<prompt> The investigation of choice to detect gastrinoma le than 5 mm size is-Endoscopic ultrasoundOctreotide scanCT scanPoal venous sampling  <response>: Investigations Upper gastrointestinal endoscopy is the investigation of choice and should be performed promptly in any dyspeptic patient with alarm features . Multiple biopsies from the edge and base of a gastric ulcer are required. Barium meal is a poor alternative, since any abnormalities must be followed by endoscopy and biopsy. Ref Davidson edition23rd pg804 