CN116413290A - Industrial CT scattering correction method - Google Patents
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Abstract
The invention relates to an industrial CT scattering correction method, which comprises the following steps: processing a dot matrix plate, and processing a through hole array vertical to the plate surface on the dot matrix plate; performing circumferential scanning on the detected samples through an industrial CT system to obtain first circumferential DR images of S detected samples; vertically placing a dot matrix plate in front of a detector of an industrial CT system to obtain second circumferential DR images of S detected samples; performing DR scanning on the dot matrix plate to obtain a dot matrix plate projection image; and calculating scattered ray distribution images according to the projection images of the dot matrix plate, carrying out scattered ray correction on each first circumferential DR image according to the scattered ray distribution images, and finally carrying out CT reconstruction by adopting the scattered ray corrected images to obtain corrected CT images. The method has low cost and easy realization.
Description
Technical Field
The invention relates to the technical field of CT image correction, in particular to an industrial CT scattering correction method.
Background
The industrial CT detection technology is a practical nondestructive detection means developed on the X-ray transmission imaging technology, is suitable for detecting the internal structure and defects of products and parts with complex structures, has the advantages of visual imaging, accurate quantification, positioning, qualitative accuracy and the like, and is widely applied to the fields of industrial nondestructive inspection, medical treatment and health and the like.
The relationship between X-rays and substances is mainly: both transmission and scattering. Wherein, the transmission refers to the capability and the intensity of the X-ray when penetrating through a substance are changed, and the radiation attenuation is generated; the attenuation rule of the rays basically accords with the Lamber-Beer law, namely the attenuation amount of the intensity of the rays in a small thickness range is proportional to the intensity of the incident rays and the thickness of a penetrating object, and industrial CT is based on the law and combines with convolution back projection and other algorithms to realize the visualization of internal structures and defects; scattering refers to the interaction of X-rays with atoms of a substance after they are incident on an object, including: the main characteristics of the photoelectric effect, compton effect, electron pair effect and Rayleigh scattering are that the X-ray deviates from the incident direction.
In the industrial CT scanning process, the X-ray receiving detector has high radiation sensitivity, so that the transmitted X-rays and scattered X-rays can be received simultaneously. However, the presence of scattered radiation is ignored in the CT reconstruction algorithm, which causes the presence of scattering artifacts in the CT image, which appear as shadows (or fringes) on the CT image, which severely interfere with the detection of internal defects. Therefore, it is necessary to study the area array industrial CT scatter correction method.
At present, scatter correction of industrial CT can be roughly classified into two main categories, hardware correction and software correction. Hardware correction is to add some correction tools on each instrument component of the X-ray imaging system, and achieve the purpose of scattering correction by physically blocking scattered rays from being received by the detector. Such as: a collimator is additionally arranged in front of the detector to block scattered X-rays generated by an object from entering the detector and a classical air gap (air gap) method is adopted, namely, the distance between an object to be irradiated and the detector is increased, and scattering components can be reduced; the software correction method is to use digital image processing method to obtain a scattering distribution map by analyzing the image itself and estimating the property of the object to be irradiated in the computer. Including convolution, deconvolution, monte carlo simulation, model estimation, and the like. However, the software correction method has complex algorithm, large calculation amount and lower efficiency. In recent years, relevant researchers at home and abroad obtain better effects by adopting a scattering correction plate method, an object+scattering correction plate image a and an individual object image b are obtained by scanning 2 times before a detected workpiece and a detector by a two-dimensional lead block point array (two-dimensional hole array lead plate), a scattering intensity distribution diagram is obtained by two-dimensional interpolation operation of the image a, and the scattering intensity distribution diagram is subtracted by the image b to obtain a scattering corrected image. It is difficult to realize wide application and popularization.
Disclosure of Invention
The technical problem to be solved by the invention is to provide an industrial CT scattering correction method with low cost aiming at the prior art.
