In order to improve the sensitivity and specificity of pre-operative imaging localization of foci in adult endogenous hyperinsulinemic hypoglycaemia (AHH) we aim to evaluate a novel promising imaging compound targeting the glucagon-like peptide-1 receptor (GLP-1R), 68Ga-NODAGA-exendin 4. With the currently used imaging techniques, only about 70-80% of insulin producing pancreatic neuroendocrine tumors (IPPNET) can be successfully visualized. Therefore, we propose to compare GLP-1R PET imaging to the standard imaging techniques in patients scheduled for surgical removal of the tumour. These highly relevant data will allow us to interpret the benefits of GLP-1R-imaging over other imaging techniques for the diagnosis of IPPNET in AHH patients. Since pre-operative localization of foci in AHH remains challenging and frequently still leading to futile surgery or unnecessary partial pancreatectomy, a more sensitive and specific imaging technique would be of great value.