Magnetic resonance imaging

Non-invasive diagnostic imaging examination, magnetic resonance imaging has numerous uses.

What is it

Also called nuclear magnetic resonance (MRI or MRI), it is a diagnostic technique introduced in the early eighties, now used in various specialties: from neurology to gastroenterology, from orthopedics to various internist specialties.

Through this diagnostic examination it is possible to acquire images of internal organs and tissues in three dimensions.

This allows to obtain a much higher resolution of the images than that obtainable with an ultrasound, and therefore detailed information on different but extremely close anatomical structures, such as muscles, tendons, cartilage and bone.

Compared to the classic computerized axial tomography (better known by the acronym TAC), in addition to ensuring better visualization, it is also decidedly less invasive and safer: unlike the latter, as well as radiographs and mammograms, magnetic resonance does not use ionizing radiation, but uses magnetic fields similar to those of magnets (at very high intensities) and radiofrequency waves similar to those used for transmissions Television.

How does that work?

For the duration of the procedure (which lasts between 30 and 40 minutes) the patient must remain lying and motionless inside the machine, which is in fact a huge tube-shaped magnet.

The examination is not painful or invasive, but in some patients it can cause some discomfort related to immobility and claustrophobia. Another source of annoyance is often the loud noises produced by the machine during operation. To remedy this, headphones or earplugs are usually provided.

It must be said that today the discomfort of claustrophobia is less in new open equipment (low field) than in high-field magnetic resonance imaging (tunnel). In any case, it is important that those suffering from severe forms of claustrophobia or anxiety, or psychiatric or neurological disorders, report the problem to radiology operators: in some cases pharmacological sedation can be used.

A small discomfort is also linked to a certain sensation of heat in some parts of the body, the perception of pulsations or involuntary contractions of some muscles: all minor problems, which are normal and should not worry.

If these disorders, as well as claustrophobia, during the execution of the procedure should prove to be important and insurmountable, it is always possible to warn the staff by means of a remote control provided to the patient: by pressing it, the operators can be warned and interrupt the examination. Moreover, the staff who maneuver the equipment always has the patient under control (he observes him through a glass or by means of cameras) and therefore has the opportunity to intervene promptly.

Since the examination is based on the production of a magnetic field, it is necessary that nothing metallic is introduced into the resonance room. Therefore on the day of the examination patients should not use cosmetics (as they may contain ferromagnetic powders), they should remove all jewelry and metal hair clips.

Buckles, piercings and dentures, hearing aids, contact lenses, wigs and orthopedic metal prostheses must also be removed. Obviously, the staff will check that the patient does not bring objects such as watches, magnetic cards, mobile phones, coins and anything containing metal with him or her into the room. To avoid inconvenience, the patient is in any case invited to take off all clothes, with the exception of underwear as long as it has no metal parts, and to wear a disposable gown and footwear.

Diagnostic significance

As mentioned, magnetic resonance imaging is used in many clinical areas: neurology, oncology, cardiology, gastroenterology and orthopedics. In the latter case, for example, magnetic resonance imaging is widely used for the diagnosis of knee, shoulder or spine pathologies.

In some contexts, such as in the study of musculoskeletal pathologies as well as central nervous system, spinal cord and brain, this examination is more useful than CT scan.

The latest MRI machines also allow more in-depth investigations in areas such as cardiology and, in gastroenterology, in the study of the organs of the abdomen. In particular, thanks to the “suspended breath” technique, it is possible to overcome the inconvenience linked to involuntary movements of the body (heartbeat, breathing, intestinal peristalsis). In this way it is now possible to obtain a precise vision, not influenced by movement.

Can anyone have an MRI?

There are some conditions that do not allow you to undergo MRI or that make it an examination at least not recommended. Here are the main ones:

1. Pregnancy. During gestation the examination is not contraindicated, although it is best to avoid it in the first 12 weeks, at least if not essential.

2. Pacemakers and implanted equipment. Wearers of cardiac pacemakers or neurostimulators cannot undergo magnetic resonance imaging: the magnetic field or the waves produced by the equipment could alter its functioning.

3. Metal structures. The examination is also forbidden to those who, following surgery, have metal structures such as stents, orthopedic components such as nails and screws, heart valves in the body: the magnetic field produced by the machine could cause a shift of seat. In case of doubt, it may be useful to use a preliminary X-ray to exclude its presence.

4. Metal splinters. Those who have worked as a turner, welder, coachbuilder or similar should pay attention to the possibility of having metal splinters in the body, even without being aware of it. The same goes for those who have been victims of major accidents or explosions: in these cases it is better to inform the operators who can prohibit the examination, especially if these parts are located near vital organs.

5. Tattoos. This is not an absolute ban: it all depends on the size and location of the tattoo and the date of execution. Even in these cases, the doctor will decide how to proceed.

6. Lens prosthesis for cataracts. No absolute ban, even in this case. Prostheses implanted after 1985 tend to be considered safe for resonance. For older prostheses, a certification from the hospital that performed the surgery is required.

7. Intrauterine devices (spiral). There are no contraindications, although a gynecological examination after the MRI is recommended to verify that the device has not moved.

8. Sickle cell anemia. Careful consideration should be made on a case-by-case basis to decide whether or not the test is compatible with this blood disorder as there is a risk of blood clots forming during exposure to the magnetic field.

Contrast media

In some cases the doctor may request that the examination be conducted with the use of a contrast agent. In this case, before execution, the patient is injected into a vein, called paramagnetic, derived from gadolinium.

By distributing itself in blood vessels and organs, it temporarily alters their molecular properties by modifying the images obtained. This technique is useful for visualizing the vessels and lesions of organs, particularly in the case of inflammatory diseases and tumors.

The use of contrast medium during magnetic resonance involves a lengthening of execution times that generally goes from 5 to 20 minutes. Generally the contrast medium is well tolerated, although caution should be exercised in patients who have had previous reactions to paramagnetic media. Although allergic reactions are very rare, in some cases a preparation can be performed in the previous days based on antiallergic drugs.

The only case that can preclude the possibility of an MRI with contrast medium is a rare disease, called systemic nephrogenic fibrosis, linked to the accumulation of gadolinium in patients with severe renal impairment. For this reason, before an MRI scan, it is always required to evaluate the state of renal function with the dosage, by means of a blood sample, of creatininemia. In addition to this examination, no specific preparation is required to perform MRI with contrast method.

The only recommendation for breastfeeding women is to collect and store before the examination the milk necessary for 24 hours after the diagnostic investigation, to be administered with the bottle to avoid the risk that the gadolinium passes to the baby. Instead, it is allowed to take the usual pharmacological therapies according to the indication of your doctor.

However, it should be noted that recently the Italian Medicines Agency (Aifa) has imposed new rules on the use of gadolinium-based paramagnetic means: starting from February 28, the use of some common products based on this substance is suspended in Italy. The decision stems from a review conducted by the European Medicines Agency which confirmed that, following the use of contrast agents, there is an accumulation of small amounts of gadolinium in brain tissues. To date, there is no evidence that gadolinium deposits in the brain cause harm to patients, however as the long-term risks are not known, EMA has recommended that the use of these contrast agents be suspended throughout the European Union with some specific exceptions for use in liver scans.