**Core Concept**
Capsule endoscopy is a diagnostic imaging technique that utilizes a small, wireless camera capsule to visualize the interior of the gastrointestinal tract, particularly the small intestine, which is difficult to access with traditional endoscopy methods.

**Why the Correct Answer is Right**
The camera capsule is swallowed, and the images it captures are transmitted to a receiver worn by the patient, providing a detailed assessment of the small intestine's mucosal surface. This is particularly useful for diagnosing conditions such as Crohn's disease, celiac disease, and obscure gastrointestinal bleeding. The capsule is designed to pass through the digestive system without causing harm, eliminating the need for invasive procedures.

**Why Each Wrong Option is Incorrect**
**Option A:** This option might seem plausible, but capsule endoscopy is not used for diagnosing conditions that require tissue sampling or biopsy, such as gastrointestinal tumors.
**Option B:** While capsule endoscopy can visualize the small intestine, it is not primarily used for therapeutic purposes, such as removing foreign bodies or performing polypectomies.
**Option C:** Capsule endoscopy is not typically used for diagnosing conditions of the upper gastrointestinal tract, such as esophagitis or gastritis, which are more commonly assessed with traditional endoscopy.

**Clinical Pearl / High-Yield Fact**
Capsule endoscopy is particularly useful for diagnosing conditions that present with non-specific symptoms, such as abdominal pain or weight loss, and can provide valuable information for guiding further management and treatment.

**Correct Answer: C. Diagnosing conditions of the small intestine.**