Methods of radiation diagnostics and their characteristics. Methods and means of radiation diagnostics

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 flow 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.

Distinguish between "soft" X-ray radiation with low energy and radiation frequency (respectively, with the largest wavelength) and "hard" X-ray radiation with high photon energy and radiation frequency, having 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 photographic 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 to carry out static, as well as dynamic, functional study of organs (for example, fluoroscopy of the stomach, excursion of the diaphragm) and to control the implementation of interventional procedures (for example, 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, USG)

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, i.e. 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 possibility of obtaining 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 patients to associate 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 with 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) 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 tracers - 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 for 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 procedure to dilate (widen) 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 location of the 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 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 currently used contrast agents 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 an examination 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 examination 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.

GENERAL PRINCIPLES OF IMAGING

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 rock paintings of the Neolithic period, in which the general scheme (image) of the phenomenon is surprisingly accurately reflected.

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 efforts 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 an X-ray examination, one must adhere to the “necessary and sufficient” rule, 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.

This is due to the use of research methods based on high technologies using a wide range of electromagnetic and ultrasonic (US) vibrations.

To date, at least 85% of clinical diagnoses are established or clarified using various methods of radiological examination. These methods are successfully used to assess the effectiveness of various types of therapeutic and surgical treatment, as well as in the dynamic monitoring of the condition of patients in the rehabilitation process.

Radiation diagnostics includes the following set of research methods:

• traditional (standard) X-ray diagnostics;
• x-ray computed tomography (RCT);
• magnetic resonance imaging (MRI);
• Ultrasound, ultrasound diagnostics (USD);
• radionuclide diagnostics;
• thermal imaging (thermography);
• interventional radiology.

Of course, over time, the listed research methods will be replenished with new methods of radiation diagnostics. These sections of radiation diagnostics are presented in the same row for a reason. They have a single semiotics, in which the leading symptom of the disease is the "shadow image".

In other words, ray diagnostics is united by skiology (skia - shadow, logos - teaching). This is a special section of scientific knowledge that studies the patterns of formation of a shadow image and develops rules for determining the structure and function of organs in the norm and in the presence of pathology.

The logic of clinical thinking in radiation diagnostics is based on the correct conduct of skiological analysis. It includes a detailed description of the properties of shadows: their position, number, size, shape, intensity, structure (drawing), the nature of the contours and displacement. The listed characteristics are determined by the four laws of skiology:

1. the law of absorption (determines the intensity of the shadow of an object depending on its atomic composition, density, thickness, as well as the nature of the X-ray radiation itself);
2. the law of summation of shadows (describes the conditions for the formation of an image due to the superposition of the shadows of a complex three-dimensional object on a plane);
3. projection law (represents the construction of a shadow image, taking into account the fact that the X-ray beam has a divergent character, and its cross section in the plane of the receiver is always greater than at the level of the object under study);
4. the law of tangentiality (determines the contour of the resulting image).

The generated x-ray, ultrasound, magnetic resonance (MP) or other image is objective and reflects the true morpho-functional state of the organ under study. The interpretation of the obtained data by a medical specialist is a stage of subjective cognition, the accuracy of which depends on the level of theoretical preparation of the researcher, the ability to clinical thinking and experience.

Traditional X-ray diagnostics

To perform a standard X-ray examination, three components are necessary:

• X-ray source (X-ray tube);
• object of study;
• receiver (converter) of radiation.

All research methods differ from each other only in the radiation receiver, which is used as an X-ray film, a fluorescent screen, a semiconductor selenium plate, a dosimetric detector.

To date, one or another system of detectors is the main radiation receiver. Thus, traditional radiography is completely transferred to the digital (digital) principle of image acquisition.

The main advantages of traditional methods of X-ray diagnostics are their availability in almost all medical institutions, high throughput, relative cheapness, the possibility of multiple studies, including for preventive purposes. The presented methods have the greatest practical significance in pulmonology, osteology, and gastroenterology.

