X線管、エックス線管

WordNet

ride or float on an inflated tube; "We tubed down the river on a hot summer day"
conduit consisting of a long hollow object (usually cylindrical) used to hold and conduct objects or liquids or gases (同)tubing
electronic device consisting of a system of electrodes arranged in an evacuated glass or metal envelope (同)vacuum_tube, thermionic vacuum tube, thermionic_tube, electron_tube, thermionic_valve
(anatomy) any hollow cylindrical body structure (同)tube-shaped structure
convey in a tube; "inside Paris, they used to tube mail"
place or enclose in a tube
provide with a tube or insert a tube into
emit as rays; "That tower rays a laser beam for miles across the sky"
(mathematics) a straight line extending from a point
a branch of an umbel or an umbelliform inflorescence
any of the stiff bony spines in the fin of a fish
cartilaginous fishes having horizontally flattened bodies and enlarged winglike pectoral fins with gills on the underside; most swim by moving the pectoral fins
the amount that a tub will hold; "a tub of water" (同)tubful
a large open vessel for holding or storing liquids (同)vat
the 24th letter of the Roman alphabet (同)x, ex
electromagnetic radiation of short wavelength produced when high-speed electrons strike a solid target (同)X-ray, X-radiation, roentgen_ray

PrepTutorEJDIC

(金属・ガラス・ゴムなどの)管,筒 / (絵の具・歯みがきなどの)チューブ / 《米》(列車・地下鉄の)トンネル / 《英》地下鉄(《米》subway) / (ラジオ・テレビなどの)真空管(vacuum tube) / (動植物の)管状器官
『光線』;熱線;放射線 / 《a ~》(希望などの)一筋(ひとすじ),ごく少量《+『of』+『名』》 / 放射状に突き出たもの;(ヒトデなどの)腕
(魚の)エイ
『おけ』,たらい / 《話》'bath 2 / (また tubful)おけ1杯[の量](の…)《+of+名》 / 《話》のろくてぶかっこうな船;《俗》でぶ,太っちょ
Christ / Christian

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/11/02 21:19:19」(JST)

wiki en

An X-ray tube is a vacuum tube, that produces X-rays. They are used in X-ray machines. X-rays are part of the electromagnetic spectrum, an ionizing radiation with wavelengths shorter than ultraviolet light. X-ray tubes evolved from experimental Crookes tubes with which X-rays were first discovered in the late 19th century, by Wilhelm Röntgen and the availability of this controllable source of X-rays created the field of radiography, the imaging of opaque objects with penetrating radiation. X-ray tubes are also used in CAT scanners, airport luggage scanners, X-ray crystallography, and for industrial inspection.

Coolidge X-ray tube, from around 1917. The heated cathode is on the left, and the anode is right. The X-rays are emitted downwards.

Types[edit]

Rotating anode tube[edit]

Simplified rotating anode tube schematic

A: Anode
C: cathode
T: Anode target
W: X-ray window

typical rotating anode X-ray tube

By thinning the tube, the anode can then be rotated by electromagnetic induction from a series of stator windings outside the evacuated tube.

Because the entire anode assembly has to be contained within the evacuated tube, heat removal is a serious problem, further exacerbated by the higher power rating available. Direct cooling by conduction or convection, as in the Coolidge tube, is difficult. In most tubes, the anode is suspended on ball bearings with silver powder lubrication which provide almost negligible cooling by conduction.

A recent development has been liquid gallium lubricated fluid dynamic bearings which can withstand very high temperatures without contaminating the tube vacuum. The large bearing contact surface and metal lubricant provide an effective method for conduction of heat from the anode.

The anode must be constructed of high temperature materials. The focal spot temperature can reach 2,500 °C (4,530 °F) during an exposure, and the anode assembly can reach 1,000 °C (1,830 °F) following a series of large exposures. Typical materials are a tungsten-rhenium target on a molybdenum core, backed with graphite. The rhenium makes the tungsten more ductile and resistant to wear from the impact of the electron beams. The molybdenum conducts heat from the target. The graphite provides thermal storage for the anode, and minimizes the rotating mass of the anode.

