The structure of the tomograph. Magnetic resonance imaging (MRI). Study of the vessels of the brain

Modern medical diagnostics is based on two types of research: applied (biological, chemical, etc.) and imaging. If the first type of research appeared from time immemorial, when a person determined the presence of a disease, as they say, “by smell and tongue”, then visualization of internal organs without damaging the body became possible only with the discovery of the property of radioactive materials to produce penetrating radiation, now known as “X-ray ".

The discoveries of physicists in the world of elementary particles gave medicine another way to obtain images of all tissues and organs of the human body without direct implementation. Magnetic resonance imaging (MRI) is one of the most advanced and continuing to develop types of obtaining information about the state of living organisms.

In the diagnosis of diseases of the spine, MRI is the leading type of imaging, because. The construction of the spinal column includes many soft tissue elements (intervertebral discs, ligaments, bags of facet joints), for which magnetic resonance imaging is the best method of “non-destructive testing”.

What is an MRI?

The basis of the imaging method of research, called "Magnetic Resonance Imaging", is one of the discoveries of quantum physics and elementary particle physics, that the nuclei of certain elements are able to emit excess energy absorbed under the influence of oriented magnetic fields and radio frequency radiation.

The phenomenon of "nuclear magnetic resonance", on which magnetic resonance research of objects (living and inanimate) is based, was discovered in 1922 during an experiment to determine "spin quantization" in electrons. It was then that physicists realized that the concept of quantum physics "spin" (the angular momentum of a particle) has a physical expression.

In the course of research on the effects of radio frequency (RF) radiation on particles in a strong magnetic field, it was found in 1937 that the cores of samples absorb RF energy of a certain frequency and radiate after the external pulse is turned off. Such an action can only be produced by particles whose nuclei have an electric charge and spin. Such properties are inherent in elements in the nucleus of which there is one "extra" proton (ie, the number of protons exceeds the number of electrons). Modern MR imaging uses the properties of several "organic" elements in research, the most popular of which is hydrogen H(1).

Being in a strong uniform magnetic field, the hydrogen nucleus, consisting of one proton, under the influence of a radio pulse emitted at a certain frequency (Larmor resonance frequency), is able to “excite”: the energy of the absorbed RF pulse transfers the hydrogen atom to a higher energy level. But this unstable state is unable to persist without external influence, and when the impulses stop, there is a return to a stable state (relaxation). In the process of this “cooling down”, the core emits an electromagnetic wave that can be detected. The rest is a matter of complex mathematical spatial calculations, during which the signal of a certain atom turns into a “pixel” with certain coordinates.

What causes the hydrogen nucleus to absorb the energy of the RF pulse? It is the interaction of the own magnetic field of the nucleus and the large, constant and oriented in a certain direction magnetic field induced around the “object of research”, created by strong electromagnets. Each nucleus of the hydrogen atom is a single magnetic system with a unique direction of the magnetic moment. The magnetic moments of all protons are forcibly oriented in the direction in which the magnetic induction vector of the external field is directed. The energy of the RF pulse emitted at a frequency coinciding with the frequency of rotation of the protons is absorbed by changing the position of the axis oriented along the general direction of the magnetic field (rotated by 90 (T1) and 180 degrees (T2)). Return to normal, i.e. "unexcited", the state with the rotation of the axis of rotation in the original direction is accompanied by the emission of an electromagnetic wave with the same frequency at which the energy was absorbed. In positions T1 and T2, the hydrogen nuclei “store” different amounts of energy, and, accordingly, the radiation power differs (the first state gives a smaller momentum than the second).

This is the simplest explanation of the essence of nuclear magnetic resonance in a single system, which is the hydrogen atom, but in dense matter, a more complex application of magnetic fields is required to obtain results. For this, additional magnetic fields, called "gradient" ones, are introduced. With their help, you can change the direction of the general magnetic field in three dimensions, which allows you to obtain images in any projection (plane) and form three-dimensional images using computer processing (as in computed x-ray tomography).

In fairness, tomography should be called "nuclear magnetic", because. It is the radiation of the nuclei of atoms that is used. But after the accident that led to the destruction of the nuclear reactor at the Chernobyl nuclear power plant and the contamination of adjacent territories with radioactive emissions, any name containing the word "nuclear" is perceived with a significant amount of unhealthy skepticism. The reduction was adopted to keep the population calm, not familiar with quantum physics.

