Coherence Based Sound Speed Aberration Correction -- with clinical validation in fetal ultrasound

TL;DR

This paper presents a clinically validated method for correcting sound speed aberrations in fetal ultrasound by estimating aberrations directly from coherence images, improving image quality without complex inversion.

Contribution

The novel contribution is a direct aberration estimation method using coherence image processing, validated in vitro, in silico, and clinically on obstetric images.

Findings

High correlation with ground truth sound speed maps

Corrected images preferred or equivalent in 72.5% of cases

Sharpness metric correlates with sound speed changes

Abstract

The purpose of this work is to demonstrate a robust and clinically validated method for correcting sound speed aberrations in medical ultrasound. We propose a correction method that calculates focusing delays directly from the observed two-way distributed average sound speed. The method beamforms multiple coherence images and selects the sound speed that maximizes the coherence for each image pixel. The main contribution of this work is the direct estimation of aberration, without the ill-posed inversion of a local sound speed map, and the proposed processing of coherence images which adapts to in vivo situations where low coherent regions and off-axis scattering represents a challenge. The method is validated in vitro and in silico showing high correlation with ground truth speed of sound maps. Further, the method is clinically validated by being applied to channel data recorded from 172 obstetric Bmode images, and 12 case examples are presented and discussed in detail. The data is recorded with a GE HealthCare Voluson Expert 22 system with an eM6c matrix array probe. The images are evaluated by three expert clinicians, and the results show that the corrected images are preferred or gave equivalent quality to no correction (1540m/s) for 72.5% of the 172 images. In addition, a sharpness metric from digital photography is used to quantify image quality improvement. The increase in sharpness and the change in average sound speed are shown to be linearly correlated with a Pearson Correlation Coefficient of 0.67.