What are the features of choice X-ray machine
High-quality and timely diagnosis is the key to successful and effective treatment. That's why in modern world Not a single medical and diagnostic institution can do without an X-ray machine.
Managers of medical centers are often faced with the question of choice. of this equipment, but how to determine which X-ray machine from the great variety of options on the market is suitable for the clinic? What parameters should you use to choose and buy an X-ray machine? How not to overpay for unnecessary functions and not miss the main thing?
Today, increasingly, outdated “film” devices are being replaced by digital X-ray machines, increasing the throughput of the room and minimizing the radiation dose. Should I make a choice in their favor or work “the old fashioned way”?
In this article we will tell you what X-ray systems are and how they differ from each other, about their advantages and features that are important to know for those who decide to buy an X-ray machine.
Types of X-ray machines
According to the operating conditions, the X-ray machine may be ward, mobile and stationary.
Specialized types of X-ray machines are also presented:
n used in operating rooms for surgical interventions - “GUS”, “C-arm”
angiography devices - “C-arm”
mammography - “mammographs”
stationary for two and three workplaces
angiographic “C-arm” “angio complexes”
CT scanners with different numbers of slices
dental x-rays for dental departments
There are also portable, small-sized devices that are used for simple X-ray examinations in an ambulance or at the patient's home. Scope of application portable devices is extremely limited due to their very low power, so they cannot replace either a mobile or, especially, a stationary X-ray machine.
Mobile X-ray units are used mainly in wards, which is why they are often called “ward X-ray machines”. The power of mobile X-ray machines ranges on average from 2.5 kW to 32 kW. The power of classic stationary devices starts from 40 kW.
Some medical centers that have significant restrictions on the installation of a stationary X-ray machine use a mobile (ward) X-ray with a power of 32 kW for radiographic examinations in the radiology department.
An X-ray machine of the U-arm type is an X-ray machine with an emitter and detector located on a single rotating stand. An X-ray transparent gurney is used for photographs in the supine position. This type of stationary X-ray machines is most often used in rooms with a small area.
X-ray systems based on a remote-controlled tripod table are the most expensive type of stationary x-ray devices. These are 3 in 1 units for the X-ray department of any modern medical institution. They allow all possible radiographic and fluoroscopic examinations to be carried out. The most common type of stationary X-ray systems in medical centers are classic two-station X-ray machines. The main components of such systems are an X-ray tube (with ceiling or floor mounting), an imaging table for the lying position, an imaging stand for the standing position, and a generator.
When purchasing an X-ray machine, it is important to decide on the profile of the research and the location of the equipment. Having chosen the type of X-ray machine, you can proceed to assessing its technical parameters.
Important technical specifications x-ray machines
Generator power
When choosing a device, you should take into account the main technical characteristics. The higher the power of the feeding device, the shorter the exposure time, the lower the radiation dose, and in some studies the higher the image quality. This is especially important when examining obese patients.
For stationary X-ray machines, the generator power range is on average from 40 kW to 80 kW. The most widely used configurations are those with a power supply of 50 kW - this is enough to carry out the vast majority of studies. But it is important to consider that the power of the generator must be consistent with the operating power of the focuses x-ray tube, which determine the operating power of the “generator - X-ray tube” system.
Generator type
When choosing an X-ray machine, it is also important to take into account the type of generator: high-frequency power supplies are characterized by a slight pulsation of the anode voltage, which increases the service life of the X-ray tube and reduces the radiation dose for the patient.
Technical solutions implemented in the design of the best modern generators provide X-ray images with high contrast and spatial resolution, as well as maximum research safety by minimizing “soft” X-ray radiation that is not involved in image formation.
X-ray tube parameters
The main characteristics of the X-ray tube itself, which are important for X-ray diagnostics, areeffective focal sizes .
The value of the theoretically achievable spatial resolution decreases as the focal size increases. With a focus size of 2 mm, according to various estimates, up to 3 pairs of lines/mm can be recognized, even if the detector has best characteristics(X-ray film, for example, allows you to distinguish 10-15 pairs of lines/mm). All tubes have two working focuses. The lower the focus size of the X-ray tube, the clearer the resulting images will be, but decreasing the focus size also reduces operating power.
It is important that the power of the X-ray machine generator matches the operating power of the foci of the supplied tube.
Another characteristic of X-ray tubes isanode heat capacity value , affecting the resource consumption of the system. The higher this indicator, the greater the number of tests before the tube overheats and the longer it will last.
When choosing a stationary X-ray machine, you should pay attention to the characteristics of the imaging table.
In the production of imaging tables with a high maximum permitted load, the most expensive and reliable components are used. Good indicator The permitted maximum load on the table is considered to be 200 kg, but some manufacturers produce optional table models with a permitted load of up to 290 kg or even higher.
The X-ray machine can also be equipped with an imaging table that has a “lift” option, which allows you to move the table surface in a vertical plane - on average in the range of 500-850 mm from the level of the floor covering.
Tube mounting options
For stationary X-ray machines with 2 workstations, there are two options for mounting the tube - on a floor stand and on the ceiling.
The most common option in private medical centers is to mount the tube on a floor stand. It is easier to install and does not have serious restrictions on the minimum ceiling height and area of the X-ray room.
Ceiling mounting of the tube is a more expensive option, including installation, but also more reliable and convenient to use. If room dimensions allow, ceiling and the budget allocated for the X-ray machine, then if there is a large planned flow of patients, it is better to choose the option of ceiling mounting of the tube.
If, with a large flow of patients, you plan to purchase an X-ray machine with a floor-mounted tube, you should pay attention to options with a reinforced floor-mounted stand.
Advantages of digital X-ray machines
IN recent years Diagnostics are increasingly carried out using new generation digital radiographic equipment. It provides instantaneous acquisition of images, eliminates the development process, allows you to store images and carry out diagnostics using computer technology.
A digital X-ray machine is distinguished by the fact that images of anatomical structures obtained using X-ray irradiation are processed digitally.
The main advantages of this modern method diagnostics can be called:
the highest quality of the resulting images: the ability to digitally process them allows you to reveal important details;
speed and ease of operation: immediately after the procedure, the image is available for analysis;
ease of storage and space saving by creating mobile and easily accessible x-ray archives,
lower cost of research due to the absence of film and reagents, and environmental safety, thanks to the elimination of the development stage.
