CN115046505A - X-ray focal spot measuring device and method for high-energy electron linear accelerator - Google Patents
X-ray focal spot measuring device and method for high-energy electron linear accelerator Download PDFInfo
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Abstract
The invention provides a device and a method for measuring X-ray focal spots of a high-energy electronic linear accelerator, wherein the device comprises a first thick metal test board, a second thick metal test board, a linear sliding table, a flat panel detector and an X-ray source of the electronic linear accelerator, a first thick metal test board or a second thick metal test board is detachably arranged on a sliding block of the linear sliding table, the linear sliding table is positioned between the flat panel detector and the X-ray source of the electronic linear accelerator, a first thick metal round hole is formed in the center of the first thick metal test board, a second thick metal round hole is formed in the center of the second thick metal test board, the method comprises the steps of collecting DR images of X-ray beams of the high-energy accelerator passing through the first thick metal round hole and the second thick metal round hole under different amplification factors to obtain a round hole edge response function, and then reconstructing an image of the X-ray focal spots of the accelerator by a filtering back-projection algorithm, the measurement of high energy electron linear accelerator X ray source focal spot size is realized to this application, and application scope is wide.
Description
Technical Field
The invention relates to the field of focal spot measurement, in particular to an X-ray focal spot measuring device and method for a high-energy electron linear accelerator.
Background
The size of an X-ray focal spot of an electronic linear accelerator is one of the key factors for determining the image quality of nondestructive testing imaging systems such as high-energy industrial CT, digital radiography DR and the like. Theoretically, the smaller the accelerator X-ray focal spot size, the sharper the image. To improve image quality, imaging systems are requiring smaller and smaller focal spot sizes from the accelerator X-ray source.
The focal spot size of a conventional low-energy X-ray source is generally measured by a pinhole camera method (GB/T25758.2-2010) or a slit camera method (GB/T25758.3-2010). However, because the size of the pinhole or the slit of the test block used in the methods is small and the thickness of the pinhole or the slit is thin, the high-energy X-rays of the electron linear accelerator can easily penetrate through the test block, so that the pinhole or the slit cannot be imaged. Therefore, the methods are not suitable for measuring the size of the focal spot of the X-ray source of the high-energy electron linear accelerator.
The currently commonly used method for measuring the focal spot size of the X-ray source of the electronic linear accelerator is a ' stacking block method ' (commonly known as ' three-Ming ' method ') in GB/T20129-2006, but the ' three-Ming ' method can only measure the transverse or longitudinal size of the focal spot, cannot display the 2D shape of the focal spot, and the measurement result is susceptible to large measurement errors caused by a plurality of main and objective factors such as nonuniformity of an accelerator radiation field, film exposure time, quality of a developed film, distance between a stack and an accelerator focus, visual misreading of personnel and the like. In addition, the X-ray focal spot of the traditional electron linear accelerator is phi 2mm, and with the progress of the accelerator technology, the X-ray focal spot size of the accelerator is smaller and smaller, so that the existing "sandwich method" is not suitable for the measurement of the focal spot size of the small-focus high-energy accelerator.
Disclosure of Invention
The invention aims to provide an X-ray focal spot measuring device of a high-energy electron linear accelerator.
The invention aims to realize the technical scheme, which comprises a first thick metal test board, a second thick metal test board, a linear sliding table, a flat panel detector, an X-ray source of an electronic linear accelerator and a computer, wherein the first thick metal test board is arranged on the first thick metal test board;
the first thick metal test board or the second thick metal test board is detachably mounted on a sliding block of the linear sliding table, the linear sliding table is located between the flat panel detector and the X-ray source of the electronic linear accelerator, and the flat panel detector, the X-ray source of the electronic linear accelerator and the computer are in data interaction;
the first thick metal testing board is provided with a first thick metal round hole at the center, the second thick metal testing board is provided with a second thick metal round hole at the center, the first thick metal testing board and the second thick metal testing board are both provided with four positioning holes, and the four positioning holes are arranged along the first thick metal round hole or the second thick metal round hole in an array mode.
Furthermore, the first thick metal test board and the second thick metal test board are both made of high atomic number and high density metal, and the diameter phi of the first thick metal round hole 1 4.0-8.0 mm; the diameter phi of the second thick metal round hole 2 20.0-80.0 mm; the thickness d of the first thick metal round hole and the second thick metal round hole is 5.0-10.0 mm; diameter phi of locating hole 3 Is 1.0-2.0 mm.
