**Core Concept**
Microcalcifications are a hallmark of ductal carcinoma in situ (DCIS) of the breast, and mammography is the primary imaging modality used for their detection. The high sensitivity of mammography in detecting microcalcifications makes it an essential tool in early breast cancer detection.

**Why the Correct Answer is Right**
Mammography uses low-energy X-rays to produce images of the breast tissue. These X-rays interact with the calcium ions in microcalcifications, producing a signal that is visible on the mammogram. The high sensitivity of mammography in detecting microcalcifications is due to its ability to resolve small changes in breast density and the presence of calcium deposits. This is particularly useful in detecting DCIS, as microcalcifications are often the only radiographic sign of this condition.

**Why Each Wrong Option is Incorrect**
**Option A:** Ultrasound is not the most sensitive investigation for DCIS, as it relies on the presence of a palpable mass or acoustic shadowing, which is not typically present in DCIS. While ultrasound can be useful in evaluating axillary lymph nodes and guiding biopsy, it is not the best choice for detecting microcalcifications.
**Option B:** MRI is highly sensitive for detecting invasive breast cancer and can be useful in evaluating the extent of disease, but it is not the most sensitive investigation for DCIS. MRI is also more expensive and less widely available than mammography.
**Option C:** Clinical examination is not a sensitive method for detecting DCIS, as the disease is often asymptomatic and may not produce a palpable mass.

**Clinical Pearl / High-Yield Fact**
Mammography is the primary imaging modality for detecting microcalcifications, which are a hallmark of DCIS. A high-quality mammogram can detect microcalcifications as small as 0.1 mm in diameter, making it an essential tool in early breast cancer detection.

**Correct Answer: C. Mammography. Mammography is the most sensitive investigation for DCIS of the breast.**