Aberration often degrades ultrasound image quality when beamforming does not account for wavefront distortions. In the past decade, local sound speed estimators have been developed for distributed aberration correction throughout a medium. Recently, iterative sound speed optimization approaches have achieved more accurate estimates than earlier approaches, but these newer methods still struggle with decreased accuracy for media with reverberation clutter and large sound speed changes. To address these challenges, we propose using a wavefield correlation (WFC) beamforming approach when performing sound speed optimization. WFC correlates simulated forward-propagated transmit wavefields and backwards-propagated receive wavefields in order to form images. This process more accurately models wave propagation in heterogeneous media and can decrease diffuse clutter due to its spatiotemporal matched filtering effect. This beamformer is implemented using auto-differentiation software to then perform gradient descent optimization, using a total-variation regularized common midpoint phase focus metric loss, on the local sound speed map used during beamforming. This approach is compared to using delay and sum (DAS) with straight-ray time delay calculations in the same sound speed optimization approach on a variety of simulated, phantom, and in vivo data with large sound speed changes and clutter. Results show that using WFC decreases sound speed estimation error, and using the estimates for aberration correction improves image resolution and contrast. These promising results have potential to improve pulse-echo imaging for challenging clinical scenarios.

翻译：当波束形成未考虑波前畸变时，像差通常会降低超声图像质量。过去十年中，已开发出局部声速估计器用于介质中的分布式像差校正。最近，迭代声速优化方法比早期方法获得了更准确的估计，但这些新方法在处理具有混响杂波和大声速变化的介质时，精度仍然会下降。为解决这些挑战，我们提出在执行声速优化时采用波场相关（WFC）波束形成方法。WFC通过关联模拟的前向传播发射波场和后向传播接收波场来形成图像。该过程能更准确地模拟波在非均匀介质中的传播，并由于其时空匹配滤波效应可减少弥散杂波。该波束形成器使用自动微分软件实现，进而对波束形成过程中使用的局部声速图执行梯度下降优化，优化采用全变分正则化的共中心点相位聚焦度量损失。该方法与在相同声速优化框架下使用延迟求和（DAS）结合直线声线时延计算的方法进行了比较，测试数据包括多种具有大声速变化和杂波的模拟、仿体和体内数据。结果表明，使用WFC降低了声速估计误差，并且利用这些估计值进行像差校正提高了图像分辨率和对比度。这些有前景的结果有望改善具有挑战性的临床场景中的脉冲回波成像。