It is also important for patients that a modern digital X-ray machine minimizes radiation exposure during the examination procedure.
X-ray machines equipped digital system, are more expensive than analog ones, but do not require a developing machine with consumables and a special darkened room for her.
The transition to digital technology can significantly increase the throughput of the X-ray room, reduce the dose load on the patient, and also reduce the waiting time for the result for the patient. It becomes possible to edit and process the resulting images to make it easier for specialists to determine the diagnosis and specifics of the disease.
A system based on semiconductor flat panel detectors is the most modern technology, which has a higher resolution.
CR systems use the principle of phosphor sensitivity. Outwardly, this is an ordinary X-ray machine, in which, instead of a film cassette, a CR cassette based on memory phosphors is used. After taking the picture, the cassette must be removed from the device and placed in a special reading device - a digitizer. At the end of the reading process, the digitizer transmits the resulting digital image to the laboratory assistant’s workstation, and the cassette will be cleaned and ready for the next study.
DR systems use semiconductor flat panel detectors. A digital X-ray machine for two workstations can be equipped with either one wireless flat-panel detector, which must be moved from the table to the image rack, or two - for both the table and the image rack.
It should be taken into account that a flat panel detector should never be dropped, and its cost makes up the majority of the entire DR system, unlike CR, where the cost of an individual cassette is insignificant.
After the image is taken, almost instantly, the flat panel detector transmits the digital image to the laboratory assistant's workstation. There is no link in the chain in the form of a digitizer, which significantly reduces the time it takes to obtain a digital image, as well as the reliability of the entire system.
Systems with a flat panel detector (DR) are more expensive than systems with cassettes with a digitizer (CR), but they are justified when there is a large flow of patients, as they significantly increase the throughput of the X-ray room, are more reliable, and also allow obtaining images of the best quality.
In addition to the laboratory assistant's workstation, which is usually included in the delivery of CR or DR systems, to equip the radiology department with a digital X-ray machine, you will need a doctor's workstation, equipped with a high-resolution medical monitor, and a special printer for printing X-ray images.
When choosing and purchasing an X-ray machine, it is advisable to take into account the presence of a network of service centers authorized by the manufacturer in Russia with a warehouse of basic spare parts that provide both warranty and post-warranty service.
Proper selection of equipment is of great importance for the full functioning of the radiology department in a private clinic.
Use: in X-ray technology. The essence of the invention: the anode contains a base made of a molybdenum alloy, which includes at least one of the elements selected from the group including niobium, tantalum and rhenium, and a target made of a tungsten alloy, the base and the target are made in the form of a coherent monocrystalline structure. 1 salary f-ly.
The invention relates to sources of X-ray radiation and can be used to create X-ray emitters with increased level power and operating resource for medical and technical purposes. Rotating anodes of an X-ray tube are known, for example for computer tomographs, made in the form of a metal disk made of a refractory alloy, for example, based on molybdenum with a layer of tungsten-rhenium alloy deposited on it. However, anodes of this type have an insufficient service life and low reliability due to recrystallization processes in work area at high thermal loads. The closest technical solution The claimed technical essence is an anode containing a molybdenum alloy base, which includes at least one of the elements selected from the group including niobium, tantalum and rhenium, and a target made of tungsten or its alloy. The disadvantage of this anode is the structural instability of dispersion-strengthened molybdenum alloys. In such materials elevated temperatures Recrystallization processes can occur intensively. Their thermal strength under cyclic conditions also has temperature limits at the anode rotation speeds used. In this case, cyclic internal stresses cause cracking of the surface of the annular working track on the anode target, which causes a decrease in the radiation intensity and the service life of the tube. Therefore, when using polycrystalline materials, in particular molybdenum-based alloys, the maximum permissible power of the X-ray emitter and its service life are determined from the condition that the mass-average temperature of the anode does not exceed 1200-1300 o C. The purpose of the invention is to increase the resistance of the anode to thermal loads. The goal is achieved by the fact that the anode disk and the target layer are made in the form of a single crystal. In addition, the use of a single-crystal alloy based on molybdenum, predominantly doped with niobium and/or tantalum in an amount of 1-9% by weight, which may also contain 0.5-9% by weight of rhenium, provides an increase in the level of heat resistance of the anode in the temperature range of 1400 -1700 o C and satisfactory workability at room temperatures. Alloys of this composition belong to alloys with a solid solution type of strengthening and are characterized by high structural stability throughout the entire temperature range of existence. Therefore, when making the anode disk from a single-crystal alloy, all processes associated with the temperature kinetics of structure development, characteristic of polycrystalline alloys, are completely excluded. These differences make it possible to raise the permissible level of average mass temperature of the disk to 1400-1600 o C. In addition, making the disk monocrystalline in such a way that its surface on the side of the target layer coincides with the close-packed crystallographic face (110) makes it possible to further increase the reliability of the anode and the permissible power for by crystal orientation. Alloying molybdenum in the above quantities with niobium, tantalum and rhenium ensures optimal thermophysical and structural properties. With quantities less than the lower level, the heat resistance is significantly reduced, and with quantities larger than the upper level, thermal conductivity is reduced. Taken together, all this makes it possible to increase the reliability of the anode and increase the power of the X-ray tube, as well as increase the service life of the anode. EXAMPLE The metal anode is made in the form of a disc made of a single crystal of a molybdenum alloy. Disc diameter is about 100 mm, thickness is about 5 mm. The surface of the disk on the target side has a taper of 12°. The disk blank was produced by the zone melting method. The target layer is made by high-temperature (1600 o C) vacuum deposition in the form of a tungsten single crystal. Preliminary thermal tests of the manufactured anodes were carried out in comparison with anodes of a known design and having the same heat capacity (X-ray tube anodes 2-30BD11-150). It was found that the power dissipation of the proposed anodes exceeds the known ones by 30-40%, which ensures an increase in the reliability of the anode, as well as the power of the X-ray tube containing the anode of the proposed design.
