Modern methods of radiation diagnostics. Radiation diagnostics. Radiation diagnostic methods What applies to radiation diagnostics

METHODS OF RADIATION DIAGNOSTICS

METHODS OF RADIATION DIAGNOSTICS
The discovery of X-rays marked the beginning of a new era in medical diagnostics - the era of radiology. Subsequently, the arsenal of diagnostic tools was replenished with methods based on other types of ionizing and non-ionizing radiation (radioisotope, ultrasound methods, magnetic resonance imaging). Year after year, radiation research methods have been improved. Currently, they play a leading role in identifying and establishing the nature of most diseases.
At this stage of study, you have a (general) goal: to be able to interpret the principles of obtaining a medical diagnostic image using various radiation methods and the purpose of these methods.
Achieving a common goal is ensured by specific goals:
be able to:
1) interpret the principles of obtaining information using x-ray, radioisotope, ultrasound research methods and magnetic resonance imaging;
2) interpret the purpose of these research methods;
3) interpret the general principles of choosing the optimal radiation research method.
It is impossible to master the above goals without basic knowledge and skills taught at the Department of Medical and Biological Physics:
1) interpret the principles of production and physical characteristics of x-rays;
2) interpret radioactivity, the resulting radiation and their physical characteristics;
3) interpret the principles of producing ultrasonic waves and their physical characteristics;
5) interpret the phenomenon of magnetic resonance;
6) interpret the mechanism of biological action of various types of radiation.

