CN116879326A - X-ray optical phase contrast imaging system and method based on multi-frequency stripes - Google Patents

X-ray optical phase contrast imaging system and method based on multi-frequency stripes Download PDF

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CN116879326A
CN116879326A CN202311146883.2A CN202311146883A CN116879326A CN 116879326 A CN116879326 A CN 116879326A CN 202311146883 A CN202311146883 A CN 202311146883A CN 116879326 A CN116879326 A CN 116879326A
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grating
molar
representing
fringe
distance
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CN116879326B (en
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徐月暑
陶思玮
匡翠方
田宗翰
柏凌
曹雯
刘旭
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ZJU Hangzhou Global Scientific and Technological Innovation Center
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    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
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    • G01N23/04Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material
    • G01N23/041Phase-contrast imaging, e.g. using grating interferometers
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/02Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
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    • G01N23/083Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and measuring the absorption the radiation being X-rays

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Abstract

The invention discloses an X-ray optical phase contrast imaging system and method based on multi-frequency stripes, wherein the system comprises: the light source focusing module is used for collecting and focusing the X-rays generated by the X-ray generating device by the focusing device; the phase grating module comprises a first grating, a second grating and a third grating which are mutually parallel, and have the same structure, the same thickness and the same grating period; the detector module comprises a scintillator, an imaging module and an image acquisition module, wherein the scintillator receives the moire fringes with different frequencies, images are formed on the surface of the scintillator to form moire fringe distribution images with different frequencies, and the image acquisition module acquires the moire fringe images; the processing module is used for decomposing to obtain an absorption contrast image, a dark field contrast image and a differential phase contrast image. The method solves the problems of low photon utilization rate, low imaging sensitivity and the like caused by poor light source coherence of the traditional taber tri-grating X-ray optical phase contrast imaging system; meanwhile, the imaging speed is high, and meanwhile, the image with higher quality can be obtained.

Description

X-ray optical phase contrast imaging system and method based on multi-frequency stripes
Technical Field
The invention relates to the field of X-ray computed radiography, in particular to an X-ray optical phase contrast radiography system and method based on multi-frequency fringes.
Background
The X-ray optical phase contrast imaging technology can solve the problem of lower image contrast in the structure composed of light elements such as carbon, hydrogen and oxygen in the traditional absorption imaging, and has wide application prospect in the fields of industrial detection, biological imaging, medical diagnosis and the like; however, because the X-ray optical phase contrast imaging technology is limited by the time and spatial coherence of a light source, and meanwhile, the technology has higher requirements on the stability of a system and the precision of system hardware, although the dependence on the light source can be greatly reduced by using a taber tri-grating interferometer, a stepping motor with hundred-nanometer precision is still required, and meanwhile, the resolution of an achievable reconstructed image is usually about tens or hundreds of micrometers, and the resolution of a traditional flat panel detector is usually limited because the pixel size of a back-end CCD cannot be continuously reduced; because two absorption gratings are used in the taber tri-grating interferometer, the utilization rate of the X-ray photons is low, and the imaging time is relatively long.
The method improves the coherence of a light source and adopts three gratings to improve the photon utilization rate, achieves the aim of shortening the imaging time, further adopts a multi-frequency fringe modulation method to reduce the requirements on system hardware and stability, and optimizes the back-end imaging to realize real-time and high-resolution X-ray optical phase contrast imaging.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides an X-ray phase contrast imaging method and system based on multi-frequency stripes.
In order to solve the technical problems, the invention is solved by the following technical scheme:
an X-ray optical phase contrast imaging system based on multi-frequency fringes, comprising: the device comprises a light source focusing module, a phase grating module, a detector module and a processing module;
the light source focusing module comprises an X-ray generating device and a focusing device, wherein X-rays generated by the X-ray generating device are collected and focused by the focusing device;
the phase grating module comprises a first grating, a second grating and a third grating, the first grating, the second grating and the third grating are mutually parallel, have the same structure, the same thickness and the same grating period, the first grating divides X-rays into a plurality of orders and carries out light splitting on different X-ray wave bands to be transmitted to the second grating, the second grating carries out secondary light splitting on the X-rays after light splitting, the second grating transmits the X-rays to the third grating after light splitting, a light field after light splitting meets the preset far field condition and forms molar fringes of a preset period, the third grating diffracts the molar fringes of the preset period to form amplified molar fringes, and the amplified molar fringes of different frequencies are generated by changing included angles between the third grating and the molar fringes of the preset period;
the detector module comprises a scintillator, an imaging module and an image acquisition module, wherein the scintillator receives moire fringes with different frequencies, the surface luminous points of the scintillator are imaged to form moire fringe distribution images with different frequencies, and the image acquisition module acquires moire fringe images of a sample to be detected under different phases;
and the processing module decomposes the moire fringe image to obtain an absorption contrast image, a dark field contrast image and a differential phase contrast image of the measured sample.
