Beam methods of diagnostics. Radiation diagnostics (X-ray, X-ray computed tomography, magnetic resonance imaging)
2.1. X-RAY DIAGNOSIS
(RADIOLOGY)
In almost all medical institutions, devices for X-ray examination are widely used. X-ray installations are simple, reliable, economical. It is these systems that still serve as the basis for diagnosing skeletal injuries, diseases of the lungs, kidneys and digestive canal. In addition, the X-ray method plays an important role in the performance of various interventional interventions (both diagnostic and therapeutic).
2.1.1. Brief description of X-ray radiation
X-rays are electromagnetic waves (flux of quanta, photons), the energy of which is located on the energy scale between ultraviolet radiation and gamma radiation (Fig. 2-1). X-ray photons have energies from 100 eV to 250 keV, which corresponds to radiation with a frequency of 3×10 16 Hz to 6×10 19 Hz and a wavelength of 0.005–10 nm. The electromagnetic spectra of x-rays and gamma rays overlap to a large extent.
Rice. 2-1.Electromagnetic radiation scale
The main difference between these two types of radiation is the way they occur. X-rays are obtained with the participation of electrons (for example, during the deceleration of their flow), and gamma rays - with the radioactive decay of the nuclei of some elements.
X-rays can be generated during deceleration of an accelerated stream of charged particles (the so-called bremsstrahlung) or when high-energy transitions occur in the electron shells of atoms (characteristic radiation). Medical devices use X-ray tubes to generate X-rays (Figure 2-2). Their main components are a cathode and a massive anode. The electrons emitted due to the difference in electrical potential between the anode and the cathode are accelerated, reach the anode, upon collision with the material of which they are decelerated. As a result, bremsstrahlung X-rays are produced. During the collision of electrons with the anode, the second process also occurs - electrons are knocked out of the electron shells of the anode atoms. Their places are occupied by electrons from other shells of the atom. During this process, a second type of X-ray radiation is generated - the so-called characteristic X-ray radiation, the spectrum of which largely depends on the anode material. Anodes are most often made of molybdenum or tungsten. There are special devices for focusing and filtering X-rays in order to improve the resulting images.
Rice. 2-2.Scheme of the X-ray tube device:
1 - anode; 2 - cathode; 3 - voltage applied to the tube; 4 - X-ray radiation
The properties of X-rays that determine their use in medicine are penetrating power, fluorescent and photochemical effects. The penetrating power of X-rays and their absorption by the tissues of the human body and artificial materials are the most important properties that determine their use in radiation diagnostics. The shorter the wavelength, the greater the penetrating power of X-rays.
There are "soft" X-rays with low energy and radiation frequency (respectively, with the largest wavelength) and "hard" X-rays with high photon energy and radiation frequency, which have a short wavelength. The wavelength of X-ray radiation (respectively, its "hardness" and penetrating power) depends on the magnitude of the voltage applied to the X-ray tube. The higher the voltage on the tube, the greater the speed and energy of the electron flow and the shorter the wavelength of the x-rays.
During the interaction of X-ray radiation penetrating through the substance, qualitative and quantitative changes occur in it. The degree of absorption of X-rays by tissues is different and is determined by the density and atomic weight of the elements that make up the object. The higher the density and atomic weight of the substance of which the object (organ) under study consists, the more X-rays are absorbed. The human body contains tissues and organs of different densities (lungs, bones, soft tissues, etc.), which explains the different absorption of X-rays. The visualization of internal organs and structures is based on the artificial or natural difference in the absorption of X-rays by various organs and tissues.
To register the radiation that has passed through the body, its ability to cause fluorescence of certain compounds and to have a photochemical effect on the film is used. For this purpose, special screens for fluoroscopy and films for radiography are used. In modern X-ray machines, special systems of digital electronic detectors - digital electronic panels - are used to register attenuated radiation. In this case, X-ray methods are called digital.
Due to the biological effect of X-rays, it is necessary to protect patients during the examination. This is achieved
the shortest possible exposure time, the replacement of fluoroscopy with radiography, the strictly justified use of ionizing methods, protection by shielding the patient and staff from exposure to radiation.
2.1.2. X-ray and fluoroscopy
Fluoroscopy and radiography are the main methods of X-ray examination. To study various organs and tissues, a number of special devices and methods have been created (Fig. 2-3). Radiography is still very widely used in clinical practice. Fluoroscopy is used less frequently due to the relatively high radiation exposure. They have to resort to fluoroscopy where radiography or non-ionizing methods for obtaining information are insufficient. In connection with the development of CT, the role of classical layered tomography has decreased. The technique of layered tomography is used in the study of the lungs, kidneys and bones where there are no CT rooms.
X-ray (gr. scopeo- consider, observe) - a study in which an x-ray image is projected onto a fluorescent screen (or a system of digital detectors). The method allows for static, as well as dynamic, functional study of organs (eg, fluoroscopy of the stomach, excursion of the diaphragm) and control of interventional procedures (eg, angiography, stenting). Currently, when using digital systems, images are obtained on the screen of computer monitors.
The main disadvantages of fluoroscopy include a relatively high radiation exposure and difficulties in differentiating "subtle" changes.
X-ray (gr. greapho- write, depict) - a study in which an x-ray image of an object is obtained, fixed on a film (direct radiography) or on special digital devices (digital radiography).
Various types of radiography (plain radiography, targeted radiography, contact radiography, contrast radiography, mammography, urography, fistulography, arthrography, etc.) are used to improve the quality and increase the amount of diagnostic
Rice. 2-3.Modern x-ray machine
information in each specific clinical situation. For example, contact radiography is used for dental imaging, and contrast radiography is used for excretory urography.
X-ray and fluoroscopy techniques can be used in the vertical or horizontal position of the patient's body in stationary or ward settings.
Conventional radiography using X-ray film or digital radiography remains one of the main and widely used examination methods. This is due to the high cost-effectiveness, simplicity and information content of the obtained diagnostic images.
When photographing an object from a fluorescent screen onto a film (usually a small size - a film of a special format), X-ray images are obtained, which are usually used for mass examinations. This technique is called fluorography. Currently, it is gradually falling into disuse due to its replacement by digital radiography.
The disadvantage of any type of X-ray examination is its low resolution in the study of low-contrast tissues. The classical tomography used for this purpose did not give the desired result. It was to overcome this shortcoming that CT was created.
2.2. ULTRASOUND DIAGNOSIS (SONOGRAPHY, ULTRASOUND)
Ultrasound diagnostics (sonography, ultrasound) is a method of radiation diagnostics based on obtaining images of internal organs using ultrasonic waves.
Ultrasound is widely used in diagnostics. Over the past 50 years, the method has become one of the most common and important, providing fast, accurate and safe diagnosis of many diseases.
Ultrasound is called sound waves with a frequency of more than 20,000 Hz. It is a form of mechanical energy that has a wave nature. Ultrasonic waves propagate in biological media. The speed of ultrasonic wave propagation in tissues is constant and amounts to 1540 m/s. The image is obtained by analyzing the signal reflected from the boundary of two media (echo signal). In medicine, frequencies in the range of 2-10 MHz are most commonly used.
Ultrasound is generated by a special transducer with a piezoelectric crystal. Short electrical pulses create mechanical oscillations of the crystal, resulting in the generation of ultrasonic radiation. The frequency of ultrasound is determined by the resonant frequency of the crystal. Reflected signals are recorded, analyzed and displayed visually on the screen of the device, creating images of the structures under study. Thus, the sensor works sequentially as an emitter and then as a receiver of ultrasonic waves. The operating principle of the ultrasonic system is shown in fig. 2-4.
