X-ray imaging apparatus and method for adjusting current supplied to filament

Abstract

The present invention provides an X-ray imaging apparatus and a method of adjusting a current supplied to a filament, the X-ray imaging apparatus comprising: an X-ray tube including an electron emission unit provided with a filament; a storage unit that stores current information acquired in advance in which the total supply time of the current supplied to the filament and an appropriate current value supplied to the filament are associated with each other; and a control unit that performs control to adjust the current supplied to the filament on the basis of the current information after a first total supply time, which is a predetermined total supply time.

Description

Technical Field

[0001] The present invention relates to an X-ray imaging apparatus and a method for adjusting the current supplied to a filament. Background Art

[0002] Conventionally, X-ray imaging apparatuses have been known. Such an apparatus is disclosed, for example, in Japanese Patent Application Laid-Open No. 2008-251300.

[0003] An X-ray inspection apparatus (X-ray imaging apparatus) disclosed in Japanese Patent Application Laid-Open No. 2008-251300 includes an X-ray tube, an X-ray detector, and a control unit. The X-ray tube includes a target and an electron emission unit provided with a filament. The X-ray tube is configured to converge an electron beam emitted from the filament by a magnetic lens in a vacuum container and inject it into the target, and emit X-rays generated in the target. The filament releases thermoelectrons by supplying current and heating. In X-ray inspection, if the current supplied to the filament is too small, sufficient tube current cannot be obtained, and the desired X-ray luminance cannot be obtained. On the other hand, if the current supplied to the filament is too large, the filament is cut off due to the advancement of filament burnout and cannot be used, thus shortening the life of the filament. Japanese Patent Application Laid-Open No. 2008-251300 discloses that before performing X-ray inspection, while sequentially increasing the current supplied to the filament, the current value (saturation filament current) when the luminance value based on the X-ray detection signal no longer changes and reaches the saturation region is explored, and the current below the explored saturation filament current value is supplied to the filament, thereby performing X-ray inspection.

[0004] However, in the process of exploring the saturation filament current before performing X-ray inspection, current is also supplied to the filament. Therefore, by the above process, the burnout of the filament also advances, thereby shortening the life of the filament. The inventors of the present application have found the following insight: Regarding the cutting off of the filament caused by the advancement of filament burnout, the filament is mostly cut off during the above process compared to when performing X-ray imaging by supplying a current below the explored saturation filament current value. Moreover, the inventors of the present application have found the following problem: suppressing the shortening of the usable period of the filament due to the process of exploring an appropriate current value supplied to the filament. Summary of the Invention

[0005] The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an X-ray imaging apparatus and a method for adjusting the current supplied to a filament, which can suppress the shortening of the usable period of the filament due to the process of exploring an appropriate current value supplied to the filament.

[0006] To achieve the above object, the X-ray imaging apparatus according to the first aspect of the present invention includes: an X-ray tube including a target and an electron emission unit provided with a filament and emitting electrons to the target; an X-ray detector for detecting X-rays emitted from the X-ray tube; a storage unit storing current information obtained in advance, which is current information establishing a correspondence between the total supply time of the current supplied to the filament for emitting electrons from the filament and an appropriate current value supplied to the filament for emitting electrons from the filament; and a control unit for performing control to adjust the current supplied to the filament based on the current information after a first total supply time which is a specified total supply time.

[0007] To achieve the above object, a method for adjusting the current supplied to the filament according to the second aspect of the present invention is a method for adjusting the current supplied to the filament in an X-ray imaging apparatus, the X-ray imaging apparatus including an X-ray tube, the X-ray tube including a target and an electron emission unit provided with a filament and emitting electrons to the target, the method for adjusting the current supplied to the filament including the following steps: obtaining in advance current information which is current information establishing a correspondence between the total supply time of the current supplied to the filament for emitting electrons from the filament and an appropriate current value supplied to the filament for emitting electrons from the filament; and adjusting the current supplied to the filament based on the current information after a first total supply time which is a specified total supply time.

[0008] In the X-ray imaging apparatus according to the first aspect and the method for adjusting the current supplied to the filament according to the second aspect, current information is obtained in advance, which is current information establishing a correspondence between the total supply time of the current supplied to the filament for emitting electrons from the filament and an appropriate current value supplied to the filament for emitting electrons from the filament, and after a first total supply time which is a specified total supply time, the current supplied to the filament is adjusted based on the current information. Thus, after the first total supply time, the process of obtaining an appropriate current value supplied to the filament by supplying current to the filament is not performed, and the current supplied to the filament is adjusted based on the previously obtained current information. Therefore, after the first total supply time, the process of supplying current to the filament to search for an appropriate current value is not performed, so that the situation of supplying current to the filament through the above process can be suppressed. As a result, the available period of the filament can be suppressed from being shortened due to the above process. In addition, after the first total supply time, the above process is not performed, and the current supplied to the filament can be appropriately adjusted based on the previously obtained current information. Description of the Drawings

[0009] Figure 1 is a schematic diagram showing the overall structure of an X-ray imaging apparatus according to an embodiment.

[0010] Figure 2It is a schematic diagram showing the structure of an X-ray tube based on an embodiment.

[0011] Figure 3 It is a graph for explaining the appropriate current value obtained in the process of exploring the appropriate current value.

[0012] Figure 4 It is a graph for explaining an example of current information.

[0013] Figure 5 It is a flowchart for explaining the control of adjusting the current supplied to the filament. Detailed Embodiment

[0014] Hereinafter, embodiments embodying the present invention will be described based on the drawings.

[0015] (Structure of X-ray Imaging Apparatus)

[0016] Refer to Figures 1 to 4 to describe the structure of the X-ray imaging apparatus 100 based on this embodiment.

