Recursively Apply Delay Multiply and Sum Beamforming Algorithm to Enhance Quality of Ultrasonic Image

A novel beamforming algorithm named delay multiply and sum (DMAS) which performance is better than the classic delay and sum (DAS) beamformer in resolution and contrast has recently been proposed. However, it is not desirable in a noisy environment. Therefore, a double stage delay multiply and sum (DS-DMAS) beamforming algorithm is proposed to address this issue. This method, however, is still not good in a noisy environment with low SNR. A new method which recursively apply the DMAS algorithm to improve the image quality is proposed by us. This approach is therefore named R-DMAS. We expand the DMAS into a number of items, and each item consists of a lot of signals. Applying DMAS to the signals in every item to generate a new signal is the second step. After that, these new synthesized signals are beamformed again by DMAS to generate the final result. Because of recursively using the DMAS beamforming algorithm, the quality of reconstructed image, in terms of resolution and contrast, is much better. A point target phantom and a hyperechoic cyst phantom are synthesized to compare the performance of R-DMAS with DAS, DMAS and DS-DMAS. The simulation results show that the R-DMAS has the narrowest main lobe and lowest side lobe especially in the far field and the contrast ratio (CR) of DAS, DMAS, DS-DMAS and R-DMAS are 10.2639, 14.7421, 20.4591 and 21.8812, respectively. The result of noise influence study exhibits that R-DMAS has the best performance among the four algorithms in the noisy environments with SNR of 6 dB, 10 dB, and 20 dB. The experimental result also shows that the image reconstructed by R-DMAS has the best resolution.