Molecular neuroimaging in the study of cognitive impairment: contribution of the cerebral blood flow SPECT with 99mTc-HMPAO and 18F-FDG PET/CT scan

The aim of this study was to analyze cerebral perfusion and glucose metabolism in patients with cognitive impairment using cerebral blood flow (99m)Tc-HMPAO SPECT and (18)F-FDG PET/CT scans. Twenty-two patients with cognitive impairment were included: 4 subjective memory complaints (SMC), 8 amnestic mild cognitive impairment (MCI), 5 prodromic Alzheimer's disease (AD) and 5 AD. In each clinical group, (99m)Tc-HMPAO SPECT and (18)F-FDG PET/CT scans were performed. (99m)Tc-HMPAO SPECT showed regions of cerebral hypoperfusion in 15 patients and was normal in 7 of the 22 patients. (18)F-FDG PET/CT scan showed cerebral regional hypometabolism in 19 patients and was normal in the other 3 patients. The distribution of abnormalities on (99m)Tc-HMPAO SPECT and (18)F-FDG PET/CT scans was similar in 9 patients (2 SMC, 2 amnestic MCI, 2 prodromic AD, and 3 AD). In 6 patients (1 amnestic MCI, 2 prodromic AD, and 3 AD), FDG hypometabolism was more extensive than the cerebral hypoperfusion. Four patients (1SMC, 3 amnestic MCI) had an abnormal (18)F-FDG PET/CT scan and normal (99m)Tc-HMPAO SPECT. There were 3 patients (1 SMC 2, amnestic MCI) with normal (99m)Tc-HMPAO SPECT and (18)F-FDG PET/CT scans. (99m)Tc-HMPAO SPECT and (18)F-FDG PET/CT scans showed cerebral hypoperfusion and hypometabolism in patients with cognitive impairment, even in patients with clinical diagnosis of SMC. In patients with a normal cerebral blood flow SPECT, brain glucose cerebral hypometabolism can be detected. In some patients, the extension of FDG hypometabolism is more pronounced than that corresponding to the hypoperfusion area.