Rice. 2-4.The principle of operation of the ultrasonic system
The greater the acoustic impedance, the greater the reflection of ultrasound. Air does not conduct sound waves, therefore, to improve signal penetration at the air/skin interface, a special ultrasonic gel is applied to the sensor. This eliminates the air gap between the patient's skin and the sensor. Strong artefacts in the study may arise from structures containing air or calcium (lung fields, bowel loops, bones and calcifications). For example, when examining the heart, the latter can be almost completely covered by tissues that reflect or do not conduct ultrasound (lungs, bones). In this case, the study of the organ is possible only through small areas on the
body surface where the organ under study is in contact with soft tissues. This area is called the ultrasonic "window". With a poor ultrasound "window", the study may be impossible or uninformative.
Modern ultrasound machines are complex digital devices. They use real-time sensors. The images are dynamic, they can observe such fast processes as breathing, heart contractions, vascular pulsation, valve movement, peristalsis, fetal movements. The position of the sensor connected to the ultrasonic device with a flexible cable can be changed in any plane and at any angle. The analog electrical signal generated in the sensor is digitized and a digital image is created.
Very important in ultrasound is the Doppler technique. Doppler described the physical effect that the frequency of sound generated by a moving object changes when it is perceived by a stationary receiver, depending on the speed, direction and nature of the movement. The Doppler method is used to measure and visualize the speed, direction and nature of the movement of blood in the vessels and chambers of the heart, as well as the movement of any other fluids.
In a Doppler study of blood vessels, continuous-wave or pulsed ultrasonic radiation passes through the area under study. When an ultrasonic beam crosses a vessel or chamber of the heart, the ultrasound is partially reflected by red blood cells. So, for example, the frequency of the reflected echo signal from the blood moving towards the sensor will be higher than the original frequency of the waves emitted by the sensor. Conversely, the frequency of the reflected echo from blood moving away from the transducer will be lower. The difference between the frequency of the received echo signal and the frequency of the ultrasound generated by the transducer is called the Doppler shift. This frequency shift is proportional to the blood flow velocity. The ultrasound device automatically converts the Doppler shift into relative blood flow velocity.
Studies that combine real-time 2D ultrasound and pulsed Doppler are called duplex studies. In a duplex exam, the direction of the Doppler beam is superimposed on a 2D B-mode image.
The modern development of the duplex study technique has led to the emergence of a technique for color Doppler blood flow mapping. Within the control volume, the stained blood flow is superimposed on the 2D image. In this case, the blood is displayed in color, and motionless tissues - in a gray scale. When blood moves towards the sensor, red-yellow colors are used, when moving away from the sensor, blue-blue colors are used. Such a color image does not carry additional information, but gives a good visual representation of the nature of the blood movement.
In most cases, for the purpose of ultrasound, it is sufficient to use sensors for percutaneous examination. However, in some cases it is necessary to bring the sensor closer to the object. For example, in large patients, sensors placed in the esophagus (transesophageal echocardiography) are used to examine the heart, in other cases, intrarectal or intravaginal sensors are used to obtain high-quality images. During the operation resort to the use of operating sensors.
In recent years, 3D ultrasound has been increasingly used. The range of ultrasound systems is very wide - there are portable devices, devices for intraoperative ultrasound and ultrasound systems of an expert class (Fig. 2-5).
In modern clinical practice, the method of ultrasound examination (sonography) is extremely widespread. This is explained by the fact that when applying the method, there is no ionizing radiation, it is possible to conduct functional and stress tests, the method is informative and relatively inexpensive, the devices are compact and easy to use.
Rice. 2-5.Modern ultrasound machine
However, the sonographic method has its limitations. These include a high frequency of artifacts in the image, a small signal penetration depth, a small field of view, and a high dependence of the interpretation of the results on the operator.
With the development of ultrasound equipment, the information content of this method is increasing.
2.3. COMPUTED TOMOGRAPHY (CT)
CT is an X-ray examination method based on obtaining layer-by-layer images in the transverse plane and their computer reconstruction.
The development of CT machines is the next revolutionary step in diagnostic imaging since the discovery of X-rays. This is due not only to the versatility and unsurpassed resolution of the method in the study of the whole body, but also to new imaging algorithms. Currently, all imaging devices use to some extent the techniques and mathematical methods that were the basis of CT.
CT has no absolute contraindications to its use (except for limitations associated with ionizing radiation) and can be used for emergency diagnosis, screening, and also as a method of clarifying diagnosis.
The main contribution to the creation of computed tomography was made by the British scientist Godfrey Hounsfield in the late 60s. XX century.
At first, CT scanners were divided into generations depending on how the X-ray tube-detectors system was arranged. Despite the multiple differences in structure, they were all called "stepping" tomographs. This was due to the fact that after each transverse cut, the tomograph stopped, the table with the patient made a “step” of a few millimeters, and then the next cut was performed.
In 1989, spiral computed tomography (SCT) appeared. In the case of SCT, an X-ray tube with detectors constantly rotates around a continuously moving table with patients.
volume. This makes it possible not only to reduce the examination time, but also to avoid the limitations of the "step-by-step" technique - skipping areas during examination due to different depths of breath holding by the patient. The new software additionally made it possible to change the slice width and the image restoration algorithm after the end of the study. This made it possible to obtain new diagnostic information without re-examination.
Since then, CT has become standardized and universal. It was possible to synchronize the injection of a contrast agent with the beginning of the movement of the table during SCT, which led to the creation of CT angiography.
In 1998, multislice CT (MSCT) appeared. Systems were created with not one (as in SCT), but with 4 rows of digital detectors. Since 2002, tomographs with 16 rows of digital elements in the detector began to be used, and since 2003, the number of rows of elements has reached 64. In 2007, MSCT appeared with 256 and 320 rows of detector elements.
On such tomographs, it is possible to obtain hundreds and thousands of tomograms in just a few seconds with a thickness of each slice of 0.5-0.6 mm. Such a technical improvement made it possible to carry out the study even for patients connected to an artificial respiration apparatus. In addition to speeding up the examination and improving its quality, such a complex problem as visualization of coronary vessels and heart cavities using CT was solved. It became possible to study the coronary vessels, the volume of the cavities and the function of the heart, and myocardial perfusion in one 5-20-second study.
The schematic diagram of the CT device is shown in fig. 2-6, and the appearance - in Fig. 2-7.
The main advantages of modern CT include: the speed of obtaining images, the layered (tomographic) nature of the images, the ability to obtain slices of any orientation, high spatial and temporal resolution.
The disadvantages of CT are the relatively high (compared to radiography) radiation exposure, the possibility of the appearance of artifacts from dense structures, movements, and the relatively low soft tissue contrast resolution.
Rice. 2-6.Scheme of the MSCT device
Rice. 2-7.Modern 64-spiral CT scanner
2.4. MAGNETIC RESONANCE
TOMOGRAPHY (MRI)
Magnetic resonance imaging (MRI) is a method of radiation diagnostics based on obtaining layer-by-layer and volumetric images of organs and tissues of any orientation using the phenomenon of nuclear magnetic resonance (NMR). The first works on obtaining images using NMR appeared in the 70s. last century. To date, this method of medical imaging has changed beyond recognition and continues to evolve. Hardware and software are being improved, methods of obtaining images are being improved. Previously, the field of use of MRI was limited only to the study of the central nervous system. Now the method is successfully used in other areas of medicine, including studies of blood vessels and the heart.
After the inclusion of NMR in the number of methods of radiation diagnostics, the adjective "nuclear" was no longer used in order not to cause associations in patients with nuclear weapons or nuclear energy. Therefore, the term "magnetic resonance imaging" (MRI) is officially used today.
NMR is a physical phenomenon based on the properties of some atomic nuclei placed in a magnetic field to absorb external energy in the radio frequency (RF) range and emit it after the cessation of exposure to the radio frequency pulse. The strength of the constant magnetic field and the frequency of the radio frequency pulse strictly correspond to each other.
