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 machine.
Managers of medical centers often face 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 features and not miss the main thing?
Today, more and more often outdated "film" devices are being replaced by digital X-ray machines, which increase the throughput of the office and minimize the radiation dose. Is it worth it to 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 radiographic devices
According to the operating conditions, the X-ray machine can be ward, mobile and stationary.
Specialized types of X-ray machines are also presented:
P used in operating rooms for surgical interventions - "GOOSE", "C-arc"
angiography devices - "C-arm"
mammographic - "mammographs"
stationary for two and three workplaces
angiographic "C-arm" "angio complexes"
computer tomography with different amount slices
dental x-rays for dental departments
There are also portable small-sized devices used for simple x-ray studies in an ambulance or at the patient's home. The scope of portable devices is extremely limited, due to their very low power, so they cannot replace either a mobile, much less a stationary X-ray machine.
Mobile x-ray units are mainly used in wards, in this regard they are often called "ward x-ray machine". The power of mobile X-ray machines ranges from 2.5 kW to 32 kW on average. The power of classic stationary devices starts from 40 kW.
Some medical centers, which 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 radiology 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 support. For images in the “lying” position, an X-ray transparent gurney is used. This type of stationary X-ray machines is most often used in rooms with a small area.
X-ray systems based on a remotely controlled tripod table are the most expensive type of stationary radiographic devices. These are 3 in 1 units for the X-ray diagnostic department of any modern medical institution. They allow you to carry out all possible radiographic and fluoroscopic studies. The most common type of stationary x-ray systems in medical centers are classic x-ray machines for two workplaces. The main components of such systems are the X-ray tube (ceiling or floor mount m), an image table - for the "lying" position, an image rack - for the "standing" position and a generator.
When buying an X-ray machine, it is important to determine the profile of research and the location of the equipment. Having chosen the type of X-ray machine, you can proceed to the assessment of its technical parameters.
Important specifications x-ray machines
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 exposure, the lower the radiation exposure, and in some studies the better the image quality. This is especially important when examining obese patients.
For stationary X-ray machines, the generator power range is on average from 40kW to 80kW. The most widely used configurations are those with a power supply of 50 kW, which is sufficient for the vast majority of studies. But it is important to take into account that the power of the generator must be consistent 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 machine, 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 life 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 resolution, as well as maximum research safety by minimizing the “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 focus sizes .
The value of the theoretically achievable spatial resolution decreases as the focus size increases. With a focus size of 2 mm different estimates up to 3 line pairs/mm can be recognized even if the detector has best performance(X-ray film, for example, allows you to distinguish between 10-15 line pairs/mm). All tubes have two working foci. The lower the focus size of the X-ray tube, the clearer the resulting images will be, but reducing the focus size also reduces the operating power.
At the same time, it is important that the power of the generator of the X-ray machine corresponds to the working power of the foci of the delivered tube.
Another characteristic of X-ray tubes isanode heat capacity value , affecting the resource intensity of the system. The higher this indicator, the more quantity studies 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.
The most expensive and reliable components are used in the production of imaging tables with a high maximum permissible load. good indicator the permitted maximum load on the table is considered to be 200kg, but some manufacturers produce optional models of tables with a permitted load of up to 290kg or even higher.
The X-ray machine can also be equipped with an imaging table with an “elevator” option that allows you to move the table surface 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 tripod and ceiling.
The most widespread in private medical centers is the option of mounting the tube on a floor stand. It is easier to install, has no serious restrictions on minimum height ceilings and the area of the x-ray room.
The ceiling mount of the tube 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 machine allow, then with a large planned flow of patients, it is better to stop at the option ceiling mount tubes.
If at big stream patients are expected to purchase an X-ray machine with a floor tube mount, you should pay attention to options with a reinforced floor stand.
Advantages of digital X-ray machines
In recent years, diagnostics are increasingly carried out using a new generation of digital radiographic equipment. It provides instant images, eliminates the development process, allows you to store images and carry out diagnostics using computer technology.
