Methods and techniques of radiation diagnostics. Modern methods of radiation diagnostics of the patient. Where is radiation diagnostics used?

2.1. X-RAY DIAGNOSTICS

(RADIOLOGY)

X-ray machines are widely used in almost all medical institutions. X-ray installations are simple, reliable and economical. It is these systems that still serve as the basis for the diagnosis of skeletal injuries, diseases of the lungs, kidneys and the alimentary 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 characteristics 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. Electromagnetic spectra of X-rays and gamma rays overlap to a large extent.

Rice. 2-1.Scale of electromagnetic radiation

The main difference between these two types of radiation is the way they occur. X-rays are produced with the participation of electrons (for example, when their flow is decelerated), and gamma rays are produced during the radioactive decay of the nuclei of some elements.

X-rays can be generated when an accelerated flow of charged particles is decelerated (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 cathode are accelerated, reaching the anode, upon collision with the material of which they are decelerated. As a result, bremsstrahlung X-ray radiation arises. 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 taken by electrons from other shells of the atom. During this process, a second type of X-ray is generated - the so-called characteristic X-ray, the spectrum of which is largely dependent on the anode material. Anodes are most often made from molybdenum or tungsten. There are special devices for focusing and filtering X-rays in order to improve the resulting images.

Rice. 2-2.X-ray tube device diagram:

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 ability, fluorescent and photochemical actions. The penetrating ability of X-rays and their absorption by 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 more penetrating the X-ray radiation.

Distinguish between "soft" X-rays with low energy and radiation frequency (respectively, with the longest wavelength) and "hard", which has high photon energy and radiation frequency, and has a short wavelength. The wavelength of X-ray radiation (respectively, its "hardness" and penetrating ability) depends on the magnitude of the voltage applied to the X-ray tube. The higher the voltage across 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 take place 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 investigated object (organ) is composed, 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. 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 transmitted through the body, its ability to cause fluorescence of certain compounds and to exert 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 for registration of attenuated radiation, special systems of digital electronic detectors are used - digital electronic panels. In this case, X-ray methods are called digital.

Due to the biological effect of X-rays, it is necessary to resort to patient protection during examination. This is achieved

the shortest possible exposure time, replacement of fluoroscopy with radiography, strictly justified use of ionizing methods, protection by shielding the patient and personnel from radiation exposure.

2.1.2. Radiography and fluoroscopy

Fluoroscopy and radiography are the main methods of X-ray examination. For the study of 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 are forced to resort to fluoroscopy where radiography or non-ionizing methods of obtaining information are insufficient. In connection with the development of CT, the role of classical layer-by-layer tomography has decreased. The technique of layer-by-layer tomography is used in the study of the lungs, kidneys and bones where there are no CT rooms.

Fluoroscopy (Greek. scopeo- consider, observe) - a study in which an X-ray image is projected onto a fluorescent screen (or a system of digital detectors). The method allows for static, as well as dynamic, functional examination of organs (for example, fluoroscopy of the stomach, excursion of the diaphragm) and control 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 relatively high radiation exposure and difficulties in differentiating "subtle" changes.

Radiography (Greek greapho- write, depict) - a study in which an X-ray image of an object is obtained, fixed on film (direct radiography) or on special digital devices (digital radiography).

Various types of radiography (plain radiography, sighting radiography, contact radiography, contrast radiography, mammography, urography, fistulography, arthrography, etc.) are used to improve the quality and increase the number of received diagnostics.

Rice. 2-3.Modern X-ray machine

technical information in each specific clinical situation. For example, contact radiography is used for dental imaging, and contrast radiography is used for excretory urography.

Radiography and fluoroscopy techniques can be used with a vertical or horizontal position of the patient's body in stationary or ward installations.

Traditional radiography using X-ray film or digital radiography remains one of the main and widely used research techniques. This is due to the high efficiency, simplicity and information content of the diagnostic images obtained.

When photographing an object from a fluorescent screen onto a film (usually a small size - special format photographic film), X-ray images are obtained, which are usually used for mass examinations. This technique is called fluorography. Currently, it is gradually being phased out due to its replacement by digital radiography.

The disadvantage of any type of X-ray examination is its low resolution when examining low-contrast tissues. Previously used for this purpose, classical tomography did not give the desired result. It was to overcome this shortcoming that CT was created.

2.2. ULTRASONIC DIAGNOSTICS (SONOGRAPHY, ultrasound)

Ultrasound diagnostics (sonography, ultrasound) is a method of radiation diagnostics based on obtaining an image 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 widespread and important, providing fast, accurate and safe diagnosis of many diseases.

Ultrasound refers to 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 propagation speed of the ultrasonic wave in the tissues is constant and amounts to 1540 m / sec. The image is obtained by analyzing the signal (echo) reflected from the boundary of two media. In medicine, frequencies in the 2-10 MHz range are most commonly used.

Ultrasound is generated by a special sensor with a piezoelectric crystal. Short electrical impulses create mechanical vibrations of the crystal, as a result of which ultrasonic radiation is generated. The ultrasound frequency is determined by the resonant frequency of the crystal. The reflected signals are recorded, analyzed and displayed visually on the device screen, creating images of the investigated structures. Thus, the sensor works consistently as an emitter and then as a receiver of ultrasonic waves. The principle of operation of the ultrasound system is shown in Fig. 2-4.

Rice. 2-4.How the ultrasound system works

The higher the acoustic impedance, the greater the reflection of the 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 artifacts on examination can arise from structures containing air or calcium (pulmonary 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 surface of the body, where the organ under study is in contact with soft tissues. This area is called an ultrasonic "window". With a poor ultrasound "window", the study may be impossible or uninformative.

Modern ultrasound machines are sophisticated digital devices. They use real-time sensors. The images are dynamic, one can observe such fast processes as respiration, cardiac contractions, vascular pulsation, valve movement, peristalsis, fetal movements. The position of the transducer 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.

