## **Core Concept**
The clinical presentation described for the 38-year-old male lawyer—abdominal pain after a fatty meal, tenderness in the right hypochondrium, and a positive Murphy's sign—is highly suggestive of **acute cholecystitis**. This condition is an inflammatory disease of the gallbladder, often caused by gallstones obstructing the cystic duct.

## **Why the Correct Answer is Right**
The correct answer, **Ultrasonography (USG)**, is the most appropriate initial imaging test for suspected acute cholecystitis. USG is highly sensitive and specific for detecting gallstones, gallbladder inflammation, and signs of cholecystitis such as a thickened gallbladder wall, pericholecystic fluid, and a positive Murphy's sign. It's non-invasive, widely available, and does not expose the patient to radiation.

## **Why Each Wrong Option is Incorrect**
- **Option A: Endoscopic Retrograde Cholangiopancreatography (ERCP)** is an invasive procedure primarily used for diagnosing and treating conditions related to the bile and pancreatic ducts. It's not a first-line diagnostic tool for acute cholecystitis.
- **Option B: Computed Tomography (CT) abdomen** can be useful in diagnosing acute cholecystitis and assessing for complications, but it's not the first-line imaging modality due to higher costs, radiation exposure, and similar diagnostic efficacy to USG for initial evaluation.
- **Option D: Magnetic Resonance Imaging (MRI)**, specifically Magnetic Resonance Cholangiopancreatography (MRCP), provides detailed images of the biliary and pancreatic ducts. While useful for certain conditions, it's not the initial test of choice for acute cholecystitis due to higher cost, limited availability, and the fact that it doesn't offer significant advantages over USG for initial diagnosis.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **Murphy's sign** is a critical physical examination finding suggestive of acute cholecystitis. The patient's pain upon deep inspiration during palpation of the right upper quadrant, which causes the inflamed gallbladder to come into contact with the examiner's fingers, is a classic sign. USG is then used to confirm the diagnosis.

## **Correct Answer:** . Ultrasonography (USG)