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  - https://doi.org/10.1002/mrm.22527
SN  - 1522-2594
VL  - 64
IS  - 2
SP  - 327
EP  - 333
PB  - Wiley-Liss
CY  - New York
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  - https://doi.org/10.1002/mrm.27731
SN  - 1522-2594
IS  - Early view
PB  - Wiley
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Fagan, Andrew J.
A1  - Bitz, Andreas
A1  - Björkman-Burtscher, Isabella M.
A1  - Collins, Christopher M.
A1  - Kimbrell, Vera
A1  - Raaijmakers, Alexander J. E.
T1  - 7T MR Safety
JF  - Journal of Magnetic Resonance Imaging (JMRI)
Y1  - 2021
U6  - https://doi.org/10.1002/jmri.27319
SN  - 1522-2586
VL  - 53
IS  - 2
SP  - 333
EP  - 346
PB  - Wiley
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Fiedler, Thomas M.
A1  - Ladd, Mark E.
A1  - Clemens, Markus
A1  - Bitz, Andreas
T1  - Safety of subjects during radiofrequency exposure in ultra-high-field magnetic resonance imaging
JF  - IEEE Letters on Electromagnetic Compatibility Practice and Applications
N2  - Magnetic resonance imaging (MRI) is one of the most important medical imaging techniques. Since the introduction of MRI in the mid-1980s, there has been a continuous trend toward higher static magnetic fields to obtain i.a. a higher signal-to-noise ratio. The step toward ultra-high-field (UHF) MRI at 7 Tesla and higher, however, creates several challenges regarding the homogeneity of the spin excitation RF transmit field and the RF exposure of the subject. In UHF MRI systems, the wavelength of the RF field is in the range of the diameter of the human body, which can result in inhomogeneous spin excitation and local SAR hotspots. To optimize the homogeneity in a region of interest, UHF MRI systems use parallel transmit systems with multiple transmit antennas and time-dependent modulation of the RF signal in the individual transmit channels. Furthermore, SAR increases with increasing field strength, while the SAR limits remain unchanged. Two different approaches to generate the RF transmit field in UHF systems using antenna arrays close and remote to the body are investigated in this letter. Achievable imaging performance is evaluated compared to typical clinical RF transmit systems at lower field strength. The evaluation has been performed under consideration of RF exposure based on local SAR and tissue temperature. Furthermore, results for thermal dose as an alternative RF exposure metric are presented.
Y1  - 2020
SN  - 2637-6423
U6  - https://doi.org/10.1109/LEMCPA.2020.3029747
VL  - 2
IS  - 3
SP  - 1
EP  - 8
PB  - IEEE
CY  - New York, NY
ER  - 
TY  - JOUR
A1  - Reinhardt, T.
A1  - Bitz, Andreas
A1  - El Ouardi, A.
A1  - Streckert, J.
A1  - Sommer, A.
A1  - Lerchl, A.
A1  - Hansen, V.
T1  - Exposure set-ups for in vivo experiments using radial waveguides
JF  - Radiation Protection Dosimetry
Y1  - 2007
U6  - https://doi.org/10.1093/rpd/ncm370
SN  - 1742-3406
VL  - 124
IS  - 1
SP  - 21
EP  - 26
ER  - 
TY  - JOUR
A1  - Sommer, Angela M.
A1  - Bitz, Andreas
A1  - Streckert, Joachim
A1  - Hansen, Volkert W.
A1  - Lerchl, Alexander
T1  - Lymphoma development in mice chronically exposed to UMTS-modulated radiofrequency electromagnetic fields
JF  - Radiation Research
Y1  - 2007
U6  - https://doi.org/10.1667/RR0857.1
SN  - 1938-5404
VL  - 168
IS  - 1
SP  - 72
EP  - 80
ER  - 
TY  - JOUR
A1  - Sukhotina, Irina
A1  - Streckert, Joachim R.
A1  - Bitz, Andreas
A1  - Hansen, Volkert W.
A1  - Lerchl, Alexander
T1  - 1800 MHz electromagnetic field effects on melatonin release from isolated pineal glands
JF  - Journal of Pineal Research
Y1  - 2006
U6  - https://doi.org/10.1111/j.1600-079X.2005.00284.x
SN  - 1600-079X
VL  - 40
IS  - 1
SP  - 86
EP  - 91
ER  - 
TY  - JOUR
A1  - Franke, Helmut
A1  - Streckert, Joachim
A1  - Bitz, Andreas
A1  - Goeke, Johannes
A1  - Hansen, Volkert
A1  - Ringelstein, E. Bernd
A1  - Nattkämper, Heiner
A1  - Galle, Hans-Joachim
A1  - Stögbauer, Florian
T1  - Effects of Universal Mobile Telecommunications System (UMTS) electromagnetic fields on the blood-brain barrier in vitro
JF  - Radiation Research
Y1  - 2005
U6  - https://doi.org/10.1667/RR3424.1
SN  - 1938-5404
VL  - 164
IS  - 3
SP  - 258
EP  - 269
ER  - 
TY  - JOUR
A1  - Wissen, M.
A1  - Bogdanski, N.
A1  - Scheer, H.-C.
A1  - Bitz, Andreas
A1  - Ahrens, G.
A1  - Gruetzner, G.
T1  - Implication of the light polarisation for UV curing of pre-patterned resists
JF  - Microelectronic Engineering
Y1  - 2005
U6  - https://doi.org/10.1016/j.mee.2004.12.099
SN  - 0167-9317
VL  - 78-79
SP  - 659
EP  - 664
ER  - 
TY  - JOUR
A1  - Ndoumbè Mbonjo Mbonjo, H.
A1  - Streckert, J.
A1  - Bitz, Andreas
A1  - Hansen, V.
A1  - Glasmachers, A.
A1  - Gencol, S.
A1  - Rozic, D.
T1  - Generic UMTS test signal for RF bioelectromagnetic studies
JF  - Bioelectromagnetics
Y1  - 2004
U6  - https://doi.org/10.1002/bem.20007
SN  - 1521-186X
VL  - 25
IS  - 6
SP  - 415
EP  - 425
ER  -