@article{YazdanbakhshSolbachBitz2012,
  author    = {Yazdanbakhsh, Pedram and Solbach, Klaus and Bitz, Andreas},
  title     = {Variable power combiner for RF mode shimming in 7-T MR imaging},
  series = {IEEE Transaction on Biomedical Engineering},
  volume    = {59},
  journal   = {IEEE Transaction on Biomedical Engineering},
  number    = {9},
  publisher = {IEEE},
  address   = {New York},
  issn      = {1558-2531},
  doi       = {10.1109/TBME.2012.2205926},
  pages     = {2549 -- 2557},
  year      = {2012},
  abstract  = {This contribution discusses the utilization of RF power in an MRI system with RF mode shimming which enables the superposition of circularly polarized modes of a transmit RF coil array driven by a Butler matrix. Since the required power for the individual modes can vary widely, mode-shimming can result in a significant underutilization of the total available RF power. A variable power combiner (VPC) is proposed to improve the power utilization: it can be realized as a reconfiguration of the MRI transmit system by the inclusion of one additional matrix network which receives the power from all transmit amplifiers at its input ports and provides any desired (combined) power distribution at its output ports by controlling the phase and amplitude of the amplifiers' input signals. The power distribution at the output ports of the VPC is then fed into the "mode" ports of the coil array Butler matrix in order to superimpose the spatial modes at the highest achievable power utilization. The VPC configuration is compared to the standard configuration of the transmit chain of our MRI system with 8 transmit channels and 16 coils. In realistic scenarios, improved power utilization was achieved from 17\% to 60\% and from 14\% to 55\% for an elliptical phantom and a region of interest in the abdomen, respectively, and an increase of the power utilization of 1 dB for a region of interest in the upper leg. In general, it is found that the VPC allows significant improvement in power utilization when the shimming solution demands only a few modes to be energized, while the technique can yield loss in power utilization in cases with many modes required at high power level.},
  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{KraffBitzBreyeretal.2011,
  author    = {Kraff, Oliver and Bitz, Andreas and Breyer, Tobias and Kruszona, Stefan and Maderwald, Stefan and Brote, Irina and Gizewski, Elke R. and Ladd, Mark E. and Quick, Harald H.},
  title     = {A transmit/receive radiofrequency array for imaging the carotid arteries at 7 Tesla: coil design and first in vivo results},
  series = {Investigative Radiology},
  volume    = {46},
  journal   = {Investigative Radiology},
  number    = {4},
  publisher = {Wolters Kluwer},
  address   = {K{\"o}ln},
  issn      = {1536-0210},
  doi       = {10.1097/RLI.0b013e318206cee4},
  pages     = {246 -- 254},
  year      = {2011},
  abstract  = {Objective: To develop a transmit/receive radiofrequency (RF) array for magnetic resonance imaging (MRI) of the carotid arteries at 7 T. The prototype is characterized in numerical simulations and bench measurements, and the feasibility of plaque imaging at 7 T is demonstrated in first in vivo images. Materials and Methods: The RF phased array coil consists of 8 surface loop coils. To allow imaging of both sides of the neck, the RF array is divided into 2 coil clusters, each with 4 overlapping loop elements. For safety validation, numerical computations of the RF field distribution and the corresponding specific absorption rate were performed on the basis of a heterogeneous human body model. To validate the coil model, maps of the transmit B1+ field were compared between simulation and measurement. In vivo images of a healthy volunteer and a patient (ulcerating plaque and a 50\% stenosis of the right internal carotid artery) were acquired using a 3-dimensional FLASH sequence with a high isotropic spatial resolution of 0.54 mm as well as using pulse-triggered proton density (PD)/T2-weighted turbo spin echo sequences. Results: Measurements of the S-parameters yielded a reflection and isolation of the coil elements of better than -18 and -13 dB, respectively. Measurements of the g-factor indicated good image quality for parallel