**Core Concept**
The investigation of choice for small intestine tumors involves a multifaceted approach, taking into account the unique anatomy and physiology of the small intestine. The small intestine's long length and thin walls make it challenging to visualize and biopsy, requiring a sensitive and specific imaging modality.

**Why the Correct Answer is Right**
The correct answer is **CT enterography**. This imaging modality uses a combination of thin-section computed tomography (CT) and oral contrast to visualize the small intestine's mucosal and submucosal layers. CT enterography is particularly useful for detecting small intestine tumors, such as carcinoids, adenocarcinomas, and lymphomas, by providing high-resolution images of the intestinal lumen and wall. The use of oral contrast helps to distend the small intestine and improve visualization, while the thin-section CT images allow for the detection of subtle abnormalities.

**Why Each Wrong Option is Incorrect**
* **Option A:** Barium follow-through study is an older imaging technique that involves swallowing a barium sulfate mixture and taking serial X-rays to visualize the small intestine's passage of barium. While it can detect some small intestine tumors, it is less sensitive than CT enterography and may not provide detailed images of the intestinal wall.
* **Option B:** Ultrasound is not typically used for small intestine tumor detection due to the small intestine's location and mobility, making it difficult to obtain clear images.
* **Option C:** MRI enterography is another imaging modality that can visualize the small intestine, but it is not as sensitive as CT enterography for detecting small intestine tumors.

**Clinical Pearl / High-Yield Fact**
When evaluating a patient with suspected small intestine tumor, it's essential to consider the patient's symptoms, such as abdominal pain, weight loss, and gastrointestinal bleeding, and to perform a thorough physical examination. CT enterography should be performed with oral and intravenous contrast to optimize tumor detection.

**Correct Answer: C. CT enterography**