CN108680589A - X-ray grating differential phase contrast 3 D cone-beam computer tomography method based on transversion malposition grating and device - Google Patents

Abstract

The invention discloses an X-ray grating differential phase contrast three-dimensional cone-beam computer tomography method and device based on a laterally dislocated grating. The method includes: arranging a Talbot-Lau three-dimensional cone-beam tomography structure with a laterally dislocated absorption grating; The two-dimensional intensity image sequence after the X-ray passes through the object is obtained with the above structure; the X-ray absorption contrast, differential phase contrast and scattering contrast are separated from the collected two-dimensional intensity image by Fourier analysis. Image sequence: Using the absorption contrast, differential phase contrast and scattering contrast filter back projection reconstruction algorithms to reconstruct the three contrast image sequences to obtain the three contrast CT slice images of the object. The invention does not need to step the absorption grating, and can obtain three kinds of contrast CT slice images with the traditional X-ray attenuation-based CT scanning method, which greatly reduces the imaging time, reduces the imaging dose, and improves the imaging efficiency and stability of the system sex.

Description

3D Cone Beam Calculation of X-ray Grating Differential Phase Contrast Based on Laterally Displaced Grating Machine tomography method and device

technical field

The invention relates to the technical field of X-ray computerized tomography, in particular to a method and device for three-dimensional cone-beam computerized tomography based on X-ray grating differential phase contrast with lateral displacement gratings.

Background technique

In the X-ray computer tomography (Computed Tomography, referred to as CT) system, the X-ray source emits X-rays, which pass through a certain area of the object to be detected from different angles, and the detectors placed opposite the ray source receive them at corresponding angles. Then, according to the different degrees of attenuation of rays at various angles, a certain reconstruction algorithm and computer operations are used to reconstruct the distribution mapping image of the ray line attenuation coefficient in the scanned area of the object, so as to realize the reconstruction of the image by projection and reproduce the object in this area without loss. The characteristics of the medium density, composition and structure morphology in the medium.

Traditional CT technology based on the principle of X-ray attenuation can only obtain absorption contrast images of the internal structure of objects, and it is difficult to obtain high-contrast images for low atomic number material structure samples. In recent years, phase-contrast imaging techniques have been proposed to improve the imaging contrast of these low-attenuation samples. For example, Yuan Qingxi et al., CT research on synchrotron radiation hard X-ray diffraction-enhanced peak position imaging, Chinese Physics C, vol.29.No.10, pp:1023-1026, 2005, realized a diffraction-enhanced phase-contrast imaging method; Pfeiffer F et al., Phase retrieval differential phase-contrast imaging with low-brilliance x-ray sources, Nature Physics, vol.2, no.4, pp.258-261, 2006, proposed a grating-based differential phase contrast method; Zanette I et al., Speckle-based x-ray phase-contrast imaging using a grating interferometer, Physical review letter, vol.112, no.25, 2014, proposed a speckle phase-contrast imaging technique. Among them, the grating-based differential phase contrast method can be realized by ordinary X-ray tubes, has great engineering application prospects, and has been extensively studied.

However, most of the existing differential phase contrast methods based on gratings are traditional methods based on the translation and stepping of absorption gratings. The imaging time is long, the dose is large, the stability is low, and the efficiency is not high, which restricts its further engineering application.

At present, no X-ray grating differential phase contrast three-dimensional cone-beam computed tomography device based on a laterally dislocated absorption grating has been found.

Contents of the invention

In order to overcome the defects of the prior art, the present invention provides a three-dimensional cone-beam computed tomography imaging method and device based on X-ray grating differential phase contrast of laterally displaced gratings.

The technical solution adopted in the present invention is: a three-dimensional cone-beam computed tomography method based on X-ray grating differential phase contrast of laterally misaligned grating, comprising the following steps:

Step 1. Obtain the two-dimensional projection image sequence after the X-ray passes through the object with the Talbort-Lau three-dimensional tomography structure based on the lateral misalignment grating; Periodically collect the two-dimensional projections of the X-rays passing through the object, and collect a two-dimensional projection image of the object in one collection cycle;

Step 2, performing Fourier transform on the two-dimensional projection image sequence to separate three contrast images of X-ray absorption contrast, differential phase contrast and scattering contrast;

Step 3, using the absorption contrast, differential phase contrast and scattering contrast filter back projection reconstruction algorithm to reconstruct the three contrast two-dimensional image sequences respectively, and obtain the absorption contrast, phase contrast and scattering contrast of the object Three kinds of CT slice images.

Further, the Talbot-Lau imaging structure of the lateral dislocation absorption grating arrangement includes:

The optical path of the Talbot-Lau imaging structure includes a total of six parts: X-ray source, source grating G0, test object, phase grating G1, absorption grating G2, detector;

The optical path parameters of the Talbot-Lau imaging structure should satisfy the following formulas (1)-(4):

kg ₁ =2g ₂ , (2)

g ₀ =g ₂ ·L/d, (3)

s<g ₂ L/2d, (4)

Among them, d represents the distance between the phase grating G1 and the absorption grating G2; k=(L+d)/L is the amplification ratio, and L is the direct distance between the source grating G0 and the phase grating G1; m represents the fractional Talbot distance of the mth order ; g ₁ is the period of the phase grating G1, λ is the wavelength of the X-ray used, g ₂ is the period of the absorption grating G2, g ₀ is the period of the source grating G0, s is the X-ray transmission allowed in each period of the source grating over the width;

The lateral dislocation absorption grating refers to the absorption grating G2 in the optical path of the Talbot-Lau imaging structure, and its relative position to the detector probes has a lateral periodic dislocation, so that multiple adjacent detector probes in the lateral direction obtain The intensity signal can be equivalent to the intensity signal obtained when a detector probe is in multiple different positions in the traditional imaging method;

For the 4 laterally adjacent detector probes, respectively marked as p ₁ , p ₂ , p ₃ , p ₄ , each probe p _x (x=1,2,3,4) has a width of w, and is dislocated in the lateral direction In the absorption grating, corresponding to a section of grating gp _x with length w, the grating period of each section of grating gp _x is g ₂ , and the gratings corresponding to adjacent detector elements have a position difference of distance f, such as adjacent detectors There is a position difference of f between the grating segments gp ₁ and gp ₂ corresponding to elements p ₁ and p ₂ , where f=g ₂ /4, the position of the gp _x grating is equivalent to the position of the absorption grating when it moves to x, adjacent 4 The positions of the absorption gratings corresponding to each detector element are different, and they are staggered by a distance f, which is called a lateral misalignment grating. The X-ray intensity signal value obtained by the detector element p _x is when the absorption grating G2 moves to the position x The collected intensity value.

Further, step 1 also includes:

In the Talbot-Lau imaging structure, when no object is placed on the turntable, the turntable rotates 360 degrees at a constant speed along the rotation center, and the imaging area is covered by the cone beam during the rotation process, and the two-dimensional projection image is collected by the detector;

In the Talbot-Lau imaging structure, when the object is placed on the turntable, the turntable rotates 360 degrees at a constant speed along the rotation center, and the imaging area is covered by the cone beam during the rotation, and the two-dimensional projection image is collected by the detector.

