TY - JOUR A1 - Kobus, Thiele A1 - Bitz, Andreas A1 - Uden, Mark J. van A1 - Lagemaat, Miram W. A1 - Rothgang, Eva A1 - Orzada, Stephan A1 - Heerschap, Arend A1 - Scheenen, Tom W. J. T1 - In vivo 31P MR spectroscopic imaging of the human prostate at 7 T: safety and feasibility JF - Magnetic Resonance in Medicine N2 - 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. Y1 - 2012 U6 - http://dx.doi.org/10.1002/mrm.24175 SN - 1522-2594 VL - 68 IS - 6 SP - 1683 EP - 1695 PB - Wiley-Liss CY - New York ER - TY - JOUR A1 - Umutlu, Lale A1 - Bitz, Andreas A1 - Maderwald, Stefan A1 - Orzada, Stephan A1 - Kinner, Sonja A1 - Kraff, Oliver A1 - Brote, Irina A1 - Ladd, Susanne C. A1 - Schroeder, Tobias A1 - Forsting, Michael T1 - Contrast-enhanced ultra-high-field liver MRI: a feasibility trial JF - European Journal of Radiology Y1 - 2013 U6 - http://dx.doi.org/10.1016/j.ejrad.2011.07.004 SN - 0720-048X VL - 82 IS - 5 SP - 760 EP - 767 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Orzada, Stephan A1 - Bitz, Andreas A1 - Schäfer, Lena C. A1 - Ladd, Susanne C. A1 - Ladd, Mark E. A1 - Maderwald, Stefan T1 - Open design eight-channel transmit/receive coil for high-resolution and real-time ankle imaging at 7 T JF - Medical Physics N2 - 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. Y1 - 2011 U6 - http://dx.doi.org/10.1118/1.3553399 SN - 2473-4209 VL - 38 IS - 3 SP - 1162 EP - 1167 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Kraff, Oliver A1 - Bitz, Andreas A1 - Kruszona, Stefan A1 - Orzada, Stephan A1 - Schaefer, Lena C. A1 - Theysohn, Jens M. A1 - Maderwald, Stefan A1 - Ladd, Mark E. A1 - Quick, Harald H. T1 - An eight-channel phased array RF coil for spine MR imaging at 7 T JF - Investigative Radiology Y1 - 2009 U6 - http://dx.doi.org/10.1097/RLI.0b013e3181b24ab7 SN - 1536-0210 VL - 44 IS - 11 SP - 734 EP - 740 PB - Lippincott Williams & Wilkins ER - TY - JOUR A1 - Rietsch, Stefan H. G. A1 - Pfaffenrot, Viktor A1 - Bitz, Andreas A1 - Orzada, Stephan A1 - Brunheim, Sascha A1 - Lazik-Palm, Andrea A1 - Theysohn, Jens M. A1 - Ladd, Mark E. A1 - Quick, Harald H. A1 - Kraff, Oliver T1 - An 8-channel transceiver 7-channel receive RF coil setup for high SNR ultrahigh-field MRI of the shoulder at 7T JF - Medical Physics Y1 - 2017 U6 - http://dx.doi.org/10.1002/mp.12612 SN - 0094-2405 IS - Article in press PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Orzada, Stephan A1 - Bitz, Andreas A1 - Johst, Sören A1 - Gratz, Marcel A1 - Völker, Maximilian N. A1 - Kraff, Oliver A1 - Abuelhaija, Ashraf A1 - Fiedler, Thomas M. A1 - Solbach, Klaus A1 - Quick, Harald H. A1 - Ladd, Mark E. T1 - Analysis of an integrated 8-Channel Tx/Rx body array for use as a body coil in 7-Tesla MRI JF - Frontiers in Physics Y1 - 2017 U6 - http://dx.doi.org/10.3389/fphy.2017.00017 SN - 2296-424X N1 - Article number 17 VL - 5 IS - Jun ER - TY - JOUR A1 - Rietsch, Stefan H. G. A1 - Brunheim, Sascha A1 - Orzada, Stephan A1 - Voelker, Maximilian N. A1 - Maderwald, Stefan A1 - Bitz, Andreas A1 - Gratz, Marcel A1 - Ladd, Mark E. A1 - Quick, Harald H. T1 - Development and evaluation of a 16-channel receive-only RF coil to improve 7T ultra-high field body MRI with focus on the spine JF - Magnetic Resonance in Medicine Y1 - 2019 U6 - http://dx.doi.org/10.1002/mrm.27731 SN - 1522-2594 IS - Early view PB - Wiley CY - Weinheim ER - TY - JOUR A1 - Orzada, Stephan A1 - Solbach, Klaus A1 - Gratz, Marcel A1 - Brunheim, Sascha A1 - Fiedler, Thomas M. A1 - Johst, Sören A1 - Bitz, Andreas A1 - Shooshtary, Samaneh A1 - Abuelhaija, Asjraf A1 - Voelker, Maximilian N. A1 - Rietsch, Stefan H. G. A1 - Kraff, Oliver A1 - Maderwald, Stefan A1 - Flöser, Martina A1 - Oehmingen, Mark A1 - Quick, Harald H. A1 - Ladd, Mark E. T1 - A 32-channel parallel transmit system add-on for 7T MRI JF - Plos one Y1 - 2019 U6 - http://dx.doi.org/10.1371/journal.pone.0222452 ER - TY - JOUR A1 - Orzada, Stephan A1 - Fiedler, Thomas M. A1 - Bitz, Andreas A1 - Ladd, Mark E. A1 - Quick, Harald H. T1 - Local SAR compression with overestimation control to reduce maximum relative SAR overestimation and improve multi-channel RF array performance JF - Magnetic Resonance Materials in Physics, Biology and Medicine N2 - 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. Y1 - 2020 SN - 1352-8661 U6 - http://dx.doi.org/10.1007/s10334-020-00890-0 IS - 34 (2021) SP - 153 EP - 164 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Fiedler, Thomas M. A1 - Orzada, Stephan A1 - Flöser, Martina A1 - Rietsch, Stefan H. G. A1 - Schmidt, Simon A1 - Stelter, Jonathan K. A1 - Wittrich, Marco A1 - Quick, Harald H. A1 - Bitz, Andreas A1 - Ladd, Mark E. T1 - Performance and safety assessment of an integrated transmitarray for body imaging at 7 T under consideration of specificabsorption rate, tissue temperature, and thermal dose JF - NMR in Biomedicine N2 - 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. KW - body imaging at 7 T MRI KW - thermal dose KW - tissue temperature KW - transmit antenna arrays Y1 - 2022 U6 - http://dx.doi.org/10.1002/nbm.4656 SN - 0952-3480 (Print) SN - 1099-1492 (Online) VL - 35 IS - 5 SP - 1 EP - 17 PB - Wiley ER -