Imaging beta amyloid deposition in vivo: Quantitative comparison of [18F]FDDNP and [11C]PIB

Introduction: Both [18F]FDDNP and [11C]PIB have been developed as PET tracers for imaging and quantifying beta-amyloid (As) fibril accumulation in Alzheimer's disease (AD) in vivo1,2. The purpose of the present study was to compare the potential value of [18F]FDDNP and [11C]PIB in the (early) diagnosis of AD by performing paired studies in the same patients. Methods: In this ongoing study, dynamic 90 minutes 3D [11C]PIB and [18F]FDDNP scans were acquired on the same day using an HR+ (Siemens) PET scanner. During both scans, continuous on-line and discrete manual sampling was performed to derive a metabolite corrected arterial plasma input curve. For each subject, volumes of interest (VOI) were defined on an individually acquired, co-registered T1 weighted structural MRI scan using an automated procedure3. Preliminary analysis of time-activity curves was performed using the simplified reference tissue model with cerebellum grey matter as reference tissue. Binding potential (BP) was used as outcome measure, in particular for areas previously associated with AD: frontal, parietal and temporal cortex. Results: At present, three AD patients, three patients with Mild Cognitive Impairment (MCI) and three age matched normal controls were included. Results are summarised in figures 1 and 2. [11C]PIB showed good contrast between AD patients and normal controls, as described previously1. In addition, the range of BP values in MCI patients was broader, probably due to the known heterogeneity of this group4. [18F]FDDNP provided less contrast between AD patients and normal controls. In AD patients, [11C]PIB BP was in general tenfold higher than [18F]FDDNP BP. Conclusion: The difference in BP between AD patients and normal controls appears to be more pronounced for [11C]PIB than for [18F]FDDNP. Further studies are needed to substantiate these preliminary findings.