Doppler sonography is very important in ultrasound examination. Doppler described the physical effect, according to which 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. Doppler is used to measure and visualize the speed, direction and nature of blood flow 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 ultrasound radiation passes through the area under study. When the ultrasound beam crosses the vessel or heart chamber, the ultrasound is partially reflected by the erythrocytes. So, for example, the frequency of the reflected echo from the blood moving towards the transducer will be higher than the original frequency of the waves emitted by the transducer. Conversely, the frequency of the reflected blood echo from the transducer will be lower. The difference between the frequency of the received echo 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 a relative blood flow velocity.

Studies that combine two-dimensional ultrasound in real time and pulsed Doppler imaging are called duplex. In a duplex examination, the direction of the Doppler beam is superimposed on the 2D B-mode image.

The modern development of the duplex examination technique has led to the emergence of a method of color Doppler blood flow mapping. Within the control volume, the stained blood flow is superimposed on a two-dimensional image. In this case, blood is displayed in color, and immobile tissues in a gray scale. When blood moves to the sensor, red-yellow colors are used, when moving away from the sensor, blue-blue colors. Such a color image does not carry additional information, but it gives a good visual representation of the nature of blood movement.

In most cases, for the purpose of conducting 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, transducers placed in the esophagus (transesophageal echocardiography) are used to examine the heart; in other cases, intrarectal or intravaginal transducers are used to obtain high-quality images. During the operation, they resort to the use of operating sensors.

In recent years, three-dimensional 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 due to the fact that when using the method, there is no ionizing radiation, there is a possibility of carrying out functional and stress tests, the method is informative and relatively inexpensive, the devices are compact and easy to use.

Rice. 2-5.Modern ultrasound apparatus

However, the sonography method has its limitations. These include a high frequency of artifacts in the image, a small depth of signal penetration, a small field of view, and a high dependence of the interpretation of results on the operator.

With the development of ultrasonic equipment, the information content of this method increases.

2.3. COMPUTER 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 after the discovery of X-rays. This is due not only to the versatility and unsurpassed resolution of the method for examining the whole body, but also to new imaging algorithms. Currently, all devices related to imaging use, to one degree or another, the techniques and mathematical methods that formed the basis of CT.

CT has no absolute contraindications to its use (except for the restrictions associated with ionizing radiation) and can be used for emergency diagnostics, screening, and also as a method of clarifying diagnostics.

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, computed tomographs were subdivided into generations depending on how the X-ray tube-detectors system was arranged. Despite numerous differences in structure, they were all called "step" tomographs. This was due to the fact that after each cross section the tomograph was stopped, the table with the patient made a "step" of several millimeters, and then the next section was performed.

In 1989, spiral computed tomography (SCT) appeared. In the case of SCT, the X-ray tube with detectors constantly rotates around the continuously moving table with the patient

volume. This allows not only to reduce the study time, but also to avoid the limitations of the “step” technique - skipping sections during the study due to the different depth 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.

From that point on, CT became standardized and versatile. It was possible to synchronize the administration of contrast medium with the beginning of table movement during SCT, which led to the creation of CT angiography.

In 1998, multislice CT (MSCT) appeared. Systems have been created not with one (as with SKT), 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, MSCTs with 256 and 320 rows of detector elements appeared.

On such tomographs, hundreds and thousands of tomograms can be obtained in just a few seconds with a thickness of each slice of 0.5-0.6 mm. This 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 difficult problem as visualization of coronary vessels and cardiac cavities using CT was solved. It became possible to study coronary vessels, the volume of cavities and cardiac function, and myocardial perfusion in one 5-20-second study.

A schematic diagram of the CT device is shown in Fig. 2-6, and the appearance is in Fig. 2-7.

The main advantages of modern CT are: speed of image acquisition, layer-by-layer (tomographic) nature of images, the ability to obtain slices of any orientation, high spatial and temporal resolution.

The disadvantages of CT are the relatively high (compared to X-ray) radiation exposure, the possibility of artifacts from dense structures, movements, and relatively low soft tissue contrast resolution.

Rice. 2-6.MSCT device diagram

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 work on obtaining images using NMR appeared in the 70s. last century. By now, this method of medical imaging has changed beyond recognition and continues to evolve. Hardware and software are being improved, and methods of obtaining images are being improved. Previously, the use of MRI was limited only to the study of the central nervous system. Now the method is successfully applied in other fields of medicine, including research 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, so as not to cause patients to associate with nuclear weapons or nuclear power. Therefore, today the term "magnetic resonance imaging" (MRI) is officially used.

NMR is a physical phenomenon based on the properties of certain atomic nuclei placed in a magnetic field to absorb external energy in the radio frequency (RF) range and emit it when the RF pulse is removed. The strength of the constant magnetic field and the frequency of the RF pulse are strictly matched to each other.

The nuclei 1H, 13C, 19F, 23Na and 31P are important for use in magnetic resonance imaging. They all have magnetic properties, which distinguishes them from non-magnetic isotopes. Hydrogen protons (1H) are most abundant in the body. Therefore, for MRI, it is the signal from the 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. In this case, the

The nucleus can be compared to a spinning top. Under the influence of a magnetic field, the rotating core makes a complex motion. The nucleus rotates around its axis, and the axis of rotation itself performs conical 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 between the populations of these two levels by protons, will be very weak. To detect this macroscopic magnetization, it is necessary to deflect its vector from the axis of the constant magnetic field. This is achieved using 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 construct 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 RF pulses with a predetermined narrow frequency range, it is possible to receive MR signals only from the selected tissue layer. The orientation of the magnetic field gradients and, accordingly, the direction of the slices can be easily set in any direction. 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 this data, you can build two or three-dimensional images.

Combinations of RF pulses of different durations and shapes are used to obtain a magnetic resonance signal. By combining different pulses, so-called pulse trains are formed, which are used to obtain images. Specialty 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

with magnetic vectors - weak signal (looks dark). Anatomical areas 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 at different 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 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.

The relaxation time of tissues - T1 and T2 - is constant. In MRI, the terms “T1-weighted image”, “T2-weighted image”, “proton-weighted image” are used, meaning 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 radiographer or doctor can influence the contrast of the images without resorting to the use of contrast media. Therefore, in MRI there is much more opportunity to change 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 abnormal tissues and improve the quality of visualization.

