Phase aberration correction by bent-ray tracing method for ultrasound computed tomography

Ultrasound computed tomography (USCT) is a promising technique for breast cancer detection. It can provide three modalities: sound speed image, attenuation image, and reflection image. The reflection image can have high-resolution, but it always be reconstructed using a pre-determined sound speed based on homogeneous assumption, and the mismatch between the pre-determined speed and real speeds of inhomogeneous tissue could result in phase aberration and degrade the image quality and resolution. In this article, we proposed and evaluated to correct phase aberration by bent-ray tracing method using sound speed image of USCT. First, sound speed image of USCT was reconstructed by first arrival picking method, bent-ray tracing method and Simultaneous Algebraic Reconstruction Technique (SART). Second, the propagation time from each element to each pixel of image was calculated by bent-ray tracing method using the sound speed image. Third, scatter-signal-delay-time was calculated and reflection image is reconstructed by using Synthetic Aperture (SA) method. For evaluation, both simulation and experiment validation were conducted. With regard to the simulation, the homogeneous point scatter simulation showed that the phase aberration might increase diameter of point-spread function (PSF) from approximate 1 to 5 mm; the complex-breast-model simulation demonstrated that the proposed method could correct phase aberration and decrease diameter of PSF from about 2 to 1 mm. With regard to the experiment, the results demonstrated that the proposed method could correct phase aberration and improve the image quality of breast phantom.