A CT scanning system and method for dynamic in situ imaging

Abstract

The present application belongs to the technical field of CT scanning imaging, in order to solve the problems of interlayer state difference and time non-comparability existing in the present in-situ scanning, a kind of dynamic in-situ imaging CT scanning system and method are proposed, the annular turntable is installed below the gantry beam;The sample table is arranged above the two-dimensional translation mechanism, and the sample table remains stationary and does not rotate during CT scanning;X-ray source-detector are installed on the annular turntable, the annular turntable rotates and drives the X-ray source-detector to rotate synchronously around the scanning center axis;While the annular turntable rotates continuously along the scanning center axis, the lifting mechanism can drive the annular turntable to ascend and descend synchronously to realize spiral scanning imaging of the measured sample.The scanning action is completed by the continuous rotation of the annular turntable and the continuous axial movement, and the spiral scanning method significantly reduces the interlayer state difference and time non-comparability.

Description

Technical Field

[0001] This invention belongs to the field of CT scanning imaging technology, and particularly relates to a dynamic in situ imaging CT scanning system and method. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] X-ray computed tomography (CT) can achieve non-destructive three-dimensional imaging based on the differences in the attenuation characteristics of materials to X-rays. It has been widely used in the characterization of internal structures and the detection of defects in fields such as industrial production, energy and chemical materials, and archaeological conservation.

[0004] Traditional industrial X-ray CT scanning systems mostly employ a single X-ray source-single detector (single optical path) structure. For dynamic / quasi-dynamic processes in multiphase media, such as capillary displacement, Haines transitions, particle rearrangement, pore-scale fluid displacement, and phase transitions, the characteristic timescales are often in the range of seconds to minutes, which is shorter than the time required for a conventional CT scan to complete a set of full-angle projections. Excessive scanning time can easily cause the sample state to span multiple evolution stages during projection acquisition, resulting in motion blur and reconstruction artifacts. This leads to inconsistencies between different projections, causing deviations in the quantitative characterization of material microstructure evolution and making it difficult to meet the requirements of dynamic four-dimensional (three-dimensional + time) imaging analysis.

[0005] On the other hand, traditional industrial CT systems typically use fixed X-ray sources and detectors, achieving full-angle projection acquisition by rotating the sample stage. However, in in-situ dynamic tests involving fluid seepage, interface migration, particle sedimentation, or weakly constrained boundary conditions, sample rotation can introduce centrifugal effects, inertial disturbances, and external pipeline / cable torsion, thereby altering fluid distribution and interface morphology, reducing the accuracy and repeatability of dynamic process observations. Simultaneously, for samples or in-situ test devices with a certain axial scale, using a layered / segmented approach to acquire three-dimensional results at different heights for stitched imaging can easily introduce inter-slice state differences and temporal incomparability. Helical scanning, however, forms a helical trajectory through "rotational scanning + axially relative continuous movement," achieving continuous axial coverage and improving scanning efficiency, thus possessing potential advantages in dynamic in-situ imaging scenarios. However, when introducing helical scanning into in-situ dynamic CT testing, sample disturbance suppression must also be considered.

[0006] In existing technologies, three sets of X-ray sources and detectors are arranged around the sample to shorten the scanning time. However, these methods still use a rotating sample stage to complete the projection acquisition, which makes it difficult to avoid the disturbance introduced by sample rotation in dynamic in-situ experiments. In addition, multiple sets of X-ray sources and detectors will inevitably have assembly errors, and this experimental method lacks a method for adjusting the optical path consistency.

[0007] Therefore, in in-situ experimental scenarios such as microscopic multiphase flow and fluid-solid phase change, there is an urgent need for a CT scanning system that can shorten CT scanning time while avoiding sample rotation disturbance, and can achieve continuous axial coverage and continuous rapid acquisition in helical scanning mode, as well as achieve optical path consistency adjustment to achieve high-precision reconstruction. Summary of the Invention

[0008] To overcome the shortcomings of the prior art, the present invention provides a dynamic in-situ imaging CT scanning system and method. The present invention shortens the scanning time while avoiding sample rotation disturbance, and achieves continuous axial coverage and continuous rapid acquisition in helical scanning mode.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a dynamic in-situ imaging CT scanning system, comprising: a two-dimensional translation mechanism, a sample stage, a ring turntable, a gantry beam, a lifting mechanism, and multiple sets of X-ray sources and detectors;

[0011] The annular turntable is installed below the gantry beam; the sample stage is positioned above the two-dimensional translation mechanism, and the sample stage remains stationary and does not rotate during CT scanning.