The schematic diagram of the MR system and the external view of the device are shown in Fig. 2-8

and 2-9.

Usually MRI scanners are classified according to the strength of the magnetic field. The strength of the magnetic field is measured in Tesla (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.MRI device diagram

Rice. 2-9.State-of-the-art 1.5 Tesla MRI system

MRI uses magnets with fields ranging from 0.2 to 3 Tesla. Currently, MR systems with fields 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 better image quality and have a larger number of programs used in clinical practice.

The main area of ​​application of MRI was the brain, and then the spinal cord. Brain tomograms allow you to get an excellent image of all structures of the brain, without resorting to additional administration of contrast. Thanks to the technical capability 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 study joints, pelvic organs, mammary glands, heart and blood vessels. For these purposes, additional special coils and mathematical methods of imaging have been developed.

A special technique allows you to record images of the heart at different phases of the cardiac cycle. If the study is carried out with

synchronization with the ECG, images of a functioning heart can be obtained. This is called a film MRI.

Magnetic resonance spectroscopy (MRS) is a non-invasive diagnostic method that allows qualitative and quantitative determination of the chemical composition of organs and tissues using nuclear magnetic resonance and the phenomenon of chemical shift.

MR spectroscopy is most often performed to obtain signals from phosphorus and hydrogen nuclei (protons). However, due to technical difficulties and the duration of its implementation, it is still rarely used in clinical practice. It should not be forgotten that the increasing use of MRI requires particular attention to patient safety issues. When examining with MR spectroscopy, the patient is not exposed to ionizing radiation, but he is exposed to electromagnetic and radio frequency radiation. Metal objects in the body of the examined person (bullets, fragments, large implants) and all electronic and mechanical devices (for example, a pacemaker) can damage the patient due to displacement or disruption (interruption) of normal operation.

Many patients experience a fear of closed spaces - claustrophobia, which leads to the inability to complete the study. Thus, all patients should be informed about the possible undesirable consequences of the study and about the nature of the procedure, and the attending physicians and radiologists before the study must interview the patient about the presence of the above items, wounds and operations. Before the examination, the patient must completely change into a special suit to exclude the ingress of metal things from the pockets of clothing into the magnet channel.

It is important to know the relative and absolute contraindications for the study.

The 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. Such contraindications are

presence of hemostatic braces, clamps and clips of other localization, decompensation of heart failure, first trimester of pregnancy, claustrophobia and the need for physiological monitoring. In such cases, the decision on the possibility of conducting an MRI is decided in each individual case based on the ratio of the magnitude of the possible risk and the expected benefit from performing 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 research in 1-4% of cases.

Like other imaging techniques, MRI is not without its drawbacks.

The significant disadvantages of MRI include the relatively long study time, the inability to accurately identify small stones and calcifications, the complexity of the equipment and its operation, and special requirements for the installation of devices (protection against interference). It is difficult to use MRI to screen patients who need equipment to keep them alive.

2.5. RADIONUCLIDE DIAGNOSTICS

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 (RFP)) and methods of 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 power analysis allows you to determine the intensity and position in space of each scintillation. This data is used to reconstruct a 2D image of the RFP propagation. The image can be presented directly on the monitor screen, on a photo or multi-format film, or recorded on a computer media.

There are several groups of radio diagnostic devices, depending on the method and type of radiation registration:

Radiometers - devices for measuring the radioactivity of the whole body;

Radiographers - devices for recording the dynamics of changes in radioactivity;

Scanners - systems for registering the spatial distribution of RFP;

Gamma cameras are devices for static and dynamic registration of the volumetric distribution of a radioactive indicator.

In modern clinics, most of the devices for radionuclide diagnostics are gamma cameras of various types.

Modern gamma cameras are a complex consisting of 1-2 large-diameter detector systems, a table for patient positioning and a computer system for accumulating and processing images (Fig. 2-10).

The next step in the development of radionuclide diagnostics was the creation of a rotary 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.Diagram of a gamma camera device

Rotary gamma cameras with one, two or three detectors are used for SPECT. Mechanical systems of tomographs allow the detectors to rotate around the patient's body in different orbits.

The spatial resolution of modern SPECT is about 5-8 mm. The second condition for performing a radioisotope study, in addition to the availability of special equipment, is the use of special radioactive indicators - radiopharmaceuticals (RFP), which are introduced into the patient's body.

A radiopharmaceutical is a radioactive chemical compound with known pharmacological and pharmacokinetic characteristics. Rather strict requirements are imposed on radiopharmaceuticals used in medical diagnostics: tropism to organs and tissues, ease of preparation, short half-life, optimal energy of gamma radiation (100-300 keV) and low radiotoxicity at relatively high permissible doses. The ideal radiopharmaceutical should be delivered only to organs or pathological foci intended for research.

Understanding the mechanisms of RFP 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 the active substance (isotope) is so small that when introduced into the body, it does not cause physiological effects or allergic reactions. Nuclear medicine uses RFPs that emit gamma rays. Sources of alpha (helium nuclei) and beta particles (electrons) are currently not used in diagnostics due to the high degree of tissue absorption and high radiation exposure.

The most commonly used in clinical practice is technetium-99t isotope (half-life - 6 hours). This artificial radionuclide is obtained immediately before the study from special devices (generators).

A radio diagnostic image, regardless of its type (statics or dynamics, planar or tomographic), always reflects the specific function of the organ under study. Essentially, it is a display of functioning tissue. It is in the functional aspect that the fundamental distinguishing feature of radionuclide diagnostics from other imaging methods lies.

RP is usually administered intravenously. For studies of ventilation of the lungs, the drug is administered by inhalation.

One of the newer tomographic radioisotope techniques in nuclear medicine is positron emission tomography (PET).

PET is based on the decay property of some short-lived radionuclides to emit positrons. A positron is a particle equal in mass to an electron, but having a positive charge. A positron, having flown through a substance of 1-3 mm and having lost the kinetic energy obtained 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 are scattered 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 aligned annihilation photons (Fig. 2-11).

