WO2020133531A1

WO2020133531A1 - X-ray dual-phase grating phase-contrast imaging system

Info

Publication number: WO2020133531A1
Application number: PCT/CN2018/125859
Authority: WO
Inventors: 李冀; 雷耀虎; 黄建衡; 刘鑫
Original assignee: 深圳大学
Priority date: 2018-12-29
Filing date: 2018-12-29
Publication date: 2020-07-02

Abstract

An X-ray dual-phase grating phase-contrast imaging system. The system comprises an X-ray tube, a source grating G 0, a phase grating and an X-ray detector which are successively arranged in the emission direction of X-rays; the phase grating comprises a first phase grating G 1 and a second phase grating G 1' which are arranged at intervals; the first phase grating G 1 and the second phase grating G 1' are located between the source grating G 0 and the X-ray detector; a self-imaging secondary source G 2 is formed after the first phase grating G 1; the X-rays emitted by the X-ray tube, the source grating G 0 and the first phase grating G 1 form a Talbot-Lau system; and the self-imaging secondary source G 2 and the second phase grating G 1' form an inverse Talbot-Lau system. According to the imaging system, the use of source gratings with small periods and high aspect ratio, and the use of absorption gratings with large area, small periods and high aspect ratio can be avoided, thereby reducing the difficulty of implementing the grating phase-contrast imaging system.

Description

X-ray dual-phase grating phase contrast imaging system

Technical field

The invention relates to a phase contrast imaging system, in particular to an X-ray dual phase grating phase contrast imaging system.

Background technique

The comparison of many X-ray phase contrast imaging technologies in the past 20 years in the world has shown that the phase contrast imaging technology based on the Tiberau interferometer can provide absorption contrast, phase contrast and dark contrast while rid of the dependence on the synchrotron radiation source. The image of the multi-contrast mechanism such as field image, reflecting the internal structure of the object, is a major change in X-ray imaging technology. It has clinical early diagnosis of lesions, the characterization of polymers in materials science, industrial and safe nondestructive testing, etc. Potential application value.

In 2006, F. Pfeiffer et al. modified the Taber interferometer based on the Taber-Laur principle and proposed to use a common X-ray source and absorption grating to form a spatially coherent array X-ray source. This not only solves the problem of partial coherent light illumination, but also improves the brightness of the light source at the same time. It is an X-ray Taber-Laur interferometer. It makes the technology get rid of the dependence on synchrotron radiation source, and may enter ordinary laboratories or even clinical, becoming a research hotspot in this field.

technical problem

Existing Taber or Taber-Laur interferometers obtain images with X-ray phase gradient as contrast. It relies on the measurement of the interference fringe shear variable. These interference fringes originate from the mutual interference of different diffracted beams of a grating (generally a phase grating) as a beam splitter. When illuminated with parallel light, these interference fringes have the same period as the beam splitting grating (or half, depending on the nature of the grating), so-called "self-imaging". When the cone beam is illuminated, the period of the interference fringe and the period of the beam splitting grating satisfy a proportional relationship of projection magnification. The geometric conditions of the spatial coherence of the X-ray source require that the period of the beam splitting grating be in the range of several microns. In this way, the period of "self-imaging" is also a few microns (slightly larger). The pixels of ordinary X-ray image detectors are in the range of 20-200 microns, that is, it is impossible to directly record such interference fringes, let alone the shear variables of fringes.

The existing interference fringe and shear detection method is to introduce another absorption grating to sample the interference fringe with a small period, that is, to form a moiré fringe to amplify the shear variable and record it. However, the production of large-area, high-aspect-ratio absorption gratings has always been a technical bottleneck. Moreover, the use of absorption gratings reduces the photon utilization efficiency, resulting in deterioration of the signal-to-noise ratio of the image signal or prolonged exposure time. Obviously, recording isophase lines without relying on the absorption grating, that is, enlarging the fringe period is the best way to solve this dilemma. However, according to the geometric conditions of spatial coherence, directly amplifying the fringes leads to the need to reduce the emission area of the light source. There are two solutions: making source gratings with smaller slits; developing structural anodes with emission scales less than a few microns. The former increases the aspect ratio more, and is more difficult to achieve (although the area is reduced); the realization of the latter is currently seen at the expense of small X-ray photon energy (copper characteristic spectrum) and power capacity.

