Temperature and SAR calculations for a human head within volume and surface coils at 64 and 300 MHz
Temperature and SAR calculations for a human head within volume and surface coils at 64 and 300 MHz
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DOI：
10.1002/jmri.20041
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发表时间：
2004-05-01
影响因子：
4.4
通讯作者：
Smith, MB
中科院分区：
文献类型：
--
作者：
Collins, CM;Liu, WZ;Smith, MB
目的：研究磁共振成像射频能量沉积过程中人体头部比能量吸收率(SAR)与温度分布的关系。材料和方法：建立了一个多组织的头部数值模型，该模型考虑了热导率、热容、灌注量、代谢热、电学性质和密度。结果：由于组织灌注率和热传导的依赖性，不同线圈的SAR和温升之间没有良好的整体空间相关性。当一个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，脑内不太可能发生显著的温度升高，尽管头部任何组织的SAR可能被超过限制。结论：在MRI中确保射频安全的尝试往往依赖于来自局部SAR水平的关于局部温度的假设。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。
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 I 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.