X-ray tube focal spot size measuring method

Abstract

To provide a simple focal spot size measuring method satisfying requirements of the fifth edition of IEC 60336 by using a two-dimensional digital X-ray sensor and reducing the number of data used for noise reduction.SOLUTION: An X-ray tube focal spot size measuring device comprises a power supply unit for driving an X-ray tube, the X-ray tube, the source of X-rays, a slit camera with a continuously uniform slit width, and a two-dimensional digital X-ray sensor. An X-ray tube focal spot size measuring method measures a focal spot size of the X-ray tube by the steps of: averaging signals having a line spread function corresponding to intensities of X-rays of a plurality of lines different in the longitudinal direction of the slit by using the X-ray tube focal spot size measuring device to calculate an averaged signal; and calculating the focal spot size on the basis of the width of two points having a prescribed ratio to a maximum value of an averaged signal having the line spread function.SELECTED DRAWING: Figure 17

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 using a digital detector and conforming to IEC60336 Edition 5.

Background Art

[0002] The focal spot characteristics of a diagnostic X-ray tube are defined in IEC60336. Up to Edition 4 of IEC60336, which was issued in 2005, it was stipulated to mainly analyze the characteristics of the focal spot using a film. However, there are many operational problems, and a reasonable measurement method to replace the film has been awaited. In recent years, since high-quality digital detectors have become easily available, in Edition 5 of IEC60336, which was issued in 2020, a digital detector has been applied to the measurement and analysis of focal spot characteristics instead of the film.

[0003] However, the concern when applying a digital detector is the quantization error. In Edition 5 of IEC60336, several requirements are stipulated to minimize the quantization error. · Requirement (1): The number of pixels in the width between two points having a value of 15% of the maximum X-ray intensity of the line spread function (LSF) is 60 or more. Or, 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 is 200 or more. · Requirement (3): The signal-to-noise ratio is 200 or more. · Requirement (4): When measuring the focal spot size, the evaluation direction is read vertically within ±1° with respect to the slit. A method for measuring the focal spot size that satisfies the above requirements (1) to (4) and uses a single-slit camera defined in Edition 4 of IEC60336 is required.

[0004] As a known example, a method of reading the shape of a cross-slit image and the shape of a pinhole image with a camera and measuring the focal spot size of an X-ray tube is disclosed in Patent Document 1. However, there is no description of a method of generating a line spread function from a single-slit image and measuring the focal spot size of an X-ray tube from the line spread function, so the method of Patent Document 1 cannot meet the requirements of IEC60336 Edition 5. Furthermore, there is a method of reducing noise to meet Requirement Item ▲2▼, but in Patent Document 1, in order to reduce the noise generated in the image, it is necessary to acquire a plurality of images and perform integration processing, so the amount of data to be handled becomes large and complicated.

Prior Art Documents

[0005]

Patent Document 1

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The first problem to be solved by the present invention is, regarding Requirement Item ▲2▼ of IEC60336 Edition 5 in the method for measuring the focal spot size of an X-ray tube, to reduce the amount of data to be handled, easily reduce the noise generated in the image, and increase the number of levels from the background level to the maximum X-ray intensity of the line spread function. The second problem to be solved by the present invention is in the method for measuring the focal spot size of an X-ray tube Regarding the requirements of IEC60336, Edition 5 ▲4▼, it is to determine the perpendicularity of the single-slit image and correct it when the single-slit image is not perpendicular.

Means for Solving the Problem

[0007] The method for measuring the focal spot size of the X-ray tube of the first invention of this case is an X-ray tube that is the X-ray source, 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 with respect to the longitudinal direction, a two-dimensional digital X-ray sensor that detects the X-rays of the slit passing through the slit of the slit camera one line at a time in a direction perpendicular to the longitudinal direction and calculates a signal having a line spread function according to the intensity of the X-rays, in an X-ray tube focal spot size measuring apparatus having a step of averaging signals having line spread functions according to the intensities of X-rays of a plurality of different lines in the longitudinal direction of the slit to calculate an averaged signal; a step of calculating the focal spot size based on the widths of two points having values of a predetermined ratio with respect to the maximum value of the averaged signal having a line spread function; It is characterized by having

[0008] The second invention of this case is the method for measuring the focal spot size of the X-ray tube of the first invention of this case wherein the predetermined ratio is 15%.

[0009] The third invention of this case is the method for measuring the focal spot size of the X-ray tube of the first invention of this case wherein the 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.

[0010] The method for measuring the focal spot size of the X-ray tube of the fourth invention of this case is an X-ray tube that is the X-ray source, a power supply unit that drives the X-ray tube, A slit camera having a slit with a width in a direction perpendicular to the longitudinal direction being continuous and uniform in the longitudinal direction, A two-dimensional digital X-ray sensor arranged on a plane in a row direction and a column direction perpendicular to the row direction, having a plurality of pixels for detecting the intensity of X-rays, A two-dimensional digital X-ray sensor angle adjustment jig for rotating the two-dimensional digital X-ray sensor on its plane, A display device, In an X-ray tube focal spot size measuring device having, Obtaining a signal having a line spread function corresponding to the intensities of X-rays of a plurality of different lines at a first predetermined interval in the longitudinal direction of the slit by the two-dimensional digital X-ray sensor; Calculating an angle between a straight line connecting a predetermined one of two points having a value of a first predetermined ratio with respect to the maximum value of a plurality of lines having a line spread function and the row direction or the column direction; Displaying on the display device when the angle is outside a predetermined angle range; Rotating the two-dimensional digital X-ray sensor using the angle adjustment jig so that the angle is within the predetermined range when the angle is outside the predetermined range; Detecting at least one line of X-rays passing through the slit of the slit camera by the two-dimensional digital X-ray sensor in a direction perpendicular to the longitudinal direction of the slit, and calculating a line spread function from the detected X-ray intensity signal; Calculating the focal spot size based on the widths of two points having a value of a second predetermined ratio with respect to the maximum value of the line spread function; Characterized by having.

[0011] The fifth invention of this case is the method for measuring the focal spot size of the X-ray tube of the fourth invention of this case In which, the step of displaying on the display device when the angle is outside the predetermined angle range is characterized in that it is a step of displaying the angle and the fact that the angle is outside the predetermined range on the display device.

