@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} } @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} } @inproceedings{BitzStreckertHansenetal.2000, author = {Bitz, Andreas and Streckert, J.R. and Hansen, V.W. and Lerchl, A.}, title = {Freely moving or restrained animals in bioelec-tromagnetic experiments - pros and cons}, series = {AP 2000 : Millennium Conference on Antennas \& Propagation, Davos, Switzerland, 9 - 14 April 2000}, booktitle = {AP 2000 : Millennium Conference on Antennas \& Propagation, Davos, Switzerland, 9 - 14 April 2000}, number = {Band 1}, editor = {Danesy, Dorothea}, publisher = {ESA Publications Division, ESTEC}, address = {Noordwijk}, pages = {489}, year = {2000}, 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{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{UmutluBitzMaderwaldetal.2013, author = {Umutlu, Lale and Bitz, Andreas and Maderwald, Stefan and Orzada, Stephan and Kinner, Sonja and Kraff, Oliver and Brote, Irina and Ladd, Susanne C. and Schroeder, Tobias and Forsting, Michael}, title = {Contrast-enhanced ultra-high-field liver MRI: a feasibility trial}, series = {European Journal of Radiology}, volume = {82}, journal = {European Journal of Radiology}, number = {5}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0720-048X}, doi = {10.1016/j.ejrad.2011.07.004}, pages = {760 -- 767}, year = {2013}, language = {en} } @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} }