**Core Concept**
The evaluation of a suspected breast mass in a patient with a breast implant requires a specific diagnostic approach to avoid complications such as implant rupture or capsular contracture. The preferred investigation should be able to accurately differentiate between a true breast mass and implant-related changes.

**Why the Correct Answer is Right**
The preferred investigation for evaluating a suspected breast mass in a patient with a breast implant is ultrasound (US). Ultrasound is a non-invasive, radiation-free imaging modality that uses high-frequency sound waves to produce detailed images of the breast tissue. It is particularly useful for differentiating between a true breast mass and implant-related changes such as implant rupture or capsular contracture. Ultrasound is also useful for guiding biopsies and fine-needle aspirations.

**Why Each Wrong Option is Incorrect**
* **Option A:** Mammography is not the preferred imaging modality for evaluating a suspected breast mass in a patient with a breast implant. This is because mammography may not provide accurate images of the implant and surrounding tissue, leading to false positives or false negatives.
* **Option B:** MRI (Magnetic Resonance Imaging) may be used in some cases to evaluate a suspected breast mass in a patient with a breast implant, but it is not the preferred initial imaging modality. MRI is more expensive and may not be readily available.
* **Option D:** CT (Computed Tomography) scans are not typically used to evaluate breast masses and are not the preferred imaging modality for this purpose.

**Clinical Pearl / High-Yield Fact**
When evaluating a suspected breast mass in a patient with a breast implant, it is essential to remember that ultrasound is the preferred initial imaging modality due to its safety, accuracy, and non-invasive nature.

**Correct Answer:** C. Ultrasound