As an embodiment, the first grating and the second grating are fixed based on a fixing device, respectively, and the first grating and the second grating are parallel;
the third grating is arranged on the rotating structure and is parallel to the first grating and the second grating respectively, and the rotating structure is used for adjusting the included angle between the third grating and the first grating and the included angle between the third grating and the second grating.
As an implementation manner, the light field distribution function of the preset far field condition is expressed as follows:
wherein ,coordinate points representing the first grating and the second grating plane, < >>The distance between the point representing the X-ray and the point of the first grating plane, +.>Representing the distance between the point of the first grating plane and the point of the second grating plane, +.>Representing the distance between the point of the second grating plane and the point of the third grating plane, +.>Representing wave vector under vacuum condition, +.>The transfer functions of the gratings are shown below:
wherein ,representing the spatial frequency of the first grating, +.>Representing the spatial frequency of the second grating, +.>Representation of/>Fourier series expansion->Grade coefficient->Representation->Fourier series expansion->And (5) a level coefficient.
As an embodiment, the preset period is expressed as follows:
wherein ,representing the period of the stripe, +.>Representing the distance of the light source to the first grating, +.>Represents the distance of the first grating to the second grating, is->Represents the distance of the second grating to the third grating, is->Representing the distance of the third grating from the image acquisition module.
As an embodiment, the period of the amplified molar stripe is expressed as follows:
wherein ,represents the period of the amplified molar stripe, +.>Representing the spatial frequency of the first grating, +.>Representing the spatial frequency of the second grating, +.>Representing the spatial frequency of the third grating, +.>Representing the distance of the light source to the first grating, +.>Represents the distance of the first grating to the second grating, is->Represents the distance of the second grating to the third grating, is->Representing the distance of the third grating from the image acquisition module.
As an implementation manner, the focusing device is an X-ray ellipsoidal mirror;
x-rays enter an X-ray ellipsoidal mirror to be converged to form light spots, the emergent direction is changed, and the light spots are used as new X-rays.
As an implementation manner, the first grating structure, the second grating structure and the third grating structure comprise a silicon substrate, a polymer anti-corrosion layer is arranged on the surface of the silicon substrate, and the polymer anti-corrosion layer is provided with grating periods corresponding to the first grating, the second grating and the third grating, wherein the polymer anti-corrosion layer comprises an alumina buffer layer and a platinum layer.
As one embodiment, the imaging module includes an objective lens, a reflecting mirror, and a tube mirror;
the objective lens is used for receiving and converging visible light converted and dispersed by the scintillator;
the reflecting mirror reflects the received visible light at a preset angle, wherein the preset angle is an included angle of an incident light path of the objective lens and the tube lens, and the preset angle is any angle.
As an embodiment, the optimizing the absorption contrast image, the differential phase contrast image, and the dark field contrast image by the processing module includes:
the background light intensity, the molar fringe contrast and the light intensity function phase are used as initial values of iterative optimization, wherein the specific expression of the light intensity function is as follows:
wherein ,indicating the background light intensity>Represents molar fringe contrast, +.>Represents the molar fringe +.>Molar fringe frequency of directional decomposition, +.>Represents the molar fringe +.>Molar fringe frequency of directional decomposition, +.>Indicating the phase of the sample to be measured,representing the phase of the light intensity function;
determining a spatial frequency of the moire pattern based on the fourier transform, and determining a moire pattern period based on the spatial frequency of the moire pattern;
optimizing the phase of a sample to be measured in the light intensity function, the background light intensity and the molar fringe contrast by a least square method through the molar fringe period and the initial value of the light intensity function phase;
reconstructing a light intensity function based on the iteratively optimized phase, background light intensity and molar fringe contrast;
and obtaining an optimized absorption contrast image, a differential phase contrast image and a dark field contrast image through the iteratively calculated background light intensity, light intensity function phase and moire contrast.
An X-ray optical phase contrast imaging method based on multi-frequency stripes is realized by an X-ray optical phase contrast imaging system based on multi-frequency stripes, the system comprises a light source focusing module, a phase grating module, a detector module and a processing module, and the method comprises the following steps:
the X-ray generating device generates X-rays which are collected and focused by the focusing device, wherein the light source focusing module comprises the X-ray generating device and the focusing device;
the first grating divides X-rays into a plurality of orders and carries out light splitting transmission on different X-ray wave bands to the second grating, the second grating carries out secondary light splitting on the X-rays after light splitting based on different energy wave bands, the second grating carries out secondary light splitting and then transmits the X-rays to the third grating, a light field after secondary light splitting meets preset far field conditions and forms molar fringes of a preset period, the third grating diffracts the molar fringes of the preset period to form amplified molar fringes, and the amplified molar fringes of different frequencies are generated by adjusting the phase of the third grating, wherein the phase grating module comprises a first grating, a second grating and a third grating, the first grating, the second grating and the third grating are parallel to each other, and the structures, the thicknesses and the grating periods are identical;
the method comprises the steps that a scintillator receives moire fringes with different frequencies, the surface luminous points of the scintillator are imaged to form moire fringe distribution images with different frequencies, an image acquisition module acquires a plurality of first moire fringe images and second moire fringe images with samples to be detected, wherein the first moire fringe images and the second moire fringe images are obtained without samples to be detected under different phases, and a detector module comprises the scintillator, an imaging module and an image acquisition module;
the processing module decomposes the molar stripe image to obtain an absorption contrast image, a dark field contrast image and a differential phase contrast image of the measured sample.