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

[0013] The seventh invention of this case is a method for measuring the focus dimension of the X-ray tube of the fourth invention or the sixth invention of this case in which the second predetermined ratio is 15%, and the first predetermined ratio is larger than the second predetermined ratio.

[0014] The eighth invention of this case is a method for measuring the focus dimension of the X-ray tube of the seventh invention of this case in which the first predetermined ratio is a predetermined ratio that is not affected by the noise of the background level of the line spread function.

[0015] The ninth invention of this case is a method for measuring the focus dimension of the X-ray tube of the sixth invention of this case in which the second predetermined interval is smaller than the first predetermined interval.

[0016] The tenth invention of this case is a method for measuring the focus dimension of the X-ray tube of the sixth invention of this case in which the first predetermined interval is larger than the second predetermined interval.

[0017] The method for measuring the focus dimension of the X-ray tube of the eleventh invention of this case is an X-ray tube that 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 continuous and uniform with respect to the longitudinal direction, A two-dimensional digital X-ray sensor arranged on a plane in a row direction and a column direction perpendicular to the row direction and having a plurality of pixels for detecting the intensity of X-rays, A two-dimensional digital X-ray sensor angle adjustment jig for rotating the two-dimensional digital X-ray sensor on its plane, A display device, A slit rotation jig including a mechanism for moving at least one slit to rotate 90° about a rotation axis perpendicular to the plane of the slit camera, In a focal dimension measuring device having an X-ray tube having a focal width and a focal length, A first step of acquiring, by a two-dimensional digital X-ray sensor, a signal having a line spread function corresponding to the intensities of X-rays of a plurality of lines different at a first predetermined interval in the longitudinal direction of the slit; A second step of calculating an angle between a straight line connecting a predetermined one of two points having values of a first predetermined ratio with respect to the maximum value of a plurality of lines having a line spread function and the row direction or the column direction; A third step of displaying on the display device when the angle is outside a predetermined angle range; A fourth step of rotating the two-dimensional digital X-ray sensor by using the angle adjustment jig so that the angle is within a predetermined range when the angle is outside the predetermined range; A fifth step of detecting, by a two-dimensional digital X-ray sensor, at least one line of X-rays that have passed through the slit of the slit camera in a direction perpendicular to the longitudinal direction of the slit, and calculating a line spread function from the detected X-ray intensity signal; A sixth step of measuring one of the focal width and the focal length of the X-ray tube based on the width of two points having values of a second predetermined ratio with respect to the maximum value of the line spread function; A seventh step of moving at least one slit to rotate 90° about a rotation axis perpendicular to the plane of the slit camera by using the slit rotation jig; An eighth step of obtaining a signal having a line spread function according to the intensities 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; A ninth step of calculating an angle between a straight line connecting a predetermined one of two points having a value of a first predetermined ratio with respect to the maximum value of a plurality of lines having a line spread function and the row direction or the column direction; A tenth step of displaying on a display device when the angle is outside a predetermined angle range; An eleventh step of rotating the two-dimensional digital X-ray sensor using an angle adjusting jig so that the angle is within a predetermined range when the angle is outside the predetermined range; A twelfth step of detecting at least one line in a direction perpendicular to the longitudinal direction of the slit of X-rays that have passed through the slit of the slit camera by a two-dimensional digital X-ray sensor, and calculating a line spread function from the detected X-ray intensity signal; A thirteenth step of calculating the other of the focal width and the focal length of the X-ray tube based on the width between two points having a value of a second predetermined ratio with respect to the maximum value of the line spread function; characterized by having.

Effect of the Invention

[0018] The first invention of this case provides the following effects ▲1▼. · Effect ▲1▼: Suitable for the requirements ▲2▼ of IEC60336, Edition 5. By averaging a signal having a line spread function according to the intensities of X-rays of a plurality of different lines in the longitudinal direction of the slit, noise can be reduced.

[0019] The second invention of this case provides the following effect ▲2▼ in addition to the effect ▲1▼. · Effect ▲2▼: By calculating the focal dimension based on the width between two points having a value of 15% with respect to the maximum value of the averaged signal having a line spread function, it is possible to measure the focal dimension that satisfies the provisions of Clause 7.2 of IEC60336, Edition 5.

[0020] The third invention of this case provides the following effect ▲3▼ in addition to the effect ▲1▼. · Effect ▲3▼: The 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, so that the focal dimension can be read by simple calculation with a small number of lines of data.

[0021] The fourth invention of this case provides the following effect ▲4▼. · Effect ▲4▼: Since the evaluation direction can be read vertically within a predetermined angle θs (±1° in IEC 60336 Edition 5) with respect to the longitudinal direction of the slit, the requirements ▲4▼ of IEC 60336 Edition 5 in the method for measuring the focal dimension of the X-ray tube can be satisfied. The definition of θs will be described later.

[0022] In addition to effect ▲4▼, the fifth invention of this case provides the following effect ▲5▼. · Effect ▲5▼: By displaying on the display device that the angle θs and the angle θs are outside the predetermined range, it is possible to grasp that the evaluation direction is outside the range of the predetermined angle θs (±1° in IEC 60336 Edition 5) from the vertical with respect to the longitudinal direction of the slit and the angle θs.

[0023] In addition to effect ▲4▼, the sixth invention of this case provides effect ▲1▼.

[0024] In addition to effects ▲1▼ and ▲4▼, the seventh invention of this case provides the following effect ▲6▼. · Effect ▲6▼: Since the first predetermined ratio is larger than the second predetermined ratio, it is possible to make it less susceptible to the influence of noise at the background level when obtaining the angle θs between the evaluation direction and the direction perpendicular to the longitudinal direction of the slit.

[0025] In addition to effects ▲1▼, ▲4▼, and ▲6▼, the eighth invention of this case provides the following effect ▲7▼. · Effect ▲7▼: Since the first predetermined ratio is a predetermined ratio that is not affected by the noise at the background level of the line spread function, the angle θs of the slit of the slit camera can be accurately calculated.

[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, even if the slit is slightly inclined, the error in the focus dimension can be reduced.

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

[0028] The eleventh invention of this case provides the following effect ▲10▼ in addition to effect ▲4▼. · Effect ▲10▼: By moving at least one slit to rotate 90° around the rotation axis perpendicular to the plane of the slit camera by means of the slit rotation jig, the measurement of the focus width and the focus length can be easily switched.

