Which of the following is an investigation of choice to diagnose gall stones?
**Core Concept**
Ultrasound abdomen is a non-invasive imaging modality that uses high-frequency sound waves to produce images of internal organs, including the gallbladder. It is particularly useful for detecting gallstones, which are small, hard deposits that can form in the gallbladder.
**Why the Correct Answer is Right**
Ultrasound abdomen is the investigation of choice for diagnosing gallstones because it is highly sensitive (95-100%) and specific (95-100%) for detecting gallstones, especially when they are small. This modality is also non-invasive, does not involve radiation, and is relatively inexpensive compared to other imaging modalities. The ultrasound probe is placed on the patient's abdomen, and the sound waves are directed towards the gallbladder to produce images of the gallstones.
**Why Each Wrong Option is Incorrect**
**Option A:** X-ray abdomen is not the investigation of choice for diagnosing gallstones because it is not sensitive enough to detect small gallstones and may not distinguish gallstones from other abdominal structures.
**Option C:** ERCP (Endoscopic Retrograde Cholangiopancreatography) is an invasive procedure that involves inserting a tube through the mouth and into the small intestine to visualize the bile and pancreatic ducts. While ERCP can diagnose gallstones, it is not the first-line investigation due to its invasive nature and potential complications.
**Option D:** MRCP (Magnetic Resonance Cholangiopancreatography) is a non-invasive imaging modality that uses magnetic resonance to visualize the bile and pancreatic ducts. While MRCP can diagnose gallstones, it is more expensive and less widely available than ultrasound abdomen.
**Clinical Pearl / High-Yield Fact**
When diagnosing gallstones, it is essential to consider the patient's symptoms, such as abdominal pain, jaundice, or fever, and to perform a thorough physical examination. Ultrasound abdomen is a quick and non-invasive way to confirm the diagnosis and guide further management.
✓ Correct Answer: B. Ultrasound abdomen.