to believe that we would be able to determine if they had smoked within the previous 12 hours. A portion of the sample was sent to an outside laboratory for quantification of urinary cannabinoid concentration via gas chromatography mass spectrometry (GCMS). In addition, all subjects completed the Addiction Severity Index (ASI), Positive and Negative Affect Scale (PANAS) (Watson et al., 1988), Beck Depression Inventory (BDI) (Beck, 1987), and the Profile of Mood States (POMS) (McNair et al., 1971) prior to their scanning sessions to evaluate their clinical state at time of testing. Prior to their participation in any study related activity, study procedures were explained and all subjects were required to read and sign an informed consent form, which described in detail the scanning procedures and which had been approved by the McLean Hospital Institutional Review Board.