History of invention, device and principle of operation

Modern magnetic resonance imaging scanners are produced in several technologically advanced countries, of which the US accounts for up to 40% of the total production. This is not accidental, because most of the major technological discoveries regarding MR imaging have been made in American research centers:

• 1937 - Professor of Columbia University (New York, USA) Isidor Rabi conducted the first experiment on the study of nuclear magnetic resonance in molecular beams;
• 1945 - two universities (Stanford and Harvard) carried out fundamental research on NMR in solid objects (F. Bloch and E. Purcell);
• 1949 - E.F. Ramsey (Columbia University) formulated the theory of chemical shift, which formed the basis of MR spectroscopy, which provided chemical laboratories with the most accurate analytical equipment;
• 1971-1977 - physicist Raymond Vagan Damadian with a group of colleagues (Brooklyn Medical Center) created the first MRI scanner and obtained an image of the internal organs of living objects (including humans). In the course of research, doctors have found that images of tumors are very different from healthy tissues. It took about 7 years to design and carry out the work;
• 1972 - Chemist Paul Lauterbur (State University of New York) obtained the first two-dimensional image using his own developments in the use of variable gradient magnetic fields.

In 1975, the Swiss physical chemist Richard Ernst proposed methods for increasing the sensitivity of MRI (using Fourier transforms, phase and frequency coding), which significantly increased the quality of two-dimensional images.

In 1977, R. Damadian presented to the scientific world the first image of a section of the human chest, made on the first MRI scanner. In the future, technology has only improved. A particularly large contribution to the development of MRI was made by the development of computer technology and programming, which made it possible to programmatically control a complex set of electromagnetic equipment and process the resulting radiation to obtain a spatial image or two-dimensional "slices" in any plane.

Currently, there are 4 types of MRI scanners:

1. On permanent magnets (small, portable, with a weak magnetic field up to 0.35 T). Allow to make "field" researches during operations. The most widely used are permanent neodymium magnets.
2. On resistive electromagnets (up to 0.6 T). Quite bulky stationary devices with a powerful cooling system.
3. Hybrid systems (on permanent and resistive magnets);
4. On superconducting electromagnets (powerful stationary systems with a cryogenic cooling system).

The highest image quality, clear and contrast, scientists get on cryogenic MRI scanners with strong magnetic fields up to 9.4 T (on average - 1.5 -3 T). But practice shows that to obtain a high-quality image, not so much a powerful field is required, but to a greater extent, fast signal processing and good contrast. With the development of software, the power of magnets in standard medical MRI scanners has been reduced to 1-1.5 T. The most powerful tomographs are made for scientific medical research.

A standard MRI scanner consists of several blocks:

1. Multiple magnet system:

• a large toroidal magnet that creates a constant field;
• gradient magnetic coils, with the help of which the direction of the magnetic induction vector is changed (“the poles are shifted”) in three dimensions. To shift the gradient, coils of various shapes and sizes were invented (8-shaped, saddle-shaped, paired (Helmgotz), Maxwell, Golay). The computer-controlled operation of single and twin coils is able to direct the moments of the nuclei in any direction or even turn around the direction originally set by the large magnet;
• shim coils needed to stabilize the overall field. Small magnetic fields of these coils compensate for extraneous pickups or possible inhomogeneity of the field created by large and gradient magnets;
• RF coil. RF coils create a magnetic field that pulsates at the resonance frequency. Three types of coils have been developed and are used: transmitting, receiving and combined (transmitting-receiving). The RF emitter is also a detector at the same time. when an external radiation created by “relaxing” protons is pointed at the coil, induction currents appear in its circuit, which are recorded as RF signals. The designs of detectors - coils are divided into two types: surface and volume, i.e. surrounding the object. The shapes depend on the methods of capturing signals, which take into account the power and directivity of the radiation. For example, the 3D birdcage coil is used to obtain better images of the head and extremities. The tomograph has several paired and single RF coils for all types and directions of RF signals.

The most powerful field is created by superconducting magnets. A large ring magnet, which creates a constant field, is immersed in a sealed vessel filled with liquefied helium (t = -269 o C). This vessel is closed in another, larger sealed vessel. A vacuum is created in the space between the two walls, which does not allow the helium to heat up even by a fraction of a degree (the number of nested vacuum vessels can be more than two). The lower the resistance in the coil wire, the higher the power of the magnetic field. It is this property that justifies the use of superconductors, the resistance in which is close to 0 Ohm.

The tomograph control system consists of devices:

• computer;
• gradient pulse programmer (forms the direction of the magnetic field by changing the amplitude and type of gradient fields);
• gradient amplifier (controls the power of gradient pulses by changing the output power of the coils);
• the source and programmer of RF pulses form the amplitude of the resonant radiation;
• The RF amplifier changes the power of the pulses to the required level.

The computer controls the field and pulse formation units, receives data from the detectors and processes it, transforming the analog signal stream into a digital "picture" that is displayed on the monitor and printed.

An MR scanner (i.e., a magnetic system) is necessarily surrounded by a shielding system from external “pickup” of electromagnetic and radio radiation, which can come from sources of radio signals and any metal objects that have fallen into a strong magnetic field. A metal mesh or solid sheet covering the walls of a room creates an electrically conductive Faraday cage screen.

