Scientific discoveries and technical inventions are transforming medicine, making many procedures safer and more accurate. Magnetic resonance imaging (MRI) is a modern method of obtaining clear images of human internal organs and tissues. The distinctive features of the procedure are that it does not create a radiation load on the body. In addition, magnetic resonance imaging (MRI) carried out with minimal preliminary preparation. This method is absolutely safe for humans and does not cause any discomfort.
History of magnetic resonance imaging (MRI) quite extensive. The first devices for carrying out this procedure appeared about 30 years ago, but then they were not yet so powerful. Science has made significant breakthroughs over the past decade with magnetic resonance imaging machines (MRI) power of 1.5 and even 3 tesla. Such powerful devices are more often used for research activities; in clinics, as a rule, equipment with a capacity of about 1.0 Tesla is used.
Conducting magnetic resonance imaging (MRI) in our clinic
The department has a modern Philips Panorama 1.0 T magnetic resonance tomograph (tomograph with an open aperture and a magnetic field strength of 1.0 Tesla). The Panorama Large Field of View MRI System is designed for maximum convenience for both patients and doctors. It has a wide open design, large field of view, wide range of clinical indications and provides high quality images. In addition, the device is equipped with a paramagnetic system for bolus intravenous administration of a contrast agent, which increases the diagnostic value of the study.
Indications for MRI use:
- diseases of the brain (vascular, inflammatory, neoplastic and other genesis), including targeted studies of the pituitary gland, orbits, cerebellar pons, paranasal sinuses;
- developmental anomalies, vascular malformations of the great vessels of the brain - MR-angiography of the arteries and veins of the brain;
- spine diseases (degenerative-dystrophic, inflammatory, neoplastic and other genesis);
- diseases of the nasopharynx, larynx, incl. lymphadenopathy of the lymph nodes of the neck;
- diseases of the abdominal organs (including with the use of a hepatospecific contrast agent);
- study of the biliary tract (MR-cholangiopancreatography);
- diseases of the pelvic organs (both in women and men);
- joint diseases (including traumatic, inflammatory and neoplastic genesis).
In connection with the growth of oncological diseases of the mammary glands, a separate study of the mammary glands should be distinguished, which makes it possible to identify non-palpable neoplastic processes, clarify the nature of nodules, recognize multifocal lesions, and assess the prevalence of the process. In addition, MRI mammography is used to clarify the condition of implants.
Research time depends on the area of study and the need for intravenous contrast enhancement, on average from 30 to 60 minutes.
Preliminary preparation It is necessary for studies of the abdominal cavity organs (on an empty stomach), for studies of the pelvic organs (preliminary cleansing of the colon) and for studies with intravenous contrast enhancement (preliminary consultation with an allergist and clarification of serum creatinine levels is advisable).
Contraindications for MRI:
ABSOLUTE CONTRAINDICATIONS
- Pacemaker, cochlear implants, other types of stimulants;
- Insulin pumps;
- Unknown metal cava filters and stents;
- Metal clips in vessels;
- Foreign metal objects (shavings, fragments, piercings, etc.).
RELATIVE CONTRAINDICATIONS
- Pregnancy;
- Severe condition of the patient;
- Claustrophobia.
Functional MRI of the brain has become widespread since the 1990s. The introduction of the technique contributed to the identification of some malignant formations (tumors), which are more difficult to identify with other methods. A feature of functional magnetic resonance imaging studies of brain tissue is the assessment of changes in blood supply due to changes in neuronal stimulation of the spinal cord and brain. The possibility of obtaining high-quality results with MRI imaging is due to increased blood flow to the region of the brain that is actively working.
Experts studied the normal activity of the cerebral cortex, the state of the tissue in tumors, which made it possible to carry out a differential diagnosis of pathology. Differences in the MR signal in normal and pathological conditions make neuroimaging an irreplaceable diagnostic method.
Neuroimaging began to be developed in 1990, when functional MRI began to be actively used to diagnose brain formations due to the high reliability, the absence of radiation exposure of the patient. The only disadvantage of the method is the need for a long stay of the patient on the diagnostic table.
Morphological bases of functional MRI of the brain
Glucose is not an important substrate for the functioning of the brain, but in its absence, the functioning of the neural channels that provide the physiological work of the brain tissue is disrupted.
