Diffusion-Weighted Magnetic Resonance Imaging in Alzheimer’s Disease

Abstract

Diffusion-weighted imaging (DWI) is a powerful new magnetic resonance imaging technique for evaluating tissue pathophysiology in vivo. We performed DWI in three orthogonal spatial directions in 10 patients with mild to moderate Alzheimer’s disease (AD) and 11 control subjects. Average apparent diffusion coefficients (ADCavg) were calculated for gray matter regions, and anisotropy indexes were calculated for white matter regions. Global measures of atrophy and white matter hyperintensities (WMH) were obtained on T₂-weighted images to control for their potential confounding effects on ADCavg and anisotropy. The measures of atrophy and WMH differed between the groups and were used as covariates in the subsequent statistical analyses. Patients with AD demonstrated diminished anisotropy in the posterior white matter (p < 0.0001) and increased ADCavg in the hippocampus (p < 0.05) when compared to the control group. Diffusion measures did not correlate with the severity of dementia. DWI provides a unique, quantitative parameter that may be sensitive to the pathophysiological and/or microstructural abnormalities that occur in AD.

Diffusion Tensor Imaging in Alzheimer’s Disease and Mild Cognitive Impairment

“…A general interpretation of these results is that diffusion changes in AD and MCI tend to occur in more posterior regions as opposed to anterior regions, as seen in normal aging [41,42]. Such increased posterior isotropic diffusion was found in a sample of AD patients [70], and differentiated AD from a sample of patients with vascular dementia [39].…”

“…Increases in MD have been reported in patients with AD in the temporal lobes [40,51], hippocampus proper [51,70], splenium of the corpus callosum [38,70], posterior cingu- lum, occipital lobes and parietal lobes [51]. Increases in isotropic diffusion in AD have been reported in the corpus callosum (particularly the splenium) [38] and temporal lobe [40].…”

In Vivo Structural Neuroanatomy of Corpus Callosum in Alzheimer's Disease and Mild Cognitive Impairment Using Different MRI Techniques: A Review

“…DWI studies on AD "all stages" patients [30,33] report no significant group differences in measurements of the anisotropy index (AI) -calculated by dividing the ADC perpendicular to the prominent callosal fiber direction by the ADC parallel to the predominant fiber direction of the CC -within the genu and splenium of the CC. On the other hand, Hanyu et al [28,29] using the same type of AI (that the authors called ADC ratio) found a decrease in the anterior (rostrum and genu) and posterior (isthmus and splenium) CC of AD "all stages" patients.…”

“…In fact, the main result mentioned above, that is atrophy mainly in the callosal anterior and posterior subregions, comes from studies of AD groups that included patients in different illness stages, ranging from mild to severe dementia [7,8,[10][11][12][14][15][16][17][18][19][23][24][25][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] and sometimes selected using different diagnostic criteria [10,14].…”

Advances in white matter imaging: A review of in vivo magnetic resonance methodologies and their applicability to the study of development and aging

“…In human studies of patients with probable Alzheimer's disease, significant changes in diffusion in white matter have been observed (Rose et al, 2000;Sandson et al, 1999). In a study of early Alzheimer's disease, Choi et al found reduced FA, increased mean diffusivity, and increased radial diffusivity in superior frontal white matter (Choi et al, 2005).…”