Functional MRI. Functional magnetic resonance imaging is an effective method for studying the brain Functional MRI

The effectiveness of treatment of the disease depends on at what stage it is started - the earlier, the better and faster the result will be. An advanced disease can have more serious consequences even if procedures are carried out to eliminate it. As for the brain, the initial stages of pathologies are very difficult to identify here, because they are not visible from the outside. For this purpose, functional MRI is used, an indispensable tool in surgery and neurology.

Functional MRI of the brain: how does it differ from conventional diagnostics?

The functional type of tomography differs from the classical one in that the indicators are taken not in a calm state, but in the process of active brain activity.

During physical activity, brain cells are better saturated with oxygen, and overall blood flow increases. This is picked up by the tomograph scanner. Registration of activity occurs due to increased magnetization of tissues - it depends on additional oxidation of glucose.

The more intense signal is compared with the indicators obtained in normal, quiet mode. A specialist uses a computer program to superimpose one three-dimensional image onto another.

The result is a complete map that captures the entire cerebral cortex, because blood in an active state allows you to view even the smallest and most distant areas. The tomogram shows parts with a diameter of half a millimeter. If you need to view them, you can enlarge them on the screen.

Signals from different cortical and subcortical structures are recorded and differentiated:

Basal ganglia.
Cingulate cortex.
Thalamus.
All types of tumors - not only their size and contours, but also the degree of penetration into the gray and white matter of the brain.

Using functional MRI, you can compare the behavior of brain cells:

At rest.
During mental work.
During physical and motor activity.

The functional type of tomography makes it possible to accurately determine the location and size of all brain centers:

Sensory.
Motor.
Rechevykh and others.

If a more accurate study is required, the patient is additionally given glucose.

Possibilities of functional MRI diagnostics

Diagnostics is used as a complement to the classical type of magnetic resonance examination - in order to clarify an unclear diagnosis, it is better to view a particular part of the brain, a section of tissue or blood vessels.

Options for using functional tomography results:

Surgery. Before brain surgery, a precise plan of action is drawn up using a tomographic map - the damage that needs to be eliminated is clearly visible on it. This allows you to avoid errors in actions and complications.
Radiology. Tomographic data makes it possible to calculate the amount of radiation required to treat cancer.
Neuropsychology. Study of failures in memory, speech apparatus, attention.
Identification of epileptic foci.
Ischemic areas are visible at an early stage - to prevent stroke.
Recognition of the initial processes of Alzheimer's and Parkinson's diseases.
The method allows you to find a connection between brain activity and dizziness.

A radiology specialist can fully decipher the data obtained as a result of the study.

When should you not do a functional MRI?

Since a powerful magnet is involved and it is necessary to lie quietly for an hour while inside a cylindrical device, there are contraindications:

Early pregnancy.
Claustrophobia.
Metal parts in and on the body - implants and prostheses that cannot be removed.
Mental illnesses due to which the patient cannot remain motionless for at least thirty minutes.

Tattoos with a metal component, small fillings and any non-magnetic materials do not pose a danger, but you need to warn your doctor about them in order to compensate for the magnetic field deviations caused by these objects and, accordingly, data distortion.

The research methodology has undoubted advantages:

High quality brain map.
Image resolution is more than three millimeters.
A convenient way to study the brain in a calm and active state.
No harm to the body - the procedure does not lead to cell death or other negative consequences.
Availability of the method - you don’t need to go abroad for this.

Informative fMRI in Moscow at a competitive price

Changes in blood flow activity are recorded by functional magnetic resonance imaging (fMRI). The method is used to determine the localization of arteries, to assess the microcirculation of the centers of vision, speech, movement, and the cortex of some other functional centers. A feature of mapping is that the patient is asked to perform certain tasks that increase the activity of the desired brain center (read, write, talk, move legs).

At the final stage, the software generates an image by summing conventional layer-by-layer tomograms and images of the brain with functional load. The complex of information is displayed by a three-dimensional model. Spatial modeling allows specialists to study the object in detail.

Together with MRI spectroscopy, the study reveals all the features of the metabolism of pathological formations.