[0017] As Figure 1 shown, the X-ray imaging apparatus 100 is an apparatus for photographing an X-ray image of a subject 90. The X-ray imaging apparatus 100 of this embodiment is used, for example, for non-destructive inspection of the subject 90. The subject 90 at this time is a specimen to be inspected.

[0018] The X-ray imaging apparatus 100 includes an X-ray tube 1, an X-ray detector 2, a subject setting unit 3, a setting unit moving mechanism 4, and a control device 20.

[0019] The X-ray tube 1 is configured to irradiate the subject 90 disposed in the subject setting unit 3 with X-rays 9. The X-ray tube 1 is configured to generate X-rays 9 by applying a high voltage. The X-ray tube 1 faces the X-ray detector 2 via the subject setting unit 3. In this embodiment, the X-ray tube 1, the subject setting unit 3, and the detector are arranged in a horizontal direction.

[0020] As Figure 2 shown, the X-ray tube 1 includes an electron emission unit 11 as a cathode, a grid electrode 12, an anode 13, an electron lens 14, an aperture 15, a target 10, a vacuum container 16, a first power supply circuit 17, and a second power supply circuit 18. The electron emission unit 11, the grid electrode 12, the anode 13, the electron lens 14, and the target 10 are housed in the vacuum container 16.

[0021] The electron emission unit 11 is configured to irradiate the target 10 with an electron beam 8. The electron emission unit 11 generates electrons by applying a current from the second power supply circuit 18. In addition, the electron emission unit 11 is configured to release the generated electrons to the target 10 to which a high voltage is applied. The electron emission unit 11 includes, for example, a filament 19 formed of a heavy metal in a coil shape or a foil shape. The filament 19 is formed of, for example, tungsten or the like.

[0022] It is configured to apply a predetermined voltage between the electron emission unit 11 and the target 10 through the first power supply circuit 17. Specifically, the electron emission unit 11 and the target 10 are connected to the first power supply circuit 17 via wirings. In addition, the electron emission unit 11 is connected to the second power supply circuit 18 via a wiring. Moreover, the filament 19 of the electron emission unit 11 is configured to be heated by being energized using the second power supply circuit 18. Thereby, an electron beam 8 (thermoelectrons) is generated from the electron emission unit 11 toward the target 10. In addition, the current supplied to the filament 19 through the second power supply circuit 18 is adjusted by the control unit 21.

[0023] The grid electrode 12 is configured to control the amount of current of the emitted electron beam 8. The grid electrode 12 is provided near the electron emission unit 11.

[0024] The anode 13 is configured to accelerate the electrons irradiated from the electron emission unit 11 by applying a voltage. The anode 13 is provided between the electron emission unit 11 and the target 10.

[0025] The electron lens 14 is configured to focus the electron beam 8 irradiated from the electron emission unit 11. In addition, the electron lens 14 is configured to cause the electron beam 8 irradiated from the electron emission unit 11 to enter the surface of the target 10 substantially perpendicularly. The electron lens 14 is provided between the electron emission unit 11 and the target 10. In the present embodiment, the electron lens 14 is an electromagnetic lens. The electromagnetic lens is an electromagnet using a coil and has magnetic poles (pole pieces) (not shown) formed so as to protrude toward the center of the hole facing the coil. The electrons irradiated from the electron emission unit 11 pass through the range (hole) surrounded by the pole pieces. In addition, the electron lens 14 for focusing the electron beam 8 is not limited to an electromagnetic lens, and may be an electrostatic lens or other known lenses.

[0026] The aperture 15 is configured to be able to adjust the passing range of electrons. The aperture 15 has an aperture hole 15a. The aperture 15 is provided between the electron emission unit 11 and the target 10. The electrons irradiated from the electron emission unit 11 and passing through the aperture hole 15a of the aperture 15 collide with the target 10.

[0027] The target 10 is configured to generate X-rays 9 when it collides with an electron beam 8 (thermal electrons) released from the electron emission unit 11. The target 10 is formed of a metal material such as tungsten, molybdenum, copper, cobalt, chromium, iron, silver, etc. The target 10 is a reflection type target. The reflection type target is a type of target in which the X-rays 9 are emitted by reflection from the surface in a direction different from the flying direction of the electron beam 8. In addition, the target 10 may also be a transmission type target. The transmission type target has a pair of (front and back) surfaces orthogonal to the electron beam 8, and is a type of target in which the X-rays 9 are emitted through the target 10 from the other surface by the collision of electrons with one surface.

[0028] The electron emission unit 11 and the target 10 are arranged inside the vacuum container 16. The inside of the vacuum container 16 is sealed in a substantially vacuum state. The vacuum container 16 is formed of a non-magnetic metal material such as stainless steel (SUS), for example. In addition, a window portion (not shown) for releasing the X-rays 9 to the outside is provided in the vacuum container 16.

[0029] As Figure 1 shown, the X-ray detector 2 is configured to detect the X-rays 9 emitted from the X-ray tube 1. The X-rays 9 emitted from the X-ray tube 1 pass through the object 90 and are incident on the detection surface of the X-ray detector 2. The X-ray detector 2 is configured to convert the detected X-rays 9 into an electrical signal. Thus, an X-ray image reflecting the transmission of the X-rays 9 through the object 90 is obtained. The X-ray detector 2 is, for example, a Flat Panel Detector (FPD). The X-ray detector 2 includes a plurality of conversion elements (not shown) and pixel electrodes (not shown) arranged on the plurality of conversion elements. The plurality of conversion elements and pixel electrodes are arranged in a matrix within the detection surface at a predetermined period (pixel pitch). The detection signal (image signal) of the X-ray detector 2 is sent to the image processing unit 5.

[0030] The object setting unit 3 is arranged between the X-ray tube 1 and the X-ray detector 2 and is configured to support the object 90. The object setting unit 3 includes a stage on which the object 90 is placed. The object 90 may be placed on the object setting unit 3 via a holding member (not shown) for holding the object 90, etc.

