EP4344358A1 - X-ray source assembly with multiple filaments - Google Patents
X-ray source assembly with multiple filaments Download PDFInfo
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- EP4344358A1 EP4344358A1 EP22197800.0A EP22197800A EP4344358A1 EP 4344358 A1 EP4344358 A1 EP 4344358A1 EP 22197800 A EP22197800 A EP 22197800A EP 4344358 A1 EP4344358 A1 EP 4344358A1
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- filament
- ray source
- filaments
- source assembly
- switches
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05G—X-RAY TECHNIQUE
- H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
- H05G1/08—Electrical details
- H05G1/26—Measuring, controlling or protecting
- H05G1/30—Controlling
- H05G1/34—Anode current, heater current or heater voltage of X-ray tube
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05G—X-RAY TECHNIQUE
- H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
- H05G1/08—Electrical details
- H05G1/10—Power supply arrangements for feeding the X-ray tube
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05G—X-RAY TECHNIQUE
- H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
- H05G1/08—Electrical details
- H05G1/60—Circuit arrangements for obtaining a series of X-ray photographs or for X-ray cinematography
Definitions
- the invention relates to the field of X-ray, and more specifically to an X-ray source assembly with multiple filaments, to a computer implemented method of controlling multiple filaments, to an imaging system comprising the X-ray source assembly and to an X-ray tube insert configured to be comprised in the X-ray source assembly.
- An X-ray tube typically includes a cathode with a focusing cup and a filament and a rotating anode.
- a tube current is applied to the filament, which heats the filament, causing the filament to expel electrons (thermionic emission), creating a space charge (or cloud a negative charge) a short distance away from the filament.
- a tube voltage is applied across the cathode and the anode and causes a beam of the electrons to accelerate from the cathode and impinge the anode.
- a grid voltage is applied to electrodes of the focusing cup to control a size of and steer the beam of electrons.
- An interaction of the electrons with the material of the anode produces heat and radiation, including X-rays, which pass through a tube window. Electrical power is supplied to the X-ray tube with a high voltage generator.
- a surface area of the anode that receives the beam of electrons is referred to as a focal spot.
- the size of the focal spot is one factor that affects the image quality of X-ray imaging.
- the focal spot size affects the spatial resolution, where a smaller focal spot size results in a greater spatial resolution than a larger focal spot size, e.g., due to less focal spot blur from geometric magnification.
- JP5395320B2 describes an X-ray tube equipped with a negative electrode having two filaments having electron emission amounts different from each other, a positive electrode target arranged oppositely to the negative electrode, and emitting an X-ray by hitting electrons emitted from the negative electrode against it, and a vacuum envelope with the negative electrode and the positive electrode target housed therein; and a control part electrically connected to the two filaments, and controlling whether the two filaments should be driven at the same time or not.
- the power chain of driving multiple filaments with sufficient speed and performance is relatively complex, costly and space consuming.
- an imaging X-ray source assembly with multiple filaments comprising:
- the X-ray source assembly makes it possible to drive and control at least two filaments with a single driver and transformer, and thereby reduce complexity of the system. Thanks to this approach, space required for the high voltage generator as well as total cost of components can be decreased. Furthermore, one independent wire instead of at least two is sufficient in the high voltage cable between the X-ray tube and the high voltage generator.
- the switch control signals are pulsed control signals, and each of the switches are configured to have a duty cycle larger than 0% and less than 100% in response to the pulsed control signal.
- the configuration of duty cycle controlled switches in combination with a common filament current set point is advantageous for controlling the multiple filaments with a single driver. With these two variables, common filament current and duty cycle, the effective current of each individual filament can be controlled.
- At least one of the plurality of switches is configured to have a duty cycle larger than 10% and less than 90% in response to the respective pulsed control signal.
- the pulsed control signal has a (maximum) pulse length smaller than a characteristic thermal response time of the respective filament. It is advantageous if the pulse length is shorter than a characteristic thermal response time of the filament in order to get a stable temperature of the filament. In this way, filament temperature fluctuations may be reduced or avoided. Duty cycled control of the filament current allows the filament to be kept on a suitable standby temperature. In this way, it can be avoided that the filament cools down too much and the filament can be quickly switched on, to emit electrons, from a standby phase without significant delay due to the thermal response. In other words, fast switching between filaments is enabled. Thermal response time in this context is a measure of how quickly the filament heats up and cools down. It may depend on aspects such as, but not limited to, filament material, purity, dimensions, surrounding vacuum etc.
- the switching frequency of the pulsed signal may be in an order of magnitude of thousands of Hz, preferably many thousands of Hz, more preferably at least 10 kHz.
- plurality of switches are semiconductor switches. Such switches are advantageous thanks to their capability of high frequency switching.
- components for such semiconductor switches include but are not limited to, metal-oxide-semiconductor field-effect transistors, silicon carbide switches, insulated-gate bipolar transistors etc.
- the X-ray source assembly further comprises an anode configured to generate X-rays when impinged with electrons at a focal spot, wherein a first one of the filaments is configured to emit electrons to impinge a first focal spot on the anode, wherein a second one of the filaments is configured to emit electrons to impinge a second focal spot on the anode, and wherein the second focal spot is different from the first focal spot in size, location and/or shape.
- Simplified control over multiple filaments according to the invention can advantageously be used with multiple focal spots, where the characteristics of each filament may be optimized to the characteristics of the focal spot.
- X-ray imaging technologies such as computed tomography, fluoroscopy etc. there is sometimes a need to rapidly switch between focal spots.
- Embodiments of the invention allows for fast switching between the focal spots.
- the invention may advantageously provide additional flexibility to focal spot control.
- control unit is connected to the filament driver via an optical fiber or wireless connection.
- an optical fiber, wireless connection or other high voltage insulating connections makes it possible to e.g. locate the control unit inside and the filament driver outside a high voltage environment of the X-ray source assembly.
- the power to switch at least one of the switches is derived from windings of the filament transformer.
- the X-ray source assembly is programmable to control the respective filament currents. This is advantageous as it allows for various protocols to be optimized for the imaging application at hand. In advance and/or during imaging for increased flexibility.