Principles of functional MRI of the brain

Magnetic resonance imaging is based on recording the altered radio frequency of hydrogen atoms in liquid media after exposure to a strong magnetic field. Classic scanning shows soft tissue components. To improve the visibility of blood vessels, intravenous contrast with the paramagnetic gadolinium is performed.

Functional MRI records the activity of individual areas of the cerebral cortex by taking into account the magnetic effect of hemoglobin. The substance, after releasing an oxygen molecule to the tissues, becomes a paramagnetic, the radio frequency of which is picked up by the sensors of the device. The more intense the blood supply to the brain parenchyma, the better the signal.

Tissue magnetization is further enhanced by glucose oxidation. The substance is necessary to ensure the processes of tissue respiration of neurons. Changes in magnetic induction are recorded by the device’s sensors and processed by a software application. High-field devices create high-quality resolution. The tomogram shows a detailed image of parts with a diameter of up to 0.5 mm in diameter.

Functional MRI studies record signals not only from the basal ganglia, cingulate cortex, and thalamus, but also from malignant tumors. Neoplasms have their own vascular network, through which glucose and hemoglobin enter the formation. Signal tracking allows you to study the contours, diameter, and depth of tumor penetration into the white or gray matter.

Functional diagnostics of MRI of the brain requires the qualifications of a radiology doctor. Different zones of the cortex are characterized by different microcirculation. Saturation with hemoglobin and glucose affects the signal quality. The structure of the oxygen molecule and the presence of alternative substitute atoms should be taken into account.

A strong magnetic field increases the half-life of oxygen. The effect works when the device power is more than 1.5 Tesla. Weaker installations cannot fail to study the functional activity of the brain.

It is better to determine the metabolic intensity of the blood supply to the tumor using high-field equipment with a power of 3 Tesla. High resolution will allow you to register a small lesion.

The effectiveness of the signal is scientifically called the “hemodynamic response.” The term is used to describe the speed of neural processes with an interval of 1-2 seconds. The blood supply to tissues is not always sufficient for functional studies. The quality of the result is improved by additional administration of glucose. After stimulation, peak saturation occurs after 5 seconds, when scanning is carried out.

Technical features of a functional MRI study of the brain

Functional MRI diagnostics are based on an increase in neuronal activity after stimulation of brain activity by a person performing a specific task. An external stimulus causes stimulation of the sensory or motor activity of a specific center.

To track the area, a gradient echo mode is enabled based on a pulsed echo-planar sequence.

Analysis of the active zone signal on MRI is done quickly. Registration of one tomogram is performed at an interval of 100 ms. Diagnostics are performed after stimulation and during the rest period. The software uses tomograms to calculate foci of neuronal activity, overlaying areas of amplified signal on a three-dimensional model of the brain at rest.

For treating physicians, this type of MRI provides information about pathophysiological processes that cannot be tracked by other diagnostic methods. The study of cognitive functions is necessary for neuropsychologists to differentiate mental and psychological diseases. The study helps to verify epileptic foci.

The final mapping map does not only show areas of increased functional stimulation. The images visualize zones of sensorimotor and auditory speech activity around the pathological focus.

Mapping the location of brain canals is called tractography. The functional significance of the location of the optic pyramidal tract before planning surgical intervention allows neurosurgeons to correctly plan the location of incisions.

What does fMRI show?

High-field MRI with functional tests is prescribed according to indications when it is necessary to study the pathophysiological basis of the functioning of the motor, sensory, visual, and auditory areas of the cerebral cortex. Neuropsychologists use research in patients with disorders of speech, attention, memory, and cognitive functions.

Using fMRI, a number of diseases are detected at the initial stage - Alzheimer's, Parkinson's, demyelination in multiple sclerosis.

Functional diagnostics in different medical centers are performed using different installations. The diagnostician knows what an MRI of the brain shows. A consultation with a specialist is required before the examination.

High quality results are achieved by scanning with a strong magnetic field. Before choosing a medical center, we recommend that you find out the type of device installed. The qualifications of a specialist who must have knowledge about the functional, structural components of the brain are important.

The future of functional MRI diagnostics in medicine

Functional studies have recently been introduced into practical medicine. The capabilities of the method are not used enough.

