What is a cardiac MRI?
Magnetic resonance imaging, or MRI, uses radiowaves and a strong magnetic field to produce clear images of internal organs and tissues without the need for radiation. The MRI machine is actually a large magnet that surrounds the patient. Cardiac MRI (sometimes referred to as CMR) generates images of the heart and coronary arteries. It is mainly used to check if your heart is getting enough blood and oxygen or to see if there is any damage to the heart muscle. MRIs may also diagnose heart defects that occur at birth, heart tumors, an enlarged heart ( cardiomyopathy), and blockages in the carotid arteries in the neck (that may lead to a stroke).
What is a cardiac MRA?
A cardiac MRA, or magnetic resonance angiography, is a noninvasive version of the angiogram. For the traditional cardiac catheterization and angiogram, a catheter is threaded into the groin and fed into the heart. A contrast dye is then injected and X-rays are taken of the heart. With cardiac MRA, there is no radiation or catheter, only the injection of contrast dye. It uses computer analysis of the images to generate a clear three-dimensional picture of the heart. Cardiac MRA is considered experimental and is not widely available. It is unlikely to replace the tried and tested gold standard of traditional cardiac catheterization, but it may help some patients avoid unnecessary invasive testing. The contrast dye used in cardiac MRI is also less likely to trigger an allergic reaction or damage the kidneys compared with the dyes used in cardiac catheterization.
What is a chemical stress cardiac MRI?
Some heart problems only show up when the heart is working hard (or stressed). Stress tests use exercise or chemicals that mimic the effect of exercise on the heart. Exercise stress is not feasible with cardiac MRI because you have to lie still in the machine throughout the test. Studies show that cardiac MRI chemical stress tests are accurate and they may be more widely used in the future.1 Currently, this test is not done very often because it is still very new and there are some safety issues that do not exist with other types of chemical stress tests. The doctor is not in the room with you during the test, and it may not be immediately obvious if you experience problems because you are hidden inside the machine.2
Who might have a cardiac MRI or MRA?
Cardiac MRI may be used in women with symptoms suggestive of heart disease such as chest pain or shortness of breath, or those at risk for heart disease who had a previous abnormal test such as an ECG or chest X-ray. Cardiac MRA is not routinely used because it is still considered experimental. Both cardiac MRI and MRA are relatively new and not widely available.
Who should not have a cardiac MRI or MRA?
If you are pregnant, you should not have a cardiac MRI or MRA. Very obese patients (330 lbs or heavier) may not fit in the MRI scanner. If you have an implanted metal device or other metallic material inside your body, you should not have any type of MRI. These objects include (but are not limited to): pacemakers, implantable cardioverter defibrillators ( ICD), intrauterine devices (IUD), artificial joints, titanium implants in the mouth, or inner ear implants.
Some cardiac patients with artificial heart valves, stents, or those who have undergone open-heart surgery should not have cardiac MRI or MRA. You should speak with your healthcare provider about whether it is all right for you to have one.