Glucose enters the cells through the vessels. At the same time, oxygen, bound by the hemoglobin molecule of erythrocytes, enters the brain. Oxygen molecules are involved in the processes of tissue respiration. After oxygen consumption by brain cells, glucose oxidation occurs. Biochemical reactions during tissue respiration contribute to a change in tissue magnetization. The induced MRI process is recorded by software, which allows you to obtain a three-dimensional image with a careful drawing of every single detail.
A change in the magnetic properties of blood occurs in almost all malignant brain formations. Excess blood flow is determined by the software and compared with normal values. Physiologically, there is a different MR signal from the cingulate cortex, thalamus, and basal ganglia.
Low flow can be seen in the parietal, lateral, frontal lobes. A change in the microcirculation of these areas greatly changes the sensitivity of the signal.
Functional diagnostics of MRI depends on the state and amount of hemoglobin in the area under study. The molecule of a substance may contain oxygen or its alternative substitutes. Under the influence of a strong magnetic field, oxygen oscillates, which distorts the signal quality. The magnetization of the channel leads to a rapid half-life of oxygen. Exposure to a strong magnetic field increases the half-life of the substance.
Based on the information, it can be concluded that there is a higher quality of the MR signal in the areas of the brain that are saturated with oxygen. Malignant brain formations have a dense vascular network, therefore they are well visualized on tomograms. For good results, the magnetic field intensity must be above 1.5 Tesla. The pulse train increases the half-life.
The activity of the MR signal recorded from the activity of neurons is called the "hemodynamic response". The term defines the speed of neural processes. The physiological value of the parameter is 1-2 seconds. This interval is insufficient for a qualitative diagnosis. To get good visualization in masses of the brain, magnetic resonance imaging is performed with additional glucose stimulation. After its introduction, the peak of activity is observed after 5 seconds.
Functional diagnostics of MRI in brain cancer
The use of MRI in neuroradiology is expanding. For the diagnosis of tumors of the brain and spinal cord, not only functional research is used. Recently, modern methods have been actively used:
Perfusion-weighted;
Diffusion;
Contrast-rich study (BOLD).
BOLD contrasting after oxygen saturation helps to diagnose the activity of the sensory, motor cortex, foci of speech of Wernicke and Broca.
The method is based on signal registration after specific stimulation. Functional diagnostics of MRI when compared with other methods (PET, emission CT, electroencephalography) Functional MRI helps to obtain a picture with spatial resolution.
To understand the essence of the graphic picture of the brain during magnetic resonance imaging, we carry out images of brain tissue after MRI after reading "raw" images (a), combining several tomograms (b).
The motor activity of the cerebral cortex after using the method of correlation coefficients makes it possible to obtain a spatial image of the results with visualization of zones of increased magnetic activity. Broca's area in functional MRI is determined after processing "raw" tomograms. Stimulating the correlation coefficients helps to generate a graph of the ratio of signal strength over a specific time period.
The following tomograms show a picture of a patient with aplastic ependymoma - a tumor with an increased shift of excitability in the area that is responsible for the activity of the functional cerebral cortex.
The graph shows the active areas in which the malignant neoplasm is localized. After receiving the tomogram data for excision of the pathological area, a subtotal resection was performed.
The following MRI scans show glioblastoma. Functional diagnostics allows high-quality visualization of this education. In this area, there is a zone responsible for the activity of the fingers of the right hand. The images show increased activity in areas after glucose stimulation. Functional magnetic resonance imaging in glioblastoma in this case made it possible to accurately visualize the localization and size of the formation. The location of the cancer in the motor cortex will result in the failure of the right fingers to move when atypical cells appear in the cerebral cortex.
In some formations, functional MRI of the brain shows several dozen different images resulting from a dynamic change in the MR signal with a distortion of up to 5%. With such a variety, it is difficult to establish the correct location of the pathological formation. To exclude the subjectivity of visual assessment, software processing of "raw" images obtained using statistical methods is required.
To obtain high-quality results in functional diagnostics of MRI, in comparison with the traditional analogue, the patient's help is required. With careful preparation, the metabolism of glucose and oxygen increases, which reduces the number of false-positive results, artifacts.
High technical equipment of magnetic resonance tomographs allows to improve the picture.
The most common use of functional magnetic resonance imaging is visualization of the main areas of activity of the cerebral cortex - visual, speech, and motor.