[0012] The X-ray source and detector are both mounted on the annular turntable. When the annular turntable rotates, it drives the X-ray source and detector to rotate synchronously around the scanning center axis.

[0013] While the annular turntable rotates continuously along the scanning center axis, the lifting mechanism can drive the annular turntable to rise and fall synchronously to perform helical scanning imaging of the sample under test.

[0014] Secondly, the present invention provides a dynamic in-situ imaging CT scanning method, comprising:

[0015] The sample to be tested is mounted on the sample stage and fixed so that it remains stationary and does not rotate during the scanning process;

[0016] Adjust the horizontal position of the X-ray source and detector according to the target resolution and field of view requirements;

[0017] The ring turntable is controlled to rotate continuously around the scanning center axis, and during the continuous rotation, the lifting mechanism is controlled to drive the ring turntable to move up and down along the scanning center axis to form a spiral scanning trajectory.

[0018] The X-ray source exposure and detector are synchronously triggered to acquire projection data in a continuous and uninterrupted manner;

[0019] The corresponding three-dimensional volume data is obtained by back-projection reconstruction of the projection data, and the three-dimensional volume data of each time period are combined into a four-dimensional imaging result in chronological order.

[0020] The above one or more technical solutions have the following beneficial effects:

[0021] In this invention, the sample remains stationary and does not rotate during the sample stage scanning process to avoid centrifugal effects, inertial disturbances, and torsion of external pipelines and cables. The scanning action is completed by the continuous rotation of the annular turntable and the continuous axial movement, forming a spiral scanning trajectory. In this way, even if the sample does not rotate, continuous coverage of a sample with a certain axial scale can be achieved. Compared with the traditional layered and segmented stitching imaging method, this spiral scanning method significantly reduces the differences in state between layers and the incomparability of time, improves the consistency of axial coverage and the overall scanning efficiency, and at the same time, it is also convenient to construct dynamic four-dimensional imaging results, thereby more realistically preserving the fluid state and interface morphology inside the sample during the in-situ dynamic process, and improving the authenticity and repeatability of the observation.

[0022] In this invention, without moving the sample position, a calibration-grade precision probe is temporarily placed at the radial center of the scanning field of view. Projected images of each optical path at multiple rotation angles are acquired for spatial coordinate calibration. The pixel coordinates of the calibrated feature points in the projection are extracted, a projection model is established, and the equivalent focal position of each optical path and the geometric offset parameters of the detector are solved by least squares. The radial drive mechanism is controlled to make fine adjustments and repeat the calibration until the threshold requirement is met. This invention avoids the problems of misalignment and reconstruction geometric artifacts in multi-optical path projection merging through optical path calibration, and achieves geometric consistency alignment of the three optical paths.

[0023] In this invention, considering that long-term use of multiple optical paths may lead to inconsistencies in intensity between optical paths due to factors such as X-ray source output attenuation, filter / collimator aging, and detector gain drift, the numerical comparability of multi-optical path projection data is ensured by normalizing the incident intensity of different optical paths.

[0024] In this invention, a joint reconstruction method is adopted, which involves independent weighting and filtering of multiple optical paths and superposition averaging during the back projection stage. This method integrates information from multiple optical paths to improve the reconstruction signal-to-noise ratio and reduce the impact of single-path noise on the reconstruction results.

[0025] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0027] Figure 1 This is a three-dimensional structural diagram of the ring gantry-type fast spiral CT scanning system suitable for dynamic in-situ imaging in Embodiment 1 of the present invention;

[0028] Figure 2 This is a front view of the ring gantry-type rapid spiral CT scanning system suitable for dynamic in-situ imaging in Embodiment 1 of the present invention;

[0029] Figure 3 This is a schematic diagram of the X-ray source and detector arrangement of the ring gantry-type fast spiral CT scanning system suitable for dynamic in-situ imaging in Embodiment 1 of the present invention.

[0030] Figure 4 This is a schematic diagram of the imaging geometry of the three-path synchronous projection acquisition of the ring gantry-type fast spiral CT scanning system suitable for dynamic in-situ imaging in Embodiment 1 of the present invention.

