Comparisons between multi-component myelin water fraction, T1w/T2w ratio, and diffusion tensor imaging measures in healthy human brain structures

Abstract

Various MRI techniques, including myelin water imaging, T1w/T2w ratio mapping and diffusion-based imaging can be used to characterize tissue microstructure. However, surprisingly few studies have examined the degree to which these MRI measures are related within and between various brain regions. Therefore, whole-brain MRI scans were acquired from 31 neurologically-healthy participants to empirically measure and compare myelin water fraction (MWF), T1w/T2w ratio, fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD) and mean diffusivity (MD) in 25 bilateral (10 grey matter; 15 white matter) regions-of-interest (ROIs). Except for RD vs. T1w/T2w, MD vs. T1w/T2w, moderately significant to highly significant correlations (p < 0.001) were found between each of the other measures across all 25 brain structures [T1w/T2w vs. MWF (Pearson r = 0.33, Spearman ρ = 0.31), FA vs. MWF (r = 0.73, ρ = 0.75), FA vs. T1w/T2w (r = 0.25, ρ = 0.22), MD vs. AD (r = 0.57, ρ = 0.58), MD vs. RD (r = 0.64, ρ = 0.61), AD vs. MWF (r = 0.43, ρ = 0.36), RD vs. MWF (r = −0.49, ρ = −0.62), MD vs. MWF (r = −0.22, ρ = −0.29), RD vs. FA (r = −0.62, ρ = −0.75) and MD vs. FA (r = −0.22, ρ = −0.18)]. However, while all six MRI measures were correlated with each other across all structures, there were large intra-ROI and inter-ROI differences (i.e., with no one measure consistently producing the highest or lowest values). This suggests that each quantitative MRI measure provides unique, and potentially complimentary, information about underlying brain tissues – with each metric offering unique sensitivity/specificity tradeoffs to different microstructural properties (e.g., myelin content, tissue density, etc.).

Myelin Measurement Using Quantitative Magnetic Resonance Imaging: A Correlation Study Comparing Various Imaging Techniques in Patients with Multiple Sclerosis

“…In NAWM, no significant correlation was found. All these studies concluded that the different quantitative techniques are at least partially correlated with each other but are sensitive to different aspects of the pathology and may provide complementary information about underlying brain tissues [53].…”

Fast and high‐resolution myelin water imaging: Accelerating multi‐echo GRASE with CAIPIRINHA

“…Although the acquisitions of these contrasts can be achieved faster and with enhanced resolution in comparison to the other approaches, other microstructural features unrelated to myelin density were shown to affect these contrasts. 65,66 The proposed framework and our study setup have limitations. The undersampling introduces a slight blurring of the images, as shown in the comparison of MWF MESE and MWF GRASE maps.…”

MR‐based age‐related effects on the striatum, globus pallidus, and thalamus in healthy individuals across the adult lifespan

“…However, while Uddin et al (2018) cite low correlations between T1w/T2w and a histologically validated technique for examining myelin, myelin water fraction (MWF), for white matter structures, they nonetheless cite moderate correlations for subcortical gray matter structures (Uddin et al, 2018(Uddin et al, , 2019. Thus, a conservative approach for using the T1w/T2w signal ratio is its use as a nonspecific biomarker of microstructure, with the use of quantitative MRI techniques, such as magnetization transfer or myelin water imaging, to parse out the effect of differential elements of the microstructure, such as myelin using MWI and iron using R2* (the short spin-spin T2 relaxation; Péran et al, 2007;Stüber et al, 2014).…”