We develop a ray-tracing theory to describe the effects of thermoacoustic lensing during high-intensity focused ultrasound (HIFU) on ultrasound images of reflectors lying distal to the HIFU focal region and discuss the application of thermal lensing effects to dose monitoring in HIFU therapy. By analyzing the effects of thermal and geometric delays of acoustic rays passing through a region of tissue undergoing localized heating, we show how the shape of a reflector distal to the heated region can be predicted and present experimental measurements in good agreement with the model. We also apply the model in reverse to estimate the thermal profile of a heated region based on a measured change in the shape of a distal reflector during HIFU delivery. As an example, we apply this technique to the measurements of thermal diffusion in porcine fat. An interesting aspect of the technique is that it can be applied to measure temperature in nonechogenic tissues as long as there is an observable reflector in the ultrasound images that is located distal to the region of localized heating.

中文翻译：

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热声透镜在高强度聚焦超声照射下对非回声组织进行超声成像

我们开发了一种射线追踪理论来描述高强度聚焦超声 (HIFU) 期间热声透镜对位于 HIFU 焦点区域远端的反射器的超声图像的影响，并讨论热透镜效应在 HIFU 治疗中的剂量监测中的应用。通过分析穿过局部加热的组织区域的声射线的热延迟和几何延迟的影响，我们展示了如何预测加热区域远端的反射器的形状，并提供与模型非常吻合的实验测量值。我们还反向应用该模型，根据 HIFU 传输期间远端反射器形状的测量变化来估计加热区域的热分布。例如，我们将此技术应用于猪脂肪热扩散的测量。