Purpose

The purpose of the present study was to develop a numerical workflow for simulating temperature increase in a high-resolution human head and torso model positioned in a whole-body magnetic resonance imaging (MRI) radio-frequency (RF) coil in the presence of a transcranial electric stimulation (tES) setup.

Methods

A customized human head and torso model was developed from medical image data. Power deposition and temperature rise (ΔT) were evaluated with the model positioned in a whole-body birdcage RF coil in the presence of a tES setup. Multiphysics modeling at 3T (123.2 MHz) on unstructured meshes was based on RF circuit, 3D electromagnetic, and thermal co-simulations. ΔT was obtained for (1) a set of electrical and thermal properties assigned to the scalp region, (2) a set of electrical properties of the gel used to ensure proper electrical contact between the tES electrodes and the scalp, (3) a set of electrical conductivity values of skin tissue, (4) four gel patch shapes, and (5) three electrode shapes.

Results

Significant dependence of power deposition and ΔT on the skin’s electrical properties and electrode and gel patch geometries was observed. Differences in maximum ΔT (> 100%) and its location were observed when comparing the results from a model using realistic human tissue properties and one with an external container made of acrylic material. The electrical and thermal properties of the phantom container material also significantly (> 250%) impacted the ΔT results.

Conclusion

Simulation results predicted that the electrode and gel geometries, skin electrical conductivity, and position of the temperature sensors have a significant impact on the estimated temperature rise. Therefore, these factors must be considered for reliable assessment of ΔT in subjects undergoing an MRI examination in the presence of a tES setup.

中文翻译：

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由于存在 3T 的经颅电刺激设置，模拟射频能量诱导的加热。

目的

本研究的目的是开发一个数值工作流程，用于模拟高分辨率人体头部和躯干模型的温度升高，该模型位于全身磁共振成像 (MRI) 射频 (RF) 线圈中，存在经颅电刺激 (tES) 设置。

方法

根据医学图像数据开发了定制的人体头部和躯干模型。在存在 tES 设置的情况下，使用放置在全身鸟笼 RF 线圈中的模型来评估功率沉积和温升 ( ΔT )。非结构化网格上的 3T (123.2 MHz) 多物理场建模基于 RF 电路、3D 电磁和热联合仿真。Δ T是为 (1) 一组分配给头皮区域的电和热特性获得的，(2) 一组用于确保 tES 电极和头皮之间正确电接触的凝胶的电特性，(3) a一组皮肤组织的电导率值，(4) 四种凝胶贴片形状，和 (5) 三种电极形状。

结果

观察到功率沉积和 Δ T对皮肤电特性和电极和凝胶贴片几何形状的显着依赖性。在比较使用真实人体组织特性的模型和使用丙烯酸材料制成的外部容器的模型的结果时，观察到最大 Δ T (> 100%) 及其位置的差异。体模容器材料的电学和热学特性也显着 (> 250%) 影响了 Δ T结果。

结论

仿真结果预测，电极和凝胶的几何形状、皮肤电导率以及温度传感器的位置对估计的温升有重大影响。因此，必须考虑这些因素，以便在存在 tES 设置的情况下对接受 MRI 检查的受试者的ΔT进行可靠评估。