Inter‐subject stability and regional concentration estimates of 3D‐FID‐MRSI in the human brain at 7 T

Abstract

Purpose: Recently, a 3D-concentric ring trajectory (CRT)-based free induction decay (FID)-MRSI sequence was introduced for fast high-resolution metabolic imaging at 7 T. This technique provides metabolic ratio maps of almost the entire brain within clinically feasible scan times, but its robustness has not yet been thoroughly investigated. Therefore, we have assessed quantitative concentration estimates and their variability in healthy volunteers using this approach.Methods: We acquired whole-brain 3D-CRT-FID-MRSI at 7 T in 15 min with 3.4 mm nominal isometric resolution in 24 volunteers (12 male, 12 female, mean age 27 ± 6 years). Concentration estimate maps were calculated for 15 metabolites using internal water referencing and evaluated in 55 different regions of interest (ROIs) in the brain. Data quality, mean metabolite concentrations, and their inter-subject coefficients of variation (CVs) were compared for all ROIs.Results: Of 24 datasets, one was excluded due to motion artifacts. The concentrations of total choline, total creatine, glutamate, myo-inositol, and N-acetylaspartate in 44 regions were estimated within quality thresholds. Inter-subject CVs (mean over

Test-retest reproducibility of human brain multi-slice 1H FID-MRSI data at 9.4 T after optimization of lipid regularization, macromolecular model and spline baseline stiffness

“…Thus, the configuration L2-MM-0.25 was chosen for presenting metabolite ratio maps in Figure 5. Since no tissue segmentation was done in this study, the concentration ratio maps can only visually be compared to previous literature, but correspond mostly well to the expected ratios of GM and WM: higher concentration in WM than GM for tCho/tCr 21,37–40,46 , mI/tCr 39,46 , NAAG/tCr 31,39,63,65 and higher concentrations in GM for Glu/tCr 31,37,38,40,46 , GABA/tCr 31,72,73 , Gln/tCr 31,74 , Tau/tCr 31,74 , Asp/tCr 31 . For some metabolites even more anatomical details are seen in the maps which correspond to the literature: NAA/tCr is higher in the corpus callosum and thalamus 37 ; tCho/tCr is concentrated higher in the frontal cortex than in the occipital lobe 21,38–40 and strongly in corpus callosum and thalamus 37 .…”

“…Since no tissue segmentation was done in this study, the concentration ratio maps can only visually be compared to previous literature, but correspond mostly well to the expected ratios of GM and WM: higher concentration in WM than GM for tCho/tCr 21,[37][38][39][40]46 , mI/tCr 39,46 , NAAG/tCr 31,39,63,65 and higher concentrations in GM for Glu/tCr 31,37,38,40,46 , GABA/tCr 31,72,73 , Gln/tCr 31,74 , Tau/tCr 31,74 , Asp/tCr 31 . For some metabolites even more anatomical details are seen in the maps which correspond to the literature: NAA/tCr is higher in the corpus callosum and thalamus 37 ; tCho/tCr is concentrated higher in the frontal cortex than in the occipital lobe 21,[38][39][40] and strongly in corpus callosum and thalamus 37 . In the literature NAA/tCr is higher in WM than GM 21,31,39,46,63 , while the transversal concentration ratio maps in Figure 5b show a rather evenly distributed NAA/tCr concentration and look similar to the maps presented in other publications 12,31 .…”

“…Maudsley et al 22 calculated mean intra-subject CVs from 5 session acquired with SE MRSI at 3T ranging from NAA/tCr: 1.8-11 % and tCho/tCr: 2.7-10.2 % for different regions and Gu et al 13 reported from 6 scans acquired with 3D MRSI ranging from NAA/tCr: 2.3-12.7 % and tCho/tCr: 2.0-7.1 % for different regions at 1.5 T. Hnilicova et al 79 calculated CVs of Glx/tCr of 4-8% and GABA+macromolecules/tCr of 6-10% (minimal-maximal value of medians) for using MEGA-LASER 3D MRSI sequence at 3T. Others reported intra-session or inter-subject CV and will not be compared 11,23,25,37 . Due to the lack of comparable high-field reproducibility studies with large volumes with more metabolites, the CVs of a single-slice study at 7T from Heckova et al 42 will be referenced.…”

“…These publications were all using acceleration techniques and showing maps of a maximum of six metabolites (tCr, tNAA/NAA, tCho, Glu, Gln, mI) for a brain volume of a maximum of 110 mm and only one paper showed NAAG for a relatively small volume of 50 mm thickness 39 . None of these ultra-high field 1 H MRSI studies investigated the intra-subject test-retest reproducibility, only one ultra-high field MRSI study investigated inter-subject reproducibility 37 . In fact there is only one 2D 1 H MRSI study at 7T that presents intra-subject test-retest data from a single slice above the corpus callosum for tNAA, tCho, tCr, mI and Glx 42 .…”

“…While the majority of ultra-high field 1 H MRSI studies cover only a single slice [28][29][30][31][32][33][34][35] , there are only very few 1 H MRSI investigations at ultra-high field strengths that show an extended coverage of the human brain [36][37][38][39][40][41] . These publications were all using acceleration techniques and showing maps of a maximum of six metabolites (tCr, tNAA/NAA, tCho, Glu, Gln, mI) for a brain volume of a maximum of 110 mm and only one paper showed NAAG for a relatively small volume of 50 mm thickness 39 .…”