- a user may interface with the programmable X-ray source assembly via a suitable computer interface and/or via communication channels as part of an imaging system.
- a programmable part of the X-ray source assembly may advantageously be on a low voltage side of the assembly to reduce complexity on the high voltage side, where space may be limited. Alternatively or in addition, a programmable part may be on a high voltage side close to the switches such that delays can be minimized for very fast switching.
- a computer implemented method of controlling a plurality of filament currents with the programmable X-ray source assembly comprising:
- a computer program which, when being executed by a computer, is adapted to cause the X-ray source assembly to carry out the above computer implemented method.
- a medical imaging system comprising the X-ray source assembly.
- the medical imaging system may be a radiography system, a computed tomography system, a fluoroscopy system, a C-arm X-ray system for interventional guidance etc.
- an X-ray tube insert comprising a plurality of filaments, configured to be comprised in the X-ray source assembly, wherein the plurality of filaments are configured to be connected to the same filament transformer, and wherein each of the plurality of filaments is configured to be connected the respective one of the plurality of switches.
- Fig. 1 schematically illustrates a conventional X-ray source assembly 100 (filament driver circuit) with two filaments FL, FS in the high voltage part 101 of the assembly, in a vacuum environment.
- Each of the filaments FL, FS may be configured to emit electrons via thermionic emission when a tube current is applied to the filament. Such a tube current heats the filament, thereby causing the filament to expel electrons.
- the emitted electrons are accelerated from the cathode filament in an electrode beam towards an anode (not shown in the figure) with a tube voltage, thereby causing generation of X-rays at the anode.
- the filaments FL, FS may be configured to generate focal spots of the same or different size, shape, location etc.
- Each of the filaments FL, FS in the X-ray source assembly 100 has a corresponding filament driver LF, SF and a corresponding transformer TL, TS.
- Each filament driver LF, SF is controlled with one or multiple processors CPU, and generates voltage to drive the corresponding filament FL, FS.
- Each filament transformer TL, TS insulates the high voltage part 101 from the low voltage part and transforms the generated voltage of the corresponding filament driver LF, SF to transfer power to the corresponding filament FL, FS.
- the assembly 100 may look relatively simple, multiple filament drivers LF, SF and transformers TL, TS lead to very bulky and complex structures.
- the example X-ray source assembly in Fig. 1 has two filaments FL, FS with corresponding drivers LF, SF and transformers TL, TS.
- an X-ray source assembly three or even more sets of filaments, filament drivers and transformers.
- Fig. 2 schematically illustrates an X-ray source assembly 200 (filament driver circuit) according to an embodiment of the invention.
- the X-ray source assembly 200 comprises multiple, at least two, filaments FL, FS, FX (shown in the figure as resistors).
- a first filament FL is configured to emit electrons when a current passes through the first filament FL.
- a second filament FS is configured to emit electrons when a current passes through the second filament FS.
- the filaments FL, FS may be configured to generate focal spots of the same or different size, shape, location etc. on an anode.
- FL may be suited to generate a large focal spot and FS may be suited to generate a smaller focal spot.
- FL and FS may also be configured to generate the same or identical focal spots.
- the X-ray source assembly 200 may also have more filaments, such as an Xth filament FX configured to emit electrons when a current passes through the Xth filament FX.
- the multiple filaments FL, FS, FX may be configured to generate different focal spots
- the X-ray source assembly 200 may also comprise electron beam optics (not shown) to focus/and or steer the electron beam from the filaments FL, FS, FX.
- the combination of multiple filaments with electron beam optics may provide increased flexibility in focal spot control.
- the X-ray source assembly 200 comprises a filament transformer T1 connected to the first filament FL and the second filament FS.
- the filament transformer T1 is also connected to additional filaments FX.
- the filament transformer T1 is configured to transfer electrical energy to the filaments FL, FS and optionally to additional filaments FX.
- the X-ray source assembly 200 comprises a filament driver FD1 configured to supply electrical energy to the first filament FL and the second filament FS via the filament transformer T1.
- the filament driver is configured to supply electrical energy to additional filaments FX via the filament transformer T1.
- the X-ray source assembly 200 comprises a first switch S1 connected to the first filament FL and configured to regulate the current through the first filament FL.
- the X-ray source assembly 200 comprises a second switch S2 connected to the second filament FS and configured to regulate the current through the second filament FS.
- the X-ray source assembly 200 comprises an Xth switch SX connected to the Xth filament FX and configured to regulate the current through the Xth filament FX.
- the switches S1, S2, SX each comprise a high part S1H, S2H, SXH and a low part S1L, S2L, SXL in series. Such switches are advantageous when regulating alternating currents through the filaments.
- other types of switches are also conceivable.
- the switches may advantageously be semiconductor switches, such as but not limited to, switches comprising metal-oxide-semiconductor field-effect transistors (MOSFET), silicon carbide switches, insulated-gate bipolar transistors etc.
- the X-ray source assembly 200 also comprises a control unit CTRL.
- the control unit CTRL is connected to the first switch S1 and the second switch S2 and the filament driver FD1.
- the control unit CTRL is configured to control the first switch S1 and the second switch S2 with a switch control signal.
- the control unit CTRL is connected to and configured to control an Xth switch, SX.
- the filaments FL, FS, FX, the switches S1, S2, SX and the control unit CTRL are located on the high voltage side 201 of the X-ray source assembly 200.
- the filament driver FD 1 and processor CPU are located on the low voltage side, insulated from the high voltage part 201 by the transformer T1.
- the control unit CTRL on the high voltage side 201 is connected to the filament driver FD1 on the low voltage side via an optical fiber 202.
- the connection may be a wireless connection or other high voltage insulating connection.
- Everything in the high voltage part 201 as illustrated in Fig. 2 is at the same voltage potential. I.e. at the cathode voltage potential of the X-ray source assembly 200.
- the multiple filaments may be fed by a secondary winding of the filament transformer T1.
- the energy provided by the filament driver FD1 can be distributed to the filaments FL, FS, FX.