Formula of invention
1. A ROTATING X-RAY TUBE ANODE comprising a base of molybdenum alloy, which includes at least one of the elements selected from the group consisting of niobium, tantalum and rhenium, and a target of tungsten or its alloy, characterized in that, for the purpose increasing the resistance of the anode to thermal loads, the base and target are made in the form of a coherent monocrystalline structure. 2. An anode according to claim 1, characterized in that the surface of the coherent single-crystal structure coincides with the plane of the crystallographic shape (110).
X-rays are created by converting the energy of electrons into photons, which occurs in an X-ray tube. The quantity (exposure) and quality (spectrum) of radiation can be adjusted by changing the current, voltage and operating time of the device.
Operating principle
X-ray tubes (photo shown in the article) are energy converters. They take it from the network and convert it into other forms - penetrating radiation and heat, the latter being an unwanted by-product. The tube is such that it maximizes photon production and dissipates heat as quickly as possible.
The tube is a relatively simple device, usually containing two fundamental elements - a cathode and an anode. When current flows from the cathode to the anode, electrons lose energy, resulting in the generation of X-rays.
Anode
The anode is the component where high-energy photons are emitted. This is a relatively massive metal element that connects to the positive pole electrical circuit. Performs two main functions:
- converts electron energy into x-rays,
- dissipates heat.
The anode material is selected to enhance these functions.
Ideally, most electrons should produce high-energy photons rather than heat. The proportion of their total energy that is converted into x-rays (efficiency) depends on two factors:
- atomic number (Z) of the anode material,
- electron energy.
Most X-ray tubes use tungsten as the anode material, which has an atomic number of 74. In addition to its large Z, this metal has several other characteristics that make it suitable for this purpose. Tungsten is unique in its ability to maintain strength when heated, has a high melting point and a low evaporation rate.
For many years the anode was made from pure tungsten. In recent years, an alloy of this metal with rhenium has begun to be used, but only on the surface. The anode itself, under a tungsten-rhenium coating, is made of lightweight material, which accumulates heat well. Two such substances are molybdenum and graphite.
X-ray tubes used for mammography are made with a molybdenum-coated anode. This material has an intermediate atomic number (Z=42), which generates characteristic photons with energies suitable for breast imaging. Some mammography devices also have a second anode made of rhodium (Z=45). This allows for increased energy and greater penetration for dense breasts.
The alloy improves long-term radiation yield - over time, the efficiency of devices with a pure tungsten anode decreases due to thermal damage to the surface.
Most anodes are shaped like beveled disks and are attached to the shaft of an electric motor, which rotates them at relatively high speeds while emitting X-rays. The purpose of rotation is to remove heat.
Focal spot
Not the entire anode is involved in the generation of X-ray radiation. It occurs on small area its surface - the focal spot. The dimensions of the latter are determined by the dimensions of the electron beam coming from the cathode. In most devices it has a rectangular shape and varies between 0.1-2 mm.
X-ray tubes are designed with a specific focal spot size. The smaller it is, the less blur and the higher the clarity of the image, and the larger it is, the better the heat is dissipated.
Focal spot size is one of the factors that must be considered when selecting X-ray tubes. Manufacturers produce devices with small focal spots when it is necessary to achieve high resolution and sufficiently low radiation. For example, this is required when examining small and thin parts of the body, such as in mammography.
X-ray tubes are generally manufactured with two focal spot sizes, large and small, which can be selected by the operator according to the imaging procedure.
Cathode
The main function of the cathode is to generate electrons and collect them into a beam directed towards the anode. Typically, it consists of a small coil of wire (thread) embedded in a cup-shaped recess.
Electrons passing through a circuit usually cannot leave the conductor and go into free space. However, they can do this if they get enough energy. A process known as thermionic emission uses heat to expel electrons from the cathode. This becomes possible when the pressure in the evacuated X-ray tube reaches 10 -6 -10 -7 mm Hg. Art. The filament heats up in the same way as the filament of an incandescent lamp when current is passed through it. The operation of the X-ray tube is accompanied by heating of the cathode to the glow temperature with the displacement of some electrons from it by thermal energy.
Balloon
The anode and cathode are contained in a sealed housing - a cylinder. The cylinder and its contents are often referred to as an insert, which has a limited lifespan and can be replaced. X-ray tubes mostly have glass bulbs, although metal and ceramic bulbs are used for some applications.
The main function of the balloon is to provide support and insulation and maintain a vacuum. The pressure in the evacuated X-ray tube at 15°C is 1.2·10 -3 Pa. The presence of gases in the cylinder would allow electricity to flow through the device freely, and not just in the form of an electron beam.
Frame
The design of the X-ray tube is such that, in addition to enclosing and supporting other components, its body serves as a shield and absorbs radiation, with the exception of the useful beam passing through the window. Its relatively large outer surface dissipates most of the heat generated inside the device. The space between the housing and the insert is filled with oil, which provides insulation and cooling.
Chain
An electrical circuit connects the tube to an energy source called a generator. The source receives power from the network and converts alternating current into direct current. The generator also allows you to adjust some circuit parameters:
- KV - voltage or electric potential;
- MA is the current that flows through the tube;
- S - duration or exposure time, in fractions of a second.
The circuit ensures the movement of electrons. They are charged with energy passing through the generator and give it to the anode. As they move, two transformations occur:
- potential electrical energy is converted into kinetic energy;
- kinetic, in turn, is converted into x-rays and heat.
Potential
When electrons enter the bulb, they have electrical potential energy, the amount of which is determined by the voltage KV between the anode and cathode. The X-ray tube operates under voltage, to create 1 KV of which each particle must have 1 keV. By adjusting KV, the operator imparts a certain amount of energy to each electron.
Kinetics
The low pressure in the evacuated X-ray tube (at 15°C it is 10 -6 -10 -7 mm Hg) allows particles to fly out from the cathode to the anode under the influence of thermionic emission and electrical force. This force accelerates them, which leads to an increase in speed and kinetic energy and a decrease in potential energy. When a particle hits the anode, its potential is lost and all its energy is converted into kinetic energy. A 100-keV electron reaches a speed exceeding half When hitting a surface, the particles slow down very quickly and lose their kinetic energy. It turns into x-rays or heat.
The electrons come into contact with individual atoms of the anode material. Radiation is generated when they interact with orbitals (X-ray photons) and with the nucleus (bremsstrahlung).
