Synthetic Aperture Focusing Technique for 3-D Ultrasound Computed Tomography

In recent years, a number of studies on ultrasound computed tomography (USCT) have been carried out in early detection of breast cancer. In this paper, synthetic aperture focusing technique (SAFT) is used in USCT system to reconstruct three dimensional images. It can provide more accurate positioning in contrast to traditional B-mode images. Spatio-temporally smoothed coherence factor (STSCF) beam forming method has applied to suppress side lobes and clutter in USCT imaging. The weighted factors can be implemented effectively to improve the image quality for USCT. The mentioned methods were verified with the radio-frequency (RF) data of the nylon thread, breast phantom and one pig heart. The RF data were captured by the USCT system developed in the Medical Ultrasound Laboratory. The main components are the ring-type transducer with 1024 elements and the channel data acquisition system. The center frequency of the transducer is 2.5 MHz. Experimental results show that the reconstructed images of the breast phantom by STSCF gets the higher signal to noise ratio (SNR) compared to delay and sum (DAS). The borders of cysts and tumors in the breast phantom can be distinguished as corresponding to magnetic resonance image (MRI). With the STSCF method, the thread targets are more clearly presented comparing with DAS while the artifact can significantly reduce. The 3-D profiles of the pig heart are also reconstructed from a series of two dimensional slices and inner structure of pig heart can be observed distinctly.