Large aperture parabolic single glass tube micro-CT system and reconstruction method thereof

Abstract

The present application relates to the technical field of micro computer tomography, and discloses a large-aperture parabolic single glass tube micro-CT system and a reconstruction method thereof, the system comprising an X-ray source, a straight-through X-ray shutter, a first lens supported by a lens support to move, a sample supported by a sample stage and an X-ray flat panel detector arranged in sequence along an optical axis; the first lens is a large-aperture parabolic glass tube lens of millimeter level, and the lens support is used for adjusting the angle, pitch and optical axis coaxiality of the first lens; an electric control platform controller is electrically connected with the lens support and the sample stage respectively, and a main control computer controls the sample stage to perform angle scanning, sub-pixel angle jitter sampling and multi-view field splicing scanning through the electric control platform controller. The present application adopts a large-aperture parabolic glass tube lens of millimeter level, and the quasi-parallel beam geometry after system regulation and control enables the micro-CT system to be compatible with parallel beam algorithm, and the image reconstruction quality of the original cone beam algorithm is retained and improved.

Description

Technical Field

[0001] This invention relates to the field of microscopic imaging technology, and in particular to a large-diameter parabolic single-glass tube micro-CT system and its reconstruction method. Background Technology

[0002] Micro-CT allows for clear visualization of the internal microstructure of samples without damaging them. It boasts extremely high resolution, reaching the micrometer (μm) level, and is applicable to research in fields such as medicine, pharmacy, biology, archaeology, materials science, electronics, and geology. Desktop micro-CT systems typically consist of a microfocus X-ray source, a sample rotation mechanism, and a two-dimensional flat panel detector. They utilize cone-beam geometry to achieve full-angle projection acquisition and often employ Feldkamp-Davis-Kress (FDK) type analytical reconstruction algorithms.

[0003] To achieve micrometer-level or even sub-micrometer-level spatial resolution, current desktop micro-CT mainly relies on two approaches: first, utilizing the imaging characteristics of cone-beam geometry; and second, employing a combination of small-focus micro-X-ray sources and high-pixel-density detectors. However, both of these approaches are constrained by factors such as focal spot size, detector pixel size, and system mechanical stability, and have reached significant bottlenecks in further improving spatial resolution and signal-to-noise ratio.

[0004] Cone-beam reconstruction is a very complex problem. The most popular reconstruction algorithm is the FDK cone-beam reconstruction algorithm, which is only an approximate formula for cone-beam reconstruction. Circular trajectory scanning cannot provide sufficient sampling for accurate cone-beam reconstruction. Therefore, this algorithm can be reasonably applied for small cone angles. When the sample height increases and the axial dimension is large, the cone angle becomes larger, and shadow artifacts and strip artifacts will appear around high-density areas (such as bone structures) during reconstruction (Reference: Feldkamp L A, Davis LC, Kress J W. Practical cone-beam algorithm[J]. Journal of the Optical Society of America A, 1984, 1(6): 612-619.).

[0005] Because the focal spot of the X-ray source has a limited size, the system exhibits a significant penumbra blurring effect, which limits the resolution improvement of micro-CT.

[0006] In contrast, parallel-beam geometry offers advantages such as simple reconstruction conditions and fewer axial artifacts. The most popular reconstruction algorithm used is called the parallel-beam filtered back-projection algorithm (Reference: Kak AC, Slaney M. Principles of computerized tomographic imaging[M]. Society for Industrial and Applied Mathematics, 2001.). However, stable quasi-parallel X-rays are difficult to obtain under the conditions of desktop micro-CT in laboratories, therefore parallel-beam CT has long relied primarily on synchrotron radiation sources. In ordinary desktop laboratories, how to obtain sufficient throughput and collimation within limited volume and cost remains an engineering challenge.

[0007] Existing laboratory beamforming control methods primarily employ pinhole / slit collimation, metal collimator arrays, or multi-capillary focusers. Pinhole / slit collimation significantly sacrifices flux; while multi-capillary beamforming can improve X-ray brightness at the sample to some extent, its multi-channel structure leads to reduced divergence and aberration superposition, making it challenging to obtain highly uniform quasi-parallel beams within the macroscopic field of view, and it is also not favorable to the geometric assumptions of the back-end reconstruction algorithm.

[0008] Existing technology 1

[0009] Existing literature: Zhou Lazhen, Xia Wenjing, Xu Qianqian, et al. A micro cone-beam CT scanner based on capillary X-ray lenses [J]. Acta Physica Sinica, 2022, 71(09):43-52. This paper discloses a micro-cone-beam computed tomography (Micro-CBCT) system based on multiple capillary focusing lenses. The system consists of a micro-focus X-ray source, an irradiation system based on capillary X-ray lenses, an amorphous silicon flat panel detector, a rotating stage, and a control computer. It acquires full-angle projection data of small animals through cone-beam geometry. The capillary X-ray lenses are used to adjust the X-ray beam diameter and irradiation uniformity to improve the system's spatial resolution, contrast resolution, and imaging uniformity. The projected data, after being processed by the FDK cone-beam reconstruction algorithm, can achieve a spatial resolution of approximately 9.1 lp / mm under a 10% modulation transfer function, which is about 1.35 times higher than that of the traditional system. At the same time, due to the suppression effect of capillary lens on the absorption and scattering of low-energy X-rays, the image uniformity deterioration caused by the hardening effect of multicolor X-ray beams is reduced to a certain extent. Its feasibility was verified in an in vivo imaging experiment in anesthetized mice.

[0010] The disadvantages of the existing technology are as follows:

[0011] 1. The system as a whole still operates under cone-beam geometry, using cone-beam projection imaging. Reconstruction relies on FDK-type cone-beam algorithms, which makes it difficult to avoid artifacts caused by incomplete sampling of the cone-beam trajectory. Furthermore, the imaging quality deteriorates significantly when the cone angle is large.

[0012] 2. The system has a limited field of view. When scanning large-volume samples, a large geometric magnification is often required to obtain high spatial resolution, which further aggravates cone-beam artifacts.