MRI in medical diagnostics

Magnetic resonance imaging is completely different from X-ray transillumination, because. it is literally not an "analog" (i.e. photographic) way of obtaining an image, but building an image using digitized data. That is, the picture that a person sees on the screen is the product of decoding many microscopically small signals that are picked up by the tomograph detector (RF coil). Each of these electromagnetic impulses has a certain power and spatial coordinates inside the body. Processing and construction of the image on the basis of the received pulses of "relaxation of protons" is carried out by a powerful computer using special programs.

MRI uses a set of RF pulse sequences that create specific modes of "excitation" of hydrogen protons in body tissues with a unique intensity of absorption and corresponding energy return. In fact, sequences are computer programs according to which RF signals are emitted with a certain amplitude and power and magnetic field gradients are controlled.

Hydrogen is the most abundant element in the body as it not only present in all organic molecules, but also, as a component of water, found in most tissues. That is why (and also because there is only one proton in the nucleus, which makes it easier to induce resonance) tomography better depicts soft tissues, in which the concentration of water is much higher. On an MRI image, bones containing very few free water molecules appear as impenetrable black areas.

Numerous experiments have shown how different the relaxation time of a proton can be if the atom in which this elementary particle is located is in a certain type of tissue. Moreover, if this tissue is healthy, the “response” time will differ significantly. It is in terms of relaxation time, i.e. the rate of return of the RF pulse, the brightness of the object is determined by the computer.

In medical diagnostics, MRI examines not only dense tissues, but also liquids: MR angiography allows you to determine the sites of thrombus formation, identify turbulences and the direction of blood flow, and measure the lumen of blood vessels. Special substances that change the response time of protons in the composition of the liquid help in the study of a liquid medium. Contrast agents contain compounds of the element "gadolinium", which has unique magnetic properties of the nuclei of atoms, for which it is called a "paramagnet".

Also, using MRI, the core temperature is measured anywhere in the body. Non-contact thermometry is based on measuring the resonant frequencies of tissues (temperature is measured on the basis of relaxation frequency deviations in hydrogen poisons in water atoms).

Imaging is based on fixing three basic parameters that protons have:

• relaxation time T1 (spin-lattice, rotation of the proton rotation axis by 90 o);
• relaxation time T2 (spin-spin, rotation of the proton rotation axis by 180 o);
• proton density (concentration of atoms in tissue).

The other two conditions that affect image contrast and brightness are sequence repeat time and echo time.

Using sequences of RF pulses with a certain power and amplitude and measuring the response time T1 and T2, researchers obtain images of the same points of the body (tissues) with different contrast and brightness. For example, a short time T1 produces a strong RF signal of relaxation, which appears as a bright spot when imaged. By combining the light characteristics of the tissue in different sequences, an increase in the concentration of water, fat, or a specific change in the characteristics of the tissue, indicating the presence of a tumor or induration, is detected.

For completeness of information about magnetic resonance imaging, it must be said that the control of magnetic fields and radio frequency impulses is not complete without "incidents", unusual-looking images. They are called "artifacts". This is any point, area, or feature that is present in an image but is not present in the body as a tissue change. The reason for the appearance of such artifacts can be:

• random pickups from unknown metal objects caught in a magnetic field;
• equipment malfunctions;
• physiological features of the body ("phantoms", spots caused by the movement of internal organs during breathing or heartbeat);
• incorrect actions of the operator.

To eliminate “artifacts”, an extraordinary calibration and testing of the equipment is carried out, the patient and the room are checked for the presence of foreign objects, and a second examination is performed in several modes.

The use of MRI in the diagnosis of diseases of the spine

The spine is the most mobile part of the musculoskeletal system. It is soft tissues that provide both mobility and integrity of the spinal system. If we count all the known and common diseases of the spine, soft tissue injuries will account for up to 90% of all diseases recorded. And if we include neurological diseases of the spinal cord and spinal nerves and various types of tumors, then the statistics will increase to 95-97%. In other words, diseases that damage the bone tissues of the vertebrae are more than rare compared to soft tissue diseases: intervertebral discs, articular capsules, ligaments and back muscles.

If we compare the symptoms of various violations of the integrity of soft tissues, the similarity will be exceptional:

• pain (local and widespread in a certain area);
• "radicular syndrome" (violations of the integrity of the spinal nerves and associated distortion of sensory signals and responses);
• various in strength paralysis (plegia), paresis and loss of sensitivity.

That is why the results of magnetic resonance imaging have a high status of "decisive word" in the imaging diagnosis of diseases of the spine. Sometimes a high-quality image of the affected area is the only way to finally confirm the diagnosis made on the basis of a preliminary examination, neurological tests and analyzes.

An indication for an MRI examination is the presence of inflammatory processes in the region of the spinal column, accompanied by an active immune response (fever, swelling of tissues, redness of the skin). Analyzes confirm the presence of an immune response, but are not able to indicate the exact location of the site of infection and inflammation. An MR tomogram with an accuracy of 1 mm establishes the coordinates of the focus, the area of ​​distribution of the inflammatory process. MRI angiograms will indicate the boundaries of vascular thrombosis and tissue edema. In the study of chronic diseases (osteochondrosis in all stages, spondylarthrosis, etc.), MRI shows exceptional utility.