As an implementation manner, the light field distribution function of the preset far field condition is expressed as follows:
wherein ,coordinate points representing the first grating and the second grating plane, < >>The distance between the point representing the X-ray and the point of the first grating plane, +.>Representing the distance between the point of the first grating plane and the point of the second grating plane, +.>Representing the distance between the point of the second grating plane and the point of the third grating plane, +.>Representing wave vector under vacuum condition, +.>The transfer functions of the gratings are shown below:
wherein ,representing the spatial frequency of the first grating, +.>Representing the spatial frequency of the second grating, +.>Representation->Fourier series expansion->Grade coefficient->Representation->Fourier series expansion->And (5) a level coefficient.
As an embodiment, the preset period is expressed as follows:
wherein ,representing the period of the stripe, +.>Representing the distance of the light source to the first grating, +.>Represents the distance of the first grating to the second grating, is->Represents the distance of the second grating to the third grating, is->Representing the distance of the third grating from the image acquisition module.
As an embodiment, the period of the amplified molar stripe is expressed as follows:
wherein ,represents the period of the amplified molar stripe, +.>Representing the spatial frequency of the first grating, +.>Representing the spatial frequency of the second grating, +.>Representing the spatial frequency of the third grating, +.>Representing the distance of the light source to the first grating, +.>Represents the distance of the first grating to the second grating, is->Represents the distance of the second grating to the third grating, is->Representing the distance of the third grating from the image acquisition module.
As an implementation manner, the method further comprises the step of optimizing the absorption contrast image, the differential phase contrast image and the dark field contrast image, specifically:
the background light intensity, the molar fringe contrast and the light intensity function phase are used as initial values of iterative optimization, wherein the specific expression of the light intensity function is as follows:
wherein ,indicating the background light intensity>Represents molar fringe contrast, +.>Represents the molar fringe +.>Molar fringe frequency of directional decomposition, +.>Represents the molar fringe +.>Molar fringe frequency of directional decomposition, +.>Indicating the phase of the sample to be measured,representing the phase of the light intensity function;
determining a spatial frequency of the moire pattern based on the fourier transform, and determining a moire pattern period based on the spatial frequency of the moire pattern;
optimizing the phase of a sample to be measured in the light intensity function, the background light intensity and the molar fringe contrast by a least square method through the molar fringe period and the initial value of the light intensity function phase;
reconstructing a light intensity function based on the iteratively optimized phase, background light intensity and molar fringe contrast;
and obtaining an optimized absorption contrast image, a differential phase contrast image and a dark field contrast image through the iteratively calculated background light intensity, light intensity function phase and moire contrast.
The invention has the remarkable technical effects due to the adoption of the technical scheme:
the method of the invention improves the coherence of the light source, realizes a rapid X-ray optical imaging system by utilizing three gratings, solves the problems of high requirement on system stability, low imaging resolution, low photon utilization rate, low imaging speed and the like of the traditional Talbow three-grating X-ray optical phase contrast imaging system, and further recovers higher-quality images by adopting a multi-frequency stripe modulation method.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions of the prior art, the drawings which are used in the description of the embodiments or the prior art will be briefly described, it being obvious that the drawings in the description below are only some embodiments of the invention, and that other drawings can be obtained according to these drawings without inventive faculty for a person skilled in the art.
FIG. 1 is an overall schematic of the system of the present invention;
FIG. 2 is a schematic diagram of the system of the present invention;
FIG. 3 is a schematic flow chart of the method of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following examples, which are illustrative of the present invention and are not intended to limit the present invention thereto.
Example 1:
an X-ray optical phase contrast imaging system based on multi-frequency fringes, as shown in fig. 1, comprising: a light source focusing module 100, a phase grating module 200, a detector module 300, and a processing module 400;
the light source focusing module 100 includes an X-ray generating device and a focusing device, and the X-rays generated by the X-ray generating device are collected and focused by the focusing device;
the phase grating module 200 comprises a first grating, a second grating and a third grating, the first grating, the second grating and the third grating are mutually parallel, have the same structure, the same thickness and the same grating period, the first grating divides the X-ray into a plurality of orders and carries out light splitting transmission on different X-ray wave bands to the second grating, the second grating carries out secondary light splitting on the X-ray after light splitting based on different energy wave bands, the second grating carries out light splitting to the third grating, the light field after light splitting meets the preset far field condition and forms molar fringes of a preset period, the third grating diffracts the molar fringes of the preset period to form amplified molar fringes, and the amplified molar fringes of different frequencies are generated by adjusting the phase of the third grating;
the detector module 300 comprises a scintillator, an imaging module and an image acquisition module, wherein the scintillator receives the moire fringes with different frequencies, the surface luminous points of the scintillator are imaged to form moire fringe distribution images with different frequencies, and the image acquisition module acquires the moire fringe images of the sample to be measured under different phases;
the processing module 400 decomposes the moire pattern to obtain an absorption contrast image, a dark field contrast image and a differential phase contrast image of the sample to be measured.
