The objectives of this study are to document the pharmacokinetics of the adequacy of DAT receptor occupancy d-MPH formulation in three doses (20 mg, 30 mg, and 40 mg) using PET scanning with C-11 Altropane as the ligand across a range of times. It has been estimated that MPH is effective when the average CNS DAT occupancy is 50% or greater. Focalin XR has been shown to be clinically effective in an analog classroom as early as 1 hour and as late as 12 hours. Therefore, it is hypothesized that the average DAT occupancy will be adequate (50% or greater) at time periods corresponding to the times of clinical efficacy.