Brief Description of the Drawings

[0029]

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Mode for Carrying Out the Invention

[0030] Hereinafter, with reference to the drawings, an embodiment of the present invention will be described in detail. This embodiment is configured as shown in Figs. 1 and 2. Fig. 1 shows the apparatus main body (focal dimension measuring device) 1 of the X-ray tube 3, and Fig. 2 shows the X-ray tube 3 with a fixed anode. In the apparatus main body (focus dimension measuring apparatus) 1 in the embodiment of FIG. 1, a power supply unit 2 and an X-ray tube 3 are connected. The oil tank 4 houses 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 column 10 and arranged on the reference axis R. The power supply unit 2 is composed of an operation condition control circuit 2-1, a high-voltage power supply 2-2, and a filament power supply 2-3. Incidentally, 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. A display device 9-1 is mounted on the computer unit 9. Incidentally, the apparatus main body 1 of the X-ray tube 3 may house the X-ray tube 3, the high-voltage power supply 2-2, the filament power supply 2-3, and the oil tank 4 in a case (not shown) to form a so-called X-ray head, or house the X-ray tube 3 and the oil tank 4 in a case (not shown), and separately place the high-voltage power supply 2-2 and the filament power supply 2-3, and connect them to the X-ray tube 3 with a cable (not shown).

[0031] FIG. 2 shows the X-ray tube 3 in the embodiment of FIG. 1. 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, there is a filament 3-4. When electric power is supplied from the filament power supply 2-3, thermoelectrons are generated by the filament 3-4, accelerated by the high-voltage power supply 2-2, and collide with the anode 3-2 to form an actual focal point 13. The point connecting the long axis L of the X-ray tube and the center of the actual focal point 13 becomes the origin 0, and the actual focal point 13 is formed on the origin 0. A line extending in the Z direction perpendicular to the origin 0 with respect to the long axis L of the X-ray tube 3 becomes the reference axis R. And, the plane along the long axis L is called a reference plane 3-5.

[0032] FIG. 3 is a schematic diagram of focus dimension measurement in the embodiment of FIG. 1. (a) shows the focus width, and (b) shows the schematic diagram when measuring the focus length. The distance n from the X-ray incident surface 6-2 of the single-slit camera 6 to the X-ray sensor imaging surface and the distance m from the X-ray incident surface 6-2 of the single-slit camera 6 to the reference plane 3-5 are arranged in a ratio of 3.5:1. In the focus width direction, the dimensions of the focus width 13-1 of the actual focus 13 and the focus width 14-1 of the effective focus 14 are the same, but in the focus length direction, the dimensions of the focus length 13-2 of the actual focus 13 and the focus length 14-2 of the effective focus 14 are different. In focus dimension measurement, it is specified in IEC60336 Edition 5 to measure the dimensions of the focus width 14-1 and the focus length 14-2 of the effective focus 14.

[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 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 6-1. Specifically, the width Ws in the direction perpendicular to the longitudinal direction of the slit 6-1 of the single-slit camera 6 is specified in Clause 5.2 of IEC60336 Edition 5. As shown in FIG. 4, it is 0.01 ± 0.002 mm, and those with a tolerance of about 20% are defined as uniform here. In Patent Document 1, since a cross-slit image 15 as shown in FIG. 6 is obtained, it does not satisfy the requirements of the slit camera required by Edition 5 of IEC60336 shown in FIGS. 4 and 5. Furthermore, in the case of the cross-slit image 15, the width Wc in the direction perpendicular to the longitudinal direction of the slit 15-1 of the cross-slit image 15 is discontinuous near the center and does not have a uniform width, so data cannot be acquired near the center of the X-ray sensor 8.

[0034] The focal spot size of the X-ray tube needs to measure the width and length, which can be achieved by rotating either the X-ray tube 3 or the single-slit camera 6 by 90°. In this embodiment, to simplify the configuration of the apparatus main body (focal spot size measuring device) 1 of the X-ray tube shown in FIG. 1, when measuring the focal width 14-1 and the focal length 14-2 of the effective focal spot 14 which is the focal spot size shown in FIG. 3, the position of the X-ray tube 3 is fixed. Therefore, when the directions of the focal width reading direction Df and the focal length reading direction D1 shown in FIG. 7 change by 90°, since it is necessary to change the direction of the single-slit camera 6, the longitudinal direction 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 rotating 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 every 90° on the same radius, and the lower plate 5-2 has protrusions 5-2-1 provided every 180° on the same radius. By fitting the recess of the upper plate 5-1 onto the protrusion of the lower plate 5-2, the single-slit camera 6 can be accurately rotated by 90°. Thereby, since the measurement of the focal spot size can be switched between the focal width reading direction Df and the focal length reading direction D1, the longitudinal direction of the slit 6-1 of the single-slit camera 6 can be arranged perpendicular to both measurements for both the focal width and the focal length. As shown in the simplified diagram representing the one-dimensional sensor and the two-dimensional sensor shown in IEC60336 Edition 5 of FIG. 9, it is necessary to arrange the longitudinal direction of the slit 6-1 of the single-slit camera 6 perpendicular to the evaluation direction 18. As described above, the longitudinal direction of the slit 6-1 of the single-slit camera 6 can be arranged perpendicular to the evaluation direction 18 in FIG. 9. In summary, by moving at least one slit 6-1 to rotate by 90° around the rotation axis perpendicular to the plane of the single-slit camera 6-1 by the single-slit camera rotating jig 5, the measurement of the focal width 14-1 and the focal length 14-2 can be easily switched.