- the switches S1, S2, SX and the filaments FL, FS, FX may advantageously be duty cycled controlled with a pulsed control signal. During the time that one switch is 'ON, the other switch or switches are 'OFF'.
- the configuration of duty cycle controlled switches in combination with a common filament current set point is advantageous for controlling the multiple filaments with a single driver.
- common filament current and duty cycle the effective current of each individual filament can be controlled.
- a set point filament current may be 9.5A and a duty cycle may be 0.63 for filament FL.
- filament FL has an effective current of around 6A and may be emitting electrons
- the filament FS has an effective current of around 3.5A and may be in standby mode.
- the pulse length of the pulsed control signal may be shorter than a characteristic thermal response time of the filaments FL, FS.
- each filament FL, FS can be quickly switched on, to emit electrons, from a standby phase without significant delay due to the thermal response, thereby enabling fast switching between the filaments FL, FS.
- the X-ray source assembly 200 comprises one or multiple processors CPU in connection with the filament driver FD1.
- the X-ray source assembly 200 may therefore be programmable, e.g. programmable to control the currents over the filaments FL, FS, FX.
- key parameters for controlling electron emission from either of the multiple filaments such as filament current set point, duty cycle and pulse length, may be programmed in advance and/or adapted during operation of the X-ray source assembly. It may be particularly advantageous to do all or most processing on the low voltage side, e.g. to reduce complexity and due to the often limited space on the high voltage side 201.
- control unit CTRL on the high voltage side 201 may comprise a Field-programmable gate array (FPGA) to decode the signals/commands from the filament driver FD1 into duty cycle for the switches S1, S2, SX.
- FPGA Field-programmable gate array
- the X-ray source assembly 200 may thus be able to execute a computer program and/or connect to external devices executing such a program. Users may directly or indirectly interact with the X-ray source assembly and/or connected external devices via a user interface. Examples of user interface types include graphical user interfaces, natural user interfaces, and so forth. For instance, a graphical user interface may accept input from a user employing input device(s) such as a keyboard, mouse, remote control, or the like and provide output on an output device such as a display. Further, a natural user interface may enable user interaction in a manner free from constraints imposed by input device such as keyboards, mice, remote controls, and the like. Rather, a natural user interface can rely on speech recognition, touch and stylus recognition, gesture recognition both on screen and adjacent to the screen, air gestures, head and eye tracking, voice and speech, vision, touch, gestures, machine intelligence, and so forth.
- Fig. 3 schematically illustrates an example of a filament driver FD1 in some more detail.
- the filament driver FD1 is shown here as a half bridge inverter with two MOSFET switches SH and SL.
- the filament driver FD1 may also be implemented using a full bridge inverter or other suitable topologies.
- a pulse generator G1 drives two gate drivers N1 and N2 to control the two MOSFET switches SH and SL.
- the pulse generator G1 may drive the gate drivers N1 and N2 with a high frequency, preferably a frequency larger than 1kHz and even more preferably larger than 10kHz. In this way, the switches SH and SL are controlled to adjust the energy for the high voltage transformer T1.
- the inductor L1 forms a resonant circuit together with capacitances C1 and C2.
- other circuits without resonant circuit may be used to drive the transformer T1.
- the fiber optics driver F2 is a frequency generator controlled by a processor CPU.
- the output signal from the fiber optics driver F2 goes via a fiber optics converter 301 to the control unit CTRL via a fiber optic connection 202 (not shown here).
- the output signal from the fiber optics driver F2 may be a fixed frequency signal with variable pulse-pause ratio or a coded frequency signal which has to be re-encoded on the high voltage side 201.
- the filament driver FD1 in Fig. 3 thus has two pulse drivers.
- the pulse generator G1 effectively determines the total power that is transferred over the transformer T1 to the filaments FL, FS, FX.
- the fiber optics driver F2 controls, via the controller CTRL, how that power is divided between the filaments FL, FS, FX.
- Fig. 4 schematically illustrates an example of a control unit CTRL.
- signals from the fiber optics driver F2, via the fiber optics connection 202 enters the control unit CTRL on the left side.
- the signals are converted into electrical signals by means of fiber optics converters 401, 402.
- the converted electrical signal is then transmitted to the respective switches S1, S2, S3, S4 via gate drivers N3, N4, N5, N6, here with NOT logic gates at N4 and N6.
- this configuration requires multiple fiber optics connections/converters to drive more than two switches S1, S2, S3, S4 and thus to drive more than two filaments.
- the fiber optics signals for 401 and 402 may need to be synchronized by the CPU in order to distribute the duty cycles or switch on time for S1 to S4.
- the maximum duty cycle per switch pair e.g. S1 and S2 or S3 and S4.
- the gate drivers N3, N4, N5, N6 and/or fiber optics converters 401,402 and/or switches S1, S2, S3, S4 may be powered by a separate power supply (not shown), or power can be harvested from the filament transformer T1 or from another form of energy harvesting.
- Fig. 5 schematically illustrates another example of a control unit CTRL.
- a single fiber optics connection 202 and fiber optics converter 501 may be used to drive more than two switches S1, S2, S3, S4 and thus to drive more than two filaments.
- the signal from the fiber optics driver F2 communicated via the fiber optics connection 202, and converted to an electric signal by the fiber optics converter 501, is encoded.
- the signal is decoded by an encoder 502 and passed on to the switches S1, S2, S3, S4 via the gate drivers N3, N4, N5, N6.
- the maximum duty cycle per switch pair e.g. S1 and S2 or S3 and S4
- the gate drivers N3, N4, N5, N6 and/or fiber optics converter 501 and/or encoder 502 and/or switches S1, S2, S3, S4 may be powered by a separate power supply (not shown), or power can be harvested from the filament transformer T1.
- Fig. 6 illustrates an example of the relation between transformer current, respective filament current and respective switch control signal over time.
- a large filament FL and a small filament FS with two switches S1, S2.
- the x-axis shows time in milliseconds.
- the gate signals for the first switch S1 and the second switch S2 are pulsed control signals, which have a duty cycle of 75% and 25%, respectively.
