CN103337443A - X-ray source for medical testing and mobile CT (computer tomography) scanner - Google Patents
X-ray source for medical testing and mobile CT (computer tomography) scanner Download PDFInfo
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- CN103337443A CN103337443A CN2013101516342A CN201310151634A CN103337443A CN 103337443 A CN103337443 A CN 103337443A CN 2013101516342 A CN2013101516342 A CN 2013101516342A CN 201310151634 A CN201310151634 A CN 201310151634A CN 103337443 A CN103337443 A CN 103337443A
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/44—Constructional features of apparatus for radiation diagnosis
- A61B6/4405—Constructional features of apparatus for radiation diagnosis the apparatus being movable or portable, e.g. handheld or mounted on a trolley
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/02—Devices for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
- A61B6/03—Computerised tomographs
- A61B6/032—Transmission computed tomography [CT]
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/40—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment with arrangements for generating radiation specially adapted for radiation diagnosis
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J35/00—X-ray tubes
- H01J35/02—Details
- H01J35/04—Electrodes ; Mutual position thereof; Constructional adaptations therefor
- H01J35/06—Cathodes
- H01J35/065—Field emission, photo emission or secondary emission cathodes
Abstract
The invention provides an X-ray source for medical testing and a mobile CT (computer tomography) scanner. The X-ray source for medical testing comprises an X-ray tube and a high voltage generator, wherein the X-ray tube comprises an anode, a cold cathode, a grid and a tube shell; the tube shell is used for supporting the anode, the cold cathode and the grid, and enabling a vacuum working environment of the anode, the cold cathode and the grid to be insulated from the outside world, and the anode is grounded; and the high voltage generator is used for providing a first electric field between the cold cathode and the grid so as to enable the cold cathode to emit electrons in a field mode, and providing a second electric field between the grid and the anode so as to accelerate the electrons emitted by the cold cathode, thereby enabling the electrons to bombard X-rays generated by the anode. The X-ray source provided by the invention can realize high-frequency pulse transmission of electron beams easily, and is high in response speed, long in service life and high in security, that is, the overall performance of the X-ray source is improved, thereby being better meeting practical application requirements such as medical testing and the like.
Description
Technical field
The present invention relates to medical instruments field, particularly a kind of medical science detects with x-ray source and mobile CT scanner.
Background technology
Along with the development of medical science technology, various medical computer tomoscanner (Computer tomography have been emerged; CT) equipment.Wherein X-ray tube is a kind of small-sized Medical CT equipment key part.Negative electrode is the core component of X-ray tube, is directly determining the performance of X-ray tube, quality such as resolution and the contrast of imaging, and the operating efficiency of complete machine.
X-ray tube is normally based on the X-ray tube of tungsten (W) silk heat emission in the prior art, namely adopt tungsten (W) silk to make the negative electrode of X-ray tube, its operation principle is tungsten (W) silk emission electronics when being heated to its working temperature, the electron bombard anode of heat emission, thus produce X ray.
At least there is following shortcoming in the X-ray tube of prior art based on the heat emission of tungsten (W) silk: the electron work functon height (φ w=4.52eV) of the tungsten that the negative electrode in the existing X-ray tube adopts, emission is little, pure tungsten material is in the time of 2200 ℃, and its heat emission current density has only 0.3A/cm2.If want to obtain bigger total emission current, usually adopt and improve cathode temperature, but improving cathode temperature can make the evaporation rate of cathode material increase, the cathode material evaporation can make tungsten filament attenuate, tungsten cathode after attenuating can make cathode temperature raise again, the cathode vaporation aggravation, thus vicious circle formed; In addition, the tungsten cathode material that is evaporated can be deposited on the shell, forms continuous or interrupted tungsten conductive film, has destroyed the dielectric strength of X-ray tube, makes that tube voltage drop is low, pipe is scrapped, and has reduced the life-span of X-ray tube; Simultaneously, this tungsten conductive film has also stopped the X ray intensity of output window, has reduced imaging sensitivity.Therefore the overall performance based on the X-ray tube of tungsten (W) silk heat emission of prior art is relatively poor, presses for a kind of novel cold cathode X-ray tube of research to replace existing X-ray tube based on hot tungsten (W) silk.
