Multifractal-dynamic reliability of white matter in rs-fMRI and relationships to gray matter

Recent studies have demonstrated the reliable detection and analysis of white matter (WM) using the resting-state functional magnetic resonance imaging (rs-fMRI) signal. This paper studies the multifractal spontaneous in WM based on the HCP test-retest datasets. Precisely: (1) multifractal in the WM; (2) the source of multifractal; (3) difference and similarity between the multifractal of WM and gray matter (GM). Results showed that WM appears to be multifractal and significantly different from GM, but the variability of brain regions in WM was smaller than that in GM. For example, in WM, ('Fornix', 'Inferior cerebellar peduncle L', 'Superior cerebellar peduncle R', 'Posterior corona radiata R', and 'Uncinate fasciculus L') had higher multifractal scores than other regions; but in GM, the degree of multifractal in the parietal lobe, occipital lobe, and parietal lobe was higher than that of different regions. Besides, the source of multifractality is primarily composed of heavy-tailed probability distributions and long-range dependence, particularly heavy-tailed probability distributions. In addition, the ICC of multifractal in GM or WM increases with the increase of sample points, but the growth trend decreases. The ICC of multifractal in GM or WM decreased with the rise of the subject numbers, but when this number was >36, the ICC did not significantly change. Besides, the ICC value of multifractal in GM and WM did not change significantly with the change of smooth size between 4 mm, 6 mm, and 8 mm full-width half-maximum. The results provide a reference for understanding the spontaneous neuronal fluctuations in WM.