PET allows quantitative assessment of the concentration of radionuclides and has more possibilities for studying metabolic processes than scintigraphy performed with gamma cameras.

PET uses isotopes of elements such as carbon, oxygen, nitrogen, fluorine. RFP labeled with these elements are natural metabolites of the body and are included in the metabolism

Rice. 2-11.PET device diagram

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 (apart from MR spectroscopy) technique for assessing metabolic and biochemical processes in vivo.

All positronic radionuclides used in medicine are ultra-short-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 often used.

Despite the fact that the first PET systems appeared in the middle of the 20th century, their clinical use is hampered by some limitations. These are the technical difficulties that arise when arranging accelerators in clinics for the production of short-lived isotopes, 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 studies 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 metabolism and tissue viability.

The common disadvantages of radioisotope methods include low spatial resolution. The use of radioactive drugs 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 device of radioisotope laboratories (especially for PET) requires special rooms, security, signaling and other precautions.

2.6. ANGIOGRAPHY

Angiography is an X-ray examination method associated with the direct injection of a contrast agent into the vessels in order to study them.

Angiography is classified into arteriography, phlebography, and lymphography. The latter, in connection with the development of methods of ultrasound, CT and MRI, is currently practically not used.

Angiography is performed in specialized X-ray rooms. These offices meet all the requirements for operating rooms. For angiography, specialized X-ray machines (angiographic installations) 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 puncture of the vessels.

Rice. 2-13.Modern angiographic unit

The main method of vascular catheterization is the Seldinger method of vessel catheterization. To perform angiography, a certain amount of a contrast agent is injected into a vessel through a catheter, and the passage of the drug through the vessels is taken.

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 a 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 devices in clinics, CT and MRI diagnostics of pathological processes in blood 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 INTERVENTIONAL RADIOLOGY

Interventional radiology is a field of medicine based on the use of methods of radiation diagnostics and special instruments for performing minimally invasive interventions for the diagnosis and treatment of diseases.

Interventional interventions are widespread in many areas of medicine, since they can often replace large surgical interventions.

The first percutaneous treatment of peripheral artery stenosis was performed by the American physician Charles Dotter in 1964. In 1977, the Swiss physician Andreas Grüntzig designed a balloon catheter and performed the procedure to dilate (dilate) the stenotic coronary artery. This method became known as balloon angioplasty.

Balloon angioplasty of coronary and peripheral arteries is currently one of the main methods of treatment of arterial stenosis and occlusion. 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 site after balloon dilatation. The expanded stent prevents re-stenosis from occurring.

Stent placement is performed after diagnostic angiography and determination of the critical narrowing site. The stent is adjusted for length and size (Figure 2-14). Using this technique, it is possible to close atrial and interventricular septal defects without major operations or to perform balloon plasty of stenoses of the aortic, mitral, tricuspid valves.

The technique of installing special filters in the inferior vena cava (cava filters) has acquired particular importance. This is necessary to prevent the entry of emboli into the vessels of the lungs in case of venous thrombosis of the lower extremities. The kava filter is a mesh structure that opens up in the lumen of the inferior vena cava and catches ascending blood clots.

Another endovascular intervention in demand in clinical practice is vascular embolization (blockage). Embolization is used to stop internal bleeding, to treat abnormal vascular anastomoses, aneurysms, or to close the vessels feeding a malignant tumor. Currently, effective artificial materials, removable balloons and steel microscopic coils are used for embolization. Usually, embolization is performed selectively so as not to cause ischemia of the surrounding tissue.

Rice. 2-14.Balloon angioplasty and stenting scheme

Interventional radiology also includes drainage of abscesses and cysts, contrasting of pathological cavities through fistulous passages, restoration of urinary tract patency in case of urinary disorders, bougienage and balloon plastic surgery for strictures (narrowing) of the esophagus and bile ducts, percutaneous thermal or cryodestruction of malignant tumors and other interventions.

After identifying a 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 tactics. 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 CONTRASTS FOR RADIATION DIAGNOSTICS

Low contrast between adjacent objects or the same density of adjacent tissues (for example, the density of blood, vascular wall, and thrombus) complicates the interpretation of images. In these cases, in radiation diagnostics, artificial contrasting is often used.

An example of enhancing the contrast of images of the organs under study is the use of barium sulfate for examining the organs of the alimentary canal. For the first time such contrasting was performed in 1909.

It was more difficult to create contrast media for intravascular administration. For this purpose, after long experiments with mercury and lead, they began to use soluble iodine compounds. The first generations of radiopaque contrast agents were imperfect. Their use caused frequent and severe (up to fatal) complications. But already in the 20-30s. XX century. a number of safer water-soluble iodine-containing preparations 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 were developed that had a low osmolarity (they did not dissociate in solution into an anion and a cation) - non-ionic contrast agents.

Modern X-ray contrast media are triiodo 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 joint cavities, into the cavity organs and under the lining of the spinal cord. For example, the introduction of contrast through the body cavity of the uterus into the tubes (hysterosalpingography) allows you to assess the inner surface of the uterine cavity and the patency of the fallopian tubes. In neurological practice, in the absence of MRI, the technique of myelography is used - the introduction of a water-soluble contrast agent under the lining 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 quick (bolus) intravenous injection of 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. Rapid diffusion of the contrast agent from the blood into the tissue occurs. During the first minute after a quick injection, a high concentration of contrast agent remains 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 patient's laboratory parameters, then they are called adverse reactions. Before examining a patient using contrast agents, it is necessary to find out whether he has allergic reactions to iodine, chronic renal failure, bronchial asthma and other diseases. The patient should be warned about the possible reaction and 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 special instructions for dealing with anaphylactic shock to prevent severe complications.

Contrast media are also used for 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 media significantly attenuate penetrating radiation, MRI drugs cause changes in the characteristics of the surrounding tissues. They are not visualized on tomograms, like X-ray contrasts, but they make it possible to reveal hidden pathological processes due to changes in magnetic parameters.

