Magnetic resonance imaging (MRI) or nuclear magnetic resonance (MRI) is a diagnostic technique that allows you to view the inside of the body through detailed images. The technique, which uses magnetic fields and radio waves, does not expose the patient to any type of ionizing radiation.
The magnetic resonance with a contrast liquid (MRI with contrast medium) involves the injection of a particular substance into a vein: it is a liquid that is distributed in the internal organs, temporarily altering their molecular properties within the magnetic field. In this way, the part of the body to be examined can be visualized highlighting the tissue and vascularity differences.
The functioning of magnetic resonance is based on the principles of quantum mechanics: simplifying the concept, atomic nuclei can be compared to many small magnets which, in the presence of an external magnetic field, tend to arrange themselves along a preferential direction (the magnetic quantum number identifies which and how many are the possible orientations when the atom is placed in a magnetic field). If radio waves are emitted, the nuclei undergo temporary changes in position: in this transitory phase, the atoms emit signals picked up by an electronic detector and transmitted to a computer, which analyzes and processes them. Since not all atomic nuclei take the same time to return to their initial position,
resonance Open magnetic resonance is performed by means of a device in which the inside of the magnet consists of a large opening: this, in addition to allowing wider movements, allows you to have a vision of the outside and not to feel forced into a cramped space. In this way, it is much easier to carry out MRI to some categories of uncomfortable patients with the use of traditional resonance imaging (closed tunnel): overweight people, the elderly, children, subjects suffering from claustrophobia.
resonance The closed magnetic resonance (the traditional one) is, instead, performed by means of a closed magnetic resonance machine, with a tunnel-shaped structure.
resonance The functional magnetic resonance (fMRI) is a particular type of magnetic resonance used, in the neuroradiological field, to detect which brain areas are activated during the performance of a certain task (speaking, reading, thinking, making a movement). The technique allows verifying whether, in or near a brain lesion, an important functional activity persists, in order to be able to preserve it. It is used for both clinical and research purposes.
Magnetic resonance is used for the diagnosis of a great variety of pathologies: the technique allows, in fact, to visualize the skeleton, the joints, and the internal organs. The quality of the results makes it possible to evaluate details that are not detectable with another diagnostic technique. For example, with the MRI exam, it is possible to investigate the state of hydration of the intervertebral discs, study the vascularization of the tissues, evaluate the health of the joints and diagnose, with considerable precision, neurological diseases and some cancers.
Most used types
Magnetic resonance imaging is used in many fields: neurosurgery, neurology, oncology, trauma, cardiology, orthopedics, gastroenterology. The most used types of MRI are:
- MRI of each joint of the upper limb (shoulder, elbow, wrist, and hand) and lower limb (hip, knee, ankle, and foot)
- MRI of the temporomandibular joints,
- MRI of the brain,
- intracranial vascular magnetic resonance, always without contrast medium (MRI of the brain)
- vascular magnetic resonance of the extracranial areas, always with contrast medium
- chest MRI,
- MRI of the pelvis,
- MRI of each skeletal segment,
- cardiac magnetic resonance,
- MRI of the abdomen (upper, lower, or complete),
- MRI of the cervical, dorsal, lumbosacral spine,
- massive facial MRI,
- MRI of the breast,
- MRI of the neck,
- magnetic resonance with cholangiography technique (MR-cholangiography),
- magnetic resonance with urographic technique (Uro-MRI),
- multiparametric magnetic resonance imaging of the prostate.
Magnetic resonance imaging is performed with the use of state-of-the-art machinery, which uses magnetic waves and radio waves. It is a non-invasive exam.
MRI usually does not require adherence to special diets or fasting (regardless of the part of the body to be examined). All the drugs that are usually used can also be taken. The doctor can provide preventive treatment to avoid risky reactions in cases of allergic subjects who must undergo an examination with contrast medium or in other specific cases.
In the preparation phase, the patient is asked to take off objects or clothing with metal parts (such as bags, belts, jewelry, piercings, hair clips, shoes, wallet), contact lenses, hearing aids. It is not allowed to bring mobile phones, credit cards, and magnetic cards which could interfere with the investigation tool.
The procedure for carrying out the resonance examination requires that the patient is made to lie down on a bed, then positioned between the poles of the magnet through electronic control. During the examination, the patient is not required to collaborate in particular, other than to relax and notify the staff (using special tools) in case of discomfort. Special earphones are provided to protect against loud and dry noises caused by the emission of radio waves. During the examination, it is normal to feel a sensation of heating in some parts of the body (to be reported to operators only if it becomes excessive). It is also possible that the magnetic field generated by the machinery, stimulating the patient’s nerve cells, causes involuntary contractions or a pulsating sensation in some muscles:
The duration of the MRI exam depends on the extent of the part of the body to be examined: on average, it ranges from 20 to 30 minutes and can even reach 40-45 minutes. In fact, many patients may find it difficult to remain motionless all the time (a necessary condition for the exam to be successful). In the post-examination phase (unless otherwise indicated by the staff), an observation period is not necessary and normal activities can be resumed immediately (except for breastfeeding women, if subjected to examination by means of contrast).
Pain on MRI: Performing an MRI does not cause pain. Only the small puncture required by the eventual injection of a contrast medium can cause slight discomfort.
When to do
The exam, therefore, allows us to explore different areas, organs, and districts of our body. But when should the magnetic resonance be done? Usually, this diagnostic technique is used in cases of:
- suspected changes in the spine (sciatica, herniated disc, health of the intervertebral discs);
- pathologies of the gastrointestinal system;
- pathologies of the muscular and osteoarticular apparatus;
- pathologies of the central and peripheral nervous system;
- pathologies of the urogenital area;
- pathologies of the cardiovascular system;
- respiratory system diseases (rare use);
- pathologies of the mammary glands.
A medical radiology technician (TSRM) performs the magnetic resonance under the direction of a specialist in Diagnostic Imaging (medical radiologist) who will subsequently acquire the exam and draw up the report.
The MRI images are displayed on a computer monitor and used by the specialist for diagnosis, which is transcribed in the report.
The results of the magnetic resonance imaging (written report and images on computer support) are delivered to the patient a few days after the examination.
Risks, side effects, and contraindications
MRI is a harmless test: only in some cases (such as in pregnancy) can it be considered potentially harmful and is used only after careful evaluation of the risks/benefits.
Risks, side effects, and contraindications: during pregnancy, magnetic resonance imaging is contraindicated or should only be performed in cases of absolute necessity, especially in the first 12 weeks. When it is necessary to inject a contrast agent, breastfeeding women should collect and store the necessary milk for 24 hours after the MRI before the examination.
Patients with cardiac pacemakers, neurostimulators, metal structures of different types (prostheses, screws, heart valves, metal preparations located near vital organs) inserted in the body following major surgical interventions cannot undergo magnetic resonance imaging: prevent the magnetic field from causing it to move to another location, altering its operation. Women who make use of use of intrauterine contraceptive means, such as the IUD, must ensure that the device has not been moved under the effect of the magnetic fields produced during the examination. The only possible risk during MRI is an allergic reaction to the substance possibly used as a contrast medium. The allergy can manifest itself with mild symptoms (nausea, vomiting, and itching) or, in exceptional cases, can trigger more serious reactions. If you have experienced such allergic reactions in the past or if you have severe kidney dysfunction, it is advisable to notify staff. Side effects are infrequent.
The absence of ionizing radiation allows the repetition of the exam even after a short time.