Technical solution

The technical problem to be solved by the present invention is to provide an X-ray dual phase grating phase contrast imaging system, which can avoid the use of a small period, high aspect ratio source grating and a large area, small period, high aspect ratio absorption grating, Reduce the difficulty of realizing grating phase contrast imaging system.

The technical solutions adopted by the present invention to solve its technical problems are:

An X-ray dual-phase grating phase contrast imaging system includes an X-ray tube, a source grating G ₀ , a phase grating and an X-ray detector arranged in sequence along the X-ray emission direction, the phase grating includes first phase gratings G arranged at intervals ₁ and a second phase grating G′ ₁ , the first phase grating G ₁ and the second phase grating G′ _{1 are} located between the source grating G ₀ and the X-ray detector, and form a self-imaging after the first phase grating G ₁ The secondary source G ₂ ; the X-rays emitted by the X-ray tube, the source grating G ₀ and the first phase grating G ₁ form a Tiberium system; the self-imaging secondary source G ₂ and the second phase grating G′ ₁ Formed the inverse Tiberium system.

Further, in the X-ray dual-phase grating phase-contrast imaging system, it is preferable that the position and period of the first phase grating G ₁ satisfy that the coherence length of the X-ray propagating to the first phase grating G ₁ after passing through the source grating G ₀ is not less than The period of the first phase grating G ₁ ; the position and period of the second phase grating G′ ₁ satisfy: the coherence length propagated from the imaging secondary source G ₂ to the second phase grating G′ ₁ is not less than the second phase grating G′ ₁ cycle

Further, in the X-ray dual phase grating phase contrast imaging system, it is preferable that the secondary source G ₂ is located at the Taber distance of the first phase grating G ₁ .

The Taber distance R _{2 of} the first phase grating G ₁ satisfies:

Where p ₁ is the period of the first phase grating G ₁ , R ₁ is the distance between the source grating G ₀ and the first phase grating G ₁ , λ is the wavelength of the X-ray, k is a constant, and for the phase of π/2 For gratings, k = 1/2, 3/2, 5/2, ..., for a phase grating of π, k = 1/8, 3/8, 5/8, ....

Further, in the X-ray dual phase grating phase contrast imaging system, it is preferable that the periods of the first phase grating G ₁ and the second phase grating G′ ₁ are the same; between the source grating G ₀ and the first phase grating G ₁ R ₁ , the distance R ₂ ′ between the second phase grating G′ ₁ and its self-imaging fringe G′ ₂ is equal;

Or the first and second phase grating G ₁ phase grating G _'1 of different periods; distance R between the source ₁ and a first grating G ₀ phase grating G _1, the second phase grating G' ₁ thereto from The distance R ₂ ′ between the imaging stripes G′ ₂ is different.

Further, in the X-ray dual phase grating phase contrast imaging system, it is preferable that the period of the self-imaging fringe of the second phase grating G′ ₁ is 20-300 μm.

Further, in the X-ray dual-phase grating phase contrast imaging system, it is preferable that the source grating G ₀ is an absorption grating that modulates incident light into coherent light, or a source grating G ₀ structure coupled to the X-ray anode target.

Further, in the X-ray dual phase grating phase contrast imaging system, it is preferable that the period of the source grating G ₀ is 5-50 μm and the duty ratio is 0.25-0.5; or the period of the source grating G ₀ is 1-5 Microns, the duty cycle is 1.

Further, in the X-ray dual phase grating phase contrast imaging system, it is preferable that the distance between the X-ray tube and the source grating G ₀ is 0 mm-100 mm; the distance between the source grating G ₀ and the first phase grating G ₁ The distance is 5 mm-1000 mm; the distance between the second phase grating G′ ₁ and the X-ray detector is 100 mm-2000 mm.

Further, in the X-ray dual-phase grating phase contrast imaging system, it is preferable that the first phase grating G ₁ and the second phase grating G′ ₁ each include an alternately arranged transmission layer and phase change layer that transmit X-rays.

Further, in the X-ray dual-phase grating phase contrast imaging system, it is preferable that the same absorption as the self-imaging fringe period G′ ₂ can be provided at the Taber distance of the second phase grating G′ ₁ in front of the X-ray detector Raster.

