**Core Concept**
Pancreatic scanning involves the use of radio-isotopes to visualize the pancreas and its functions. The radio-isotope used should have a suitable half-life, allowing for optimal imaging while minimizing radiation exposure. In this context, the radio-isotope should be taken up by the pancreas or its secretions, enabling accurate visualization.

**Why the Correct Answer is Right**
Technetium-99m (Tc99) is commonly used in various nuclear medicine applications, but it is not the preferred choice for pancreatic scanning. Selenium-75 (Se75), on the other hand, is a suitable radio-isotope for pancreatic scanning due to its ability to be taken up by the pancreas and its secretions. Se75 is primarily used to label mebrofenin, a bile acid derivative that is secreted by the pancreas and intestines, allowing for accurate visualization of the pancreas.

**Why Each Wrong Option is Incorrect**
**Option B:** Chromium-51 (Cr51) is primarily used in labeling red blood cells for blood volume determination, not for pancreatic scanning.

**Option C:** Iodine-131 (I131) is used for thyroid imaging and treatment, not for pancreatic scanning.

**Option D:** Although Technetium-99m (Tc99) has a wide range of applications in nuclear medicine, it is not the preferred choice for pancreatic scanning.

**Clinical Pearl / High-Yield Fact**
When performing pancreatic scanning, it is essential to use a radio-isotope that is taken up by the pancreas or its secretions, allowing for accurate visualization. Selenium-75 (Se75) and mebrofenin are a suitable combination for this purpose.

**Correct Answer:**
✓ Correct Answer: A. Se75