Summary of the invention
Provide hereinafter about brief overview of the present invention, in order to basic comprehension about some aspect of the present invention is provided.Should be appreciated that this general introduction is not about exhaustive general introduction of the present invention.It is not that intention is determined key of the present invention or pith, neither be intended to limit scope of the present invention.Its purpose only is that the form of simplifying provides some concept, with this as the preorder of discussing after a while in greater detail.
The invention provides a kind of medical science and detect with x-ray source and mobile CT scanner, in order to improve the overall performance of x-ray source, can satisfy application demands such as medical science detection.
On the one hand, the present invention provide a kind of medical science to detect to use x-ray source, comprising:
X-ray tube comprises anode, cold cathode, grid and shell; Described shell be used for to support described anode, cold cathode and grid, and makes vacuum working environment and the external insulation of described anode, cold cathode and grid, described plus earth;
High pressure generator, be used between described cold cathode and described grid, providing first electric field to make described cold cathode field emission electron, and between described grid and described anode, provide second electric field to accelerate the electronics of described cold cathode emission, make it to bombard described anode and produce X ray.
On the other hand, the present invention also provides a kind of mobile CT scanner, comprises aforesaid medical science detection x-ray source.
X-ray source adopts cold cathode in the technical scheme provided by the invention, and is provided with grid between anode and cold cathode, because the protection of grid, most of air ion can't directly clash into cold cathode, therefore can reduce cold cathode by the probability of radiation damage; In addition, by the voltage control that grid is applied, also can realize the conducting of cold cathode emission or by control, can be easy to realize the pulse emission of electron beam that response speed is fast, long service life.When modes such as adopting the pulse exposure image is worked, can significantly reduce the projected angle number of degrees and the radiation dose of sampling, and can effectively suppress to rotate pseudo-shadow, and then better satisfy practical application request such as medical science detection.In addition, owing to adopt the cold cathode X-ray tube with grid, the electric field action that cooperates high pressure generator to apply, and with plus earth, make x-ray source can be easy to realize the high-frequency impulse emission of electron beam, response speed is fast, long service life, fail safe is higher, has namely overcome the intrinsic shortcoming of existing hot filament x-ray source, improve the overall performance of x-ray source, can better satisfy practical application request such as medical science detection.
Description of drawings
In order to be illustrated more clearly in the embodiment of the invention or technical scheme of the prior art, to do to introduce simply to the accompanying drawing of required use in embodiment or the description of the Prior Art below, apparently, accompanying drawing in describing below only is some embodiments of the present invention, for those of ordinary skills, under the prerequisite of not paying creative work, can also obtain other accompanying drawing according to these accompanying drawings.
The medical science that Figure 1A-Figure 1B provides for the embodiment of the invention detects the optional structural representation with x-ray source;
SEM photo, the field emission characteristic of a kind of optional diode LaB6 pointed cone field emission array that Fig. 2 A-Fig. 2 C provides for the embodiment of the invention;
SEM photo, the field emission characteristic of a kind of optional triode LaB6 pointed cone field emission array that Fig. 3 A-Fig. 3 C provides for the embodiment of the invention;
A kind of X-ray tube anode model example that Fig. 4 provides for the embodiment of the invention;
The maximum withstand current of the anode that Fig. 5 provides for the embodiment of the invention is with tungsten alloy sheet varied in thickness curve example;
The relation curve example of the electron beam incident angle that Fig. 6 provides for the embodiment of the invention (perhaps target surface inclination angle) and photon yield;
The X-ray tube that Fig. 7 provides for the embodiment of the invention is at the image-forming principle schematic diagram that detects as medical science such as Cranial Computed Tomography scanning imageries;
When the target surface inclination angle 5 that Fig. 8 provides for the embodiment of the invention is spent, with the distribution curve example of the photon surface density of the different angles of target surface;
The distribution curve example of the quantity of X-ray in the exit facet vertical with the electron beam incident direction under the different target surfaces inclination angle that Fig. 9 provides for the embodiment of the invention;
The embodiment of the invention target surface inclination angle that provides and the relation curve example that can be used for the X-ray subnumber of imaging are provided Figure 10.