Further, it also includes:

Perform image analysis on the two-dimensional projection image sequence according to formulas (5)-(14) to obtain three contrast two-dimensional projection image sequences:

I ₁ (x,z,θ)=I(x-1,z,θ), (5)

I ₂ (x,z,θ)=I(x,z,θ), (6)

I ₃ (x,z,θ)=I(x+1,z,θ), (7)

I ₄ (x,z,θ)=I(x+2,z,θ), (8)

phase(x,z,θ)=φ ^s (x,z,θ)-φ ^r (x,z,θ), (13)

Among them, x is the abscissa of the point in the two-dimensional projection; z is the vertical coordinate of the point in the two-dimensional projection, and θ is the projection angle of the two-dimensional projection image; I(x,z,θ) is the point in the two-dimensional projection (x,z) intensity value at projection angle θ; I ₁ (x,z,θ), I ₂ (x,z,θ), I ₃ (x,z,θ), I ₄ (x,z, θ) represent 4 different intensity values of the point (x, z) at the projection angle θ respectively, simulating the point (x, z) in the projection angle θ of the traditional grating differential phase contrast image when the absorption grating is in 4 different steps The intensity value when entering the position; M represents the number of different intensity values in a point (x, z), M=4; a ₀ (x, z, θ) is the point (x, z) at the projection angle θ The mean value of the sinusoidal curve fitted by 4 different intensity values; a ₁ (x, z, θ) is the amplitude of the sinusoidal curve fitted by the 4 different intensity values of the point (x, z) at the projection angle θ Size; φ(x,z,θ) is the phase value of the sinusoidal curve fitted by the point (x,z) at 4 different intensity values of the projection angle θ; Indicates the value of a ₀ (x,z,θ) when the test object is not placed at the projection angle θ, Indicates the value of a ₀ (x,z,θ) when the test object is placed at the projection angle θ; Indicates the value of a ₁ (x,z,θ) when the test object is not placed at the projection angle θ, Indicates the a ₁ (x, z, θ) value when the test object is placed at the projection angle θ; φ ^r (x, z, θ) indicates the φ(x, z, θ) value when the test object is not placed at the projection angle θ , φ ^s (x, z, θ) represents the value of φ(x, z, θ) when the test object is placed at the projection angle θ; abs(x, z, θ) is the absorption at the point (x, z) at the projection angle θ The value of the contrast; phase(x,z,θ) is the value of the differential phase contrast at the projection angle θ point (x,z); dark(x,z,θ) is the projection angle θ point (x,z) Values for scatter contrast imaging.

Further, use the absorption contrast, differential phase contrast and scattering contrast filter back projection reconstruction algorithm to reconstruct the three contrast two-dimensional image sequences respectively, and obtain the absorption contrast, phase contrast and scattering contrast of the object Three kinds of CT slice images, including:

Perform image analysis on the two-dimensional projection image sequence according to formulas (15)-(17) to obtain three contrast two-dimensional projection image sequences:

Among them, a(x,y,z), p(x,y,z) and d(x,y,z) are respectively the reconstructed absorption contrast slice image, phase contrast slice image and scattering contrast slice image; abs(s,v,θ), phase(s,v,θ) and dark(s,v,θ) represent the two-dimensional projection of absorption contrast, differential phase contrast and scattering contrast under the projection angle θ respectively, s , v are the coordinates of the intersection between the pixel point on the detector and the ray source and the virtual detector placed at the rotation axis; ξ is the angle between the ray and the central ray; D is the distance from the ray source to the virtual detector plane ; y′ is the distance from the reconstructed image pixel to the virtual detector plane; h _a (s), h _p (s) and h _d (s) are the two-dimensional projections of absorption contrast, differential phase contrast and scattering contrast, respectively The filter, which is defined as formula (18)-(19):

h _a (s)=|s|, (18)

h _d (s)=|s|, (20)

Another aspect of the present invention is to provide an X-ray grating differential phase contrast three-dimensional cone-beam computed tomography device based on a laterally misaligned grating, including:

An acquisition module, configured to acquire a sequence of two-dimensional projection images collected by the detector. The sequence of two-dimensional projection images is during the rotation of the object along the axial direction. After the projection of the rays transmitted through the object, the detector periodically collects A plurality of two-dimensional projection images obtained, and one sampling period corresponds to one two-dimensional projection image of the object;

The calculation module is used to perform Fourier transform on the two-dimensional projection image sequence to obtain the absorption contrast, differential phase contrast and scattering contrast two-dimensional projection sequence; using the absorption contrast, differential phase contrast and scattering contrast three Three-dimensional CT slice images are obtained by reconstructing three contrast two-dimensional projection sequences with a contrast filtering inverse reconstruction algorithm.

Further, the Talbot-Lau imaging structure of the lateral dislocation absorption grating arrangement includes:

The optical path of the Talbot-Lau imaging structure includes a total of six parts: X-ray source, source grating G0, test object, phase grating G1, absorption grating G2, detector;

The optical path parameters of the Talbot-Lau imaging structure should satisfy the following formulas (1)-(4):

kg ₁ =2g ₂ , (2)

g ₀ =g ₂ ·L/d, (3)

s<g ₂ L/2d, (4)

Among them, d represents the distance between the phase grating G1 and the absorption grating G2; k=(L+d)/L is the amplification ratio, and L is the direct distance between the source grating G0 and the phase grating G1; m represents the fractional Talbot distance of the mth order ; g ₁ is the period of the phase grating G1, λ is the wavelength of the X-ray used, g ₂ is the period of the absorption grating G2, g ₀ is the period of the source grating G0, s is the X-ray transmission allowed in each period of the source grating over the width;

The lateral dislocation absorption grating refers to the absorption grating G2 in the optical path of the Talbot-Lau imaging structure, and its relative position to the detector probes has a lateral periodic dislocation, so that multiple adjacent detector probes in the lateral direction obtain The intensity signal can be equivalent to the intensity signal obtained when a detector probe is in multiple different positions in the traditional imaging method;

For the 4 laterally adjacent detector probes, respectively marked as p ₁ , p ₂ , p ₃ , p ₄ , each probe p _x (x=1,2,3,4) has a width of w, and is dislocated in the lateral direction In the absorption grating, corresponding to a section of grating gp _x with length w, the grating period of each section of grating gp _x is g ₂ , and the gratings corresponding to adjacent detector elements have a position difference of distance f, such as adjacent detectors There is a position difference of f between the grating segments gp ₁ and gp ₂ corresponding to elements p ₁ and p ₂ , where f=g ₂ /4, the position of the gp _x grating is equivalent to the position of the absorption grating when it moves to x, adjacent 4 The positions of the absorption gratings corresponding to each detector element are different, and they are staggered by a distance f, which is called a lateral misalignment grating. The X-ray intensity signal value obtained by the detector element p _x is when the absorption grating G2 moves to the position x The collected intensity value.

Further, the acquisition module also includes:

In the Talbot-Lau imaging structure, when no object is placed on the turntable, the turntable rotates 360 degrees at a constant speed along the rotation center, and the imaging area is covered by the cone beam during the rotation process, and the two-dimensional projection image is collected by the detector;

In the Talbot-Lau imaging structure, when the object is placed on the turntable, the turntable rotates 360 degrees at a constant speed along the rotation center, and the imaging area is covered by the cone beam during the rotation, and the two-dimensional projection image is collected by the detector.