Scientists are developing techniques for visualizing dreams and reading minds using functional MRI. It is proposed to use tomography to develop a method of communication with paralyzed people.

Neuronal excitability;
Mental activity;
Degree of saturation of the cerebral cortex with oxygen and glucose;
The amount of deoxylated hemoglobin in the capillaries;
Areas of blood flow expansion;
Level of oxyhemoglobin in blood vessels.

Advantages of the study:

High-quality temporary picture;
Spatial resolution higher than 3 mm;
Possibility of studying the brain before and after stimulation;
Harmlessness (when compared with PET);
Lack of invasiveness.

The widespread use of functional MRI of the brain is limited by the high cost of equipment, each single examination, the impossibility of directly measuring neuronal activity, and cannot be done on patients with metallic inclusions in the body (vascular clips, ear implants).

Registration of the functional metabolism of the cerebral cortex has great diagnostic value, but is not an accurate indicator for the dynamic assessment of changes in the brain during treatment, after surgery.

Functional magnetic resonance imaging of the brain is a type of study that allows you to measure the hemodynamic reactions of blood flow caused by the functioning of the organ.

In modern medicine, this is one of the main methods for studying brain processes.

Principles of functional MRI of the brain

Functional MRI will help identify pathologies in significant areas of the brain. The principle of operation of the device is quite simple: the brain consumes energy and the more active this process is, the more nutrients and oxygen it needs to receive. All this enters the organ through the bloodstream. It is MRI that helps to see areas with slow and increased blood circulation and understand how the brain copes with a particular problem.

Diagnostic measures associated with nuclear magnetic resonance, including functional tomography, have the following advantages:

The image displayed on the device's screen is very clear. The study is considered not only one of the most accurate, but also provides a picture of the highest quality.
Short duration of the study. The magnetic field has a high intensity, which makes it possible to significantly reduce diagnostic time. This is especially convenient for people suffering from neurodegenerative pathologies, mental illnesses (BD).
High accuracy of results. If surgical intervention on an organ is required, it is important for the doctor to obtain reliable information about the condition and location of the tumor, which will eliminate motor, speech, visual and other disorders after its excision. With the help of functional MRI, you can accurately assess the risk of such consequences and make a final decision about the resectability of the tumor.

Based on the characteristics of the changes identified using functional magnetic resonance imaging, one can determine the prognosis of a particular disease and the effectiveness of the treatment.

Technical features

The magnetic resonance imaging apparatus consists of:

table for patient placement;
a computer with a monitor to which the image is supplied;
radiofrequency and gradient system;
magnet.

A constant magnetic field with a force expressed in Tesla (T) is supplied from the magnet. Taking into account the strength, the apparatus is divided into low-field, medium-field, high-field, and ultra-high-field. In modern medicine, the most popular is a high-field tomograph with a power of 1.5 Tesla.

Considering the design, the device is divided into closed and open. The first is presented in the form of a tunnel into which a table with a bedridden patient is placed. In open devices there is no tunnel, which makes it possible to prescribe diagnostics to people who have a phobia of closed spaces.

Indications and contraindications for fMRI

Classification of MRI according to functional criteria allows us to divide the study into several types:

brain examination: with the help of it, a detailed image of the hemispheres and brainstem is obtained for the presence of neoplasms, infectious and inflammatory lesions, and congenital anomalies;
research: using MRI, they study the internal structure of the brain, detect tumor-like neoplasms in the gland;
head examination (including MRI of the cervical spine with functional tests, MRI of the temporomandibular joints with functional tests): in this case, the cause can be diagnosed if it does not give an accurate result.

In addition, diagnostics are prescribed to identify foci and determine the cause of impairment of functions such as memory, speech, attention. Functional MRI is an effective way to identify some pathologies that occur at stage 1, for example, to identify areas with, diagnose diseases, etc.

Despite the prevalence of the method, it has contraindications for use, which are divided into absolute and relative. Among the first:

presence of a pacemaker;
the presence of ferromagnetic or electronic implants in the middle ear;
the presence of a ferromagnetic Ilizarov apparatus.

