## **Core Concept**
The use of ultrasonography for diagnosing gallstones relies on the principle that gallstones, being solid, reflect ultrasound waves, creating characteristic echoes. The size of the gallstone that can be confidently diagnosed depends on the resolution of the ultrasound equipment and the skill of the operator.

## **Why the Correct Answer is Right**
The correct answer, , indicates that a gallstone of 2 mm in size can be confidently diagnosed using ultrasonography. This is because modern ultrasound technology, especially high-frequency ultrasound probes, has improved resolution that allows for the detection of small gallstones. Generally, stones larger than 2 mm are usually detectable with high sensitivity and specificity.

## **Why Each Wrong Option is Incorrect**
- **Option A:** . This option suggests a much larger size, which, while easily diagnosable, does not represent the smallest size that can be confidently diagnosed.
- **Option B:** . This option suggests an even smaller size than the correct answer but might not be confidently diagnosable with all ultrasound equipment, especially if the resolution is not optimal.
- **Option D:** . This option suggests a larger size than the correct answer and, similar to Option A, does not represent the smallest size.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the sensitivity of ultrasound for detecting gallstones is high, especially for stones >2 mm. However, very small stones (<1 mm) or sludge might not be reliably detected. The presence of gallstones is a significant risk factor for acute and chronic gallbladder disease. ## **Correct Answer:** .