Radionuclide tests are considered safe. However, during the test you will be exposed to some radiation.
Every day we are exposed to a small amount of radiation which occurs naturally in the environment. Our risk of cancer can increase if we're exposed to plenty of radiation, but the amounts used in these tests are small.
Your doctor will only suggest you have the test if he or she feels it's really necessary, and if its benefits outweigh any risks.
Types of radionuclide tests
There are two types of radionuclide tests: a myocardial perfusion scan and a computerised tomography (CT) scan. There are lots of different names for these tests.
The names we mention below are some of the more common ones. If the name of your test isn't mentioned here, check with your doctor or radiographer what your test involves.
Myocardial perfusion scan
This is also known as a thallium scan, MIBI scan, MPS or technetium scan. A camera takes pictures to:
- look at the pumping action of your heart
- look at the flow of blood to your heart muscle
- see how your heart functions when it has to work harder - for example, when you're being more active, or
- help diagnose coronary heart disease (CHD).
What happens during a myocardial perfusion scan?
There are two parts to the test - stress and rest.
For the stress part, you will be given an injection of a small amount of isotope (radioactive substance) and be asked to exercise on an exercise bike or treadmill. Or, you may be given a drug that stimulates your heart to beat faster (this is useful if you cannot do much exercise).
A large camera, positioned close to your chest, picks up the gamma rays sent out by the isotope as it passes through your heart. The camera takes pictures of the different parts of your heart.
For the rest part, you will be given a small amount of isotope while you're resting. The camera will then take the same sort of pictures as before.
Various isotopes are used, including technetium and thallium.
During the test, the staff will monitor your heart rate and check your blood pressure.
When might I be offered this test?
You may be offered this test if you haven't previously been diagnosed with CHD and you go to A&E with chest pain. If the doctors think it's very likely that your chest pain is caused by CHD this test may be used to confirm if you have CHD.
You may also be offered this test if you have CHD and your doctor wants to find out if you'll benefit from having a procedure such as an angioplasty or coronary bypass graft.
CT scans (computerised tomography)
A CT scan is also known as a CAT scan. It's a sophisticated type of X-ray, which can produce detailed images of your heart. It can look at:
- the pumping action of your heart
- the structure of your heart - its muscle, valves and coronary arteries (the arteries that supply your heart muscle with blood and oxygen)
- the flow of blood through your heart and your coronary arteries.
A CT scan can see how well your heart is working and can help to diagnose various heart conditions such as an enlarged heart, heart valve problems or coronary heart disease (CHD).
This test can also measure how much calcium there is in your coronary arteries - this is called a coronary calcium scan. The higher your calcium score, the higher your risk of having CHD. If you have a high or medium calcium score, you may need further tests. If you have a low calcium score, it's unlikely that you have CHD.
What happens during the test?
You will need to lie on a bed under the CT scanner. Usually, at the start of the scan, some dye (called a contrast) will be injected into your arm. This allows the camera to easily see the heart's structure and blood flow. This may cause a warm, flushing sensation which some people find unpleasant.
You may be given a medicine to slow your heart rate down. This is to ensure that the doctors are able to get the best possible image of your heart.
How long the test is, depends on the type of scanner used and why you are having the scan.
When might I be offered this test?
You may be offered a CT scan if doctors are not entirely sure that your chest pain is caused by CHD. So this test is often used to make sure that you don't have CHD.
If your doctor is reasonably sure that you do have CHD, he or she is more likely to offer you a myocardial perfusion scan or a conventional angiogram.