Communication energy
Each electron inside an atom has a certain binding energy, which depends on the size of the latter and the level at which the particle is located. Binding energy plays an important role in the generation of characteristic x-rays and is necessary to remove an electron from an atom.
Bremsstrahlung
Bremsstrahlung produces greatest number photons. Electrons penetrating the anode material and passing near the nucleus are deflected and slowed down by the atomic force of attraction. Their energy, lost during this meeting, appears in the form of an x-ray photon.
Spectrum
Only a few photons have energy close to that of electrons. For most of them it is lower. Let us assume that there is a space, or field, surrounding the nucleus in which the electrons experience a “braking” force. This field can be divided into zones. This gives the nuclear field the appearance of a target with an atom at the center. An electron hitting any point on the target experiences deceleration and generates an X-ray photon. Particles that strike closest to the center are impacted the most and therefore lose the most energy, producing the highest-energy photons. Electrons entering the outer zones experience more and generate quanta with lower energy. Although the zones are the same width, what do they have different area, depending on the distance to the nucleus. Since the number of particles falling on a given zone depends on its total area, it is obvious that the outer zones capture more electrons and create more photons. Using this model, the energy spectrum of X-ray radiation can be predicted.
Emax of photons of the main spectrum of bremsstrahlung radiation corresponds to Emax of electrons. Below this point, as the energy of the quanta decreases, their number increases.
A significant number of low energy photons are absorbed or filtered as they attempt to pass through the anode surface, tube window, or filter. Filtration, as a rule, depends on the composition and thickness of the material through which the beam passes, which determines the final shape of the low-energy spectrum curve.
KV influence
The high-energy part of the spectrum is determined by the voltage in the X-ray tubes, kV (kilovolts). This is because it determines the energy of the electrons reaching the anode, and photons cannot have a potential greater than this. At what voltage does the X-ray tube operate? The maximum photon energy corresponds to the maximum applied potential. This voltage may change during exposure due to AC mains current. In this case, E max of the photon is determined by the peak voltage of the oscillation period KV p .
In addition to the quantum potential, KV p determines the amount of radiation created by a given number of electrons hitting the anode. Since the overall efficiency of bremsstrahlung increases due to an increase in the energy of bombarding electrons, which is determined by KV p, it follows that KV p affects the efficiency of the device.
Changing KV p, as a rule, changes the spectrum. Total area under the energy curve represents the number of photons. Without a filter, the spectrum is a triangle, and the amount of radiation is proportional to the square of KV. With a filter, increasing the KV also increases photon penetration, which reduces the percentage of radiation filtered. This leads to an increase in radiation output.
Characteristic radiation
The type of interaction that produces characteristic radiation involves the collision of high-speed electrons with orbital ones. An interaction can only occur when the incoming particle has an E k greater than the binding energy in the atom. When this condition is met and a collision occurs, the electron is knocked out. In this case, a vacancy remains, filled by a particle of a higher energy level. As the electron moves, it releases energy, which is emitted in the form of an x-ray quantum. This is called characteristic radiation, since E of the photon is the characteristic chemical element, from which the anode is made. For example, when an electron from the K-level of tungsten with E bond = 69.5 keV is knocked out, the vacancy is filled by an electron from the L-level with E bond = 10.2 keV. The characteristic X-ray photon has an energy equal to the difference between these two levels, or 59.3 keV.
In fact, a given anode material gives rise to a range of characteristic X-ray energies. This is because electrons at different energy levels (K, L, etc.) can be knocked out by bombarding particles, and vacancies can be filled from different energy levels. Although filling L-level vacancies generates photons, their energies are too low to be used in diagnostic imaging. Each characteristic energy is given a designation that indicates the orbital in which the vacancy occurred, with a subscript that indicates the source of the electron occupancy. The subscript alpha (α) indicates the occupancy of an electron from the L level, and beta (β) indicates the occupancy from the M or N level.
- Tungsten spectrum. The characteristic radiation of this metal produces a mixture of several discrete energies, while the bremsstrahlung radiation creates a continuous distribution. The number of photons produced by each characteristic energy differs in that the probability of filling a K-level vacancy depends on the orbital.
- Spectrum of molybdenum. Anodes made from this metal used for mammography produce two fairly intense characteristic X-ray energies: K-alpha at 17.9 keV, and K-beta at 19.5 keV. The optimal spectrum of X-ray tubes, allowing to achieve the best balance between contrast and for an average-sized breast, is achieved at E f = 20 keV. However, bremsstrahlung is produced at high energies. Mammography equipment uses a molybdenum filter to remove the unwanted part of the spectrum. The filter works on the K-edge principle. It absorbs radiation that exceeds the binding energy of electrons at the K-level of the molybdenum atom.
- Spectrum of rhodium. Rhodium has atomic number 45 and molybdenum 42. Therefore the characteristic X-ray emission from a rhodium anode will have slightly higher energy than molybdenum and more penetrating. This is used to obtain images of dense breasts.
Anodes with dual surface areas, molybdenum-rhodium, allow the operator to select a distribution optimized for the mammary glands different sizes and density.
Effect of KV on the spectrum
The value of KV greatly influences the characteristic radiation, since it will not be produced if KV is less than the energy of the K-level electrons. When the KV exceeds this threshold value, the amount of radiation is generally proportional to the difference between the tube KV and the threshold KV.
The energy spectrum of the photons of the X-ray beam emerging from the device is determined by several factors. As a rule, it consists of quanta of inhibitory and characteristic interactions.
The relative composition of the spectrum depends on the anode material, KV and filter. In a tube with a tungsten anode, characteristic radiation is not formed at KV< 69,5 кэВ. При более высоких значениях КВ, используемых в диагностических исследованиях, характеристическое излучение увеличивает суммарную радиацию до 25%. В молибденовых устройствах оно может составить большую часть общего объема генерации.
Efficiency
Only a small portion of the energy delivered by electrons is converted into radiation. The main share is absorbed and converted into heat. Radiation efficiency is defined as the proportion of the total radiated energy from the total electrical energy imparted to the anode. The factors that determine the efficiency of an X-ray tube are the applied voltage KV and the atomic number Z. An approximate relationship is as follows:
- Efficiency = KV x Z x 10 -6.
