The PiB PET scanning was performed within 16 weeks of the clinical screening and cognitive testing. The PiB PET data were acquired as recently described.16 (link) The PET imaging was conducted using an ECAT HR+ scanner (Siemens/CTI Molecular Imaging, Malvern, Pennsylvania) (3-dimensional mode; 15.2-cm field-of-view; 63 planes; reconstructed image resolution of approximately 6 mm). The scanner was equipped with a Neuroinsert (CTI PET Systems, Knoxville, Tennessee) to reduce the contribution of scattered photons.38 Data were reconstructed using filtered back-projection (Fourier rebinning/2-dimensional back projection; 3-mm Hann filter) and corrected for photon attenuation (68Ge-68Ga [germanium 68–gallium 68] rods), scatter,39 and radioactive decay. The participant’s head was immobilized to minimize motion during the scan. The PiB was injected intravenously (mean [SD], 14.3 [2.2] mCi for 20 seconds; mean [SD] specific activity,1.4[0.8] Ci/μmol), and dynamic PET scanning was performed for 90 minutes (34 time frames).
Regions of interest (ROIs) were defined on the coregistered magnetic resonance image as described previously40 (link) and included the following: frontal lobe; anterior cingulate gyrus (ACG); lateral temporal, mesial temporal, occipital, parietal, precuneus cortex (PRC)/posterior cingulate gyrus (PCG), and sensorimotor cortices; and anterior-ventral striatum. A cerebellar ROI was used as the reference region and a pons ROI was included as an example of nonspecific retention in white matter. A global mean of 6 regions (GBL6) was calculated as the arithmetic mean of the PiB binding index of the frontal lobe, ACG, PRC, lateral temporal, and parietal cortices and striatum.