Localization in insulinoma is best with -

The insulinoma might be localized by noninvasive means, using ultrasound, CT scan, or MRI techniques. An indium-111 pentetreotide scan is more sensitive than ultrasound, CT, or MRI for detection of somatostatin receptor positive tumors, but not a good diagnostic tool for insulinomas. An endoscopic ultrasound has a sensitivity of 40-93% (depending on the location of the tumor) for detecting insulinomas. Sometimes, angiography with percutaneous transhepatic pancreatic vein catheterization to sample the blood for insulin levels is required. Calcium can be injected into selected aeries to stimulate insulin release from various pas of the pancreas, which can be measured by sampling blood from their respective veins. The use of calcium stimulation improves the specificity of this test. During surgery to remove an insulinoma, an intraoperative ultrasound can sometimes localize the tumor, which helps guide the surgeon in the operation and has a higher sensitivity than noninvasive imaging tests. Ref Davidson edition23rd pg840