TY  - JOUR
A1  - Umutlu, Lale
A1  - Orzada, Stephan
A1  - Kinner, Sonja
A1  - Maderwald, Stefan
A1  - Bronte, Irina
A1  - Bitz, Andreas
A1  - Kraff, Oliver
A1  - Ladd, Susanne C.
A1  - Antoch, Gerald
A1  - Ladd, Mark E.
A1  - Quick, Harald H.
A1  - Lauenstein, Thomas C.
T1  - Renal imaging at 7 Tesla: preliminary results
JF  - European Radiology
N2  - Objective
To investigate the feasibility of 7T MR imaging of the kidneys utilising a custom-built 8-channel transmit/receive radiofrequency body coil.

Methods
In vivo unenhanced MR was performed in 8 healthy volunteers on a 7T whole-body MR system. After B0 shimming the following sequences were obtained: 1) 2D and 3D spoiled gradient-echo sequences (FLASH, VIBE), 2) T1-weighted 2D in and opposed phase 3) True-FISP imaging and 4) a T2-weighted turbo spin echo (TSE) sequence. Visual evaluation of the overall image quality was performed by two radiologists.

Results
Renal MRI at 7T was feasible in all eight subjects. Best image quality was found using T1-weighted gradient echo MRI, providing high anatomical details and excellent conspicuity of the non-enhanced vasculature. With successful shimming, B1 signal voids could be effectively reduced and/or shifted out of the region of interest in most sequence types. However, T2-weighted TSE imaging remained challenging and strongly impaired because of signal heterogeneities in three volunteers.

Conclusion
The results demonstrate the feasibility and diagnostic potential of dedicated 7T renal imaging. Further optimisation of imaging sequences and dedicated RF coil concepts are expected to improve the acquisition quality and ultimately provide high clinical diagnostic value.
Y1  - 2011
SN  - 1432-1084
VL  - 21
IS  - 4
SP  - 841
EP  - 849
PB  - Springer
CY  - Berlin
ER  - 
TY  - JOUR
A1  - Kraff, Oliver
A1  - Bitz, Andreas
A1  - Kruszona, Stefan
A1  - Orzada, Stephan
A1  - Schaefer, Lena C.
A1  - Theysohn, Jens M.
A1  - Maderwald, Stefan
A1  - Ladd, Mark E.
A1  - Quick, Harald H.
T1  - An eight-channel phased array RF coil for spine MR imaging at 7 T
JF  - Investigative Radiology
Y1  - 2009
U6  - http://dx.doi.org/10.1097/RLI.0b013e3181b24ab7
SN  - 1536-0210
VL  - 44
IS  - 11
SP  - 734
EP  - 740
PB  - Lippincott Williams & Wilkins
ER  - 
TY  - JOUR
A1  - Rietsch, Stefan H. G.
A1  - Pfaffenrot, Viktor
A1  - Bitz, Andreas
A1  - Orzada, Stephan
A1  - Brunheim, Sascha
A1  - Lazik-Palm, Andrea
A1  - Theysohn, Jens M.
A1  - Ladd, Mark E.
A1  - Quick, Harald H.
A1  - Kraff, Oliver
T1  - An 8-channel transceiver 7-channel receive RF coil setup for high SNR ultrahigh-field MRI of the shoulder at 7T
JF  - Medical Physics
Y1  - 2017
U6  - http://dx.doi.org/10.1002/mp.12612
SN  - 0094-2405
IS  - Article in press
PB  - Wiley
CY  - Hoboken
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  - Rietsch, Stefan H. G.
A1  - Brunheim, Sascha
A1  - Orzada, Stephan
A1  - Voelker, Maximilian N.
A1  - Maderwald, Stefan
A1  - Bitz, Andreas
A1  - Gratz, Marcel
A1  - Ladd, Mark E.
A1  - Quick, Harald H.
T1  - Development and evaluation of a 16-channel receive-only RF coil to improve 7T ultra-high field body MRI with focus on the spine
JF  - Magnetic Resonance in Medicine
Y1  - 2019
U6  - http://dx.doi.org/10.1002/mrm.27731
SN  - 1522-2594
IS  - Early view
PB  - Wiley
CY  - Weinheim
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  - 
TY  - JOUR
A1  - Orzada, Stephan
A1  - Fiedler, Thomas M.
A1  - Bitz, Andreas
A1  - Ladd, Mark E.
A1  - Quick, Harald H.
T1  - Local SAR compression with overestimation control to reduce maximum relative SAR overestimation and improve multi-channel RF array performance
JF  - Magnetic Resonance Materials in Physics, Biology and Medicine
N2  - Objective
In local SAR compression algorithms, the overestimation is generally not linearly dependent on actual local SAR. This can lead to large relative overestimation at low actual SAR values, unnecessarily constraining transmit array performance.

Method
Two strategies are proposed to reduce maximum relative overestimation for a given number of VOPs. The first strategy uses an overestimation matrix that roughly approximates actual local SAR; the second strategy uses a small set of pre-calculated VOPs as the overestimation term for the compression.

Result
Comparison with a previous method shows that for a given maximum relative overestimation the number of VOPs can be reduced by around 20% at the cost of a higher absolute overestimation at high actual local SAR values.

Conclusion
The proposed strategies outperform a previously published strategy and can improve the SAR compression where maximum relative overestimation constrains the performance of parallel transmission.
Y1  - 2020
SN  - 1352-8661
U6  - http://dx.doi.org/10.1007/s10334-020-00890-0
IS  - 34 (2021)
SP  - 153
EP  - 164
PB  - Springer
CY  - Heidelberg
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  - 
TY  - JOUR
A1  - Orzada, Stephan
A1  - Maderwald, Stefan
A1  - Poser, Benedikt Andreas
A1  - Bitz, Andreas
A1  - Quick, Harald H.
A1  - Ladd, Mark E.
T1  - RF excitation using time interleaved acquisition of modes (TIAMO) to address B1 inhomogeneity in high-field MRI
JF  - Magnetic Resonance in Medicine
N2  - As the field strength and, therefore, the operational frequency in MRI is increased, the wavelength approaches the size of the human head/body, resulting in wave effects, which cause signal decreases and dropouts. Several multichannel approaches have been proposed to try to tackle these problems, including RF shimming, where each element in an array is driven by its own amplifier and modulated with a certain (constant) amplitude and phase relative to the other elements, and Transmit SENSE, where spatially tailored RF pulses are used. In this article, a relatively inexpensive and easy to use imaging scheme for 7 Tesla imaging is proposed to mitigate signal voids due to B1 field inhomogeneity. Two time-interleaved images are acquired using a different excitation mode for each. By forming virtual receive elements, both images are reconstructed together using GRAPPA to achieve a more homogeneous image, with only small SNR and SAR penalty in head and body imaging at 7 Tesla.
Y1  - 2010
U6  - http://dx.doi.org/10.1002/mrm.22527
SN  - 1522-2594
VL  - 64
IS  - 2
SP  - 327
EP  - 333
PB  - Wiley-Liss
CY  - New York
ER  -