Renal calculi (kidney stones) are a common indication for renal ultrasound, particularly as a radiation-free alternative to CT in specific populations. Renal stones appear as echogenic foci with posterior acoustic shadowing within the collecting system. Ultrasound also evaluates for hydronephrosis, a complication of obstructing stones.
Limitations
While ultrasound has high specificity for renal stones when a posterior shadow is present, sensitivity is lower than CT, particularly for ureteral stones. Renal ultrasound is especially preferred for pregnant patients and children to avoid radiation exposure.