@article{UmutluOrzadaKinneretal.2011,
  author    = {Umutlu, Lale and Orzada, Stephan and Kinner, Sonja and Maderwald, Stefan and Bronte, Irina and Bitz, Andreas and Kraff, Oliver and Ladd, Susanne C. and Antoch, Gerald and Ladd, Mark E. and Quick, Harald H. and Lauenstein, Thomas C.},
  title     = {Renal imaging at 7 Tesla: preliminary results},
  series = {European Radiology},
  volume    = {21},
  journal   = {European Radiology},
  number    = {4},
  publisher = {Springer},
  address   = {Berlin},
  issn      = {1432-1084},
  pages     = {841 -- 849},
  year      = {2011},
  abstract  = {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.},
  language  = {en}
}
@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{HansenBitzStreckert1999,
  author    = {Hansen, Volkert W. and Bitz, Andreas and Streckert, Joachim R.},
  title     = {RF Exposure of Biological Systems in Radial Waveguides},
  series = {IEEE Transactions on Electromagnetic Compatibility},
  volume    = {41},
  journal   = {IEEE Transactions on Electromagnetic Compatibility},
  number    = {4},
  issn      = {1558-187X},
  doi       = {10.1109/15.809852},
  pages     = {487 -- 493},
  year      = {1999},
  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}
}
@article{FiedlerLaddBitz2017,
  author    = {Fiedler, Thomas M. and Ladd, Mark E. and Bitz, Andreas},
  title     = {RF safety assessment of a bilateral four-channel transmit/receive 7 Tesla breast coil: SAR versus temperature limits},
  series = {Medical Physics},
  volume    = {44},
  journal   = {Medical Physics},
  number    = {1},
  doi       = {10.1002/mp.12034},
  pages     = {143 -- 157},
  year      = {2017},
  language  = {en}
}
@inproceedings{BitzKobusScheenenetal.2013,
  author    = {Bitz, Andreas and Kobus, Thiele and Scheenen, Tom W. J. and Ladd, Mark E.},
  title     = {RF Safety of the Combination of a 31P Tx/Rx Endorectal Coil \& a 1H Tx/Rx Body Array for 31P MRSI of the Prostate at 7T (311.)},
  series = {20th Annual ISMRM scientific meeting and exhibition 2012 : Melbourne, Australia, 5 - 11 May 2012},
  booktitle = {20th Annual ISMRM scientific meeting and exhibition 2012 : Melbourne, Australia, 5 - 11 May 2012},
  number    = {Volume 1},
  publisher = {Curran},
  address   = {Red Hook, NY},
  isbn      = {978-1-62276-943-8},
  issn      = {1545-4428},
  pages     = {311},
  year      = {2013},
  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}
}
@article{FiedlerLaddBitz2017,
  author    = {Fiedler, Thomas M. and Ladd, Mark E. and Bitz, Andreas},
  title     = {SAR Simulations \& Safety},
  series = {NeuroImage},
  journal   = {NeuroImage},
  number    = {Epub ahead of print},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {1053-8119},
  doi       = {10.1016/j.neuroimage.2017.03.035},
  year      = {2017},
  language  = {en}
}
@article{UmutluKraffFischeretal.2013,
  author    = {Umutlu, Lale and Kraff, Oliver and Fischer, Anja and Kinner, Sonja and Maderwald, Stefan and Nassenstein, Kai and Nensa, Felix and Gr{\"u}neisen, Johannes and Orzada, Stephan and Bitz, Andreas and Forsting, Michael and Ladd, Mark E. and Lauenstein, Thomas C.},
  title     = {Seven-Tesla MRI of the female pelvis},
  series = {European Radiology},
  volume    = {23},
  journal   = {European Radiology},
  number    = {9},
  publisher = {Springer},
  address   = {Berlin},
  issn      = {1432-1084},
  doi       = {10.1007/s00330-013-2868-0},
  pages     = {2364 -- 2373},
  year      = {2013},
  language  = {en}
}
@inproceedings{BitzStreckertHansenetal.2001,
  author    = {Bitz, Andreas and Streckert, J. and Hansen, V.W. and Stogbauer, F.},
  title     = {Shielded RF-exposure system with an integrated LF-measuring system for in vitro experiments with cell-layers},
  series = {Proceedings of the Ebea 2001 : 5th International Congress of the European Bioelectromagnetics Association (Ebea) ; 6-8 September 2001, Marina Congress Center, Helsinki, Finland},
  booktitle = {Proceedings of the Ebea 2001 : 5th International Congress of the European Bioelectromagnetics Association (Ebea) ; 6-8 September 2001, Marina Congress Center, Helsinki, Finland},
  editor    = {Hietanen, Maila and Jokela, Kari and Juutilainen, Jukka and Työterveyslaitos,},
  publisher = {Finnish Institute of Occupational Health},
  address   = {Helsinki},
  isbn      = {9789518024401},
  pages     = {67 -- 68},
  year      = {2001},
  language  = {en}
}