Purpose: To evaluate diffusional changes of the corticospinal tract (CST) in patients with idiopathic normal pressure hydrocephalus (iNPH) by neurite orientation dispersion and density imaging (NODDI).
Materials and methods: Nineteen patients with iNPH and 12 healthy controls were included. Diffusion MRI data for NODDI were acquired with a 3-T system, using 32 motion-probing gradient directions with six b-values (from 0 to 2500 s/mm2). The orientation dispersion index (ODI), intra-cellular volume fraction (Vic), and isotropic volume fraction (Viso) of the CST were calculated by tract-specific analysis in patients and controls. We also measured the fractional anisotropy (FA) and apparent diffusion coefficient (ADC).
Results: The ODI of the CST (0.087 ± 0.024 vs. 0.183 ± 0.051, P < 0.01, Mann-Whitney U test) and Vic of the CST (0.551 ± 0.061 vs. 0.628 ± 0.038, P < 0.01, Mann-Whitney U test) were significantly lower in iNPH patients than in healthy controls. In receiver-operating characteristic analysis, the area under the curve (AUC) of the ODI and FA were not significantly different (Fig. 4a, 0.987 vs. 0.904, P = 0.061), and the AUC of the Vic and ADC also showed no significant difference (Fig. 4b, 0.864 vs. 0.912, P = 0.194).
Conclusion: The NODDI can effectively evaluate the condition of neurites in the CST of iNPH patients, and the ODI could be clinically useful in the diagnosis of iNPH.
Keywords: Diffusion MRI; Idiopathic normal pressure hydrocephalus; Neurite orientation dispersion and density imaging; Tract-specific analysis.