Multivariate Analysis of Nerve Microstructure

Statistical analysis was performed using GraphPad Prism 9 (GraphPad Software Inc., San Diego, United States). The Shapiro-Wilk test was used to evaluate the groups for normality. Because normality and equal variance assumptions were met, the fascicular eigenvalues (D₁, D₂, and D₃), as well as their derived indices (MD, FA, and D_||/D_⊥), were compared by two-way analysis of variance (ANOVA) followed by Tukey’s posthoc test when appropriate. When comparing DT indices of the perineurium, interfascicular epineurium, and nerve CSA one-way ANOVA followed by Tukey’s posthoc test was employed. The fascicular variability of FA was assessed using the coefficient of variation and then compared between fascicles and within fascicles with two-way ANOVA followed by Tukey’s posthoc test when appropriate. To determine the correlations between the DT indices and parameters at the fascicular level, linear regression was performed for each nerve sample then coefficients were compared using a one-sample t-test. The change of nerve FA in subsequent slices was calculated with linear regression. For the assessment of an intra-observer agreement, one-way ICC was used (Koo and Li, 2016 (link)). Differences were deemed statistically significant at p < 0.05. Data are given as means ± standard deviations, ranges, or percentages when appropriate.