Mapping the average speed of sound in synthetic aperture ultrasound imaging.

A method to map the average speed of sound in a heterogeneous medium was proposed. First, an equation was derived relating the phase aberration to the average speed of sound. Then, this equation was applied to study the average speed in a uniform phantom in simulations. An initial delay on the order of microseconds was found to affect the speed-map close to the surface. Next, a method was proposed to estimate this initial delay. Average speed and initial delay methods were validated in experimental studies in a uniform and two-layered phantoms. This proposed method has improved the image contrast and spatial resolution.