What are the features of the choice X-ray machine
High-quality and timely diagnostics 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 apparatus.
Medical center managers are often faced with the question of choosing 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 are the parameters to choose and buy an X-ray machine? How not to overpay for unnecessary functions and not miss the main thing?
Today, more and more obsolete "film" machines are being replaced by digital X-ray machines, increasing the throughput of the office and minimizing the radiation dose. Is it worth making a choice in their favor or working "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 have decided to buy an X-ray machine.
Types of X-ray machines
In accordance with the operating conditions, the X-ray machine can to be ward, mobile and stationary.
Specialized types of X-ray machines are also presented:
NS used in operating rooms for surgical interventions - "GUS", "S-arc"
apparatus for angiography - "S-arc"
mammography - "mammographers"
stationary for two and three workplaces
angiographic "S-arc" "angio complexes"
computed tomographs with different amounts slices
dental x-rays for dental departments
There are also portable, small-sized units used for simple X-rays in an ambulance or at a patient's home. The field of application of portable devices is extremely limited, due to their very low power, therefore, they cannot replace either a mobile, let alone a stationary X-ray device.
Mobile X-ray units are used mainly in wards, which is why they are often called "ward X-ray apparatus". The power of mobile X-ray machines is 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 X-ray examinations in the X-ray department.
The X-ray apparatus of the U-arm type is an X-ray apparatus with an emitter and a detector located on a single rotating stand. An X-ray transparent trolley is used for taking pictures in the "lying" position. This type of stationary X-ray machine is most often used in rooms with a small area.
X-ray systems based on a telecontrolled tripod table are the most expensive type of stationary X-ray apparatus. These are 3-in-1 installations for the X-ray diagnostic department of any modern medical institution... They allow you to carry out all possible X-ray and fluoroscopic examinations. The most common type of stationary X-ray system in medical centers is the classic two-seat X-ray unit. The main components of such systems are an X-ray tube (with a ceiling or floor mount m), a table of pictures - for a "lying" position, a stand of pictures - for a "standing" position and a generator.
When buying an X-ray machine, it is important to determine the research profile and the location of the equipment. Having chosen the type of the X-ray apparatus, one can proceed to the assessment of its technical parameters.
Important specifications X-ray apparatus
Generator power
When choosing a device, you should also take into account the main technical characteristics. The higher the power of the power supply, the less time the exposure, the lower the radiation exposure, and with some examinations 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 widespread are configurations with a power supply of 50 kW - this is enough for the vast majority of studies. But it is important to take into account that the generator power must be matched with the operating power of the X-ray tube foci, which determine the operating power of the "generator-X-ray tube" system.
Generator type
When choosing an X-ray apparatus, it is also important to take into account the type of generator: high-frequency power supplies are characterized by a small ripple of the anode voltage, which increases the resource of the X-ray tube and reduces the radiation dose for the patient.
The technical solutions implemented in the design of the best modern generators provide X-ray images with high contrast and spatial resolutions, as well as maximum research safety due to minimization of "soft" X-ray radiation that does not participate in the formation of the image.
X-ray tube parameters
The main characteristics of the X-ray tube itself, which are important for X-ray diagnostics, areeffective focus sizes .
The value of theoretically achievable spatial resolution decreases with increasing focus size. With a focus size of 2 mm in different estimates up to 3 line pairs / mm can be recognized, even if the detector has best performance(X-ray film, for example, can distinguish 10-15 line pairs / mm). All tubes have two working focuses. The lower the value of the focus size of the X-ray tube, the clearer the images will be, but decreasing the focus size also reduces the operating power.
In this case, it is important that the power of the X-ray apparatus generator corresponds to the operating power of the foci of the supplied tube.
Another characteristic of X-ray tubes isthe value of the heat capacity of the anode affecting the resource intensity of the system. The higher this indicator, the more quantity research until 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 image table.
The most expensive and reliable components are used in the production of picture tables with a high maximum permissible load. A good indicator the permissible maximum table load is considered to be 200 kg, but some manufacturers produce optional table models with a permissible load of up to 290 kg or even higher.
