Focus on: CT scans of the heart
Computerised tomography (CT) has been around since the 1970s. There are two ways in which a CT scan can be used for the heart – one is a CT coronary angiogram and the other is a CT calcium score.
A CT scan produces multiple images of the heart from different angles, which the doctor can then see on a computer screen. The images are picked up using detectors. The greater the number of detectors – the UK’s most commonly used version has 64 – the clearer the image and the more useful it is in helping the doctor to make a diagnosis.
CT coronary angiogram
What is it?
A CT coronary angiogram is used to measure the blood flow through the coronary arteries. Similar to a conventional coronary angiogram, a CT coronary angiogram involves injecting an iodine-based dye into your bloodstream to highlight your blood vessels.
However, unlike the traditional angiogram, which is a sophisticated x-ray of the arteries, the dye is injected into a small vein in your arm rather than an artery in your groin. You may also be given some medication to slow down your heartbeat, making it easier to take images.
Discover what to expect in a cath lab, where angiograms are carried out.
When you would have one
The CT coronary angiogram is useful if your cardiologist thinks that it’s unlikely that you have coronary heart disease but he or she can’t explain what’s causing your symptoms. So it’s often used to out rule coronary heart disease rather than to confirm it. It can also be useful if you have heart failure but you doctor doesn’t know why.
If your doctor thinks you do have coronary heart disease, you’ll be more likely to have a traditional angiogram.
Another reason you may need a CT coronary angiogram is if your doctor suspects you may have an abnormality in the structure of your heart.
CT calcium score
What is it?
A CT scan can also measure the amount of calcified, or hardened, plaques in the arteries, which is usually explained as a calcium score of low, moderate or high. Unlike a CT angiogram, a calcium score doesn’t involve a dye.
When you would have one
As with the CT coronary angiogram, it’s often used to rule out coronary heart disease. A low calcium score is useful because it indicates that it’s highly unlikely that you have coronary heart disease.
However, a moderate or high score isn’t that useful as sometimes moderate or high calcium plaques don’t cause problems and there’s no evidence that treating people with these scores has any benefit.
In a nutshell, a CT calcium score is useful when the doctor can’t explain what’s causing the symptoms but thinks you’re unlikely to have coronary heart disease.
You may be given a calcium score if you’re not suitable for a CT angiogram (see Who shouldn’t have a CT scan, below). It’s also used a lot in private screening because it’s cheap, quick and simple to do.
Who shouldn’t have a CT scan
Unlike the MRI scan, CT scans expose you to radiation, so they aren’t suitable for pregnant women.
The CT angiogram may not be suitable for patients with kidney problems because the dye can worsen kidney function. It’s also not suitable for anyone who’s allergic to the dye or for anyone with severe asthma as the dye can cause narrowing of airways.
Because of the radiation, it should be carried out only when really necessary.
What to expect
If you’re having the CT angiogram, the dye will be injected into your arteries by a small needle inserted at the level of your elbow or in the back of your hand.
For both scans, you’ll be asked to lie on a narrow bed, which is then moved inside the scanner. The scanner is shaped a bit like a doughnut in that it’s a large round hole through which the bed is moved until the scanner is over your chest with your head, shoulders and legs sticking out. You’ll be asked to lie still and hold your breath for a few seconds at a time. This is a pain-free test that will last for less than 10 minutes.