1. Bright spots: Kidney stones show up on ultrasound as bright echogenic foci (white spots) within the substance of the kidney. If the stones are larger than 3 or 4 mm there will be a darker area behind the stone representing an acoustical shadow.. Bright spots: Kidney stones show up on ultrasound as bright echogenic foci (white spots) within the substance of the kidney. If the stones are larger than 3 or 4 mm there will be a darker area behind the stone representing an acoustical shadow.