The relationship between efficiency and KV has a specific impact on the practical use of X-ray equipment. Due to the heat generated, the tubes have a certain limit on the number electrical energy, which they can dissipate. This imposes a limitation on the power of the device. As KV increases, however, the amount of radiation produced per unit of heat increases significantly.
The dependence of X-ray generation on the composition of the anode is of only academic interest, since most devices use tungsten. The exception is molybdenum and rhodium, used in mammography. The efficiency of these devices is significantly lower than tungsten ones due to their lower atomic number.
Efficiency
The efficiency of an X-ray tube is defined as the amount of irradiation, in milliroentgens, delivered to a point in the center of the useful beam at a distance of 1 m from the focal spot for every 1 mAs of electrons passing through the instrument. Its value expresses the ability of the device to convert the energy of charged particles into x-rays. Allows you to determine the exposure of the patient and the image. Like efficiency, device efficiency depends on a number of factors, including KV, voltage waveform, anode material and degree of surface damage, filter, and time in use of the device.
KV control
The KV voltage effectively controls the output of the X-ray tube. Generally, the output is assumed to be proportional to the square of KV. Doubling the KV increases the exposure by 4 times.
Waveform
The waveform describes the way in which KV changes over time as radiation is generated due to the cyclical nature of the power supply. Several are used various forms waves General principle is: the less the KV shape changes, the more efficiently X-rays are produced. Modern equipment uses generators with a relatively constant KV.
X-ray tubes: manufacturers
Oxford Instruments produces various devices, including glass with power up to 250 W, potential 4-80 kV, focal spot up to 10 microns and a wide range of anode materials, including Ag, Au, Co, Cr, Cu, Fe, Mo, Pd, Rh, Ti, W.
Varian offers more than 400 different types of medical and industrial X-ray tubes. Other well-known manufacturers are Dunlee, GE, Philips, Shimadzu, Siemens, Toshiba, IAE, Hangzhou Wandong, Kailong, etc.
Svetlana-Roentgen X-ray tubes are produced in Russia. In addition to traditional devices with a rotating and stationary anode, the company produces devices with a cold cathode controlled by the light flux. The advantages of the device are as follows:
- operation in continuous and pulse modes;
- inertia;
- regulation of intensity by LED current;
- spectrum purity;
- possibility of obtaining X-ray radiation of varying intensities.
GOST R 55771-2013
NATIONAL STANDARD OF THE RUSSIAN FEDERATION
MEDICAL ELECTRICAL PRODUCTS
X-ray computer tomographs. Technical requirements for public procurement
Medical electrical equipment. Angiography X-ray equipment. Technical requirements for government purchases
OKS 11.040.50
Date of introduction 2015-01-01
Preface
1 DEVELOPED by the Federal State Budgetary Institution "All-Russian Research and Testing Institute of Medical Equipment" Federal service for supervision in the field of healthcare and social development (FSBI "VNIIIMT" of Roszdravnadzor)
2 INTRODUCED by the Technical Committee for Standardization TC 411 "Apparatus and equipment for radiation diagnostics, therapy and dosimetry"
3 APPROVED AND ENTERED INTO EFFECT by Order of the Federal Agency for Technical Regulation and Metrology dated November 8, 2013 N 1549-st
4 INTRODUCED FOR THE FIRST TIME
The rules for the application of this standard are established in GOST R 1.0-2012 (section 8). Information about changes to this standard is published in the annual (as of January 1 of the current year) information index "National Standards", and the official text of changes and amendments is published in the monthly information index "National Standards". In case of revision (replacement) or cancellation of this standard, the corresponding notice will be published in the next issue of the information index "National Standards". Relevant information, notices and texts are also posted in the information system public use- on the official website of the Federal Agency for Technical Regulation and Metrology on the Internet (gost.ru)
Introduction
Introduction
This standard establishes the basic requirements that must be contained in the technical specifications for public procurement of X-ray computed tomographs intended for obtaining layer-by-layer images and 3D images (XCT).
When conducting competitive bidding, tender assignments for the purchase of electronic equipment in a number of cases include technical requirements that do not correspond to the purpose of the purchased equipment: either overly specific and redundant, or indirectly related to its consumer properties. This standard aims to streamline the current practice of training technical requirements for government procurement.
There are no international analogues to the standard. This standard reflects the specifics of domestic forms of public procurement of high-tech medical equipment and can only be a national document.
1 Application area
This standard establishes general requirements for the preparation of technical specifications (TOR) and their execution during public procurement of medical equipment (MO): X-ray computer tomographs designed to obtain layer-by-layer images and 3D images (XCT).
This standard is a private standard in relation to GOST R 55719-2013 "Medical electrical products. Requirements for the content and execution of technical specifications for competitive documentation for public procurement of high-tech medical equipment."
This standard applies to tenders for state and municipal procurement by the Ministry of Defense for the provision of medical care. The standard does not apply to non-state procurement by the Ministry of Defense.
This standard applies to RKT.
The standard does not apply to tomosynthesis devices.
2 Normative references
This standard uses normative references to the following national standards:
GOST R 55719-2013 Medical electrical products. Requirements for the content and execution of technical specifications for competitive documentation during public procurement of high-tech medical equipment
GOST R 50267.0-92 (IEC 601-1-88) Medical electrical products. Part 1. General safety requirements
GOST R 50267.0.2-2005 (IEC 60601-1-2:2001) Medical electrical products. Part 1-2. General safety requirements. Electromagnetic compatibility. Requirements and test methods
GOST R 50267.32-99 (IEC 60601-2-32-94) Medical electrical products. Part 2. Particular safety requirements for auxiliary equipment X-ray machines
GOST R IEC 60601-1-2010
GOST R IEC 60601-2-28-2013
GOST R IEC 60601-2-44-2013
GOST R IEC/TO 60788-2009
Note - When using this standard, it is advisable to check the validity of the reference standards in the public information system - on the official website of the Federal Agency for Technical Regulation and Metrology for Standardization on the Internet or according to the annually published information index "National Standards", which was published as of January 1 of the current year, and according to the releases of the monthly information index "National Standards" for the current year. If an undated reference standard is replaced, it is recommended that the current version of that standard be used, taking into account any changes made to that version. If a dated reference standard is replaced, it is recommended to use the version of that standard with the year of approval (adoption) indicated above. If, after the approval of this standard, a change is made to the reference standard to which a dated reference is given, affecting the provision to which the reference is given, then this provision is recommended to be applied without taking into account this change. If the reference standard is canceled without replacement, then the provision in which the reference is given to it, it is recommended to apply in the part not affecting this reference.