Further, the calculation module uses Fourier analysis method to separate three kinds of images of X-ray absorption contrast, differential phase contrast and scattering contrast from the collected two-dimensional intensity images, including:

Perform image analysis on the two-dimensional projection image sequence according to formulas (5)-(14) to obtain three contrast two-dimensional projection image sequences:

I ₁ (x,z,θ)=I(x-1,z,θ), (5)

I ₂ (x,z,θ)=I(x,z,θ), (6)

I ₃ (x,z,θ)=I(x+1,z,θ), (7)

I ₄ (x,z,θ)=I(x+2,z,θ), (8)

phase(x,z,θ)=φ ^s (x,z,θ)-φ ^r (x,z,θ), (13)

Among them, x is the abscissa of the point in the two-dimensional projection; z is the vertical coordinate of the point in the two-dimensional projection, and θ is the projection angle of the two-dimensional projection image; I(x,z,θ) is the point in the two-dimensional projection (x,z) intensity value at projection angle θ; I ₁ (x,z,θ), I ₂ (x,z,θ), I ₃ (x,z,θ), I ₄ (x,z, θ) represent 4 different intensity values of the point (x, z) at the projection angle θ respectively, simulating the point (x, z) in the projection angle θ of the traditional grating differential phase contrast image when the absorption grating is in 4 different steps The intensity value when entering the position; M represents the number of different intensity values in a point (x, z), M=4; a ₀ (x, z, θ) is the point (x, z) at the projection angle θ The mean value of the sinusoidal curve fitted by 4 different intensity values; a ₁ (x, z, θ) is the amplitude of the sinusoidal curve fitted by the 4 different intensity values of the point (x, z) at the projection angle θ Size; φ(x,z,θ) is the phase value of the sinusoidal curve fitted by the point (x,z) at 4 different intensity values of the projection angle θ; Indicates the value of a ₀ (x,z,θ) when the test object is not placed at the projection angle θ, Indicates the value of a ₀ (x,z,θ) when the test object is placed at the projection angle θ; Indicates the value of a ₁ (x,z,θ) when the test object is not placed at the projection angle θ, Indicates the a ₁ (x, z, θ) value when the test object is placed at the projection angle θ; φ ^r (x, z, θ) indicates the φ(x, z, θ) value when the test object is not placed at the projection angle θ , φ ^s (x, z, θ) represents the value of φ(x, z, θ) when the test object is placed at the projection angle θ; abs(x, z, θ) is the absorption at the point (x, z) at the projection angle θ The value of the contrast; phase(x,z,θ) is the value of the differential phase contrast at the projection angle θ point (x,z); dark(x,z,θ) is the projection angle θ point (x,z) Values for scatter contrast imaging.

Further, the calculation module uses the absorption contrast, differential phase contrast and scattering contrast filter back projection reconstruction algorithms to respectively perform image reconstruction on three kinds of contrast two-dimensional image sequences, and obtain the absorption contrast, phase contrast and scattering contrast of the object. Contrast three CT slice images, including:

Perform image analysis on the two-dimensional projection image sequence according to formulas (15)-(17) to obtain three contrast two-dimensional projection image sequences:

Among them, a(x,y,z), p(x,y,z) and d(x,y,z) are respectively the reconstructed absorption contrast slice image, phase contrast slice image and scattering contrast slice image; abs(s,v,θ), phase(s,v,θ) and dark(s,v,θ) represent the two-dimensional projection of absorption contrast, differential phase contrast and scattering contrast under the projection angle θ respectively, s , v are the coordinates of the intersection between the pixel point on the detector and the ray source and the virtual detector placed at the rotation axis; ξ is the angle between the ray and the central ray; D is the distance from the ray source to the virtual detector plane ; y′ is the distance from the reconstructed image pixel to the virtual detector plane; h _a (s), h _p (s) and h _d (s) are the two-dimensional projections of absorption contrast, differential phase contrast and scattering contrast, respectively The filter, which is defined as formula (18)-(19):

h _a (s)=|s|, (18)

h _d (s)=|s|, (20)

Compared with the prior art, the present invention has the following advantages: (1) the present invention can solve the problem of multiple exposures at one projection angle and reduce the radiation dose; (2) avoid grating stepping in the process of projection imaging at one angle , eliminating the errors caused by mechanical jitter; (3) Only one exposure imaging is required at each angle to obtain three-dimensional tomographic images of object absorption contrast, phase contrast and scattering contrast.

Description of drawings

Fig. 1 is a flow chart of a three-dimensional cone-beam computed tomography method based on an X-ray grating differential phase contrast provided by an embodiment of the present invention;

Fig. 2 is a schematic diagram of a three-dimensional cone-beam computed tomography system based on an X-ray grating differential phase contrast provided by an embodiment of the present invention;

Fig. 3 is a schematic diagram of the structure of a novel laterally dislocated absorption grating provided by an embodiment of the present invention;

Fig. 4 is a two-dimensional projection image of the X-ray grating differential phase contrast three-dimensional cone beam computed tomography method based on the laterally dislocated absorption grating;

Fig. 5 is four two-dimensional projection images of the traditional X-ray grating differential phase contrast imaging method;

Figure 6 is the absorption contrast, differential phase contrast and scattering contrast images obtained by the X-ray grating differential phase contrast three-dimensional cone beam computed tomography method based on the laterally dislocated absorption grating;

Figure 7 is the absorption contrast, differential phase contrast and scattering contrast images obtained by the traditional X-ray grating differential phase contrast imaging method;

Fig. 8 is a CT image of the three-dimensional cone beam computed tomography method based on the X-ray grating differential phase contrast provided by the embodiment of the present invention;

Fig. 9 is a CT image of the traditional X-ray grating differential phase contrast imaging method.

Fig. 10 is a structural diagram of an X-ray grating differential phase contrast three-dimensional cone-beam computed tomography device based on a laterally dislocated absorption grating provided by an embodiment of the present invention.

In the figure: 20 is the X-ray source, 21 is the X-ray beam, 22 is the source grating G0, 23 is the object to be measured, 24 is the phase grating G1, 25 is the lateral displacement absorption grating G2, 26 is the detector, 27 is the computer, 100 is an X-ray cylindrical three-dimensional cone-beam computed tomography device, 101 is an acquisition module, and 102 is a calculation module.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Fig. 1 is a flow chart of the X-ray grating differential phase contrast three-dimensional cone-beam computed tomography method based on the laterally dislocated absorption grating provided by the embodiment of the present invention; the embodiment of the present invention is aimed at the existing X-ray absorption contrast CT imaging and X-ray Grating differential phase contrast CT imaging, the slice image has only one contrast or can obtain three kinds of contrast but requires multiple exposures at one projection angle, large radiation dose, long imaging time, low efficiency, and large mechanical vibration errors. An X-ray grating differential phase contrast three-dimensional cone-beam computed tomography method based on a laterally dislocated absorption grating is provided, and the specific steps of the method are as follows:

Step S101 , using the Talbort-Lau three-dimensional tomography structure proposed by the present invention based on the lateral misalignment grating to acquire a sequence of two-dimensional projection images after X-rays pass through the object. The two-dimensional projection sequence is a two-dimensional projection of the object after the detector periodically collects X-rays passing through the object during the axial rotation of the object, and acquires a two-dimensional projection image of the object in one collection cycle .