[0031] In the figure, 1 is the sample stage, 2 is the two-dimensional translation mechanism, and 3 is the test sample or in-situ test equipment.

[0032] 4. First vertical support column; 5. Second vertical support column; 6. First lifting guide column; 7. Second lifting guide column; 8. Gantry beam; 9. Circular fixed frame; 10. Circular turntable; 11. Turntable drive mechanism.

[0033] 12. First X-ray source; 13. Second X-ray source; 14. Third X-ray source;

[0034] 15. First detector; 16. Second detector; 17. Third detector;

[0035] 18. First radial sliding guide rail; 19. Second radial sliding guide rail; 20. Third radial sliding guide rail; 21. Fourth radial sliding guide rail; 22. Fifth radial sliding guide rail; 23. Sixth radial sliding guide rail.

[0036] 24. First radial drive mechanism; 25. Second radial drive mechanism; 26. Third radial drive mechanism; 27. Fourth radial drive mechanism; 28. Fifth radial drive mechanism; 29. ​​Sixth radial drive mechanism. Detailed Implementation

[0037] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0038] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations of the present invention.

[0039] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0040] Example 1

[0041] This embodiment discloses a CT scanning system suitable for dynamic in situ imaging, including: a sample stage 1, a lifting mechanism, a circular turntable, an X-ray source, a detector, and an electronic control unit;

[0042] The X-ray source and detector are both connected to the electronic control unit; vertical support columns are set on both sides of the sample stage 1.

[0043] The annular turntable 10 is set inside the annular fixed frame 9 and rotates with it. The annular fixed frame 9 is installed below the gantry beam 8. The turntable drive mechanism 11 drives the annular turntable 10 to rotate continuously around the scanning center axis.

[0044] The lifting mechanism includes: a vertical support column and a lifting guide column. The gantry beam 8 is supported by the lifting guide column. The lifting guide column is sleeved and slidably engaged with the vertical support column, so that the gantry beam 8 and its load-bearing components can be lifted and lowered vertically as a whole, so as to realize the height adjustment of the plane of the X-ray source-detector system.

[0045] Both the X-ray source and the detector are mounted on the annular turntable 10. The detector and the X-ray source are respectively set in the circumferential relative positions of the annular turntable 10 so that when the annular turntable 10 rotates, it drives the X-ray source and the detector to rotate synchronously around the scanning center axis. The sample stage 1 is set above the two-dimensional translation mechanism 2 and is used to place the test sample or the in-situ test equipment 3. The sample stage 1 remains stationary and does not rotate during the scanning process. The electronic control unit is used to synchronously control the exposure of multiple X-ray sources and the triggering of multiple detectors during the continuous rotation of the annular turntable 10, so as to realize the continuous and uninterrupted acquisition of projection data to meet the requirements of dynamic in-situ four-dimensional CT imaging.

[0046] Before scanning, the lifting guide column drives the gantry beam 8 to adjust its position vertically and drives the annular fixed frame 9 and the annular turntable 10 installed below it to rise and fall synchronously to complete the vertical setting of the scanning field of view. During the scanning process, the lifting guide column drives the annular turntable to move continuously along the scanning center axis while the annular turntable 10 rotates continuously to form a spiral scanning trajectory and achieve continuous axial coverage.

[0047] like Figure 1 and Figure 2 As shown, the vertical support columns include a first vertical support column 4 and a second vertical support column 5; the two vertical support columns are respectively set on both sides of the sample stage 1; the lifting guide columns include a first lifting guide column 6 and a second lifting guide column 7, which are respectively sleeved and slidably engaged with the two vertical support columns; the two lifting guide columns are used to support the gantry beam 8 and the annular fixing frame 9 and the annular turntable 10 below it. The gantry beam 8 is supported by the lifting guide columns, forming a gantry-type load-bearing structure, which is used to provide rigid support and installation reference for the annular fixing frame 9.

[0048] While the turntable drive mechanism 11 enables the ring turntable 10 to rotate continuously, the ring turntable 10 can be driven to move continuously along the scanning center axis direction by the lifting guide column, thereby forming a spiral scanning trajectory and achieving continuous axial coverage.

