MRI - Magnetic resonance (exams)

Content

Introduction

Nuclear magnetic resonance, also known as magnetic resonance imaging (MRI), is an imaging technique that exploits the magnetic properties of the nuclei of certain chemical elements. In particular, it is a non-invasive diagnostic technique that uses non-ionizing radiation and is particularly used for soft tissue investigations.

To date, the extensive research conducted has not highlighted any risks to human health and therefore MRI is considered a widely used medical procedure capable of producing detailed images of different parts of the human body.

MRI is currently used for the study of a large number of tumor, cardiological, neurological, infectious and inflammatory diseases. In addition, this technique is also used for minor problems related to traumatic or degenerative pathology, such as the injury of the menisci in the knee or the rotator cuff in the shoulder; for the identification of surgical or radiotherapy plans; to follow the effect of a drug treatment.

Unlike other imaging techniques such as radiographs, computed axial tomography (CT), positron emission tomography (PET), etc., MRI does not use ionizing radiation and is therefore preferred for repeated investigations over a short distance.Furthermore, compared to other imaging techniques, MRI makes the non-bony structures of the body, i.e. soft tissues, such as the brain, spinal cord and nerve endings, muscles, ligaments, tendons, etc. clearly visible.

However, it is important to remember that in many cases MRI cannot replace other techniques and that it is often complementary to other investigations or even useless for diagnostic purposes.

In some cases it may be necessary to use a contrast medium, always non-radioactive, which is administered intravenously after the doctor has evaluated some parameters including renal function, allergies, etc.

The test

The fundamental element of an MRI device is the magnet, which produces a strong static magnetic field (even tens of thousands of times greater than the Earth's magnetic field). The huge magnet is shaped like a tube and has a cavity open to both. the ends. This cavity is large enough to accommodate a bed where the patient is positioned and the part of the body to be examined is positioned in the center of the magnet.

The instrumentation is controlled by a radiologist and by technical personnel specialized in performing MRI investigations. The staff starts and controls the examination in a room other than that in which the patient is located because the sophisticated electronic control and processing equipment they must be placed away from the magnetic field so that they do not suffer interference during operation.

The mechanism underlying the MRI technique exploits the magnetic properties of the nuclei of some chemical elements and in particular of the hydrogen of the water present in the tissues.
At the center of each hydrogen atom there is an even smaller particle called a proton that acts like a very small magnet.When the protons of the nuclei are exposed to a magnetic field of a much higher intensity than the Earth's, they move orienting themselves according to it (for example like a compass needle), acquire energy and remain in this "forced" equilibrium state .
This equilibrium can be altered by a specific radiofrequency pulse which in MRI is supplied through an antenna positioned in the vicinity of the area to be analyzed. After this emission, the protons change their energetic state and subsequently, with different speeds, return to their state of equilibrium (resonance). This resonance can be detected by appropriate receivers and, with a complex electronic apparatus and appropriate software, is processed and transformed into an "image."

The investigation can last from a few minutes to more than an hour. This depends on how much and what information is needed by the physician requesting the examination and by the radiologist to carry out a correct report.

Before scanning

Generally, in order to carry out this type of exam it is not necessary to follow any particular preparation. However, in order to have all the necessary information, it is essential that the patient discusses with their trusted doctor. In addition, before the examination the patient must complete a questionnaire regarding their health status. This helps the medical staff to ensure that the patient carries out the scan safely. Once the questionnaire is completed, they will also be asked to give consent by signing some forms It is important to fill in the questionnaire carefully, discussing with your doctor if you have any doubts.

Since MRI equipment produces strong magnetic fields, it is important not to enter the magnet with metal objects, whether in direct contact with the body or in clothing, such as watches, jewelry, earrings and necklaces, piercings, hearing aids, wigs (some wigs contain traces of metal). For the same reason, it is necessary to inform if you have dental prostheses, artificial heart valves, devices implanted in the ear or eye (cochlear or ocular), battery-operated devices that control the heartbeat (pacemaker), of metal clips inserted following surgery, etc. Any valuables should generally be kept safe.
In some cases it is required to remove cosmetics from the face and eyes.

In order to analyze some tissues and blood vessels in more detail it may be necessary to inject a contrast agent. However, the use of these agents in some patients can be dangerous. Therefore, some tests may be required before MRI is performed. In addition, the patient should report any problems with kidney failure, blood clotting, or particular allergic reactions to staff. The administration of the contrast medium can give a sensation of heat, but you must not be frightened and remain still so as not to invalidate the result.

In general, if MRI with contrast is performed, it may be necessary not to eat or drink up to four hours before the scan and if the examination involves sedation / anesthesia, fasting from solid and liquid foods for at least 6-8 hours is required.

In some cases, special preparations may be required for specific organs to be investigated. Although it is essential to discuss with your doctor, you can generally take your usual personal medications.

Breastfeeding women, if the use of contrast medium is foreseen for the examination, should collect and store the necessary milk before the examination for the 24 hours following the investigation, to avoid the risk that the substance passes to the baby. .

An MRI is a painless procedure, so usually no anesthesia or pain medication is needed. However, if the patient is claustrophobic (unable to stay indoors), they may ask for mild sedation to relax before starting. . In this case he will have to be taken home by a relative or friend (the patient cannot drive). The general anesthetic is given only if the patient is unable to remain still voluntarily.

While scanning

The patient can speak to the staff through an intercom located inside the equipment and will be monitored via a monitor throughout the examination.

In addition, the patient will also have a button available to call for help or simply to draw the attention of the staff. In special cases, a companion may be allowed to stay in the room, especially if the subject is a child, provided that all the compatibility requirements with the magnetic field are met.

Usually the patient will have to wear clothes without metal zippers, closures, buttons, insoles, belts, buckles, bra wires, metal staples applied to clothes brought to the laundry, etc. In some cases it is necessary to wear a hospital gown during the procedure .

To prevent the images from being illegible, it is very important to stay still throughout the measurement. Sometimes you are asked to hold your breath for a short time.

During the examination, the instrument can produce annoying noises, due to physical phenomena intrinsic to the technique. The patient may be equipped with ear plugs or headphones.In some cases it is also possible to listen to music.

After scanning

An MRI exam is usually done through an outpatient procedure, which means the patient will not have to stay in the hospital overnight.
After scanning, you can resume normal activities immediately.

Results

The images produced during the scan will need to be studied by a radiologist (a physician who specializes in interpreting diagnostic imaging) and possibly discussed with other specialists. This means that it is unlikely that the patient will know the results immediately, except for special emergencies.

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