TEMPERATURE AND SAR CALCULATIONS FOR A HUMAN HEAD WITHIN VOLUME AND SURFACE COI

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 目的 目的：研究射频能量沉积过程中人体头部比能量吸收率(SAR)与温度分布之间的关系。 材料和方法 建立了头部的多组织数值模型，该模型考虑了导热系数、热容、灌注量、代谢热、电学性质和密度。对不同线圈在不同频率下的SAR和由此产生的温升进行了计算。 结果 由于组织相关的灌注率和热传导，在SAR和温度升高之间没有良好的整体空间相关性。当体积线圈被驱动以诱导头部平均SAR水平为3.0或3.2W/kg时，由于其高灌注率，大脑不太可能出现显著的温度升高，尽管头部任何1g组织的SAR可能被超过限制。 结论 在磁共振成像中确保射频安全的尝试通常依赖于对当地SAR水平的局部温度的假设。然而，本地SAR和本地气温之间的关系并不是一帆风顺的。在由于脉冲序列要求而需要高SAR水平的情况下，由于温度和安全性之间更直接的关系，所以温度计算可能比SAR计算更可取。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Purpose To examine relationships between specific energy absorption rate (SAR) and temperature distributions in the human head during radio frequency energy deposition in MRI. Materials and Methods A multi-tissue numerical model of the head was developed that considered thermal conductivity, heat capacity, perfusion, heat of metabolism, electrical properties, and density. Calculations of SAR and the resulting temperature increase were performed for different coils at different frequencies. Results Because of tissue-dependant perfusion rates and thermal conduction, there is not a good overall spatial correlation between SAR and temperature increase. When a volume coil is driven to induce a head average SAR level of either 3.0 or 3.2 W/kg, it is unlikely that a significant temperature increase in the brain will occur due to its high rate of perfusion, although limits on SAR in any 1 g of tissue in the head may be exceeded. Conclusion Attempts to ensure RF safety in MRI often rely on assumptions about local temperature from local SAR levels. The relationship between local SAR and local temperature is not, however, straightforward. In cases where high SAR levels are required due to pulse sequence demands, calculations of temperature may be preferable to calculations of SAR because of the more direct relationship between temperature and safety.