In order to evaluate the difference in beta cell mass in morbidly obese patients with type 2 diabetes mellitus (T2D) before and after Roux-en-Y gastric bypass (RYGB), investigators aim to compare quantitative PET imaging of the pancreas in this patient group before and after surgery. Investigators propose to measure the uptake of 68Ga-NODAGA-exendin-4 in the pancreatic beta cells of these patients. Furthermore, investigators aim to compare uptake of the radiolabeled tracer to beta cell function measured by laboratory parameters. These highly relevant data will provide investigators with more information on the contribution of the beta cells to the mechanisms behind resolution of T2D after bariatric surgery and on the prognostic value of pre-operative beta cell mass determination to T2D resolution. This might be of great interest for the assessment of RYGB as an alternative therapy in patients with T2D and a BMI <35, who currently do not meet the international guidelines for bariatric surgery.