Computed ultrasound tomography in echo mode (CUTE) allows determining the spatial distribution of speed-of-sound (SoS) inside tissue using handheld pulse-echo ultrasound (US). This technique is based on measuring the changing phase of beamformed echoes obtained under varying transmit (Tx) and/or receive (Rx) steering angles. The SoS is reconstructed by inverting a forward model describing how the spatial distribution of SoS is related to the spatial distribution of the echo phase shift. Thanks to the straight-ray approximation, this forward model is linear and can be inverted in real-time when implemented in a state-of-the art system. Here we demonstrate that the forward model must contain two features that were not taken into account so far: (a) the phase shift must be detected between pairs of Tx and Rx angles that are centred around a set of common mid-angles, and (b) it must account for an additional phase shift induced by the offset of the reconstructed position of echoes. In a phantom study mimicking hepatic and cancer imaging, we show that both features are required to accurately predict echo phase shift among different phantom geometries, and that substantially improved quantitative SoS images are obtained compared to the model that has been used so far. The importance of the new model is corroborated by a preliminary volunteer result.

中文翻译：

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定量脉冲回波声速成像的改进前向模型

回波模式 (CUTE) 下的计算机超声断层扫描允许使用手持脉冲回波超声 (US) 确定组织内声速 (SoS) 的空间分布。该技术基于测量在变化的发射 (Tx) 和/或接收 (Rx) 转向角下获得的波束成形回波的变化相位。SoS 是通过反转一个前向模型来重建的，该模型描述了 SoS 的空间分布如何与回波相移的空间分布相关。由于直线近似，这个前向模型是线性的，并且在最先进的系统中实现时可以实时反转。在这里，我们证明前向模型必须包含两个目前尚未考虑的特征：(a) 必须在以一组公共中角为中心的 Tx 和 Rx 角对之间检测相移，并且 (b) 它必须考虑由回波重建位置的偏移引起的额外相移. 在模拟肝脏和癌症成像的体模研究中，我们表明需要这两个特征来准确预测不同体模几何结构之间的回波相移，并且与迄今为止使用的模型相比，获得了显着改进的定量 SoS 图像。初步的志愿者结果证实了新模型的重要性。我们表明，需要这两个特征来准确预测不同体模几何结构之间的回声相移，并且与迄今为止使用的模型相比，获得了显着改进的定量 SoS 图像。初步的志愿者结果证实了新模型的重要性。我们表明，需要这两个特征来准确预测不同体模几何结构之间的回声相移，并且与迄今为止使用的模型相比，获得了显着改进的定量 SoS 图像。初步的志愿者结果证实了新模型的重要性。