The digital x-ray machine is characterized in that the images of anatomical structures obtained by means of x-ray irradiation are digitally processed.
The main advantages of this modern method diagnostics are:
the highest quality of the received images: the possibility of their digital processing allows to reveal 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 research costs 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 processor 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 is easier for specialists to determine the diagnosis and specifics of the disease.
The semiconductor flat panel detector system is the most modern technology, which has 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 memory phosphors is used instead of a film cassette. After the picture is taken, the cassette must be removed from the device and placed in a special reader - a digitizer. At the end of the reading process, the digitizer transmits the received digital image to the laboratory assistant's workstation, while the cassette will be cleaned and ready for the next study.
DR systems use semiconductor flat panel detectors. The two-station digital X-ray machine can be equipped with either one wireless flat panel detector, which must be moved from the table to the imaging rack, or two - both for the table and for the imaging rack.
At the same time, 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, in contrast to CR, where the cost of a single cassette is negligible.
After the snapshot, almost instantly, the 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.
Flat panel detector (DR) systems are more expensive than digitizer cassette (CR) systems, but they are justified with a large flow of patients, as 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 assistant's workstation, 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 X-ray department in a private clinic.
Usage: in X-ray technology. The essence of the invention: the anode contains a molybdenum alloy base, which includes at least one of the elements selected from the group including niobium, tantalum and rhenium, and a tungsten alloy target, the base and the target are made in the form of a connected single-crystal structure. 1 z.p. f-ly.
The invention relates to sources of x-rays and can be used to create x-ray emitters with increased level power and work resource for medical and technical purposes. Rotating X-ray tube anodes are known, for example, for CT scanners, 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 working area at high thermal loads. The closest technical solution to 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-hardened molybdenum alloys. Recrystallization processes can proceed intensively in such materials at elevated temperatures. Their thermal strength under cyclic exposure 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 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 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 about With and satisfactory workability at room temperatures. Alloys of this composition belong to alloys with a solid-solution type of hardening and are characterized by high structural stability over the entire temperature range of existence. Therefore, when the anode disk is made of a single-crystal alloy, all processes associated with the temperature kinetics of structure development, which are characteristic of polycrystalline alloys, are completely excluded. These differences make it possible to raise the permissible level of the mass-average temperature of the disk to 1400-1600 ° C. In addition, the implementation of the disk as single-crystal so 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 allowable power for account of the orientation of the crystal. Alloying of molybdenum in the above amounts with niobium, tantalum, and rhenium ensures optimal thermal and structural properties. At amounts less than the lower level, the heat resistance is significantly reduced, and at amounts greater than the upper level, thermal conductivity decreases. 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 from a molybdenum alloy single crystal. Disc diameter about 100 mm, thickness about 5 mm. The surface of the disk on the target side has a taper of 12 o. The disc 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 known design and having the same heat capacity (X-ray tube anodes 2-30BD11-150). It has been found that the proposed anodes exceed the known anodes by 30-40% in terms of power dissipation, which ensures an increase in the reliability of the anode, as well as the power of an X-ray tube containing an anode of the claimed design.
Claim
1. A ROTATING X-RAY TUBE 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, characterized in that, for the purpose increase the resistance of the anode to thermal loads, the base and the target are made in the form of a connected single-crystal structure. 2. The anode according to claim 1, characterized in that the surface of the connected single-crystal structure coincides with the plane of the crystallographic shape (110).
GOST R 55771-2013
NATIONAL STANDARD OF THE RUSSIAN FEDERATION
MEDICAL ELECTRICAL PRODUCTS
Tomographs are X-ray computer. Technical requirements for public procurement
medical electrical equipment. Angiography X-ray equipment. Technical requirements for government 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 Equipment" Federal Service for Health Supervision and social development(FGBU "VNIIIMT" of Roszdravnadzor)
2 INTRODUCED by the Technical Committee for Standardization TK 411 "Apparatus and equipment for radiation diagnostics, therapy and dosimetry"
3 APPROVED AND PUT 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 set out 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 - in the monthly information index "National Standards". In case of revision (replacement) or cancellation of this standard, a corresponding notice will be published in the next issue of the information index "National Standards". Relevant information, notification and texts are also placed 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 should be contained in the terms of reference for public procurement of X-ray computed tomographs designed to obtain layered images and 3D images (RCT).
