X-rays are produced as a result. History of discovery and applications of X-rays

• The higher the voltage is applied to the poles of the tube, the stronger the potential difference appears on them, therefore, the kinetic energy of moving electrons will be higher. The voltage on the tube determines the speed of the electrons and the force of their collision with the anode material, therefore, the voltage determines the wavelength of the resulting X-ray radiation.

Classification of x-ray tubes

1. By appointment
1. Diagnostic
2. Therapeutic
3. For structural analysis
4. For transillumination
2. By design
1. By focus

• Single-focus (one spiral on the cathode, and one focal spot on the anode)
• Bifocal (two spirals of different sizes on the cathode, and two focal spots on the anode)

1. By type of anode

• Stationary (fixed)
• Rotating

X-rays are used not only for radiodiagnostic purposes, but also for therapeutic purposes. As noted above, the ability of X-ray radiation to suppress the growth of tumor cells makes it possible to use it in radiation therapy of oncological diseases. Apart from medical field applications, X-ray radiation has found wide application in the engineering and technical field, materials science, crystallography, chemistry and biochemistry: for example, it is possible to identify structural defects in various products (rails, welds, etc.) using X-ray radiation. The type of such research is called defectoscopy. And at airports, railway stations and other crowded places, X-ray television introscopes are actively used to scan hand luggage and luggage for security purposes.

Depending on the type of anode, X-ray tubes differ in design. Due to the fact that 99% of the kinetic energy of the electrons is converted into thermal energy, during the operation of the tube, the anode is significantly heated - the sensitive tungsten target often burns out. The anode is cooled in modern x-ray tubes by rotating it. The rotating anode has the shape of a disk, which distributes heat evenly over its entire surface, preventing local overheating of the tungsten target.

The design of X-ray tubes also differs in focus. Focal spot - the section of the anode on which the working X-ray beam is generated. It is subdivided into the real focal spot and the effective focal spot ( rice. 12). Due to the angle of the anode, the effective focal spot is smaller than the real one. Different focal spot sizes are used depending on the size of the image area. The larger the image area, the wider the focal spot must be to cover the entire image area. However, a smaller focal spot produces better image clarity. Therefore, when producing small images, a short filament is used and the electrons are directed to a small area of ​​the anode target, creating a smaller focal spot.

Rice. 9 - x-ray tube with a stationary anode.
Rice. 10 - X-ray tube with a rotating anode.
Rice. 11 - X-ray tube device with a rotating anode.
Rice. 12 is a diagram of the formation of a real and effective focal spot.

1. 
   High penetrating ability - able to penetrate certain media. X-rays penetrate best through gaseous media (lung tissue), but poorly penetrate through substances with high electron density and large atomic mass (bones in humans).
2. 
   Fluorescence - glow. In this case, the energy of X-rays is converted into the energy of visible light. Currently, the principle of fluorescence underlies the device of intensifying screens designed for additional illumination of X-ray film. This allows you to reduce the radiation load on the body of the patient under study.
3. 
   Photochemical - the ability to induce various chemical reactions.
4. 
   Ionizing ability - under the influence of X-rays, ionization of atoms occurs (decomposition of neutral molecules into positive and negative ions that make up an ion pair.
5. 
   Biological - damage to cells. For the most part, it is due to the ionization of biologically significant structures (DNA, RNA, protein molecules, amino acids, water). Positive biological effects - antitumor, anti-inflammatory.

1. 
   Beam tube device

X-rays are produced in an X-ray tube. An X-ray tube is a glass container with a vacuum inside. There are 2 electrodes - cathode and anode. The cathode is a thin tungsten spiral. The anode in the old tubes was a heavy copper rod, with a bevelled surface facing the cathode. On the beveled surface of the anode, a plate of refractory metal was soldered - the mirror of the anode (the anode is very hot during operation). In the center of the mirror is focus of x-ray tube This is where X-rays are produced. The smaller the focus value, the clearer the contours of the subject being shot are. Small focus is considered 1x1 mm, and even less.

In modern X-ray machines, electrodes are made from refractory metals. Typically, tubes with a rotating anode are used. During operation, the anode is rotated by a special device, and the electrons flying from the cathode fall into the optical focus. Due to the rotation of the anode, the position of the optical focus changes all the time, so such tubes are more durable and do not wear out for a long time.

