Magnetic resonance imaging (MRI)

Cardiac MRI is an imaging procedure that provides doctors with detailed pictures of the heart, including the chambers and valves, without patients having to undergo cardiac catheterisation. The test uses no radiation and therefore is ideal for repeated investigations that are needed in patients with congenital heart disease.

How does it work?

The MRI machine looks like a long, narrow tube. When the patient is placed inside the tube, he or she is surrounded by a magnetic field. The human body is made up of different elements, which can be magnetised. For example, the human body contains a large amount of hydrogen atoms, which can be used for image generating. The MRI machine's magnetic field excites the hydrogen atoms in the body, which in turn creates a small radio signal. A computer reads the radio signal and turns it into an image that can be seen on a computer monitor.

Different types of MRI

A magnetic resonance angiography (MRA) is a type of test that allows the study of blood vessels leading to the heart. It can usually provide doctors with very clear images of the blood vessels without exposing the patient to radiation. In some cases, a harmless dye can be used to make the images even clearer. If a contrast dye is needed, it will be injected (usually in the patient’s arm) for 1–2 minutes, and then more scans will be done.

Procedure

No special preparation is needed before the patient has an MRI.
The MRI machine will surround the patient during the test, and some people can feel closed in or claustrophobic. The patient will have to lie still, and they might be asked to hold their breath briefly while the technician takes pictures of the heart.

Indications

For patients with congenital heart disease or with suspicion of having this disease, MRI is indicated in the following cases:

General cases

• Anatomical or functional assessment in case of further doubts after echocardiographic or angiohaemodynamic study
• Before cardiac catheterisation in complex malformations
• Follow-up studies in case echocardiography does not provide complete information and the catheterisation is considered inappropriate since no vascular pressure or resistance data are needed

Specific cases

• Anomalies of the aortic arch, rings and slings
• Anomalies of the pulmonary arteries and veins
• Shunt lesions like atrial and ventricular septal defects, PDA
• Quantification of heart size and function
• Quantifications of valvular regurgitations
• Assessment of coronary anomalies

Value of the test and limitations

An MRI is a completely painless test. Because the MRI machine uses magnetism, the patient is not exposed to any radiation as they would be with an X-ray machine. MRI cannot be done, however, if the patient has a pacemaker.