A cone beam CT device radiation source focal point center position calibration block and calibration method

Abstract

A kind of cone beam CT equipment radiation source focal point center position calibration block, including pressing plate A, pressing plate B;Multiple heavy metal material thin plates and multiple wave-transparent material thin plates are placed alternately superimposed, tiled between pressing plate A, pressing plate B, multiple heavy metal material thin plates and multiple wave-transparent material thin plates between pressing plate A, pressing plate B are tightly laminated by fastening bolt, form multiple slit passageways.A kind of cone beam CT equipment radiation source focal point center position calibration method, comprising the following steps: S1: establishing plane rectangular coordinate system in area imaging of area detector;S2: the imaging position x-axis coordinate calibration of radiation source focal point center on area detector;S3: the imaging position y-axis coordinate calibration of radiation source focal point center on area detector;S4: complete the imaging position calibration of radiation source focal point center on area detector.

Description

Technical Field

[0001] This invention relates to a calibration block and calibration method for measuring and adjusting the imaging position of the focal point of a cone-beam CT scanner's X-ray source on an area array detector. It can be used for rapid on-site testing and adjustment of the imaging position of the X-ray source focal point in a cone-beam CT scanner. Background Technology

[0002] When using a cone-beam CT scanner to acquire images of a workpiece, if the imaging position of the X-ray source's focal center on the area array detector deviates significantly from the center of the detector, it will result in poor image acquisition quality, low accuracy of 3D model reconstruction, and large dimensional measurement errors in the image processing software, making accurate measurement and normal use impossible. For initial use, periodic calibration, equipment replacement, and before high-precision image acquisition, the imaging position of the X-ray source's focal center on the area array detector must be calibrated and adjusted to ensure complete alignment between the X-ray source's focal center and the center of the area array detector. Alternatively, while meeting measurement accuracy and usage requirements, the imaging position of the X-ray source's focal center on the area array detector can be adjusted to ensure that its deviation from the detector center is within the allowable error range.

[0003] The standard GB / T 25758.3-2010, "Nondestructive Testing of Industrial X-ray Systems - Focus Characteristics - Part 3: Slit Camera Radiographic Method," specifies a method for measuring the focus of an industrial X-ray system using slit camera radiography. While the slit test block and measurement method specified in the standard can determine the size of the X-ray source focus, it cannot measure the deviation of the X-ray source focus center from the center of the area array detector. Furthermore, the slit test block specified in the standard is a single-slit type, requiring high precision in its placement and the angle between the X-ray beam and the slit's axis of symmetry. This complex testing process cannot meet the practical needs for rapid on-site testing and adjustment, quick calibration, and simple, convenient operation. Summary of the Invention

[0004] The purpose of this invention is to provide a calibration block and calibration method for the focal point position of a cone-beam CT device, so as to achieve accurate and rapid calibration of the imaging position of the focal point of the radiation source on the array detector.

[0005] The technical solution of the present invention is as follows: A cone-beam CT equipment X-ray source focal point center position calibration block includes a clamping plate A and a clamping plate B; multiple layers of heavy metal material thin plates and multiple layers of wave-transparent material thin plates are alternately stacked and laid flat between the clamping plate A and the clamping plate B, and the multiple layers of heavy metal material thin plates and multiple layers of wave-transparent material thin plates between the clamping plate A and the clamping plate B are tightly laminated by fastening bolts to form multiple narrow slit passages.

[0006] The clamping plate A, clamping plate B, the thin plate of heavy metal material, and the thin plate of wave-transparent material are all square.

[0007] A method for calibrating the focal point of a cone-beam CT scanner includes the following steps:

[0008] S1: Based on the pixel array and specific acquisition mode of the area array detector, take the horizontal direction of the area array detector as the x-axis, the vertical direction as the y-axis, and the coordinates of the first pixel array point P on the lower left side of the area array detector as (1,1), and establish a plane rectangular coordinate system in the area array detector imaging region.

