Multi‐center reproducibility of neurochemical profiles in the human brain at 7 T

Abstract

Purpose To harmonize data acquisition and post-processing of single voxel proton magnetic resonance spectroscopy (1H-MRS) at 7 Tesla (7T), and to determine metabolite concentrations, accuracy and reproducibility of metabolite levels in the adult human brain. Experimental This study was performed in compliance with local Institutional Human Ethics Committees. The same seven subjects were each examined twice using four different 7T MR-systems from two different vendors using an identical semi-LASER spectroscopy sequence. Neurochemical profiles were obtained from the posterior cingulate cortex (GM) and the corona radiata (WM). Spectra were analyzed with LCModel, and sources of variation in concentrations (‘subject’, ‘institute’ & ‘random’) were identified with a variance components analysis. Results Concentrations of 10-11 metabolites, which were corrected for T1, T2, Magnetization Transfer-effects and partial volume effects, were obtained with mean Cramér-Rao Lower Bounds below 20%. Data variances and mean concentrations in GM and WM were comparable for all institutions. The primary source of variance for glutamate, myo-inositol, scyllo-inositol, total creatine and total choline was between-subjects. Variance sources for all other metabolites were associated to within-subject and system noise, except for total N-acetylaspartate, glutamine and glutathione, which related to differences in signal-to-noise and in shimming performance between vendors. Conclusion After multi-center harmonization of acquisition and post-processing protocols, metabolite concentrations and size and sources of their variations were established for neurochemical profiles in the healthy brain at 7T, which can be used as guidance in future studies quantifying metabolite and neurotransmitter concentrations with 1H-MRS at ultra-high magnetic field.

Quantitativein vivoneurochemical profiling in humans: where are we now?

“…This ability of 1 H-MRS to map the actual inter-subject variability in metabolite concentration in a specific brain region was demonstrated by a strong correlation between metabolite levels of individual subjects determined at 4 T and 7 T ( Figure 6). Similar results were found in a recent multi-centre study that focused on the accuracy and reproducibility of neurochemical profiles in the human brain at 7 T. 27 This study was performed at four different institutions (University Duisburg-Essen, University of Minnesota, Leiden University Medical Center and University Medical Center Utrecht) using 7T MRI scanners from two different vendors (Philips or Siemens). The same seven subjects were each examined twice at each site using the same protocol: FASTMAP B 0 shimming, semi-LASER localization sequence 33 combined with VAPOR water suppression, 25,34 LCModel metabolite quantification.…”

“…For this reason, automatic VOI positioning methods have been developed for 1 H-MRS. 64 These regional differences in metabolite concen- 27 This was possible by implementing the same MRS methodology including data acquisition and processing (FASTMAP shimming, semi-LASER localization sequence, VAPOR water suppression, LCModel processing). There is an ongoing multi-centre effort (NIH grant: Partnership for MRS biomarker development, PI: Gü lin € Oz, University of Minnesota) that seeks to simplify the operator input necessary to acquire MRS data, to make it robust and user-friendly and to make it available for all major clinical MR platforms.…”

Big GABA: Edited MR spectroscopy at 24 research sites

“…These focuses have included: unedited, short-TE MRS (Deelchand et al, 2015); low-field MRS (Träber et al, 2006); ultra-high field MRS (van de Bank, 2015); absolute quantification (Bovée et al, 1998; De Beer et al, 1998; Keevil et al, 1998; Soher et al, 1996); MRSI (Sabati et al, 2015; Wijnen et al, 2010); body MRS (Bolan et al, 2016; Scheenen et al, 2011); brain tumor classification (García-Gómez et al, 2009; Julià-Sapé et al, 2006; Tate et al, 2003; Vicente et al, 2013); and HIV-associated dementia (Chang et al, 2004; Lee et al, 2003; Sacktor et al, 2005). Even for short-TE methods, the degree of agreement between sites and scanners is highly dependent on the degree of acquisition homogeneity.…”

The dynamics of cortical GABA in human motor learning

“…MRS data were acquired using a semi-LASER sequence (van de Bank et al, 2015): TR=5000 ms, TE=36 ms, 20x20x20 mm voxel, 64 averages per block, TA=5 mins 20 secs, using VAPOR (VAriable Power RF pulses with Op mized Relaxa on delays) water suppression (Tkác et al, 1999). The VOI was manually posi oned in the le M1, covering the whole hand knob (Yousry et al, 1997) ( Figure 1D) and excluding the dura.…”