Increasing demand for high-performance Computed tomography (CT) scanning and angiography systems has driven development of very high performance medical X-ray tubes. Contemporary CT tubes have power ratings of up to 100 kW and anode heat capacity of 6 MJ, yet retain an effective focal spot area of less than 1 mm².

Microfocus X-ray tubes[edit]

Some X-ray examinations (such as, e.g., non-destructive testing and 3-D microtomography) need very high-resolution images and do therefore require X-ray tubes that can generate very small focal spot sizes, typically below 50 µm in diameter. These tubes are called microfocus X-ray tubes.

There are two basic types of microfocus X-ray tubes: solid-anode tubes and metal-jet-anode tubes.

Solid-anode microfocus X-ray tubes are in principle very similar to the Coolidge tube, but with the important distinction that care has been taken to be able to focus the electron beam into a very small spot on the anode. Many microfocus X-ray sources operate with focus spots in the range 5-20 µm, but in the extreme cases spots smaller than 1 µm may be produced.

The major drawback of solid-anode microfocus X-ray tubes is the very low power they operate at. In order to avoid melting of the anode the electron-beam power density must be below a maximum value. This value is somewhere in the range 0.4-0.8 W/µm depending on the anode material.^[1] This means that a solid-anode microfocus source with a 10 µm electron-beam focus can operate at a power in the range 4-8 W.

In metal-jet-anode microfocus X-ray tubes the solid metal anode is replaced with a jet of liquid metal, which acts as the electron-beam target. The advantage of the metal-jet anode is that the maximum electron-beam power density is significantly increased. Values in the range 3-6 W/µm have been reported for different anode materials (gallium and tin).^[2]^[3] In the case with a 10 µm electron-beam focus a metal-jet-anode microfocus X-ray source may operate at 30-60 W.

The major benefit of the increased power density level for the metal-jet X-ray tube is the possibility to operate with a smaller focal spot, say 5 µm, to increase image resolution and at the same time acquire the image faster, since the power is higher (15-30 W) than for solid-anode tubes with 10 µm focal spots.

Physics[edit]

Spectrum of the X-rays emitted by an X-ray tube with a rhodium target, operated at 60 kV. The smooth, continuous curve is due to bremsstrahlung, and the spikes are characteristic K lines for rhodium atoms.

As with any vacuum tube, there is a cathode, which emits electrons into the vacuum and an anode to collect the electrons, thus establishing a flow of electrical current, known as the beam, through the tube. A high voltage power source, for example 30 to 150 kilovolts (kV), is connected across cathode and anode to accelerate the electrons. The X-ray spectrum depends on the anode material and the accelerating voltage.^[4]

In many applications, the current flow (typically in the range 1 mA to 1 A) is able to be pulsed on for between about 1 ms to 1 s. This enables consistent doses of X-rays, and taking snapshots of motion. Until the late 1980s, X-ray generators were merely high-voltage, AC to DC variable power supplies. In the late 1980s a different method of control was emerging, called high speed switching. This followed the electronics technology of switching power supplies (aka switch mode power supply), and allowed for more accurate control of the X-ray unit, higher quality results, and reduced X-ray exposures.

Electrons from the cathode collide with the anode material, usually tungsten, molybdenum or copper, and accelerate other electrons, ions and nuclei within the anode material. About 1% of the energy generated is emitted/radiated, usually perpendicular to the path of the electron beam, as X-rays. The rest of the energy is released as heat. Over time, tungsten will be deposited from the target onto the interior surface of the tube, including the glass surface. This will slowly darken the tube and was thought to degrade the quality of the X-ray beam, but research has suggested there is no effect.^[5] Eventually, the tungsten deposit may become sufficiently conductive that at high enough voltages, arcing occurs. The arc will jump from the cathode to the tungsten deposit, and then to the anode. This arcing causes an effect called "crazing" on the interior glass of the X-ray window. As time goes on, the tube becomes unstable even at lower voltages, and must be replaced. At this point, the tube assembly (also called the "tube head") is removed from the X-ray system, and replaced with a new tube assembly. The old tube assembly is shipped to a company that reloads it with a new X-ray tube.

The X-ray photon-generating effect is generally called the Bremsstrahlung effect, a contraction of the German bremsen for braking, and strahlung for radiation.