The X-ray machine can also be equipped with an image table with an "elevator" option, which allows the table surface to be moved in a vertical plane - on average, in the range of 500-850 mm from the floor level.
Tube mounting options
Stationary X-ray machines for 2 workplaces have two options for mounting the tube - on a floor stand and on a ceiling.
The most common option in private medical centers is the option of mounting the tube on a floor stand. It is easier to install, does not have serious restrictions on minimum height ceilings and areas of the X-ray room.
Ceiling tube mounting is a more expensive option, including installation, but also more reliable and convenient to use. If the dimensions of the room, the ceiling and the budget allocated for the X-ray apparatus allow, then with a large planned flow of patients it is better to choose the option ceiling mount tube.
If at large stream patients are expected to purchase an X-ray device with a floor tube mount, you should pay attention to options with a reinforced floor stand.
Benefits of digital X-ray machines
In recent years, diagnostics have been increasingly carried out using digital X-ray equipment of a new generation. It provides instant acquisition of images, eliminates the development process, allows you to store images and carry out diagnostics using computer technology.
The digital X-ray apparatus differs in that the images of anatomical structures obtained using X-ray irradiation are digitally processed.
The main advantages of this modern method diagnostics can be called:
the highest quality of the obtained images: the possibility of their digital processing allows revealing important details;
speed and convenience of work: immediately after the procedure, the image is available for analysis;
Convenience of storage and space saving due to the creation of mobile and easily accessible X-ray archives,
lower cost of research due to the absence of film and reagents, and environmental safety, due 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 with a digital system are more expensive than analog ones, but they do not require a developing machine with consumables and a special darkened room for it.
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 obtained images, so that it would be easier for specialists to determine the diagnosis and the specifics of the disease.
A system based on semiconductor flat detectors is the most modern technology with a higher resolution.
CR systems apply the principle of phosphor sensitivity. Outwardly, this is a conventional X-ray machine, in which a CR-cassette based on storage phosphors is used instead of a film cassette. After taking a 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 transfers the obtained digital image to the laboratory assistant's workstation, while the cassette will be cleaned and ready for the next examination.
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 X-ray rack, or two - for both the table and the X-ray rack.
It should be borne in mind that a flat-panel detector should never be dropped, and its cost makes up a large part of the entire DR-system, in contrast to CR, where the cost of a single cassette is insignificant.
After a snapshot, almost instantly, a flat-panel detector transmits a digital image to the laboratory assistant's workstation. There is no link in the chain in the form of a digitizer (digitizer), which significantly reduces the time for obtaining 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 digitizer cassettes (CR), but they are justified with a large flow of patients, since they significantly increase the throughput of the X-ray room, are more reliable, and also provide the best image quality.
In addition to the laboratory technician's workstation, usually included with CR or DR systems, to equip the radiology department with a digital X-ray machine, you will need a doctor's workstation, complete with a high-resolution medical monitor, and a special printer for printing X-ray images.
When choosing and buying 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.
Competent selection of equipment is of great importance for the full functioning of the X-ray department in a private clinic.
Usage: in X-ray engineering. The essence of the invention: the anode contains a base of a molybdenum alloy, which includes at least one of the elements selected from the group including niobium, tantalum and rhenium, and a target from a tungsten alloy, the base and the target are made in the form of a coherent monocrystalline structure. 1 wp f-ly.