The optical path parameters of the Talbot-Lau three-dimensional tomography structure should satisfy the following formulas (1)-(4):

kg ₁ =2g ₂ , (2)

g ₀ =g ₂ ·L/d, (3)

s<g ₂ L/2d, (4)

Among them, d represents the distance between the phase grating G1 and the absorption grating G2; k=(L+d)/L is the amplification ratio, and L is the direct distance between the source grating G0 and the phase grating G1; m represents the fractional Talbot distance of the mth order ; g ₁ is the period of the phase grating G1, λ is the wavelength of the X-ray used, g ₂ is the period of the absorption grating G2, g ₀ is the period of the source grating G0, s is the X-ray transmission allowed in each period of the source grating over the width.

Fig. 2 is a schematic diagram of the three-dimensional cone beam computed tomography system based on the X-ray grating differential phase contrast provided by the embodiment of the present invention; as shown in Fig. 2, the X-ray grating differential phase contrast The three-dimensional cone-beam computed tomography system includes: X-ray source 20, X-ray beam 21, source grating G0 22, object to be measured 23, phase grating G1 24, transverse dislocation absorption grating G2 25, detector 26, and computer 27. Wherein, the detector 26 and the X-ray source 20 are respectively connected to a computer 27 . The computer 27 is used to control the intensity and time of the X-ray beam 21 generated by the X-ray source 20, and to control the detector 26 to collect two-dimensional intensity images. The X-ray beam 21 produced by the X-ray source 20 is transmitted through the object to be measured 23 after passing through the source grating G0 22, and the imaging area of the object to be measured 23 is covered by the X-ray beam 21, and the X-ray beam 21 passes through the phase grating G1 24 and absorbs the lateral displacement The signal modulated by the grating G2 25 is collected by the detector 26 . After the acquisition is completed, the computer 27 controls the detector 26 to stop sampling, controls the X-ray source 20 to stop generating X-rays, and the three-dimensional cone-beam computer tomography system based on the X-ray grating differential phase contrast of the laterally misaligned grating completes the imaging at one projection angle. One projection imaging. The whole tomographic imaging process is as follows: at each projection angle, in the Talbot-Lau three-dimensional tomographic imaging structure, the object 23 to be measured is not placed first, and the computer 27 controls the detector 26 to collect the two-dimensional intensity image at this time; Then the object 23 to be measured is placed in the Talbot-Lau imaging optical path to ensure that the object is completely covered by the X-ray beam 21 in the test area, and the computer 27 controls the detector 26 to collect the X-ray signal after the attenuation of the object 23 to be measured. Intensity image; the projection angle covers 360 degrees, and after the above-mentioned acquisition is performed at each projection angle, the acquisition of a tomographic two-dimensional projection image sequence is completed.

Fig. 3 is a schematic diagram of the structure of a novel laterally dislocated absorption grating provided by an embodiment of the present invention.

Step S102 , performing Fourier transform on the two-dimensional projection image sequence to separate three contrast image sequences of X-ray absorption contrast, differential phase contrast and scattering contrast.

The computer 27 performs Fourier transform on the two-dimensional projection image sequence collected by the detector to separate three contrast image sequences of X-ray absorption contrast, differential phase contrast and scattering contrast, including:

Perform image analysis on the two-dimensional projection image sequence according to formulas (5)-(14) to obtain three contrast two-dimensional projection image sequences:

I ₁ (x,z,θ)=I(x-1,z,θ), (5)

I ₂ (x,z,θ)=I(x,z,θ), (6)

I ₃ (x,z,θ)=I(x+1,z,θ), (7)

I ₄ (x,z,θ)=I(x+2,z,θ), (8)

phase(x,z,θ)=φ ^s (x,z,θ)-φ ^r (x,z,θ), (13)

Among them, x is the abscissa of the point in the two-dimensional projection; z is the vertical coordinate of the point in the two-dimensional projection, and θ is the projection angle of the two-dimensional projection image; I(x,z,θ) is the point in the two-dimensional projection (x,z) intensity value at projection angle θ; I ₁ (x,z,θ), I ₂ (x,z,θ), I ₃ (x,z,θ), I ₄ (x,z, θ) represent 4 different intensity values of the point (x, z) at the projection angle θ respectively, simulating the point (x, z) in the projection angle θ of the traditional grating differential phase contrast image when the absorption grating is in 4 different steps The intensity value when entering the position; M represents the number of different intensity values in a point (x, z), M=4; a ₀ (x, z, θ) is the point (x, z) at the projection angle θ The mean value of the sinusoidal curve fitted by 4 different intensity values; a ₁ (x, z, θ) is the amplitude of the sinusoidal curve fitted by the 4 different intensity values of the point (x, z) at the projection angle θ Size; φ(x,z,θ) is the phase value of the sinusoidal curve fitted by the point (x,z) at 4 different intensity values of the projection angle θ; Indicates the value of a ₀ (x,z,θ) when the test object is not placed at the projection angle θ, Indicates the value of a ₀ (x,z,θ) when the test object is placed at the projection angle θ; Indicates the value of a ₁ (x,z,θ) when the test object is not placed at the projection angle θ, Indicates the a ₁ (x, z, θ) value when the test object is placed at the projection angle θ; φ ^r (x, z, θ) indicates the φ(x, z, θ) value when the test object is not placed at the projection angle θ , φ ^s (x, z, θ) represents the value of φ(x, z, θ) when the test object is placed at the projection angle θ; abs(x, z, θ) is the absorption at the point (x, z) at the projection angle θ The value of the contrast; phase(x,z,θ) is the value of the differential phase contrast at the projection angle θ point (x,z); dark(x,z,θ) is the projection angle θ point (x,z) Values for scatter contrast imaging.

Step S103, using the absorption contrast, differential phase contrast and scattering contrast filter back projection reconstruction algorithms to reconstruct the three contrast two-dimensional image sequences respectively, and obtain the absorption contrast, phase contrast and scattering contrast of the object Three kinds of CT slice images, including:

Perform image analysis on the two-dimensional projection image sequence according to formulas (15)-(17) to obtain three contrast two-dimensional projection image sequences:

Among them, a(x,y,z), p(x,y,z) and d(x,y,z) are respectively the reconstructed absorption contrast slice image, phase contrast slice image and scattering contrast slice image; abs(s,v,θ), phase(s,v,θ) and dark(s,v,θ) represent the two-dimensional projection of absorption contrast, differential phase contrast and scattering contrast under the projection angle θ respectively, s , v are the coordinates of the intersection between the pixel point on the detector and the ray source and the virtual detector placed at the rotation axis; ξ is the angle between the ray and the central ray; D is the distance from the ray source to the virtual detector plane ; y′ is the distance from the reconstructed image pixel to the virtual detector plane; h _a (s), h _p (s) and h _d (s) are the two-dimensional projections of absorption contrast, differential phase contrast and scattering contrast, respectively The filter, which is defined as formula (18)-(19):

h _a (s)=|s|, (18)

h _d (s)=|s|, (20)

Compared with the existing X-ray absorption contrast CT technology and X-ray grating differential phase contrast CT technology, the embodiment of the present invention can only use one exposure imaging at each projection angle, and finally reconstruct the object absorption contrast, The tomographic images of phase contrast and scattering contrast have simple steps and do not require high-precision movement of the absorption grating during the imaging process, which significantly reduces imaging time, reduces radiation dose, and improves imaging efficiency.

