Local specific absorption rate in brain tumors at 7 tesla

Abstract

Purpose MR safety at 7 Tesla relies on accurate numerical simulations of transmit electromagnetic fields to fully assess local specific absorption rate (SAR) safety. Numerical simulations for SAR safety are currently performed using models of healthy patients. These simulations might not be useful for estimating SAR in patients who have large lesions with potentially abnormal dielectric properties, e.g., brain tumors. Theory and Methods In this study, brain tumor patient models are constructed based on scans of four patients with high grade brain tumors. Dielectric properties for the modeled tumors are assigned based on electrical properties tomography data for the same patients. Simulations were performed to determine SAR. Results Local SAR increases in the tumors by as much as 30%. However, the location of the maximum 10-gram averaged SAR typically occurs outside of the tumor, and thus does not increase. In the worst case, if the tumor model is moved to the location of maximum electric field intensity, then we do observe an increase in the estimated peak 10-gram SAR directly related to the tumor. Conclusion Peak local SAR estimation made on the results of a healthy patient model simulation may underestimate the true peak local SAR in a brain tumor patient.