To obtain images of the internal structures of the human body nuclear magnetic resonance (MRI) is used. This medical diagnostic procedure uses radio waves that pass through the area of the body to be studied and that are subjected to the effect of a magnetic field during the exploration. Allows to obtain high quality and detailed images, which helps the doctor to detect variations in the shape, consistency, and size of the organs, and this can greatly facilitate the diagnosis.
What does it consist of?
MRI uses a powerful magnetic field, radiofrequency waves, and a computer program that allows the captured signals to be transformed into a series of very detailed images of the organs, soft tissues, bones, and practically the rest of the internal structures of the body. Unlike CT, MRI does not use ionizing radiation, that is, X-rays. Radiofrequency waves realign the hydrogen atoms in the body, without causing any chemical changes in the tissues. As the hydrogen atoms return to their usual position, they give off different amounts of energy that varies depending on the type of body tissue they came from. This energy is captured and creates, by means of a computer program, an image of the scanned tissues.
How it is performed?
Performing a nuclear magnetic resonance may be indicated when other simpler diagnostic tests, such as an x-ray or ultrasound, did not allow a definitive diagnosis. NMR is very useful to study:
- Tumor masses and cysts.
- Soft tissue tears.
- Heart attacks.
- Intracranial or cardiac lesions.
- Large arterial vessels.
- Glands (pancreas, thyroid, adrenals).
- Abdominal organs (liver, bile ducts, spleen, kidneys).
- Soft structures of the joints and muscles (tendons, ligaments).
To perform a nuclear magnetic resonance, the patient’s jewelry and metal objects should be removed or that have magnetic stripes like credit cards or phones. Carrying out the test involves subjecting the patient to a magnetic field, therefore, any metallic object can cause alterations in the capture of the images.
The patient must remain relaxed and motionless all the time. Performing an MRI takes longer than performing a CT scan. The examination takes between three-quarters of an hour and just over an hour, depending on the anatomical structure studied. Sometimes it may be necessary to sedate the patient to improve relaxation. Loud noises such as knocking and clanking are heard during the test. The patient is provided with hearing protection to muffle the sound of the examination.
What if I suffer from claustrophobia or it anguishes me to be locked up?
It is important that if you suffer from claustrophobia, inform the medical team in advance since the patient must be immobile for a long time inside the MRI machine, which is a closed structure. Today, however, there are open MRI machines that make performing the test less burdensome. In any case, the patient always has a button at hand that he can press to temporarily stop the test if necessary.
WHEN IS CONTRAST INJECTED?
Sometimes it is necessary to inject contrast to improve the images. The contrast material most commonly used for an MRI exam contains a metal called gadolinium, which can be used in patients with allergies to iodinated contrast. It is much less common for a patient to have an allergy to the gadolinium-based contrast material used for MRI than to the iodinated contrast used for CT. However, even if the patient had an allergy to the gadolinium contrast, said contrast could be used after the administration of appropriate medication.
In the case of women…
Women must always inform of the possibility of being pregnant. MRI has been used since the 1980s without any report of a harmful effect on pregnant women or their babies. However, because the fetus will be in a strong magnetic field, pregnant women should not have this exam during the first three to four months of pregnancy, unless it is assumed that the potential benefit of performing MRI outweighs outweigh the possible risks. The use of gadolinium contrast, however, is contraindicated in pregnant women unless absolutely necessary for medical treatment.
Is it a safe procedure?
In most cases, the MRI exam is safe for patients with metal implants, except for a few types. An MRI cannot be performed if you are a carrier of:
- Cochlear (ear) implant.
- Some types of clips are used for brain aneurysms.
- Some types of coils are placed inside blood vessels.
- Almost all defibrillators and cardiac pacemakers.
Some implants may interfere with the exam or pose a potential risk when subjected to the powerful magnet of the MRI. Some implanted devices require a short period of time after placement(about six weeks) before an MRI can be done safely. Some of these implants are:
- Artificial heart valves.
- Implantable access routes to administer medications (port-a-cath).
- Artificial limbs or metal prostheses for the joints.
- Implantable nerve stimulators.
- Metal clips, screws, plates, stents, or surgical staples.
Magnetic resonance imaging is, therefore, a safe test that allows us to obtain a lot of information. However, as always, it should be the doctor who decides if it is the most appropriate test for the problem to be studied. Also, MRI is never an emergency test, unless acute spinal cord compression is thought to be present.