TY  - JOUR
A1  - Orzada, Stephan
A1  - Ladd, Mark E.
A1  - Bitz, Andreas
T1  - A method to approximate maximum local SAR in multichannel transmit MR systems without transmit phase information
JF  - Magnetic Resonance in Medicine
N2  - Purpose
To calculate local specific absorption rate (SAR) correctly, both the amplitude and phase of the signal in each transmit channel have to be known. In this work, we propose a method to derive a conservative upper bound for the local SAR, with a reasonable safety margin without knowledge of the transmit phases of the channels.

Methods
The proposed method uses virtual observation points (VOPs). Correction factors are calculated for each set of VOPs that prevent underestimation of local SAR when the VOPs are applied with the correct amplitudes but fixed phases.

Results
The proposed method proved to be superior to the worst-case calculation based on the maximum eigenvalue of the VOPs. The mean overestimation for six coil setups could be reduced, whereas no underestimation of the maximum local SAR occurred. In the best investigated case, the overestimation could be reduced from a factor of 3.3 to a factor of 1.7.

Conclusion
The upper bound for the local SAR calculated with the proposed method allows a fast estimation of the local SAR based on power measurements in the transmit channels and facilitates SAR monitoring in systems that do not have the capability to monitor transmit phases
Y1  - 2016
U6  - http://dx.doi.org/10.1002/mrm.26398
SN  - 1522-2594
VL  - 78
IS  - 2
SP  - 805
EP  - 811
PB  - International Society for Magnetic Resonance in Medicine
ER  - 
TY  - JOUR
A1  - Fiedler, Thomas M.
A1  - Ladd, Mark E.
A1  - Bitz, Andreas
T1  - RF safety assessment of a bilateral four-channel transmit/receive 7 Tesla breast coil: SAR versus temperature limits
JF  - Medical Physics
Y1  - 2017
U6  - http://dx.doi.org/10.1002/mp.12034
N1  - This article is corrected by:
Errata: Erratum: “RF safety assessment of a bilateral four-channel transmit/receive 7 Tesla breast coil: SAR versus tissue temperature limits” [Med. Phys. 44(1), 143–157 (2017)] Volume 44, Issue 2, 772
VL  - 44
IS  - 1
SP  - 143
EP  - 157
ER  - 
TY  - JOUR
A1  - Noureddine, Yacine
A1  - Kraff, Oliver
A1  - Ladd, Mark E.
A1  - Wrede, Karsten H.
A1  - Chen, Bixia
A1  - Quick, Harald H.
A1  - Schaefers, Gregor
A1  - Bitz, Andreas
T1  - In vitro and in silico assessment of RF-induced heating around intracranial aneurysm clips at 7 Tesla
JF  - Magnetic Resonance in Medicine
Y1  - 2017
U6  - http://dx.doi.org/10.1002/mrm.26650
SN  - 1522-2594
IS  - Early view
PB  - Wiley
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Fiedler, Thomas M.
A1  - Ladd, Mark E.
A1  - Bitz, Andreas
T1  - SAR Simulations & Safety
JF  - NeuroImage
Y1  - 2017
U6  - http://dx.doi.org/10.1016/j.neuroimage.2017.03.035
SN  - 1053-8119
IS  - Epub ahead of print
PB  - Elsevier
CY  - Amsterdam
ER  -