Further, in the X-ray dual phase grating phase contrast imaging system, it is preferred that the X-ray tube is an X-ray tube that emits X-ray photons with an energy range of 8 keV-70 keV.

Beneficial effect

The X-ray dual-phase grating phase contrast imaging system of the present invention can realize phase contrast imaging by using an ordinary X-ray source, a large period source grating, and two phase gratings. Regarding the two phase gratings provided by the present invention-the first phase The grating G ₁ and the second phase grating G′ ₁ have a large degree of linkage between the periods of all gratings and the distance between them. The phase grating of the present invention is a dual-phase grating, which is composed of two A single-phase grating phase contrast imaging system is combined to form a Tiberium and inverse Tiberium imaging system. The Tiberium system can provide structured light with a period of micrometers. Then, the inverse Tiberium system can obtain a large period Self-imaging stripes. In addition, a large-period absorption grating can be used as a sampling grating, thereby greatly reducing the difficulty of manufacturing an absorption grating with a large area and a high aspect ratio.

In order to avoid the production of small-scale light sources and large-area, small-period, high-aspect-ratio absorption gratings, dual-phase grating phase contrast imaging systems use images (interference fringes) generated by ordinary Taber-Lao systems as "self-imaging secondary sources". The adjustment of the period size of the "self-imaging secondary source" can be obtained by adjusting the period of the source grating and the phase grating of the Taber-Lao system and the distance between them. When the period is small, the second phase grating is used. It is possible to obtain a self-imaging fringe with a large period in a short distance. If the fringes at this time are still not enough to be detected, a large area of absorption grating can be added to assist detection. However, due to the large period of the absorption grating, the aspect ratio is not large, so it is not difficult to manufacture.

BRIEF DESCRIPTION

The present invention will be further described below with reference to the drawings and embodiments. In the drawings:

FIG. 1 is a schematic structural diagram of an embodiment of the present invention;

2 is a schematic structural diagram of another implementation manner of an example of the present invention;

3 is a schematic diagram of structural analysis of an embodiment of the present invention;

4 is a Moiré fringe obtained by the present invention;

5 is the fringe contrast along the horizontal line of the embodiment of the present invention;

Figures 6a-6c are the absorption image, phase contrast image and dark field image in the phase contrast experiment.

Best Mode of the Invention

In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific embodiments of the present invention will now be described in detail with reference to the drawings.

As shown in FIG. 1, an X-ray dual-phase grating phase contrast imaging system of the present invention includes an X-ray tube, a source grating G0, a phase grating and an X-ray detector arranged in sequence along the X-ray emission direction. The phase grating The first phase grating G1 and the second phase grating G'1 are arranged at intervals. Specifically, as shown in FIG. 1, from left to right are: X-ray tube, source grating G0, first phase grating G1, second phase grating G′1 and X-ray detector.

Specifically, the first phase grating G1 and the second phase grating G′1 are located between the source grating G0 and the X-ray detector, and the position and period of the first phase grating G1 satisfy: X-rays propagate through the source grating G0 The coherence length to the first phase grating G1 is not less than the period of the first phase grating G1. In this way, his self-imaging is formed at the Taber distance of the first phase grating G1, that is, the self-imaging secondary source G2 is obtained. This self-imaging secondary source G2 is a virtual source, thereby illuminating the second phase grating G'1. Similarly, the position of the second phase grating G′1 is related to the period and the period of the virtual source, that is, the position and period of the second phase grating G′1 satisfy: the self-imaging secondary source G2 propagates to the second phase grating G′1 The coherence length at is no less than the period of the second phase grating G'1.

The above structure of the imaging system of the present invention is actually a Tiberium system and an inverse Tiberium system, wherein the X-rays emitted by the X-ray tube, the source grating G0 and the first phase grating G1 form a Tiberium system, which can provide a period It is micron-level structured light, that is, self-imaging secondary source G2. Next, an inverse Tiberau system is formed by the self-imaging secondary source G2 and the second phase grating G′1, and finally detected by the X-ray detector. This scheme can provide sufficient magnification for the fringes and obtain large-period self-imaging fringes so that they can be directly resolved by the X-ray detector.