The technical scheme adopted for solving the technical problems is as follows: an industrial CT scattering correction method is characterized by comprising the following steps:
step 1, processing a dot matrix plate, and processing a through hole array vertical to the plate surface on the dot matrix plate;
the through hole array comprises m rows and n columns of through holes which are distributed at equal intervals, and m and n are positive integers;
step 2, performing circumferential scanning on the detected sample through an industrial CT system to obtain S first circumferential DR images of the detected sample, and marking the pixel value of the pixel point (x, y) in the S first circumferential DR images as A s (x, y), S ε 1, 2 … S; the industrial CT system comprises an X-ray machine, a placing table and a detector, wherein the X-ray machine, the placing table and the detector are sequentially arranged at intervals;
step 3, vertically placing the dot matrix plate in the step 1 in front of a detector of the industrial CT system, performing circumferential scanning on the detected sample by adopting the scanning process same as that in the step 2 to obtain second circumferential DR images of S detected samples, and marking the pixel value of the pixel point (x, y) in the second circumferential DR image of the S as B s (x,y)，B s (x, y) and A s The scan angles of (x, y) are the same;
step 4, performing DR scanning on the dot matrix plate by adopting the scanning process same as that in the step 2 to obtain a dot matrix plate projection image;
step 5, calculating a scattered ray distribution image;
the specific steps of the scattered ray distribution image calculation are as follows:
step 5-1, performing binarization processing on the projected image of the dot matrix plate to obtain a projected binarized image of the dot matrix plate;
step 5-2, numbering each through hole on the dot matrix plate, wherein i and j are respectively corresponding to the serial numbers corresponding to the rows and columns of the dot matrix plate, i epsilon {1, 2, … m }, j epsilon {1, 2, … n };
step 5-3, searching pixel positions occupied by each through hole on the dot matrix board in the dot matrix board projection binarized image, and classifying the pixel positions occupied by each through hole into a first subclass Ck i,j Calculating the centroid position of each through hole after imaging on the dot matrix plate projection binarization image;
step 5-4, calculating the image gray values of the centroid position of each through hole in the second circumferential DR image and the first circumferential DR image, which are respectively marked as B s (x,y) i,j And A s (x,y) i,j ；
Step 5-5, projecting a pixel size V of the binarized image according to the dot matrix plate cal Calculating the pixel number occupied by the through hole aperture d of the dot matrix plate
Step 5-6, obtaining the center of mass of each through hole,
a circle of radius and classifying pixel positions within the circle as a second subclass Cy i,j Find Cy belonging to the second subclass i,j But not of the first subclass Ck i,j Extracting the points belonging to the second subclass Cy from the second circumferential DR image i,j But not of the first subclass Ck i,j The gray value of the position corresponding to the point of (2) is calculated as the average value of the gray values of all the points, and k is set s i,j ；
Step 5-7, calculating the scattering value l of the mass center position of each through hole in each second circumferential DR image s i,j ；l s i,j The calculation formula of (2) is as follows:
l s i,j ＝A s (x,y) i,j -B s (x,y) i,j -k s i,j ；
step 5-8, calculating scattered ray distribution images of each first circumferential DR image by adopting a two-dimensional interpolation method according to the scattering value of the mass center position of each through hole in each second circumferential DR image, and marking the pixel value of which the pixel point in the scattered ray distribution image of the s-th first circumferential DR image is (x, y) as E s (x,y)；
Step 6, carrying out scattered ray correction on each first circumferential DR image to obtain S images after scattered ray correction; wherein the pixel value of the pixel point (x, y) in the s-th scattering corrected image is A s (x,y)-E s (x,y)；
And 7, performing CT reconstruction by adopting S scattered ray corrected images to obtain corrected CT images.
In this scheme, the thickness of the point array plate in the step 1 is determined according to the highest energy of the X-ray machine in the industrial CT system.
Preferably, the lattice plate material is steel;
when the highest energy of the X-ray machine is 50keV-150keV, the thickness of the lattice plate is 5mm;
when the highest energy of the X-ray machine is 150keV-250keV, the thickness of the lattice plate is 10mm;
when the highest energy of the X-ray machine is 250keV-350keV, the thickness of the lattice plate is 15mm;
the thickness of the lattice plate is 20mm when the highest energy of the X-ray machine is 350-450 keV.
Further, when the lattice plate material is other than steel, the lattice plate thickness D x The calculation formula is as follows:
wherein D is 1 The thickness of the lattice plate when the material of the lattice plate is steel; ρ 1 Representing the density of the steel; ρ x Representing the density of other materials.
Further, the scanning process in the step 3 includes tube voltage, tube current, amplification ratio, focal spot size and integration time.
In this scheme, the mass center position calculation mode of each through hole in step 5-3 after imaging on the dot matrix plate projection binarization image is as follows: and calculating the average value of pixel positions occupied by the through holes in the dot matrix plate projection binarization image, wherein the average value is the centroid position of the through holes.
Compared with the prior art, the invention has the advantages that: the traditional method has the defects that the processing difficulty is high, the cost is high and the time is long because the radial hole array plate is required to be adopted, the problem is solved by processing the through hole array vertical to the plate surface on the lattice plate, and the scattering value of the mass center position of each through hole is calculated in the scattered ray distribution image calculation mode through the image processing mode, so that the purpose of scattering correction is realized. Therefore, the method is low in cost, easy to implement and high in scattering correction precision.