In order to prove the effect of the above-mentioned embodiment, the embodiment of the present invention carried out the following experiments, and the experimental steps are as follows:

(1) Set the experimental conditions. The source grating G0, phase grating G1 and absorption grating G2 in this experiment are designed under the condition that the X-ray energy is 28keV. The period of the source grating G0 is 14 microns; the period of the phase grating G1 is 3.5 microns; the period of the absorption grating G2 is 2.0 microns. The distance between the source grating G0 and the phase grating G1 is 1400 mm, and the distance between the phase grating G1 and the absorption grating G2 is 200 mm, corresponding to the 5th fractional Talbot distance (m=5). The size of the 2D intensity image is 307*652.

(2) Arrange the Talbot-Lau imaging structure according to the Talbot-Lau imaging optical path parameter requirements.

(3) According to the set parameters, the computer controls the rotation of the turntable, and the detector collects the projection data before and after placing the object to be measured, and generates a two-dimensional projection image sequence according to the projection data.

(4) The computer uses the Fourier analysis method to separate the three image sequences of absorption contrast, differential phase contrast and scattering contrast on the two-dimensional projection image sequence according to the above formulas (5)-(14).

(5) The computer performs image reconstruction on the separated absorption contrast, differential phase contrast and scattering contrast image sequences of the object according to the above formulas (15)-(20) to obtain the tomographic images of the three contrasts of the object.

Figure 4 is the two-dimensional projection image obtained by the X-ray grating differential phase contrast three-dimensional cone-beam computed tomography system based on the lateral displacement grating; Figure 6 is the X-ray grating differential phase contrast three-dimensional cone beam computer layer based on the lateral displacement grating The two-dimensional projection images of absorption contrast, differential phase contrast and scattering contrast analyzed by the imaging system; Fig. 8 is the reconstruction of the CT image obtained by the three-dimensional cone-beam computer tomography system based on the X-ray grating differential phase contrast with lateral displacement grating. image. It can be seen from Figures 4, 6 and 8 that the X-ray grating differential phase contrast 3D cone-beam computed tomography system based on the laterally misaligned grating can correctly separate the three-contrast two-dimensional projection images of the object and reconstruct the three-dimensional image of the object. A contrast tomographic image.

Figure 5 is the two-dimensional projection image obtained by the traditional X-ray grating differential phase contrast imaging method; Figure 7 is the absorption contrast, differential phase contrast and scattering contrast analyzed by the traditional X-ray grating differential phase contrast imaging method 3D projection image; FIG. 9 is a CT image reconstructed by a traditional X-ray grating differential phase contrast computer tomography system. It can be clearly observed from Figure 5 that the traditional X-ray grating differential phase contrast imaging method requires four exposures to the object, which greatly increases the imaging time and radiation dose, and significantly reduces the imaging efficiency.

As can be seen from Figures 4, 5, 6, 7, 8 and 9, the embodiment of the present invention can quickly and correctly perform three-dimensional imaging of the object in terms of absorption contrast, phase contrast and scattering contrast, and only one exposure is required at each projection angle The projection imaging process can be realized without multiple exposures of the traditional grating differential imaging method, which reduces the imaging time, significantly reduces the radiation dose, reduces the error caused by mechanical jitter, and improves the efficiency of three contrast imaging. The process is simple and easy accomplish.

Fig. 10 is a structural diagram of an X-ray grating differential phase contrast three-dimensional cone-beam computed tomography device based on a laterally misaligned grating provided by an embodiment of the present invention. The X-ray grating differential phase contrast three-dimensional cone-beam computer tomography device provided by the embodiment of the present invention can execute the processing flow provided by the embodiment of the three-contrast three-dimensional cone-beam computer tomography method of the object, as shown in the figure As shown in 10, the X-ray grating differential phase contrast three-dimensional cone-beam computed tomography device 100 based on the transverse misalignment grating includes an acquisition module 101 and a calculation module 102, wherein the acquisition module 101 is used to acquire the two-dimensional projection collected by the detector Image sequence; the calculation module 102 is used to perform Fourier analysis on the two-dimensional projection image sequence to separate three contrast projection image sequences, and reconstruct three contrast tomographic images using three contrast filter de-reconstruction algorithms.

Compared with the existing X-ray absorption contrast CT technology and X-ray grating differential phase contrast CT technology, the embodiment of the present invention can only use one exposure imaging at each projection angle, and finally reconstruct the object absorption contrast, The tomographic images of phase contrast and scattering contrast have simple steps and do not require high-precision movement of the absorption grating during the imaging process, which significantly reduces imaging time, reduces radiation dose, and improves imaging efficiency.

The acquisition module 101 needs to arrange the various devices according to the Talbot-Lau imaging optical path parameter requirements, and the detector collects the two-dimensional intensity image of the object to be measured.

The optical path parameters of the Talbot-Lau imaging structure should satisfy the following formulas (1)-(4):

kg ₁ =2g ₂ , (2)

g ₀ =g ₂ ·L/d, (3)

s<g ₂ L/2d, (4)

Among them, d represents the distance between the phase grating G1 and the absorption grating G2; k=(L+d)/L is the amplification ratio, and L is the direct distance between the source grating G0 and the phase grating G1; m represents the fractional Talbot distance of the mth order ; g ₁ is the period of the phase grating G1, λ is the wavelength of the X-ray used, g ₂ is the period of the absorption grating G2, g ₀ is the period of the source grating G0, s is the X-ray transmission allowed in each period of the source grating over the width.

The calculation module 102 performs image analysis on the two-dimensional projection image sequence according to formulas (5)-(14) to obtain three contrast two-dimensional projection image sequences:

I ₁ (x,z,θ)=I(x-1,z,θ), (5)

I ₂ (x,z,θ)=I(x,z,θ), (6)

I ₃ (x,z,θ)=I(x+1,z,θ), (7)

I ₄ (x,z,θ)=I(x+2,z,θ), (8)

phase(x,z,θ)=φ ^s (x,z,θ)-φ ^r (x,z,θ), (13)

