A magnetic resonance (MR) shear wave elastography technique that uses transient acoustic radiation force impulses from a focused ultrasound (FUS) transducer and a sinusoidal-shaped MR displacement encoding strategy is presented. Using this encoding strategy, an analytic expression for calculating the shear wave speed in a heterogeneous medium was derived. Green’s function-based simulations were used to evaluate the feasibility of calculating shear wave speed maps using the analytic expression. Accuracy of simulation technique was confirmed experimentally in a homogeneous gelatin phantom. The elastography measurement was compared to harmonic MR elastography in a homogeneous phantom experiment and the measured shear wave speed values differed by less than 14%. This new transient elastography approach was able to map the position and shape of inclusions sized from 8.5 to 14 mm in an inclusion phantom experiment. These preliminary results demonstrate the feasibility of using a straightforward analytic expression to generate shear wave speed maps from MR images where sinusoidal-shaped motion encoding gradients are used to encode the displacement-time history of a transiently propagating wave-packet. This new measurement technique may be particularly well suited for performing elastography before, during, and after MR-guided FUS therapies since the same device used for therapy is also used as an excitation source for elastography.

提出了一种磁共振 (MR) 剪切波弹性成像技术，该技术使用来自聚焦超声 (FUS) 换能器的瞬态声辐射力脉冲和正弦形 MR 位移编码策略。使用这种编码策略，导出了计算异质介质中剪切波速度的解析表达式。Green 的基于函数的模拟用于评估使用解析表达式计算横波速度图的可行性。模拟技术的准确性在均质明胶体模中通过实验得到证实。弹性成像测量与均匀体模实验中的谐波 MR 弹性成像进行了比较，测得的剪切波速度值相差不到 14%。这种新的瞬态弹性成像方法能够在夹杂物体模实验中绘制尺寸为 8.5 至 14 毫米的夹杂物的位置和形状。这些初步结果证明了使用简单的解析表达式从 MR 图像生成剪切波速度图的可行性，其中正弦形运动编码梯度用于编码瞬态传播波包的位移时间历史。这种新的测量技术可能特别适合在 MR 引导的 FUS 治疗之前、期间和之后执行弹性成像，因为用于治疗的相同设备也用作弹性成像的激发源。这些初步结果证明了使用简单的解析表达式从 MR 图像生成剪切波速度图的可行性，其中正弦形运动编码梯度用于编码瞬态传播波包的位移时间历史。这种新的测量技术可能特别适合在 MR 引导的 FUS 治疗之前、期间和之后执行弹性成像，因为用于治疗的相同设备也用作弹性成像的激发源。这些初步结果证明了使用简单的解析表达式从 MR 图像生成剪切波速度图的可行性，其中正弦形运动编码梯度用于编码瞬态传播波包的位移时间历史。这种新的测量技术可能特别适合在 MR 引导的 FUS 治疗之前、期间和之后执行弹性成像，因为用于治疗的相同设备也用作弹性成像的激发源。