Andrzej Liebert1, Moritz Zaiss2, Rene Gumbrecht3, Katharina Tkotz1, Peter Linz1, Benjamin Schmitt3, Frederik B Laun1, Arnd Doerfler4, Michael Uder1, Armin M Nagel1,5,6. 1. Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Germany. 2. High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany. 3. Siemens Healthcare GmbH, Erlangen, Germany. 4. Department of Neuroradiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Germany. 5. Institute of Medical Physics, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Germany. 6. Division of Medical Physics in Radiology, German Cancer Research Centre (DKFZ), Heidelberg, Germany.
Abstract
PURPOSE: To mitigate B 1 + inhomogeneity in quantitative CEST MRI at ultra-high magnetic field strengths (B0 ≥ 7 Tesla) using a parallel transmit system. METHODS: Multiple interleaved mode saturation employs interleaving of 2 complementary phase sets during the saturation pulse train. Phase differences of 45° (first mode) and 90° (second mode) between 2 adjacent transmitter coil channels are used. The influence of the new saturation scheme on the CEST contrast was analyzed using Bloch-McConnell simulations. The presented method was verified in phantom and in vivo measurements of the healthy human brain. The relayed nuclear Overhauser effect was evaluated, and the inverse magnetic transfer ratio metric was calculated. Results were compared to a published B 1 + correction method. All measurements were conducted on a whole-body 7 Tesla MRI system using an 8 transmitter and 32 receiver channel head coil. RESULTS: Simulations showed that the inverse magnetic transfer ratio metric contrast of relayed nuclear Overhauser effect shows a smaller dependency on the relative amplitudes of the 2 different modes than the contrasts of Cr and amide proton transfer. Measurements of an egg white phantom showed markedly improved homogeneity compared to the uncorrected inverse magnetic transfer ratio metric (relayed nuclear Overhauser effect) images and slightly improved results compared to B 1 + corrected images. In vivo multiple interleaved mode saturation images showed similar contrast compared to B 1 + corrected images. CONCLUSION: Multiple interleaved mode saturation can be used as a simple method to mitigate B 1 + inhomogeneity effects in CEST MRI at ultra-high magnetic field strengths. Compared to previous B 1 + correction methods, acquisition time can be reduced because an additional scan, usually required for B 1 + correction, can be omitted.
PURPOSE: To mitigate B 1 + inhomogeneity in quantitative CEST MRI at ultra-high magnetic field strengths (B0 ≥ 7 Tesla) using a parallel transmit system. METHODS: Multiple interleaved mode saturation employs interleaving of 2 complementary phase sets during the saturation pulse train. Phase differences of 45° (first mode) and 90° (second mode) between 2 adjacent transmitter coil channels are used. The influence of the new saturation scheme on the CEST contrast was analyzed using Bloch-McConnell simulations. The presented method was verified in phantom and in vivo measurements of the healthy human brain. The relayed nuclear Overhauser effect was evaluated, and the inverse magnetic transfer ratio metric was calculated. Results were compared to a published B 1 + correction method. All measurements were conducted on a whole-body 7 Tesla MRI system using an 8 transmitter and 32 receiver channel head coil. RESULTS: Simulations showed that the inverse magnetic transfer ratio metric contrast of relayed nuclear Overhauser effect shows a smaller dependency on the relative amplitudes of the 2 different modes than the contrasts of Cr and amide proton transfer. Measurements of an egg white phantom showed markedly improved homogeneity compared to the uncorrected inverse magnetic transfer ratio metric (relayed nuclear Overhauser effect) images and slightly improved results compared to B 1 + corrected images. In vivo multiple interleaved mode saturation images showed similar contrast compared to B 1 + corrected images. CONCLUSION: Multiple interleaved mode saturation can be used as a simple method to mitigate B 1 + inhomogeneity effects in CEST MRI at ultra-high magnetic field strengths. Compared to previous B 1 + correction methods, acquisition time can be reduced because an additional scan, usually required for B 1 + correction, can be omitted.
Authors: Paul S Jacobs; Blake Benyard; Abigail Cember; Ravi Prakash Reddy Nanga; Quy Cao; M Dylan Tisdall; Neil Wilson; Sandhitsu Das; Kathryn A Davis; John Detre; David Roalf; Ravinder Reddy Journal: Magn Reson Med Date: 2022-08-15 Impact factor: 3.737
Authors: David Leitão; Raphael Tomi-Tricot; Pip Bridgen; Tom Wilkinson; Patrick Liebig; Rene Gumbrecht; Dieter Ritter; Sharon L Giles; Ana Baburamani; Jan Sedlacik; Joseph V Hajnal; Shaihan J Malik Journal: Magn Reson Med Date: 2022-03-10 Impact factor: 3.737