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  - 
TY  - JOUR
A1  - Fiedler, Thomas M.
A1  - Orzada, Stephan
A1  - Flöser, Martina
A1  - Rietsch, Stefan H. G.
A1  - Schmidt, Simon
A1  - Stelter, Jonathan K.
A1  - Wittrich, Marco
A1  - Quick, Harald H.
A1  - Bitz, Andreas
A1  - Ladd, Mark E.
T1  - Performance and safety assessment of an integrated transmitarray for body imaging at 7 T under consideration of specificabsorption rate, tissue temperature, and thermal dose
JF  - NMR in Biomedicine
N2  - In this study, the performance of an integrated body-imaging array for 7 T with 32 radiofrequency (RF) channels under consideration of local specific absorption rate (SAR), tissue temperature, and thermal dose limits was evaluated and the imaging performance was compared with a clinical 3 T body coil.

Thirty-two transmit elements were placed in three rings between the bore liner and RF shield of the gradient coil. Slice-selective RF pulse optimizations for B1 shimming and spokes were performed for differently oriented slices in the body under consideration of realistic constraints for power and local SAR. To improve the B1+ homogeneity, safety assessments based on temperature and thermal dose were performed to possibly allow for higher input power for the pulse optimization than permissible with SAR limits.

The results showed that using two spokes, the 7 T array outperformed the 3 T birdcage in all the considered regions of interest. However, a significantly higher SAR or lower duty cycle at 7 T is necessary in some cases to achieve similar B1+ homogeneity as at 3 T. The homogeneity in up to 50 cm-long coronal slices can particularly benefit from the high RF shim performance provided by the 32 RF channels. The thermal dose approach increases the allowable input power and the corresponding local SAR, in one example up to 100 W/kg, without limiting the exposure time necessary for an MR examination.

In conclusion, the integrated antenna array at 7 T enables a clinical workflow for body imaging and comparable imaging performance to a conventional 3 T clinical body coil.
KW  - body imaging at 7 T MRI
KW  - thermal dose
KW  - tissue temperature
KW  - transmit antenna arrays
Y1  - 2022
U6  - http://dx.doi.org/10.1002/nbm.4656
SN  - 0952-3480 (Print)
SN  - 1099-1492 (Online)
VL  - 35
IS  - 5
SP  - 1
EP  - 17
PB  - Wiley
ER  -