What is Magnetic Resonance Angiography (MRA)?
Magnetic resonance imaging (MRI) is a radiological technique of producing fine detailed images of the body without exposure to radiation. The radiofrequency waves generated in the presence of a strong magnetic field can generate cross sectional images which are then reconstructed as 3 dimensional pictures by a computer. Magnetic Resonance Angiography (MRA) is a variant of the same technique that helps to visualize the blood vessels in the body. The images of the blood vessels are extremely detailed and can be viewed in all dimensions. The dye injected can help visualize blood vessels in most parts of the body. MRA is frequently the test of choice in individuals with a stroke, aneurysm and blood vessel problems in diabetics.
What are some common uses of MRA?
- Assess blood circulation in the brain after a stroke
- Determine the status of carotid arteries (cause of stroke)
- Determine the presence of aneurysm and fistulas in the brain, spleen, kidney, lungs
- Determine disease of the heart and its branches
- Identify disease of the aorta and its branches
- Identify the blood supply to the kidney, liver, lungs
- Identify disease of blood vessels in the legs
- Identify causes of decreased blood flow to the arms
- Confirm disorders identified by ultrasound
Are there any preparation(s) required for the procedure?
There are no special overnight preparations except that one should not eat for 2-3 hrs before the procedure. One should wear loose comfortable clothing with no metal buttons or zippers. Because the strong magnetic field used in MRA can affect the performance of medical devices, one should let the technologist know if she or he has any of the following:
- infusion ports
- ear implants
- artificial limb prosthesis
- surgical clips
- metal pins
For those workers who have been exposed to metal, a prior x ray is always done to ensure that there are no imbedded foreign metals. All patients are asked to sign a consent form confirming that none they have no metal implants.
Are there any metals which are not affected by MRA?
Yes; there area some magnetic resonance compatible metallic implants and these include orthopedic prosthesis which poses no risk. Dyes used in tattoos may contain iron and could heat up during MRI scan, but this is rarely a problem.
Is there contrast used during MRI?
Yes, Some MRI studies use oral or injected contrast material called gandolium. Unlike the dye used in CT scans, this is a non iodine based contrast dye and less toxic. The dye used in MRA has a very low incidence of side effects. However those who have allergies should not have the dye injected. To evaluate blood vessels with MRA, contrast is always required for better imaging.
What other details about MRA should one be aware of?
People who tend to be claustrophobic might become uncomfortable if examined by an enclosed MRA unit, and may find it hard to lie still during the exam. A sedative will relieve anxiety in this situation, but probably only one in twenty patients will require such medication. Another option is to use an open MRA unit.
One is asked to remove all metal objects including jewelry, pens, watches and hairpins. You may wear a hospital gown during the exam, or may be allowed to keep your own clothing if it is loose-fitting and has no metal fasteners. If you are or may be pregnant, an MRA should not be done.
What does the MRA equipment look like?
The MRA is a closed, cylinder-shaped compartment in which the patient must lie still for periods lasting several minutes. Recent MRA technology has led to the development of open MRA which does not generate a claustrophobic feeling. These open MRA are also useful for obese patients.
However, the images generated by the open MRA are usually of a lower quality compared to the closed MRA.
How does the procedure work?
The basis of MRA is to generate radio waves at high magnetic frequencies. MRA images depict differences in the content and distribution of water in various tissues. MRA can easily distinguish between different types of tissue within the same organ and can clearly display the fine anatomical detail. Most of the large blood vessels can be seen in great detail with MRA. The MRA obtains images in sections and these sections are then constructed into 3 dimensional images by a computer.
How is the procedure performed?
Upon arrival at the suite, one is asked to lie on a flat table which moves back and forth. An intravenous is started in the arm. The table then moves into the MRA tunnel. When one is positioned and comfortable he imaging is started. The technologist is able to view you through a mirror and can talk to you through a speaker phone. Most MRA facilities allow for a friend or relative to be inside the room during the procedure. Because the MRA makes a loud noise, it is advisable to bring in a pair of ear plus. Some individual may feel claustrophobic because of the closed tunnel. Some of these individuals may require a sedate to help calm the nerves.
The procedure usually takes 15-20 minutes. During the imaging, one is asked not to breathe to prevent any motion artifacts. After the procedure, one may go home and resume all normal activities.
Who interprets the results and how do I get them?
The results of an MRA are available within 30 minutes after completion of the test; if prior appointment has been made with the radiologist then the results can be available right away. In most cases, however, the report is sent to the family physicians.
What are the advantages versus disadvantages of MRA?
- MRA can show excellent anatomy of the blood vessels without the patient undergoing conventional angiogram. There is no need of placing a large needle in the groin.
- MRA is much faster than a conventional angiogram and the recovery is immediate.
- MRA is less expensive than a conventional angiogram.
- There is no exposure to radiation with MRA.
- The contrast dye used in MRA is non-iodine and has much less toxicity.
- MRA can be used in individuals who are unable to tolerate the dye (either renal failure or allergy).
- MRA can identify the blood vessel disease, its severity and hopefully, decrease unnecessary surgery.
- MRA scan takes less than 10-15 minutes and useful for the elderly, children and injured.
- The contrast material sometimes used for MRI does not contain iodine, and therefore is far less likely to produce an allergic reaction than the contrast materials used for conventional x-rays and CT scanning.
- MRA is not associated with any outward toxicity but it does induce a feeling of claustrophobia. Open MRA are available but the imaging quality is poor.
- Because of the claustrophobic feeling, some individuals may require sedation.
- MRA can not be done in individuals with implanted medical devices.
- MRI is slightly more expensive than CT scans.
- MRI is also difficult to perform in very obese individual or individuals who are not able to lie down flat.
- patient movement can induce motion artifacts.
- MRA should not be done in pregnant females because of the risk of fetal injury.
- MRA can frequently over diagnose vascular disease.
- MRA is not adequate to visualize blood vessels in the distal parts of the legs or hands.
- Individuals with any medical devices are unable to undergo MRA.
- MRI is slightly more expensive than CT scans.
What are the limitations of MRA?
MRI is not offered to women who are pregnant. Even though there are no reports of harm to the fetus, the potential of damage to the fetus are always present. The MRI is only done for a pregnant female when the benefits of the procedure override the risks of pregnancy.
An alternative choice may be to use Ultrasound imaging.
Findings on MRI always need to be interpreted along with the individual's physical findings and information from other tests.
Plaque cannot always be identified with MRA because MRA can't detect calcium as well as CT scan.
All individuals with metal clips, implanted medical pacemakers, ear implants can not undergo MRA.
A significant number of patients complain of a claustrophobic feeling during an MRA.
MRA is not the gold standard for imaging all blood vessels in the body. Conventional angiogram is.
What is the cost of an MRA?
MRA is more expensive than other imaging methods. The average cost of an MRA of the spine may range from $600 - $1000.
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By ScanDirectory.com Staff
Updated: August 17, 2007