Combined magnetic resonance imaging and single-photon emission tomography scanning in the discrimination of Alzheimer's disease from age-matched controls

Objective: To compare the utility of temporal lobe magnetic resonance imagi ng (MRI) and single-photon emission tomography (SPET) scanning in discrimin ating between subjects with Alzheimer's disease (AD) and age-matched contro ls. Methods: Thirty subjects with NINCDS-ADRDA AD (23 probable AD, 5 possib le AD, 2 definite AD) and 22 age- and sex-matched controls underwent TI-wei ghted coronal MRI scanning (0.3 T) and technetium 99m-HMPAO SPET scanning. MRI scans were analyzed using a digitizer system with volumes of hippocampu s, amygdala, entorhinal cortex, parahippocampal gyrus, and whole cerebral c ortex calculated. From SPET scans, regional cerebral blood flow (rCBF) was assessed in anterior and posterior frontal, parietal, occipital, and mesial temporal cortex using a region of interest analysis with the cerebellum as a reference area. Results: Using MRI, the areas that best separated groups were left hippocampal and left amygdala volume, resulting in correct class ification (patient vs. control) in 79% of cases (sensitivity 77%, specifici ty 82%). Exactly the same proportion of subjects were correctly classified by SPET, with the most discriminating rCBF changes being left parietal and right posterior frontal. Combining information from both scans improved the proportion of correctly classified subjects in a discriminant function to 90% (sensitivity 93%, specificity 86%; only 2 AD and 3 controls misclassifi ed). All AD subjects had abnormalities on MRI and/or SPET (sensitivity for combined examinations 100%), while abnormalities on both MRI and SPET had a positive predictive value of 100% for dementia (including the detection of one control subject who later had dementia). Significant correlations betw een MRI and SPET measures were seen in control subjects but not in patients . Conclusion: Both 0.3 T MRI and single rotating gamma camera SPET were equ ally useful in separating AD subjects from age-matched controls, although t he combination of both significantly enhanced discrimination. In particular , all AD subjects had abnormalities on either MRI or SPET and both techniqu es may have an important role in assisting with clinical diagnosis, though replication in other centers and examination of differentiation of AD from other causes of dementia need to be examined.