title: A method to enhance the sensitivity of DTI analyses to group differences: a validation study with comparison to voxelwise analyses.
abstract: Studies of white matter (WM) abnormalities in psychiatric and neurological disorders often use the analysis package Tract-Based Spatial Statistics (TBSS). However, with small samples and/or subtle effects, a study using the standard TBSS approach can be underpowered. For such cases, a new method is presented that summarizes global differences between TBSS-derived fractional anisotropy (FA) images with a single paired t-statistic, estimating the degrees of freedom using spatial autocorrelation. The sensitivity of the method is demonstrated by using well-known aging effects on FA as a proxy for disease effects. Sixty healthy subjects were divided equally into younger- (YA), middle- (MA), and older-aged (OA) groups and significant global differences were demonstrated in the YA versus OA (all N ≥ 4, FA difference≈0.023), MA versus OA (all N≥4, FA difference≈0.017), and YA versus MA (FA difference≈0.005 at N=20) comparisons. In contrast, no significant difference could be detected in the YA versus MA comparison using voxelwise TBSS analysis with the full sample (N=20 per group). This method should facilitate localizing analyses in the direction of a proven group difference while providing clinically relevant information about pathophysiologic processes globally affecting WM.
authors.affiliation: University of Texas Health Science Center, San Antonio, TX, USA. matthew-cykowski@ouhsc.edu
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Cykowski
authors.forename: Jack L
authors.initials: JL
authors.lastname: Lancaster
authors.forename: Peter T
authors.initials: PT
authors.lastname: Fox
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D016880:Anisotropy; D001921:Brain / Q000033:anatomy & histology*; D001931:Brain Mapping; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D013223:Statistics as Topic