What is a hyperintense signal? MRI

People first started talking about MRI at the end of the 20th century, although at first the technique was called NMR - nuclear magnetic resonance. Subsequently, as technology improved, the name was changed to MRI - magnetic resonance imaging.

In the 21st century, diagnosing brain pathology without MRI is unthinkable. The most advanced option is fMRI or functional MRI. It allows you to evaluate not only organic, anatomical changes in the nervous tissue, but also provides information about the function of the brain regions of interest.

The phenomenon of nuclear magnetic resonance was demonstrated by an American scientist Isidor Isaac Rabi in 1937, while he was working on the team developing the atomic bomb.

TO practical medicine Rabi's "magnetic resonance detection method" was only adapted in 1971. In Brooklyn medical center, USA. Physicist Raymond Damadian, experimenting on rats, discovered differences between normal and tumor tissues with magnetic resonance.

Physical justification of the method

In the normal state, the magnetic field of an atom is zero: the positive charge of protons is balanced by the negative charge of electrons.

But when atoms are placed in a strong magnetic field and irradiated with a radiofrequency pulse, the charge on the protons changes. Some of them have more energy than at rest. Once the RF pulse is turned off, the accumulated “excess” energy is released. And these impulses, the transition of atomic nuclei from a high energy level to a normal one, can be detected.

The larger the molecule, the slower it accumulates and releases kinetic energy. The difference is calculated in microseconds and their fractions, but special equipment is capable of recording this difference in time. The main thing is to have something to compare with, a benchmark.

Water was chosen as this sample. It is everywhere in the human body. And its molecules in any tissue give the same so-called time. longitudinal relaxation.

The received data is summarized, processed by a computer and displayed on the monitor screen. An image is made up of pixels, which are the unit of image. The brightness of a pixel is proportional to the voxel - the degree of magnetization in a given unit of volume. The combination of pixels on a monitor screen forms an image. The characteristics of the picture depend on how much water there is in a particular tissue.

In addition, the use of special contrasts based on paramagnetic ions increases the resolution of the technique and promotes better visualization and differentiation of tissues.

Contrasting

The advantage of MRI is that it provides an image of the body part of interest without the need to change body position.

Nowadays, a rare earth metal, gadolinium, is used as a basis for contrast. To make it non-toxic to humans, a chelate complex of gadolinium with derivatives of ethylenediaminetetraacetic acid (with diethylenetriaminepentaacetic acid) is synthesized.

Contrast is administered intravenously. The standard dosage is 0.1 mmol/kg. Optimal contrast is observed on T1-weighted images.

Diagnostic capabilities

Initially, the MRI showed a static anatomical picture. Similar to CT, but with better differentiation of soft tissues.

Since the 80s, diffusion-weighted MRI has been introduced into medical practice, which makes it possible to evaluate the processes of water diffusion in tissues. This technique has found application both in terms of detecting ischemia and regarding any functional abnormalities.

The technique is based on the difference in the magnetic properties of oxy and deoxyhemoglobin, as well as a change in the magnetic properties of tissue due to different blood supply. For neurologists, fMRI allows them to assess functional state brain tissue.

A competitor to functional MRI is PET. This technique requires the use of toxic and expensive radioisotope pharmaceuticals.

Magnetic resonance imaging is non-invasive and has a minimal list of contraindications. Functional MRI can be repeated multiple times, making it an excellent tool for patient monitoring.

Ischemic stroke

Direct signs of brain hypoxia are changes in the diffusion coefficient of signal intensity in individual (affected) areas and signs of edema. Indirect ones include changes in the lumen of blood vessels.

A decrease in the coefficient of observed diffusion is caused by a disorder of tissue metabolism under conditions of oxygen starvation. The second factor is the decrease in temperature in this area.

Early signs

The first signs of acute ischemia, on MRI, appear after 6 to 8 hours. In fact, in all patients, by the end of the day, the signal intensity in the affected area increases in T2 mode.

Initially, the lesion has a heterogeneous structure and unclear boundaries. On days 2–3, the signal remains heterogeneous, but acquires a homogeneous structure. Here it becomes difficult to differentiate the area of ​​edema and, in fact, the lesion. In T1 mode, after 24 hours, the signal intensity decreases.

Indirect signs of ischemia are detected from the first minutes of its development.

These signs include:

• the appearance of intra-arterial isointense or hyperintense signal from cross section vessel;
• a combination of an isointense signal in the lumen of the vessel and a hyperintense signal along the periphery of the lesion;
• no signal loss effect, since such a phenomenon is normally characteristic of blood flow.

In the first hours, using MRI, with a sufficient degree of probability, one can judge the reversibility of the ischemic focus. To do this, diffusion-weighted and T2 images are evaluated.

If the observed diffusion coefficient (ODC) is low and there is no change in the signal in T2 mode, then in the first hours of a stroke one can count on the reversibility of the pathology.

If, along with low CDI in T2 mode, the lesion is intense, one should talk about the irreversibility of the lesion.

Further evolution of the MR signal: with a decrease in the area of ​​edema and the beginning of the resorption phase from the second week, the lesion again becomes heterogeneous. From the beginning of week 4, relaxation time increases again, with a corresponding increase in signal intensity in T2 mode. By the time the cystic cavity forms, by 7-8 weeks, the MR signal corresponds to that of the cerebrospinal fluid.

When using contrast during the acute period of a stroke, up to 6-8 hours, the contrast does not accumulate in the affected area. This is probably due to the preservation of the blood-brain barrier. Accumulation of contrast agent is noted in the later period of stroke, and before the formation of a cystic cavity. After this, the contrast again ceases to accumulate in the lesion.

Hemorrhagic stroke

The image of the lesion in hemorrhagic stroke on MRI depends on the ratio of oxyhemoglobin and deoxyhemoglobin, which have different magnetic properties. The dynamics of this process can be observed by evaluating images in T1 and T2 modes.

In the most acute stage, due to the high content of oxyhemoglobin, the hematoma is visualized as an isointense and hypointense focus.

With the onset of the acute period, oxyhemoglobin is converted to deoxyhemoglobin. In T2 mode, this is manifested by the formation of a low-density focus.

In the subacute period, deoxyhemoglobin turns into methemoglobin. These changes can be assessed in T1 mode, an increase in signal intensity is noted.

In the late stage, the level continues to increase and erythrocyte lysis occurs. Also, the amount of water in the resulting cavity increases. Such processes cause the formation of a hyperintense focus in both T1 and T2 modes.

IN chronic stage, hemosiderin and ferritin are deposited in macrophages, which are located in the capsule of the lesion. On MRI it appears as a dark ring around the hematoma on T2.

Damage to the white matter of the brain

There is a difference between biochemical phenomena in the white and gray matter of the brain. And it makes it possible to differentiate one from the other.

Gray matter contains more water, and white contains more lipids. This allows them to be confidently distinguished during MRI.

However no specific signs which would allow a clear diagnosis to be formulated after the examination. Therefore, the present picture on the monitor must be correlated with the clinical manifestations of the pathology nervous system.

Let us consider the typical manifestations of white matter damage in diseases of the nervous system.

Multiple sclerosis

Regarding this pathology, MRI is very informative. The procedure reveals multiple foci of increased density, located asymmetrically, deep in the white matter. The typical localization of such foci is along the periphery of the ventricles of the brain (periventricular), in the corpus callosum and stem structures, and the cerebellum.

When the spinal cord is damaged, similar lesions are detected in T2 mode. In the case of retrobulbar neuritis in multiple sclerosis, MRI shows increased signal from the optic nerves.

Using contrast, you can establish how long ago the process is. Fresh lesions readily accumulate contrast, unlike indifferent old ones.

In order to establish a diagnosis of multiple sclerosis with a high probability based on MRI, two signs must be found. Firstly, foci of typical localization (subtentorial, periventricular, and cortical), and at least one of them must accumulate contrast. Secondly, lesions with a diameter of more than 5 mm must be found.

Acute disseminated encephalomyelitis

This pathology appears on MRI as large foci of increased signal. They are located, as a rule, in the deep, subcortical sections of the white matter and tend to merge with each other.

Neurosarcoidosis

MRI reveals diffuse lesions with typical localization:

• chiasm (where the optic nerves cross);
• pituitary;
• bottom of the third ventricle.

Also, neurosarcoidosis often affects the meninges.

Subacute sclerosing panencephalitis

This pathology is manifested by foci of increased density in T2 mode. They are located mainly in the basal ganglia and along the periphery of the ventricles of the brain.

Brain tumors

The features of the lesion identified on MRI depend on the ratio of extracellular and intracellular fluid in the formation. Therefore, the size of the formation obtained on MRI does not always correspond to the actual extent of the spread of tumor cells.

A number of diagnostic criteria have been developed to judge the nature of the tumor by its manifestations on MRI.

Tumors of adipose tissue are relatively rare. Neoplasms that produce isointense signals (eg, meningiomas) or hyperintense lesions (eg, gliomas) are more common.

Calcifications appear as low-intensity foci. Acute hemorrhages are visualized as an area of ​​reduced T2 signal. In the subacute and chronic periods, hemorrhages give a T2 signal of increased intensity.

The degree of malignancy of a space-occupying lesion can also be judged by its boundaries.

Thus, smooth and clear edges at the lesion are more indicative of the benign quality of the formation.

Malignant tumors have blurred outlines, reflecting the infiltrating nature of growth.