- the switches S1, S2 results in a corresponding respective duty cycled controlled filament current for the large filament FL and the small filament SL.
- the total power over the filaments is regulated with the transformer T1.
- the transformer current is an alternating current with, in this case, constant amplitude and frequency.
- the combination of total power over the filaments and the duty cycle determines the effective respective filament currents.
- the set-point current in this case is 4 A
- the effective large filament current is around 3 A
- the effective small filament current is around 1 A.
- the sufficiently large frequency of the pulsed control signals allows the filaments to be kept on a relatively stable temperature, without cooling down too much. It is appreciated that the examples of filament currents, duty cycles, number of filaments etc. are only non-limiting examples for illustration. Many variations are possible to best fit the application at hand.
- Fig. 7 schematically (no circuit diagram) illustrates an X-ray source insert 600, according to an embodiment of the invention.
- Such an X-ray source insert 600 may be configured to be included in an X-ray source assembly with a single filament driver FD1 and a control unit CTRL to drive two or more filaments FL, FS.
- the insert 600 is enclosed by a vacuum envelope 601, such that the insert can be sealed under a high vacuum.
- the vacuum envelope 601 may form e.g. a glass or metal enclosure.
- the insert comprises a cathode 602 with two or more filaments FL, FS.
- the filaments are configured to be connected to a filament transformer T1 outside of the insert.
- the filaments FL, FS are also configured to be connected to their respective switches S1, S2.
- the example in Fig. 7 illustrates two filaments FS, FL configured to be connected to two switches S1, S2.
- the insert 600 comprises three or more filaments, where each Xth filament FX is configured to be connected to a respective switch SX.
- the insert in Fig. 7 also includes an anode 603.
- the anode is 603 configured to generate X-rays when impinged with electrons in an electron beam (not shown) emitted from one of the filaments FS, FL at a focal spot on the anode 603.
- the anode 603 may advantageously be a rotating anode, rotated by a rotor apparatus 604.
- the anode 603 may also be a non-rotating anode for low power applications. In the latter case, not rotor apparatus 604 is required.
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Abstract
The present invention relates to an imaging X-ray source assembly (200) with multiple filaments (FL, FS). The X-ray source assembly comprises a plurality of filaments (FL, FS, FX) configured to emit electrons when a respective current passes through the filament (FL, FS, FX); a filament transformer (T1) configured to transfer electrical energy to the plurality of filaments (FL, FS, FX); a filament driver (FD1) configured to supply electrical energy to the plurality of filaments (FL, FS, FX) via the filament transformer (T1); a plurality of switches (S1, S2, SX) each connected to a respective one of the filaments (FL, FS, FX) and configured to regulate the respective current through the respective filament (FL, FS, FX); and a control unit (CTRL) connected to the plurality of switches (S1, S2, SX) and the filament driver (FD1), wherein the control unit (CTRL) is configured to control the plurality of switches (S1, S2, SX) by respective switch control signals.
Description
- The invention relates to the field of X-ray, and more specifically to an X-ray source assembly with multiple filaments, to a computer implemented method of controlling multiple filaments, to an imaging system comprising the X-ray source assembly and to an X-ray tube insert configured to be comprised in the X-ray source assembly.
- X-ray tubes are used for a variety of medical and industrial imaging processes. An X-ray tube typically includes a cathode with a focusing cup and a filament and a rotating anode. A tube current is applied to the filament, which heats the filament, causing the filament to expel electrons (thermionic emission), creating a space charge (or cloud a negative charge) a short distance away from the filament. A tube voltage is applied across the cathode and the anode and causes a beam of the electrons to accelerate from the cathode and impinge the anode. Sometimes a grid voltage is applied to electrodes of the focusing cup to control a size of and steer the beam of electrons. An interaction of the electrons with the material of the anode produces heat and radiation, including X-rays, which pass through a tube window. Electrical power is supplied to the X-ray tube with a high voltage generator.
- A surface area of the anode that receives the beam of electrons is referred to as a focal spot. The size of the focal spot is one factor that affects the image quality of X-ray imaging. For example, the focal spot size affects the spatial resolution, where a smaller focal spot size results in a greater spatial resolution than a larger focal spot size, e.g., due to less focal spot blur from geometric magnification.
- Many X-ray tubes available have more than one filament. In order to supply all individual filaments with electrical energy, complex drivers are necessary.
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JP5395320B2 - The power chain of driving multiple filaments with sufficient speed and performance is relatively complex, costly and space consuming.
- It is therefore an object of the invention to provide an X-ray source assembly with reduced cost and space required for driving multiple filaments.
- The invention is defined by the independent claims. Advantageous embodiments are defined in the dependent claims.
- According to a first aspect of the invention, there is provided an imaging X-ray source assembly with multiple filaments, the X-ray source assembly comprising:
- a plurality of filaments configured to emit electrons when a respective current passes through the filament;
- a filament transformer configured to transfer electrical energy to the plurality of filaments;
- a filament driver configured to supply electrical energy to the plurality of filaments via the filament transformer;
- a plurality of switches each connected to a respective one of the filaments and configured to regulate the respective current through the respective filament; and
- a control unit connected to the plurality of switches and the filament driver, wherein the control unit is configured to control the plurality of switches by respective switch control signals.
- The X-ray source assembly makes it possible to drive and control at least two filaments with a single driver and transformer, and thereby reduce complexity of the system. Thanks to this approach, space required for the high voltage generator as well as total cost of components can be decreased. Furthermore, one independent wire instead of at least two is sufficient in the high voltage cable between the X-ray tube and the high voltage generator.
- In an embodiment of the invention, the switch control signals are pulsed control signals, and each of the switches are configured to have a duty cycle larger than 0% and less than 100% in response to the pulsed control signal. The configuration of duty cycle controlled switches in combination with a common filament current set point is advantageous for controlling the multiple filaments with a single driver. With these two variables, common filament current and duty cycle, the effective current of each individual filament can be controlled.
- In an embodiment of the invention, at least one of the plurality of switches is configured to have a duty cycle larger than 10% and less than 90% in response to the respective pulsed control signal.