The range of photonic energies emitted by the system can be adjusted by changing the applied voltage, and installing aluminum filters of varying thicknesses. Aluminum filters are installed in the path of the X-ray beam to remove "soft" (non-penetrating) radiation. The number of emitted X-ray photons, or dose, are adjusted by controlling the current flow and exposure time.

Simply put, the high voltage controls X-ray penetration, and thus the contrast of the image. The tube current and exposure time affect the dose and therefore the darkness of the image.

Heat unit[edit]

In radiography, in particular in radiology, a heat unit is a usual unit derived from the Joule and measuring the quantity of heat in a device, in particular the thermal energy that an X-ray tube must be able to support and dissipate during and after an exam.

Historically, this unit comes from the need to express a quantity of energy whatever the waveform of the electrical source power (direct or pulsating). The heat produced in these devices is (in Joule) :

In radiography voltage is usually expressed in (thousands of volts peak), the effective current in mA and the time in seconds:

w being the waveform ratio. With a full-wave rectification of a sine wave it equals , thus the practical unit:

1 HU = 0.707 J or

1.4 HU = 1 J ^[6]

History[edit]

Crookes tube[edit]

Crookes X-ray tube from early 1900s. The cathode is on the right, the anode is in the center with attached heat sink at left. The electrode at the 10 o'clock position is the anticathode. The device at top is a 'softener' used to regulate the gas pressure.

Historically, X-rays were discovered radiating from experimental discharge tubes called Crookes tubes invented by British physicist William Crookes and others. As the medical and other uses of X-rays became apparent, workshops began to manufacture specialized Crookes tubes to produce X-rays. These were the first X-ray tubes. These first generation cold cathode or Crookes X-ray tubes were used until the 1920s.

Crookes tubes generated the electrons needed to create X-rays by ionization of the residual air in the tube, instead of a heated filament, so they were partially but not completely evacuated. They consisted of a glass bulb with around 10⁻⁶ to 5×10⁻⁸ atmospheric pressure of air (0.1 to 0.005 Pa). An aluminum cathode plate at one end of the tube created a beam of electrons, which struck a platinum anode target at the center generating X-rays. The anode surface was angled so that the X-rays would radiate through the side of the tube. The cathode was concave so that the electrons were focused on a small (~1 mm) spot on the anode, approximating a point source of X-rays, which resulted in sharper images. The tube had a third electrode, an anticathode connected to the anode. It improved the X-ray output, but the method by which it achieved this is not understood. A more common arrangement used a cupped plate anticathode (similar in construction to the cathode) in line with the anode such that the anode was between the cathode and the anticathode.

To operate, a DC voltage of a few kilovolts to as much as 100 kV was applied between the anodes and the cathode, usually generated by an induction coil, or for larger tubes, an electrostatic machine. This created and then accelerated a small number of ions from the low pressure gas in the tube. These struck further gas atoms, knocking electrons off them, creating more positive ions in a chain reaction. All the positive ions were attracted to the cathode. When they struck it, they knocked electrons out of the metal, which were accelerated along with the electrons knocked from the gas atoms toward the anode target. When these high speed electrons struck the atoms of the anode, they created X-rays by one of two processes, either Bremsstrahlung or X-ray fluorescence.

Crookes tubes were unreliable. As time passed, the residual air would be absorbed by the walls of the tube, reducing the pressure. This increased the voltage across the tube, generating 'harder' X-rays, until eventually the tube stopped working. To prevent this, 'softener' devices were used (see picture). A small tube attached to the side of the main tube contained a mica sleeve or chemical that released a small amount of gas when heated, restoring the correct pressure.

The glass envelope of the tube would blacken in use due to the X-rays affecting its structure.

Coolidge tube[edit]

Coolidge side-window tube (scheme)

C: filament/cathode (-)
A: anode (+)
W_in and W_out: water inlet and outlet of the cooling device

typical fixed-anode X-ray tube

The Crookes tube was improved by William Coolidge in 1913. The Coolidge tube, also called hot cathode tube, is the most widely used. It works with a very good quality vacuum (about 10⁻⁴ Pa, or 10⁻⁶ Torr).

