Tissue correction for GABA‐edited MRS: Considerations of voxel composition, tissue segmentation, and tissue relaxations

Abstract

Purpose To develop a tissue correction for GABA-edited MRS that appropriately addresses differences in voxel gray matter (GM), white matter (WM) and cerebrospinal fluid (CSF) fractions. Methods Simulations compared the performance of tissue correction approaches. Corrections were then applied to in vivo data from sixteen healthy volunteers, acquired at 3T. GM, WM and CSF fractions were determined from T1-weighted images. Corrections for CSF content, GM/WM GABA content, and water relaxation of the three compartments are combined into a single, fully corrected measurement. Results Simulations show that CSF correction increases the dependence of GABA measurements on GM/WM fraction, by an amount equal to the fraction of CSF. Furthermore, GM correction substantially (and non-linearly) increases the dependence of GABA measurements on GM/WM fraction, for example, by a factor of over four when the voxel GM tissue fraction is 50%. At this tissue fraction, GABA is over estimated by a factor of 1.5. For the in vivo data, correcting for voxel composition increased measured GABA values (p<0.001 for all regions), but did not reduce inter-subject variance (p>0.5 for all regions). Corrected GABA values differ significantly based on the segmentation procedure used (p<0.0001) and tissue parameter assumptions made (p<0.0001). Conclusion We introduce a comprehensive tissue correction factor that adjusts GABA measurements to correct for different voxel compositions of GM, WM, and CSF.

Global brain atrophy and metabolic dysfunction in LGI1 encephalitis: A prospective multimodal MRI study

“…The CSF corrected concentration of the following metabolites were calculated in all MRS voxels [23][24][25]: total N-acetylaspartate (tNAA), total choline (tCho), total creatine (tCr), myoinositole (Ins) and glutamine/glutamate (Glx). Detailed evaluation is described in Supplementary Materials and Methods.…”

“…The binary masks of the MRS voxels were constructed in the native coordinate space of the MPRAGE image using Gannet software suite [24]. Average CSF content of the spectroscopy voxel was then calculated using the CSF image resulting from FAST and the binary mask of the voxel using fslstats.…”

Impact of tissue correction strategy on GABA-edited MRS findings

“…How the heterogeneity of white and gray matter atrophy impacts cognitive decline is unclear (7). The impact of this dynamic, regionally variant atrophy necessitates a sophisticated consideration of voxel tissue composition to ensure that the age-related GABA+ changes are not unduly impacted by the tissue composition of the measurement voxel (14). The current study implements and compares different tissue corrections for GABA+ in the context of healthy aging.…”

“…The current study implements and compares different tissue corrections for GABA+ in the context of healthy aging. Specifically, the most commonly used approach, the CSF-correction, a more recently proposed tissue correction, here referred to as the α-correction (14), and no tissue correction are compared.…”

“…Tissue composition of MRS voxels has a significant impact on metabolite quantification (14–16), as metabolite levels (and reference signals) differ between tissue and CSF, but also between gray and white matter. Tissue correction is applied to account for the differences in signal between different tissues within a voxel; however both the use of the term and implementation of the method are inconsistently applied.…”