Healthy urinary tract. Coloured X-ray urogram of human kidneys, ureters and bladder. The two yellow branched structures (at top) are collecting ducts of the kidneys. Descending from these are the long ureters (which have been computer enhanced); they carry urine to the bladder. The blue structure between the hip bones (at bottom) is a pool of urine that has collected in the bladder. Urograms are made by injecting the body with a substance opaque to X-rays and then taking an X-ray after the kidneys have had enough time to remove this substance from the blood. The test may be carried out to look for abnormalities like kidney stones.