X-ray tube focal spot size measurement method

Abstract

An object of the present invention is to provide a simple focal spot dimension measurement method that satisfies the requirements of IEC60336 5th edition by using a two-dimensional digital X-ray sensor and reduces the amount of data used for noise reduction. [Solution] Using an X-ray tube focal spot dimension measuring device consisting of a power supply unit that drives the X-ray tube, an X-ray tube that is the source of X-rays, a slit camera with a continuously uniform slit width, and a two-dimensional digital X-ray sensor, the focal spot dimension of the X-ray tube is measured by the steps of averaging signals having a line spread function corresponding to the X-ray intensities of multiple different lines in the longitudinal direction of the slit to calculate an averaged signal, and calculating the focal spot dimension based on the width of two points having a value of a predetermined ratio to the maximum value of the averaged signal having the line spread function.

Description

[Technical field]

[0001] The present invention relates to a method for measuring the focal spot size of an X-ray tube, and more particularly to a method for measuring the focal spot size of an X-ray tube that uses a digital detector and complies with IEC60336 5th Edition. [Background technology]

[0002] The focal characteristics of diagnostic X-ray tube devices are specified in IEC 60336. Until the 4th edition of IEC 60336, published in 2005 (Non-Patent Document 1), it was specified that the focal characteristics should be analyzed mainly using film, but many operational problems exist, and a rational measurement method to replace film is awaited. In recent years, high-quality digital detectors have become easily available, so in the 5th edition of IEC 60336, published in 2020 (Non-Patent Document 2), digital detectors are now used instead of films to measure and analyze focal characteristics.

[0003] However, one concern when applying digital detectors is discretization error. IEC60336 5th Edition specifies several requirements to minimize discretization error. Requirement 1: The number of pixels between two points having a value of 15% of the maximum X-ray intensity of the line spread function (LSF) is 60 or more. Alternatively, the number of pixels is 30 or more and less than 60, and linear interpolation is applied. · Requirement 2: The number of levels from the background level to the maximum X-ray intensity of the line spread function must be 200 or more. · Requirement ▲3▼: The signal-to-noise ratio must be 200 or greater. · Requirement ▲4▼: When measuring the focal dimension, the evaluation direction must be read perpendicular to the slit within ±1°. There is a demand for a method to measure the focal length using a single slit camera as specified in IEC 60336, 4th edition, which satisfies the above requirements (1) to (4).

[0004] As a known example, Patent Document 1 discloses a method for measuring the focal spot dimension of an X-ray tube by reading the shape of a cross slit image or the shape of a pinhole image with a camera. However, there is no description of a method for generating a line spread function from a single slit image and measuring the focal spot dimension of an X-ray tube from the line spread function, so the method in Patent Document 1 cannot meet the requirements of IEC60336 5th Edition. Furthermore, while there is a method for reducing noise to meet requirement 2, Patent Document 1 requires the acquisition and integration of multiple images to reduce noise generated in the image, which results in a large amount of data to be handled and becomes complicated. [Prior art documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 9-17342 [Non-Patent Document 1] IEC60336:2005 Medical electrical equipment-X-ray tube assemblies for medical diagnosis-Characteristics of focal spots [Non-Patent Document 2] IEC60336:2020{Ed5.0}b Medical electrical equipment-X-ray tube assemblies for medical diagnosis-Focal spot dimensions and related characteristics Summary of the Invention [Problem to be solved by the invention]

[0006] The first problem to be solved by the present invention is to increase the number of levels from the background level to the maximum X-ray intensity of the line spread function by simply reducing noise generated in an image with a small amount of data to be handled, in relation to requirement 2 of IEC 60336, 5th edition, in a method of measuring the focal spot dimension of an X-ray tube. The second problem to be solved by the present invention is to determine the verticality of a single-slit image and correct the single-slit image when it is not vertical, in relation to requirement 4 of IEC 60336, 5th edition, in a method of measuring the focal spot dimension of an X-ray tube. [Means for solving the problem]

[0007] The method for measuring the focal spot size of an X-ray tube according to the first aspect of the present invention is as follows: An X-ray tube, which is the source of X-rays; A power supply unit that drives the X-ray tube; a slit camera having a slit whose width in a direction perpendicular to the longitudinal direction is continuously uniform along the longitudinal direction; a two-dimensional digital X-ray sensor that detects X-rays that have passed through a slit of a slit camera for a predetermined period of time, line by line, in a direction perpendicular to the longitudinal direction, and calculates a signal having a line spread function according to the intensity of the X-ray; In an apparatus for measuring focal spot dimensions of an X-ray tube, A step of averaging signals having a line spread function corresponding to the intensities of X-rays of a plurality of different lines in a longitudinal direction of the slit to calculate an averaged signal; calculating a focal spot size based on a width of two points having a predetermined ratio to a maximum value of an average signal having a line spread function; The present invention is characterized by having the following.

[0008] The second invention is a method for measuring the focal spot size of an X-ray tube according to the first invention. The predetermined ratio is 15%.

[0009] The third invention is a method for measuring the focal spot size of an X-ray tube according to the first invention. In the present invention, the pixels of the two-dimensional digital X-ray sensor are arranged in a direction perpendicular to the longitudinal direction of the slit and in the longitudinal direction of the slit.

[0010] The fourth aspect of the present invention is an X-ray tube focal spot size measuring method. An X-ray tube, which is the source of X-rays; A power supply unit that drives the X-ray tube; a slit camera having a slit whose width in a direction perpendicular to the longitudinal direction is continuously uniform along the longitudinal direction; a two-dimensional digital X-ray sensor having a plurality of pixels arranged on a plane in a row direction and a column direction perpendicular to the row direction, the pixels detecting the intensity of X-rays; a two-dimensional digital X-ray sensor angle adjustment tool for rotating the two-dimensional digital X-ray sensor on its plane; A display device; In an apparatus for measuring focal spot dimensions of an X-ray tube, acquiring a signal having a line spread function corresponding to the intensity of X-rays of a plurality of different lines at a first predetermined interval in the longitudinal direction of the slit by a two-dimensional digital X-ray sensor; calculating an angle between a line connecting a predetermined one of two points having a first predetermined ratio to a maximum value of a plurality of lines having a line spread function and the row direction or column direction; a step of displaying on a display device when the angle falls outside a predetermined angle range; when the angle falls outside a predetermined range, rotating the two-dimensional digital X-ray sensor using an angle adjustment jig so that the angle falls within the predetermined range; a step of detecting at least one line of X-rays that have passed through a slit of a slit camera for a predetermined period of time in a direction perpendicular to the longitudinal direction of the slit by a two-dimensional digital X-ray sensor, and calculating a line spread function from a signal of the detected X-ray intensity; calculating a focal spot size based on the widths of two points having a second predetermined ratio to the maximum value of the line spread function; The present invention is characterized by having the following.

[0011] The fifth invention is a method for measuring the focal spot size of an X-ray tube according to the fourth invention. In the method, the step of displaying on a display device when the angle falls outside a range of a predetermined angle is a step of displaying on a display device the angle and a fact that the angle has fallen outside the predetermined range.