- In an embodiment of invention, the pulsed control signal has a (maximum) pulse length smaller than a characteristic thermal response time of the respective filament. It is advantageous if the pulse length is shorter than a characteristic thermal response time of the filament in order to get a stable temperature of the filament. In this way, filament temperature fluctuations may be reduced or avoided. Duty cycled control of the filament current allows the filament to be kept on a suitable standby temperature. In this way, it can be avoided that the filament cools down too much and the filament can be quickly switched on, to emit electrons, from a standby phase without significant delay due to the thermal response. In other words, fast switching between filaments is enabled. Thermal response time in this context is a measure of how quickly the filament heats up and cools down. It may depend on aspects such as, but not limited to, filament material, purity, dimensions, surrounding vacuum etc. The switching frequency of the pulsed signal may be in an order of magnitude of thousands of Hz, preferably many thousands of Hz, more preferably at least 10 kHz.
- In an embodiment of the invention, plurality of switches are semiconductor switches. Such switches are advantageous thanks to their capability of high frequency switching. Examples of components for such semiconductor switches include but are not limited to, metal-oxide-semiconductor field-effect transistors, silicon carbide switches, insulated-gate bipolar transistors etc.
- In an embodiment of the invention, the X-ray source assembly further comprises an anode configured to generate X-rays when impinged with electrons at a focal spot, wherein a first one of the filaments is configured to emit electrons to impinge a first focal spot on the anode, wherein a second one of the filaments is configured to emit electrons to impinge a second focal spot on the anode, and wherein the second focal spot is different from the first focal spot in size, location and/or shape. Simplified control over multiple filaments according to the invention can advantageously be used with multiple focal spots, where the characteristics of each filament may be optimized to the characteristics of the focal spot. Such as, but not limited to, a large focus filament that emits electrons impinging a large focus focal spot and a small focus filament that emits electrons impinging a small focus focal spot. In X-ray imaging technologies such as computed tomography, fluoroscopy etc. there is sometimes a need to rapidly switch between focal spots. E.g. but not limited to cardiovascular applications. Embodiments of the invention allows for fast switching between the focal spots. In addition, e.g. in combination with grid electrodes or other electron beam optics, the invention may advantageously provide additional flexibility to focal spot control.
- In an embodiment of the invention, the control unit is connected to the filament driver via an optical fiber or wireless connection. Such an optical fiber, wireless connection or other high voltage insulating connections makes it possible to e.g. locate the control unit inside and the filament driver outside a high voltage environment of the X-ray source assembly.
- In an embodiment of the invention, the power to switch at least one of the switches is derived from windings of the filament transformer. By harvesting power for the switches from the same filament transformer that is used to transfer energy to the filaments, the need for additional power sources to drive the switches can be avoided. Other forms of energy harvesting, such as but not limited to solar, thermal, kinetic energy harvesting are also conceivable.
- In an embodiment for the invention, the X-ray source assembly is programmable to control the respective filament currents. This is advantageous as it allows for various protocols to be optimized for the imaging application at hand. In advance and/or during imaging for increased flexibility. A user may interface with the programmable X-ray source assembly via a suitable computer interface and/or via communication channels as part of an imaging system. A programmable part of the X-ray source assembly may advantageously be on a low voltage side of the assembly to reduce complexity on the high voltage side, where space may be limited. Alternatively or in addition, a programmable part may be on a high voltage side close to the switches such that delays can be minimized for very fast switching.
- According to a second aspect of the invention, there is provided a computer implemented method of controlling a plurality of filament currents with the programmable X-ray source assembly, the method comprising:
- controlling, via the filament driver, supply of electrical energy to the plurality of filaments via the filament transformer; and
- controlling, via the control unit, the plurality of switches by the respective switch control signals.
- According to a further aspect of the invention, there is a computer program, which, when being executed by a computer, is adapted to cause the X-ray source assembly to carry out the above computer implemented method.
- According to a further aspect of the invention, there is a computer readable medium having stored thereon the computer program mentioned above.
- According to a third aspect of the invention, there is provided a medical imaging system comprising the X-ray source assembly. The medical imaging system may be a radiography system, a computed tomography system, a fluoroscopy system, a C-arm X-ray system for interventional guidance etc.
- According to a fourth aspect of the invention, there is provided an X-ray tube insert comprising a plurality of filaments, configured to be comprised in the X-ray source assembly, wherein the plurality of filaments are configured to be connected to the same filament transformer, and wherein each of the plurality of filaments is configured to be connected the respective one of the plurality of switches.