1. X-ray research methods
X-ray examination still plays an important role in the diagnosis of human diseases. It is based on the varying degrees of absorption of X-rays by various tissues and organs of the human body. The rays are absorbed to a greater extent in the bones, to a lesser extent - in parenchymal organs, muscles and body fluids, even less - in fatty tissue and are almost not retained in gases. In cases where nearby organs equally absorb x-rays, they are not distinguishable during x-ray examination. In such situations, artificial contrast is resorted to. Consequently, X-ray examination can be carried out under conditions of natural contrast or artificial contrast. There are many different x-ray examination techniques.
The (general) goal of studying this section is to be able to interpret the principles of obtaining x-ray images and the purpose of various x-ray examination methods.
1) interpret the principles of image acquisition using fluoroscopy, radiography, tomography, fluorography, contrast research techniques, computed tomography;
2) interpret the purpose of fluoroscopy, radiography, tomography, fluorography, contrast research techniques, computed tomography.
1.1. X-ray
Fluoroscopy, i.e. obtaining a shadow image on a translucent (fluorescent) screen is the most accessible and technically simple research technique. It allows us to judge the shape, position and size of the organ and, in some cases, its function. By examining the patient in various projections and body positions, the radiologist obtains a three-dimensional understanding of the human organs and the identified pathology. The more radiation is absorbed by the organ or pathological formation being examined, the fewer rays hit the screen. Therefore, such an organ or formation casts a shadow on the fluorescent screen. And vice versa, if an organ or pathology is less dense, then more rays pass through them, and they hit the screen, causing it to become clear (glow).
The fluorescent screen glows faintly. Therefore, this study is carried out in a darkened room, and the doctor must adapt to the dark within 15 minutes. Modern X-ray machines are equipped with electron-optical converters that amplify and transmit the X-ray image to a monitor (TV screen).
However, fluoroscopy has significant disadvantages. Firstly, it causes significant radiation exposure. Secondly, its resolution is much lower than radiography.
These disadvantages are less pronounced when using X-ray television scanning. On the monitor you can change the brightness and contrast, thereby creating better viewing conditions. The resolution of such fluoroscopy is much higher, and the radiation exposure is less.
However, any screening is subjectivity. All physicians must rely on the expertise of the radiologist. In some cases, to objectify the study, the radiologist takes radiographs during the copy. For the same purpose, a video recording of the study using X-ray television scanning is also carried out.
1.2. Radiography
Radiography is a method of x-ray examination in which an image is obtained on x-ray film. The radiograph is a negative in relation to the image visible on the fluoroscopic screen. Therefore, light areas on the screen correspond to dark areas on the film (so-called highlights), and vice versa, dark areas correspond to light areas (shadows). Radiographs always produce a planar image with the summation of all points located along the ray path. To obtain a three-dimensional representation, it is necessary to take at least 2 photographs in mutually perpendicular planes. The main advantage of radiography is the ability to document detectable changes. In addition, it has significantly greater resolution than fluoroscopy.
In recent years, digital radiography has found application, in which special plates serve as X-ray receivers. After exposure to X-rays, a latent image of the object remains on them. When scanning plates with a laser beam, energy is released in the form of a glow, the intensity of which is proportional to the dose of absorbed x-ray radiation. This glow is recorded by a photodetector and converted into digital format. The resulting image can be displayed on a monitor, printed on a printer and saved in the computer's memory.
1.3. Tomography
Tomography is an x-ray method for layer-by-layer examination of organs and tissues. On tomograms, in contrast to x-rays, images of structures located in any one plane are obtained, i.e. the summation effect is eliminated. This is achieved through the simultaneous movement of the X-ray tube and film. The advent of computed tomography has sharply reduced the use of tomography.
1.4. Fluorography
Fluorography is usually used to conduct mass screening X-ray examinations, especially to detect lung pathology. The essence of the method is to photograph an image from an X-ray screen or an electron-optical amplifier screen onto photographic film. The frame size is usually 70x70 or 100x100 mm. On fluorograms, image details are visible better than with fluoroscopy, but worse than with radiography. The radiation dose received by the subject is also greater than with radiography.
1.5. Methods of X-ray examination under artificial contrast conditions
As mentioned above, a number of organs, especially hollow ones, absorb X-rays almost equally with the surrounding soft tissues. Therefore, they are not detected during X-ray examination. For visualization, they are artificially contrasted by injecting a contrast agent. Most often, various liquid iodide compounds are used for this purpose.
In some cases, it is important to obtain an image of the bronchi, especially in cases of bronchiectasis, congenital bronchial defects, or the presence of an internal bronchial or bronchopleural fistula. In such cases, a study using contrasting bronchial tubes - bronchography - helps to establish a diagnosis.
Blood vessels are not visible on conventional x-rays, with the exception of the pulmonary vessels. To assess their condition, angiography is performed - an X-ray examination of blood vessels using a contrast agent. During arteriography, a contrast agent is injected into the arteries, and during venography, into the veins.
When a contrast agent is injected into an artery, the image normally shows the phases of blood flow sequentially: arterial, capillary and venous.
Contrast studies are of particular importance when studying the urinary system.
There are excretory (excretory) urography and retrograde (ascending) pyelography. Excretory urography is based on the physiological ability of the kidneys to capture iodinated organic compounds from the blood, concentrate them and excrete them in the urine. Before the study, the patient needs appropriate preparation - bowel cleansing. The study is carried out on an empty stomach. Usually 20-40 ml of one of the urotropic substances is injected into the cubital vein. Then, after 3-5, 10-14 and 20-25 minutes, pictures are taken. If the secretory function of the kidneys is reduced, infusion urography is performed. In this case, the patient is slowly injected with a large amount of contrast agent (60–100 ml), diluted with a 5% glucose solution.
Excretory urography makes it possible to evaluate not only the pelvis, calyces, ureters, general shape and size of the kidneys, but also their functional state.
In most cases, excretory urography provides sufficient information about the renal-pelvic system. But still, in isolated cases, when this fails for some reason (for example, with a significant decrease or absence of kidney function), ascending (retrograde) pyelography is performed. To do this, a catheter is inserted into the ureter to the desired level, right up to the pelvis, a contrast agent (7-10 ml) is injected through it and pictures are taken.
To study the biliary tract, percutaneous transhepatic cholegraphy and intravenous cholecystocholangiography are currently used. In the first case, the contrast agent is injected through a catheter directly into the common bile duct. In the second case, the contrast administered intravenously in hepatocytes mixes with bile and is excreted with it, filling the bile ducts and gallbladder.
To assess the patency of the fallopian tubes, hysterosalpingography (metroslpingography) is used, in which a contrast agent is injected through the vagina into the uterine cavity using a special syringe.
A contrast X-ray technique for studying the ducts of various glands (mammary, salivary, etc.) is called ductography, and various fistulous tracts are called fistulography.
The digestive tract is studied under artificial contrast conditions using a suspension of barium sulfate, which the patient takes orally when examining the esophagus, stomach and small intestine, and is administered retrogradely when examining the colon. Assessment of the condition of the digestive tract is necessarily carried out by fluoroscopy with a series of radiographs. The study of the colon has a special name - irrigoscopy with irrigography.
1.6. CT scan
Computed tomography (CT) is a method of layer-by-layer X-ray examination, which is based on computer processing of multiple X-ray images of layers of the human body in cross section. Around the human body, multiple ionization or scintillation sensors are located around the circumference, capturing X-ray radiation that has passed through the subject.
Using a computer, the doctor can enlarge the image, highlight and enlarge its various parts, determine the dimensions and, what is very important, estimate the density of each area in conventional units. Information about tissue density can be presented in the form of numbers and histograms. To measure density, the Hounswild scale with a range of over 4000 units is used. The density of water is taken as the zero density level. The density of bones ranges from +800 to +3000 H units (Hounswild), parenchymal tissue - within 40-80 H units, air and gases - about -1000 H units.
Dense formations on CT are visible lighter and are called hyperdense, less dense formations are visible lighter and are called hypodense.
Contrast agents are also used to enhance contrast in CT scans. Intravenously administered iodide compounds improve the visualization of pathological foci in parenchymal organs.
An important advantage of modern computed tomographs is the ability to reconstruct a three-dimensional image of an object using a series of two-dimensional images.
2. Radionuclide research methods
The possibility of obtaining artificial radioactive isotopes has made it possible to expand the scope of application of radioactive tracers in various branches of science, including medicine. Radionuclide imaging is based on recording the radiation emitted by a radioactive substance inside the patient. Thus, what is common between X-ray and radionuclide diagnostics is the use of ionizing radiation.
Radioactive substances, called radiopharmaceuticals (RPs), can be used for both diagnostic and therapeutic purposes. All of them contain radionuclides - unstable atoms that spontaneously decay with the release of energy. An ideal radiopharmaceutical accumulates only in organs and structures targeted for imaging. The accumulation of radiopharmaceuticals can be caused, for example, by metabolic processes (the carrier molecule may be part of a metabolic chain) or by local perfusion of the organ. The ability to study physiological functions in parallel with the determination of topographic and anatomical parameters is the main advantage of radionuclide diagnostic methods.
For imaging, radionuclides that emit gamma rays are used, since alpha and beta particles have low tissue penetration.
Depending on the degree of radiopharmaceutical accumulation, a distinction is made between “hot” foci (with increased accumulation) and “cold” foci (with reduced or no accumulation).
There are several different methods for radionuclide testing.
The (general) goal of studying this section is to be able to interpret the principles of obtaining radionuclide images and the purpose of various radionuclide research methods.
To do this you need to be able to:
1) interpret the principles of image acquisition during scintigraphy, emission computed tomography (single-photon and positron);
2) interpret the principles of obtaining radiographic curves;
2) interpret the purpose of scintigraphy, emission computed tomography, radiography.
Scintigraphy is the most common radionuclide imaging method. The study is carried out using a gamma camera. Its main component is a disc-shaped scintillation crystal of sodium iodide of large diameter (about 60 cm). This crystal is a detector that captures the gamma radiation emitted by the radiopharmaceutical. In front of the crystal on the patient's side there is a special lead protective device - a collimator, which determines the projection of radiation onto the crystal. Parallel located holes on the collimator facilitate the projection onto the surface of the crystal of a two-dimensional display of the radiopharmaceutical distribution on a scale of 1:1.
Gamma photons hitting a scintillation crystal cause flashes of light (scintillation) on it, which are transmitted to a photomultiplier tube, which generates electrical signals. Based on the registration of these signals, a two-dimensional projection image of the radiopharmaceutical distribution is reconstructed. The final image can be presented in analogue format on photographic film. However, most gamma cameras can also create digital images.
Most scintigraphic studies are performed after intravenous administration of a radiopharmaceutical (the exception is inhalation of radioactive xenon during inhalation lung scintigraphy).
Lung perfusion scintigraphy uses 99mTc-labeled albumin macroaggregates or microspheres, which are retained in the smallest pulmonary arterioles. Images are obtained in direct (anterior and posterior), lateral and oblique projections.
Skeletal scintigraphy is performed using Tc99m-labeled diphosphonates that accumulate in metabolically active bone tissue.
To study the liver, hepatobiliscintigraphy and hepatoscintigraphy are used. The first method studies the biliary and biliary function of the liver and the condition of the biliary tract - their patency, storage and contractility of the gallbladder, and is a dynamic scintigraphic study. It is based on the ability of hepatocytes to absorb certain organic substances from the blood and transport them in the bile.
Hepatoscintigraphy - static scintigraphy - allows you to assess the barrier function of the liver and spleen and is based on the fact that stellate reticulocytes of the liver and spleen, purifying the plasma, phagocytose particles of the radiopharmaceutical colloid solution.
To study the kidneys, static and dynamic nephroscintigraphy is used. The essence of the method is to obtain an image of the kidneys by fixing nephrotropic radiopharmaceuticals in them.
2.2. Emission computed tomography
Single photon emission computed tomography (SPECT) is especially widely used in cardiology and neurology practice. The method is based on rotating a conventional gamma camera around the patient's body. Registration of radiation at various points of the circle allows one to reconstruct a sectional image.
Positron emission tomography (PET), unlike other radionuclide examination methods, is based on the use of positrons emitted by radionuclides. Positrons, having the same mass as electrons, are positively charged. The emitted positron immediately interacts with a nearby electron (a reaction called annihilation), resulting in two gamma-ray photons traveling in opposite directions. These photons are recorded by special detectors. The information is then transferred to a computer and converted into a digital image.
PET makes it possible to quantify the concentration of radionuclides and thereby study metabolic processes in tissues.
2.3. Radiography
Radiography is a method of assessing the function of an organ through external graphic recording of changes in radioactivity above it. Currently, this method is used mainly to study the condition of the kidneys - radiorenography. Two scintigraphic detectors record radiation over the right and left kidneys, the third – over the heart. A qualitative and quantitative analysis of the obtained renograms is carried out.
3. Ultrasound research methods
Ultrasound refers to sound waves with a frequency above 20,000 Hz, i.e. above the hearing threshold of the human ear. Ultrasound is used in diagnostics to obtain sectional images (slices) and measure the speed of blood flow. The most commonly used frequencies in radiology are in the range of 2-10 MHz (1 MHz = 1 million Hz). The ultrasound imaging technique is called sonography. The technology for measuring blood flow velocity is called Dopplerography.
The (general) goal of studying this section is to learn to interpret the principles of obtaining ultrasound images and the purpose of various ultrasound research methods.
To do this you need to be able to:
1) interpret the principles of obtaining information during sonography and Dopplerography;
2) interpret the purpose of sonography and Dopplerography.
3.1. Sonography
Sonography is carried out by passing a narrowly directed ultrasound beam through the patient's body. Ultrasound is generated by a special transducer, usually placed on the patient's skin over the anatomical area being examined. The sensor contains one or more piezoelectric crystals. Applying an electric potential to a crystal leads to its mechanical deformation, and mechanical compression of the crystal generates an electric potential (inverse and direct piezoelectric effect). Mechanical vibrations of the crystal generate ultrasound, which is reflected from various tissues and returns back to the transducer as an echo, generating mechanical vibrations of the crystal and therefore electrical signals of the same frequency as the echo. This is how the echo is recorded.
The intensity of the ultrasound gradually decreases as it passes through the patient's body tissue. The main reason for this is the absorption of ultrasound in the form of heat.
The unabsorbed portion of the ultrasound may be scattered or reflected back to the transducer by tissue as an echo. The ease with which ultrasound can pass through tissue depends partly on the mass of the particles (which determines the density of the tissue) and partly on the elastic forces that attract the particles to each other. The density and elasticity of a fabric together determine its so-called acoustic resistance.
The greater the change in acoustic impedance, the greater the reflection of ultrasound. A large difference in acoustic impedance exists at the soft tissue-gas interface, and almost all ultrasound is reflected from it. Therefore, a special gel is used to eliminate air between the patient's skin and the sensor. For the same reason, sonography does not allow visualization of the areas located behind the intestines (since the intestines are filled with gas) and the lung tissue containing air. There is also a relatively large difference in acoustic impedance between soft tissue and bone. Most bony structures thus preclude sonography.
The simplest way to display the recorded echo is the so-called A-mode (amplitude mode). In this format, echoes from different depths are represented as vertical peaks on a horizontal depth line. The strength of the echo determines the height or amplitude of each of the peaks shown. The A-mode format provides only a one-dimensional image of changes in acoustic impedance along the line of passage of the ultrasound beam and is used in diagnostics to an extremely limited extent (currently only for examining the eyeball).
An alternative to A-mode is M-mode (M - motion, movement). In this image, the depth axis on the monitor is oriented vertically. Various echoes are reflected as dots, the brightness of which is determined by the strength of the echo. These bright dots move across the screen from left to right, thereby creating bright curves that show the changing position of reflective structures over time. M-mode curves provide detailed information about the dynamic behavior of reflective structures located along the ultrasound beam. This method is used to obtain dynamic one-dimensional images of the heart (chamber walls and heart valve leaflets).
The most widely used mode in radiology is B-mode (B - brightness). This term means that the echo is depicted on the screen in the form of dots, the brightness of which is determined by the strength of the echo. B-mode provides a two-dimensional sectional anatomical image (slice) in real time. Images are created on the screen in the form of a rectangle or sector. The images are dynamic and can show phenomena such as respiratory movements, vascular pulsations, heartbeats and fetal movements. Modern ultrasound machines use digital technology. The analog electrical signal generated in the sensor is digitized. The final image on the monitor is represented by shades of gray scale. Lighter areas are called hyperechoic, darker areas are called hypo- and anechoic.
3.2. Dopplerography
Measuring blood flow velocity using ultrasound is based on the physical phenomenon that the frequency of sound reflected from a moving object changes compared to the frequency of the sent sound when received by a stationary receiver (Doppler effect).
During Doppler examination of blood vessels, an ultrasound beam generated by a special Doppler sensor is passed through the body. When this beam crosses a vessel or cardiac chamber, a small part of the ultrasound is reflected from red blood cells. The frequency of the echo waves reflected from these cells moving towards the sensor will be higher than the waves emitted by the sensor itself. The difference between the frequency of the received echo and the frequency of the ultrasound generated by the transducer is called the Doppler frequency shift, or Doppler frequency. This frequency shift is directly proportional to the speed of blood flow. When measuring flow, the frequency shift is continuously measured by the instrument; Most of these systems automatically convert the change in ultrasound frequency into relative blood flow velocity (for example, in m/s), using which the true blood flow velocity can be calculated.
The Doppler frequency shift usually lies within the frequency range audible to the human ear. Therefore, all Doppler equipment is equipped with speakers that allow you to hear the Doppler frequency shift. This "flow sound" is used both to detect vessels and to semi-quantitatively assess the nature of blood flow and its speed. However, such a sound display is of little use for accurate speed estimation. In this regard, a Doppler study provides a visual display of flow velocity - usually in the form of graphs or in the form of waves, where the y-axis is velocity and the abscissa is time. In cases where the blood flow is directed towards the sensor, the Dopplerogram graph is located above the isoline. If the blood flow is directed away from the sensor, the graph is located below the isoline.
There are two fundamentally different options for emitting and receiving ultrasound when using the Doppler effect: constant wave and pulsed. In continuous wave mode, the Doppler sensor uses two separate crystals. One crystal continuously emits ultrasound, while the other receives echoes, allowing very high speeds to be measured. Since velocities are simultaneously measured over a large range of depths, it is not possible to selectively measure velocities at a specific, predetermined depth.
In pulsed mode, the same crystal emits and receives ultrasound. Ultrasound is emitted in short pulses and echoes are recorded during the waiting periods between pulse transmissions. The time interval between the transmission of the pulse and the reception of the echo determines the depth at which velocities are measured. Pulsed Doppler can measure flow velocities in very small volumes (called control volumes) located along the ultrasound beam, but the highest velocities available for measurement are significantly lower than those that can be measured using continuous wave Doppler.
Currently, radiology uses so-called duplex scanners, which combine sonography and pulsed Dopplerography. With duplex scanning, the direction of the Doppler beam is superimposed on the B-mode image, and thus it is possible, using electronic markers, to select the size and location of the control volume along the direction of the beam. By moving the electronic cursor parallel to the direction of blood flow, the Doppler shift is automatically measured and the true flow velocity is displayed.
Color visualization of blood flow is a further development of duplex scanning. Colors are superimposed on the B-mode image to show the presence of moving blood. Fixed tissues are displayed in shades of a gray scale, and vessels are displayed in color (shades of blue, red, yellow, green, determined by the relative speed and direction of blood flow). The color image gives an idea of ​​the presence of various vessels and blood flows, but the quantitative information provided by this method is less accurate than with continuous wave or pulsed Doppler studies. Therefore, color visualization of blood flow is always combined with pulsed Doppler ultrasound.
4. Magnetic resonance research methods
The (general) goal of studying this section is to learn to interpret the principles of obtaining information from magnetic resonance research methods and interpret their purpose.
To do this you need to be able to:
1) interpret the principles of obtaining information from magnetic resonance imaging and magnetic resonance spectroscopy;
2) interpret the purpose of magnetic resonance imaging and magnetic resonance spectroscopy.
4.1. Magnetic resonance imaging
Magnetic resonance imaging (MRI) is the “youngest” of radiological methods. Magnetic resonance imaging scanners allow you to create cross-sectional images of any part of the body in three planes.
The main components of an MRI scanner are a strong magnet, a radio transmitter, a radio frequency receiving coil, and a computer. The inside of the magnet is a cylindrical tunnel large enough to fit an adult inside.
MR imaging uses magnetic fields ranging from 0.02 to 3 Tesla (tesla). Most MRI scanners have a magnetic field oriented parallel to the long axis of the patient's body.
When a patient is placed inside a magnetic field, all the hydrogen nuclei (protons) in his body turn in the direction of this field (like a compass needle aligned with the Earth's magnetic field). In addition, the magnetic axes of each proton begin to rotate around the direction of the external magnetic field. This rotational motion is called precession, and its frequency is called the resonant frequency.
Most protons are oriented parallel to the external magnetic field of the magnet ("parallel protons"). The rest precess antiparallel to the external magnetic field (“antiparallel protons”). As a result, the patient's tissues are magnetized and their magnetism is oriented exactly parallel to the external magnetic field. The amount of magnetism is determined by the excess of parallel protons. The excess is proportional to the strength of the external magnetic field, but it is always extremely small (on the order of 1-10 protons per 1 million). Magnetism is also proportional to the number of protons per unit volume of tissue, i.e. proton density. The enormous number (about 1022 per ml of water) of hydrogen nuclei contained in most tissues provides magnetism sufficient to induce an electric current in the receiving coil. But a prerequisite for inducing current in the coil is a change in the strength of the magnetic field. This requires radio waves. When short electromagnetic radiofrequency pulses are passed through the patient's body, the magnetic moments of all protons rotate by 90º, but only if the frequency of the radio waves is equal to the resonant frequency of the protons. This phenomenon is called magnetic resonance (resonance - synchronous oscillations).
The sensing coil is located outside the patient. The magnetism of the tissue induces an electrical current in the coil, and this current is called the MR signal. Tissues with large magnetic vectors induce strong signals and appear bright - hyperintense on the image, while tissues with small magnetic vectors induce weak signals and appear dark - hypointense on the image.
As stated earlier, contrast in MR images is determined by differences in the magnetic properties of tissues. The magnitude of the magnetic vector is primarily determined by the proton density. Objects with a small number of protons, such as air, induce a very weak MR signal and appear dark in the image. Water and other liquids should appear on MR images as having a very high proton density. However, depending on the mode used to obtain the MR image, fluids can produce either bright or dark images. The reason for this is that the contrast of the image is determined not only by the proton density. Other parameters also play a role; the two most important of them are T1 and T2.
Several MR signals are needed to reconstruct an image, i.e. Several radiofrequency pulses must be transmitted through the patient's body. In the interval between the application of pulses, the protons undergo two different relaxation processes - T1 and T2. The rapid attenuation of the induced signal is partly a result of T2 relaxation. Relaxation is a consequence of the gradual disappearance of magnetization. Liquids and fluid-like tissues typically have long T2 times, while solid tissues and substances typically have short T2 times. The longer T2, the brighter (lighter) the fabric looks, i.e. gives a more intense signal. MR images in which contrast is predominantly determined by differences in T2 are called T2-weighted images.
T1 relaxation is a slower process compared to T2 relaxation, which consists in the gradual alignment of individual protons along the direction of the magnetic field. In this way, the state preceding the radiofrequency pulse is restored. The T1 value largely depends on the size of the molecules and their mobility. As a rule, T1 is minimal for tissues with molecules of medium size and average mobility, for example, adipose tissue. Smaller, more mobile molecules (as in liquids) and larger, less mobile molecules (as in solids) have a higher T1 value.
Tissues with minimal T1 will induce the strongest MR signals (eg, adipose tissue). This way, these fabrics will be bright in the image. Tissues with maximum T1 will accordingly induce the weakest signals and will be dark. MR images in which contrast is predominantly determined by differences in T1 are called T1-weighted images.
Differences in the strength of MR signals obtained from different tissues immediately after exposure to a radiofrequency pulse reflect differences in proton density. In proton density-weighted images, tissues with the highest proton density induce the strongest MR signal and appear brightest.
Thus, in MRI there is much more opportunity to change the contrast of images than in alternative techniques such as computed tomography and sonography.
As mentioned, RF pulses only induce MR signals if the pulse frequency exactly matches the resonant frequency of the protons. This fact makes it possible to obtain MR signals from a pre-selected thin layer of tissue. Special coils create small additional fields so that the strength of the magnetic field increases linearly in one direction. The resonant frequency of protons is proportional to the strength of the magnetic field, so it will also increase linearly in the same direction. By delivering radiofrequency pulses with a predetermined narrow frequency range, it is possible to record MR signals only from a thin layer of tissue, the range of resonant frequencies of which corresponds to the frequency range of the radio pulses.
In MR imaging, the signal intensity of static blood is determined by the selected “weighting” of the image (in practice, static blood is in most cases visualized as bright). In contrast, circulating blood practically does not generate an MR signal, thus being an effective “negative” contrast agent. The lumens of blood vessels and the chambers of the heart appear dark and are clearly demarcated from the brighter stationary tissues surrounding them.
There are, however, special MRI techniques that make it possible to display circulating blood as bright and stationary tissue as dark. They are used in MR angiography (MRA).
Contrast agents are widely used in MRI. All of them have magnetic properties and change the intensity of the image of the tissues in which they are located, shortening the relaxation (T1 and/or T2) of the protons surrounding them. The most commonly used contrast agents contain the paramagnetic metal ion gadolinium (Gd3+) bound to a carrier molecule. These contrast agents are administered intravenously and are distributed throughout the body similar to water-soluble X-ray contrast agents.
4.2. Magnetic resonance spectroscopy
An MR unit with a magnetic field strength of at least 1.5 Tesla allows for magnetic resonance spectroscopy (MRS) in vivo. MRS is based on the fact that atomic nuclei and molecules in a magnetic field cause local changes in the strength of the field. The nuclei of atoms of the same type (for example, hydrogen) have resonant frequencies that vary slightly depending on the molecular arrangement of the nuclei. The MR signal induced after exposure to a radiofrequency pulse will contain these frequencies. As a result of frequency analysis of a complex MR signal, a frequency spectrum is created, i.e. amplitude-frequency characteristic showing the frequencies present in it and the corresponding amplitudes. Such a frequency spectrum can provide information about the presence and relative concentration of different molecules.
Several types of nuclei can be used in MRS, but the two most frequently studied are hydrogen (1H) and phosphorus (31P) nuclei. A combination of MR imaging and MR spectroscopy is possible. In vivo MRS allows one to obtain information about important metabolic processes in tissues, but this method is still far from routine use in clinical practice.

