@article{OrzadaMaderwaldPoseretal.2010, author = {Orzada, Stephan and Maderwald, Stefan and Poser, Benedikt Andreas and Bitz, Andreas and Quick, Harald H. and Ladd, Mark E.}, title = {RF excitation using time interleaved acquisition of modes (TIAMO) to address B1 inhomogeneity in high-field MRI}, series = {Magnetic Resonance in Medicine}, volume = {64}, journal = {Magnetic Resonance in Medicine}, number = {2}, publisher = {Wiley-Liss}, address = {New York}, issn = {1522-2594}, doi = {10.1002/mrm.22527}, pages = {327 -- 333}, year = {2010}, abstract = {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.}, language = {en} } @article{RietschBrunheimOrzadaetal.2019, author = {Rietsch, Stefan H. G. and Brunheim, Sascha and Orzada, Stephan and Voelker, Maximilian N. and Maderwald, Stefan and Bitz, Andreas and Gratz, Marcel and Ladd, Mark E. and Quick, Harald H.}, title = {Development and evaluation of a 16-channel receive-only RF coil to improve 7T ultra-high field body MRI with focus on the spine}, series = {Magnetic Resonance in Medicine}, journal = {Magnetic Resonance in Medicine}, number = {Early view}, publisher = {Wiley}, address = {Weinheim}, issn = {1522-2594}, doi = {10.1002/mrm.27731}, year = {2019}, language = {en} } @article{FaganBitzBjoerkmanBurtscheretal.2021, author = {Fagan, Andrew J. and Bitz, Andreas and Bj{\"o}rkman-Burtscher, Isabella M. and Collins, Christopher M. and Kimbrell, Vera and Raaijmakers, Alexander J. E.}, title = {7T MR Safety}, series = {Journal of Magnetic Resonance Imaging (JMRI)}, volume = {53}, journal = {Journal of Magnetic Resonance Imaging (JMRI)}, number = {2}, publisher = {Wiley}, address = {Weinheim}, issn = {1522-2586}, doi = {10.1002/jmri.27319}, pages = {333 -- 346}, year = {2021}, language = {en} } @article{FiedlerLaddClemensetal.2020, author = {Fiedler, Thomas M. and Ladd, Mark E. and Clemens, Markus and Bitz, Andreas}, title = {Safety of subjects during radiofrequency exposure in ultra-high-field magnetic resonance imaging}, series = {IEEE Letters on Electromagnetic Compatibility Practice and Applications}, volume = {2}, journal = {IEEE Letters on Electromagnetic Compatibility Practice and Applications}, number = {3}, publisher = {IEEE}, address = {New York, NY}, isbn = {2637-6423}, doi = {10.1109/LEMCPA.2020.3029747}, pages = {1 -- 8}, year = {2020}, abstract = {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.}, language = {en} } @inproceedings{BitzStreckertHansenetal.2000, author = {Bitz, Andreas and Streckert, J. and Hansen, V.W. and Buschmann, J.}, title = {RF exposure of non restrained animals in an overmoded radial waveguide}, series = {22nd BEMS Annual Meeting, Munich, Germany, 2000}, booktitle = {22nd BEMS Annual Meeting, Munich, Germany, 2000}, publisher = {Bioelectromagnetics Society}, address = {Frederick, MD}, pages = {63}, year = {2000}, language = {en} } @inproceedings{BitzKlompLadd2009, author = {Bitz, Andreas and Klomp, D.W. and Ladd, M.E.}, title = {Experimental and numerical determination of SAR and temperature distribution of a human endorectal coil for MR imaging of the prostate at 7T (903.)}, series = {16th annual ISMRM scientific meeting and exhibition 2008 : Toronto, Ontario, Canada, 3 - 9 May 2008}, booktitle = {16th annual ISMRM scientific meeting and exhibition 2008 : Toronto, Ontario, Canada, 3 - 9 May 2008}, publisher = {Curran}, address = {Red Hook, NY}, isbn = {978-1-61567-196-0}, year = {2009}, language = {en} } @inproceedings{BitzElOuardiStreckertetal.2005, author = {Bitz, Andreas and El Ouardi, A. and Streckert, J. and Hansen, V.}, title = {Efficient calculation of human exposure in front of base station antennas by a combination of the FDTD and Hybrid(2)-method}, series = {Proceedings of the 16th International Zurich Symposium on Electromagnetic Compatibility, Topical Meeting on Biomedical EMC, Zurich, Switzerland, February 2005}, booktitle = {Proceedings of the 16th International Zurich Symposium on Electromagnetic Compatibility, Topical Meeting on Biomedical EMC, Zurich, Switzerland, February 2005}, publisher = {ETH Zentrum}, address = {Z{\"u}rich}, isbn = {3-9521199-9-7}, pages = {115 -- 118}, year = {2005}, language = {en} } @inproceedings{BitzAlaydrusStreckertetal.2002, author = {Bitz, Andreas and Alaydrus, M. and Streckert, J. and Hansen, V.}, title = {Combination of the hybrid/sup [2]/-method and the FDTD-method for solution of boundary value problems with electrically large and high-resolution bodies}, series = {IEEE Antennas and Propagation Society International Symposium (IEEE Cat. No.02CH37313) 2002 : San Antonio, TX, USA, 16-21 June}, booktitle = {IEEE Antennas and Propagation Society International Symposium (IEEE Cat. No.02CH37313) 2002 : San Antonio, TX, USA, 16-21 June}, publisher = {IEEE}, address = {Piscataway, NJ}, isbn = {0-7803-7330-8}, doi = {10.1109/APS.2002.1018209}, pages = {278 -- 281}, year = {2002}, language = {en} } @inproceedings{BitzAlaydrusStreckertetal.2002, author = {Bitz, Andreas and Alaydrus, M. and Streckert, J. and Hansen, V.W.}, title = {Absorption rates inside human body due to radiated electro-magnetic fields of multi-band base station antennas. Boundary value problems with electrically large and high-resolution bodies}, series = {24th BEMS Annual Meeting, Quebec City, Quebec, Canada, 23 - 27 June 2002}, booktitle = {24th BEMS Annual Meeting, Quebec City, Quebec, Canada, 23 - 27 June 2002}, publisher = {Bioelectromagnetics Society}, address = {Frederick, MD}, pages = {40 -- 41}, year = {2002}, language = {en} } @inproceedings{BitzAlaydrusStreckertetal.2001, author = {Bitz, Andreas and Alaydrus, M. and Streckert, J. and Hansen, V.W.}, title = {Base station antennas embedded in complex environments: rf exposure in controlled areas}, series = {23rd BEMS Annual Meeting, St. Paul, Minnesota, USA, 49-50, June 2001}, booktitle = {23rd BEMS Annual Meeting, St. Paul, Minnesota, USA, 49-50, June 2001}, publisher = {Bioelectromagnetics Society}, address = {Frederick, MD}, pages = {49 -- 50}, year = {2001}, language = {en} }