In one embodiment, the first and second gratings are fixed based on a fixing device and the first and second gratings are made parallel, respectively;
the third grating is arranged on the rotating structure and is parallel to the first grating and the second grating respectively, and the rotating structure is used for adjusting the phase of the third grating.
Referring to fig. 2, a specific multi-frequency fringe based X-ray optical phase contrast imaging system is provided, comprising an X-ray light pipe 1, an X-ray ellipsoidal mirror 2, a first grating 3, a second grating 4, a third grating 5, a scintillator 6, a high power objective lens 7, a mirror 8, a tube mirror 9, and a camera 10, wherein the first grating 3 and the second grating 4 are both arranged on a dry plate frame, and the third grating 5 is arranged on a rotatable slide clamp.
The first grating 3 and the second grating 4 are imaged by using a high-power objective lens and a camera in a manner of polishing the side surfaces of the visible light, the angles of the first grating 3 and the second grating 4 are adjusted, so that the first grating 3 and the second grating 4 are completely parallel, and the third grating 5 is also adjusted, so that the three are completely parallel at first.
All optical elements in the imaging system are arranged above the guide rail so as to ensure that the optical elements are placed on a straight line and are convenient to adjust, the guide rail is fixed on the optical platform, and the fixed position of the guide rail is preferably the position with the strongest X-ray emergent intensity so as to obtain the optimal mole stripes and amplified mole stripes.
Referring to the specific structure of fig. 2, divergent X-rays emitted by the X-ray tube 1 are collected by the ellipsoidal mirror 2, photons with a total internal reflection angle smaller than or equal to the total internal reflection angle are converged by the ellipsoidal mirror, and a new light source is generated by focusing; the focused X-rays reach the first grating 3 after diffraction and are split to form X-rays with different primary diffraction orders and continue diffraction propagation to reach the second grating 4; the second grating 4 again performs secondary light splitting on the X-rays after light splitting, and generates different secondary diffraction orders among the same primary diffraction orders and propagates the same secondary diffraction orders until reaching the third grating 5; the interaction between the different secondary diffraction orders of the different primary diffraction orders and the third grating 5 is carried out, and then diffraction is carried out to the scintillator 6; the scintillator 6 converts the generated X-ray molar fringes into visible light, and the luminous points on the scintillator 6 diverge and are converged after passing through the objective lens 7; the propagation to the mirror 8 produces a reflection of 90 °; passes through the tube mirror 9 and is further converged and hit at a certain point on the target surface of the camera 10; an image of the scintillator is obtained by a camera, and a moire distribution image of the X-rays is obtained.
The X-ray is generated by an X-ray light tube of a high-power rotary anode target, free electrons are generated by a heating filament of a high-voltage circuit in the X-ray light tube, the free electrons are accelerated to the anode from a cathode to bombard the target material by a high-voltage circuit to generate X-ray characteristic radiation and bremsstrahlung radiation, and the energy near 99% of the bombarded part can be converted into heat, so that the rotating motor rotates the anode for accelerating heat dissipation. The generated X-rays are emitted from the light pipe after passing through the beryllium window and are collected by the rear-end X-ray ellipsoidal mirror, and a new light source is generated at the rear-end focal position of the X-ray ellipsoidal mirror to illuminate the rear-end light path. The X-rays pass through the three gratings to generate amplified molar fringes and then are projected to the scintillator. The third grating 5 is rotated to produce moire fringes of different frequencies for subsequent image restoration and reconstruction.
The scintillator converts X-rays into visible light and is imaged by a high power objective lens in combination with a tube lens into a camera. Because X-rays can cause radiation damage to the QCSMOS, a reflector is arranged behind the high-power objective lens, so that the light path turns 90 degrees and then is imaged into the QCSMOS through a tube lens. The scintillator is placed at the depth of field position of the high-power objective lens, and the rear end face of the objective lens is connected with the camera through the sleeve and the cage structure, so that the influence of external stray light on imaging is further reduced under the condition of ensuring the stability of the system.
In the process of using the high-power objective lens, the actual requirement that imaging objects with different sizes can be imaged is considered to be met, so that the high-power objective lens can be switched to different multiplying powers and even can be switched to a reduced double telecentric lens, and clear imaging can be realized by readjusting the distance between the scintillator and the objective lens and the working distance and depth of field position of the objective lens.
The first grating and the second grating are both arranged on the dry plate clamp, and the third grating is arranged on the rotatable slide clamp. The first grating and the second grating are imaged by utilizing the high-power objective lens and the camera in a mode of polishing the first grating and the second grating by using the visible light side, and the angles of the first grating and the second grating on the dry plate clamp are adjusted, so that the first grating and the second grating are completely parallel. The slide clamp of the third grating is adjusted so that the three are completely parallel at first.
