**Core Concept**
Acute osteomyelitis is a bacterial infection of the bone, typically caused by Staphylococcus aureus. The investigation of choice should ideally provide early detection, diagnosis, and assessment of the extent of bone involvement.

**Why the Correct Answer is Right**
The investigation of choice for acute osteomyelitis is a **Bone Scan**, specifically a technetium-99m methylene diphosphonate (99mTc-MDP) scan. This nuclear medicine test detects increased bone turnover, which is a hallmark of osteomyelitis. The 99mTc-MDP scan can identify areas of abnormal bone metabolism, such as increased uptake in infected bones. The scan is highly sensitive and can detect osteomyelitis earlier than other imaging modalities, such as X-rays or CT scans.

**Why Each Wrong Option is Incorrect**
* **Option A:** MRI is more sensitive for detecting soft tissue involvement and marrow edema, but it may not be as widely available or cost-effective as a bone scan.
* **Option B:** X-rays are not sensitive for detecting early osteomyelitis and may not show abnormalities until 2-3 weeks after the onset of symptoms.
* **Option C:** CT scans can detect bone destruction and abscesses, but they may not be as sensitive as a bone scan for detecting early osteomyelitis.

**Clinical Pearl / High-Yield Fact**
In cases of suspected osteomyelitis, a bone scan can provide a rapid and accurate diagnosis, guiding further management and treatment. Remember that a bone scan is particularly useful in the early stages of osteomyelitis, when other imaging modalities may still be normal.

**Correct Answer: A. Bone Scan**