CN116518879A - Sample 4D reconstruction method and system based on micro CT-hyperspectral dual-mode imaging - Google Patents

Sample 4D reconstruction method and system based on micro CT-hyperspectral dual-mode imaging Download PDF

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CN116518879A
CN116518879A CN202310784836.4A CN202310784836A CN116518879A CN 116518879 A CN116518879 A CN 116518879A CN 202310784836 A CN202310784836 A CN 202310784836A CN 116518879 A CN116518879 A CN 116518879A
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sample
hyperspectral
detected
projection
annular
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CN116518879B (en
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余乐俊
刘谦
吴丹
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Hainan University
Sanya Research Institute of Hainan University
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Hainan University
Sanya Research Institute of Hainan University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
    • G—PHYSICS
    • G01—MEASURING; TESTING
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    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T19/00—Manipulating 3D models or images for computer graphics
    • G06T19/20—Editing of 3D images, e.g. changing shapes or colours, aligning objects or positioning parts
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    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00—Image analysis
    • G06T7/30—Determination of transform parameters for the alignment of images, i.e. image registration
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2200/00—Indexing scheme for image data processing or generation, in general
    • G06T2200/08—Indexing scheme for image data processing or generation, in general involving all processing steps from image acquisition to 3D model generation
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    • G06T2207/10—Image acquisition modality
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    • G06T2207/10081—Computed x-ray tomography [CT]
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Abstract

The invention relates to the technical field of machine vision phenotype detection, in particular to a sample 4D reconstruction method and system based on micro CT-hyperspectral dual-mode imaging, wherein the reconstruction method comprises the following steps: the method comprises the steps that a flat panel detector assembly collects a plurality of X-ray projection images of a sample to be detected at different rotation angles within a rotation range, and a hyperspectral camera shoots an annular hyperspectral projection image of the sample to be detected within the rotation range; and the workstation generates a 4D model of the sample to be tested according to the received X-ray projection images and the annular hyperspectral projection images of the sample to be tested. According to the invention, through synchronous acquisition of the ray projection diagram and the annular hyperspectral projection diagram, the acquisition efficiency of phenotype data based on CT imaging and hyperspectral imaging can be improved, and through registration of the CT three-dimensional model and the hyperspectral image, a high-precision 4D sample model with internal structure and external texture information can be obtained, so that the dimension and breadth of phenotype data acquisition can be improved.

Description

Sample 4D reconstruction method and system based on micro CT-hyperspectral dual-mode imaging
Technical Field
The invention relates to the technical field of machine vision phenotype detection, in particular to a sample 4D reconstruction method and system based on micro CT-hyperspectral dual-mode imaging.
Background
In recent years, remote sensing technology and computer vision technology greatly promote the development of the field of phenotype research, and the acquisition of phenotype data is gradually changed from an inefficient and lossy traditional manual mode to high-throughput and lossless automatic phenotype measurement. Modern phenotype detection methods mainly acquire sample images by means of visible light, infrared, fluorescence, hyperspectral, X-ray/CT and other imaging modes, and then extract sample phenotype shape parameters from the sample images by adopting a traditional or deep learning-based image processing method. The imaging methods such as visible light, infrared, fluorescence and the like can only acquire sample surface information but cannot detect internal structures, CT imaging can reconstruct the internal structures of the samples but cannot acquire surface textures, the phenotype information acquired by a single imaging mode is limited, and the existing phenotype detection method has a large lifting space in measurement breadth and dimension. The reflected light imaging and the transmission imaging are integrated, so that the external texture information and the internal structure of the sample can be obtained at the same time, the dimension of phenotype data acquisition can be effectively expanded, and the data mining potential is improved. CT and hyperspectral imaging are typical of two imaging techniques, namely transmitted light and reflected light, and are widely used in phenotypic studies, but these studies are usually performed by a single CT device or hyperspectral device, and the acquired data has a low dimension. In addition, the existing CT-hyperspectral dual-mode imaging system is complex in operation process, a ray projection image and a hyperspectral image cannot be shot at the same time, and the acquisition efficiency of phenotype data is low.