Also, a direct indication for the use of MRI are symptoms indicating the possible formation of abscesses in the epidural region: severe localized pain, "radicular syndrome", progressive loss of sensation and paralysis of the limbs and internal organs.

Infectious diseases that can damage all types of tissues (tuberculosis, osteomyelitis) require a comprehensive study using MRI and computed tomography (CT). On MRI tomograms, lesions of the nervous tissues, cartilaginous intervertebral discs, and articular capsules are detected. CT complements the overall picture with data on the destruction of bone tissues of the vertebral bodies and processes.

Injuries to the spinal cord and tissues close to them (blood vessels, meninges, internal periosteum of the spinal canal) require multilateral and painstaking MRI studies, because most of the disorders of the nervous tissues are associated with the formation of tumors (benign and cancerous), occasionally - abscesses (epidural and subdural). Studies of magnetic resonance imaging were originally aimed at identifying tumor formations in the central nervous system. Long-term observations and systematization of accumulated experience allow researchers to determine emerging neoplasms at the first stage, “in their infancy”.

The development of scanner technology is aimed at increasing the detail, contrast and brightness of the image of objects of any size, as well as the fastest possible data acquisition after the emission of an RF pulse. A modern MRI scanner is able to "show" ongoing processes in real time: heartbeat, movement of fluids, respiration, muscle contraction, formation of a blood clot. Small open MRI scanners with permanent magnets allow operations with a minimum level of damage to surface tissues (interventional MRI).

Computer programming makes it possible to build a three-dimensional image on a monitor screen or using laser technology, based on data received from a scanner.

The direction of MRI studies of the spine in a vertical position is developing. The mobile unit is equipped with a table that changes position by 90°, which allows you to record changes in the spinal column in real time with an increase in vertical loads. Such data are especially valuable in the study of injuries (fractures of various types) and spondylolisthesis.

According to the reviews of those who underwent the examination, they do not experience any pain. The biggest impression on them is the noise that the equipment creates: "a strong knock in the walls of the tunnel, as if a perforator is working nearby." This rotates the moving part of the permanent magnet.

Contraindications

An unambiguous obstacle to an MRI examination is the presence in the patient's body of implants and devices containing metals that have the properties of ferromagnets to any extent. For information: only pure titanium, used to create vertebral fixation systems, does not have magnetic properties.

The presence in the patient's body of a pacemaker, a cochlear implant with electronic equipment and metal parts will immediately cause disturbances in the magnetic field, which will create an "artifact" on the tomogram. In addition, the electronic device will fail, causing maximum damage to the owner. The presence in the body of artificial joints, pins, staples, or even fragments of metal left after the injury will lead to the same result. Some chemical compounds that make up tattoo inks also have ferromagnetic properties (in particular, microscopic particles can heat up in a strong magnetic field, which leads to burns of the deep layers of the epidermis).

During the examination, the patient is required to remain as immobile as possible for a sufficiently long time. An obstacle to an MRI can be mental instability, certain phobias (claustrophobia, for example), which will cause a shock, hysteria, and involuntary mobility in the subject.

To improve image quality, contrast agents (gadolinium compounds) can be used, the properties of which are not yet fully understood. For example, how they can affect the development of the fetus during the first three months of pregnancy. Therefore, examinations of pregnant women requiring the use of contrast agents are not recommended. In addition, in people with individual physiological intolerance, these drugs can cause an unexpected anaphylactic reaction.

The improvement of technology using the phenomenon of nuclear magnetic resonance provides physicians, chemists and biologists with a powerful tool for studying current processes in a living organism and searching for pathologies at the earliest stages of development.

Related Articles

One of the most modern methods of studying the human body is MRI. The layered image of tissues with this method is possible due to such a phenomenon as nuclear-magnetic resonance (NMR). Despite the terrible name, this research method has nothing to do with radiation.

What is the point?

Earlier diagnostic procedures (X-ray and CT) are contraindicated for some patients due to radiation exposure. MRI is based on the properties of a magnetic field.

NMR effect was opened in the middle of the last century. It has been proven that the nuclei of individual atoms absorb the energy of an electromagnetic pulse, convert it into a radio signal, which is then emitted.

In medicine, this method was applied only after 30 years. In the eighties, the world congress of radiologists was held in the capital of France. It was then that scientists demonstrated the first MRI machines based on the NMR of hydrogen, the most naturally occurring element. The received signals are processed by a computer program, after which the radiologist receives images of tissue sections.

The method is being developed and improved, and its fields of application are expanding. Today, MRI is successfully used to diagnose pathologies of the spine, blood vessels, abdominal and pelvic organs, heart, and musculoskeletal system.

What are the advantages of the method?

1. Non-invasive;
2. informative;
3. No complications;
4. Safety;
5. Virtually no preparation needed;
6. 3D images.

What is an MRI machine?