[0009] S2: calibrate the x-axis coordinates of the imaging position of the X-ray source focal center on the area array detector. Place a calibration block vertically on the stage between the X-ray source and the area array detector, with the side of the calibration block close to the area array detector. The planes of clamping plates A and B are perpendicular to the area array detector. Adjust the horizontal relative positions of the X-ray source, stage, area array detector, and calibration block until the area array detector can acquire a DR image of the calibration block with a vertical bright line. Extract the grayscale curve of the entire image arbitrarily along line A parallel to the x-axis within the y-axis region y2 and y3 of the calibration block's bright line. Correlate the pixel values ​​of this grayscale curve along the x-axis with the pixel coordinates of the area array detector along the x-axis. Based on the changes in the grayscale values ​​of the image along line A, find the abrupt change point of the grayscale value on the grayscale curve corresponding to the vertical bright line. Draw a perpendicular line from this abrupt change point to the x-axis. The pixel coordinate value corresponding to the foot of the perpendicular along the x-axis is xA. xA is the x-axis coordinate of the imaging position of the X-ray source focal center on the area array detector.

[0010] S3: Calibrate the y-axis coordinate of the imaging position of the X-ray source focal center on the area array detector. Place a calibration block horizontally on the stage between the X-ray source and the area array detector, with the side of the calibration block close to the area array detector. Adjust the relative height of the X-ray source, stage, and area array detector until the area array detector can acquire a DR image of the calibration block with a horizontal bright line. Extract the grayscale curve of the entire image arbitrarily along line B parallel to the y-axis within the x-axis region x2 and x3 of the bright line of the calibration block. Correlate the pixel values ​​of the grayscale curve in the y-axis direction with the pixel coordinate values ​​in the y-axis direction of the area array detector. Based on the change of the image grayscale value on line B, find the grayscale value change point on the grayscale curve corresponding to the horizontal bright line. Draw a perpendicular line from this change point to the y-axis. The pixel coordinate value in the y-axis direction corresponding to the foot of the perpendicular is yB. ​​yB is the y-axis coordinate of the imaging position of the X-ray source focal center on the area array detector.

[0011] S4: Compare the obtained coordinates (xA, yB) with the coordinates (x1, y1) of the center of the array detector. If the coordinates are consistent or the position deviation of the coordinates is within the allowable range of this measurement, the calibration of the imaging position of the X-ray source focal center on the array detector is completed.

[0012] In step S1, all pixel array points within the imaging area of ​​the area array detector are assigned corresponding coordinate values ​​in a Cartesian coordinate system.

[0013] In S1, the smallest pixel array interval is defined as one smallest scale division.

[0014] In step S4, if the coordinate points are consistent or the positional deviation of the coordinate points is not within the allowable range of this measurement, the physical positions of the X-ray source, stage, and array detector are adjusted accordingly. Steps S1 to S3 are repeated until the image position coordinates (xA, yB) of the X-ray source focal center on the array detector are consistent with the center position coordinates (x1, y1) of the array detector, or the positional deviation of the coordinate points is within the allowable range of this measurement.

[0015] The significant advantages of this invention are: by employing a calibration block with a multi-slit stacked structure, the accuracy requirements for the placement of the calibration block are reduced when calibrating the imaging position of the X-ray source focal center on the area array detector, overcoming the drawback of requiring highly precise placement of a single slit test block for calibration testing. Based on the pixel array and specific acquisition mode of the area array detector, all pixel array points within the imaging area of ​​the area array detector are assigned corresponding coordinate values ​​in a Cartesian coordinate system. The imaging position coordinates of the X-ray source focal center on the area array detector are found by corresponding gray-scale value abrupt changes on the DR image gray-scale curve. This simplifies the on-site calibration method for the imaging position of the X-ray source focal center on the area array detector, optimizes the calibration operation process and steps, and effectively improves the efficiency of detection and calibration. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the calibration block structure;

[0017] Figure 2 A schematic diagram illustrating the establishment of a planar rectangular coordinate system within the imaging region of the area array detector;

[0018] Figure 3 A schematic diagram showing the positional relationship between the X-ray source, calibration block, stage, and array detector when calibrating the X-ray source focal center's imaging position on the array detector using the x-axis coordinate.