[0012] The sixth invention is a method for measuring the focal spot size of an X-ray tube according to the fourth invention. in the method, the step of detecting at least one line of X-rays that have passed through a slit of a slit camera for a predetermined period in a direction perpendicular to the longitudinal direction of the slit by a two-dimensional digital X-ray sensor and calculating a line spread function from a signal of detected X-ray intensity is a step of detecting multiple different lines of X-rays that have passed through a slit of a slit camera for a predetermined period in a direction perpendicular to the longitudinal direction of the slit by a two-dimensional digital X-ray sensor, averaging signals having line spread functions corresponding to the intensities of X-rays for the multiple different lines at a second predetermined interval in the longitudinal direction of the slit to calculate an averaged signal, The step of calculating the focal dimension based on the width of two points having a second predetermined ratio value to the maximum value of the line spread function is characterized by being a step of calculating the focal dimension based on the width of two points having a second predetermined ratio value to the maximum value of the averaged signal having the line spread function.

[0013] The seventh aspect of the present invention is a method for measuring the focal spot size of an X-ray tube according to the fourth or sixth aspect of the present invention. In the method, the second predetermined ratio is 15%, and the first predetermined ratio is greater than the second predetermined ratio.

[0014] The eighth aspect of the present invention is the seventh aspect of the present invention, which is a method for measuring the focal spot size of an X-ray tube. The first predetermined ratio is a predetermined ratio that is not affected by noise at a background level of the line spread function.

[0015] The ninth aspect of the present invention is the method for measuring the focal spot size of an X-ray tube according to the sixth aspect of the present invention. In the above, the second predetermined interval is smaller than the first predetermined interval.

[0016] The tenth aspect of the present invention is the sixth aspect of the present invention. wherein the first predetermined interval is greater than the second predetermined interval.

[0017] The method for measuring the focal spot size of an X-ray tube according to the eleventh aspect of the present invention is as follows: An X-ray tube, which is the source of X-rays; A power supply unit that drives the X-ray tube; a slit camera having a slit whose width in a direction perpendicular to the longitudinal direction is continuously uniform along the longitudinal direction; a two-dimensional digital X-ray sensor having a plurality of pixels arranged on a plane in a row direction and a column direction perpendicular to the row direction, the pixels detecting the intensity of X-rays; a two-dimensional digital X-ray sensor angle adjustment tool for rotating the two-dimensional digital X-ray sensor on its plane; A display device; a slit rotation tool having a mechanism for moving at least one slit so as to rotate it 90° around a rotation axis perpendicular to the plane of the slit camera; In a focal dimension measuring device for measuring the focal width and focal length of an X-ray tube having A first step of acquiring signals having a line spread function corresponding to the intensities of X-rays of a plurality of different lines at a first predetermined interval in a longitudinal direction of a slit by a two-dimensional digital X-ray sensor; a second step of calculating an angle between a line connecting a predetermined one of two points having a value that is a first predetermined ratio to a maximum value of a plurality of lines having a line spread function and the row direction or column direction; a third step of displaying on a display device when the angle falls outside a predetermined angle range; a fourth step of rotating the two-dimensional digital X-ray sensor using an angle adjustment jig when the angle falls outside a predetermined range so that the angle falls within the predetermined range; a fifth step of detecting at least one line of X-rays that have passed through the slit of the slit camera for a predetermined period of time in a direction perpendicular to the longitudinal direction of the slit by a two-dimensional digital X-ray sensor, and calculating a line spread function from a signal of the detected X-ray intensity; a sixth step of measuring one of a focal width and a focal length of the x-ray tube based on the width of two points having a second predetermined ratio to a maximum value of the line spread function; a seventh step of moving at least one slit by a slit rotation jig so as to rotate the slit by 90° around a rotation axis perpendicular to a plane of the slit camera; an eighth step of acquiring signals having a line spread function according to the intensities of X-rays of different lines at first predetermined intervals in the longitudinal direction of the slit by the two-dimensional digital X-ray sensor; a ninth step of calculating an angle between a line connecting a predetermined one of two points having a value that is a first predetermined ratio to a maximum value of a plurality of lines having a line spread function and the row direction or column direction; a tenth step of displaying on a display device when the angle falls outside a predetermined angle range; an eleventh step of rotating the two-dimensional digital X-ray sensor by using an angle adjustment jig when the angle falls outside the predetermined range so that the angle falls within the predetermined range; a twelfth step of detecting, by a two-dimensional digital X-ray sensor, at least one line of X-rays that have passed through a slit of the slit camera for a predetermined period in a direction perpendicular to the longitudinal direction of the slit, and calculating a line spread function from a signal of the detected X-ray intensity; a thirteenth step of calculating the other of the focal width and the focal length of the X-ray tube based on the width of two points having a second predetermined ratio to the maximum value of the line spread function; The present invention is characterized by having the following. Effect of the Invention

[0018] The first invention provides the following effect (1). Effect ▲1▼: This satisfies requirement ▲2▼ of IEC 60336, 5th edition, and reduces noise by averaging signals that have a line spread function corresponding to the intensities of multiple different lines of X-rays in the longitudinal direction of the slit.

[0019] The second invention of this case provides the following effect (2) in addition to effect (1). Effect 2: By calculating the focal spot size based on the width of two points having a value of 15% of the maximum value of the averaged signal having a line spread function, it is possible to measure the focal spot size in accordance with the provisions of Section 7.2 of IEC 60336, 5th edition.

[0020] The third invention provides the following effect (3) in addition to effect (1). Effect 3: The multiple pixels of the 2D digital X-ray sensor are arranged in a direction perpendicular to the longitudinal direction of the slit, and are also arranged in the longitudinal direction of the slit, so that the focal spot dimensions can be read with simple calculations using data from a small number of lines.

[0021] The fourth aspect of the present invention provides the following effect (4). Effect ▲4▼: The evaluation direction can be read perpendicularly to the longitudinal direction of the slit within a specified angle θs (±1° in IEC 60336, 5th edition), satisfying requirement ▲4▼ of IEC 60336, 5th edition for the focal spot dimension measurement method of X-ray tubes. The definition of θs will be described later.

[0022] The fifth invention provides the following effect (5) in addition to effect (4). Effect 5: By displaying on the display device the angle θs and the fact that the angle θs is outside the specified range, it is possible to grasp that the evaluation direction is outside the range of the specified angle θs (±1° in IEC 60336, 5th edition) from perpendicular to the longitudinal direction of the slit and that angle θs.

[0023] The sixth invention provides effect (1) in addition to effect (4).

[0024] The seventh invention provides the following effect (6) in addition to effects (1) and (4). Effect 6: Since the first predetermined ratio is greater than the second predetermined ratio, the angle θs between the evaluation direction and the direction perpendicular to the longitudinal direction of the slit is less susceptible to the influence of background level noise when determining the angle θs.

[0025] The eighth invention provides the following effect (7) in addition to the effects (1), (4), and (6). Effect (7): Since the first predetermined ratio is a predetermined ratio that is not affected by noise at the background level of the line spread function, the slit angle θs of the slit camera can be calculated with high accuracy.

[0026] The ninth invention of this case provides the following effect (8) in addition to effects (1) and (4). Effect (8): Since the second predetermined interval is smaller than the first predetermined interval, the error in the focal spot size can be reduced even if the slit is slightly tilted.