The diagnostic apparatus consists of a large tube in the form of a cylinder and a magnet located around it. The patient lies down on a table moving inside the tube. Today, medicine has various types of tomographs at its disposal, including those with open sides and a shortened tunnel. The capabilities of the latest models of devices are very large: with their help, clear images of various parts of the body are obtained. However, not all studies can be carried out with the same quality on different types of tomographs, for example, on an open one. In each case, expert advice is needed. After scanning, the image is processed by a computer located in another room adjacent to the machine.

Should I be afraid of testing?

An MRI study is performed during hospitalization of the patient, as well as on an outpatient basis. The human body is fixed with straps motionless on a special table. Radio wave devices are placed near the examined part of the body.

Sometimes the procedure is performed with contrast. In this case, the contrast agent is injected into the blood through a catheter.

At the end of the preparatory measures, the patient is moved to the center of the magnet. The medical staff goes to another room where the computer is located. It is used to process tomographic data. The sounds (clicks) of the device indicate the beginning of the scan. During this time, it is important to remain still. In pauses, the patient can relax a little, but, nevertheless, it is necessary to remain still.

After the procedure, the catheter is removed. As a rule, the study takes place within 45 minutes.

Side effects of the study

• • In general, the MRI procedure is painless. However, the patient may feel uncomfortable from lying still.
  • There are people who are afraid of closed space. Such patients are recommended tomography of an open type. Your doctor may also suggest taking sedatives. But there are few such people - 1/20 of all those surveyed.
  • The temperature of the part of the body that is being studied may increase. You should not worry, as this is quite normal.
  • Some people are worried about loneliness: after all, the radiologist and other medical staff are in the next room. Others are afraid that their possible ill health will go unnoticed by the doctor. However, there is no need to worry: the study provides for the possibility of communication between the patient and the medical staff.

• The scanner buzzes quite loudly, so the patient is offered to use headphones or ear plugs.
• During the installation of the catheter and the supply of a contrast agent, the patient may experience discomfort. There is also the possibility of a metallic taste in the mouth.
• Very rarely, a patient is allergic to a contrast agent: itching, eye irritation. Sometimes he starts to feel sick, there is pain. This must be reported to the doctor.
• Nursing mothers are advised to stop breastfeeding for at least a day after the contrast agent enters the bloodstream. All this time it is necessary to express milk from each breast. It is believed that in 24 hours this substance is completely eliminated from the body. Although according to some reports, the components of the contrast agent are not toxic to the child. But, as they say, God saves the safe!

Video: MRI procedure

Study of the vessels of the brain

To date, several modes and programs have been developed for conducting MRI of cerebral vessels. The doctor notes the method of examination in the patient's medical history and points in the direction of MRI. Therefore, it is important that a visit to a medical facility precedes the MRI procedure of the brain. When drawing up a research plan, the specialist will definitely take into account all contraindications.

One of the safest and at the same time effective ways to study the brain is the MRI method. As a result of MRI of cerebral vessels, not only their structure, but also their functional state is assessed. Usually, the radiologist gets a fairly clear image of the vessels, but in some difficult cases, the study is carried out with contrast.

As a result of the study, it is possible to make many sections of the problem area, obtain its image in different planes, and consider the specifics of blood flow. The desired part of the investigated vessel can be identified in a certain projection.

When is a tomographic examination of the head performed?

The main indications for MRI of the brain vessels include:

Possibilities, which are opened using the MRI method:

• The study helps to draw up the right treatment plan;
• The course of treatment is monitored;
• The diagnosis is specified;
• Pathology is recognized at the earliest stages of its development.

MRI of the vessels of the head visualizes not only the vessels themselves, but also the tissues surrounding them. Moreover, this happens without the use of x-rays and contrast material used in the case of computed tomography.

The method helps to determine the exact localization of blood clots, damage to the walls of blood vessels,.

Without a doubt, the MRI method, due to its safety and high information content, is superior to earlier diagnostic methods: CT and radiography. An MRI of the brain vessels can be done at any medical institution that has the appropriate equipment.

Video: MRI of the brain

Spine examination

If in the recent past it was possible to study the state of the spinal column only with the help of radiographic methods (which is not always safe), then the method of magnetic resonance imaging that appeared later became a real breakthrough in diagnosis. In fact, medicine has reached a whole new level. With the help of this non-invasive technique, the development of the pathological process in dynamics is studied. Get three-dimensional sections of problem areas. The resulting images are displayed on a computer monitor, then the images can be printed and placed in the medical history.

Typically, MRI of the spine is prescribed to clarify the diagnosis of pain in the back or legs. With the help of the MR-tomography method it is possible:

1. Detect damage to intervertebral discs;
2. Determine the degree of pressure on the nerve roots of the damaged disc;
3. Diagnose congenital pathology of the organ under study;
4. Determine violations in the movement of blood in a particular part of the spine;
5. Diagnose tumors of bone and nervous tissue;
6. Identify narrowing of the spinal canal;
7. See traumatic injuries in nerve fibers;
8. Detect metastases of malignant tumors of the lungs, prostate, breast;
9. Find changes in nerve fibers that have occurred as a result of diseases;
10. Identify foci of inflammation, osteoporosis;
11. Find the area of ​​the spine affected by the infection.