The invention relates to sources of x-ray radiation and can be used to create x-ray emitters with elevated level capacity and resource of work for medical and technical purposes. Known are rotating anodes of an X-ray tube, 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 insufficient service life and low reliability due to recrystallization processes in working area at high thermal loads. The closest technical solution to the claimed technical essence is an anode containing a base of molybdenum alloy, 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-hardened molybdenum alloys. In such materials, at elevated temperatures, recrystallization processes can occur intensively. Their thermal strength under cyclic exposure also has temperature limits at the used anode rotation speeds. In this case, cyclic internal stresses cause cracking of the surface of the annular working track on the anode target, which leads to a decrease in the radiation intensity and the service life of the tube. Therefore, when using polycrystalline materials, in particular alloys based on molybdenum, the maximum allowable power of the X-ray emitter and its service life are determined from the condition that the average mass temperature of the anode does not exceed 1200-1300 ° C. The aim of the invention is to increase the anode's resistance 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 monocrystalline alloy based on molybdenum, predominantly alloyed 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 heat resistance of the anode in the temperature range 1400 -1700 o C and satisfactory workability at room temperature. Alloys of this composition belong to alloys with a solid solution type of hardening and are characterized by high structural stability in the entire temperature range of existence. Therefore, when the anode disk is made of a monocrystalline alloy, all processes associated with the temperature kinetics of the development of the structure, characteristic of polycrystalline alloys, are completely excluded. These differences make it possible to raise the permissible level of the average mass temperature of the disk to 1400-1600 o C. In addition, the design of the disk is monocrystalline so that its surface on the side of the target layer coincides with the close-packed crystallographic face (110), which makes it possible to further increase the reliability of the anode and the permissible power for account of the orientation of the crystal. Doping of molybdenum in the above amounts 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, the thermal conductivity decreases. 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 disk made of a single crystal of molybdenum alloy. The disc diameter is about 100 mm, the thickness is about 5 mm. The surface of the disc from the side of the target has a taper of 12 °. The disk blank was obtained 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 (anodes of an X-ray tube 2-30BD11-150). It was found that in terms of power dissipation, the proposed anodes surpass the known ones by 30-40%, which provides an increase in the reliability of the anode, as well as the power of the X-ray tube containing the anode of the claimed design.
Claim
1. A ROTATING X-RAY TUBE ANODE comprising a molybdenum alloy base containing at least one of the elements selected from the group consisting of niobium, tantalum and rhenium, and a tungsten or its alloy target, characterized in that, for the purpose increasing the resistance of the anode to thermal loads, the base and the target are made in the form of a coherent monocrystalline structure. 2. Anode according to claim 1, characterized in that the surface of the connected monocrystalline structure coincides with the plane of the crystallographic form (110).
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 governmental purchases
OKS 11.040.50
Introduction date 2015-01-01
Foreword
1 DEVELOPED by the Federal State Budgetary Institution "All-Russian Research and Testing Institute of Medical Technology" Federal Service on supervision in the field of health care 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 PUT INTO EFFECT by the Order of the Federal Agency for Technical Regulation and Metrology of November 8, 2013 N 1549-st
4 INTRODUCED FOR THE FIRST TIME
The rules for the application of this standard are set out in GOST R 1.0-2012 (section 8). Information on 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, notice and texts are also posted in the information system. common 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 terms of reference for government procurement of X-ray computed tomographs intended for obtaining layer-by-layer images and 3D images (RKT).
When conducting competitive bidding, tenders for the purchase of RKT in a number of cases include technical requirements that do not correspond to the purpose of the purchased equipment: either excessively specified and redundant, or indirectly related to its consumer properties. This standard aims to streamline the established practice of preparing technical requirements for public 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 area of use
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 (RKT).
This standard is a private standard in relation to GOST R 55719-2013 "Medical electrical devices. Requirements for the content and design of technical specifications for tender documentation for public procurement of high-tech medical equipment."
This standard applies to tendering for state and municipal procurement of medical services for the provision of medical care. The standard does not apply to non-government procurement of medical organizations.
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 equipment. Requirements for the content and execution of technical specifications for tender documentation for public procurement of high-tech medical equipment
GOST R 50267.0-92 (IEC 601-1-88) Medical electrical equipment. Part 1. General safety requirements
GOST R 50267.0.2-2005 (IEC 60601-1-2: 2001) Medical electrical equipment. Part 1-2. General safety requirements. Electromagnetic compatibility. Requirements and test methods
GOST R 50267.32-99 (IEC 60601-2-32-94) Medical electrical equipment. Part 2. Particular safety requirements for auxiliary equipment of 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 operation of 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 for the issues of the monthly information index "National Standards" for the current year. If the referenced standard to which an undated reference is given is replaced, it is recommended that the current version of that standard be used, subject to any changes made to that version. If the referenced standard to which the dated reference is given is replaced, then it is recommended to use the version of that standard with the above year of approval (acceptance). If, after the approval of this standard, a change is made to the referenced 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 that does not affect this link.