The mechanism of action of these agents is based on changes in the relaxation time of the tissue site. Most of these drugs are based on gadolinium. Contrast agents based on iron oxide are used much less frequently. These substances have different effects on the signal intensity.

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-containing ones. There are only a few reports of serious anaphylactic reactions to these substances. Despite this, close monitoring of the patient after the injection is necessary and the availability of resuscitation equipment available. 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 central nervous system, only areas devoid of this barrier are normally contrasted, for example, the pituitary gland, pituitary funnel, cavernous sinuses, dura mater and mucous membranes of the nose and paranasal sinuses. Damage and destruction of the BBB lead to the penetration of paramagnetic contrast agents into the extracellular space and a local change in T1 relaxation. This is observed in a number of pathological processes in the central nervous system, such as tumors, metastases, cerebrovascular accidents, infections.

In addition to MRI studies of the central nervous system, contrast enhancement is used to diagnose diseases of the musculoskeletal system, heart, liver, pancreas, kidneys, adrenal glands, pelvic organs and mammary glands. These studies are being carried out

it is much less common than with pathology of the central nervous system. To perform MR angiography and study organ perfusion, a contrast agent must be 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. As with other contrast media, ultrasound contrast media must be of low toxicity and be rapidly eliminated from the body. The drugs of the first generation did not pass through the capillary bed of the lungs and were destroyed in it.

The contrast media used now enter the systemic circulation, which makes it possible to use them to improve the quality of images of internal organs, amplify 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.

Special attention should be paid to the prevention and treatment of severe complications. The incidence 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 therapeutic measures.

With moderate reactions, the above symptoms may also be accompanied by a decrease in blood pressure, the occurrence of tachycardia, vomiting, urticaria. It is necessary to provide symptomatic treatment (usually the introduction of antihistamines, antiemetics, sympathomimetics).

In severe reactions, anaphylactic shock may occur. An urgent need for resuscitation

tii 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 thyroid dysfunction;

With severe diabetes mellitus, pheochromocytoma, multiple myeloma.

It is also customary to refer to the risk group in relation to the risk of developing adverse reactions to young children and elderly people.

The prescribing physician should carefully assess the risk / benefit ratio of contrasting studies and take the necessary precautions. A radiologist performing a study in a patient with a high risk of adverse reactions to a contrast agent is obliged to warn the patient and the attending physician about the dangers of using contrast agents and, if necessary, replace the study with another one that does not require contrasting.

The X-ray room should be equipped with everything necessary for carrying out resuscitation measures and combating anaphylactic shock.

Radiation diagnostics, radiation therapy are two components of radiology. In modern medical practice, they are used more and more often. This can be explained by their excellent information content.

Radiation diagnostics is a practical discipline that studies the use of various kinds of radiation in order to detect and recognize a large number of diseases. It helps to study the morphology and functions of normal and diseased organs and systems of the human body. There are several types of radiation diagnostics, and each of them is unique in its own way and allows you to detect diseases in different areas of the body.

Radiation diagnostics: types

Today there are several methods of radiation diagnostics. Each of them is good in its own way, as it allows you to conduct research in a specific area of ​​the human body. Types of radiation diagnostics:

• X-ray diagnostics.
• Radionuclide research.
• CT scan.
• Thermography.

These methods of research of radiation diagnostics can allow to give out data on the state of health of the patient only in the area that they are investigating. But there are also more advanced methods that give more detailed and extensive results.

Modern diagnostic method

Modern radiation diagnostics is one of the fastest growing medical specialties. It is directly related to the general progress of physics, mathematics, computing, computer science.

Radiation diagnostics is a science that uses radiation that helps to study the structure and functioning of normal and disease-damaged organs and systems of the human body in order to prevent and recognize the disease. This diagnostic method plays an important role both in the examination of patients and in radiological treatment procedures, which depend on information obtained during the research.

Modern methods of radiation diagnostics make it possible to identify pathology in a specific organ with maximum accuracy and help find the best way to treat it.

Varieties of diagnostics

Innovative diagnostic methods include a large number of diagnostic imaging and differ from each other in the physical principles of data acquisition. But the general essence of all techniques lies in the information that is obtained by processing transmitted, emitted or reflected electromagnetic radiation or mechanical vibrations. Depending on which of the phenomena are the basis of the resulting image, radiation diagnostics is divided into the following types of studies:

• X-ray diagnostics is based on the ability to absorb X-rays by tissues.
• It is based on the reflection of a beam of directed ultrasonic waves in tissues towards the sensor.
• Radionuclide - characterized by the emission of isotopes that accumulate in tissues.
• The magnetic resonance method is based on the emission of radio frequency radiation, which occurs during the excitation of unpaired atomic nuclei in a magnetic field.
• Infrared research - spontaneous emission of infrared radiation by tissues.

Each of these methods allows you to accurately identify pathology in human organs and gives more chances for a positive outcome of treatment. How does radiation diagnostics reveal pathology in the lungs, and what can be detected with its help?

Lung examination

Diffuse lung damage is changes in both organs, which are scattered foci, an increase in tissue volume, and in some cases, a combination of these two conditions. Thanks to X-ray and computer research methods, it is possible to determine pulmonary diseases.

Only modern research methods make it possible to quickly and accurately establish a diagnosis and start surgical treatment in a hospital setting. In our time of modern technologies, radiation diagnostics of the lungs is of great importance. It is very difficult to make a diagnosis according to the clinical picture in most cases. This is due to the fact that lung pathologies are accompanied by severe pain, acute respiratory failure and hemorrhage.

But even in the most severe cases, urgent radiation diagnostics comes to the aid of doctors and patients.

When is the study indicated?

The X-ray diagnostic method allows you to quickly identify the problem in the event of a life-threatening situation for the patient that requires urgent intervention. An urgent x-ray can be helpful in many cases. It is most often used for damage to bones and joints, internal organs and soft tissues. Injuries to the head and neck, abdomen and abdominal cavity, chest, spine, hip and long bones are very dangerous for humans.

The X-ray method is prescribed to the patient immediately after the anti-shock therapy is performed. It can be carried out directly in the admission department using a mobile device, or the patient is delivered to the X-ray room.

