Anisotropic regularization of ultrasound pulse-echo tomography for reconstruction of speed-of-sound and tissue heterogeneity through abdominal layers

Regularization has a critical impact on the performance of pulse-echo computed-tomography and is a key component of the speed-of-sound (SoS) reconstruction pipeline. We investigate SoS reconstruction accuracy through heterogeneous abdominal models. We propose anisotropic regularization approaches, which integrate available gradient information for both Tikhonov (L2) and Total Variation (L1) regularizers. Our results show that different target clinical applications, for instance, quantification of focal lesions or diffuse disease may benefit from different regularization approaches. Reconstruction of SoS distributions through abdominal layers was feasible in limited-angle ray tracing simulations, with Pearson coefficient r = 0.909 for estimation of SoS baseline (mean) and r = 0.66 for estimation of SoS heteroaeneity (std. deviation).