- These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
-
-
Fig. 1 schematically illustrates a conventional multi-filament X-ray source assembly. -
Fig. 2 schematically illustrates an X-ray source assembly, according to an embodiment of the invention. -
Fig. 3 schematically illustrates a filament driver, according to an embodiment of the invention. -
Fig. 4 schematically illustrates a control unit according to an embodiment of the invention. -
Fig. 5 schematically illustrates a control unit according to an embodiment of the invention. -
Fig. 6 illustrates an example of the relation between transformer current, respective filament current and respective switch control signal, according to an embodiment of the invention. -
Fig. 7 schematically illustrates an X-ray source insert, according to an embodiment of the invention. -
Fig. 1 schematically illustrates a conventional X-ray source assembly 100 (filament driver circuit) with two filaments FL, FS in thehigh voltage part 101 of the assembly, in a vacuum environment. Each of the filaments FL, FS may be configured to emit electrons via thermionic emission when a tube current is applied to the filament. Such a tube current heats the filament, thereby causing the filament to expel electrons. As described in the background section, the emitted electrons are accelerated from the cathode filament in an electrode beam towards an anode (not shown in the figure) with a tube voltage, thereby causing generation of X-rays at the anode. The filaments FL, FS may be configured to generate focal spots of the same or different size, shape, location etc. on the anode. For example, FL may be suited to generate a large focal spot and FS may be suited to generate a smaller focal spot. Each of the filaments FL, FS in theX-ray source assembly 100 has a corresponding filament driver LF, SF and a corresponding transformer TL, TS. Each filament driver LF, SF is controlled with one or multiple processors CPU, and generates voltage to drive the corresponding filament FL, FS. Each filament transformer TL, TS insulates thehigh voltage part 101 from the low voltage part and transforms the generated voltage of the corresponding filament driver LF, SF to transfer power to the corresponding filament FL, FS. Although schematically theassembly 100 may look relatively simple, multiple filament drivers LF, SF and transformers TL, TS lead to very bulky and complex structures. The example X-ray source assembly inFig. 1 has two filaments FL, FS with corresponding drivers LF, SF and transformers TL, TS. However, it is also possible that an X-ray source assembly three or even more sets of filaments, filament drivers and transformers. -
Fig. 2 schematically illustrates an X-ray source assembly 200 (filament driver circuit) according to an embodiment of the invention. TheX-ray source assembly 200 comprises multiple, at least two, filaments FL, FS, FX (shown in the figure as resistors). A first filament FL is configured to emit electrons when a current passes through the first filament FL. A second filament FS is configured to emit electrons when a current passes through the second filament FS. The filaments FL, FS may be configured to generate focal spots of the same or different size, shape, location etc. on an anode. For example, FL may be suited to generate a large focal spot and FS may be suited to generate a smaller focal spot. However, FL and FS may also be configured to generate the same or identical focal spots. TheX-ray source assembly 200 may also have more filaments, such as an Xth filament FX configured to emit electrons when a current passes through the Xth filament FX. Although the multiple filaments FL, FS, FX, may be configured to generate different focal spots, theX-ray source assembly 200 may also comprise electron beam optics (not shown) to focus/and or steer the electron beam from the filaments FL, FS, FX. The combination of multiple filaments with electron beam optics may provide increased flexibility in focal spot control. - The
X-ray source assembly 200 comprises a filament transformer T1 connected to the first filament FL and the second filament FS. Optionally, the filament transformer T1 is also connected to additional filaments FX. The filament transformer T1 is configured to transfer electrical energy to the filaments FL, FS and optionally to additional filaments FX. TheX-ray source assembly 200 comprises a filament driver FD1 configured to supply electrical energy to the first filament FL and the second filament FS via the filament transformer T1. Optionally, the filament driver is configured to supply electrical energy to additional filaments FX via the filament transformer T1. TheX-ray source assembly 200 comprises a first switch S1 connected to the first filament FL and configured to regulate the current through the first filament FL. TheX-ray source assembly 200 comprises a second switch S2 connected to the second filament FS and configured to regulate the current through the second filament FS. Optionally, theX-ray source assembly 200 comprises an Xth switch SX connected to the Xth filament FX and configured to regulate the current through the Xth filament FX. In this example, the switches S1, S2, SX each comprise a high part S1H, S2H, SXH and a low part S1L, S2L, SXL in series. Such switches are advantageous when regulating alternating currents through the filaments. However, other types of switches are also conceivable. The switches may advantageously be semiconductor switches, such as but not limited to, switches comprising metal-oxide-semiconductor field-effect transistors (MOSFET), silicon carbide switches, insulated-gate bipolar transistors etc. TheX-ray source assembly 200 also comprises a control unit CTRL. The control unit CTRL is connected to the first switch S1 and the second switch S2 and the filament driver FD1. The control unit CTRL is configured to control the first switch S1 and the second switch S2 with a switch control signal. Optionally, the control unit CTRL is connected to and configured to control an Xth switch, SX. - In the example in
Fig. 2 , the filaments FL, FS, FX, the switches S1, S2, SX and the control unit CTRL are located on thehigh voltage side 201 of theX-ray source assembly 200. Thefilament driver FD 1 and processor CPU are located on the low voltage side, insulated from thehigh voltage part 201 by the transformer T1. The control unit CTRL on thehigh voltage side 201 is connected to the filament driver FD1 on the low voltage side via anoptical fiber 202. Alternatively, the connection may be a wireless connection or other high voltage insulating connection. Everything in thehigh voltage part 201 as illustrated inFig. 2 is at the same voltage potential. I.e. at the cathode voltage potential of theX-ray source assembly 200. The multiple filaments may be fed by a secondary winding of the filament transformer T1. By controlling the multiple switches S1, S2, SX and their respective on and off time, the energy provided by the filament driver FD1 can be distributed to the filaments FL, FS, FX. The switches S1, S2, SX and the filaments FL, FS, FX may advantageously be duty cycled controlled with a pulsed control signal. During the time that one switch is 'ON, the other switch or switches are 'OFF'. - The configuration of duty cycle controlled switches in combination with a common filament current set point is advantageous for controlling the multiple filaments with a single driver. With these two variables, common filament current and duty cycle, the effective current of each individual filament can be controlled. As a non-limiting example with two filaments FL and FS, a set point filament current may be 9.5A and a duty cycle may be 0.63 for filament FL. In this example, filament FL has an effective current of around 6A and may be emitting electrons, whereas the filament FS has an effective current of around 3.5A and may be in standby mode. The pulse length of the pulsed control signal may be shorter than a characteristic thermal response time of the filaments FL, FS. In this way duty cycled control of the filament current then allows the filaments to be kept on a suitable standby temperature when off, without cooling down too much. Thus, each filament FL, FS can be quickly switched on, to emit electrons, from a standby phase without significant delay due to the thermal response, thereby enabling fast switching between the filaments FL, FS.