In the Coolidge tube, the electrons are produced by thermionic effect from a tungsten filament heated by an electric current. The filament is the cathode of the tube. The high voltage potential is between the cathode and the anode, the electrons are thus accelerated, and then hit the anode.

There are two designs: end-window tubes and side-window tubes.

End window tubes usually have "transmission target" which is thin enough to allow X-rays to pass through the target (X-rays are emitted in the same direction as the electrons are moving.) In one common type of end-window tube, the filament is around the anode ("annular" or ring-shaped), the electrons have a curved path.(half of a toroid)

What is special about side-window tubes is:

An Electrostatic Lens to focus the beam onto a very small spot on the anode
The anode is specially designed to dissipate the heat and wear resulting from this intense focused barrage of electrons. Some anodes are:
- Mechanically spun to increase the area heated by the beam.(Medical "rotating anode")
- Cooled by circulating coolant. (indirectly on most rotating anodes)

The anode is precisely angled at 1-20 degrees off perpendicular to the electron current so as to allow escape of some of the X-ray photons which are emitted essentially perpendicular to the direction of the electron current.
The anode is usually made out of tungsten or molybdenum.
The tube has a window designed for escape of the generated X-ray photons.

The power of a Coolidge tube usually ranges from 0.1 to 18 kW.

Hazards of X-ray production from vacuum tubes[edit]

Two high Voltage rectifier tubes capable of producing X-rays

Any vacuum tube operating at several thousand volts or more can produce X-rays as an unwanted byproduct, raising safety issues.^[7]^[8] The higher the voltage, the more penetrating the resulting radiation and the more the hazard. Color televisions and computer CRT displays operate at 30-40 kilovolts, making them the main concern among household appliances. Historically, concern has focused less on the cathode ray tube, since its thick glass envelope is impregnated with several pounds of lead for shielding, than on high voltage (HV) rectifier and voltage regulator tubes inside. In the late 1960s it was found that a failure in the HV supply circuit of some General Electric TVs could leave excessive voltages on the regulator tube, causing it to emit X-rays.^{[citation needed]} The models were recalled and the ensuing scandal caused the US agency responsible for regulating this hazard, the Center for Devices and Radiological Health of the Food and Drug Administration (FDA), to require that all TVs include circuits to prevent excessive voltages in the event of failure.^{[citation needed]} This hazard was eliminated with the advent of all solid state TVs, which have no tubes beside the CRT. Since 1969 the FDA has limited TV X-ray emission to 0.5 mR (milliroentgen) per hour.

Patents[edit]

Coolidge, U.S. Patent 1,211,092, "X-ray tube"
Langmuir, U.S. Patent 1,251,388, "Method of and apparatus for controlling X-ray tubes
Coolidge, U.S. Patent 1,917,099, "X-ray tube"
Coolidge, U.S. Patent 1,946,312, "X-ray tube"

References[edit]

^ D. E. Grider, A Wright, and P. K. Ausburn (1986), “Electron beam melting in microfocus x-ray tubes”, J. Phys. D: Appl. Phys. 19: 2281-2292
^ M. Otendal, T. Tuohimaa, U. Vogt, and H. M. Hertz (2008), “A 9 keV electron-impact liquid-gallium-jet x-ray source”, Rev. Sci. Instrum. 79: 016102
^ T. Tuohimaa, M. Otendal, and H. M. Hertz (2007), “Phase-contrast x-ray imaging with a liquid-metal-jet-anode microfocus source”, Appl. Phys. Lett. 91: 074104
^ Diagram of continuum and characteristic lines
^ John G. Stears, Joel P. Felmlee, and Joel E. Gray (September 1986), "cf., Half-Value-Layer Increase Owing to Tungsten Buildup in the X-ray Tube: Fact or Fiction", Radiology 160 (3): 837–838
^ Perry Sprawls, Ph.D. X-Ray Tube Heating and Cooling, from The web-based edition of The Physical Principles of Medical Imaging, 2nd Ed.
^ "We want you to know about television radiation". Center for Devices and Radiological Health, US FDA. 2006. Retrieved 2007-12-24. ^{[dead link]}
^ Pickering, Martin. "An informal history of X-ray protection". sci.electronics.repair FAQ. Retrieved 2007-12-24.