X-ray computed tomography

Three decades have passed since CT was used in clinical practice. It is unlikely that the authors of this method, A. Cormack and G. Hounsfield, who received the Nobel Prize in 1979 for its development, could have imagined how fast the growth of their scientific ideas would be and what a lot of questions this invention would pose to clinicians.

Each CT scanner consists of five main functional systems:

1. a special stand called a gantry, which contains an x-ray tube, mechanisms for forming a narrow beam of radiation, dosimetric detectors, as well as a system for collecting, converting and transmitting pulses to an electronic computer (computer). In the center of the tripod there is a hole where the patient is placed;
2. a patient table that moves the patient within the gantry;
3. computer storage and data analyzer;
4. tomograph control panel;
5. display for visual control and image analysis.

Differences in the designs of tomographs are primarily due to the choice of scanning method. To date, there are five varieties (generations) of X-ray computed tomography. Today, the main fleet of these devices is represented by devices with a spiral scanning principle.

The principle of operation of an X-ray computed tomograph is that the part of the human body of interest to the doctor is scanned by a narrow beam of X-ray radiation. Special detectors measure the degree of its attenuation by comparing the number of photons at the entrance and exit from the studied area of ​​the body. The measurement results are transferred to the computer memory, and according to them, in accordance with the absorption law, the radiation attenuation coefficients for each projection are calculated (their number can be from 180 to 360). At present, absorption coefficients according to the Hounsfield scale have been developed for all tissues and organs in the norm, as well as for a number of pathological substrates. The reference point in this scale is water, the absorption coefficient of which is taken as zero. The upper limit of the scale (+1000 HU) corresponds to the absorption of X-rays by the cortical layer of the bone, and the lower one (-1000 HU) to air. Below, as an example, some absorption coefficients for various body tissues and fluids are given.

Obtaining accurate quantitative information not only about the size and spatial arrangement of organs, but also about the density characteristics of organs and tissues is the most important advantage of CT over traditional methods.

When determining indications for the use of RCT, one has to take into account a significant number of different, sometimes mutually exclusive factors, finding a compromise solution in each specific case. Here are some provisions that determine the indications for this type of radiation study:

• the method is additional, the feasibility of its use depends on the results obtained at the stage of the primary clinical and radiological examination;
• the feasibility of computed tomography (CT) is clarified by comparing its diagnostic capabilities with other, including non-radiation, research methods;
• the choice of RCT is influenced by the cost and availability of this technique;
• it should be taken into account that the use of CT is associated with radiation exposure to the patient.

The diagnostic capabilities of CT will undoubtedly expand as hardware and software improve, allowing for real-time examinations. Its importance has increased in X-ray surgical interventions as a control tool during surgery. Computed tomographs have been built and are beginning to be used in the clinic, which can be placed in the operating room, intensive care unit or intensive care unit.

Multispiral computed tomography (MSCT) is a technique that differs from spiral in that one revolution of the X-ray tube produces not one, but a whole series of slices (4, 16, 32, 64, 256, 320). Diagnostic advantages are the ability to perform lung tomography at one breath-hold in any of the phases of inhalation and exhalation, and consequently, the absence of “silent” zones when examining moving objects; the availability of building various planar and volumetric reconstructions with high resolution; the possibility of performing MSCT angiography; performing virtual endoscopic examinations (bronchography, colonoscopy, angioscopy).

Magnetic resonance imaging

MRI is one of the newest methods of radiation diagnostics. It is based on the phenomenon of the so-called nuclear magnetic resonance. Its essence lies in the fact that the nuclei of atoms (primarily hydrogen), placed in a magnetic field, absorb energy, and then are able to emit it into the external environment in the form of radio waves.

The main components of the MP tomograph are:

• a magnet that provides a sufficiently high field induction;
• radio transmitter;
• receiving radio frequency coil;

To date, the following areas of MRI are actively developing:

1. MR spectroscopy;
2. MR angiography;
3. the use of special contrast agents (paramagnetic fluids).

Most MP tomographs are configured to detect the radio signal of hydrogen nuclei. That is why MRI has found the greatest use in recognizing diseases of organs that contain a large amount of water. Conversely, the study of the lungs and bones is less informative than, for example, CT.