[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 the intensity of X-rays with the sensor and digitizes it, 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. In the two-dimensional digital X-ray sensor 8, it is an arrangement of consecutive pixels 8-1 parallel to the x'(row) direction or parallel to the y'(column) direction, and what detects the X-ray intensity of each pixel 8-1 of the two-dimensional digital X-ray sensor 8 is called one line. Each of the numbers 1, 2, 3, ···, 2217800 in the pixel 8-1 numbers the pixels 8-1 in the x'(row) direction. Also, the two numbers in the parentheses below are the coordinates in the x'(row) direction and the y'(column) direction. The smaller the size of the pixel 8-1, the more advantageous it is for discretization, and in this embodiment, it is 20um×20um. Fig. 11(a) is the X-ray image 11 of the single-slit camera 6 obtained by the two-dimensional digital X-ray sensor 8, and no image processing peculiar to the two-dimensional digital X-ray sensor 8 is performed. In the X-ray image 11, the single-slit image 11-1 is blackened by the X-rays passing through the slit 6-1 of the single-slit camera 6. When the X-ray intensity is illustrated along any one line 11-2, a line spread function (LSF) 17 as shown in Fig. 11(b) is obtained. The part with strong X-ray intensity is the slit part 17-1, and the part with weak X-ray intensity is the non-irradiated part 17-2. In section 7.2 of IEC60336 Edition 5, as shown in Fig. 12, when measuring the focal dimension, it is stipulated to read the width of the two positions of the value 17-5 which is 15% of the maximum X-ray intensity of the line spread function (LSF) 17 which is the second predetermined ratio. The width of the two positions of the value 17-5 which is 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 dimension. The magnification E is obtained by n / m shown in Fig. 3, and in this embodiment, the magnification E = 3.5. From the above, the plurality of 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 by being arranged in the longitudinal direction of the slit 6-1, the focal dimension can be read with one line of data. However, the line spread function (LSF) 17 used for reading the focal dimension contains noise, and it is necessary to reduce the noise in order to perform measurements conforming to IEC60336 Edition 5. The noise reduction method will be described in detail in

[0038] .

[0036] FIG. 13(a) shows the positional relationship between the single-slit image when the angle θ obtained by the two-dimensional digital X-ray sensor in the measurement in the focal length direction is not within ±1° and the pixels of the corresponding two-dimensional digital X-ray sensor. 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 arrangement of the pixels 8-1 from which data is being read is defined as the read line 12. In order 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 with an interval of 100 rows of pixels 8-1 in the y' (column) coordinate direction at a first predetermined interval, and the data of the pixels 8-1 of the two-dimensional digital X-ray sensor 8 is calculated to obtain graphs of 10 line spread functions (LSF) 17 corresponding to the data of 10 read lines 12. The direction of this read line 12 coincides with the evaluation direction 18. FIG. 13(b) shows a total of 10 line spread functions (LSF) 17 corresponding to each read line 12 in FIG. 13(a). For the 10 line spread functions (LSF) 17, the pixel 8-1 positions of the value 17-6 which is 60% of the maximum X-ray intensity, which is the first predetermined ratio, are acquired on the x'-y' coordinates. The reason for setting the value 17-6 as 60% of the maximum X-ray intensity, which is the first predetermined ratio, is to avoid being affected by the noise of the background level 17-4 described in

[0038] . Since the first predetermined ratio is larger than the second predetermined ratio, when obtaining the angle θs between the evaluation direction 18 and the direction perpendicular to the longitudinal direction of the slit 6-1, it is possible to make it less susceptible to the influence of the noise of the background level 17-4. When the pixel 8-1 value of 60% of the maximum X-ray intensity, which is the first predetermined ratio, 17-6 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%. An approximate straight line 16 parallel to the longitudinal direction of the single-slit image 11-1 is obtained from the ten coordinate groups thus obtained by the least squares method. The approximate straight line 16 parallel to the longitudinal direction of the single-slit image 11-1 lies 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 the angle θ is obtained from the y'-axis parallel to the y' (column) direction. Since the first predetermined ratio is a predetermined ratio that is not affected by the 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 accurately calculated. θs will be described later in

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

[0037] The requirements recommended in IEC60336 Edition 5, Clause 6.3.1 to limit the error caused by discretization to about 1% are Requirements ▲1▼ to ▲3▼. Requirement ▲1▼ is whether the number of pixels 8-1 in the width of the 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, it is cleared by setting the size of the pixel 8-1 of the two-dimensional digital X-ray sensor 8 and the magnification E. By adopting a magnification ratio E = 3.5 and using a two-dimensional digital X-ray sensor 8 with a side length of 20 um for 1 pixel 8-1, in the case of a 0.4 mm focal spot X-ray tube, the number of pixels 8-1 between two points having a value 17-5 which is 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 claim 1 is satisfied. Since the number of pixels 8-1 between two points having a value 17-5 which is 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 for measuring the focal spot size of a 0.4 mm focal spot X-ray tube. However, in this embodiment, linear interpolation is applied so as to be applicable to measuring the focal spot size of an X-ray tube with a smaller focal spot. Claim 2 is that the number of levels from the background level 17-4 to the maximum X-ray intensity 17-3 of the line spread function (LSF) 17 is 200 or more. How this is realized in this embodiment will be

[0038] described later. Claim 3 is that the signal-to-noise ratio is 200 or more. 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 Co., Ltd., and since the signal-to-noise ratio is 700, the requirement of claim 3 is satisfied.

