay multiply and sum beamforming (ZPF-DMAS) weighted by space-time smoothing coherence factor (StS-CF) has been proved to enhance the image contrast resolution than the traditional delay and sum method. However, the large number of virtual received signals may increase the computational cost of this method in ultrasound computed tomography (USCT) with ring array. Here, a method with less computation amount is proposed in USCT: the received signals are separated into different groups by their spatial lag; the groups form a new smaller size receive aperture; StS-CF is finally applied to the new receive aperture. CIRS model 055A is tested to compare the performances of the proposed method and ZPF-DMAS. The results show that the computational complexity has been reduced by N*B*D((M2–3M)/2+1) multiplications, supposing there are N ultrasound waves transmitted, B scan lines, D imaging points on each line and M-element receive aperture. StS-CF with a subarray size of L = 16 (far less than half the receive aperture) and P = 5 time samples gives the best result in USCT, which is different from that in linear array B-mode imaging. The proposed method can enhance contrast ratio about 6.3 dB and 5.7 dB for the cystic mass and dense mass than ZPF-DMAS, respectively.