of HU who were current heroin users and not under any treatment, the HU were under a methadone treatment and had no illicit drug use during the treatment as confirmed by their care takers. Among the 12 HU under the treatment, 9 were in the detoxification phase (entering the program within one week before the scanning, mean = 2.1 days, SD = 1.8), while the remaining 3 were in a relatively stable maintenance phase (one had been in the program for 2 months and the other two for 6 months). All methadone-treated participants were under daily methadone administrations and their last methadone uses were at least 12 hours before the scanning.