In the imaging system, all optical elements in the imaging system are arranged above a guide rail so as to ensure that the optical elements are arranged on a straight line to facilitate subsequent adjustment, and the guide rail is fixed on an optical platform, and the fixed position of the guide rail is preferably the position with the strongest X-ray emergent intensity.
The system uses an ellipsoidal mirror to focus X-rays to obtain a light source with high spatial coherence so as to improve the resolution of imaging, uses three gratings in the system, is easy to manufacture, can greatly improve the photon utilization rate of the X-rays, has photon numbers in unit time of more than four times that of a traditional Talbow three grating system, improves the imaging speed of X-ray optical phase contrast imaging, uses a multi-frequency stripe recovery solving algorithm, can get rid of the dependence of the system on a high-precision electric control displacement table, can recover to obtain high-quality images in a manual rotation mode, and reduces the system cost. The scintillator is combined with the high-power objective lens, the tube lens and the camera to build the X-ray indirect detector, so that the resolution of an imaging end can be improved, further high-resolution imaging is realized, the objective lens in the design can be switched at will, and different imaging requirements can be met. High-resolution fast X-ray optical phase contrast imaging with low system requirements is realized.
In one embodiment, the focusing device is an X-ray ellipsoidal mirror; x-rays enter an X-ray ellipsoidal mirror to be converged to form light spots, the emergent direction is changed, and the light spots are used as new X-rays.
That is, by collecting the X-rays entering the ellipsoidal mirror after exiting, the direction of the X-rays is changed by the ellipsoidal surface type and the principle of total internal reflection. Wherein, the X-ray smaller than the total internal reflection angle can be changed in direction by the ellipsoidal surface type, and the X-ray larger than the total internal reflection angle can be completely absorbed. Since the X-ray ellipsoidal mirror has two focal points in geometry, by setting the position of the X-ray focal spot as the front focal point, a focused smaller X-ray spot is obtained at the position of the rear focal point of the X-ray ellipsoidal mirror. Because the focal spot of the X-ray light source has a certain size, the size of the focal spot can be enlarged and reduced by designing the long and short axes of the X-ray ellipsoidal mirror and designing the corresponding ellipsoidal surface according to the wavelength of the X-ray.
To achieve far-field X-ray optical phase contrast imaging to increase imaging sensitivity, the X-ray polychromatic far-field optical phase contrast imaging method requires the use of three gratings with periods on the order of hundred nanometers. To achieve the purposes ofThe height of the grating is typically on the order of microns and the aspect ratio of the fabricated grating is about 30. And the three gratings have the same structure and comprise a silicon substrate, and the surface of the silicon substrate is provided with a poly-crystalAnd the polymer anti-corrosion layer is provided with grating periods corresponding to the first grating, the second grating and the third grating, wherein the polymer anti-corrosion layer comprises an alumina buffer layer and a platinum layer.
Specifically, a nano-imprint technology is used for extruding a corresponding period on the surface of a silicon substrate with a polymer anti-corrosion layer, and then a deep silicon etching technology is used for etching a grating structure with a corresponding thickness. Because the silicon surface can not be electroplated with gold, an alumina buffer layer and a platinum layer are grown on the etched silicon surface in a magnetron sputtering mode, and finally gold with corresponding thickness is electroplated in an electroplating mode to serve as a phase shift material to generate pi phase shift.
The X-ray light spot at the focus after being focused by the ellipsoidal mirror can be used as a new X-ray light source, and three gratings are placed at the rear end of the light source to realize X-ray polychromatic far-field optical phase contrast imaging. Wherein the three grating periods are all hundred nanometers, and the periods are identical. The first grating is used as a beam splitting grating to divide X-rays into a plurality of orders, and the X-rays are transmitted to the second grating after being split according to different X-ray wave bands, the second grating is used for carrying out beam splitting treatment on the X-rays of different orders, and meanwhile, beam splitting transmission is carried out according to different energy wave bands to reach the third grating. Since the period of three gratings is in the order of hundred nanometers, the distance between two adjacent gratings is in the order of meters. Therefore, the light field before reaching the third grating through two spectroscopic propagation meets the far field condition, and the light field distribution function of the preset far field condition is expressed as follows:
wherein ,coordinate points representing the first grating and the second grating plane, < >>The distance between the point representing the X-ray and the point of the first grating plane, +.>Representing the distance between the point of the first grating plane and the point of the second grating plane, +.>Representing the distance between the point of the second grating plane and the point of the third grating plane, +.>Representing wave vector under vacuum condition, +.>The transfer functions of the gratings are shown below:
wherein ,representing the spatial frequency of the first grating, +.>Representing the spatial frequency of the second grating, +.>Representation->Fourier series expansion->Grade coefficient->Representation->Fourier series expansion->And (5) a level coefficient.
The preset period is expressed as follows:
wherein ,representing the period of the stripe, +.>Representing the distance of the light source to the first grating, +.>Represents the distance of the first grating to the second grating, is->Represents the distance of the second grating to the third grating, is->Representing the distance of the third grating from the image acquisition module.