[0019] Figure 4 A schematic diagram showing the relationship between the extraction position and coordinate value of the vertical bright line and grayscale curve in the DR image when calibrating the image position of the focal center of the X-ray source on the array detector using the x-axis coordinate;

[0020] Figure 5 A schematic diagram showing the positional relationship between the X-ray source, calibration block, stage, and array detector when calibrating the y-axis coordinate of the imaging position of the X-ray source focal center on the array detector.

[0021] Figure 6 A schematic diagram showing the relationship between the extraction position and coordinate value of the horizontal bright line and grayscale curve in the DR image when calibrating the y-axis coordinate of the imaging position of the X-ray source focal center on the array detector;

[0022] In the diagram: 1. Clamping plate A; 2. Fastening bolt; 3. Thin sheet of heavy metal material; 4. Thin sheet of wave-transparent material; 5. Clamping plate B; 6. X-ray source; 7. Area array detector; 8. Calibration block; 9. Stage Detailed Implementation

[0023] A cone-beam CT X-ray source focal point center position calibration block and calibration method, comprising:

[0024] like Figure 1 As shown, multiple layers of heavy metal material sheets 3 and multiple layers of wave-transparent material sheets 4 are alternately stacked and laid flat between clamping plates A1 and B5. The multiple layers of heavy metal material sheets 3 and multiple layers of wave-transparent material sheets 4 between clamping plates A1 and B5 are tightly laminated with fastening bolts 2 to form multiple narrow slit passages, ensuring that the X-ray beam can pass through the calibration block at different height positions, reducing the accuracy requirements for the height position of the calibration block.

[0025] The clamping plate A1, clamping plate B5, heavy metal material plate 3, and wave-transparent material plate 4 are all square. The assembled calibration block is a cuboid structure. When placed horizontally, the height of the calibration block should be significantly less than the length and width of the calibration block.

[0026] Calibration method:

[0027] S1: Based on the pixel array and specific acquisition mode of the area array detector 7, with the horizontal direction of the area array detector 7 as the x-axis and the vertical direction as the y-axis, and the minimum pixel array interval as one minimum scale, and with the coordinates of the first pixel array point P on the lower left side of the imaging area of ​​the area array detector 7 as (1,1), establish a planar rectangular coordinate system within the imaging area of ​​the area array detector 7, such as... Figure 2 As shown, all pixel array points within the imaging area of ​​the area array detector 7 are assigned corresponding coordinate values ​​in a Cartesian coordinate system.

[0028] S2: When calibrating the x-axis coordinate of the imaging position of the focal center of X-ray source 6 on the array detector 7, a calibration block 8 is vertically placed on the stage 9 between X-ray source 6 and array detector 7, with the side of calibration block 8 close to array detector 7. The plane of calibration block clamping plate A1 or clamping plate B5 is perpendicular to array detector 7. Figure 3As shown; adjust the horizontal relative positions of the X-ray source 6, stage 9, area array detector 7, and calibration block 8 until the area array detector 7 can acquire a DR image of the calibration block 8 with a vertical bright line; arbitrarily extract the grayscale curve of the entire image along line A parallel to the x-axis within the y-axis region y2 and y3 of the calibration block's bright line, as shown. Figure 4 As shown, the pixel values ​​in the x-axis direction of the grayscale curve are associated with the pixel coordinates in the x-axis direction of the area array detector 7. Based on the change in the grayscale value of the image on line A, the grayscale value change point on the grayscale curve corresponding to the vertical bright line is found. A perpendicular line is drawn from the change point to the x-axis, and the pixel coordinate value in the x-axis direction corresponding to the foot of the perpendicular is xA. xA is the x-axis coordinate of the imaging position of the focal center of the X-ray source on the area array detector.