[0013] Existing technology 2

[0014] Chinese patent CN209784229U discloses a CT imaging system based on a lead glass square multi-capillary lens. The system consists of an X-ray source, a rotating stage, a lead glass square multi-capillary lens, and a CCD camera arranged sequentially along the optical axis. The object to be scanned is placed on the rotating stage, with the lens positioned close to the sample. The lead glass square lens is composed of multiple square lead glass sub-tubes, the size of which corresponds one-to-one with the CCD pixel unit. This sub-tube is used to magnify the projected image of the sample, increasing the magnification without increasing the blurriness of the projection, thereby improving the resolution of the CT image.

[0015] The disadvantages of the existing technology 2 are as follows:

[0016] 1. This system still belongs to the traditional cone-beam CT structure, only adding a magnifying lens behind the sample, and does not solve the penumbra blur caused by the actual size of the X-ray source.

[0017] 2. The artifact problem caused by cone beam projection itself has not been solved either.

[0018] 3. Its imaging field of view is limited by the aperture of the multi-capillary lens and the one-to-one correspondence with the CCD pixels, which is not conducive to imaging large-field samples.

[0019] To overcome the physical limitations of detector pixels, researchers have explored methods such as super-resolution reconstruction based on sub-pixel dithering for upsampling, iterative reconstruction based on constraints or priors, and deep learning reconstruction utilizing learned priors. These methods can improve reconstruction quality to some extent, but they typically do not change the front-end beam geometry and system transfer characteristics, and remain constrained in areas such as conical beam artifact handling and reconstruction stability.

[0020] In summary, existing desktop micro-CT scanners suffer from at least the following common technical problems:

[0021] (1) Artifacts caused by large-angle conical beam geometry limit the accuracy of sample reconstruction;

[0022] (2) High magnification and small focal spot scheme lead to insufficient throughput and reduced field of view (FOV);

[0023] (3) The FDK algorithm is essentially an approximation algorithm. The smaller the cone angle, the more accurate the reconstruction. The larger the cone angle, the more severe the artifacts in the reconstructed image. There is a lack of practical beamforming methods that can take into account large aperture, high throughput and near-parallel beams under laboratory conditions. It is difficult to directly utilize the algorithmic advantages of small cone angle cone beams or parallel beams to reconstruct the internal structure of microscopic samples with high precision. Summary of the Invention

[0024] To overcome or alleviate one or more of the above-mentioned technical problems, the present invention aims to provide a large-aperture parabolic single-glass tube micro-CT system and its usage method. This system provides a large-aperture, near-parallel X-ray beam profile scheme that can be achieved under ordinary laboratory conditions. Combined with targeted sample scanning and jitter sampling strategies, it improves the X-ray flux at the sample, increases the projection resolution at each angle, and improves the accuracy of the reconstructed image, thereby enhancing the imaging quality and application versatility of desktop micro-CT.

[0025] This invention provides the following technical solution:

[0026] A large-aperture parabolic single-glass tube micro-CT system includes an X-ray source arranged sequentially along the optical axis, a direct X-ray shield, a first lens that moves via a lens holder, a sample supported by a sample stage, and an X-ray flat panel detector.

[0027] The first lens is a large-diameter parabolic glass tube lens with a diameter of millimeters. The lens holder is used to adjust the angle, pitch, and optical axis coaxiality of the first lens. The electronic control platform controller is electrically connected to the lens holder and the sample stage respectively. The main control computer controls the sample stage to perform angle scanning, sub-pixel angle jitter sampling, and multi-field stitching scanning through the electronic control platform controller.

[0028] The X-ray source control power supply provides high-voltage drive for the X-ray source, which generates a micro-focus cone-shaped diverging X-ray beam. After being shielded by the direct X-ray shielding device, the beam enters the first lens, where it undergoes single total internal reflection to shape the X-rays into a quasi-parallel X-ray beam with a certain ring width at the exit of the first lens. This beam irradiates the sample on the sample stage, and the X-rays passing through the sample form a two-dimensional projection image on the X-ray flat panel detector. The X-ray flat panel detector transmits the acquired signal to the main control computer via a data line. The main control computer performs synchronous control, controlling the angle jitter of the sample stage, and controlling the acquisition, cropping, stitching, and fusion of the projection image at the sample, as well as subsequent quasi-parallel beam reconstruction processing.

[0029] According to some possible implementations, the inner wall of the first lens is a parabolic channel structure, which guides the incident X-rays through a single total internal reflection within the critical angle range, so that a quasi-parallel beam is generated at the exit of the first lens. The geometric parameters of the first lens, such as the inlet diameter, outlet diameter, length, and parabolic equation parameters, are obtained through critical angle calculation and ray tracing optimization.

[0030] According to some possible implementations, the sample stage is driven by the electronic control platform controller controlled by the main control computer to perform high-precision rotational scanning around the vertical optical axis, micro-displacement along the X direction for field stitching, lifting and lowering adjustment along the Z direction for height positioning and field stitching in the Z direction, and small-amplitude angle jitter sampling at each nominal angle.

[0031] According to some possible implementations, the detection pixel size of the X-ray flat panel detector is selected according to the required resolution and system geometry. Its output signal is transmitted to the main control computer via a data line, and the main control computer performs real-time data acquisition, dark field or flat field correction and buffer management.

[0032] According to some possible implementations, the synchronous control of the main control computer includes: the start-up and shutdown and exposure control of the X-ray source; the rotation, angle jitter and X / Z direction translation of the sample stage; the data acquisition, trigger timing and parameter configuration of the X-ray flat panel detector, used to execute projection domain registration, sub-pixel angle jitter fusion, multi-field projection stitching and back-end reconstruction algorithms, using quasi-parallel beam geometry, the back-end reconstruction uses parallel beam filtering back projection or equivalent small cone angle cone beam FDK type algorithms to obtain high-precision three-dimensional volume data.

[0033] On the other hand, the present invention provides a reconstruction method for the above-mentioned large-diameter parabolic single-glass tube micro-CT system, which includes the following steps:

[0034] S1: Start the X-ray source and adjust the position of the first lens by adjusting the lens holder to form a stable quasi-parallel beam; after the sample is placed on the sample stage, adjust the sample stage to adjust the height and center position of the sample; adjust the sample stage at each nominal angle to perform sub-pixel angle jitter sampling and obtain 2~3 frames of projection with different micro-perturbation angles; after completing the 180° scan, move the sample stage along the X or Z direction to achieve multi-field stitching.

