A way to visualize the renal (kidney) veins using contrast material and X-rays. The veins are not normally seen in an X-ray , so a contrast material is injected into the vein so it may be seen. For renal venography the contrast material is injected into the renal vein. X-rays are a form of electromagnetic radiation (like radio waves or light). The wavelength is very short and is capable of penetrating the body and producing a shadow picture of the structures inside the body. Some of the X-rays are absorbed by the body tissues, while other X-rays will pass through. The denser tissues, such as bone, appear on the film as white. Less dense tissues, such as muscles, appear as gray; and air on the X-ray appear as black. See also renal arteriography .