Double-energy-point double-magnification imaging device and method based on time-broadening framing camera

Abstract

The invention belongs to the field of X-ray imaging, and provides a double-energy-point double-magnification imaging device and method based on a time broadening type framing camera, and the device comprises a pinhole sheet and the time broadening type framing camera; the method comprises the steps of pinhole piece and time broadening type framing camera imaging, geometric mapping model construction, distortion correction function fitting and image calibration. According to the invention, photoelectron imaging and transmission light imaging are realized at the same time by using the time-broadening framing camera, so that two spatially corresponding images are formed; the difference between electron acceleration and focusing characteristics in the time-broadening framing camera can be reflected by comparing the size and distortion difference of the straight-through light image and the photoelectron image, and dual-channel response mutual calibration is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of X-ray imaging, in particular to a dual-energy-point dual-magnification imaging device and method based on a time-stretch framing camera. BACKGROUND

[0002] Microchannel plate, abbreviated as MCP. Photoelectric conversion and electron imaging are one of the core technologies in high-energy radiation diagnosis, material analysis and ultrafast process detection. In the prior art, incident photons or radiation signals generate photoelectrons through the photocathode of the time-stretch framing camera, and the spatial information of the target is obtained through the MCP multiplication imaging of the time-stretch framing camera. In the traditional design, metal thin film cathodes such as gold cathodes and semi-transparent cathodes are mainly used as photoelectric conversion interfaces, and the design goal is to achieve high quantum efficiency and stable photoelectron emission performance.

[0003] However, with the increasing application of photoelectron imaging systems, it is gradually found in experiments that after pinhole imaging, part of the incident light can directly pass through the conversion structure of the time-stretch framing camera and form a weak transmission image on the rear-end imaging system. This direct transmission light imaging has been ignored as noise or background signal in the past, but in the system of micron-thick metal film or thin cathode, the proportion of this direct transmission light can reach 10% to 40% of the incident energy. In fact, it has the same spatial mapping relationship as photoelectron imaging, but it has undergone different transmission paths and amplification mechanisms. The current common time-stretch framing camera electron imaging system mainly relies on magnetic lenses to realize electron focusing. In this system, the electrons from the photocathode move in the magnetic field and are gathered to form an image. Its imaging characteristics are affected by the initial energy distribution of the electrons, the uniformity of the magnetic field, and the cathode-image plane geometry. If the incident light signal contains photons of different energies or different emission layer depths, it will cause the photoelectron energy distribution to widen, resulting in different magnifications and aberrations in the imaging system, making the final image appear blurred or distorted. Because the direct transmission light image and the electron image correspond to the same incident signal in spatial distribution, the size difference, distortion characteristics and brightness change between them contain the implicit information of the electron energy distribution and the space-time characteristics of the electric field in the imaging system. In theory, this dual-channel imaging can obtain the photoelectron distribution and the direct transmission light distribution at the same time, thereby forming two images that can be mutually referenced. However, other types of framing cameras cannot observe separate direct transmission light images and photoelectron images in this process due to the close relative position of the MCP and the cathode microstrip in the design. SUMMARY

[0004] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a dual-energy-point dual-magnification imaging device and method based on a time-stretch framing camera, which solves the problem that the prior art cannot simultaneously obtain photoelectron imaging and direct transmission light imaging information.

[0005] To achieve the above object, the present application provides the following scheme:

[0006] A dual-energy-point dual-magnification imaging device based on a time-stretch framing camera, comprising: a pinhole sheet, a time-stretch framing camera (photocathode, magnetic lens coil, drift tube, MCP, and imaging screen);

[0007] The pinhole sheet is fixed between the X-ray source and the photocathode of the time-stretch framing camera; the angle between the normal line of the photocathode of the time-stretch framing camera and the main optical axis of the drift tube of the time-stretch framing camera is less than 5°; the direction of the magnetic field lens optical axis generated by the magnetic lens coil of the time-stretch framing camera coincides with the main optical axis of the drift tube of the time-stretch framing camera;

[0008] The pinhole sheet of the time-stretch framing camera is used to perform pinhole imaging on the incident light emitted by the X-ray source on the surface of the photocathode of the time-stretch framing camera;

[0009] Preferably, the pinhole sheet is a 50-micron tantalum sheet; the aperture size of the pinhole sheet is 20 microns.

[0010] Preferably, the material of the photocathode of the time-stretch framing camera is gold; the thickness of the photocathode is 100 nm.