[0049] like Figures 1 to 3 As shown, the annular fixing frame 9 is installed below the gantry beam 8, and the annular turntable 10 is set inside the annular fixing frame 9 and can rotate continuously around the scanning center axis, and can rotate continuously for multiple revolutions. Multiple sets of X-ray source-detector assemblies are arranged on the annular turntable 10. In this embodiment, three sets of X-ray source-detector assemblies are set, including: a first X-ray source 12 and a first detector 15, a second X-ray source 13 and a second detector 16, and a third X-ray source 14 and a third detector 17. The three sets of X-ray sources and three sets of detectors are evenly arranged at 120° circumference along the annular turntable 10, and the distances from the three detectors to the sample being tested are equal, as are the distances from the three X-ray sources to the sample being tested. Furthermore, the X-ray sources and detectors are one-to-one and arranged circumferentially opposite each other, enabling the annular turntable 10 to achieve multi-angle synchronous projection acquisition of the test sample or in-situ experimental equipment 3 during continuous rotation, thus improving acquisition efficiency.

[0050] like Figure 3As shown, the annular turntable 10 is equipped with a radial sliding guide assembly for mounting the X-ray source and detector positions, including: a first radial sliding guide 18, a second radial sliding guide 19, a third radial sliding guide 20, a fourth radial sliding guide 21, a fifth radial sliding guide 22, and a sixth radial sliding guide 23; the annular turntable 10 is also equipped with a radial drive mechanism assembly for adjusting the X-ray source and detector positions, including: a first radial drive mechanism 24, a second radial drive mechanism 25, a third radial drive mechanism 26, a fourth radial drive mechanism 27, a fifth radial drive mechanism 28, and a sixth radial drive mechanism 29; wherein, the first X-ray source 12, the second X-ray source 13, the third X-ray source 14, the first detector 15, the second detector 16, and the third detector... 17 is respectively installed on the first radial sliding guide rail 18, the second radial sliding guide rail 19, the third radial sliding guide rail 20, the fourth radial sliding guide rail 21, the fifth radial sliding guide rail 22, and the sixth radial sliding guide rail 23; the first radial sliding guide rail 18, the second radial sliding guide rail 19, the third radial sliding guide rail 20, the fourth radial sliding guide rail 21, the fifth radial sliding guide rail 22, and the sixth radial sliding guide rail 23 are respectively connected to the first radial drive mechanism 24, the second radial drive mechanism 25, the third radial drive mechanism 26, the fourth radial drive mechanism 27, the fifth radial drive mechanism 28, and the sixth radial drive mechanism 29, which can realize the adjustment of the X-ray source and the detector along the radial direction of the frame, thereby realizing the setting of the magnification of the CT scan field of view and providing adjustment margin for subsequent geometric calibration.

[0051] like Figure 4 As shown, before the actual scanning, the gantry beam 8 and the annular fixed frame 9 below it are moved vertically by the lifting guide column to adjust the height so that the test sample or in-situ test equipment 3 appears at the scanning field of view.

[0052] like Figure 4 As shown, in the actual scanning, each X-ray source emits a cone-beam X-ray. The X-ray passes through the test sample or in-situ test equipment 3 and reaches the corresponding detector, which receives the X-ray and forms a projection image. The projection image is synchronously acquired by the electronic control unit and transmitted to the computer for storage and subsequent reconstruction processing.

[0053] like Figure 1 and Figure 2 As shown, the sample stage 1 is set on the two-dimensional translation mechanism 2, which is used to realize the X and Y bidirectional position adjustment of the test sample or in-situ test equipment 3 in the horizontal plane, so as to complete the centering of the sample center and the scanning center and the fine positioning of the scanning area.

[0054] The test sample or in-situ test equipment 3 can be a conventional exposed sample, a mechanical loading test device, a seepage test device, a temperature control test device or a combination thereof. The sample stage 1 remains stationary and does not rotate during the scanning process, and does not move axially continuously with the vertical lifting mechanism, thereby avoiding the disturbance to the fluid seepage, phase change or structural evolution process caused by the traditional "rotating sample" method, which is conducive to maintaining the authenticity and repeatability of the in-situ test state.