Drawings
FIG. 1 is a schematic view of a matrix board in an embodiment of the present invention;
FIG. 2 is a first circumferential DR image of a sample to be inspected at an angle according to an embodiment of the present invention;
FIG. 3 is a second circumferential DR image of the sample under test at the same angle as in FIG. 2;
FIG. 4 is a projected image of a panel in an embodiment of the present invention;
FIG. 5 is a view of a projected binary image of a panel array in accordance with an embodiment of the present invention;
FIG. 6 is an enlarged view of a portion of FIG. 4 in accordance with an embodiment of the present invention;
FIG. 7 is a schematic diagram of points belonging to the second subclass but not belonging to the first subclass according to the embodiment of the present invention;
FIG. 8 is a graph showing images before and after scatter correction in an embodiment of the present invention; wherein (a) is an image before scatter correction and (b) is an image after scatter correction.
Detailed Description
The invention is described in further detail below with reference to the embodiments of the drawings.
The industrial CT scattering correction method in the embodiment comprises the following steps:
step 1, processing a dot matrix plate, and processing a through hole array vertical to the plate surface on the dot matrix plate;
the through hole array comprises m rows and n columns of through holes which are distributed at equal intervals, and m and n are positive integers; the smaller the hole diameter d of the through hole of the dot matrix plate is, the better, generally 1-3mm (diameter) is adopted; the range of the pitch of the through holes (the center distance of circles of the two through holes) is 1.5-3 times of the aperture of the through holes, and the longitudinal pitch and the transverse pitch are kept consistent and distributed at equal intervals; manufacturing a hole array vertical to the plate surface by adopting a machining mode and the like;
in the embodiment, the thickness of the dot matrix board is determined according to the highest energy (tube voltage) of an X-ray machine in an industrial CT system, and when the dot matrix board is selected as steel;
when the highest energy of the X-ray machine is 50keV-150keV, the thickness of the lattice plate is 5mm;
when the highest energy of the X-ray machine is 150keV-250keV, the thickness of the lattice plate is 10mm;
when the highest energy of the X-ray machine is 250keV-350keV, the thickness of the lattice plate is 15mm;
when the highest energy of the X-ray machine is 350keV-450keV, the thickness of the lattice plate is 20mm;
in the embodiment, the highest energy (tube voltage) of an X-ray machine in an industrial CT system for experiments is 90kV, a dot matrix plate with the thickness of 5mm is manufactured by adopting stainless steel, the diameter of a through hole is 3mm, the center distance of the through hole is 9mm, and a specific physical diagram of the dot matrix plate is shown in figure 1;
when the lattice plate material is other than steel, the thickness D of the lattice plate x The calculation formula is as follows:
wherein D is 1 The thickness of the lattice plate when the material of the lattice plate is steel; ρ 1 Representing the density of the steel; ρ x Representing the density of other materials; the specific materials of the dot matrix plate are replaced according to actual needs;
step 2, performing circumferential scanning on the detected sample through an industrial CT system to obtainObtaining first circumferential DR images of S detected samples, and marking the pixel value of the pixel point (x, y) in the S first circumferential DR images as A s (x, y), S ε 1, 2 … S; the industrial CT system comprises an X-ray machine, a placing table and a detector, wherein the placing table and the detector are sequentially arranged; the specific imaging mode of the industrial CT system is known to those skilled in the art, and will not be described in detail herein;
before circumferential scanning, adjusting detection process parameters according to the characteristics of the detected object, such as material, density, size and the like; obtaining a first circumferential DR image of a detected sample at a certain angle as shown in FIG. 2;
step 3, vertically placing the dot matrix plate in the step 1 in front of a detector of the industrial CT system, performing circumferential scanning on the detected sample by adopting the scanning process same as that in the step 2 to obtain second circumferential DR images of S detected samples, and marking the pixel value of the pixel point (x, y) in the second circumferential DR image of the S as B s (x,y)，B s (x, y) and A s The scan angles of (x, y) are the same;
the lattice plate is parallel to the detector, and is placed close to the detector as much as possible, but the distance between the lattice plate and the detector is not particularly required; the scanning process in this embodiment includes tube voltage, tube current, amplification ratio, focal spot size, and integration time; acquiring a second circumferential DR image with the same angle as in the step 2, as shown in FIG. 3;
