Somatostatin receptor antagonists are emerging agents in molecular imaging of neuroendocrine tumors. There're two main antagonist peptides, namely JR11 and LM3, which can be coupled with different chelators, DOTA and NODAGA. Previous studies by our and other groups have revealed the different diagnostic performances of these tracers. However, head-to-head comparison data is still missing. In this study, we aim to evaluate the diagnostic performance of four different antagonists, that is, NODAGA-LM3, DOTA-LM3, and NODAGA-JR11, all labeled with gallium-68.

Patients will be randomly assigned into two arms:

Arm A : 68Ga-NODAGA-LM3 and 68Ga-DOTA-LM3 Arm B : 68Ga-NODAGA-LM3 and 68Ga-NODAGA-JR11

In each arm, patients will undergo PET/CT using assigned tracers. Lesion detection, lesion SUV, and the tumor-to-background ratio will be compared.

Inclusion Criteria:

• Written informed consent.
• Patients of either gender, aged ≥ 18 years.
• Histologically confirmed diagnosis of well-differentiated neuroendocrine tumor.
• A diagnostic computed tomography (CT) or magnetic resonance imaging (MRI) of the tumor region within the previous 6 months prior to dosing day is available.
• At least 1 measurable lesion based on RECIST v1.1.
• Blood test results as follows (White blood cell: ≥ 3*10^9/L, Hemoglobin: ≥ 8.0 g/dL, Platelets: ≥ 50x10^9/L, Alanine aminotransferase / Aspartate aminotransferase / Alkaline phosphatase: ≤ 5 times the upper limit of normal (ULN), Bilirubin: ≤ 3 times ULN)
• Serum creatinine: within normal limits or < 120 μmol/L for patients aged 60 years or older.
• Calculated Glomerular filtration rate (GFR) ≥ 45 mL/min.

Exclusion Criteria:

• Known hypersensitivity to Gallium-68, to NODAGA, to DOTA, to LM3, to JR11 or to any of the excipients of Gallium-68 DOTA-LM3, Gallium-68 NODAGA-LM3, or Gallium-68 NODAGA-JR11.
• Presence of active infection at screening or history of serious infection within the previous 6 weeks.
• Therapeutic use of any somatostatin analog, including long-acting Sandostatin (within 28 days) and short-acting Sandostatin (within 2 days) prior to study imaging. If a patient is on long-acting Sandostatina, then a wash-out phase of 28 days is required before the injection of the study drug. If a patient is on short-acting Sandostatin, then a wash-out phase of 2 days is required before the injection of the study drug.
• Any neuroendocrine tumor-specific treatment between scans.
• Proofs of negative somatostatin receptor expression by previous scans or Immunohistochemical staining results.
• Prior or planned administration of a radiopharmaceutical within 8 half-lives of the radionuclide used on such radiopharmaceutical including at any time during the current study.
• Pregnant or breast-feeding women.
• Current history of any malignancy other than neuroendocrine tumor; patients with a secondary tumor in remission of > 5 years can be included.
• Any mental condition rendering the patient unable to understand the nature, scope, and possible consequences of the study, and/or evidence of an uncooperative attitude.

The details of patient groups will be sealed in sequentially numbered, opaque, sealed envelopes generated by Xuezhu Wang from the nuclear medicine department, Peking Union Medical College Hospital, who will not participate in other parts of the study.