Relative contraindications include:

the presence of a non-ferromagnetic implant in the inner ear;
presence of hemostatic clips;
development of heart failure in the stage of decompensation;
pregnancy in the 1st trimester;
fear of being in a closed space (phobia);
severe mental disorder or general condition;
the presence of a tattoo, which is made using a dye containing metal compounds;
presence of dentures and braces.

Tomography using a contrast agent is not performed with concomitant hemolytic anemia, hypersensitivity to contrast, with chronic liver failure, or during pregnancy.

Stages of the procedure

Before fMRI, a blood test for creatinine, its quantitative indicator, is required. You need to take your passport, a referral from a doctor and the results of previous diagnostic tests with you to the office.

During the procedure, no physical sensations or other discomfort arise. There is only noise, which can not be heard by wearing special earplugs or headphones.

A person must remove all metal objects from himself and leave them in a specially designated place. Next, the subject lies down on the apparatus table and puts on earplugs (or headphones). If necessary, the required part of the body is fixed.

In exceptional cases, if a person is unable to remain still, he is given general anesthesia. To increase the information content of the results, it may be necessary to administer intravenous contrast.

The duration of the study varies from 10 to 30 minutes. You can receive diagnostic results in just a few minutes.

Where can I get a functional MRI and how much does it cost?

Computed tomography machines are installed in many private and public medical institutions. The cost of the study starts from 4-5 thousand rubles. If a contrast analysis is required, the price rises to 7-8 thousand rubles.

Functional magnetic resonance imaging is an effective method for diagnosing the brain, allowing a detailed examination of the organ for specific pathologies. However, before carrying out it, it is necessary to weigh all the pros and cons, and also exclude contraindications. This is the only way to get reliable results.

Functional magnetic resonance imaging(fMRI) is an MRI technique that measures the hemodynamic response (change in blood flow) associated with neuronal activity. fMRI does not allow us to see the electrical activity of neurons directly, but does so indirectly, thanks to the phenomenon of neurovascular interaction. This phenomenon represents a regional change in blood flow in response to the activation of nearby neurons, since when their activity increases, they need more oxygen and nutrients brought by the blood flow.

Basic principles of fMRI. fMRI is a neuroimaging technique that uses oxy-hemoglobin and deoxy-hemoglobin in blood vessels as an endogenous contrast agent. The principle of BOLD contrast (blood oxygenation level dependent contrast) discovered by Seiji Ogawa in 1990 is used. BOLD contrast is the difference in MR signal in images using gradient sequences depending on the percentage of deoxyhemoglobin. The BOLD fMRI technique is as follows: an increase in neuronal activity causes a local increase in oxygen consumption. This leads to an increase in the level of the paramagnetic deoxyhemoglobin, which reduces the level of the fMRI signal. But after a few seconds, neuronal activity also causes an increase in cerebral blood flow and blood volume, which leads to an increase in arterial blood flow and therefore an increase in oxyhemoglobin, which increases the fMRI signal level. For as yet unknown reasons, the amount of oxygenated blood that flows in response to neuronal activity greatly exceeds metabolic oxygen consumption. This kind of overcompensation of oxyhemoglobin leads to a change in the ratio of oxyhemoglobin to deoxyhemoglobin, which is measured and is the basis for the BOLD fMRI signal.

There are two main methods for performing fMRI: [ 1 ] with the measurement of the functional activity of the cerebral cortex when performing a specific task compared to its activity at rest/with a control task (the so-called task-fMRI); [ 2 ] with measurement of the functional activity of the cerebral cortex at rest (the so-called resting state fMRI - RS-fMRI).

When conducting an fMRI study with a specific paradigm, the tasks that the subject performs can be different: motor, visual, cognitive, speech, etc. After fMRI, the obtained functional data are subjected to statistical analysis. The result is information about activation zones in the form of color maps superimposed on anatomical data, and the same data can be presented in digital format indicating the statistical significance of the activation zone, its volume and the coordinates of its center in stereotaxic space. However, in the last 10 years, resting fMRI (fMRI) has attracted increasing interest from researchers. The principle of its operation remains the same as with classical fMRI (task-fMRI). The only difference is the absence of any paradigms in fMRI (i.e., active tasks or influences presented to the patient). During fMRI, the subject is in a resting state in the MRI scanner and is instructed to relax as much as possible and not think about anything in particular. In various studies, there are different views regarding whether the subject needs to close his eyes or not. Proponents of leaving the eyes open argue that it prevents the subject from falling asleep.