[0035] S2: All projected images are sent to the main control computer for cropping, registration, fusion, and reconstruction, specifically including the following steps:

[0036] S21: Perform flat field correction and noise suppression on the original projection, and trim the effective imaging area according to the beam width of the quasi-parallel beam exit;

[0037] S22: When the field of view is insufficient, grayscale matching and edge registration are performed on the projections of adjacent positions to achieve large field of view stitching;

[0038] S23: Subpixel dithered projections upsampled at the same angle are fused into a higher resolution projection.

[0039] S24: Based on the characteristics of quasi-parallel beams, select any of the following image reconstruction methods: Parallel beam reconstruction method: Treat the cropped projection as a parallel beam projection and directly reconstruct the 3D image using a filtered back projection method; Small cone angle reconstruction method: Equivalent the quasi-parallel beam to a small cone angle cone beam model and reconstruct it using an improved FDK algorithm based on small cone angle expansion.

[0040] S3: Outputs high-resolution, wide-field-of-view 3D micro-CT images.

[0041] According to some possible implementations, the small cone angle cone bundle reconstruction method in step S24 includes the following steps:

[0042] The quasi-parallel beam exit has a small divergence, with a small angle θ between the edge rays and the optical axis. d According to the principles of light reversibility and geometric optics, if the two edge rays of the quasi-parallel beam are extended in the "reverse" direction, they will inevitably intersect at a point on the optical axis. Therefore, this point can be defined as the equivalent virtual focus Ov. The tiny cone-shaped beam emitted from this equivalent focus coincides with the quasi-parallel beam at the lens exit. It is the cone angle of the equivalent small cone angle cone bundle, referring to the cone angle size corresponding to the equivalent mapping of the quasi-parallel bundle to a small cone angle cone bundle. When the equivalent mapping is valid, it should satisfy: This allows the quasi-parallel beam to be directly mapped to a small cone-angle cone beam, thus enabling the use of small cone-angle FDK-type cone beam reconstruction algorithms. From similar triangles, we can obtain:

[0043] (1)

[0044] In the above formula, the quasi-parallel beam divergence angle θ d , beam width D out Virtual focus position L vf

[0045] therefore,

[0046] (2)

[0047] This is the focal position of the equivalent "small cone angle cone beam light source"; in the equivalent model, the distance between the detector and the virtual focal point is obtained by extending the edge rays of the aligned parallel beam in the opposite direction and intersecting them at a point on the optical axis. Because the optical path is controlled by the glass tube, this point is not the same as the SDD (source to detector distance) of the real scene. This point is defined as the virtual focal point Ov.

[0048] From standard conical bundle geometry:

[0049] (3)

[0050] In the above formula, The cone angle of the equivalent small cone angle cone bundle,

[0051] Substitution

[0052] θ cone = θ d (4)

[0053] get:

[0054] (5)

[0055] In the above formula, This represents the maximum illumination range formed by the small cone-angled beam on the flat panel detector. Using the virtual focus-detector distance, the equivalent cone-beam projection geometry and reconstruction algorithm are precisely constructed.

[0056] According to some possible implementations, the subpixel angle jitter sampling in step S1 is implemented under approximately parallel beam geometry. The small angle perturbation Δθ corresponds to a subpixel displacement Δu≈SDD·Δθ in the detector domain, where SDD is the distance from the sample to the detector. This calculation formula satisfies the upper limit of Δθ for upsampling in adjacent frames. The typical value of Δu is selected from within 1 / 2 or 1 / 3 of the pixel size of the X-ray flat panel detector. The angle jitter of the subpixel angle jitter sampling is superimposed with the X and Z translation jitter to form a two-dimensional or three-dimensional subpixel sampling grid.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] The large-aperture parabolic single-glass tube micro-CT system and its reconstruction method provided by this invention employ a large-aperture parabolic single-glass tube lens. The large-aperture parabolic single-glass tube lens determines the inlet / outlet diameter, length, and parabolic generatrix based on the working energy and the critical angle of total internal reflection to achieve high reflectivity and high beam uniformity. This glass tube lens is used to convert the X-ray cone beam used for scanning samples in traditional desktop micro-CT into an approximately parallel beam, enabling the system to perform image reconstruction using an improved small cone-angle cone beam, or directly using a parallel beam scanning method combined with a parallel beam reconstruction algorithm. A multi-frame projection acquisition, registration, and fusion method based on sub-pixel angle jitter (which can be combined with translation jitter) is used to improve the effective projection resolution and achieve super-resolution reconstruction. Under the premise of fixed source-lens-detector geometry, a large field of view acquisition is achieved by using sample X and Z translation for multi-field stitching scanning; the present invention also provides an imaging and reconstruction process suitable for approximately parallel beam / small cone angle geometry, including projection correction, field stitching, jitter fusion, and image reconstruction methods using parallel beam or improved small cone angle cone beam reconstruction algorithms;

[0059] By combining large-field sample scanning with stage control and multi-projection fusion imaging based on angle jitter, the imaging quality of desktop micro-CT can be significantly improved.

[0060] The adjusted quasi-parallel beam geometry enables this micro-CT system to be compatible with parallel beam algorithms while preserving and improving the imaging quality of the original cone-beam FDK-type algorithms. Specifically:

[0061] (1) Artifact suppression:

[0062] By using a single parabolic glass tube to modulate the cone-shaped diverging beam emitted from the X-ray source into an approximately parallel beam, artifacts in the reconstructed image of the cone beam are significantly reduced.

[0063] (2) Penumbra blur suppression:

[0064] Parallel illumination guided by the lens significantly suppresses the geometric expansion and penumbra blurring effects caused by the finite focal spot, improves the system modulation transfer function (MTF) and edge sharpness, and makes the imaging details clearer.

[0065] (4) Gain and field of view are adjustable:

[0066] The lens geometry parameters (focal length, aperture, length) can be flexibly designed and adjusted, so that the system's light flux gain and quasi-parallel beam size can be optimized and matched according to different CT modes or sample sizes, thereby adapting to various micro-CT imaging needs.

