Distributed aberration correction in handheld ultrasound based on tomographic estimates of the speed of sound

Phase aberration is one the key sources of image degradation in handheld B-mode ultrasound imaging. Sound speed heterogeneities create phase aberrations in the image by inducing additional tissue-dependent delays and diffractive effects that conventional beamforming does not incorporate. For this reason, the Fourier split-step angular spectrum method is used to simulate pressure fields in a heterogeneous sound speed medium and create B-mode images based on the cross-correlation of transmitted and received wavefields. Because the strongest aberrations are caused by a laterally varying sound speed profile, this work presents a new sound speed estimator that can be used to correct for aberrations in laterally varying media. Phantom experiments show a 58-76% improvement in point target resolution and a 2.5x improvement in contrast-to-noise ratio because of the proposed sound speed estimation and phase aberration correction scheme.