Embodiment
For the purpose, technical scheme and the advantage that make the embodiment of the invention clearer, below in conjunction with the accompanying drawing in the embodiment of the invention, technical scheme in the embodiment of the invention is clearly and completely described, obviously, described embodiment is the present invention's part embodiment, rather than whole embodiment.The element of describing in an accompanying drawing of the present invention or a kind of execution mode and feature can combine with element and the feature shown in one or more other accompanying drawing or the execution mode.Should be noted that for purpose clearly, omitted the parts that have nothing to do with the present invention, those of ordinary skills are known and expression and the description of processing in accompanying drawing and the explanation.Based on the embodiment among the present invention, the every other embodiment that those of ordinary skills obtain under the prerequisite of not paying creative work belongs to the scope of protection of the invention.
The medical science that Figure 1A provides for the embodiment of the invention detects the optional structural representation with x-ray source.Shown in Figure 1A, the medical science that the embodiment of the invention provides detects and comprises with x-ray source: and X-ray tube and high pressure generator (High Voltage Power Supply, HVPS).
X-ray tube comprises: anode 1, cold cathode 2, grid 3 and shell 4; Described shell 4 is used for supporting described anode 1, cold cathode 2 and grid 3, and makes vacuum working environment and the external insulation of anode 1, cold cathode 2 and grid 3, anode 1 ground connection, and grid 3 is between anode 1 and cold cathode 3.
High pressure generator is used for providing first electric field to make cold cathode 2 field emission electrons between cold cathode 2 and grid 3, and provides second electric field to accelerate the electronics of cold cathode 2 emissions between grid 3 and anode 1, makes it to bombard anode 1 and produces X ray.
The x-ray source that present embodiment provides adopts cold cathode, and is provided with grid between anode and cold cathode, because the protection of grid, most of air ion can't directly clash into cold cathode, as shown in Figure 1B, therefore can reduce cold cathode by the probability of radiation damage; In addition, by the voltage control that grid is applied, also can realize the conducting of cold cathode emission or by control, can be easy to realize the pulse emission of electron beam that response speed is fast, long service life.When modes such as adopting the pulse exposure image is worked, can significantly reduce the projected angle number of degrees and the radiation dose of sampling, and can effectively suppress to rotate pseudo-shadow, and then better satisfy practical application request such as medical science detection.For target forms better protection, optional, grid can be the wire netting grid that adopts wire netting to make.
Further, the x-ray source that present embodiment provides makes the cold cathode field emission electron by first electric field that high pressure generator provides between cold cathode and grid, and second electric field that between grid and anode, provides by high pressure generator, accelerate the electronics that cold-cathode field is launched, make it to bombard anode and produce X ray.Owing to adopt the cold cathode X-ray tube with grid, the electric field action that cooperates high pressure generator to apply, and with plus earth, make x-ray source can be easy to realize the high-frequency impulse emission of electron beam, response speed is fast, long service life, and fail safe is higher, overcome the intrinsic shortcoming of existing hot filament x-ray source, can better satisfy practical application request such as medical science detection.
Optionally, the relevant parameter of first electric field that high pressure generator applies between cold cathode and grid for example: the direct voltage of 500v-1000v, be higher than the power of 50w, operating frequency 300Hz-3000Hz, pulse duty factor is 20%-80%.This scheme can effectively improve the beam intensity of cold-cathode field emission.
Optionally, the relevant parameter of second electric field that high pressure generator applies between grid and anode for example: be higher than the direct voltage of 140kv, the tube current of 2mA-16mA is higher than the power of 2000W.Plus earth.This scheme can effectively be accelerated the electronics that cold-cathode field is launched, and makes it to bombard anode and produces more X-ray, improves X ray intensity.
Optionally, cold cathode comprises: substrate and be formed at carbon nano-tube emission array on the described substrate.With the carbon nanotube cathod that carbon nano-tube is made as cathode material, hot filament negative electrode of the prior art relatively is a kind of cold cathode.The principle that produces X ray based on the X-ray tube of carbon nano-tube is: field emission takes place and produces electronics in carbon nanotube cathod under first effect of electric field, and electronics accelerates to bombard anode under second electric field, thus the generation X ray.Carbon nano-tube has very low field emission and opens electric field strength (1-3V/ μ m) and very high field emission (～1A/cm
2), can be at common condition of high vacuum degree (～10
-5Pa) long-term stable operation under, the response time is nanosecond order, launches continuously 10000 hours, beam intensity only reduces by 5%.Therefore, this scheme adopts carbon nano-tube development X-ray tube can be easy to realize the high-frequency impulse emission of electron beam, and response speed is fast, long service life, overcome the intrinsic shortcoming of existing hot filament x-ray source thus, can better satisfy practical application request such as medical science detection.