[0027] The tenth invention provides the following effect (9) in addition to the effects (1) and (4). Effect (9): Since the first predetermined interval is greater than the second predetermined interval, the slit angle θs of the slit camera can be calculated more accurately.

[0028] The eleventh invention provides the following effect (10) in addition to effect (4). Effect 10: The slit rotation jig allows at least one slit to be rotated 90° around a rotation axis perpendicular to the plane of the slit camera, making it easy to switch between measurements of focal width and focal length. [Brief description of the drawings]

[0029] [Figure 1] 1 is an overall view of an X-ray tube focal spot dimension measuring device according to an embodiment of the present invention. [Diagram 2] Schematic diagram of a fixed anode X-ray tube. [Diagram 3] Schematic diagram of focal dimension measurement for focal width (a) and focal dimension measurement for focal length (b) [Figure 4] Cross-sectional view of a single slit camera specified in IEC60336 4th edition or IEC60336 5th edition. [Diagram 5]Plan view of a single slit camera specified in IEC60336 4th edition or IEC60336 5th edition. [Figure 6] FIG. 1 is a simplified diagram of the shape of a focal image photographed using the cross slit used in Patent Document 1. [Figure 7] A perspective view showing the axes and directions related to focal dimension measurement as specified in IEC 60336 4th edition or IEC 60336 5th edition. [Figure 8] Plan view showing the mechanism for rotating the single slit camera by 90° to switch between focal width and focal length when measuring focal dimensions. [Figure 9] Simplified diagram of the use of a one-dimensional sensor (left) and a two-dimensional sensor (right) shown in Figure 6-Alignment of the receptor of the DIGITAL FOCAL SPOT DETECTOR with respect to the slit diaphragm of IEC60336 5th Edition. [Figure 10] Schematic diagram showing pixel positions of a two-dimensional digital X-ray sensor. [Figure 11] A simplified diagram showing an arbitrary line in an X-ray image of a slit acquired by a 2D digital X-ray sensor (a), and a graph showing the line spread function obtained along the arbitrary line (b). [Figure 12] A graph showing the line spread function (LSF) specified in IEC60336 5th edition. [Figure 13] This shows the positional relationship between the single slit image and the corresponding pixels of the two-dimensional digital X-ray sensor when the angle θ acquired by the two-dimensional digital X-ray sensor in the measurement of the focal length direction is not within ±1°. This is a simplified diagram (a) showing an X-ray image, and a schematic diagram (b) showing the line spread function corresponding to each reading line of the simplified diagram (a). [Figure 14] This shows the positional relationship between the single slit image and the corresponding pixels of the two-dimensional digital X-ray sensor when the angle θ obtained by the two-dimensional digital X-ray sensor in the measurement of the focal length direction is within ±1°. (a) is a simplified diagram showing an X-ray image, and (b) is a schematic diagram showing the line spread function corresponding to each reading line of the simplified diagram (a). [Figure 15] (a) is a simplified diagram of an X-ray image showing 10 read lines when measuring focal spot dimensions, (b) is a graph showing the line spread functions of the first and tenth lines of the simplified diagram (a), and (c) is a graph showing the line spread function obtained by averaging the line spread functions of the ten lines of (a). [Figure 16] FIG. 13 is a plan view showing a 2D digital X-ray sensor angle adjustment jig provided with a mechanism for adjusting the angle of the 2D digital X-ray sensor. [Figure 17] 2 is an operation flowchart of the X-ray tube focal spot dimension measuring device shown in FIG. 1 . [Figure 18] This shows the positional relationship between the single slit image and the corresponding pixels of the two-dimensional digital X-ray sensor when the angle θ acquired by the two-dimensional digital X-ray sensor in measurement in the focal spot width direction is not within ±1°, and shows (a) a simplified diagram showing the entire two-dimensional digital X-ray sensor, and (b) a schematic diagram showing the line spread function corresponding to each reading line in (a) [Figure 19] 18 is a detailed flowchart of an angle determination portion of the flowchart in FIG. 17. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] An embodiment of the present invention will be described in detail below with reference to the drawings. This embodiment is configured as shown in Figures 1 and 2. Figure 1 shows the main body (focus dimension measuring device) 1 of the X-ray tube 3, and Figure 2 shows the X-ray tube 3 with a fixed anode. In the main body (focus dimension measuring device) 1 of the embodiment of FIG. 1, a power supply unit 2 and an X-ray tube 3 are connected. An oil tank 4 contains the X-ray tube 3 together with insulating oil (not shown), and electrically insulates the X-ray tube 3 from the outside. The X-ray tube 3, a single slit camera 6, which is a form of a slit camera, and a two-dimensional digital X-ray sensor 8 are installed on a support 10 and arranged on a reference axis R. The power supply unit 2 is composed of an operating condition control circuit 2-1, a high-voltage power supply 2-2, and a filament power supply 2-3. The single slit camera 6 is fixed to a single slit camera rotation jig 5, which is a form of a slit rotation jig, and the two-dimensional digital X-ray sensor 8 is fixed to a two-dimensional digital X-ray sensor angle adjustment jig 7. The two-dimensional digital X-ray sensor 8 is connected to a computer unit 9. The computer unit 9 is equipped with a display device 9-1. The main body 1 of the X-ray tube 3 may be configured as a so-called X-ray head by housing the X-ray tube 3, high-voltage power supply 2-2, filament power supply 2-3, and oil vat 4 in a case (not shown), or the X-ray tube 3 and oil vat 4 may be housed in a case (not shown) with the high-voltage power supply 2-2 and filament power supply 2-3 placed separately and connected to the X-ray tube 3 by cables (not shown).

[0031] 2 shows the X-ray tube 3 in the embodiment of FIG. 1, and the X-ray tube 3 has an X-ray output window 3-1, an anode 3-2, and a cathode 3-3. Inside the cathode 3-3 is a filament 3-4, and when power is supplied from the filament power supply 2-3, thermal electrons are generated in the filament 3-4, which are accelerated by the high-voltage power supply 2-2 and form a real focal point 13 when they collide with the anode 3-2. The point connecting the major axis L of the X-ray tube and the center of the real focal point 13 becomes the origin 0, and the real focal point 13 is formed on the origin 0. A line extending in the Z direction perpendicular to the major axis L of the X-ray tube 3 from the origin 0 becomes the reference axis R. The plane along the long axis L is called the reference plane 3-5.

[0032] FIG. 3 is a schematic diagram of focal dimension measurement in the embodiment of FIG. 1, where (a) shows a schematic diagram of focal width measurement, and (b) shows a schematic diagram of focal length measurement. The single slit camera 6 is arranged so that the distance n from the X-ray incidence surface 6-2 to the X-ray sensor image receiving surface and the distance m from the X-ray incidence surface 6-2 of the single slit camera 6 to the reference surface 3-5 have a ratio of 3.5:1. In the focal width direction, the focal width 13-1 of the real focus 13 and the focal width 14-1 of the effective focus 14 have the same dimensions, but in the focal length direction, the focal length 13-2 of the real focus 13 and the focal length 14-2 of the effective focus 14 have different dimensions. In focal dimension measurement, it is specified in IEC60336 5th edition that the dimensions of the focal width 14-1 and focal length 14-2 of the effective focus 14 should be measured.

