Venograms are a subset of a larger class of X-ray exams called angiography. Angiography in general is the X-ray study of the blood vessels in your body. Venograms deal strictly with the veins as opposed to the arteries, most commonly the veins in your legs, though other sets of veins can be examined. These studies are generally done when your doctor has reason to suspect a blood clot or other blockage of one of the more important vessels.
Since blood vessels in general do not show up on X-rays, a "dye," or contrast medium, must be injected into the veins being studied. This contrast medium is an organic iodine solution, meaning that the iodine is bound to compounds similar to those found in living organisms. While venograms can be performed on just about any part of your body, they all are done using a similar style, and venograms of the leg are the most common.
When performing a venogram of the leg, the radiologist and technologist doing your study will have you remove your pants, shoes, and socks, and put on a hospital gown. You will then be placed on an X-ray table that has been tilted up to between 30 and 45 degrees. Two tourniquets will be placed around your leg, one down near the ankle, and one up high on the thigh. These tourniquets are not to stop the blood flow in your leg, but rather to slow it down so that adequate X-rays may be obtained. The radiologist will then start an IV in your foot and slowly inject the contrast medium into it while the technologist quickly takes a series of images. Another common version of this exam will have the technologist injecting the contrast medium through the IV in the foot while the radiologist films the study using fluoroscopy. The advantage of this method used at Emory is that we can do a "subtraction" study, in which a computer uses a special filter to remove from the X-ray images everything except the veins being studied and the outlines of the major bones that can act as landmarks to identify where problem areas may lie.