The purpose of the lead-in phase is to identify patients who do not achieve abstinence in response to behavioral treatment. Subsequently, two matched subgroups of participants (half who achieved abstinence and half who did not achieve abstinence) will undergo the [11C] raclopride displacement PET brain imaging procedure. This procedure allows the measurement of dopamine release in response to a single dose of methylphenidate, and the investigators will determine if failure to achieve abstinence during the lead-in period is associated low dopamine transmission.