Department of Physics, University of Alberta, 11322-89th Avenue, Edmonton, Alberta T6G 2G7, Canada.
Phys Med Biol. 2010 Feb 7;55(3):735-46. doi: 10.1088/0031-9155/55/3/013. Epub 2010 Jan 13.
The integration of medical linear accelerators (linac) with magnetic resonance imaging (MRI) systems is advancing the current state of image-guided radiotherapy. The MRI in these integrated units will provide real-time, accurate tumor locations for radiotherapy treatment, thus decreasing geometric margins around tumors and reducing normal tissue damage. In the real-time operation of these integrated systems, the radiofrequency (RF) coils of MRI will be irradiated with radiation pulses from the linac. The effect of pulsed radiation on MRI radio frequency (RF) coils is not known and must be studied. The instantaneous radiation induced current (RIC) in two different MRI RF coils were measured and presented. The frequency spectra of the induced currents were calculated. Some basic characterization of the RIC was also done: isolation of the RF coil component responsible for RIC, dependence of RIC on dose rate, and effect of wax buildup placed on coil on RIC. Both the time and frequency characteristics of the RIC were seen to vary with the MRI RF coil used. The copper windings of the RF coils were isolated as the main source of RIC. A linear dependence on dose rate was seen. The RIC was decreased with wax buildup, suggesting an electronic disequilibrium as the cause of RIC. This study shows a measurable RIC present in MRI RF coils. This unwanted current could be possibly detrimental to the signal to noise ratio in MRI and produce image artifacts.
医学线性加速器（linac）与磁共振成像（MRI）系统的整合正在推进图像引导放射治疗的现状。这些集成单元中的 MRI 将为放射治疗提供实时、准确的肿瘤位置，从而减少肿瘤周围的几何边界，并减少正常组织损伤。在这些集成系统的实时操作中，MRI 的射频（RF）线圈将受到来自 linac 的辐射脉冲的照射。脉冲辐射对 MRI 射频（RF）线圈的影响尚不清楚，必须进行研究。测量并呈现了两个不同的 MRI RF 线圈中的瞬时辐射感应电流（RIC）。计算了感应电流的频谱。还对 RIC 进行了一些基本特性分析：分离负责 RIC 的 RF 线圈组件、RIC 对剂量率的依赖性以及放置在线圈上的蜡堆积对 RIC 的影响。RIC 的时间和频率特性都随所使用的 MRI RF 线圈而变化。RF 线圈的铜绕组被隔离为 RIC 的主要来源。观察到与剂量率呈线性关系。随着蜡堆积的增加，RIC 减小，这表明 RIC 的产生是由于电子失衡。这项研究表明，MRI RF 线圈中存在可测量的 RIC。这种不需要的电流可能对 MRI 的信噪比有害，并产生图像伪影。