Disclosure of Invention
In view of the fact that the phenotype data which can be obtained by a single imaging mode is limited, the invention provides a sample 4D reconstruction method and a sample 4D reconstruction system based on micro CT-hyperspectral dual-mode imaging, and accurate spatial positioning of hyperspectral information is achieved while the internal fault structure of a sample is reconstructed, so that a 4D sample model with both internal structure and external texture information is obtained.
The invention provides a sample 4D reconstruction method based on micro CT-hyperspectral dual-mode imaging, which comprises the following steps:
the work station sends a control instruction to the PLC controller so that the object carrying rotary table with the sample to be tested is arranged to rotate at equal intervals;
when the object carrying rotary table with the sample to be measured is placed and rotated at equal intervals, the micro focal spot ray source emits X rays so that the X rays penetrate through the sample to be measured and reach the flat panel detector assembly;
the flat panel detector component receives X rays to acquire a plurality of X-ray projection images of the sample to be detected at different rotation angles within a rotation range, and the hyperspectral camera shoots an annular hyperspectral projection image of the sample to be detected within the rotation range;
the flat panel detector component and the hyperspectral camera respectively transmit the collected multiple X-ray projection images and the photographed annular hyperspectral projection images to a workstation;
And the workstation generates a 4D model of the sample to be tested according to the received X-ray projection images and the annular hyperspectral projection images of the sample to be tested.
Preferably, before the step of emitting X-rays by the micro focal spot radiation source, the method further comprises: positioning the rotation axis of the sample to be detected by adopting a plumb line on the reference object, so that the plumb line of the reference object coincides with the rotation axis of the sample to be detected; the orientation of the hyperspectral camera is adjusted so that the slit of the hyperspectral camera is aligned with the rotation axis of the sample to be measured.
Preferably, the step of positioning the rotation axis of the sample to be measured by using the plumb line on the reference object so that the plumb line of the reference object coincides with the rotation axis of the sample to be measured includes: fixing a visible light camera right above the characteristic pattern of the reference object, shooting the characteristic pattern of the reference object through the visible light camera, and calculating the center point position of the characteristic pattern of the reference object; and translating the reference object along the horizontal direction, so that the drift amount of the center point of the characteristic pattern of the reference object is minimized, and the plumb line on the reference object is overlapped with the rotation axis of the sample to be detected.
Preferably, after the step of adjusting the orientation of the hyperspectral camera, the method further comprises: the rotation center of a bottom plate of the calibration object is moved to a rotation shaft of a sample to be tested, and a calibration annular hyperspectral projection graph of the calibration object is shot in the process of rotating the calibration object for one circle; based on the calibrated annular hyperspectral projection graph, the internal and external parameters of the hyperspectral camera are calculated according to the corresponding relation between the actual coordinates of the feature points on the calibrated object and the projected pixel coordinates.
Preferably, the step of moving the rotation center of the bottom plate of the calibration object to the rotation axis of the sample to be measured, and shooting the calibration annular hyperspectral projection chart of the calibration object in the process of rotating the calibration object once comprises the following steps: placing a calibration object on an object carrying rotary table to enable the calibration object to rotate at a constant speed, wherein the calibration object comprises a bottom plate and thin rods vertically fixed on the bottom plate, rings with different colors at intervals are formed on the bottom plate, textures with different colors at intervals are formed on the thin rods, connecting lines of the bottom ends of the thin rods and the central point of the bottom plate are distributed at equal angles, and the distances between the bottom ends of the thin rods and the central point of the bottom plate are sequentially increased; moving the center of the bottom plate of the calibration object to the rotation axis of the sample to be tested to coincide; and shooting a calibration annular hyperspectral projection graph of the calibration object in the process of rotating the calibration object for one circle.
Preferably, the step of calculating the internal and external parameters of the hyperspectral camera based on the calibrated annular hyperspectral projection graph according to the corresponding relation between the actual coordinates of the feature points on the calibration object and the projected pixel coordinates comprises the following steps: establishing characteristic points of the calibration object based on the boundary of the alternate rings on the bottom plate and the texture edge of the thin rod; based on the calibrated annular hyperspectral projection graph, calculating the internal and external parameters of the hyperspectral camera according to the corresponding relation between the actual coordinates of the feature points on the calibrated object and the projected pixel coordinates; the internal and external parameters of the hyperspectral camera comprise equivalent focal length, principal point coordinates, rotation angles from a world coordinate system to a camera coordinate system and translation components from the world coordinate system to the camera coordinate system.
