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If we compare the human body with a computer, the brain, of course, is its “central processing unit”. Like a control point of control, this central organ of the nervous system is involved in the implementation of almost all processes in the human body. The study, diagnosis and treatment of the brain is carried out, first of all, by a neurologist.
And, if earlier his entire research arsenal consisted of a primitive hammer and a needle for testing sensitivity, today, thanks to the achievements of mathematics, physics, biology, computer engineering, this specialist has access to the most modern methods for studying a complex system called the “human brain”, including magnetic – resonant tomography.
How it works and why it is carried out
The essence of magnetic resonance imaging, which is usually denoted by the abbreviation MRI, is the impact on the human body of a magnetic field and radio frequency pulses that scan it slice by section, and allow you to get a high-precision and clear image of internal organs and tissues in three projections – sagittal, axial, coronal.
Initially, this technology owes its appearance to the phenomenon of NMR – nuclear magnetic resonance, discovered in 1946 during joint research by Harvard and Stanford specialists.
The phenomenon is that the nuclei of certain substances, such as hydrogen, can absorb or launch the energy of radio frequency pulses, provided that these substances are in a magnetic field, and the frequency of the pulses coincides with the frequency of rotation of these nuclei.
Each fragment and particle of the examined tissue or organ has its own NMR frequency. It is this value that is converted into the image of the tomogram.
Already in 1973, as a result of the analysis, study and development of this method, the first MRI image was obtained – an image of two vessels filled with water.
Photographed by Paul Lauterbur. His colleague, Peter Mansfield, was the first to show how a radio signal received from an MRI spectrometer is converted into an image. Both scientists in 2003 received the Nobel Prize for their achievements in this field.
Since that time, the method of magnetic resonance imaging has gained popularity and is highly valued to this day.
It is prescribed in various situations, in order to:
- research on symptoms of probable or diagnosed head injuries;
- checking for symptoms that indicate the likelihood of brain damage from Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and other diseases. These symptoms may include confusion, changes in consciousness, impaired behavioral responses;
- checking for hydrocephalus;
- detection and study of tumors, infectious lesions, abscesses, encephalitis or meningitis;
- examination of the optic and auditory nerves.
MRI can be done with or without contrast. In the first case, the subject is injected with special dyes, which in the pictures give a clearer and more detailed image of the brain tissue.
Allocate MRI of cerebral vessels as an independent type of examination – MR angiography. According to the technique, methods of preparation and contraindications, MR angiography does not differ from MRI of the brain, while it gives a complete picture of the state of the arteries and veins of the brain, and MRI of the brain allows you to diagnose disorders in the brain tissue. Both procedures can be performed with contrast.
Indications for the appointment of magnetic resonance imaging of the brain
The first thing a doctor pays attention to when a new patient comes to see him is his complaints. Suspicious symptoms, for example, pathological deviations in behavior, consciousness, sensations, reactions, may be the basis for referral to an MRI of the brain. These deviations include:
- regular, frequent headaches of unknown etiology;
- periodic fainting;
- confusion of thoughts, clouding and disorders of consciousness;
- Feeling dizzy with slight exertion or at rest;
- causeless decrease in visual acuity and hearing, tinnitus;
- violations of the sensitivity of the facial nerves, pain, tingling, numbness of the facial muscles;
- frequent nosebleeds;
- decreased ability to concentrate.
Single manifestations of such conditions are unlikely to be a cause for serious concern, but if there is a regularity and / or persistence of symptoms, a combination of several of the above sensations, the doctor may need magnetic resonance imaging data.
In addition, the examination will need to be completed if, according to other indications, the doctor has suspicions of multiple sclerosis, parasitic, infectious or inflammatory lesions, tumors and neoplasms in the brain, acute or chronic cerebrovascular accident, brain aneurysms, pituitary tumor, vascular pathologies.
Who should not have an MRI of the brain
The entire group of prohibitions on MRI is divided into two parts – the first includes relative prohibitions when it is undesirable to do an MRI, but if there is an urgent need, if there are no alternative options, the doctor can allow the procedure.
The second group consists of absolute contraindications, in the presence of which MRI should be forgotten – no doctor will simply give permission for it.
In the first group – the risk group – pregnant women in the first trimester, since during this period the fetus is most susceptible to any negative influence from the outside, and doctors prefer not to expose it once again to any effects unusual for the body. In addition, the implementation of the procedure for those who suffer from claustrophobia is questionable.
During an MRI, it is very important to remain calm and completely still, and a person with a phobia of closed spaces cannot guarantee either one or the other. In this case, the way out of the situation is to carry out the procedure on an open tomograph.
