QUANTITATIVE-ANALYSIS OF PET AND MRI DATA IN NORMAL AGING AND ALZHEIMERS-DISEASE - ATROPHY WEIGHTED TOTAL BRAIN METABOLISM AND ABSOLUTE WHOLE-BRAIN METABOLISM AS RELIABLE DISCRIMINATORS

Average whole brain metabolic rates, when corrected for brain atrophy, are similar between patients with Alzheimer's disease (AD) and age-ma tched controls. To elucidate the relationship between reduced cognitiv e function and cerebral metabolism in patients with AD, we hypothesize d that the absolute amount of glucose used by the entire brain may pro ve to be a more reliable indicator of the disease than metabolic rates calculated for a unit of brain weight. Twenty patients with the proba ble diagnosis of AD and 17 similarly aged controls underwent F-18-fluo rodeoxyglucose positron emission tomography (FDG-PET) studies as well as magnetic resonance imaging (MRI) within a few days of each other. A verage metabolic rates, when corrected for atrophy, were 3.91 +/- 1.02 and 4.43 +/- 0.87 (mg of glucose per 1 00 cc brain tissue per min +/- s.d.) respectively for AD patients and controls. Two other indices we re determined, atrophy weighted total brain metabolism (calculated by multiplying the brain volume, determined by MR analysis, by the averag e metabolic rate) and absolute whole brain metabolism (calculated by m ultiplying the brain volume by the average metabolic rate corrected fo r atrophy). The former showed a very significant difference between th e two groups (29.96 +/- 7.90 for AD patients compared to 39.1 +/- 7.0 for controls, p < 0.001). Atrophy weighted total brain metabolism also correlated very well with mini mental status exam (MMSE) scores (r = 0.59, p < 0.01). Absolute whole brain metabolism was significantly dif ferent between AD and control groups and correlated well with MMSE. Th ese data demonstrate that although the metabolic rate per unit weight of the brain is unchanged in AD compared to controls, atrophy weighted total brain metabolism and absolute whole brain metabolism are signif icantly affected. Both indices may prove to be a sensitive correlate f or cognitive dysfunction in AD.