Background: Central nicotinic acetylcholine receptors (nAChRs) mediate a variety of brain functions and have been implicated in the pathophysiology of Alzheimer's and Parkinson's diseases, other CNS disorders (Tourette's syndrome, epilepsy, etc.), and nicotine dependence. These receptors are the primary target for the action of nicotine, which is believed to cause tobacco dependence. The availability of a suitable agent that could image nAChRs with PET in humans would allow scientists to monitor the nAChRs in vivo for the purpose of determining their roles in the pathogenesis of neurodegenerative diseases and nicotine dependence.