3 Terms and definitions
This standard uses terms according to GOST R IEC 60601-1, GOST R IEC 60601-2-44 and GOST R IEC/TO 60788, as well as the following terms with corresponding definitions:
3.1 warranty period: The period of time during which the manufacturer guarantees the stability of product quality indicators during operation, subject to compliance with operating rules.
Note 1 - Within warranty period The manufacturer is responsible for hidden and obvious defects, unless otherwise provided by the agreement (contract).
Note 2 - The manufacturer, at the request of the customer, is obliged to eliminate them free of charge, unless he proves that the defects were the result of circumstances for which he is not responsible.
3.2 standard (assigned) service life: The calendar duration of operation, upon reaching which the operation of the facility must be terminated, regardless of its technical condition.
Note - Upon expiration of the assigned resource (service life), the object must be removed from service and a decision must be made, provided for by the relevant regulatory and technical documentation, - sending it for repair, decommissioning, destruction, inspection and establishing a new assigned period.
4 General requirements for the content of technical specifications for public procurement of medical equipment
4.1 Technical specifications are developed by the customer. The technical specifications determine the subject of the MO purchase order.
Responsibility for the completeness and sufficiency of the technical specifications lies with the customer.
4.2 When preparing technical specifications for the purchase of medical equipment, it is prohibited to indicate specific trademarks, service marks, brand names, patents, utility models, industrial designs, appellations of origin of goods or names of the manufacturer (except for cases indicated separately).
5 Main technical characteristics indicated in the terms of reference for the auction
5.1 The following are the characteristics (parameters) that should be included in the terms of reference for public procurement of RKT:
- supply voltage, V;
- power consumption, kW, not less;
- spiral type RCT (if available);
- number of detector lines;
- minimum time for one rotation of the X-ray tube, s, no more;
- minimum thickness cut, mm, no more;
- maximum field scanning, mm;
- heat capacity of the X-ray tube, MHU;
- x-ray tube cooling rate, kHU/min;
- rated power of the X-ray generator, kW, not less;
- gantry hole diameter, mm;
- density measurement range, Hounsfield e, not less;
- data collection matrix, no worse;
- image reconstruction time, image/s, not less;
- image matrix, no worse;
- contrast sensitivity, %, not less;
- spatial resolution, line pairs/cm, no less;
- load capacity of the table for the patient, kg, not less;
- range of vertical movement of the table for the patient, mm, not less;
- range of horizontal movement of the patient, not less;
- speed of movement of the table for the patient, mm/s;
- software: basic and special.
Notes
1 Most clinical routine examinations can be performed on a 16-slice X-ray CT scan. Tomographs with a large number of slices (64, 128 or more) per revolution of the X-ray tube are intended for more complex studies (cardiac) and for a certain group of patients (for example, children). The more lines of detectors the RCT contains, the faster the collection of information for a given 3D image occurs, which is especially important for the cardiovascular system. When studying a heart that is in constant and rapid motion, synchronization with an ECG is used. However, with an increase in the number of detector lines and, consequently, the number of X-ray CT slices, the radiation dose to the patient increases and the image quality deteriorates due to radiation scattered by the object. To reduce the patient's radiation dose, certain RCT operating modes and special dose modulation programs are used depending on the patient's build, age, and gender.
2 When purchasing, the customer determines the type of RCT depending on the profile of the medical institution and the type of research performed and is responsible for this.
5.2 List regulatory documents, which the RKT must comply with, is given in Appendix A.
6 Requirements for the preparation of technical specifications
6.1 An example of medical and technical characteristics of RCT is given in Appendix B.
6.2 It is possible to include additional requirements justified by the customer from the standpoint of conducting the necessary research in accordance with the profile of the medical institution.
Appendix A (mandatory). List of regulatory documents that an X-ray computed tomograph must comply with
Appendix A
(required)
Table A.1
Designation | Name |
Medical electrical products. Part 1. General safety requirements taking into account the main functional characteristics |
|
Medical electrical products. Part 2-28. Particular safety requirements taking into account the basic functional characteristics of medical diagnostic X-ray emitters |
|
Medical electrical products. Part 2-44. Particular safety requirements taking into account the basic functional characteristics of X-ray computed tomographs |
|
Medical electrical products. Dictionary |
|
Radiation safety standards |
|
Hygienic requirements to the construction and operation of X-ray rooms, devices and conducting X-ray examinations |
Appendix B (for reference). An example of medical and technical characteristics of an X-ray computed tomograph
Appendix B
(informative)
Table B.1
Characteristic name | Value for 64-slice X-ray CT | Value for 16-slice RCT |
Scan Options |
||
Scan area | Whole body, head |
|
Scanning system, 360°/rotation | Continuous rotation |
|
Spiral scan while the patient table is moving | Continuous scanning |
|
Minimum X-ray tube rotation time, s | ||
Maximum scanning field, mm | ||
Cut thickness, mm | ||
Spiral scan |
||
Maximum time of one scan, s, not less | ||
Minimum speed for spiral scanning, mm/s, no more | ||
Maximum speed during helical scanning, mm/s | ||
Gantry |
||
Aperture diameter, cm, not less | ||
Laser positioning | ||
Gantry movement control, remote and manual | ||
Detector |
||
Number of simultaneously obtained slices, pcs. | ||
Minimum thickness of one cut, mm, no more | ||
X-ray tube |
||
Heat capacity of the X-ray tube, MHU, not less | ||
X-ray tube cooling rate, kHU/min, not less | ||
Minimum focus size, mm, no more | ||
X-ray generator |
||
Rated power, kW, not less | ||
Range of changes in anode voltage, kV | ||
Range of changes in anode current, mA | ||
Patient table |
||
Electromechanical and manual drive | ||
Opportunity remote control movement of the table | ||
Range of vertical movement, cm | ||
Maximum horizontal movement, cm, not less | ||
Table deck width, cm, not less | ||
Table movement speed, mm/m | ||
Image Options |
||
Data collection matrix, no worse | ||
Reconstruction time, image/s, not less | ||
Image matrix, no worse | ||
Low contrast resolution at 0.3%, no less | ||
High contrast resolution (at 250 mA anode current, 120 kV ANODIC VOLTAGE, 0.5 s scan time, 1 mm slice thickness) | ||
Catphan phantom with a diameter of 20 cm | ||
Software |
||
Basic package | ||
Dose modulation protocols | ||
Cardio package | ||
Synchronization with ECG | ||
Axial cardiography | ||
Arrhythmia correction | ||
Pediatric protocols | ||
Beam taper correction software | ||
Special software | According to customer needs |
|
Checking for calcification of coronary vessels | ||
Vascular examination | ||
Cardiac parameters | ||
Pulmonary function test | ||
Characteristics of the power supply network |
||
Supply voltage, V | 3-phase, 380 | 3-phase, 380 |
Power consumption, kW, not less | ||
Warranty period of operation, years, not less | ||
Standard service life, years, not less |
||
UDC 621.86.1:616-073.7:006.354 OKS 11.040.50
Key words: X-ray tomograph, tomographic plane, tomographic slice, computed tomography dose index, image
_______________________________________________________________________________
Electronic document text
prepared by Kodeks JSC and verified against:
official publication
M.: Standartinform, 2014
Application of accelerators
And X-ray devices
Tutorial
to course design
Saint Petersburg
Publishing house SPbSETU "LETI"
UDC ___________
BBK____________
I00 Gryaznov A.Yu., Potrakhov N.N. Application of accelerators and X-ray devices: Textbook. allowance. St. Petersburg: Publishing house of St. Petersburg Electrotechnical University "LETI", 2006, 46 p.