Important for use in magnetic resonance imaging are the 1H, 13C, 19F, 23Na and 31P nuclei. All of them have magnetic properties, which distinguishes them from non-magnetic isotopes. Hydrogen protons (1H) are the most abundant in the body. Therefore, for MRI, it is the signal from hydrogen nuclei (protons) that is used.
Hydrogen nuclei can be thought of as small magnets (dipoles) with two poles. Each proton rotates around its own axis and has a small magnetic moment (magnetization vector). The rotating magnetic moments of nuclei are called spins. When such nuclei are placed in an external magnetic field, they can absorb electromagnetic waves of certain frequencies. This phenomenon depends on the type of nuclei, the strength of the magnetic field, and the physical and chemical environment of the nuclei. At the same time, the behavior
the nucleus can be compared to a spinning top. Under the action of a magnetic field, the rotating nucleus performs a complex movement. The nucleus rotates around its axis, and the axis of rotation itself performs cone-shaped circular motions (precesses), deviating from the vertical direction.
In an external magnetic field, nuclei can be either in a stable energy state or in an excited state. The energy difference between these two states is so small that the number of nuclei at each of these levels is almost identical. Therefore, the resulting NMR signal, which depends precisely on the difference in the populations of these two levels by protons, will be very weak. To detect this macroscopic magnetization, it is necessary to deviate its vector from the axis of the constant magnetic field. This is achieved by a pulse of external radio frequency (electromagnetic) radiation. When the system returns to the equilibrium state, the absorbed energy (MR signal) is emitted. This signal is recorded and used to build MR images.
Special (gradient) coils located inside the main magnet create small additional magnetic fields in such a way that the field strength increases linearly in one direction. By transmitting radio frequency pulses with a predetermined narrow frequency range, it is possible to receive MR signals only from a selected layer of tissue. The orientation of the magnetic field gradients and, accordingly, the direction of the slices can be easily set in any direction. The signals received from each volumetric image element (voxel) have their own, unique, recognizable code. This code is the frequency and phase of the signal. Based on these data, two or three-dimensional images can be built.
To obtain a magnetic resonance signal, combinations of radio frequency pulses of various durations and shapes are used. By combining various pulses, so-called pulse sequences are formed, which are used to obtain images. Special pulse sequences include MR hydrography, MR myelography, MR cholangiography, and MR angiography.
Tissues with large total magnetic vectors will induce a strong signal (look bright), and tissues with small
magnetic vectors - weak signal (looks dark). Anatomical regions with few protons (eg air or compact bone) induce a very weak MR signal and thus always appear dark in the image. Water and other liquids have a strong signal and appear bright in the image, with varying intensities. Soft tissue images also have different signal intensities. This is due to the fact that, in addition to the proton density, the nature of the signal intensity in MRI is also determined by other parameters. These include: the time of spin-lattice (longitudinal) relaxation (T1), spin-spin (transverse) relaxation (T2), motion or diffusion of the medium under study.
Tissue relaxation time - T1 and T2 - is a constant. In MRI, the concepts of "T1-weighted image", "T2-weighted image", "proton-weighted image" are used, indicating that the differences between tissue images are mainly due to the predominant action of one of these factors.
By adjusting the parameters of the pulse sequences, the radiologist or doctor can influence the contrast of images without resorting to contrast agents. Therefore, in MR imaging, there are significantly more opportunities for changing the contrast in images than in radiography, CT or ultrasound. However, the introduction of special contrast agents can further change the contrast between normal and pathological tissues and improve the quality of imaging.
Schematic diagram of the MR-system device and the appearance of the device are shown in fig. 2-8
and 2-9.
Typically, MR scanners are classified according to the strength of the magnetic field. The strength of the magnetic field is measured in teslas (T) or gauss (1T = 10,000 gauss). The strength of the Earth's magnetic field ranges from 0.7 gauss at the pole to 0.3 gauss at the equator. For cli-
Rice. 2-8.Scheme of the MRI device
Rice. 2-9.Modern MRI system with a field of 1.5 Tesla
Magnetic MRI uses magnets with fields ranging from 0.2 to 3 Tesla. Currently, MR systems with a field of 1.5 and 3 T are most often used for diagnostics. Such systems account for up to 70% of the world's equipment fleet. There is no linear relationship between field strength and image quality. However, devices with such a field strength give a better image quality and have a greater number of programs used in clinical practice.
The main field of application of MRI was the brain, and then the spinal cord. Brain tomograms allow you to get a great image of all brain structures without resorting to additional contrast injection. Due to the technical ability of the method to obtain an image in all planes, MRI has revolutionized the study of the spinal cord and intervertebral discs.
Currently, MRI is increasingly used to examine the joints, pelvic organs, mammary glands, heart and blood vessels. For these purposes, additional special coils and mathematical methods for imaging have been developed.
A special technique allows you to record images of the heart in different phases of the cardiac cycle. If the study is carried out with
synchronization with the ECG, images of the functioning heart can be obtained. This study is called cine-MRI.
Magnetic resonance spectroscopy (MRS) is a non-invasive diagnostic method that allows you to qualitatively and quantitatively determine the chemical composition of organs and tissues using nuclear magnetic resonance and the chemical shift phenomenon.
MR spectroscopy is most often performed to obtain signals from phosphorus and hydrogen nuclei (protons). However, due to technical difficulties and duration, it is still rarely used in clinical practice. It should not be forgotten that the increasing use of MRI requires special attention to patient safety issues. When examined using MR spectroscopy, the patient is not exposed to ionizing radiation, but he is affected by electromagnetic and radio frequency radiation. Metal objects (bullets, fragments, large implants) and all electromechanical devices (for example, a pacemaker) located in the body of the person being examined can harm the patient due to displacement or disruption (cessation) of normal operation.
Many patients experience a fear of closed spaces - claustrophobia, which leads to the inability to perform the study. Thus, all patients should be informed about the possible undesirable consequences of the study and the nature of the procedure, and the attending physicians and radiologists must interrogate the patient before the study for the presence of the above objects, injuries and operations. Before the examination, the patient must completely change into a special suit to prevent metal items from getting into the magnet channel from the pockets of clothing.
It is important to know the relative and absolute contraindications to the study.
Absolute contraindications to the study include conditions in which its conduct creates a life-threatening situation for the patient. This category includes all patients with the presence of electronic-mechanical devices in the body (pacemakers), and patients with the presence of metal clips on the arteries of the brain. Relative contraindications to the study include conditions that can create certain dangers and difficulties during MRI, but in most cases it is still possible. These contraindications are
the presence of hemostatic staples, clamps and clips of other localization, decompensation of heart failure, the first trimester of pregnancy, claustrophobia and the need for physiological monitoring. In such cases, the decision on the possibility of MRI is decided in each individual case based on the ratio of the magnitude of the possible risk and the expected benefit from the study.
Most small metal objects (artificial teeth, surgical sutures, some types of artificial heart valves, stents) are not a contraindication to the study. Claustrophobia is an obstacle to the study in 1-4% of cases.
Like other imaging modalities, MRI is not without its drawbacks.
Significant disadvantages of MRI include a relatively long examination time, the inability to accurately detect small stones and calcifications, the complexity of the equipment and its operation, and special requirements for the installation of devices (protection from interference). MRI makes it difficult to examine patients who need equipment to keep them alive.
2.5. RADIONUCLIDE DIAGNOSIS
Radionuclide diagnostics or nuclear medicine is a method of radiation diagnostics based on the registration of radiation from artificial radioactive substances introduced into the body.
For radionuclide diagnostics, a wide range of labeled compounds (radiopharmaceuticals (RP)) and methods for their registration with special scintillation sensors are used. The energy of the absorbed ionizing radiation excites flashes of visible light in the sensor crystal, each of which is amplified by photomultipliers and converted into a current pulse.
Signal strength analysis allows you to determine the intensity and position in space of each scintillation. These data are used to reconstruct a two-dimensional image of the distribution of radiopharmaceuticals. The image can be presented directly on the monitor screen, on a photo or multi-format film, or recorded on a computer medium.
