Al18F-NOTA-octreotide PET Imaging in Neuroendocrine Tumors

Inclusion Criteria: * Subject is aged over 18 years. * Signed Informed Consent. * Subject is diagnosed with a histologically and/or cytologically confirmed neuroendocrine tumor of all grades of gastroenteropancreatic, pulmonary, neural crest or unknown primary origin. * Subject should have at least one known tumoral lesion below the level of the submandibular and parotid glands with either a minimum size of 1 cm in at least one dimension on morphological imaging (CT, MRI, ultrasound), or a maximal standardized uptake value (SUVmax) of at least 10 on 68Ga-DOTA-SSA PET, in both cases performed within 4 months prior to study scan. A positive lesion is defined as a volume of increased tracer uptake compared to background, deemed to be caused by the presence of NET cells, and that is unlikely to be attributed to physiological or benign etiology (e.g. inflammation, blood pool retention, excretion, etc.). * Subject should have a routine clinical 68Ga-DOTA-SSA PET/CT performed within three months prior to the study scan or scheduled within three months after the study scan. * Female subjects should be (a) post-menopausal, or (b) surgically sterile, or (c) using effective contraceptive with negative pregnancy test. Exclusion Criteria: Part A and B: * Subject has a previous or ongoing recurrent or chronic disease, other than a neuroendocrine tumor, at high risk to interfere with the performance or evaluation of the trial according to the judgement of the investigator. * Subject has had exposure to ionizing radiation (\> 1 mSv) in other research studies within the last 12 months. * Subject has recently (\< 30 days or 5 times the plasma half-life of the investigated drug, whichever is longest) participated or is simultaneously participating in another prospective interventional clinical trial. * Subject is unwilling to avoid unusual, unaccustomed, or strenuous physical activity (i.e. weight lifting, running, bicycling) beginning 4 days prior to tracer injection up to 1 day after tracer injection. * Subject is potentially pregnant (urinary hCG test can be performed in case of doubt) or is breast-feeding. * Subject is unwilling or unable to perform all of the study procedures, or is considered unsuitable in any way by the principal investigator. * Subject does not understand the study procedure. * Subject is mentally or legally incapacitated. Only for part B: * Subject has a contra-indication for MR scanning. * Subject suffers from claustrophobia or cannot tolerate confinement during PET/MR scanning. * Subject has an impaired renal function: estimated glomerular filtration rate (eGFR) \< 30 ml/min/1.73m² (the last known value may not date from more than 3 months prior to the study PET/MR; if not available a blood analysis may be performed as part of the trial). * Subject suffers from diseases for which butylhyoscine bromide (Buscopan®) is contra-indicated: glaucoma, paralytic ileus, severe colitis ulcerosa or myasthenia gravis.