Molecular Neuroimaging in the Study of Cognitive Impairment: Contribution of the Cerebral Blood Flow SPECT with 99mTc-HMPAO and 18F-FDG PET/CT Scan

Objective

The aim of this study was to analyze cerebral perfusion and glucose metabolism in patients with cognitive impairment using cerebral blood flow ^99mTc-HMPAO SPECT and ¹⁸F-FDG PET/CT scans.

Material and methods

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, ^99mTc-HMPAO SPECT and ¹⁸F-FDG PET/CT scans were performed.

Results

^99mTc-HMPAO SPECT showed regions of cerebral hypoperfusion in 15 patients and was normal in 7 of the 22 patients. ¹⁸F-FDG PET/CT scan showed cerebral regional hypometabolism in 19 patients and was normal in the other 3 patients. The distribution of abnormalities on ^99mTc-HMPAO SPECT and ¹⁸F-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 (1 SMC, 3 amnestic MCI) had an abnormal ¹⁸F-FDG PET/CT scan and normal ^99mTc-HMPAO SPECT. There were 3 patients (1 SMC, 2 amnestic MCI) with normal ^99mTc-HMPAO SPECT and ¹⁸F-FDG PET/CT scans.

Conclusion

^99mTc-HMPAO SPECT and ¹⁸F-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.