Among them, x is the abscissa of the point in the two-dimensional projection; z is the vertical coordinate of the point in the two-dimensional projection, and θ is the projection angle of the two-dimensional projection image; I(x,z,θ) is the point in the two-dimensional projection (x,z) intensity value at projection angle θ; I ₁ (x,z,θ), I ₂ (x,z,θ), I ₃ (x,z,θ), I ₄ (x,z, θ) represent 4 different intensity values of the point (x, z) at the projection angle θ respectively, simulating the point (x, z) in the projection angle θ of the traditional grating differential phase contrast image when the absorption grating is in 4 different steps The intensity value when entering the position; M represents the number of different intensity values in a point (x, z), M=4; a ₀ (x, z, θ) is the point (x, z) at the projection angle θ The mean value of the sinusoidal curve fitted by 4 different intensity values; a ₁ (x, z, θ) is the amplitude of the sinusoidal curve fitted by the 4 different intensity values of the point (x, z) at the projection angle θ Size; φ(x,z,θ) is the phase value of the sinusoidal curve fitted by the point (x,z) at 4 different intensity values of the projection angle θ; Indicates the value of a ₀ (x,z,θ) when the test object is not placed at the projection angle θ, Indicates the value of a ₀ (x,z,θ) when the test object is placed at the projection angle θ; Indicates the value of a ₁ (x,z,θ) when the test object is not placed at the projection angle θ, Indicates the a ₁ (x, z, θ) value when the test object is placed at the projection angle θ; φ ^r (x, z, θ) indicates the φ(x, z, θ) value when the test object is not placed at the projection angle θ , φ ^s (x, z, θ) represents the value of φ(x, z, θ) when the test object is placed at the projection angle θ; abs(x, z, θ) is the absorption at the point (x, z) at the projection angle θ The value of the contrast; phase(x,z,θ) is the value of the differential phase contrast at the projection angle θ point (x,z); dark(x,z,θ) is the projection angle θ point (x,z) Values for scatter contrast imaging.

The calculation module 102 performs image analysis on the two-dimensional projection image sequence according to formulas (15)-(17) to obtain three contrast two-dimensional projection image sequences:

Among them, a(x,y,z), p(x,y,z) and d(x,y,z) are respectively the reconstructed absorption contrast slice image, phase contrast slice image and scattering contrast slice image; abs(s,v,θ), phase(s,v,θ) and dark(s,v,θ) represent the two-dimensional projection of absorption contrast, differential phase contrast and scattering contrast under the projection angle θ respectively, s , v are the coordinates of the intersection between the pixel point on the detector and the ray source and the virtual detector placed at the rotation axis; ξ is the angle between the ray and the central ray; D is the distance from the ray source to the virtual detector plane ; y′ is the distance from the reconstructed image pixel to the virtual detector plane; h _a (s), h _p (s) and h _d (s) are the two-dimensional projections of absorption contrast, differential phase contrast and scattering contrast, respectively The filter, which is defined as formula (18)-(19):

h _a (s)=|s|, (18)

h _d (s)=|s|, (20)

Compared with the existing X-ray absorption contrast CT technology and X-ray grating differential phase contrast CT technology, the embodiment of the present invention can only use one exposure imaging at each projection angle, and finally reconstruct the object absorption contrast, The tomographic images of phase contrast and scattering contrast have simple steps and do not require high-precision movement of the absorption grating during the imaging process, which significantly reduces imaging time, reduces radiation dose, and improves imaging efficiency.

The X-ray grating differential phase contrast three-dimensional cone-beam computed tomography device provided by the embodiment of the present invention can be specifically used to execute the method embodiment provided in FIG. 1 above, and the specific functions will not be repeated here.

The embodiment of the present invention can quickly perform two-dimensional projection imaging on the absorption contrast, differential phase contrast and scattering contrast of the object, and reconstruct three-dimensional tomographic images of the three contrasts. Only one exposure is required at each projection angle. Three kinds of contrast two-dimensional projection images can be separated, the imaging time is reduced, the radiation dose is reduced, the error caused by mechanical vibration is eliminated, and the imaging efficiency is improved.

In summary, compared with the existing CT technology, the embodiment of the present invention can perform three-dimensional tomographic imaging of objects with three contrasts: absorption contrast, phase contrast, and scattering contrast; the steps are simple, and at each projection angle Only one exposure is needed, and there is no need to step through the absorption grating multiple times to obtain three-contrast two-dimensional projection images; the time for two-dimensional projection imaging is reduced; the radiation dose is reduced; errors caused by mechanical jitter are eliminated; imaging efficiency.

In the several embodiments provided by the present invention, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only illustrative. For example, the division of the units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components can be combined or May be integrated into another system, or some features may be ignored, or not implemented. In another point, the mutual coupling or direct coupling or communication connection shown or discussed may be through some interfaces, and the indirect coupling or communication connection of devices or units may be in electrical, mechanical or other forms.

The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or may be distributed to multiple network units. Part or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, each unit may exist separately physically, or two or more units may be integrated into one unit. The above-mentioned integrated units can be implemented in the form of hardware, or in the form of hardware plus software functional units.

The above-mentioned integrated units implemented in the form of software functional units may be stored in a computer-readable storage medium. The above-mentioned software functional units are stored in a storage medium, and include several instructions to make a computer device (which may be a personal computer, server, or network device, etc.) or a processor (processor) execute the methods described in various embodiments of the present invention. partial steps. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (Read-Only Memory, ROM), random access memory (Random Access Memory, RAM), magnetic disk or optical disk and other various media that can store program codes. .

Those skilled in the art can clearly understand that for the convenience and brevity of description, only the division of the above-mentioned functional modules is used as an example for illustration. The internal structure of the system is divided into different functional modules to complete all or part of the functions described above. For the specific working process of the device described above, reference may be made to the corresponding process in the foregoing method embodiments, and details are not repeated here.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: It is still possible to modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the various embodiments of the present invention. scope.

Claims (10)