External links[edit]

X-ray Tube - A Radiograph of an X-ray Tube
The Cathode Ray Tube site
NY State Society of Radiologic Sciences
Collection of X-ray tubes by Grzegorz Jezierski of Poland
Excillum AB, a manufacturer of metal-jet-anode microfocus x-ray tubes

UpToDate Contents

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English Journal

An investigation of automatic exposure control calibration for chest imaging with a computed radiography system.

Moore CS1, Wood TJ, Avery G, Balcam S, Needler L, Beavis AW, Saunderson JR.Author information 1Radiation Physics Department, Queen's Centre for Oncology and Haematology, Castle Hill Hospital, Hull and East Yorkshire Hospitals NHS Trust, Castle Road, Hull, HU16 5JQ, UK.AbstractThe purpose of this study was to examine the use of three physical image quality metrics in the calibration of an automatic exposure control (AEC) device for chest radiography with a computed radiography (CR) imaging system. The metrics assessed were signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and mean effective noise equivalent quanta (eNEQm), all measured using a uniform chest phantom. Subsequent calibration curves were derived to ensure each metric was held constant across the tube voltage range. Each curve was assessed for its clinical appropriateness by generating computer simulated chest images with correct detector air kermas for each tube voltage, and grading these against reference images which were reconstructed at detector air kermas correct for the constant detector dose indicator (DDI) curve currently programmed into the AEC device. All simulated chest images contained clinically realistic projected anatomy and anatomical noise and were scored by experienced image evaluators. Constant DDI and CNR curves do not appear to provide optimized performance across the diagnostic energy range. Conversely, constant eNEQm and SNR do appear to provide optimized performance, with the latter being the preferred calibration metric given as it is easier to measure in practice. Medical physicists may use the SNR image quality metric described here when setting up and optimizing AEC devices for chest radiography CR systems with a degree of confidence that resulting clinical image quality will be adequate for the required clinical task. However, this must be done with close cooperation of expert image evaluators, to ensure appropriate levels of detector air kerma.
Physics in medicine and biology.Phys Med Biol.2014 May 7;59(9):2307-24. doi: 10.1088/0031-9155/59/9/2307. Epub 2014 Apr 15.
The purpose of this study was to examine the use of three physical image quality metrics in the calibration of an automatic exposure control (AEC) device for chest radiography with a computed radiography (CR) imaging system. The metrics assessed were signal-to-noise ratio (SNR), contrast-to-noise ra
PMID 24732020

Estimation of mean glandular dose for contrast enhanced digital mammography: factors for use with the UK, European and IAEA breast dosimetry protocols.

Dance DR1, Young KC.Author information 1NCCPM, Medical Physics Department, Royal Surrey County Hospital, Guildford GU2 7XX, UK. Department of Physics, University of Surrey, Guildford GU2 7XH, UK.AbstractThe UK, European and IAEA protocols for breast dosimetry in mammography use tabulations of conversion factors, which relate measurements of incident air kerma to the mean glandular dose to the breast. To supplement the existing tabulations, a Monte Carlo computer program has been used to calculate conversion factors for the high-energy spectra used for contrast enhanced digital mammography. The calculations were made for the x-ray spectra from a tungsten target (tube voltage range 40-50 kV) filtered by 0.28, 0.30 and 0.32 mm of copper, and from molybdenum and rhodium targets (tube voltage range 40-49 kV), each filtered by 0.30 mm of copper. The g-factors for all of these spectra were plotted for each breast thickness as a function of half value layer (HVL) and were found to lie on smooth curves within 0.3%. These reflect the fact that the characteristic x-rays present in the spectra from molybdenum and rhodium are heavily filtered and all the spectra are essentially Bremsstrahlung. As a consequence, the s-factor previously used in the dosimetry protocols to adjust for different target/filter combinations can be taken as unity for all of the spectra considered. Tables of g-factors and c-factors are provided for breast thicknesses in the range 20-110 mm and HVLs in the range 2.4-3.6 mm of aluminium. The tables of c-factors are given for breast glandularities in the range 0.1%-100% and for typical glandularities for women in the age bands 40-49 and 50-64 attending the UK national breast screening programme.
Physics in medicine and biology.Phys Med Biol.2014 May 7;59(9):2127-37. doi: 10.1088/0031-9155/59/9/2127. Epub 2014 Apr 4.
The UK, European and IAEA protocols for breast dosimetry in mammography use tabulations of conversion factors, which relate measurements of incident air kerma to the mean glandular dose to the breast. To supplement the existing tabulations, a Monte Carlo computer program has been used to calculate c
PMID 24699200

Validation of CT doses of SPECT/CT and PET/CT hybrid devices: lessons learned.