Functional MRI examination of the brain - clinical experiments
Visual stimulation of cortical zones using functional MRI according to the J.Belliveau method involves visual stimulation using bolus contrasting with gadolinium. The approach makes it possible to register the drop in the echo signal due to the different sensitivity between the contrast passing through the vessels and the surrounding tissues.
Clinical studies have found that visual stimulation of the cortical zones in the light and in the dark is accompanied by a difference in activity of about 30%. Such data were obtained from animal studies.
The experiments were based on the method for determining the signal obtained from deoxyhemoglobin, which has paramagnetic properties. During the first 5 minutes after glucose stimulation of brain activity, the process of anaerobic glycolysis is activated.
Stimulation leads to an increase in the perfusion activity of neurons, since microcirculation after the intake of glucose is significantly enhanced due to a decrease in the concentration of deoxyhemoglobin, a substance that carries carbon dioxide.
On T2-weighted tomograms, an increase in signal activity is traced - the technique is called BOLD-contrasting.
This functional contrasting technique is not perfect. When planning neurosurgical operations on tumors, routine and functional research is required.
The complexity of functional magnetic resonance imaging lies in the patient's need to perform activating actions. To do this, through the intercom, the operator transmits the task, which the person must do with special care.
Patient training should be performed prior to functional MRI examination. Mental rest, preparation of physical activity is required in advance.
Statistical processing of the results, if done correctly, makes it possible to thoroughly examine "raw" tomograms, to compose a three-dimensional image on their basis. For a competent assessment of the values, it is necessary to carry out not only a structural, but also a functional assessment of the state of the cerebral cortex. The examination results are assessed simultaneously by a neurosurgeon and a neurologist.
The introduction of MRI with functional tests into mass medical practice is not allowed by the following restrictions:
1. High requirements for the tomograph;
2. Lack of standardized developments regarding assignments;
3. The appearance of false results, artifacts;
4. Execution of involuntary movements by a person;
5. The presence of metal objects in the body;
6. The need for additional auditory and visual stimulants;
7. High sensitivity of metals to echo-planar sequences.
These contraindications limit the spread of the study, but they can be eliminated by carefully developing recommendations for MRI.
The main goals of functional magnetic resonance imaging are:
Analysis of the localization of the pathological focus to predict the course of surgical intervention with a tumor, assess the functional activity;
Craniotomy planning in areas away from the areas of the main brain activity (visual, speech, motor, sensory);
Selecting a group of people for invasive mapping.
Functional studies significantly correlate with direct stimulation of the cortical activity of the brain tissue with special electrodes.
Functional MRI is of the greatest interest for Russian doctors, since mapping in our country is just beginning to develop. For planning operational activity, magnetic resonance imaging with functional tests is of great interest.
Thus, functional studies of MRI in our country are at the level of practical tests. Frequent use of the procedure is observed in supratentorial tumors, when MRI examination is a necessary addition to the preoperative stage.
In conclusion, let us highlight the modern aspects of the development of the "brain-computer" technology. On the basis of this technology, a "computer symbiosis" is being developed. The combination of electroencephalography and MRI allows you to create a complete picture of the functioning of the brain. By superimposing one study on another, a high-quality picture is obtained, indicating the relationship between the anatomical and functional characteristics of the neurons.
Magnetic resonance imaging is indispensable in the diagnosis of many diseases and allows you to obtain detailed visualization of internal organs and systems.
The MRI department of the NAKFF clinic in Moscow is equipped with a high-field Siemens MAGNETOM Aera tomograph with an open tunnel design. The power of the tomograph is 1.5 Tesla. The equipment allows examining people weighing up to 200 kg, the width of the apparatus tunnel (aperture) - 70 cm brain. The cost of diagnostics is affordable, while the value of the results obtained is incredibly high. In total, more than 35 types of magnetic resonance imaging are performed.
After MRI diagnostics, the doctor conducts a conversation with the patient and issues a disc with a recording. The conclusion is sent by e-mail.
Preparation
Most magnetic resonance imaging studies do not require special training. However, for example, for MRI of the abdomen and pelvic organs, it is recommended to refrain from eating and drinking for 5 hours before the examination.
Before visiting the center of magnetic resonance imaging (on the day of the study), you must wear comfortable clothing without any metal elements.
