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

Ashley D. Harris, Nicolaas A.J. Puts, Richard A.E. Edden
2015 Journal of Magnetic Resonance Imaging  
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
more » ... e 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.
doi:10.1002/jmri.24903 pmid:26172043 pmcid:PMC4615266 fatcat:eyevdcyg75bz3nczptaok7oe6u