The technique makes it possible to determine the presence of a space-occupying lesion in the brain, even when it is not visible during routine examination. Indirect signs of a tumor include:

• deformation of the convolutions of the brain;
• anomalies of the ventricular system;
• internal hydrocephalus;
• displacement of brain structures from their anatomical location.

For clarifying and differential diagnosis, contrast is used.

Tumor differentiation

Thanks to MRI, it becomes possible to predict in advance which part has become the source of tumor cells. This helps distinguish a primary node from a metastatic lesion.

Meningiomas

As a rule, they appear as an isointense signal in T1 mode. A slight increase in the signal in T2 mode is characteristic of angioblastic meningiomas. Fibroblastic meningiomas exhibit an isointense or hypointense signal.

In such conditions, the above-described indirect signs. And also – contrast. Contrast readily accumulates in meningioma, and during MRI it appears as a homogeneous formation with clear boundaries.

Any magnetic field can induce an electric current in the coil, but the prerequisite for this is a change in the strength of the field. When short EM radiofrequency pulses M are passed through the patient's body along the y-axis, the field of radio waves causes the M moments of all protons to rotate clockwise around this axis. In order for this to happen, it is necessary that the frequency of the radio waves be equal to the Larmor frequency of protons. This phenomenon is called nuclear magnetic resonance. Resonance is understood as synchronous oscillations, and in this context this means that in order to change the orientation of the magnetic moments of protons M, the fields of protons and radio waves must resonate, i.e. have the same frequency.

After transmitting a 90-degree pulse, the tissue magnetization vector (M) induces an electrical current (MR signal) in the receiving coil. The receiving coil is placed outside the anatomical area under study, oriented in the direction of the patient, perpendicular to B0. When M rotates in the x-y planes, it induces a current in the coil E, and this current is called the MR signal. These signals are used to reconstruct images of MR slices.

In this case, tissues with large magnetic vectors will induce strong signals and appear bright in the image, while tissues with small magnetic vectors will induce weak signals and will appear dark in the image.

Image contrast: proton density, T1- and T2-weighted. Contrast in MR images is determined by differences in the magnetic properties of tissues or, more precisely, differences in the magnetic vectors rotating in x-y plane and inducing currents in the receiving coil. The magnitude of the tissue magnetic vector is primarily determined by the proton density. Anatomical areas with a low number of protons, such as air, always induce a very weak MR signal and thus always appear dark on the image. Water and other liquids, on the other hand, should appear bright on MR images as having a very high proton density. However, it is not. Depending on the imaging technique used, liquids can produce either bright or dark images. The reason for this is that the contrast of the image is determined not only by the proton density. Several other parameters play a role; the two most important of them are T1 and T2.

Rice.

Between arriving MP pulses, protons undergo two relaxation times T1 and T2, which are based on the loss of magnetic voltage on the x-y plane (Mxy) and its restoration along the z axis (Mz).

Maximum tissue magnetism, z-oriented (Mz), depends on proton density, so the relative strength of MP signals determined immediately after delivery of a 90° pulse or after recovery of Mz allows proton density-weighted imaging to be constructed. T1 - relaxation reflects the gradual restoration of nuclear magnetism and the orientation of individual hydrogen protons in the direction Bo = > (z axis) to their original position, which was inherent in them by providing a 90 ° impulse. As a result, after turning off the 90° pulse, the tissue magnetic moment increases along the z axis with increasing acceleration from 0 to the maximum value Mz, which is determined by the proton density of the tissue. T1 is defined as the time during which M restores its original value by 63%. After 4-5 time intervals equal to T1 have passed, Mz is completely restored. The shorter the T1, the faster the recovery. The physical basis of T1 relaxation is the exchange of thermal energy between molecules. T1 - relaxation time depends on the size of the molecules and their mobility. In dense tissues with large immobile molecules, protons retain their position for a long time, contain energy, and few weak impulses occur, so T1 is long. In a liquid, the position of protons changes faster and thermal energy is released faster, therefore T1 - relaxation in a liquid with small molecules, moves quickly, is short and is accompanied by a significant number of electromagnetic pulses of varying strengths. In parenchymal tissues, T1 relaxation is about 500 ms, varying widely depending on the characteristics of their structure. In adipose tissue with molecules of average size and mobility, T1 is short and the number of impulses is greatest. Images whose contrast is based on T1 differences in adjacent tissues are called T1-weighted images.

The physical basis of T2 relaxation is the interaction of tissue magnetism with protons. T2 is an indicator of the gradual decay of tissue magnetism on the x-y (mxy) plane after eliminating the 90° pulse and is defined as the time during which the mxy has lost 63% of its maximum tension. After 4-5 time intervals equal to T2 have passed, the moss completely disappears. The T2 time interval varies depending on physical and chemical properties fabrics. Thick fabrics have stable internal magnetic fields, and therefore the precession of protons in them quickly decays, and the induction of energy quickly decreases, sending a lot electromagnetic waves different frequencies, so T2 is short. In liquids, internal magnetic fields are unstable and quickly become equal to 0, affecting the precession of protons to a lesser extent. Therefore, the frequency of protons in procession in the liquid is high, the electromagnetic pulses are weak, and the T2 relaxation is relatively long. In parenchymal tissues, T2 is about 50 ms, i.e. 10 times shorter than TE. Variations in T2 time affect the magnitude of electromagnetic pulses (MP). Therefore, the image built on their calculation is called T2 - weighted image. Its detection is hampered by signals from the TE, so registration of a T2-weighted image is achieved by introducing a time interval - echo time (TO) between the 90 ° pulse and the measurement of the MP induced by it. The echo time of the moss gradually decreases due to T2 relaxation. By recording the amplitude of the MP signal at the end of the echo time, the T2 difference in various tissues is determined.

19145 0

Magnetic resonance, or, as it was and is still called in the natural sciences, nuclear magnetic resonance (NMR), is a phenomenon first mentioned in the scientific literature in 1946 by US scientists F. Bloch and E. Purcell. Following the inclusion of NMR as a medical imaging modality, the word "nuclear" was dropped. The modern name of the method, magnetic resonance imaging (MRI), was transformed from the earlier name - NMR solely for reasons of marketing and radiophobia of the population. The main elements of a magnetic resonance imaging scanner are: a magnet that generates a strong magnetic field; emitter of radio frequency pulses; a receiving coil-detector that picks up the response signal from tissues during relaxation; a computer system for converting signals received from a detector coil into an image displayed on a monitor for visual evaluation.

The MRI method is based on the NMR phenomenon, the essence of which is that nuclei located in a magnetic field absorb the energy of radio frequency pulses, and when the pulse ends, they emit this energy when transitioning to their original state. The magnetic field induction and the frequency of the applied radio frequency pulse must strictly correspond to each other, i.e. be in resonance.

The role of classical x-ray examination is limited by the ability to obtain images of bone structures only. At the same time, bone changes in the TMJ, as a rule, appear in the later stages of the disease, which does not allow timely assessment of the nature and severity of the pathological process. In the 1970-1980s, arthrotomography with contrast of the joint cavity was used to diagnose discoligamentary changes, which as an interventional procedure has now been replaced by studies that are more informative for the doctor and not burdensome for the patient. Widely used in modern clinic X-ray CT allows a detailed assessment of the structure of the bones that form the TMJ, but the sensitivity of this method in diagnosing changes in the intra-articular disc is too low. At the same time, MRI as a non-invasive technique allows you to objectively assess the condition of the soft tissue and fibrous structures of the joint and, above all, the structure of the intra-articular disc. However, despite the high information content, MRI of the TMJ does not have a standardized methodology for performing research and analyzing detected disorders, which gives rise to discrepancies in the data obtained.

Under the influence of a strong external magnetic field, a total magnetic moment is created in the tissues, coinciding in direction with this field. This occurs due to the directional orientation of the nuclei of hydrogen atoms (representing dipoles). The higher the magnetic field strength, the greater the magnetic moment in the object under study. When performing a study, the area under study is exposed to radio pulses of a certain frequency. In this case, hydrogen nuclei receive an additional quantum of energy, which causes them to rise to a higher energy level. The new energy level is at the same time less stable, and when the radio pulse ends, the atoms return to their previous position - less energetically capacious, but more stable. The process of transition of atoms to their original position is called relaxation. During relaxation, the atoms emit a response quantum of energy, which is detected by a sensing detector coil.

The radio pulses that influence the “zone of interest” during scanning are different (they are repeated with different frequencies, they deflect the magnetization vector of the dipoles at different angles, etc.). Accordingly, the response signals of atoms during relaxation are not the same. A distinction is made between the so-called longitudinal relaxation time, or T1, and the transverse relaxation time, or T2. Time T1 depends on the size of the molecules that contain hydrogen dipoles, on the mobility of these molecules in tissues and liquid environments. T2 time largely depends on the physical and chemical properties of tissues. Based on the relaxation times (T1 and T2), T|- and Tg-weighted images (WI) are obtained. The fundamental thing is that the same tissues have different contrast on T1 and T2 WI. For example, fluid has a high MR signal (white on tomograms) on T2 WI and a low MR signal (dark gray, black) on T1 WI. Adipose tissue (in fiber, the fatty component of cancellous bone) has a high intensity MR signal (white) on both T1 and T2 WI. By changing the intensity of the MR signal on T1 and T2 VI of various structures, one can judge their qualitative structure (cystic fluid).