When conducting competitive bidding, tender assignments for the purchase of RCT in a number of cases include technical requirements that do not correspond to the purpose of the purchased equipment: either overly specified and redundant, or indirectly related to its consumer properties. This standard aims to streamline the established practice of preparing specifications for public procurement.
There are no international analogues of 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 layered images and 3D images (RKT).
This standard is a private standard in relation to GOST R 55719-2013 "Medical electrical products. Requirements for the content and design of technical specifications for tender documentation during public procurement of high-tech medical equipment."
This standard applies to tenders for state and municipal purchases of the Ministry of Defense for the provision of medical care. The standard does not apply to non-government procurement of MO.
This standard applies to RKT.
This standard does not cover devices for tomosynthesis.
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 design 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 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 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 validity 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 on issues of the monthly information index "National Standards" for the current year. If an undated referenced reference standard has been replaced, it is recommended that the current version of that standard be used, taking into account any changes made to that version. If the reference standard to which the dated reference is given is replaced, then it is recommended to use the version of this standard with the year of approval (acceptance) indicated above. 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 referenced standard is canceled without replacement, then the provision in which the reference is given on 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 the 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 the 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 normative (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 - After 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, decommissioning, destruction, verification and setting a new appointed time.
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. The TOR determines the subject of the MO purchase order.
Responsibility for the completeness and sufficiency of the TOR lies with the customer.
4.2 When preparing TOR for the purchase of MO, it is prohibited to indicate specific trademarks, service marks, trade names, patents, utility models, industrial designs, appellations of origin or manufacturer's names (except as otherwise specified separately).
5 The 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 the public procurement of RCT:
- supply voltage, V;
- power consumption, kW, not less;
- spiral type RKT (if available);
- number of detector lines;
- 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;
- density measurement range, Hounsfield units, not less;
- data collection matrix, not worse;
- image reconstruction time, image/s, not less;
- image matrix, not worse;
- contrast sensitivity, %, not less;
- spatial resolution, pairs of lines/cm, not 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 16-slice CT. Tomographs with a large number of slices (64, 128 or more) per rotation of the X-ray tube are designed for more complex studies (cardiology) and for a specific group of patients (for example, children). The more lines of detectors the CT contains, the faster information is collected for a given 3D image, which is especially important for the cardiovascular system. In the study of the heart, which is in constant and rapid motion, synchronization with the ECG is used. However, with an increase in the number of detector lines and, consequently, the number of XCT 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 operating modes of the CT 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 being carried out and is responsible for this.
5.2 The list of regulatory documents that the RCT must comply with is given in Appendix A.
6 Requirements for the execution of technical specifications
6.1 An example of the 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 studies in accordance with the profile of the medical institution.
