This prospective, single-center, double-blinded study investigates the biodistribution, dosimetry, safety, and diagnostic ability of Al18F-NOTA-LM3 in patients with well-differentiated neuroendocrine tumors. And compares the diagnostic ability of Al18F-NOTA-LM3 with 68Ga-DOTATATE PET/CT and 68Ga-NODAGA-LM3 PET/CT. Clinical management will also be compared using different imaging modalities.

Somatostatin receptors (SSTR), especially SSTR subtype 2 (SSTR2), are highly expressed in well-differentiated neuroendocrine tumors (NETs). Radiolabeled somatostatin analogs, including 68Ga-DOTATATE, are widely used for NET imaging and play essential roles in primary tumor seeking, staging, as well as management. SSTR antagonists have recently emerged as another type of somatostatin analog and showed better performance than analogs. Our previous studies exhibited better diagnostic efficacy of 68Ga-DOTA-LM3, 68Ga-DOTA-JR11, and 68Ga-NODAGA-LM3 compared to 68Ga-DOTATATE, especially liver metastasis.

18F-labeled radiotracers have shown several advantages compared to 68Ga-labelled tracers, including increased cyclotron production, lower positron energy, and longer half-life when compared to 68Ga, theoretically to the benefit of image quality. The purpose of this study is to investigate the biodistribution, safety, and diagnostic ability of Al18F-NOTA-LM3 in patients with well-differentiated neuroendocrine tumors. And compare the diagnostic ability of Al18F-NOTA-LM3 with 68Ga-DOTATATE PET/CT and 68Ga-NODAGA-LM3 PET/CT. Clinical management related to imaging will also be compared.

Patients with histologically confirmed well-differentiated neuroendocrine tumors (G1 and G2) will be recruited in this study. All patients will be randomized into two arms (A and B): Patients in arm A performed Al18F-NOTA-LM3 and 68Ga-DOTATATE. Patients in arm B performed Al18F-NOTA-LM3 and 68Ga-NODAGA-LM3. The first eight patients will undergo serial PET scans at 5, 15, 30, 45, 60, and 120 min after injection of Al18F-NOTA-LM3. The following patients will perform a whole-body PET/CT scan at 60-90 minutes after injection of Al18F-NOTA-LM3. All patients a whole-body PET/CT scan at 40-60 minutes after administering 68Ga-DOTATATE or 68Ga-NODAGA-LM3. For each patient, the two pet scans should be done within a week and the interval between the two scans should be at least 24h in case of mutual interference.

The images were reviewed by 2 experienced nuclear medicine physicians who were masked to all patients' clinical information. The results were based on consensus, with any discrepant result resolved by a consensus image interpretation by a third senior physician.

The biodistribution, dosimetry, safety, and diagnostic ability of Al18F-NOTA-LM3 will be explored. The diagnostic ability of Al18F-NOTA-LM3 with 68Ga-DOTATATE PET/CT and 68Ga-NODAGA-LM3 PET/CT will be compared. We will also compare the clinical management using different imaging modalities.

Inclusion Criteria:

• Patients aged 18 to 80 years.
• Histologically proven, well-differentiated, NETs (G1 or G2).
• No long-acting somatostatin analog treatment within 4 weeks.
• No PRRT treatment within 8 weeks.

Exclusion Criteria:

• Combined with other types of tumors.
• Severe liver or renal dysfunction (ALT/AST≥5 ULN, GFR<30ml/min).
• Active infection.
• Pregnant or breast-feeding women.
• Inability to perform PET/CT scans.

The images of patients will be reviewed by 2 experienced nuclear medicine physicians and they will be masked to all patients' clinical information.