[0031] The setting unit moving mechanism 4 is configured to move the object setting unit 3 in two mutually orthogonal directions in the horizontal plane or in the vertical direction. The setting unit moving mechanism 4 includes a motor (not shown) for moving the object setting unit 3 serving as a stage, etc.

[0032] The control device 20 includes, for example, a personal computer (PC). The control device 20 includes a control unit 21, an image processing unit 5, a storage unit 22, and an input / output unit 23. The control device 20 is connected to a display device 24 and an input device 25.

[0033] The control unit 21 includes, for example, a processor such as a Central Processing Unit (CPU). By executing application programs stored in the storage unit 22, the control unit 21 controls the setting of imaging conditions, the start and stop of imaging, the operation of the X-ray tube 1, and the control of the process for searching for an appropriate current value in the X-ray imaging apparatus 100. In addition, details of the above-mentioned process will be described later.

[0034] In addition, the control unit 21 is configured to adjust the current supplied to the filament 19 based on the current information 30 after a first total supply time which is a prescribed total supply time. Specifically, the control unit 21 is configured to adjust the current supplied to the filament 19 based on the appropriate current value obtained through the process of searching for an appropriate current value before the first total supply time, and to adjust the current supplied to the filament 19 based on the current information 30 during a second total supply time after the first total supply time. In addition, details of the current information 30 and the control for adjusting the current supplied to the filament 19 based on the current information 30 will be described later.

[0035] The image processing unit 5 includes, for example, a processor such as a Graphics Processing Unit (GPU) or a Field-Programmable Gate Array (FPGA) configured for image processing. The image processing unit 5 acquires data of an X-ray image from the X-ray detector 2. The image processing unit 5 is configured to perform prescribed image processing on the acquired data of the X-ray image.

[0036] The storage unit 22 is configured to include a volatile storage device and a non-volatile storage device. The storage unit 22 stores various programs. In addition, the storage unit 22 stores the previously acquired current information 30, an offset value table, and a correction value table. Here, in this specification, the “previously acquired” in the “previously acquired current information 30” does not mean “acquired after the manufacture of the X-ray imaging apparatus 100 or before the start of the first X-ray examination after the X-ray imaging apparatus 100 is shipped from the factory”. For example, it means “acquired by the manufacturer of the X-ray imaging apparatus 100 through experiments commonly for each model or type of the X-ray imaging apparatus 100”. In addition, details of the offset value table and the correction value table will be described later.

[0037] The input / output unit 23 includes various interfaces for inputting / outputting signals to / from the control device 20. The input / output unit 23 is connected to the display device 24 and the input device 25. The display device 24 is, for example, a liquid crystal display device or the like. The input device 25 includes a keyboard, a mouse, and the like. The image processing unit 5 acquires a detection signal (image signal) from the X-ray detector 2 via the input / output unit 23.

[0038] (Processing for searching for an appropriate current value)

[0039] The processing for searching for an appropriate current value will be described.

[0040] In X-ray imaging, in order to obtain an image with a desired X-ray luminance, it is important to set the current supplied to the filament 19 to an appropriate value. When the current supplied to the filament 19 is too small, a sufficient tube current cannot be obtained, and the desired X-ray luminance cannot be obtained. On the other hand, when the current supplied to the filament 19 is too large, due to the advancement of the burnout of the filament 19, the filament 19 is cut off and cannot be used, thereby shortening the life of the filament 19. Therefore, the control unit 21 performs a process of obtaining an appropriate current value supplied to the filament 19 by supplying current to the filament 19. The said process is performed at every prescribed third total supply time interval set in advance. The total supply time refers to the total supply time of supplying current to the filament 19 in order to release electrons from the filament 19. The said process may also be performed based on an input operation performed by the user.

[0041] Before the first total supply time from the start of use of the filament 19, the control unit 21 obtains an appropriate current value through the process of searching for an appropriate current value. Here, an oxide film is formed on the filament 19 before the start of use. Due to the formed oxide film, the appropriate current value in the filament 19 immediately after the start of use is unstable. The control unit 21 performs the said process before the first total supply time, and obtains an appropriate current value supplied to the filament 19 by supplying current to the filament 19. The first total supply time is the total supply time predicted to stabilize the variation of the appropriate current value obtained through the said process due to the oxide film of the filament 19 being peeled off by use. As an example, the first total supply time is 96 hours. In addition, the first total supply time is not limited to 96 hours, and may be shorter than 96 hours or longer than 96 hours.

[0042] In the process of searching for an appropriate current value, the control unit 21 sequentially increases the current supplied to the filament 19 via the second power supply circuit 18, and obtains the change of the luminance value based on the X-ray detection signal obtained by the X-ray detector 2 with respect to the increase of the current supplied to the filament 19. Figure 3It is a diagram showing the relationship between the current supplied to the filament 19 and the X-ray brightness. When the current supplied to the filament 19 is small, as the current supplied to the filament 19 increases, the brightness value based on the X-ray detection signal also increases. Moreover, when the current supplied to the filament 19 increases, the change amount of the brightness value based on the X-ray detection signal soon becomes small and tends to reach the saturation region. When a current exceeding the current value reaching the saturation region is supplied to the filament 19, the X-ray brightness remains substantially unchanged, but since the filament 19 becomes hot, it promotes the evaporation or consumption of the filament 19, so the life of the filament 19 is shortened.

[0043] For example, when the control unit 21 measures the brightness value based on the X-ray detection signal while sequentially increasing the current supplied to the filament 19, when the measured values at multiple consecutive measurement points converge within a preset allowable variation range, it is determined that the current value has reached the saturation region. Then, the control unit 21 obtains 80% of the current value at the time of reaching the saturation region as the appropriate current value.