[0033] FIG. 4 is a cross-sectional view of the single slit camera 6 in the embodiment of FIG. 1, and FIG. 5 is a plan view of the single slit camera 6 in the embodiment of FIG. 1. The width Ws of the single slit camera 6 in the direction perpendicular to the longitudinal direction of the slit 6-1 is continuous and uniform in the longitudinal direction of the slit 6-1. The width Ws of the single slit camera 6 in the direction perpendicular to the longitudinal direction of the slit 6-1 is specifically specified in IEC 60336, 5th edition, section 5.2, and is 0.01±0.002 mm as shown in FIG. 4, and is defined as having a tolerance of about 20% here. Since Patent Document 1 obtains a cross slit image 15 as shown in FIG. 6, it does not satisfy the requirements of the slit camera required by the IEC 60336, 5th edition, shown in FIG. 4 and FIG. 5. Furthermore, in the case of the cross slit image 15, the width Wc of the cross slit image 15 in the direction perpendicular to the longitudinal direction of the slit 15-1 is discontinuous near the center and does not have a uniform width, so data cannot be obtained near the center of the X-ray sensor 8.

[0034] The focal dimension of the X-ray tube needs to be measured in terms of width and length, which can be performed by rotating either the X-ray tube 3 or the single slit camera 6 by 90°. In this embodiment, in order to simplify the configuration of the X-ray tube device body (focal dimension measuring device) 1 shown in FIG. 1, the position of the X-ray tube 3 is fixed when measuring the focal width 14-1 and focal length 14-2 of the effective focal spot 14, which are the focal dimension shown in FIG. 3. Therefore, when the orientation of the focal width reading direction Df and the focal length reading direction Dl shown in FIG. 7 changes by 90°, the orientation of the single slit camera 6 needs to be changed, so the longitudinal orientation of the single slit camera 6 is rotated by 90° using the single slit camera rotating jig 5 shown in FIG. 8. The single-slit camera rotation jig 5 shown in Fig. 8 is composed of an upper plate 5-1 and a lower plate 5-2. The upper plate 5-1 has recesses 5-1-1 provided at 90° intervals on the same radius, and the lower plate 5-2 has protrusions 5-2-1 provided at 180° intervals on the same radius. The single-slit camera 6 is rotated precisely 90° by fitting the recesses of the upper plate 5-1 into the protrusions of the lower plate 5-2. This allows the focal dimension measurement to be switched between the focal width reading direction Df and the focal length reading direction Dl, so that the length direction of the slit 6-1 of the single-slit camera 6 can be arranged perpendicular to both the focal width and focal length measurements. As shown in the simplified diagram of one-dimensional and two-dimensional sensors shown in IEC 60336, 5th edition in Figure 9, the longitudinal direction of the slit 6-1 of the single slit camera 6 must be positioned perpendicular to the direction of evaluation 18. As a result, the longitudinal direction of the slit 6-1 of the single slit camera 6 can be arranged to be perpendicular to the direction of evaluation 18 in Fig. 9. In summary, by using the single slit camera rotation jig 5 to move at least one slit 6-1 so as to rotate it 90° around a rotation axis perpendicular to the plane of the single slit camera 6-1, it is possible to easily switch between the measurements of the focal width 14-1 and the focal length 14-2.

[0035] Fig. 10 is a schematic diagram showing the position of pixel 8-1 of the two-dimensional digital X-ray sensor 8 in the embodiment of Fig. 1. The two-dimensional digital X-ray sensor 8 reads and digitizes the intensity of X-rays with a sensor, and obtains an image in which the X-ray intensity of each pixel 8-1 is shaded. The pixels 8-1 of the two-dimensional digital X-ray sensor 8 are arranged two-dimensionally with 1300 in the x' (row) direction and 1706 in the y' (column) direction, and the x' (row) direction and the y' (column) direction are orthogonal to each other. In the two-dimensional digital X-ray sensor 8, the pixels 8-1 are arranged in parallel to the x' (row) direction or the y' (column) direction, and the detection of the X-ray intensity of each pixel 8-1 of the two-dimensional digital X-ray sensor 8 is called one line. The numbers 1, 2, 3, ..., 2217800 in the pixels 8-1 are the numbering of the pixels 8-1 in the x' (row) direction. The two numbers in parentheses below them are the coordinates in the x' (row) direction and the y' (column) direction. The smaller the size of the pixels 8-1, the more advantageous it is for discretization, and in this embodiment, the size is 20um x 20um. FIG. 11(a) shows an X-ray image 11 of the single slit camera 6 acquired by the two-dimensional digital X-ray sensor 8, and image processing specific to the two-dimensional digital X-ray sensor 8 has been performed. In the X-ray image 11, the single slit image 11-1 is darkened by the X-ray that passed through the slit 6-1 of the single slit camera 6. When the X-ray intensity is plotted along an arbitrary line 11-2, a line spread function (LSF) 17 is obtained as shown in FIG. 11(b). The part with high X-ray intensity is the slit part 17-1, and the part with low X-ray intensity is the non-irradiated part 17-2. In IEC60336 5th edition, section 7.2 specifies that when measuring the focal spot size, the width of two positions of the value 17-5 of 15% of the maximum X-ray intensity of the line spread function (LSF) 17, which is the second predetermined ratio, is read as shown in FIG. 12. The width of two positions of the value 17-5 of 15% of the maximum X-ray intensity of the line spread function (LSF) 17, which is the second predetermined ratio, is a width enlarged from the actual focal spot size. The magnification factor E is calculated by n / m shown in FIG. 3, and in this embodiment, the magnification factor E=3.5. As described above, the pixels 8-1 of the two-dimensional digital X-ray sensor 8 are arranged in a direction perpendicular to the longitudinal direction of the slit 6-1, and are arranged in the longitudinal direction of the slit 6-1, so that the focal spot size can be read with one line of data. However, the line spread function (LSF) 17 used to read the focal spot size contains noise, and it is necessary to reduce the noise in order to perform measurements conforming to the IEC 60336 5th edition. The noise reduction method will be described in detail in

[0038] .

