## **Core Concept**
The question tests knowledge on diagnostic modalities for detecting skeletal metastasis. Skeletal metastasis refers to the spread of cancer to the bones, a common occurrence in various malignancies. The diagnostic tests listed are used to detect bone metastases.

## **Why the Correct Answer is Right**
**Option C: Whole-body MRI** is considered highly sensitive for detecting skeletal metastasis, especially in the early stages. MRI provides excellent soft-tissue contrast and can image the bone marrow directly, allowing for the detection of metastatic lesions before they cause significant bone destruction or become apparent on other imaging modalities. It is particularly useful for assessing the spine and for detecting lesions in the bone marrow.

## **Why Each Wrong Option is Incorrect**
- **Option A: Bone Scan** is a commonly used method for detecting skeletal metastases, especially for cancers like prostate, breast, and lung. However, it may not be as sensitive as MRI for early marrow involvement and can have false negatives, especially in the spine.
- **Option B: PET-CT** combines the functional information of PET with the anatomical detail of CT. While highly useful for detecting metastases and assessing cancer spread, its sensitivity for purely skeletal metastases, especially in early stages, may not surpass that of MRI.
- **Option D: Conventional Radiographs** is the least sensitive method for detecting early skeletal metastases. It often requires significant bone destruction (about 50% or more of bone density loss) before lesions become apparent.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **whole-body MRI** is particularly advantageous for detecting skeletal metastases without the need for ionizing radiation, making it a preferred option for long-term follow-up and in certain patient populations.

## **Correct Answer: C. Whole-body MRI**