Longitudinal Assessment of Intravoxel Incoherent Motion Diffusion-Weighted MRI Metrics in Cognitive Decline.

Background: Advanced diffusion-based MRI biomarkers may provide insight into microstructural and perfusion changes associated with neurodegeneration and cognitive decline.
Purpose: To assess longitudinal microstructural and perfusion changes using apparent diffusion coefficient (ADC) and intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) parameters in cognitively impaired (CI) and healthy control (HC) groups.
Study Type: Prospective/longitudinal.
Population: Twelve CI patients (75% female) and 13 HC subjects (69% female).
Field Strength/sequence: 3 T; Spin-Echo-IVIM-DWI.
Assessment: Two MRI scans were performed with a 12-month interval. ADC and IVIM-DWI metrics (diffusion coefficient [D] and perfusion fraction [f]) were generated from monoexponential and biexponential fits, respectively. Additionally, voxel-based correlations were evaluated between change in Montreal Cognitive Assessment (ΔMoCA) and baseline imaging parameters.
Statistical Tests: Analysis of covariance with sex and age as covariates was performed for main effects of group and time (false discovery rate [FDR] corrected) with post hoc comparisons using Bonferroni correction. Partial-η ² and Hedges' g were used for effect-size analysis. Spearman's correlations (FDR corrected) were used for the relationship between ΔMoCA score and imaging. P < 0.05 was considered statistically significant.
Results: Significant differences were found for the main effects of group (HC vs. CI) and time. For group effects, higher ADC, IVIM-D, and IVIM-f were observed in the CI group compared to HC (ADC: 1.23 ± 0.08 ^. 10 ^-3 vs. 1.09 ± 0.07 ^. 10 ^-3  mm ² /sec; IVIM-D: 0.82 ± 0.01 ^. 10 ^-3 vs. 0.73 ± 0.01 ^. 10 ^-3  mm ² /sec; and IVIM-f: 0.317 ± 0.008 vs. 0.253 ± 0.009). Significantly higher ADC, IVIM-D, and IVIM-f values were observed in the CI group after 12 months (ADC: 1.45 ± 0.05 ^. 10 ^-3 vs. 1.50 ± 0.07 ^. 10 ^-3  mm ² /sec; IVIM-D: 0.87 ± 0.01 ^. 10 ^-3 vs. 0.94 ± 0.02 ^. 10 ^-3  mm ² /sec; and IVIM-f: 0.303 ± 0.007 vs. 0.332 ± 0.008), but not in the HC group at large effect size. ADC, IVIM-D, and IVIM-f negatively correlated with ΔMoCA score (ρ = -0.49, -0.51, and -0.50, respectively).
Data Conclusion: These findings demonstrate that longitudinal differences between CI and HC cohorts can be measured using IVIM-based metrics.
Level of Evidence: 2 TECHNICAL EFFICACY STAGE: 2.
(© 2022 International Society for Magnetic Resonance in Medicine.)