Zhang Zhongshuai, Michaelis Thomas, Frahm Jens
Biomedizinische NMR Forschungs GmbH am Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany.
DZHK (German Center for Cardiovascular Research), partner site Göttingen, Göttingen, Germany.
Quant Imaging Med Surg. 2017 Apr;7(2):251-258. doi: 10.21037/qims.2017.03.03.
Optimal control of minimally invasive interventions by hyperthermia requires dynamic temperature mapping at high temporal resolution.
Based on the temperature-dependent shift of the proton resonance frequency (PRF), this work developed a method for real-time MRI thermometry which relies on highly undersampled radial FLASH MRI sequences with iterative image reconstruction by regularized nonlinear inversion (NLINV). As a first step, the method was validated with use of a temperature phantom and organs (swine kidney) subjected to heating by warm water or a pulsed laser source.
The temperature maps obtained by real-time PRF MRI demonstrate good accuracy as independently controlled by fiber-optic temperature sensors. Moreover, the dynamic results demonstrate both excellent sensitivity to single laser pulses (20 ms duration, 6 J energy output) and high temporal resolution, i.e., 200 ms acquisition times per temperature map corresponding to a rate of 5 frames per second. In addition, future extensions to applications were prepared by addressing the breathing-related motion problem by a pre-recorded library of reference images representative of all respiratory states.
The proposed method for real-time MRI thermometry now warrants further developments towards MRI monitoring of thermal interventions in animals.
通过热疗对微创干预进行最佳控制需要高时间分辨率的动态温度映射。
基于质子共振频率（PRF）随温度的变化，本研究开发了一种实时MRI测温方法，该方法依赖于通过正则化非线性反演（NLINV）进行迭代图像重建的高度欠采样径向FLASH MRI序列。第一步，该方法通过使用温度模型和经温水或脉冲激光源加热的器官（猪肾）进行了验证。
通过实时PRF MRI获得的温度图显示出良好的准确性，这由光纤温度传感器独立控制。此外，动态结果表明该方法对单个激光脉冲（持续时间20毫秒，能量输出6焦耳）具有出色的灵敏度和高时间分辨率，即每个温度图的采集时间为200毫秒，对应于每秒5帧的速率。此外，通过使用代表所有呼吸状态的预记录参考图像库解决与呼吸相关的运动问题，为未来扩展到其他应用做好了准备。
所提出的实时MRI测温方法现在值得进一步发展，以用于动物热干预的MRI监测。