[0055] In this embodiment, the sample stage remains stationary and does not rotate during the scanning process to avoid centrifugal effects, inertial disturbances, and torsion of external pipelines / cables. At the same time, the system adopts continuous rotation of the ring turntable, combined with continuous and uninterrupted projection acquisition, to reduce the sudden changes in state and inconsistencies between projection states caused by start-stop during traditional CT scanning. This allows for a more realistic preservation of the fluid state and interface morphology inside the sample during the in-situ dynamic process, improving the realism and repeatability of the observation.

[0056] In this embodiment, a spiral scanning trajectory is formed by the continuous rotation and axial continuous movement of the annular turntable, which achieves continuous coverage of test samples or in-situ test equipment with axial dimensions without rotating the test sample. Compared with layered or segmented stitching imaging, it significantly reduces the differences in state between layers and the incomparability of time, improves the consistency of axial coverage and scanning efficiency, and facilitates the construction of dynamic four-dimensional (three-dimensional + time) imaging results.

[0057] Example 2

[0058] Based on the dynamic in-situ imaging CT scanning system in Embodiment 1, this embodiment also discloses a dynamic in-situ imaging CT scanning method, including the following steps:

[0059] S1. Sample stage preparation: Install the sample to be tested or the in-situ testing equipment on the sample stage, complete the connection of external pipelines, cables and sensors, and fix the sample so that it remains stationary and does not rotate during the scanning process.

[0060] S2. Scanning Field of View Setting: Adjust the height of the annular fixed stage to adjust the height of the X-ray source-detector assembly; control the two-dimensional translation mechanism to adjust the sample position so that the area to be scanned is within the detector's field of view; control the radial drive mechanism on the annular turntable to adjust the horizontal position parameters of the X-ray source and detector according to the target resolution and field of view requirements.

[0061] S3. Three-light path coordinate calibration: Given the inevitable assembly tolerances and relative pose differences among the three X-ray source-detector components, this embodiment introduces a three-light path coordinate calibration and automatic collimation correction process based on metrology-grade precision probes to avoid the problems of misalignment in the merging of three-light path projections and ghosting artifacts in reconstruction, thereby achieving geometric consistency alignment of the three-light paths and writing the calibration results into the reconstructed geometric model.

[0062] Without moving the sample, a calibration-grade precision stylus is temporarily positioned at the radial center of the scanning field of view, and optical samples are collected at multiple rotation angles. β The projected image is used for spatial coordinate calibration; the pixel coordinates of the calibration feature points in the projection are extracted, the projection model is established, and the equivalent focal position of each optical path and the geometric offset parameters of the detector are solved by least squares to form a reconstructed geometric model and write it into the electronic control unit; when the calibration residual exceeds the preset threshold, the electronic control unit controls the radial drive mechanism to make fine adjustments and repeat the calibration until the threshold requirement is met.

[0063] S3-1 projection model.

[0064] Assume a precision probe includes M The nth calibration feature point, the nth i The three-dimensional coordinates of each feature point in the calibration target coordinate system are: ,in .

[0065] For the first k Optical path ( The rotation angle of the annular turntable around the scanning center axis From the calibration projection image acquired below, extract the observed pixel coordinate vector of the feature point on the detector:

[0066]

[0067] in, and These are the pixel coordinates in the horizontal and vertical directions of the detector, respectively; The rotation angle of the annular turntable around the scanning center axis; β The set of values ​​of is denoted as (Right now ),in This indicates the number of angles used during calibration.

[0068] Establish the first k Cone-beam geometric projection prediction model of the optical path:

[0069]

[0070] in, The pixel coordinate vector is predicted by the cone-beam geometric projection prediction model; For the first The set of geometric parameters of the optical path serves as the cone-beam geometric projection operator. The parameters to be solved include at least the equivalent focal position parameters and the detector geometric offset parameters of the optical path. This is a cone-beam geometric projection operator used to project 3D feature points. At a given rotation angleβ With geometric parameters Mapped to the detector pixel coordinate system under certain conditions; The least squares optimization in step S3-2 is performed using the observed pixel coordinates. The result is obtained by reverse calculation, and iteratively updated under the threshold criterion in step S3-3 until the accuracy requirement is met.

[0071] S3-2 parameter solution: Minimize reprojection error based on least squares.