In the Tiberium system, labor conditions can be written as:

Where p0, p1, and p2 are the periods of the source grating G0, the first phase grating G1, and the self-imaging secondary source G2, respectively. The constant α is 1 or 2, the specific value depends on the first phase grating G1 is π/2 grating Π grating.

The Taber distance R2 of the first phase grating G1 satisfies:

Where p1 is the period of the first phase grating G1, R1 is the distance between the source grating G0 and the first phase grating G1, λ is the X-ray wavelength, k is a constant, and for the π/2 phase grating, k=1 /2, 3/2, 5/2, ..., for a phase grating of π, k = 1/8, 3/8, 5/8, ....

Functionally, the source grating G0 of the Tiberium system modulates the incident light into coherent light that satisfies the imaging conditions, so a self-imaging secondary source will be formed after the first phase grating G1. The self-imaging fringes of these self-imaging secondary sources can be used as the “light source” of the subsequent inverse Tiberau system, that is, as shown in FIG. 3, the self-imaging sub-grid is formed after the first phase grating G1 and before the second phase grating G′1 Level source.

The periods of the first phase grating G1 and the second phase grating G′1 may be the same or different. Preferably, the period p1 of the first phase grating G1 is the same as the period p1′ of the second phase grating G′1 (p1′=p1). That is, a symmetrical Tiberium system and an inverse Tiberium system are formed. The symmetrically placed Tiberium and inverse Tiberium systems are selected, so that only two specifications of gratings are required, while the traditional Tiberium systems require three specifications of gratings. The invention reduces the number of grating specifications. The spacing R1 between the source grating G0 and the first phase grating G1, the spacing R2' between the second phase grating G′1 and the self-imaging fringes G′2 formed by them are equal (R1=R2′), and the first The interval R2 between the phase grating G1 and the formed self-imaging secondary source and the interval R1′ between the self-imaging secondary source and the second phase grating G′1 are equal (R2=R1′).

The period of the self-imaging fringes of the second phase grating G'1 is 20-300 microns.

The following describes the specific structure of the present invention in detail:

The X-ray tube is selected to produce an X-ray beam with an X-ray energy range of 17 keV to 70 keV, a large radiation flux and a wide emission angle.

The source grating G0 is an absorption grating that modulates incident light into coherent light. The source grating G0 has a modulation effect on the X-rays generated by the X-ray tube. The modulated X-rays are a group of parallel line arrays, and each line is an X-ray line source.

The structure of the source grating G0 is as follows: a transmission layer and an absorption material layer are alternately arranged on the substrate, and the width ratio of the absorption material layer and the transmission layer is 2:1 to 4:1. The area should cover the entire imaging field of view. The base material is selected from silicon. The shape of the silicon substrate is adapted to the imaging field of view. The absorption material layer is selected from gold, bismuth, gold-tin alloy and other materials.

Preferably, the source grating G0 is a large-period source grating, and the period of the source grating is 5-50 microns, and the duty ratio is 0.25-0.5; for example, the line width of X-rays after modulation by the source grating is 5-100 microns The optimized numerical range is 10-20 microns; its length range is 0.3-2mm, and the optimized range is 0.6-1.2mm. The line emitter array has a duty cycle range of 0.1-0.5 and an optimized duty cycle of 0.2-0.35.

Further, in the X-ray dual-phase grating phase contrast imaging system, it is preferable that the distance between the X-ray tube and the source grating G0 is 0mm-100mm; the distance between the source grating G0 and the first phase grating G1 The distance is 2 mm-1000 mm; the distance between the second phase grating G′1 and the X-ray detector is 100 mm-2000 mm. The positions and sizes of the above devices can be designed and calculated according to actual needs, and any data within the above range can meet the needs of the present invention without specifying a certain data.

The first phase grating G1 and the second phase grating G′1 are a microstructure composed of a fully transparent layer and a phase change layer spaced on the base material. That is, it is preferable that the first phase grating G1 and the second phase grating G′1 each include an alternating transmission layer and a phase change layer that transmit X-rays. The phase change layer is made of silicon, aluminum, nickel, gold It is made of other materials, such as air and photoresist. By changing the thickness of the grating, the photon energy corresponding to the center wavelength can be adjusted within the range of 17-70 keV, and the allowable X-ray bandwidth is ±20%. The first phase grating G1 and the second phase grating G′1 have a diffractive effect. The X-rays modulated by the source grating G0 pass through the first phase grating G1 to generate diffraction, which minimizes the 0th order diffracted light energy and ±1st order diffracted light energy The largest, ±1st order diffracted light interacts to produce a differential interference effect.

