@article{OrzadaLaddBitz2016,
  author    = {Orzada, Stephan and Ladd, Mark E. and Bitz, Andreas},
  title     = {A method to approximate maximum local SAR in multichannel transmit MR systems without transmit phase information},
  series = {Magnetic Resonance in Medicine},
  volume    = {78},
  journal   = {Magnetic Resonance in Medicine},
  number    = {2},
  publisher = {International Society for Magnetic Resonance in Medicine},
  issn      = {1522-2594},
  doi       = {10.1002/mrm.26398},
  pages     = {805 -- 811},
  year      = {2016},
  abstract  = {Purpose To calculate local specific absorption rate (SAR) correctly, both the amplitude and phase of the signal in each transmit channel have to be known. In this work, we propose a method to derive a conservative upper bound for the local SAR, with a reasonable safety margin without knowledge of the transmit phases of the channels. Methods The proposed method uses virtual observation points (VOPs). Correction factors are calculated for each set of VOPs that prevent underestimation of local SAR when the VOPs are applied with the correct amplitudes but fixed phases. Results The proposed method proved to be superior to the worst-case calculation based on the maximum eigenvalue of the VOPs. The mean overestimation for six coil setups could be reduced, whereas no underestimation of the maximum local SAR occurred. In the best investigated case, the overestimation could be reduced from a factor of 3.3 to a factor of 1.7. Conclusion The upper bound for the local SAR calculated with the proposed method allows a fast estimation of the local SAR based on power measurements in the transmit channels and facilitates SAR monitoring in systems that do not have the capability to monitor transmit phases},
  language  = {en}
}
@article{MaasVosLagemaatetal.2014,
  author    = {Maas, Marnix C. and Vos, Eline K. and Lagemaat, Miriam W. and Bitz, Andreas and Orzada, Stephan and Kobus, Thiele and Kraff, Oliver and Maderwald, Stefan and Ladd, Mark E. and Scheenen, Tom W. J.},
  title     = {Feasibility of T₂-weighted turbo spin echo imaging of the human prostate at 7 tesla},
  series = {Magnetic Resonance in Medicine},
  volume    = {71},
  journal   = {Magnetic Resonance in Medicine},
  number    = {5},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1522-2594},
  doi       = {10.1002/mrm.24818},
  pages     = {1711 -- 1719},
  year      = {2014},
  abstract  = {Purpose To demonstrate that high quality T₂-weighted (T2w) turbo spin-echo (TSE) imaging of the complete prostate can be achieved routinely and within safety limits at 7 T, using an external transceive body array coil only. Methods Nine healthy volunteers and 12 prostate cancer patients were scanned on a 7 T whole-body system. Preparation consisted of B₀ and radiofrequency shimming and localized flip angle calibration. T₁ and T₂ relaxation times were measured and used to define the T2w-TSE protocol. T2w imaging was performed using a TSE sequence (pulse repetition time/echo time 3000-3640/71 ms) with prolonged excitation and refocusing pulses to reduce specific absorption rate. Results High quality T2w TSE imaging was performed in less than 2 min in all subjects. Tumors of patients with gold-standard tumor localization (MR-guided biopsy or prostatectomy) were well visualized on 7 T imaging (n = 3). The number of consecutive slices achievable within a 10-g averaged specific absorption rate limit of 10 W/kg was ≥28 in all subjects, sufficient for full prostate coverage with 3-mm slices in at least one direction. Conclusion High quality T2w TSE prostate imaging can be performed routinely and within specific absorption rate limits at 7 T with an external transceive body array.},
  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}
}
@article{KraffWredeSchoembergetal.2013,
  author    = {Kraff, Oliver and Wrede, Karsten H. and Schoemberg, Tobias and Dammann, Philipp and Noureddine, Yacine and Orzada, Stephan and Ladd, Mark E. and Bitz, Andreas},
  title     = {MR safety assessment of potential RF heating from cranial fixation plates at 7 T},
  series = {Medical Physics},
  volume    = {40},
  journal   = {Medical Physics},
  number    = {4},
  publisher = {Wiley},
  address   = {Hoboken},
  issn      = {2473-4209},
  doi       = {10.1118/1.4795347},
  pages     = {042302-1 -- 042302-10},
  year      = {2013},
  language  = {en}
}
