<prompt> Neuroendocrinal tumors NET can be best detected by :PET scanHRCT scanMRIRadionuclide scan  <response>: Ans. is d i.e. Radio nucleotide scan Somatostatin receptor scintigraphy SRS type of radio nucleotide scan is now the imaging modality of choice for localizing both primary and metastatic NET tumor. - HarrisonNeuroendocrine for NET tumors refers to two types of tumor:Carcinoids Pancreatic endocrine tumors PETs e.g. Insulinoma Gastrinoma VIPomas GRFomas Somatostatinoma etc.SRS is an investigating modality for localizing the NETs as are CT, MRI, Endoscopic USNote that it not a diagnostic investigation.Diagnosis of NETs, is made by detecting the peptides or amines or their metabolites secreted by the tumors, in urine or serum.For e.g. -In carcinoid tumor - Serotonin5-HIAA Best5-HTP5-TGlucagonoma - Elevated plasma glucagon levelSomatostatinoma - Elevated plasma level of somatostatinInvestigating modalities for localization of NET tumors:CT ScanMRITransabdominal USSelective angiographySRSEndoscopic USSRS is the imaging modality of choice for localizing both primary and metastatic NET tumors.Insulinomas are an exception to this :They have low densities of SST receptors, therefore SRS is not effective modality for them.Best modality for localizing insulinomas is Endoscopic US.Also note that though SRS is the imaging modality of choice for localizing the NETs, it does not provide reliable information on tumor size CT MRI are much better. 