The study is not accompanied by radioactive exposure of the patient and staff. Nothing is known for sure about the negative (from a biological point of view) effect of magnetic fields with induction, which is used in modern tomographs. Certain limitations of the use of MRI must be taken into account when choosing a rational algorithm for radiological examination of a patient. These include the effect of "pulling" metal objects into the magnet, which can cause a shift of metal implants in the patient's body. An example is metal clips on vessels, the shift of which can lead to bleeding, metal structures in the bones, spine, foreign bodies in the eyeball, etc. The work of an artificial pacemaker during MRI can also be impaired, so examination of such patients is not allowed.

Ultrasound diagnostics

Ultrasonic devices have one distinctive feature. The ultrasonic sensor is both a generator and a receiver of high-frequency oscillations. The basis of the sensor is piezoelectric crystals. They have two properties: the supply of electrical potentials to the crystal leads to its mechanical deformation with the same frequency, and its mechanical compression from reflected waves generates electrical impulses. Depending on the purpose of the study, various types of sensors are used, which differ in the frequency of the generated ultrasound beam, their shape and purpose (transabdominal, intracavitary, intraoperative, intravascular).

All ultrasound techniques are divided into three groups:

• one-dimensional study (sonography in A-mode and M-mode);
• two-dimensional study (ultrasound scanning - B-mode);
• dopplerography.

Each of the above methods has its own options and is used depending on the specific clinical situation. For example, M-mode is especially popular in cardiology. Ultrasound scanning (B-mode) is widely used in the study of parenchymal organs. Without Dopplerography, which makes it possible to determine the speed and direction of fluid flow, a detailed study of the chambers of the heart, large and peripheral vessels is impossible.

Ultrasound has practically no contraindications, as it is considered harmless to the patient.

Over the past decade, this method has undergone unprecedented progress, and therefore it is advisable to single out new promising directions for the development of this section of radiodiagnosis.

Digital ultrasound involves the use of a digital image converter, which increases the resolution of the devices.

Three-dimensional and volumetric image reconstructions increase diagnostic information content due to better spatial anatomical visualization.

The use of contrast agents makes it possible to increase the echogenicity of the studied structures and organs and to achieve their better visualization. These drugs include "Ehovist" (microbubbles of gas introduced into glucose) and "Echogen" (a liquid from which, after its introduction into the blood, microbubbles of gas are released).

Color Doppler imaging, in which stationary objects (such as parenchymal organs) are displayed in shades of gray scale, and vessels in color scale. In this case, the shade of color corresponds to the speed and direction of blood flow.

Intravascular ultrasound not only makes it possible to assess the state of the vascular wall, but also, if necessary, to perform a therapeutic effect (for example, crush an atherosclerotic plaque).

Somewhat apart in ultrasound is the method of echocardiography (EchoCG). This is the most widely used method for non-invasive diagnostics of heart diseases, based on the registration of the reflected ultrasound beam from moving anatomical structures and real-time image reconstruction. There are one-dimensional EchoCG (M-mode), two-dimensional EchoCG (B-mode), transesophageal examination (PE-EchoCG), Doppler echocardiography using color mapping. The algorithm for applying these echocardiography technologies allows obtaining sufficiently complete information about the anatomical structures and function of the heart. It becomes possible to study the walls of the ventricles and atria in various sections, non-invasively assess the presence of zones of contractility disorders, detect valvular regurgitation, study blood flow rates with the calculation of cardiac output (CO), valve opening area, and a number of other important parameters, especially in the study of heart disease.

Radionuclide diagnostics

All methods of radionuclide diagnostics are based on the use of so-called radiopharmaceuticals (RP). They are a kind of pharmacological compound that has its own "fate", pharmacokinetics in the body. Moreover, each molecule of this pharmaceutical compound is labeled with a gamma-emitting radionuclide. However, RFP is not always a chemical substance. It can also be a cell, for example, an erythrocyte labeled with a gamma emitter.

