Objective: To use diffusion kurtosis MRI with NODDI to assess brain cortex microstructure in Parkinson’s patients and localize disease related changes.

Background: Cortical atrophy has been shown in Parkinson’s disease (PD) using structural MRI. However, early microstructural events have not been extensively studied. NODDI estimates the tissue volume fraction of dendrites and axons (neurites), the degree of directional dispersion of the neurites, and the tissue fraction of free water. Assessing longitudinal changes accompanied by disease progression will reflect the temporal and spatial microstructural changes at the level of cell bodies and myelin, and allow regional changes to be associated with cognitive decline.

Method: PD patients (n=16) and age-matched healthy controls (HC, n=8) were recruited. At baseline, subjects performed the Montreal Cognitive Assessment (MoCA) and symbol digit modality task (SDM), to asses overall cognition and information processing speed, respectively. Motor severity of PD patients was measured by the Unified Parkinson Disease Rating Scale. For diffusion MRI, three different diffusion gradient strengths were used (b=711, 2000 and 2855 s/mm²) with a total of 160 directions. Diffusion data were fitted using the Neurite Orientation and Dispersion Density Imaging (NODDI) to estimate the intracellular volume fraction (ICVF) and the orientation dispersion index (ODI).

Results: Using FreeSurfer segmentation of cortical regions, we extracted ICVF and ODI from 34 bilateral cortical regions and compared them between groups, accounting for age and cortical thickness. Our results show PD patients have lower ICVF and ODI in major limbic and association areas, compared to controls. Areas with estimated reduction in fraction of dendrites and axons included the right inferior parietal (p=0.023), right inferior temporal (p=0.023), right middle temporal (p=0.022), right lateral occipital (p=0.041), right and left fusiform (p=0.03) and left entorhinal cortex (p=0.024). ICVF in the fusiform and entorhinal cortices were positively correlated with scores on the MoCA and SDMT.

Conclusion: These results demonstrate cortical microstructural changes accompanying detectable cortical thinning and suggest that ICVF may be a sensitive biomarker for tracking disease pathology in key cortical areas. Furthermore, reduction in ICVF correlates to cognitive decline.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/diffusion-magnetic-resonance-imaging-with-neurite-orientation-and-dispersion-imaging-noddi-detects-early-localized-cortex-disruption-in-parkinsons-disease/