Exact hr scanner

Details on the acquisition and post-processing of the PiB-PET examinations have been previously described (Johnson et al., 2014 (link); Okonkwo et al., 2014 (link)). Briefly, 3-dimensional PiB-PET data were acquired on a Siemens EXACT HR+ scanner (Siemens AG, Erlangen, Germany). Imaging consisted of a 6-minute transmission scan and a 70-minute dynamic scan upon bolus injection. Post-processing was based on an in-house automated pipeline (Floberg et al., 2012 (link)). We derived distribution volume ratio (DVR) maps from the PiB images using the Logan method, with a cerebellar gray matter reference (Price et al., 2005 (link)).
An anatomical atlas (Tzourio-Mazoyer et al., 2002 (link)) was used to extract quantitative DVR data from eight bilateral regions of interest (ROIs) that are sensitive to Aβ accumulation (Rosario et al., 2011 (link)). These ROIs were the precuneus, posterior cingulate, orbitofrontal cortex, anterior cingulate, angular gyrus, supramarginal gyrus, middle temporal gyrus, and superior temporal gyrus. The DVR data from the ROIs were combined to form a composite measure of global Aβ load. The time interval between the PET scan and the GXT was 3.10 ± .47 years. GXT was subsequent to the PiB-PET scan for all 69 participants.

For the second research question, participants were selected who underwent a 70-minute dynamic [¹¹C]Pittsburgh compound B (PiB) scan on a Siemens EXACT HR+ scanner (and prior to 2015, a T1-weighted magnetic resonance imaging (MRI) scan on a GE 3.0 T MR750 using an 8-channel head coil). Neuroimaging was completed, on average, 1.4 years (SD = 1.4) after the first visit at which story recall was administered (median visit 2). [¹¹C]PiB radiosynthesis, acquisition and reconstruction parameters, image processing and quantification have been described previously (Johnson et al., 2014 (link)). Briefly, the PET time series was motion corrected, de-noised, and co-registered to T1-w MRI. Time-activity curves were extracted from the co-registered PET data in subject MRI space from gray matter restricted Anatomic Labeling atlas (AAL, Tzourio-Mazoyer, Landeau, et al., 2002) regions of interest (ROIs) warped to MRI space and used to estimate ROI-level distribution volume ratios (DVRs; Logan Graphical Analysis, cerebellum GM reference region, ®k₂ =0.149 min⁻¹; (Logan et al., 1996 (link); Lopresti et al., 2005 (link)). PiB positivity was ascertained by applying a threshold to the mean DVR (global PiB) across eight bilateral ROIs (global DVR ≥ 1.19) (Racine et al., 2016 ).