Non-Gaussian Diffusion Imaging Shows Brain Myelin and Axonal Changes in Obstructive Sleep Apnea

Abstract

Objective: Obstructive sleep apnea (OSA) is accompanied by brain changes in areas that regulate autonomic, cognitive, and mood functions, which were initially examined by Gaussian-based diffusion tensor imaging measures, but can be better assessed with non-Gaussian measures. We aimed to evaluate axonal and myelin changes in OSA using axial (AK) and radial kurtosis (RK) measures.

Materials and methods: We acquired diffusion kurtosis imaging data from 22 OSA and 26 controls; AK and RK maps were calculated, normalized, smoothed, and compared between groups using analysis of covariance.

Results: Increased AK, indicating axonal changes, emerged in the insula, hippocampus, amygdala, dorsolateral pons, and cerebellar peduncles and showed more axonal injury over previously identified damage. Higher RK, showing myelin changes, appeared in the hippocampus, amygdala, temporal and frontal lobes, insula, midline pons, and cerebellar peduncles and showed more widespread myelin damage over previously identified injury.

Conclusions: Axial kurtosis and RK measures showed widespread changes over Gaussian-based techniques, suggesting a more sensitive nature of kurtoses to injury.

Conflict of interest statement

Conflicts of interest: None

Figures

Figure 1. 3D whole-brain demonstrating altered axial and radial kurtosis

Brain sites with significantly increased axial (A) and radial (B) kurtosis values in obstructive sleep apnea compared to control subjects. Sites are overlaid onto a 3D whole-brain cortical surface for anatomical identification, and are shown in different axial, coronal, and sagittal views.

Figure 2. Brain regions showing altered axial kurtosis

3D brain sites showing regions with higher axial kurtosis values in obstructive sleep apnea over control subjects. These sites included the right middle cerebellar peduncle (a), hippocampus (b), parietal white matter (c, o), mid corona radiata (d), ventral temporal cortex extending to cerebellar cortex (e), unilateral dorsolateral pons (f), mid, caudal temporal cortices (g, h), hippocampus extending to amygdala (i, j) mid and posterior insular cortices extending to external capsule and ventral putamen (k, l), left internal capsule extending to the thalamus (m), left internal capsule extending to caudate (p), occipital cortex (n, t), and lateral parietal cortex extending to midline (s). Images are in neurological convention (L, left; R, right), and color bar represents t-statistic values.

Figure 3. Brain regions showing altered radial kurtosis

3D brain regions with increased radial kurtosis values in obstructive sleep apnea over control subjects. These regions appeared in the midline pons, extending to the middle cerebellar peduncle (a), ventral, mid, dorsal temporal cortex extending to temporal white matter (b), temporal white matter extending to the hippocampus (c, d), inferior frontal orbital cortex (e), parietal cortex (f, n), midline frontal cortex (g), hippocampus extending to amygdala (i, h), cerebellar vermis (j), insular cortex extending to external capsule and ventral putamen (m, l). Figure conventions are same as in Figure 2.