In case of neck and head injuries, an overview X-ray is performed, if necessary, special images of individual parts of the skull are added. In specialized institutions, you can conduct a rapid angiography of the vessels of the brain.

When the chest is injured, the diagnosis begins with a survey done with a direct and side view. In case of abdominal and pelvic injuries, an examination should be carried out using contrasting.

Also, an urgent one is carried out for other pathologies: acute abdominal pain, coughing up blood and bleeding from the digestive tract. If the data is not enough to establish an accurate diagnosis, computed tomography is prescribed.

Rarely, X-ray diagnostics are used in cases of suspicion of the presence of foreign bodies in the respiratory tract or digestive tract.

For all types of injuries and in difficult cases, it may be necessary to conduct not only computed tomography, but also magnetic resonance imaging. Only the attending doctor can prescribe this or that study.

Advantages of radiation diagnostics

This research method is considered one of the most effective, therefore, considering its advantages, I would like to highlight the following:

• Under the influence of rays, tumor neoplasms decrease, some of the cancer cells die, and the rest stop dividing.
• Many vessels from which food comes to overgrow.
• Most of the positive aspects are in the treatment of certain types of cancer: lung, ovary and thymus.

But not only the positive aspects of this method have, there are also negative aspects.

Cons of radiation diagnosis

Most doctors believe, as amazing as this research method is, it also has its negative sides. These include:

• Side effects that occur during therapy.
• Low sensitivity to radioactive radiation of organs such as cartilage, bones, kidneys and brain.
• Maximum sensitivity of the intestinal epithelium to this radiation.

Radiation diagnostics showed good results in detecting pathology, but it is not suitable for every patient.

Contraindications

This research method is not suitable for all patients with cancer. It is prescribed only in some cases:

• The presence of a large number of metastases.
• Radiation sickness.
• Growth of cancer roots into the largest vessels and organs of the reproductive system.
• Fever.
• Severe condition of the patient with severe intoxication.
• Extensive oncological lesion.
• Anemia, leukopenia, and thrombocytopenia.
• Breakdown of cancerous growths with bleeding.

Conclusion

Radiation diagnostics have been in use for several years and have shown very good results in quick diagnosis, especially in difficult cases. Thanks to its use, it was possible to determine the diagnoses of very serious patients. Even with its shortcomings, there are no other studies that have yielded such results. Therefore, we can say for sure that at present, radiation diagnostics is in the first place.

Radiation diagnostics is the science of using radiation to study the structure and function of normal and pathologically altered human organs and systems for the prevention and diagnosis of diseases.

The Role of Radiology

in the training of a doctor and in medical practice in general is constantly increasing. This is due to the creation of diagnostic centers, as well as diagnostic departments equipped with computer and magnetic resonance tomographs.

It is known that most (about 80%) of diseases are diagnosed with the help of radiation diagnostic devices: ultrasound, X-ray, thermographic, computer and magnetic resonance imaging devices. The lion's share in this list belongs to X-ray devices, which have many varieties: basic, universal, fluorographs, mammographs, dental, mobile, etc. In connection with the exacerbation of the problem of tuberculosis, the role of preventive fluorographic examinations in order to diagnose this ailment in the early stages has especially increased recently. ...

There is one more reason that made the problem of X-ray diagnostics urgent. The share of the latter in the formation of the collective dose of irradiation of the population of Ukraine due to artificial sources of ionizing radiation is about 75%. To reduce the patient's radiation dose, modern X-ray machines incorporate X-ray image intensifiers, but these in Ukraine today are less than 10% of the available fleet. And it is quite impressive: as of January 1998, more than 2,460 X-ray departments and rooms functioned in medical institutions of Ukraine, where 15 million X-ray diagnostic and 15 million fluorographic examinations of patients were performed annually. There is reason to assert that the state of this branch of medicine determines the health of the entire nation.

The history of the formation of radiation diagnostics

Over the past century, radiation diagnostics has undergone rapid development, transformation of methods and equipment, has won a solid position in diagnostics and continues to amaze with its truly inexhaustible capabilities.
The founder of radiation diagnostics, the X-ray method appeared after the discovery of X-ray radiation in 1895, which gave rise to the development of a new medical science - radiology.
The first objects of research were the skeletal system and respiratory organs.
In 1921, the method of radiography at a given depth was developed - layer by layer, and tomography was widely introduced into practice, which significantly enriched diagnostics.

In the eyes of one generation, within 20-30 years, radiology emerged from dark rooms, the image from the screens passed to television monitors, and then was transformed into digital on a computer monitor.
In the 70-80s, revolutionary transformations took place in radiation diagnostics. New methods of image acquisition are being introduced into practice.

This stage is characterized by the following features:

1. By switching from one type of radiation (X-ray) used to obtain an image to others:

• ultrasonic radiation
• long-wave infrared electromagnetic radiation (thermography)
• radio frequency radiation (NMR - nuclear magnetic resonance)

1. Using a computer for signal processing and imaging.
2. The transition from a single-stage image to scanning (sequential registration of signals from different points).

The ultrasound method of research came into medicine much later than the X-ray one, but it developed even more rapidly and became indispensable due to its simplicity, the absence of contraindications due to its harmlessness to the patient and high information content. In a short time, the path was passed from gray-scale scanning to methods with a color image and the possibility of studying the vascular bed - Doppler sonography.

One of the methods - radionuclide diagnostics has also become widespread in recent years due to low radiation exposure, atraumaticity, non-allergy, a wide range of studied phenomena, the possibility of combining static and dynamic techniques.

One of the actively developing branches of modern clinical medicine is radiation diagnostics. This is facilitated by constant progress in the field of computer technology and physics. Thanks to highly informative non-invasive examination methods that provide detailed visualization of internal organs, doctors are able to identify diseases at different stages of their development, including before the onset of pronounced symptoms.