[0036] Figure 13(a) shows the positional relationship between a single-slit image and the corresponding pixels of the two-dimensional digital X-ray sensor when the angle θ acquired by the two-dimensional digital X-ray sensor in the measurement in the focal length direction is not within ±1°. Each pixel 8-1 of the two-dimensional digital X-ray sensor 8 corresponds to each pixel image 11-3 of the X-ray image 11. Here, a row of pixels 8-1 from which data is read is defined as a read line 12. To capture the inclination of the single slit image 11-1, it is easier to capture the inclination by acquiring the data of the entire single slit image 11-1. In this embodiment, data of 10 read lines 12 is acquired at intervals of 100 rows of pixels 8-1 in the y' (column) coordinate direction, which is the first predetermined interval, and the data of the pixels 8-1 of the two-dimensional digital X-ray sensor 8 is calculated to obtain a graph of 10 line spread functions (LSFs) 17 corresponding to the data of the 10 read lines 12. The direction of the read lines 12 coincides with the direction of evaluation 18. FIG. 13(b) shows a total of 10 line spread functions (LSFs) 17 corresponding to each read line 12 in FIG. 13(a). The pixel 8-1 position of the value 17-6 of 60% of the maximum X-ray intensity, which is the first predetermined ratio, is acquired on the x'-y' coordinate for the 10 line spread functions (LSFs) 17. The reason for using the value 17-6 of 60% of the maximum X-ray intensity, which is the first predetermined ratio, is to avoid the influence of noise of the background level 17-4 described in

[0038] . Since the first predetermined ratio is larger than the second predetermined ratio, it is possible to reduce the influence of noise of the background level 17-4 when obtaining the angle θs between the evaluation direction 18 and the direction perpendicular to the longitudinal direction of the slit 6-1. If the pixel 8-1 value of the value 17-6 of 60% of the maximum X-ray intensity, which is the first predetermined ratio, cannot be obtained, the x'-y' coordinates of the value 17-6 of 60% of the maximum X-ray intensity, which is the first predetermined ratio, are calculated by linear interpolation from the coordinates of the two pixels closest to 60%. From the group of 10 coordinates thus obtained, an approximation line 16 parallel to the longitudinal direction of the single slit image 11-1 is obtained by the least squares method. An angle θ is obtained from the approximation line 16 parallel to the longitudinal direction of the single slit image 11-1 and the y' axis, which is on the plane of the X-ray image 11 of the slit 6-1 acquired by the two-dimensional digital X-ray sensor 8 and is parallel to the y' (column) direction. Since the first predetermined ratio is a predetermined ratio that is not affected by noise of the background level 17-4 of the line spread function (LSF) 17, the angle θs of the slit 6-1 of the single slit camera 6 can be calculated with high accuracy. θs will be described later in

[0039] . If the range of the x'-y' coordinates is too narrow, the angle θ cannot be obtained, so the size of the two-dimensional digital X-ray sensor 8 must be large enough to obtain the angle θ. Figure 14 shows an X-ray image 11 when the angle θ with the y' (row) direction is within ±1°. In the case of Figure 14, the angle θ with the x' (row) direction can be said to be 90±1°.

[0037] Requirements 1 to 3 are recommended in IEC 60336, 5th edition, section 6.3.1 to limit the error caused by discretization to about 1%. Requirement 1 is that the number of pixels 8-1 in the width between two positions of the value 17-5 of 15% of the maximum X-ray intensity of the line spread function (LSF) 17, which is the second predetermined ratio, is 60 or more, or is 30 or more and less than 60, and linear interpolation is applied. In this embodiment, this requirement is met by setting the size of the pixels 8-1 of the two-dimensional digital X-ray sensor 8 and the magnification ratio E. By adopting a magnification ratio E=3.5 and using a two-dimensional digital X-ray sensor 8 with one pixel 8-1 having a side of 20 um, in the case of a 0.4 mm focal point X-ray tube, the number of pixels 8-1 in the width between two points having a value 17-5 of 15% of the maximum X-ray intensity of the line spread function (LSF) 17, which is the second predetermined ratio, is 60 or more. Therefore, the requirement of requirement ▲1▼ is satisfied. Since the number of pixels 8-1 in the width between two points having a value 17-5 of 15% of the maximum X-ray intensity of the line spread function (LSF) 17, which is the second predetermined ratio, is 60 or more, linear interpolation is not required in measuring the focal spot dimension of a 0.4 mm focal point X-ray tube. However, linear interpolation is applied in this embodiment so that it can also be used to measure the focal spot dimension of an X-ray tube with a smaller focal spot. Requirement ▲2▼ is that the number of levels from the background level 17-4 of the line spread function (LSF) 17 to the maximum X-ray intensity 17-3 is 200 or more. How this is achieved in this embodiment is as follows.

[0038] This will be explained later. Requirement 3 is that the signal-to-noise ratio be 200 or greater. This is determined by the performance of the two-dimensional digital X-ray sensor 8. The two-dimensional digital X-ray sensor 8 used in this embodiment is S15683-13 manufactured by Hamamatsu Photonics KK, and has a signal-to-noise ratio of 700, so it satisfies requirement (3).

[0038] Regarding the number of levels between the background level 17-4 of the line spread function (LSF) 17 and the maximum X-ray intensity 17-3, which corresponds to the above-mentioned requirement 2, being 200 or more, in this embodiment, this is realized by averaging signals having a line spread function (LSF) 17 corresponding to the X-ray intensities of multiple different lines in the longitudinal direction of the slit 6-1 to reduce noise. As shown in Fig. 5, the width Ws in the direction perpendicular to the longitudinal direction of the slit 6-1 of the single slit camera 6 is continuous and uniform in the longitudinal direction of the slit, so the longitudinal width Wi of the single slit image 11-1 shown in Fig. 15(a) is also continuous and uniform in the longitudinal direction of the slit. Since the longitudinal width Wi of the single slit image 11-1 shown in Fig. 15(a) is the same, the line spread function (LSF) 17 according to the X-ray intensity obtained by detecting each line in the direction perpendicular to the longitudinal direction of the single slit image 11-1 theoretically has the same shape for multiple different read lines 12 of the single slit image 11-1. In this embodiment, data for ten reading lines 12 is acquired at intervals of one row of pixels 8-1 in the y' (column) coordinate direction, which is the second predetermined interval in FIG. 10, and the data for the pixels 8-1 of the two-dimensional digital X-ray sensor 8 is calculated to acquire a graph of ten line spread functions (LSFs) 17 corresponding to the data for the ten reading lines 12 shown in FIG. 15. FIG. 15(b) shows the line spread function (LSF) 17 of the first line and the line spread function (LSF) 17 of the tenth line among the read lines 12. Spike-like noise occurs in each line spread function (LSF) 17, and since the spike-like noise appears differently in the first line and the tenth line, it can be seen that it is random noise. This random noise is electrical noise caused by the variation in sensitivity of each pixel 8-1, the thermal noise of each pixel 8-1, and the circuit that reads out the signal for each pixel 8-1, and increases the background level 17-4. For example, in the case of the line spread function (LSF) 17 of the first line shown in FIG. 15(b), the maximum X-ray intensity 17-3 is 221 [LSB] and the background level 17-4 is 55 [LSB], so that the number of levels between the background level 17-4 and the maximum X-ray intensity 17-3, which is 200 or more, cannot be secured. In the case of the line spread function (LSF) 17 of the 10th line, the maximum X-ray intensity 17-3 is 247 [LSB] and the background level 17-4 is 38 [LSB], so that the number of levels between the background level 17-4 and the maximum X-ray intensity 17-3 is 200 or more, but the maximum X-ray intensity 17-3 is apparently larger due to the influence of noise, and there are also places in the non-irradiated part 17-2 that exceed the value 17-5 of 15% of the maximum X-ray intensity due to the influence of noise, so that an error occurs in reading the focal spot dimension. It is necessary to reduce noise to eliminate these effects and perform stable and accurate reading. In order to reduce noise, a line spread function (LSF) 17 corresponding to the intensity of X-rays including the variation in sensitivity of each pixel 8-1 obtained by detecting one line at a time in a direction perpendicular to the longitudinal direction of the single slit image 11-1 is obtained for multiple lines, 10 lines in this embodiment, and the outputs of multiple different pixels 8-1 arranged in the longitudinal direction, 10 pixels 8-1 in this embodiment, are averaged, and the variation in sensitivity of each pixel 8-1 is reduced by averaging. A line spread function corresponding to the intensity of X-rays including electrical noise obtained by detecting one line at a time in a direction perpendicular to the longitudinal direction of the single slit image 11-1 is obtained for 10 lines, and the outputs of 10 different pixels 8-1 arranged in the longitudinal direction are averaged, and the electrical noise is also reduced by averaging. By averaging the data for 10 lines, the random noise can be reduced to about 1 / √(10) compared to the data for one line. FIG. 15(c) shows the line spread function (LSF) 17 obtained by averaging data for 10 lines. The maximum X-ray intensity 17-3 is 222 [LSB] and the background level 17-4 is 13 [LSB]. Therefore, requirement 2 is met by averaging data for 10 lines. In order to satisfy requirement 2, noise reduction is performed by averaging, and the focal dimension is calculated based on the width between two points that have a value of 15% of the maximum value of the averaged signal having a line spread function (LSF) 17, thereby making it possible to measure the focal dimension in accordance with the provisions of Section 7.2 of IEC 60336, 5th Edition. The method of reducing noise by averaging data for 10 lines described above reduces noise by only processing data of signals having a line spread function in an image, compared to the conventional method of reducing noise using data of the entire image, so that the number of data to be processed can be reduced, and the software capacity can be reduced and the operating speed can be increased. Therefore, the first problem is solved in order to reduce noise generated in an image with a small amount of data to be processed, increase the number of levels from the background level to the maximum X-ray intensity of the line spread function, and satisfy requirement 2. In the present embodiment, the read line 12 in FIG. 15(a) reads data for 10 lines at intervals of one row in the y' (column) coordinate direction, which is the second predetermined interval, and obtains 10 graphs of the line spread function (LSF) 17 from the data of pixel 8-1 of the two-dimensional digital X-ray sensor 8. Since the second specified interval of one row in the y' (column) coordinate direction is smaller than the first specified interval of 100 rows, even if the single-slit image 11-1 is slightly tilted, the deviation of each line spread function (LSF) 17 in the x' (row) coordinate direction is small, the error when averaging is small, and the error in the focal spot dimension can be reduced. In other words, since the first predetermined interval of 100 lines is greater than the second predetermined interval of 1 line, the angle θs of the slit 6-1 of the single slit camera 6 can be calculated more accurately. This makes it easier to capture the inclination of the single slit image 11-1. In this embodiment, since the two-dimensional digital X-ray sensor 8 generally has high reliability near the center, when measuring the focal spot dimension, data is acquired near the center of the two-dimensional digital X-ray sensor 8. The second predetermined interval may be continuous reading without any interval, in other words, the second predetermined interval may be 0 lines.

