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. 2017 Apr;38(4):1780-1790.
doi: 10.1002/hbm.23481. Epub 2016 Dec 23.

Test-retest reliability and concurrent validity of in vivo myelin content indices: Myelin water fraction and calibrated T1 w/T2 w image ratio

Muzamil Arshad  1   2 , Jeffrey A Stanley  1 , Naftali Raz  2   3
Affiliations

Test-retest reliability and concurrent validity of in vivo myelin content indices: Myelin water fraction and calibrated T1 w/T2 w image ratio

Muzamil Arshad et al. Hum Brain Mapp. 2017 Apr.

Abstract

In an age-heterogeneous sample of healthy adults, we examined test-retest reliability (with and without participant repositioning) of two popular MRI methods of estimating myelin content: modeling the short spin-spin (T2 ) relaxation component of multi-echo imaging data and computing the ratio of T1 -weighted and T2 -weighted images (T1 w/T2 w). Taking the myelin water fraction (MWF) index of myelin content derived from the multi-component T2 relaxation data as a standard, we evaluate the concurrent and differential validity of T1 w/T2 w ratio images. The results revealed high reliability of MWF and T1 w/T2 w ratio. However, we found significant correlations of low to moderate magnitude between MWF and the T1 w/T2 w ratio in only two of six examined regions of the cerebral white matter. Notably, significant correlations of the same or greater magnitude were observed for T1 w/T2 w ratio and the intermediate T2 relaxation time constant, which is believed to reflect differences in the mobility of water between the intracellular and extracellular compartments. We conclude that although both methods are highly reliable and thus well-suited for longitudinal studies, T1 w/T2 w ratio has low criterion validity and may be not an optimal index of subcortical myelin content. Hum Brain Mapp 38:1780-1790, 2017. © 2017 Wiley Periodicals, Inc.

Keywords: MRI; Simpson paradox; T2 relaxation; brain water mobility; white matter.

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Figures

Figure 1
Figure 1
Design diagram of the reliability trials.
Figure 2
Figure 2
Plots of associations between Myelin Water Fraction, geomT2iew and T1w/T2w ratio (multiplied by 100) for all regions of interest, and their aggregation. Values are based on the mean of the right and left side except for the genu and splenium. *P < 0.05; **P < 0.008. [Color figure can be viewed at http://wileyonlinelibrary.com]
See this image and copyright information in PMC

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