[0029] S3: When calibrating the y-axis coordinate of the imaging position of the X-ray source focal center on the array detector, a calibration block 8 is horizontally placed on the stage 9 between the X-ray source 6 and the array detector 7, with the side of the calibration block 8 close to the array detector 7. Figure 5 As shown; adjust the relative height of the X-ray source 6, stage 9, and array detector 7 until the array detector 7 can acquire the DR image of the calibration block 8 with a horizontal bright line; arbitrarily extract the grayscale curve of the entire image along line B parallel to the y-axis within the x-axis region x2 and x3 of the calibration block's bright line, as shown. Figure 6 As shown, the pixel values ​​in the y-axis direction of the grayscale curve are associated with the pixel coordinate values ​​in the y-axis direction of the area array detector. Based on the change in the grayscale value of the image on line B, the grayscale value change point on the grayscale curve corresponding to the horizontal bright line is found. A perpendicular line is drawn from this change point to the y-axis, and the pixel coordinate value in the y-axis direction corresponding to the foot of the perpendicular is yB. ​​yB is the y-axis coordinate of the imaging position of the focal center of the X-ray source on the area array detector.

[0030] S4: Compare the obtained coordinates (xA, yB) with the center coordinates (x1, y1) of the area array detector 7. If the coordinates match or the deviation is within the allowable range for this measurement, the calibration of the imaging position of the X-ray source focal center on the area array detector is complete. Otherwise, adjust the physical positions of the X-ray source 6, stage 9, and area array detector 7 accordingly, and repeat S1 to S3 until the imaging position coordinates (xA, yB) of the X-ray source focal center on the area array detector match the center coordinates (x1, y1) of the area array detector or the deviation is within the allowable range for this measurement. This completes the calibration of the imaging position of the X-ray source focal center on the area array detector.

[0031] The following examples further illustrate the present invention.

[0032] Use such as Figure 1The calibration block shown is used to correct and calibrate the imaging position of the X-ray source focal center on the area array detector. The heavy metal material plate 3 is made of tungsten, lead, or similar materials with absorption properties to ensure that the X-ray beam cannot penetrate the heavy metal material plate 3 to reach the area array detector. The wave-transparent material plate 4 is made of polyester, resin, or similar materials that are easily penetrated by X-rays to ensure that the X-ray beam can penetrate the wave-transparent material plate to reach the area array detector for imaging.

[0033] Multiple layers of heavy metal material sheets 3 and multiple layers of wave-transparent material sheets 4 are alternately stacked and laid flat between clamping plates A1 and B5. The layers are then tightly laminated using fastening bolts 2, forming multiple slit pathways within a height H1 that allow multiple X-ray beams to pass through. When the calibration block is placed horizontally, a DR image with horizontal bright lines can be generated on the area array detector as long as the horizontal X-ray beam is adjusted within the height H1 range. When the calibration block is placed vertically, a DR image with vertical bright lines can be generated on the area array detector as long as the vertical X-ray beam is adjusted within the width H1 range. This overcomes the drawback of requiring highly precise positioning of a single slit test block for calibration testing, effectively improving calibration and testing efficiency and shortening equipment position adjustment time.

[0034] Using a cone-beam X-ray scanning method, an area array detector with a pixel array size of 4096×4096 is used to acquire images in a 4096×4096 mode, and to correct the imaging position of the X-ray source focal center on the area array detector. In this image acquisition mode, the horizontal direction of the area array detector is used as the x-axis, the vertical direction as the y-axis, and the smallest pixel array interval is used as one minimum scale. The coordinates of the first smallest pixel array point p on the lower left side of the area array detector's imaging region are (1,1). A planar rectangular coordinate system is established within the area array detector's imaging region, as follows: Figure 2 As shown. The pixel coordinates (x1, y1) of the center point k of this area array detector in the above coordinate system are (2048, 2048). If an area array detector with a pixel array size of 4096×4096 is used, and image acquisition is performed in a 2048×2048 mode, the imaging position correction of the X-ray source focal center on the area array detector is performed. In this image acquisition mode, the horizontal direction of the area array detector is taken as the x-axis, the vertical direction as the y-axis, the interval between two smallest pixel arrays is taken as one smallest scale, and the coordinates of the area point p formed by the four smallest pixel array points on the lower left side of the area array detector's imaging area are (1,1). A planar rectangular coordinate system is established within the area array detector's imaging area, as shown. Figure 2 As shown. The pixel coordinates (x1, y1) of the center point k of this area array detector in the above coordinate system are (1024, 1024).