Preferably, the step of establishing the feature points of the calibration object based on the boundary between the spaced rings on the base plate and the grain edges of the thin rods comprises the following steps: measuring the radius of the outer edge of each ring on the bottom plate to obtain a first group of characteristic point plane coordinates; and measuring the height of the edge of each fine rod texture relative to the bottom plate to obtain a second group of characteristic point plane coordinates.
Preferably, the step of generating a 4D model of the sample to be measured by the workstation from the received plurality of X-ray projections and the annular hyperspectral projection of the sample to be measured comprises: the workstation adopts an FDK algorithm, and a fault diagram of each height of the sample to be detected is obtained according to the sequence reconstruction of a plurality of X-ray projection diagrams of the sample to be detected; the workstation performs foreground segmentation on the fault diagrams of the heights of the sample to be detected, and a CT three-dimensional model of the sample to be detected is generated; and the workstation performs registration according to the CT three-dimensional model of the sample to be detected and the annular hyperspectral projection graph to generate a 4D model of the sample to be detected.
The invention also provides a sample 4D reconstruction system based on micro CT-hyperspectral dual-mode imaging, which comprises: the object carrying rotary table is used for placing the sample to be tested and driving the sample to be tested to rotate; a micro focal spot ray source for emitting X-rays to a sample to be measured; the flat panel detector component is used for receiving the attenuated X-rays after penetrating through the sample to be detected, and obtaining a plurality of X-ray projection images of different rotation angles of the sample to be detected after the sample to be detected rotates one circle; the hyperspectral camera is positioned on one side of the sample to be detected, a slit of the hyperspectral camera is aligned with a rotating shaft of the sample to be detected, the hyperspectral camera is used for shooting the sample to be detected, and after the sample to be detected rotates for one circle, an annular hyperspectral projection diagram of the sample to be detected is obtained; the working station is used for controlling the start and stop of the object carrying rotary table, the acquisition of a ray projection image, the acquisition of an annular hyperspectral projection image, the reconstruction of a CT three-dimensional model and the completion of the reconstruction of a 4D model of a sample to be detected based on the CT three-dimensional model and the annular hyperspectral projection image; and the PLC is used for realizing communication between the workstation and the servo motor and driver, and further controlling the start and stop of the object carrying rotary table.
Preferably, the workstation comprises at least one processor; and a memory communicatively coupled to the at least one processor; the memory stores instructions executable by the at least one processor to enable the at least one processor to perform the micro-CT-hyperspectral dual mode imaging-based sample 4D reconstruction method of the present invention.
Compared with the prior art, the invention has the following beneficial effects:
according to the invention, through synchronous acquisition of the ray projection diagram and the annular hyperspectral projection diagram, the acquisition efficiency of phenotype data based on CT-hyperspectral dual-mode imaging can be improved, and through registration of CT imaging data and hyperspectral data, a high-precision 4D sample model with internal structure and external texture information can be obtained, so that the dimension and breadth of phenotype data acquisition are improved.
Drawings
FIG. 1 is a schematic diagram of a sample 4D reconstruction system based on micro CT-hyperspectral dual-mode imaging according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a structure of a reference object provided according to an embodiment of the present invention;
FIG. 3 is a schematic illustration of a feature pattern of a reference object provided in accordance with an embodiment of the present invention;
FIG. 4 is a schematic view of the structure of an adjusting bracket provided according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a calibration object according to an embodiment of the present invention;
FIG. 6 is a schematic view of the structure from the top view of FIG. 5;
FIG. 7 is a schematic flow chart of a sample 4D reconstruction method based on micro CT-hyperspectral dual-mode imaging according to an embodiment of the present invention;
FIG. 7a is a flow chart of a method for aligning a slit with a rotation axis of a sample to be measured according to an embodiment of the present invention;
FIG. 7b is a flowchart of a method for calculating internal and external parameters of a hyperspectral camera according to an embodiment of the present invention;
fig. 8 is a schematic diagram of a single-frame imaging model of a hyperspectral camera provided according to an embodiment of the present invention.
