Patient-specific SAR models and in vivo validation

Introduction For parallel transmission, traditional safety concepts need to be re-assessed, as the local specific absorption rate (SAR) becomes a limiting safety constraint [1] that depends on the pulse design as well as on the individual patient anatomy. Whereas the whole-body SAR can be monitored during the scan, the local SAR cannot be measured in clinical practice. Instead, numerical simulations are usually performed for safety approval. In recent years, a number of generic body models have been developed for this purpose (e.g. [2,3]). However, the local SAR is dependent on the subject-specific anatomy and the body pose inside the scanner. Furthermore, these models have, to our knowledge, never been validated in vivo. Therefore, it is highly desirable to provide additional, subject-specific body models for comparative SAR studies. In this work, a method for generating dielectric body models from MR scans was developed, consisting of the following steps: (1) Whole-body images are acquired, (2) a water-fat separation is performed, (3) segmentation into three tissue classes is carried out, and (4) FDTD models are created. The simulation results are validated against measured B1 field maps.