[0044] In addition, in the process of exploring the appropriate current value, it is necessary to obtain the brightness value based on the X-ray detection signal in a state where the object 90 is not photographed in the X-ray image. Therefore, in this process, while sequentially increasing the current supplied to the filament 19 in a state where the object 90 is not provided on the stage, the brightness value based on the X-ray detection signal obtained by the X-ray detector 2 is obtained. Therefore, during the execution of the above process, the X-ray photography for non-destructive inspection with the object 90 provided on the stage is interrupted.

[0045] (Adjustment of the current supplied to the filament before the first total supply time)

[0046] The control unit 21 adjusts the current supplied to the filament 19 based on the appropriate current value obtained through the process of exploring the appropriate current value before the first total supply time.

[0047] The control unit 21 obtains an appropriate current value through the process of exploring the appropriate current value at every prescribed third total supply time interval during the period from the start of use of the filament 19 to before the first total supply time. As an example, the prescribed third total supply time interval is a 24-hour (total supply time) interval. In addition, the prescribed third total supply time interval is not limited to 24 hours and can be shorter or longer than 24 hours.

[0048] Here, when the diameter of the aperture hole 15a provided in the aperture 15 is small, the X-ray focus of the target 10 becomes smaller than when the diameter of the aperture hole 15a is large. Therefore, by limiting the direction of the irradiated X-ray 9, an X-ray image with a clear outline and improved resolution can be generated, but since the X-ray amount decreases, an X-ray image with a low brightness value is generated.

[0049] Therefore, in order to increase the brightness value, an offset value for fine-tuning an appropriate current value is preset according to the diameter of the aperture hole 15a of the aperture 15. In the storage unit 22, an offset value table is stored, that is, an offset value table in which the diameter of the aperture hole 15a provided in the aperture 15 is associated with the offset value with respect to the appropriate current value obtained by the process of searching for the appropriate current value. The control unit 21 adjusts the current supplied to the filament 19 by referring to the offset value table, based on the appropriate current value obtained by the above process and the offset value based on the diameter of the aperture hole 15a provided in the aperture 15. Specifically, the control unit 21 adds the offset value to the obtained appropriate current value to adjust the current supplied to the filament 19. That is, during the period before the first total supply time from the start of use of the filament 19, the control unit 21 obtains an appropriate current value by the above process at every prescribed third total supply time interval, and adds the offset value to the obtained appropriate current value to adjust the current supplied to the filament 19.

[0050] (Current information)

[0051] Refer to Figure 4 to describe the current information 30.

[0052] The current information 30 is information in which the total supply time of the current supplied to the filament 19 to release electrons from the filament 19 is associated with the appropriate current value of the current supplied to the filament 19 to release electrons from the filament 19. Specifically, the current information 30 is information in which the total supply time is associated with the appropriate current value, and the appropriate current value is obtained based on the brightness value of the X-ray detection signal detected by the X-ray detector 2 while supplying current to the filament 19 at every prescribed second total supply time interval and increasing the supplied current. The current information 30 is obtained in advance and stored in the storage unit 22. In addition, the current information 30 can be stored in the storage unit 22 either before the X-ray imaging apparatus 100 is shipped or after the X-ray imaging apparatus 100 is shipped. Further, the current information 30 stored in the storage unit 22 can be configured to be updatable or can be configured to be replaceable with new current information 30.

[0053] The current information 30 is information on the total supply time of the appropriate current value obtained based on the measured data and obtained through processing to explore the appropriate current value. Specifically, the current information 30 is an approximate curve, that is, in a graph where the vertical axis represents the information on the appropriate current value at the total supply time supplied to the filament 19, and the horizontal axis represents the total supply time of the current supplied to the filament 19, it is an approximate curve calculated based on the plot points in the graph as the appropriate current value with respect to the total supply time.

[0054] The process of exploring the appropriate current value performed when obtaining the current information 30 in advance is carried out at a prescribed second total supply time interval. That is, the appropriate current value is obtained through the above-mentioned process carried out at every prescribed second total supply time interval. As an example, the prescribed second total supply time interval is a 2-hour (total supply time) interval. In addition, the prescribed second total supply time interval is not limited to a 2-hour interval, and can be an interval shorter than the 2-hour interval or an interval longer than the 2-hour interval. For example, the prescribed second total supply time interval can be a 0.5-hour interval, a 1-hour interval, a 4-hour interval, or an 8-hour interval.

[0055] In addition, in obtaining the current information 30, the measured data in which the filament 19 is not cut off before reaching the predicted maximum usable time (predicted life of the filament 19) of the filament 19 is used. In obtaining the current information 30, the measured data in which the filament 19 is cut off and cannot be used before reaching the predicted maximum usable time of the filament 19 is not used.

[0056] As the appropriate current value with respect to the total supply time obtained through the first process of exploring the appropriate current value performed when obtaining the current information 30 in advance, an initial value is set. As an example, "160" is set as the initial value as the obtained appropriate current value with respect to the total supply time. In addition, the initial value is not limited to "160".

[0057] Then, an approximate curve of the plot representing the appropriate current value obtained through the process of exploring the appropriate current value carried out at every prescribed second total supply time interval is calculated. The calculated approximate curve is stored in the storage unit 22 as the current information 30.

[0058] Obtain two pieces of current information 30. Regarding the current information 30, obtain the following two pieces of current information 30: the current information 30 obtained based on the measured data obtained under the condition of setting the tube voltage of the X-ray tube 1 to 120 kV and the tube current to 50 μA, and the current information 30 obtained based on the measured data obtained under the condition of setting the tube voltage of the X-ray tube 1 to 120 kV and the tube current to 100 μA. Store the two pieces of current information 30 obtained in the storage unit 22.

[0059] (Adjustment of the current supplied to the filament during the second total supply time after the first total supply time)

[0060] The control unit 21 obtains an appropriate current value through a process of searching for an appropriate current value during the first total supply time, and during the second total supply time after the first total supply time, adjusts the current supplied to the filament 19 based on the appropriate current value obtained during the first total supply time and the current information 30 previously obtained and stored in the storage unit 22.