5. General principles for choosing the optimal radiation research method
The purpose of studying this section corresponds to its name - to learn to interpret the general principles of choosing the optimal radiation research method.
As shown in the previous sections, there are four groups of radiation research methods - x-ray, ultrasound, radionuclide and magnetic resonance. To effectively use them in diagnosing various diseases, a physician must be able to choose from this variety of methods the optimal one for a specific clinical situation. In this case, one should be guided by the following criteria:
1) informativeness of the method;
2) the biological effect of radiation used in this method;
3) accessibility and cost-effectiveness of the method.

Information content of radiation research methods, i.e. their ability to provide the doctor with information about the morphological and functional state of various organs is the main criterion for choosing the optimal radiation research method and will be covered in detail in the sections of the second part of our textbook.
Information about the biological effect of radiation used in one or another radiation research method refers to the initial level of knowledge and skills mastered in the course of medical and biological physics. However, given the importance of this criterion when prescribing a radiation method to a patient, it should be emphasized that all x-ray and radionuclide methods are associated with ionizing radiation and, accordingly, cause ionization in the tissues of the patient’s body. If these methods are carried out correctly and the principles of radiation safety are observed, they do not pose a threat to human health and life, because all changes caused by them are reversible. At the same time, their unreasonably frequent use can lead to an increase in the total radiation dose received by the patient, an increase in the risk of tumors and the development of local and general radiation reactions in his body, which you will learn in detail from the courses of radiation therapy and radiation hygiene.
The main biological effect of ultrasound and magnetic resonance imaging is heating. This effect is more pronounced with MRI. Therefore, the first three months of pregnancy are regarded by some authors as an absolute contraindication for MRI due to the risk of fetal overheating. Another absolute contraindication to the use of this method is the presence of a ferromagnetic object, the movement of which can be dangerous for the patient. The most important are intracranial ferromagnetic clips on blood vessels and intraocular ferromagnetic foreign bodies. The greatest potential danger associated with them is bleeding. The presence of pacemakers is also an absolute contraindication for MRI. The functioning of these devices may be affected by the magnetic field and, furthermore, electrical currents may be induced in their electrodes that can heat the endocardium.
The third criterion for choosing the optimal research method - accessibility and cost-effectiveness - is less important than the first two. However, when referring a patient for examination, any doctor should remember that he should start with more accessible, common and less expensive methods. Compliance with this principle is, first of all, in the interests of the patient, who will be diagnosed in a shorter time.
Thus, when choosing the optimal radiation research method, the doctor should mainly be guided by its information content, and from several methods that are similar in information content, prescribe the one that is more accessible and has less impact on the patient’s body.