Further, in the X-ray dual-phase grating phase contrast imaging system, preferably, the X-ray detector is a flat panel detector or adopts an indirect way to detect X-rays. The X-ray detector is an existing product, which is not described here. Repeat again.

Further, it is preferable that an absorption grating G′ 2 is provided in front of the X-ray detector at a Taber distance of the second phase grating G′ 1. When the source grating G0 and the first phase grating G1 and the second phase grating G′1 have a suitable fit, the self-imaging fringe period formed by the reverse Tiberau system is relatively large, not less than twice the pixel size of the X-ray detector, That is, it can be directly resolved. In this case, the above-mentioned absorption grating G′ 2 can be omitted. When the period of the self-imaging fringes formed by the reverse Tiberau system is less than twice the size of the X-ray detector, then the above absorption grating G′ 2 cannot be omitted. In fact, at the position of the absorption grating G′2, if the resolution of the X-ray detector used is still insufficient to resolve the self-imaging fringes formed by the inverse Tiberau system at this position (the advantage of the dual-phase grating imaging system of the present invention is If the fringe period becomes larger (about tens of microns or even larger), an absorption grating G′2 should be used. The period of the absorption grating G′2 is equal to the period of the self-imaging fringes formed by the inverse Tiberau system, as shown in Figure 2 In front of the X-ray detector, there is an absorption grating G′2. In this way, moiré fringes can be formed to facilitate detection by the X-ray detector, and at the same time, the fabrication of the absorption grating G′ 2 with such a large period is also relatively difficult.

The present invention is preferably applicable to a large-period source grating G0, and also to a small-period source grating G0.

Equation (2) can be transformed into:

among them:

In (3), R1 and R2 can be exchanged, and (1) p0 and p2 can be exchanged, that is, a small period of source grating G0 can obtain a large period of self-imaging fringes. The source grating G0 is a small period source grating G0, and the period of the source grating G0 is 1-5 microns, and the duty ratio is 1.

In addition to the above embodiments, in other embodiments, the periods of the first phase grating G1 and the second phase grating G′1 are different; the distance R1 between the source grating G0 and the first phase grating G1, the second The distance R2' between the phase grating G'1 and its self-imaging fringes G'2 is different.

The following is a detailed description with a specific embodiment:

As shown in FIG. 2-3, an X-ray dual-phase grating phase contrast imaging system includes an X-ray tube and a source grating G0, which are arranged in sequence along the X-ray emission direction (from left to right as shown in FIG. 1). The first phase grating G1, the second phase grating G'1, the absorption grating G'2 and the X-ray detector, the position and size of each device are: R1 = R2' = 0.763m, R2 = R1' = 0.101m, p1 '=p1=5.6 μm, p2′=p0=24 μm, the source grating G0 has a duty ratio of 25%, and a depth of 130 μm. The absorption grating has a duty ratio of 50% and a depth of 130 μm. Both absorption materials used are bismuth. The X-ray wavelength used is 0.043 nm, that is, the photon energy is 28 keV, and the corresponding thicknesses of the first phase grating G1 and the second phase grating are both 36 μm. The above embodiment is only a specific implementation manner, and the position and size of each device can be designed and calculated according to actual needs, which is not limited by the present invention.

The effective focal spot area of the X-ray source emitted by the X-ray tube is 1×0.8 mm 2, the applied voltage is 40 kV, and the current is 4 mA.

The flat panel detector is used as the X-ray detector, and the pixel size of the X-ray detector is 74.8 μm. The exposure time is 3s. As shown in FIG. 4, the displayed field of view is the overlapping part of the absorption grating (diameter: 10.5cm) and the area of the X-ray detector (11.5×6.5cm2). By measuring the pixel values on the horizontal line in FIG. 4, the fringe contrast can be calculated to be about 17%. Therefore, we can infer the self-imaging period at G2′. As shown in Figure 5, the fringe contrast along the horizontal line.