Annex A (mandatory). List of regulatory documents that an X-ray computed tomograph must comply with
Annex A
(mandatory)
Table A.1
Designation | Name |
Medical electrical products. Part 1: General safety requirements with respect to essential functional characteristics |
|
Medical electrical products. Part 2-28. Particular safety requirements, taking into account the main functional characteristics of medical diagnostic X-ray emitters |
|
Medical electrical products. Part 2-44. Particular safety requirements, taking into account the main functional characteristics for X-ray computed tomography |
|
Medical electrical products. Dictionary |
|
Radiation safety standards |
|
Hygienic requirements for the design and operation of X-ray rooms, apparatus and X-ray examinations |
Appendix B (informative). An example of the medical and technical characteristics of an X-ray computed tomograph
Annex B
(reference)
Table B.1
Characteristic name | Significance for 64-slice CT | Significance 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 |
|
Minimum X-ray tube turnover time, s | ||
Maximum scanning field, mm | ||
Cut thickness, mm | ||
spiral scan |
||
Maximum time of one scan, s, not less | ||
Minimum speed during helical scanning, mm/s, no more | ||
Maximum speed during helical scanning, mm/s | ||
Gantry |
||
Aperture diameter, cm, not less than | ||
Positioning with a laser | ||
Gantry movement control remote and manual | ||
Detector |
||
The number of simultaneously obtained sections, pcs. | ||
Minimum thickness of one cut, mm, no more | ||
x-ray tube |
||
Heat capacity of X-ray tube, MHU, not less than | ||
X-ray tube cooling rate, kHU/min, not less than | ||
Minimum focus size, mm, no more | ||
X-ray generator |
||
Rated power, kW, not less | ||
Anode voltage range, kV | ||
Anode current range, mA | ||
Patient table |
||
Electromechanical and manual drive | ||
Opportunity remote control table movement | ||
Vertical movement range, cm | ||
Maximum horizontal movement, cm, not less than | ||
Table deck width, cm, not less than | ||
Table travel speed, mm/m | ||
Image Options |
||
Data acquisition matrix, no worse | ||
Reconstruction time, image/s, not less than | ||
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 | ||
Cardio package | ||
Synchronization with ECG | ||
Axial cardiography | ||
Arrhythmia correction | ||
protocols pediatric | ||
Beam taper correction software | ||
Special software | According to customer's needs |
|
Checking for calcification of coronary vessels | ||
Vascular examination | ||
Cardiac parameters | ||
Lung function test | ||
Characteristics of the power network |
||
Supply voltage, V | 3-phase, 380 | 3-phase, 380 |
Power consumption, kW, not less | ||
Warranty period of operation, years, not less | ||
Normative service life, years, not less |
||
UDC 621.86.1:616-073.7:006.354 OKS 11.040.50
Keywords: X-ray tomograph, tomographic plane, tomographic slice, computed tomography dose index, image
_______________________________________________________________________________
Electronic text of the document
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 of Saint-Petersburg Electrotechnical University "LETI"
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I00 Gryaznov A.Yu., Potrakhov N.N. The use of accelerators and X-ray devices: Proc. allowance. St. Petersburg: SPbGETU "LETI", 2006, 46 p.
Designed for students of specialty 200300 and direction 654100, and may also be useful to engineering and technical workers in this field of knowledge.
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Reviewers: laboratory of technical means non-destructive testing Moscow Institute of Radioelectronic Equipment; ch. engineer of CJSC "ELTECH-Med" V.M. Mukhin
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ISBN 0-0000-0000-0 © Saint Petersburg Electrotechnical University "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, the 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 objects under study on initial stage X-ray ion tubes were used in the development of X-ray technology. The work of Lilienfeld and especially Coolidge (1912 - 1913) led to the creation of electron tubes with a thermionic cathode, which subsequently received exceptionally great development.
At the moment, thanks to the 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 the widest range practical problems of various kinds: X-ray diffraction and X-ray spectral analyses, X-ray diffraction of fast processes, research of phase and elemental composition for industrial and scientific purposes, quality control of microelectronics and semiconductor products, X-ray location, X-ray luminescent separation rocks, X-ray lithography and much more.
The symbol for X-ray devices (marking) is defined in OST 11.073.807-82 “Vacuum devices. The system of symbols "and reflects the purpose, and sometimes the main parameters of the devices. In accordance with the OST, the symbol includes a combination of numbers and letters: digit \ letters \ digit \ - digit.
For X-ray tubes for industrial transillumination and structural and spectral analysis, the first digit means the maximum allowable power during continuous operation in kilowatts. This is followed by a letter indicating the method of protection against radiation: "P" - complete protection is provided; "B" - required additional protection elements of the casing or monoblock of the apparatus. The next letter indicates the scope: "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 indicates the nature (method) of forced cooling: "B" - water; "K" - air; "M" - oil. The absence of a 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 transillumination tubes, the next figure (written with a hyphen) indicates the maximum allowable anode voltage in kilovolts. For tubes of structural and spectral analysis, the last element symbol(written with a hyphen) 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 covers for equipment of old and new modifications). Information about the difference in design is given in the passport for the device and in advertising messages.