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 purpose of preventing and diagnosing diseases.

The role of radiation diagnostics

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 imaging scanners.

It is known that most (about 80%) diseases are diagnosed using radiation diagnostic devices: ultrasound, X-ray, thermography, 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. Due to the worsening problem of tuberculosis, the role of preventive fluorographic examinations has recently especially increased in order to diagnose this disease in the early stages .

There is another reason that made the problem of X-ray diagnostics relevant. The share of the latter in the formation of the collective radiation dose 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 include X-ray image intensifiers, but in Ukraine today there are less than 10% of the existing fleet. And it is very impressive: in medical institutions of Ukraine, as of January 1998, there were over 2,460 x-ray departments and rooms, 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.

History of the development of radiation diagnostics

Over the last century, radiation diagnostics has undergone rapid development, transformation of methods and equipment, has gained a strong position in diagnostics and continues to amaze with its truly inexhaustible capabilities.
The ancestor 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 study were the skeletal system and respiratory organs.
In 1921, a technique for radiography at a given depth—layer by layer—was developed, and tomography came into widespread practice, significantly enriching diagnostics.

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

This stage is characterized by the following features:

1. Transition from one type of radiation (X-ray) used to obtain an image to another:

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

1. Using a computer for signal processing and image construction.
2. Transition from a single image to scanning (sequential recording of signals from different points).

The ultrasound research method came to medicine much later than the X-ray method, 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 its high information content. In a short time, we have gone from grey-scale scanning to techniques with color images and the ability to study the vascular bed - Dopplerography.

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

Send your good work in the knowledge base is simple. Use the form below

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

Posted on http://allbest.ru

Introduction

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 purpose of preventing and recognizing diseases.

All treatments used in radiation diagnostics are divided into non-ionizing and ionizing.

Non-ionizing radiation is electromagnetic radiation of various frequencies that does not cause ionization of atoms and molecules, i.e. their disintegration into oppositely charged particles - ions. These include thermal (infrared - IR) radiation and resonant radiation, which occurs in an object (the human body) placed in a stable magnetic field under the influence of high-frequency electromagnetic pulses. Also include ultrasonic waves, which are elastic vibrations of the medium.

Ionizing radiation can ionize atoms of the environment, including atoms that make up human tissue. All these radiations are divided into two groups: quantum (i.e., consisting of photons) and corpuscular (consisting of particles). This division is largely arbitrary, since any radiation has a dual nature and, under certain conditions, exhibits either the properties of a wave or the properties of a particle. Quantum ionizing radiation includes bremsstrahlung (X-ray) radiation and gamma radiation. Corpuscular radiation includes beams of electrons, protons, neutrons, mesons and other particles.

To obtain a differentiated image of tissues that absorb radiation approximately equally, artificial contrast is used.

There are two ways to contrast organs. One of them is the direct (mechanical) introduction of a contrast agent into the organ cavity - into the esophagus, stomach, intestines, into the lacrimal or salivary ducts, bile ducts, urinary tracts, into the uterine cavity, bronchi, blood and lymphatic vessels or into the cellular space, surrounding the organ under study (for example, into the retroperitoneal tissue surrounding the kidneys and adrenal glands), or by puncture into the parenchyma of the organ.

The second contrast method is based on the ability of some organs to absorb a substance introduced into the body from the blood, concentrate and secrete it. This principle - concentration and elimination - is used in X-ray contrasting of the excretory system and biliary tract.

The basic requirements for radiocontrast substances are obvious: creation of high image contrast, harmlessness when introduced into the patient’s body, and rapid removal from the body.

The following contrast agents are currently used in radiology practice.

1. Preparations of barium sulfate (BaSO4). An aqueous suspension of barium sulfate is the main preparation for studying the digestive canal. It is insoluble in water and digestive juices and is harmless. Used as a suspension in a concentration of 1:1 or higher - up to 5:1. To give the drug additional properties (slowing down the sedimentation of solid barium particles, increasing adhesion to the mucous membrane), chemically active substances (tannin, sodium citrate, sorbitol, etc.) are added to the aqueous suspension; gelatin and food cellulose are added to increase viscosity. There are ready-made official preparations of barium sulfate that meet all of the above requirements.

2. Iodine-containing solutions of organic compounds. This is a large group of drugs, which are mainly derivatives of certain aromatic acids - benzoic, adipic, phenylpropionic, etc. The drugs are used for contrasting blood vessels and heart cavities. These include, for example, urografin, trazograf, triombrast, etc. These drugs are secreted by the urinary system, so they can be used to study the pyelocaliceal complex of the kidneys, ureters, and bladder. Recently, a new generation of iodine-containing organic compounds has appeared - nonionic (first monomers - Omnipaque, Ultravist, then dimers - iodixanol, iotrolan). Their osmolarity is significantly lower than ionic ones, and approaches the osmolarity of blood plasma (300 my). As a result, they are significantly less toxic than ionic monomers. A number of iodine-containing drugs are captured from the blood by the liver and excreted in the bile, so they are used for contrasting the biliary tract. To contrast the gallbladder, iodide preparations are used that are absorbed in the intestine (cholevid).

3. Iodized oils. These preparations are an emulsion of iodine compounds in vegetable oils (peach, poppy). They have gained popularity as tools used in the study of bronchi, lymphatic vessels, uterine cavity, and fistula tracts. Ultra-liquid iodized oils (lipoidol) are especially good, which are characterized by high contrast and have little irritation to tissues. Iodine-containing drugs, especially the ionic group, can cause allergic reactions and have a toxic effect on the body

General allergic manifestations are observed in the skin and mucous membranes (conjunctivitis, rhinitis, urticaria, swelling of the mucous membrane of the larynx, bronchi, trachea), cardiovascular system (low blood pressure, collapse), central nervous system (convulsions, sometimes paralysis), kidneys (violation of excretory function). These reactions are usually transient, but can reach a high degree of severity and even lead to death. In this regard, before introducing iodine-containing drugs into the blood, especially high-osmolar ones from the ionic group, it is necessary to conduct a biological test: carefully inject 1 ml of a radiocontrast drug intravenously and wait 2-3 minutes, carefully monitoring the patient’s condition. Only in the absence of an allergic reaction is the main dose administered, which varies from 20 to 100 ml in different studies.

4. Gases (nitrous oxide, carbon dioxide, ordinary air). Only carbon dioxide can be used for injection into the blood due to its high solubility. When administered into body cavities and cellular spaces, nitrous oxide is also used to avoid gas embolism. It is permissible to introduce ordinary air into the digestive canal.

1.X-ray methods

X-rays were discovered on November 8, 1895. Professor of physics at the University of Würzburg Wilhelm Conrad Roentgen (1845-1923).

The X-ray method is a method of studying the structure and function of various organs and systems, based on qualitative and/or quantitative analysis of a beam of X-ray radiation passed through the human body. X-ray radiation generated in the anode of the X-ray tube is directed at the patient, in whose body it is partially absorbed and scattered, and partially passes through

X-rays are one of the types of electromagnetic waves with a length of approximately 80 to 10~5 nm, which occupy a place in the general wave spectrum between ultraviolet rays and -rays. The speed of propagation of X-rays is equal to the speed of light 300,000 km/s.

X-rays are formed at the moment of collision of a stream of accelerated electrons with the anode substance. When electrons interact with a target, 99% of their kinetic energy is converted into thermal energy and only 1% into x-ray radiation. An X-ray tube consists of a glass cylinder into which 2 electrodes are soldered: a cathode and an anode. The air has been pumped out of the glass balloon: the movement of electrons from the cathode to the anode is possible only under conditions of relative vacuum. The cathode has a filament, which is a tightly twisted tungsten spiral. When electric current is applied to the filament, electron emission occurs, in which electrons are separated from the filament and form an electron cloud near the cathode. This cloud is concentrated at the focusing cup of the cathode, which sets the direction of electron motion. The cup is a small depression in the cathode. The anode, in turn, contains a tungsten metal plate onto which electrons are focused - this is where X-rays are produced. There are 2 transformers connected to the electronic tube: a step-down and a step-up. A step-down transformer heats the tungsten coil with low voltage (5-15 volts), resulting in electron emission. A step-up, or high-voltage, transformer fits directly to the cathode and anode, which are supplied with a voltage of 20-140 kilovolts. Both transformers are placed in the high-voltage block of the X-ray machine, which is filled with transformer oil, which ensures cooling of the transformers and their reliable insulation. After an electron cloud has been formed using a step-down transformer, the step-up transformer is turned on, and high-voltage voltage is applied to both poles of the electrical circuit: a positive pulse to the anode, and a negative pulse to the cathode. Negatively charged electrons are repelled from the negatively charged cathode and tend to the positively charged anode - due to this potential difference, a high speed of movement is achieved - 100 thousand km/s. At this speed, electrons bombard the tungsten plate of the anode, completing an electrical circuit, resulting in x-rays and thermal energy. X-ray radiation is divided into bremsstrahlung and characteristic. Bremsstrahlung occurs due to a sharp slowdown in the speed of electrons emitted by a tungsten helix. Characteristic radiation occurs at the moment of restructuring of the electronic shells of atoms. Both of these types are formed in the X-ray tube at the moment of collision of accelerated electrons with atoms of the anode substance. The emission spectrum of an X-ray tube is a superposition of bremsstrahlung and characteristic X-rays.

Properties of X-rays.

1. Penetrating ability; Due to their short wavelength, X-rays can penetrate objects that are impenetrable to visible light.

2. Ability to be absorbed and dispersed; When absorbed, part of the X-rays with the longest wavelength disappears, completely transferring their energy to the substance. When scattered, it deviates from the original direction and does not carry useful information. Some of the rays pass completely through the object with a change in their characteristics. Thus, an image is formed.

3. Cause fluorescence (glow). This phenomenon is used to create special luminous screens for the purpose of visual observation of X-ray radiation, sometimes to enhance the effect of X-rays on a photographic plate.

4. Have a photochemical effect; allows you to record images on photosensitive materials.

5. Cause ionization of the substance. This property is used in dosimetry to quantify the effect of this type of radiation.

6. They spread in a straight line, which makes it possible to obtain an X-ray image that follows the shape of the material being studied.

7. Capable of polarization.

8. X-rays are characterized by diffraction and interference.

9. They are invisible.

Types of X-ray methods.

