Magnetic resonance imaging (MRI) is a modern non-invasive technique that allows you to visualize the internal structures of the body. It is based on the effect of nuclear magnetic resonance – the reaction of atomic nuclei to the impact of electromagnetic waves in a magnetic field. It makes it possible to obtain a three-dimensional image of any tissues of the human body. It is widely used in various fields of medicine: gastroenterology, pulmonology, cardiology, neurology, otolaryngology, mammology, gynecology, etc. Due to its high information content, safety and reasonable price, MRI occupies a leading position in the list of techniques used to diagnose diseases and pathological conditions of various organs and systems.
The date of the creation of MRI is traditionally considered to be 1973, when the American physicist and radiologist P. Lauterbourg published an article on this topic. However, the history of MRI began much earlier. In the 40s of the twentieth century, Americans F. Bloch and R. Purcell independently described the phenomenon of nuclear magnetic resonance. In the early 50s, both scientists received the Nobel Prize for their discoveries in physics. In 1960, the Soviet military applied for a patent describing an analogue of an MRI machine, but the application was rejected “for unrealizability”.
After the publication of the Lottery article, MRI began to develop rapidly. A little later, P. Mansfield carried out work on improving image acquisition algorithms. In 1977, the American scientist R. Damadian created the first device for MRI studies and tested it. In American clinics, the first MRI machines appeared in the 80s of the last century. By the beginning of the 90s, there were already about 6 thousand such devices in the world.
Currently, MRI is a medical technique without which it is impossible to imagine modern diagnostics of diseases of the abdominal cavity, joints, brain, blood vessels, spine, spinal cord, kidneys, retroperitoneal space, female genital organs and other anatomical structures. MRI makes it possible to detect even minor changes characteristic of the early stages of diseases, assess the structure of organs, measure blood flow velocity, determine the activity of various parts of the brain, carry out precise localization of pathological foci, etc.
Principles of visualization
The MRI is based on the phenomenon of nuclear magnetic resonance. The nuclei of chemical elements are peculiar magnets that rotate rapidly around their axis. When entering an external magnetic field, the axes of rotation of the nuclei shift in a certain way, the nuclei begin to rotate in accordance with the direction of the lines of force of this field. This phenomenon is called a procession. When irradiated with radio waves of a certain frequency (coinciding with the frequency of the procession) the nuclei absorb the energy of radio waves.
When the irradiation ceases, the nuclei return to their normal state, the absorbed energy is released, creating electromagnetic vibrations recorded using a special device. The MRI machine registers the energy released by the nuclei of hydrogen atoms. This makes it possible to detect any changes in the concentration of water in the tissues of the body and, thus, obtain images of almost any organs. Certain limitations during MRI arise when trying to visualize tissues with a low water content (bones, bronchoalveolar structures) – in such cases, the images are not informative enough.
Types of MRI
Taking into account the studied area , the following types of MRI can be distinguished:
- MRI of the head (brain, pituitary gland and paranasal sinuses).
- MRI of the chest organs (lungs and heart).
- MRI of the abdominal cavity and retroperitoneal space (pancreas, liver, biliary tract, kidneys, adrenal glands and other organs located in this area).
- MRI of the pelvic organs (urinary tract, prostate and female genital organs).
- MRI of the musculoskeletal system (spine, bones and joints).
- MRI of soft tissues, including mammary glands, soft tissues of the neck (salivary glands, thyroid gland, larynx, lymph nodes and other structures), muscles and fatty tissue of various areas of the human body.
- Vascular MRI (cerebral vessels, limb vessels, mesenteric vessels and lymphatic system).
- MRI of the whole body. It is usually used at the stage of diagnostic search in case of suspected metastatic lesion of various organs and systems.
MRI can be performed both without the use of, and with the use of a contrast agent. In addition, there are special techniques that allow us to assess the temperature of tissues, the movement of intracellular fluid, the functional activity of the brain areas responsible for speech, movement, vision, memory.
MRI is usually used at the final stage of diagnosis, after radiography and other first-line diagnostic tests. MRI is used to clarify the diagnosis, differential diagnosis, accurate assessment of the severity and prevalence of pathological changes, preparation of a conservative therapy plan, determination of the need and scope of surgical intervention, as well as dynamic monitoring during treatment and in the long term.