Perhaps, optional, cold cathode comprises substrate and is formed at LaB6 pointed cone field emission array on the described substrate.In all hexaborides, the LaB6 nano material has the best physicochemical property and electron emission capability, lot of experiment results shows, the work function of LaB6 nano material is that 2.4-2.8eV is 4.52eV far below the pure tungsten negative electrode, have advantages such as strong, the anti-ion bombardment of anti-poisoning capability ability is strong, chemical property stable, the life-span is long, can satisfy the selection requirement of field-transmitting cathode.In addition, though LaB6 pointed cone field emission array is to work in the X-ray tube, can't realize absolute vacuum in the X-ray tube under vacuum state, still have the little air molecule.These air molecules by high-power electron beam ionization after, can might bombard negative electrode, thereby cause the radiation damage of negative electrode to cathode direction acceleration under the highfield effect in pipe.Because the ability of the anti-ion of LaB6 nano material bombardment is strong, the chemical stability height, so based on the X-ray tube of LaB6 nano material field emission other X-ray tubes relatively, working life is longer, performance is also comparatively stable and reliable.Therefore, this scheme is launched (FieldEmission Arrays with the LaB6 nano material as the X-ray tube field, FEAs) tip materials of negative electrode, the LaB6 pointed cone field emission array that makes thus a large amount of electronics that but field emission produces under electric field action, improve electronic beam current intensity, the X ray that the electron bombard anode produces is highly stable, the X ray that makes these electron bombard anodes produce has consistency, be conducive to improve definition and the resolution of x-ray imaging, reduction is to the radiation dose of measured object, and be convenient to realize the miniaturization of X-ray tube, can satisfy the design requirement as portable medical checkout equipments such as mobile CT scanner.
For example: described LaB6 pointed cone field emission array comprises: diode LaB6 pointed cone field emission array, described diode LaB6 pointed cone field emission array comprises: silicon tip awl diode array and the LaB6 nano material film layer that covers on the silicon tip poppet surface.A kind of scanning electron microscopy (Scanning Electron Microscope of optional diode LaB6 pointed cone field emission array, SEM) photo is shown in Fig. 2 A and Fig. 2 B, its field emission characteristic is shown in Fig. 2 C, when anode voltage 1500V, the emission current 32mA of X-ray tube, the average emitted electric current of amounting to the unicuspid awl is 0.1 μ A, and threshold field is 8.0V/ μ m.As seen, adopt diode LaB6 pointed cone field emission array to have lower threshold field as the X-ray tube of negative electrode, extra electric field required when namely reaching the stable emission of X ray is less, can be at common condition of high vacuum degree (～10
-5Pa) long-term stable operation under can be easy to realize the high-frequency impulse emission of electron beam, and response speed is fast, long service life, and be conducive to reduce power consumption, reduce the radiation dose to measured object, have advantages such as environmental protection, health, can better satisfy practical application request such as medical science detection.
Again for example: described LaB6 pointed cone field emission array comprises: triode LaB6 pointed cone field emission array, described triode LaB6 pointed cone field emission array comprises: silica-based, be formed on described on silica-based the vestibule array, be distributed in the molybdenum pointed cone array in each vestibule and cover the lip-deep LaB6 nano material film of each molybdenum pointed cone layer.The SEM photo of a kind of optional triode LaB6 pointed cone field emission array of employing traditional handicraft (as the Spindt method) preparation as shown in Figure 3A, the SEM photo of a kind of optional triode LaB6 pointed cone field emission array of employing mask oxidation technology (LOCOS method) preparation is shown in Fig. 3 B, its field emission characteristic is shown in Fig. 3 C, when anode voltage 1500V, the emission of X-ray tube is 0.6A/cm
2, amount to unicuspid awl average emitted electric current 0.24 μ A.As seen, adopt triode LaB6 pointed cone field emission array to have very low field emission unlatching electric field strength and very high field emission as the X-ray tube of negative electrode, can be at common condition of high vacuum degree (～10
-5Pa) long-term stable operation under can be easy to realize the high-frequency impulse emission of electron beam, and response speed is fast, long service life, and be conducive to reduce power consumption, reduce the radiation dose to measured object, have advantages such as environmental protection, health, can better satisfy practical application request such as medical science detection.