[0039] In IEC60336 5th edition, section 5.5.4 states that "The direction of evaluation for the FOCAL SPOT width or length shall be oriented normal to the direction of the diaphragm slit to within ±1°.", and it is stipulated that when measuring the focal dimension, the evaluation direction 18 should be read perpendicular to the slit 6-1 of the single slit camera 6 within ±1°, which corresponds to requirement ▲4▼. However, as shown in Fig. 9, if the sensor used for reading is a one-dimensional sensor, the one-dimensional sensor must be arranged within ±1° (θs) in the vertical direction to the longitudinal direction of the slit 6-1 of the single slit camera 6, but if the sensor used for reading is a two-dimensional sensor, it is sufficient that the evaluation direction (direction of evaluation) 18 is perpendicular to the slit 6-1 of the single slit camera 6 within ±1° (θs) even if the two-dimensional sensor is not arranged within ±1° in the vertical direction to the longitudinal direction of the slit 6-1 of the single slit camera 6.

[0040] By positioning the two-dimensional digital X-ray sensor 8 so that the direction of the reading line 12 and the evaluation direction 18 are the same, the angle δ2 (= 90° ± 1° (θ)) between the direction of the reading line 12 and the single slit image 11-1 shown in Figure 14 becomes the same as the angle δ1 (= 90° ± 1° (θs)) between the evaluation direction 18 and the slit 6-1 in the standard shown in Figure 9, and the θ in angle δ2 and the θs in angle δ1 become the same. Therefore, in this embodiment, requirement {circumflex over (4)} is satisfied by calculating whether θ is within ±1° (θs) and controlling it so that it is within ±1°.

[0041] As a method of making the reading line 12 perpendicular to the slit 6-1 of the single slit camera 6 within ±1° using a two-dimensional sensor (two-dimensional digital X-ray sensor 8 in this embodiment), there is a method of acquiring the X-rays that have passed through the slit 6-1 of the single slit camera 6 with the two-dimensional digital X-ray sensor 8, calculating the angle θ of the single slit image 11-1 projected on the obtained X-ray image 11 by calculation in software, determining the position of the pixel 8-1 of the two-dimensional digital X-ray sensor 8 that is arranged perpendicular to the single slit image 11-1, and acquiring the data of this pixel 8-1 to read perpendicular to the single slit image 11-1 within ±1°. There is also a method of calculating the angle θ on the X-ray image 11 by calculation in software, correcting the inclination of the single slit image 11-1, making it parallel to the y' (column) direction of the two-dimensional digital X-ray sensor 8, and acquiring the data of the pixel 8-1 arranged in the X' (row) direction to read perpendicular to the single slit image 11-1 within ±1°. As described above, it is possible to read the single-slit image 11-1 acquired by the two-dimensional digital X-ray sensor 8 perpendicularly to the single-slit image 11-1 within ±1° when the image is tilted by calculation within the software, but this requires complex calculations. In this embodiment, as a method for easily reading the single-slit image 11-1 perpendicularly using the two-dimensional digital X-ray sensor 8, a method is used in which the pixels 8-1 aligned in the x' (row) direction of the two-dimensional digital X-ray sensor 8 are positioned within ±1° in the vertical direction relative to the longitudinal direction of the single-slit image 11-1, thereby reading the single-slit image 11-1 perpendicularly to within ±1° without calculation within the software. As a result, the focal spot dimensions can be read if there is at least one line consisting of pixels 8-1 arranged in the x' (row) direction of the two-dimensional digital X-ray sensor 8, and if noise reduction by averaging as shown in

[0038] is taken into consideration, the focal spot dimensions can be read if 2 to 10 lines are used. However, if the two-dimensional sensor is not positioned within ±1° in the vertical direction relative to the longitudinal direction of the slit 6-1 of the single-slit camera 6 and the focal dimension is measured by calculation within the software, as can be seen from the right side of Figure 9, 10 or more lines made up of pixels 8-1 lined up in the x' (row) direction of the two-dimensional digital X-ray sensor 8 will be required. Therefore, by using the method of this embodiment, the focal spot size can be read by simple calculations using data from a small number of lines. The pixels 8-1 arranged in the x' (row) direction of the two-dimensional digital X-ray sensor 8 can be positioned within ±1° in the vertical direction relative to the longitudinal direction of the single-slit image 11-1 by determining the angle θ using the method described in

[0036] , and displaying on the display device 9-1 the angle θs and the fact that the angle θs is outside the specified range, thereby making it possible to grasp that the evaluation direction 18 is outside the range of the specified angle θs (±1° in IEC 60336, 5th edition) from perpendicular to the longitudinal direction of the slit 6-1 and that the angle θs is outside the specified range. As a result, in this embodiment, θ in angle δ2 is the same as θs in angle δ1 of the evaluation direction and slit in the standard, and evaluation direction 18 can be read perpendicular to the longitudinal direction of slit 6-1 within a specified angle θs (±1° in IEC 60336, 5th edition), thereby satisfying requirement ▲4▼ of IEC 60336, 5th edition for the focal spot dimension measurement method of an X-ray tube.

