Development of Non-Invasive Temperature Monitoring for RF Interstitial Hyperthermia Using an 0.2-T Open MR-Apparatus

非侵入性的、实时监测温度变化分布的技术已经成为热疗的理想方法之一。本研究的目的是评估在极低磁场(0.2-T)的射频间质热疗中使用体模和动物使用相位映射方法进行温度映射的可行性。实验使用的是使用头表面线圈的0.2T磁共振介入放射学设备。以植物油容器为对比物，观察磁场偏移量。用梯度回波相图法测量了化学位移的变化。射频间质热疗的功率由射频发生器提供，频率为9.0~13.5 MHz，功率为2~7W。(1)磁场起伏的空间分布：测量油模中的相位差分布。空间分辨率为1.56×1.56×5 mm~3。(2)将4.5 mm的CuSO4溶液模体用微波加热到80℃，然后对冷却过程中的相位差图像进行处理，得到温度系数。测得温度系数为-0.0096 ppm/℃。(3)将5只新西兰大白兔麻醉后固定，以验证该系统的有效性。将间质电极插入兔的大腿。射频电源和温度处理交替进行。重建的温度图像在5秒内进行处理，验证了0.2-T开放式磁共振系统准实时处理温度变化分布成像的可行性。本研究结果提示，这种低端场扫描仪在射频间质热疗中监测体内体温的临床应用是可能的。

The technique of a non-invasive, real-time monitoring of the temperature change distribution has been one of the desired methods in performing hyperthermia treatment. The purpose of this study was to estimate the feasibility of temperature mapping using the phase mapping method during RF interstitial hyperthermia with a very low magnetic field(0.2-T) using phantoms and animals.The experiments were performed with a 0.2-T MR unit for interventional radiology using a head surface coil. Vegetable oil containers were used as comparative substance to observe the magnetic field deviation. The chemical shift change was measured with the phase mapping method using a gradient echo process. For RF interstitial hyperthermia, the power was supplied by a RF generator, which was driven at a frequency between 9.0 and 13.5 MHz, with the power of 2 to 7 W. (1)The spatial distribution of the magnetic field fluctuation : measured as phase difference distribution in an oil phantom. The spatial resolution was 1.56 x 1.56 x 5 mm3. (2)To obtain the temperature coefficient, 4.5mM CuSO4 solution phantoms were warmed up to 80℃ by microwave, then the phase difference images were processed during the cooling. The temperature coefficient obtained was -0.0096 ppm/℃. (3)Anesthetized and immobilized five New Zealand- White rabbits were used to confirm the efficacy of this system. The interstitial electrode was inserted into the rabbit's thigh. The RF power supply and temperature processing were performed alternately. The reconstructed temperature images were processed in 5 seconds.Feasibility of the temperature change distribution imaging with the 0.2-T open MR system with a quasi-real-time processing was demonstrated. The results shown in the present study suggest the possibility of clinical applications of such low-end field scanners to monitor the internal body temperature during RF interstitial hyperthermia.