1. A three-dimensional cone-beam computed tomography method based on X-ray grating differential phase contrast of lateral displacement grating, it is characterized in that, comprises the steps: Step 1. Obtain the two-dimensional projection image sequence after the X-ray passes through the object with the Talbort-Lau three-dimensional tomography structure based on the lateral misalignment grating. The two-dimensional projection image sequence is during the rotation of the object along the axial direction. Collecting the two-dimensional projection of the X-ray after passing through the object, and collecting a two-dimensional projection image of the object in one collection cycle; Step 2, performing Fourier transform on the two-dimensional projection image sequence to separate three contrast images of X-ray absorption contrast, differential phase contrast and scattering contrast; Step 3, using the absorption contrast, differential phase contrast and scattering contrast filter back projection reconstruction algorithm to reconstruct the three contrast two-dimensional image sequences respectively, and obtain the absorption contrast, phase contrast and scattering contrast of the object Three kinds of CT slice images. 2. The X-ray grating differential phase contrast three-dimensional cone-beam computed tomography method based on the laterally misplaced grating according to claim 1, wherein the Talbot-Lau imaging structure is arranged in the laterally misplaced absorption grating, comprising: The optical path of the Talbot-Lau imaging structure includes a total of six parts: X-ray source, source grating G0, test object, phase grating G1, absorption grating G2, detector; The optical path parameters of the Talbot-Lau imaging structure should satisfy the following formulas (1)-(4): kg ₁ =2g ₂ , (2) g ₀ =g ₂ ·L/d, (3) s<g ₂ L/2d, (4) Among them, d represents the distance between the phase grating G1 and the absorption grating G2; k=(L+d)/L is the amplification ratio, and L is the direct distance between the source grating G0 and the phase grating G1; m represents the fractional Talbot distance of the mth order ; g ₁ is the period of the phase grating G1, λ is the wavelength of the X-ray used, g ₂ is the period of the absorption grating G2, g ₀ is the period of the source grating G0, s is the X-ray transmission allowed in each period of the source grating over the width; The lateral dislocation absorption grating refers to the absorption grating G2 in the optical path of the Talbot-Lau imaging structure, and its relative position to the detector probes has a lateral periodic dislocation, so that multiple adjacent detector probes in the lateral direction obtain The intensity signal can be equivalent to the intensity signal obtained when a detector probe is in multiple different positions in the traditional imaging method; For the 4 laterally adjacent detector probes, respectively marked as p ₁ , p ₂ , p ₃ , p ₄ , each probe p _x (x=1,2,3,4) has a width of w, and is dislocated in the lateral direction In the absorption grating, corresponding to a section of grating gp _x with length w, the grating period of each section of grating gp _x is g ₂ , and the gratings corresponding to adjacent detector elements have a position difference of distance f, such as adjacent detectors There is a position difference of f between the grating segments gp ₁ and gp ₂ corresponding to elements p ₁ and p ₂ , where f=g ₂ /4, the position of the gp _x grating is equivalent to the position of the absorption grating when it moves to x, adjacent 4 The positions of the absorption gratings corresponding to each detector element are different, and they are staggered by a distance f, which is called a lateral misalignment grating. The X-ray intensity signal value obtained by the detector element p _x is when the absorption grating G2 moves to the position x The collected intensity value. 3. The X-ray grating differential phase contrast three-dimensional cone-beam computed tomography method based on laterally misaligned gratings according to claim 1, wherein step 1 also includes: In the Talbot-Lau imaging structure, when no object is placed on the turntable, the turntable rotates 360 degrees at a constant speed along the rotation center, and the imaging area is covered by the cone beam during the rotation process, and the two-dimensional projection image is collected by the detector; In the Talbot-Lau imaging structure, when the object is placed on the turntable, the turntable rotates 360 degrees at a constant speed along the rotation center, and the imaging area is covered by the cone beam during the rotation, and the two-dimensional projection image is collected by the detector. 4. The X-ray grating differential phase contrast three-dimensional cone-beam computed tomography method based on laterally misaligned grating according to claim 1, characterized in that, it is separated from the collected two-dimensional intensity image by Fourier analysis method Three kinds of images including X-ray absorption contrast, differential phase contrast and scattering contrast can be produced, including: Perform image analysis on the two-dimensional projection image sequence according to formulas (5)-(14) to obtain three contrast two-dimensional projection image sequences: I ₁ (x,z,θ)=I(x-1,z,θ), (5) I ₂ (x,z,θ)=I(x,z,θ), (6) I ₃ (x,z,θ)=I(x+1,z,θ), (7) I ₄ (x,z,θ)=I(x+2,z,θ), (8) phase(x,z,θ)=φ ^s (x,z,θ)-φ ^r (x,z,θ), (13) Among them, x is the abscissa of the point in the two-dimensional projection; z is the vertical coordinate of the point in the two-dimensional projection, and θ is the projection angle of the two-dimensional projection image; I(x,z,θ) is the point in the two-dimensional projection (x,z) intensity value at projection angle θ; I ₁ (x,z,θ), I ₂ (x,z,θ), I ₃ (x,z,θ), I ₄ (x,z, θ) represent 4 different intensity values of the point (x, z) at the projection angle θ respectively, simulating the point (x, z) in the projection angle θ of the traditional grating differential phase contrast image when the absorption grating is in 4 different steps The intensity value when entering the position; M represents the number of different intensity values in a point (x, z), M=4; a ₀ (x, z, θ) is the point (x, z) at the projection angle θ The mean value of the sinusoidal curve fitted by 4 different intensity values; a ₁ (x, z, θ) is the amplitude of the sinusoidal curve fitted by the 4 different intensity values of the point (x, z) at the projection angle θ Size; φ(x,z,θ) is the phase value of the sinusoidal curve fitted by the point (x,z) at 4 different intensity values of the projection angle θ; Indicates the value of a ₀ (x,z,θ) when the test object is not placed at the projection angle θ, Indicates the value of a ₀ (x,z,θ) when the test object is placed at the projection angle θ; Indicates the value of a ₁ (x,z,θ) when the test object is not placed at the projection angle θ, Indicates the a ₁ (x, z, θ) value when the test object is placed at the projection angle θ; φ ^r (x, z, θ) indicates the φ(x, z, θ) value when the test object is not placed at the projection angle θ , φ ^s (x, z, θ) represents the value of φ(x, z, θ) when the test object is placed at the projection angle θ; abs(x, z, θ) is the absorption at the point (x, z) at the projection angle θ The value of the contrast; phase(x,z,θ) is the value of the differential phase contrast at the projection angle θ point (x,z); dark(x,z,θ) is the projection angle θ point (x,z) Values for scatter contrast imaging. 5. The X-ray grating differential phase contrast three-dimensional cone-beam computed tomography method based on lateral misalignment grating according to claim 1, characterized in that, using absorption contrast, differential phase contrast and scattering contrast filter back projection The reconstruction algorithm performs image reconstruction on three kinds of contrast two-dimensional image sequences respectively, and obtains three kinds of CT slice images of the object absorption contrast, phase contrast and scattering contrast, including: Perform image analysis on the two-dimensional projection image sequence according to formulas (15)-(17) to obtain three contrast two-dimensional projection image sequences: Among them, a(x,y,z), p(x,y,z) and d(x,y,z) are respectively the reconstructed absorption contrast slice image, phase contrast slice image and scattering contrast slice image; abs(s,v,θ), phase(s,v,θ) and dark(s,v,θ) represent the two-dimensional projection of absorption contrast, differential phase contrast and scattering contrast under the projection angle θ respectively, s , v are the coordinates of the intersection between the pixel point on the detector and the ray source and the virtual detector placed at the rotation axis; ξ is the angle between the ray and the central ray; D is the distance from the ray source to the virtual detector plane ; y′ is the distance from the reconstructed image pixel to the virtual detector plane; h _a (s), h _p (s) and h _d (s) are the two-dimensional projections of absorption contrast, differential phase contrast and scattering contrast, respectively The filter of , which is defined as formula (18)-(19): h _a (s)=|s|, (18) _hd (s)=|s|, (20) . 