The invention also aims to provide an X-ray focal spot measuring method of the high-energy electron linear accelerator.
The invention is realized by the technical scheme that the X-ray focal spot measuring device adopting the high-energy electron linear accelerator comprises the following specific steps:
1) data acquisition: gather the first DR image when first thick metal round hole geometry enlargies m times respectively to and the second DR image when the thick metal round hole of second hugs closely flat panel detector, wherein: m is belonged to [5,10 ];
2) extracting an edge diffusion function: respectively intercepting the round hole images of the primary DR image and the secondary DR image, and respectively and uniformly extracting a edge diffusion functions (ESF) along the circumferential direction of the round hole edge of the round hole image syn (μ,θ)、ESF s ′ yn (μ,θ)；
3) Calculating a focal spot 2D image: by applying an edge diffusion function ESF syn (μ,θ)、ESF s ′ yn (mu, theta) calculating the line spread function LSF focus (mu, theta), and then using Radon inverse transform or parallel beam filtering back projection to LSF focus (u, theta) is reconstructed to obtain focal spot f (x, y) distribution, namely a focal spot 2D image;
4) calculating the focal spot size: and respectively taking the number of pixels with the gray value more than b% of the maximum value along the length direction and the width direction of the focal spot 2D image, calculating the length value and the width value of the focal spot 2D image according to the pixel size, and dividing by the geometric magnification factor m to obtain the actual length and the width of the focal spot.
Further, the data acquisition in the step 1) comprises the following specific steps:
1-1) installing a first thick metal test board on a sliding block of the linear sliding table, and adjusting the distance SOD between the first thick metal test board and an X-ray source of an electronic linear accelerator and the distance SDD between the X-ray source of the electronic linear accelerator and a flat panel detector to ensure that the gray values of images of four positioning holes of the first thick metal test board are equal and the geometric magnification of a first thick metal round hole is equal
m∈[5,10]Performing DR shooting on the first thick metal round hole for the first time to obtain a DR image;
1-2) replacing the first thick metal test plate with a second thick metal test plate, wherein the diameter phi of the second thick metal round hole (7) 2 Is m phi 1 And translating the second thick metal test plate to enable the second thick metal test plate to be tightly attached to the flat panel detector, and carrying out DR shooting on the second thick metal round hole for the second time to obtain a secondary DR image.
Further, the specific steps of extracting the edge diffusion function in the step 2) are as follows:
2-1) intercepting a round hole image from the primary DR image, and uniformly extracting a edge diffusion functions ESF (extreme short-range intensity) along the circumferential direction of the round hole edge of the round hole image intercepted from the primary DR image syn (μ, θ), wherein: a is>180；
The edge spread function ESF syn (mu, theta) is an edge spread function ESF of focal spot formation in a primary DR image focus (mu, theta) andedge Spread Function (ESF) formed by thick metal round hole circle Convolution of (μ, θ):
in the formula, mu is a pixel coordinate of the detector system;
2-2) intercepting the circular hole image of the secondary DR image, and uniformly extracting a edge diffusion functions ESF 'along the circumferential direction of the edge of the circular hole of the secondary DR image intercepting circular hole image' syn (μ,θ)；
The edge diffusion function ESF' syn (mu, theta) is equal to the edge diffusion function ESF 'formed by the thick metal round hole in secondary DR shooting' circle (μ,θ)。
Further, the specific steps of calculating the focal spot 2D image in step 3) are:
3-1) to ESF respectively syn (μ,θ)、ESF′ syn (μ, θ) fourier transform:
F syn (w,θ)＝F focus (w,θ)·F circle (w,θ)
F′ syn (μ,θ)＝F′ circle (μ,θ)
in the formula, F syn (w,θ)、F focus (w,θ)、F circle (w, θ) are each ESF syn (μ,θ)、ESF focus (μ,θ)、ESF circle Fourier transform of (. mu.,. theta.) F' circle (mu, theta) is ESF' circle A Fourier transform of (μ, θ), then:
to F focus Performing inverse Fourier transform to obtain the ESF focus (μ, θ) is:
ESF focus (μ,θ)＝F -1 (F focus (w,θ))
edge spread function ESF for focal spot formation focus (μ,Theta) obtaining a linear spread function LSF of the focal spot by partial derivation focus (μ, θ) is:
will LSF focus (u, θ) assembling the sets into a two-dimensional sinogram;
3-2) using Radon inverse transform or parallel beam filtering back projection to LSF focus And (u, theta) sets form a two-dimensional sinogram for reconstruction, and focal spot f (x, y) distribution, namely a focal spot 2D image, is obtained.
