A lymphangiogram is used to evaluate the possible spread of cancers and the effectiveness of cancer therapy. The X-rays may also help determine the cause of swelling in an arm or leg and check for parasitic diseases. The test is performed by injecting blue dye into an area to be tested. The blue dye helps to locate the lymphatic vessels where the catheter will be placed. Once the lymph vessels are found, contrast medium is injected through the catheter and X-rays are taken to monitor its progress as it spreads through the lymph system up the legs, into the groin, and along the back of the abdominal cavity. The next day, another set of X-rays is taken.