Contraindications
Contraindications to magnetic resonance imaging are associated with the fact that during the study a powerful magnetic field is formed that can affect electronics and metals. Based on this, an absolute contraindication to MRI is the presence of:
- pacemaker;
- neurostimulator;
- electronic middle ear implant;
- metal clips on vessels;
- insulin pumps.
Installed pacemaker, neurostimulator, electronic middle ear implant, metal clips on the vessels, insulin pumps.
Restrictions on conducting
If you have large metal structures installed (for example, a joint endoprosthesis), you will need a document on the possibility and safety of MRI. This can be a certificate for an implant (usually issued after the operation) or a certificate from the surgeon who performed the intervention. Most of these structures are made of medical grade titanium, which does not interfere with the procedure. But, in any case, before the examination, tell the doctor of the radiation diagnostics department about the presence of foreign objects in the body - crowns in the oral cavity, piercings, and even tattoos (in the latter, metal-containing paints could be used).
The price of magnetic resonance imaging depends on the part of the body being examined and the need for additional procedures (for example, the introduction of contrast). So an MRI of the brain will cost more than a tomography of one hand. Sign up for a study by phone in Moscow: +7 495 266-85-01 or leave a request on the website.
Magnetic resonance imaging (MRI) is a method of obtaining tomographic medical images for non-invasive examination of internal organs and tissues, based on the phenomenon of nuclear magnetic resonance (NMR). The technology appeared several decades ago, and today it is possible to undergo examination with such a device in many modern clinics. However, scientists continue to work to improve the accuracy of the technology and develop new, more efficient systems. , Senior Researcher at the Max Planck Institute in Tübingen (Germany), is one of the leading specialists who develops new sensors for experimental ultra-high-field MRI. The day before, he held a special course on the master's program " RF systems and devices»From ITMO University, and in an interview with ITMO.NEWS he spoke about his work and how new research in the field of MRI will help make the diagnosis of diseases more effective.
For the past few years, you have worked for the High-field Magnetic Resonance department of the Max Planck Institute. Please tell us what your current research is about?
I am developing new radio frequency (RF) sensors for MRI. What is MRI is probably already known to most people, because over the past 40 years, since this technology was developed, it managed to come to a huge number of clinics and become an indispensable diagnostic tool. But even today, people are working to improve this technology by developing new MRI systems.
An MRI is primarily a huge cylindrical magnet into which a patient or volunteer is placed to obtain a three-dimensional image. But before you can create this image, you need to do a lot of research work. It is conducted by engineers, physicists, doctors and other specialists. I am one of the links in this chain and am engaged in research at the intersection of physics and engineering. More specifically, we are developing sensors for ultra-high-field experimental MRI, which is used at the stage of excitation, reception and processing of the signal obtained as a result of the physical effect of NMR.
One of the main directions is the development of new experimental ultra-high-field MRI systems, that is, using a higher constant magnetic field, which can improve image resolution or reduce scan time, which is very important for many clinical studies and diagnostics.
Conventional clinical tomographs use constant fields up to 3 T, but now experimental tomographs with a magnetic field of 7 T and higher are appearing. It is customary to call tomographs with a magnetic field of 7 T and higher ultra-high-field. There are already about a hundred tomographs with a field of 7 T in the world, but developments are underway to further increase the magnetic field. For example, we have a 9.4 T MRI machine at the Max Planck Institute in Tübingen.
But even with the transition from 7 to 9.4 T, many technical problems arise that require serious scientific and technical developments, including the calculation and design of sensors for a new generation of MRI.
What are these difficulties?
Increasing the constant magnetic field results in a corresponding increase in the frequency of the RF sensors. For example, clinical 3T tomographs use sensors with a resonant frequency of about 120 MHz, while 7T tomographs require sensors with a frequency of 300 MHz. This primarily leads to a shortening of the RF field wavelength in human tissues. If the frequency of 120 MHz corresponds approximately to a wavelength of 35-40 centimeters, then at a frequency of 300 MHz it decreases to about 15 cm, which is much smaller than the size of the human body.
As a result of this effect, the sensitivity of RF sensors can be severely distorted when studying large objects (longer than wavelength). This leads to difficulties in the interpretation of images and the diagnosis of clinical diseases and pathologies. In a field of 9.4 T, which corresponds to a sensor frequency of 400 MHz, all these problems become even more critical.
That is, such pictures become virtually unreadable?