[0072] Based on the observed pixel coordinates in step S3-1 Predicted pixel coordinates obtained from the cone-beam geometric projection prediction model The reprojection error is minimized using the least squares method to solve the problem. Optimal geometric parameters of the optical path:

[0073]

[0074] in, For the first k The set of geometric parameters of the optical path, the initial values ​​of which are given by the system structure assembly measurement values; For the first k The optimal set of geometric parameters obtained by solving the optical path; arg min represents the parameter values ​​that minimize the objective function. Represents the Euclidean norm; This represents the pixel reprojection error vector of the feature point at that angle.

[0075] S3-3 Threshold Criterion and Closed-Loop Repeat Calibration.

[0076] Definition of the first k Optical path calibration residual (RMS pixel error):

[0077]

[0078] in, For the first k The root mean square pixel error of the optical path; The pixel coordinate vector is predicted by the cone-beam geometric projection prediction model; M represents the coordinates of the observed pixels; M represents the number of calibrated feature points. β Let be the rotation angle of the annular turntable around the scanning center axis. β The set of values ​​of is denoted as ,Right now .

[0079] set up ε A preset pixel-level threshold is used, with the maximum residual of the three optical paths as the criterion. When At this time, the electronic control unit adjusts the distance between the specified X-ray source and the corresponding detector, and / or the height of the lifting guide column, based on the offset parameters obtained in step S3-2, to compensate for assembly errors and motion deviations; after fine-tuning, it re-acquires the calibration projection and repeats steps S3-1 and S3-2 to update the geometric parameters of each optical path. ; until satisfied , to optimize geometric parameters Write to the electronic control unit and reconstruct the geometric model.

[0080] S4. Spiral Continuous Projection Acquisition: According to the set rotation speed, axial movement speed and total number of projections required, the ring turntable is controlled to rotate continuously around the scanning center axis and rotate multiple times. During the continuous rotation, the lifting guide column is controlled to drive the ring turntable to move continuously along the scanning center axis to form a spiral scanning trajectory. The electronic control unit synchronously controls the X-ray source exposure and the detector to trigger acquisition, so as to acquire projection data in a continuous and uninterrupted manner. The sample is kept stationary during the acquisition process.

[0081] S5, Multi-source projection normalization.

[0082] Given that long-term use of multiple optical paths may lead to inconsistencies in intensity scale between optical paths due to factors such as X-ray source output attenuation, filter / collimator aging, and detector gain drift, this step normalizes the incident intensity of different optical paths to ensure the numerical comparability of multi-optical path projection data.

[0083] The raw projection intensity data obtained in step S4 is subjected to dark field correction and flat field correction, and the incident intensity of different optical paths is normalized to obtain the line integral projection data used for reconstruction. For the case of simultaneous acquisition via three optical paths, the first... k Optical path projection is defined as:

[0084]

[0085] in, Indicates the optical path number. For the first k Light path incident intensity, For the first k Optical path detector at rotation angle β With detector pixel coordinates The intensity of X-rays received at that location, For the first k The optical path corresponds to the ray path. For the first k The distribution of linear attenuation coefficients corresponding to the optical path.

[0086] Through the above normalization and logarithmic transformation, the original intensity projection is converted into line integral projection data, providing input for S6.

[0087] In this embodiment, normalization processing can effectively reduce the systematic intensity difference between optical paths, reduce the risk of brightness bias and fringe artifacts during the joint reconstruction of three optical paths, and improve the stability and repeatability of the superimposed reconstruction of three optical paths.

[0088] S6, Three-path spiral compensation FDK 3D reconstruction algorithm.

[0089] Based on the reconstructed geometric model and calibration parameters obtained in step S3, and using the three-light path integral projection constructed in step S5 as input, geometric weighting and filtering are sequentially performed on each projection path. During helical scanning, the annular turntable rotates while simultaneously moving continuously along the axial direction; therefore, the axial position varies with the rotation angle. β Changes. Therefore, an axial displacement varying with the angle is introduced into the back-projection geometric mapping. This enables the reconstruction of the three-path superposition back projection under the spiral trajectory condition.

[0090] S6-1 Geometric Weighted Scaling.

[0091] For the first k Optical path projection is subjected to geometric correlation weighting to obtain weighted projection data. :

[0092]

[0093] in, For the first k Distance from the X-ray source to the detector in the optical path; For the first k The pixel coordinates of the optical path detector are used as independent variables to index the projected image; For the first k The center pixel coordinates of the optical path detector, and .

