Peripheral nerve diffusion tensor imaging (DTI). Normal values and demographic determinants in a cohort of 60 healthy individuals

To identify demographic determinants of peripheral nerve diffusion tensor imaging (DTI) and to establish normal values for fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD), and mean diffusivity (MD). Sixty subjects were examined at 3 Tesla by single-shot DTI. FA, AD, RD, and MD were collected for the sciatic, tibial, median, ulnar, and radial nerve and were correlated with demographic variables. Mean FA of all nerves declined with increasing age (r = -0.77), which could be explained by RD increasing (r = 0.56) and AD declining (r = -0.40) with age. Moreover, FA was inversely associated with height (r = -0.28), weight (r = -0.38) and BMI (r = -0.35). Although FA tended to be lower in men than women (p = 0.052), this difference became completely negligible after adjustment to body weight. A multiple linear regression model for FA was calculated with age and weight as predictors (defined by backward variable selection), yielding an R² = 0.71 and providing a correction formula to adjust FA for age and weight. Peripheral nerve DTI parameters depend on demographic variables. The most important determinants age and weight should be considered in all studies employing peripheral nerve DTI. (orig.)