Kidney stone. Coloured abdominal X-ray showing a kidney stone (small pale rounded area just right of the vertebral column at upper right) in a male patient's left ureter. The stone (small blue dot) is just to the right of the backbone (blocks down centre). Each of the two kidneys (not seen) has a ureter that channels urine to the bladder (not seen). Kidney stones are deposits of calcium salts that can cause intense pain as they pass through the urinary system. If not passed, they may need to be broken up with ultrasonic waves. The lower ribs (top centre) and pelvis (bottom centre) are also seen.