How are x-rays obtained? First, the cathode filament is heated. To do this, using a step-down transformer, the voltage on the tube is reduced from 220 to 12-15V. The cathode filament heats up, the electrons in it begin to move faster, some of the electrons go beyond the filament and a cloud of free electrons forms around it. After that, a high voltage current is turned on, which is obtained using a step-up transformer. In diagnostic X-ray machines, high voltage current is used from 40 to 125 KV (1KV=1000V). The higher the voltage on the tube, the shorter the wavelength. When a high voltage is turned on, a large potential difference is obtained at the poles of the tube, the electrons “break off” from the cathode and rush to the anode at high speed (the tube is the simplest charged particle accelerator). Thanks to special devices, the electrons do not scatter to the sides, but fall into almost one point of the anode - the focus (focal spot) and are decelerated in the electric field of the anode atoms. When the electrons decelerate, electromagnetic waves arise, i.e. X-rays. Thanks to a special device (in old tubes - the bevel of the anode), x-rays are directed to the patient in the form of a divergent beam of rays, a "cone".

1. 
   X-ray imaging

X-ray film is a layered structure, the main layer is a polyester composition up to 175 microns thick, coated with a photographic emulsion (silver iodide and bromide, gelatin).

1. 
   Film development - silver is restored (where the rays passed through - blackening of the film area, where they lingered - lighter areas)
2. 
   Fixer - washing out silver bromide from areas where the rays passed through and did not linger.

1. 
   The device of a modern radiological room

1. The X-ray room itself, where the apparatus is located and the patients are examined. The area of ​​the X-ray room must be at least 50 m2

2. Control room, where the control panel is located, with the help of which the X-ray laboratory assistant controls the entire operation of the device.

3. A photographic laboratory where cassettes are loaded with film, images are developed and fixed, they are washed and dried. A modern method of photo processing of medical X-ray films is the use of roller-type processors. In addition to undoubted convenience in work, processors provide high stability of the photo processing process. The time of a complete cycle from the moment the film enters the processing machine to the receipt of a dry X-ray pattern ("from dry to dry") does not exceed several minutes.

4. Doctor's office, where the radiologist analyzes and describes the radiographs taken.

1. 
   Methods of protection for medical personnel and for patients from x-ray radiation

3 main protection methods: protection by shielding, distance and time.

1 .Shield protection:

X-rays are placed in the path of special devices made of materials that absorb x-rays well. It can be lead, concrete, barite concrete, etc. The walls, floor, ceiling in X-ray rooms are protected, made of materials that do not transmit rays into neighboring rooms. The doors are protected with lead material. The observation windows between the X-ray room and the control room are made of leaded glass. The x-ray tube is placed in a special protective casing that does not let x-rays through, and the rays are directed to the patient through a special "window". A tube is attached to the window, which limits the size of the x-ray beam. In addition, the X-ray machine diaphragm is installed at the exit of the rays from the tube. It consists of 2 pairs of plates perpendicular to each other. These plates can be moved and moved apart like curtains. In this way, the irradiation field can be increased or decreased. The larger the irradiation field, the greater the harm, therefore aperture is an important part of protection, especially in children. In addition, the doctor himself is irradiated less. And the quality of the pictures will be better. Another example of shielding is sewn up - those parts of the body of the subject that are not currently subject to shooting should be covered with sheets of lead rubber. There are also aprons, skirts, gloves made of special protective material.

2 .Protection by time:

The patient should be irradiated during x-ray examination for as little time as possible (hurry, but not to the detriment of diagnosis). In this sense, images give a lower radiation load than transillumination, because. very slow shutter speeds (time) are used in the pictures. Time protection is the main way to protect both the patient and the radiologist himself. When examining patients, the doctor, ceteris paribus, tries to choose a research method that takes less time, but not to the detriment of diagnosis. In this sense, fluoroscopy is more harmful, but, unfortunately, it is often impossible to do without fluoroscopy. So in the study of the esophagus, stomach, intestines, both methods are used. When choosing a research method, we are guided by the rule that the benefits of research should be greater than the harm. Sometimes, due to the fear of taking an extra picture, errors in diagnosis occur, treatment is incorrectly prescribed, which sometimes costs the patient's life. It is necessary to remember about the dangers of radiation, but do not be afraid of it, it is worse for the patient.

