Magnetic Resonance Angiogram (MRA) is a diagnostic tool used to produce images of the blood vessels in the body. In this article, we shall discuss in detail about how a MRA test is conducted, when it is recommended, the risks involved, and more.
A magnetic resonance imaging technique, the MRA is used to examine the condition of blood vessels and the flow of blood to different parts of the body. Sometimes, a MRA image can provide better information than an ultrasound image or an X-ray image. This diagnostic procedure is used to detect mineral or cholesterol deposits, clots and damages in the walls of the blood vessels.
Deposit of substances, such as cholesterol in the blood vessels, especially arteries, can increase the risk of a heart attack. MRA is generally used to monitor the renal arteries, cranial arteries and the arteries of the lower extremities. During the test, the subject is made to lie inside a Magnetic Resonance Imaging (MRI) machine and the resulting images are stored in the computer memory, which can be accessed later, if necessary.
Principle
The magnet field inside the MRI tube, combined with the radio waves generated, changes the configuration of the hydrogen atoms in the body. This change in configuration is then fed into a computer, which then generates three-dimensional images of the blood vessels. The difference between MRI and MRA is that while a MRI image shows both, blood vessels and the surrounding tissue, you can see only blood vessels in a MRA image.
Techniques
There are three techniques to carry out the process of magnetic angiography. These methods are as follows.
Contrast Enhanced MRA Test
In contrast enhanced MRA, a gadolinium based contrast agent is injected into the veins, and the moment the contrast agent first reaches the arteries, images are taken. This can result in very high-resolution images. However, the most important factor here is the timing. Also, the amount of contrast agent used, should be as small as possible for higher image quality.
Phase Contrast MRA Test
In this method, special bipolar phase-encoding gradient pairs are used. The bipolar gradient pairs are nothing but varying magnetic fields that alter the phase of the magnetic field generated by the MRI machine. The velocity of the gradient is set as the highest possible velocity of blood flow. The stationary tissues in the body acquire zero net phase due to zero velocity. The phase sensitive imagery depicts vascular flow or flow of blood through the blood vessels. This technique also helps in the analysis of quantitative blood flow.
Inflow or Time-of-Flight MRA Test
This technique is based on the principle of signals that indicate the flow of blood into the blood vessels. In the images obtained by inflow angiogram, blood flowing in the blood vessels is prominently distinguished from the surrounding stationary tissue. This method is best used for images of the arteries in the head and neck.
Who Cannot Take the Test
If you suffer from one of the following medical conditions, then you need to talk to your doctor before undergoing this test.
- If you are prone to allergies, the contrast agent used may trigger them.
- If you are pregnant.
- If you have devices such as a pacemaker, defibrillator, prosthetics or metal parts inside your body, or if you have any iron-based pigment tattoos,etc.
- If you are claustrophobic, that is, you are afraid of enclosed spaces. In this case, your doctor might recommend an open MRI scanner.
- If you are suffering from diseases such as sickle-cell anemia.
How to Prepare for MRA Test
Here are a few things you need to keep in mind before undergoing this test for clearer test results.
- Be on an empty stomach before going for the test.
- Completely abstain from tobacco and alcohol before the test.
- Do not take any iron supplements on the day of the test.
- Once inside the MRI machine, remain completely still.
An MRA scan may take anywhere between half an hour to two hours.
Results
Abnormal test results indicate partial or complete blockage of blood vessels due to deposit of cholesterol and minerals. It may also indicate a bulge or damage to the walls of the blood vessels. Usually, you can collect your test results from your doctor within 1 or 2 days.
There are several new developments in this field with new techniques such as fresh blood imaging, 4D dynamic MR angiography and blood-oxygen-level dependent (BOLD) venography. MRA is an expensive test but its major advantage is that it does not involve the use of any harmful radiation, and is a relatively safe medical procedure. However, it is important to consult your doctor before going ahead with this test.