There are many radiopharmaceuticals. Hence the variety of methodological approaches in radionuclide diagnostics, when the use of a certain radiopharmaceutical dictates a specific research methodology. The development of new radiopharmaceuticals and the improvement of existing radiopharmaceuticals is the main direction in the development of modern radionuclide diagnostics.

If we consider the classification of radionuclide research methods from the point of view of technical support, then we can distinguish three groups of methods.

Radiometry. Information is presented on the display of the electronic unit in the form of numbers and compared with the conditional norm. Usually, slow physiological and pathophysiological processes in the body are studied in this way (for example, the iodine-absorbing function of the thyroid gland).

Radiography (gamma chronography) is used to study fast processes. For example, the passage of blood with the introduced radiopharmaceutical through the chambers of the heart (radiocardiography), the excretory function of the kidneys (radiorenography), etc. Information is presented in the form of curves, designated as "activity - time" curves.

Gamma tomography is a technique designed to obtain images of organs and body systems. It comes in four main options:

1. Scanning. The scanner allows, line by line passing over the area under study, to perform radiometry at each point and put information on paper in the form of strokes of various colors and frequencies. It turns out a static image of the organ.
2. Scintigraphy. A high-speed gamma camera allows you to follow in dynamics almost all the processes of passage and accumulation of radiopharmaceuticals in the body. The gamma camera can acquire information very quickly (with a frequency of up to 3 frames per 1 s), so dynamic observation becomes possible. For example, the study of blood vessels (angioscintigraphy).
3. Single photon emission computed tomography. The rotation of the detector block around the object allows to obtain sections of the organ under study, which significantly increases the resolution of gamma tomography.
4. Positron emission tomography. The youngest method based on the use of radiopharmaceuticals labeled with positron-emitting radionuclides. When they are introduced into the body, the interaction of positrons with the nearest electrons (annihilation) occurs, as a result of which two gamma quanta are “born”, flying oppositely at an angle of 180 °. This radiation is registered by tomographs according to the principle of "coincidence" with very precise topical coordinates.

A novelty in the development of radionuclide diagnostics is the appearance of combined hardware systems. Now the combined positron emission and computed tomography (PET/CT) scanners are being actively used in clinical practice. At the same time, both an isotope study and CT are performed in one procedure. Simultaneous acquisition of accurate structural-anatomical information (using CT) and functional information (using PET) significantly expands diagnostic capabilities, primarily in oncology, cardiology, neurology, and neurosurgery.

A separate place in radionuclide diagnostics is occupied by the method of radiocompetitive analysis (in vitro radionuclide diagnostics). One of the promising directions of the method of radionuclide diagnostics is the search for so-called tumor markers in the human body for early diagnosis in oncology.

thermography

The thermography technique is based on the registration of natural thermal radiation of the human body by special detectors-thermal imagers. Remote infrared thermography is the most common, although thermography methods have now been developed not only in the infrared, but also in the millimeter (mm) and decimeter (dm) wavelength ranges.

The main disadvantage of the method is its low specificity in relation to various diseases.

Interventional radiology

The modern development of radiation diagnostic techniques has made it possible to use them not only for recognizing diseases, but also for performing (without interrupting the study) the necessary medical manipulations. These methods are also called minimally invasive therapy or minimally invasive surgery.

The main areas of interventional radiology are:

1. X-ray endovascular surgery. Modern angiographic complexes are high-tech and allow the medical specialist to superselectively reach any vascular pool. Interventions such as balloon angioplasty, thrombectomy, vascular embolization (for bleeding, tumors), long-term regional infusion, etc., become possible.
2. Extravasal (extravascular) interventions. Under the control of X-ray television, computed tomography, ultrasound, it became possible to perform drainage of abscesses and cysts in various organs, to perform endobronchial, endobiliary, endourinal and other interventions.
3. Aspiration biopsy under radiation control. It is used to establish the histological nature of intrathoracic, abdominal, soft tissue formations in patients.

