Magnetic Resonance Angiography (MRA) is a non-invasive medical imaging technique. It is a specialized form of Magnetic Resonance Imaging (MRI) designed to visualize blood vessels. MRA provides detailed images of arteries and veins, helping assess blood flow and detect conditions like blockages, narrowing, or widening of blood vessels.
How MRA Works
MRA operates by utilizing a powerful magnetic field and radio waves to generate images. The strong magnetic field aligns protons within the body’s water molecules. Short bursts of radio waves are then emitted, temporarily knocking these aligned protons out of alignment.
As the radio waves are turned off, the protons realign with the magnetic field, releasing energy signals. These signals are detected by the MRA machine and translated into detailed cross-sectional images. For MRA, the technique capitalizes on the movement of blood, as flowing blood produces distinct signals that highlight the vessels.
Key Uses of MRA
MRA is employed to identify a range of vascular conditions. It detects aneurysms, which are abnormal bulges or weaknesses in artery walls that carry a risk of rupture. The technique also pinpoints blockages or narrowing of arteries, known as stenosis, which can impede blood flow.
MRA examines arteries in the brain and neck, such as the carotid arteries, to assess for plaque buildup that could lead to a stroke. It also evaluates blood vessels supplying the kidneys, lungs, heart, and limbs for issues like reduced blood flow or malformations. This imaging helps diagnose conditions like atherosclerosis, a hardening of the arteries, and to plan for medical interventions or surgeries.
What to Expect During an MRA
Before an MRA, patients are advised to remove all metal objects, including jewelry, watches, and metallic fasteners, as these can interfere with the magnetic field. Fasting instructions might be provided depending on the area being imaged. You may be asked to wear a hospital gown or clothing free of metal.
During the procedure, you will lie on a movable table that slides into a tunnel-shaped scanner. The MRA machine produces loud knocking or buzzing noises, so earplugs or headphones are often provided. The scan often lasts an hour or more. A contrast agent, gadolinium, may be injected into a vein to enhance the visibility of blood vessels. Inform the medical staff about any metal implants, such as pacemakers or joint replacements, or if you experience claustrophobia, as accommodations can often be made.
MRA Compared to Other Imaging
MRA is a type of Magnetic Resonance Imaging (MRI), but its specific focus is visualizing blood vessels, distinguishing it from a general MRI which images various soft tissues and organs. Both MRA and standard MRI utilize strong magnetic fields and radio waves, avoiding ionizing radiation.
MRA also differs from Computed Tomography Angiography (CTA), another common method for imaging blood vessels. CTA uses X-rays and an iodine-based contrast material, exposing patients to ionizing radiation. MRA relies on the magnetic properties of the body and often uses a gadolinium-based contrast, which is generally less likely to cause allergic reactions than the iodine contrast. Each imaging technique offers unique advantages, and the choice depends on diagnostic needs and patient considerations.