In modern radiation diagnostics, the MRI method is considered the most sensitive in detecting changes in soft tissue structures. This method allows you to obtain images in any plane without changing the position of the patient’s body, and is harmless to humans.

However, there are contraindications to performing MRI related to the damaging effects of the magnetic field and radio pulses on some devices (heart pacemakers, hearing aids). It is not recommended to perform MRI if the patient has metal implants, terminals, foreign bodies. Since most MRI scanners are a closed space (magnet tunnel), performing the examination on patients with claustrophobia is extremely difficult or impossible. Another disadvantage of MRI is the long examination time (depending on software tomograph from 30 minutes to 1 hour).

Since both joints function as a single unit, it is imperative to conduct a bilateral examination. It is important to use a coil (surface) of small diameter (8-10 cm), which allows you to obtain maximum spatial resolution. When positioning the coil, its center is located 1 - 1.5 cm ventral to the external auditory canal (Fig. 3.33).

MR examination technique.

Scanning begins with the mouth closed (in the position of habitual occlusion), and then with the mouth open up to 3 cm to determine the maximum physiological displacement of the intra-articular disc and articular head. To hold the open mouth in a stable position, retainers made of non-magnetic material are used.

Rice. 3.33. Positioning of the detector coil during MRI.
C - coil; TMJ - TMJ; EAC - external auditory canal.

The standard MR examination protocol includes performing parasagittal T1 and T2 VIs, paracoronal T1 VIs in the occlusion position, parasagittal T1 VIs with open mouth and kinematics of the joint (scanning is performed in several phases with gradual opening of the mouth from closed to maximum open position). Parasagittal sections are planned along a plane perpendicular to the long axis of the articular head. The study area includes the external auditory canal, the bottom of the temporal fossa, the ascending branch lower jaw. This projection is preferable for studying the intra-articular disc and differentiating other intra-articular structures.

T1 VI allows one to clearly differentiate the shape, structure, and degree of disc degeneration, identify changes in the lateral pterygoid muscle (including fibrosis in the upper abdomen), and assess the condition of the bilaminar zone and ligaments, as well as bone structures. After obtaining T1 WI, T2 WI are performed, similar in scanning geometry (direction of the scanning plane, thickness of the slices and spaces between them, size of the field of view). T2 V-I allows one to clearly detect even minimal amounts of fluid in the upper and lower parts of the joint, swelling of the bilaminar zone and periarticular soft tissues.

The next stage of the study is obtaining parasagittal T1-weighted scans with the mouth open. This sequence helps to assess the mobility of the intra-articular disc, the displacement of the disc and the articular head relative to each other. The optimal amount of mouth opening is 3 cm, when the head of normal mobility moves under the apex of the articular tubercle. Paracoronal (frontal) sections are made parallel to the long axis of the articular heads in the occluded position. These views are preferred for assessing lateral disc displacement, articular head configuration, and deformation.

Parasagittal T2 VIs have lower anatomical and topographic resolution compared to T1 VIs. But T2 VI is more sensitive and preferable for detecting intra-articular fluid in various pathological conditions.

If the TMJ is changed secondary, and the primary process is localized in the surrounding tissues, T2-weighted tomograms are performed in the axial projection, as well as T1-weighted tomograms in the axial and frontal projections before and after contrast enhancement ( intravenous administration contrast agents containing gadolinium chylates). Contrast enhancement is advisable in cases of damage to the TMJ due to rheumatoid processes.

Rapid sequences of the method are used in the study of joint kinematics to assess the position of the disc and articular head in 5 different phases of mouth opening: from the occlusion position (1st phase) to the maximum open mouth (5th phase).

Rice. 3.34. T1 VI in oblique agittal projection. Normal relationship of articular structures with central occlusion. In the diagram, the arrow indicates the central zone of the disc and the vector of the chewing load.

Static MRI scans allow the position of the disc and head to be assessed in only two positions. Kinematics gives a clear idea of ​​the mobility of joint structures during the gradual opening of the mouth.

Normal MR anatomy. Oblique sagittal scans allow visualization articular head like a convex structure. On T1 low-intensity imaging, the cortical layer of the bone elements of the joint, as well as the fibrous cartilage of the articular surfaces, is clearly distinguished from the fat-containing trabecular component of the bone. The articular head and fossa have clear, rounded contours. In the position of central occlusion (closed mouth), the articular head is located in the center of the glenoid fossa. In this case, the maximum width of the joint space is 3 mm, the distance between the surface of the head to the anterior and posterior parts of the articular fossa is the same.

The intraarticular disc is visualized as a biconcave structure of low intensity and homogeneous structure (Fig. 3.34). A mild increase in the signal intensity of the posterior parts of the disc is observed in 50% of unchanged discs and should not be considered as a pathology without corresponding changes in shape and position.

In the occlusion position, the disc is located between the head and the posterior slope of the articular tubercle. Normally, the upper pole of the head in the occlusion position is at the 12 o’clock position and the anteroposterior deviation should not exceed 10°.

The anterior portions of the bilaminar structure are attached to the posterior portion of the disc and connect the disc to the posterior portions of the joint capsule.

The low-intensity signal of the disc and the high-intensity signal of the bilaminar zone on T1 V I make it possible to clearly differentiate the contours of the disc.

The TMJ functions as a combination of two joints. When the mouth begins to open, the articular head makes rotational movements in the lower parts of the joint.

Rice. 3.35. T1 VI in oblique agittal projection. Normal position of intra-articular structures with the mouth open. The articular disc is under the tip of the articular tubercle, the central zone of the disc is between the tips of the tubercle and the head.

With further opening of the mouth, the disc continues to shift forward due to the traction of the lateral pterygoid muscle. When the mouth is fully open, the head reaches the top of the articular tubercle, the disc completely covers the articular head, and between the head and the top of the articular tubercle there is an intermediate zone of the disc (Fig. 3.35).

Rice. 3.36. T1 VI in oblique coronal projection. Normal relationship of articular structures with central occlusion. The disc covers the articular head like a cap.

The oblique projection allows us to identify medial or lateral displacement of the disc. The disc is defined as a low-intensity structure covering the articular head like a cap (Fig. 3.36). This projection is preferable for identifying the lateralization of the position of the head, as well as for assessing the condition of the subchondral parts of its bone structure, and detecting intra-articular osteophytes.

V.A. Khvatova
Clinical gnathology

On a series of T1 and T2 weighted MR tomograms in three projections, sub- and supratentorial structures are visualized.

In the white matter of the brain, a few foci are T2 hyperintense, FLAIR and T1 isointense without perifocal edema, up to 0.3 cm in size.

The lateral ventricles of the brain are symmetrical, not dilated, without periventricular edema. III ventricle not expanded. The fourth ventricle is not dilated or deformed.

The internal auditory canals are not dilated.

The chiasmal area is without features, the pituitary gland is not enlarged in size, the pituitary tissue has a normal signal. The chiasmal cistern is not changed. The pituitary funnel is not displaced. The basal cisterns are not dilated or deformed.

Subarachnoid convexital spaces and grooves are not widened. The lateral fissures of the brain are symmetrical and not widened.

The cerebellar tonsils are located at the level of the foramen magnum

CONCLUSION: MR picture of a few foci of gliosis in the white matter of the brain (foci of discirculatory dystrophy).

Please tell me what this diagnosis means? Why is this dangerous? What's the prognosis? What are foci of discirculatory dystrophy?

The neurologist prescribed me:

- “Mexidol” 125 mg 1 tablet x 3 times a day (1 month).

- “Phenibut” 250 mg x 2 times a day, afternoon and evening (1 month).

- “Cavinton forte” 10 mg x 3 times a day (3 months).

- “Indap” 2.5 mg in the morning (continuously).

- “Berlipril” 5 mg for blood pressure above 130 mmHg.

Sanatorium-resort treatment (“Uvildy”, “Ust-Kachka”).

Baths, saunas, and increased insolation are contraindicated.

But when the weather changes and when I get nervous, the headaches start again for 2-3 days. What do you recommend?

Magnetic resonance imaging - Diagnosis and treatment

The phenomenon of nuclear magnetic resonance was demonstrated by Rabi et all. In 1939 and 1971, R. Damadian showed the differences between normal and tumor tissues with magnetic resonance, which served as an impetus for the active introduction of the method into practical medicine.

Physical basis of the method

In the absence of external magnetic fields, the spins of the protons of the nucleus are oriented randomly, as a result of which their total magnetic moment is zero. When an object is placed in a magnetic field and irradiated with a radio frequency pulse, the energy level of protons changes, i.e. the transition of some protons from a “low” energy level to a “higher” one and their orientation relative to the external magnetic field. After the cessation of the radio frequency pulse, the excited protons return to their original level, while giving off kinetic energy to the crystal lattice.

There are differences in the degree of longitudinal relaxation between large and small molecules. In particular, water molecules have a longer longitudinal relaxation time than organic molecules. The degree of water content in tissues, as well as the molecular spectrum of the substances included in their composition, determines, in a simplified version, the physical basis of the method. The received data is summarized and displayed on the monitor screen. An image is made up of pixels, which are the unit of image. The brightness of a pixel is proportional to the voxel - the degree of magnetization in a given unit of volume. The combination of pixels on a monitor screen forms an image.

