Vanderbilt University Institute of Imaging Science, Nashville, Tennessee.
Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee.
Magn Reson Med. 2020 Mar;83(3):1016-1024. doi: 10.1002/mrm.27987. Epub 2019 Sep 4.
To reduce temperature errors due to water motion in transcranial MR-guided focused ultrasound (tcMRgFUS) ablation.
In tcMRgFUS, water is circulated in the transducer bowl around the patient's head for acoustic coupling and heat removal. The water moves during sonications that are monitored by MR thermometry, which causes it to alias into the brain and create temperature errors. To reduce these errors, a two-dimensional excitation pulse was implemented in a gradient-recalled echo thermometry sequence. The pulse suppresses water signal by selectively exciting the brain only, which reduces the imaging FOV. Improvements in temperature precision compared to the conventional full-FOV scan were evaluated in healthy subject scans outside the tcMRgFUS system, gel phantom scans in the system with heating, and in 2×-accelerated head phantom scans in the system without heating.
In vivo temperature precision (standard deviation of temperature errors) outside the tcMRgFUS system was improved 43% on average, due to the longer TR and TE of the reduced-FOV sequence. In the phantom heating experiments, the hot spot was less distorted in the reduced-FOV scans, and background temperature precision was improved 59% on average. In the accelerated head phantom temperature reconstructions, temperature precision was improved 89% using the reduced-FOV sequence.
Reduced-FOV temperature imaging alleviates temperature errors due to water bath motion in tcMRgFUS, and enables accelerated temperature mapping with greater precision.
减少经颅磁共振引导聚焦超声（tcMRgFUS）消融中因水动造成的温度误差。
在 tcMRgFUS 中，水在环绕患者头部的换能器碗中循环，以实现声耦合和热量去除。水在磁共振测温监测的声处理过程中移动，这会导致其伪影进入大脑并产生温度误差。为了减少这些误差，在梯度回波测温序列中实现了二维激发脉冲。该脉冲通过选择性地仅激发大脑来抑制水信号，从而减小成像视野。在 tcMRgFUS 系统外的健康受试者扫描、系统内加热凝胶体模扫描以及系统内无加热 2×加速头部体模扫描中，评估了与传统全视野扫描相比，该方法在温度精度方面的改进。
在 tcMRgFUS 系统外，由于缩短了重复时间（TR）和回波时间（TE），降低视野序列的平均温度精度标准差提高了 43%。在体模加热实验中，减少视野扫描中热点的变形程度，背景温度精度平均提高了 59%。在加速头部体模温度重建中，使用减少视野序列后温度精度提高了 89%。
减少视野温度成像减轻了 tcMRgFUS 中水浴运动造成的温度误差，并实现了具有更高精度的加速温度测绘。