Phase contrast experiment:

Taking lemon as a sample, the parameters of the imaging system of the present invention are the same as those obtained when the Moiré fringe is obtained, except that the X-ray detector is replaced with a visible light CCD (Spectral Instruments), 4096×4096 pixels, 9 μm/pixel and scintillator CsI ( Tl) (thickness: 400 μm) coupling through 2:1 light cone. A voltage value of 40 kV and a current value of 4 mA were applied to the X-ray source, the exposure time was set to 60 s, the image effective area was 70×70 mm2, and the absorption, phase contrast, and dark field images of lemon were obtained by the 4-step phase shift method, as shown in Figure 6a -6c shown.

The above-mentioned phase contrast and dark field images show that the dual phase grating phase contrast imaging of the present invention can be performed like an ordinary Tiberium system. And because the dual-phase grating system is composed of a Tiberium and an inverse Tiberium system, while retaining the advantages of the two systems, they abandon their respective shortcomings. That is to allow the use of large-period source gratings, avoiding the production of small-period source gratings. More importantly, the system can greatly amplify interference fringes, for example, it can be amplified to a period of tens of microns or even hundreds of microns, thereby avoiding the production of small period absorption gratings, and even using a flat panel X-ray detector can directly Distinguish.

Claims

An X-ray dual-phase grating phase contrast imaging system, including an X-ray tube, a source grating G0, a phase grating and an X-ray detector arranged in sequence along the X-ray emission direction, characterized in that the phase grating includes first intervals A phase grating G1 and a second phase grating G′1, the first phase grating G1 and the second phase grating G′1 are located between the source grating G0 and the X-ray detector, and form a self-imaging order after the first phase grating G1 Level source G2; the X-ray emitted by the X-ray tube, the source grating G0 and the first phase grating G1 form a Tiberium system; the self-imaging secondary source G2 and the second phase grating G′1 form an inverse Tiberium system .
The X-ray dual-phase grating phase contrast imaging system according to claim 1, wherein the position and period of the first phase grating G 1 satisfy: make X-rays propagate to the first phase grating after passing through the source grating G 0 The coherence length at G 1 is not less than the period of the first phase grating G 1 ; the position and period of the second phase grating G′ 1 satisfy: the self-imaging secondary source G 2 propagates to the position of the second phase grating G′ 1 The coherence length is not less than the period of the second phase grating G′ 1 .
The X-ray dual-phase grating phase contrast imaging system according to claim 1, wherein the self-imaging secondary source G 2 is located at the Taber distance of the first phase grating G 1 .
The X-ray dual-phase grating phase contrast imaging system according to claim 1, wherein the periods of the first phase grating G1 and the second phase grating G'1 are the same; the source grating G0 and the first phase grating The distance R1 between G1 and the distance R2′ between the second phase grating G′1 and the self-imaging fringes G′2 formed by it are equal;

Or the periods of the first phase grating G1 and the second phase grating G'1 are different; the distance R1 between the source grating G0 and the first phase grating G1, the second phase grating G'1 and the self-imaging fringes formed by them The distance R2' between G'2 is different.
The X-ray dual-phase grating phase contrast imaging system according to claim 4, wherein the period of the self-imaging fringes G'2 formed by the second phase grating G'1 is 20-300 microns.
The X-ray dual-phase grating phase contrast imaging system of claim 1, wherein the source grating G0 is an absorption grating that modulates incident light into coherent light, or a source grating coupled to an X-ray anode target structure.
The X-ray dual-phase grating phase contrast imaging system according to claim 1, wherein the period of the source grating G0 is 1-50 microns, and the duty ratio is 0.25-0.5.
The X-ray dual-phase grating phase contrast imaging system according to claim 1, wherein the distance between the X-ray tube and the source grating G0 is 0mm-100mm; the source grating G0 and the first phase The distance between the grating G1 is 5mm-1000mm; the distance between the second phase grating G'1 and the X-ray detector is 100mm-2000mm.
The X-ray dual-phase grating phase contrast imaging system according to claim 1, wherein each of the first phase grating G1 and the second phase grating G'1 includes an alternating transmission layer for transmitting X-rays And phase change layer.
The X-ray dual-phase grating phase contrast imaging system according to claim 1, wherein a periodic and self-imaging can be provided in front of the X-ray detector and at the Taber distance of the second phase grating G′1 The absorption grating with the same fringe G'2.