1.X-ray (X-ray).

Radiography is a method of x-ray examination in which a fixed x-ray image of an object is obtained on a solid medium. Such media can be X-ray film, photographic film, digital detector, etc.

Film radiography is performed either on a universal X-ray machine or on a special stand designed only for this type of research. The inner walls of the cassette are covered with intensifying screens, between which the X-ray film is placed.

Intensifying screens contain a phosphor, which glows under the influence of X-ray radiation and, thus acting on the film, enhances its photochemical effect. The main purpose of intensifying screens is to reduce exposure, and therefore radiation exposure, to the patient.

Depending on the purpose, intensifying screens are divided into standard, fine-grained (they have a fine phosphor grain, reduced light output, but very high spatial resolution), which are used in osteology, and high-speed (with large phosphor grains, high light output, but reduced resolution), which used when conducting research in children and fast-moving objects, such as the heart.

The body part being examined is placed as close to the cassette as possible to reduce projection distortion (basically magnification) that occurs due to the divergent nature of the X-ray beam. In addition, this arrangement provides the necessary image sharpness. The emitter is installed so that the central beam passes through the center of the body part being removed and is perpendicular to the film. In some cases, for example, when examining the temporal bone, an inclined position of the emitter is used.

Radiography can be performed in a vertical, horizontal and inclined position of the patient, as well as in a lateral position. Filming in different positions allows us to judge the displacement of organs and identify some important diagnostic signs, such as the spread of fluid in the pleural cavity or fluid levels in intestinal loops.

Technique for recording X-ray radiation.

Scheme 1. Conditions for conventional radiography (I) and teleradiography (II): 1 - X-ray tube; 2 - beam of X-rays; 3 - object of study; 4 - film cassette.

Obtaining an image is based on the attenuation of X-ray radiation as it passes through various tissues and its subsequent recording on X-ray sensitive film. As a result of passing through formations of different densities and compositions, the radiation beam is scattered and decelerated, and therefore an image of varying degrees of intensity is formed on the film. As a result, the film produces an averaged, summation image of all tissues (shadow). It follows from this that in order to obtain an adequate x-ray, it is necessary to study radiologically heterogeneous formations.

An image that shows a part of the body (head, pelvis, etc.) or an entire organ (lungs, stomach) is called a survey. Images in which an image of the part of the organ of interest to the doctor is obtained in the optimal projection, most advantageous for studying a particular detail, are called targeted. Pictures can be single or serial. The series may consist of 2-3 radiographs, which record different conditions of the organ (for example, gastric peristalsis).

An X-ray photograph is a negative in relation to the image visible on a fluorescent screen when transilluminated. Therefore, transparent areas on an x-ray are called dark (“darkenings”), and dark ones are called light (“clearances”). The X-ray image is summative, planar. This circumstance leads to the loss of the image of many elements of the object, since the image of some parts is superimposed on the shadow of others. This leads to the basic rule of x-ray examination: examination of any part of the body (organ) must be carried out in at least two mutually perpendicular projections - frontal and lateral. In addition to them, images in oblique and axial (axial) projections may be needed.

For X-ray image analysis, an X-ray image is recorded on an illuminating device with a bright screen - a negatoscope.

Previously, selenium plates were used as X-ray image receivers, which were charged on special devices before exposure. The image was then transferred to writing paper. The method is called electroradiography.

In electron-optical digital radiography, the X-ray image obtained in a television camera, after amplification, is transferred to an analog-digital one. All electrical signals carrying information about the object under study are converted into a series of numbers. The digital information then enters the computer, where it is processed according to pre-compiled programs. Using a computer, you can improve the quality of the image, increase its contrast, clear it of noise, and highlight details or contours of interest to the doctor.

The advantages of digital radiography include: high image quality, reduced radiation exposure, the ability to save images on magnetic media with all the ensuing consequences: ease of storage, the ability to create organized archives with quick access to data and transmit images over distances - like inside a hospital, and beyond.

Disadvantages of radiography: the presence of ionizing radiation that can have a harmful effect on the patient; The information content of classical radiography is significantly lower than such modern medical imaging methods as CT, MRI, etc. Conventional X-ray images reflect the projection layering of complex anatomical structures, that is, their summation X-ray shadow, in contrast to the layer-by-layer series of images obtained by modern tomographic methods. Without the use of contrast agents, radiography is not informative enough to analyze changes in soft tissues that differ little in density (for example, when studying the abdominal organs).

2. Fluoroscopy (x-ray scanning)

Fluoroscopy is a method of x-ray examination in which an image of an object is obtained on a luminous (fluorescent) screen. The intensity of the glow at each point of the screen is proportional to the number of X-ray quanta that hit it. On the side facing the doctor, the screen is covered with lead glass, protecting the doctor from direct exposure to X-ray radiation.

X-ray television transmission is used as an improved method of fluoroscopy. It is performed using an X-ray image intensifier (IIA), which includes an X-ray electron-optical converter (X-ray electron-optical converter) and a closed-circuit television system.

X-ray scope

The REOP is a vacuum flask, inside of which, on one side, there is an X-ray fluorescent screen, and on the opposite side, a cathodoluminescent screen. An electric accelerating field with a potential difference of about 25 kV is applied between them. The light image that appears during transillumination on the fluorescent screen is transformed at the photocathode into a stream of electrons. Under the influence of the accelerating field and as a result of focusing (increasing the flux density), the energy of the electrons increases significantly - several thousand times. Getting on the cathodoluminescent screen, the electron flow creates a visible image on it, similar to the original one, but very bright.

This image is transmitted through a system of mirrors and lenses to a transmitting television tube - a vidicon. The electrical signals arising in it are sent for processing to the television channel unit, and then to the screen of a video control device or, more simply, to the TV screen. If necessary, the image can be recorded using a video recorder.

3. Fluorography

Fluorography is a method of x-ray examination that involves photographing an image from an x-ray fluorescent screen or an electron-optical converter screen onto small-format photographic film.

Fluorography provides a reduced image of an object. There are small-frame (for example, 24×24 mm or 35×35 mm) and large-frame (in particular, 70×70 mm or 100×100 mm) techniques. The latter approaches radiography in diagnostic capabilities. Fluorography is used mainly to study the chest organs, mammary glands, and skeletal system.

With the most common method of fluorography, reduced X-ray images - fluorograms - are obtained using a special X-ray machine - a fluorograph. This machine has a fluorescent screen and an automatic roll film movement mechanism. Photographing the image is carried out using a camera on this roll film with a frame size of 70X70 or 100X 100 mm.

On fluorograms, image details are captured better than with fluoroscopy or X-ray television transmission, but slightly worse (4-5%) compared to conventional radiographs.

For verification studies, fluorographs of stationary and mobile types are used. The first are placed in clinics, medical units, dispensaries, and hospitals. Mobile fluorographs are mounted on automobile chassis or in railway cars. Shooting in both fluorographs is carried out on roll film, which is then developed in special tanks. Special gastrofluorographs have been created to examine the esophagus, stomach and duodenum.

Finished fluorograms are examined with a special flashlight - a fluoroscope, which magnifies the image. From the general population of those examined, individuals are selected whose fluorograms indicate pathological changes. They are sent for additional examination, which is carried out on x-ray diagnostic units using all the necessary x-ray research methods.

Important advantages of fluorography are the ability to examine a large number of people in a short time (high throughput), cost-effectiveness, ease of storing fluorograms, and allows early detection of minimal pathological changes in organs.

The use of fluorography turned out to be most effective for identifying hidden lung diseases, primarily tuberculosis and cancer. The frequency of verification surveys is determined taking into account the age of people, the nature of their work activity, local epidemiological conditions

4. Tomography

Tomography (from the Greek tomos - layer) is a method of layer-by-layer x-ray examination.

In tomography, due to the movement of the X-ray tube at a certain speed during shooting, the film produces a sharp image of only those structures that are located at a certain, predetermined depth. Shadows of organs and formations located at a shallower or greater depth are “blurred” and do not overlap the main image. Tomography facilitates the identification of tumors, inflammatory infiltrates and other pathological formations.

The tomography effect is achieved through continuous movement during imaging of two of the three components of the X-ray emitter-patient-film system. Most often, the emitter and film move while the patient remains motionless. In this case, the emitter and the film move in an arc, a straight line or a more complex trajectory, but always in opposite directions. With such a movement, the image of most of the details on the x-ray image turns out to be unclear, smeared, and the image is sharp only of those formations that are located at the level of the center of rotation of the emitter-film system.

Structurally, tomographs are made in the form of additional stands or a special device for a universal rotating stand. If you change the level of the center of rotation of the emitter-film system on the tomograph, then the level of the selected layer will change. The thickness of the selected layer depends on the amplitude of movement of the above-mentioned system: the larger it is, the thinner the tomographic layer will be. The usual value of this angle is from 20 to 50°. If a very small displacement angle is chosen, on the order of 3-5°, then an image of a thick layer, essentially an entire zone, is obtained.

Types of tomography

Linear tomography (classical tomography) is a method of x-ray examination with which you can take a picture of a layer lying at a certain depth of the object under study. This type of research is based on the movement of two of three components (X-ray tube, X-ray film, object of study). The system closest to modern linear tomography was proposed by Maer; in 1914, he proposed moving the X-ray tube parallel to the patient’s body.

Panoramic tomography is a method of x-ray examination with which you can obtain an image of a curved layer lying at a certain depth of the object under study.

In medicine, panoramic tomography is used to study the facial skull, primarily in diagnosing diseases of the dental system. Using the movement of the X-ray emitter and film cassette along special trajectories, an image in the form of a cylindrical surface is isolated. This allows you to obtain an image showing all the patient’s teeth, which is necessary for prosthetics and is useful for periodontal disease, in traumatology and a number of other cases. Diagnostic studies are performed using pantomographic dental devices.

Computed tomography is a layer-by-layer X-ray examination based on computer reconstruction of the image obtained by circular scanning of an object (Pє English scan - scan quickly) with a narrow beam of X-ray radiation.

CT machine

Computed tomography (CT) images are produced using a narrow, rotating beam of X-rays and a system of sensors arranged in a circle called a gantry. Passing through tissue, radiation is attenuated according to the density and atomic composition of these tissues. On the other side of the patient there is a circular system of X-ray sensors, each of which converts radiation energy into electrical signals. After amplification, these signals are converted into a digital code, which is stored in the computer's memory. The recorded signals reflect the degree of attenuation of the X-ray beam in any one direction.

