What is an MRI scan?

Magnetic resonance imaging (MRI) is increasingly used to diagnose and give information on heart conditions. Professor John Greenwood tells Senior Cardiac Nurse Emily McGrath what a cardiac MRI scan involves.

Cardiac MRI illustration

Why would I have a cardiac MRI scan?

We use cardiac MRI to diagnose a wide range of heart conditions. These include coronary heart disease, congenital heart disease (in children and adults), inherited heart conditions (such as hypertrophic cardiomyopathy or dilated cardiomyopathy), heart valve disease and cardiac tumours.

Cardiac MRI gives good information about the severity of a particular heart condition and helps identify how the person is likely to do in the future

There is increasingly strong evidence that cardiac MRI is very good for complex cases and for diagnosing conditions where other tests have been ambiguous. It provides high-resolution images and can give very accurate measurements of the heart. It is also very safe, which is particularly important as some patients, such as those with complex congenital heart disease, need multiple scans over time.

We know from BHF-funded research that cardiac MRI is a more reliable diagnostic test than some traditional tests. So it can be a very cost-effective test for the NHS. It also gives good information about the severity of a particular heart condition and helps identify how the person is likely to do in the future. This can help with planning medical or surgical treatments.

Will I have an echocardiogram beforehand?

Typically, yes, but not in all cases. Echocardiogram is a quick, reliable and portable test. If it picks up something more complex, or the imaging is unclear, then patients may be referred for cardiac MRI. Increasingly though, cardiac MRI is the first and only test that needs to be done.

Is cardiac MRI becoming more common?

Yes. Most UK hospitals now have access to cardiac MRI, and the number of scans being done is growing at around 15–20 per cent per year. It’s been growing at that rate for about a decade.

What does an MRI scan involve?

The scanner is a large machine with a hole in the middle. You will lie down on a table and go inside. It can be a bit noisy, so we give patients headphones and they can listen to music while they are inside. You will usually be asked to hold your breath several times during the test, so images can be taken while your chest is still.

The scan could be as short as 15 minutes or up to an hour, depending on the type of problem being addressed.

Do I need to do anything to prepare?

Most UK hospitals now have access to cardiac MRI, and the number of scans being done is growing

No. We just need to check if patients have any implanted devices (such as pacemakers or ICDs) or metalwork in their body. Most devices are now MRI compatible – it is usually only older devices that cause a problem, so we check the make and model number. Having metal in your body doesn’t necessarily mean you can’t have an MRI, but it’s important we know about it so we can avoid any risks and ensure it won’t affect the scan quality. You need to remove metal objects like watches, belts and jewellery and wear a hospital gown for the procedure.

Will an MRI scan hurt?

You might feel a prick in your wrist or hand if we need to inject dye, but otherwise no.

Professor John Greenwood with an MRI scanner

Professor John Greenwood with an MRI scanner

What are the risks around MRI scans?

Mainly around implanted devices and metalwork (see above). MRI scans use an extremely strong magnetic field, which can move iron-containing objects with great force. That’s why it’s important to tell us about any metal objects in your body. If you’re not sure, we can do an X-ray to check.

There are potential risks around the contrast agent (dye) that is sometimes used, but this is only if you have kidney problems, as your kidneys need to remove the dye from your body. So you’ll have a blood test for kidney function before the scan. We typically reduce the dose or avoid it altogether in patients who have severe kidney problems.

Is an MRI scan safe in pregnancy?

There are no known risks, but we usually avoid MRI in the first trimester, just to be on the safe side. In fact, there are published cases of MRI being used on babies in the womb. In pregnant or breast-feeding women we try to avoid using a contrast agent.

Is there anyone that this test wouldn’t be suitable for?

It might not be suitable for those who are extremely obese (if they are unable to fit inside the scanner), very claustrophobic patients or those with non-MRI compatible devices in their body – but this is fairly unusual.

Cardiac MRI is now being used in clinical trials around the world to improve patient diagnosis and test new drugs and medical procedures

Will I need further tests after my MRI scan?

That depends on the condition that you have. Often, you will have had a variety of other tests already, so you may not need any other imaging tests to make the diagnosis. However, you may need more tests to monitor your condition.

What are the latest developments in MRI scanning?

The manufacturers are making MRI scanners that can scan much faster thanks to advances in computer software. This will reduce or eliminate the need for you to keep holding your breath while inside the scanner. Because MRI images provide such exquisite detail, cardiac MRI is now being used in clinical trials around the world to improve patient diagnosis and test new drugs and medical procedures. 

Professor John Greenwood

  • Professor of Cardiology, University of Leeds and Consultant Cardiologist, Leeds Teaching Hospitals NHS Trust.
  • Researches diagnosis and treatment of stable and unstable coronary artery disease, especially involving cardiac MRI.
  • Led BHF-funded CE-MARC study 2006–12, to see whether cardiac MRI could improve the diagnosis of patients with suspected coronary heart disease.
  • Led BHF-funded CE-MARC-2 clinical trial 2012–17, to see if cardiac MRI could improve the management of patients with suspected coronary heart disease.

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