Nineteen tobacco smokers and 20 age-matched nonsmokers were included in the study. Smokers who participated in scans at different times since the last cigarette were equivalent in age, level of nicotine dependence (as assessed by the FTND at intake), cigarettes smoked per day, and years of smoking (Table 1). Plasma cotinine and nicotine levels and carbon monoxide measurements were negligible in nonsmokers and in smokers were highest at 1 day of abstinence and decreased over time, confirming abstinence from smoking (Table 1).
