What is a myocardial perfusion imaging test?
Myocardial perfusion imaging (MPI) is a non-invasive imaging test that shows how well blood flows through your heart muscle. It can show areas of the heart muscle that aren’t getting enough blood flow. It can also show how well the heart muscle is pumping. This test is often called a nuclear stress test.
There are two types of MPI: single photon emission computed tomography (SPECT) and positron emission tomography (PET).
MPI is useful in people with chest discomfort to see if the pain comes from lack of blood flow to the heart muscle caused by narrowed or blocked heart (coronary) arteries. This type of pain is known as angina. MPI doesn’t show the heart arteries themselves but can tell your health care professional if and how many arteries are blocked. The test can also show if you’ve previously had a heart attack.
If you have chest pain and an abnormal MPI test, the next step may be performing a coronary angiogram (PDF). If the MPI test is normal, your health care professional will look into other causes of your chest pain.
Why do people have MPI tests?
MPI tests can help your health care professional find out if you:
- Have narrowed or blocked heart arteries.
- Have heart damage from a heart attack.
- Should have a coronary angiogram.
- Would benefit from a coronary stent or bypass surgery to treat your chest discomfort or help your heart pump normally.
The MPI test can also show:
- If a heart procedure you had to improve blood flow (stent, bypass) is working.
- How well your heart can handle physical activity.
If the test is normal, it means that no blood flow problems were found and your heart is functioning properly. An abnormal result may mean that heart disease is present. Discuss the findings with your health care professional and whether more testing will be needed and how severe the condition is.
What are the risks of an MPI test?
MPI tests are generally safe for most people. MPI studies expose you to a low dose of radiation. Experts disagree if radiation at such low doses can cause cancer, but the possibility exists that no dose of radiation, however low, is completely safe. Discuss whether or not to undergo the test with your health care professional based on your risk of heart disease. If you’re pregnant or think you might be pregnant, or if you’re a nursing mother, tell your health care professional before you have this test. It could harm your baby.
How do I prepare for my MPI test?
- Tell your health care professional about any medicines you take, including over-the-counter medicines, herbs and vitamins. They may ask you not to take them before the test.
- Don’t eat certain foods, such as caffeine-containing beverages (i.e., coffee, tea and soft drinks) or chocolate for 24 hours before your test if your told not to. The test may have to be postponed or cancelled if you drink caffeine.
- You may be instructed to avoid eating and drinking after midnight before your test.
- Wear comfortable, loose-fitting clothing and comfortable shoes.
What happens during my MPI test?
Specially trained technicians usually perform the test in a hospital or clinic with special equipment.
- The technician places small pads (electrodes) on your chest, arms and legs. The pads have wires that hook up to a machine to record your electrocardiogram (ECG or EKG). The ECG keeps track of your heartbeat during your test and is used to tell the camera when to take a picture.
- You’ll wear a cuff around your arm to track of your blood pressure.
- The technician will put an intravenous line (IV) in your arm.
- You’ll exercise on either a treadmill or a stationary bicycle.
- If you can’t exercise, your IV will be connected to a bag that has a medicine to widen the arteries in your heart or make it go faster, similar to when you exercise. This is called a chemical stress test.
- When you reach your peak activity level, you’ll stop and receive a small amount of radioactive material (tracer) through the IV.
- You’ll lie still on a table for 10-30 minutes while the gamma camera takes pictures of your heart. Several scans are done during that time to provide pictures of thin slices of your entire heart from all angles. It’s important to hold still with your arms above your head while the pictures are being taken.
- During the resting part of the test, you’ll receive more tracer and another set of pictures will be taken. This set of images will be compared to the images taken after exercise or stress.
- Some forms of the test don’t use stress or exercise but take sets of resting images with a tracer.
The test takes between three and four hours. Some labs may do the resting part of the test first or do the resting and exercise tests on different days.
What happens after my MPI test?
- You can usually go back to your normal activities as directed by your heath care professional.
- Drink plenty of water to flush the radioactive material from your body.
- Make an appointment with your health care professional to discuss the test results and next steps.
- Ask for a note confirming your recent MPI test if you plan on travelling within a few days after your test. The radioactive material still in your body may trigger alarms in the airport.