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 share 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, followed by its 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 built in: 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 the 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 (to heat up the cathode coil, a voltage of 10-15 volts is required), a high-voltage transformer (the tube itself requires a voltage of 40 to 120 kV), 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 health 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. Computed radiography), X-ray image amplifier - 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 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 studied organ 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, due to anatomical, topographic and skiological features, we cannot get a complete picture of the anatomical characteristics of the organ under study in standard projections. These are oblique projections (intermediate between straight 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

BELARUSIAN STATE MEDICAL UNIVERSITY

"Methods of Radiation Diagnostics"

MINSK, 2009

1. Methods that regulate the size of the resulting image

These include teleroentgenography and direct magnification of the x-ray image.

Teleroentgenography ( shot at a distance). The main objective of the method is to reproduce an x-ray image, the dimensions of which in the image are close to the true dimensions of the object under study.

In conventional radiography, when the focal length is 100 cm, only those details of the object being photographed that are located directly at the cassette are slightly enlarged. The farther the detail is from the film, the greater the degree of magnification.

Method: the object of study and the cassette with the film are moved away from the X-ray tube to a much greater distance than with conventional radiography, up to 1.5-2 m, and when examining the facial skull and dentoalveolar system, up to 4-5 m. film is formed by the central (more parallel) X-ray beam (Scheme 1).

Scheme 1. Conditions for conventional radiography (I) and teleradiography (II):

1 - x-ray tube; 2 - a beam of x-rays;

3 - object of study; 4 - film cassette.

Indications: the need to reproduce the image of the object, the dimensions of which are as close as possible to the true ones - the study of the heart, lungs, maxillofacial region, etc.

Direct magnification of the x-ray image is achieved as a result of increasing the object-film distance during radiography.

Indications: the technique is more often used to study fine structures - the osteoarticular apparatus, the pulmonary pattern in pulmonology.

Method: The film cassette is moved away from the object at a focal length of 100 cm. The diverging X-ray beam in this case reproduces an enlarged image. The degree of such an increase can be determined using the formula: k = H /h, where k is the direct magnification factor, H is the distance from the focus of the X-ray tube to the film plane, equal to 100 cm; h is the distance from the focus of the tube to the object (in cm). The best quality enlarged image is obtained using a coefficient in the range of 1.5-1.6 (Scheme 3).

When performing the direct magnification method, it is advisable to use an X-ray tube with a microfocus (0.3 × 0.3 mm or less). The small linear dimensions of the focus reduce the geometric blurring of the image and improve the clarity of structural elements.

2. Methods of spatial research

These include linear and computed tomography, panoramic tomography, panoramic sonography.

Linear tomography - method of layer-by-layer research with obtaining an image of an object (organ) at a given depth. It is carried out with synchronous movement in opposite directions of the X-ray tube and the film cassette along parallel planes along a stationary object at an angle of 30-50°. There are longitudinal tomography (Scheme 4), transverse and with a complex motion cycle (circular, sinusoidal). The thickness of the detected slice depends on the size of the tomographic angle and is often 2-3 mm, the distance between the slices (tomographic step) is set arbitrarily, usually 0.5-1 cm.

Linear tomography is used to study the respiratory organs, the cardiovascular system, the abdominal cavity and retroperitoneal organs, the osteoarticular apparatus, etc.

In contrast to linear tomography, tomographs with a complex cycle of movement of the X-ray tube and film cassettes (S-shaped, ellipsoid) are also used.

Linear zoning - layer-by-layer study (tomography) on a linear tomograph at a small angle (8-10°) of the X-ray tube movement. The slice thickness is 10-12 mm, the tomographic step is 1-2 cm.

Panoramic zoning — layer-by-layer examination of the facial skull using a special multi-program panoramic device, when turned on, the x-ray tube makes a uniform movement around the facial region of the head, while the image of the object (upper and lower jaws, pyramids of the temporal bones, upper cervical vertebrae) is recorded by a narrow x-ray beam on a curved shape face cassette with film.