[0067] (5) Subpixel angle jitter improves resolution:

[0068] By introducing minute angular jitter at each nominal projection angle and utilizing subpixel-level angular perturbation to achieve upsampling and fusion of projection information, the projection resolution and reconstructed image resolution can be improved without changing the detector pixel size.

[0069] (6) Multi-field-of-view splicing extended FOV:

[0070] By employing a multi-field stitching scanning method that involves translating the sample along the X and Z directions, a large field of view projection acquisition can be achieved without moving the light source and detector, effectively expanding the scanning range of the system.

[0071] (7) Coating and assembly are easier to achieve:

[0072] The large-diameter parabolic tube structure facilitates inner wall coating and can improve total internal reflection efficiency; its installation position and incident angle can be adjusted according to the system geometry, which is beneficial for optical axis calibration and system integration.

[0073] (8) Algorithm-assisted enhancement of imaging performance:

[0074] The ring beam formed by parabolic guidance exhibits predictable non-uniformity in energy distribution. This characteristic can be utilized through projection correction or signal enhancement algorithms to achieve local signal enhancement or adaptive gain compensation, thereby further improving the image signal-to-noise ratio and local resolution.

[0075] (9) Multiple algorithms can be used for reconstruction:

[0076] This invention can perform image reconstruction using improved small cone angle cone beams under approximate parallel beam geometry, or directly using parallel beam filtering back projection (FBP) and iterative algorithms.

[0077] (10) The project is simple to implement and the cost is controllable:

[0078] The system employs a single parabolic glass tube lens structure, resulting in a compact overall design, easy assembly, and significantly lower cost compared to multi-capillary or multi-lens array solutions. This makes it suitable for the promotion and integrated application of desktop micro-CT systems under ordinary laboratory conditions. Attached Figure Description

[0079] Figure 1 This is a schematic diagram of the structure of a large-diameter parabolic single-glass tube micro-CT system provided in an embodiment of the present invention.

[0080] Figure 2 The equivalent virtual focus Ov and detector coverage width D of the small cone beam provided in the embodiments of the present invention detector .

[0081] Figure 3The working principle and structural diagram of the parabolic glass tube provided in the embodiments of the present invention are shown.

[0082] In the picture:

[0083] 1-X-X-ray source; 2-X-ray source control power supply; 3-Direct X-ray shield; 4-First lens; 5-Lens support; 6-Sample stage; 7-X-ray flat panel detector; 8-Electrical control platform controller; 9-Main control computer. Detailed Implementation

[0084] The technical concept and key points of this invention are as follows:

[0085] 1. System Overview

[0086] The system of the present invention includes a micro-focal X-ray source arranged sequentially along the same optical axis, a large-aperture parabolic single glass tube lens with adjustment and fixing brackets, a sample stage, and a micron-level X-ray flat panel detector; the sample stage includes a sub-pixel-level rotation mechanism and a high-precision translation mechanism along the X and Z directions; the system is equipped with a control unit for synchronously controlling exposure, rotation stepping, angle jittering, and translation stitching, and completing projection, registration, projection fusion, and image reconstruction.

[0087] 2. Parabolic single-glass tube lens

[0088] The inner wall of the single-glass tube lens is a parabolic channel structure, employing total internal reflection of X-rays on the glass surface to shape the conical diverging beam from the X-ray source into an approximately parallel beam. The large-diameter inlet of the lens is used to receive a large solid angle flux. The parabolic generatrix parameters are set based on the critical angle of total internal reflection calculated from the source energy and the material dispersion constant. The lens shape and length are optimized according to the working distance and system layout, ensuring that the reflected approximately parallel X-ray beam irradiates the sample, thereby significantly suppressing or avoiding out-of-layer crosstalk caused by the cone beam geometry and cone beam artifacts that are sensitive to FDK-type algorithms.

[0089] The lens is a single, compact unit, mounted between the light source and the sample, and coaxial with the system's optical axis. The lens's inner wall surface shape error and roughness are controlled to ensure high reflectivity and low scattering within the grazing incident angle range, thereby achieving better beam shape uniformity and coherence retention. Material selection and geometric parameters can be designed and calibrated based on the operating energy.

[0090] 3. Multi-field translation and stitching of samples

[0091] To overcome the field-of-view limitations imposed by geometric magnification, this invention employs a multi-field-of-view stitching strategy involving two-dimensional translation of the sample's X and Z axes without moving the light source, lenses, or detector. The sample is divided into several adjacent sub-regions. For each sub-region, a projection acquisition of 0–180° (or 0–360°) is performed independently, followed by translation to the next sub-region until the target field of view is covered. For multiple sub-region projections at the same projection angle, sub-projection domain clipping and registration stitching are used to generate the entire projection frame at that angle. This allows for the acquisition of a large field-of-view projection sequence while maintaining system geometry, simplifying the control process.

[0092] 4. Subpixel angle jitter

[0093] Building upon traditional X and Z translation subpixel dithering (2×2, 3×3, or higher densities), this invention proposes a subpixel angle dithering strategy: at each nominal projection angle, a tiny angular perturbation (2–3 frames per angle) is introduced, causing a subpixel-level relative displacement between adjacent frames in the projection domain. The dithering amplitude is determined based on system geometry, detector pixel size, and sample-detector distance, enabling stable subpixel-level subpixel registration and super-resolution fusion between adjacent frames, thereby achieving upsampling of projection resolution without altering the hardware pixels.

[0094] Angular jitter is implemented under approximate parallel beam geometry: a small-angle perturbation Δθ corresponds to a subpixel displacement Δu ≈ SDD·Δθ (small-angle approximation) in the detector domain, where SDD is the distance from the sample to the detector. This allows calculation of the upper limit of Δθ for upsampling between adjacent frames; preferably, Δu is controlled within 1 / 2 or 1 / 3 of the pixel size of the X-ray flat panel detector to balance information gain and registration stability. This strategy can be superimposed with X and Z translation jitter to form a two-dimensional or three-dimensional subpixel sampling grid. Before image reconstruction, this method establishes a connection between the projections of two adjacent frames through subpixel angular jitter, thereby overcoming the physical limitations of the X-ray flat panel detector pixels and improving projection resolution. To the best of our knowledge, similar methods only involve translating the X-ray source, sample, or detector to achieve subpixel upsampling; the angular jitter implementation method proposed in this application is the first of its kind.

