Abstract: The study explored the diagnosis standard to evaluate the degree of dementia of Alzheimer disease(AD)according to the comparison between AD patients and the normal. PET scan was performed after 40 minutes of injection of 18 F-FDG. The mean counts of bilateral frontal, parietal, temporal, occipital lobe, cerebellum, basal ganglion and the ratio of the above brain lobes via cerebellum were calculated in both AD patients and the normal. The counts ratio of the cerebral lobes, basal ganglion and thalamus via cerebellum was quite stable in the normal, with varying coeffient ranging from 2.78% to 8.95%. The AD patient's hypometabolism was judged according to the normal's standard with mean minus 2 s. The result showed that 4 out of 6 belonged to the mild, 6 out of 7 were middle, 4 out of 4 were severe in the AD patients. At the same time, the specific of the normal was 100%. The range of hypometabolism increased with the severity degree of dementia in 17 AD cases. There was hypometabolism only in the parietal in the mild cases, but hypometabolism occurred not only in the parietal but also in the temporal and the frontal in the middle and severe AD cases. The counts ratio between the left frontal lobe via the cerebellum was a very important index to distinguish between the middle AD patients and severe AD ones according to the degree of hypometabolism. Combining the hypometabolism scope with hypometabolism degree of counts ratio of the parietal, frontal and temporal lobes via the cerebellum could make the diagnosis of AD and evaluate the degree of dementia in a better way.

Key words: Alzheimer disease, 18 F-FDG, positron emission tomography, brain image, diagnosis, degree evaluation