Cardiac MRI uses a magnetic field rather than X-rays. Its particular strength is tissue characterisation — it can say something about the state of the heart muscle itself, not only its shape and movement.

That makes it useful when the question is about the muscle: whether it is scarred, inflamed, thickened, infiltrated, or has been affected by a previous event. It is also the reference standard for measuring the volumes and function of both ventricles.

It is a longer scan than CT, usually 45 to 60 minutes, and it requires lying still inside a tube while the scanner makes loud knocking noises. Contrast is often given through a cannula in the arm.

MRI is not suitable for everyone. Some implanted devices and metal fragments are a contraindication, and severe claustrophobia can make the scan difficult. This is checked carefully beforehand.

What to expect

A detailed safety questionnaire is completed before the scan, covering implants, devices and previous surgery.
The scan usually takes 45 to 60 minutes and you will be asked to hold your breath at intervals.
The scanner is loud. Ear protection is provided.
Contrast is often given through a cannula in the arm.