[0095] 5. Projection Preprocessing and Reconstruction

[0096] Data processing includes: dark field / flat field correction, artifact suppression, geometric calibration, projection domain registration and fusion; super-resolution fusion of multiple subframes caused by angular jitter to obtain high-resolution projection at each nominal angle; stitching together the projections of multiple field-of-view sub-regions at the same angle to obtain the entire projection sequence; and, under approximately parallel beam geometry, using parallel beam filtered back projection (FBP) or equivalent small cone angle cone beam FDK-type algorithms to complete volume data reconstruction.

[0097] 6. Control and Synchronization

[0098] The control unit sends synchronous trigger commands to the X-ray source, detector, rotary stage, and translation stage, executing them in the sequence of "angle → angle jitter subframe → (complete one revolution) → translation to the next sub-region". Exposure parameters can be adaptively adjusted between different sub-regions and jitter sampling to balance flux, noise, and dose.

[0099] The present invention will now be described in detail with reference to embodiments and accompanying drawings. However, it should be understood that the embodiments and drawings are for illustrative purposes only and do not constitute any limitation on the scope of protection of the present invention. All reasonable modifications and combinations included within the inventive spirit of the present invention fall within the scope of protection of the present invention.

[0100] The present invention will be further described below with reference to the accompanying drawings.

[0101] Example 1

[0102] like Figure 1 As shown, the large-aperture parabolic single-glass tube micro-CT system provided in this embodiment includes an X-ray source 1, an X-ray source control power supply 2, a direct-through X-ray shield 3, a first lens 4, a lens support 5, a sample stage 6, an X-ray flat panel detector 7, an electronic control platform controller 8, and a main control computer 9.

[0103] 1) Light source and front-end beamforming unit

[0104] X-ray source 1 is provided with stable high-voltage excitation by X-ray source control power supply 2 to generate a microfocus cone-shaped diverging X-ray beam. Its position is arranged along the optical axis of the system, and its operating voltage, current, and exposure parameters are adjusted by X-ray source control power supply 2 to ensure stable output from the light source.

[0105] A direct-through X-ray blocker 3 is installed at the front end of the X-ray source 1 to shield the direct light from the center of the source, thereby reducing uncontrolled X-ray background signals. The direct-through X-ray blocker 3 can be made of high-density metal material, and its aperture can be designed according to the size of the focal spot of the source.

[0106] 2) Parabolic glass tube bundle unit

[0107] A first lens 4 is placed after the through X-ray blocker 3.

[0108] The first lens, 4, is a large-aperture parabolic glass tube lens with an inner wall that forms a parabolic channel structure. It can guide incident X-rays through single total internal reflection within the critical angle range, producing a quasi-parallel beam at the lens exit. Single reflection exhibits high reflection efficiency. The lens's geometric parameters (inlet diameter, outlet diameter, length, and parabolic equation parameters) are obtained through critical angle calculation and ray tracing optimization.

[0109] The lens holder 5 is used to mount and precisely adjust the spatial position of the through X-ray blocker 3 and the first lens 4, including their angle, pitch, and optical axis coaxiality. The lens holder 5 employs a three-dimensional adjustment mechanism to ensure that the blocker intercepts the through X-rays while ensuring that the lens exit beam irradiation range can irradiate the movement range of the subsequent sample stage 6.

[0110] 3) Sample scanning unit

[0111] The sample is mounted on the sample stage 6, which is driven by the electronic control platform controller 8 to achieve: high-precision rotational scanning around the vertical optical axis; micro-displacement along the X direction for field stitching; lifting adjustment along the Z direction for height positioning and field stitching in the Z direction; and micro-amplitude sub-pixel angle jitter sampling at each nominal angle.

[0112] The sample stage 6 is driven by the electronic control platform controller 8. The electronic control platform controller 8 executes preset angle stepping, angle perturbation, X / Z translation, multi-area scanning and other actions according to the motion commands issued by the main control computer 9, and has high repeatability positioning accuracy.

[0113] 4) Detector Unit and Data Acquisition

[0114] The quasi-parallel beam passes through the sample and reaches the X-ray flat panel detector 7, which is used to acquire a two-dimensional projection image. The detector pixel size can be selected according to the required resolution and system geometry, featuring high-speed exposure and high dynamic range. Typical options include:

[0115] The signal output by the X-ray flat panel detector 7 is directly transmitted to the main control computer 9 via a data cable, and the main control computer performs real-time data acquisition, dark field / flat field correction and buffer management.

[0116] 5) Main control computer and imaging software

[0117] The main control computer 9 is used to synchronously control the entire system, including: starting and stopping the X-ray source and exposure control; rotation, angle jitter and X / Z direction translation of the sample stage 6; data acquisition, trigger timing and parameter configuration of the X-ray flat panel detector 7.

[0118] The main control computer 9 is also used to perform projection domain registration, subpixel angle dithering fusion, multi-field projection stitching, and back-end reconstruction algorithms. Because this invention uses quasi-parallel beam geometry, the reconstruction can directly use parallel beam filtering back projection or a cone-beam FDK-type algorithm equivalent to a small cone angle to obtain high-precision three-dimensional volume data.

[0119] 6) Imaging operation procedure

[0120] The basic imaging operation procedure of the large-diameter parabolic single-glass tube micro-CT system provided in this embodiment is as follows:

[0121] 1. Start the X-ray source 1 and adjust the position of the first lens 4 to form a stable quasi-parallel beam;

[0122] 2. After placing the sample on the sample stage 6, adjust its height and center position;

[0123] 3. Perform angle jitter sampling at each nominal angle to obtain 2–3 frames of projection with different perturbation angles;

[0124] 4. After completing the 180° scan, move the sample stage 6 along the X or Z direction to achieve multi-field stitching;

[0125] 5. Send all projections to the main control computer 9 for cropping, registration, blending, and reconstruction;

[0126] 6. Output high-resolution, wide-field-of-view 3D micro-CT images.