3 .Protection distance:

According to the quadratic law of light, the illumination of a given surface is inversely proportional to the square of the distance from the light source to the illuminated surface. In relation to X-ray examination, this means that the radiation dose is inversely proportional to the square of the distance from the focus of the X-ray tube to the patient (focal length). With an increase in the focal length by 2 times, the radiation dose decreases by 4 times, with an increase in the focal length by 3 times, the radiation dose decreases by 9 times.

A focal length of less than 35 cm is not allowed for fluoroscopy. The distance from the walls to the X-ray machine must be at least 2 m, otherwise secondary rays are formed that occur when the primary beam of rays hits the surrounding objects (walls, etc.). For the same reason, extra furniture is not allowed in X-ray rooms. Sometimes, when examining seriously ill patients, the personnel of the surgical and therapeutic departments help the patient stand behind the screen for transillumination and stand next to the patient during the examination, supporting him. As an exception, this is allowed. But the radiologist must make sure that the nurses and nurses helping the sick put on a protective apron and gloves and, if possible, do not stand close to the patient (protection by distance). If several patients came to the X-ray room, they are called to the procedural room by 1 person, i.e. There should only be 1 person at a time in the study.

1. 
   Physical bases of radiography and fluorography. Their shortcomings and advantages. Advantages of digital over film.

For diagnostic radiography, it is advisable to take pictures in at least two projections. This is due to the fact that the radiograph is a flat image of a three-dimensional object. And as a result, the localization of the detected pathological focus can be established only with the help of 2 projections.

The quality of the resulting X-ray image is determined by 3 main parameters. The voltage applied to the X-ray tube, the current strength and the operating time of the tube. Depending on the studied anatomical formations, and the weight and size data of the patient, these parameters can vary significantly. There are average values ​​for different organs and tissues, but it should be borne in mind that the actual values ​​will differ depending on the apparatus where the examination is performed and the patient who is being X-rayed. An individual table of values ​​is compiled for each device. These values ​​are not absolute and are adjusted as the study progresses. The quality of the images performed is largely dependent on the ability of the radiographer to adequately adapt the table of average values ​​to a particular patient.

The most common way to record an X-ray image is to fix it on an X-ray sensitive film and then develop it. Currently, there are also systems that provide digital data recording. Due to the high cost and complexity of manufacturing, this type of equipment is somewhat inferior to analog equipment in terms of prevalence.

X-ray film is placed in special devices - cassettes (they say - the cassette is loaded). The cassette protects the film from visible light; the latter, like x-rays, has the ability to reduce metallic silver from AgBr. Cassettes are made of a material that does not transmit light, but transmits x-rays. Inside the cassettes are intensifying screens, the film is laid between them; when taking a picture, not only the X-rays themselves fall on the film, but also the light from the screens (the screens are covered with fluorescent salt, so they glow and enhance the action of the X-rays). This allows you to reduce the radiation load on the patient by 10 times.

When taking a picture, x-rays are directed to the center of the object being photographed (centration). After shooting in a photo lab, the film is developed in special chemicals and fixed (fixed). The fact is that on those parts of the film that were not hit by x-rays during the shooting or there were few of them, silver was not restored, and if the film is not placed in a fixer (fixer) solution, then when examining the film, silver is restored under the influence of visible light. Sveta. The entire film will turn black and no image will be visible. When fixing (fixing), unreduced AgBr from the film goes into the fixer solution, so there is a lot of silver in the fixer, and these solutions are not poured out, but surrendered to X-ray centers.

A modern method of photo processing of medical X-ray films is the use of roller-type processors. In addition to undoubted convenience in work, processors provide high stability of the photo processing process. The time of a complete cycle from the moment the film enters the processing machine to the receipt of a dry X-ray pattern ("from dry to dry") does not exceed several minutes.
X-rays are an image made in black and white - a negative. Black - areas with low density (lungs, stomach gas bubble. White - with high density(bones).
Fluorography- The essence of FOG is that with it, an image of the chest is first obtained on a fluorescent screen, and then a picture is taken not of the patient himself, but of his image on the screen.

Fluorography gives a reduced image of the object. There are small frame (eg 24×24 mm or 35×35 mm) and large frame (eg 70×70 mm or 100×100 mm) techniques. The latter, in terms of diagnostic capabilities, approaches radiography. FOG is used for preventive examination of the population(hidden diseases such as cancer and tuberculosis are detected).

Both stationary and mobile fluorographic devices have been developed.

