Istituto Nazionale di Ricerca Metrologica, Torino, Italy.
Phys Med Biol. 2019 Dec 13;64(24):245006. doi: 10.1088/1361-6560/ab5428.
This work focuses on the in silico evaluation of the energy deposed by MRI switched gradient fields in bulk metallic implants and the consequent temperature increase in the surrounding tissues. An original computational strategy, based on the subdivision of the gradient coil switching sequences into sub-signals and on the time-harmonic electromagnetic field solution, allows to realistically simulate the evolution of the phenomena produced by the gradient coils fed according to any MRI sequence. Then, Pennes' bioheat equation is solved through a Douglas-Gunn time split scheme to compute the time-dependent temperature increase. The procedure is validated by comparison with laboratory results, using a component of a realistic hip implant embedded within a phantom, obtaining an agreement on the temperature increase better than 5%, lower than the overall measurement uncertainty. The heating generated inside the body of a patient with a unilateral hip implant when undergoing an Echo-Planar Imaging (EPI) MRI sequence is evaluated and the role of the parameters affecting the thermal results (body position, coil performing the frequency encoding, effects of thermoregulation) is discussed. The results show that the gradient coils can generate local increases of temperature up to some kelvin when acting without radiofrequency excitation. Hence, their contribution in general should not be disregarded when evaluating patients' safety.
这项工作专注于对大块金属植入物中 MRI 切换梯度场所沉积的能量以及周围组织随之产生的温升进行计算机模拟评估。一种基于将梯度线圈切换序列细分为子信号以及时谐电磁场解的原始计算策略，可以根据任何 MRI 序列逼真地模拟梯度线圈产生的现象的演变。然后，通过 Douglas-Gunn 时间分裂方案求解彭内斯生物传热方程，以计算随时间变化的温升。该方法通过与实验室结果进行比较得到验证，使用嵌入在模型中的实际髋关节植入物的一部分，在温升方面的一致性优于 5%，低于整体测量不确定度。评估了单侧髋关节植入物患者在进行回波平面成像 (EPI) MRI 序列时体内产生的加热情况，并讨论了影响热结果的参数（体位、执行频率编码的线圈、体温调节的影响）的作用。结果表明，梯度线圈在没有射频激励的情况下工作时会产生高达几开尔文的局部温升。因此，在评估患者安全性时，通常不应忽视它们的贡献。
