基于回波平移序列的快速三维磁共振温度成像方法

高强度聚焦超声（HIFU）是一种无创的热消融疗法，为保证其安全性和有效性，需要一种精度高、速度快的测温方法在其治疗过程中对温度进行监控.基于质子共振频率位移（PRFS）的磁共振温度成像（MRT）对温度具有较高的灵敏度，且与温度具有良好的线性关系，因此常被用于引导HIFU治疗.然而在实际应用中，HIFU治疗的最大隐患在于可能造成表皮灼伤，并且灼伤区域可能与焦点区域相隔较远.因此MRT的监控范围十分重要.本文基于三维回波平移成像序列，结合可控混叠的空间并行成像技术，实现了时间分辨率为3 s的快速三维温度成像.为了验证该方法的精度，本文首先设计了仿体降温实验，利用光纤温度计验证回波平移序列测温的准确度和精确度.然后在室温条件下扫描离体猪肉组织，对比加速前后的MRT的测温精确度.在HIFU加热条件下扫描离体猪肉组织，对比加速前后的MRT的测温准确度.结果显示，本文提出的方法可以在3 s内完成三维温度精准测量，对于HIFU治疗的安全监控具有重要意义.

Fast Three-Dimensional Magnetic Resonance Thermometry Using an Echo-Shifted Gradient-Recalled Sequence

High-intensity focused ultrasound (HIFU) is a noninvasive thermal ablation therapy. Thermometry techniques with high precision and temporal resolution are needed to ensure the safety and effectiveness of HIFU. The magnetic resonance thermometry (MRT) technique based on proton resonance frequency shift (PRFS) shows good linearity with and high sensitivity to temperature change, and is frequently used in HIFU therapy. In practice, HIFU may have a potential danger of causing unwanted skin burns far away from the focus of ultrasound irradiation. It is therefore desirable to increase the spatial coverage of MRT measurements to include the skins. In this work, a fast three-dimensional (3D) MRT technique was developed based on an echo-shifted gradient-recalled sequence with controlled aliasing in volumetric parallel imaging. Phantom experiments were first used to calibrate the accuracy and precision of temperature measurements made by the proposed technique to those obtained by an optical fiber thermometer. Pork tissues were then scanned at room temperature to determine the precision of temperature measurements before and after imaging acceleration. The pork tissues were also scanned under the condition of HIFU heating to compare the accuracy of temperature measurements with or without imaging acceleration.