[0061] In the non-destructive inspection using the X-ray imaging apparatus 100, when performing X-ray imaging under the same X-ray imaging conditions as any one of the two pieces of current information 30, the control unit 21 adjusts the current supplied to the filament 19 based on the current information 30 under the same X-ray imaging conditions during the second total supply time after the first total supply time. Additionally, in the non-destructive inspection using the X-ray imaging apparatus 100, when performing X-ray imaging using a tube current different from 50 μA and 100 μA, the control unit 21 performs linear interpolation processing on the two pieces of current information 30, and during the second total supply time after the first total supply time, adjusts the current supplied to the filament 19 based on the current information 30 on which the linear interpolation processing has been performed.

[0062] After the control unit 21 obtains an appropriate current value during the first total supply time, it obtains a correction value based on the obtained appropriate current value and the appropriate current value in the current information 30 during the first total supply time.

[0063] The control unit 21 obtains a correction value based on, for example, the difference between the appropriate current value obtained at the first total supply time and the appropriate current value in the current information 30 at the first total supply time, the diameter of the aperture hole 15a of the aperture 15 of the X-ray tube 1, and the offset value based on the diameter of the aperture hole 15a of the aperture 15. In the storage unit 22, a correction value table in which the difference between the appropriate current values, the diameter of the aperture hole 15a, and the offset value based on the diameter of the aperture hole 15a are associated with the correction value is stored. The control unit 21 obtains the correction value by referring to the correction value table. In addition, the items associated with the correction value in the correction value table are not limited to the above. Further, the control unit 21 may be configured to obtain the correction value not based on the correction value table but based on a relational expression for calculating the correction value from the difference between the appropriate current values, the diameter of the aperture hole 15a, and the offset value based on the diameter of the aperture hole 15a.

[0064] Then, the control unit 21 adjusts the current supplied to the filament 19 at the second total supply time based on the obtained correction value and the appropriate current value at the second total supply time in the current information 30. Specifically, the control unit 21 adds or divides the obtained correction value by the appropriate current value at the second total supply time in the current information 30 to adjust the current supplied to the filament 19.

[0065] In addition, after the first total supply time, the control unit 21 adjusts the current supplied to the filament 19 at every prescribed first total supply time interval based on the obtained correction value and the appropriate current value in the current information 30. As an example, the prescribed first total supply time interval is a 2-hour (total supply time) interval. In addition, the prescribed first total supply time interval is not limited to a 2-hour interval, and may be an interval shorter than the 2-hour interval or an interval longer than the 2-hour interval.

[0066] In addition, after the first total supply time, the control unit 21 shortens the first total supply time interval for adjusting the current supplied to the filament 19 as the total supply time becomes longer. As an example, before the total supply time of 500 hours where the slope of the appropriate current value obtained through the process of searching for an appropriate current value in the measured data with respect to the total supply time is small, the specified first total supply time interval is set to 2 hours (total supply time) interval. After 500 hours where the slope is large, the specified first total supply time interval is changed to 0.5 hours (total supply time) interval. The control unit 21 adjusts the current supplied to the filament 19 every specified first total supply time interval. In addition, the timing of the change of the specified first total supply time interval is not limited to the total supply time of 500 hours, and can be shorter than 500 hours or longer than 500 hours. Also, the number of times of the change of the specified first total supply time interval can be not once but multiple times. In addition, the changed specified first total supply time interval is not limited to the 0.5-hour interval, and can be an interval shorter than the 0.5-hour interval or an interval longer than the 0.5-hour interval.

[0067] Therefore, after the first total supply time, the control unit 21 adds or divides the obtained correction value by the appropriate current value of the second total supply time in the current information 30 every specified first total supply time interval to adjust the current supplied to the filament 19. That is, after the first total supply time, the control unit 21 does not perform the process of searching for an appropriate current value, but adjusts the current supplied to the filament 19 based on the current information 30. Therefore, in the adjustment of the current supplied to the filament 19, the object 90 placed on the stage does not need to be moved from the stage. In addition, the control unit 21 can perform the adjustment process of the current supplied to the filament 19 in the background. For these reasons, after the first total supply time, it is not necessary to interrupt the X-ray imaging for non-destructive inspection for the adjustment process of the current supplied to the filament 19.

[0068] (Control of Adjustment of Current Supplied to Filament)

[0069] Refer to Figure 5 to describe the control of the adjustment of the current supplied to the filament 19 by the control unit 21 (X-ray imaging method). The current information 30 is pre-stored in the storage unit 22. In addition, in the case of receiving an input operation indicating the end of X-ray imaging, the control of the adjustment of the current supplied to the filament 19 by the control unit 21 and the control of X-ray imaging end. Also, as long as the order of each step does not conflict with each other, they can be swapped before and after or executed simultaneously.

[0070] In step S1, in a state where the object 90 is not set on the stage, the control unit 21 obtains an appropriate current value through a process of searching for an appropriate current value. Thereafter, the process proceeds to step S2.

[0071] In step S2, the control unit 21 adjusts the current supplied to the filament 19 based on the appropriate current value obtained through the above process. Thereafter, the process proceeds to step S3.

[0072] In step S3, in a state where the object 90 is set on the stage, the control unit 21 performs X-ray photography. Thereafter, the process proceeds to step S4.

[0073] In step S4, the control unit 21 determines whether a predetermined third total supply time interval has elapsed since the start of the above process. If the predetermined third total supply time interval has elapsed since the start of the above process (Yes in step S4), the process proceeds to step S5. If the predetermined third total supply time interval has not elapsed since the start of the above process (No in step S4), the process returns to step S3.