As an embodiment, the period of the amplified molar stripe is expressed as follows:
wherein ,represents the period of the amplified molar stripe, +.>Representing the spatial frequency of the first grating, +.>Representing the spatial frequency of the second grating, +.>Representing the spatial frequency of the third grating, +.>Representing the distance of the light source to the first grating, +.>Represents the distance of the first grating to the second grating, is->Represents the distance of the second grating to the third grating, is->Representing the distance of the third grating from the image acquisition module.
In one embodiment, the detector module includes a scintillator, a high power objective lens, and a camera. The scintillator converts the incident X-rays into visible light, and the high-power objective lens images the luminous points on the surface of the scintillator to the camera to realize point-to-point imaging. The problem that the resolution of the traditional flat panel detector is limited due to the fact that the size of the CCD pixel at the rear end cannot be reduced can be solved by combining the high-resolution scintillator with the high-power objective lens, and the resolution of the system is further improved.
In one embodiment, the processing module optimizes the absorption contrast image, the differential phase contrast image, and the dark field contrast image, comprising:
the background light intensity, the molar fringe contrast and the light intensity function phase are used as initial values of iterative optimization, wherein the specific expression of the light intensity function is as follows:
wherein ,indicating the background light intensity>Represents molar fringe contrastDegree (f)>Represents the molar fringe +.>Molar fringe frequency of directional decomposition, +.>Represents the molar fringe +.>Molar fringe frequency of directional decomposition, +.>Indicating the phase of the sample to be measured,representing the phase of the light intensity function;
determining a spatial frequency of the moire pattern based on the fourier transform, and determining a moire pattern period based on the spatial frequency of the moire pattern;
optimizing the phase of a sample to be measured in the light intensity function, the background light intensity and the molar fringe contrast by a least square method through the molar fringe period and the initial value of the light intensity function phase;
reconstructing a light intensity function based on the iteratively optimized phase, background light intensity and molar fringe contrast;
and obtaining an optimized absorption contrast image, a differential phase contrast image and a dark field contrast image through the iteratively calculated background light intensity, light intensity function phase and moire contrast.
Example 2:
as shown in fig. 3, the multi-frequency-fringe-based X-ray optical phase contrast imaging method is implemented by a multi-frequency-fringe-based X-ray optical phase contrast imaging system, wherein the system comprises a light source focusing module, a phase grating module, a detector module and a processing module, and the method comprises the following steps:
the X-ray generating device generates X-rays which are collected and focused by the focusing device, wherein the light source focusing module comprises the X-ray generating device and the focusing device;
the first grating divides X-rays into a plurality of orders and carries out light splitting transmission on different X-ray wave bands to the second grating, the second grating carries out secondary light splitting on the X-rays after light splitting based on different energy wave bands, the second grating carries out secondary light splitting and then transmits the X-rays to the third grating, a light field after secondary light splitting meets preset far field conditions and forms molar fringes of a preset period, the third grating diffracts the molar fringes of the preset period to form amplified molar fringes, and the amplified molar fringes of different frequencies are generated by adjusting the phase of the third grating, wherein the phase grating module comprises a first grating, a second grating and a third grating, the first grating, the second grating and the third grating are parallel to each other, and the structures, the thicknesses and the grating periods are identical;
the method comprises the steps that a scintillator receives moire fringes with different frequencies, the surface luminous points of the scintillator are imaged to form moire fringe distribution images with different frequencies, an image acquisition module acquires a plurality of first moire fringe images and second moire fringe images with samples to be detected, wherein the first moire fringe images and the second moire fringe images are obtained without samples to be detected under different phases, and a detector module comprises the scintillator, an imaging module and an image acquisition module;
the processing module decomposes the molar stripe image to obtain an absorption contrast image, a dark field contrast image and a differential phase contrast image of the measured sample.
Furthermore, considering that the system needs to meet the actual requirement of imaging objects with different sizes, the high-power objective lens in the system can be switched to different multiplying powers, and the aim of clear imaging is achieved by adjusting the distance between the scintillator and the high-power objective lens and the working distance and depth of field position of the high-power objective lens, and the QCMOS detector can be a common CCD, a common CMOS, SCMOS, EMCCD or the like.
The foregoing is merely a preferred embodiment of the present invention, and the present invention has been disclosed in the above description of the preferred embodiment, but is not limited thereto. Any person skilled in the art can make many possible variations and modifications to the technical solution of the present invention or modifications to equivalent embodiments using the methods and technical contents disclosed above, without departing from the scope of the technical solution of the present invention. Therefore, any simple modification, equivalent variation and modification of the above embodiments according to the technical substance of the present invention still fall within the scope of the technical solution of the present invention.

