Patent Application
20170221670
1. Field of the Invention
The present invention relates to a fluid injector for x-ray tubes and a method to provide a liquid anode by liquid metal injection, with a device to inject fluid from an opening in a chamber of the device as a fluid jet generated by an arrangement to change the volume within the chamber, and comprising a reservoir to store the anode material, which is fluidically connected by a pipe with the chamber of the device.
2. Description of the Related Art
X-rays are used, for example, in clinical diagnostics and visualization. Usually, x-rays are generated by applying a high voltage to an x-ray tube. The x-ray tube is a capsulated device comprising vacuum and with an electron source, i.e., cathode as well with an electron target, i.e., anode.
Electrons emitted from the cathode are accelerated by an applied high voltage between anode and cathode, and hit the anode at a high velocity, i.e., energy. A high thermal load is generated at the anode material of the x-ray tube as an impact of the electron beam.
The interaction of electrons with anode material is accompanied by radiation, the so called “Bremsstrahlung” with a continuous spectrum and the “Characteristic” radiation with a discrete monochromatic spectrum. The “Bremsstrahlung” radiation spectrum is inefficient for various diagnostic applications in healthcare. Only some portion of the “Bremsstrahlung” radiation spectrum is used for quality imaging, while low energy photons overexpose the patient without contribution to the image quality. More than 99% of electron energy is converted into heat in the anode material, leading to a high amount of thermal load at the target material. This is especially the case when the x-ray focal spot is in the range of micrometers in diameter, to obtain high resolution x-ray images.
To reduce the thermal load at the anode, the target material can be changed rapidly in order not to accumulate the thermal load in a specific volume part of the target material. The most effective ways to provide rapidly changing anode material facing the electron beam are the use of rotating or moving solid state anodes, and another way is the use of a target formed by a flowing liquid material, such as a high Z material or a combination of a low and high Z material.
U.S. Pat. No. 3,836,805A, DE 3 429 799A1 and U.S. Pat. No. 6,735,283B2 disclose conventional x-ray cubes with rotating anodes are known from the state of the art. The limiting factor in the described arrangements is the maximum of rotational frequency, which is sensible to external acceleration for example of the whole tube, and it is difficult to fabricate tubes with a reliable transmission microfocus source.
U.S. Pat. No. 8,170,179B2, U.S. Pat. No. 7,929,667B1 and U.S. Pat. No. 7,412,032B2 also disclose conventional x-ray tubes with liquid metal in form of a jet used as anode are also known from the state of the art. The advantages of a liquid jet as a target material are the excellent heat transfer properties of liquid metals and the possibility to generate thin and fast liquid jets flowing free in vacuum or inside an electron- and x-ray transparent casing, such as with a jet with less than 0.1 mm diameter and more than 50 m/s velocity of the liquid flow. The disadvantage of the described arrangements is the use of complex recirculation systems, comprising pumps for high temperature liquid metal. The flow rate of liquid metal is limited by the pumps, the reliability of the arrangement is limited and pumps increase costs and complexity.
It is an object of the present invention to provide a fluid injector for x-ray tubes and a method to provide a liquid anode by liquid metal injection solving the above described problems. Particularly, it is an object of the invention to provide an injector and a method to use the injector to produce x-rays, preventing high thermal loads, without moving parts such as valves, with a simple and easy to use configuration, with low complexity and long lasting without substantial wear, and which has a cost-effective production.
These and other objects and advantages are achieved in accordance with the invention by a fluid injector for x-ray tubes and a method to provide a liquid anode in which the fluid injector for x-ray tubes to provide a liquid anode by liquid metal injection in accordance with the present invention comprises a device to inject fluid from an opening in a chamber of the device as a fluid jet, generated by an arrangement to change the volume within the chamber. The fluid injector further comprises a reservoir to store the anode material, which is fluidically connected by a pipe with the chamber. The pipe comprises a part formed in the fluid flow direction with a shape to block fluid flow from the chamber to the reservoir during injection. The described fluid injector in accordance with the present invention solves the above described problems. Particularly, the fluid injector provides a liquid anode by liquid metal injection to an x-ray tube for the generation of x-rays, which prevents high thermal loads. The injector has a simple and easy to use configuration, with low complexity. The described injector is long lasting without substantial wear, and cost-effective in its production due to no moving parts with high wear, such as pumps or valves. The configuration of the injector without valves and pumps allows its use with a high frequency of injection. The injector is reliable and due to the fast change of anode material in contact with an electron beam, the summing up of thermal load is reduced in the material. X-rays can be produced with high intensity and focused, without a high level of effort.