• A person with dentures (with regard to dentures, their presence is not a contraindication), a pacemaker and other metal-containing inclusions;
• Patients with convulsive syndrome and;
• People with a mental disorder;
• Patients with claustrophobia;
• Those who may develop an allergic reaction to contrast.

There is no need to prepare for the procedure. Naturally, the patient will have to remove all metal objects, as he will be in a strong magnetic field.

Examination of the cervical spine

One of the most complex and important nodes of the human body is the cervical spine. In this place there are many blood vessels, nerve and muscle fibers, vertebral elements. With their pathology, all body systems suffer. Sometimes diseases are accompanied by similar symptoms, therefore, in order to make the correct diagnosis, an MRI procedure of the cervical spine and neck vessels is prescribed.

Indications for an MRI of the spine

1. Dystrophic-degenerative changes in the tissues of the spine;
2. neck injury;
3. Congenital anomalies of the organ;
4. Suspicions of hernia and displacement of the vertebral discs;
5. Spondyloarthritis, osteomyelitis, spondylitis;
6. Suspicion of metastases;
7. Upcoming spinal surgery.

These diseases are manifested by pain in the hands, ringing in the ears, numbness of the neck, impaired hearing and vision, and fluctuations in blood pressure. MRI of the vessels of the neck allows you to identify the causes of disruption of the body.

MRI of the heart

The cardiovascular system in the body has a special role - blood circulation. Thanks to the work of the heart, blood enters all the cells of the human body and brings oxygen to them. Even small disturbances in the operation of this system can lead to irreversible health consequences. These organs wear out faster than others: the heart is in constant motion, and the vessels experience an impulse load.

There is no doubt that the heart and blood vessels must be helped. How? First, follow the regime, eat healthy foods, give up bad habits. And secondly, time to do research. Detecting a problem in the early stages, no secret, gives a better chance of recovery. MRI of the coronary vessels and heart will provide an opportunity to find all the problems in the system. And according to the results of the examination, the doctor will prescribe the correct treatment.

The MRI method is absolutely safe for cardiac activity. The magnetic field is harmless to the myocardium, vascular walls, heart rate. After the study, there are no residual effects.

Heart examination shows:

• Changes in the structure of the heart and the entire coronary system;
• Decrease or increase in blood flow. Blood supply depends on the intake of drugs, hormonal drugs, load, stress;
• Stenosis or cholesterol deposits: even the slightest violation of the capacity of the arteries worsens cardiac activity;
• Changes in the functions of the heart chambers;
• Pathological changes in the myocardium;
• Violations in the structure and operation of the valve system;
• Formations (benign and malignant);
• (congenital or acquired);
• Postoperative conditions of vessels and heart.

Healthy heart (left) and well-detected by MRI (right)

The difficulty in examining the heart is that this organ cannot be motionless. Breathing also affects the result of the scan. To make high-quality images, it is necessary to use high-power tomographs. Therefore, in the study of the cardiovascular system, devices are used that can create a magnetic field strength of more than 1.5 Tesla. This allows you to take pictures of slices no thicker than 1 mm. And for a clearer picture, the study can be carried out with contrast.

On such tomographs, a three-dimensional high-quality image is obtained. Vessels and surrounding tissues are viewed at any depth and from a variety of angles. Heart rate and magnetic field strength in modern MRI machines are synchronized. The study of vessels is carried out both in statics and in dynamics.

Absolute contraindications:

1. The presence in the body of electronic devices (ferromagnetic ear implants, pacemakers);
2. Metal implants, clips, staples;

Relative contraindications:

1. Claustrophobia;
2. Postoperative condition that requires the use of supporting equipment;
3. Pregnancy (first trimester);
4. Unhealthy muscle activity.

Abdominal diagnostics

Usually, for diagnosing pathologies of organs located in the peritoneal cavity, it is not MRI that is prescribed, but other research methods. For example, CT scanners better distinguish between the gallbladder and intestines. Fibrogastroscopy has proven itself well in the study of the stomach. However, soft tissues are better seen by an MRI scanner. Therefore, in order to clarify the diagnosis regarding the bile ducts, blood vessels, adrenal glands, liver, an MRI is prescribed. With the help of the method, it is possible to identify the exact location of the organ, its shape and size, to detect the painful process, as well as the connection of the latter with neighboring organs.

Thrombosis of the liver veins on MRI

MRI is a rather expensive procedure, therefore it is prescribed only if necessary as an addition to the studies.