@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{OrzadaJohstMaderwaldetal.2013,
  author    = {Orzada, Stephan and Johst, S{\"o}ren and Maderwald, Stefan and Bitz, Andreas and Solbach, Klaus and Ladd, Mark E.},
  title     = {Mitigation of B1(+) inhomogeneity on single-channel transmit systems with TIAMO},
  series = {Magnetic Resonance in Medicine},
  volume    = {70},
  journal   = {Magnetic Resonance in Medicine},
  number    = {1},
  publisher = {Wiley},
  address   = {Weinheim},
  issn      = {1522-2594},
  doi       = {10.1002/mrm.24453},
  pages     = {290 -- 294},
  year      = {2013},
  language  = {en}
}
@article{OrzadaBitzSchaeferetal.2011,
  author    = {Orzada, Stephan and Bitz, Andreas and Sch{\"a}fer, Lena C. and Ladd, Susanne C. and Ladd, Mark E. and Maderwald, Stefan},
  title     = {Open design eight-channel transmit/receive coil for high-resolution and real-time ankle imaging at 7 T},
  series = {Medical Physics},
  volume    = {38},
  journal   = {Medical Physics},
  number    = {3},
  publisher = {Wiley},
  address   = {Hoboken},
  issn      = {2473-4209},
  doi       = {10.1118/1.3553399},
  pages     = {1162 -- 1167},
  year      = {2011},
  abstract  = {Purpose: At 1.5 T, real-time MRI of joint movement has been shown to be feasible. However, 7 T, provides higher SNR and thus an improved potential for parallel imaging acceleration. The purpose of this work was to build an open, U-shaped eight-channel transmit/receive microstrip coil for 7 T MRI to enable high-resolution and real-time imaging of the moving ankle joint. Methods: A U-shaped eight-channel transmit/receive array for the human ankle was built.urn:x-wiley:00942405:mp3399:equation:mp3399-math-0001-parameters and urn:x-wiley:00942405:mp3399:equation:mp3399-math-0002-factor were measured. SAR calculations of different ankle postures were performed to ensure patient safety. Inhomogeneities in the transmit field consequent to the open design were compensated for by the use of static RF shimming. High-resolution and real-time imaging was performed in human volunteers. Results: The presented array showed good performance with regard to patient comfort and image quality. High acceleration factors of up to 4 are feasible without visible acceleration artifacts. Reasonable image homogeneity was achieved with RF shimming. Conclusions: Open, noncylindrical designs for transmit/receive coils are practical at 7 T and real-time imaging of the moving joint is feasible with the presented coil design.},
  language  = {en}
}
@article{KraffBitzKruszonaetal.2009,
  author    = {Kraff, Oliver and Bitz, Andreas and Kruszona, Stefan and Orzada, Stephan and Schaefer, Lena C. and Theysohn, Jens M. and Maderwald, Stefan and Ladd, Mark E. and Quick, Harald H.},
  title     = {An eight-channel phased array RF coil for spine MR imaging at 7 T},
  series = {Investigative Radiology},
  volume    = {44},
  journal   = {Investigative Radiology},
  number    = {11},
  publisher = {Lippincott Williams \& Wilkins},
  issn      = {1536-0210},
  doi       = {10.1097/RLI.0b013e3181b24ab7},
  pages     = {734 -- 740},
  year      = {2009},
  language  = {en}
}
@article{RietschPfaffenrotBitzetal.2017,
  author    = {Rietsch, Stefan H. G. and Pfaffenrot, Viktor and Bitz, Andreas and Orzada, Stephan and Brunheim, Sascha and Lazik-Palm, Andrea and Theysohn, Jens M. and Ladd, Mark E. and Quick, Harald H. and Kraff, Oliver},
  title     = {An 8-channel transceiver 7-channel receive RF coil setup for high SNR ultrahigh-field MRI of the shoulder at 7T},
  series = {Medical Physics},
  journal   = {Medical Physics},
  number    = {Article in press},
  publisher = {Wiley},
  address   = {Hoboken},
  issn      = {0094-2405},
  doi       = {10.1002/mp.12612},
  year      = {2017},
  language  = {en}
}
@article{OrzadaBitzJohstetal.2017,
  author    = {Orzada, Stephan and Bitz, Andreas and Johst, S{\"o}ren and Gratz, Marcel and V{\"o}lker, Maximilian N. and Kraff, Oliver and Abuelhaija, Ashraf and Fiedler, Thomas M. and Solbach, Klaus and Quick, Harald H. and Ladd, Mark E.},
  title     = {Analysis of an integrated 8-Channel Tx/Rx body array for use as a body coil in 7-Tesla MRI},
  series = {Frontiers in Physics},
  volume    = {5},
  journal   = {Frontiers in Physics},
  number    = {Jun},
  issn      = {2296-424X},
  doi       = {10.3389/fphy.2017.00017},
  year      = {2017},
  language  = {en}
}