X-ray examination of any part of the urinary (urinary bladder) tract after introduction of a radiopaque substance (often an organic iodine derivative) that casts an X-ray shadow. This contrast (contrast medium) fluid, which passes quickly into the urine, may be taken orally or injected intravenously. It may also be injected directly into the area being examined. Tumours, tuberculous abscesses, kidney stones, and obstruction by prostatic enlargement may be detected by this method. Specific types of urography include pyelography (examination of the kidney and ureter) and cystography (examination of the bladder). Motion-picture “voiding cystograms” provide evidence of gross reflux of urine into the ureters and pelvis of the kidney during voiding.