[0035] When calibrating the x-axis coordinate of the imaging position of the X-ray source focal center on the array detector, a calibration block 8 is vertically placed on the stage 9 between the X-ray source 6 and the array detector 7. The side of the calibration block 8 is as close as possible to the array detector 7, and the plane of the calibration block clamping plate A1 or clamping plate B5 is perpendicular to the array detector. Figure 3 As shown; adjust the horizontal relative positions of the X-ray source 6, stage 9, area array detector 7, and calibration block 8 until the area array detector 7 can acquire a DR image of the calibration block 8 with a vertical bright line; arbitrarily extract the grayscale curve of the entire image along line A parallel to the x-axis within the y-axis region y2 and y3 of the calibration block's bright line, as shown. Figure 4 As shown, the pixel values ​​in the x-axis direction of the grayscale curve are associated with the pixel coordinates in the x-axis direction of the area array detector 7. Based on the change in the grayscale value of the image on line A, the grayscale value change point on the grayscale curve corresponding to the vertical bright line in the DR image is found. A perpendicular line is drawn from this change point to the x-axis, and the pixel coordinate value in the x-axis direction corresponding to the foot of the perpendicular is xA. xA is the x-axis coordinate of the imaging position of the focal center of the X-ray source on the area array detector, such as xA=1967.

[0036] When calibrating the y-axis coordinate of the imaging position of the X-ray source focal center on the array detector, a calibration block 8 is horizontally placed on the stage 9 between the X-ray source 6 and the array detector 7, with the side of the calibration block 8 as close as possible to the array detector 7. Figure 5 As shown; adjust the relative height of the X-ray source 6, stage 9, and array detector 7 until the array detector 7 can acquire the DR image of the calibration block 8 with a horizontal bright line; arbitrarily extract the grayscale curve of the entire image along line B parallel to the y-axis within the x-axis region x2 and x3 of the calibration block's bright line, as shown. Figure 6 As shown, the pixel values ​​in the y-axis direction of the grayscale curve are associated with the pixel coordinate values ​​in the y-axis direction of the area array detector. Based on the change in the grayscale value of the image on line B, the grayscale value change point on the grayscale curve corresponding to the horizontal bright line in the DR image is found. A perpendicular line is drawn from this change point to the y-axis, and the pixel coordinate value in the y-axis direction corresponding to the foot of the perpendicular is yB. ​​yB is the y-axis coordinate of the imaging position of the focal center of the X-ray source on the area array detector, such as yB=2043.

[0037] The obtained coordinates of the imaging position of the X-ray source focal center on the array detector 7 (xA, yB), i.e. (1967, 2043), are compared with the coordinates of the center position of the array detector 7 (x1, y1), i.e. (2048, 2048). If there is a deviation in the coordinate values, and the deviation is within the allowable range of this measurement, the calibration of the imaging position of the X-ray source focal center on the array detector 7 is completed. Otherwise, the physical positions of the X-ray source, turntable, and detector are adjusted accordingly, and the above steps are repeated until the imaging position of the X-ray source focal center on the array detector 7 is (2048, 2048) or the difference is adjusted to an acceptable range. The calibration of the imaging position of the X-ray source focal center on the array detector of this device is then completed.

