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Magnetic resonance imaging (MRI) is an imaging test that is used to visualize inside of a part of the body, which allows a diagnosis to be made, or the patient’s state of health to be assessed. 

What is Magnetic Resonance Imaging?

Magnetic resonance imaging is a technique that employs a powerful magnet and radiofrequency waves to create a detailed view of the internal structures inside our bodies. The patient lies on a mobile table which then slides inside the scanning equipment.

How does it work?

Unlike radiography and computed tomography (CT), magnetic resonance imaging uses magnets and radiofrequency waves instead of X-rays or radioactive substances.

The signals generated by the magnetic field rebound inside the body and the computer records the different responses returned by each tissue. As such several images can be generated during a single examination.

What is it used for?

Magnetic resonance imaging is used to obtain anatomical and functional images of the human body which subsequently help to reach a diagnosis or to evaluate a patient’s general state of health. The technique is used to assess a wide variety of complaints, from ruptured ligaments to tumours, and is also well-suited to brain and spinal cord examinations.

How is it performed?

During the test, the healthcare professional will help position the patient on a mobile table which is then introduced inside the machine. It is important for the patient to remain perfectly still so that the equipment can capture good quality images. Patients will receive instructions and be under the supervision of healthcare professionals until the test is finished. It may sometimes be necessary to administer a contrast medium into a vein in the arm or hand in order to visualise certain parts of the body in greater detail. Note that the test can last between 20 and 40 minutes.

The healthcare professionals will ask you to sign an informed consent form and, at all times, inform you about the test and answer any questions you may have. If you do not fill in a consent form, then you may be asked to complete a safety questionnaire (between the doctor and the patient) which guarantees there are no contraindications for placing you inside a magnetic field.

Doctors will consider sedation for paediatric examinations or whenever patients do not collaborate.

How do I prepare for an magnetic resonance imaging?

Most cases do not require any special preparation. Certain situations may require the administration of a contrast agent and therefore you should ask the healthcare professional if you need to fast.

It is very important to tell the doctor and/or radiologist if you have a pacemaker fitted as you will not be able to undergo the test. If you have any other type of metal prosthesis, ferromagnetic material or even a dental prosthesis, then you should also report this information so it can be considered before deciding whether the test is appropriate.

You should remove all metal objects before entering the MRI suite (e.g. jewellery, piercings, watch, hair clips and pins, zips, buttons, bank cards, etc.). You should not wear any make-up or nail polish.

Special situations

You may not be able to do the test if you have:

  • a pacemaker
  • brain aneurysm clips
  • certain types of artificial heart valves
  • inner ear (cochlear) implants
  • recently implanted artificial joints
  • certain types of vascular stents

Always tell the healthcare professional or technical personnel if:

  • you are pregnant
  • you are breastfeeding
  • you may be allergic to the contrast agent
  • you suffer from claustrophobia
  • you have severe kidney failure
  • you have previously received a Liver Transplant
  • you have previously undergone surgery

Who performs the test?

The radiology technicians will perform and supervise the test at all times. Although there is a lot of noise, you can talk in the pauses between each image acquisition series. You will also be given a buzzer to call the technician’s attention if necessary.

Who interprets the results?

A doctor specialising in radiology.

What can I expect to feel during the test?

The test is harmless; even if administered a contrast agent you will not feel anything in particular. You may notice a slight feeling of warmth throughout your entire body. Patients should remain very still during the test. You will also wear hearing protection to reduce the sound produced by the equipment.

If you have claustrophobia, then you should report this to the healthcare professional so they may decide how to approach the test. You may be administered a mild sedative or perform the test with an open machine.

Substantiated information by:

Laura Oleaga Zufiría

Published: 20 February 2018
Updated: 22 February 2024


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