This work presents the first quantitative ultrasonic sound speed images of ex vivo limb cross-sections containing both soft tissue and bone using Full Waveform Inversion (FWI) with level set (LS) and travel time regularization. The estimated bulk sound speed of bone and soft tissue are within 10% and 1%, respectively, of ground truth estimates. The sound speed imagery shows muscle, connective tissue and bone features. Typically, ultrasound tomography (UST) using FWI is applied to imaging breast tissue properties (e.g. sound speed and density) that correlate with cancer. With further development, UST systems have the potential to deliver volumetric operator independent tissue property images of limbs with non-ionizing and portable hardware platforms. This work addresses the algorithmic challenges of imaging the sound speed of bone and soft tissue by combining FWI with LS regularization and travel time methods to recover soft tissue and bone sound speed with improved accuracy and reduced soft tissue artifacts when compared to conventional FWI. The value of leveraging LS and travel time methods is realized by evidence of improved bone geometry estimates as well as promising convergence properties and reduced risk of final model errors due to un-modeled shear wave propagation. Ex vivo bulk measurements of sound speed and MRI cross-sections validates the final inversion results.

中文翻译：

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皮质骨和软组织的定量声速成像：观察数据集的结果

这项工作提出了第一个定量的超声波声速图像使用具有水平集 (LS) 和行程时间正则化的全波形反演 (FWI) 获得包含软组织和骨骼的离体肢体横截面。骨骼和软组织的估计体积声速分别在地面实况估计的 10% 和 1% 以内。声速图像显示肌肉、结缔组织和骨骼特征。通常，使用 FWI 的超声断层扫描 (UST) 用于对与癌症相关的乳腺组织特性（例如声速和密度）进行成像。随着进一步的发展，UST 系统有可能通过非电离和便携式硬件平台提供与体积操作员无关的肢体组织属性图像。这项工作通过将 FWI 与 LS 正则化和传播时间方法相结合来解决对骨骼和软组织声速成像的算法挑战，以恢复软组织和骨骼声速，与传统 FWI 相比，具有更高的准确性并减少了软组织伪影。利用 LS 和旅行时间方法的价值通过改进骨骼几何估计的证据以及有希望的收敛特性以及由于未建模的剪切波传播而降低最终模型错误的风险来实现。声速和 MRI 横截面的体外批量测量验证了最终的反演结果。