MRV or MR venogram, is a test that looks for narrowing or clot in the veins throughout the body. It is used most commonly in the brain, abdomen, and pelvis. In the brain, an unexplained headache and risk factors for clot formation, may prompt a search for clot in the major veins of the brain. In patients with swelling in the legs, MRV of the abdomen and pelvis can look for clot in the major veins draining the legs, abdomen and pelvis. It can also detect congenital abnormalities in the veins than can lead to leg swelling, such as May-Thurner syndrome. MRV can also evaluate for pelvic congestion syndrome, a condition causing pelvic pain in women that is associated with enlarged, varicose pelvic veins.