Purpose: (18)F-Florbetapir (AV-45/Amyvid) is a novel positron emission tomography (PET) tracer for imaging plaque pathology in Alzheimer's disease (AD), while PET images of fluorodeoxyglucose (FDG) for cerebral glucose metabolism can provide complementary information to amyloid plaque images for diagnosis of AD. The goal of this preliminary study was to investigate the perfusion-like property of relative cerebral blood flow estimates (R(1)) and summed early-phase AV-45 images [perfusion AV-45 (pAV-45)] and optimize the early time frame for pAV-45.
Methods: Dynamic AV-45 PET scans (0-180 min) were performed in seven subjects. pAV-45, late-phase AV-45, and FDG images were spatially normalized to the Montreal Neurological Institute template aided by individual MRI images, and the corresponding standardized uptake value ratio (SUVR) was computed. The R(1) images were derived from a simplified reference tissue model. Correlations between regional and voxelwise R(1) and the corresponding FDG images were calculated. An optimization of time frames of pAV-45 was conducted in terms of correlation to FDG images. The optimal early time frame was validated in a separate cohort.
Results: The regional distribution in the R(1) images correlated well (R = 0.91) to that of the FDG within subjects. Consistently high correlation was noted across a long range of time frames. The maximal correlation of pAV-45 to FDG SUVR of R = 0.95 was observed at the time frame of 1-6 min, while the peak correlation of R = 0.99 happened at 0-2 min between pAV-45 and R(1). A similar result was achieved in the validation cohort.
Conclusion: Preliminary results showed that the distribution patterns of R(1) and pAV-45 images are highly correlated with normalized FDG images, and the initial 5-min early time frame of 1-6 min is potentially useful in providing complementary FDG-like information to the amyloid plaque density by late-phase AV-45 images.