I wouldn't say that. More precisely, in some cases this makes it difficult to interpret them. However, there are groups that are developing techniques for obtaining MR images of the entire human body. However, the tasks of our group are focused primarily on the study of the brain.
Exactly what opportunities does UHF MRI research open up for medicine?
As you know, with an MRI, a person must lie still: if you start to move during the measurements, the picture will turn out to be distorted. At the same time, some MRI techniques can take up to an hour, and it is clear that it is difficult not to move during all this time. The increased sensitivity of ultra-high-field tomographs makes it possible to obtain images not only with higher resolution, but also much faster. This is primarily important in the study of children and elderly patients.
It should also be said about the possibilities for magnetic resonance spectroscopy ( MRS, a method that allows you to determine the biochemical changes of tissues in various diseases by the concentration of certain metabolites - approx. ed. ).
In MRI, the main signal source is the hydrogen atoms of the water molecules. But, besides this, there are other hydrogen atoms found in other molecules that are important for the functioning of the human body. Examples include various metabolites, neurotransmitters, etc. Measurement of the spatial distribution of these substances using MRS can provide useful information for the study of pathologies associated with metabolic disorders in the human body. Often the sensitivity of clinical tomographs is insufficient for their study due to their low concentration and, as a consequence, a smaller signal.
In addition to this, one can observe the NMR signal not only from hydrogen atoms, but also from other magnetic atoms, which are also very important for the diagnosis of diseases and medical research. However, firstly, their NMR signal is much weaker due to the lower gyromagnetic ratio and, secondly, their natural content in the human body is much less than hydrogen atoms. The increased sensitivity of UHF MRI is extremely important for MRI.
Another important area of MRI techniques, for which increased sensitivity is critically important, is functional MRI - an important technique for cognitive studies of the human brain.
So far, the vast majority of clinics in the world do not have high-field tomographs. What are the prospects that tomographs 7 T, and then 9 T will be able to be used in routine diagnostics?
In order for the tomograph to come to the clinic, it must be certified, checked for safety conditions, and appropriate documentation must be drawn up. This is a rather complicated and lengthy procedure. So far, there is only one company in the world that has begun to certify not only the sensors that we make, but also the device itself. This is Siemens.
There are 7 T tomographs, there are not so many of them, and they cannot yet be called completely clinical. What I named is a preclinical option, but this device is already certified, that is, it can potentially be used in clinics.
Predicting when 9.4 T tomographs will appear in clinics is even more difficult. The main problem here is the possible local heating of tissues by the RF field of the sensor due to a strong decrease in the wavelength. One of the important areas of engineering research in UHF MRI is the detailed numerical simulation of this effect to ensure patient safety. Despite the fact that such studies are carried out within the framework of scientific institutions, the transition to clinical practice requires additional research.
How is the cooperation between the Max Planck Institute and ITMO University currently being built? What joint results have you already managed to get?
The work is progressing very well. Now working with us, a postgraduate student at ITMO University. We recently published an article in one of the leading journals on the technical development of MRI. In this paper, we experimentally validated the results of previous theoretical studies to improve the sensitivity of UHF RF sensors through the use of modified and optimized dipole antennas. The result of this work, in my opinion, turned out to be very promising.
Now we are also working on several more articles that are devoted to the use of similar methods, but for other tasks. And recently Georgy received a grant for a trip to Germany. Next month he will come to us for six months, and we will continue to work together to further develop sensors for MRI.
This week you gave a special course in the Master's program in Radio Frequency Systems and Devices. What are the main topics that you covered?
The course focuses on the various technical aspects of developing MRI transducers. There are many subtleties in this area that need to be known, so I have presented a number of basic techniques that are used to design and manufacture these sensors. In addition, I presented a lecture on my latest developments. In total, the course includes eight lectures of two academic hours, which are designed for four days. There is also a demo at the end to help explain these techniques more clearly.
Master's students are now in the process of choosing their future direction, so I think this course will give them additional information to assess their prospects.
And if we talk about education in the field of MRI technologies in general, what, in your opinion, are the knowledge and skills required of such specialists today?
Despite the fact that our field has now become very popular and promising for use in clinical diagnostics, there are no engineering courses that would train highly specialized specialists involved in the manufacture of MRI coils. A gap has formed. And I think that together we can just fill it.
Elena Menshikova
News portal editorial staff
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