A detailed scan of the heart muscle, chambers and blood flow that does not use X-ray radiation.
Cardiac MRI uses a strong magnetic field and radio waves to take detailed pictures of the heart. It is also known as cardiovascular magnetic resonance, usually shortened to CMR.
The scan shows the size and shape of the heart, how well it pumps and what the heart muscle is made of. It can detect inflammation and scar that may not be visible on an echocardiogram.
Cardiac MRI is often helpful when assessing an enlarged, thickened or weakened heart, suspected cardiomyopathy, possible myocarditis, damage after a heart attack, unexplained ECG or echocardiogram changes, congenital conditions, the pericardium and selected aortic problems.
It is not automatically a better version of an echocardiogram or cardiac CT. These scans answer different questions.
CMR measures chamber size, heart-muscle thickness and how much blood the ventricles pump with each beat.
The scan may show swelling, inflammation, fibrosis or scar. Its pattern can help distinguish different causes of heart-muscle injury.
Selected scans include medication stress to assess blood flow. CMR can also show permanently scarred and potentially viable heart muscle.
One of the main strengths of cardiac MRI is its ability to examine the heart muscle itself, sometimes called tissue characterisation. An MRI pattern is not always a diagnosis on its own. The images need to fit with the symptoms, ECG, blood tests, medical history and other scans.
CMR can also assess complex congenital heart conditions, blood flow through the heart and major vessels, the pericardium and selected valve or aortic problems.
You lie on a table that moves into a tunnel-shaped scanner. ECG stickers are placed on the chest so the scanner can time the images to the heartbeat.
The scanner makes loud tapping and knocking sounds, so you are given hearing protection. You can speak to the radiographer throughout and will have a buzzer if you need assistance.
You need to keep still and hold your breath for short periods. Tell the referring clinician and MRI team beforehand if claustrophobia may be a problem.
Some scans use gadolinium-based contrast through a small cannula. It can help show inflammation, scar and blood flow, but is not needed for every scan. The team will check kidney function and any previous contrast reaction.
Because MRI uses a strong magnet, the team must know about pacemakers, defibrillators, medical devices, previous operations involving metal, metal fragments and electronic implants. Many modern cardiac devices can be scanned under controlled conditions, but the exact device and leads must be checked first.
The report may describe chamber size, left and right ventricular pumping function, heart-muscle thickness and movement, inflammation, fibrosis or scar, blood flow if this was assessed, and abnormalities involving the pericardium, aorta or congenital anatomy.
Image quality can be reduced by an irregular heartbeat, movement or difficulty holding your breath. Some implants may prevent scanning or require a specialist pathway.
A normal cardiac MRI can be reassuring, but it does not exclude every heart condition or record intermittent rhythm problems. A small finding may have little significance in one patient but matter in another, so the report must be interpreted in clinical context.
Often the first scan for valves, chamber size and pumping function, and may provide all the information needed.
Usually better for showing plaque and narrowing inside the coronary arteries.
Stress imaging may be used when the question is whether blood flow becomes insufficient under stress.
Dr Mark Cassar achieved Level 3 accreditation in cardiovascular magnetic resonance and reports cardiac MRI in clinical practice. He interprets the images alongside the patient’s symptoms, examination, ECG, blood tests and previous scans.
This matters because technical phrases in an MRI report can sound more definite than they are. A small area of scar after a previous heart attack, a pattern suggesting inflammation and an uncertain finding in an otherwise normal heart require different responses.
The clinical question is whether the scan explains the problem and whether the result should change care. The next step may be reassurance, follow-up imaging, treatment, family assessment or another investigation. The heart scans compared guide explains how CMR differs from other tests.
Yes. CMR stands for cardiovascular magnetic resonance. Cardiac MRI is the more familiar term for the same type of scan.
No. It uses a magnetic field and radio waves rather than X-rays, so there is no exposure to ionising radiation.
Not always. Some scans use gadolinium-based contrast to assess inflammation, scar or blood flow. The scanning team decides whether it is needed and suitable.
Possibly. Many modern devices can be scanned under defined conditions, but the exact device and leads must be checked beforehand.
A standard cardiac MRI does not show the inside of the coronary arteries as directly as CTCA. It can show previous heart-muscle damage, and stress CMR can assess blood flow.
Claustrophobia can make the scan difficult, and an irregular rhythm may reduce image quality. Tell the referring clinician and MRI service in advance.
If cardiac MRI has been suggested, or you would like an existing result explained in context, Dr Mark Cassar can review the clinical question and advise on appropriate next steps.