Reference numerals: the flat panel detector comprises a flat panel detector assembly 1, a lifting table 2, a translation table 3, a carrying rotary table 4, a sample to be detected 5, a micro focal spot radiation source 6, a radiation source cooling device 7, a hyperspectral camera 8, an adjusting bracket 9, a halogen light source 10, a workstation 11, a PLC (programmable logic controller) 12, a double-shaft translation base 13-1, a flat panel 13-2, a flat panel support 13-3, a characteristic pattern 13-4, a plumb line 13-5, a plumb 13-6, an adapter plate 14-1, a lifting support 14-2, a rotary table 14-3, a linear translation table 14-4, a bottom plate 15-1 and a thin rod 15-2.
Detailed Description
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, like modules are denoted by like reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, detailed description thereof will not be repeated
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not to be construed as limiting the invention.
Fig. 1 shows a structure of a sample 4D reconstruction system based on micro CT-hyperspectral dual mode imaging according to an embodiment of the present invention.
As shown in fig. 1, a sample 4D reconstruction system based on micro CT-hyperspectral dual-mode imaging according to an embodiment of the present invention includes a flat panel detector assembly 1, a lifting table 2, a translation table 3, a carrying rotary table 4, a micro focal spot radiation source 6, a radiation source cooling device 7, a hyperspectral camera 8, an adjusting bracket 9, a halogen light source 10, a workstation 11, a PLC controller 12, a reference object and a calibration object.
The sample 5 to be measured is placed on the carrying rotary table 4, and the sample 5 to be measured is driven to rotate at equal intervals through the carrying rotary table 4.
The micro focal spot radiation source 6 is located at one side of the object carrying rotary table 4 and is used for emitting X-rays to the sample 5 to be tested. The micro focal spot ray source 6 mainly comprises a cathode filament, a vacuum pressurizing cavity anode target and the like, and is used for emitting stable X-ray beams to a sample to be tested, and the ray energy distribution and total energy of the X-ray beams are determined by voltages at two ends of the pressurizing cavity and currents passing through two ends of the filament. The micro focal spot radiation source 6 is independently placed beside the radiation source cooling device 7, and the micro focal spot radiation source 6 is cooled by the radiation source cooling device 7, so as to prevent the micro focal spot radiation source 6 from being damaged due to overheating.
The flat panel detector assembly 1 is positioned on the other side of the object carrying rotary table 4, a plurality of X-ray projection images of the sample 5 to be detected at different rotation angles are collected through the flat panel detector assembly 1, and a CT three-dimensional model is reconstructed based on the X-ray projection images. The flat panel detector assembly 1 comprises a flat panel detector, a scintillator and a CCD, wherein the flat panel detector is used for receiving the X-rays attenuated after penetrating through a sample to be detected, converting the X-ray energy into optical signals through the scintillator, and converting the optical signals into image data through the CCD.
The carrying rotary table 4 is placed on the translation table 3, and the movement of the carrying rotary table 4 is realized through the translation table 3 so as to adjust the distance between the carrying rotary table 4 and the flat panel detector assembly 1. The translation stage 3 is realized by any mechanism for realizing linear motion, the carrying rotary table 4 is realized by any mechanism for realizing rotation, and the specific structures of the translation stage 3 and the carrying rotary table 4 are not specifically limited in the invention, but all belong to the prior art.
The flat panel detector assembly 1 is placed on the lifting table 2, the height of the flat panel detector assembly 1 is adjusted through the lifting table 2, the movement of the carrying rotary table 4 is realized through the adjustment of the translation table 3, and the distance between the carrying rotary table 4 and the flat panel detector assembly 1 is adjusted, so that a sample 5 to be detected can be in an X-ray shooting view under each rotation angle. The lifting platform 2 is realized by any mechanism for realizing lifting movement, and belongs to the prior art.
The hyperspectral camera 8 is located on one side of the sample 5 to be measured, and the slit of the hyperspectral camera 8 is aligned with the rotation axis of the sample 5 to be measured. After the sample 5 to be measured rotates for one circle, the hyperspectral camera 8 can shoot to obtain an annular hyperspectral projection image of the sample 5 to be measured.
The hyperspectral camera 8 is placed on the adjusting bracket 9, the hyperspectral camera 8 can rotate around three non-coplanar shafts and translate along a certain fixed direction by the adjusting bracket 9, and the slit of the hyperspectral camera 8 is aligned with the rotating shaft of the sample 5 to be measured by adjusting the position of the hyperspectral camera 8 by the adjusting bracket 9.
