Hr scanner

Scans were acquired with a Siemens (Knoxville, TN) HR+ scanner in three-dimensional mode [reconstructed full width at half-maximum (FWHM) resolution, ~5.5 mm in-plane and 5.0 mm axially], with septa retracted and scatter correction. Participants were positioned in the PET scanner gantry, and an intravenous (antecubital) line was placed in the right arm. A light forehead restraint was used to eliminate intra-scan head movement. [¹¹C]-carfentanil was synthesized at high specific activity by the reaction of [¹¹C]-methyliodide and a nonmethyl precursor as described previously.^{37 (link)} 15 +/− 1 mCi (555 +/− 55 MBq) were administered during the scan. Receptor occupancy by carfentanil was calculated to be between 0.2 and 0.6% for brain regions with low, intermediate, and high MOR concentrations, based on the mass of carfentanil administered and the known concentration of opioid receptors in the postmortem human brain.^{20 (link); 27 (link)} Fifty percent of the [¹¹C]-carfentanil dose was administered as a bolus, and the remaining 50% was administered by continuous infusion for the remainder of the study. Twenty-eight frames of images were acquired over 90 min with an increasing duration (30 seconds up to 10 minutes).

PET scans were acquired with a Siemens (Knoxville, TN) HR+ scanner in 3-D mode (reconstructed full-width at half maximum resolution, ∼5.5 mm in-plane and 5.0 mm axially). Radiotracer synthesis and image acquisition, coregistration and reconstruction protocols were identical to those used previously (Weiland et al., 2014 (link)). Briefly, images were reconstructed, attenuation and motion corrected, and co-registered to each other (Minoshima et al., 1993 (link)). Time points were then decay-corrected during data reconstruction. Approximately 15 millicuries (mCi) was administered for each scan (<40 μg total cold mass for raclopride). Fifty percent of the radiotracer dose was administered as a bolus with the remainder delivered as a continuous infusion which allows for more rapid equilibration across compartments and is achieved within 5 min of radiotracer administration (Watabe et al., 2000). Twenty-eight image frames were acquired over 90 minutes with an increasing duration (30 seconds up to 10 minutes).