[0094] S6-2 Collaborative Filtering and Two-Dimensional Convolutional Filtering.

[0095] Weighted projection data Perform collaborative filtering and two-dimensional convolutional filtering to obtain filtered projection data. :

[0096]

[0097] in, For the integral variable in the two-dimensional convolution kernel, it corresponds to the input pixel coordinates scanned by the convolution kernel on the detector plane; This is a two-dimensional filtering kernel function.

[0098] S6-3 spiral axial displacement and three-path superposition back projection reconstruction.

[0099] To accommodate the geometric changes caused by the continuous axial movement of the X-ray source-detector assembly during helical scanning, the relationship between the X-ray source-detector assembly and the rotation angle during helical scanning is defined. β The axial displacement is This is to reduce misalignment artifacts caused by axial movement.

[0100] Preferably, when the frame moves at an angular velocity ω Continuous rotation and with axial velocity v z When moving at a constant speed along the central axis:

[0101]

[0102] in, The starting angle and starting axial position are the values ​​corresponding to this projection sequence.

[0103] Set the integration angle range to the angle window corresponding to this segment of the projection sequence. (Preferably, a ring of windows is selected, i.e.) The reconstructed 3D voxel values ​​are obtained by superimposing the three optical paths and backprojecting. :

[0104]

[0105] in, For the first k Distance from the X-ray source to the center of rotation in the optical path; The filtered projection data is obtained through interpolation. get; voxel point At rotation angle β The first obtained through geometric mapping k The sampling coordinates of the optical path detector satisfy:

[0106]

[0107] in, For the first k The optical path has a fixed azimuth angle, preferably .

[0108] S6-4 Three-Path Reconstruction Results Output.

[0109] The reconstructed 3D volume data is subjected to artifact removal and data format normalization, and the angle window is output. The corresponding three-dimensional volume data results provide three-dimensional volume data with a single time window for the subsequent construction of four-dimensional dynamic sequences (step S7).

[0110] This embodiment employs a joint reconstruction method that combines independent weighting and filtering of three optical paths with superposition averaging during the back projection stage. This method integrates information from multiple optical paths to improve the reconstruction signal-to-noise ratio and reduce the impact of single-path noise on the reconstruction results.

[0111] S7. Construction and Output of Four-Dimensional Dynamic Sequences:

[0112] According to the preset time acquisition window, the continuous projection data acquired during the spiral continuous scanning process in step S4 is divided into multiple time periods. The projection sequence; where each time period corresponds to a helical segment on the helical scanning trajectory and covers a preset axial scanning range. For each time period... t Step S5 is performed on the three-light-path projection to construct line integral projection data, and step S6 is performed to realize the three-light-path superposition back projection reconstruction, thereby obtaining the three-dimensional volume data corresponding to the time period. The three-dimensional volume data from each time period are arranged in chronological order to form a four-dimensional imaging result. The data is then imported into image processing software for artifact removal, intensity consistency correction, and data format standardization batch processing, ultimately outputting 4D imaging data for dynamic evolution process analysis.

[0113] Preferably, the time acquisition window can be a sliding overlapping window to further improve the time resolution and reduce motion artifacts caused by dynamic processes.

