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 - TY - JOUR A1 - Fagan, Andrew J. A1 - Bitz, Andreas A1 - Björkman-Burtscher, Isabella M. A1 - Collins, Christopher M. A1 - Kimbrell, Vera A1 - Raaijmakers, Alexander J. E. T1 - 7T MR Safety JF - Journal of Magnetic Resonance Imaging (JMRI) Y1 - 2021 U6 - http://dx.doi.org/10.1002/jmri.27319 SN - 1522-2586 VL - 53 IS - 2 SP - 333 EP - 346 PB - Wiley CY - Weinheim 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 - Ladd, Mark E. A1 - Clemens, Markus A1 - Bitz, Andreas T1 - Safety of subjects during radiofrequency exposure in ultra-high-field magnetic resonance imaging JF - IEEE Letters on Electromagnetic Compatibility Practice and Applications N2 - Magnetic resonance imaging (MRI) is one of the most important medical imaging techniques. Since the introduction of MRI in the mid-1980s, there has been a continuous trend toward higher static magnetic fields to obtain i.a. a higher signal-to-noise ratio. The step toward ultra-high-field (UHF) MRI at 7 Tesla and higher, however, creates several challenges regarding the homogeneity of the spin excitation RF transmit field and the RF exposure of the subject. In UHF MRI systems, the wavelength of the RF field is in the range of the diameter of the human body, which can result in inhomogeneous spin excitation and local SAR hotspots. To optimize the homogeneity in a region of interest, UHF MRI systems use parallel transmit systems with multiple transmit antennas and time-dependent modulation of the RF signal in the individual transmit channels. Furthermore, SAR increases with increasing field strength, while the SAR limits remain unchanged. Two different approaches to generate the RF transmit field in UHF systems using antenna arrays close and remote to the body are investigated in this letter. Achievable imaging performance is evaluated compared to typical clinical RF transmit systems at lower field strength. The evaluation has been performed under consideration of RF exposure based on local SAR and tissue temperature. Furthermore, results for thermal dose as an alternative RF exposure metric are presented. Y1 - 2020 SN - 2637-6423 U6 - http://dx.doi.org/10.1109/LEMCPA.2020.3029747 VL - 2 IS - 3 SP - 1 EP - 8 PB - IEEE CY - New York, NY 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 - Schmidt, Katharina A1 - Forkmann, Katarina A1 - Schultz, Heidrun A1 - Gratz, Marcel A1 - Bitz, Andreas A1 - Wiech, Katja A1 - Bingel, Ulrike T1 - Enhanced Neural Reinstatement for Evoked Facial Pain Compared With Evoked Hand Pain JF - The Journal of Pain Y1 - 2019 U6 - http://dx.doi.org/10.1016/j.jpain.2019.03.003 SN - 1526-5900 IS - In Press, Corrected Proof PB - Elsevier CY - Amsterdam 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 - Noureddine, Yacine A1 - Kraff, Oliver A1 - Ladd, Mark E. A1 - Wrede, Karsten A1 - Chen, Bixia A1 - Quick, Harald H. A1 - Schaefers, Georg A1 - Bitz, Andreas T1 - Radiofrequency induced heating around aneurysm clips using a generic birdcage head coil at 7 Tesla under consideration of the minimum distance to decouple multiple aneurysm clips JF - Magnetic Resonance in Medicine Y1 - 2019 U6 - http://dx.doi.org/10.1002/mrm.27835 SN - 1522-2594 IS - Early view SP - 1 EP - 17 PB - Wiley CY - Weinheim ER - TY - JOUR A1 - Fiedler, Thomas M. A1 - Ladd, Mark E. A1 - Bitz, Andreas T1 - SAR Simulations & Safety JF - NeuroImage Y1 - 2017 U6 - http://dx.doi.org/10.1016/j.neuroimage.2017.03.035 SN - 1053-8119 IS - Epub ahead of print PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Noureddine, Yacine A1 - Kraff, Oliver A1 - Ladd, Mark E. A1 - Wrede, Karsten H. A1 - Chen, Bixia A1 - Quick, Harald H. A1 - Schaefers, Gregor A1 - Bitz, Andreas T1 - In vitro and in silico assessment of RF-induced heating around intracranial aneurysm clips at 7 Tesla JF - Magnetic Resonance in Medicine Y1 - 2017 U6 - http://dx.doi.org/10.1002/mrm.26650 SN - 1522-2594 IS - Early view PB - Wiley CY - Weinheim ER - TY - JOUR A1 - Fiedler, Thomas M. A1 - Ladd, Mark E. A1 - Bitz, Andreas T1 - RF safety assessment of a bilateral four-channel transmit/receive 7 Tesla breast coil: SAR versus temperature limits JF - Medical Physics Y1 - 2017 U6 - http://dx.doi.org/10.1002/mp.12034 N1 - This article is corrected by: Errata: Erratum: “RF safety assessment of a bilateral four-channel transmit/receive 7 Tesla breast coil: SAR versus tissue temperature limits” [Med. Phys. 44(1), 143–157 (2017)] Volume 44, Issue 2, 772 VL - 44 IS - 1 SP - 143 EP - 157 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 - Schmidt, K. A1 - Forkmann, K. A1 - Sinke, C. A1 - Gratz, M. A1 - Bitz, Andreas A1 - Bingel, U. T1 - The differential effect of trigeminal vs. peripheral pain stimulation on visual processing and memory encoding is influenced by pain-related fear JF - NeuroImage N2 - Compared to peripheral pain, trigeminal pain elicits higher levels of fear, which is assumed to enhance the interruptive effects of pain on concomitant cognitive processes. In this fMRI study we examined the behavioral and neural effects of trigeminal (forehead) and peripheral (hand) pain on visual processing and memory encoding. Cerebral activity was measured in 23 healthy subjects performing a visual categorization task that was immediately followed by a surprise recognition task. During the categorization task subjects received concomitant noxious electrical stimulation on the forehead or hand. Our data show that fear ratings were significantly higher for trigeminal pain. Categorization and recognition performance did not differ between pictures that were presented with trigeminal and peripheral pain. However, object categorization in the presence of trigeminal pain was associated with stronger activity in task-relevant visual areas (lateral occipital complex, LOC), memory encoding areas (hippocampus and parahippocampus) and areas implicated in emotional processing (amygdala) compared to peripheral pain. Further, individual differences in neural activation between the trigeminal and the peripheral condition were positively related to differences in fear ratings between both conditions. Functional connectivity between amygdala and LOC was increased during trigeminal compared to peripheral painful stimulation. Fear-driven compensatory resource activation seems to be enhanced for trigeminal stimuli, presumably due to their exceptional biological relevance. Y1 - 2016 U6 - http://dx.doi.org/10.1016/j.neuroimage.2016.03.026 SN - 1053-8119 VL - 134 SP - 386 EP - 395 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Lagemaat, Miriam W. A1 - Breukels, Vincent A1 - Vos, Eline K. A1 - B., Adam A1 - Uden, Mark J. van A1 - Orzada, Stephan A1 - Bitz, Andreas A1 - Maas, Marnix C. A1 - Scheenen, Tom W. J. T1 - ¹H MR spectroscopic imaging of the prostate at 7T using spectral-spatial pulses JF - Magnetic Resonance in Medicine N2 - Purpose To assess the feasibility of prostate ¹H MR spectroscopic imaging (MRSI) using low-power spectral-spatial (SPSP) pulses at 7T, exploiting accurate spectral selection and spatial selectivity simultaneously. Methods A double spin-echo sequence was equipped with SPSP refocusing pulses with a spectral selectivity of 1 ppm. Three-dimensional prostate ¹H-MRSI at 7T was performed with the SPSP-MRSI sequence using an 8-channel transmit array coil and an endorectal receive coil in three patients with prostate cancer and in one healthy subject. No additional water or lipid suppression pulses were used. Results Prostate ¹H-MRSI could be obtained well within specific absorption rate (SAR) limits in a clinically feasible time (10 min). Next to the common citrate signals, the prostate spectra exhibited high spermine signals concealing creatine and sometimes also choline. Residual lipid signals were observed at the edges of the prostate because of limitations in spectral and spatial selectivity. Conclusion It is possible to perform prostate ¹H-MRSI at 7T with a SPSP-MRSI sequence while using separate transmit and receive coils. This low-SAR MRSI concept provides