**Core Concept**
The investigation of choice to visualize gallbladder pathologies involves imaging modalities that can provide detailed information about the gallbladder and its surrounding structures. **Ultrasound** is a non-invasive, cost-effective, and widely available imaging modality that is particularly useful for gallbladder visualization.

**Why the Correct Answer is Right**
Ultrasound is the preferred imaging modality for gallbladder pathologies due to its ability to provide real-time images and detect gallstones, gallbladder inflammation, and other abnormalities. The **transabdominal ultrasound** probe is typically used to visualize the gallbladder, and **doppler ultrasound** can be used to assess blood flow in the liver and gallbladder. Additionally, ultrasound is particularly sensitive for detecting gallstones, which are a common cause of gallbladder pathologies.

**Why Each Wrong Option is Incorrect**
**Option A:** Computed Tomography (CT) scan is not the primary imaging modality for gallbladder pathologies, although it can be used to evaluate more complex cases or when ultrasound findings are inconclusive.
**Option B:** Magnetic Resonance Cholangiopancreatography (MRCP) is a specialized imaging modality that is typically used to evaluate the biliary and pancreatic ducts, rather than the gallbladder itself.
**Option C:** X-ray is not a useful imaging modality for gallbladder pathologies, as it is not sensitive for detecting gallstones or other abnormalities.

**Clinical Pearl / High-Yield Fact**
A key clinical correlation is that patients with suspected gallbladder pathologies should have an ultrasound examination as the first-line imaging modality, as it is highly sensitive for detecting gallstones and other abnormalities.

**Correct Answer: A. Ultrasound.