There are several groups of radiodiagnostic devices depending on the method and type of registration of radiation:
Radiometers - devices for measuring the radioactivity of the whole body;
Radiographs - devices for recording the dynamics of changes in radioactivity;
Scanners - systems for registering the spatial distribution of radiopharmaceuticals;
Gamma cameras are devices for static and dynamic registration of the volumetric distribution of a radioactive tracer.
In modern clinics, most devices for radionuclide diagnostics are gamma cameras of various types.
Modern gamma cameras are a complex consisting of 1-2 systems of large-diameter detectors, a patient positioning table and a computer system for image acquisition and processing (Fig. 2-10).
The next step in the development of radionuclide diagnostics was the creation of a rotational gamma camera. With the help of these devices, it was possible to apply the method of layer-by-layer study of the distribution of isotopes in the body - single-photon emission computed tomography (SPECT).
Rice. 2-10.Scheme of the gamma camera device
Rotating gamma cameras with one, two or three detectors are used for SPECT. The mechanical systems of tomographs allow the detectors to be rotated around the patient's body in different orbits.
The spatial resolution of modern SPECT is about 5-8 mm. The second condition for performing a radioisotope study, in addition to the availability of special equipment, is the use of special radioactive indicators - radiopharmaceuticals (RP), which are introduced into the patient's body.
A radiopharmaceutical is a radioactive chemical compound with known pharmacological and pharmacokinetic characteristics. Quite strict requirements are imposed on radiopharmaceuticals used in medical diagnostics: affinity for organs and tissues, ease of preparation, short half-life, optimal gamma radiation energy (100-300 kEv) and low radiotoxicity at relatively high allowable doses. An ideal radiopharmaceutical should only reach the organs or pathological foci intended for investigation.
Understanding the mechanisms of radiopharmaceutical localization serves as the basis for an adequate interpretation of radionuclide studies.
The use of modern radioactive isotopes in medical diagnostic practice is safe and harmless. The amount of active substance (isotope) is so small that when administered to the body, it does not cause physiological effects or allergic reactions. In nuclear medicine, radiopharmaceuticals emitting gamma rays are used. Sources of alpha (helium nuclei) and beta particles (electrons) are currently not used in diagnostics due to the high tissue absorption and high radiation exposure.
The most commonly used in clinical practice is the technetium-99t isotope (half-life - 6 hours). This artificial radionuclide is obtained immediately before the study from special devices (generators).
A radiodiagnostic image, regardless of its type (static or dynamic, planar or tomographic), always reflects the specific function of the organ under study. In fact, this is a display of a functioning tissue. It is in the functional aspect that the fundamental distinguishing feature of radionuclide diagnostics from other imaging methods lies.
RFP is usually administered intravenously. For studies of lung ventilation, the drug is administered by inhalation.
One of the new tomographic radioisotope techniques in nuclear medicine is positron emission tomography (PET).
The PET method is based on the property of some short-lived radionuclides to emit positrons during decay. A positron is a particle equal in mass to an electron, but having a positive charge. A positron, having flown in a substance of 1-3 mm and having lost the kinetic energy received at the moment of formation in collisions with atoms, annihilates with the formation of two gamma quanta (photons) with an energy of 511 keV. These quanta scatter in opposite directions. Thus, the decay point lies on a straight line - the trajectory of two annihilated photons. Two detectors located opposite each other register the combined annihilation photons (Fig. 2-11).
PET makes it possible to quantify the concentration of radionuclides and has more opportunities for studying metabolic processes than scintigraphy performed using gamma cameras.
For PET, isotopes of elements such as carbon, oxygen, nitrogen, and fluorine are used. Radiopharmaceuticals labeled with these elements are natural metabolites of the body and are included in the metabolism
Rice. 2-11.Diagram of the PET device
substances. As a result, it is possible to study the processes occurring at the cellular level. From this point of view, PET is the only method (except for MR spectroscopy) for assessing metabolic and biochemical processes in vivo.
All positron radionuclides used in medicine are ultrashort-lived - their half-life is calculated in minutes or seconds. The exceptions are fluorine-18 and rubidium-82. In this regard, fluorine-18-labeled deoxyglucose (fluorodeoxyglucose - FDG) is most commonly used.
Despite the fact that the first PET systems appeared in the middle of the 20th century, their clinical use is hindered due to some limitations. These are the technical difficulties that arise when accelerators for the production of short-lived isotopes are installed in clinics, their high cost, and the difficulty in interpreting the results. One of the limitations - poor spatial resolution - was overcome by combining the PET system with MSCT, which, however, makes the system even more expensive (Fig. 2-12). In this regard, PET examinations are carried out according to strict indications, when other methods are ineffective.
The main advantages of the radionuclide method are high sensitivity to various types of pathological processes, the ability to assess the metabolism and viability of tissues.
The general disadvantages of radioisotope methods include low spatial resolution. The use of radioactive preparations in medical practice is associated with the difficulties of their transportation, storage, packaging and administration to patients.
Rice. 2-12.Modern PET-CT system
The organization of radioisotope laboratories (especially for PET) requires special facilities, security, alarms and other precautions.
2.6. ANGIOGRAPHY
Angiography is an X-ray method associated with the direct injection of a contrast agent into the vessels in order to study them.
Angiography is divided into arteriography, phlebography and lymphography. The latter, due to the development of ultrasound, CT and MRI methods, is currently practically not used.
Angiography is performed in specialized x-ray rooms. These rooms meet all the requirements for operating rooms. For angiography, specialized X-ray machines (angiographic units) are used (Fig. 2-13).
The introduction of a contrast agent into the vascular bed is carried out by injection with a syringe or (more often) with a special automatic injector after vascular puncture.
Rice. 2-13.Modern angiographic unit
The main method of vessel catheterization is the Seldinger method of vessel catheterization. To perform angiography, a certain amount of a contrast agent is injected into the vessel through the catheter and the passage of the drug through the vessels is filmed.
A variant of angiography is coronary angiography (CAG) - a technique for examining the coronary vessels and chambers of the heart. This is a complex research technique that requires special training of the radiologist and sophisticated equipment.
Currently, diagnostic angiography of peripheral vessels (for example, aortography, angiopulmonography) is used less and less. In the presence of modern ultrasound machines in clinics, CT and MRI diagnostics of pathological processes in the vessels is increasingly carried out using minimally invasive (CT angiography) or non-invasive (ultrasound and MRI) techniques. In turn, with angiography, minimally invasive surgical procedures (recanalization of the vascular bed, balloon angioplasty, stenting) are increasingly performed. Thus, the development of angiography led to the birth of interventional radiology.
2.7 INTERVENTION RADIOLOGY
Interventional radiology is a field of medicine based on the use of radiation diagnostic methods and special tools to perform minimally invasive interventions to diagnose and treat diseases.
Interventional interventions are widely used in many areas of medicine, as they can often replace major surgical interventions.
The first percutaneous treatment of peripheral artery stenosis was performed by the American physician Charles Dotter in 1964. In 1977, the Swiss physician Andreas Gruntzig constructed a balloon catheter and performed a dilatation (expansion) procedure on a stenotic coronary artery. This method became known as balloon angioplasty.
Balloon angioplasty of the coronary and peripheral arteries is currently one of the main methods for the treatment of stenosis and occlusion of the arteries. In case of recurrence of stenosis, this procedure can be repeated many times. To prevent re-stenosis at the end of the last century, endo-
vascular prostheses - stents. A stent is a tubular metal structure that is placed in a narrowed area after balloon dilatation. An expanded stent prevents re-stenosis from occurring.
Stent placement is carried out after diagnostic angiography and determination of the site of critical constriction. The stent is selected according to length and size (Fig. 2-14). Using this technique, it is possible to close defects of the interatrial and interventricular septa without major operations or to perform balloon plasty of stenoses of the aortic, mitral, and tricuspid valves.