[0011] Preferably, a dual-energy-point dual-magnification imaging method based on a time-stretch framing camera, comprising:

[0012] Imaging the incident light emitted by the X-ray source on the surface of the photocathode of the time-stretch framing camera by using the pinhole sheet to obtain pinhole imaging;

[0013] Converting the pinhole imaging into photoelectrons by using the photocathode of the time-stretch framing camera through photoelectric effect, and setting the photons not absorbed by the photocathode as transmission light signals;

[0014] Inputting the photoelectrons and the transmission light signals into the drift tube of the time-stretch framing camera; the angle between the normal line of the photocathode and the main optical axis of the drift tube is less than 5°; the direction of the magnetic field lens optical axis generated by the magnetic lens coil coincides with the main optical axis of the drift tube;

[0015] Imaging the transmission light signals output by the drift tube by using the front end of the MCP of the time-stretch framing camera to obtain straight-through light images;

[0016] Constructing a geometric mapping model between the straight-through light images and the photoelectron images according to an image registration algorithm;

[0017] Calculating the boundary offset of each block of the straight-through light images and the photoelectron images and fitting the offset field by using the geometric mapping model to obtain a distortion correction function;

[0018] The photoelectron image is calibrated by using a distortion correction function to obtain a distortion corrected image.

[0019] The following technical effects are disclosed in the present application:

[0020] The application provides a dual-energy-point dual-magnification imaging device and method based on a time expansion framing camera, solves the problem that existing methods cannot simultaneously acquire photoelectron imaging and straight-through light imaging information through a time expansion framing (photoelectric cathode, magnetic lens coil, MCP, and imaging screen), realizes photoelectron imaging and transmission light imaging simultaneously in the same camera structure, solves the problem that the final image of the existing method is blurred or distorted by comparing the size and distortion difference between the straight-through light image and the photoelectron image, and realizes dual-channel response calibration. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0022] Figure 1 The imaging structure diagram provided for the embodiments of the present application;

[0023] Figure 2 The result display diagram provided for the embodiments of the present application.

[0024] Explanation of reference signs:

[0025] 1- pinhole sheet, 2- time expansion framing camera. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0027] The purpose of the present application is to provide a dual-energy-point dual-magnification imaging device and method based on a time expansion framing camera, which solves the problem that existing methods cannot simultaneously acquire photoelectron imaging and straight-through light imaging information.

[0028] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0029] Figure 1 An imaging structure diagram provided for an embodiment of the present invention, such as... Figure 1 As shown, the present invention provides a dual-energy point dual-magnification imaging device based on a time-stretching slat camera, comprising: a pinhole plate 1 and a time-stretching slat camera 2;

[0030] The pinhole plate 1 is fixed between the X-ray source and the photocathode; the angle between the normal of the photocathode and the principal optical axis of the drift tube is less than 5°; the direction of the magnetic field lens optical axis generated by the magnetic lens coil coincides with the direction of the principal optical axis of the drift tube;

[0031] The pinhole plate 1 is used to perform pinhole imaging of the incident light emitted by the X-ray source on the surface of the photocathode; the drift tube is used to transmit the photoelectrons and the photons not absorbed by the photocathode.

[0032] Optionally, the pinhole sheet 1 is a 50-micrometer tantalum sheet; the aperture size of the pinhole sheet 1 is 20 micrometers.

[0033] Preferably, the photocathode is made of gold; the thickness of the photocathode is 100 nm.

[0034] Furthermore, a dual-energy point dual-magnification imaging method based on a time-stretching framing camera 2 includes:

[0035] Pinhole imaging is obtained by using a pinhole plate 1 to image the incident light emitted from the X-ray source on the surface of the photocathode.

[0036] The pinhole imaging is converted into photoelectrons using the photocathode via the photoelectric effect, and the photons not absorbed by the photocathode are set as transmitted light signals.

[0037] The photoelectrons and the transmitted light signal are input into the drift tube, and the angle between the normal of the photocathode and the principal optical axis of the drift tube is less than 5°; the direction of the magnetic field lens optical axis generated by the magnetic lens coil coincides with the direction of the principal optical axis of the drift tube.

[0038] The transmitted light signal output from the drift tube is imaged using the front end of the MCP to obtain a direct-penetrating light image;

[0039] A geometric mapping model between the through-light image and the photoelectron image is constructed based on the image registration algorithm;

[0040] Using the geometric mapping model, the boundary offset and offset field fitting are performed on each block of the through-beam image and the photoelectron image to obtain the distortion correction function;

[0041] The photoelectron image is calibrated using the distortion correction function to obtain a distortion-corrected image.