X-ray computed tomography ( CT) is a modern, rapidly progressing method. Transverse layer-by-layer sections are made of any part of the body (brain, organs of the chest, abdominal cavities and retroperitoneal space, etc.) using a narrow x-ray beam with a circular motion of the x-ray tube X-ray computed tomography.

The method allows obtaining images of several transverse sections (up to 25) with different tomographic steps (from 2 to 5 mm and more). The density of various organs is fixed by special sensors, mathematically processed by a PC and reproduced on the display screen in the form of a cross section. Differences in the density of the structure of organs are automatically objectified using a special Hounsfield scale, which gives high accuracy to information about any organ or in a selected “zone of interest”.

When using spiral CT, the image is recorded in the PC memory continuously (Scheme 2).

Scheme 2. X-ray spiral computed tomography.

A special PC program allows you to reconstruct the obtained data in any other plane or reproduce a three-dimensional image of an organ or a group of organs.

Taking into account the high diagnostic efficiency of RCT and the worldwide recognized authority of the method, it should, however, be remembered that the use of modern RCT is associated with a significant radiation exposure to the patient, which leads to an increase in the collective (population) effective dose. The latter, for example, in the study of the chest (25 layers with 8 mm pitch) corresponds to 7.2 mSV (for comparison, the dose for conventional radiography in two projections is 0.2 mSV). Thus, the radiation exposure during CT is 36-40 times higher than the dose of conventional two-projection radiography, for example, of the chest. This circumstance dictates the strict necessity of using RCT exclusively for strict medical indications.

3. Motion registration methods

The methods of this group are used in the study of the heart, esophagus, diaphragm, ureters, etc. The methods of this group include: x-ray kymography, electroroentgen kymography, x-ray cinematography, x-ray television, video magnetic recording.

VCR ( VZ) is a modern method of dynamic research. It is carried out in the process of fluoroscopy through an image intensifier tube. The image in the form of a television signal is recorded by a video recorder on a magnetic tape and, by repeated viewing, allows you to carefully study the function and anatomical features (morphology) of the organ under study without additional exposure to the patient.

X-ray kymography - method of registration of oscillatory movements (functional displacement, pulsation, peristalsis) of the external contours of various organs (heart, blood vessels, esophagus, ureter, stomach, diaphragm).

Between the object and the X-ray film, a grating of horizontally arranged lead strips 12 mm wide with narrow slots between them (1 mm) is installed. During the picture, the grating is set in motion and X-rays pass only through the gaps between the plates. In this case, the movements of the contour of the shadow, for example, the heart, are reproduced in the form of teeth of various shapes and sizes. According to the height, shape and nature of the teeth, it is possible to assess the depth, rhythm, speed of movements (pulsation) of the organ, and determine the contractility. The shape of the teeth is specific to the ventricles of the heart, atria and blood vessels. However, the method is outdated and has limited application.

Electroroentgenokymography. One or more sensitive photocells (sensors) are placed in front of the screen of the X-ray machine and, during fluoroscopy, they are installed on the contour of a pulsating or contracting object (heart, blood vessels). With the help of sensors, when the outer contours of the pulsating organ move, a change in the brightness of the screen glow is recorded and displayed on the screen of an oscilloscope or in the form of a curve on a paper tape. The method is outdated and is used to a limited extent.

X-ray cinematography ( RCMGR) is a method of capturing an X-ray image of a pulsating or moving organ (heart, blood vessels, contrasting of hollow organs and vessels, etc.) using a movie camera from the screen of an electron-optical converter. The method combines the capabilities of radiography and fluoroscopy and allows you to observe and record processes at a speed inaccessible to the eye - 24-48 frames / sec. A film projector with frame-by-frame analysis is used to view a movie. The RCMGR method is cumbersome and costly and is not currently used due to the introduction of a simpler and cheaper method - video magnetic recording of an X-ray image.