The part of the pipe with a shape to block fluid flow from the chamber to the reservoir during injection can be formed in the fluid flow direction with a curved and/or angled shape, particularly as repeated loops of the pipe, particularly in spiral form.
This form is easy and cost-effective to produce, especially with commercially available pipe material, and is effective in blocking fluid flow from the chamber to the reservoir during injection, particularly short injection phases with high frequency alternating to refilling phases. The fluidic connection between the chamber and the reservoir can be an uninterrupted direct connection through the pipe and/or permanent. That is, there are no valves or other fluidically disrupting components arranged in the fluidic connection between the chamber and the reservoir. A pipe with a curved and/or angled shape without moving parts such as valves is easy to use, cheap to produce, and reliable, without high complexity, and is long lasting due to no moving parts, which reduces wear. The pipe can comprise a part having a spiral shape with a number of full loops in the range of 5 to 15 and/or a predefined radius of curvature and cross-section to result in a limited and/or turbulent fluid flow in a direction toward the reservoir in a phase of injection and to a laminar fluid flow in direction to the chamber during a refilling phase. The repeated loops are quite able to block fluid flow back to the reservoir during injection, even when fluid would flow with high velocity in a pipe without loops.
Turbulent flow is blocking fluid from flowing back to the reservoir from the injector chamber during injection. A laminar flow allows a good refilling of the chamber with fluid from the reservoir due to a good flow of fluid from the reservoir to the device with the chamber. A number of loops between 5 to 15 is high enough to block fluid flow during injection and low enough to allow a good fluid flow within the pipe during refilling without high resistance to the fluid flow. Depending among others on the kind of fluid used, the dimensions of the device to inject fluid and of the reservoir, the material of the pipe, the cross-section and radius of curvature as well as the number of loops needed to block fluid flow during injection can be calculated and pre-determined. The fluid can be and/or can comprise a liquid metal, particularly Gallium and/or a Gallium alloy and/or Lithium and/or a Lithium alloy. These materials are particularly suitable as anode materials for x-ray generation. The device can be configured for high pressure pulsed fluid injection, particularly with an injection frequency in the range of 10 to 1000 Hz. At this frequency, the use of valves is difficult to handle and involves a high amount of wear. The curved and/or angled shape part in the pipe is particularly able to block fluid flow during injection due to a hydraulic hammer effect.
The arrangement to change the volume within the chamber can comprise a metal sheet, a membrane and/or a piezo element for a volume change within the chamber, particularly with a frequency in the range of 10 to 1000 Hz and/or to produce a high pressure within the chamber for pulsed fluid injection through the opening. The device to inject fluid can comprise a nozzle cup, particularly with a sharp edge orifice, and/or a clamped circular membrane, and/or a piston particularly driven by a piezo-actuator. Such a configuration of the device enables the injection of a jet of anode material with a small cross section at high frequencies.
The injector and/or components of the injector, particularly the opening, can be arrangeable in or fluidically connectable to the inner part of a vacuum tube, to inject fluid as anode material into and/or to an electron beam, particularly generated by an electron source. The method to provide a liquid anode by liquid metal injection in an x-ray tube in accordance with the present invention, particularly using a fluid injector as described before, comprises a step of injecting liquid metal as a fluid jet from an opening of a chamber comprised of a device to inject fluid in the direction towards an electron beam. The injection is generated by changing the volume of the chamber with an arrangement producing a high pressure in the fluid in the chamber. The method further comprises a step of refilling the chamber with liquid metal from a reservoir, where the liquid metal flow from the reservoir to the chamber through a pipe.
The liquid metal flow in the pipe can be laminar during refilling and at least partly turbulent during injection, particularly with liquid metal flow in the pipe limited by a part of the pipe with a curved and/or angled shape in the flow direction during injection. The curved and/or angled shape can take the form of repeated loops of the pipe, particularly in spiral form, i.e., formed as a spiral.
