There is provided a radiolabelled peptide-based compound for diagnostic imaging using positron emission tomography (PET). The compound may thus be used for diagnosis of malignant diseases. The compound is particularly useful for imaging of somatostatin overexpression in tumors, wherein the compound is capable of being imaged by PET when administered with a target dose in the range of 150-350 MBq, such as 150-250 MBq, preferable in the range of 191- 210 MBq.