- In the example in
Fig. 2 theX-ray source assembly 200 comprises one or multiple processors CPU in connection with the filament driver FD1. TheX-ray source assembly 200 may therefore be programmable, e.g. programmable to control the currents over the filaments FL, FS, FX. Thus, key parameters for controlling electron emission from either of the multiple filaments, such as filament current set point, duty cycle and pulse length, may be programmed in advance and/or adapted during operation of the X-ray source assembly. It may be particularly advantageous to do all or most processing on the low voltage side, e.g. to reduce complexity and due to the often limited space on thehigh voltage side 201. However, it is conceivable that there may also be at least some processing and/or programming in the control unit CTRL on thehigh voltage side 201. This may be advantageous to avoid signal delays to the switches S1, S2, SX. As an example, the control unit CTRL on the high voltage side may comprise a Field-programmable gate array (FPGA) to decode the signals/commands from the filament driver FD1 into duty cycle for the switches S1, S2, SX. - The
X-ray source assembly 200 may thus be able to execute a computer program and/or connect to external devices executing such a program. Users may directly or indirectly interact with the X-ray source assembly and/or connected external devices via a user interface. Examples of user interface types include graphical user interfaces, natural user interfaces, and so forth. For instance, a graphical user interface may accept input from a user employing input device(s) such as a keyboard, mouse, remote control, or the like and provide output on an output device such as a display. Further, a natural user interface may enable user interaction in a manner free from constraints imposed by input device such as keyboards, mice, remote controls, and the like. Rather, a natural user interface can rely on speech recognition, touch and stylus recognition, gesture recognition both on screen and adjacent to the screen, air gestures, head and eye tracking, voice and speech, vision, touch, gestures, machine intelligence, and so forth. -
Fig. 3 schematically illustrates an example of a filament driver FD1 in some more detail. The filament driver FD1 is shown here as a half bridge inverter with two MOSFET switches SH and SL. However, the filament driver FD1 may also be implemented using a full bridge inverter or other suitable topologies. In the example inFig. 3 , a pulse generator G1 drives two gate drivers N1 and N2 to control the two MOSFET switches SH and SL. The pulse generator G1 may drive the gate drivers N1 and N2 with a high frequency, preferably a frequency larger than 1kHz and even more preferably larger than 10kHz. In this way, the switches SH and SL are controlled to adjust the energy for the high voltage transformer T1. In this example, the inductor L1 forms a resonant circuit together with capacitances C1 and C2. Alternatively or additionally, other circuits without resonant circuit may be used to drive the transformer T1. The fiber optics driver F2 is a frequency generator controlled by a processor CPU. The output signal from the fiber optics driver F2 goes via afiber optics converter 301 to the control unit CTRL via a fiber optic connection 202 (not shown here). The output signal from the fiber optics driver F2 may be a fixed frequency signal with variable pulse-pause ratio or a coded frequency signal which has to be re-encoded on thehigh voltage side 201. The filament driver FD1 inFig. 3 thus has two pulse drivers. The pulse generator G1 effectively determines the total power that is transferred over the transformer T1 to the filaments FL, FS, FX. The fiber optics driver F2 controls, via the controller CTRL, how that power is divided between the filaments FL, FS, FX. -
Fig. 4 schematically illustrates an example of a control unit CTRL. In this example, signals from the fiber optics driver F2, via thefiber optics connection 202 enters the control unit CTRL on the left side. The signals are converted into electrical signals by means offiber optics converters -
Fig. 5 schematically illustrates another example of a control unit CTRL. In this example a singlefiber optics connection 202 andfiber optics converter 501 may be used to drive more than two switches S1, S2, S3, S4 and thus to drive more than two filaments. In this case, the signal from the fiber optics driver F2, communicated via thefiber optics connection 202, and converted to an electric signal by thefiber optics converter 501, is encoded. The signal is decoded by anencoder 502 and passed on to the switches S1, S2, S3, S4 via the gate drivers N3, N4, N5, N6. In this example "four-switch configuration" the maximum duty cycle per switch pair (e.g. S1 and S2 or S3 and S4) is 50%. The gate drivers N3, N4, N5, N6 and/orfiber optics converter 501 and/orencoder 502 and/or switches S1, S2, S3, S4 may be powered by a separate power supply (not shown), or power can be harvested from the filament transformer T1. -
Fig. 6 illustrates an example of the relation between transformer current, respective filament current and respective switch control signal over time. In this example for control of two filaments, a large filament FL and a small filament FS, with two switches S1, S2. The x-axis shows time in milliseconds. As seen in the bottom of the chart, in this example the gate signals for the first switch S1 and the second switch S2 are pulsed control signals, which have a duty cycle of 75% and 25%, respectively. When either of the switches is "ON", the other is "OFF". The control of the switches S1, S2, results in a corresponding respective duty cycled controlled filament current for the large filament FL and the small filament SL. The total power over the filaments is regulated with the transformer T1. As shown in the figure, the transformer current is an alternating current with, in this case, constant amplitude and frequency. Similarly to the example described inFig. 2 , the combination of total power over the filaments and the duty cycle determines the effective respective filament currents. For illustration, if the set-point current in this case is 4 A, the effective large filament current is around 3 A and the effective small filament current is around 1 A. The sufficiently large frequency of the pulsed control signals allows the filaments to be kept on a relatively stable temperature, without cooling down too much. It is appreciated that the examples of filament currents, duty cycles, number of filaments etc. are only non-limiting examples for illustration. Many variations are possible to best fit the application at hand. -
Fig. 7 schematically (no circuit diagram) illustrates anX-ray source insert 600, according to an embodiment of the invention. Such an X-ray source insert 600 may be configured to be included in an X-ray source assembly with a single filament driver FD1 and a control unit CTRL to drive two or more filaments FL, FS. In the example inFig. 7 , theinsert 600 is enclosed by avacuum envelope 601, such that the insert can be sealed under a high vacuum. Thevacuum envelope 601 may form e.g. a glass or metal enclosure. The insert comprises acathode 602 with two or more filaments FL, FS. The filaments are configured to be connected to a filament transformer T1 outside of the insert. The filaments FL, FS are also configured to be connected to their respective switches S1, S2. The example inFig. 7 illustrates two filaments FS, FL configured to be connected to two switches S1, S2. However, it is also conceivable that theinsert 600 comprises three or more filaments, where each Xth filament FX is configured to be connected to a respective switch SX. The insert inFig. 7 also includes ananode 603. The anode is 603 configured to generate X-rays when impinged with electrons in an electron beam (not shown) emitted from one of the filaments FS, FL at a focal spot on theanode 603. Theanode 603 may advantageously be a rotating anode, rotated by arotor apparatus 604. However, theanode 603 may also be a non-rotating anode for low power applications. In the latter case, notrotor apparatus 604 is required. - It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and/or by means of a suitably programmed processor. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. Measures recited in mutually different dependent claims may advantageously be used in combination.