Of particular importance is the technique of installing special filters in the inferior vena cava (cava filters). This is necessary to prevent the entry of emboli into the vessels of the lungs during thrombosis of the veins of the lower extremities. The cava filter is a mesh structure that, opening in the lumen of the inferior vena cava, catches ascending blood clots.
Another endovascular intervention that is in demand in clinical practice is embolization (blockage) of blood vessels. Embolization is used to stop internal bleeding, treat pathological vascular anastomoses, aneurysms, or to close vessels that feed a malignant tumor. Currently, effective artificial materials, removable balloons and microscopic steel coils are used for embolization. Usually, embolization is performed selectively so as not to cause ischemia of surrounding tissues.
Rice. 2-14.Scheme of performing balloon angioplasty and stenting
Interventional radiology also includes drainage of abscesses and cysts, contrasting of pathological cavities through fistulous tracts, restoration of urinary tract patency in urinary disorders, bougienage and balloon plastics in case of strictures (narrowings) of the esophagus and bile ducts, percutaneous thermal or cryodestruction of malignant tumors and other interventions.
After identifying the pathological process, it is often necessary to resort to such a variant of interventional radiology as a puncture biopsy. Knowledge of the morphological structure of education allows you to choose an adequate treatment strategy. Puncture biopsy is performed under X-ray, ultrasound or CT control.
Currently, interventional radiology is actively developing and in many cases allows avoiding major surgical interventions.
2.8 IMAGING CONTRAST AGENTS
Low contrast between adjacent objects or the same density of adjacent tissues (for example, the density of blood, vascular wall and thrombus) makes it difficult to interpret images. In these cases, in radiodiagnosis, artificial contrast is often used.
An example of increasing the contrast of images of the organs under study is the use of barium sulfate to study the organs of the alimentary canal. The first such contrasting was performed in 1909.
It was more difficult to create contrast agents for intravascular injection. For this purpose, after long experiments with mercury and lead, soluble iodine compounds began to be used. The first generations of radiopaque agents were imperfect. Their use caused frequent and severe (even fatal) complications. But already in the 20-30s. 20th century a number of safer water-soluble iodine-containing drugs for intravenous administration have been created. The widespread use of drugs in this group began in 1953, when a drug was synthesized, the molecule of which consisted of three iodine atoms (diatrizoate).
In 1968, substances with low osmolarity (they did not dissociate into an anion and cation in solution) were developed - non-ionic contrast agents.
Modern radiopaque agents are triiodine-substituted compounds containing three or six iodine atoms.
There are drugs for intravascular, intracavitary and subarachnoid administration. You can also inject a contrast agent into the cavity of the joints, into the abdominal organs and under the membranes of the spinal cord. For example, the introduction of contrast through the uterine cavity into the tubes (hysterosalpingography) allows you to evaluate the inner surface of the uterine cavity and the patency of the fallopian tubes. In neurological practice, in the absence of MRI, the myelography technique is used - the introduction of a water-soluble contrast agent under the membranes of the spinal cord. This allows you to assess the patency of the subarachnoid spaces. Other methods of artificial contrasting should be mentioned angiography, urography, fistulography, herniography, sialography, arthrography.
After a rapid (bolus) intravenous injection of a contrast agent, it reaches the right heart, then the bolus passes through the vascular bed of the lungs and reaches the left heart, then the aorta and its branches. There is a rapid diffusion of the contrast agent from the blood into the tissues. During the first minute after a rapid injection, a high concentration of contrast agent is maintained in the blood and blood vessels.
Intravascular and intracavitary administration of contrast agents containing iodine in their molecule, in rare cases, can have an adverse effect on the body. If such changes are manifested by clinical symptoms or change the laboratory parameters of the patient, then they are called adverse reactions. Before examining a patient with the use of contrast agents, it is necessary to find out if he has allergic reactions to iodine, chronic renal failure, bronchial asthma and other diseases. The patient should be warned about the possible reaction and about the benefits of such a study.
In the event of a reaction to the administration of a contrast agent, the office staff must act in accordance with the special instructions for combating anaphylactic shock in order to prevent serious complications.
Contrast agents are also used in MRI. Their use began in recent decades, after the intensive introduction of the method into the clinic.
The use of contrast agents in MRI is aimed at changing the magnetic properties of tissues. This is their essential difference from iodine-containing contrast agents. While X-ray contrast agents significantly attenuate penetrating radiation, MRI preparations lead to changes in the characteristics of surrounding tissues. They are not visualized on tomograms, like x-ray contrasts, but they allow revealing hidden pathological processes due to changes in magnetic indicators.
The mechanism of action of these agents is based on changes in the relaxation time of a tissue site. Most of these drugs are made on the basis of gadolinium. Contrast agents based on iron oxide are used much less frequently. These substances affect the intensity of the signal in different ways.
Positive (shortening the T1 relaxation time) are usually based on gadolinium (Gd), and negative ones (shortening the T2 time) based on iron oxide. Gadolinium-based contrast agents are considered safer than iodine-based contrast agents. There are only a few reports of serious anaphylactic reactions to these substances. Despite this, careful monitoring of the patient after the injection and availability of resuscitation equipment are necessary. Paramagnetic contrast agents are distributed in the intravascular and extracellular spaces of the body and do not pass through the blood-brain barrier (BBB). Therefore, in the CNS, only areas devoid of this barrier are normally contrasted, for example, the pituitary gland, the pituitary funnel, the cavernous sinuses, the dura mater, and the mucous membranes of the nose and paranasal sinuses. Damage and destruction of the BBB lead to the penetration of paramagnetic contrast agents into the intercellular space and local changes in T1 relaxation. This is noted in a number of pathological processes in the central nervous system, such as tumors, metastases, cerebrovascular accidents, infections.
In addition to MR studies of the central nervous system, contrast is used to diagnose diseases of the musculoskeletal system, heart, liver, pancreas, kidneys, adrenal glands, pelvic organs and mammary glands. These studies are carried out
significantly less than in CNS pathology. To perform MR angiography and study organ perfusion, a contrast agent is injected with a special non-magnetic injector.
In recent years, the feasibility of using contrast agents for ultrasound studies has been studied.
To increase the echogenicity of the vascular bed or parenchymal organ, an ultrasound contrast agent is injected intravenously. These can be suspensions of solid particles, emulsions of liquid droplets, and most often - gas microbubbles placed in various shells. Like other contrast agents, ultrasound contrast agents should have low toxicity and be rapidly eliminated from the body. The drugs of the first generation did not pass through the capillary bed of the lungs and were destroyed in it.
The contrast agents currently used enter the systemic circulation, which makes it possible to use them to improve the quality of images of internal organs, enhance the Doppler signal and study perfusion. There is currently no final opinion on the advisability of using ultrasound contrast agents.
Adverse reactions with the introduction of contrast agents occur in 1-5% of cases. The vast majority of adverse reactions are mild and do not require special treatment.
Particular attention should be paid to the prevention and treatment of severe complications. The frequency of such complications is less than 0.1%. The greatest danger is the development of anaphylactic reactions (idiosyncrasy) with the introduction of iodine-containing substances and acute renal failure.
Reactions to the introduction of contrast agents can be conditionally divided into mild, moderate and severe.
With mild reactions, the patient has a feeling of heat or chills, slight nausea. There is no need for medical treatment.
With moderate reactions, the above symptoms may also be accompanied by a decrease in blood pressure, the occurrence of tachycardia, vomiting, and urticaria. It is necessary to provide symptomatic medical care (usually - the introduction of antihistamines, antiemetics, sympathomimetics).
In severe reactions, anaphylactic shock may occur. Urgent resuscitation is needed
ties aimed at maintaining the activity of vital organs.
