Comparative evaluation of wavefront coherence imaging methods in the presence of clutter

There are a number of mechanisms that contribute to poor image quality in ultrasonic imaging. Numerous algorithms have been designed to compensate for phase aberrations, but recently it was shown that reverberation clutter plays a significant role in degrading image quality. We have developed a novel imaging technique that is capable of differentiating ultrasonic signals corrupted by clutter, named Short-Lag Spatial Coherence (SLSC) imaging. The method relies of the spatial coherence of the echo wavefronts. Ultrasound images from a full-wave, nonlinear wave propagation simulation of low contrast lesions were used to demonstrate our coherence imaging method and compare it images generated by methods such as the generalized coherence factor (GCF) and the wavefront similarity factor (WSF). Signal-to-clutter ratio (SCR) of the images were adjusted via impedance mismatch of the intervening abdominal layer in the simulation. Results demonstrate that SLSC imaging yielded better contrast-to-noise ratio than B-mode, GCF, and WSF. When phase aberration was removed, all coherence imaging methods demonstrated stable CNR as a function of SCR, while B-mode imaging degraded linearly with decreasing SCR. In vivo images of a human carotid artery show superior visualization of carotid anatomy with the coherence imaging methods, however SLSC imaging yielded superior contrast and CNR of targets over all other imaging methods.