Diffusion tensor tractography-based analysis of the pyramidal tract in patients with amyotrophic lateral sclerosis

Abstract

BACKGROUND AND PURPOSE: We attempted to measure DTI parameters of the brainstem pyramidal tract using two approaches, ie, simple ROI and tract-specific analyses. Results obtained for healthy subjects and ALS patients were compared. METHODS: DTI was performed using a single shot SE-EPI with 25 noncollinear diffusion gradient directions (b= 1000 second/mm(2)) and with no diffusion gradient on a 3.0-T MR system in 10 ALS patients and in 8 age- and sex-matched normal controls. To delineate the brainstem pyramidal tract, tractography was performed using two ROIs, ie, a seed ROI at the cerebral peduncle (ROI-1) and a target ROI at the lower pons (ROI-2). ROI-1 was subsequently restricted to voxels that contained streamlines in the tract reconstruction, thus creating a sub-ROI. RESULTS: Mean fractional anisotropy (FA) and mean diffusivity values were highly reproducible by tract specific analysis, whereas simple ROI analysis yielded larger variabilities between operators. FA values were significantly lower in ALS patients than in normal controls in the tractography-derived sub-ROI (P= .01), but not in the seed or target ROIs. CONCLUSIONS: These results suggest, compared with simple ROI analysis, that tract-specific analysis using DTI fiber-tracking is more reliable and sensitive for detecting upper motor neuron pathology in ALS.