Sera T1, Porubszky T, Papos M, Elek R, Besenyi Z, Gion K, Bartha A, Pellet S, Pavics L.Author information 1aDepartment of Nuclear Medicine, University of Szeged bEuromedic Diagnostics, Szeged c'Frédéric Joliot-Curie' National Research Institute for Radiobiology and Radiohygiene, Budapest, Hungary.AbstractThe aim of the study was to check the validity of computed tomographic (CT) doses exhibited by SPECT/CT and PET/CT hybrid devices. Dose measurements were taken from four SPECT/CT and four PET/CT cameras commercially available from different manufacturers. A calibrated ionization chamber was placed in whole-body or head phantoms for the acquisition of CT images with clinically used parameters. Computed tomography dose index (CTDIvol) values were calculated according to the IEC 60601-2-44:1999 formula. The measured CTDIvol doses were compared with those preprogrammed by the manufacturer. In the case of the whole-body phantom, the differences between the measured and displayed values varied between -31 and +24% [European document RP162 (2012) sets up the limit for acceptance criterion as ±20%]. The head phantom data showed either an agreement between -10 and +24%, or an underestimation by two-fold. The latter seemed to be because, while preprogramming the doses, the manufacturer had used the whole-body phantom instead of a proper head phantom. The results of the work demonstrate the need for individual dosimetric calibration of every single X-ray tube. Dosimetric checks should be included in the regular quality control programmes of the SPECT/CT and PET/CT devices. Special attention should be paid to head-and-neck and paediatric protocols, in which the use of a head phantom is recommended for dose calibration.
Nuclear medicine communications.Nucl Med Commun.2014 May;35(5):534-8. doi: 10.1097/MNM.0000000000000087.
The aim of the study was to check the validity of computed tomographic (CT) doses exhibited by SPECT/CT and PET/CT hybrid devices. Dose measurements were taken from four SPECT/CT and four PET/CT cameras commercially available from different manufacturers. A calibrated ionization chamber was placed i
PMID 24499726

Japanese Journal

X-ray Photon Counting Using 100 MHz Ready-Made Silicon P--Intrinsic--N X-ray Diode and Its Application to Energy-Dispersive Computed Tomography

Kodama Hajime,Watanabe Manabu,Sato Eiichi,Oda Yasuyuki,Hagiwara Osahiko,Matsukiyo Hiroshi,Osawa Akihiro,Enomoto Toshiyuki,Kusachi Shinya,Sato Shigehiro,Ogawa Akira
Jpn J Appl Phys 52(7), 072202-072202-6, 2013-07-25
… X-ray photons are directly detected using a 100 MHz ready-made silicon P--intrinsic--N X-ray diode (Si-PIN-XD). … The Si-PIN-XD is shielded using an aluminum case with a 25-μm-thick aluminum window and a BNC connector. …
NAID 150000107331

Low-Dose-Rate Computed Tomography System Utilizing 25 mm/s-Scan Silicon X-ray Diode and Its Application to Iodine K-Edge Imaging Using Filtered Bremsstrahlung Photons

Matsushita Ryo,Sato Eiichi,Yanbe Yutaka,Chiba Hiraku,Maeda Tomoko,Hagiwara Osahiko,Matsukiyo Hiroshi,Osawa Akihiro,Enomoto Toshiyuki,Watanabe Manabu,Kusachi Shinya,Sato Shigehiro,Ogawa Akira,Onagawa Jun
Jpn J Appl Phys 52(3), 032202-032202-5, 2013-03-25
… A low-dose-rate X-ray computed tomography (CT) system is useful for reducing absorbed dose for patients. … The CT system with a tube current of sub-mA was developed using a silicon X-ray diode (Si-XD). …
NAID 150000106544