PIB-PET-imaging was performed to assess Aβ accumulation in the brain. The PET-scanning protocol has been described previously elsewhere [6 (link)]. The dynamic 90 min [11C]PIB-PET scan was performed using a brain-dedicated high-resolution PET scanner, the ECAT HRRT (Siemens Medical Solutions, Knoxville, TN, USA). [11C]PIB was manufactured as previously reported [42 (link)] in high molar radioactivity (mean 680 MBq/nmol (SD±240)) at the time of injection utilizing in-target produced [11C]methane.
Voxel-by-voxel [11C]PIB standardized uptake values (SUV) were calculated using imaging data from 60 to 90 minutes after the tracer injection. Automated region of interest (ROI) generation was conducted using FreeSurfer software (version 5.3.0, http://freesurfer.net/) and individual T1 weighted MRI data as input. Six ROIs were formed (parietal cortex, prefrontal cortex, anterior cingulum, posterior cingulum, precuneus, lateral temporal cortex based on brain regions where Aβ has been shown to first accumulate in early AD [43–45 (link)]. SUV ratios (SUVRs) were obtained by using the cerebellar cortex as a reference region. A composite cortical PIB score was calculated as the average PIB SUVR over all six ROIs.