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

该子项目是利用 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得主要资金， 因此可以在其他CRISP条目中表示。列出的机构是 中心，不一定是研究者的机构。 目的 研究MRI中射频能量沉积过程中人体头部的比能量吸收率（SAR）与温度分布之间的关系。 材料和方法 一个多组织的头部的数值模型，考虑导热系数，热容，灌注，代谢热，电性能和密度。对不同频率下的不同线圈进行SAR计算和由此产生的温升。 结果 由于组织依赖性灌注率和热传导，SAR和温度升高之间没有良好的整体空间相关性。当驱动体积线圈以诱导3.0或3.2 W/kg的头部平均SAR水平时，由于其高灌注率，不太可能发生脑中的显著温度升高，尽管可能超过头部任何1 g组织中的SAR限值。 结论 确保MRI中RF安全性的尝试通常依赖于根据局部SAR水平对局部温度的假设。然而，局部SAR和局部温度之间的关系并不简单。在由于脉冲序列要求而需要高SAR水平的情况下，由于温度与安全性之间的关系更直接，温度计算可能优于SAR计算。

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.