X-ray pneumopolygraphy ( RPPG) - a technique designed to study the functional characteristics of the respiratory system - the function of external respiration. Two images of the lungs on the same x-ray film (in the phase of maximum inhalation and exhalation) are taken through a special grid of I.S. Amosov. The latter is a raster of square lead plates (2×2 cm) arranged in a checkerboard pattern. After the first image (on inspiration), the raster is shifted by one square, the unimaged areas of the lungs are opened, and the second image is taken (on exhalation). RPPG data allow assessing the qualitative and quantitative indicators of the function of external respiration - lung tissue densitometry, planimetry and amplimetry both before and after the treatment, as well as determining the reserve capacity of the bronchopulmonary apparatus with a stress test.

Due to the relatively high radiation exposure to the patient, the technique has not been widely used.

4. Methods of radionuclide diagnostics

Radionuclide (radioisotope) diagnostics is an independent scientifically substantiated clinical branch of medical radiology, which is designed to recognize pathological processes in individual organs and systems using radionuclides and labeled compounds. Research is based on the possibility of recording and measuring radiation from radiopharmaceuticals (RP) introduced into the body or radiometry of biological samples. The radionuclides used for this differ from their analogues - stable elements contained in the body or entering it with food, only in physical properties, i.e. ability to decay and emit radiation. These studies, using small indicator amounts of radioactive nuclides, cycle elements in the body without affecting the course of physiological processes. The advantage of radionuclide diagnostics, in comparison with other methods, is its versatility, since studies are applicable to determine diseases and injuries of various organs and systems, the ability to study biochemical processes and anatomical and functional changes, i.e. the whole complex of probable disorders that often occur in various pathological conditions.

Especially effective is the use of radioimmunological examinations, the implementation of which is not accompanied by the introduction of radiopharmaceuticals to the patient and, therefore, excludes radiation exposure. Given the fact that studies are carried out more often with blood plasma, these techniques are called radioimmunoassay (RIA) in vitro. In contrast to this technique, other methods of radionuclide diagnostics in vivo are accompanied by the administration of the radiopharmaceutical to the patient, mainly by the intravenous route. Such studies are naturally accompanied by radiation exposure to the patient.

All methods of radionuclide diagnostics can be divided into groups:

fully ensuring the diagnosis of the disease;

determining violations of the function of the organ or system under study, on the basis of which a plan for further examination is developed;

revealing the features of the anatomical and topographic position of the internal organs;

allowing to obtain additional diagnostic information in the complex of clinical and instrumental examination.

A radiopharmaceutical is a chemical compound containing in its molecule a certain radioactive nuclide, approved for administration to a person for diagnostic purposes. Each radiopharmaceutical undergoes clinical trials, after which it is approved by the Pharmacological Committee of the Ministry of Health. When choosing a radioactive nuclide, certain requirements are usually taken into account: low radiotoxicity, a relatively short half-life, a convenient condition for detecting gamma radiation, and the necessary biological properties. Currently, the following nuclides have found the widest use in clinical practice for labeling: Se -75, In -Ill, In -113m, 1-131, 1-125, Xe-133, Au -198, Hg -197, Tc -99m . The most suitable for clinical research are short-lived radionuclides: Tc-99t and In-113t, which are obtained in special generators in a medical institution immediately before use.

Depending on the method and type of registration of radiation, all radiometric instruments are divided into the following groups:

to register the radioactivity of individual samples of various biological media and samples (laboratory radiometers);

to measure the absolute radioactivity of samples or solutions of radionuclides (dose calibrators);

to measure the radioactivity of the body of the examined or individual organ of the patient (medical radiometers);

to register the dynamics of the movement of radiopharmaceuticals in organs and systems with the presentation of information in the form of curves (radiographs);

to register the distribution of radiopharmaceuticals in the patient's body or in the examined organ with obtaining data in the form of images (scanners) or in the form of distribution curves (profile scanners);

to register the dynamics of movement, as well as to study the distribution in the body of the patient and the studied organ of the radiopharmaceutical (scintillation gamma camera).

Methods of radionuclide diagnostics are divided into methods of dynamic and static radionuclide research.