[0127] During operation, the X-ray source 1 is driven by a stable high voltage supplied by the X-ray source control power supply 2. The cone-shaped diverging X-ray beam emitted by the source is first processed by the through-through X-ray blocker 3, which is used to shield ineffective direct light and limit the effective irradiation area of ​​the beam. The beam processed by the through-through X-ray blocker 3 enters the first lens 4. The first lens 4 completes the modulation of the X-ray through a single total internal reflection, so that it forms a quasi-parallel X-ray beam with a certain ring width at the exit of the first lens 4.

[0128] The lens holder 5 is used to adjust and maintain the precise position of the first lens 4 and the X-ray blocker 3 in the optical axis direction to ensure that the collimated beam stably illuminates the sample on the sample stage 6. The sample stage 6 has high-precision rotation function and translation function in the X and Z directions. The main control computer 9 sends instructions to the electronic control platform controller 8, which performs angle scanning, sub-pixel angle jitter sampling, and multi-field stitching scanning.

[0129] The X-rays passing through the sample form a two-dimensional projection image on the X-ray flat panel detector 7. The signal from the X-ray flat panel detector 7 is transmitted to the main control computer 9 via a data cable. The main control computer 9 is used to realize the synchronous control of the system, control the rotation angle jitter of the rotary table, control the acquisition, cropping, stitching and fusion of the projection image at the sample, and subsequent image reconstruction processing.

[0130] The design concept of image reconstruction processing is explained as follows:

[0131] (1) In this embodiment, the quasi-parallel beam formed by the parabolic single-glass tube lens is regarded as an equivalent small-cone-angle cone beam emanating from the virtual focal point. The divergence angle θ of the quasi-parallel beam is used. d With beam width D outThe virtual focus position L can be uniquely determined. vf And calculate the detector coverage width D based on the system source-detector distance SDD. detector To achieve higher reconstruction accuracy, an FDK-type cone-beam reconstruction algorithm with small cone angles is implemented. For example... Figure 3 The working principle of the parabolic glass tube is explained as follows:

[0132] The quasi-parallel beam exit has a small divergence, with a small angle θ between the edge rays and the optical axis. d Based on the reversibility of light and the principles of geometric optics: if the two marginal rays of a quasi-parallel beam are extended in the "reverse" direction (backwards), they must intersect at a point on the optical axis. Therefore, this point can be defined as: the equivalent virtual focus Ov, from which a tiny cone-shaped beam with a conical angle emanates, coinciding with the quasi-parallel beam at the lens exit. Here, It is the cone angle of the equivalent small cone angle cone bundle, referring to the cone angle size corresponding to the equivalent mapping of the quasi-parallel bundle to a small cone angle cone bundle. When the equivalent mapping is valid, it should satisfy: This allows quasi-parallel beams to be directly mapped to small-cone-angle cone beams, thus enabling the use of small-cone-angle FDK-type cone beam reconstruction algorithms. From similar triangles, we can obtain:

[0133] (1)

[0134] In the above formula, the quasi-parallel beam divergence angle θ d , beam width D out Virtual focus position L vf

[0135] therefore,

[0136] (2)

[0137] This is the focal point of the equivalent "small cone-angle cone beam source". In the equivalent model, the distance from the detector to the virtual focal point is determined by extending the edge rays of the aligned parallel beam in the opposite direction and finding a point on the optical axis where they intersect. Because the optical path is controlled by the glass tube, this point is not the same as the actual SDD (source-to-detector distance) of the system. This point is defined as the virtual focal point Ov.

[0138] From standard conical bundle geometry:

[0139] (3)

[0140] In the above formula, The cone angle of the equivalent small cone angle cone bundle,

[0141] Substitution

[0142] θ cone = θ d(4)

[0143] get:

[0144] (5)

[0145] In the above formula, This represents the maximum illumination range formed by the small cone-angled beam on the flat panel detector. Virtual focus-detector distance

[0146] This allows for the accurate construction of equivalent cone-beam projection geometry and reconstruction algorithms.

[0147] Appendix Figure 2 The equivalent virtual focus Ov and detector coverage width D of the small cone beam detector .

[0148] (2) Thanks to its good divergence, parallel beam projection and reconstruction algorithms can also be used directly.

[0149] Projection correction method: Due to errors in the rotation axis during the rotation projection sampling process, it is necessary to correct the projection image of each frame.

[0150] Field stitching method: The first lens is a large-aperture parabolic glass tube lens. The large aperture refers to a significantly larger aperture compared to a parabolic capillary with a conventional micron-level quasi-parallel beam ring width.

[0151] The first lens provided in this embodiment enables the adjusted parallel beam loop width to reach the millimeter level (the millimeter-level first lens refers to the loop width W of the annular parallel beam after lens adjustment in this example being approximately 1 millimeter, where "approximately" indicates an error within ±5%). Therefore, to increase usability and enable projection scanning of small samples at the millimeter level, a field-of-view (FOV) stitching method is used to increase the FOV.

[0152] The first lens 4 is constructed with an inner wall parabolic channel, and its generatrix satisfies:

[0153] (6)

[0154] In the above formula, r is the cross-sectional radius of the rotating parabolic glass tube, z is the axial coordinate along the optical axis, and P is the parabola parameter;

[0155] Lens materials and coatings are based on the working energy E k Determine the critical angle θ for total internal reflection c The inlet radius is determined by the following formula:

[0156] (7)

[0157] In the above formula, the inlet radius R if1 is the distance from the X-ray source point to the lens entrance plane (equivalent focal length / design working distance); the critical angle for total internal reflection θ c。

[0158] The effective incident light rays from the source point are such that the grazing incident angle does not exceed θ. c A single total internal reflection occurs during guidance; the parabolic parameter P is determined by the following formula:

[0159] (8)

[0160] Given a lens length L, the exit radius R0 is determined by the following formula:

[0161] (9)

[0162] Thus, the inlet diameter d is obtained. in =2R i and export diameter d out：

[0163] d out =2R o (10)

[0164] And the quasi-parallel beam loop width W:

[0165] W = R o - R i (11)

[0166] This method ensures the acquisition of high-throughput, low-divergence quasi-parallel beams under laboratory microfocus X-ray source conditions.

