Ho H S
Center for Devices and Radiological Health, Food and Drug Administration, HFZ-133, 9200 Corporate Boulevard, Rockville, MD 20850, USA.
J Magn Reson Imaging. 2001 Oct;14(4):472-7. doi: 10.1002/jmri.1209.
Magnetic resonance (MR) imaging has become a commonly accepted medical procedure. Manufacturers of medical implant devices are submitting claims that their devices are safe and effective in a MR environment. This paper concentrates on the issue of heating of patients due to the interaction of metallic implants with the strong radiofrequency (RF) magnetic field produced by the MR scanner. The commercially available program XFDTD was used to calculate the specific absorption rate (SAR) distribution in a realistic model of the human body. The body contained a metallic implant and was exposed to RF magnetic fields at 64 MHz from a model of a MR birdcage body coil. The results of the calculation showed that the magnitude of the increased heating of tissues due to the presence of the metallic implant depended on the dimensions, orientation, shape, and location of the metallic implant in the patient. This increased heating of surrounding tissues primarily concentrates in a small volume near the tip of the metallic wire. When the whole-body SAR was normalized to 1 W/kg, a calculated value of 41 W/kg was obtained at this location if the absorption was averaged over 1 g of tissue. However, a maximum value of 310 W/kg was calculated when the absorption was averaged over 1/8 g of tissue.
磁共振（MR）成像已成为一种普遍接受的医疗程序。医疗植入设备制造商声称他们的设备在MR环境中是安全有效的。本文着重探讨金属植入物与MR扫描仪产生的强射频（RF）磁场相互作用导致患者发热的问题。使用商业软件XFDTD计算人体真实模型中的比吸收率（SAR）分布。该人体模型包含一个金属植入物，并暴露于来自MR鸟笼式体线圈模型的64 MHz RF磁场中。计算结果表明，由于金属植入物的存在，组织发热增加的程度取决于金属植入物在患者体内的尺寸、方向、形状和位置。周围组织这种增加的发热主要集中在金属丝尖端附近的小体积区域。当全身SAR归一化为1 W/kg时，如果在1 g组织上平均吸收，则在该位置获得的计算值为41 W/kg。然而，当在1/8 g组织上平均吸收时，计算出的最大值为310 W/kg。