[0074] In step S5, the control unit 21 determines whether the total supply time since the start of using the filament 19 has become the first total supply time. If it has become the first total supply time (Yes in step S5), the process proceeds to step S6. If it has not become the first total supply time (No in step S5), the process returns to step S1.

[0075] In step S6, in a state where the object 90 is not set on the stage, the control unit 21 obtains an appropriate current value through a process of searching for an appropriate current value. Thereafter, the process proceeds to step S7.

[0076] In step S7, the control unit 21 adjusts the current supplied to the filament 19 based on the appropriate current value obtained through the above process. Thereafter, the process proceeds to step S8.

[0077] In step S8, the control unit 21 determines whether a predetermined first total supply time interval has elapsed since the start of the adjustment of the current supplied to the filament 19 last time. If the predetermined first total supply time interval has elapsed since the start of the adjustment of the current supplied to the filament 19 last time (Yes in step S8), the process proceeds to step S9. If the predetermined first total supply time interval has not elapsed since the start of the adjustment of the current supplied to the filament 19 last time (No in step S8), step S8 is repeated.

[0078] In step S9, the control unit 21 adjusts the current supplied to the filament 19 based on the current information 30. Thereafter, the process returns to step S8.

[0079] (Effect of this embodiment)

[0080] In this embodiment, the following effects can be obtained.

[0081] In the X-ray imaging apparatus 100 and the method of adjusting the current supplied to the filament 19 according to this embodiment, current information 30 is obtained in advance, that is, current information 30 in which the total supply time of the current supplied to the filament 19 for releasing electrons from the filament 19 is associated with an appropriate current value supplied to the filament 19 for releasing electrons from the filament 19. After the first total supply time which is a specified total supply time, the current supplied to the filament 19 is adjusted based on the current information 30. Thus, after the first total supply time, instead of performing the process of obtaining an appropriate current value supplied to the filament 19 by supplying current to the filament 19, the current supplied to the filament 19 is adjusted based on the previously obtained current information 30. Therefore, after the first total supply time, the process of supplying current to the filament 19 to search for an appropriate current value is not performed, and thus the situation where current is supplied to the filament 19 by the above process can be suppressed. As a result, shortening of the usable period of the filament 19 due to the above process can be suppressed. In addition, after the first total supply time, without performing the above process, the current supplied to the filament 19 can be appropriately adjusted based on the previously obtained current information 30.

[0082] In addition, in the X-ray imaging apparatus 100 according to the above embodiment, by configuring as follows, further effects as described below can be obtained.

[0083] That is, in this embodiment, as described above, the control unit 21 is configured to adjust the current supplied to the filament 19 based on an appropriate current value obtained by the following process, that is, a process of obtaining an appropriate current value supplied to the filament 19 by supplying current to the filament 19, before the first total supply time, and to adjust the current supplied to the filament 19 based on the current information 30 at a second total supply time after the first total supply time. Thus, before the first total supply time, since the appropriate current value is unstable, the current supplied to the filament 19 can be adjusted based on the appropriate current value obtained by the above process for the currently used filament 19. In addition, at the second total supply time after the first total supply time, since the appropriate current value is stable, the current supplied to the filament 19 can be adjusted based on the previously obtained current information 30.

[0084] In addition, in the present embodiment, as described above, the control unit 21 is configured to obtain an appropriate current value through the above processing at the first total supply time, and adjust the current supplied to the filament 19 based on the appropriate current value obtained at the first total supply time and the current information 30 at the second total supply time. Thus, based on the appropriate current value obtained through the above processing actually measured at the first total supply time and the previously obtained current information 30, the current supplied to the filament 19 can be adjusted with good accuracy.

[0085] In addition, in the present embodiment, as described above, the control unit 21 is configured to obtain a correction value based on the appropriate current value among the appropriate current value obtained at the first total supply time and the current information 30 at the first total supply time, and adjust the current supplied to the filament 19 at the second total supply time based on the obtained correction value and the appropriate current value at the second total supply time in the current information 30. Thus, based on the obtained correction value and the appropriate current value at the second total supply time in the current information 30, the current supplied to the filament 19 can be adjusted with good accuracy at the second total supply time.

[0086] In addition, in the present embodiment, as described above, the control unit 21 is configured to, after the first total supply time, adjust the current supplied to the filament 19 based on the appropriate current value in the current information 30 at every prescribed first total supply time interval. Thus, by adjusting the current supplied to the filament 19 based on the appropriate current value in the current information 30 at every prescribed first total supply time interval, it is possible to effectively suppress the shortening of the usable period of the filament 19 due to the above processing.

[0087] In addition, in the present embodiment, as described above, the control unit 21 is configured to shorten the first total supply time interval for adjusting the current supplied to the filament 19 as the total supply time becomes longer after the first total supply time. Thus, for the filament 19 whose wire diameter gradually becomes thinner as the total supply time becomes longer, the first total supply time interval is shortened to adjust the current supplied to the filament 19, so that it is possible to more effectively suppress the shortening of the usable period of the filament 19 due to the above processing.

[0088] In addition, in the present embodiment, as described above, the current information 30 is information on appropriate current values with respect to the total supply time obtained in advance based on measured data, and the control unit 21 is configured to adjust the current supplied to the filament 19 based on the information on appropriate current values obtained in advance based on measured data after the first total supply time. Thus, through the current information 30 obtained in advance based on measured data, the current supplied to the filament 19 can be adjusted with good accuracy.

[0089] In addition, in the present embodiment, as described above, the current information 30 is information in which the total supply time is associated with an appropriate current value, and the appropriate current value is obtained while supplying current to the filament 19 at every prescribed second total supply time interval and increasing the supplied current, based on the luminance value of the X-ray detection signal detected by the X-ray detector 2. The control unit 21 is configured to adjust the current supplied to the filament 19 based on the current information 30 after the first total supply time. Thereby, after the first total supply time, the current supplied to the filament 19 can be adjusted more accurately based on the current information 30 in which the total supply time is associated with the appropriate current value.