imaging acceleration factors up to 2.4. A similar distribution and a very good match of the absolute values were found between the measured and simulated B1+ transmit RF field for the validation of the coil model. In vivo images revealed good signal excitation of both sides of the neck and a high vessel-to-background image contrast for the noncontrast-enhanced 3-dimensional FLASH sequence. Imaging at 7 T could depict the extent of stenosis, and revealed the disruption and ulcer of the plaque. Conclusions: This study demonstrates that 2 four-channel transmit/receive RF arrays for each side of the neck is a suitable concept for in vivo MRI of the carotid arteries at 7 Tesla. Further studies are needed to explore and exploit the full potential of 7 T high-field MRI for carotid atherosclerotic plaque imaging.},
  language  = {en}
}
@article{NdoumbeMbonjoMbonjoStreckertBitzetal.2004,
  author    = {Ndoumb{\`e} Mbonjo Mbonjo, H. and Streckert, J. and Bitz, Andreas and Hansen, V. and Glasmachers, A. and Gencol, S. and Rozic, D.},
  title     = {Generic UMTS test signal for RF bioelectromagnetic studies},
  series = {Bioelectromagnetics},
  volume    = {25},
  journal   = {Bioelectromagnetics},
  number    = {6},
  issn      = {1521-186X},
  doi       = {10.1002/bem.20007},
  pages     = {415 -- 425},
  year      = {2004},
  language  = {en}
}
@article{SommerStreckertBitzetal.2004,
  author    = {Sommer, Angela M. and Streckert, Joachim and Bitz, Andreas and Hansen, Volkert W. and Lerchl, Alexander},
  title     = {No effects of GSM-modulated 900 MHz electromagnetic fields on survival rate and spontaneous development of lymphoma in female AKR/J mice},
  series = {BMC Cancer},
  volume    = {77},
  journal   = {BMC Cancer},
  number    = {4},
  doi       = {10.1186/1471-2407-4-77},
  year      = {2004},
  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{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}
}
@inproceedings{BitzKraffOrzadaetal.2012,
  author    = {Bitz, Andreas and Kraff, O. and Orzada, S. and Maderwald, S. and Brote, I. and Johst, S. and Ladd, E.},
  title     = {Assessment of RF Safety of Transmit Coils at 7 Tesla by Experimental and Numerical Procedures (490.)},
  series = {19th annual ISMRM scientific meeting and exhibition 2011 : Montreal, Quebec, Canada, 7 - 13 May 2011},
  booktitle = {19th annual ISMRM scientific meeting and exhibition 2011 : Montreal, Quebec, Canada, 7 - 13 May 2011},
  number    = {Volume 1},
  publisher = {Curran},
  address   = {Red Hook, NY},
  isbn      = {978-1-61839-284-8},
  pages     = {475},
  year      = {2012},
  language  = {en}
}
@inproceedings{BitzKraffOrzadaetal.2010,
  author    = {Bitz, Andreas and Kraff, O. and Orzada, S. and Maderwald, S. and Brote, I. and Ladd, M.},
  title     = {Experimental and Numerical Assessment of RF Safety of Transmit Coils at 7 Tesla},
  series = {ISMRM workshop on MR safety 2010 : RF heating of the human in MRI : workshop series. The Washington County Historic Courthouse, Stillwater, Minnesota, USA, 15 - 17 October 2010},
  booktitle = {ISMRM workshop on MR safety 2010 : RF heating of the human in MRI : workshop series. The Washington County Historic Courthouse, Stillwater, Minnesota, USA, 15 - 17 October 2010},
  isbn      = {978-1-62276-088-6},
  pages     = {195},
  year      = {2010},
  language  = {en}
}
@inproceedings{SchwankeHoefkenSchuba2017,
  author    = {Schwanke, Peter and H{\"o}fken, Hans-Wilhelm and Schuba, Marko},
  title     = {Security Analysis of the ADS Protocol of a Beckhoff CX2020 PLC},
  pages     = {1 -- 5},
  year      = {2017},
  abstract  = {ICSs (Industrial Control Systems) and its subset SCADA systems (Supervisory Control and Data Acquisition) are getting exposed to a constant stream of new threats. The increasing importance of IT security in ICS requires viable methods to assess the security of ICS, its individual components, and its protocols. This paper presents a security analysis with focus on the communication protocols of a single PLC (Programmable Logic Controller). The PLC, a Beckhoff CX2020, is examined and new vulnerabilities of the system are revealed. Based on these findings recommendations are made to improve security of the Beckhoff system and its protocols.},
  language  = {en}
}