Optionally, described anode 1 comprises: anode bodies 11 and be located at target surface 12 on the anode bodies 11.By the choose reasonable anode material, can effectively improve the maximum beam intensity that it bears, preferred, described anode bodies is the copper anode body, described target surface is the tungsten alloy target surface.
In X-ray tube, the electronics of cold cathode emission strikes after electric field accelerates and produces X ray on the plate target, and wherein the energy of electron beam more than 99% changes into heat and be deposited in the anode, only is transformed into X ray less than about 1% energy.If electronics can not get scattering and disappearing timely and effectively at a large amount of heats that plate target produces, the temperature rise on plate target surface is very fast, and in a short period of time, the surfacing of plate target will melt, and causes X-ray tube to damage.Therefore, the heat-resisting and heat dispersion of plate target has directly influenced the use of X-ray tube.
Optionally, can adopt fixed anode conceptual design X-ray tube, i.e. X-ray tube middle-jiao yang, function of the spleen and stomach fixed anode very.The advantage of this scheme is effectively to reduce the weight and volume of x-ray source, and reduces the manufacturing of X-ray tube and use difficulty.
Relate generally to following different materials in the development process of X-ray tube:
Table 1: material characteristic parameter
From the performance of material as can be known, the fusing point height of tungsten, but heat conductivility is poor; The good heat conductivity of copper, but fusing point is low.Though all than tungsten, copper height, its atomic number is low for graphite fusing point and specific heat, the generation efficient of X ray is low.Therefore, can adopt copper to do anode bodies, to utilize its good heat-conducting, adopt the tungsten alloy sheet to do target surface, to utilize its high-melting-point performance.
Because the performance of copper and tungsten is inconsistent, the thickness of tungsten alloy sheet is a key parameter of anode design.If the tungsten alloy sheet is too thick, heat has little time to transmit, and then the tungsten alloy sheet may melt earlier; If the tungsten alloy sheet is too thin, heat passes to copper at once, and then copper may melt earlier.No matter which kind of situation occurs, and all can have influence on the operate as normal of X-ray tube.Therefore, the thickness of tungsten alloy sheet need be selected optimal value.
In order to calculate the optimal thickness value of tungsten alloy sheet, can use the tungsten alloy sheet of hot analysis software simulation different-thickness under the beam pulse bombardment of varying strength, the temperature rising curve of tungsten alloy sheet and adjacent metal copper, and the transmittance process of heat in anode, the relation between research material thickness, electronic beam current intensity and the temperature.Because the heat of electron beam generates low than with under the constant current state under the intensity under the pulse condition, in order to leave surplus to design, we mainly simulate the parameter under the constant current state.
The physical model of anode is illustrated in fig. 4 shown below: the physical dimension of copper anode body is
The target surface material is tungsten, and the diameter of tungsten alloy sheet is
Focus diameter is
The thickness range of tungsten alloy sheet is 20 μ m～2mm, and x-ray tube voltage is 140kV, and current range is 2mA～10mA.
Can use ANSYS12 to set up X-ray tube anode FEM (finite element) model, carry out CALCULATION OF THERMAL, the thickness by change tungsten alloy sheet and current strength are come the Temperature Distribution on the computational analysis anode.
Electron beam is beaten on the tungsten surface, and its focus diameter is
The top layer mean depth that electronics enters tungsten is 5 μ m, and electronics is at the small volume Nei Shengre of this section.The method that applies thermal force has two kinds: a kind of is the imposed load method of having simplified, and load is applied on the whole, namely at the center of tungsten
The surface on apply thermal force, can calculate the heat flow size that applies on the whole according to voltage and current; Another method is one innings of actual conditions imposed load, and thermal force is applied on the body, namely
Cylinder on.The coefficient of overall heat transmission is directly proportional with area, because S
Surf=π r
2=0.785mm
2, S
Vol=π r
2+ 2 π rh=0.8007mm
2If the mode of load with face load applied the two error
Can ignore.Find the solution conveniently for modeling, at this applying method that uses face load, computing formula is as follows:
In the following formula: Q---heat output or heat flow in the time t.
