nuclear cardiology

myocardial perfusion imaging

Coronary Artery Disease (CAD) is a narrowing of the blood vessels that supply blood and oxygen to the heart.  The narrowing is usually caused by fatty deposits inside the coronary arteries that lead to the heart.  Such narrowing can restrict the heart from pumping efficiently, cause chest pain, and lead to serious problems such as heart attack or death.

Nuclear Imaging is a common procedure given to millions of people every year.  This safe and useful test will help your physician see whether you have CAD.

What Is Nuclear Imaging?
Nuclear myocardial perfusion imaging (MPI) is a procedure that lets your physician look at the flow of blood to the heart muscle.  Let’s break it down.

Nuclear refers to the tracer that is injected into your bloodstream.  This tracer contains a small amount of radiation similar to that used in a common x-ray.

Myocardial refers to the heart muscle (myocardium).

Perfusion refers to the passage of blood through the circulatory system.

Imaging refers to the computer-generated pictures taken during the test by a special camera.

What Information Can Be Learned From This Procedure?

Nuclear MPI will help your physician determine:

  1. If your heart is receiving enough blood.
  2. If you have CAD.
  3. If more tests are necessary.

How Does Nuclear MPI Work?

A nuclear MPI test is performed in two parts: when the heart is at rest and when it is at stress. 

PART 1.  When the patient enters the clinic, a small IV catheter is started in the hand or arm. A small amount of a radioactive imaging agent (tracer) is injected into the IV by the nuclear medicine technologist. Images are taken of the blood flow to the muscle of the heart after a 45 minute waiting period. The first set of images shows the heart while relaxed and is referred to as “at rest”. 

PART 2.  The heart is stressed.  The arteries are expanded (dilated) either by exercise on a treadmill or by using a prescription medication such as Lexiscan or Adenosine.  Patients who are unable to exercise on a treadmill can receive a medication that creates an effect on the heart that is similar to exercise.  Healthy coronary arteries dilate more than unhealthy narrow arteries.  Once the blood vessels are dilated, a small amount of a radioactive imaging agent is injected into the IV catheter.  Images will be taken by a special camera after the stress test and will show if any part of your heart is not getting enough blood. The second set of images shows the pictures of the heart when the blood vessels are dilated and is referred to as “at stress”.  

The two sets of images are processed on a computer then compared by your cardiologist.  A heart with healthy coronary arteries shows little or no difference between images taken during stress and those taken at rest.  In a heart with narrow arteries, images taken during stress are different from those taken at rest.

What Can You Do To Prepare For The Test?

  1. *Ask your physician for special instructions if you are a diabetic on insulin or oral hypoglycemic medications.
  2. *Ask your physician whether you should stop taking any medications prior to the test.
  3. *Do not eat for 4 hours prior to the test.
  4. *Refrain from consuming products containing caffeine for 24 hours before the test.  Certain ingredients in foods and medications may interfere with the test.  Foods such as chocolate and cocoa and even ”caffeine-free” colas and soft drinks still contain some caffeine as well as some OTC drugs like Anacin or Excedrin.
  5. *Be prepared to spend 3-4 hours in the clinic for testing.
  6. *Wear comfortable clothes and shoes appropriate for brisk exercise on a treadmill.
  7. *Do not apply any creams, lotions, or powder to your chest area on the day of your test.
  8. *Inform your physician if you have a history of wheezing, asthma, or chronic lung disease.

What If I Need Medication To Dilate My Arteries?
A pharmaceutical stress test is administered if you are unable to exercise adequately. A blood pressure cuff is placed on one arm, and a small intravenous needle is inserted in your other arm.  Small round pads will be gently attached to your chest.  The pads are attached to wires that lead to an electrocardiograph (ECG). A drug that dilates your blood vessels will be administered over a short period of time. During this time, your physician will continue to monitor your heart.  You may experience side effects similar to exercise, including flushing, chest pressure/pain, and/or shortness of breath.  This is to be expected and not cause for alarm.  Most adverse affects usually resolve quickly and spontaneously after the infusion has stopped.

What Happens During Imaging?
For approximately 15-20 minutes, you will rest on your back with your arms comfortably extended above your head.  The camera is then used to take images of the blood flow of your heart.  The camera will not come in contact with your body, and doesn’t hurt or emit any radiation.

Is Nuclear MPI Safe?
Like many people, you may be worried about the radioactive tracer you will receive during the test.  That’s very understandable.  But you can feel comfortable about nuclear MPI.  The radiation amount is the same or less than what you would receive during a typical x-ray, and your body quickly eliminates it through natural means.

If you have any questions, don’t hesitate to ask your physician or nuclear medicine technologist. He or she can tell you everything you need to know about your nuclear MPI test.