Minimal angular compounding required for coherence-based sound speed estimation with plane wave ultrasound imaging

Conventional ultrasound beamforming assumes a uniform sound speed of 1540 m/s, which neglects tissue heterogeneity and results in phase aberrations and image degradation. Our recently introduced coherence-based sound speed estimation approach overcomes this limitation by assessing the short-lag spatial coherence within a coherent region of interest and selecting the sound speed that maximizes coherence, initially demonstrated after compounding images from 75 steered plane wave angles. However, using fewer angles will reduce required processing times. This study investigates the minimum number of steered angles necessary to implement our coherence-based sound speed estimation approach. In experiments with tissue-mimicking phantoms, a minimum of three steered plane wave angles was necessary to produce a similar full width at half maximum (FWHM) to that obtained with 75 angles, representing FWHM improvements of 67.19% over a sound speed of 1540 m/s and 65.31% over a speckle brightness maximization method. In vivo testing on the brachioradialis muscle demonstrated that the coherence-based method achieved a mean amplitude artifact reduction of 4.73 dB when compared to the same region in an image produced with a sound speed of 1540 m/s, using three angles in both cases. Overall, a minimum of 3-7 angles can be employed to estimate sound speeds using our coherence-based approach for plane wave images. Results have the potential to improve ultrasound imaging workflows and enhance diagnostic accuracy in clinical practice.