This study is a single centre non-randomized non-blinded phase II prospective cohort study including 50 participants. The objective of this study is to directly compare 68Ga-HA-DOTATATE, 18F-DOPA, and 18F-FDG activity in patients with metastatic neuroendocrine tumors (NETs) on a lesion-by-lesion basis. The investigators will determine the prevalence of concordant versus discordant disease. Secondary objectives include assessing the standardized uptake value (SUV) and determining if there is any correlation between discordance and disease progression.

Inclusion Criteria:

• History of biopsy proven neuroendocrine tumor including (but not limited to): gastrointestinal NET, pancreatic NET, pulmonary NET, NET unknown primary, pheochromocytoma, paraganglioma, medullary thyroid cancer, medulloblastoma, meningioma
• At least two abnormal 68Ga-HA-DOTATATE positive lesions suspected to represent neuroendocrine tumor (at least tow lesions with SUVmax > SUV meanliver).
• Age greater or equal to 40
• Ability to provide written informed consent prior to participation in the study

Exclusion Criteria:

• Weight > 225 kg (weight limitation of PET/CT scanner)
• Inability to scan (ie. extreme claustrophobia) or inability to lie still for imaging
• Any medical condition, serious inter-current illness, or other extenuating circumstance that, in the opinion of the investigator or attending department physician, may significantly interfere with study performance or interpretation
• Previous allergic reaction to 18F-DOPA
• Lack of intravenous access
• Pregnant
• Breastfeeding
• Less than 40 years old