MRA of the Lower Extremity (Runoff)
Basics: What is an MRA of the Lower Extremity?
MRA stands for “magnetic resonance angiography”. In short, MRA of the lower extremities is a relatively quick (30 minutes), extremely accurate noninvasive test (other than the IV), to get a close look at the arteries in your legs. It is extremely good at finding narrowed or blocked arteries, which leads to poor circulation (ischemia), and pain (claudication). Note: MRA of the lower extremities is usually obtained at the same time as a MRA of the Pelvis.
MRA of the lower extremity (& Pelvis) is most important for patients with claudication, which is pain in the legs with exertion, due to the muscles not getting enough oxygenated blood. An example would be pain in the calves after walking a few blocks. This is usually due to narrowing from atherosclerosis, the same process that causes narrowing of the coronary blood vessels in the heart (heart attack), as well as the vessels of the neck and head (stroke).
The standard test for many years has been an invasive angiogram (runoff). Now, however, an MRA of the lower extremities is actually preferred over an angiogram because it provides extremely accurate 3D images, while an invasive runoff is still only 2D. An MRA it is not invasive, does not use radiation, and the MRI dye/contrast has no known effects on the kidneys (other than in extremely unusual cases), whereas an invasive angiogram uses a type of dye that may damage the kidneys in patients with renal failure. As is the case in other areas of the body, there is absolutely no reason to perform a standard diagnostic angiogram of the legs (runoff), unless the physician is going into to fix something. This may include putting a stent in, or using a machine to shave plaque from the vessels, or perhaps to open up a clogged artery in a leg with medicine. Additionally, the average bill for an invasive angiogram (which must be performed at a hospital) may top $10,000, whereas a non-invasive MRA of the lower extremities is less than $2000.
For Patients: Why would a physician order an expensive and invasive angiogram, which uses radiation, instead of a better and less expensive, non radiation based, non-invasive test? There are a number of reasons. A few years back, 3T MRA was not available, and many physicians don’t realize that this is a cheaper, better, safer test. Even many vascular and interventional surgeons are not aware of this fact. Some vascular and interventional surgeons who rely on the angiograms are slow to change. You (the patient) need to take the initiative here and insist on receiving a better, cheaper, and noninvasive test.
Answers to commonly asked questions about MRA of the Lower Extremity/Runoff:
Q: How do I decide between an MRA of the lower extremities or a CTA?
A: An MRA is always preferred over a CTA unless the patient cannot be exposed to a high power magnet (due to a pacemaker, etc.). MRA uses no radiation and the bone images in a CTA make that much more difficult to read. Also, patients with renal insufficiently may be put at a risk for sustaining further injury to the kidneys from CTA contrast (dye). If the patient cannot undergo an MRA, then CTA is still an excellent exam and should be sought instead of an invasive angiography.
Discussion of images above:
The above pictures are from an MRA of the lower extremity with runoff performed on a patient (62 year old male) who complained of significant pain in his left leg upon walking further than a short distance, or climbing stairs. The study includes the lower abdominal aorta, the ilium, common femoral and superficial femoral arteries, as well as the three main arteries in the calf, which lead to the ankles.
This individual’s study shows narrowing of the right common iliac artery and severe narrowing that indicates an atherosclerotic disease of the left superficial femoral artery in the left thigh. Although there is “3 vessel runoff” to both ankles, this man is not receiving adequate blood flow to his left leg. A next logical step in the patient's treatment plan would be to consider a revascularization procedure, probably a femoral to popliteal bypass graft. This study provides excellent information, which deems an invasive angiogram to be unnecessary.