A special feature of MRI is that it is possible to obtain images in different planes without changing the position of the patient’s body. To improve image quality and differential diagnosis use the contrast method using paramagnetic ions. Currently, a rare earth metal, gadolinium, is used to prevent side effects on the human body; this metal is used as a chelate complex with derivatives of ethylenediaminetetraacetic acid (for example, with diethylenetriaminepentaacetic acid). The drug is usually used at a dose of 0.1 mmol/kg, which is administered intravenously. Optimal contrast is observed on T1-weighted images. Since the 80s, diffusion-weighted MRI has been introduced into medical practice, which makes it possible to evaluate the processes of water diffusion in tissues. This technique has found application in the study of ischemic processes in tissues.

Recently, the so-called functional MRI method has been used. The technique is based on the difference in the magnetic properties of oxy- and deoxyhemoglobin, as well as changes in the magnetic properties of tissue with changes in blood supply. This technique allows you to assess the functional state of brain tissue. Unlike PET, there is no need to use radiopharmaceuticals. The technique is non-invasive, functional MRI can be repeated several times. All of the above determines the prospects for the development of functional MRI.

Ischemic stroke

Direct signs include changes in the coefficient of observed diffusion of signal intensity, signs of edema, and indirect signs include changes in the lumen of blood vessels. The decrease in the observed diffusion coefficient is associated with metabolic disorders in the ischemic zone, as well as with a decrease in temperature in this area. The first signs of signal changes appear 6–8 hours after the development of acute ischemia. By the end of the day, almost all patients experience an increase in signal intensity in the affected area in T2 mode.

Initially, the lesion has a heterogeneous structure and unclear boundaries. On days 2–3, the signal remains heterogeneous, but acquires a homogeneous structure, which makes it difficult to differentiate the edema zone and the lesion itself. In T1 mode, signal changes are manifested by a decrease in its intensity, which can be observed after 1 day.

Indirect signs of ischemia can be detected from the first minutes of its development. These signs include: the appearance of an intra-arterial isointense or hyperintense signal from the cross-section of the vessel, with a possible combination of an isointense signal in the lumen of the vessel and a hyperintensive signal along the periphery of the lesion. Other indirect signs include the absence of signal loss effect (which is normally characteristic of blood flow). In the first hours, using MRI, it is possible to judge with a sufficient degree of probability the reversibility of the ischemic focus. For this purpose, diffusion-weighted images and T2 images are evaluated. Moreover, if the observed diffusion coefficient (ODC) is low and there is no change in the signal in the T2 mode, then in the first hours of the stroke we can talk about its reversibility. If, along with low CDI in T2 mode, the lesion is sufficiently intense, we can talk about the irreversibility of the lesion.

Further evolution of the MR signal: with a decrease in the area of ​​edema and the beginning of the resorption phase from the second week, the lesion again becomes heterogeneous. From the beginning of week 4, relaxation time increases again, with a corresponding increase in signal intensity in T2 mode. With the formation of a cystic cavity by 7-8 weeks, the MR signal corresponds to that of the cerebrospinal fluid. When using the contrast method in the acute period of a stroke, up to 6-8 hours, the lesion usually does not accumulate contrast, which is probably due to the preservation of the blood-brain barrier. Later, the accumulation of contrast agent is noted, until the formation of a cystic cavity, when the lesion again stops accumulating contrast.

Hemorrhagic stroke

The image of the lesion in hemorrhagic stroke on MRI depends on the ratio of oxyhemoglobin and deoxyhemoglobin, which have different magnetic properties. The dynamics of this process can be observed by evaluating images in T1 and T2 modes.

The most acute stage of hematoma is manifested by an isointense or hypointense focus, which is associated with the presence of oxyhemoglobin. In the acute period, oxyhemoglobin turns into deoxyhemoglobin, which is accompanied by the formation of a low-density focus in T2 mode. In the subacute period, deoxyhemoglobin turns into methemoglobin. These changes can be assessed in T1 mode, and an increase in signal intensity is observed. In the late stage, along with the formation of methemoglobin, lysis of red blood cells occurs, and the amount of water in the cavity increases. This condition causes the appearance of a hyperintense focus in both T1 and T2. In the chronic stage, hemosiderin and ferritin are deposited in macrophages, which are located in the capsule of the lesion. At the same time, on MRI we get an image of a dark ring around the hematoma in T2 mode.

Damage to the white matter of the brain

The biochemical characteristics of brain tissue make it possible to differentiate the white and gray matter of the brain. So white matter contains more lipids and less water compared to gray matter, which is what MRI images are based on. At the same time, MRI is a nonspecific research method for lesions of the white matter of the brain, therefore, when obtaining an image, it is necessary to correlate it with the clinical picture. Let us consider the manifestations of white matter damage in major diseases of the nervous system.

Multiple sclerosis. MRI is very informative in this disease. With this disease, foci of increased density are identified, which, when the brain is damaged, are multiple, located asymmetrically, usually periventricularly in the deep white matter, in the corpus callosum, trunk (usually the bridge and cerebral peduncles), and cerebellum. Damage to the spinal cord is manifested by corresponding foci of increased density in T2 mode. It is also possible to increase the MR signal from the optic nerves if the disease manifests itself as retrobulbar neuritis. To determine the age of a lesion, contrast is used, while fresh lesions can accumulate contrast, old ones do not. There are a number of complex criteria that allow a fairly accurate diagnosis of multiple sclerosis. This is, firstly, the presence of foci of subtentorial, periventricular, and cortical localization, while at least one foci must accumulate contrast. Secondly, periventricular and subtentorial lesions larger than 5 mm.

Acute disseminated encephalomyelitis. This disease is characterized by the presence on MRI of extensive foci of increased MR signal in the T2 mode, which are located in the deep and subcortical sections of the white matter; the peculiarity is that these foci are prone to fusion.

Neurosarcoidosis. MRI reveals diffuse lesions in the area of ​​the chiasm, pituitary gland, hypothalamus, and the floor of the 3rd ventricle; the meninges are often affected.

Subacute sclerosing panencephalitis. This disease is manifested by foci of increased density in T2 mode with the foci located in the basal ganglia and periventricularly.

Brain tumors

The appearance of a lesion on MRI depends on the ratio of extracellular and intracellular fluid in the formation; therefore, the size of the lesion obtained on MRI does not always correspond to the area of ​​tumor cell spread. There are a number of criteria that allow you to determine the nature of the image and, based on these data, judge the nature of the tumor.

First, the image intensity of the lesion is assessed. Thus, tumors from adipose tissue, as well as those containing a large amount of lipids, are characterized by a decrease in relaxation time, which in the T1 mode is manifested by an intense signal. Tumors of adipose tissue are relatively rare. Tumors that produce isointense signals (eg, meningiomas) or hyperintense lesions (eg, gliomas) are more common.

The nature of the resulting image is also assessed; two options are possible: the structure of the image can be homogeneous or heterogeneous. For benign tumors characterized by a homogeneous image on MRI. For malignant tumors, a heterogeneous image is more typical, which reflects the processes of necrosis, hemorrhages in the tumor tissue, and the possible presence of calcifications. Calcifications appear as foci of low intensity, hemorrhages appear as an area of ​​reduced signal in T2 mode (with acute development of hemorrhage), in the subacute and chronic period of hemorrhage they give a signal of increased intensity in T2 mode.

By the nature of the tumor boundaries one can judge the degree of malignancy of the space-occupying lesion. Thus, an education with clear edges is more indicative of the good quality of the education. Malignant tumors are characterized by unclear boundaries, which often reflect infiltrative growth.

There are a number of signs by which one can judge the origin of a space-occupying formation. Tumors from the meninges and skull bones are characterized by the presence of cerebrospinal fluid gaps between the tumor tissue and the deformed area of ​​the brain; the base of the tumor is wider at the site of attachment to the bones of the skull; hyperostosis is also possible in this area. There are a number of so-called indirect signs of a tumor. These include deformation of the convolutions of the brain, the ventricular system, including internal hydrocephalus. For differential diagnosis, contrast injection is used.

Meningiomas often present with an isointense signal on T1. In T2 mode, a slight increase in signal is typical for angioblastic meningiomas; for fibroblastic meningiomas, an isointense or hypointense signal is more typical. In such conditions, indirect signs that were described earlier, as well as contrast, become of great importance. Contrast accumulates quite quickly in meningioma and during MRI it looks like a homogeneous formation with clear boundaries.

Tumors from brain tissue (glial row). Benign astrocytomas manifest as a homogeneous signal with increased density on T2 and isointense or hypointense signal on T1 (Fig. 1).

Aplastic astrocytomas manifest themselves with a heterogeneous signal, which reflects their structure - a tendency to cystic degeneration and the formation of hemorrhages into the tumor tissue. Glioblastomas, as the most malignant formations, are manifested by pronounced heterogeneity (reflection of areas of necrosis, hemorrhages). The boundaries are unclear, the tumor itself is not differentiated from the surrounding area of ​​edema, and during contrast, the contrast accumulates heterogeneously in the tumor tissue.

Pituitary tumors. The main manifestation of a pituitary tumor is the presence on MRI of a formation of reduced and increased density in T1 and T2 modes in the projection of the pituitary gland. In the presence of a small adenoma (less than 1 cm in size), the so-called indirect signs indicating the growth of a space-occupying formation become of great importance - this is an upward displacement of the diaphragm of the sella turcica, deformation of the pituitary infundibulum, etc.

