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Tissue correction for GABA‐edited MRS: Considerations of voxel composition, tissue segmentation, and tissue relaxations
Author(s) -
Harris Ashley D.,
Puts Nicolaas A.J.,
Edden Richard A.E.
Publication year - 2015
Publication title -
journal of magnetic resonance imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.563
H-Index - 160
eISSN - 1522-2586
pISSN - 1053-1807
DOI - 10.1002/jmri.24903
Subject(s) - voxel , white matter , cerebrospinal fluid , brain tissue , nuclear medicine , nuclear magnetic resonance , in vivo , fractionation , chemistry , magnetic resonance imaging , biomedical engineering , physics , pathology , biology , medicine , chromatography , radiology , microbiology and biotechnology
Purpose To develop a tissue correction for GABA‐edited magnetic resonance spectroscopy (MRS) that appropriately addresses differences in voxel gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) fractions. Materials and Methods Simulations compared the performance of tissue correction approaches. Corrections were then applied to in vivo data from 16 healthy volunteers, acquired at 3T. GM, WM, and CSF fractions were determined from T 1 ‐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 nonlinearly) 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 overestimated 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 intersubject 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. J. Magn. Reson. Imaging 2015;42:1431–1440.