The advantage of this method is its security. Carrying out the procedure without the use of x-rays allows it to be used even when examining pregnant women. If it is necessary to conduct an additional study, then the procedure can be repeated without fear of complications. Also, when studying the state of the vessels in the abdominal cavity, it is not necessary to use a contrast agent, which makes this method indispensable for allergy sufferers. Of course, if it is necessary to examine in more detail the cellular structures of organs, to determine their blood supply, then it is possible to use contrasting. However, only a doctor should decide this.

What does MRI reveal?

• Fatty degeneration of the liver, cirrhosis;
• Tumors of various nature;
• Bleeding, infection, inflammation;
• Obstruction of the bile ducts;
• Cholesterol deposits and other causes of impaired blood flow in the vessels;
• Accumulation of fluid in the abdominal cavity.

Important! The patient should not refuse an additional clarifying procedure - MRI of the abdominal organs, if prescribed by a doctor.

MR-tomography of vessels of extremities

In the arterial and venous bed of the lower extremities, circulatory disorders may occur. To determine the degree of this violation will help MRI of the vessels of the legs. Based on the results of the study, it is possible to draw a conclusion about vascular injuries, anomalies in their development, diseases, predict subsequent manifestations of the disease and prescribe the most appropriate method of treatment.

thrombosis of the vessels of the legs on the MRI image

Absolute and relative contraindications for MRI of the vessels of the legs are the same as for the diagnosis of other organs (MRI of the vessels of the kidneys, abdomen, heart).

The use of MRI in the study of the knee joints

About 70% of all lower extremity injuries occur in the knee joints. This can happen to people of any age and lead to a complete loss of performance.

MRI of the knee joint is currently used to clarify the diagnosis of the following injuries:

• Ligament damage;
• Rupture of the meniscus;
• Tendon injury.

MRI not only confirms this or that injury, but also shows more complex changes occurring in the tissues.

Why MRI?

The most used methods for examining the vessels of the legs are computed tomography and MRI.

The safest of these methods are MRI and Doppler sonography. It should be noted the high information content of both one and the other method. However, the advantage of MRI is that, based on the results of the study, the patient and his doctor receive a three-dimensional, detailed, detailed image of all the elements of interest.

When compared with MRI and CT, they are both reliable and can be successfully used to make a correct diagnosis. The main difference between MRI and CT is the absence of x-rays. Therefore, there are much fewer contraindications for MRI, and the method can be recommended to a larger circle of patients, even to pregnant women.

Video: comparison of MRI with CT

Among the variety of diagnostic methods, MRI occupies a special place. Maximum benefits and minimum contraindications make it the method of choice. However, the final conclusions, by definition, should be made only by a doctor.

The image of this device is familiar to everyone who watches medical TV programs and news from the world of science. Still would! After all, it allows you to perform such “tricks” that were not even dreamed of 30 years ago by any doctor of radiation diagnostics.

Once upon a time, the only way to "look inside the body" was an X-ray examination. Flat black-and-white pictures and a lot of “places on the body map” that are inaccessible to x-rays.

Now the doctor has at his disposal devices that allow him to "scan" a person and depict his inner world in the most detailed way on the monitor screen - in color and even in "slicing", like a store sausage. The method is called magnetic resonance imaging (MRI).

Magic Secrets

A person consists of 60–80% water, in the molecules of which, as is known, there are hydrogen atoms. When exposed to a powerful magnetic field, they begin to emit certain waves. Moreover, they are different - depending on which tissues the “magnetized” atoms are located in.

This physical process is the basis of MRI. A person is placed in a magnetic field, the radiation is fixed and the received signals are transformed into a color three-dimensional image.

With any pathology, the water situation in our body changes, which means that the picture becomes different. This is why the MRI eye is often referred to as the all-seeing eye.

In medicine, a large number of instrumental research methods are used, some of which are, in fact, universal, which makes it possible to diagnose many pathologies from various classification groups of human diseases. This is the MRI machine, which allows you to visualize body tissues without using radiation exposure. However, what is MRI and what is the structure of the device, its principle of operation, a small number of people know. But such ignorance does not prevent most patients from undergoing such diagnostic procedures.

The structure of the MRI scanner and the principle of operation

The MRI machine is a large magnet. The human body is located in its cavity, which is protected by a plastic case. At the same time, such a study of tissues does not lead to the onset of pathological conditions, because it does not ionize the substances that make up the basis of the body structure. A strong device acts directly on protons. These particles are hydrogen ions, which are part of water - the most common substance in the human body.

The water content in different tissues of the human body has its differences. Its smallest amount is in the bones and connective tissue, while muscle and fat are characterized by a higher concentration of fluid. The brain tissue, as well as the parenchyma of internal organs, differs in the same indicators. At the same time, due to the difference in the water content, the construction of boundaries between heterogeneous tissues is achieved on a virtual image, which is formed after a signal is sent to the computer.