[0038] Regarding the fact that the number of levels from the background level 17-4 to the maximum X-ray intensity 17-3 of the line spread function (LSF) 17 corresponding to claim 2 above is 200 or more, in this embodiment, signals having a line spread function (LSF) 17 corresponding to the X-ray intensities of a plurality of different lines in the longitudinal direction of the slit 6-1 are averaged to reduce noise, thereby realizing it. As shown in FIG. 5, since 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, the width Wi in the longitudinal direction 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 width Wi in the longitudinal direction of the single-slit image 11-1 shown in FIG. 15(a) is the same width, the line spread function (LSF) 17 corresponding to the intensity of the X-rays obtained by detecting one line at a time in the direction perpendicular to the longitudinal direction of the single-slit image 11-1 theoretically has the same shape in a plurality of different reading lines 12 of the single-slit image 11-1. In this embodiment, in FIG. 10, data of 10 reading lines 12 are acquired with a pixel 8-1 interval of one row in the y'(column) coordinate direction that is the second predetermined interval, and the data of the pixels 8-1 of the two-dimensional digital X-ray sensor 8 are calculated to obtain graphs of 10 line spread functions (LSF) 17 corresponding to the data of the 10 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 reading lines 12. Spike-like noise occurs in each line spread function (LSF) 17, and since the appearance of this spike-like noise is different between the first line and the tenth line, it can be seen that it is random noise. This random noise is due to variations in the sensitivity of each pixel 8-1, thermal noise of each pixel 8-1, and electrical noise caused by the circuit that reads the signal for each pixel 8-1, and it 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 it becomes impossible to ensure a level number of 200 or more from the background level 17-4 to the maximum X-ray intensity 17-3. In the case of the line spread function (LSF) 17 at the 10th line, the maximum X-ray intensity 17-3 is 247 [LSB], and the background level 17-4 is 38 [LSB]. Therefore, more than 200 levels can be ensured from the background level 17-4 to the maximum X-ray intensity 17-3. However, the maximum X-ray intensity 17-3 is apparently increased in the apparent maximum X-ray intensity 17-3 due to the influence of noise. In addition, in the non-irradiated portion 17-2, there is a portion exceeding the value 17-5 which is 15% of the maximum X-ray intensity due to the influence of noise, so an error occurs in the reading of the focal dimension. In order to eliminate these influences and perform stable and accurate reading, it is necessary to reduce noise. In order to reduce noise, the 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 the direction perpendicular to the longitudinal direction of the single slit image 11-1 is acquired for a plurality of lines, in this embodiment, 10 lines. The outputs of a plurality of different pixels 8-1 arranged in the longitudinal direction, in this embodiment, 10 pixels 8-1 are averaged, and the variation in sensitivity of each pixel 8-1 is reduced by the averaging. The line spread function corresponding to the intensity of X-rays including electrical noise obtained by detecting one line at a time in the direction perpendicular to the longitudinal direction of the single slit image 11-1 is acquired for 10 lines, and the outputs of 10 different pixels 8-1 arranged in the longitudinal direction are averaged, and the electrical noise is simultaneously reduced by the 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 the data for 10 lines. The maximum X-ray intensity 17-3 is 222 [LSB], and the background level 17-4 is 13 [LSB]. Therefore, by averaging the data for 10 lines, the requirements of claim 2 are satisfied. In order to satisfy the requirements of claim 2, by performing noise reduction by averaging, the focal dimension can be measured satisfying the provisions of item 7.2 of IEC 60336, fifth edition, by calculating the focal dimension based on the width between two points having a value of 15% with respect to the maximum value of the averaged signal having the line spread function (LSF) 17. The method of averaging the data for 10 lines described above to reduce noise only handles the data of the signal with the line spread function in the image to perform noise reduction, compared with the method of reducing noise using the data of the entire conventional image. Therefore, the number of data to be handled can be reduced, and the reduction of the software capacity and the increase of the operation speed can be realized. Thus, the number of data to be handled is small, and the noise generated in the image can be easily reduced. The number of levels from the background level to the maximum X-ray intensity of the line spread function is increased to satisfy Requirement 2, and the first problem is solved. The reading line 12 in Fig. 15(a) reads 10 lines of data with an interval of one line in the y'(column) coordinate direction, which is the second predetermined interval, in this embodiment, and 10 graphs of the line spread function (LSF) 17 are obtained from the data of the pixel 8-1 of the two-dimensional digital X-ray sensor 8. Since the one-line interval in the y'(column) coordinate direction, which is the second predetermined interval, is smaller than the 100-line interval, which is the first predetermined interval, even if the single-slit image 11-1 is slightly tilted, the deviation in the x'(row) coordinate direction of each line spread function (LSF) 17 becomes smaller, the error at the time of averaging becomes smaller, and the error of the focal dimension can be reduced. In other words, since the 100-line interval, which is the first predetermined interval, is larger than the one-line interval, which is the second predetermined interval, the angle θs of the slit 6-1 of the single-slit camera 6 can be calculated more accurately. It becomes easier to capture the tilt of the single-slit image 11-1. In this embodiment, generally, the two-dimensional digital X-ray sensor 8 has high reliability near the center. Therefore, when measuring the focal dimension, data is acquired near the center of the two-dimensional digital X-ray sensor 8. The second predetermined interval may be read continuously without an interval. In other words, the second predetermined interval may be zero lines.

[0039] In paragraph 5.5.4 of the 5th edition of IEC60336, it is stated 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°." When measuring the focal dimension, the evaluation direction 18 is specified to be read perpendicular to the slit 6-1 of the single-slit camera 6 within ±1°, which corresponds to requirement item ▲4▼. However, as shown in Fig. 9, when the sensor for reading is a one-dimensional sensor, the one-dimensional sensor must be arranged within ±1°(θs) in the vertical direction with respect to the longitudinal direction of the slit 6-1 of the single-slit camera 6. When the sensor for reading is a two-dimensional sensor, it is stated that as long as the evaluation direction (direction of evaluation) 18 is perpendicular to the slit 6-1 of the single-slit camera 6 within ±1°(θs), it is not necessary to arrange the two-dimensional sensor within ±1° in the vertical direction with respect to the longitudinal direction of the slit 6-1 of the single-slit camera 6.

[0040] By arranging 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 shown in Fig. 14 and the single-slit image 11-1 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 Fig. 9, and the θ in the angle δ2 and the θs in the angle δ1 are the same. Therefore, in this embodiment, it is calculated whether θ is within ±1°(θs) and controlled to be within ±1° to satisfy requirement item ▲4▼.

[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 (in this embodiment, the two-dimensional digital X-ray sensor 8), X-rays passing through the slit 6-1 of the single-slit camera 6 are acquired by the two-dimensional digital X-ray sensor 8, the angle θ of the single-slit image 11-1 projected on the obtained X-ray image 11 is calculated by an operation within software, the position of the pixel 8-1 of the two-dimensional digital X-ray sensor 8 arranged perpendicular to the single-slit image 11-1 is determined, and by acquiring the data of this pixel 8-1, there is a method of performing reading perpendicular to the single-slit image 11-1 within ±1°. Also, by calculating the angle θ on the X-ray image 11 by an operation within 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 then acquiring the data of the pixels 8-1 arranged in the X’ (row) direction, there is also a method of performing reading perpendicular to the single-slit image 11-1 within ±1°. As described above, it is possible to perform reading perpendicular to the single-slit image 11-1 within ±1° with the single-slit image 11-1 obtained by the two-dimensional digital X-ray sensor 8 being in an inclined state by an operation within software, but it requires complex calculations. In this embodiment, as a method of easily performing reading perpendicular to the single-slit image 11-1 using the two-dimensional digital X-ray sensor 8, by arranging the pixels 8-1 arranged in the x’ (row) direction of the two-dimensional digital X-ray sensor 8 within ±1° in the vertical direction with respect to the longitudinal direction of the single-slit image 11-1, a method of performing reading perpendicular to the single-slit image 11-1 within ±1° without performing an operation within software is used. Thereby, if there is at least one line composed of the pixels 8-1 arranged in the x’ (row) direction of the two-dimensional digital X-ray sensor 8, the focal dimension can be read. Considering performing noise reduction by averaging as shown in