[0042] Specifically, in this embodiment, a series of pinhole arrays are fabricated on a 50-micrometer-thick tantalum sheet with a aperture size of 20 micrometers and a fixed spacing, so as to perform pinhole X-ray imaging on the photoelectric microstrip surface of the time-stretched framing camera 2 and to perform imaging on the MCP of the subsequent time-stretched framing camera 2.

[0043] Preferably, this embodiment is based on two known quantities: the energy response coefficient (photon energy and efficiency of photoelectron generation) of the time-stretched framing camera 2 photoelectric microstrip (cathode) and the transmittance of incident X-rays by the microstrip thickness (given by the linear attenuation coefficient of the material). Since the photoelectric absorption coefficient of gold is extremely strong in the range of 0.5 keV to 2 keV and has a rapid decrease in the range of 2 keV to 5 keV, a gold photoelectric microstrip with a thickness of hundreds of nanometers will absorb low-energy X-rays (less than 5 keV) to generate photoelectron images, while high-energy signals still have a significant transmission component after passing through the gold cathode. Therefore, there is a dual-energy response region, which can be used for dual-energy imaging of the time-stretched framing camera 2.

[0044] Furthermore, when incident light shines on the cathode surface of the time-stretching framing camera 2, the cathode surface absorbs part of the incident photon energy and releases photoelectrons through the photoelectric effect. The photoelectrons will be accelerated and focused in the magnetic lens system; the unabsorbed photons penetrate the metal cathode layer and the drift space.

[0045] Specifically, a vacuum drift space is set at the rear end of the cathode, and a modulated electric field is set in the drift space to accelerate photoelectrons. The electron image is then focused onto a microchannel plate (MCP) by a magnetic lens.

[0046] Preferably, the MCP is positioned at the end of the drift tube to simultaneously receive drift electrons and transmitted light signals. The MCP amplifies the photoelectron signals to form a first image (photoelectron image), while an angle of less than 5° is set between the optical axis of the magnetic field lens and the principal optical axis to allow transmitted light to form a second image (through-light image) at the front end of the MCP. An imaging screen or optical recording system is coupled to the MCP to record the dual-image distribution; a fluorescent screen and a CCD structure can be used.

[0047] Furthermore, the coordinates of the obtained through-line image (high-energy reference image) are: And the coordinates of the electronic image (the image requiring correction) are A mapping function is established to estimate the local magnification and distortion field matrix. A calibration target with periodic edge boundaries (grid, aperture array, line scale, or stepped filter edge) is selected or prepared to ensure clear corresponding structures in both channels. A mapping model for the two signals is obtained using a set of control points with clear corresponding structures. For small distortions, a linear mapping model is used, and the distortion field is solved using the least squares method. For large distortions, a high-order polynomial model can be used to fit the mapping, or a high-degree-of-freedom TPS or RBF model can be used to obtain a smooth nonlinear mapping result. The relationship between the distortion field, magnetic field strength, and inhomogeneity is obtained through calibration iterations, enabling self-calibration of magnetic field inhomogeneity in the experiment via secondary imaging. By comparing the geometric magnification of the two images and the distance between the two image planes, the magnification of the imaging system is self-calibrated using the magnification calculation formula. The two images with different energy ranges acquired correspond to different types of physical processes during the study.

[0048] Specifically, Figure 1 This is a diagram of the imaging structure of this embodiment, including a pinhole plate 1 that uses the pinhole imaging principle. The pinhole plate 1 is located between the photocathode and the X-ray source, and the distance between them is relatively fixed. The photocathode is located behind the pinhole plate 1 and is installed close to one side of the drift tube, with its normal direction forming a small angle with the main axis of the drift tube. When X-rays are imaged on the photocathode, the generated photoelectrons can directly enter the drift tube for drifting. A magnetic lens coil is fixedly installed on the outside of the drift tube, and a uniform magnetic field is formed inside the drift tube by current to achieve magnetic lens imaging. The MCP is installed on the other side of the drift tube, and its installation position is consistent with the focusing imaging position, where photoelectrons are multiplied. A fluorescent screen is installed close to the rear end of the MCP, where the multiplied photoelectrons generate light signals, which are collected by a collection device installed behind the fluorescent screen. All connections are hard connections, and the accuracy of the relative positions must be ensured to reduce imaging errors caused by positional errors.