K---be pyroconductivity.
T---temperature.
A---contact area.
D---the distance between two planes.
In X-ray tube work, because heat loss through conduction and heat loss through radiation take place simultaneously, so can calculate the influence that their antianode temperature rise.
In actual use, whole X-ray tube all is placed into insulation in the oil, cooling.Because the conductive coefficient of oil is very little, therefore in X-ray tube work, heat mainly is stored on the anode.Behind the end of scan, through just cooling down after a while.So when modeling, can ignore the cooling effect of oil earlier.Can calculate Temperature Distribution on the anode by hot emulation, and then estimate the heat loss through radiation of whole anode.High-temperature area was very little during temperature of anode distributed, and mainly concentrated on the electron beam focus, and the temperature on overwhelming majority surface is lower than 468 ℃.
According to Si Difen-Boltzmann's theorem:
E is radioactive force, and unit is W/m
2
ε is the radiance of object;
C is blackbody coefficient, 5.67W/ (m
2K
4);
T is the body surface temperature.
According to 3300 degrees centigrade of electron beam focus temps, other surface temperatures are 400 ℃ and estimate that then the radiant power of anode is:
P
Radiation=A
TungstenE
Tungsten+ A
CopperE
Copper
=(π * r*r) * ε
Tungsten* c* (T
Tungsten/ 100)
4+ (2* π * r
1* r
1+ 2* π * r
1* * ε h)
Copper* c* (T
Copper/ 100)
4
=92.17(W)
The input power of anode is 1050W, P so
Radiation/ P=0.0658, the proportion that the power of radiation accounts for input power is very little, can neglect.
Be the simulation result of ignoring heat loss through radiation and insulating oil heat loss through conduction below.According to designing requirement, the maximum duration of finishing a CT scan is 30s, so in when scanning, X-ray tube must continuous firing 30s, this be foundation, calculates the tungsten alloy sheet thickness of optimum and the maximum Constant Electric Current flow valuve that can tolerate.
As seen from Figure 5, under the situation of continuous incident electron, when tungsten alloy sheet thickness was 400～500 μ m, maximum withstand current was 7.5mA.The left side of curve peak in the drawings, copper is fusing earlier, the right, the tungsten alloy sheet is fusing earlier.
For pulse working mode, under the different duty, the tungsten alloy sheet of same thickness the maximum surge current that can tolerate increase along with the minimizing of duty ratio.
Consider the useful life of plate target, and the pulse working mode of electron beam, it is 400-500um that the embodiment of the invention will be selected the thickness of tungsten alloy target surface for use, for example preferred 0.5mm is the preferred thickness value of tungsten alloy sheet.
Optionally, as shown in Figure 7, the anode 1 of X-ray tube comprises anode bodies 11 and target surface 12.Target surface 12 relative reference directions are formed with predetermined target surface inclination alpha, and reference direction is vertical with the electron impact direction, as shown in Figure 7.
The target surface inclination alpha is a key parameter, and it will directly have influence on photoyield, Effective focus size, heat distribution and the transmission etc. of X-ray tube.For the variation of studying the target surface inclination angle influence to yield and the angular distribution of X-ray, can adopt Monte Carlo method that it has been carried out analog computation.For example used the EGS software simulation 1 * 10
7The tungsten target of the electron bombard different angle of individual 140keV, the spatial distribution of having added up photoyield and photon.The relation of target surface inclination angle and photon yield is seen Fig. 6.As can be seen from Figure 6, the target surface inclination angle is more little, and X-ray yield is more high.
But, whether the smaller the better the target surface inclination angle is, and this need carry out careful analysis.Final utilization is with X-ray within the approximately perpendicular fladellum of electron beam incident direction in the CT scan process, and this part X-ray is only (as shown in Figure 7) that really contributes for the CT imaging, so X-ray in this angular range is The more the better.
