@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{OrzadaFiedlerBitzetal.2020, author = {Orzada, Stephan and Fiedler, Thomas M. and Bitz, Andreas and Ladd, Mark E. and Quick, Harald H.}, title = {Local SAR compression with overestimation control to reduce maximum relative SAR overestimation and improve multi-channel RF array performance}, series = {Magnetic Resonance Materials in Physics, Biology and Medicine}, journal = {Magnetic Resonance Materials in Physics, Biology and Medicine}, number = {34 (2021)}, publisher = {Springer}, address = {Heidelberg}, isbn = {1352-8661}, doi = {10.1007/s10334-020-00890-0}, pages = {153 -- 164}, year = {2020}, abstract = {Objective In local SAR compression algorithms, the overestimation is generally not linearly dependent on actual local SAR. This can lead to large relative overestimation at low actual SAR values, unnecessarily constraining transmit array performance. Method Two strategies are proposed to reduce maximum relative overestimation for a given number of VOPs. The first strategy uses an overestimation matrix that roughly approximates actual local SAR; the second strategy uses a small set of pre-calculated VOPs as the overestimation term for the compression. Result Comparison with a previous method shows that for a given maximum relative overestimation the number of VOPs can be reduced by around 20\% at the cost of a higher absolute overestimation at high actual local SAR values. Conclusion The proposed strategies outperform a previously published strategy and can improve the SAR compression where maximum relative overestimation constrains the performance of parallel transmission.}, language = {en} } @article{OrzadaSolbachGratzetal.2019, author = {Orzada, Stephan and Solbach, Klaus and Gratz, Marcel and Brunheim, Sascha and Fiedler, Thomas M. and Johst, S{\"o}ren and Bitz, Andreas and Shooshtary, Samaneh and Abuelhaija, Asjraf and Voelker, Maximilian N. and Rietsch, Stefan H. G. and Kraff, Oliver and Maderwald, Stefan and Fl{\"o}ser, Martina and Oehmingen, Mark and Quick, Harald H. and Ladd, Mark E.}, title = {A 32-channel parallel transmit system add-on for 7T MRI}, series = {Plos one}, journal = {Plos one}, doi = {10.1371/journal.pone.0222452}, year = {2019}, language = {en} } @article{RietschBrunheimOrzadaetal.2019, author = {Rietsch, Stefan H. G. and Brunheim, Sascha and Orzada, Stephan and Voelker, Maximilian N. and Maderwald, Stefan and Bitz, Andreas and Gratz, Marcel and Ladd, Mark E. and Quick, Harald H.}, title = {Development and evaluation of a 16-channel receive-only RF coil to improve 7T ultra-high field body MRI with focus on the spine}, series = {Magnetic Resonance in Medicine}, journal = {Magnetic Resonance in Medicine}, number = {Early view}, publisher = {Wiley}, address = {Weinheim}, issn = {1522-2594}, doi = {10.1002/mrm.27731}, year = {2019}, 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} } @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{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{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{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} }