In what cases is fMRI performed??

First, for purely scientific purposes: this is a study of the functioning of the normal brain and its functional asymmetry. This technique has revived the interest of researchers in mapping brain functions: without resorting to invasive interventions, you can see which areas of the brain are responsible for a particular process. Perhaps the greatest advances have been made in our understanding of higher cognitive processes, including attention, memory, and executive functions. Such studies have made it possible to use fMRI for practical purposes far from medicine and neuroscience (as a lie detector, in marketing research, etc.).

Secondly, fMRI is beginning to be actively used in practical medicine, in particular, for preoperative mapping of basic functions (motor, speech) before neurosurgical interventions for space-occupying brain lesions or intractable epilepsy. As a rule, motor areas for the arms and legs, tongue, as well as speech areas - Broca's and Wernicke's - are assessed: their presence, location relative to the lesion, the presence of homologues in the healthy hemisphere, compensatory increase in activation in the opposite hemisphere of the cerebrum or secondary zones. This information helps neurosurgeons assess the risk of postoperative neurological deficit, choose the most convenient and least traumatic access, and suggest the extent of resection.

Third, researchers are also trying to introduce fMRI into routine clinical practice for various neurological and psychiatric diseases. The main goal of numerous works in this area is to assess changes in the functioning of the brain in response to damage to one or another of its areas - loss and (or) switching of zones, their displacement, etc., as well as dynamic observation of the restructuring of activation zones in response to drug therapy therapy and (or) rehabilitation measures. Ultimately, fMRI studies conducted on patients of various categories can help determine the prognostic value of various options for functional restructuring of the cortex to restore impaired functions and develop optimal treatment algorithms.

Additional information on fMRI:

article “Advanced neuroimaging technologies” by M.A. Piradov, M.M. Tanashyan, M.V. Krotenkova, V.V. Bryukhov, E.I. Kremneva, R.N. Konovalov; Federal State Budgetary Institution "Scientific Center of Neurology" (journal "Annals of Clinical and Experimental Neurology" No. 4, 2015) [read];

article “Functional magnetic resonance imaging” E.I. Kremneva, R.N. Konovalov, M.V. Krotenkova; Scientific Center of Neurology of the Russian Academy of Medical Sciences, Moscow (journal “Annals of Clinical and Experimental Neurology” No. 1, 2011) [read];

article “The use of functional magnetic resonance imaging in the clinic” Belyaev A., Peck Kung K., Brennan N., Kholodny A.; Memorial Sloan-Kettering Cancer Center, Functional MRI Laboratory, Department of Radiology, New York, USA (Russian electronic journal of radiology, No. 1, 2014) [read];

article “Functional magnetic resonance imaging at rest: new opportunities for studying the physiology and pathology of the brain” by E.V. Seliverstova, Yu.A. Seliverstov, R.N. Konovalov, S.N. Illarioshkin FSBI "Scientific Center of Neurology" RAMS, Moscow (journal "Annals of Clinical and Experimental Neurology" No. 4, 2013) [read];

article “Functional magnetic resonance imaging at rest: possibilities and future of the method” by Yu.A. Seliverstov, E.V. Seliverstova, R.N. Konovalov, M.V. Krotenkova, S.N. Illarioshkin, Scientific Center of Neurology of the Russian Academy of Medical Sciences, Moscow (Bulletin of the National Society for the Study of Parkinson's Disease and Movement Disorders, No. 1, 2014) [read];

article “Functional magnetic resonance imaging and neuroscience” by M.B. Stark, A.M. Korostyshevskaya, M.V. Rezakova, A.A. Savelov; Institute of Molecular Biology and Biophysics of the Siberian Branch of the Russian Academy of Medical Sciences, Novosibirsk; Institute "International Tomographic Center" SB RAS, Novosibirsk; NPF "Computer biocontrol systems", Novosibirsk (magazine "Advances of Physiological Sciences", No. 1, 2012) [read]