Evaluation of the Specific Absorption Rate for Simultaneous Multi-Frequency RF Excitations in 7-T Magnetic Resonance Imaging

Radiofrequency (RF) safety in magnetic resonance imaging (MRI) is mainly verified using the specific absorption rate (SAR) in research involving humans. Universal MRI scanners measure the distribution of the hydrogen nucleus ¹H; hence, RF safety previously focused on the single frequency at which ¹H resonates. However, MRI technology is gradually transforming into simultaneous multi-frequency (MF) RF excitation to provide significant information related to biochemical changes in addition to morphological changes. These changes necessitate close monitoring of RF safety by considering other SAR aspects. This study proposes three evaluation methods for estimating the SAR value: summation of the SAR values of individual peaks, using the SAR value of the highest individual peak, and using the peak of the combined SAR for simultaneous RF excitation under MF RF excitation. This method, which is environmentally friendly, can be applied to various approaches for evaluating the RF safety in MF MRI applications.