Gellermann Johanna, Wlodarczyk Waldemar, Ganter Hildegard, Nadobny Jacek, Fähling Horst, Seebass Martin, Felix Roland, Wust Peter
Department of Radiation Medicine, Charité Medical School, Berlin, Germany.
Int J Radiat Oncol Biol Phys. 2005 Jan 1;61(1):267-77. doi: 10.1016/j.ijrobp.2004.05.009.
This study investigates the feasibility and accuracy of noninvasive magnetic resonance (MR) monitoring for a system that includes a multiantenna applicator for part-body hyperthermia (SIGMA-Eye applicator, BSD-2000/3D) and a 1.5 Tesla MR tomograph (Siemens Magnetom Symphony).
A careful electrical decoupling enabled simultaneous operation of both systems, the hyperthermia system (100 MHz, up to 1600 W) and the MR tomograph (63.9 MHz). We used the phase data sets of a gradient echo sequence (long echo time TE = 20 ms) according to the proton frequency shift (PFS) method to determine MR temperature changes. Data postprocessing and visualization was conducted in the software platform AMIRA-HyperPlan. Heating was evaluated in an elliptical Lucite cylinder of 50 cm length filled with tissue-equivalent agarose and a skeleton made from low-dielectric material to simulate the heterogeneity of a real patient. Multiple catheters were included longitudinally for direct thermometry (using Bowman high-impedance thermistors). The phantom was positioned in the 24-antenna applicator SIGMA-Eye employing the integrated water bolus (filled with deionized water) both for coupling the radiated power into the lossy medium and to enable a correction procedure based on direct temperature measurements.
In eight phantom experiments we monitored the heating in the applicator not only by repetitive acquisition of three-dimensional MR datasets, but also by measuring temperature-time curves directly at selected spatial positions. For the correction, we specified regions in the bolus. Direct bolus temperatures at fixed positions were taken to aim at best possible agreement between MR temperatures and these direct temperature-time curves. Then we compared additional direct temperature-position scans (thermal maps) for each experiment with the MR temperatures along these probes, which agreed satisfactorily (averaged accuracy of +/- 0.4-0.5 degrees C). The deviations decreased with decreasing observation time, temperature increase, and thermal load to the surroundings (corresponding to bolus heating)-estimating a resolution of, at best, +/- 0.2-0.3 degrees C. The acquired MR temperature distributions give also insight into limitations and control possibilities of regional hyperthermia (annular phased array technology) for various tumor sites.
On-line MR monitoring of regional hyperthermia by using the PFS method is feasible in a phantom setup and can be further developed for clinical applications.
本研究调查了一种系统的无创磁共振（MR）监测的可行性和准确性，该系统包括用于局部热疗的多天线 applicator（SIGMA-Eye applicator，BSD-2000/3D）和一台 1.5 特斯拉 MR 断层扫描仪（西门子 Magnetom Symphony）。
通过仔细的电气去耦实现了两个系统的同时运行，即热疗系统（100MHz，高达 1600W）和 MR 断层扫描仪（63.9MHz）。我们根据质子频率偏移（PFS）方法使用梯度回波序列（长回波时间 TE = 20ms）的相位数据集来确定 MR 温度变化。数据后处理和可视化在软件平台 AMIRA-HyperPlan 中进行。在一个 50cm 长的椭圆形有机玻璃圆柱体中进行加热评估，该圆柱体填充有组织等效琼脂糖和由低介电材料制成的骨架，以模拟真实患者的异质性。纵向包含多个导管用于直接测温（使用 Bowman 高阻抗热敏电阻）。体模放置在采用集成水囊（填充去离子水）的 24 天线 applicator SIGMA-Eye 中，既用于将辐射功率耦合到有损耗介质中，也用于基于直接温度测量实现校正程序。
在八个体模实验中，我们不仅通过重复采集三维 MR 数据集来监测 applicator 中的加热情况，还通过在选定空间位置直接测量温度-时间曲线来进行监测。为了进行校正，我们在水囊中指定了区域。采用固定位置的直接水囊温度以力求 MR 温度与这些直接温度-时间曲线之间达到最佳一致。然后我们将每个实验的额外直接温度-位置扫描（热图）与沿这些探头的 MR 温度进行比较，二者吻合良好（平均精度为±0.4 - 0.5℃）。偏差随着观察时间的减少、温度的升高以及对周围环境的热负荷（对应于水囊加热）的降低而减小 - 估计最佳分辨率为±0.2 - 0.3℃。所获取的 MR 温度分布还深入了解了针对各种肿瘤部位的区域热疗（环形相控阵技术）的局限性和控制可能性。
在体模设置中，使用 PFS 方法对区域热疗进行在线 MR 监测是可行的，并且可以进一步开发用于临床应用。
