Ultrasound Computed Tomography (USCT) reflection imaging can provide information on the anatomical structure of the breast and assist the screening and early diagnosis of breast cancer. Because of the individual differences of the breasts, the USCT reflection image reconstruction may need different sound speeds. To address this problem, we propose a strategy to extract the average breast sound speeds of each slice through the USCT prescan process and then use them for the formal scan reconstruction. In the prescan process, the signals trasmit through the coupling agent only and the signal transmits through the coupling agent and the breast are selected first. Then the maximum value-based time of flight (TOF) extraction method is used to obtain the corresponding sound speeds, respectively. After that, the average sound speeds of the agent and the breasts can be calculated as the size of the coupling agent is known. Finally, the average breast sound speed of each slice is utilized for the formal scan reconstruction. Image clarity evaluation functions, such as Tenengrad gradient function, Brenner gradient function, and Discrete Cosine Transform (DCT) function are used to analyze the image reconstruction results of one slice from one dense breast and one fatty breast under the empirical sound speed(1540m/s) and the calculated sound speed. The calculated sound speeds of the fatty and dense breast were 1470m/s and 1516m/s, respectively. The normalized DCT values, Brenner and Tenengrad gradient values of the fatty and dense breast, which were reconstructed under the calculated sound speed were about 25%, 63%, 56% and 2%, 15%, 16% higher than the ones under the empirical sound speed.

 

USCT,prescan,sound speed estimation