Due to the adoption of the technical scheme, the invention has the following advantages:
1. according to the method, the edge response function of the circular hole is obtained by the method that the X-ray beam of the high-energy accelerator penetrates through the metal circular hole with a certain thickness, the image of the X-ray focal spot of the accelerator is reconstructed by the filtering back-projection algorithm, the measurement of the X-ray focal spot size of the X-ray source of the high-energy electron linear accelerator is realized, and the application range is wide.
2. According to the method, the edge response functions of the first thick metal round hole and the second thick metal round hole at different positions are measured, the Fourier transform of convolution of the two functions is equivalent to the product operation of the Fourier transform of the two corresponding functions, errors caused by the thickness of the metal round hole test plate are corrected, and visual and quantifiable accurate measurement of the focal spot of the high-energy electron linear accelerator is realized.
3. This application is through surveying the board setting with first, the thick metal of second respectively on sharp slip table, makes first, the thick metal of second survey the board and can carry out the removal of a plurality of positions to realize the DR shooting of different positions, provide the support for the measurement of focal spot.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the means of the instrumentalities and combinations particularly pointed out hereinafter.
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The drawings of the present invention are described below.
Fig. 1 is a flow chart of a focal spot measurement method according to the present invention.
Fig. 2 is a schematic structural diagram of a first DR photographing of the focal spot measuring device of the present invention.
Fig. 3 is a schematic structural diagram of a second DR photographing of the focal spot measuring device of the present invention.
FIG. 4 is a schematic structural diagram of a first thick metal circular hole test board according to the present invention.
FIG. 5 is a schematic structural view of a second thick metal circular hole testing board according to the present invention.
FIG. 6 is a graph of edge diffusion functions of the first and second thick metal circular holes formed at different positions according to the present invention.
FIG. 7 is a DR image of a thick metal circular hole in a primary DR image of the present invention.
Fig. 8 is a schematic diagram of extracting the edge profile of the first thick metal circular hole DR image along the radial direction according to the present invention.
Fig. 9 is a sinogram of a set of focal line spreading functions in accordance with the present invention.
Fig. 10 is a reconstructed focal spot 2D map of the present invention.
Fig. 11 is a schematic view of focal spot size quantization according to the present invention.
In the figure: 1-a first thick metal test plate; 2-a second thick metal test plate; 3-a linear sliding table; 4-a flat panel detector; 5-electron linear accelerator X-ray source; 6-a first thick metal circular hole; 7-a second thick metal circular hole; (ii) a 8-positioning holes.
Detailed Description
The invention is further illustrated by the following figures and examples.
Example 1:
the device for measuring the X-ray focal spot of the high-energy electron linear accelerator shown in the figures 2 to 5 is characterized by comprising a first thick metal test board 1, a second thick metal test board 2, a linear sliding table 3, a flat panel detector 4, an electron linear accelerator X-ray source 5 and a computer, wherein the computer is not shown;
the first thick metal test plate 1 or the second thick metal test plate 2 is detachably mounted on a sliding block of the linear sliding table 3, the linear sliding table 3 is located between the flat panel detector 4 and the X-ray source 5 of the electronic linear accelerator, and the flat panel detector 4 and the X-ray source 5 of the electronic linear accelerator interact with the computer;
first thick metal round hole 6 has been seted up at the center department of first thick metal testing board 1, second thick metal round hole 7 has been seted up at the center department of second thick metal testing board 2, all be provided with four locating hole 8 on first thick metal testing board 1 and the second thick metal testing board 2, four locating hole 8 are followed first thick metal round hole 6 or the array setting of second thick metal round hole 7.
In the embodiment of the invention, image reconstruction and processing software is arranged on the computer, and focal spot measurement of the X-ray of the high-energy electron linear accelerator is carried out through the acquired DR image.
As an embodiment of the present invention, the first thick metal test board 1 and the second thick metal test board 2 are made of high atomic number and high density metal (lead, tungsten, etc.), as shown in fig. 3 and 4, the diameter Φ of the first thick metal circular hole 6 is Φ 1 Is 6.0 mm; the diameter phi of the second thick metal round hole 7 2 Is 48.0 mm; the thickness d of the first thick metal round hole 6 and the second thick metal round hole 7 are both 7.5 mm; diameter phi of the positioning hole 8 3 Is 1.5 mm.