3 Terms and definitions
This standard uses the 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 appropriate definitions:
3.1 warranty period of operation: The period of time during which the manufacturer guarantees the stability of the product quality indicators during operation, provided that the operating rules are observed.
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 the occurrence of which he is not responsible.
3.2 standard (assigned) service life: Calendar duration of operation, upon reaching which the operation of the facility must be terminated regardless of its technical condition.
Note - Upon the expiration of the assigned resource (service life), the object must be withdrawn from operation and a decision must be made, provided for by the relevant regulatory and technical documentation, - sending for repair, write-off, destruction, verification and establishment of a new assigned period.
4 General requirements for the content of the terms of reference for public procurement of medical equipment
4.1 TK is developed by the customer. TK determines the subject of placing an order for the purchase of MO.
The customer is responsible for the completeness and sufficiency of the TK.
4.2 When preparing the TK for the purchase of MO, it is prohibited to indicate specific trademarks, service marks, brand names, patents, utility models, industrial designs, appellations of origin or manufacturer's names (except for cases specified separately).
5 Main technical characteristics specified in the terms of reference for the auction
5.1 The following are the characteristics (parameters) that should be included in the TOR for public procurement of RCT:
- supply voltage, V;
- power consumption, kW, not less;
- spiral type RCT (if any);
- the number of detector lines;
- the minimum time of one revolution of the X-ray tube, s, no more;
- minimum thickness cut, mm, no more;
- maximum scanning field, mm;
is the heat capacity of the X-ray tube, MHU;
- X-ray tube cooling rate, kHU / min;
- rated power X-ray generator, kW, not less;
- gantry hole diameter, mm;
- range of density measurement, Hounsfield units, not less;
- data collection matrix, not worse;
- image reconstruction time, images / s, not less;
- image matrix, not worse;
- contrast sensitivity,%, not less;
- spatial resolution, pairs of lines / cm, not less;
- carrying capacity of the table for the patient, kg, not less;
- the range of vertical movement of the table for the patient, mm, not less;
- the 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 (edit)
1 Most clinical routine examinations can be performed on 16-slice CT. Tomographs with a large number of slices (64, 128 and more) in one revolution of the X-ray tube are designed for more complex studies (cardiac) and for a certain group of patients (for example, children). The more lines of detectors the RKT contains, the faster information is collected for a given 3D image, which is especially important for the cardiovascular system. When examining the heart, which is in constant and rapid movement, synchronization with the ECG is used. However, with an increase in the number of detector lines and, consequently, the number of RCT slices, the patient's radiation dose increases and the image quality deteriorates due to the radiation scattered by the object. To reduce the patient's radiation dose, certain modes of RKT operation and special dose modulation programs are used, depending on the patient's complexion, age, gender.
2 When purchasing, the customer determines the type of RCT depending on the profile of the medical institution and the type of research being carried out and is responsible for this.
