**Core Concept**
The underlying principle being tested is the use of nuclear medicine imaging techniques, specifically **scintigraphy**, to diagnose certain conditions. **Tc99m Pertechnetate** is a radiopharmaceutical used in various diagnostic scans.

**Why the Correct Answer is Right**
Tc99m Pertechnetate scintigraphy is used to diagnose conditions like **Meckel's diverticulum**, a congenital anomaly of the small intestine. This radiopharmaceutical accumulates in the mucoid cells of the diverticulum, allowing for its visualization.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is not associated with Tc99m Pertechnetate scintigraphy.
**Option B:** Incorrect as it is not typically diagnosed using this method.
**Option C:** Incorrect because it does not relate to the use of Tc99m Pertechnetate.

**Clinical Pearl / High-Yield Fact**
Tc99m Pertechnetate scintigraphy is particularly useful in pediatric patients to diagnose **Meckel's diverticulum**, which can cause gastrointestinal bleeding due to the presence of ectopic gastric mucosa.

**Correct Answer:** D. Meckel's Diverticulum.