Example 2:
as shown in fig. 1, a method for measuring an X-ray focal spot of a high-energy electron linear accelerator adopts the device for measuring an X-ray focal spot of a high-energy electron linear accelerator in embodiment 1, and includes the following specific steps:
1) data acquisition: gather the first DR image when first thick metal round hole 6 geometry enlargies m times respectively to and the second DR image when thick metal round hole 7 of second hugs closely the flat panel detector, wherein: m is belonged to [5,10 ];
1-1) as shown in fig. 6(a), a first thick metal test board 1 is installed on the slide block of the linear sliding table 3, and the distance SOD between the first thick metal test board 1 and the X-ray source 5 of the electron linear accelerator and the distance SDD between the X-ray source 5 of the electron linear accelerator and the flat panel detector 4 are adjusted to enable four positioning holes 8 of the first thick metal test board 1 to have imagesThe gray values are equal and the geometric magnification of the first thick metal round hole 6 is
m∈[5,10]Performing a first DR photographing on the first thick metal round hole 6 to obtain a first DR image, as shown in fig. 7;
1-2) As shown in FIG. 6(b), the first thick metal test plate 1 is replaced with a second thick metal test plate 2, the diameter phi of the second thick metal circular hole 7 2 Is m phi 1 And translating the second thick metal test plate 2 to enable the second thick metal test plate to be tightly attached to the flat panel detector 4, and carrying out DR shooting on the second thick metal round hole 7 for the second time to obtain a secondary DR image.
In the embodiment of the invention, the magnification m is 8, and the diameter phi of the first thick metal round hole 6 1 Is 6.0 mm; diameter phi of second thick metal round hole 7 2 Is 48.0 mm; the intensity distribution f (X, y) of X-rays emitted by the focal spot of the X-ray source 5 of the high-energy electron linear accelerator is obtained, and the flat panel detector 4 receives the X-rays to obtain a gray level image of the circular hole. An Edge Spread Function (ESF) of the circular hole, the ESF being related to the focal spot size, the thickness d of the thick metal circular hole, the position of the thick metal circular hole, etc. When the second thick metal test board 2 is tightly attached to the flat panel detector 4, the geometric magnification factor 1 is required to enlarge the diameter phi of the second thick metal round hole 2 to ensure that the ambiguity caused by the second thick metal round hole 2 and the second thick metal round hole 1 is the same 1 Is m phi 1 。
2) Extracting an edge diffusion function: as shown in fig. 8, circular hole images are respectively cut out from the primary and secondary DR images, and a edge spread functions ESF are respectively and uniformly extracted along the circumferential direction of the circular hole edge of the circular hole image syn (μ,θ)、ESF′ syn (mu, theta), and the specific steps are as follows:
2-1) intercepting a round hole image from the primary DR image, and uniformly extracting a edge diffusion functions ESF (extreme short-range intensity) along the circumferential direction of the round hole edge of the round hole image intercepted from the primary DR image syn (μ, θ), wherein: a is>180；
The edge spread function ESF syn (mu, theta) is an edge spread function ESF of focal spot formation in a primary DR image focus (mu, theta) and a first thicknessEdge spread function ESF formed by metal circular hole 6 circle Convolution of (μ, θ):
in the formula, mu is a pixel coordinate of a flat panel detector 4 system;
2-2) intercepting the circular hole image of the secondary DR image, and uniformly extracting a edge diffusion functions ESF 'along the circumferential direction of the edge of the circular hole of the secondary DR image intercepting circular hole image' syn (μ,θ)；
The edge diffusion function ESF' syn (mu, theta) is equal to the edge diffusion function ESF 'formed by the second thick metal circular hole 7 in the secondary DR shooting' circle (μ,θ)。
In the present example, when the SDD is 1 m and is much larger than the focal spot size (0.4-2.0 mm), the edge diffusion function ESF 'measured on the flat panel detector 5 in the secondary DR shooting' syn (mu, theta) is due to bore thickness, i.e. ESF' syn (μ,θ)＝ESF′ circle (μ,θ)。