Currently, film fluorography is gradually being replaced by digital. Digital methods make it possible to simplify work with an image (an image can be displayed on a monitor screen, printed, transmitted over a network, stored in a medical database, etc.), reduce radiation exposure to the patient and reduce the cost of additional materials (film, developer for films).

A conventional film chest fluorogram provides the patient with an average individual radiation dose of 0.5 millisievert (mSv) per procedure (digital fluorogram - 0.05 mSv), while a film radiograph - 0.3 mSv per procedure (digital radiograph - 0 .03 mSv), and computed tomography of the chest - 11 mSv per procedure. Magnetic resonance imaging does not carry radiation exposure

Benefits of radiography

1. 
   Wide availability of the method and ease of research.
2. 
   Most studies do not require special patient preparation.
3. 
   Relatively low cost of research.
4. 
   The images can be used for consultation with another specialist or in another institution (unlike ultrasound images, where a second examination is necessary, since the images obtained are operator-dependent).

1. 
   Static image - the complexity of assessing the function of the body.
2. 
   The presence of ionizing radiation that can have a harmful effect on the patient.
3. 
   The informativeness of classical radiography is much lower than such modern methods of medical imaging as CT, MRI, etc. Ordinary x-ray images reflect the projection layering of complex anatomical structures, that is, their summation x-ray shadow, in contrast to the layered series of images obtained by modern tomographic methods.
4. 
   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 abdominal organs).

1. 
   Physical bases of roentgenoscopy. Disadvantages and advantages of the method

In modern conditions, the use of a fluorescent screen is not justified due to its low luminosity, which makes it necessary to conduct research in a well-darkened room and after a long adaptation of the researcher to the dark (10-15 minutes) to distinguish a low-intensity image.

Now fluorescent screens are used in the design of X-ray image intensifier, which increases the brightness (glow) of the primary image by about 5,000 times. With the help of an electron-optical converter, the image appears on the monitor screen, which significantly improves the quality of diagnostics, does not require darkening of the X-ray room.

Advantages of fluoroscopy
The main advantage over radiography is the fact of the study in real time. This allows you to evaluate not only the structure of the organ, but also its displacement, contractility or extensibility, the passage of a contrast agent, and fullness. The method also allows you to quickly assess the localization of some changes, due to the rotation of the object of study during transillumination (multi-projection study).

Fluoroscopy allows you to control the implementation of some instrumental procedures - catheter placement, angioplasty (see angiography), fistulography.

The resulting images can be placed on a regular CD or network storage.

With the advent of digital technologies, 3 main disadvantages inherent in traditional fluoroscopy have disappeared:

Relatively high radiation dose compared to radiography - modern low-dose devices have left this disadvantage in the past. The use of pulsed scan modes further reduces the dose load by up to 90%.

Low spatial resolution - on modern digital devices, the resolution in scopy mode is only slightly inferior to the resolution in radiographic mode. In this case, the ability to observe the functional state of individual organs (heart, lungs, stomach, intestines) "in dynamics" is of decisive importance.

The impossibility of documenting research - digital imaging technologies make it possible to save research materials, both frame-by-frame and as a video sequence.

Fluoroscopy is performed mainly in the X-ray diagnosis of diseases of the internal organs located in the abdominal and chest cavities, according to the plan that the radiologist draws up before the start of the study. Sometimes, the so-called survey fluoroscopy is used to recognize traumatic bone injuries, to clarify the area to be radiographed.

Contrast fluoroscopic examination

Artificial contrast greatly expands the possibilities of fluoroscopic examination of organs and systems where tissue densities are approximately the same (for example, abdomen, whose organs transmit X-rays to approximately the same extent and therefore have low contrast). This is achieved by introducing into the lumen of the stomach or intestines an aqueous suspension of barium sulfate, which does not dissolve in digestive juices, is not absorbed by the stomach or intestines and is excreted naturally in a completely unchanged form. The main advantage of barium suspension is that, passing through the esophagus, stomach and intestines, coats their inner walls and gives a complete picture of the nature of elevations, depressions and other features of their mucous membrane on the screen or film. The study of the internal relief of the esophagus, stomach and intestines contributes to the recognition of a number of diseases of these organs. With more tight filling, it is possible to determine the shape, size, position and function of the organ under study.

1. 
   Mammography - the basics of the method, indications. Advantages of digital mammography over film.

2. differential diagnosis between cancer and benign dyshormonal hyperplasia (FAM) of the breast;

3. assessment of the growth of the primary tumor (single node or multicentric cancerous foci);

4.Dynamic dispensary monitoring of the state of the mammary glands after surgery.