The essence of radiation diagnostics

It is customary to call radiation diagnostics a branch of medicine associated with the use of ionizing and non-ionizing radiation in order to detect anatomical and functional changes in the body and to identify congenital and acquired diseases. There are such types of radiation diagnostics:

• X-ray, implying the use of X-rays: fluoroscopy, radiography, computed tomography (CT), fluorography, angiography;
• ultrasound, associated with the use of ultrasonic waves: ultrasound examination (ultrasound) of internal organs in 2D, 3D, 4D formats, Doppler sonography;
• magnetic resonance, based on the phenomenon of nuclear magnetic resonance - the ability of a substance containing nuclei with nonzero spin and placed in a magnetic field to absorb and emit electromagnetic energy: magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS);
• radioisotope, involving the registration of radiation emanating from radiopharmaceuticals introduced into the patient's body or into the biological fluid contained in a test tube: scintigraphy, scanning, positron emission tomography (PET), single-photon emission tomography (SPECT), radiometry, radiography;
• thermal, associated with the use of infrared radiation: thermography, thermal tomography.

Modern methods of radiation diagnostics allow obtaining flat and volumetric images of human internal organs, therefore they are called intrascopic ("intra" - "inside something"). They provide clinicians with about 90% of the information they need to make a diagnosis.

In what cases is radiation diagnostics contraindicated?

Studies of this type are not recommended for patients who are in a coma and in serious condition, combined with fever (increased to 40-41 ̊C body temperature and chills), suffering from acute hepatic and renal failure (loss of the organs' ability to fully perform their functions), mental illness, extensive internal bleeding, open pneumothorax (when air during breathing freely circulates between the lungs and the external environment through damage to the chest).

However, sometimes a CT scan of the brain is required for urgent indications, for example, for a patient in a coma in the differential diagnosis of strokes, subdural (the area between the dura mater and arachnoid) and subarachnoid (the cavity between the pia mater and arachnoid) hemorrhages.

The thing is that CT is performed very quickly, and it "sees" the volume of blood inside the skull much better.

This allows you to make a decision about the need for urgent neurosurgical intervention, and during CT, you can provide the patient with resuscitation benefits.

X-ray and radioisotope studies are accompanied by a certain level of radiation exposure on the patient's body. Since the dose of radiation, although small, can adversely affect the development of the fetus, X-ray and radioisotope radiation examination during pregnancy is contraindicated. If one of these types of diagnostics is assigned to a woman during lactation, she is recommended to stop breastfeeding for 48 hours after the procedure.

Magnetic resonance imaging studies are not associated with radiation, therefore they are allowed for pregnant women, but they are nevertheless carried out with caution: during the procedure there is a risk of excessive heating of the amniotic fluid, which can harm the child. The same goes for infrared diagnostics.

An absolute contraindication to magnetic resonance imaging is the presence of metal implants and a pacemaker in the patient.

Ultrasound diagnostics has no contraindications, therefore it is allowed for both children and pregnant women. Transrectal ultrasound (TRUS) is not recommended only for patients with rectal lesions.

Where are radiation methods of examination used?

Radiation diagnostics is widely used in neurology, gastroenterology, cardiology, orthopedics, otolaryngology, pediatrics and other branches of medicine. The features of its use, in particular, the leading instrumental research methods prescribed to patients in order to identify diseases of various organs and their systems, will be discussed further.

The use of radiation diagnostics in therapy

Radiation diagnostics and therapy are closely related branches of medicine. According to statistics, among the problems with which patients most often turn to physicians are diseases of the respiratory and urinary systems.

Radiography remains the main method of primary examination of the chest organs.
This is due to the fact that X-ray radiation diagnostics of respiratory diseases is inexpensive, fast and highly informative.

Regardless of the presumed disease, overview pictures are immediately taken in two projections - direct and lateral during a deep breath. Evaluate the nature of the darkening / clarification of the pulmonary fields, changes in the vascular pattern and roots of the lungs. Additionally, images in oblique projection and on exhalation can be performed.

To determine the details and nature of the pathological process, X-ray studies with contrast are often prescribed:

• bronchography (contrasting of the bronchial tree);
• angiopulmonography (contrast study of the vessels of the pulmonary circulation);
• pleurography (contrasting of the pleural cavity) and other methods.

Radiation diagnostics for pneumonia, suspicion of fluid accumulation in the pleural cavity or thromboembolism (blockage) of the pulmonary artery, the presence of tumors in the mediastinal area and subpleural parts of the lungs is often performed using ultrasound.

If the above methods did not allow to detect significant changes in the lung tissue, but at the same time the patient has alarming symptoms (shortness of breath, hemoptysis, the presence of atypical cells in the sputum), CT of the lungs is prescribed. Radiation diagnostics of pulmonary tuberculosis of this type allows obtaining volumetric layered images of tissues and detecting the disease even at the stage of its inception.

If it is necessary to investigate the functional abilities of an organ (the nature of ventilation of the lungs), including after transplantation, carry out differential diagnostics between benign and malignant neoplasms, check the lungs for the presence of metastases of cancer of another organ, radioisotope diagnostics (scintigraphy, PET or other methods are used) ...

The tasks of the imaging service, which operates under local and regional health departments, include monitoring medical staff compliance with research standards. This is necessary, since if the order and frequency of diagnostic procedures are violated, excessive radiation can cause burns on the body, contribute to the development of malignant neoplasms and deformities in children in the next generation.

If radioisotope and X-ray examinations are performed correctly, the doses of emitted radiation are insignificant, incapable of causing disturbances in the functioning of the adult human body. Innovative digital equipment, which replaced the old X-ray machines, has significantly reduced the level of radiation exposure. For example, the radiation dose for mammography varies in the range from 0.2 to 0.4 mSv (millisievert), for chest x-rays - from 0.5 to 1.5 mSv, and for CT of the brain - from 3 to 5 mSv.

The maximum human exposure dose is 150 mSv per year.

The use of radiopaque contrast agents in radiation diagnostics helps to protect areas of the body that are not examined from radiation. For this purpose, a lead apron and tie are put on the patient before the X-ray. To prevent a radiopharmaceutical injected into the body before radioisotope diagnostics from accumulating and being excreted faster with urine, the patient is advised to drink plenty of water.