A pulsed liquid metal injection, particularly with a frequency of injection pulses in the range of 10 to 1000 Hz, can be followed in time by refilling the chamber with liquid metal from the reservoir, particularly the metal liquidized by heating up solid metal in the reservoir. The metal can be liquidized according to the amount needed for liquid injection. The electron beam can converge at the injected liquid metal jet, particularly pulsed liquid metal jet, in an angle of substantially 90 degree. Electrons hitting the liquid metal, i.e., anode target material yield energy to the material resulting in thermal load and x-ray generation. Due to the movement of material the target material hit by the electron beam is changing, preventing respectively reducing the summing up of the thermal load in a specific volume element of material. An angle of substantially 90 degrees of electron beam impact to the liquid metal let can results in a high x-ray yield, particularly in the transmission mode. Depending on the energy distribution, geometrical restrictions and other circumstances, other angles of coincidence are also possible. The electron beam can converge at the injected liquid metal jet, where the liquid metal acts as an anode material and/or target, and x-rays are generated. Particularly, the electron beam hits the target with high intensity in a small volume of metal and/or with low thermal load at the injected metal.
During injection, a piston driven by a piezo-actuator can produce high pressure in the chamber by compressing a hydraulic fluid, volume, deforming a membrane, particularly a clamped circular membrane, to reduce the volume of the chamber with liquid metal being ejected from the chamber through an opening, particularly as a nozzle cup with sharp edge orifice, and liquid metal being blocked from flowing to the reservoir by a part of the pipe with curved and/or angled shape.
The advantages in connection with the described method to provide a liquid anode by liquid metal injection in an x-ray tube in accordance with the present invention are similar to the previously, in connection with the fluid injector described advantages and vice versa.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.
The present invention is further described hereinafter reference to illustrated embodiments shown in the accompanying drawings, in which:
In
The device 2 comprises a chamber 3 filled with fluid in liquid form to be injected. The volume of the chamber 3 is, for example, in the range of 1 cm3. The fluid is a liquid metal that is used as an anode, such as a Gallium based alloy or a Lithium based alloy. Injected means ejected from the chamber 3 via an opening 4 in the chamber 3 to the outside of the chamber 3, i.e., the outside of the device 2. The device 2 comprises an arrangement 5 to change the volume within the chamber 3. The arrangement 5 can be or comprise, for example, a piezo-electric device, formed to reduce the volume of the chamber 3 particularly after applying a first electrical voltage. The volume reduction increases the pressure in the chamber 3 and a stream of liquid with a flow direction 8, as shown in
In a next step the arrangement 5, for example, the piezo-electric device can increase the volume of the chamber 3, for example, after applying a second electrical voltage, particularly with an opposite sign of the electrical voltage. The volume increase leads to a pressure reduction in the chamber 3. Liquid is sucked from the reservoir 6, which is filled with liquid, through the pipe 7 to the chamber 3 of the device 2. The chamber 3 is refilled with liquid metal and the process can re-start from the beginning, thus injecting liquid. As a result, a pulsed injection of liquid metal can be generated continuously or interrupted. Various periods of injection and refilling can be chosen according to the needs during application of the fluid injector 1. The injection and refilling can be periodical with the same time intervals or with changing time intervals. The pressure in the reservoir 6 is chosen to be low enough, such that the surface tension at the opening 4 is not overcome without moving parts of the arrangement 5. As long as the pressure in the reservoir 6 is below a limit, set by the diameter of opening 4 and liquid surface tension, no liquid leaves the fluid injector 1. The limit depends among others from the environment of the liquid injector 1, particularly the pressure, for example, in vacuum.
For a laminar liquid flow during refilling, which results in a liquid flow with low friction and a high refilling rate, the cross section of the pipe is larger than the cross section of the opening 4 in the chamber 3. With the circular diameter of the opening 4 D1 and pipe 7 D2, an example for an inner diameter of the pipe D2 is 200 Micrometer and a diameter of the opening 4 D1 is 50 Micrometer.
For the liquid flow to be blocked during injection, the time interval to refill is, for example, in the order of ten times longer than the time interval to inject. A short time interval to inject liquid, i.e., eject liquid from the chamber 3, results from a fast volume change by the arrangement 5, thus inducing a liquid flow pulse breaking through the opening 4 after overcoming the surface tension of the liquid and pushing liquid in the pipe 7 in the direction from the chamber 3 to the reservoir 6. The liquid pushed rapidly into the pipe 7 from the camber 3, particularly into the pipe with higher cross-section than the cross-section of the opening 4, results in a kind of hydraulic hawser and/or turbulent flow, which is blocked by the spiral part 9 of the pipe 7. In contrast, the more slow laminar flow during refilling is not or at least only very minimally reduced by the spiral part 9 of the pipe 7.
