Figure 3.

Distribution of white matter water diffusivities and FW fraction in relation with OSA severity. The average value of clusters showing significant group differences was extracted and estimated against the logarithm of the AHI. Both a linear and a quadratic fit were observed for (a) MD, (b) RD, and (c) AD. This was not the case for (d) AD specifically in the corpus callosum. For the (e) FW fraction fitted for CSF volume, a trend was observed for the quadratic fit (p = .064). Overall, these curve estimations showed that both linear and curvilinear relations are significant for MD, RD, and AD with OSA severity, suggesting a high level of heterogeneity in the moderate to severe OSA group. AHI values corresponding to the mild OSA group are showed in gray. AD, axial diffusivity; AHI, apnea–hypopnea index; CSF, cerebrospinal fluid; FW, free‐water; MD, mean diffusivity; OSA, obstructive sleep apnea; RD, radial diffusivity