Summing up

In modern medicine, radiation diagnostics in emergency conditions, in the detection of acute and chronic diseases of organs, in the detection of tumor processes plays a leading role. Thanks to the intensive development of computer technology, it is possible to constantly improve diagnostic techniques, making them safer for the human body.

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 RADIATION DIAGNOSTICS.

Chapter 1.

Radiological methods.

Radiation diagnostics deals with the use of various types of penetrating radiation, both ionization and non-ionization, in order to identify diseases of internal organs.

Radiation diagnostics currently reaches 100% of use in clinical methods of 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 in which the methods are listed determines the chronological sequence of the introduction of each of them into medical practice. The specific gravity of methods of radiation diagnostics according to the WHO today is: 50% ultrasound, 43% RD (X-ray 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 internal organs using X-ray radiation directed at the object of study, having a high penetrating ability, with its subsequent registration after leaving the object by any X-ray receiver, with the help of which a shadow image of the organ under study is obtained directly or indirectly.

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 of 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 waves - propagation at the speed of light

(300,000 km / sec), straightness of propagation, interference and diffraction, luminescent and photochemical action, X-ray radiation also has distinctive properties, which led to their use in medical practice: this is the penetrating ability - X-ray diagnostics is based on this property, and biological action is a constituent essence of X-ray therapy .. The penetrating ability, in addition to the wavelength ("stiffness"), 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 cylinder in which two electrodes are built: 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 rpm 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 is closed and electrons fly to the anode at a speed of up to 30,000 km / s, 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: inhibitory and characteristic. The bremsstrahlung 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 quanta of bremsstrahlung X-ray radiation of low rigidity. The characteristic fraction is obtained due to the penetration of electrons to the atomic nuclei of the anode, which results in knocking out 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 great penetrating ability. 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 customary to designate, the X-ray diagnostic complex (RDK) 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 thermal energy in a large amount formed during the operation of the tube (otherwise the anode will quickly collapse). The cooling systems are transformer oil, air cooling with fans, or a combination of both.

The next block of the RDK - x-ray power supply, which includes a low-voltage transformer (a voltage of 10-15 volts is needed to warm up the cathode spiral), a high-voltage transformer (the tube itself requires a voltage of 40 to 120 kV), rectifiers (for efficient operation of the tube, a direct current is needed) 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; a diaphragm, which forms an X-ray beam according to the size of the removed organ; screening grating, which cuts off scattered rays arising in the patient's body in order to improve the sharpness of the image.

Tripod (s) are used to position the patient, and in some cases, the X-ray tube .. There are stands intended only for X-ray - X-ray, and universal, on which you can carry out both X-ray and fluoroscopy .. The X-ray diagnostic complex can include a different number of stands - one, two , three, which is determined by the complete set of the RDK, depending on the profile of the medical facility.

X-ray receiver (s)... The receivers used are a fluorescent screen for transillumination, an X-ray film (for radiography), amplifying screens (the film in a cassette is located between two amplifying screens), memory screens (for luminescent s. Computer radiography), an X-ray image amplifier - URI, detectors (when using digital technologies).

1.5. X-ray imaging technologies currently exist in three flavors:

direct analog,

indirect analog,

digital (digital).

With direct analog technology(Fig. 3) X-rays coming from the X-ray tube and passing through the investigated area of ​​the body are unevenly weakened, since along the X-ray beam, tissues and organs with different atomic

and specific gravity and various thicknesses. 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 fall into the zone of passage of the rays. This image is studied (interpreted) either directly on a fluorescent screen or on an X-ray film after it has been chemically treated. This technology is based on the classic (traditional) methods of X-ray diagnostics:

fluoroscopy (fluoroscopy abroad), radiography, linear tomography, fluorography.

Fluoroscopy is currently used mainly in the study of the gastrointestinal tract. Its advantages are a) the study of the functional characteristics of the investigated organ in real time 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 low resolution, so it is always combined with radiography ..

X-ray 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 roentgenogram), b) minimal radiation exposure, since the exposures during the acquisition of an image are mainly tenths and hundredths of a second, c ) the objectivity of obtaining information, since the roentgenogram can be analyzed by other, more qualified specialists, d) the possibility of studying the dynamics of the pathological process using roentgenograms taken at different periods of the illness, e) the roentgenogram is a legal document. The disadvantages of an X-ray image include incomplete topographic and functional characteristics of the examined organ.

Usually, in radiography, two projections are used, which are called standard: direct (front and back) and lateral (right and left). The projection is determined by the adherence of the film cassette to the body surface. For example, if the cassette for chest X-ray is located at the front surface of the body (in this case, the X-ray tube will be located at the back), then such a projection will be called a direct front; if the cassette is positioned along the posterior surface of the body, a direct posterior projection is obtained. In addition to standard projections, there are additional (atypical) projections, which are used in cases where in standard projections, due to anatomical, topographic and skialological features, we cannot get a complete picture of the anatomical characteristics of the organ under study. These are oblique projections (intermediate between the direct and lateral), axial (in this case, the X-ray beam is directed along the axis of the body or the organ under study), tangential (in this case, the X-ray beam is directed tangentially to the surface of the organ being removed). So, in oblique projections, hands, feet, sacroiliac joints, stomach, duodenum, etc. are removed, in the axial - 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 for X-ray diagnostics, different positions of the patient are used, which is determined by the research method or the patient's condition. The main position is orthoposition- vertical position of the patient in the horizontal direction of X-rays (used for X-ray and fluoroscopy of the lungs, stomach, fluorography). Other positions are trochoposition- horizontal position of the patient with the vertical course of the X-ray beam (used for X-ray of bones, intestines, kidneys, in the study of patients in serious condition) and lateroposition- horizontal position of the patient with the horizontal direction of X-rays (used with special research methods).

Linear tomography(X-ray 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), in the process of X-ray imaging, the X-ray tube moves over the surface of the examined organ at an angle of 30, 45 or 60 degrees for 2-3 seconds, and the cassette with the film at the same time moves in the opposite direction. The center of their rotation is the selected organ layer at a certain depth from its surface, the depth is