Absolute contraindications completely exclude the possibility of examining a patient with an MRI scanner. Among them, the presence of a pacemaker, installed heart valve prostheses, ferromagnetic devices and implants, metal implants, knitting needles, fragments, hemostatic clips of cerebral vessels, the presence of an inner ear prosthesis, tattoos containing metal compounds in the pigment, if MRI with contrast is necessary, severe renal insufficiency and allergic reactions to the components of the contrast agent.
How to prepare for an MRI of the brain
When prescribing a procedure, the doctor conducts a survey and examination of the patient, finds out the presence or absence of contraindications, which the patient himself can tell about, informs him of information about how the procedure will take place, and answers all questions. Usually no special training is given. If you need to conduct an MRI of the brain on an empty stomach, the doctor will warn you about it.
All removable metal dentures, metal jewelry and accessories must be removed before the procedure.
The subject may be given special clothing during the scan, or allowed to stay in their own if it has a loose cut and does not contain metal fittings and parts.
It is necessary to inform the X-ray laboratory technician about all recent illnesses, operations, and cases of allergies. Women need to notify their doctor if they are pregnant.
The process of performing an MRI of the brain
The MRI machine is a horizontally positioned cylinder with thick walls and a narrow bore. There are holes at both ends of the loop. Before starting the procedure, the patient is placed on the tomograph table in the “lying on his back” position, asked to take a completely relaxed position. There are also so-called open tomographs – devices open on the sides allow you to examine people with obesity, as well as those who have claustrophobia. However, their diagnostic abilities are somewhat lower than standard, closed tomographs.
If the examination involves the use of a contrast agent, then a native study is performed first, then the patient is rolled out, a contrast agent is injected intravenously and scanning is started. A variant of delayed contrasting is possible: when scanning is carried out after the introduction of contrast in 10-15 minutes. The drug contains gadolinium salt, a rare earth metal. This element provides contrast coloration in the images, increasing the signal intensity. It enters the patient’s body through a special syringe or catheter with an automatic dispenser, if the introduction should be carried out gradually.
The patient is fastened with soft straps to ensure his complete immobility – otherwise, the resulting images will be blurry, respectively, useless. Around his head are placed special coils that emit radio frequency pulses.
If the subject is uncomfortable with the noise of the operating MRI machine (characteristic buzzing, knocking, crackling), he is given ear plugs or headphones, after which the table with the patient is pushed into the space of the tomograph, and the X-ray technician is removed to the next room, from where he has the opportunity to observe the process.
The tomograph takes a series of images that are processed by a special computer program. These will form the final image. The whole procedure usually takes from 10-20 minutes (without contrast) to 35-40 minutes (with contrast). In the process of one scan, the device takes information from about 20 levels or slices. The cut step is 4-5 mm. The informativeness and accuracy of the examination result depends on many parameters, such as: how high is the magnetic field strength of the tomograph, measured in Tesla; slice thickness, number of programs used during the study.
The procedure is so painless and safe that it is prescribed not only for adults, but also for children, unlike, for example, computed tomography. You can undergo an examination with a magnetic resonance tomograph in a hospital, clinic or specialized medical diagnostic centers.
After the end of the procedure, the radiologist deciphers the images and draws up a conclusion on the examination. It is this document that will become the basis for the doctor to develop treatment tactics if changes were detected as a result of MRI.
In the process of interpreting the images, the doctor clearly understands what he can see on them, and what you need to pay special attention to, as he knows well what the MRI shows.
The tomogram displays the presence of primary or secondary tumors of various etiologies, as well as external manifestations of the deep work of the brain, its general condition and functional characteristics, foci of diseases, injuries and post-traumatic changes. In addition, MRI images can be used to examine the vascular system of the brain and the state of the pituitary gland.
Magnetic resonance imaging of the brain is a scanning technology that has opened up new possibilities for the study of this organ. With its help, doctors can now get to the deepest tissues of the brain, study the structure and functioning of tissues, nerves, blood vessels, without using invasive examination methods for this.
Scientists and doctors recognize MRI as the most modern diagnostic technique: magnetic resonance imaging does not use X-rays for scanning, therefore, it does not expose a person to radiation exposure, so it can be done quite often without fear of the negative effects of radiation.
The tomograph produces clear and high-quality images, by which the doctor can determine pathologies and diseases at almost any stage of their development, often even if other examination methods do not detect problems.
The relative disadvantages of MRI are only its high price (for example, a CT scan of the brain can cost about 1,5-2 times cheaper), as well as strict requirements regarding the immobility of the patient during the procedure.
If during computed tomography this issue is not so critical, then for the most effective MRI images, absolutely complete immobility is required during the entire procedure, which can be quite difficult for the patient to follow.