The halogen light source 10 is located at one side of the hyperspectral camera 8, and the halogen light source 10 provides a stable light source for hyperspectral imaging required by the hyperspectral camera 8.
The workstation 11 is used for controlling the start and stop of the object carrying rotary table 4, the acquisition of a ray projection image, the acquisition of an annular hyperspectral projection image, the reconstruction of a CT three-dimensional model and the completion of the reconstruction of a 4D model of a sample to be detected based on the registration of the CT three-dimensional model and the annular hyperspectral projection image.
The workstation 11 comprises at least one processor and a memory communicatively coupled to the at least one processor; the memory stores instructions executable by the at least one processor to enable the at least one processor to perform a 4D model reconstruction method of the sample 5 to be measured.
The workstation 11 is in the form of a general purpose computing device. The workstation 11 is intended to represent various forms of digital computers, such as laptops, desktops, personal digital assistants, servers, blade servers, mainframes, and other appropriate computers. The electronic device may also represent various forms of mobile devices, such as personal digital processing, cellular telephones, smartphones, wearable devices, and other similar computing devices. The components shown herein, their connections and relationships, and their functions, are meant to be exemplary only, and are not meant to limit implementations of the inventions described and/or claimed herein.
The PLC controller 12 is configured to implement communication between the workstation 11 and the servo motor and driver, and further control start and stop of the cargo turntable 4.
The alignment of the slit of the hyperspectral camera 8 with the rotation axis of the sample 5 to be measured is achieved by the cooperation of the reference object and the adjusting bracket 9.
Fig. 2 shows a structure of a reference object provided according to an embodiment of the present invention.
As shown in fig. 2, the reference object includes a biaxial translation base 13-1, a flat plate 13-2, a flat plate support 13-3, a characteristic pattern 13-4, a plumb line 13-5, and a plumb 13-6, the flat plate 13-2 is fixed to an upper moving part of the biaxial translation base 13-1 through the flat plate support 13-3, the characteristic pattern 13-4 is formed on an upper surface of the flat plate 13-2, the plumb 13-6 is released through the plumb line 13-5 at a position corresponding to a center point of the characteristic pattern 13-4 on a lower surface of the flat plate 13-2, and textures of different colors are formed on the plumb line 13-5. The biaxial translation base 13-1 is a prior art, and its specific structure is not described here again.
Fig. 3 shows a feature pattern of a reference object provided according to an embodiment of the present invention.
As shown in fig. 3, the feature pattern includes two sets of circles of different colors, each set including two opposing circles of the same color, for example, two opposing blue circles and two opposing green circles, and the plumb 13-6 is released downward at the intersection point of the centroid line of the two blue circles and the centroid line of the two green circles, and in addition, the outer circle is red, and the remaining lines are black. Of course, the present invention may also be used to find the center point of the feature pattern 13-4 by different shapes. For example, two green circles are replaced with two blue triangles.
It should be noted that, the present invention can detect the center point of the feature pattern by color or shape, and if the feature pattern is not a circle, but another shape, the position of the released plumb line must be the intersection point of the centroid lines of two sets of opposite shapes.
It should also be noted that, if other asymmetric pattern configurations are used, the term "center point" may not be literally used, because the intersection point of two sets of centroid lines is most likely not at the exact center of the entire feature pattern.
Fig. 4 shows a structure of an adjusting bracket provided according to an embodiment of the present invention.
As shown in fig. 4, the adjusting bracket 9 includes an adapter plate 14-1, a lifting support 14-2, a rotary table 14-3 and a linear translation stage 14-4, the rotary table 14-3 is fixedly connected with a moving part of the linear translation stage 14-4, the bottom end of the lifting support 14-2 is fixed on the rotary table 14-3, the top end of the lifting support 14-2 supports the adapter plate 14-1, and the hyperspectral camera 8 is placed on the adapter plate 14-1. The lifting support 14-2, the rotary table 14-3 and the linear translation table 14-4 are all of the prior art, and the specific structure thereof is not described herein.
Before the annular hyperspectral projection image is acquired by the hyperspectral camera 8, the internal and external parameters of the hyperspectral camera 8 are required to be calibrated, and the calibration of the internal and external parameters of the hyperspectral camera 8 is realized by a calibration object.