[0090] In addition, in the present embodiment, as described above, the first total supply time is the total supply time predicted to stabilize the variation of the appropriate current value obtained by the above-described processing due to the peeling of the oxide film of the filament 19. The control unit 21 is configured to adjust the current supplied to the filament 19 based on the current information 30 after the first total supply time. Thereby, after the first total supply time when the variation of the appropriate current value is stable, the current supplied to the filament 19 can be appropriately adjusted based on the current information 30.

[0091] [Modification Example]

[0092] Furthermore, it should be considered that the embodiments disclosed herein are illustrative in all respects and not restrictive. The scope of the present invention is shown by the claims rather than the description of the embodiments, and also includes all modifications (modification examples) within the meaning and scope equivalent to the claims.

[0093] For example, in the above-described embodiment, an example in which the X-ray imaging apparatus is used for non-destructive inspection is shown, but the present invention is not limited thereto. For example, the X-ray imaging apparatus may also be configured for medical use. The object to be imaged at this time is a living body to be inspected.

[0094] In addition, in the above-described embodiment, an example in which there are two pieces of current information is shown, but the present invention is not limited thereto. For example, there may be only one standard piece of current information, or three or more different pieces of current information may be provided as the current information.

[0095] In addition, in the above-described embodiment, an example is shown in which two pieces of current information are obtained: current information obtained based on measured data obtained under the condition of setting the tube voltage of the X-ray tube to 120 kV and the tube current to 50 μA, and current information obtained based on measured data obtained under the condition of setting the tube voltage of the X-ray tube to 120 kV and the tube current to 100 μA. However, the present invention is not limited thereto. For example, the values of the tube voltage and the tube current under the condition of the measured data of the current information are not limited to the above, and the values of the tube voltage and the tube current under the condition of the measured data of the current information may also be other values.

[0096] In addition, in the above-described embodiment, an example is shown in which the control unit adjusts the current supplied to the filament based on the appropriate current value obtained through the process of searching for the appropriate current value before the first total supply time. However, the present invention is not limited thereto. For example, the control unit may not adjust the current supplied to the filament before the first total supply time, or may be configured to adjust the current supplied to the filament based on the appropriate current value obtained through other known methods before the first total supply time.

[0097] In addition, in the above-described embodiment, an example is shown in which the control unit adjusts the current supplied to the filament based on the appropriate current value obtained through the process of searching for the appropriate current value and the current information at the first total supply time. However, the present invention is not limited thereto. For example, the control unit may also be configured to adjust the current supplied to the filament based on the appropriate current value obtained through the above process and the current information before the first total supply time.

[0098] In addition, in the above-described embodiment, an example is shown in which the control unit obtains a correction value based on the difference in the appropriate current value, the diameter of the aperture, and the offset value, and adjusts the current supplied to the filament based on the obtained correction value and the current information. However, the present invention is not limited thereto. For example, the control unit may also be configured to obtain the difference in the appropriate current value and adjust the current supplied to the filament based on the obtained difference in the appropriate current value and the current information.

[0099] In addition, in the above-described embodiment, an example is shown in which the control unit shortens the first total supply time interval as the total supply time becomes longer. However, the present invention is not limited thereto. For example, the first total supply time interval after the first total supply time may also be constant.

[0100] In addition, in the above-described embodiment, an example is shown in which the current information is information in which the total supply time is associated with an appropriate current value, that is, an appropriate current value obtained while supplying current to the filament at every prescribed second total supply time interval and increasing the supplied current according to the luminance value based on the X-ray detection signal. However, the present invention is not limited thereto. For example, the appropriate current value in the current information may not be obtained while supplying current to the filament at every prescribed second total supply time interval and increasing the supplied current according to the luminance value based on the X-ray detection signal.

[0101] In addition, in the above-described embodiment, an example is shown in which the current information is an approximate curve, that is, an approximate curve calculated from a plot obtained by plotting appropriate current values with respect to the total supply time, which are obtained in advance based on measured data, on a graph. However, the present invention is not limited thereto. For example, the current information may be a table in which the total supply time and appropriate current values obtained in advance based on measured data are associated with each other. For example, in addition, the current information may be configured such that data such as X-ray imaging conditions is input into a pre-trained model created using various machine learning methods including deep learning, and the result of obtaining an appropriate current value with respect to the total supply time is output.

[0102] [Embodiment]

[0103] Those skilled in the art should understand that the illustrative embodiments are specific examples of the following embodiments.

[0104] (Item 1)

[0105] An X-ray imaging apparatus, comprising:

[0106] an X-ray tube including a target and an electron emission unit provided with a filament and emitting electrons to the target;

[0107] an X-ray detector detecting X-rays emitted from the X-ray tube;

[0108] a storage unit storing current information, that is, pre-acquired current information in which the total supply time of the current supplied to the filament to emit electrons from the filament is associated with an appropriate current value for emitting electrons from the filament; and

[0109] a control unit controlling to adjust the current supplied to the filament based on the current information after a first total supply time which is a prescribed total supply time.

[0110] (Item 2)

[0111] The X-ray imaging apparatus according to Item 1, wherein the control unit is configured to, before the first total supply time, adjust the current supplied to the filament based on the appropriate current value obtained by a process of obtaining the appropriate current value supplied to the filament by supplying current to the filament, and at a second total supply time after the first total supply time, adjust the current supplied to the filament based on the current information.

[0112] (Item 3)

[0113] The X-ray imaging apparatus according to Item 2, wherein the control unit is configured to obtain the appropriate current value by the process at the first total supply time, and at the second total supply time, adjust the current supplied to the filament based on the appropriate current value obtained at the first total supply time and the current information.