Craniopharyngiomas. The MRI picture is determined by the histological structure of the tumor - craniopharyngioma usually has a heterogeneous structure in the form of nodules, cystic cavities, and calcifications. These features determine the picture on MRI. Cystic cavities appear with different signals in T1 and T2 modes, respectively; the tumor parenchyma appears hypointense in T1 mode and hyperintense in T2 mode.

Rathke's pouch cysts. The picture depends on the content of the cyst; if it is serous content, then in the T1 image the signal is hypointense, and in the T2 image it is hyperintense. With mucosal content in T1 and T2 modes, the signal will be of increased intensity. When contrasted, cysts do not accumulate contrast.

Neuromas. The main manifestation of a neuroma on MRI is the presence of a space-occupying formation of an isointense or hypointense nature of a homogeneous (small tumor) or heterogeneous (large tumor) structure (Fig. 2). Neuroma accumulates contrast unevenly.

Tumor metastases to the brain. The main manifestation of metastasis is the presence of a focus of increased intensity on the tomogram in T2 mode. When contrasting, contrast accumulates along the periphery of the tumor with the formation of ring-shaped structures (crown effect).

Inflammatory diseases of the nervous system

Meningitis. The structure of the resulting image depends on the nature of the pathological process, i.e., on the nosological form of meningitis. With serous meningitis, signs of dilation of the ventricular system and subarachnoid spaces may appear on MRI. With purulent meningitis, dilation of the ventricles of the brain and subarachnoid spaces is also noted; foci of increased intensity may appear in the brain parenchyma in T2 mode as a sign of inflammation. When contrast is administered, it accumulates mainly in the meninges. A feature of tuberculous meningitis is the appearance on the tomogram of a low-intensity focus surrounded by a high-intensity signal. These signs are manifestations of tuberculoma. Typically these lesions are located at the base of the brain.

Encephalitis. A characteristic manifestation is the appearance of a focus of increased intensity in the T2 mode in the substance of the brain, along with the above-described signs of meningitis.

Brain abscess. Before the formation of the capsule, the abscess on the tomogram looks like a focus of increased density in T2 mode heterogeneous structure. The capsule appears in T2 mode in the form of a rim of reduced density. The contrast accumulates in the abscess “tissue” and its capsule.

Hereditary diseases of the nervous system

Parkinson's disease is manifested by signs of atrophy of subcortical structures: caudate nucleus, globus pallidus, substantia nigra, Lewis nucleus, etc. In the presence of vascular pathology, which is more often noted in parkinsonism syndrome, the tomogram shows multiple lacunar infarctions, localized, including in the area of ​​subcortical structures, as well as leukoaraiosis. With Huntington's chorea, signs of atrophy of the caudate nucleus and globus pallidus are noted. Olivopontocerebellar degeneration is characterized by the presence of signs of atrophy in the white matter of the cerebellum, medulla oblongata, and pons. With hereditary cerebellar ataxia signs of atrophy of the cerebellum (its cortical parts and vermis) are noted. The role of MRI is also high in patients with autism, epilepsy, intracranial hypertension, attention deficit hyperactivity disorder (ADHD), psychomotor and speech development, minimal brain dysfunction (MCD), migraine headaches.

What is signal intensity?

The concept of intensity refers to the brightness of the signal generated by a particular tissue. Brighter (whiter) tissues are hyperintense, darker ones are hypointense. Tissues that fall somewhere in the middle of this scale are isointense.

These terms are typically applied to the signal of a lesion relative to surrounding tissue (eg, tumor is hyperintense relative to adjacent muscle tissue). Note that the term intensity is used rather than density, which is used in CT or conventional radiography.

10. Describe the signal intensity of fat and water on Ti- and T2-weighted iso-

Fat is bright (hyperintense) on T1-weighted images and less bright on T2-weighted images (Figure 6-1). Water is dark on T1-weighted images and bright on T2-weighted images. These points are important to remember because most pathological processes are associated with increased water content and are therefore hyperintense on T2-weighted images and hypointense on T1. A mnemonic rule may come in handy: Entrance Ticket for Two (white water for T-two).

11. What other tissues, besides fat, are bright in Ti-weighted images?

Blood (methemoglobin for subacute hemorrhages), protein-like substances, melanin and gadolinium (MRI contrast agent).

12. List what appears dark on T2-weighted images.

Calcium, gas, chronic hemorrhages (hemosiderin), mature fibrous tissue.

13. What is unique about the signal intensity of a hematoma?

The intensity of the blood signal changes over time as the properties of hemoglobin change (i.e., as oxyhemoglobin is converted to deoxyhemoglobin and methemoglobin). This position is useful for determining the duration of the hemorrhagic process. Acute hemorrhages (oxy- or deoxyhemoglobin) are hypointense or isointense on T1-weighted images, whereas subacute hemorrhages are

Rice. 6-1. Signal intensity on MRI. T1-weighted (A) and T2-weighted (B) sagittal images of the knee showing comparative signal intensities of fat (F) and joint fluid (f). Note that fluid appears brighter and fat appears less bright on T2-weighted images

hyperintense. Hemosiderin deposits in chronic hematomas are hypointense under all operating modes (types of pulse sequences).

Describe the appearance of blood vessels on MRI.

Vessels with flowing blood appear as a lack of signal, giving a dark circular or tubular appearance, respectively, on transverse or longitudinal images. Exceptions to this rule include vessels with slow blood flow and special types of pulse sequences (gradient echo), in which the blood vessels appear bright.

15. How can you tell whether you are seeing a T1-weighted or a T2-weighted image?

some TE - about 20 ms, high TE - about 80 ms. Low TR - about 600 ms, high

TR - about 3000 ms. T1-weighted images have low TE and low TR, for

In T2-weighted images, both of these parameters have high values. Weighted

Proton density images have low TE and high TR.

Knowing the signal characteristics of water and fat helps, especially when specific TRs and TEs are not indicated in the image. Look for fluid-containing structures such as the ventricles of the brain, bladder, or cerebrospinal fluid. If the fluid is bright, it is most likely T2-weighted, and if it is dark, it is most likely T1-weighted. If the fluid is bright but the rest of the image does not appear T2-weighted and the TE and TR are low, you are likely dealing with a gradient-echo image.

Magnetic resonance angiography. The principles of MRI allow the use of the unique properties of flowing blood. Images are generated that show only structures with flowing blood; all other structures on them are suppressed (Fig. 6-2). These principles can be modified so that only vessels with a certain direction of blood flow (for example, arteries rather than veins) will be displayed. MRI is useful in evaluating patients with suspected cerebrovascular disease (circle of Willis or carotid arteries) and when deep vein thrombosis is suspected. There are certain limitations and artifacts of MRA, especially when applied outside the central nervous system.

Interpretation of tomogram results

On a series of MR tomograms, weighted by T1, T2WI, FLAIR, SWI and DWI (factors: b-0, B-500, b-1000) in three projections, sub- and supratentorial structures are visualized.

The midline structures are not displaced.

In the subcortical parts of the right frontal lobe, parasagittal are noted

single, adjacent zones of local slight decrease in signal on T2VI and SWI, measuring up to 0.3×0.4×0.2 cm (frontal, sagittal, vertical).

In the white matter of the frontal lobes, subcortically, isolated small

foci of increased signal on T2WI, FLAIR and isointense signal on T1WI,

up to 0.2-0.3 cm in size, without signs of perifocal edema.

The lateral ventricles of the brain are of normal size and quite symmetrical (D=S). III

ventricle up to 0.2-0.4 cm wide. Moderate expansion of the suprasellar

tanks. The fourth ventricle and basal cisterns are not changed. Chiasmal area without

features. The pituitary tissue has a normal signal, with an uneven height of up to 0.3-

A moderate expansion of the perivascular spaces of Virchow-Robin and

intrathecal spaces of the optic nerves.

The subarachnoid convexital space is moderately unevenly expanded, mainly in the area of ​​the frontal and parietal lobes. The cerebellar tonsils are located at the level of the foramen magnum.

There is an increase in signal intensity on T2WI from the cells of the left mastoid process, measuring up to 3.1×4.5×3.7 cm, probably due to the phenomena of edema.

Focal changes in the white matter of the brain. MRI diagnostics

DIFFERENTIAL DIAGNOSIS OF WHITE MATTER LESIONS

The differential diagnostic range of white matter diseases is very long. MRI-detected lesions may reflect normal age-related changes, but most white matter lesions arise during life and as a result of hypoxia and ischemia.

Multiple sclerosis is considered the most common inflammatory disease, which is characterized by damage to the white matter of the brain. Most common viral diseases, leading to the appearance of similar lesions are progressive multifocal leukoencephalopathy and herpesvirus infection. They are characterized by symmetrical pathological areas that need to be differentiated from intoxication.

The complexity of differential diagnosis in some cases necessitates an additional consultation with a neuroradiologist to obtain a second opinion.

WHAT DISEASES ARE FOCIED IN THE WHITE MATTER?

