Evaluation of 10-minute post-injection ¹¹C-PiB PET and its correlation with ¹⁸F-FDG PET in older adults who are cognitively healthy, mildly impaired, or with probable Alzheimer’s disease

Objective:

Positron emission tomography (PET) allows in vivo evaluation of molecular targets in neurodegenerative diseases, such as Alzheimer’s disease. Mild cognitive impairment is an intermediate stage between normal cognition and Alzheimer-type dementia. In vivo fibrillar amyloid-beta can be detected in PET using [¹¹C]-labeled Pittsburgh compound B (¹¹C-PiB). In contrast, [¹⁸F]fluoro-2-deoxy-d-glucose (¹⁸F-FDG) is a neurodegeneration biomarker used to evaluate cerebral glucose metabolism, indicating neuronal injury and synaptic dysfunction. In addition, early cerebral uptake of amyloid-PET tracers can determine regional cerebral blood flow. The present study compared early-phase ¹¹C-PiB and ¹⁸F-FDG in older adults without cognitive impairment, amnestic mild cognitive impairment, and clinical diagnosis of probable Alzheimer’s disease.

Methods:

We selected 90 older adults, clinically classified as healthy controls, with amnestic mild cognitive impairment, or with probable Alzheimer’s disease, who underwent an ¹⁸F-FDG PET, early-phase ¹¹C-PiB PET and magnetic resonance imaging. All participants were also classified as amyloid-positive or -negative in late-phase ¹¹C-PiB. The data were analyzed using statistical parametric mapping.

Results:

We found that the probable Alzheimer’s disease and amnestic mild cognitive impairment group had lower early-phase ¹¹C-PiB uptake in limbic structures than ¹⁸F-FDG uptake. The images showed significant interactions between amyloid-beta status (negative or positive). However, early-phase ¹¹C-PiB appears to provide different information from ¹⁸F-FDG about neurodegeneration.

Conclusions:

Our study suggests that early-phase ¹¹C-PiB uptake correlates with ¹⁸F-FDG, irrespective of the particular amyloid-beta status. In addition, we observed distinct regional distribution patterns between both biomarkers, reinforcing the need for more robust studies to investigate the real clinical value of early-phase amyloid-PET imaging.

Positron emission tomography; amyloid; [¹¹C]-labeled Pittsburgh compound B; perfusion; cerebral glucose metabolism; [¹⁸F]fluoro-2-deoxy-d-glucose; aging, neuroimaging