phno_amthTest-retest Reproducibility of [11C]PHNO PET Using the Constant Infusion

To determine amphetamine-induced DA release in tobacco smokers while currently smoking and during acute withdrawal and in nonsmokers. Twenty healthy men and women tobacco smokers and twenty healthy nonsmokers will be recruited. Each subject will participate in 1 MRI and up to 2 [11C]PHNO PET scans. On the PET study day subjects will participate in two [11C]PHNO scans (ideally, the two PET scans will be carried out in the same day). Three hours before the second PET scan, amphetamine (0.5 mg/kg, PO) will be administered. In smokers, the set of scans will occur at 10-21 days of smoking abstinence. Smoking abstinence will be determined by carbon monoxide and urine cotinine (a breakdown product of nicotine in cigarette smoke) levels. Subjects will be asked to breathe into a breathalyzer to measure carbon monoxide and to provide a urine sample to measure cotinine. Smoking abstinence will be confirmed by carbon monoxide and cotinine levels that are reduced as compared to actively smoking. We hypothesize that smokers at 10-21 days of withdrawal will have amphetamine-induced DA release that is blunted compared to healthy nonsmokers. Magnetic resonance imaging (MRI) scans (3 T) will be collected in each subject to co-register PET and MRI for image analysis. Within two weeks of the PET study, an MRI will be acquired at the Yale University MRI Center. Subjects will be taken through a ferromagnetic metal detector before entering the scan room. The acquisition sequence is a 3D fast spoiled grass (FSPGR) MR pulse sequence with an IR prep of 300 ms. (TE= 3.3 ms, flip angle=17 degrees; slice thickness= 1.2 mm) optimized for delineating gray matter/white matter/CSF boundaries. The small voxel size (0.93 X 1.2 X 0.93 mm) provides high-resolution volumetric images. MR images provide a matching anatomical atlas for creating individualized region-of-interest templates for each subject. Subject preparation consists of two intravenous (IV) catheterizations and immobilization of the head. PET scans are acquired as subjects rest using an HRRT PET scanner (207 slices, resolution better than 3 mm FWHM). This resolution permits visualization of the PHNO and raclopride uptake in the ventral/dorsal striatum, in globus pallidus (GP) and substantia nigra (SN). A transmission scan using an orbiting 137Cs point-source is obtained for each emission scan. Motion correction will be performed dynamically with measurements from the Vicra (NDI Systems, Waterloo, Ontario) used by a dedicated list-mode reconstruction algorithm.