论文标题
对7T间隙平行传输电磁安全模拟所需的最小组织组数量的研究
An investigation into the minimum number of tissue groups required for 7T in-silico parallel transmit electromagnetic safety simulations in the human head
论文作者
论文摘要
目的：允许特定的吸收率（SAR）放置脉冲序列设计的安全限制，尤其是在超高场（$ \ geq 7 $ tesla）。由于受试者间的可变性，通常会根据标准人类模型保守估算SAR，该模型包括应用安全余量以确保安全操作。减少限制的一种方法是从其分段的MR图像中创建更准确的主体模型。这项研究使用电磁模拟来研究准确确定人头中SAR所需的最小组织组数量。 方法：根据组织的电导率，拼接性和组织的质量密度，将完全表征的电磁体模型具有47种组织类型的组织类型分组为不同的组织簇。使用平行传输（PTX）头线线圈内部模型的电磁模拟用于确定所需的组织簇的最小数量，以准确确定受试者特异性的SAR。然后，使用两个额外的良好电磁人体模型评估已鉴定的组织簇。 结果：发现至少需要4个簇和空气才能进行准确的SAR估计。这些组织簇以灰质，脂肪，皮质骨和脑脊液为中心。对于所有三个模拟模型，PTX最大10GSAR始终确定为<12％的误差，相对于完整的47-Tissue模型。 结论：在7T时使用PTX时，至少需要4个簇和空气来产生人头的准确个性化SAR模拟。
Purpose: Safety limits for the permitted Specific Absorption Rate (SAR) place restrictions on pulse sequence design, especially at ultra-high fields ($\geq 7$ tesla). Due to inter-subject variability, the SAR is usually conservatively estimated based on standard human models that include an applied safety margin to ensure safe operation. One approach to reducing the restrictions is to create more accurate subject-specific models from their segmented MR images. This study uses electromagnetic simulations to investigate the minimum number of tissue groups required to accurately determine SAR in the human head. Methods: Tissue types from a fully characterized electromagnetic human model with 47 tissue types in the head and neck region were grouped into different tissue clusters based on the conductivities, permittivities, and mass densities of the tissues. Electromagnetic simulations of the head model inside a parallel transmit (pTx) head coil at 7T were used to determine the minimum number of required tissue clusters to accurately determine the subject-specific SAR. The identified tissue clusters were then evaluated using two additional well-characterized electromagnetic human models. Results: A minimum of 4 clusters plus air was found to be required for accurate SAR estimation. These tissue clusters are centered around gray matter, fat, cortical bone, and cerebrospinal fluid. For all three simulated models the pTx maximum 10gSAR was consistently determined to within an error of <12% relative to the full 47-tissue model. Conclusion: A minimum of 4 clusters plus air are required to produce accurate personalized SAR simulations of the human head when using pTx at 7T.