[0114] (Item 4)

[0115] The X-ray imaging apparatus according to Item 3, wherein the control unit is configured to obtain a correction value based on the appropriate current value among the appropriate current value obtained at the first total supply time and the current information at the first total supply time, and at the second total supply time, adjust the current supplied to the filament based on the obtained correction value and the appropriate current value in the current information at the second total supply time.

[0116] (Item 5)

[0117] The X-ray imaging apparatus according to any one of Items 1 to 4, wherein the control unit is configured to, after the first total supply time, at every prescribed first total supply time interval, adjust the current supplied to the filament based on the appropriate current value in the current information.

[0118] (Item 6)

[0119] The X-ray imaging apparatus according to Item 5, wherein the control unit is configured to, after the first total supply time, as the total supply time becomes longer, shorten the first total supply time interval for adjusting the current supplied to the filament.

[0120] (Item 7)

[0121] The X-ray imaging apparatus according to any one of Items 1 to 6, wherein the current information is information on the appropriate current value with respect to the total supply time, which is obtained in advance based on measured data.

[0122] The control unit is configured to adjust the current supplied to the filament based on the information of the appropriate current value obtained in advance based on the measured data after the first total supply time.

[0123] (Item 8)

[0124] According to the X-ray imaging apparatus according to Item 7, wherein the current information is information in which the total supply time and the appropriate current value are correlated, and the appropriate current value is obtained while supplying current to the filament at every prescribed second total supply time interval and increasing the supplied current, based on the luminance value of the X-ray detection signal detected by the X-ray detector.

[0125] The control unit is configured to adjust the current supplied to the filament based on the current information after the first total supply time.

[0126] (Item 9)

[0127] According to the X-ray imaging apparatus according to any one of Items 2 to 4, wherein the first total supply time is the total supply time predicted to stabilize the variation of the appropriate current value obtained by the processing due to the peeling of the oxide film of the filament.

[0128] The control unit is configured to adjust the current supplied to the filament based on the current information after the first total supply time.

[0129] (Item 10)

[0130] A method for adjusting the current supplied to a filament, which is a method for adjusting the current supplied to a filament in an X-ray imaging apparatus, the X-ray imaging apparatus including an X-ray tube, the X-ray tube including a target and an electron emission unit provided with the filament and emitting electrons to the target, the method for adjusting the current supplied to the filament including the following steps:

[0131] Pre-obtaining the following current information, that is, current information in which the total supply time of the current supplied to the filament for releasing electrons from the filament and the appropriate current value of the current supplied to the filament for releasing electrons from the filament are correlated; and

[0132] After the first total supply time as the prescribed total supply time, adjusting the current supplied to the filament based on the current information.

Claims

1. An X-ray imaging apparatus, comprising: an X-ray tube including a target and an electron emission section provided with a filament for emitting electrons to the target; an X-ray detector for detecting X-rays emitted from the X-ray tube; a storage section storing current information obtained in advance, which is information establishing a correspondence between the total supply time of the current supplied to the filament for emitting electrons from the filament and an appropriate current value for emitting electrons from the filament; and a control section for controlling to adjust the current supplied to the filament based on the current information after a first total supply time which is a prescribed total supply time.

2. The X-ray imaging apparatus according to claim 1, wherein the control section is configured to, before the first total supply time, adjust the current supplied to the filament based on the appropriate current value obtained by a process of obtaining the appropriate current value supplied to the filament by supplying current to the filament, and at a second total supply time after the first total supply time, adjust the current supplied to the filament based on the current information.

3. The X-ray imaging apparatus according to claim 2, wherein the control section is configured to obtain the appropriate current value by the process at the first total supply time, and at the second total supply time, adjust the current supplied to the filament based on the appropriate current value obtained at the first total supply time and the current information.

4. The X-ray imaging apparatus according to claim 3, wherein the control section is configured to obtain a correction value based on the appropriate current value obtained at the first total supply time and the appropriate current value in the current information at the first total supply time, and based on the obtained correction value and the appropriate current value in the current information at the second total supply time, adjust the current supplied to the filament at the second total supply time.

5. The X-ray imaging apparatus according to claim 1, wherein the control section is configured to, after the first total supply time, adjust the current supplied to the filament based on the appropriate current value in the current information at every prescribed first total supply time interval.

6. The X-ray imaging apparatus according to claim 5, wherein the control section is configured to, after the first total supply time, shorten the first total supply time interval for adjusting the current supplied to the filament as the total supply time becomes longer.

7. The X-ray imaging apparatus according to claim 1, wherein the current information is information of the appropriate current value with respect to the total supply time obtained in advance based on measured data, and the control section is configured to, after the first total supply time, adjust the current supplied to the filament according to the information of the appropriate current value obtained in advance based on measured data.

8. The X-ray imaging apparatus according to claim 7, wherein The current information is information that establishes a correspondence between the total supply time and the appropriate current value, and the appropriate current value is obtained based on a luminance value of an X-ray detection signal detected by the X-ray detector while supplying current to the filament at every prescribed second total supply time interval and increasing the supplied current. The control unit is configured to adjust the current supplied to the filament based on the current information after the first total supply time.

9. The X-ray imaging apparatus according to claim 2, wherein the first total supply time is a total supply time predicted to stabilize fluctuations in the appropriate current value obtained through the processing due to peeling of the oxide film of the filament. The control unit is configured to adjust the current supplied to the filament based on the current information after the first total supply time.

10. A method for adjusting a current supplied to a filament, the method for adjusting a current supplied to a filament in an X-ray imaging apparatus including an X-ray tube having a target and an electron emission unit provided with the filament and emitting electrons to the target, the method for adjusting a current supplied to the filament including the steps of: previously obtaining current information, that is, current information that establishes a correspondence between the total supply time of the current supplied to the filament for electron emission from the filament and the appropriate current value of the current supplied to the filament for electron emission from the filament; and after a first total supply time as the prescribed total supply time, adjusting the current supplied to the filament based on the current information.

Images