Claims

1. A method for calibrating the center position of the X-ray source focal spot in a cone-beam CT scanner, characterized in that: Includes the following steps: S1: Based on the pixel array and specific acquisition mode of the area array detector, take the horizontal direction of the area array detector as the x-axis, the vertical direction as the y-axis, and the coordinates of the first pixel array point P on the lower left side of the area array detector as (1,1), and establish a plane rectangular coordinate system in the area array detector imaging region. S2: calibrate the x-axis coordinates of the imaging position of the X-ray source focal center on the area array detector. Place a calibration block vertically on the stage between the X-ray source and the area array detector, with the side of the calibration block close to the area array detector. The planes of clamping plates A and B are perpendicular to the area array detector. Adjust the horizontal relative positions of the X-ray source, stage, area array detector, and calibration block until the area array detector can acquire a DR image of the calibration block with a vertical bright line. Extract the grayscale curve of the entire image arbitrarily along line A parallel to the x-axis within the y-axis region y2 and y3 of the calibration block's bright line. Correlate the pixel values ​​of this grayscale curve along the x-axis with the pixel coordinates of the area array detector along the x-axis. Based on the changes in the grayscale values ​​of the image along line A, find the abrupt change point of the grayscale value on the grayscale curve corresponding to the vertical bright line. Draw a perpendicular line from this abrupt change point to the x-axis. The pixel coordinate value corresponding to the foot of the perpendicular along the x-axis is xA. xA is the x-axis coordinate of the imaging position of the X-ray source focal center on the area array detector. S3: Calibrate the y-axis coordinate of the imaging position of the X-ray source focal center on the area array detector. Place a calibration block horizontally on the stage between the X-ray source and the area array detector, with the side of the calibration block close to the area array detector. Adjust the relative height of the X-ray source, stage, and area array detector until the area array detector can acquire a DR image of the calibration block with a horizontal bright line. Extract the grayscale curve of the entire image arbitrarily along line B parallel to the y-axis within the x-axis region x2 and x3 of the bright line of the calibration block. Correlate the pixel values ​​of the grayscale curve in the y-axis direction with the pixel coordinate values ​​in the y-axis direction of the area array detector. Based on the change of the image grayscale value on line B, find the grayscale value change point on the grayscale curve corresponding to the horizontal bright line. Draw a perpendicular line from this change point to the y-axis. The pixel coordinate value in the y-axis direction corresponding to the foot of the perpendicular is yB. ​​yB is the y-axis coordinate of the imaging position of the X-ray source focal center on the area array detector. S4: Compare the obtained coordinates (xA, yB) with the center position coordinates (x1, y1) of the array detector (7). If the coordinates are consistent or the position deviation of the coordinates is within the allowable range of this measurement, the calibration of the imaging position of the X-ray source focal center on the array detector is completed. In step S1, all pixel array points within the imaging area of ​​the area array detector are assigned corresponding coordinate values ​​in a Cartesian coordinate system; the minimum pixel array interval is defined as one minimum scale division. In step S4, if the coordinate points are consistent or the positional deviation of the coordinate points is not within the allowable range of this measurement, the physical positions of the X-ray source, the stage, and the array detector are adjusted accordingly, and steps S1 to S3 are repeated until the imaging position coordinates (xA, yB) of the X-ray source focal center on the array detector are consistent with the center position coordinates (x1, y1) of the array detector or the positional deviation of the coordinate points is within the allowable range of this measurement.

2. A calibration block for the focal point position of a cone-beam CT scanner, applied to the method described in claim 1, characterized in that: Includes clamping plate A and clamping plate B; multiple layers of heavy metal material thin plates and multiple layers of wave-transparent material thin plates are alternately stacked and laid flat between clamping plate A and clamping plate B, and the multiple layers of heavy metal material thin plates and multiple layers of wave-transparent material thin plates between clamping plate A and clamping plate B are tightly laminated by fastening bolts; The clamping plate A, clamping plate B, the thin plate of heavy metal material, and the thin plate of wave-transparent material are all square.

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