The majority of renal calculi are radiopaque and can be visualized with which imaging modality?

• A. X-ray
• B. Ultrasound
• C. CT
• D. MRI

Answer: (C)

Most renal calculi contain calcium, which makes them radiopaque. Because of this, they typically show up on plain abdominal X-ray (a KUB film). The mention of radiopacity points you toward X-ray as the modality that visualizes the majority of stones. While non-contrast CT is extremely sensitive and can detect all stone types (including radiolucent ones like certain uric acid stones), the fact that most stones are radiopaque means plain X-ray will demonstrate the majority. Ultrasound can detect many stones but is less reliable for small stones or in certain locations, and MRI is not used for stone detection. So the imaging modality that visualizes the majority of renal calculi is X-ray.