The aim of study is to investigate neural biomarkers of ACT efficiency in patients with SB disorder. Patients having a history of SB within previous year were randomized in an ACT program (21 patients) or relaxation program (21 patients) during 7 weeks. Before and after the completion of the group, they performed 3 tasks during fMRI: implicit emotional visualization, Cyberball game, motivational task Investigators will compare cerebral activations between groups, between pre and post intervention as well as measure baseline cerebral activations associated with improvement of suicidal ideation during follow up.