Foundation of Research on Information Technologies in Society (IT'IS), 8004 Zurich, Switzerland. Department of Information Technology and Electrical Engineering, ETH Zurich, 8092 Zurich, Switzerland.
Phys Med Biol. 2020 Apr 6;65(7):075004. doi: 10.1088/1361-6560/ab7507.
Electromagnetic (EM) radiofrequency (RF) safety testing of elongated active implantable medical devices (AIMD) during magnetic resonance imaging (MRI) requires an RF response model of the implant to assess a wide range of exposure conditions. The model must be validated using a sufficiently large set of incident tangential electric field ([Formula: see text]) conditions that provide diversified exposure. Until now, this procedure was very time consuming and often resulted in poorly defined [Formula: see text] conditions. In this paper, we propose a test field diversity (TFD) validation method that provides more diverse exposure conditions of high fidelity, thereby decreasing the number of implant routings to be tested. The TFD method is based on the finding that the amplitude and phase of [Formula: see text] along a single lead path in a cylindrical phantom can be sufficiently varied by changing the polarization of the incident 64 and 128 MHz magnetic fields inside standard birdcage test coils. The method is validated, its benefits are demonstrated, and an uncertainty budget is developed. First, the numerically determined field conditions were experimentally verified. The RF transfer function of a 90 cm long spinal cord stimulator was successfully validated with the TFD approach and excitation conditions that cover a > 10 dB dynamic range of RF-heating enhancement factors (for identical trajectory-averaged incident field strength). The new TFD method yields an improved and reliable validation of the AIMD RF response model with low uncertainty, i.e. < 1.5 dB, for both 1.5 and 3.0 T evaluations.
在磁共振成像（MRI）期间对细长的有源植入式医疗器械（AIMD）进行电磁（EM）射频（RF）安全性测试，需要对植入物的 RF 响应模型进行评估，以评估广泛的暴露条件。该模型必须使用足够大的一组入射切向电场（[Formula: see text]）条件进行验证，这些条件提供多样化的暴露。到目前为止，该过程非常耗时，并且常常导致定义不明确的[Formula: see text]条件。在本文中，我们提出了一种测试场多样性（TFD）验证方法，该方法提供了更具多样化和高保真度的暴露条件，从而减少了需要测试的植入物布线数量。TFD 方法基于这样的发现，即在圆柱形仿体中的单个引线路径上，[Formula: see text]的幅度和相位可以通过改变标准鸟笼测试线圈内部入射的 64 和 128 MHz 磁场的极化来充分改变。该方法进行了验证，展示了其优势，并制定了不确定度预算。首先，通过实验验证了数值确定的场条件。使用 TFD 方法和激励条件成功地对 90 厘米长的脊髓刺激器的射频传输函数进行了验证，该激励条件涵盖了 >10 dB 的射频加热增强因子的动态范围（对于相同的轨迹平均入射场强）。新的 TFD 方法可改善和可靠地验证 AIMD 的 RF 响应模型，其不确定度<1.5 dB，适用于 1.5 和 3.0 T 的评估。