Design and technology
modern x-ray tube
The main units of a modern X-ray tube are the cathode unit, the vacuum shell and the anode unit.
The cathode assembly is designed to generate an electron beam of a given shape. The design of the cathode assembly includes current-carrying wires, a cathode holder, current-carrying racks, a filament, a cathode screen, and an insulator.
As electron sources, either a direct-heated thermionic 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. The current-carrying wires are led to the insulated stand and to the cathode holder and are led out of the vacuum envelope.
In order for the emitted electron flow to have a certain shape all the way from the cathode to the anode target, the design of the cathode unit is an electron-optical system. The effect of electron beam focusing is provided by a certain shape of the hole in the cathode screen. To tube cathodes, along with the general requirements for cathodes of electrovacuum devices (provide the necessary and stable emission current during the entire service life, be well degassed and not worsen the vacuum in the device in operating modes, have a sufficient service life, etc.), a number of special requirements: stability of operation at a high field strength on the cathode surface and the possibility of adjusting the emission current over a wide range.
Pointed Extended Flat spiral
Rice. 1. Designs 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 cylinder is made by blowing into special shapes, allowing to form the required configuration of the cylinder with sufficient accuracy. The connection of the electrodes with the cylinder 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 shells
The middle part of the cylinder is expanded to increase the dielectric strength. In this case, 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 radiation is supposed to be released, the wall thickness is reduced by grinding - a specific outlet window is created. Another option is to use an exhaust port made of vacuum tight beryllium.
The anode units of X-ray tubes are intended directly for the generation of X-rays. The anode of an x-ray tube is an electrode that acts as a target or carries the target of the tube. Part of the X-ray emission arising during electron deceleration on the target, intended for beneficial use and enclosed in a solid angle, the top of which lies in the center of the real 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, anodes can be made massive or perforated. A 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 removed 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 is subject to the requirements of high melting temperature and low vapor pressure at high temperature. In tubes designed to produce bremsstrahlung, the targets are made of tungsten. To obtain characteristic radiation of a certain hardness (tubes for X-ray diffraction analysis and X-ray spectral analysis), targets are made from various materials (chromium, iron, copper, molybdenum, silver, etc.).
Rice. 3. The design of the anode unit of massive type
1 – target, 2 – anode body, 3 – central cooling tube,
4 - connecting covar ring, 5 - edge of the glass container
In some cases, the target as a 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 manufacture 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 installed at the required angle. Then, a copper billet, previously cleaned of impurities, is put into the crucible. Melting of copper in a crucible is carried out in a vacuum furnace with electrical heating or by means of high-frequency currents under a quartz hood. Depending on the mass of the anodes, melting modes are selected in such a way that the copper body of the anode has a coarse-grained structure. After melting, the anode blank is processed mechanically, giving it the required configuration. The design of the anode-cooling device depends on the mode of operation, the power of the tube, and some other factors. Radiator cooling is used in x-ray tubes operating in the intermittent mode of medium power (several hundred watts).
A flange is attached to the copper body of the anode with the target by welding, through which the anode assembly is connected to the tube cylinder. The radiator is fixed on the anode shank by a shrink fit 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-finned. Oil, water or air can be used as the cooling medium. Depending on the design of the emitters and operating modes, cooling can be forced (by means of pumps) or natural. In tubes of high (up to 4 kW) power, operating in a long continuous mode, flow-through liquid cooling systems are used. Water or transformer oil is used as a coolant. 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 snail, contributes to a better washing of the hottest end part of the cooled surface with liquid, and also increases the heat exchange surface. Therefore, the scroll cooling system is able to dissipate higher power. Volute cooling systems typically use transformer oil as the coolant, which also acts as an insulator for the X-ray tube from the grounded housing or transformer oil tank that houses the tube. The cooling system usually uses water directly from the water supply, the anode assembly is grounded.
