Myocardial Perfusion Imaging Test: PET and SPECT

What is a myocardial perfusion imaging test?

Myocardial perfusion imaging is an imaging test that shows how well blood flows through your heart muscle. It can show areas 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: positron emission tomography (PET) and single photon emission computed tomography (SPECT). The main difference between a PET and a SPECT scan is the radioactive tracer used during the procedure.  

Positron Emission Tomography (PET)

What is a cardiac PET scan?

A PET scan of the heart is an imaging test that uses nuclear medicine. Radioactive tracers produce pictures of your heart. Health care professionals use PET scans to diagnose coronary artery disease (CAD) and damage due to a heart attack. PET scans can show healthy and damaged heart muscle. They are also used to help find out if you will benefit from:

• Percutaneous coronary intervention (PCI) such as angioplasty and stenting
• Coronary artery bypass surgery (CABG)

Why do I need it?

A PET scan can diagnose or detect many conditions, including:

• Coronary artery disease
• Low blood flow in the heart
• Improved blood flow to the heart after a procedure
• Non-ischemic and ischemic cardiomyopathy
• Benign and malignant cardiac tumors
• Effects of chemotherapy on known malignant tumors
• Cardiac diseases such as cardiac sarcoidosis

How does a PET scan work?

A radioactive tracer is injected. It is tagged with a small amount of radioactive material. An image of your heart is created by tracking how your body reacts to the tracer.

Your health care professional can tell whether your heart muscle is functioning by how well it takes up and uses the different tracers.

What are the risks of cardiac PET?

Cardiac PET is safe for most people. The amount of radiation is small. Your body will get rid of it through your kidneys or stool. Drink plenty of water to flush it out of your system. If you’re pregnant or think you might be , 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 the scan?

• Tell your health care team about any medications you take, including over-the-counter medications, herbs and vitamins. You may be asked not to take some of them before the test.
• If you have diabetes and take insulin, ask how much you should take before the scan and what you should eat. Your blood sugar levels will be monitored during the test. Test results are not always correct in people with diabetes.
• You may also be asked to avoid certain foods and drinks, such as caffeine or alcohol, for 24 hours before your test.
• Don’t eat, and drink only water for four to six hours before your test.
• Wear comfortable, loose-fitting clothing, and don’t wear jewelry or other metal objects.
• Tell your health care team if you’re:
  • Pregnant
  • Allergic to injected dyes
  • Afraid of tight spaces
  • Have anxiety about being enclosed

What happens after my PET scan?

• Ask your health care professional if you can go back to your normal activities right away.
• Drink plenty of water for the next 24 hours to flush the radioactive material from your body.
• Make an appointment with your health care professional to discuss test results and next steps.

Single Photon Emission Computed Tomography (SPECT)

What is a cardiac SPECT scan?

A SPECT scan of the heart is a nuclear imaging test. Radioactive tracers are injected into the blood to make pictures of your heart. Health care professionals use SPECT to diagnose coronary artery disease and find out if a heart attack has occurred. SPECT, also called a myocardial perfusion scan, can show how well blood flows to the heart and how well the heart is working.

Why do people have cardiac SPECT scans?

SPECT scans show areas of your heart with low blood flow at rest or during exercise. This helps your health care professional find out:

• If you have coronary artery disease
• If you have scar tissue from a heart attack
• How well bypass surgery or other heart procedures worked

How does a SPECT scan work?

A small amount of radioactive tracer is injected into your bloodstream. The tracer produces energy inside your body. A special camera picks up signals from the tracer, and a computer converts them into pictures of blood flow through your heart.

SPECT scans can be done while you rest and during an exercise stress test, called a nuclear stress test. The stress test gives your health care professional a better idea of how well your heart handles work. If you can’t exercise, you may get medication to increase the blood flow in your heart as if you were exercising. This is called a chemical or pharmacologic stress test.

• If the test is normal during both exercise and rest, blood flow through the coronary arteries is normal.
• The test may show normal blood flow  at rest but not after exercise. This may be due to a blockage in one or more coronary arteries.
• The test may be abnormal during both exercise and rest. This means that not enough blood is flowing to that area of the heart at any time.
• The lack of tracer may mean the cells in that area are dead from a prior heart attack. Other imaging tests may be needed to assess this.
• SPECT scans can also show how well your heart’s lower pumping chamber is working.

What are the risks of a cardiac SPECT scan?

A cardiac SPECT scan is safe for most people.

• Some people may have a treatable allergic reaction to the tracer.
• If you have coronary heart disease, you may feel chest pain during the stress test.
• Other rare complications include irregular heartbeat, low blood pressure and heart attack.

If you’re pregnant or think you might be pregnant, tell your health care professional. They may have you wait until after your pregnancy for the scan if it’s not urgent. If you’re a nursing mother, pump enough milk for a couple of days of feedings before your scan or feed your baby formula for one to two days after the scan.

How do I prepare for a cardiac SPECT scan?

• Tell your health care professional about any medications you take, including over-the-counter medications, herbs and vitamins. They may ask you not to take them before the test.
• You may be asked not to have caffeine for 24 hours before your test.
• Don’t eat and drink only water for four to six hours before your test.
• Wear loose-fitting clothing and comfortable shoes if you are having an exercise stress test.

What happens during a cardiac SPECT scan?

A doctor and nuclear medicine technologist usually perform the scan in a hospital or clinic using special equipment.

• The technician will place small disks or pads (electrodes) on your chest, arms and legs. The EKG has electrodes with wires that connect to a machine that records your heartbeat.
• You’ll wear a cuff around your arm to track your blood pressure.
• The technician will put an IV line in your arm. The tracer will be injected through the IV.
• For a resting scan, you’ll lie on a table. A special camera will move around your chest and convert the tracer’s signals into pictures.
• For a nuclear stress test, you’ll walk on a treadmill or ride a stationary bicycle. Then you’ll lie on the table for more pictures. If you can’t exercise, you’ll receive medication through the IV to increase the blood flow in your heart. The tests may take about an hour.

What happens after my SPECT scan?

• You can usually go back to your normal activities right away.
• Drink plenty of water for the next few days. This will help flush the radioactive material from your body.
• Make an appointment with your health care professional to discuss the test results and next steps.