Fig. 5 and 6 respectively show structures of calibration objects with different viewing angles according to an embodiment of the present invention.
As shown in fig. 5 and 6, the calibration object is composed of a bottom plate 15-1 and a plurality of thin rods 15-2 vertically fixed on the bottom plate, rings with different colors being alternately formed on the bottom plate 15-1, textures with different colors being alternately formed on each thin rod 15-2, the connecting lines of the bottom end of each thin rod 15-2 and the central point of the bottom plate 15-1 are distributed at equal angles, and the distance between the bottom end of the thin rod 15-2 and the central point of the bottom plate 15-1 is sequentially increased.
The above details the sample 4D reconstruction system based on micro CT-hyperspectral dual-mode imaging provided by the embodiment of the present invention, corresponding to the sample 4D reconstruction system described above, and the second embodiment of the present invention further provides a sample 4D reconstruction method implemented by using the sample 4D reconstruction system based on micro CT-hyperspectral dual-mode imaging.
Fig. 7 shows a flow of a sample 4D reconstruction method based on micro CT-hyperspectral dual mode imaging according to an embodiment of the present invention.
As shown in fig. 7, the sample 4D reconstruction method based on micro CT-hyperspectral dual-mode imaging mainly includes the following steps:
in step 701, the workstation sends a control instruction to the PLC controller, so that the carrying turntable 4 rotates at equal intervals, and a sample to be measured is placed on the carrying turntable.
In this step, first, the sample 5 to be measured may be placed on the pre-prepared carrying turntable 4, and then, an instruction is sent to the PLC controller 12 through the workstation 11 to implement equidistant rotation of the carrying turntable 4, so as to implement synchronous acquisition of the radial projection map and the annular hyperspectral projection map through the flat panel detector assembly 1 and the hyperspectral camera 8 in one rotation time of the sample 5 to be measured in the subsequent step, so as to greatly improve the acquisition efficiency of the phenotype data based on the CT-hyperspectral dual-mode imaging.
Before the sample 4D reconstruction system based on micro CT-hyperspectral dual-mode imaging is used for dual-mode image shooting for the first time, the slit of the hyperspectral camera 8 is aligned with the rotation axis of the sample 5 to be measured, and then the internal and external parameters of the hyperspectral camera are calibrated.
It can be appreciated that after alignment and calibration, the same set of sample 4D reconstruction system based on micro CT-hyperspectral dual mode imaging is reused without any change in the system.
Specifically, the slit of the hyperspectral camera 8 is aligned with the rotation axis of the sample 5 to be measured in order to maximize the acquisition of the surface information of the sample 5 to be measured by the hyperspectral camera 8. The slit of the hyperspectral camera 8 is aligned with the rotation axis of the sample 5 to be measured, i.e. the rotation axis of the sample 5 to be measured is located within the imaging plane of the hyperspectral camera 8. Since adjusting the orientation of the hyperspectral camera by eye observation alone cannot align the slit to the accuracy required for data registration, the present invention adopts the reference object shown in fig. 2 and the adjustment bracket 9 shown in fig. 4 to align the slit of the hyperspectral camera 8 with the rotation axis of the sample 5 to be measured.
Fig. 7a shows the flow of the alignment method in the present invention.
As shown in fig. 7a, the alignment method includes the steps of:
and step 11, positioning the rotating shaft by adopting the plumb line on the reference object, namely enabling the plumb line of the reference object to coincide with the rotating shaft.
In the implementation process, first, a visible light camera may be fixed directly above a feature pattern of a reference object, the feature pattern of the reference object is photographed by the visible light camera, and a center point position of the feature pattern of the reference object is calculated. The specific operation steps are as follows:
(1) The top surface of the carrying rotary table 4 is adjusted to be completely horizontal by adopting a level gauge, and the rotating shaft of the sample 5 to be tested is in the vertical direction at the moment.
(2) The reference object is placed on the leveled object carrying rotary table 4, and an instruction is sent by the workstation 11 to rotate the object carrying rotary table 4 at a constant speed.
(3) A visible light camera is fixed right above the characteristic pattern 13-4 of the reference object, and the characteristic pattern 13-4 is photographed by the visible light camera, at this time, the console terminal of the workstation 11 displays the characteristic pattern 13-4 photographed by the visible light camera in real time.