The following methods of radiation diagnostics of breast cancer have been introduced into medical practice: mammography, ultrasound, computed tomography, magnetic resonance imaging, color and power Doppler, mammography-guided stereotaxic biopsy, and thermography.

X-ray mammography
Currently, in the world, in the vast majority of cases, X-ray projection mammography, film (analogue) or digital, is used to diagnose female breast cancer (BC).

The procedure takes no more than 10 minutes. For the shot, the chest should be fixed between two planks and slightly compressed. The picture is taken in two projections so that you can accurately determine the location of the neoplasm, if it is found. Because symmetry is one of the diagnostic factors, both breasts should always be examined.

MRI mammography

Complaints about retraction or bulging of any part of the gland

Discharge from the nipple, changing its shape

Soreness of the mammary gland, its swelling, resizing

Benign breast tumors (particularly fibroadenoma)

Inflammatory processes (mastitis)

Mastopathy

Tumors of the genital organs

Diseases of the endocrine glands (thyroid, pancreas)

Infertility

Obesity

History of breast surgery

Advantages of digital mammography over film:

Reduction of dose loads during X-ray studies;

Improving the efficiency of research, allowing to identify previously inaccessible pathological processes (possibility of digital computer image processing);

Possibilities of using telecommunication networks for transmitting images for the purpose of remote consultation;

Achievement of economic effect during mass research.

X-ray radiation, from the point of view of physics, is electromagnetic radiation, the wavelength of which varies in the range from 0.001 to 50 nanometers. It was discovered in 1895 by the German physicist W.K. Roentgen.

By nature, these rays are related to solar ultraviolet. Radio waves are the longest in the spectrum. They are followed by infrared light, which our eyes do not perceive, but we feel it as heat. Next come the rays from red to purple. Then - ultraviolet (A, B and C). And right behind it are x-rays and gamma rays.

X-ray can be obtained in two ways: by deceleration in the matter of charged particles passing through it and by the transition of electrons from the upper layers to the internal ones when energy is released.

Unlike visible light, these rays are very long, so they are able to penetrate opaque materials without being reflected, refracted, or accumulated in them.

Bremsstrahlung is easier to obtain. Charged particles emit electromagnetic radiation when braking. The greater the acceleration of these particles and, consequently, the sharper the deceleration, the more X-rays are produced, and the wavelength becomes shorter. In most cases, in practice, they resort to the generation of rays in the process of deceleration of electrons in solids. This allows you to control the source of this radiation, avoiding the danger of radiation exposure, because when the source is turned off, the X-ray emission completely disappears.

The most common source of such radiation - The radiation emitted by it is inhomogeneous. It contains both soft (long-wave) and hard (short-wave) radiation. Soft is characterized by being completely absorbed human body, therefore, such X-ray radiation brings harm twice as much as hard. With excessive electromagnetic radiation in the tissues of the human body, ionization can damage cells and DNA.

The tube is with two electrodes - a negative cathode and a positive anode. When the cathode is heated, electrons evaporate from it, then they are accelerated in an electric field. Colliding with the solid matter of the anodes, they begin deceleration, which is accompanied by the emission of electromagnetic radiation.

X-ray radiation, the properties of which are widely used in medicine, is based on obtaining a shadow image of the object under study on a sensitive screen. If the diagnosed organ is illuminated with a beam of rays parallel to each other, then the projection of shadows from this organ will be transmitted without distortion (proportionally). In practice, the radiation source is more like a point source, so it is located at a distance from the person and from the screen.

To receive a person is placed between the x-ray tube and the screen or film, acting as radiation receivers. As a result of irradiation, bone and other dense tissues appear in the image as clear shadows, look more contrast against the background of less expressive areas that transmit tissues with less absorption. On x-rays, a person becomes "translucent".

As X-rays propagate, they can be scattered and absorbed. Before absorption, the rays can travel hundreds of meters in the air. In dense matter, they are absorbed much faster. Human biological tissues are heterogeneous, so their absorption of rays depends on the density of the tissue of the organs. absorbs rays faster than soft tissues, because it contains substances that have large atomic numbers. Photons (individual particles of rays) are absorbed by different tissues of the human body in different ways, which makes it possible to obtain a contrast image using X-rays.