Quantification of Human Brain Metabolites using Two-Dimensional J-Resolved Metabolite-Cycled semiLASER at 9.4 T
Saipavitra Murali-Manohar1,2, Tamas Borbath1,2, Andrew Martin Wright1,3, and Anke Henning1,4
1High Field Magentic Resonance, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany, 2Faculty of Science, University of Tuebingen, Tuebingen, Germany, 3IMPRS for Cognitive Neuroscience, Tuebingen, Germany, 4Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, United States
2D J-resolved metabolite cycled semiLASER is implemented at 9.4 T in the human brain and the spectral fitting is performed using ProFit2.0 for in vivo data. Quantification of metabolites is performed using internal water referencing after accounting for relaxation effects and tissue content.
Figure 2: a) Two-dimensional J-resolved MC semiLASER spectrum (TEstart: 24 ms, TR: 6000 ms, $$$n$$$=85, $$$∆t$$$=2 ms) acquired at 9.4T from a Braino phantom. Lactate peaks at 1.31 and 4.09 ppm (maximum separated in the upfield proton spectrum) were considered to calculate reduction in the intensity of the J-refocused peaks according to the equation given in Lin et al17. This resulted in 86% reduction in the intensity and hence, there are barely any J-refocused peaks in the spectrum. b) Two-dimensional J-resolved MC semiLASER spectrum from a representative subject acquired at 9.4T.
Figure 1: a) 2D J-resolved MC semiLASER sequence implemented at 9.4 T. The excitation and adiabatic pulse bandwidths are 8000Hz. This leads to a chemical shift displacement of 10% between NAA (2.008 ppm) and mI (4.05 ppm). This means that even after accounting for the displacement in all three directions still there is a 73% voxel overlap occurring in the voxels for the two mentioned resonances. b) High-resolution MP2RAGE images showing the voxel positioning for the acquisition of in vivo data. Tissue segmentation resulted in GM/WM/CSF content: 67.3 ± 8.6/ 28.5 ± 8.6/ 3.7 ± 1.5%.