Intended for students of specialty 200300 and direction 654100, and can also be useful to engineering and technical workers in this field of knowledge.
UDC ___________
BBK____________
Reviewers: laboratory technical means non-destructive testing Moscow Institute radio-electronic equipment; Ch. engineer of ZAO ELTECH-Med V.M. Mukhin
Approved
Editorial and Publishing Council of the University
as guidelines
ISBN 0-0000-0000-0 © SPbSETU "LETI", 2006
INTRODUCTION
X-ray equipment occupies one of the leading places among the means used to study the structure of matter, non-destructive quality control of products, radiation technology, the study of fast processes and solving other scientific and technical problems. Functionality and the technical level of X-ray equipment are largely determined by the parameters of the radiation sources used in it - X-ray tubes.
Historically the first areas practical use X-ray radiation was used for medical diagnostics and transillumination of materials. To obtain shadow pictures of the objects under study, at the initial stage of development of X-ray technology, ion X-ray tubes were used. The work of Lilienfeld and especially Coolidge (1912 - 1913) led to the creation of electron tubes with a thermionic cathode, which later received exceptional development.
On at the moment Thanks to advances in vacuum technology and technology, X-ray tubes have been significantly improved. The developed range of existing X-ray tubes makes it possible to solve a wide range of practical problems of various kinds: X-ray structural and X-ray spectral analyses, X-ray diffraction of fast processes, study of phase and elemental composition for industrial and scientific purposes, quality control of microelectronics and semiconductor products, X-ray ranging, X-ray luminescence separation of rocks, X-ray lithography and much more.
The symbol of X-ray devices (marking) is defined in OST 11.073.807-82 “Electrovacuum devices. System of symbols" and reflects the purpose, and sometimes the main parameters of the devices. In accordance with OST, the symbol includes a combination of numbers and letters: number \ letters \ number \ - number.
For X-ray tubes for industrial transmission and structural and spectral analysis, the first digit indicates the maximum permissible power during long-term operation in kilowatts. This is followed by a letter indicating the method of protection against radiation: “P” - complete protection is provided; “B” - additional protection is required by elements of the casing or monoblock of the device. The following letter indicates the area of application: “P” - for industrial transillumination; “X” - for spectral analysis; “C” - for structural analysis; “M” - for medical x-raying; "T" - for therapy; "D" - for flaw detection.
The third letter indicates the nature (method) of forced cooling: “B” - water; “K” - air; "M" - oil. The absence of the third letter means cooling by natural convection or radiation. The number following the letters indicates the serial number of the device in this group.
For industrial screening tubes, the next number (written with a hyphen) indicates the maximum permissible anode voltage in kilovolts. For structural and spectral analysis tubes, the last element symbol(spelled with a hyphen) is the symbol for the anode target material. Sometimes, after the standard designation of the tube, a Roman numeral is added in brackets, indicating the external design of the device (if required various designs protective covers equipment of old and new modifications). Information about the difference in design is given in the device passport and in advertising messages.
Design and technology
modern x-ray tube
The main components of a modern X-ray tube are the cathode assembly, the vacuum shell and the anode assembly.
The cathode unit is designed to generate an electron flow of a given shape. The design of the cathode assembly includes current-carrying wires, a cathode holder, current-carrying posts, a filament, a cathode screen and an insulator.
Either a directly heated thermal cathode or a field emission emitter is mainly used as sources of electrons. The cathode is attached (by welding or mechanically) to molybdenum posts, one of which is attached to the cathode holder and has electrical contact with it, and the other is mechanically fixed to the cathode holder, but is separated from it by an insulator. Current-carrying wires are brought to the insulated stand and to the cathode holder and taken out outside the vacuum shell.
In order for the emitted electron flow to have a certain shape along the entire path from the cathode to the anode target, the design of the cathode assembly is an electron-optical system. The effect of focusing the electron beam is ensured by a certain shape of the hole in the cathode screen. To the tube cathodes, along with general requirements The cathodes of electric vacuum devices (provide the necessary and stable emission current during the entire service life, are well degassed and do not deteriorate the vacuum in the device in operating conditions, have a sufficient service life, etc.), are subject to a number of special requirements: stability of operation at high voltage fields on the cathode surface and the possibility of adjusting the emission current over a wide range.
Pointed Extended Flat spiral
Rice. 1. Cathode designs
The vacuum shell of the X-ray tube is designed to separate the vacuum volume of the device from the external environment, secure the electrodes in a certain position and isolate them from each other. The cylinder is made by blowing in special forms, allowing you to form the required configuration of the cylinder with sufficient accuracy. The electrodes are connected to the cylinder by soldering. In this case, the cathode and anode units assembled on glass legs are hermetically connected to the cylinder on special brewing machines.