[0049] Furthermore, Figure 2The results of this embodiment are illustrated in the diagram. It is evident that the actual intensity distribution of the image differs due to the different energy points. This allows for dual-energy point analysis of X-ray emission information, analysis of signal energy characteristics, and verification of the system's geometric magnification and the uniformity of the drift tube's focusing. By measuring the spacing between the imaging pinholes and the imaging distance, the spatial alignment of the images is determined. The overall imaging magnification can be self-calibrated using the ratio. Since the dual-channel images originate from the same incident light field, their spatial geometries (such as aperture shape, spot center, and boundary contour) have a one-to-one correspondence. Through image registration algorithms (such as centroid localization, edge matching, or cross-correlation matching), a geometric mapping model between the electron image and the through-light image is established. By calculating the boundary offset of each region, the aberration distribution of the magnetic lens system at different locations can be reflected. By fitting the offset field (such as using a polynomial or radial basis function model), a distortion correction function is obtained, which quantitatively reflects the degree of imaging distortion of the magnetic lens. Because the cathode allows some high-energy rays to pass through, and because the cathode has different response efficiencies to X-rays of different energy bands, it will form an image on the image plane that responds to different energy bands. By comparing the intensity of the two images, the intensity difference between the low-energy signal and the high-energy signal and the uniformity of the incident source energy distribution can be determined.

[0050] The beneficial effects of this invention are as follows:

[0051] (1) The present invention realizes both photoelectronic imaging and transmitted light imaging in the same camera structure, forming two spatially corresponding images, providing direct data for studying magnetic field distribution and cathode characteristics.

[0052] (2) The electronic image and the optical image correspond to particle / photon channels with different energies. By comparing their size and distortion differences, this invention can reflect the differences in electron acceleration and focusing characteristics in the drift tube, and realize the mutual calibration of the dual-channel response.

[0053] (3) The present invention does not require the addition of a complex time scanning or external modulation system and has good system compatibility.

[0054] (4) The dual imaging channels of the present invention can be used to verify the focusing uniformity, cathode transmission stability and system geometric magnification of time-stretched framing cameras, providing a self-calibration means for high-precision imaging systems.

[0055] (5) This invention is not only applicable to time-stretching framing cameras, but can also be extended to visible light or electronic imaging systems, requiring only adjustment of the cathode material and thickness according to the energy range.

[0056] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0057] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A dual-energy, dual-magnification imaging device based on a time-stretching framing camera, characterized in that, include: Pinhole film and time-expanded framing camera; The pinhole plate is fixed between the X-ray source and the time-stretching framing camera; the angle between the normal of the photocathode of the time-stretching framing camera and the principal optical axis is less than 5°; The pinhole plate is used to perform pinhole imaging of the incident light emitted from the X-ray source on the surface of the photocathode of the time-stretching framing camera; the time-stretching framing camera is used to simultaneously image photoelectrons and photons not absorbed by the photocathode.

2. The dual-energy, dual-magnification imaging device based on a time-stretching framing camera according to claim 1, characterized in that, The pinhole sheet is a 50-micrometer tantalum sheet; the pore size of the pinhole sheet is 20 micrometers.

3. The dual-energy, dual-magnification imaging device based on a time-stretching framing camera according to claim 1, characterized in that, The photocathode is made of gold; the thickness of the photocathode is 100 nm.

4. A dual-energy, dual-magnification imaging method based on a time-stretching framing camera, characterized in that, The method applied to the dual-energy, dual-magnification imaging device based on a time-stretching framing camera as described in claim 1 includes: Pinhole imaging is obtained by using a pinhole plate on the photocathode surface of a time-stretching framing camera to image the incident light emitted from an X-ray source. The pinhole imaging is converted into photoelectrons using the photocathode through the photoelectric effect, and the photons not absorbed by the photocathode are set as transmitted light signals; the angle between the normal of the photocathode and the principal optical axis of the time-stretched framing camera is less than 5°. The transmitted light signal is imaged using the time-stretched framing camera to obtain a direct-penetrating light image and a photoelectron image, and the direct-penetrating light image and the photoelectron image are received using an imaging screen; A geometric mapping model between the through-light image and the photoelectron image is constructed based on the image registration algorithm; Using the geometric mapping model, the boundary offset and offset field fitting are performed on each block of the through-beam image and the photoelectron image to obtain the distortion correction function; The photoelectron image is calibrated using the distortion correction function to obtain a distortion-corrected image.

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