[0038] , if there are 2 to 10 lines, the focal dimension can be read. However, when measuring the focal dimension by calculation within software without arranging the two-dimensional sensor within ±1° in the vertical direction with respect to the longitudinal direction of the slit 6-1 of the single-slit camera 6, as can be seen from the right side of FIG. 9, 10 or more lines are required for the lines composed of the pixels 8-1 arranged in the x' (row) direction of the two-dimensional digital X-ray sensor 8. Therefore, by using the method of this embodiment, the focal dimension can be read by simple calculation with data of a small number of lines. Regarding the arrangement of the pixels 8-1 arranged in the x' (row) direction of the two-dimensional digital X-ray sensor 8 within ±1° in the vertical direction with respect to the longitudinal direction of the single-slit image 11-1, the angle θ is obtained by the method described in

[0036] , and the fact that the angle θs and the angle θs are outside the predetermined range is displayed on the display device 9-1, so that it can be grasped that the evaluation direction 18 is outside the range of a predetermined angle θs (±1° in IEC 60336, 5th edition) from the vertical with respect to the longitudinal direction of the slit 6-1 and the angle θs. As described above, in this embodiment, θ in the angle δ2, the evaluation direction in the standard, and θs in the angle δ1 of the slit are the same, and the evaluation direction 18 can be read vertically within a predetermined angle θs (±1° in IEC 60336, 5th edition) with respect to the longitudinal direction of the slit 6-1. Therefore, the requirements of item ▲4▼ of IEC 60336, 5th edition in the method for measuring the focal dimension of the X-ray tube can be satisfied.

[0042] FIG. 16 is a diagram showing a two-dimensional digital X-ray sensor angle adjustment jig 7 capable of adjusting the angle of the two-dimensional digital X-ray sensor. By fixing the two-dimensional digital X-ray sensor 8 to the two-dimensional digital X-ray sensor angle adjustment jig 7 and rotating the two-dimensional digital X-ray sensor angle adjustment screw 7-1 clockwise or counterclockwise, the two-dimensional digital X-ray sensor 8 can be rotated with respect to the rotation axis R'. By rotating the two-dimensional digital X-ray sensor 8, the position of the pixels 8-1 arranged in the x'(row) direction of the two-dimensional digital X-ray sensor 8 can be adjusted with respect to the longitudinal direction of the single-slit image 11-1, thus solving the second problem. The rotation axis R' does not have to coincide with the reference axis R, but it is easier to adjust the position of the pixels 8-1 arranged 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 if it is as close as possible to the reference axis R.

[0043] Figure 17 is an operation flowchart of this embodiment. In S1, the computer unit 9 is operated to start image acquisition in order to measure the focal length 14-2 with the two-dimensional digital X-ray sensor 8. In S2, the operation condition control unit 2-1 is operated to start X-ray exposure. In S3, when the set time (5 seconds in this embodiment) has elapsed, the exposure is terminated. In S4, the capture of the dark image is started. The dark image is an image without X-ray exposure. In S5, when the set time (5 seconds in this embodiment) has elapsed, the capture of the dark image is terminated. In S6, dark subtraction correction is started. When using the two-dimensional digital X-ray sensor 8, since the sensor reacts to X-rays in the atmosphere, it is necessary to perform image processing specific to the two-dimensional digital X-ray sensor 8 of subtracting the dark image from the X-ray exposed image. In S7, it is confirmed that the dark subtraction correction has been completed. In S8, the data of each pixel 8-1 of the reading line 12 shown in Fig. 13(a) is output from the image on which the dark subtraction correction has been performed. In S9, the angle θ between the approximate straight line 16 parallel to the longitudinal direction of the single-slit image 11-1 shown in Fig. 13(a) and the y'-axis parallel to the y'(column) direction 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 is calculated, and the pass / fail is determined. In S9-1, when the angle is within ±1°, OK is displayed on the display device 9-1. In S9-2, when the angle is not within ±1°, NG is displayed on the display device 9-1. When NG is displayed on the display device 9-1, after mechanically adjusting the angle of the X-ray sensor 8, return to S1. S10 displays the angle θ on the display device 9-1. When the angle determination in S11 is OK, it outputs the 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. 14(a). In order to reduce the noise of the line spread function (LSF) 17 for reading the focus size, S12 averages the data of the line spread function (LSF) 17 in each reading line 12 shown in FIG. 15(a). S13 performs linear interpolation to interpolate the data between the pixels 8-1 of each reading line 12. S14 divides the width of the 15% value 17-5 of the maximum X-ray intensity, which is the second predetermined ratio of the averaged line spread function (LSF) 17 obtained from the averaged data, by the magnification factor E = 3.5 to define the focal length 14-2 of the effective focal spot 14. S15 rotates the single-slit camera 6 by 90°. 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. S17 operates the operation condition control unit 2-1 to start X-ray irradiation. S18 terminates the irradiation when the set time (5 seconds in this embodiment) has elapsed. S19 starts capturing a dark image. S20 terminates the capture of the dark image when the set time (5 seconds in this embodiment) has elapsed. S21 starts dark subtraction correction. S22 confirms that the dark subtraction correction has ended. S23 outputs the data of each pixel 8-1 of the reading line 12 shown in FIG. 18(a) from the image subjected to dark subtraction correction. S24 calculates the angle θ between the approximate 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 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 determines pass or fail. When the angle of S24-1 is within ±1°, the display device 9-1 displays OK. When the angle of S24-2 is not within ±1°, the display device 9-1 displays NG. When NG is displayed on the display device 9-1, after mechanically adjusting the angle of the two-dimensional digital X-ray sensor 8, return to S16. Here, it can also be confirmed that the single-slit camera 6 can be rotated 90°. S25 displays the angle θ on the display device 9-1. When the angle determination is OK in S26, each pixel 8-1 data of the reading line 12 near the center of the two-dimensional digital X-ray sensor 8 shown in Fig. 15(a) is output. In S27, in order to reduce the noise of the line spread function (LSF) 17 for reading the focal dimension, the data of the reading line 12 shown in Fig. 15(a) is averaged. S28 performs linear interpolation to interpolate the data between the pixels 8-1 of each reading line 12. In S29, 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 is divided by the magnification factor E = 3.5 to define the focal width 14-1 of the effective focal point 14.