MRI of the head is prescribed to study bones, superficial soft tissues and intracranial structures. The technique is used to detect pathological changes in the brain, pituitary gland, intracranial vessels and nerves, ENT organs, paranasal sinuses and soft tissues of the head. MRI is used in the diagnosis of congenital anomalies, inflammatory processes, primary and secondary oncological lesions, traumatic injuries, diseases of the inner ear, eye pathology, etc. The procedure can be performed with or without contrast.
MRI of the chest organs is used in the study of the structure of the heart, lungs, trachea, large vessels and bronchi, pleural cavity, esophagus, thymus gland and lymph nodes of the mediastinum. Indications for MRI are myocardial and pericardial lesions, vascular disorders, inflammatory processes, cysts and tumors of the thoracic and mediastinal organs. MRI can be performed with or without the use of a contrast agent. It is uninformative in the study of alveolar tissue.
MRI of the abdominal cavity and retroperitoneal space is prescribed to study the structure of the pancreas, liver, biliary tract, intestines, spleen, kidneys, adrenal glands, mesenteric vessels, lymph nodes and other structures. Indications for MRI are developmental abnormalities, inflammatory diseases, traumatic injuries, gallstone disease, urolithiasis, primary tumors, metastatic neoplasms, other diseases and pathological conditions.
Pelvic MRI is used in the study of the rectum, ureters, bladder, lymph nodes, intrabasic fiber, prostate gland in men, ovaries, uterus and fallopian tubes in women. Indications for the study are malformations, traumatic injuries, inflammatory diseases, volumetric processes, stones in the bladder and ureters. MRI does not provide radiation load on the body, so it can be used to diagnose diseases of the reproductive system even during gestation.
MRI of the musculoskeletal system is prescribed for the study of bone and cartilage structures, muscles, ligaments, joint capsules and synovial membranes of various anatomical zones, including joints, bones, a certain part of the vertebral column or the entire spine. MRI can diagnose a wide range of developmental abnormalities, traumatic injuries, degenerative-dystrophic diseases, as well as benign and malignant lesions of bones and joints.
Vascular MRI is used in the study of cerebral vessels, peripheral vessels, vessels involved in the blood supply to internal organs, as well as the lymphatic system. MRI is indicated for malformations, traumatic injuries, acute and chronic disorders of cerebral circulation, aneurysms, lymphedema, thrombosis and atherosclerotic vascular lesions of the extremities and internal organs.
Pacemakers and other implanted electronic devices, large metal implants and Ilizarov devices are considered as absolute contraindications to MRI. The list of relative contraindications to MRI includes prosthetic heart valves, non-metallic middle ear implants, cochlear implants, insulin pumps and tattoos using ferromagnetic dyes. In addition, relative contraindications to MRI are the first trimester of pregnancy, claustrophobia, decompensated heart disease, general serious condition, motor agitation and inability of the patient to follow the doctor’s instructions due to impaired consciousness or mental disorders.
MRI with contrast is contraindicated for allergies to contrast agents, chronic renal failure and anemia. MRI using a contrast agent is not prescribed during gestation. During lactation, the patient is asked to express milk in advance and refrain from feeding for 2 days after the study (until the end of the withdrawal of contrast from the body). The presence of titanium implants is not a contraindication for any type of MRI, since titanium does not have ferromagnetic properties. The technique can also be used in the presence of an intrauterine device.
Preparation for MRI
Most studies do not require special training. For several days before the pelvic MRI, you should refrain from using gas-forming products. To reduce the amount of gas in the intestine, activated charcoal and other similar drugs can be used. Some patients are shown an enema or taking laxatives (as directed by a doctor). Shortly before the start of the study, it is necessary to empty the bladder.
When conducting any type of MRI, it is necessary to provide the doctor with the results of other studies (radiography, ultrasound, CT, laboratory tests). Before starting the MRI, you should take off your clothes with metal elements and all metal objects: hairpins, jewelry, watches, dentures, etc. In the presence of metal implants and implanted electronic devices, it is necessary to inform the specialist about their type and location.
Methodology of conducting
The patient is placed on a special table that moves into the tunnel of the tomograph. In contrast-enhanced MRI, a contrast agent is pre-injected into the vein. Throughout the study, the patient can contact the doctor using a microphone installed inside the tomograph. During the procedure, the MRI machine creates a slight noise. At the end of the study, the patient is asked to wait until the doctor examines the data obtained, since in some cases additional images may be required to create a more complete picture. Then the specialist prepares a conclusion and passes it to the attending physician or gives it to the patient.