Rice. 2. Types of vacuum shells
The middle part of the cylinder is expanded to increase electrical strength. At the same time, the expansion of the middle part helps to reduce the specific thermal load on the glass surface due to thermal radiation from the cathode and anode. The length of the cylinder is selected taking into account the operating voltage of the tube and the environment in which it will be operated. In the place where the radiation is supposed to be released, the wall thickness is reduced by grinding - a specific outlet window is created. Another option is to use a vacuum-dense beryllium exhaust port.
The anode units of X-ray tubes are designed directly to generate X-ray radiation. The anode of an X-ray tube is the electrode that performs the functions of a target or carries the target of the tube. Part of the X-ray radiation arising from the deceleration of electrons on the target, intended for beneficial use and enclosed in a solid angle, the vertex of which lies in the center of the actual focal spot, is called the working radiation beam of the tube. Geometric characteristics the working radiation beam (its direction and solid angle) depend on the design of the X-ray tube and its anode.
Structurally, the anodes can be made massive or perforated. The massive anode consists of an anode body and a target (composite anode). The material of the anode body must have high thermal conductivity, since heat is transferred through the anode body to the cooling device. Most often, the anode body is made of copper, which has a fairly high melting point (1360 K), good vacuum properties, high heat capacity and thermal conductivity. The target applied to the anode surface requires a high melting point and low vapor pressure at high temperatures. In tubes designed to produce bremsstrahlung radiation, the targets are made of tungsten. To obtain characteristic radiation of a certain hardness (tubes for X-ray structural analysis and X-ray spectral analysis), targets are made from various materials(chrome, iron, copper, molybdenum, silver, etc.).
Rice. 3. Design of a massive anode assembly
1 – target, 2 – anode body, 3 – central cooling tube,
4 - connecting kovar ring, 5 - edge of the glass container
In some cases, the target is structural element is absent in the tube, and its functions are performed by the surface of the anode body (homogeneous anode). The main requirement in the manufacture of a massive anode with a target is good thermal contact between the target and the anode body. This requirement is met by various technological methods: vacuum melting, diffusion welding, electrochemical or plasma deposition. Vacuum melting is used to produce anodes with massive refractory targets made of tungsten, molybdenum or rhodium. For melting, a dismountable graphite crucible in the form of a glass is used, on the bottom of which a target is installed at the required angle. Then a copper cylindrical blank, previously cleaned of contaminants, is placed into the crucible. Copper smelting in a crucible is carried out in a vacuum furnace with electric heating or through high frequency currents under a quartz cap. Depending on the mass of the anodes, melting modes are selected so that the copper body of the anode has a coarse-crystalline structure. After melting, the anode blank is processed mechanically, giving it the required configuration. The design of the anode cooling device depends on the operating mode, tube power and some other factors. In X-ray tubes operating in the mode of intermittent switching on of medium power (several hundred watts), radiator cooling is used.
A flange is welded to the copper body of the anode with the target, through which the anode assembly is connected to the tube cylinder. The radiator is fixed to the anode shank by a shrink fit after pumping out the tube. For the purpose of reliable thermal contact, the mating surfaces of the anode and radiator body are carefully processed. To increase the heat transfer surface, the radiator is multi-finned. Oil, water or air can be used as a cooling medium. Depending on the design of the emitters and operating modes, cooling can be forced (using pumps) or natural. In high-power (up to 4 kW) tubes operating in long-term continuous mode, flow liquid cooling systems are used. Water or transformer oil is used as a refrigerant. In both cooling systems, the liquid enters the anode cavity through a tube located on its axis, washes the inner wall of the cavity directly, spreading through the channels of a special bifilar spiral soldered to the end part of the cooled surface. The spiral, called a volute, helps to better wash the hottest end part of the cooled surface with liquid, and also increases the heat exchange surface. Therefore, the volute cooling system is capable of delivering higher power. Volute cooling systems typically use transformer oil as a coolant, which simultaneously serves as insulation for the X-ray tube from the grounded housing or transformer oil tank in which the tube is located. The system usually uses water directly from the water supply for cooling, and the anode assembly is grounded.
In stationary and mobile equipment for flaw detection, X-ray tubes of an end design with a cover on the anode are most often used. They typically operate in the voltage range 160 - 320 kV and are characterized by high power, reaching 4 kW. Design feature These devices have a massive copper case on the anode.
Rice. 4. Anode with cover.
1 – cover, 2 – electron beam, 3 – exhaust window, 4 – radiation, 5 – anode
The cover serves to reduce the intensity of unused X-ray radiation and prevents secondary electrons knocked out of the target from reaching the glass shell of the device, helping to increase the electrical strength and reliability of the tube. Sometimes, to enhance the protective properties of the cover, it is made of a material with additives of heavy elements, for example, tungsten, or is equipped with internal screens in the form of cylinders made of molybdenum or tantalum. A directed working X-ray beam is released through a special hole in the case, which is closed with a beryllium or titanium disk, and then passes through the tube cylinder. Anodes of powerful X-ray tubes of this type for stationary equipment, as a rule, have forced oil cooling
Course project assignment
The goal of the course design is to calculate the thermal, electrical and radiation characteristics of an X-ray tube, as well as to develop the main elements of its design.
1. Obtain a variant of the task, which will indicate the basic data for the calculation and design of the X-ray tube (for example, the variant from Table 1):
Type and purpose of the tube.
Operating voltage of the tube.
Rated power of the tube.
Tube target material.
2. Familiarize yourself and bring brief description the basic requirements for the cathode and anode assemblies, the vacuum shell of the tube and the outlet windows of modern X-ray tubes.
3. Calculate the electrical strength for a given X-ray tube.
Determine the interelectrode distance.
Determine the surface area where breakdowns are likely.
Determine the relative position, configuration of the electrodes and their distance from the shell.
Determine the maximum anode temperature at the rated power of the tube.
5. Determine the radiation characteristics of the X-ray tube.
6. Make an assembly drawing of a given X-ray tube indicating the main components. Provide specification.
Table 1
Sample assignment options