In stationary and mobile equipment for flaw detection, X-ray tubes of end design with a cover on the anode are most often used. They usually operate in the voltage range of 160 - 320 kV and are characterized by high power, reaching 4 kW. Design feature of these devices is a massive copper case 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 the secondary electrons knocked out of the target from reaching the glass shell of the device, thereby increasing the electrical strength and reliability of the tube. Sometimes, to enhance the protective properties of the cover, it is made from a material with additives of heavy elements, such as tungsten, or it is provided with internal screens in the form of cylinders made of molybdenum or tantalum. The 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 balloon. The 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 the 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 the calculation and design of an 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 short description the basic requirements for cathode and anode assemblies, the vacuum shell of the tube and the 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 radiation characteristics of the x-ray tube.
6. Run Assembly drawing of a given X-ray tube, indicating the main constituent components. Bring specification.
Table 1
Approximate task options
X-ray emitter for medical diagnostics is an oil-filled metal casing with an X-ray tube. An X-ray tube is a flask made of heat-resistant glass, inside of which a thermal cathode and an anode are placed in a high vacuum (Fig.
2.3). The hot cathode is heated by passing through a tungsten filament 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, a flow of electrons is created that bombards the anode surface. The electron beam is focused by an electrostatic system into a small focal spot on the anode surface.
The electrons ionize the atoms of the anode material, slow down and stop. Most of the energy transferred by electrons to the anode is converted into heat, 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 exit windows of the flask and casing, the filter, the collimating device, and then through the patient to the receiver.
X-rays propagating in other directions are absorbed by the tube casing. The whole structure of the tube is mounted on a tripod, providing ease of its positioning. The collimator is necessary 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 - radiolucent window; 5 - vacuum; 6 - cathode block; 7 - high voltage cable; 8 - soldering process; 9 - lead case; 10 - glass flask; 11 - target; 12 - anode; 13 - heat shield; 14 - molybdenum holder; 15 - oil expansion diaphragm
On fig. 2.4. clearly presented appearance of a typical rotating anode x-ray tube for a general purpose x-ray machine.
The design of the thermal cathode unit and the electron-optical system plays a very important role, since the image blur 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 coming to the anode.
The cathode (most often directly heated) is a tungsten spiral, which is installed in a nickel capsule. This capsule supports the filament and is shaped so 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 top (Fig. 2.4, 2.5).
The exit window receives those x-rays that travel approximately at right angles to the direction of the electron beam, so that the x-rays at the receiver surface have a square cross section, even if the electron beam bombarding the target is well collimated.
Rice. 2.4. X-ray tube with rotating anode:
1 - bulb, 2 - cathode assembly, 3 - oblique (conical) anode, 4 - rotor and bearing assembly
The angle of inclination of the anode surface q is chosen 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 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 an electron beam in X-ray machines can reach approximately 100 kV ´ 300 mA = 30 kW. This problem can be solved in such a way that the electron flux falls on the surface of the rotating anode, and the focus strip moves along the periphery of the anode disk. For general purpose tubes, the anode rotation speed is about 3000 rpm, and the anode disk diameter is about 10 cm.
Rice. 2.5. Scheme of the X-ray diagnostic system
The anode is usually made from tungsten, although molybdenum is used for special applications requiring 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 be large, since the bremsstrahlung output from the anode increases with atomic number, and the X-ray spectrum, generated by the element with a large atomic number, well suited for imaging more massive parts of the body. To increase the life of an X-ray tube, a tungsten-rhenium alloy (in a ratio of 90:10) is often used. This reduces the destruction of the anode surface (in the form of microcracks) caused by prolonged cyclic heating and cooling processes.
Rice. 2.6. Use of a beveled anode to reduce the effective size of the focal spot. The electron beam width 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 disk has a high total heat capacity. The large heat capacity associated with an increase in the size and weight of the anode makes it possible to achieve shorter time intervals between exposures. For tubes operating in a stressed mode, the anode heat capacity 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 the return heat flow and protects the rotor bearings from overheating. The 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 anode rotation electric drive is arranged according to the principle induction motor, and the rotor, rigidly connected to the anode, rotates inside the flask in a high vacuum, and the stator is located outside and cooled with oil.