Rotating around the patient, the X-ray emitter “views” his body from different angles, for a total of 360°. By the end of the rotation of the emitter, all signals from all sensors are recorded in the computer memory. The duration of rotation of the emitter in modern tomographs is very short, only 1-3 s, which makes it possible to study moving objects.

Along the way, the tissue density in individual areas is determined, which is measured in conventional units - Hounsfield units (HU). The density of water is taken as zero. Bone density is +1000 HU, air density is -1000 HU. All other tissues of the human body occupy an intermediate position (usually from 0 to 200-300 HU).

Unlike a conventional X-ray, which best shows bones and air-bearing structures (lungs), computed tomography (CT) also clearly shows soft tissues (brain, liver, etc.), this makes it possible to diagnose diseases in the early stages , for example, to detect a tumor while it is still small and amenable to surgical treatment.

With the advent of spiral and multispiral tomographs, it became possible to perform computed tomography of the heart, blood vessels, bronchi, and intestines.

Benefits of X-ray computed tomography (CT):

H high tissue resolution - allows you to evaluate the change in the radiation attenuation coefficient within 0.5% (in conventional radiography - 10-20%);

There is no overlap of organs and tissues - there are no closed areas;

H allows you to assess the ratio of organs in the area under study

A package of application programs for processing the resulting digital image allows you to obtain additional information.

Disadvantages of computed tomography (CT):

There is always a small risk of developing cancer from overexposure. However, the possibility of an accurate diagnosis outweighs this minimal risk.

There are no absolute contraindications to computed tomography (CT). Relative contraindications to computed tomography (CT): pregnancy and early childhood, which is associated with radiation exposure.

Types of computed tomography

Spiral X-ray computed tomography (SCT).

The principle of operation of the method.

Spiral scanning consists of rotating the X-ray tube in a spiral and simultaneously moving the table with the patient. Spiral CT differs from conventional CT in that the speed of table movement can be different depending on the purpose of the study. At higher speeds, the scanning area is larger. The method significantly reduces procedure time and reduces radiation exposure to the patient's body.

The principle of operation of spiral computed tomography on the human body. Images are obtained using the following operations: The required width of the X-ray beam is set in the computer; The organ is scanned with an X-ray beam; Sensors catch pulses and convert them into digital information; Information is processed by computer; The computer displays information on the screen in the form of an image.

Advantages of spiral computed tomography. Increasing the speed of the scanning process. The method increases the area of ​​study in a shorter time. Reducing the radiation dose to the patient. The ability to obtain a clearer and higher-quality image and detect even the most minimal changes in body tissues. With the advent of new generation tomographs, the study of complex areas has become accessible.

Spiral computed tomography of the brain shows the vessels and all components of the brain with detailed accuracy. Also a new achievement was the ability to study the bronchi and lungs.

Multislice computed tomography (MSCT).

In multislice tomographs, X-ray sensors are located around the entire circumference of the installation and the image is obtained in one rotation. Thanks to this mechanism, there is no noise, and the procedure time is reduced compared to the previous type. This method is convenient when examining patients who cannot remain motionless for a long time (small children or patients in critical condition). Multispiral is an improved type of spiral. Spiral and multispiral tomographs make it possible to perform studies of blood vessels, bronchi, heart and intestines.

Operating principle of multislice computed tomography. Advantages of the multislice CT method.

H High resolution, allowing even minor changes to be seen in detail.

H Speed ​​of research. Scanning does not exceed 20 seconds. The method is good for patients who are unable to remain motionless for a long time and who are in critical condition.

Ch Unlimited opportunities for research on patients in serious condition who need constant contact with a doctor. The ability to construct two-dimensional and three-dimensional images that allow you to obtain the most complete information about the organs being studied.

No noise during scanning. Thanks to the device’s ability to complete the process in one revolution.

Ch Radiation dose has been reduced.

CT angiography

CT angiography provides a layer-by-layer series of images of blood vessels; Based on the data obtained, a three-dimensional model of the circulatory system is built through computer post-processing with 3D reconstruction.

5. Angiography

Angiography is a method of contrast X-ray examination of blood vessels. Angiography studies the functional state of blood vessels, circuitous blood flow and the extent of the pathological process.

Angiogram of cerebral vessels.

Arteriogram

Arteriography is performed by puncture of the vessel or its catheterization. The puncture is used to study the carotid arteries, arteries and veins of the lower extremities, the abdominal aorta and its large branches. However, the main method of angiography at present is, of course, catheterization of the vessel, which is performed according to the technique developed by the Swedish doctor Seldinger

The most common procedure is catheterization of the femoral artery.

All manipulations during angiography are carried out under X-ray television control. A contrast agent is injected under pressure through a catheter into the artery being examined using an automatic syringe (injector). At the same moment, high-speed X-ray imaging begins. The photographs are developed immediately. Once the test is successful, the catheter is removed.

The most common complication of angiography is the development of a hematoma in the catheterization area, where swelling appears. A severe but rare complication is peripheral artery thromboembolism, the occurrence of which is indicated by limb ischemia.

Depending on the purpose and site of administration of the contrast agent, aortography, coronary angiography, carotid and vertebral arteriography, celiacography, mesentericography, etc. are distinguished. To perform all these types of angiography, the end of a radiopaque catheter is inserted into the vessel being examined. The contrast agent accumulates in the capillaries, causing the intensity of the shadow of the organs supplied by the vessel under study to increase.

Venography can be performed by direct and indirect methods. In direct venography, a contrast agent is introduced into the blood by venipuncture or venosection.

Indirect contrasting of veins is carried out in one of three ways: 1) by introducing a contrast agent into the arteries, from which it reaches the veins through the capillary system; 2) injection of a contrast agent into the bone marrow space, from which it enters the corresponding veins; 3) by introducing a contrast agent into the parenchyma of an organ by puncture, while the images show the veins draining blood from this organ. There are a number of special indications for venography: chronic thrombophlebitis, thromboembolism, post-thrombophlebitic changes in the veins, suspected abnormal development of venous trunks, various disorders of venous blood flow, including due to insufficiency of the valvular apparatus of the veins, wounds of the veins, conditions after surgical interventions on the veins.

A new technique for x-ray examination of blood vessels is digital subtraction angiography (DSA). It is based on the principle of computer subtraction (subtraction) of two images recorded in the computer memory - images before and after the introduction of a contrast agent into the vessel. Here, add an image of the vessels from the general image of the part of the body being studied, in particular, remove interfering shadows of soft tissues and skeleton and quantitatively assess hemodynamics. Less radiopaque contrast agent is used, so vascular images can be obtained with a large dilution of the contrast agent. This means that it is possible to inject a contrast agent intravenously and obtain a shadow of the arteries on a subsequent series of images without resorting to catheterization.

To perform lymphography, a contrast agent is injected directly into the lumen of the lymphatic vessel. The clinic currently performs mainly lymphography of the lower extremities, pelvis and retroperitoneum. A contrast agent - a liquid oil emulsion of an iodide compound - is injected into the vessel. X-rays of the lymphatic vessels are taken after 15-20 minutes, and X-rays of the lymph nodes - after 24 hours.

RADIONUCLIDE RESEARCH METHOD

The radionuclide method is a method of studying the functional and morphological state of organs and systems using radionuclides and indicators labeled with them. These indicators - they are called radiopharmaceuticals (RP) - are introduced into the patient’s body, and then, using various instruments, the speed and nature of their movement, fixation and removal from organs and tissues are determined.

In addition, pieces of tissue, blood and secretions of the patient can be used for radiometry. Despite the introduction of negligible amounts of the indicator (hundredths and thousandths of a microgram) that do not affect the normal course of life processes, the method has extremely high sensitivity.

When choosing a radiopharmaceutical for research, the doctor must first of all take into account its physiological orientation and pharmacodynamics. It is imperative to take into account the nuclear physical properties of the radionuclide included in its composition. To obtain images of organs, only radionuclides emitting Y-rays or characteristic x-rays are used, since these radiations can be recorded by external detection. The more gamma quanta or X-ray quanta are formed during radioactive decay, the more effective a given radiopharmaceutical is in diagnostic terms. At the same time, the radionuclide should emit as little as possible corpuscular radiation - electrons that are absorbed in the patient’s body and do not participate in obtaining images of organs. Radionuclides whose half-life is several tens of days are considered long-lived, several days - medium-lived, several hours - short-lived, several minutes - ultra-short-lived. There are several ways to obtain radionuclides. Some of them are formed in reactors, some in accelerators. However, the most common method for obtaining radionuclides is generator, i.e. production of radionuclides directly in the laboratory of radionuclide diagnostics using generators.

A very important parameter of a radionuclide is the energy of electromagnetic radiation quanta. Quanta of very low energies are retained in tissues and, therefore, do not reach the detector of a radiometric device. Quanta of very high energies partially pass through the detector, so the efficiency of their registration is also low. The optimal range of quantum energy in radionuclide diagnostics is considered to be 70-200 keV.

All radionuclide diagnostic studies are divided into two large groups: studies in which radiopharmaceuticals are introduced into the patient’s body - in vivo studies, and studies of blood, pieces of tissue and patient secretions - in vitro studies.

LIVER SCINTIGRAPHY - carried out in static and dynamic modes. In the static mode, the functional activity of the cells of the reticuloendothelial system (RES) of the liver is determined, in the dynamic mode - the functional state of the hepatobiliary system. Two groups of radiopharmaceuticals (RPs) are used: to study liver RES - colloidal solutions based on 99mTc; for the study of hepatobiliary compound based on imidodiacetic acid 99mTc-HIDA, mezide.

HEPATOSCINTIGRAPHY is a technique for visualizing the liver using a scintigraphic method on a gamma camera in order to determine the functional activity and amount of functioning parenchyma when using colloidal radiopharmaceuticals. 99mTc colloid is administered intravenously with an activity of 2 MBq/kg. The technique allows you to determine the functional activity of reticuloendothelial cells. The mechanism of radiopharmaceutical accumulation in such cells is phagocytosis. Hepatoscintigraphy is performed 0.5-1 hour after administration of the radiopharmaceutical. Planar hepatoscintigraphy is performed in three standard projections: anterior, posterior and right lateral.