[0044] Fig. 19 is a detailed flow of the angle determination part in the flowchart of Fig. 17. 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 flows in the focal length direction and the focal width direction are the same, they are shown together in Fig. 19. S8-1 and S23-1 generate a 10-line line spread function (LSF) 17 from each pixel data of the reading line 12 shown in Fig. 13(a). S8-2 and S23-2 identify each maximum X-ray intensity 17-3 from the 10-line line spread function (LSF) 17. S8-3 and S23-3 identify the 60% value 17-6 of each maximum X-ray intensity, which is the first predetermined ratio of the 10 lines, from each maximum X-ray intensity 17-3. S8-4 and S23-4 identify the x'-y' coordinates of the 60% value 17-6 of each maximum X-ray intensity, which is a first predetermined ratio, from the 60% value 17-6 of each maximum X-ray intensity in each line spread function (LSF) 17. S8-5 and S23-5 connect the pixel 8-1 positions on the left side of the 60% value 17-6 of each maximum X-ray intensity, which is a first predetermined ratio of 10 lines, and draw an approximate straight line 16 parallel to the longitudinal direction of the single slit image 11-1 on the x'-y' coordinate plane. S8-6 determines the angle θ of the approximate straight line 16 parallel to the longitudinal direction of the single slit image 11-1 with reference to the y' axis of the X-ray image 11. S23-6 determines the angle θ of the approximate straight line 16 parallel to the longitudinal direction of the single slit image 11-1 with reference to the x' axis of the X-ray image 11. 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 a first predetermined ratio of 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 the approximate straight line 16 parallel to the longitudinal direction of the single slit image 11-1 with reference to the y' axis of the X-ray image. S23-8 determines the angle θ of the approximate straight line 16 parallel to the longitudinal direction of the single slit image 11-1 with reference to the x' axis of the X-ray image. S9 and S24 start the angle determination based on the obtained angle θ. When the angles θ of the approximate straight line on the left side and the approximate straight line on the right side of the X-ray image are both within ±1°, it is determined that the y' axis or the x' axis of the two-dimensional digital X-ray sensor 8 can be arranged parallel to the longitudinal direction of the single slit image 11-1 within ±1°.

[0045] In this embodiment, a single slit camera rotation jig 5 is used to rotate one slit 6-1 by 90° to detect the focal width and the focal length. However, a single slit camera 6 in which two slits 6-1 are independently arranged vertically at 90° so as not to intersect each other can be used. The two slits 6-1 are rotated by 90° around a rotation axis perpendicular to the plane of the single slit camera rotation jig 5, and linearly moved in the X direction and / or the Y direction shown in FIG. 8 to detect the focal width and the focal length. In this case, the distance between the two slits 6-1 needs to be ensured to be 2.5 mm or more, and can be read from the plan view of the single-slit camera 6 defined in IEC60336 Edition 4 or IEC60336 Edition 5 shown in FIG. 5.

[0046] Summarizing the present invention, it is an object to provide a simple focal spot size measurement method that satisfies the requirements of IEC60336 Edition 5 using a two-dimensional digital X-ray sensor 8 and reduces the amount of data used for noise reduction. As a means for solving the problem, an X-ray tube focal spot size measuring apparatus 1 including a power supply unit for driving an X-ray tube, an X-ray tube as an X-ray generation source, a single-slit camera 6 having a continuously uniform slit width, and a two-dimensional digital X-ray sensor 8 is used. A step of averaging signals having a line spread function 17 corresponding to the intensities of X-rays of a plurality of different lines in the longitudinal direction of the slit 6-1 to calculate an averaged signal; and a step of calculating the focal spot size based on the widths of two points having a value of a predetermined ratio with respect to the maximum X-ray intensity 17-3 of the averaged signal having the line spread function 17. This is a means for measuring the focal spot size of the X-ray tube 3.

Explanation of Signs

[0047] 1 Apparatus main body (focal spot size measuring apparatus) 2 Power supply unit 2-1 Operation 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 jig 5-1 Upper plate 5-1-1 Concave portion 5-2 Lower plate 5-2-1 Convex portion 6 Single-slit camera 6-1 Slit 6-2 X-ray incident surface 7 Two-Dimensional Digital X-Ray Sensor Angle Adjustment Fixture 7-1 Two-Dimensional Digital X-Ray Sensor Angle Adjustment Screw 8 Two-Dimensional Digital X-Ray Sensor 8-1 Pixel 8-2 X-Ray Sensor Image-Receiving Surface 9 Computer Unit 9-1 Display Device 10 Support Column 11 X-Ray Image 11-1 Single-Slit Image 11-2 Arbitrary One Line 11-3 Pixel Image 12 Reading Line 13 Actual Focus 13-1 Focus Width 13-2 Focus Length 14 Effective Focus 14-1 Focus Width 14-2 Focus Length 15 Cross-Slit Image 15-1 Slit 16 Approximate Straight Line 17 Line Spread Function (LSF) 17-1 Slit Portion 17-2 Non-Irradiated Portion 17-3 Maximum X-Ray Intensity 17-4 Background Level 17-5 Value of 15% of the Maximum X-Ray Intensity 17-6 Value of 60% of the Maximum X-Ray Intensity 18 Evaluation Direction Df Focus Width Reading Direction D1 Focus Length Reading Direction E Magnification Given in n / m L Long Axis of the X-Ray Tube 0 Origin: Center of the Effective Focus in the X-Ray Tube 0’ Origin’: Center of the Single Slit 0’’ Origin’’: Center of the Two-Dimensional Digital X-Ray Sensor R Reference Axis R’ Rotation Axis S Symmetry Axis Width in the direction perpendicular to the longitudinal direction of the slit of the Wc cross slit image Width in the direction perpendicular to the longitudinal direction of the slit of the single slit camera Ws Longitudinal width of the single slit image Wi Distance k to the farthest effective focal point end of the single slit camera Distance m between the X-ray incident surface and the reference surface of the single slit camera Distance n from the X-ray incident surface to the X-ray sensor imaging surface of the single slit camera Distance p to the nearest effective focal point end of the single slit camera Coordinate x' in the row direction with respect to the pixel arrangement of the two-dimensional digital X-ray sensor Coordinate y' in the column direction with respect to the pixel arrangement of the two-dimensional digital X-ray sensor Angle θ in the y' (column) direction with respect to the pixel arrangement of the two-dimensional digital X-ray sensor for the single slit image Angle θs from the direction perpendicular to the slit of the single slit camera Angle δ1 in the evaluation direction with respect to the slit of the single slit camera Angle δ2 in the reading line direction with respect to the single slit image