Claims (14)

1. An X-ray optical phase contrast imaging system based on multi-frequency fringes, comprising: the device comprises a light source focusing module, a phase grating module, a detector module and a processing module;
the light source focusing module comprises an X-ray generating device and a focusing device, wherein X-rays generated by the X-ray generating device are collected and focused by the focusing device;
the phase grating module comprises a first grating, a second grating and a third grating, the first grating, the second grating and the third grating are mutually parallel, have the same structure, the same thickness and the same grating period, the first grating divides X-rays into a plurality of orders and carries out light splitting on different X-ray wave bands to be transmitted to the second grating, the second grating carries out secondary light splitting on the X-rays after light splitting, the second grating transmits the X-rays to the third grating after light splitting, a light field after light splitting meets the preset far field condition and forms molar fringes of a preset period, the third grating diffracts the molar fringes of the preset period to form amplified molar fringes, and the amplified molar fringes of different frequencies are generated by changing included angles between the third grating and the molar fringes of the preset period;
the detector module comprises a scintillator, an imaging module and an image acquisition module, wherein the scintillator receives the moire fringes with different frequencies, the surface luminous points of the scintillator are imaged to obtain moire distribution images with different frequencies, and the image acquisition module acquires the moire fringe images containing a sample to be detected;
and the processing module decomposes the moire fringe image to obtain an absorption contrast image, a dark field contrast image and a differential phase contrast image of the measured sample.
2. The multi-band fringe based X-ray optical phase contrast imaging system of claim 1 wherein the first and second gratings are fixed based on a fixture and the first and second gratings are made parallel, respectively;
the third grating is arranged on the rotating structure and is parallel to the first grating and the second grating respectively, and the rotating structure is used for adjusting the included angle between the third grating and the first grating and the included angle between the third grating and the second grating.
3. The multi-frequency-fringe-based X-ray optical phase-contrast imaging system of claim 1, wherein the light field distribution function of the preset far-field condition is represented as follows:
wherein ,coordinate points representing the first grating and the second grating plane, < >>The distance between the point representing the X-ray and the point of the first grating plane, +.>Representing the distance between the point of the first grating plane and the point of the second grating plane, +.>Representing the distance between the point of the second grating plane and the point of the third grating plane, +.>Representing wave vector under vacuum condition, +.>The transfer functions of the gratings are shown below:
wherein ,representing the spatial frequency of the first grating, +.>Representing the spatial frequency of the second grating, +.>Representation->Fourier series expansion->Grade coefficient->Representation->Fourier series expansion->And (5) a level coefficient.
4. The multi-band fringe-based X-ray optical phase contrast imaging system of claim 3, wherein said preset period is represented as follows:
wherein ,representing the period of the stripe, +.>Representing the distance of the light source to the first grating, +.>Represents the distance of the first grating to the second grating, is->Represents the distance of the second grating to the third grating, is->Representing the distance of the third grating from the image acquisition module.
5. The multi-band fringe based X-ray optical phase contrast imaging system of claim 4, wherein a period of said magnified molar fringes is represented as follows:
wherein ,represents the period of the amplified molar stripe, +.>Representing the spatial frequency of the first grating, +.>Representing the spatial frequency of the second grating, +.>Representing the spatial frequency of the third grating, +.>Representing the distance of the light source to the first grating, +.>Represents the distance of the first grating to the second grating, is->Represents the distance of the second grating to the third grating, is->Representing the distance of the third grating from the image acquisition module.
6. The multi-frequency fringe based X-ray optical phase contrast imaging system of claim 1, wherein said focusing means is an X-ray ellipsoidal mirror;
x-rays enter an X-ray ellipsoidal mirror to be converged to form light spots, the emergent direction is changed, and the light spots are used as new X-rays.
7. The multi-band fringe based X-ray optical phase contrast imaging system of claim 1, wherein the first grating structure, the second grating structure, and the third grating structure comprise a silicon substrate having a polymer resist layer disposed on a surface thereof, the polymer resist layer having a grating period corresponding to the first grating, the second grating, and the third grating, wherein the polymer resist layer comprises an alumina buffer layer and a platinum layer.
8. The multi-band fringe based X-ray optical phase contrast imaging system of claim 1, wherein said imaging module comprises an objective lens, a mirror, and a tube lens;
the objective lens is used for receiving and converging visible light converted and dispersed by the scintillator;
the reflecting mirror reflects the received visible light at a preset angle, wherein the preset angle is an included angle of an incident light path of the objective lens and the tube lens, and the preset angle is any angle.
9. The multi-band fringe based X-ray optical phase contrast imaging system of claim 1, wherein the processing module optimizes an absorption contrast image, a differential phase contrast image, and a dark field contrast image, comprising:
the background light intensity, the molar fringe contrast and the light intensity function phase are used as initial values of iterative optimization, wherein the specific expression of the light intensity function is as follows:
wherein ,indicating the background light intensity>Represents molar fringe contrast, +.>Represents the molar fringe +.>Molar fringe frequency of directional decomposition, +.>Represents the molar fringe +.>Molar fringe frequency of directional decomposition, +.>Indicating the phase of the sample to be measured,representing the phase of the light intensity functionA bit;
determining a spatial frequency of the moire pattern based on the fourier transform, and determining a moire pattern period based on the spatial frequency of the moire pattern;
optimizing the phase of a sample to be measured in the light intensity function, the background light intensity and the molar fringe contrast by a least square method through the molar fringe period and the initial value of the light intensity function phase;
reconstructing a light intensity function based on the phase, the background light intensity and the molar fringe contrast of the sample to be measured after iterative optimization;
and obtaining an optimized absorption contrast image, a differential phase contrast image and a dark field contrast image through the iteratively calculated background light intensity, light intensity function phase and moire contrast.