The number of windings of the spiral 9, the cross-section for fluid flow in the pipe 7 in relation to the cross-section of opening 4 and/or the volume of the chamber 3, particularly depending on the speed of volume change by the arrangement 5 and/or the time interval for refilling and injection, are calculated and/or predefined to get an injection of liquid from the device 2, particularly overcoming the surface tension of the liquid at opening 4, and to result in a blocking of liquid flow in the pipe 7 at the spiral part 9 during injection. The values, particularly the cross-section, i.e., inner cross-section of the pipe 7, the refilling time period and the number of windings of the spiral 9 are chosen to result during refilling in a laminar liquid flow to refill the chamber 3 from the reservoir 6 without or with little flow resistance and/or friction losses. A good refilling results from the described fluid injector 1 during refilling, with a high amount of injected liquid without and/or with little liquid flowing from the chamber 3 to the reservoir 6 during injection.
With a second voltage applied to the piezo-actuator, for example, with a negative sign, the piston 12 moves up, in the direction away from the membrane 11. The hydraulic liquid volume is expanded, which deforms the membrane 11 towards the piston 12. The membrane 11 expands the liquid to be injected in the chamber 3, which decreases the pressure slowly to suck/extract liquid from the reservoir 6 via the pipe 7 to the chamber 3 without overcoming the surface tension of the liquid at the opening 10. No vacuum or air with low pressure is sucked into the chamber 3 via the opening 10. A slow movement of the membrane 11, i.e., slow expansion of the volume in chamber 3 and liquid sucking/extracting, results in a laminar liquid flow in the pipe 7 without blocking of the liquid by the spiral part 9. The chamber 3 is refilled with liquid from the reservoir 6, to be ready for the next injection. The process can be repeated as long liquid is in the reservoir 6, which can be refilled.
The refilling of chamber 3 can be actively, directly induced by the arrangement 5 with liquid flow synchronous with the movements of arrangement 5. In high frequency operation, the refilling can be slow over time after a fast movement of arrangement 5 induces a pressure difference between chamber 3 and reservoir 6.
With piezo-electric stacks, high frequency movements are possible, depending on the electric voltage change and its frequency. Typical expansion distances of piezo-electric stacks in the arrangement 5 are, for example, in the range of 0.1 mm, with a force in the range of 50 kN, creating pressure up to 500 to 1000 Atm. This allows high pressure injection in pulsed manner at high frequencies, such as 10 to 1000 Hz. At high voltage changes, a linear piezo-actuator is able to expand and/or contract with high frequency, pushing and/or pulling a piston 12 with high constant force. This force is converted to high pressure changes of, for example, a hydraulic liquid in a hydraulic liquid volume 13. A pressure difference between hydraulic liquid volume 13 and chamber 3 deforms, for example, a clamped disc membrane, particularly made of a thin steel sheet. The deformation induces high or low pressure in the chamber 3, inducing the liquid metal injection pulse respectively refilling.
The dimension of opening 10 in a chamber 3 is, for example, in the order of 0.01 to 0.1 mm and can be produced, for example, by laser drilling. The opening 10 can have conical shape with a cone base at the inner side of chamber 3, to provide a vena contracts flow. High injection pressure and small diameter of the opening 10 enable a high speed microjet.
The fluid injector 1 as shown in
The change of direction of liquid flow in the pipe 7 part with curved and/or angled shape 9, with the pipe 7 being curved and/or angled shaped along the fluid flow direction, will cause significant hydraulic losses in addition to frictional losses occurring in the pipe 7 along the length of the pipe 7. These losses during the injection phase are orders of magnitude higher than during the refilling phase. This is caused by the fact that during injection the liquid outflow will be turbulent opposite to a laminar low speed refilling flow, i.e., charging of the chamber 3. A part of the pipe with the spiral shape 9 can be made, i.e., produced by spiraling a capillary tube with, for example, an inner diameter of 0.1 to 1 mm around a cylindrical rod with, for example, a diameter of 16 mm. A spiraled tube with 1 mm inner diameter and 2 mm outer diameter with 15×360 grad full turns will results in a pipe 7 with a length of approximately 0.85 m, and in 60×90 curved and/or angled shaped parts. Hydraulic losses in the curved and/or angled shape parts, which can also be called elbows and sum up to the spiral part 9, will give rise to additional 50% losses compared to pure frictional losses in the pipe 7, assuming high speed turbulent flow when the pressure difference between the device 2 and reservoir 6 is high, such as 100 Atm. During refilling, i.e., the charge phase, the curved and/or angled shape parts will not generate any additional losses due to the laminar regime of the liquid flow.
