How do non-contrast CT and ultrasound contribute to kidney stone evaluation?

• A. Non-Contrast CT is Highly Sensitive for Detecting Stones; Ultrasound Can Show Hydronephrosis and Echogenic Stones With Acoustic Shadowing
• B. Ultrasound Is More Sensitive Than CT for Stones
• C. CT Is Used Only After Ultrasound; Ultrasound Cannot Detect Stones
• D. CT Is Used to Evaluate Kidney Function; Ultrasound Measures Urine Flow

Answer: (A)

Non-contrast CT is the most sensitive way to detect kidney stones because it directly images the urinary tract and can identify stones of all compositions and locations with high accuracy and speed. Ultrasound complements this by showing the downstream effect of a stone: hydronephrosis, which indicates obstruction, and, in some cases, stones themselves as bright echogenic foci with posterior acoustic shadowing. While ultrasound is safer (no radiation) and useful in settings like pregnancy or bedside evaluation, it isn’t as consistently definitive for stone detection as non-contrast CT. So the combination works this way: CT confirms presence, size, and exact location of stones; ultrasound assesses obstruction and acute impact, guiding urgent management while minimizing radiation exposure when appropriate.