3) Calculating a focal spot 2D image: by means of the edge-to-edge diffusion function ESF syn (μ,θ)、ESF′ syn (mu, theta) calculating the line spread function LSF focus (mu, theta), and then using Radon inverse transform or parallel beam filtering back projection to LSF focus (u, θ) is reconstructed to obtain focal spot f (x, y) distribution, i.e. focal spot 2D image, and the specific steps are as follows:
3-1) since the Fourier transform of the convolution of two functions is equivalent to the product of the Fourier transforms of the corresponding two functions, the ESF is separately addressed syn (μ,θ)、ESF′ syn (μ, θ) fourier transform:
F syn (w,θ)＝F focus (w,θ)·F circle (w,θ)
F′ syn (μ,θ)＝F′ circle (μ,θ)
in the formula, F syn (w,θ)、F focus (w,θ)、F circle (w, θ) are each ESF syn (μ,θ)、ESF focus (μ,θ)、ESF circle Fourier transform of (. mu.,. theta.) F' circle (mu, theta) is ESF' circle A Fourier transform of (μ, θ), then:
to F focus Performing inverse Fourier transform to obtain the ESF focus (μ, θ) is:
ESF focus (μ,θ)＝F -1 (F focus (w,θ))
edge spread function ESF for focal spot formation focus (mu, theta) partial derivation to obtain the line spread function LSF of the focal spot focus (μ, θ) is:
as shown in fig. 9, LSF is applied focus (u, θ) assembling the sets into a two-dimensional sinogram;
3-2) using Radon inverse transform or parallel beam filtering back projection to LSF focus And (u, theta) sets form a two-dimensional sinogram for reconstruction, and focal spot f (x, y) distribution, namely a focal spot 2D image, is obtained.
In the examples of the present invention, ESF focus (μ, θ) is the convolution of focal spot f (x, y) with step function H, i.e.:
ESF focus (μ,θ)＝∫∫f(x,y)H(mx+u)dxdy
thus, a line spread function LSF can be obtained focus The relationship of (μ, θ) to focal spot f (x, y) is:
from the above formula, LSF focus (u, θ) is the Radon transform of the focal spot f (x, y) in the direction perpendicular to the edge of the metal circular hole, thus using the inverse Radon transform or parallel beam filtering on the LSF focus (u, theta) set composition into two dimensionsThe sinogram is backprojected to reconstruct the focal spot f (x, y) distribution, resulting in a focal spot 2D image as shown in fig. 10.
4) Calculating the focal spot size: as shown in fig. 11, the number of pixels with gray values greater than b% of the maximum value is taken along the length and width directions of the focal spot 2D image, the length L and width W values of the focal spot 2D image can be calculated according to the pixel sizes, and then the values are divided by the geometric magnification factor m, so as to obtain the actual focal spot length (L) and width (W).
In the embodiment of the invention, the value of b% is 10%.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.
Claims (6)
1. The X-ray focal spot measuring device of the high-energy electron linear accelerator is characterized by comprising a first thick metal test board (1), a second thick metal test board (2), a linear sliding table (3), a flat panel detector (4), an X-ray source (5) of the electron linear accelerator and a computer;
the first thick metal testing plate (1) or the second thick metal testing plate (2) is detachably mounted on a sliding block of the linear sliding table (3), the linear sliding table (3) is located between the flat panel detector (4) and the X-ray source (5) of the electronic linear accelerator, and the flat panel detector (4) and the X-ray source (5) of the electronic linear accelerator interact with the computer;
first thick metal round hole (6) have been seted up in the center department that first thick metal surveyed board (1), second thick metal round hole (7) have been seted up in the center department that the thick metal of second surveyed board (2), all be provided with four locating hole (8) on first thick metal survey board (1) and the thick metal of second survey board (2), four locating hole (8) are followed first thick metal round hole (6) or the thick metal round hole of second (7) array setting.
2. The device for measuring X-ray focal spot of the high-energy electron linear accelerator according to claim 1, wherein the first thick metal test board (1) and the second thick metal test board (2) are made of high atomic number and high density metal, and the diameter phi of the first thick metal round hole (6) is 1 4.0-8.0 mm; the diameter phi of the second thick metal round hole (7) 2 20.0-80.0 mm; the thickness d of the first thick metal round hole (6) and the second thick metal round hole (7) is 5.0-10.0 mm; diameter phi of the positioning hole (8) 3 Is 1.0-2.0 mm.