Fig. 8 is target surface inclination angle 5 when spending, with the photon surface density of the different angles of target surface.As can be seen from Figure 8, along with the increase of target surface angle, the surface density of photon is more and more littler, the X-ray subnumber that namely can be used for imaging is fewer and feweri.Therefore, though the total photon yield when target surface inclination angle 5 is spent is very high, but very low with the photon surface density at target surface angle 85 degree places.
Quantity to X-ray in the exit facet vertical with the electron beam incident direction under the different target surfaces inclination angle is added up, and statistics is seen Fig. 9.As can be seen from Figure 9, along with the increase at target surface inclination angle, the number of photons of exit facet increases thereupon, but reaches maximum about 45 degree, just begins then to reduce.
In the CT imaging, what influence faultage image resolution is the effective focal spot of X-ray tube, rather than actual focal spot.Suppose the parallel incident of electron beam, then the relation between the Effective focus size d after actual focal spot size L and the projection is as follows:
d＝Lsinα
As can be seen from the above equation, if when the size L of actual focal spot is difficult to reduce, can control the size d of effective focal spot by reducing the target surface inclination alpha.
If the density of the electron beam unit cross-sectional area of incident can't improve, according to following formula as can be known, reduce the sum that the target surface inclination alpha might improve imaging X-ray but increase electronic beam current width h.
d＝htgα
The density of the focal spot size of remaining valid and electron beam unit cross-sectional area is constant, and target surface inclination angle and the relation curve that can be used between the X-ray subnumber of imaging are seen Figure 10.
As can be seen from Figure 10, the target surface inclination angle is more little, can effectively increase the X-ray quantum count that can be used for imaging by increasing the electronic beam current width.But in conjunction with preceding figure as can be known, at this moment, the total amount of the electronic beam current of incident significantly increases, and then has increased the heat that anode is accepted, and this will propose challenge to the heat radiation of X-ray tube.Therefore, the target surface inclination angle of anode determines and need seek a kind of balance between the heat of the X-ray quantum count that can be used for imaging and incident electron.Through taking all factors into consideration, the target surface inclination angle is preferably 11 degree, shown in Figure 1A.
Optionally, the X-ray tube total length in above-described embodiment is less than or equal to 120mm, and/or, the total weight of x-ray source is less than 25kg, with the slimline of abundant assurance X-ray tube, can be easy to carry, conveniently be applicable to particular surroundingss such as carrier-borne, vehicle-mounted, FAMB.
Optionally, the maximum gauge in above-described embodiment is less than or equal to 60mm.Further preferably, the distance at pointed cone top is less than or equal to 10um in the anode in above-described embodiment and the negative electrode.Can guarantee the premium properties of X-ray tube like this.
In addition, the present invention also provides a kind of mobile CT scanner, and this moves the medical science detection x-ray source that CT scanner comprises that above-mentioned arbitrary embodiment provides, and produces X ray by this x-ray source and detects human bodies such as brain are carried out medical science.
In the various embodiments described above of the present invention, the sequence number of embodiment or sequencing do not represent the quality of embodiment just to being convenient to description.Description to each embodiment all emphasizes particularly on different fields, and does not have the part of detailed description among certain embodiment, can be referring to the associated description of other embodiment.
One of ordinary skill in the art will appreciate that: all or part of step that realizes said method embodiment can be finished by the relevant hardware of program command, aforesaid program can be stored in the computer read/write memory medium, this program is carried out the step that comprises said method embodiment when carrying out; And aforesaid storage medium comprises: various media that can be program code stored such as read-only memory (Read-Only Memory is called for short ROM), random access memory (Random Access Memory is called for short RAM), magnetic disc or CD.
In embodiment such as apparatus and method of the present invention, obviously, after can decomposing, make up and/or decompose, each parts or each step reconfigure.These decomposition and/or reconfigure and to be considered as equivalents of the present invention.Simultaneously, in the above in the description to the specific embodiment of the invention, can in one or more other execution mode, use in identical or similar mode at the feature that a kind of execution mode is described and/or illustrated, combined with the feature in other execution mode, or the feature in alternative other execution mode.
Should emphasize that term " comprises/comprise " existence that refers to feature, key element, step or assembly when this paper uses, but not get rid of the existence of one or more further feature, key element, step or assembly or additional.