10. The X-ray optical phase contrast imaging method based on the multi-frequency fringes is realized by an X-ray optical phase contrast imaging system based on the multi-frequency fringes, and the system comprises a light source focusing module, a phase grating module, a detector module and a processing module, and is characterized by comprising the following steps:
the X-ray generating device generates X-rays which are collected and focused by the focusing device, wherein the light source focusing module comprises the X-ray generating device and the focusing device;
the first grating divides X-rays into a plurality of orders and carries out light splitting transmission on different X-ray wave bands to the second grating, the second grating carries out secondary light splitting on the X-rays after light splitting based on different energy wave bands, the second grating carries out secondary light splitting and then transmits the X-rays to the third grating, a light field after secondary light splitting meets preset far field conditions and forms molar fringes of a preset period, the third grating diffracts the molar fringes of the preset period to form amplified molar fringes, and the amplified molar fringes of different frequencies are generated by adjusting the phase of the third grating, wherein the phase grating module comprises a first grating, a second grating and a third grating, the first grating, the second grating and the third grating are parallel to each other, and the structures, the thicknesses and the grating periods are identical;
the method comprises the steps that a scintillator receives moire fringes with different frequencies, the surface luminous points of the scintillator are imaged to form moire fringe distribution images with different frequencies, an image acquisition module acquires a plurality of first moire fringe images without a tested sample and a second moire fringe image with the tested sample, and a detector module comprises the scintillator, an imaging module and an image acquisition module;
the processing module decomposes the molar stripe image to obtain an absorption contrast image, a dark field contrast image and a differential phase contrast image of the measured sample.
11. The multi-frequency-fringe-based X-ray optical phase contrast imaging method of claim 10, wherein the light field distribution function of the preset far-field condition is expressed as follows:
wherein ,coordinate points representing the first grating and the second grating plane, < >>The distance between the point representing the X-ray and the point of the first grating plane, +.>Representing the distance between the point of the first grating plane and the point of the second grating plane, +.>Representing the distance between the point of the second grating plane and the point of the third grating plane, +.>Representing wave vector under vacuum condition, +.>Representing the transfer function of the grating, e.gThe following steps:
wherein ,representing the spatial frequency of the first grating, +.>Representing the spatial frequency of the second grating, +.>Representation->Fourier series expansion->Grade coefficient->Representation->Fourier series expansion->And (5) a level coefficient.
12. The multi-band fringe based X-ray optical phase contrast imaging method of claim 10 wherein said preset period is represented as follows:
wherein ,representing the period of the stripe, +.>Representing the distance of the light source to the first grating, +.>Represents the distance of the first grating to the second grating, is->Represents the distance of the second grating to the third grating, is->Representing the distance of the third grating from the image acquisition module.
13. The multi-band fringe based X-ray optical phase contrast imaging method of claim 10 wherein the period of said magnified molar fringes is represented as follows:
wherein ,represents the period of the amplified molar stripe, +.>Representing the spatial frequency of the first grating, +.>Representing the spatial frequency of the second grating, +.>Representing the spatial frequency of the third grating, +.>Representing the distance of the light source to the first grating, +.>Represents the distance of the first grating to the second grating, is->Represents the distance of the second grating to the third grating, is->Representing the distance of the third grating from the image acquisition module.
14. The multi-band fringe based X-ray optical phase contrast imaging method of claim 10, further comprising the step of optimizing an absorption contrast image, a differential phase contrast image, and a dark field contrast image, in particular:
the background light intensity, the molar fringe contrast and the light intensity function phase are used as initial values of iterative optimization, wherein the specific expression of the light intensity function is as follows:
wherein ,indicating the background light intensity>Represents molar fringe contrast, +.>Represents the molar fringe +.>Molar fringe frequency of directional decomposition, +.>Represents the molar fringe +.>Molar fringe frequency of directional decomposition, +.>Indicating the phase of the sample to be measured,representing the phase of the light intensity function;
determining a spatial frequency of the moire pattern based on the fourier transform, and determining a moire pattern period based on the spatial frequency of the moire pattern;
optimizing the phase of a sample to be measured in the light intensity function, the background light intensity and the molar fringe contrast by a least square method through the molar fringe period and the initial value of the light intensity function phase;
reconstructing a light intensity function based on the iteratively optimized phase, background light intensity and molar fringe contrast;
and obtaining an optimized absorption contrast image, a differential phase contrast image and a dark field contrast image through the iteratively calculated background light intensity, light intensity function phase and moire contrast.
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