With pressure inside chamber 3 being increased very fast, the effect of the hydraulic hammer in the pipe 7 will appear, particularly in the spiral part 9 of the pipe 7. This effect originates from the fact that any disturbances in the liquid propagates through the liquid with a finite speed, which corresponds to the specific velocity of sound in the liquid, depending on physical and thermodynamics properties of the liquid and mechanical properties of the pipe 7. Due to the hydraulic hammer effect, a compression wave moves in direction from the device 2 to the reservoir 6, and an expansion wave moves in the reverse direction. Liquid is accelerated behind the front of the waves, taking a certain period of time to establish the outflow of the liquid to the reservoir 6. The propagation of shock waves in spiraled tubes is more complex than in straight tubes. This fact requires additional time to establish the outflow, minimizing total liquid losses during the injection and increasing a possible operating frequency.
This allows an operation of the device 2 in pulse mode, with a high frequency depending on the ratio of liquid loss during injection and compensation during refilling. Spiraled pipes 9 are easy to manufacture and limit the liquid outflow to the reservoir 7, i.e., storage tank, during the injection phase when the flow regime is turbulent, but do not bring any essential liquid flow losses during refilling when the flow regime is laminar.
Due to reduced thermal load, less “Bremsstrahlung” and a higher specific x-ray radiation with well defined wave length can be produced. A well defined, specific wavelength of x-rays increases the resolution of, for example, x-ray computer tomographs or other x-ray examination devices.
To produce an x-ray image, just or only one anode material injection can be used for the imaging. The amount of anode material stored in reservoir 6 can last for a lifetime of an x-ray examination device. Alternatively, it can also be refilled. The fluid injector 1 in accordance with the present invention for x-ray tubes can be attached to the x-ray tube or arranged within the x-ray tube. The entire system can be part of an x-ray examination device, for example, built into the device. The compact set-up of the fluid injector 1, without moving parts such as valves, enables a set-up of an x-ray tube comprising the injector 1, with long lifetime.
The above described features of embodiments according to the present invention can be combined with each other and/or can be combined with embodiments known from the state of the art. For example, the dimension of components of the fluid injector 1 and frequencies for injection can be chosen according to the kind of liquid metal used as the anode material and according to the application of the x-ray tube. The membrane material can, for example, be instead of steel made of other metals and/or non metallic materials. The fluid injector 1 can be used in inert atmosphere instead of a vacuum, where the atmosphere influences the surface tension of the fluid and necessary dimensions of the opening 4, 10. The x-ray produced can be a microfocus x-ray. The liquid injector 1 can replace complex and bulky pump based recirculation systems, which are used for liquid metal injection. The operation mode of the liquid metal injector 1 can be pulsed mode, with a frequency depending on the ratio of liquid loss in chamber 3 during injection and compensation during refilling, i.e., charging. A valueless injector 1 is able to generate thin, high speed liquid jets, which can be utilized as the anode material for microfocus x-ray generation. The use of an injector 1 without moving parts such as valves increases the system reliability in comparison to tubes with rotating anodes or to liquid anode tubes with high pressure pumps. The injector 1 in accordance with the present invention is not sensitive to external acceleration, thus improving operational limits for different applications, for example, in computer tomography with fast rotating gantries.
The use of liquid metallic jets as the anode material allows the application of significantly higher loads to x-ray tubes compared with conventional microfocus solutions. The use of optimised combinations of different components of metallic alloys, for example, Lithium and Lanthanum, results in an optimised x-ray spectrum, which is essential for a high image quality and a low patient dose load during medical diagnostics.
Next, the chamber (3) is refilled with liquid metal from a reservoir (6), as indicated in step 420. In accordance with the invention, the injected liquid metal flows from the reservoir (6) to the chamber (3) through a pipe (7).
While there have been shown, described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the methods described and the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognised that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.
This is a U.S. national stage of application No. PCT/RU2014/000522 filed 17 Jul. 2014.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/RU2014/000522 | 7/17/2014 | WO | 00 |