-
- 100, 200
- X-ray source assembly
- 101, 201
- High voltage part
- 202
- Fiber optic connection
- 301, 401, 402, 501
- Fiber optics converter
- 502
- Encoder
- 600
- X-ray source insert
- 601
- Vacuum envelope
- 602
- Cathode
- 603
- Anode
- 604
- Rotor apparatus
- C1, C2
- Capacitance
- CPU
- Processor
- CTRL
- Control unit
- F2
- Fiber optics driver
- FL, FS, FX
- Filament
- G1
- Pulse generator
- L1
- Inductance
- LF, SF, FD1
- Filament driver
- N1, N2, N3, N4, N5, N6
- Gate driver
- S1, S2, S3, S4, SX, SH, SL
- Switch
- TL, TS, T1
- Transformer
Claims (14)
- An imaging X-ray source assembly (200) with multiple filaments, the X-ray source assembly (200) comprising:- a plurality of filaments (FL, FS, FX) configured to emit electrons when a respective current passes through the filament (FL, FS, FX);- a filament transformer (T1) configured to transfer electrical energy to the plurality of filaments (FL, FS, FX);- a filament driver (FD1) configured to supply electrical energy to the plurality of filaments (FL, FS, FX) via the filament transformer (T1);- a plurality of switches (S1, S2, SX) each connected to a respective one of the filaments (FL, FS, FX) and configured to regulate the respective current through the respective filament (FL, FS, FX); and- a control unit (CTRL) connected to the plurality of switches (S1, S2, SX) and the filament driver (FD1), wherein the control unit (CTRL) is configured to control the plurality of switches (S1, S2, SX) by respective switch control signals.
- The X-ray source assembly according to Claim 1, wherein the switch control signals are pulsed control signals, and wherein each of the switches (S1, S2, SX) is configured to have a duty cycle larger than 0% and less than 100% in response to the pulsed control signal.
- The X-ray source assembly according to Claim 2, wherein at least one of the plurality of switches (S1, S2, SX) is configured to have a duty cycle larger than 10% and less than 90% in response to the respective pulsed control signal.
- The X-ray source assembly according to Claim 2 or 3, wherein the pulsed control signal has a pulse length smaller than a characteristic thermal response time of the respective filament (FL, FS).
- The X-ray source assembly according to any of the preceding claims, wherein the switches (S1, S2, SX) are semiconductor switches.
- The X-ray source assembly according to any of the preceding claims, the X-ray source assembly further comprising an anode (603) configured to generate X-rays when impinged with electrons at a focal spot, wherein a first one of the filaments (FL) is configured to emit electrons to impinge a first focal spot on the anode (603), a second one of the filaments (FS) is configured to emit electrons to impinge a second focal spot on the anode (603), and wherein the second focal spot is different from the first focal spot in size, location and/or shape.
- The X-ray source assembly according to any of the preceding claims, wherein the control unit (CTRL) is connected to the filament driver via an optical fiber (202) or wireless connection.
- The X-ray source assembly according to any of the preceding claims, wherein power to switch at least one of the switches (S1, S2) is derived from windings of the filament transformer (T1).
- The X-ray source assembly according to any preceding claim, wherein the X-ray source assembly is programmable to control the respective filament currents.
- A computer implemented method of controlling a plurality of respective filament currents with the X-ray source assembly according to claim 9, the method comprising:- controlling, via the filament driver (FD1), supply of electrical energy to the plurality of filaments (FL, FS, FX) via the filament transformer (T1); and- controlling, via the control unit (CTRL), the plurality of respective switches (S1, S2, SX) by respective switch control signals.
- A computer program, which, when being executed by a computer, is adapted to cause the X-ray source assembly to carry out the computer implemented method according to claim 10.
- A computer readable medium having stored thereon the computer program of claim 11.
- A medical imaging system comprising the X-ray source assembly of claims 1 to 9.
- An X-ray tube insert (600) comprising a plurality of filaments (FL, FS, FX), configured to be comprised in the X-ray source assembly as claimed in any of claim 1 to 9, wherein the plurality of filaments (FL, FS, FX) are configured to be connected to the same filament transformer (T1), and wherein each of the plurality of filaments (FL, FS, FX) is configured to be connected to the respective one of the plurality of switches (S1, S2, SX).
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP22197800.0A EP4344358A1 (en) | 2022-09-26 | 2022-09-26 | X-ray source assembly with multiple filaments |
PCT/EP2023/075718 WO2024068346A1 (en) | 2022-09-26 | 2023-09-19 | X-ray source assembly with multiple filaments |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
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EP22197800.0A EP4344358A1 (en) | 2022-09-26 | 2022-09-26 | X-ray source assembly with multiple filaments |
Publications (1)
Publication Number | Publication Date |
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EP4344358A1 true EP4344358A1 (en) | 2024-03-27 |
Family
ID=83457369
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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EP22197800.0A Pending EP4344358A1 (en) | 2022-09-26 | 2022-09-26 | X-ray source assembly with multiple filaments |
Country Status (2)
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EP (1) | EP4344358A1 (en) |
WO (1) | WO2024068346A1 (en) |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4811375A (en) * | 1981-12-02 | 1989-03-07 | Medical Electronic Imaging Corporation | X-ray tubes |
JP5395320B2 (en) | 2006-08-07 | 2014-01-22 | 株式会社東芝 | X-ray tube device |
Family Cites Families (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP4312495B2 (en) * | 2003-04-17 | 2009-08-12 | オリジン電気株式会社 | X-ray tube filament heating device |
-
2022
- 2022-09-26 EP EP22197800.0A patent/EP4344358A1/en active Pending
-
2023
- 2023-09-19 WO PCT/EP2023/075718 patent/WO2024068346A1/en unknown
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4811375A (en) * | 1981-12-02 | 1989-03-07 | Medical Electronic Imaging Corporation | X-ray tubes |
JP5395320B2 (en) | 2006-08-07 | 2014-01-22 | 株式会社東芝 | X-ray tube device |
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