Claims

1. an X-ray tube which is a source of X-rays, a power supply unit for driving the X-ray tube, a slit camera having a slit whose width in a direction perpendicular to the longitudinal direction is continuous and uniform with respect to the longitudinal direction, a two-dimensional digital X-ray sensor arranged on a plane in a row direction and a column direction perpendicular to the row direction, and having a plurality of pixels for detecting the intensity of X-rays, a two-dimensional digital X-ray sensor angle adjustment jig for rotating the two-dimensional digital X-ray sensor on its plane, a display device, in an X-ray tube focal spot size measuring apparatus having: a step of acquiring, by the two-dimensional digital X-ray sensor, a signal having a line spread function corresponding to the intensities of X-rays of a plurality of different lines at a first predetermined interval in the longitudinal direction of the slit; a step of calculating an angle between a straight line connecting a predetermined one of two points having values of a first predetermined ratio with respect to the maximum value of a plurality of lines having the line spread function and the row direction or the column direction; a step of displaying on the display device when the angle is outside a predetermined angle range; a step of rotating the two-dimensional digital X-ray sensor using the angle adjustment jig so that the angle is within a predetermined angle range when the angle is outside the predetermined angle range; a step of detecting, by the two-dimensional digital X-ray sensor, at least one line of X-rays that have passed through the slit of the slit camera in a direction perpendicular to the longitudinal direction of the slit, and calculating a line spread function from the detected X-ray intensity signal; a step of calculating a focal spot size based on the width of two points having values of a second predetermined ratio with respect to the maximum value of the line spread function; characterized by comprising. A method for measuring the focal spot size of an X-ray tube.

2. The method for measuring the focal spot size of an X-ray tube according to claim 1, wherein the step of displaying on the display device when the angle is outside a predetermined angle range is a step of displaying on the display device the angle and the fact that the angle is outside the predetermined range.

3. In claim 1, the step of detecting, by a two-dimensional digital X-ray sensor, X-rays that have passed through the 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 the detected X-ray intensity signals is a step of detecting, by a two-dimensional digital X-ray sensor, X-rays that have passed through the slit of the slit camera for a predetermined period in a plurality of different lines in a direction perpendicular to the longitudinal direction of the slit, and averaging signals having line spread functions corresponding to the intensities of the X-rays in the plurality of 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 widths of two points having values of a second predetermined ratio with respect to the maximum value of the line spread function is a step of calculating the focal dimension based on the widths of two points having values of a second predetermined ratio with respect to the maximum value of the averaged signal having the line spread function. A method for measuring the focal dimension of an X-ray tube, characterized in that.

4. In claim 1 or claim 3, the second predetermined ratio is 15%, and the first predetermined ratio is larger than the second predetermined ratio. A method for measuring the focal dimension of an X-ray tube, characterized in that.

5. In claim 4, the first predetermined ratio is a predetermined ratio that is not affected by the noise of the background level of the line spread function. A method for measuring the focal dimension of an X-ray tube, characterized in that.

6. In claim 3, the second predetermined interval is smaller than the first predetermined interval. A method for measuring the focal dimension of an X-ray tube, characterized in that.

7. In claim 3, the first predetermined interval is larger than the second predetermined interval. A method for measuring the focal dimension of an X-ray tube, characterized in that.

8. An X-ray tube that is a source of X-rays, A power supply unit that drives the X-ray tube, A slit camera having at least one slit whose width in a direction perpendicular to the longitudinal direction is continuous and uniform in 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, for detecting the intensity of X-rays, A two-dimensional digital X-ray sensor angle adjustment jig for rotating the two-dimensional digital X-ray sensor on its plane, A display device, A slit rotation jig including a mechanism for moving at least one slit so as to rotate 90° about 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 the above, A first step of obtaining a signal having a line spread function according to the intensities of a plurality of different lines of X-rays at a first predetermined interval in the longitudinal direction of the slit by a two-dimensional digital X-ray sensor; A second step of calculating an angle between a straight line connecting a predetermined one of two points having a value of a first predetermined ratio with respect to the maximum value of a plurality of lines having a line spread function and the row direction or the column direction; A third step of displaying on a display device when the angle is outside a predetermined angle range; A fourth step of rotating the two-dimensional digital X-ray sensor by using an angle adjustment jig so that the angle is within the predetermined range when the angle is outside 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 by the two-dimensional digital X-ray sensor in a direction perpendicular to the longitudinal direction of the slit, and calculating a line spread function from the detected X-ray intensity signal; A sixth step of calculating one of the focal width and the focal length of the X-ray tube based on the width between two points having a value of a second predetermined ratio with respect to the 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 90° about a rotation axis perpendicular to the plane of the slit camera; An eighth step of obtaining a signal having a line spread function according to the intensities of a plurality of different lines of X-rays at a first predetermined interval in the longitudinal direction of the slit by a two-dimensional digital X-ray sensor; A ninth step of calculating an angle between a straight line connecting a predetermined one of two points having a value of a first predetermined ratio with respect to the maximum value of a plurality of lines having a line spread function and the row direction or the column direction; A tenth step of displaying on a display device when the angle is outside a predetermined angle range; An eleventh step of rotating the two-dimensional digital X-ray sensor by using an angle adjustment jig so that the angle is within the predetermined range when the angle is outside the predetermined range; A twelfth step of detecting at least one line of X-rays that have passed through the slit of the slit camera by the two-dimensional digital X-ray sensor in a direction perpendicular to the longitudinal direction of the slit, and calculating a line spread function from the detected X-ray intensity signal; A thirteenth step of calculating the other of the focal width and the focal length of the X-ray tube based on the width between two points having a value of a second predetermined ratio with respect to the maximum value of the line spread function; An X-ray tube focal dimension measurement method, characterized by comprising the above steps.

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