[0167] The specific implementation steps of the technical solution are as follows:

[0168] 1. Selection of materials and working energy:

[0169] 1.1 The working energy of this design is set to the characteristic X-rays of the metal target excited by the microfocus X-ray source: E k Corresponding X-ray wavelengths (keV–Å relationship): .

[0170] 1.2 Optical constants and critical angle of total internal reflection of reflective materials: Using iridium (Ir) as the inner wall reflective material (coating material), the imaginary part β and real part δ of the refractive index are calculated based on the atomic scattering factor of Ir at this working energy, and then the critical angle of total internal reflection is calculated: .

[0171] Summary of material selection principles: Given a working energy E k Under these conditions, high Z-reflectivity coatings / materials (such as Ir, Pt, Au, etc.) should be preferred, based on their δ(E) kCalculate the critical angle θ for total internal reflection. c The generatrix of the lens parabola and the aperture must ensure that the angle of incidence of light rays is ≤ θ. c This enables highly efficient single-shot total internal reflection guidance.

[0172] 1.3 Surface Shape Error and Roughness Requirements: A surface shape error er is introduced, which shifts the grazing incidence angle by changing the local surface normal vector. In a parabolic single-glass tube lens, this shift causes an angular deviation of approximately 2er in the reflection direction, resulting in additional divergence in the quasi-parallel beam at the lens exit; when the local grazing incidence angle exceeds the critical angle θ for total internal reflection... c At the same time, it also causes photon loss and energy attenuation. Surface roughness Ser is included in the reflectivity attenuation term; roughness causes reflectivity attenuation: The inner wall of the lens needs to be controlled within the Å level for roughness and 10⁻⁻⁶. 5 Only when the surface shape error is within the order of rad can it be achieved when θ ≤ θ c To ensure high reflectivity and low scattering under grazing incidence conditions.

[0173] 2. Geometric structure and parametric relationships of a parabolic single-glass tube lens: The designed lens generatrix satisfies the paraboloid of revolution relationship: Where r is the cross-sectional radius of the parabolic glass tube, z is the axial coordinate along the optical axis, and P is the parabolic parameter. Corresponding shape curve: Where P is the parabola parameter, determined by the inlet radius and the critical angle: parabola parameter .

[0174] 2.1 Key geometric design parameters: f1 is the distance from the X-ray source point to the lens entrance plane (equivalent focal length / design working distance); L is the effective length of the lens; f2 is the working distance from the lens exit to the sample.

[0175] 2.2 The inlet diameter is determined by the critical angle: Inlet radius: , inlet diameter: .

[0176] 2.3 The outlet diameter is determined by the extension length of the parabolic surface, and the outlet radius is: Outlet diameter: .

[0177] 2.4 Effective beam width (ring width) of quasi-parallel beam: This ring width corresponds to the effective annular illumination area width of the quasi-parallel beam at the exit in the system, and is also the width of the subsequent D... out( The effective beamwidth of the quasi-parallel beam is a direct reference for measurement / calibration.

[0178] 2.5 A direct-pass light blocker is used to block direct-pass light that propagates in a straight line along the optical axis without undergoing total internal reflection against the inner wall of the parabolic surface. The direct-pass light forms a central spot at the lens exit, the radius of which is determined by geometric similarity relations: (12)

[0179] Based on f1, L, R o The radius of the central spot, Rbs, was calculated. After the blocker shields the central region, only one total internal reflection-guided annular quasi-parallel beam is allowed to pass through, thereby reducing the background and improving the imaging contrast.

[0180] 3. Specific data description of the large-diameter parabolic glass tube: Based on the current design's working energy and Ir total internal reflection critical angle, the lens aperture is: Inlet aperture... Export caliber Given the lens length L, the effective beam width (ring width) of the quasi-parallel beam is calculated as W. The effective beam width of the quasi-parallel beam is approximately 1 mm, belonging to the millimeter-level large-diameter single-tube parabolic X-ray beam lens. It can receive a solid angle flux much greater than that of traditional parabolic capillary tubes, achieving a millimeter-level irradiation range.

[0181] In other embodiments, alternatives include:

[0182] 1. A multi-capillary parallel lens array or a metal collimator array is used to achieve the control from a cone beam to a quasi-parallel beam.

[0183] 2. Obtain an ideal parallel beam using a synchrotron radiation device.

[0184] However, the aforementioned alternative 1 involves multiple total internal reflections of X-rays, and its X-ray transmission efficiency is far lower than that of the single reflection and efficiency of the parabolic single glass tube; furthermore, the X-ray divergence is worse than that of the parabolic single glass tube.

[0185] The aforementioned alternative solution 2 relies on large-scale equipment, which is difficult to implement under ordinary laboratory conditions. Therefore, the above two alternative solutions are difficult to achieve the overall effect of "large aperture + high throughput + near-parallel beam geometry + multi-field stitching and angle jitter" in this invention under ordinary laboratory desktop conditions, and thus it is difficult to achieve the technical purpose of this invention under the same conditions.

[0186] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A large-diameter parabolic single-glass tube micro-CT system, characterized in that: It includes an X-ray source arranged sequentially along the optical axis, a through X-ray blocker, a first lens that moves via a lens holder, a sample supported by a sample stage, and an X-ray flat panel detector. The first lens is a large-diameter parabolic glass tube lens with a diameter of millimeters. The lens holder is used to adjust the angle, pitch, and optical axis coaxiality of the first lens. The electronic control platform controller is electrically connected to the lens holder and the sample stage respectively. The main control computer controls the sample stage to perform angle scanning, sub-pixel angle jitter sampling, and multi-field stitching scanning through the electronic control platform controller. The X-ray source control power supply provides high-voltage drive for the X-ray source, which generates a micro-focus cone-shaped diverging X-ray beam. After the direct light from the center of the light source is shielded by the direct-through X-ray blocker, the beam enters the first lens. The X-rays are shaped by a single total internal reflection, forming a quasi-parallel X-ray beam with a certain ring width at the exit of the first lens. This beam irradiates the sample on the sample stage. The X-rays passing through the sample form a two-dimensional projection image on the X-ray flat panel detector. The X-ray flat panel detector transmits the acquired signal to the main control computer via a data line. The main control computer performs synchronous control, controlling the angle jitter of the sample stage, and controlling the acquisition, cropping, stitching, and fusion of the projection image at the sample, as well as subsequent quasi-parallel beam reconstruction processing. The sample stage is driven by the electronic control platform controller controlled by the main control computer to perform high-precision rotational scanning around the vertical optical axis, micro-displacement along the X direction for field stitching, lifting and lowering adjustment along the Z direction for height positioning and field stitching in the Z direction, and small-amplitude angle jitter sampling at each nominal angle.

