Functional imaging in mild cognitive impairment and early Alzheimer's disease: is it pertinent?

Neuroimaging techniques, namely positron emission tomography (PET), single photon emission computed tomography (SPECT), and magnetic resonance imaging (MRI) are increasingly used to study mild cognitive impairment (MCI) and its conversion to dementia, as well as early Alzheimer's disease (AD). Despite an important overlap of the various imaging parameter values between MCI,early AD and controls, some markers may help clinical diagnosis in individual patients. For example,the combination of significantly reduced hippocampal volume and brain hypometabolism in a MCI patient establishes the anatomical and functional features seen in dementia. In association with clinical information, the topographic localization of the hypometabolism will help to precise the type of dementia. Functional brain activation studies using functional MRI and PET are not used for clinical purpose, but they allow to determine the differences between control and pathological states and thus to characterize the functional abnormalities specific to the disease. Finally, the use of biomarkers of the neuropathological lesions constitutes the most promising tool to accurately diagnose MCI and early AD patients.