Focal changes of vascular origin

• Atherosclerosis
• Hyperhomocysteinemia
• Amyloid angiopathy
• Diabetic microangiopathy
• Hypertension
• Migraine

• Multiple sclerosis
• Vasculitis: systemic lupus erythematosus, Behcet's disease, Sjögren's disease
• Sarcoidosis
• Inflammatory bowel diseases (Crohn's disease, ulcerative colitis, celiac disease)

Infectious diseases

• HIV, syphilis, borreliosis (Lyme disease)
• Progressive multifocal leukoncephalopathy
• Acute disseminated (disseminated) encephalomyelitis (ADEM)

Intoxications and metabolic disorders

• Poisoning carbon monoxide, vitamin B12 deficiency
• Central pontine myelinolysis

• Radiation therapy related
• Post-concussion lesions

• Caused by metabolic disorders (they are symmetrical in nature and require differential diagnosis with toxic encephalopathies)

Can be observed normally

• Periventricular leukoaraiosis, grade 1 according to the Fazekas scale

MRI OF THE BRAIN: MULTIPLE FOCAL CHANGES

The images reveal multiple pinpoint and “spotty” lesions. Some of them will be discussed in more detail.

Watershed-type heart attacks

• The main difference between heart attacks (strokes) of this type is the predisposition to localize foci in only one hemisphere on the border of large blood supply basins. The MRI shows an infarction in the deep rami basin.

Acute disseminated encephalomyelitis (ADEM)

• The main difference: the appearance of multifocal areas in the white matter and in the area of ​​the basal ganglia the day after an infection or vaccination. As with multiple sclerosis, ADEM may involve the spinal cord, arcuate fibers, and corpus callosum; in some cases, lesions may accumulate contrast. The difference from MS is that they are large in size and occur predominantly in young patients. The disease has a monophasic course

• It is characterized by the presence of small lesions 2-3 mm in size, simulating those in MS, in a patient with a skin rash and influenza-like syndrome. Other features include hyperintense signal from the spinal cord and contrast enhancement in the root zone of the seventh pair of cranial nerves.

Sarcoidosis of the brain

• The distribution of focal changes in sarcoidosis is very similar to that in multiple sclerosis.

Progressive multifocal leukoencephalopathy (PML)

• Demyelinating disease caused by John Cunningham virus in immunocompromised patients. The key feature is white matter lesions in the area of ​​the arcuate fibers that do not enhance with contrast and have a volumetric effect (unlike lesions caused by HIV or cytomegalovirus). Pathological areas in PML can be unilateral, but more often they occur on both sides and are asymmetrical.

• Key sign: hyperintense signal on T2WI and hypointense on FLAIR

• For zones of a vascular nature, deep localization in the white matter is typical, with no involvement of the corpus callosum, as well as the juxtaventricular and juxtacortical areas.

DIFFERENTIAL DIAGNOSTICS OF MULTIPLE FOCI, ENHANCED WITH CONTRAST

MRI scans demonstrated multiple pathological zones accumulating contrast agent. Some of them are described in more detail below.

• Most vasculitis is characterized by the occurrence of point focal changes that are enhanced by contrast. Damage to cerebral vessels is observed in systemic lupus erythematosus, paraneoplastic limbic encephalitis, b. Behçet, syphilis, Wegener's granulomatosis, b. Sjögren, as well as with primary angiitis of the central nervous system.

• It occurs more often in patients of Turkish origin. A typical manifestation of this disease is the involvement of the brain stem with the appearance of pathological areas that are enhanced by contrast in the acute phase.

Watershed type infarction

• Peripheral marginal zone infarcts may be enhanced by early contrast enhancement.

PERIVASCULAR SPACES OF VIRCHOW-ROBIN

On the left, a T2-weighted tomogram shows multiple high-intensity lesions in the basal ganglia region. On the right, in FLAIR mode, their signal is suppressed and they appear dark. On all other sequences they are characterized by the same signal characteristics as cerebrospinal fluid (in particular, a hypointense signal on T1 WI). This signal intensity, combined with the localization of the described process, are typical signs of Virchow-Robin spaces (also known as criblures).

Virchow-Robin spaces surround penetrating leptomeningeal vessels and contain cerebrospinal fluid. Their typical location is considered to be the region of the basal ganglia; they are also typically located near the anterior commissure and in the center of the brain stem. On MRI, the signal from the Virchow-Robin spaces in all sequences is similar to the signal from the cerebrospinal fluid. In FLAIR mode and on proton density-weighted tomograms, they give a hypointense signal, in contrast to lesions of a different nature. Virchow-Robin spaces are small in size, with the exception of the anterior commissure, where the perivascular spaces may be larger.

MR imaging can reveal both dilated perivascular Virchow-Robin spaces and diffuse hyperintense areas in the white matter. This MRI excellently illustrates the differences between Virchow-Robin spaces and white matter lesions. In this case, the changes are pronounced to a significant extent; the term “sieve state” (etat crible) is sometimes used to describe them. Virchow-Robin spaces increase with age, as well as with hypertension as a result of the atrophic process in the surrounding brain tissue.

NORMAL AGE CHANGES IN WHITE MATTER ON MRI

Expected age-related changes include:

• Periventricular “caps” and “stripes”
• Moderate atrophy with widening of the sulci and ventricles of the brain
• Point (and sometimes even diffuse) disturbances of the normal signal from brain tissue in the deep white matter (grades 1 and 2 according to the Fazekas scale)

Periventricular “caps” are areas of hyperintense signal located around the anterior and posterior horns of the lateral ventricles, caused by blanching of myelin and dilation of the perivascular spaces. Periventricular “strips” or “rims” are thin linear areas located parallel to the bodies of the lateral ventricles, caused by subependymal gliosis.

Magnetic resonance imaging demonstrated a normal age-related pattern: widening of the sulci, periventricular “caps” (yellow arrow), “stripes” and punctate lesions in the deep white matter.

The clinical significance of age-related brain changes is not well understood. However, there is an association between lesions and some risk factors for cerebrovascular disorders. One of the most significant risk factors is hypertension, especially in older people.

Degree of white matter involvement according to the Fazekas scale:

1. Light degree – spot areas, Fazekas 1
2. Medium degree – confluent areas, Fazekas 2 (changes in the deep white matter can be regarded as the age norm)
3. Severe degree – pronounced drainage areas, Fazekas 3 (always pathological)

DISCIRCULATORY ENCEPHALOPATHY ON MRI

Focal white matter changes of vascular origin are the most common MRI finding in elderly patients. They arise due to disturbances in blood circulation through small vessels, which is the cause of chronic hypoxic/dystrophic processes in the brain tissue.

A series of MRI scans shows multiple hyperintense areas in the white matter of the brain in a patient suffering from hypertension.

The MR tomograms presented above visualize disturbances in the MR signal in the deep parts of the cerebral hemispheres. It is important to note that they are not juxtaventricular, juxtacortical, or located in the corpus callosum. Unlike multiple sclerosis, they do not affect the cerebral ventricles or cortex. Considering that the likelihood of developing hypoxic-ischemic lesions is a priori higher, we can conclude that the presented lesions are most likely of vascular origin.

Only in the presence of clinical symptoms directly indicating an inflammatory, infectious or other disease, as well as toxic encephalopathy, does it become possible to consider focal changes in the white matter in connection with these conditions. Suspicion of multiple sclerosis in a patient with similar abnormalities on MRI, but without clinical signs, is considered unfounded.

The presented MRI scans did not reveal any pathological areas in the spinal cord. In patients suffering from vasculitis or ischemic diseases, the spinal cord is usually not changed, while in patients with multiple sclerosis, in more than 90% of cases, pathological disorders in the spinal cord. If the differential diagnosis between vascular lesions and multiple sclerosis is difficult, for example in elderly patients with suspected MS, MRI of the spinal cord may be useful.

Let's return again to the first case: focal changes were detected on MRI scans, and now they are much more obvious. There is widespread involvement of the deep parts of the hemispheres, but the arcuate fibers and corpus callosum remain intact. Ischemic white matter abnormalities may manifest as lacunar infarcts, border zone infarcts, or diffuse hyperintense zones in the deep white matter.

Lacunar infarctions result from sclerosis of arterioles or small penetrating medullary arteries. Border zone infarctions result from atherosclerosis of larger vessels, such as carotid obstruction or hypoperfusion.

Structural disorders of the cerebral arteries, such as atherosclerosis, are observed in 50% of patients over 50 years of age. They can also be found in patients with normal blood pressure, but are more common in hypertensive patients.

SARCOIDOSIS OF THE CENTRAL NERVOUS SYSTEM

The distribution of pathological areas on the presented MRI scans is extremely reminiscent of multiple sclerosis. In addition to deep white matter involvement, juxtacortical lesions and even Dawson's fingers are visualized. As a result, a conclusion was made about sarcoidosis. It is not for nothing that sarcoidosis is called the “great imitator”, because it surpasses even neurosyphilis in its ability to simulate the manifestations of other diseases.

On T1-weighted tomograms with contrast enhancement with gadolinium preparations, performed on the same patient as in the previous case, pinpoint areas of contrast accumulation in the basal ganglia are visualized. Similar areas are observed in sarcoidosis and can also be found in systemic lupus erythematosus and other vasculitides. Typical of sarcoidosis in this case is leptomeningeal enhancement (yellow arrow), which occurs as a result of granulomatous inflammation of the pia and arachnoid membranes.

Another typical manifestation in this same case is linear contrast enhancement (yellow arrow). It results from inflammation around the Virchow-Robin spaces and is also considered a form of leptomeningeal enhancement. This explains why in sarcoidosis the pathological zones have a similar distribution to multiple sclerosis: small penetrating veins pass through the Virchow-Robin spaces, which are affected in MS.