the opportunity to increase spatial resolution of MRSI within reasonable scan times. Y1 - 2016 U6 - http://dx.doi.org/10.1002/mrm.25569 SN - 1522-2594 VL - 75 IS - 3 SP - 933 EP - 945 PB - International Society for Magnetic Resonance in Medicine ER - TY - JOUR A1 - Orzada, Stephan A1 - Ladd, Mark E. A1 - Bitz, Andreas T1 - A method to approximate maximum local SAR in multichannel transmit MR systems without transmit phase information JF - Magnetic Resonance in Medicine N2 - 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 Y1 - 2016 U6 - http://dx.doi.org/10.1002/mrm.26398 SN - 1522-2594 VL - 78 IS - 2 SP - 805 EP - 811 PB - International Society for Magnetic Resonance in Medicine ER - TY - JOUR A1 - Chen, Bixia A1 - Schoemberg, Tobias A1 - Kraff, Oliver A1 - Dammann, Philipp A1 - Bitz, Andreas A1 - Schlamann, Marc A1 - Quick, Harald H. A1 - Ladd, Mark E. A1 - Sure, Ulrich A1 - Wrede, Karsten H. T1 - Cranial fixation plates in cerebral magnetic resonance imaging: a 3 and 7 Tesla in vivo image quality study JF - Magnetic Resonance Materials in Physics, Biology and Medicine N2 - Objective This study assesses and quantifies impairment of postoperative magnetic resonance imaging (MRI) at 7 Tesla (T) after implantation of titanium cranial fixation plates (CFPs) for neurosurgical bone flap fixation. Materials and methods The study group comprised five patients who were intra-individually examined with 3 and 7 T MRI preoperatively and postoperatively (within 72 h/3 months) after implantation of CFPs. Acquired sequences included T₁-weighted magnetization-prepared rapid-acquisition gradient-echo (MPRAGE), T₂-weighted turbo-spin-echo (TSE) imaging, and susceptibility-weighted imaging (SWI). Two experienced neurosurgeons and a neuroradiologist rated image quality and the presence of artifacts in consensus reading. Results Minor artifacts occurred around the CFPs in MPRAGE and T2 TSE at both field strengths, with no significant differences between 3 and 7 T. In SWI, artifacts were accentuated in the early postoperative scans at both field strengths due to intracranial air and hemorrhagic remnants. After resorption, the brain tissue directly adjacent to skull bone could still be assessed. Image quality after 3 months was equal to the preoperative examinations at 3 and 7 T. Conclusion Image quality after CFP implantation was not significantly impaired in 7 T MRI, and artifacts were comparable to those in 3 T MRI. Y1 - 2016 U6 - http://dx.doi.org/10.1007/s10334-016-0548-1 SN - 1352-8661 VL - 29 IS - 3 SP - 389 EP - 398 PB - Springer CY - Berlin ER - TY - JOUR A1 - Bank, Bart L. van de A1 - Orzada, Stephan A1 - Smits, Frits A1 - Lagemaat, Miriam W. A1 - Rodgers, Christopher T. A1 - Bitz, Andreas A1 - Scheenen, Tom W. J. T1 - Optimized (31) P MRS in the human brain at 7 T with a dedicated RF coil setup JF - NMR in Biomedicine Y1 - 2015 U6 - http://dx.doi.org/10.1002/nbm.3422 SN - 1099-1492 VL - 28 IS - 11 SP - 1570 EP - 1578 PB - Wiley CY - Weinheim ER - TY - JOUR A1 - Noureddine, Yacine A1 - Bitz, Andreas A1 - Ladd, Mark E. A1 - Thürling, Markus A1 - Ladd, Susanne C. A1 - Schaefers, Gregor A1 - Kraff, Oliver T1 - Experience with magnetic resonance imaging of human subjects with passive implants and tattoos at 7 T: a retrospective study JF - Magnetic Resonance Materials in Physics, Biology and Medicine Y1 - 2015 U6 - http://dx.doi.org/10.1007/s10334-015-0499-y SN - 1352-8661 VL - 28 IS - 6 SP - 577 EP - 590 PB - Springer CY - Berlin ER - TY - JOUR A1 - Lagemaat, Miriam W. A1 - Maas, Marnix C. A1 - Vos, Eline K. A1 - Bitz, Andreas A1 - Orzada, Stephan A1 - Weiland, Elisabeth A1 - Uden, Mark J. van A1 - Kobus, Thiele A1 - Heerschap, Arend A1 - Scheenen, Tom W. J. T1 - (31) P MR spectroscopic imaging of the human prostate at 7 T: T1 relaxation times, Nuclear Overhauser Effect, and spectral characterization JF - Magnetic Resonance in Medicine Y1 - 2015 U6 - http://dx.doi.org/10.1002/mrm.25209 SN - 1522-2594 VL - 73 IS - 3 SP - 909 EP - 920 PB - Wiley CY - Weinheim ER -