The following categories of patients belong to the high-risk group. These are the patients:
With severe impairment of kidney and liver function;
With a burdened allergic history, especially those who had adverse reactions to contrast agents earlier;
With severe heart failure or pulmonary hypertension;
With severe dysfunction of the thyroid gland;
With severe diabetes mellitus, pheochromocytoma, myeloma.
The risk group in relation to the risk of developing adverse reactions is also commonly referred to as young children and the elderly.
The prescribing physician should carefully evaluate the risk/benefit ratio when performing contrast studies and take the necessary precautions. A radiologist performing a study in a patient with a high risk of adverse reactions to a contrast agent must warn the patient and the attending physician about the dangers of using contrast agents and, if necessary, replace the study with another one that does not require contrast.
The X-ray room should be equipped with everything necessary for resuscitation and the fight against anaphylactic shock.
The problems of disease are more complex and difficult than any others that a trained mind has to deal with.
A majestic and endless world spreads around. And each person is also a world, complex and unique. In different ways, we strive to explore this world, to understand the basic principles of its structure and regulation, to know its structure and functions. Scientific knowledge is based on the following research methods: morphological method, physiological experiment, clinical research, radiation and instrumental methods. However scientific knowledge is only the first basis of diagnosis. This knowledge is like sheet music for a musician. However, using the same notes, different musicians achieve different effects when performing the same piece. The second basis of diagnosis is the art and personal experience of the doctor.“Science and art are as interconnected as the lungs and the heart, so if one organ is perverted, then the other cannot function correctly” (L. Tolstoy).
All this emphasizes the exceptional responsibility of the doctor: after all, every time at the patient's bedside he makes an important decision. Constant improvement of knowledge and the desire for creativity - these are the features of a real doctor. “We love everything - both the heat of cold numbers, and the gift of divine visions ...” (A. Blok).
Where does any diagnosis begin, including radiation? With deep and solid knowledge about the structure and functions of the systems and organs of a healthy person in all the originality of his gender, age, constitutional and individual characteristics. “For a fruitful analysis of the work of each organ, it is necessary first of all to know its normal activity” (IP Pavlov). In this regard, all chapters of the III part of the textbook begin with a summary of the radiation anatomy and physiology of the relevant organs.
Dream of I.P. Pavlova to embrace the majestic activity of the brain with a system of equations is still far from being realized. In most pathological processes, diagnostic information is so complex and individual that it has not yet been possible to express it by a sum of equations. Nevertheless, re-examination of similar typical reactions has allowed theorists and clinicians to identify typical syndromes of damage and diseases, to create some images of diseases. This is an important step on the diagnostic path, therefore, in each chapter, after describing the normal picture of organs, the symptoms and syndromes of diseases that are most often detected during radiodiagnosis are considered. We only add that it is here that the doctor's personal qualities are clearly manifested: his observation and ability to discern the leading lesion syndrome in a motley kaleidoscope of symptoms. We can learn from our distant ancestors. We have in mind the Neolithic rock paintings, which surprisingly accurately reflect the general scheme (image) of the phenomenon.
In addition, each chapter gives a brief description of the clinical picture of a few of the most common and severe diseases that the student should get acquainted with both at the Department of Radiation Diagnostics.
CI and radiation therapy, and in the process of supervising patients in therapeutic and surgical clinics in senior courses.
The actual diagnosis begins with an examination of the patient, and it is very important to choose the right program for its implementation. The leading link in the process of recognizing diseases, of course, remains a qualified clinical examination, but it is no longer limited to examining the patient, but is an organized, purposeful process that begins with an examination and includes the use of special methods, among which radiation occupies a prominent place.
Under these conditions, the work of a doctor or a group of doctors should be based on a clear program of action, which provides for the application of various methods of research, i.e. each doctor should be armed with a set of standard schemes for examining patients. These schemes are designed to provide high reliability of diagnostics, economy of forces and resources of specialists and patients, priority use of less invasive interventions and reduction of radiation exposure to patients and medical personnel. In this regard, in each chapter, schemes of radiation examination are given for some clinical and radiological syndromes. This is only a modest attempt to outline the path of a comprehensive radiological examination in the most common clinical situations. The next task is to move from these limited schemes to genuine diagnostic algorithms that will contain all the data about the patient.
In practice, alas, the implementation of the examination program is associated with certain difficulties: the technical equipment of medical institutions is different, the knowledge and experience of doctors is not the same, and the patient's condition. “Wits say that the optimal trajectory is the trajectory along which the rocket never flies” (N.N. Moiseev). Nevertheless, the doctor must choose the best way of examination for a particular patient. The noted stages are included in the general scheme of the patient's diagnostic study.
Medical history and clinical picture of the disease
Establishing indications for radiological examination
The choice of the method of radiation research and preparation of the patient
Conducting a radiological study
Analysis of the image of an organ obtained using radiation methods
Analysis of the function of the organ, carried out using radiation methods
Comparison with the results of instrumental and laboratory studies
Conclusion
In order to effectively conduct radiation diagnostics and correctly evaluate the results of radiation studies, it is necessary to adhere to strict methodological principles.
First principle: any radiation study must be justified. The main argument in favor of performing a radiological procedure should be the clinical need for additional information, without which a complete individual diagnosis cannot be established.
Second principle: when choosing a research method, it is necessary to take into account the radiation (dose) load on the patient. The guidance documents of the World Health Organization provide that an X-ray examination should have undoubted diagnostic and prognostic effectiveness; otherwise, it is a waste of money and a health hazard due to the unjustified use of radiation. With equal informativeness of methods, preference should be given to the one in which there is no exposure of the patient or it is the least significant.
Third principle: when conducting a radiological examination, it is necessary to adhere to the rule “necessary and sufficient”, avoiding unnecessary procedures. The procedure for performing the necessary studies- from the most gentle and easy to more complex and invasive (from simple to complex). However, we should not forget that sometimes it is necessary to immediately perform complex diagnostic interventions due to their high information content and importance for planning the treatment of the patient.
Fourth principle: when organizing a radiological study, economic factors (“cost-effectiveness of methods”) should be taken into account. Starting the examination of the patient, the doctor is obliged to foresee the costs of its implementation. The cost of some radiation studies is so high that their unreasonable use can affect the budget of a medical institution. In the first place, we put the benefit for the patient, but at the same time we have no right to ignore the economics of the medical business. Not to take it into account means to organize the work of the radiation department incorrectly.
Science is the best modern way of satisfying the curiosity of individuals at the expense of the state.
Radiation diagnostics in the last three decades has made significant progress, primarily due to the introduction of computed tomography (CT), ultrasound (ultrasound) and magnetic resonance imaging (MRI). However, the initial examination of the patient is still based on traditional imaging methods: radiography, fluorography, fluoroscopy. Traditional radiation research methods are based on the use of X-rays, discovered by Wilhelm Conrad Roentgen in 1895. He did not consider it possible to derive material benefit from the results of scientific research, since “... his discoveries and inventions belong to mankind, and. they must not be hindered in any way by patents, licenses, contracts, or the control of any group of people.” Traditional radiological research methods are called projection imaging methods, which, in turn, can be divided into three main groups: direct analog methods; indirect analog methods; digital methods. In direct analog methods, an image is formed directly in a medium that perceives radiation (X-ray film, fluorescent screen), the reaction of which to radiation is not discrete, but constant. The main analog research methods are direct radiography and direct fluoroscopy. Direct radiography- the basic method of radiation diagnostics. It lies in the fact that X-rays that have passed through the patient's body create an image directly on the film. X-ray film is coated with a photographic emulsion with silver bromide crystals, which are ionized by photon energy (the higher the radiation dose, the more silver ions are formed). This is the so-called latent image. In the process of development, metallic silver forms dark areas on the film, and in the process of fixing, silver bromide crystals are washed out, transparent areas appear on the film. Direct radiography produces static images with the best spatial resolution possible. This method is used to obtain chest x-rays. Currently, direct radiography is rarely used also to obtain a series of full-format images in cardioangiographic studies. Direct fluoroscopy (transmission) is that the radiation that has passed through the patient's body, hitting the fluorescent screen, creates a dynamic projection image. Currently, this method is practically not used due to the low brightness of the image and the high dose of radiation to the patient. Indirect fluoroscopy almost completely replaced the translucency. The fluorescent screen is part of an electron-optical converter, which amplifies the brightness of the image by more than 5000 times. The radiologist got the opportunity to work in daylight. The resulting image is displayed on a monitor and can be recorded on film, VCR, magnetic or optical disk. Indirect fluoroscopy is used to study dynamic processes, such as contractile activity of the heart, blood flow through the vessels
Literature.
