**Core Concept**
The initial investigation for suspected gallbladder stones involves evaluating symptoms, risk factors, and laboratory findings to identify the most appropriate diagnostic test. Ultrasonography is a non-invasive, cost-effective imaging modality that provides valuable information about gallbladder morphology and function.

**Why the Correct Answer is Right**
Ultrasonography is the preferred initial imaging modality for suspected gallbladder stones due to its high sensitivity and specificity for detecting gallstones, gallbladder inflammation, and other biliary pathologies. It can also assess liver morphology, bile ducts, and nearby structures. The sonographic features of gallstones include hyperechoic foci with posterior shadowing and acoustic attenuation.

**Why Each Wrong Option is Incorrect**
* **Option A:** Endoscopic Ultrasound (EUS) is a more invasive and expensive procedure typically reserved for patients with suspected malignant biliary obstruction or for guiding fine-needle aspiration.
* **Option B:** Abdominal X-rays are not sensitive or specific for detecting gallstones and are often used to evaluate other abdominal pathologies.
* **Option C:** Magnetic Resonance Cholangiopancreatography (MRCP) is an excellent imaging modality for visualizing bile ducts and pancreatic ducts but is more expensive and less readily available than ultrasonography.

**Clinical Pearl / High-Yield Fact**
When ordering imaging for suspected gallbladder stones, it's essential to remember that ultrasonography should be the initial test of choice due to its non-invasive nature, high diagnostic accuracy, and cost-effectiveness.

**Correct Answer: C. Magnetic Resonance Cholangiopancreatography (MRCP) is an excellent imaging modality for visualizing bile ducts and pancreatic ducts but is more expensive and less readily available than ultrasonography.