Bariatric surgery (BS) is currently the most effective treatment in severe obesity. However, a considerable percentage of patients undergoing BS fail to lose sufficient weight or regain weight after initial weight loss during long-term follow-up, which may be attributed to personality traits and pathological eating behaviour. Previous positron emission tomography (PET) studies have shown reduced dopamine D2 receptor availability in obese patients and upregulation of this availability following successful BS in the brain's reward system. Dopamine D2 receptor availability in patients with unsuccessful BS has not been investigated to date.

Inclusion Criteria:

• Bariatric surgery 24-36 months prior to the study
• Adult (over 18y old)
• Mentally capable to understand the consequences of the procedure and make his or her own choice without coercion
• Able to undergo PET and MRI, according to the investigator's assessment
• Native speaking
• Able to participate in follow-up
• Written informed consent

Exclusion Criteria:

• Presence of a DSM-IV axis 1 disorder
• The use of drugs that bind to dopamine D2/3 receptors, including various classes of antipsychotics and antidepressants
• History of stroke, brain tumor, Parkinson's Disease or dementia
• History of head trauma with loss of consciousness
• Alcohol or substance abuse in the last 6 months
• Alcohol consumption 24h prior to PET scanning
• Smoking or other forms of nicotine intake 12 hours prior to PET scanning
• Use of anorectic drugs in the last 6 months
• Current pregnancy
• Medication for Diabetes Mellitus
• Claustrophobia
• The presence of implanted metal objects of the type which may concentrate radiofrequency fields or cause tissue damage from twisting in a magnetic field (such as certain implanted devices, shrapnel, ocular metal shavings)
• Patients with a bodyweight > 200kg will be excluded to ensure the maximum load of the camera bed of the PET-scanner (227 kg) is not exceeded.