**Investigation of Choice in Stress Fracture**

**Core Concept**
A stress fracture is a type of bone injury that occurs due to repetitive stress or overuse, leading to a micro-crack in the bone. Accurate diagnosis is essential to prevent further injury and promote proper healing. The investigation of choice for stress fractures should ideally be non-invasive, sensitive, and specific.

**Why the Correct Answer is Right**
The investigation of choice in stress fractures is a **Bone Scan**. A bone scan involves the injection of a small amount of radioactive material, which is then detected by a special camera. This technique is highly sensitive in detecting areas of increased bone turnover, which occurs in response to stress fractures. The bone scan can identify stress fractures in their early stages, even before they become visible on X-rays. This is because stress fractures cause an increase in bone metabolism, leading to increased uptake of the radioactive material.

**Why Each Wrong Option is Incorrect**
**Option A:** X-Ray - While X-rays can eventually show a stress fracture, they are often normal in the early stages. X-rays are not the investigation of choice for stress fractures due to their limited sensitivity.

**Option B:** MRI - While MRI is highly sensitive in detecting stress fractures, it is not the investigation of choice due to its high cost and limited availability. MRI is typically reserved for cases where the diagnosis is unclear or other imaging modalities are inconclusive.

**Option C:** CT Scan - CT scans can be useful in detecting stress fractures, especially in the weight-bearing bones of the lower extremities. However, they are not the investigation of choice due to their high radiation dose and limited availability.

**Clinical Pearl / High-Yield Fact**
Stress fractures are often seen in athletes who participate in high-impact sports, such as running or jumping. The most common sites for stress fractures are the metatarsals, tibia, and femur.

**Correct Answer:** B. MRI.