In the photo on the right: a typical type of skin rash that occurs when bitten by a tick (left) that carries spirochetes.

Lyme disease, or borreliosis, is caused by spirochetes (Borrelia Burgdorferi), the infection is transmitted by ticks, and infection occurs through transmission (by sucking on a tick). First of all, with borreliosis, a skin rash does not occur. After several months, the spirochetes can infect the central nervous system, resulting in abnormal white matter lesions resembling those seen in multiple sclerosis. Clinically, Lyme disease is manifested by acute symptoms of the central nervous system (including paresis and paralysis), and in some cases transverse myelitis may occur.

The key sign of Lyme disease is the presence of small lesions measuring 2-3 mm, simulating the picture of multiple sclerosis, in a patient with a skin rash and influenza-like syndrome. Other findings include spinal cord hyperintensity and contrast enhancement of the seventh cranial nerve (root entry zone).

PROGRESSIVE MULTIFOCAL LEUCOENCEPHALOPATHY DUE TO NATALIZUMAB

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease caused by John Cunningham virus in immunocompromised patients. Natalizumab is an anti-alpha-4 integrin monoclonal antibody drug approved for the treatment of multiple sclerosis due to its clinical and MRI benefit.

A relatively rare but serious side effect of taking this drug is an increased risk of developing PML. The diagnosis of PML is based on clinical manifestations, detection of viral DNA in the central nervous system (in particular, in the cerebrospinal fluid), and on data from imaging methods, in particular MRI.

Compared to patients with PML due to other causes, such as HIV, MRI findings in natalizumab-associated PML may be described as uniform and fluctuating.

Key diagnostic signs for this form of PML:

• Focal or multifocal zones in the subcortical white matter, located supratentorially with the involvement of arcuate fibers and gray matter of the cortex; Less commonly affected is the posterior fossa and deep gray matter
• Characterized by a hyperintense signal on T2
• On T1, areas may be hypo- or isointense depending on the severity of demyelination
• In approximately 30% of patients with PML, focal changes enhance with contrast. High signal intensity on DWI, especially at the edges of lesions, reflects active infection and cellular edema

MRI shows signs of PML due to natalizumab. Images courtesy of Bénédicte Quivron, La Louviere, Belgium.

Differential diagnosis between progressive MS and natalizumab-associated PML can be challenging. Natalizumab-associated PML is characterized by the following disorders:

• FLAIR has the greatest sensitivity in detecting changes in PML
• T2-weighted sequences allow visualization of specific aspects of PML lesions, such as microcysts
• T1-weighted images with and without contrast are useful for determining the degree of demyelination and detecting signs of inflammation
• DWI: to determine active infection

Differential diagnosis of MS and PML

MRI diagnosis of brain diseases

The brain regulates and coordinates the work of all organs and systems human body, ensures their connection, uniting them into a single whole. However, as a result of the pathological process, the functioning of the brain is disrupted, and thereby entails a malfunction in the functioning of other organs and systems, which is manifested by characteristic symptoms.

The most frequent symptoms brain damage:

1. Headache- the most common symptom indicating irritation of pain receptors, the cause of which can be varied. However, the MRI method, by assessing the structure of the brain, can reveal the cause or exclude most diseases.

Structural changes detected using MRI studies can be interpreted within the limits of the method and the location of the pathological process can be extremely accurately localized.

2. Dizziness is a symptom indicating a disturbance in the pressure in the arteries of the brain, damage to the brain stem or the vestibular apparatus of the middle ear.

These anatomical regions of the brain are clearly visible on MRI and are subject to structural analysis.

3. Impaired coordination and balance. This symptom is often associated with circulatory disorders in the area of ​​the brain stem and cerebellum; there may also be other causes affecting these parts of the brain, for example, a tumor, metastasis or an inflammatory process.

4. Symptoms of irritation of the meninges, manifested in photophobia, hyperreflexia, muscle spasms. This symptom complex is associated with subarachnoid hemorrhage (acute bleeding from an aneurysm) or with an acute inflammatory disease affecting the membranes of the brain (meningitis).

Brain diseases

Dyscirculatory encephalopathy is a chronic disorder cerebral circulation caused by decreased inflow arterial blood to the brain, occurring against the background of atherosclerotic lesions of the artery wall, or against the background of arterial hypertension.

MR semiotics of dyscirculatory encephalopathy includes the presence of foci of gliosis in the white matter of the cerebral hemispheres, located predominantly subcortically (having a hyperintense signal on T2 and TIRM/FLAIR sequences and isointense on T1); along the contour of the lateral ventricles – zones of gliosating changes (leukoaraiosis).

MRI of the brain (normal)

Discircular encephalopathy on MRI

Stroke is an acute cerebrovascular accident (CVA) associated with a sudden disruption of arterial blood flow to an area of ​​the brain due to acute thrombosis/embolism of an artery or a drop in blood pressure.

MR semiotics of stroke depends on the stage of the pathological process. It should be noted that there is no consensus regarding the timing of a diagnostically significant change in the MR signal. A number of authors believe that this is 8 hours from the onset of the disease, others are inclined to think that this period begins no earlier than an hour. Thus, early changes reflecting the ischemic process in the brain parenchyma are changes in the MR signal in T2 and local edema in T1.

MR imaging of intracerebral hemorrhages has its own characteristics, depending on the stage of the process. In the first hours after hemorrhage, only oxyhemoglabin is present in the hematoma, which does not affect the intensity of the T1 and T2 signal. Therefore, the hematoma is usually isointense with gray matter on T1-weighted images and hyperintense on T2-weighted images, due to the presence of a predominantly protein-rich aqueous component. In the following hours, when oxyhemoglobin turns into deoxyhemoglobin and remains in this form for two days, on T1-WI the hematoma remains isointense with respect to the brain substance, and on T2-WI the hyperintense signal changes to low. In the subacute stage, oxidation of gmoglobin occurs with the formation of methemoglobin, which has a pronounced paramagnetic effect. Therefore, there is an increase in the intensity of the MR signal on T1-WI along the periphery of the hematoma with a gradual spread to the center. At the beginning of the subacute stage, methemoglobin is located intracellularly, as a result of which the hematoma is hypointense on T2-weighted images, but already hyperintense on T1-weighted images. In a later period, the hemolysis that occurs leads to the release of methemoglabin from the cells. Therefore, the hematoma is hyperintense on both T2 and T1-weighted images. At the end of the subacute and beginning of the chronic stage, a low-signal zone begins to form along the periphery of the hematoma, caused by the deposition of iron in the form of hemosiderin around the hemorrhage. At this stage, the hematoma has an increased T1 signal from the center and a decreased T2 signal from the periphery. Hemosiderin deposits can persist for many years.

MRI makes it possible to detect ischemic and hemorrhagic strokes in the first hours of the disease, which is extremely important for choosing appropriate treatment tactics and reducing the severity of the consequences of this disease.

Ischemic stroke on MRI

MRI shows the area of ​​damage in the brain after a stroke

MRI shows decreased or absent blood flow through the arteries

Brain tumor is a disease characterized by the growth of pathological tissue from any part of the brain, compressing nerve centers, causing increased intracranial pressure and accompanied by a variety of nonspecific clinical manifestations.

Malignant tumor on MRI

Benign tumor brain tumor on MRI

The MR semiotics of brain tumors is diverse and depends on the histological characteristics of the tumor itself. Signs of a pathological brain formation detected using MRI can be divided into direct and indirect.

MRI with contrast allows better visualization of metastases

Direct signs include various types of changes in the intensity of MR signals:

Heterogeneously altered MR signal,

Isointense MR signal (i.e. without signal change).

Indirect (secondary) signs include:

Lateral dislocation of the midline structures of the brain and choroid plexus,

Displacement, compression, change in size and deformation of the ventricle;

Blockage of the cerebrospinal fluid pathways with the development of occlusive hydrocephalus,

Displacement, deformation, narrowing of the basal cisterns of the brain,

Perifocal swelling of the brain substance (i.e. swelling along the periphery of the tumor).

If a brain tumor is suspected, an MRI examination is performed with additional contrast enhancement.

Demyelinating brain lesion

Demyelinating diseases of the brain are one of the most socially and economically significant problems in modern neurology. The most common demyelinating disease of the central nervous system, multiple sclerosis (MS), affects people of young working age and quickly leads to their disability.

The MR semiotics of this pathology is characterized by the presence of foci (plaques) of multiple sclerosis in the white matter of the brain, and only a small proportion of foci (5-10%) are located at the border of gray and white matter, or in the gray matter. On T1-weighted images, the lesions are isontense - without a change in the signal, or hypointense - with a decrease in signal intensity like “black holes”, which characterizes the chronicity of the process.

Typical localization of MS lesions in the brain:

Areas adjacent to the superolateral corner of the lateral ventricles

brain stem,

Inflammatory diseases

Encephalitis is an inflammatory disease of the white matter of the brain. If the pathological process spreads to the gray matter of the brain, they speak of encephalomyelitis.

The Clinic of Nervous Diseases knows a large number of types of encephalitis. The main etiological factor of this disease is infection. According to the anatomical distribution, encephalitis can be diffuse or focal. Primary encephalitis is an independent disease (tick-borne, acute disseminated encephalomyelitis); secondary – a complication of an existing pathological process (measles, influenza encephalitis, rheumatic encephalitis, as a complication in patients with AIDS, etc.). A separate group of secondary encephalitis consists of post-vaccination encephalitis - encephalitis that developed after vaccination.