5.2 The list of normative documents that the RCT must comply with is given in Appendix A.
6 Requirements for the design of technical specifications
6.1 An example of medical and technical characteristics of the 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). The list of normative documents that an X-ray computed tomograph must comply with
Appendix A
(required)
Table A.1
Designation | Name |
Medical electrical equipment. Part 1. General safety requirements taking into account basic functional characteristics |
|
Medical electrical equipment. Part 2-28. Particular safety requirements taking into account the main functional characteristics of medical diagnostic X-ray emitters |
|
Medical electrical equipment. Part 2-44. Particular safety requirements, taking into account the main functional characteristics for X-ray computed tomographs |
|
Medical electrical equipment. Dictionary |
|
Radiation safety standards |
|
Hygienic requirements for the design and operation of X-ray rooms, apparatus and X-ray examinations |
Appendix B (reference). An example of medical and technical characteristics of an X-ray computed tomograph
Appendix B
(reference)
Table B.1
Description of characteristics | Value for 64-slice CT | Value for 16-slice CT |
Scan options |
||
Scan area | Whole body, head |
|
Scanning system, 360 ° / rotation | Continuous rotation |
|
Spiral scan while moving the patient table | Continuous scan |
|
X-ray tube minimum turnaround time, s | ||
Maximum scanning field, mm | ||
Slice thickness, mm | ||
Spiral scan |
||
Maximum time of one scan, s, not less | ||
Minimum speed for spiral scanning, mm / s, no more | ||
Maximum speed during spiral scanning, mm / s | ||
Gantry |
||
Aperture diameter, cm, not less | ||
Laser positioning | ||
Remote and manual gantry movement control | ||
Detector |
||
Number of slices obtained at the same time, pcs. | ||
Minimum thickness of one cut, mm, no more | ||
X-ray tube |
||
X-ray tube heat capacity, 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 variation of anode voltage, kV | ||
Range of variation of anode current, mA | ||
Patient table |
||
Electromechanical and manual drive | ||
Possibility remote control table movement | ||
Vertical movement range, 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, images / s, not less | ||
Image matrix, no worse | ||
Low contrast resolution at 0.3%, not less | ||
High contrast resolution (at anode current 250 mA, ANODE VOLTAGE 120 kV, scan time 0.5 s, slice thickness 1 mm) | ||
Phantom Catphan with a diameter of 20 cm | ||
Software |
||
Basic package | ||
Dose modulation protocols | ||
Cardiopackage | ||
Synchronization with ECG | ||
Axial cardiography | ||
Arrhythmia correction | ||
Pediatric protocols | ||
Beam taper correction software | ||
Special software | According to customer needs |
|
Checking the calcification of the coronary vessels | ||
Vascular examination | ||
Cardiac parameters | ||
Lung function test | ||
Power supply characteristics |
||
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 text of the document
prepared by JSC "Kodeks" and verified by:
official publication
M .: Standartinform, 2014
Application of accelerators
And x-ray instruments
Tutorial
to course design
St. Petersburg
Publishing house SPbGETU "LETI"
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I00 Gryaznov A.Yu., Potrakhov N.N. Application of accelerators and X-ray devices: Textbook. allowance. SPb .: Publishing house of ETU "LETI", 2006, 46 p.
Designed for students of specialty 200300 and direction 654100, and can also be useful to engineering and technical workers in this area of knowledge.
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Reviewers: laboratory of technical means non-destructive testing Moscow Institute of Radio-Electronic Equipment; ch. engineer of CJSC "ELTECH-Med" V.M. Mukhin
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ISBN 0-0000-0000-0 © SPbGETU "LETI", 2006
INTRODUCTION
X-ray equipment occupies one of the leading places in a number of tools used to study the structure of matter, non-destructive quality control of products, radiation technology, study of fast processes and the solution of other scientific and technical problems. The functionality and 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 were medical diagnostics and transillumination of materials. To obtain shadow pictures of the investigated objects on initial stage In the 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 were subsequently extremely developed.
At the moment, thanks to the successes of vacuum technology and technology, X-ray tubes have been significantly improved. The developed range of existing X-ray tubes allows you to solve the widest range practical tasks of various kinds: X-ray structural and X-ray spectral analyzes, X-ray diffraction of fast processes, study of the phase and elemental composition for industrial and scientific purposes, quality control of microelectronic and semiconductor technology products, X-ray location, X-ray luminescence separation rocks, X-ray lithography and much more.
Conventional designation of X-ray devices (marking) is defined in OST 11.073.807-82 “Electrovacuum devices. The 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: digit \ letters \ digit \ - digit.