It should be noted that at last: though above the present invention and the advantage thereof of having described in detail is to be understood that and can carries out various changes, alternative and conversion under the situation that does not exceed the spirit and scope of the present invention that limited by appended claim.And scope of the present invention is not limited only to the specific embodiment of the described process of specification, equipment, means, method and step.The one of ordinary skilled in the art will readily appreciate that from disclosure of the present invention, can use according to the present invention and carry out and process, equipment, means, method or the step essentially identical function of corresponding embodiment described herein or acquisition result essentially identical with it, existing and that will be developed in the future.Therefore, appended claim is intended to comprise such process, equipment, means, method or step in their scope.
Claims (10)
1. a medical science detects and uses x-ray source, it is characterized in that, comprising:
X-ray tube comprises anode, cold cathode, grid and shell; Described shell be used for to support described anode, cold cathode and grid, and makes vacuum working environment and the external insulation of described anode, cold cathode and grid, described plus earth;
High pressure generator, be used between described cold cathode and described grid, providing first electric field to make described cold cathode field emission electron, and between described grid and described anode, provide second electric field to accelerate the electronics of described cold cathode emission, make it to bombard described anode and produce X ray.
2. medical science according to claim 1 detects and uses x-ray source, it is characterized in that,
The relevant parameter of described first electric field comprises: the direct voltage of 500v-1000v, be higher than the power of 50w, and operating frequency 300Hz-3000Hz, pulse duty factor is 20%-80%; And/or,
The relevant parameter of described second electric field comprises: be higher than the direct voltage of 140kv, the tube current of 2mA-16mA is higher than the power of 2000W.
3. medical science according to claim 1 and 2 detects and uses x-ray source, it is characterized in that,
Described cold cathode comprises: substrate and be formed at carbon nano-tube emission array on the described substrate;
Perhaps,
Described cold cathode comprises: substrate and be formed at LaB6 pointed cone field emission array on the described substrate.
4. medical science according to claim 3 detects and uses x-ray source, it is characterized in that,
Described LaB6 pointed cone field emission array comprises: diode LaB6 pointed cone field emission array, and described diode LaB6 pointed cone field emission array comprises: silicon tip awl diode array and the LaB6 nano material film layer that covers on the silicon tip poppet surface;
Perhaps,
Described LaB6 pointed cone field emission array comprises: triode LaB6 pointed cone field emission array, described triode LaB6 pointed cone field emission array comprises: silica-based, be formed on described on silica-based the vestibule array, be distributed in the molybdenum pointed cone array in each vestibule and cover the lip-deep LaB6 nano material film of each molybdenum pointed cone layer.
5. medical science according to claim 3 detects and uses x-ray source, it is characterized in that described anode is fixed anode or rotatable anode.
6. medical science according to claim 5 detects and use x-ray source, it is characterized in that described fixed anode comprises: the copper anode body of fixing and be fixed in tungsten alloy target surface on the described copper anode body.
7. medical science according to claim 6 detects and uses x-ray source, it is characterized in that described tungsten alloy target surface relative reference direction is formed with predetermined target surface inclination angle, and described reference direction is vertical with the electron impact direction.
8. medical science according to claim 7 detects and uses x-ray source, it is characterized in that the thickness of described tungsten alloy target surface is 400-500um, and/or described target surface inclination angle is 11 degree.
9. medical science according to claim 3 detects and uses x-ray source, it is characterized in that, described X-ray tube total length is less than or equal to 120mm, and/or, the maximum gauge of described X-ray tube is less than or equal to 60mm, and/or the distance at described anode and described cold cathode top is less than or equal to 10um, and/or the total weight of described x-ray source is less than 25kg.
10. a mobile CT scanner is characterized in that, comprises arbitrary described medical science detection x-ray source as claim 1-9.
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| CN201310151634.2A CN103337443B (en) | 2013-04-27 | 2013-04-27 | Medical science detects with x-ray source and mobile CT scanner |
| PCT/CN2013/076000 WO2014172932A1 (en) | 2013-04-27 | 2013-05-21 | X-ray source for medical detection, and movable ct scanner |
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| WO2014172932A1 (en) | 2014-10-30 |
| CN103337443B (en) | 2016-05-18 |
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