Ultrasound can be useful for detecting _____ renal calculi.

• A. Radiolucent
• B. Radiopaque
• C. Calcified
• D. Obstructive

Answer: (A)

Ultrasound is able to detect stones that do not show up on X-ray because it relies on acoustic properties rather than radiodensity. Some renal calculi, such as uric acid stones, are radiolucent on plain radiographs due to their lack of calcium, so they aren’t seen on X-ray scans. But on ultrasound, a stone appears as a bright echogenic focus with posterior acoustic shadowing, allowing detection even when the stone is radiolucent. This makes ultrasound particularly useful for identifying radiolucent renal calculi. Radiopaque or calcified stones are typically visible on X-ray, and ultrasound flags signs of obstruction like hydronephrosis but doesn’t define radiodensity.