This is a technique for visualizing the liver using a scintigraphic method on a gamma camera to determine the functional activity of hepatocytes and the biliary system using a radiopharmaceutical based on imidodiacetic acid.

HEPATOBILISTICINTIGRAPHY

99mTc-HIDA (mesida) is administered intravenously with an activity of 0.5 MBq/kg after the patient is laid down. The patient lies on his back under a gamma camera detector, which is installed as close as possible to the surface of the abdomen so that the entire liver and part of the intestine are in its field of view. The study begins immediately after intravenous administration of the radiopharmaceutical and lasts 60 minutes. Simultaneously with the introduction of radiopharmaceuticals, recording systems are turned on. At the 30th minute of the study, the patient is given a choleretic breakfast (2 raw chicken yolks). Normal hepatocytes quickly take up the drug from the blood and excrete it with bile. The mechanism of radiopharmaceutical accumulation is active transport. The passage of the radiopharmaceutical through the hepatocyte normally takes 2-3 minutes. The first portions of it appear in the common bile duct after 10-12 minutes. At 2-5 minutes, the scintigrams show the hepatic and common bile duct, and after 2-3 minutes - the gallbladder. Maximum radioactivity over the liver is normally recorded approximately 12 minutes after administration of the radiopharmaceutical. By this time, the radioactivity curve reaches its maximum. Then it takes on the character of a plateau: during this period, the rates of uptake and removal of radiopharmaceuticals are approximately balanced. As the radiopharmaceutical is excreted in the bile, the radioactivity of the liver decreases (by 50% in 30 minutes), and the intensity of radiation above the gallbladder increases. But very little radiopharmaceuticals are released into the intestines. To induce emptying of the gallbladder and assess the patency of the bile ducts, the patient is given a choleretic breakfast. After this, the image of the gallbladder progressively decreases, and an increase in radioactivity is recorded above the intestines.

Radioisotope study of the kidneys and urinary tract radioisotope scintigraphy biliary liver.

It consists of assessing renal function, it is carried out on the basis of a visual picture and quantitative analysis of the accumulation and excretion of radiopharmaceuticals by the renal parenchyma secreted by the tubular epithelium (Hippuran-131I, Technemag-99mTc) or filtered by the renal glomeruli (DTPA-99mTc).

Dynamic renal scintigraphy.

A technique for visualizing the kidneys and urinary tract using a scintigraphic method on a gamma camera in order to determine the parameters of accumulation and elimination of nephrotropic radiopharmaceuticals through the tubular and glomerular elimination mechanisms. Dynamic renoscintigraphy combines the advantages of simpler techniques and has greater capabilities due to the use of computer systems for processing the obtained data.

Kidney scan

It is used to determine the anatomical and topographical features of the kidneys, the localization of the lesion and the extent of the pathological process in them. Based on the selective accumulation of 99mTc - cyton (200 MBq) by normally functioning kidney parenchyma. They are used when there is a suspicion of a volumetric process in the kidney caused by a malignant tumor, cyst, cavity, etc., to identify congenital kidney anomalies, select the extent of surgical intervention, and assess the viability of the transplanted kidney.

Isotope renography

It is based on external registration of g-radiation over the kidney area from intravenous 131I - hippuran (0.3-0.4 MBq), which is selectively captured and excreted by the kidneys. Indicated in the presence of urinary syndrome (hematuria, leukocyturia, proteinuria, bacteriuria, etc.), pain in the lumbar region, pastosity or swelling on the face, legs, kidney injury, etc. Allows a separate assessment for each kidney of the speed and intensity of secretory and excretory function , determine the patency of the urinary tract, and by blood clearance - the presence or absence of renal failure.

Radioisotope study of the heart, myocardial scintigraphy.

The method is based on assessing the distribution in the heart muscle of an intravenously administered radiopharmaceutical, which is incorporated into intact cardiomyocytes in proportion to coronary blood flow and metabolic activity of the myocardium. Thus, the distribution of the radiopharmaceutical in the myocardium reflects the state of coronary blood flow. Areas of the myocardium with normal blood supply create a picture of uniform distribution of the radiopharmaceutical. Areas of the myocardium with limited coronary blood flow due to various reasons are defined as areas with reduced radiotracer uptake, that is, perfusion defects.

The method is based on the ability of radionuclide-labeled phosphate compounds (monophosphates, diphosphonates, pyrophosphate) to be included in mineral metabolism and accumulate in the organic matrix (collagen) and the mineral part (hydroxylapatite) of bone tissue. The distribution of radiophosphates is proportional to blood flow and the intensity of calcium metabolism. Diagnosis of pathological changes in bone tissue is based on visualization of foci of hyperfixation or, less commonly, defects in the accumulation of labeled osteotropic compounds in the skeleton.

5. Radioisotope study of the endocrine system, scintigraphy of the thyroid gland

The method is based on visualization of functioning thyroid tissue (including abnormally located) using radiopharmaceuticals (Na131I, technetium pertechnetate), which are absorbed by the epithelial cells of the thyroid gland along the pathway of inorganic iodine uptake. The intensity of inclusion of radionuclide tracers in the gland tissue characterizes its functional activity, as well as individual sections of its parenchyma (“hot” and “cold” nodes).

Scintigraphy of the parathyroid glands

Scintigraphic visualization of pathologically altered parathyroid glands is based on the accumulation of diagnostic radiopharmaceuticals in their tissue, which have an increased tropism for tumor cells. Detection of enlarged parathyroid glands is carried out by comparing scintigraphic images obtained with maximum accumulation of the radiopharmaceutical in the thyroid gland (thyroid phase of the study) and with its minimum content in the thyroid gland with maximum accumulation in the pathologically altered parathyroid glands (parathyroid phase of the study).

Breast scintigraphy (mammoscintigraphy)

Diagnosis of malignant neoplasms of the mammary glands is carried out by a visual picture of the distribution in the gland tissue of diagnostic radiopharmaceuticals, which have an increased tropism for tumor cells due to the increased permeability of the histohematic barrier in combination with a higher cell density and higher vascularization and blood flow, compared with unchanged breast tissue ; peculiarities of metabolism of tumor tissue - increased activity of membrane Na+-K+ ATPase; expression of specific antigens and receptors on the surface of the tumor cell; increased protein synthesis in a cancer cell during proliferation in a tumor; phenomena of degeneration and cell damage in breast cancer tissue, due to which, in particular, the content of free Ca2+, products of damage to tumor cells and intercellular substance is higher.

The high sensitivity and specificity of mammoscintigraphy determine the high predictive value of the negative conclusion of this method. Those. the absence of accumulation of the radiopharmaceutical in the studied mammary glands indicates the probable absence of tumor viable proliferating tissue in them. In this regard, according to the world literature, many authors consider it sufficient not to perform a puncture study on a patient in the absence of accumulation of 99mTc-Technetril in a nodular “doubtful” pathological formation, but only to observe the dynamics of the condition for 4 - 6 months.

Radioisotope study of the respiratory system

Lung perfusion scintigraphy

The principle of the method is based on visualization of the capillary bed of the lungs using technetium-labeled albumin macroaggregates (MAA), which, when administered intravenously, embolize a small part of the lung capillaries and are distributed proportionally to the blood flow. MAA particles do not penetrate into the lung parenchyma (interstitially or alveolarly), but temporarily occlude capillary blood flow, while 1:10,000 of the pulmonary capillaries are embolized, which does not affect hemodynamics and pulmonary ventilation. Embolization lasts for 5-8 hours.

Ventilation of the lungs with aerosol

The method is based on inhalation of aerosols obtained from radiopharmaceuticals (RPs), quickly eliminated from the body (most often a solution of 99m-Technetium DTPA). The distribution of radiopharmaceuticals in the lungs is proportional to regional pulmonary ventilation; increased local accumulation of radiopharmaceuticals is observed in places of air flow turbulence. The use of emission computed tomography (ECT) makes it possible to localize the affected bronchopulmonary segment, which on average increases the diagnostic accuracy by 1.5 times.

Alveolar membrane permeability

The method is based on determining the clearance of a radiopharmaceutical solution (RP) 99m-Technetium DTPA from the entire lung or an isolated bronchopulmonary segment after aerosol ventilation. The rate of removal of radiopharmaceuticals is directly proportional to the permeability of the pulmonary epithelium. The method is non-invasive and easy to perform.

Radionuclide diagnostics in vitro (from the Latin vitrum - glass, since all studies are carried out in test tubes) refers to microanalysis and occupies a borderline position between radiology and clinical biochemistry. The principle of the radioimmunological method is the competitive binding of the desired stable and similar labeled substances with a specific perceptive system.

The binding system (most often these are specific antibodies or antiserum) interacts simultaneously with two antigens, one of which is the desired one, the other is its labeled analogue. Solutions are used that always contain more labeled antigen than antibodies. In this case, a real struggle between labeled and unlabeled antigens for connection with antibodies takes place.

In vitro radionuclide analysis began to be called radioimmunological, since it is based on the use of immunological antigen-antibody reactions. Thus, if an antibody rather than an antigen is used as the labeled substance, the analysis is called immunoradiometric; if tissue receptors are taken as the binding system, they say orradioreceptor analysis.

Radionuclide research in vitro consists of 4 stages:

1. The first stage is mixing the biological sample being analyzed with reagents from the kit containing antiserum (antibodies) and a binding system. All manipulations with solutions are carried out with special semi-automatic micropipettes; in some laboratories they are carried out using automatic machines.

2. The second stage is incubation of the mixture. It continues until dynamic equilibrium is achieved: depending on the specificity of the antigen, its duration varies from several minutes to several hours and even days.

3. The third stage is the separation of free and bound radioactive matter. For this purpose, the sorbents included in the kit are used (ion exchange resins, carbon, etc.), which precipitate heavier antigen-antibody complexes.

4. The fourth stage is radiometry of samples, construction of calibration curves, determination of the concentration of the desired substance. All this work is performed automatically using a radiometer equipped with a microprocessor and a printing device.

Ultrasound research methods.

Ultrasound examination (ultrasound) is a diagnostic method based on the principle of reflection of ultrasonic waves (echolocation) transmitted to tissues from a special sensor - an ultrasound source - in the megahertz (MHz) ultrasound frequency range, from surfaces with different permeability for ultrasonic waves . The degree of permeability depends on the density and elasticity of the tissue.