However, what is MRI, on the basis of what physical principle does this device operate? This type of differentiation of the structure of the human body is realized due to the mechanism of action. They are dipoles, which in a magnetic field take on a certain type of orientation. The MRI cycle itself consists in creating a magnetic field and conditions for ordering the arrangement of water molecules, after which a radio wave is launched along the magnetic field, causing the molecules to vibrate, which are amplified due to the emerging resonance.

MRI of the head, examination of the brain

In the diagnosis of diseases and degenerative lesions, it is of great importance, because it allows with a high degree of probability to determine the exact localization of the process, the amount of damage or neoplasm, to identify the vessel in which the thrombus is located. At the same time, the main approach to conducting this study is not how to diagnose, because the basis of tomography is the formulation of the question “what?” and answer to it. Such an MRI, made after a preliminary diagnosis, allows you to increase the information content of the study, because the doctor already assumes what exactly he will look for. At the same time, among the target pathologies that can be detected by MRI of the brain, there are tumor, traumatic, and infectious diseases. Also, magnetic resonance imaging is able to diagnose complications that arise during the development of the above diseases.

What is MRI of the spine

MRI of the spine and spinal cord is a method of instrumental research that involves the visualization of all anatomical formations at a certain level. Modern devices make it possible to carry out various virtual sections of individual parts of the body. This makes it possible to assess the anatomical structure of the spinal canal, intervertebral foramina in various areas. The study is also included because such an MRI allows you to see its structure, because the inductance of the magnetic field in the coil of the device is approximately 1.5 Tesla. The use of tomography helps to determine the presence of tumor formations in the membranes of the brain or in its tissue with appropriate symptoms.

The principle of this diagnostic procedure is the phenomenon of NMR (nuclear magnetic resonance), with which you can get a layered image of the organs and tissues of the body.
Nuclear magnetic resonance is a physical phenomenon, which consists in the special properties of the nuclei of atoms. With the help of a pulse of radio frequency nature in an electromagnetic field, energy is emitted in the form of a special signal. The computer displays and captures this energy.
NMR makes it possible to know everything about the human body due to the saturation of the latter with hydrogen atoms and the magnetic properties of body tissues. It is possible to determine where this or that hydrogen atom is located due to the vector direction of the proton parameters, which are divided into two phases located on opposite sides, as well as their dependence on the magnetic moment.

The principle of operation of the MRI machine is based on magnetic fields, the strength of which is tens of thousands of times greater than the strength of the earth's magnetic field, but they do not adversely affect human health.
How is an MRI done? How is the procedure

The MRI machine is located in a special room with a window through which the doctor observes the process. While the device is in operation, there is no one in the room; if necessary, the patient can consult a doctor over the speakerphone. All that is required of the subject is to lie still, as movements distort the picture of the images.

If MRIs are done for overweight people, the equipment makes less noise due to the weak magnet of low-field machines.

It is necessary to take into account one important nuance. During the procedure, the patient is placed inside the tomograph, which is a tunnel-shaped magnet. There are people who are afraid of closed spaces. This fear can be of varying intensity - from a little anxiety to panic. Some medical institutions have open tomographs for such categories of patients. If there is no such scanner, then you need to tell the doctor about your problems, he will prescribe a sedative before the study.

What kind of research is best suited for

Magnetic resonance imaging is indispensable in the diagnosis of such conditions:

• many ailments of an inflammatory nature, for example, of the genitourinary organs;
• disorders of the brain and spinal cord (pathologies of the nervous system, pituitary gland);
• tumors, both benign and malignant;
• provides the most accurate data on metastases, allows you to see even the smallest ones that are invisible in other studies. Helps to find out whether they decrease after the therapy or, conversely, increase;
• pathologies of the cardiac and vascular systems (vascular disorders, heart defects);
• injuries of organs and soft tissues;
• to determine the effectiveness of the surgical treatment, chemotherapy and radiation;
• infectious processes in the joints and bones.

Why does an MRI make noise?

What is accompanied by an MRI? The examination procedure is not accompanied by any physical sensations, except for the noise and rare clicks of the apparatus. The noise is quite loud, so the patient is given comfortable headphones or ear plugs. Many patients fall asleep during the procedure.

The machine makes noise during operation, just like any other mechanical device, this is normal.
After the MRI procedure, how long will the description be ready? The result is ready in a few minutes, after which the doctor interprets the data and makes a final conclusion. The whole process takes no more than one hour. Innovative types of MRI machines are characterized by lower noise levels.

What sounds does a working MRI scanner make?

It is a high-sensitivity, low-noise signal amplifier that operates at ultra-high frequencies. The recorded response undergoes changes - conversion from MHz to kHz (from high to low frequencies).

The doctor observes the patient through a special window or with a video camera. If necessary, by pressing a button, you can give a signal and talk to the doctor through the intercom.
There are cases when a contrast agent is injected intravenously to obtain an accurate result. There are no side effects in this procedure.
Within thirty minutes, the patient receives a ready-made conclusion and pictures.

During the MRI, a buzzing or rhythmic thumping noise is heard due to the operation of the magnet.