2. The large-diameter parabolic single-glass tube micro-CT system according to claim 1, characterized in that: The inner wall of the first lens is a parabolic channel structure, which guides the incident X-rays through a single total internal reflection within the critical angle range, so that a quasi-parallel beam is generated at the exit of the first lens. The geometric parameters of the first lens, such as the inlet diameter, outlet diameter, length, and parabolic equation parameters, are obtained through critical angle calculation and ray tracing optimization.

3. The large-diameter parabolic single-glass tube micro-CT system according to claim 1, characterized in that: The size of the X-ray flat panel detector is selected according to the required resolution and system geometry. Its output signal is transmitted to the main control computer via a data line, and the main control computer performs real-time data acquisition, dark field or flat field correction and buffer management.

4. The large-diameter parabolic single-glass tube micro-CT system according to claim 3, characterized in that: The synchronous control of the main control computer includes: the start-up and shutdown and exposure control of the X-ray source; the rotation, angle jitter and X / Z direction translation of the sample stage; and the data acquisition, triggering timing and parameter configuration of the X-ray flat panel detector, which is used to execute projection domain registration, sub-pixel angle jitter fusion, multi-field projection stitching and back-end reconstruction algorithms. Quasi-parallel beam geometry is adopted, and the back-end reconstruction uses algorithms including parallel beam filtering back projection or equivalent small cone angle cone beam FDK type algorithms to obtain high-precision three-dimensional volume data.

5. A reconstruction method for a large-aperture parabolic single-glass tube micro-CT system according to any one of claims 1 to 4, characterized in that: Includes the following steps: S1: Start the X-ray source and adjust the position of the first lens by adjusting the lens holder to form a stable quasi-parallel beam; after the sample is placed on the sample stage, adjust the sample stage to adjust the height and center position of the sample; adjust the sample stage at each nominal angle to perform sub-pixel angle jitter sampling and obtain 2~3 frames of projection with different micro-perturbation angles; after completing the 180° scan, move the sample stage along the X or Z direction to achieve multi-field stitching. S2: All projected images are sent to the main control computer for cropping, registration, fusion, and reconstruction, specifically including the following steps: S21: Perform flat field correction and noise suppression on the original projection, and trim the effective imaging area according to the beam width of the quasi-parallel beam exit; S22: When the field of view is insufficient, grayscale matching and edge registration are performed on the projections of adjacent positions to achieve large field of view stitching; S23: Subpixel dithered projections upsampled at the same angle are fused into a higher resolution projection. S24: Based on the characteristics of quasi-parallel beams, select any of the following image reconstruction methods: Parallel beam reconstruction method: Treat the cropped projection as a parallel beam projection and directly reconstruct the 3D image using a filtered back projection method; Small cone angle reconstruction method: Equivalent the quasi-parallel beam to a small cone angle cone beam model and reconstruct it using an improved FDK algorithm based on small cone angle expansion. S3: Outputs high-resolution, wide-field-of-view 3D micro-CT images.

6. The reconstruction method according to claim 5, characterized in that: The small cone angle cone-beam reconstruction method described in step S24 includes the following steps: The quasi-parallel beam exit has a small divergence, with a small angle θ between the edge rays and the optical axis. d According to the principles of reversibility of light and geometric optics, if the two edge rays of the quasi-parallel beam are extended in the "reverse" direction, they will inevitably intersect at a point on the optical axis. Therefore, this point can be defined as the equivalent virtual focus Ov. The tiny cone-shaped beam emitted from this equivalent focus coincides with the quasi-parallel beam at the lens exit. It is the cone angle of the equivalent small cone angle cone bundle, referring to the cone angle size corresponding to the equivalent mapping of the quasi-parallel bundle to a small cone angle cone bundle. When the equivalent mapping is valid, it should satisfy: This allows the quasi-parallel beam to be directly mapped to a small cone-angle cone beam, thus enabling the use of small cone-angle FDK-type cone beam reconstruction algorithms. From similar triangles, we can obtain: （1） In the above formula, the quasi-parallel beam divergence angle θ d , beam width D out Virtual focus position L vf ; therefore, （2） This is the focal point of the equivalent "small cone-angle cone beam light source"; in the equivalent model, the intersection of the quasi-parallel beam edge rays extended in the opposite direction on the optical axis is defined as the virtual focal point. Because the glass tube modulates the light path, the position of the virtual focus does not correspond to the physical light source position in the actual experiment; therefore, the distance from the virtual focus to the detector is... This is not equivalent to the actual distance from the source to the detector (SDD). From standard conical bundle geometry: （3） In the above formula, The cone angle of the equivalent small cone angle cone bundle is substituted into... i cone = θ d (4) get: （5） In the above formula, This represents the maximum illumination range formed by the small cone-angled beam on the flat panel detector. For the virtual focus-detector distance, an equivalent cone-beam projection geometry and reconstruction algorithm are constructed.

7. The reconstruction method according to claim 5, characterized in that: The sub-pixel angle jitter sampling described in step S1 is implemented under approximately parallel beam geometry, and the small angle perturbation Δθ corresponds to the sub-pixel displacement in the detector domain. ,in, The distance from the sample to the detector is represented by the formula; the formula satisfies the upper limit of Δθ for upsampling in adjacent frames; the typical value of Δu is selected from within 1 / 2 or 1 / 3 of the pixel size of the X-ray flat panel detector; the angle jitter of the subpixel angle jitter sampling is superimposed with the X and Z translation jitter to form a two-dimensional or three-dimensional subpixel sampling grid.

Images