[0114] Those skilled in the art will recognize that the units and algorithm steps described in conjunction with the embodiments herein can be implemented in electronic hardware or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0115] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A dynamic in-situ imaging CT scanning method, characterized in that, include: The test sample or in-situ testing equipment is mounted on the sample stage and fixed so that the sample remains stationary and does not rotate during the scanning process; Adjust the horizontal position of the X-ray source and detector according to the target resolution and field of view requirements; The ring turntable is controlled to rotate continuously around the scanning center axis, and during the continuous rotation, the lifting mechanism is controlled to drive the ring turntable to move up and down along the scanning center axis to form a spiral scanning trajectory. The X-ray source exposure and detector are synchronously triggered to acquire projection data in a continuous and uninterrupted manner; Back-projection reconstruction is performed on the projection data under a specified time window to obtain the corresponding three-dimensional volume data. The three-dimensional volume data of each time window are combined into a four-dimensional imaging result in chronological order. This also includes: calibrating the multiple optical paths of multiple X-ray source-detector sets, specifically: Without moving the sample position, the calibration-grade precision stylus is positioned at the radial center of the scanning field of view, and projection images of each optical path are acquired at multiple rotation angles. Extract the pixel coordinates of the calibrated feature points in the projected image, establish the projection model, and solve the geometric parameters of each optical path by least squares. Adjust the lifting mechanism and / or the distance between the X-ray source and the detector according to the geometric parameters of each optical path. After fine-tuning, re-acquire and calibrate the projection and update the geometric parameters of each optical path until the accuracy requirements are met. Specifically, the projected data is back-projected and reconstructed to obtain the corresponding three-dimensional volume data. The three-dimensional volume data from each time period are then arranged in chronological order to form a four-dimensional imaging result. The continuous projection data acquired during the spiral continuous scanning process is divided into multiple time periods; each time period corresponds to a spiral segment on the spiral scanning trajectory and covers a preset axial scanning range. For each time period, construct line integral projection data for the multi-path projection separately; Based on the reconstructed line integral projection data, geometric weighting and filtering are performed sequentially on each projection path; An axial displacement that varies with the angle is introduced into the back projection geometric mapping to achieve three-path superposition back projection reconstruction under the condition of spiral trajectory. The three-dimensional volume data from each time period are arranged in chronological order to form a four-dimensional imaging result; Among them, the reconstructed three-dimensional voxel values ​​are obtained by three-path superposition back projection. : voxel point At rotation angle β The first obtained through geometric mapping k The sampling coordinates of the optical path detector satisfy: in, For the first k The optical path has a fixed azimuth angle; among which, For the first k Distance from the X-ray source to the center of rotation in the optical path; The filtered projection data is obtained through interpolation. get; The rotation angle of the annular turntable around the scanning center axis; Starting angle, ; For the first k Pixel coordinates of the optical path detector; This represents the axial displacement that varies with the angle.

2. The CT scanning method for dynamic in-situ imaging as described in claim 1, characterized in that, For each time period, line integral projection data is constructed for the multi-path projection, specifically as follows: Dark field correction and flat field correction are performed on the acquired raw projection intensity data, and the incident intensity of different optical paths is normalized to obtain the line integral projection data used for reconstruction.

3. A dynamic in-situ imaging CT scanning system, employing the dynamic in-situ imaging CT scanning method as described in any one of claims 1-2, characterized in that, include: Two-dimensional translation mechanism, sample stage, ring turntable, gantry beam, lifting mechanism, multiple sets of X-ray sources and detectors; The annular turntable is installed below the gantry beam; the sample stage is positioned above the two-dimensional translation mechanism, and the sample stage remains stationary and does not rotate during CT scanning. The X-ray source and detector are both mounted on the annular turntable. When the annular turntable rotates, it drives the X-ray source and detector to rotate synchronously around the scanning center axis. While the annular turntable rotates continuously along the scanning center axis, the lifting mechanism can drive the annular turntable to rise and fall synchronously to perform helical scanning imaging of the sample under test.

4. The dynamic in-situ imaging CT scanning system as described in claim 3, characterized in that, The multiple X-ray source-detector system includes a first X-ray source and a first detector, a second X-ray source and a third detector, and a third X-ray source and a third detector. The first X-ray source, the second X-ray source, and the third X-ray source are evenly distributed in a ring with a 120° interval around the scanning center axis, and the distances of the three X-ray source-detectors to the sample being tested are equal.

5. The dynamic in-situ imaging CT scanning system as described in claim 3, characterized in that, The lifting mechanism includes a vertical support column and a lifting guide column; the vertical support column and the lifting guide column are sleeved and slidably engaged, and the lifting guide column is used to support the annular turntable.

6. The dynamic in-situ imaging CT scanning system as described in claim 5, characterized in that, It also includes an electronic control unit, which is used to control the rotation of the annular turntable and simultaneously control the lifting mechanism to drive the annular turntable to move continuously along the scanning center axis during the continuous rotation of the annular turntable. It also simultaneously controls the exposure of the X-ray source and the triggering acquisition of the detector to achieve continuous and uninterrupted acquisition of projection data in the spiral scanning mode.

7. The dynamic in-situ imaging CT scanning system as described in claim 4, characterized in that, The X-ray source and detector are respectively mounted on radial sliding rails, which are used to adjust the distance between the corresponding X-ray source and the corresponding detector, thereby setting the CT scan field of view and magnification.

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