**Core Concept**
Mammography is the primary imaging modality for breast cancer screening, including detection of ductal carcinoma in-situ (DCIS). The sensitivity of mammography for DCIS detection is influenced by various factors, including the size and location of the lesion, as well as the quality of the mammogram.

**Why the Correct Answer is Right**
Magnetic Resonance Imaging (MRI) is considered the most sensitive investigation for detecting DCIS of the breast. This is due to its ability to provide detailed images of the breast tissue, including the ductal structures, and its sensitivity to changes in tissue architecture and perfusion. MRI can detect DCIS lesions that are not visible on mammography, making it a valuable tool for high-risk patients and those with dense breast tissue. The use of contrast agents in MRI allows for the identification of areas of increased perfusion, which can be indicative of malignant lesions.

**Why Each Wrong Option is Incorrect**
**Option A:** Mammography is the primary screening tool for breast cancer, but its sensitivity for detecting DCIS is lower than that of MRI, particularly for lesions smaller than 1 cm. Mammography may not detect calcifications associated with DCIS, especially in dense breast tissue.

**Option B:** Ultrasound is useful for evaluating palpable breast masses and differentiating between cystic and solid lesions, but it is not as sensitive as MRI for detecting DCIS. Ultrasound may not detect calcifications or small lesions, making it less effective for DCIS detection.

**Option C:** Tomosynthesis, also known as digital breast tomosynthesis (DBT), is an advanced mammography technique that provides 3D images of the breast. While DBT improves the detection of breast cancers compared to conventional mammography, its sensitivity for detecting DCIS is still lower than that of MRI.

**Clinical Pearl / High-Yield Fact**
MRI is the most sensitive investigation for detecting DCIS, particularly in high-risk patients and those with dense breast tissue. However, its use should be limited to cases where mammography and ultrasound are inconclusive or when a more detailed evaluation is needed.

**Correct Answer: C. MRI**