For X-ray tubes for industrial transmission and structural and spectral analyzes, the first digit indicates the maximum permissible power during continuous operation in kilowatts. This is followed by a letter denoting the method of protection against radiation: "P" - full protection is provided; "B" - required additional protection elements of the casing or monoblock of the device. The next letter denotes the field of application: "P" - for industrial transillumination; "X" - for spectral analysis; "C" - for structural analysis; "M" - for medical transillumination; "T" - for therapy; "D" - for flaw detection.
The third letter denotes the nature (method) of forced cooling: "B" - water; "K" - air; "M" stands for oil. The absence of the third letter means cooling by natural convection or radiation. The number following the letters denotes the serial number of the device in this group.
For industrial transillumination tubes, the following figure (written with a hyphen) indicates the maximum permissible anode voltage in kilovolts. For tubes of structural and spectral analysis the last element symbol(hyphenated) is the anode target material symbol. Sometimes, after the standard designation of the tube, a Roman numeral in brackets is added, indicating the external design of the device (if this is required by various designs of protective casings of equipment of old and new modifications). Information about the difference in design is given in the data sheet for the device and in advertising messages.
Design and technology
modern x-ray tube
The main assemblies of a modern X-ray tube are the cathode assembly, vacuum cladding and anode assembly.
The cathode assembly is designed to form an electron flow of a given shape. The design of the cathode assembly includes live wires, cathode holder, live posts, filament, cathode screen and insulator.
As sources of electrons, either a direct-heated hot cathode or a field-emitter is mainly used. 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 separated from it by an insulator. Current-carrying wires are led to the insulated rack and to the cathode holder and taken out outside the vacuum sheath.
In order for the emitted electron flow to have a definite shape all the way from the cathode to the anode target, the design of the cathode assembly is an electron-optical system. The focusing effect of the electron beam provides a certain shape of the hole in the cathode screen. For the cathodes of the tubes, along with the general requirements for the cathodes of electrovacuum devices (to provide the necessary and stable emission current during the entire service life, to degass well and not to worsen the vacuum in the device in operating modes, to have a sufficient service life, etc.), a number of special requirements: stability of operation at high field strength on the cathode surface and the possibility of adjusting the emission current over a wide range.
Sharp Extended Flat spiral
Rice. 1. Design of cathodes
The vacuum shell of the X-ray tube is designed to separate the vacuum volume of the device from external environment, fixing the electrodes in a certain position and isolating them from each other. The balloon is made by blowing into special shapes that allow you to form the required configuration of the balloon with sufficient accuracy. The connection of the electrodes to the balloon is carried out by soldering. At the same time, collected on glass legs the cathode and anode units are hermetically connected to the cylinder on special welding machines.
Rice. 2. Types of vacuum casings
The middle part of the balloon is expanded to increase the dielectric strength. In this case, the expansion of the middle part helps to reduce the specific heat 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 the grinding method - a specific outlet window is created. Another option is to use a high-density beryllium outlet.
The anode assemblies of the X-ray tubes are designed directly for generating X-rays. The anode of an X-ray tube is an electrode that acts as a target or carries the target of a tube. Part of the X-ray radiation arising from the deceleration of electrons on the target, intended for useful use and enclosed in a solid angle, the top of which lies in the center of the actual focal spot, is called the working radiation beam of the tube. The geometric characteristics of 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 shot through. The massive anode consists of an anode body and a target (composite anode). The material of the anode body must have a 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 sufficiently high melting point (1360 K), good vacuum properties, high heat capacity and thermal conductivity. The target applied to the anode surface is required to have a high melting point and low vapor pressure at high temperatures. In tubes intended for obtaining bremsstrahlung radiation, 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 of various materials (chromium, iron, copper, molybdenum, silver, etc.).
Rice. 3. The structure of the anode unit of massive type
1 - target, 2 - anode body, 3 - central cooling tube,
4 - connecting kovar ring, 5 - the edge of the glass container
In some cases, the target as a structural element in the tube is absent, and its function is 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 by electrochemical or plasma deposition. Vacuum melting is used for the manufacture of anodes with massive refractory targets made of tungsten, molybdenum or rhodium. For melting, a collapsible graphite crucible in the form of a glass is used, on the bottom of which a target is set at the required angle. Then a copper billet, previously cleaned of contamination, is inserted into the crucible. Melting of copper in a crucible is carried out in a vacuum furnace with electric heating or by means of high-frequency currents under a quartz cap. Depending on the mass of the anodes, the 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. Radiator cooling is used in X-ray tubes operating in the mode of intermittent switching of average power (several hundred watts).
