White matter fiber-based analysis of T1w/T2w ratio map

Abstract

Purpose To develop, test, evaluate and apply a novel tool for the white matter fiber-based analysis of T1w/T2w ratio maps quantifying myelin content. Background The cerebral white matter in the human brain develops from a mostly non-myelinated state to a nearly fully mature white matter myelination within the first few years of life. High resolution T1w/T2w ratio maps are believed to be effective in quantitatively estimating myelin content on a voxel-wise basis. We propose the use of a fiber-tract-based analysis of such T1w/T2w ratio data, as it allows us to separate fiber bundles that a common regional analysis imprecisely groups together, and to associate effects to specific tracts rather than large, broad regions. Methods We developed an intuitive, open source tool to facilitate such fiber-based studies of T1w/T2w ratio maps. Via its Graphical User Interface (GUI) the tool is accessible to non-technical users. The framework uses calibrated T1w/T2w ratio maps and a prior fiber atlas as an input to generate profiles of T1w/T2w values. The resulting fiber profiles are used in a statistical analysis that performs along-tract functional statistical analysis. We applied this approach to a preliminary study of early brain development in neonates. Results We developed an open-source tool for the fiber based analysis of T1w/T2w ratio maps and tested it in a study of brain development.

Interactive effect of age and APOE-ε4 allele load on white matter myelin content in cognitively normal middle-aged subjects

“…We hypothesized that subjects at risk of developing AD would show negatively affected ratio values in regions matching the ones observed in diffusion imaging taking T1w/T2w ratios as indirect measures of myelin content. T1w/T2w ratio has been extensively used in previous research as a non-quantitative descriptor of cortical myelination, but rarely in WM studies (Chen et al, 2017). Results from this present study show significant decreases of this ratio in APOE -ε4 carriers in extended regions of the WM in a cognitively normal population.…”

Mapping myelin in white matter with T1-weighted/T2-weighted maps: discrepancy with histology and other myelin MRI measures

“…Myelin is present in the cortex, but it is most abundant in the cerebral white matter (Shafee et al 2015 ), and the ratio of T1-weighted/T2-weighted (T1w/T2w) MRI images has been suggested as a reliable and straightforward in vivo method to map myelin in the cerebral cortex (Glasser and Van Essen, 2011 ). Some studies have even applied T1w/T2w to white matter tracts in the neonatal (Lee et al 2015 ; Chen et al 2017 ) and adult brain (Colmenares et al 2021 ). However, upon comparison with other myelin mapping imaging modalities, including Myelin Water Fraction (MWF), T1w/T2w ‘may be not an optimal index of subcortical myelin content’ (Arshad et al 2017 ), and its use as a myelin marker has been criticized (Uddin et al 2018 , 2019 ).…”

Empirical Transmit Field Bias Correction of T1w/T2w Myelin Maps

“…For this reason, Voxel Based Morphometry (VBM) style analyses are never appropriate in T1w/T2w studies of the cerebral cortex. Skeletonized methods such as Tract-Based-Spatial-Statistics (TBSS; Smith et al, 2006) offer the best option for voxelwise white matter analysis (e.g., Operto et al, 2019), though tractography-based tract analyses would likely be even better (Chen et al, 2017; Thompson et al, 2020).…”

“…Importantly, however, it is NOT appropriate to attempt "VBMstyle" analyses of these T1w/T2w ratio volumes in lieu of proper surface-based cortical analyses for reasons described elsewhere (Glasser et al, 2016b;Coalson et al, 2018), and also because partial volume effects of CSF, grey matter, and white matter will completely dominate the differential effects of myelin content in traditional volume-based analyses (i.e., the differences in T1w/T2w ratio between tissues are much larger than those within tissues). Skeletonized methods such as Tract-Based-Spatial-Statistics (TBSS; Smith et al, 2006) offer the best option for voxelwise white matter analysis (e.g., Operto et al, 2019), though tractography-based tract analyses would likely be even better (Chen et al, 2017;Thompson et al, 2020).…”