Diffusion and perfusion MR imaging in cases of Alzheimer's disease: Correlations with cortical atrophy and lesion load

BACKGROUND AND PURPOSE: Perfusion and diffusion-weighted MR imaging are pow erful new imaging techniques for evaluating tissue pathophysiology in assoc iation with many neurologic disorders, such as neurodegenerative diseases. The purpose of our study was to evaluate the sensitivity and specificity of dynamic susceptibility contrast-enhanced MR imaging and diffusion-weighted MR imaging in cases of Alzheimer's disease and to assess the role of atrop hy in the quantification of cortical perfusion. METHODS: Thirty-nine participants were studied: 18 patients with moderate c ognitive impairment with probable Alzheimer's disease, 16 patients with mil d impairment with possible or probable Alzheimer's disease, and 15 group-ma tched elderly healthy comparison volunteers Relative values of temporoparie tal, sensorimotor, and hippocampal regional cerebral blood volume (rCBV) we re measured as a percentage of cerebellar rCBV, and group classification wa s assessed with logistic regression. Brain atrophy was used as a covariate to assess its role in rCBV quantification. Regions of interest placed on or ientation-independence apparent diffusion coefficient maps allowed the calc ulation of apparent diffusion coefficient values and relative anisotropic i ndices of the head of the caudate nuclei, thalamus, parietal, frontal, and hippocampal cortices bilaterally, genu and splenium of corpus callosum, and anterior and posterior white matter in patients with Alzheimer's disease a nd in control volunteers. RESULTS: Temporoparietal rCBV ratios were reduced bilaterally in the patien ts with Alzheimer's disease. Sensitivity was 91% in moderately affected pat ients with Alzheimer's disease and 90% in patients with mild cases. Specifi city was 87% in healthy comparison volunteers. Lower values of sensitivity and specificity were obtained for sensorimotor (73%, 50%, and 67%, respecti vely) and hippocampal cortices (80%, 80%, and 65%, respectively). Using bra in atrophy as a covariate, patients with Alzheimer's disease still showed a statistically significant reduction of rCBV compared with control voluntee rs. Diffusion-weighted MR imaging analysis only showed a trend, with no sta tistic significance, of reduction of anisotropy in posterior white matter. CONCLUSION: Dynamic susceptibility contrast-enhanced MR imaging of rCBV may be an alternative to nuclear medicine imaging for the evaluation of patien ts with Alzheimer's disease. When brain atrophy is used as a covariate, dif ferences in rCBV still persist between patients with Alzheimer's disease an d control volunteers, suggesting that perfusion impairment is unrelated to atrophy. No significant results for either white or gray matter were obtain ed using diffusion-weighted MR imaging.