[0042] 16 is a diagram showing a 2D digital X-ray sensor angle adjustment jig 7 that can adjust the angle of the 2D digital X-ray sensor. By fixing a 2D digital X-ray sensor 8 to the 2D digital X-ray sensor angle adjustment jig 7 and turning the 2D digital X-ray sensor angle adjustment screw 7-1 clockwise or counterclockwise, the 2D digital X-ray sensor 8 can be rotated around the rotation axis R'. By rotating the two-dimensional digital X-ray sensor 8, the positions of the pixels 8-1 aligned in the x' (row) direction of the two-dimensional digital X-ray sensor 8 with respect to the longitudinal direction of the single-slit image 11-1 can be adjusted, thereby solving the second problem. There is no problem if the rotation axis R' does not coincide with the reference axis R, but it is easier to adjust the positions of the pixels 8-1 aligned in the x' (row) direction of the two-dimensional digital X-ray sensor 8 with respect to the longitudinal direction of the single-slit image 11-1 by making the rotation axis R as close as possible to the reference axis R.

[0043] FIG. 17 is a flowchart showing the operation of this embodiment. S1 operates the computer unit 9 and starts image acquisition to measure the focal length 14-2 with the two-dimensional digital X-ray sensor 8. S2 operates the operating condition control unit 2-1 to start X-ray irradiation. S3 ends the exposure when a set time (5 seconds in this embodiment) has elapsed. S4 starts capturing a dark image. A dark image is an image without X-ray exposure. S5 ends the capture of the dark image when a set time (5 seconds in this embodiment) has elapsed. S6 starts dark subtraction correction. When using the two-dimensional digital X-ray sensor 8, the sensor reacts to X-rays in the atmosphere, so it is necessary to perform image processing specific to the two-dimensional digital X-ray sensor 8, which subtracts a dark image from an image exposed to X-rays. S7 confirms that the dark subtraction correction is completed. S8 outputs data of each pixel 8-1 of the read line 12 shown in FIG. 13(a) from the image that has been subjected to the dark subtraction correction. S9 is located on the plane of the approximated straight line 16 parallel to the longitudinal direction of the single-slit image 11-1 shown in Figure 13(a) and the X-ray image 11 of the single-slit camera 6 acquired by the two-dimensional digital X-ray sensor 8, and calculates the angle θ between the y' axis parallel to the y' (column) direction to judge pass / fail. If the angle is within ±1°, S9-1 displays OK on the display device 9-1. If the angle is not within ±1°, S9-2 displays NG on the display device 9-1. If NG is displayed on the display device 9-1, the angle of the X-ray sensor 8 is mechanically adjusted, and then the process returns to S1. S10 displays the angle θ on the display device 9-1. If the angle determination is OK, S11 outputs data of each pixel 8-1 of a reading line 12 near the center of the two-dimensional digital X-ray sensor 8 shown in FIG. 14(a). In order to reduce noise in the line spread function (LSF) 17 for reading the focal spot size, S12 averages data of the line spread function (LSF) 17 for each read line 12 shown in FIG. 15(a). S13 performs linear interpolation to interpolate data between pixels 8-1 of each read line 12. S14 defines the focal length 14-2 of the effective focal point 14 by dividing the width of the 15% value 17-5 of the maximum X-ray intensity, which is a second predetermined ratio of the averaged line spread function (LSF) 17 obtained from the averaged data, by the expansion ratio E = 3.5. S15 rotates the single slit camera 6 by 90 degrees. S16 operates the computer unit 9 to start image acquisition in order to measure the focal width 14-1 with the two-dimensional digital X-ray sensor 8. In step S17, the operating condition control unit 2-1 is operated to start X-ray irradiation. In step S18, the exposure is terminated when a set time (5 seconds in this embodiment) has elapsed. S19 starts capturing dark images. S20 ends the capture of the dark image when a set time (5 seconds in this embodiment) has elapsed. S21 starts the dark subtraction correction. In step S22, it is confirmed that the dark subtraction correction is completed. S23 outputs data of each pixel 8-1 of the read line 12 shown in FIG. 18(a) from the image that has been subjected to the dark subtraction correction. S24 is on the plane of the X-ray image 11 of the single-slit camera 6 acquired by the two-dimensional digital X-ray sensor 8, and calculates the angle θ between the approximated straight line 16 parallel to the longitudinal direction of the single-slit image 11-1 shown in FIG. 18(a) and the X' axis parallel to the x' (column) direction, and judges pass / fail. If the angle is within ±1°, S24-1 displays OK on the display device 9-1. If the angle is not within ±1°, S24-2 displays NG on the display device 9-1. If NG is displayed on the display device 9-1, the angle of the two-dimensional digital X-ray sensor 8 is mechanically adjusted, and then the process returns to S16. Here, it can also be seen that the single slit camera 6 can be rotated by 90 degrees. S25 displays the angle θ on the display device 9-1. If the angle determination is OK, S26 outputs data of each pixel 8-1 of the reading line 12 near the center of the two-dimensional digital X-ray sensor 8 shown in FIG. 15(a). S27 averages the data of the read line 12 shown in FIG. 15(a) to reduce noise in the line spread function (LSF) 17 that reads the focal spot size. S28 performs linear interpolation to interpolate data between pixels 8-1 of each read line 12. S29 defines the focal width 14-1 of the effective focal point 14 by dividing the width of the 15% value 17-5 of the maximum X-ray intensity of the averaged line spread function (LSF) 17 obtained from the averaged data by the expansion ratio E = 3.5.

