TY  - JOUR
AU  - Fiedler, Thomas
AU  - Ladd, Mark
AU  - Bitz, Andreas
TI  - RF safety assessment of a bilateral four-channel transmit/receive 7 Tesla breast coil: SAR versus tissue temperature limits.15
JO  - Medical physics
VL  - 44
IS  - 1
SN  - 0094-2405
CY  - New York, NY
M1  - DKFZ-2017-00080
SP  - 143 - 157
PY  - 2017
AB  - The purpose of this work was to perform an RF safety evaluation for a bilateral four-channel transmit/receive breast coil and to determine the maximum permissible input power for which RF exposure of the subject stays within recommended limits. The safety evaluation was done based on SAR as well as on temperature simulations. In comparison to SAR, temperature is more directly correlated with tissue damage, which allows a more precise safety assessment. The temperature simulations were performed by applying three different blood perfusion models as well as two different ambient temperatures. The goal was to evaluate whether the SAR and temperature distributions correlate inside the human body and whether SAR or temperature is more conservative with respect to the limits specified by the IEC.A simulation model was constructed including coil housing and MR environment. Lumped elements and feed networks were modeled by a network co-simulation. The model was validated by comparison of S-parameters and B1(+) maps obtained in an anatomical phantom. Three numerical body models were generated based on 3 Tesla MRI images to conform to the coil housing. SAR calculations were performed and the maximal permissible input power was calculated based on IEC guidelines. Temperature simulations were performed based on the Pennes bioheat equation with the power absorption from the RF simulations as heat source. The blood perfusion was modeled as constant to reflect impaired patients as well as with a linear and exponential temperature-dependent increase to reflect two possible models for healthy subjects. Two ambient temperatures were considered to account for cooling effects from the environment.The simulation model was validated with a mean deviation of 3
LB  - PUB:(DE-HGF)16
C6  - pmid:28102957
DO  - DOI:10.1002/mp.12034
UR  - https://inrepo02.dkfz.de/record/119325
ER  -