Diagnostic role of 11C-Pittsburgh compound B retention patterns and glucose metabolism by fluorine-18-fluorodeoxyglucose PET/CT in amnestic and nonamnestic mild cognitive impairment patients.

OBJECTIVE: Amyloid imaging clinically is usually reported as positive or negative, and the role of amyloid topography has not been studied before. To evaluate in a clinical setting the regional distribution patterns of C-Pittsburgh compound B (C-PIB) and the fluorine-18-fluorodeoxyglucose (F-FDG) uptake in patients with mild cognitive impairment (MCI), we designed this study. METHODS: We studied 81 consecutive MCI patients, 64 amnestic (A-MCI) and 17 nonamnestic (NA-MCI) by C-PIB and F-FDG PET/computed tomography, by visual analysis. PIB retention was classified according to the regional distribution into the following patterns: A (frontal, lateral temporal, basal ganglia and anterior cingulate) and B (global retention). F-FDG images were considered positive only if temporoparietal hypometabolism consistent with Alzheimer's disease was observed. RESULTS: In 42 of the 64 A-MCI, C-PIB was positive. Twelve of the 42 positive A-MCI showed an A-pattern, all F-FDG negative, and 30 a B-pattern, 10 F-FDG positive and 20 F-FDG negative. Of the 17 NA-MCI, C-PIB was positive in three and F-FDG was positive in one. The different proportion of C-PIB positivity in A-MCI and NA-MCI was highly significant (P<0.001). CONCLUSION: Two different C-PIB patterns were observed in MCI patients and for the A-pattern, glucose hypometabolism consistent with Alzheimer's disease is highly unlikely. These findings may contribute towards a better selection of patients for future potential treatments and also to optimize the use of F-FDG-PET/CT.

Aortic 18F-FDG PET/CT uptake pattern at 60 min (early) and 180 min (delayed) acquisition in a control population: a visual and semiquantitative comparative analysis.

18F-Fluoro-2-deoxy-D-glucose (F-FDG) PET/CT acquisition is generally performed 60 min after injection. The normal biodistribution pattern of F-FDG includes activity in the aortic territory due to blood pool activity, which could interfere in the diagnosis of aortic diseases by overlapping the wall uptake. The aim of the study was to evaluate the change over time of F-FDG uptake by the aortic wall and the activity in the lumen in a control population and to establish normal reference values. This prospective study included 15 control patients (mean age: 58.2 years). PET/CT was acquired 60 min (early scan) and 180 min (delayed scan) after an F-FDG injection at a dose of 7 MBq/kg. A visual and semiquantitative analysis of the F-FDG aortic wall uptake was carried out, and lumen activity and the aortic wall to lumen ratio [target-to-background ratio (TBR)] were determined. In the visual analysis all patients showed F-FDG activity at the aortic territory at 60 and 180 min. The pattern of uptake at 60 min was diffuse in all 15 patients (100%), without delineation of the aortic wall uptake; however, at 180 min the uptake pattern of the aortic wall changed to lineal in 14 patients (93.3%). The aortic wall maximum standardized uptake value decreased from 2.07±0.34 to 1.7±0.46 during the delayed acquisition (P=0.0279) and the lumen maximum standardized uptake value decreased highly significantly (1.99±0.35 vs. 1.36±0.32, P=0.0001). Therefore, TBR also increased highly significantly from 1.04±0.06 to 1.25±0.16 (P<0.0001). The high decrease in blood pool activity from 60 to 180 min provides a better delineation of the aortic wall uptake, which corresponds to the normal pattern at that time. The TBR increased significantly at 180 min, and 1.25±0.16 is suggested as the threshold for diagnostic purposes, especially for the diagnosis of vasculitis.