Department of Electrical and Computer Engineering, University of Houston, Houston, TX 77204, United States of America.
Phys Med Biol. 2018 Jul 6;63(13):135020. doi: 10.1088/1361-6560/aacbf2.
A typical cochlear implant system under magnetic resonance imaging (MRI) procedures may couple with the radio frequency (RF) electromagnetic field (EMF) and results in an intensified electric field at the lead tip. As a result, the RF energy deposited in human tissues around the lead tip may induce heating and cause tissue damage concerns. The purpose of this work is to evaluate the RF-EMF-induced heating for cochlear implant system in 1.5 T MRI coil and highlight the factors that have significant effects on the heating. The potential factors involved in the RF-EMF-induced heating including the lead type, lead trajectory, human model and MRI landmark. In this paper, the RF-EMF-induced heating for three types of leads is evaluated in two virtual human models. A total of 24 lead trajectories and 23 anatomical landmark positions are studied using the transfer function method. The average temperature rise for all the studied cases in the human models is 0.79 °C, and the maximum value is 2.80 °C for a maximum whole-body average specific absorption rate of 2 W kg in an RF body coil. It is found that the lead trajectory and MRI landmark are two primary influencing factors. The maximum temperature rises for different lead trajectories can vary from 0.82 to 2.80 °C. A difference in heating of 2.80 °C is observed when the landmark changes from -100 to 700 mm. This work demonstrates that it is necessary to take these factors into account when evaluating the RF-EMF-induced heating for implanted medical devices.
在磁共振成像（MRI）过程中，典型的人工耳蜗植入系统可能会与射频（RF）电磁场（EMF）耦合，并在导联尖端产生强化电场。结果，沉积在导联尖端周围人体组织中的 RF 能量可能会引起加热并导致组织损伤。这项工作的目的是评估 1.5T MRI 线圈中人工耳蜗植入系统的射频电磁场诱导加热，并强调对加热有显著影响的因素。涉及射频电磁场诱导加热的潜在因素包括导联类型、导联轨迹、人体模型和 MRI 解剖标志。本文在两个虚拟人体模型中评估了三种导联的射频电磁场诱导加热。使用传递函数方法研究了 24 条导联轨迹和 23 个解剖标志位置。在人体模型中，所有研究病例的平均温升为 0.79°C，在射频体线圈中全身平均比吸收率最大值为 2W/kg 时，最大温升为 2.80°C。结果表明，导联轨迹和 MRI 解剖标志是两个主要影响因素。不同导联轨迹的最大温升范围从 0.82°C 到 2.80°C。当解剖标志从-100mm 变化到 700mm 时，加热差异为 2.80°C。这项工作表明，在评估植入式医疗设备的射频电磁场诱导加热时，有必要考虑这些因素。