Test questions.
Magnetic resonance imaging (MRI).
X-ray computed tomography (CT).
Ultrasound examination (ultrasound).
Radionuclide diagnostics (RND).
X-ray diagnostics.
Part I. GENERAL QUESTIONS OF RADIO DIAGNOSIS.
Chapter 1.
Methods of radiation diagnostics.
Radiation diagnostics deals with the use of various types of penetrating radiation, both ionization and non-ionization, in order to detect diseases of internal organs.
Radiation diagnostics currently reaches 100% of the use in clinical methods for examining patients and consists of the following sections: X-ray diagnostics (RDI), radionuclide diagnostics (RND), ultrasound diagnostics (US), computed tomography (CT), magnetic resonance imaging (MRI) . The order of listing methods determines the chronological sequence of the introduction of each of them into medical practice. The proportion of methods of radiation diagnostics according to WHO today is: 50% ultrasound, 43% RD (radiography of the lungs, bones, breast - 40%, X-ray examination of the gastrointestinal tract - 3%), CT - 3%, MRI -2 %, RND-1-2%, DSA (digital subtraction arteriography) - 0.3%.
1.1. The principle of X-ray diagnostics consists in visualization of the internal organs with the help of X-ray radiation directed at the object of study, which has a high penetrating power, with its subsequent registration after leaving the object by any X-ray receiver, with the help of which a shadow image of the organ under study is directly or indirectly obtained.
1.2. X-rays are a type of electromagnetic waves (these include radio waves, infrared rays, visible light, ultraviolet rays, gamma rays, etc.). In the spectrum of electromagnetic waves, they are located between ultraviolet and gamma rays, having a wavelength from 20 to 0.03 angstroms (2-0.003 nm, Fig. 1). For X-ray diagnostics, the shortest-wavelength X-rays (the so-called hard radiation) with a length of 0.03 to 1.5 angstroms (0.003-0.15 nm) are used. Possessing all the properties of electromagnetic oscillations - propagation at the speed of light
(300,000 km / s), straightness of propagation, interference and diffraction, luminescent and photochemical effects, X-rays also have distinctive properties that led to their use in medical practice: this is penetrating power - X-ray diagnostics is based on this property, and biological action is a component the essence of X-ray therapy. Penetrating power, in addition to the wavelength (“hardness”), depends on the atomic composition, specific gravity and thickness of the object under study (inverse relationship).
1.3. x-ray tube(Fig. 2) is a glass vacuum vessel in which two electrodes are embedded: a cathode in the form of a tungsten spiral and an anode in the form of a disk, which rotates at a speed of 3000 revolutions per minute when the tube is in operation. A voltage of up to 15 V is applied to the cathode, while the spiral heats up and emits electrons that rotate around it, forming a cloud of electrons. Then voltage is applied to both electrodes (from 40 to 120 kV), the circuit closes and electrons fly to the anode at a speed of up to 30,000 km/sec, bombarding it. In this case, the kinetic energy of flying electrons is converted into two types of new energy - the energy of X-rays (up to 1.5%) and the energy of infrared, thermal, rays (98-99%).
The resulting x-rays consist of two fractions: bremsstrahlung and characteristic. Braking rays are formed as a result of the collision of electrons flying from the cathode with the electrons of the outer orbits of the anode atoms, causing them to move to the inner orbits, which results in the release of energy in the form of bremsstrahlung x-ray quanta of low hardness. The characteristic fraction is obtained due to the penetration of electrons to the nuclei of the anode atoms, resulting in the knocking out of quanta of characteristic radiation.
It is this fraction that is mainly used for diagnostic purposes, since the rays of this fraction are harder, that is, they have a large penetrating power. The proportion of this fraction is increased by applying a higher voltage to the x-ray tube.
1.4. X-ray diagnostic apparatus or, as it is now commonly called, the X-ray diagnostic complex (RDC) consists of the following main blocks:
a) x-ray emitter,
b) X-ray feeding device,
c) devices for the formation of x-rays,
d) tripod(s),
e) X-ray receiver(s).
X-ray emitter consists of an X-ray tube and a cooling system, which is necessary to absorb the thermal energy generated in large quantities during the operation of the tube (otherwise the anode will quickly collapse). Cooling systems include transformer oil, air cooling with fans, or a combination of both.
The next block of the RDK - x-ray feeder, which includes a low-voltage transformer (a voltage of 10-15 volts is required to heat the cathode spiral), a high-voltage transformer (a voltage of 40 to 120 kV is required for the tube itself), rectifiers (a direct current is needed for efficient operation of the tube) and a control panel.
Radiation shaping devices consist of an aluminum filter that absorbs the “soft” fraction of x-rays, making it more uniform in hardness; diaphragm, which forms an X-ray beam according to the size of the removed organ; screening grating, which cuts off the scattered rays arising in the patient's body in order to improve the sharpness of the image.
tripod(s)) serve to position the patient, and in some cases, the X-ray tube. , three, which is determined by the configuration of the RDK, depending on the profile of the medical facility.
X-ray receiver(s). As receivers, a fluorescent screen is used for transmission, x-ray film (for radiography), intensifying screens (the film in the cassette is located between two intensifying screens), memory screens (for fluorescent s. computer radiography), x-ray image intensifier - URI, detectors (when using digital technologies).
1.5. X-ray Imaging Technologies currently available in three versions:
direct analog,
indirect analog,
digital (digital).
With direct analog technology(Fig. 3) X-rays coming from the X-ray tube and passing through the area of the body under study are attenuated unevenly, since along the X-ray beam there are tissues and organs with different atomic
and specific gravity and different thickness. Getting on the simplest X-ray receivers - an X-ray film or a fluorescent screen, they form a summation shadow image of all tissues and organs that have fallen into the zone of passage of the rays. This image is studied (interpreted) either directly on a fluorescent screen or on X-ray film after its chemical treatment. Classical (traditional) methods of X-ray diagnostics are based on this technology:
fluoroscopy (fluoroscopy abroad), radiography, linear tomography, fluorography.
Fluoroscopy currently used mainly in the study of the gastrointestinal tract. Its advantages are a) the study of the functional characteristics of the organ under study on a real-time scale and b) a complete study of its topographic characteristics, since the patient can be placed in different projections by rotating him behind the screen. Significant disadvantages of fluoroscopy are the high radiation load on the patient and the low resolution, so it is always combined with radiography.
Radiography is the main, leading method of X-ray diagnostics. Its advantages are: a) high resolution of the x-ray image (pathological foci 1-2 mm in size can be detected on the x-ray), b) minimal radiation exposure, since the exposures during the acquisition of the image are mainly tenths and hundredths of a second, c ) the objectivity of obtaining information, since the radiograph can be analyzed by other, more qualified specialists, d) the possibility of studying the dynamics of the pathological process from radiographs made in different periods of the disease, e) the radiograph is a legal document. The disadvantages of an X-ray image include incomplete topographic and functional characteristics of the organ under study.