[0044] FIG. 19 shows a detailed flow of the angle determination part in the flow chart of FIG. The detailed flow of the angle determination part starts from S8 in the focal length direction and from S23 in the focal width direction. Since the flow is similar in the focal length direction and the focal width direction, they are shown together in FIG. S8-1 and S23-1 generate a 10-line line spread function (LSF) 17 from each pixel data of the read line 12 shown in FIG. 13(a). S8-2 and S23-2 identify the maximum X-ray intensity 17-3 from the 10-line line spread function (LSF) 17. S8-3 and S23-3 specify 60% values ​​17-6 of the maximum X-ray intensities, which are a first predetermined ratio of the 10 lines from the maximum X-ray intensities 17-3. S8-4 and S23-4 specify the x'-y' coordinates of the 60% value 17-6 of each maximum X-ray intensity in each line spread function (LSF) 17 from the 60% value 17-6 of each maximum X-ray intensity, which is a first predetermined ratio. S8-5 and S23-5 draw an approximate straight line 16 on the x'-y' coordinate plane that connects the pixel 8-1 position to the left of the 60% value 17-6 of each maximum X-ray intensity, which is the first predetermined ratio of the 10 lines, and is parallel to the longitudinal direction of the single slit image 11-1. S8-6 determines the angle θ of an approximate straight line 16 parallel to the longitudinal direction of the single slit image 11-1 with respect to the y' axis of the X-ray image 11 as a reference. In step S23-6, the x'-axis of the X-ray image 11 is used as a reference to find the angle θ of an approximated straight line 16 parallel to the longitudinal direction of the single-slit image 11-1. S8-7 and S23-7 connect the pixel 8-1 positions on the right side of the 60% value 17-6 of each maximum X-ray intensity, which is the first predetermined ratio of the 10 lines, and draw an approximate straight line 16 parallel to the longitudinal direction of the single slit image 11-1. S8-8 determines the angle θ of an approximate straight line 16 parallel to the longitudinal direction of the single slit image 11-1 with respect to the y' axis of the X-ray image. In step S23-8, the x'-axis of the X-ray image is used as a reference to determine the angle θ of an approximated straight line 16 parallel to the longitudinal direction of the single-slit image 11-1. In steps S9 and S24, angle determination is started based on the obtained angle θ. When the angle θ between the approximate straight lines on the left and right sides of the X-ray image is both within ±1°, it is determined that the y'-axis or x'-axis of the two-dimensional digital X-ray sensor 8 has been positioned parallel to the longitudinal direction of the single-slit image 11-1 within ±1°.

[0045] In this embodiment, one slit 6-1 is rotated 90° using a single-slit camera rotation jig 5 to detect the focal width and focal length, but it is also possible to use a single-slit camera 6 that is independently arranged perpendicular to the camera so that the two slits 6-1 do not cross each other, and to detect the focal width and focal length by linearly moving the two slits 6-1 in the X direction and / or Y direction shown in FIG. 8 so as to rotate them 90° around a rotation axis perpendicular to the plane of the single-slit camera rotation jig 5. In this case, the distance between the two slits 6-1 must be 2.5 mm or more, which can be seen from the plan view of the single slit camera 6 defined in IEC 60336 4th edition or IEC 60336 5th edition shown in FIG.

[0046] To summarize the present invention, the objective of the present invention is to provide a simple focal spot dimension measurement method that satisfies the requirements of IEC 60336 5th edition using a 2D digital X-ray sensor 8 and reduces the number of data items used for noise reduction. The means for solving the objective is to use an X-ray tube focal spot dimension measurement device 1 that is composed of a power supply unit that drives the X-ray tube, an X-ray tube that is a source of X-rays, a single slit camera 6 with a continuously uniform slit width, and a 2D digital X-ray sensor 8, and to perform focal spot dimension measurement of an X-ray tube 3 by a step of averaging a signal having a line spread function 17 corresponding to the X-ray intensities of multiple lines that differ in the longitudinal direction of a slit 6-1 to calculate an averaged signal, and a step of calculating a focal spot dimension based on the width of two points that have a predetermined ratio to the maximum X-ray intensity 17-3 of the averaged signal having the line spread function 17. [Explanation of symbols]

[0047] 1. Main unit of the device (focus dimension measuring device) 2 Power supply section 2-1 Operating condition control circuit 2-2 High voltage power supply 2-3 Filament power supply 3 X-ray tube 3-1 X-ray output window 3-2 Anode 3-3 Cathode 3-4 Filament 3-5 Reference plane 4 Oil tank 5 Single slit camera rotation fixture 5-1 Upper plate 5-1-1 Recess 5-2 Lower plate 5-2-1 Convex part 6 Single-slit camera 6-1 Slit 6-2 X-ray entrance surface 7 2D digital X-ray sensor angle adjustment jig 7-1 2D digital X-ray sensor angle adjustment screw 8 2D digital X-ray sensor 8-1 pixels 8-2 X-ray sensor image receiving surface 9 Computer Department 9-1 Display device 10 pillars 11 X-ray image 11-1 Single slit image 11-2 Any one line 11-3 Pixel images 12 Reading Lines 13 Real focus 13-1 Focal width 13-2 Focal length 14 Effective Focus 14-1 Focal width 14-2 Focal length 15 Cross slit image 15-1 Slit 16 Approximate straight line 17 Line Spread Function (LSF) 17-1 Slit section 17-2 Non-irradiated area 17-3 Maximum X-ray intensity 17-4 Background level 17-5 15% of maximum X-ray intensity 17-6 60% of maximum X-ray intensity 18 Direction of Evaluation Df Focal width reading direction Dl Focal length reading direction E Magnification factor given by n / m Long axis of L X-ray tube O Origin: Center of the effective focal spot in the X-ray tube O'Origin': Center of a single slit O''Origin'': Center of 2D digital X-ray sensor R reference axis R' rotation axis S Symmetry axis Wc Width of the cross slit image in the direction perpendicular to the longitudinal direction of the slit Ws: The width of the single slit camera in the direction perpendicular to the longitudinal direction Wi: Longitudinal width of a single slit image k is the distance to the edge of the effective focal point farthest from the single slit camera m Distance between the X-ray incidence surface of the single slit camera and the reference surface n is the distance from the X-ray incidence surface of the single slit camera to the X-ray sensor image receiving surface p Distance to the edge of the effective focal point closest to the single slit camera x' is the row coordinate for the pixel arrangement of the two-dimensional digital X-ray sensor y' is the column coordinate of the pixel arrangement of the two-dimensional digital X-ray sensor θ Pixel arrangement of a two-dimensional digital X-ray sensor for a single slit image Angle in the y' (column) direction θs Angle from the vertical direction to the slit of a single slit camera δ1 Angle of the evaluation direction relative to the slit of the single slit camera δ2 Angle of the reading line direction to the single slit image

Claims

1. An X-ray tube which is a source of X-rays; A power supply unit that drives the X-ray tube; a slit camera having a slit whose width in a direction perpendicular to the longitudinal direction is continuously uniform along the longitudinal direction; a two-dimensional digital X-ray sensor that detects X-rays that have passed through a slit of a slit camera for a predetermined period of time, line by line, in a direction perpendicular to the longitudinal direction of the slit, and calculates a signal having a line spread function according to the intensity of the X-rays; In an apparatus for measuring focal spot dimensions of an X-ray tube, A step of averaging signals having a line spread function corresponding to the intensities of X-rays of a plurality of lines different in a longitudinal direction of the slit to calculate an averaged signal; calculating a focal spot size based on a width of two points having a predetermined ratio to a maximum value of an average signal having a line spread function; 1. A method for measuring a focal spot dimension of an X-ray tube, comprising:

2. 2. The method of claim 1, wherein the predetermined ratio is 15%.

3. 2. The method for measuring the focal spot dimension of an X-ray tube according to claim 1, wherein a plurality of pixels of the two-dimensional digital X-ray sensor are arranged in a direction perpendicular to the longitudinal direction of the slit and are arranged in the longitudinal direction of the slit.

Images