A flange is welded to the copper body of the anode with the target, by means of which the anode assembly is connected to the tube cylinder. The radiator is shrink-fitted to the anode shank after the tube has been evacuated. For the purpose of reliable thermal contact, the mating surfaces of the anode body and the radiator are carefully processed. To increase the heat exchange surface, the radiator is multi-ribbed. The cooling medium can be oil, water or air. Depending on the design of the emitters and operating modes, cooling can be forced (by means of pumps) or natural. In tubes of large (up to 4 kW) power, operating in a long-term continuous mode, flow-through 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 the cochlea, promotes better liquid washing over the hottest end part of the cooled surface, and also increases the heat exchange surface. Therefore, the volute cooling system is capable of dissipating higher power. Volute cooling systems typically use transformer oil as the refrigerant, which also insulates the X-ray tube from the grounded housing or transformer oil tank that houses the tube. The system usually uses water directly from the water supply for cooling, the anode assembly is grounded.
In stationary and mobile equipment for flaw detection, X-ray tubes of an end structure with a cover on the anode are most often used. They usually operate in the 160 - 320 kV voltage range and are characterized by high power up to 4 kW. Design feature of these devices is a massive copper sheath on the anode.
Rice. 4. Anode with a cover.
1 - cover, 2 - electron beam, 3 - outlet 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 entering the glass shell of the device, thereby increasing the dielectric 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 equipped with internal screens in the form of cylinders of molybdenum or tantalum. A directed working X-ray beam is emitted through a special hole in the cover, which is closed by a beryllium or titanium disk, and then passes through the tube balloon. Anodes of powerful X-ray tubes of this type for stationary equipment, as a rule, have forced oil cooling.
Assignment for a course project
The purpose of the course design is to calculate the thermal, electrical and radiation characteristics of an X-ray tube, as well as the development of the main elements of its design.
1. Get a variant of the task, which will indicate the basic data for calculating and designing an X-ray tube (for example, an option from Table 1):
The type and purpose of the tube.
Tube working voltage.
The nominal power of the tube.
Tube target material.
2. Get acquainted and bring short description basic requirements for cathode and anode assemblies, vacuum tube shell and outlet windows of modern X-ray tubes.
3. Calculate the dielectric strength for a given X-ray tube.
Determine the interelectrode distance.
Determine the surface area on which breakdowns are likely.
Determine the relative position, configuration of the electrodes and their distance from the shell.
Define maximum temperature anode at the rated power of the tube.
5. Determine the characteristics of the X-ray tube radiation.
6. Execute Assembly drawing a given X-ray tube with an indication of the main constituent components. Bring the specification.
Table 1
Sample job options
The X-ray emitter for medical diagnostics is an oil-filled metal casing with an X-ray tube. An X-ray tube is a heat-resistant glass flask, inside which a hot cathode and an anode are placed in a high vacuum (Fig.
2.3). The hot cathode is heated by passing through a tungsten coil electric current... In the process of thermionic emission of the cathode and due to the presence of a potential difference between the cathode and the anode of 25–150 kV, an electron flux is generated that bombard the anode surface. The electron beam is focused by the electrostatic system into a small focal spot on the anode surface.
Electrons ionize atoms of the anode material, slow down and stop. Most of the energy transferred by electrons to the anode is converted into thermal energy, and only a small part of it (less than 1%) is converted into bremsstrahlung and characteristic X-rays. Some of these X-rays pass through the outlet windows of the flask and the casing, the filter, the collimating device, and then through the patient to the receiver.
X-rays from other directions are absorbed by the tube casing. The entire tube structure is mounted on a tripod for easy positioning. A collimator is required to control the size and direction of the X-ray beam.