The MR semiotics of inflammatory diseases of the brain is diverse.

Should I get an MRI of my brain?

A large number of diseases of the central nervous system occur latently, that is, they do not manifest themselves outwardly; there may be rare cases of headache attacks of varying intensity, decreased concentration, decreased memory, as well as other minor symptoms that are considered by doctors as “astheno- vegetative syndrome”, most often different diagnoses are made, and treatment does not bring the desired result.

At the same time, MRI can detect any, even minimal, structural disorders in the anatomy of the brain, each of which can have a large clinical significance. Early diagnosis of any disease can provide not only its correct treatment, but can also provide the opportunity for its complete healing.

In addition, if you have already had an MRI of the brain and, based on the conclusion of a radiologist, you have questions, for example, it is not clear what specific terms mean or you doubt the correctness of the diagnosis and want to clarify it by obtaining a second independent opinion from a doctor and a transcript of the images, then send us your question or pictures and we will be happy to help.

Second opinion of medical experts

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In recent years, significant changes have occurred in the diagnosis of pathologies of the brain and spinal cord. This is due to the introduction of magnetic resonance and computed tomography. The diagnostic capabilities of these methods are many times greater than those of previously used methods (ventriculography, cerebral angiography, spondylography).

With the help of CT and MRI, it is possible to determine the exact localization of the pathological focus, its relationship to blood vessels and bone structures.

However, none of the methods, including magnetic resonance and computed tomography, can completely replace other research methods. In this regard, it is necessary to adhere to a certain algorithm in the examination in order to obtain the maximum amount of necessary information for the clinician.

Demyelinating processes (including multiple sclerosis)

Diagnostic capabilities of magnetic resonance imaging

The capabilities of MRI are great, and the limitations of its use are caused only by the high cost and, in connection with this, low availability of the method.

Magnetic resonance imaging occupies a special place in the diagnosis of brain pathology. After all, almost any organic pathology can be diagnosed using this method.

Indications for MRI are:

• Prolonged headaches of unspecified etiology
• Volumetric formations of the brain, tumors, suspicion of their presence
• Traumatic brain injuries
• Congenital anomalies and hereditary diseases
• Demyelinating processes
• Inflammatory diseases of the brain and spinal cord
• Control of treatment (surgical, medicinal)
• Cerebral blood supply disorders, vascular diseases and anomalies
• Pathology of the cerebrospinal fluid system
• Epilepsy, noneleptic seizures of unspecified origin.

The diagnostic search in each case has its own specifics, so the radiology doctor needs to understand the reasons for performing an MRI. The research technique and the use of contrast agents depend on this.

MRI is used to diagnose:

• Benign and malignant tumors, even in the early stages, their exact size, type of blood supply and growth, and relationship with surrounding tissues are determined. These data form the basis for determining the type of tumor process and choosing treatment tactics.
• Clinical data indicating multiple sclerosis and other demyelinating processes are confirmed only by magnetic resonance imaging data. In this case, diagnosis is possible after the first episode of the disease.
• To assess the state of blood supply to the brain, detect hemorrhagic and ischemic changes, as well as vascular anomalies, the optimal research method is magnetic resonance imaging with contrast.
• Inflammatory processes of the brain and its membranes, tissue swelling, impaired outflow of cerebrospinal fluid.
• For the diagnosis of traumatic brain injury in acute period MRI remains an auxiliary method, but in the subacute period and for the diagnosis of long-term consequences it is of key importance.

What does a brain MRI show?

Angiomas

Cavernous angioma on an MRI image

On tomograms they appear as multinodular formations of mixed signal intensity, surrounded by a hypointense rim. When contrast is administered, the picture is not specific: it is possible to detect an avascular lesion or an area with arteriovenous shunting.

Arteriovenous malformation

Arteriovenous malformation of cerebral vessels

The anomaly is quite common. Interest in it is also caused by the fact that it is a common cause of subarachnoid hemorrhages. The MRI picture is characterized by the presence of a lesion various shapes reduced intensity. When an arteriovenous malformation is detected, it is necessary to detect a feeding vessel, which is clearly shown by MRI of the brain with contrast (magnetic resonance angiography). It is also important to determine the number of feeding vessels, their course, and whether they supply blood to the adjacent brain tissue.

Aneurysms

During the study, they are distinguished by the absence of a signal from rapid blood flow. This sign is not pathognomonic, since compact bone tissue on tomograms can have this appearance. To confirm, a contrast study is used, in which a “defect” effect is observed in the central part of the aneurysm. If there is a mural thrombus, it gives a bright signal on T1-weighted tomograms.

Strokes

They are visualized within a few hours during an MRI. This makes this type of research a priority. Early tomograms reveal the disappearance of the “empty flow” effect in the arteries of the affected area. Parenchymal accumulation of contrast is observed already from 3–4 days, however contrast is still rarely used for strokes.

Demyelinating processes (including multiple sclerosis)

Effectively diagnosed using MRI. In the acute phase, demyelinating processes are characterized by the accumulation of a contrast agent in a central or peripheral manner. On conventional tomograms, there is a decrease in signal intensity on T1-weighted images and a hyperintense signal on T2-weighted images.

MRI for multiple sclerosis

Chronic demyelinating process

It has no manifestations on T1-weighted images and when using contrast agents, and changes on T2-weighted images are nonspecific. To diagnose multiple sclerosis, a table of criteria has been developed, based on which the presence and intensity of the process can be judged by the number of foci accumulating contrast agent and their location.

Meningitis

On conventional tomograms it has no distinctive signs, especially in the first days of the disease. Contrast is required for MRI diagnostics. Post-contrast images show increased signal in areas of inflammation. With the development of complications of the inflammatory process, the focus of abscess formation is visualized quite clearly, which makes MRI an indispensable research method in this area. However, MRI data do not allow us to determine the etiological agent and, accordingly, are not decisive when choosing etiotropic therapy.

Brain tumors

They have a number of common signs on tomograms. These include:

• uniform or local increase in MR signal intensity
• decrease in signal intensity on tomograms
• heterogeneity of structures due to areas of increased and decreased signal intensity
• dislocation of structures relative to the midline
• deformation, displacement of the ventricles of the brain
• occlusive hydrocephalus.

Despite a number of common signs, each tumor has its own distinctive signs on tomograms.

Astrocytoma

It is a tumor with an infiltrative type of growth and a tendency to form areas of cystic degeneration and hemorrhages. In this regard, it appears heterogeneous on tomograms, with an increased signal intensity on T2-weighted images. In this case, the true size of the tumor may exceed the lesion on T2 tomograms. The use of contrast makes it possible to assess the true size of the tumor, its structure, and the ratio of the solid and cystic components.

Glioblastoma

On T1-weighted image it appears hypointense, and on T2-weighted image there is uneven signal enhancement with a brighter area of ​​necrosis in the center. On post-contrast images, accumulation of contrast is observed along the periphery of the tumor; areas of necrosis do not accumulate contrast. The detection of feeding vessels along the periphery and arteriovenous shunts indicates the malignancy of the process.

Meningioma

Characteristic signs of meningiomas are: the presence of a wide base of the tumor, its adherence to the hard meninges. On T2-weighted images, the tumor has a uniformly increased signal intensity; in the presence of foci of calcification, hypointense foci are determined. When contrast is administered, its uniform accumulation is observed, with a maximum level in the first 5 minutes after administration.

Adenoma

Pituitary adenoma on MRI

In the diagnosis of adenomas, MRI is of key importance. On T1-weighted images they have a hypointense signal, and on T2-weighted images they have a moderately increased signal. When contrast is applied, an uneven, intense accumulation of the contrast agent occurs.
MRI diagnostics of traumatic brain injuries with brain damage in the acute period is inferior in information content to CT, but in the diagnosis of long-term consequences it occupies a leading position.

Brain contusions

Brain contusion on MRI

They have several variants of the MR picture: single foci of increased signal intensity; multiple small punctate foci of increased intensity on E1 and T2-weighted images; heterogeneous round or oval areas of increased signal intensity. During the resolution process, the options transform among themselves.

Epidural hematomas

Epidural hematomas on MRI

They have a biconvex or plano-convex shape, subdural hematomas have a crescent shape. Both types of hematomas have a moderately increased signal intensity on T2 tomograms in the acute stage with increased signal in the subacute stage on T1 and T2-weighted images. Chronic hematomas are characterized by a gradual decrease in signal as it resolves.

Diffuse axonal injuries

Tomograms are characterized by an increase in brain volume, compression of the subarachnoid space, lesions have increased echogenicity. Over time, the inflammation passes and the signal intensity decreases. In the long-term period, hyperintense foci of hemorrhage are visualized, which can persist for several years.

Injuries and fractures of the bones of the vault and base of the skull

They are also well visualized using magnetic resonance imaging, but due to the high cost of the method, cheaper radiation diagnostic methods are used.

The introduction of magnetic resonance imaging in the diagnosis of brain pathology has expanded the list of diagnosed pathologies and, accordingly, treatment options. The method has been used quite recently, so data is currently being accumulated and diagnostic capabilities are being assessed. But now there is no doubt that the widespread use of the method will make it possible to diagnose many diseases on initial stage