Simunić D, Wach P, Renhart W, Stollberger R
Graz University of Technology, Institute of Biomedical Engineering, Graz, Austria.
IEEE Trans Biomed Eng. 1996 Jan;43(1):88-94. doi: 10.1109/10.477704.
Finite Element Method (FEM) using 26-node isoparametric finite elements was applied for modeling saddle-shaped head coils used in Magnetic Resonance Imaging (MRI) generating linearly polarized radiofrequency (RF) pulses at 64 MHz. The human head was modeled from MR scans of a volunteer and additional information were taken from Atlas of Sectional Human Anatomy. The physical dimensions of the head coil and the head permit a calculation of the outside magnetic field by a quasistatic approach. Of course, a full-wave approach was applied within the head. Values of specific energy--specific absorption (SA)--as well as of specific power--specific absorption rate (SAR)--were calculated by the method, simulating the real exposure conditions during MRI. Although the results of the used numerical method were compared previously to the results of the analytical solution with homogeneous sphere and to the results of RF measurements on heterogeneous phantom, a comparison between the numerical results of the modeled human head and in vivo measurements performed on the human head of the volunteer was made once more. Since the results are in excellent agreement, they argue for the correctness of the numerical method. The "worst-case" temperature elevations delta theta of the "hot-spots" were calculated, as well. Finally, the results of SA, SAR, and delta theta are compared to the existing recommendations.
采用26节点等参有限元的有限元方法（FEM），对用于磁共振成像（MRI）的鞍形头部线圈进行建模，该线圈可在64MHz频率下产生线性极化射频（RF）脉冲。根据一名志愿者的磁共振扫描数据对人体头部进行建模，并从《人体断面解剖图谱》中获取其他信息。头部线圈和头部的物理尺寸允许通过准静态方法计算外部磁场。当然，在头部内部采用了全波方法。通过该方法计算比能量——比吸收率（SA）以及比功率——比吸收率（SAR），模拟MRI过程中的实际暴露条件。尽管之前已将所使用数值方法的结果与均匀球体解析解的结果以及非均匀体模上的射频测量结果进行了比较，但还是再次对模拟人体头部的数值结果与对志愿者头部进行的体内测量结果进行了比较。由于结果高度吻合，这证明了数值方法的正确性。还计算了“热点”的“最坏情况”温度升高量Δθ。最后，将SA、SAR和Δθ的结果与现有建议进行了比较。
