Ultrasound tomography (UST) is an emerging technique that uses methods similar to computed tomography (CT) to generate the images using sound signals. It is well suited for inferring the acoustic properties of a volume of tissue from measurements made along a surface surrounding the tissue. Unlike the x-rays used in conventional CT, sound is purely wave-like. Tomographic techniques that process sound data must, therefore, take into account wave propagation phenomena such as reection, refraction, and diraction. In an inhomogeneous medium, ultrasound pulses do not travel in straight lines, thereby complicating the tomographic inversion and placing additional burden on the computational requirements. e need for a high level of computing power and associated data-processing capability has been a major historical factor in limiting the development of UST compared to CT and other tomographic methods. For this reason, UST has not completely lived up to its early promise. However, in recent years, thanks to the increasing processing power of both computers and electronics, the landscape has changed dramatically.