TY  - JOUR
A1  - Orzada, Stephan
A1  - Johst, Sören
A1  - Maderwald, Stefan
A1  - Bitz, Andreas
A1  - Solbach, Klaus
A1  - Ladd, Mark E.
T1  - Mitigation of B1(+) inhomogeneity on single-channel transmit systems with TIAMO
JF  - Magnetic Resonance in Medicine
Y1  - 2013
U6  - http://dx.doi.org/10.1002/mrm.24453
SN  - 1522-2594
VL  - 70
IS  - 1
SP  - 290
EP  - 294
PB  - Wiley
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Yazdanbakhsh, Pedram
A1  - Solbach, Klaus
A1  - Bitz, Andreas
T1  - Variable power combiner for RF mode shimming in 7-T MR imaging
JF  - IEEE Transaction on Biomedical Engineering
N2  - This contribution discusses the utilization of RF power in an MRI system with RF mode shimming which enables the superposition of circularly polarized modes of a transmit RF coil array driven by a Butler matrix. Since the required power for the individual modes can vary widely, mode-shimming can result in a significant underutilization of the total available RF power. A variable power combiner (VPC) is proposed to improve the power utilization: it can be realized as a reconfiguration of the MRI transmit system by the inclusion of one additional matrix network which receives the power from all transmit amplifiers at its input ports and provides any desired (combined) power distribution at its output ports by controlling the phase and amplitude of the amplifiers’ input signals. The power distribution at the output ports of the VPC is then fed into the “mode” ports of the coil array Butler matrix in order to superimpose the spatial modes at the highest achievable power utilization. The VPC configuration is compared to the standard configuration of the transmit chain of our MRI system with 8 transmit channels and 16 coils. In realistic scenarios, improved power utilization was achieved from 17% to 60% and from 14% to 55% for an elliptical phantom and a region of interest in the abdomen, respectively, and an increase of the power utilization of 1 dB for a region of interest in the upper leg. In general, it is found that the VPC allows significant improvement in power utilization when the shimming solution demands only a few modes to be energized, while the technique can yield loss in power utilization in cases with many modes required at high power level.
Y1  - 2012
U6  - http://dx.doi.org/10.1109/TBME.2012.2205926
SN  - 1558-2531
VL  - 59
IS  - 9
SP  - 2549
EP  - 2557
PB  - IEEE
CY  - New York
ER  - 
TY  - JOUR
A1  - Orzada, Stephan
A1  - Bitz, Andreas
A1  - Johst, Sören
A1  - Gratz, Marcel
A1  - Völker, Maximilian N.
A1  - Kraff, Oliver
A1  - Abuelhaija, Ashraf
A1  - Fiedler, Thomas M.
A1  - Solbach, Klaus
A1  - Quick, Harald H.
A1  - Ladd, Mark E.
T1  - Analysis of an integrated 8-Channel Tx/Rx body array for use as a body coil in 7-Tesla MRI
JF  - Frontiers in Physics
Y1  - 2017
U6  - http://dx.doi.org/10.3389/fphy.2017.00017
SN  - 2296-424X
N1  - Article number 17
VL  - 5
IS  - Jun
ER  - 
TY  - JOUR
A1  - Orzada, Stephan
A1  - Solbach, Klaus
A1  - Gratz, Marcel
A1  - Brunheim, Sascha
A1  - Fiedler, Thomas M.
A1  - Johst, Sören
A1  - Bitz, Andreas
A1  - Shooshtary, Samaneh
A1  - Abuelhaija, Asjraf
A1  - Voelker, Maximilian N.
A1  - Rietsch, Stefan H. G.
A1  - Kraff, Oliver
A1  - Maderwald, Stefan
A1  - Flöser, Martina
A1  - Oehmingen, Mark
A1  - Quick, Harald H.
A1  - Ladd, Mark E.
T1  - A 32-channel parallel transmit system add-on for 7T MRI
JF  - Plos one
Y1  - 2019
U6  - http://dx.doi.org/10.1371/journal.pone.0222452
ER  -