Ultrasonic waves are elastic vibrations of a medium with a frequency that lies above the range of sounds audible to humans - above 20 kHz. The upper limit of ultrasonic frequencies can be considered 1 - 10 GHz. Ultrasound waves are non-ionizing radiation and, in the range used in diagnostics, do not cause significant biological effects

To generate ultrasound, devices called ultrasound emitters are used. The most widespread are electromechanical emitters based on the phenomenon of the inverse piezoelectric effect. The inverse piezoelectric effect consists of mechanical deformation of bodies under the influence of an electric field. The main part of such an emitter is a plate or rod made of a substance with well-defined piezoelectric properties (quartz, Rochelle salt, ceramic material based on barium titanate, etc.). Electrodes are applied to the surface of the plate in the form of conductive layers. If an alternating electrical voltage from a generator is applied to the electrodes, the plate, thanks to the inverse piezoelectric effect, will begin to vibrate, emitting a mechanical wave of the corresponding frequency.

Similar documents

X-ray diagnostics is a way of studying the structure and functions of human organs and systems; research methods: fluorography, digital and electroradiography, fluoroscopy, computed tomography; chemical action of x-rays.

abstract, added 01/23/2011


Diagnostic methods based on recording the radiation of radioactive isotopes and labeled compounds. Classification of types of tomography. Principles of using radiopharmaceuticals in diagnostics. Radioisotope study of renal urodynamics.

training manual, added 12/09/2010


Calculation of the power of an ultrasonic emitter, which provides the possibility of reliable registration of the boundaries of biological tissues. The strength of the anode current and the magnitude of the x-ray voltage in the Coolidge electron tube. Finding the decay rate of thallium.

test, added 06/09/2012


The principle of obtaining an ultrasound image, methods of its registration and archiving. Symptoms of pathological changes on ultrasound. Ultrasound technique. Clinical applications of magnetic resonance imaging. Radionuclide diagnostics, recording devices.

presentation, added 09/08/2016


Introduction of X-rays into medical practice. Methods for radiological diagnosis of tuberculosis: fluorography, fluoroscopy and radiography, longitudinal, magnetic resonance and computed tomography, ultrasound and radionuclide methods.

abstract, added 06/15/2011


Instrumental methods of medical diagnostics for X-ray, endoscopic and ultrasound examinations. The essence and development of research methods and methods for conducting them. Rules for preparing adults and children for the examination procedure.

abstract, added 02/18/2015


Determination of the need and diagnostic value of radiological research methods. Characteristics of radiography, tomography, fluoroscopy, fluorography. Features of endoscopic research methods for diseases of internal organs.

presentation, added 03/09/2016


Types of X-ray examinations. An algorithm for describing healthy lungs, examples of images of lungs with pneumonia. The principle of computed tomography. Use of endoscopy in medicine. The procedure for performing fibrogastroduodenoscopy, indications for its use.

presentation, added 02/28/2016


Biography and scientific activity of V.K. Roentgen, the history of his discovery of X-rays. Characteristics and comparison of two main methods in medical x-ray diagnostics: fluoroscopy and radiography. Examination of the gastrointestinal tract and lungs.

abstract, added 03/10/2013


Main sections of radiation diagnostics. Technical progress in diagnostic radiology. Artificial contrast. The principle of obtaining an x-ray image, as well as a sectional plane during tomography. Ultrasound research technique.

Literature.

Test questions.

Magnetic resonance imaging (MRI).

X-ray computed tomography (CT).

Ultrasound examination (ultrasound).

Radionuclide diagnostics (RND).

X-ray diagnostics.

Part I. GENERAL ISSUES IN RADIATION DIAGNOSTICS.

Chapter 1.

Radiation diagnostic methods.

Radiation diagnostics deals with the use of various types of penetrating radiation, both ionizing and non-ionizing, 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 (USD), 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 share of radiological diagnostic methods according to WHO today is: 50% ultrasound, 43% X-ray (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. Principle of X-ray diagnostics consists of visualizing internal organs using x-ray radiation directed at the object of study, which has a high penetrating ability, with its subsequent registration after leaving the object by some 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 (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 vibrations - 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: it is penetrating ability - X-ray diagnostics is based on this property, and biological action is a component the essence of X-ray therapy.. Penetrating ability, in addition to 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 cylinder 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 rpm when the tube is operating. 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 speeds 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. Bremsstrahlung rays are formed as a result of the collision of electrons flying from the cathode with electrons of the outer orbits of the atoms of the anode, causing them to move to inner orbits, which results in the release of energy in the form of quanta of bremsstrahlung X-ray radiation of low hardness. The characteristic fraction is obtained due to the penetration of electrons into the nuclei of the anode atoms, which results in the knocking out of characteristic radiation quanta.

It is this fraction that is mainly used for diagnostic purposes, since the rays of this fraction are harder, that is, they have greater penetrating power. The proportion of this fraction is increased by applying a higher voltage to the X-ray tube.

1.4. X-ray diagnostic machine or, as it is now commonly referred to, the X-ray diagnostic complex (RDC) consists of the following main blocks:

a) X-ray emitter,

b) X-ray feeding device,

c) devices for generating 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 generated in large quantities during operation of the tube (otherwise the anode will quickly collapse). Cooling systems use transformer oil, air cooling with fans, or a combination of both.

The next block of the RDK is x-ray feeding device, which includes a low-voltage transformer (to heat up the cathode spiral, a voltage of 10-15 volts is required), a high-voltage transformer (for the tube itself, a voltage of 40 to 120 kV is required), rectifiers (for efficient operation of the tube, direct current is required) 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 organ being removed; screening grid, which cuts off scattered rays arising in the patient’s body in order to improve image sharpness.

Tripod(s)) serve to position the patient, and in some cases, the X-ray tube. There are stands intended only for radiography - radiographic, and universal, on which both radiography and fluoroscopy can be carried out. , three, which is determined by the configuration of the RDK depending on the profile of the healthcare 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), storage screens (for luminescent s. computer radiography), an X-ray image intensifier - URI, detectors (when using digital technologies).

1.5. X-ray imaging technologies Currently there are three versions:

direct analog,

indirect analog,

digital (digital).

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

and specific gravity and different thicknesses. When they fall on the simplest X-ray receivers - 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 X-ray film after its chemical processing. Classical (traditional) X-ray diagnostic methods are based on this technology:

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

X-ray currently used mainly in the study of the gastrointestinal tract. Its advantages are a) the study of the functional characteristics of the organ under study 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 exposure to the patient and 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 when receiving the image are mainly tenths and hundredths of a second, c ) objectivity of obtaining information, since the radiograph can be analyzed by other, more qualified specialists, d) the ability to study the dynamics of the pathological process from radiographs taken at different periods of the disease, e) the radiograph is a legal document. The disadvantages of an x-ray include incomplete topographical and functional characteristics of the organ being studied.

Typically, radiography uses two projections, which are called standard: direct (front and back) and lateral (right and left). The projection is determined by the proximity of the film cassette to the surface of the body. For example, if the cassette for a chest x-ray is located at the anterior surface of the body (in this case, the x-ray tube will be located at the back), then such a projection will be called direct anterior; if the cassette is located along the posterior surface of the body, a direct posterior projection is obtained. In addition to standard projections, there are additional (atypical) projections that are used in cases where in standard projections, due to anatomical, topographical and skialological features, we cannot obtain a complete picture of the anatomical characteristics of the organ under study. These are oblique projections (intermediate between direct and lateral), axial (in this case, the X-ray beam is directed along the axis of the body or organ under study), tangential (in this case, the X-ray beam is directed tangentially to the surface of the organ being photographed). Thus, 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 projection - the nasal bone, zygomatic bone , frontal sinuses, etc.

In addition to projections, during X-ray diagnostics, different positions of the patient are used, which is determined by the research technique or the patient’s condition. The main position is orthoposition– 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 trichoposition– horizontal position of the patient with a vertical course of the X-ray beam (used for radiography of bones, intestines, kidneys, when studying patients in serious condition) and lateroposition- horizontal position of the patient with the horizontal direction of the x-rays (used for special research techniques).

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 radiography, 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, and at the same time the film cassette moves in the opposite direction. The center of their rotation is the selected layer of the organ at a certain depth from its surface, the depth is

Radiation diagnostics has made significant progress in the last three decades, primarily due to the introduction of computed tomography (CT), ultrasound (US), and magnetic resonance imaging (MRI). However, the initial examination of the patient is still based on traditional imaging methods: radiography, fluorography, fluoroscopy. Traditional radiation research methods are based on the use of X-rays discovered by Wilhelm Conrad Roentgen in 1895. He did not consider it possible to derive material benefit from the results of scientific research, since “... his discoveries and inventions belong to humanity, and. they shall not be hindered in any way by patents, licenses, contracts, or the control of any group of people.” Traditional X-ray research methods are called projection visualization methods, which, in turn, can be divided into three main groups: direct analogue methods; indirect analogue methods; digital methods. In direct analogue methods, the image is formed directly in a radiation-receiving medium (X-ray film, fluorescent screen), the reaction of which to radiation is not discrete, but constant. The main analogue research methods are direct radiography and direct fluoroscopy. Direct radiography– basic method of radiation diagnostics. It consists in the fact that X-rays passing through the patient's body create an image directly on the film. X-ray film is coated with a photographic emulsion containing silver bromide crystals, which are ionized by photon energy (the higher the radiation dose, the more silver ions are formed). This is the so-called latent image. During the developing process, metallic silver forms dark areas on the film, and during the fixing process, the silver bromide crystals are washed out and transparent areas appear on the film. Direct radiography produces static images with the best possible spatial resolution. This method is used to obtain chest x-rays. Currently, direct radiography is rarely used to obtain a series of full-format images in cardiac angiographic studies. Direct fluoroscopy (transillumination) lies in the fact that the radiation passing through the patient’s body, hitting the fluorescent screen, creates a dynamic projection image. Currently, this method is practically not used due to the low brightness of the image and the high radiation dose to the patient. Indirect fluoroscopy almost completely replaced transillumination. The fluorescent screen is part of an electron-optical converter, which enhances the image brightness by more than 5000 times. The radiologist was able to work in daylight. The resulting image is reproduced by the monitor and can be recorded on film, video recorder, magnetic or optical disk. Indirect fluoroscopy is used to study dynamic processes, such as contractile activity of the heart, blood flow through the vessels