Assessment of Pancreatic Beta Cell Mass and Function by Positron Emission Tomography Imaging in Human Diabetes Mellitus

Inclusion Criteria: * Age ≥18 years; ≤ 75 years * Both sexes * Good health * Absence of exclusion criteria * Able to understand methods, goals, and implications of the research and of delivering a free, written informed consent Exclusion Criteria: * Hemoglobin \< 12 g/dl * HbA1c \> 10% * Pregnancy or breast-feeding * If not in menopause, women not using effective birth control methods or not willing to undergo a pregnancy test * History of severe psychiatric disorder or alcohol abuse * Recent head traumas (\<6 months) * Active neurologic diseases * Claustrophobia * Active malignant neoplasms * Severe kidney and/or liver disease * Recent (\<6 months) major adverse cardiovascular events * Heart failure (class NYHA 3-4) * Drugs known to affect beta cell function and/or insulin sensitivity * Current or past treatment with GLP1R-agonists * Intolerance to exenatide * Endocrine diseases, other than diabetes mellitus, known to affect beta cell function and/or insulin sensitivity, except well controlled hypothyroidism or adrenal insufficiency * COPD on day time oxygen therapy * Any current acute disease