Imaging age-related cognitive decline: A comparison of diffusion tensor and magnetization transfer MRI.

PURPOSE: To determine which MR technique was the most sensitive to age-related white matter damage. We compared both diffusion tensor imaging (DTI) and magnetization transfer (MT) maps to determine which technique correlated most strongly with cognitive function in a middle-aged and elderly community population. MATERIALS AND METHODS: In all, 64 healthy subjects (aged 50-90) underwent MRI and neuropsychology. Histograms were generated for white matter mean diffusivity (MD), fractional anisotropy (FA), and MT ratio (MTR). White matter hyperintensity volume (WMH) and brain volume were also determined. Composite neuropsychological scores were derived for 4 cognitive domains (executive function, working memory, episodic memory, and information processing speed). RESULTS: All MRI parameters correlated with age (FA r = 0.726, P < 0.001; MD r = -0.619 P < 0.001, MTR r = -0.566, P < 0.001, WMH r = 0.511, P < 0.001). All MRI parameters correlated with cognition, but DTI, and particularly FA, correlated most strongly. Adding DTI parameters explained more variance in cognition than WMH alone; the increase was greatest with FA, which alone explained 45%, 33%, and 25% of the variance in cognition for information processing speed, episodic memory, and executive function, respectively. CONCLUSION: DTI appears the most sensitive imaging parameter to determine age-related white matter damage. The stronger relationship with FA suggests that axonal damage is important in age-related cognitive decline.