Glucagon-like peptide-1 receptor (GLP-1R) is a kind of G protein coupled receptor which regulate the insulin secretion and serves as potential target in the diagnosis of functional pancreas neuroendocrine tumor. The aim of this study was the clinical evaluation of a potential GLP-1R targeted tracer 68Ga-NOTA-MAL-Cys39-exendin-4 for the detection of insulinoma.

Since GLP-1R is expressed in human β-cells and highly overexpressed in insulinomas，multiple GLP-1R-targeted radiopharmaceuticals were devoted to insulinoma localization imaging.68Ga-NOTA-MAL-Cys39-exendin-4 is an optimal probe targeting GLP-1R. A single dose of 111-185 Mega-Becquerel (MBq) 68Ga-NOTA-MAL-Cys39-exendin-4 will be injected intravenously. Visual and semiquantitative method will be used to assess the PET/CT images.The investigators will determine the use of 68Ga-NOTA-MAL-Cys39-exendin-4 PET/CT in the detection of insulinomas, and to compare its diagnostic value with conventional imaging.

Inclusion Criteria:

1. The patient volunteers and signs an informed consent form.
2. age ≥18 and ≤75 years old;
3. Patients with hypoglycaemia in the presence of neuroglycopenic symptoms and documented Whipple's triad;
4. Biochemically proven endogenous hyperinsulinemic hypoglycaemia (plasma glucose concentration <3.0 mM, insulin >3 µU/ml, and C-peptide >0.6 ng/ml);
5. Conventional imaging within 3 month.

Exclusion Criteria:

1. Having a history of allergy to similar drugs, allergic constitution or suffering from allergic diseases;
2. Breast feeding;
3. Pregnancy or the wish to become pregnant within 6 months;
4. Renal function: serum creatinine > 3.0 mg/dl;
5. Any medical condition that, in the opinion of the investigator, may significantly interfere with study compliance.