Cardiac MRI (CMR) at Shrewsbury Hospital

What is a cardiac MRI?

A cardiac MRI, also called a CMR scan, uses strong magnets and radio waves to take detailed pictures of your heart. It's a painless, non-invasive scan that shows your heart's chambers, valves and muscles, and it doesn't use any radiation.

Why might I need a cardiac MRI?

Your doctor may suggest this scan:

• to find out why you're having symptoms such as chest pain, breathlessness or fainting
• to diagnose conditions such as congenital heart disease, cardiomyopathy (heart muscle disease), heart valve disease, or growths (tumours) in the heart
• to check for damage after a heart attack, or areas where blood flow to the heart muscle is reduced
• to help plan treatment, or see how well an existing treatment is working.

What are the benefits of a cardiac MRI?

• It doesn't use any radiation, unlike a CT scan or X-ray
• It gives very detailed, high-quality images from different angles, which can sometimes show disease more clearly than other scans
• It's painless and generally very safe
• It can show the structure and function of your heart together, including chambers, valves, muscle and blood flow, all from one scan.

Are there different types of cardiac MRI?

A standard scan gives a structural assessment, an overview of your heart's chambers, valves and major vessels.

Your doctor might also request a stress perfusion scan, where you're given medicine through a vein to make your heart beat faster, similar to exercising, so your team can see how it copes under pressure.

A viability scan uses contrast dye to show which areas of heart muscle have a healthy blood supply and which have scarring, for example after a heart attack.

How do I prepare for a cardiac MRI?

In the days before your scan:

• tell your team about any medical implants, such as a pacemaker, defibrillator, heart valve replacement, or any other metal in your body, as the strong magnet can affect these
• let them know if you're pregnant, have kidney problems, or weigh more than around 102kg (16 stone), since these can affect how the scan is done
• if you're having a stress perfusion scan, avoid caffeine for 24 hours beforehand, as it can interfere with the medication used
• on the day, remove jewellery, watches, hearing aids and anything metal, and leave electronic devices and cards in a locker. You can usually eat, drink and take your normal medication as usual
• if you feel anxious in small spaces, mention this in advance. You may be offered a mild sedative, in which case you'll need someone to drive you home afterwards.

What happens during a cardiac MRI?

1. You lie on a bed that slides into a tunnel-shaped scanner, which is open at both ends.
2. Sticky pads may be placed on your chest to track your heartbeat, and a belt around your chest to monitor your breathing.
3. If you're having contrast dye, this is given through a small tube (cannula) in your arm. For a stress scan, medicine to speed up your heart rate is given the same way.
4. You'll need to lie still and may be asked to hold your breath for short periods, since movement can blur the images.
5. The scanner is loud, with tapping or knocking sounds. You can usually have earplugs or listen to music, and there's a buzzer to alert the team if you need them.
6. The whole scan can take up to 90 minutes, depending on how many images are needed.

What happens after a cardiac MRI?

You can usually go home and return to your normal activities straight away. If you had contrast dye, drink plenty of water for 24 hours afterwards to help flush it out of your system.

If you were given a sedative, you'll need someone to drive you home, and you shouldn't drive, drink alcohol or operate machinery for 24 hours.

The doctor who arranged your scan will usually discuss the results with you once they're ready, and a report should be sent to your GP.

What are the risks of a cardiac MRI?

• A heart MRI itself carries no significant risk and doesn't use radiation, though the strong magnetic field means it may not be suitable if you have certain metal implants or devices
• If you have contrast dye, you might notice a metallic taste, or some bruising where the needle went in; rarely, people have nausea, a headache or an allergic reaction
• If you're having a stress perfusion scan, the medication used to speed up your heart can cause temporary chest tightness, breathlessness or a flushing feeling, which settles quickly once it's stopped
• If you had a sedative, you may feel drowsy for a while afterwards.