3. An X-ray focal spot measuring method of a high-energy electron linear accelerator is characterized in that the X-ray focal spot measuring device of the high-energy electron linear accelerator as claimed in any one of claims 1 or 2 is adopted, and the specific steps are as follows:
1) data acquisition: gather the first DR image when first thick metal round hole geometry enlargies m times respectively to and the second DR image when the thick metal round hole of second hugs closely flat panel detector, wherein: m is belonged to [5,10 ];
2) extracting an edge diffusion function: respectively intercepting the round hole images of the primary DR image and the secondary DR image, and respectively and uniformly extracting a edge diffusion functions (ESF) along the circumferential direction of the round hole edge of the round hole image syn (μ,θ)、ESF′ syn (μ,θ)；
3) Calculating a focal spot 2D image: by means of the edge-to-edge diffusion function ESF syn (μ,θ)、ESF′ syn (mu, theta) calculating the line spread function LSF focus (mu, theta), and then using Radon inverse transform or parallel beam filtering back projection to LSF focus (u, theta) is reconstructed to obtain focal spot f (x, y) distribution, namely a focal spot 2D image;
4) calculating the focal spot size: and respectively taking the number of pixels with the gray value more than b% of the maximum value along the length direction and the width direction of the focal spot 2D image, calculating the length value and the width value of the focal spot 2D image according to the pixel size, and dividing by the geometric magnification factor m to obtain the actual length and the width of the focal spot.
4. The method for measuring the X-ray focal spot of the high-energy electron linear accelerator according to claim 3, wherein the data acquisition in the step 1) comprises the following specific steps:
1-1) installing a first thick metal test board on a sliding block of the linear sliding table, and adjusting the distance SOD between the first thick metal test board and an X-ray source of an electronic linear accelerator and the distance SDD between the X-ray source of the electronic linear accelerator and a flat panel detector to ensure that the gray values of images of four positioning holes of the first thick metal test board are equal and the geometric magnification of a first thick metal round hole is equal
Performing first DR shooting on the first thick metal round hole to obtain a first DR image;
1-2) replacing the first thick metal test plate with a second thick metal test plate, wherein the diameter phi of the second thick metal round hole (7) 2 Is m phi 1 And translating the second thick metal test plate to enable the second thick metal test plate to be tightly attached to the flat panel detector, and carrying out DR shooting on the second thick metal round hole for the second time to obtain a secondary DR image.
5. The method for measuring the X-ray focal spot of the high-energy electron linear accelerator according to claim 3, wherein the step of extracting the edge spread function in the step 2) comprises the following specific steps:
2-1) intercepting the circular hole image of the primary DR image, and uniformly extracting a edge diffusion functions ESF along the circumferential direction of the circular hole edge of the primary DR image intercepted circular hole image syn (μ, θ), wherein: a is>180；
The edge spread function ESF syn (mu, theta) is an edge spread function ESF of focal spot formation in a primary DR image focus (mu, theta) and edge diffusion function ESF formed by thick metal round holes circle Convolution of (μ, θ):
in the formula, mu is a pixel coordinate of the detector system;
2-2) intercepting the circular hole image of the secondary DR image, and uniformly extracting a edge diffusion functions ESF 'along the circumferential direction of the edge of the circular hole of the secondary DR image intercepting circular hole image' syn (μ,θ)；
The edge diffusion function ESF' syn (mu, theta) is equal to the edge diffusion function ESF 'formed by the thick metal round hole in secondary DR shooting' circle (μ,θ)。
6. The method for measuring the X-ray focal spot of the high-energy electron linear accelerator according to claim 3, wherein the specific step of calculating the 2D image of the focal spot in the step 3) is as follows:
3-1) to ESF respectively syn (μ,θ)、ESF′ syn (μ, θ) fourier transform:
F syn (w,θ)＝F focus (w,θ)·F circle (w,θ)
F′ syn (μ,θ)＝F′ circle (μ,θ)
in the formula, F syn (w,θ)、F focus (w,θ)、F circle (w, θ) are respectively ESF syn (μ,θ)、ESF focus (μ,θ)、ESF circle Fourier transform of (. mu.,. theta.) F' circle (mu, theta) is ESF' circle A Fourier transform of (μ, θ), then:
to F focus Performing inverse Fourier transform to obtain the ESF focus (μ, θ) is:
ESF focus (μ,θ)＝F -1 (F focus (w,θ))
edge spread function ESF for focal spot formation focus (mu, theta) partial derivation to obtain the line spread function LSF of the focal spot focus (μ, θ) is:
will LSF focus (u, θ) assembling the sets into a two-dimensional sinogram;
3-2) using Radon inverse transform or parallel beam filtering back projection to LSF focus And (u, theta) sets form a two-dimensional sinogram for reconstruction, and focal spot f (x, y) distribution, namely a focal spot 2D image, is obtained.
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