Usually, radiography uses two projections, which are called standard: direct (anterior and posterior) and lateral (right and left). The projection is determined by the belonging of the film cassette to the surface of the body. For example, if the chest x-ray cassette is located at the anterior surface of the body (in this case, the x-ray tube will be located behind), then such a projection will be called direct anterior; if the cassette is located along the back surface of the body, a direct rear projection is obtained. In addition to standard projections, there are additional (atypical) projections that are used in cases where in standard projections, due to anatomical, topographic and skiological features, we cannot get a complete picture of the anatomical characteristics of the organ under study. These are oblique projections (intermediate between direct and lateral), axial (in this case, the x-ray beam is directed along the axis of the body or the organ under study), tangential (in this case, the x-ray beam is directed tangentially to the surface of the organ being removed). So, in oblique projections, the hands, feet, sacroiliac joints, stomach, duodenum, etc. are removed, in the axial projection - the occipital bone, calcaneus, mammary gland, pelvic organs, etc., in the tangential - the bones of the nose, zygomatic bone , frontal sinuses, etc.
In addition to projections, different positions of the patient are used in X-ray diagnostics, which is determined by the research technique or the patient's condition. The main position is orthoposition- the vertical position of the patient with a horizontal direction of x-rays (used for radiography and fluoroscopy of the lungs, stomach, and fluorography). Other positions are trochoposition- the horizontal position of the patient with the vertical course of the x-ray beam (used for radiography of bones, intestines, kidneys, in the study of patients in serious condition) and lateroposition- the horizontal position of the patient with the horizontal direction of x-rays (used for special research methods).
Linear tomography(radiography of the organ layer, from tomos - layer) is used to clarify the topography, size and structure of the pathological focus. With this method (Fig. 4), during X-ray exposure, the X-ray tube moves over the surface of the organ under study at an angle of 30, 45 or 60 degrees for 2-3 seconds, while the film cassette moves in the opposite direction at the same time. The center of their rotation is the selected layer of the organ at a certain depth from its surface, the depth is
State Institution "Ufa Research Institute of Eye Diseases" of the Academy of Sciences of the Republic of Belarus, Ufa
The discovery of X-rays marked the beginning of a new era in medical diagnostics - the era of radiology. Modern methods of radiation diagnostics are divided into X-ray, radionuclide, magnetic resonance, ultrasound.
The X-ray method is a method of studying the structure and function of various organs and systems, based on the qualitative and quantitative analysis of the X-ray beam that has passed through the human body. X-ray examination can be carried out in conditions of natural contrast or artificial contrast.
X-ray is simple and not burdensome for the patient. A radiograph is a document that can be stored for a long time, used for comparison with repeated radiographs and presented for discussion to an unlimited number of specialists. Indications for radiography must be justified, since X-ray radiation is associated with radiation exposure.
Computed tomography (CT) is a layer-by-layer X-ray study based on computer reconstruction of an image obtained by circular scanning of an object with a narrow X-ray beam. A CT scanner is able to distinguish tissues that differ from each other in density by only half a percent. Therefore, a CT scanner provides about 1000 times more information than a conventional x-ray. With spiral CT, the emitter moves in a spiral in relation to the patient's body and captures a certain volume of the body in a few seconds, which can subsequently be represented by separate discrete layers. Spiral CT initiated the creation of new promising imaging methods - computed angiography, three-dimensional (volumetric) imaging of organs, and, finally, the so-called virtual endoscopy, which became the crown of modern medical imaging.
The radionuclide method is a method for studying the functional and morphological state of organs and systems using radionuclides and tracers labeled with them. Indicators - radiopharmaceuticals (RP) - are injected into the patient's body, and then with the help of devices they determine the speed and nature of their movement, fixation and removal from organs and tissues. Modern methods of radionuclide diagnostics are scintigraphy, single photon emission tomography (SPET) and positron emission tomography (PET), radiography and radiometry. The methods are based on the introduction of radiopharmaceuticals that emit positrons or photons. These substances introduced into the human body accumulate in areas of increased metabolism and increased blood flow.
The ultrasound method is a method for remotely determining the position, shape, size, structure and movement of organs and tissues, as well as pathological foci using ultrasound radiation. It can register even slight changes in the density of biological media. Thanks to this, the ultrasound method has become one of the most popular and accessible studies in clinical medicine. Three methods are most widely used: one-dimensional examination (sonography), two-dimensional examination (sonography, scanning) and dopplerography. All of them are based on the registration of echo signals reflected from the object. With the one-dimensional A-method, the reflected signal forms a figure in the form of a peak on a straight line on the indicator screen. The number and location of peaks on the horizontal line corresponds to the location of the ultrasound-reflecting elements of the object. Ultrasound scanning (B-method) allows you to get a two-dimensional image of organs. The essence of the method is to move the ultrasonic beam over the surface of the body during the study. The resulting series of signals is used to form an image. It appears on the display and can be recorded on paper. This image can be subjected to mathematical processing, determining the dimensions (area, perimeter, surface and volume) of the organ under study. Dopplerography allows non-invasive, painless and informative recording and evaluation of the blood flow of the organ. The high information content of color Doppler mapping, which is used in the clinic to study the shape, contours and lumen of blood vessels, has been proven.
Magnetic resonance imaging (MRI) is an extremely valuable research method. Instead of ionizing radiation, a magnetic field and radio frequency pulses are used. The operating principle is based on the phenomenon of nuclear magnetic resonance. By manipulating gradient coils that create small additional fields, you can record signals from a thin tissue layer (up to 1 mm) and easily change the direction of the cut - transverse, frontal and sagittal, obtaining a three-dimensional image. The main advantages of the MRI method include: the absence of radiation exposure, the ability to obtain an image in any plane and perform three-dimensional (spatial) reconstructions, the absence of artifacts from bone structures, high resolution imaging of various tissues, and the almost complete safety of the method. A contraindication to MRI is the presence of metallic foreign bodies in the body, claustrophobia, convulsions, the patient's serious condition, pregnancy and lactation.
The development of radiation diagnostics also plays an important role in practical ophthalmology. It can be argued that the organ of vision is an ideal object for CT due to pronounced differences in the absorption of radiation in the tissues of the eye, muscles, nerves, vessels, and retrobulbar fatty tissue. CT allows you to better examine the bone walls of the orbits, to identify pathological changes in them. CT is used for suspected orbital tumor, exophthalmos of unknown origin, injuries, foreign bodies of the orbit. MRI makes it possible to examine the orbit in different projections, it allows you to better understand the structure of neoplasms inside the orbit. But this technique is contraindicated when metal foreign bodies get into the eye.
The main indications for ultrasound are: damage to the eyeball, a sharp decrease in the transparency of light-conducting structures, detachment of the choroid and retina, the presence of foreign intraocular bodies, tumors, damage to the optic nerve, the presence of areas of calcification in the membranes of the eye and the area of the optic nerve, dynamic monitoring of the treatment , study of the characteristics of blood flow in the vessels of the orbit, studies before MRI or CT.
X-ray is used as a screening method for injuries of the orbit and lesions of its bone walls to detect dense foreign bodies and determine their localization, diagnose diseases of the lacrimal ducts. Of great importance is the method of X-ray examination of the paranasal sinuses adjacent to the orbit.
Thus, in the Ufa Research Institute of Eye Diseases in 2010, 3116 X-ray examinations were performed, including patients from the clinic - 935 (34%), from the hospital - 1059 (30%), from the emergency room - 1122 (36%) %). 699 (22.4%) special studies were performed, which include the study of the lacrimal ducts with contrast (321), non-skeletal radiography (334), detection of the localization of foreign bodies in the orbit (39). Chest radiography in inflammatory diseases of the orbit and eyeball was 18.3% (213), and paranasal sinuses — 36.3% (1132).
conclusions. Radiation diagnostics is a necessary part of the clinical examination of patients in ophthalmological clinics. Many of the achievements of traditional X-ray examination are increasingly receding before the improving capabilities of CT, ultrasound, and MRI.