6. An X-ray grating differential phase contrast three-dimensional cone-beam computed tomography device based on a laterally misaligned grating, characterized in that it comprises: An acquisition module, configured to acquire a sequence of two-dimensional projection images collected by the detector. The sequence of two-dimensional projection images is during the rotation of the object along the axial direction. After the projection of the rays transmitted through the object, the detector periodically collects A plurality of two-dimensional projection images obtained, and one sampling period corresponds to one two-dimensional projection image of the object; The calculation module is used to perform Fourier transform on the two-dimensional projection image sequence to obtain the two-dimensional projection sequence of absorption contrast, differential phase contrast and scattering contrast; use the cone beam reconstruction algorithm to perform three-dimensional contrast two-dimensional projection Image reconstruction is performed sequentially to obtain a three-dimensional CT slice image corresponding to the object cylinder. 7. The X-ray grating differential phase contrast three-dimensional cone-beam computed tomography device based on a laterally misplaced grating according to claim 6, wherein the Talbot-Lau imaging structure is arranged in the laterally misplaced absorption grating, comprising: The optical path of the Talbot-Lau imaging structure includes a total of six parts: X-ray source, source grating G0, test object, phase grating G1, absorption grating G2, detector; The optical path parameters of the Talbot-Lau imaging structure should satisfy the following formulas (1)-(4): kg ₁ =2g ₂ , (2) g ₀ =g ₂ ·L/d, (3) s<g ₂ L/2d, (4) Among them, d represents the distance between the phase grating G1 and the absorption grating G2; k=(L+d)/L is the amplification ratio, and L is the direct distance between the source grating G0 and the phase grating G1; m represents the fractional Talbot distance of the mth order ; g ₁ is the period of the phase grating G1, λ is the wavelength of the X-ray used, g ₂ is the period of the absorption grating G2, g ₀ is the period of the source grating G0, s is the X-ray transmission allowed in each period of the source grating over the width; The lateral dislocation absorption grating refers to the absorption grating G2 in the optical path of the Talbot-Lau imaging structure, and its relative position to the detector probes has a lateral periodic dislocation, so that multiple adjacent detector probes in the lateral direction obtain The intensity signal can be equivalent to the intensity signal obtained when a detector probe is in multiple different positions in the traditional imaging method; For the 4 laterally adjacent detector probes, respectively marked as p ₁ , p ₂ , p ₃ , p ₄ , each probe p _x (x=1,2,3,4) has a width of w, and is dislocated in the lateral direction In the absorption grating, corresponding to a section of grating gp _x with length w, the grating period of each section of grating gp _x is g ₂ , and the gratings corresponding to adjacent detector elements have a position difference of distance f, such as adjacent detectors There is a position difference of f between the grating segments gp ₁ and gp ₂ corresponding to elements p ₁ and p ₂ , where f=g ₂ /4, the position of the gp _x grating is equivalent to the position of the absorption grating when it moves to x, adjacent 4 The positions of the absorption gratings corresponding to each detector element are different, and they are staggered by a distance f, which is called a lateral misalignment grating. The X-ray intensity signal value obtained by the detector element p _x is when the absorption grating G2 moves to the position x The collected intensity value. 8. The X-ray grating differential phase contrast three-dimensional cone-beam computed tomography device based on laterally misaligned gratings according to claim 7, wherein the acquisition module further comprises: In the Talbot-Lau imaging structure, when no object is placed on the turntable, the turntable rotates 360 degrees at a constant speed along the rotation center, and the imaging area is covered by the cone beam during the rotation process, and the two-dimensional projection image is collected by the detector; In the Talbot-Lau imaging structure, when the object is placed on the turntable, the turntable rotates 360 degrees at a constant speed along the rotation center, and the imaging area is covered by the cone beam during the rotation, and the two-dimensional projection image is collected by the detector. 9. The X-ray grating differential phase contrast three-dimensional cone-beam computed tomography device based on the lateral misalignment grating according to claim 7, characterized in that, the calculation module uses Fourier analysis method from the collected two-dimensional In the intensity image, three kinds of images are separated: X-ray absorption contrast, differential phase contrast and scattering contrast, including: Perform image analysis on the two-dimensional projection image sequence according to formulas (5)-(14) to obtain three contrast two-dimensional projection image sequences: I ₁ (x,z,θ)=I(x-1,z,θ), (5) I ₂ (x,z,θ)=I(x,z,θ), (6) I ₃ (x,z,θ)=I(x+1,z,θ), (7) I ₄ (x,z,θ)=I(x+2,z,θ), (8) phase(x,z,θ)=φ ^s (x,z,θ)-φ ^r (x,z,θ), (13) Among them, x is the abscissa of the point in the two-dimensional projection; z is the vertical coordinate of the point in the two-dimensional projection, and θ is the projection angle of the two-dimensional projection image; I(x,z,θ) is the point in the two-dimensional projection (x,z) intensity value at projection angle θ; I ₁ (x,z,θ), I ₂ (x,z,θ), I ₃ (x,z,θ), I ₄ (x,z, θ) represent 4 different intensity values of the point (x, z) at the projection angle θ respectively, simulating the point (x, z) in the projection angle θ of the traditional grating differential phase contrast image when the absorption grating is in 4 different steps The intensity value when entering the position; M represents the number of different intensity values in a point (x, z), M=4; a ₀ (x, z, θ) is the point (x, z) at the projection angle θ The mean value of the sinusoidal curve fitted by 4 different intensity values; a ₁ (x, z, θ) is the amplitude of the sinusoidal curve fitted by the 4 different intensity values of the point (x, z) at the projection angle θ Size; φ(x,z,θ) is the phase value of the sinusoidal curve fitted by the point (x,z) at 4 different intensity values of the projection angle θ; Indicates the value of a ₀ (x,z,θ) when the test object is not placed at the projection angle θ, Indicates the value of a ₀ (x,z,θ) when the test object is placed at the projection angle θ; Indicates the value of a ₁ (x,z,θ) when the test object is not placed at the projection angle θ, Indicates the a ₁ (x, z, θ) value when the test object is placed at the projection angle θ; φ ^r (x, z, θ) indicates the φ(x, z, θ) value when the test object is not placed at the projection angle θ , φ ^s (x, z, θ) represents the value of φ(x, z, θ) when the test object is placed at the projection angle θ; abs(x, z, θ) is the absorption at the point (x, z) at the projection angle θ The value of the contrast; phase(x,z,θ) is the value of the differential phase contrast at the projection angle θ point (x,z); dark(x,z,θ) is the projection angle θ point (x,z) Values for scatter contrast imaging. 10. The X-ray grating differential phase contrast three-dimensional cone-beam computed tomography device based on laterally displaced gratings according to claim 6, wherein the calculation module uses absorption contrast, differential phase contrast and scattering contrast The degree filter back projection reconstruction algorithm performs image reconstruction on three kinds of contrast two-dimensional image sequences respectively, and obtains three kinds of CT slice images of the object absorption contrast, phase contrast and scattering contrast, including: Perform image analysis on the two-dimensional projection image sequence according to formulas (15)-(17) to obtain three contrast two-dimensional projection image sequences: Among them, a(x,y,z), p(x,y,z) and d(x,y,z) are respectively the reconstructed absorption contrast slice image, phase contrast slice image and scattering contrast slice image; abs(s,v,θ), phase(s,v,θ) and dark(s,v,θ) represent the two-dimensional projection of absorption contrast, differential phase contrast and scattering contrast under the projection angle θ respectively, s , v are the coordinates of the intersection between the pixel point on the detector and the ray source and the virtual detector placed at the rotation axis; ξ is the angle between the ray and the central ray; D is the distance from the ray source to the virtual detector plane ; y′ is the distance from the reconstructed image pixel to the virtual detector plane; h _a (s), h _p (s) and h _d (s) are the two-dimensional projections of absorption contrast, differential phase contrast and scattering contrast, respectively The filter of , which is defined as formula (18)-(19): h _a (s)=|s|, (18) h _d (s)=|s|, (20).