962 ecat exact hr pet scanner

All participants older than 35 years, excluding 3 (aged 44, 58, and 60, final n = 157) underwent a 60-minute dynamic Pittsburgh compound B (PIB) PET scan following injection of ~10 mCi PIB. The PIB PET imaging procedure has been described in detail (Mintun et al., 2006 (link); Su et al., 2013 (link)), and was conducted with a Siemens model 962 ECAT EXACT HR+ PET scanner (Siemens/CTI, Knoxville, KY) or on a Siemens Biograph 40 PET/CT scanner (Siemens/CTI, Knoxville, KY). Standard uptake value ratios (SUVR) with the cerebellar cortex as reference were calculated from regions of interest with PIB-positivity defined as the mean cortical SUVR (from predefined prefrontal, parietal, and temporal regions of interest) > 1.42, a value commensurate with a mean cortical binding potential of 0.18 as defined previously for a similar cohort (Mintun et al., 2006 (link)).

In all individuals, ¹⁸F-FDG and ¹⁵O PET scans were performed on a Siemens model 962 ECAT EXACT HR+ PET scanner as described previously (Vaishnavi et al., 2010 (link); Vlassenko et al., 2010 (link)). All subjects underwent one FDG scan and two sets of ¹⁵O-CO, ¹⁵O-H₂O, and ¹⁵O-O₂ scans.
FDG scans were performed after injection of ~5 mCi of FDG. Cerebral blood volume (CBV) was measured with a 5-min emission scan beginning 2 min after brief inhalation of ~75 mCi of [¹⁵O]CO in room air. Dynamic scans of 3 min were acquired after injection of ~50 mCi [¹⁵O]H₂O in saline or inhalation of 60 mCi of [¹⁵O]O₂ in room air. The CMRO₂ parametric image was derived from these ¹⁵O scans and corrected for CBV.
The local-to-global images obtained as described above for CMRGlc, CMRO₂, and CBF were summarized to the FreeSurfer ROIs. These were then multiplied by age-specific literature-based whole brain estimates for each of the metabolic parameters (Goyal et al., 2014 (link); Goyal et al., 2017 (link)).
AG was defined by subtracting the oxidative fraction of CMRGlc, calculated by dividing molar CMRO₂ by six, from total molar CMRGl (Goyal et al., 2017 (link)):
$$\text{AG}=[\text{CMRGlc}-({\text{CMRO}}_2÷6)].$$