step 4, performing DR scanning on the dot matrix plate by adopting the scanning process same as that in the step 2 to obtain a dot matrix plate projection image, and marking the pixel value of which the pixel point is (x, y) in the dot matrix plate projection image as D (x, y); the projected image of the dot matrix plate is shown in fig. 4;
step 5, calculating a scattered ray distribution image;
the specific steps of the scattered ray distribution image calculation are as follows:
step 5-1, performing binarization processing on the projected image of the dot matrix plate to obtain a projected binarized image of the dot matrix plate;
the threshold value of the image binarization can be selected by adopting an automatic or manual setting method, wherein the automatic method is preferably a maximum inter-class variance method, and the obtained dot matrix plate projection binarization image is shown in figure 5;
step 5-2, numbering each through hole on the dot matrix plate, wherein i and j are respectively corresponding to the serial numbers corresponding to the rows and columns of the dot matrix plate, i epsilon {1, 2, … m }, j epsilon {1, 2, … n };
step 5-3, searching pixel positions occupied by each through hole on the dot matrix board in the dot matrix board projection binarized image, and classifying the pixel positions occupied by each through hole into a first subclass Ck i,j Calculating the centroid position of each through hole after imaging on the dot matrix plate projection binarization image;
the mass center position calculation mode of each through hole after imaging on the dot matrix plate projection binarization image is as follows: calculating the average value of pixel positions occupied by the through holes in the dot matrix plate projection binarization image, wherein the average value is the centroid position of the through holes;
step 5-4, calculating the image gray values of the centroid position of each through hole in the second circumferential DR image and the first circumferential DR image, which are respectively marked as B s (x,y) i,j And A s (x,y) i,j ；
Step 5-5, projecting a pixel size V of the binarized image according to the dot matrix plate cal Calculating the pixel number occupied by the through hole aperture d of the dot matrix plate
In the present embodiment, the pixel size V cal The aperture d of the dot matrix plate=3 mm, and the number of pixels occupied by the aperture is calculated to be 20;
step 5-6, obtaining the center of mass of each through hole,
a circle of radius and classifying pixel positions within the circle as a second subclass Cy i,j Find Cy belonging to the second subclass i,j But not of the first subclass Ck i,j Extracting the points belonging to the second subclass Cy from the second circumferential DR image i,j But not of the first subclass Ck i,j The gray value of the position corresponding to the point of (2) is calculated as the average value of the gray values of all the points, and k is set s i,j ；
Fig. 6 is a partial enlarged view of the projected image of the dot matrix plate, and it can be seen from fig. 6 that: when the through hole is at the edge position, the through hole is deformed, thereby forming an inclined hole as shown in fig. 6; for this purpose, the calculation in step 5-6 is used to find Cy belonging to the second subclass i,j But not of the first subclass Ck i,j The gray value average value of the corresponding positions of all the points in the grid region in the second circumferential DR image is calculated, so that the accuracy of scattering correction can be effectively improved;
step 5-7, calculating the scattering value l of the mass center position of each through hole in each second circumferential DR image s i,j ；l s i,j The calculation formula of (2) is as follows:
l s i,j ＝A s (x,y) i,j -B s (x,y) i,j -k s i,j ；
step 5-8, calculating scattered ray distribution images of each first circumferential DR image by adopting a two-dimensional interpolation method according to the scattering value of the mass center position of each through hole in each second circumferential DR image, and marking the pixel value of which the pixel point in the scattered ray distribution image of the s-th first circumferential DR image is (x, y) as E s (x,y)；
The two-dimensional interpolation method is the prior art and is not developed here;
step 6, carrying out scattered ray correction on each first circumferential DR image to obtain S images after scattered ray correction; wherein the pixel value of the pixel point (x, y) in the s-th scattering corrected image is A s (x,y)-E s (x,y)；
And 7, performing CT reconstruction by adopting S scattered ray corrected images to obtain corrected CT images.
The CT reconstruction method in step 7 is the prior art, and will not be described in detail herein. Fig. 8 (a) is an effect diagram before the scatter correction; fig. 8 (b) is an effect diagram after the scattering correction.
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that it will be apparent to those skilled in the art that several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the scope of the invention.
