@article{KobusBitzUdenetal.2012,
  author    = {Kobus, Thiele and Bitz, Andreas and Uden, Mark J. van and Lagemaat, Miram W. and Rothgang, Eva and Orzada, Stephan and Heerschap, Arend and Scheenen, Tom W. J.},
  title     = {In vivo 31P MR spectroscopic imaging of the human prostate at 7 T: safety and feasibility},
  series = {Magnetic Resonance in Medicine},
  volume    = {68},
  journal   = {Magnetic Resonance in Medicine},
  number    = {6},
  publisher = {Wiley-Liss},
  address   = {New York},
  issn      = {1522-2594},
  doi       = {10.1002/mrm.24175},
  pages     = {1683 -- 1695},
  year      = {2012},
  abstract  = {31P MR spectroscopic imaging of the human prostate provides information about phosphorylated metabolites that could be used for prostate cancer characterization. The sensitivity of a magnetic field strength of 7 T might enable 3D 31P MR spectroscopic imaging with relevant spatial resolution in a clinically acceptable measurement time. To this end, a 31P endorectal coil was developed and combined with an eight-channel 1H body-array coil to relate metabolic information to anatomical location. An extensive safety validation was performed to evaluate the specific absorption rate, the radiofrequency field distribution, and the temperature distribution of both coils. This validation consisted of detailed Finite Integration Technique simulations, confirmed by MR thermometry and Burn:x-wiley:07403194:media:MRM24175:tex2gif-stack-1 measurements in a phantom and in vivo temperature measurements. The safety studies demonstrated that the presence of the 31P endorectal coil had no influence on the specific absorption rate levels and temperature distribution of the external eight-channel 1H array coil. To stay within a 10 g averaged local specific absorption rate of 10 W/kg, a maximum time-averaged input power of 33 W for the 1H array coil was allowed. For transmitting with the 31P endorectal coil, our safety limit of less than 1°C temperature increase in vivo during a 15-min MR spectroscopic imaging experiment was reached at a time-averaged input power of 1.9 W. With this power setting, a second in vivo measurement was performed on a healthy volunteer. Using adiabatic excitation, 3D 31P MR spectroscopic imaging produced spectra from the entire prostate in 18 min with a spatial resolution of 4 cm3. The spectral resolution enabled the separate detection of phosphocholine, phosphoethanolamine, inorganic phosphate, and other metabolites that could play an important role in the characterization of prostate cancer.},
  language  = {en}
}
@article{KlompBitzHeerschapetal.2009,
  author    = {Klomp, D. W. J. and Bitz, Andreas and Heerschap, A. and Scheenen, T. W. J.},
  title     = {Proton spectroscopic imaging of the human prostate at 7 T},
  series = {NMR in Biomedicine},
  volume    = {22},
  journal   = {NMR in Biomedicine},
  number    = {5},
  issn      = {1099-1492},
  doi       = {10.1002/nbm.1360},
  pages     = {495 -- 501},
  year      = {2009},
  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}
}
@article{FrankeStreckertBitzetal.2005,
  author    = {Franke, Helmut and Streckert, Joachim and Bitz, Andreas and Goeke, Johannes and Hansen, Volkert and Ringelstein, E. Bernd and Nattk{\"a}mper, Heiner and Galle, Hans-Joachim and St{\"o}gbauer, Florian},
  title     = {Effects of Universal Mobile Telecommunications System (UMTS) electromagnetic fields on the blood-brain barrier in vitro},
  series = {Radiation Research},
  volume    = {164},
  journal   = {Radiation Research},
  number    = {3},
  issn      = {1938-5404},
  doi       = {10.1667/RR3424.1},
  pages     = {258 -- 269},
  year      = {2005},
  language  = {en}
}
@article{FiedlerOrzadaFloeseretal.2022,
  author    = {Fiedler, Thomas M. and Orzada, Stephan and Fl{\"o}ser, Martina and Rietsch, Stefan H. G. and Schmidt, Simon and Stelter, Jonathan K. and Wittrich, Marco and Quick, Harald H. and Bitz, Andreas and Ladd, Mark E.},
  title     = {Performance and safety assessment of an integrated transmitarray for body imaging at 7 T under consideration of specificabsorption rate, tissue temperature, and thermal dose},
  series = {NMR in Biomedicine},
  volume    = {35},
  journal   = {NMR in Biomedicine},
  number    = {5},
  publisher = {Wiley},
  issn      = {0952-3480 (Print)},
  doi       = {10.1002/nbm.4656},
  pages     = {1 -- 17},
  year      = {2022},
  abstract  = {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.},
  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{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}
}
@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{ElQuardiStreckertBitzetal.2011,
  author    = {El Quardi, A. and Streckert, J. and Bitz, Andreas and M{\"u}nkner, S. and Engel, J. and Hansen, V.},
  title     = {New fin-line devices for radiofrequency exposure of small biological samples in vitro allowing whole-cell patch clamp recordings},
  series = {Bioelectromagnetics},
  volume    = {32},
  journal   = {Bioelectromagnetics},
  number    = {2},
  publisher = {Wiley},
  address   = {Weinheim},
  issn      = {1521-186X},
  doi       = {10.1002/bem.20621},
  pages     = {102 -- 112},
  year      = {2011},
  abstract  = {The development and analysis of three waveguides for the exposure of small biological in vitro samples to mobile communication signals at 900 MHz (GSM, Global System for Mobile Communications), 1.8 GHz (GSM), and 2 GHz (UMTS, Universal Mobile Telecommunications System) is presented. The waveguides were based on a fin-line concept and the chamber containing the samples bathed in extracellular solution was placed onto two fins with a slot in between, where the exposure field concentrates. Measures were taken to allow for patch clamp recordings during radiofrequency (RF) exposure. The necessary power for the achievement of the maximum desired specific absorption rate (SAR) of 20 W/kg (average over the mass of the solution) was approximately Pin = 50 mW, Pin = 19 mW, and Pin = 18 mW for the 900 MHz, 1800 MHz, and 2 GHz devices, respectively. At 20 W/kg, a slight RF-induced temperature elevation in the solution of no more than 0.3 °C was detected, while no thermal offsets due to the electromagnetic exposure could be detected at the lower SAR settings (2, 0.2, and 0.02 W/kg). A deviation of 10\% from the intended solution volume yielded a calculated SAR deviation of 8\% from the desired value. A maximum ±10\% variation in the local SAR could occur when the position of the patch clamp electrode was altered within the area where the cells to be investigated were located.},
  language  = {en}
}