Static radionuclide research allows to determine the anatomical and topographic state of internal organs, to establish the position, shape, size and presence of non-functioning areas or, conversely, pathological foci of increased function in individual organs and tissues and is used in cases where it is necessary:

clarify the topography of internal organs, for example, in the diagnosis of malformations;

identify tumor processes (malignant or benign);

determine the volume and degree of damage to an organ or system.

To perform static radionuclide studies, radiopharmaceuticals are used, which, after being introduced into the patient's body, are characterized either by a stable distribution in organs and tissues, or by a very slow redistribution. Studies are performed on scanners (scanning) or on gamma cameras (scintigraphy). Scanning and scintigraphy have approximately equal technical capabilities in assessing the anatomical and topographic state of internal organs, but scintigraphy has some advantages.

Dynamic radionuclide study allows to evaluate the radiation of radiopharmaceutical redistribution and is a fairly accurate way to assess the state of the function of internal organs. Indications for their use include:

clinical and laboratory data on a possible disease or damage to the cardiovascular system, liver, gallbladder, kidneys, lungs;

the need to determine the degree of dysfunction of the investigated oran before treatment, during treatment;

the need to study the preserved function of the investigated oran when substantiating the operation.

The most widely used for dynamic radionuclide studies are radiometry and radiography, which are methods for continuously recording changes in activity. At the same time, the methods, depending on the purpose of the study, received various names:

radiocardiography - registration of the speed of passage through the chambers of the heart to determine the minute volume of the left ventricle and other parameters of cardiac activity;

radiorenography - registration of the rate of passage of the radiopharmaceutical through the right and left kidneys for the diagnosis of violations of the secretory-excretory function of the kidneys;

radiohepatography - registration of the rate of passage of the radiopharmaceutical through the liver parenchyma to assess the function of polygonal cells;

radioencephalography - registration of the rate of passage of the radiopharmaceutical through the right and left hemispheres of the brain to detect cerebrovascular accident;

radiopulmonography - registration of the rate of passage of the radiopharmaceutical through the right and left lung, as well as through individual segments to study the ventilation function of each lung and its individual segments.

In vitro radionuclide diagnostics, in particular radioimmunoassay (RIA), is based on the use of labeled compounds that are not introduced into the body of the test subject, but are mixed in a test tube with the patient's analyzed medium.

Currently, RIA methods have been developed for more than 400 compounds of various chemical nature and are used in the following areas of medicine:

in endocrinology for diagnosing diabetes mellitus, pathology of the pituitary-adrenal and thyroid systems, identifying the mechanisms of other endocrine-metabolic disorders;

in oncology for the early diagnosis of malignant tumors and monitoring the effectiveness of treatment by determining the concentration of alpha-fetoprotein, cancer embryonic antigen, as well as more specific tumor markers;

in cardiology for the diagnosis of myocardial infarction, by determining the concentration of myoglobin, monitoring treatment with drugs dogixin, digitokosin;

in pediatrics to determine the causes of developmental disorders in children and adolescents (determination of self-tropic hormone, thyroid-stimulating hormone of the pituitary gland);

in obstetrics and gynecology to monitor the development of the fetus by determining the concentration of estriol, progesterone, in the diagnosis of gynecological diseases and identifying the causes of female infertility (determination of luteinizing and follicle-stimulating hormone);

in allergology to determine the concentration of immunoglobulins E and specific reagins;

in toxicology to measure the concentration of drugs and toxins in the blood.

A special place in radiation diagnostics is occupied by research methods that are not associated with the use of ionizing radiation sources, which have been widely used in practical healthcare in recent decades. These include methods: ultrasound (ultrasound), magnetic resonance imaging (MRI) and medical thermography (thermal imaging).

Literature

1. Radiation diagnostics. / ed. Sergeeva I.I., Minsk: BSMU, 2007

2. Tikhomirova T.F. Technology of radiation diagnostics, Minsk: BSMU, 2008.

3. Boreyka S.B., X-ray technique, Minsk: BSMU, 2006.

4. Novikov V.I. Technique of radiation diagnostics, SPb, SPbMAMO, 2004.