Rice. 2.3. Rotating anode X-ray tube design:
1 - thermal switch; 2 - high voltage cable; 3 - cathode of direct heating; 4 - X-ray transparent window; 5 - vacuum; 6 - cathode block; 7 - high voltage cable; 8 - branch line; 9 - lead case; 10 - glass flask; 11 - target; 12 - anode; 13 - heat shield; 14 - holder made of molybdenum; 15 - oil expansion diaphragm
In fig. 2.4. graphically presented appearance a typical rotating anode X-ray tube for a general purpose X-ray machine.
The design of the hot cathode assembly and the electron-optical system plays a very important role, since the blurriness of the image largely depends on the size of the focal spot on the anode surface, and the output radiation power of the tube is determined by the electron current entering the anode.
The cathode (most often directly heated) is a tungsten coil, which is installed in a nickel capsule. This capsule supports the filament and is shaped such that the generated electric field focuses the electrons into a narrow beam. The rotating anode has a conical surface with an obtuse angle at the apex (Fig. 2.4, 2.5).
The exit window receives those X-rays that are approximately at right angles to the direction of the electron beam, so that on the surface of the receiver the X-rays have a square cross section, even if the electron flux bombarding the target is well collimated.
Rice. 2.4. Rotating anode X-ray tube:
1 - flask, 2 - cathode assembly, 3 - beveled (conical) anode, 4 - rotor and bearing assembly
The angle of inclination of the anode surface q is selected based on the purpose of the tube and varies depending on the requirements for the size of the field and focal spot, as well as for the output power of the tube (Fig. 2.6). For general purpose X-ray tubes, the angle q is about 17 °.
In many cases, the anode is beveled at two different angles, as well as two filaments to select either a narrow or wide focal spot, and to provide increased tube reliability.
Since most of the energy given off by the electron flow to the anode is converted into heat, one of the most important problems is the problem of its reduction and its rapid removal and dissipation. Indeed, the power of the electron beam in X-ray diagnostic devices can reach approximately 100 kV ´ 300 mA = 30 kW. This problem can be solved in such a way that the flow of electrons falls on the surface of the rotating anode, and the focal strip moves along the periphery of the anode disk. For general-purpose tubes, the rotation speed of the anode is about 3000 rpm, and the diameter of the anode disk is about 10 cm.
Rice. 2.5. X-ray diagnostic system diagram
The anode is typically made of tungsten, although molybdenum is used for special applications that require low photon energy X-rays. The atomic number of tungsten is Z = 74, tungsten has the necessary thermal conductivity and heat capacity, as well as a high melting point. It is important that the atomic number of the anode material is large, since the output of bremsstrahlung from the anode increases with the atomic number, and the X-ray spectrum, created by element with a higher atomic number, well suited for imaging more massive body parts. Tungsten-rhenium alloy (90:10 ratio) is often used to extend the life of the X-ray tube. This reduces the destruction of the anode surface (in the form of microcracking) caused by prolonged cyclic heating and cooling processes.
Rice. 2.6. Use of a beveled anode to reduce the effective focal spot size. The width of the electron beam is lcosq, while the size of the focal spot, measured relative to the central axis of the radiation field, is lsin q.
It is important that the anode disc has a high total heat capacity. The high heat capacity associated with an increase in the size and mass of the anode makes it possible to achieve shorter time intervals between exposures. For tubes operating in a stressed mode, the heat capacity of the anode can be increased by introducing a molybdenum substrate, since molybdenum has a higher specific heat capacity than tungsten (Table 2.1).
Table 2.1 Properties of molybdenum and tungsten
The anode disc is mounted on a thin molybdenum rod, which reduces heat return and protects the rotor bearings from overheating. Heat is removed from the rotating anode mainly by radiation to the glass bulb and then, due to thermal conductivity, to the transformer oil filling the casing.
The electric drive of the anode rotation is arranged according to the principle asynchronous motor, moreover, the rotor, rigidly connected to the anode, rotates inside the flask in a high vacuum, and the stator is located outside and is cooled by oil.