Claims (6)
1. An industrial CT scattering correction method is characterized by comprising the following steps:
step 1, processing a dot matrix plate, and processing a through hole array vertical to the plate surface on the dot matrix plate;
the through hole array comprises m rows and n columns of through holes which are distributed at equal intervals, and m and n are positive integers;
step 2, performing circumferential scanning on the detected sample through an industrial CT system to obtain S first circumferential DR images of the detected sample, and marking the pixel value of the pixel point (x, y) in the S first circumferential DR images as A s (x, y), S ε 1, 2 … S; the industrial CT system comprises an X-ray machine, a placing table and a detector, wherein the X-ray machine, the placing table and the detector are sequentially arranged at intervals;
step 3, vertically placing the dot matrix plate in the step 1 in front of a detector of the industrial CT system, performing circumferential scanning on the detected sample by adopting the scanning process same as that in the step 2 to obtain second circumferential DR images of S detected samples, and marking the pixel value of the pixel point (x, y) in the second circumferential DR image of the S as B s (x,y)，B s (x, y) and A s The scan angles of (x, y) are the same;
step 4, performing DR scanning on the dot matrix plate by adopting the scanning process same as that in the step 2 to obtain a dot matrix plate projection image;
step 5, calculating a scattered ray distribution image;
the specific steps of the scattered ray distribution image calculation are as follows:
step 5-1, performing binarization processing on the projected image of the dot matrix plate to obtain a projected binarized image of the dot matrix plate;
step 5-2, numbering each through hole on the dot matrix plate, wherein i and j are respectively corresponding to the serial numbers corresponding to the rows and columns of the dot matrix plate, i epsilon {1, 2, … m }, j epsilon {1, 2, … n };
step 5-3, searching pixel positions occupied by each through hole on the dot matrix board in the dot matrix board projection binarized image, and classifying the pixel positions occupied by each through hole into a first subclass Ck i,j Calculating the centroid position of each through hole after imaging on the dot matrix plate projection binarization image;
step 5-4, calculating the image gray values of the centroid position of each through hole in the second circumferential DR image and the first circumferential DR image, which are respectively marked as B s (x,y) i,j And A s (x,y) i,j ；
Step 5-5, projecting a pixel size V of the binarized image according to the dot matrix plate cal Calculating the pixel number occupied by the through hole aperture d of the dot matrix plate
Step 5-6, obtaining the center of mass of each through hole,
a circle of radius and classifying pixel positions within the circle as a second subclass Cy i,j Find Cy belonging to the second subclass i,j But not of the first subclass Ck i,j Extracting the points belonging to the second subclass Cy from the second circumferential DR image i,j But not of the first subclass Ck i,j The gray value of the position corresponding to the point of (2) is calculated as the average value of the gray values of all the points, and k is set s i,j ；
Step 5-7, calculating the scattering value l of the mass center position of each through hole in each second circumferential DR image s i,j ；l s i,j The calculation formula of (2) is as follows:
l s i,j ＝A s (x,y) i,j -B s (x,y) i,j -k s i,j ；
step 5-8, calculating each first through hole centroid position according to the scattering value of each through hole centroid position in each second circumferential DR image by adopting a two-dimensional interpolation methodThe scattered ray distribution image of the first circumferential DR image is marked as E, wherein the pixel value of the pixel point (x, y) in the scattered ray distribution image of the second circumferential DR image is marked as E s (x,y)；
Step 6, carrying out scattered ray correction on each first circumferential DR image to obtain S images after scattered ray correction; wherein the pixel value of the pixel point (x, y) in the s-th scattering corrected image is A s (x,y)-E s (x,y)；
And 7, performing CT reconstruction by adopting S scattered ray corrected images to obtain corrected CT images.
2. The industrial CT scatter correction method of claim 1, wherein: the thickness of the point array plate in the step 1 is determined according to the highest energy of an X-ray machine in an industrial CT system.
3. The industrial CT scatter correction method of claim 2, wherein: the lattice plate is made of steel;
when the highest energy of the X-ray machine is 50keV-150keV, the thickness of the lattice plate is 5mm;
when the highest energy of the X-ray machine is 150keV-250keV, the thickness of the lattice plate is 10mm;
when the highest energy of the X-ray machine is 250keV-350keV, the thickness of the lattice plate is 15mm;
the thickness of the lattice plate is 20mm when the highest energy of the X-ray machine is 350-450 keV.
4. The industrial CT scatter correction method of claim 3 wherein: when the lattice plate material is other materials than steel, the thickness D of the lattice plate x The calculation formula is as follows:
wherein D is 1 The thickness of the lattice plate when the material of the lattice plate is steel; ρ 1 Representing the density of the steel; ρ x Representing the density of other materials。
5. The industrial CT scatter correction method according to any one of claims 1 to 4, wherein: the scanning process in step 3 includes tube voltage, tube current, amplification ratio, focal spot size and integration time.
6. The industrial CT scatter correction method of claim 5 wherein: the mass center position calculation mode of each through hole after imaging on the dot matrix plate projection binarization image in the step 5-3 is as follows: and calculating the average value of pixel positions occupied by the through holes in the dot matrix plate projection binarization image, wherein the average value is the centroid position of the through holes.
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