And secondly, the reference object can be horizontally translated, so that the drift amount of the center point of the characteristic pattern of the reference object is minimized, and the plumb line on the reference object is overlapped with the rotation axis of the sample to be measured. The specific operation steps are as follows:
(1) And calculating the intersection point of the connecting line of the centers of mass of the two opposite patterns on the characteristic pattern 13-4 and the connecting line of the centers of mass of the other two opposite patterns to obtain the pixel coordinate of the right center of the characteristic pattern 13-4 (namely the position of the central point of the characteristic pattern 13-4).
(2) Tracking the movement track of the center point of the characteristic pattern 13-4, and translating the reference object along the X or Y direction so as to minimize the drift amount of the center point of the reference object.
When the reference object is placed on the object carrying rotary table 4 to rotate during alignment, and the center point of the feature pattern is not moved to the rotary shaft, the motion track of the center point is a circle, wherein the center point of the circle is positioned on the rotary shaft, the closer the center point is to the rotary shaft, the smaller the circle radius of the motion track is, and after the reference object is moved to the rotary shaft, the center point is kept at a point, namely, the so-called 'drift amount' is minimized.
(3) Since the vertex of the plumb line 13-5 coincides with the position of the center point of the feature pattern 13-4, when the amount of drift of the center point of the feature pattern 13-4 during the rotational movement is minimized, the plumb line 13-5 coincides with the rotational axis of the sample 5 to be measured.
(4) And evacuating the visible light camera.
It can be appreciated that the present invention achieves positioning of the rotational axis using the plumb line on the reference object such that the plumb line of the reference object coincides with the rotational axis by tracking the center point motion trajectory of the feature pattern 13-4, and translating the reference object in the X or Y direction.
And step 12, when the plumb line of the reference object is coincident with the rotation axis, adjusting the azimuth of the hyperspectral camera so that the slit of the hyperspectral camera is aligned with the rotation axis.
In the step, firstly, slit single-frame imaging results can be displayed in real time in hyperspectral camera acquisition control software, and the hyperspectral camera 8 is translated through the adjusting bracket 9, so that the slit of the hyperspectral camera 8 can observe plumb lines 13-5; the orientation of the hyperspectral camera 8 is then further fine-tuned, when the range of plumb lines 13-5 that the slit can observe is maximized, indicating that the slit of the hyperspectral camera 8 is aligned with the axis of rotation of the sample 5 to be measured. It can be seen that in this step, the slit of the hyperspectral camera can be aligned with the plumb line by adjusting the orientation of the hyperspectral camera, that is, indirectly, the slit of the hyperspectral camera 8 is aligned with the rotation axis of the sample 5 to be measured.
Next, the internal and external parameters of the hyperspectral camera 8 can be calculated. The calculation of the internal and external parameters of the hyperspectral camera 8 is for the registration of the subsequent CT three-dimensional model with the annular hyperspectral projection map.
The invention simplifies a single-frame imaging model of the hyperspectral camera 8 into the two-dimensional condition aperture imaging shown in fig. 8, and calculates the internal and external parameters of the hyperspectral camera 8 by adopting a special calibration object based on the simplified imaging model.
As shown in FIG. 8, the world coordinate system is recorded asThe camera coordinate system is->The image coordinate system is OX, the pixel coordinate system is +.>，/>For the optical axis of the hyperspectral camera 8, the world coordinate system +.>The axis coincides with the rotation axis of the sample 5 to be measured, since the slit of the hyperspectral camera 8 is aligned with the rotation axis of the sample 5 to be measured, therefore +.>And->Two coplanar straight lines are to be +.>And->The plane is defined as the hyperspectral camera imaging plane, and the world coordinate system is specified>The axis is within the hyperspectral camera imaging plane and perpendicular to +.>。
One point in the world coordinate systemThe projection formula of the image point m (u) to this point is:
；
in the case of the formula (1),is an internal reference matrix of a camera>Is an external reference matrix->For an equivalent focal length,f is a cameraFocal length, dx is the camera CCD single pixel size, < >>For principal point coordinates, +.>For the rotation angle of the world coordinate system to the camera coordinate system, +.>And->Is a translational component of the world coordinate system to the camera coordinate system.
Equation (1) can be written as:
；
recording deviceWherein->，/>，/>，，/>，/>；
If the correspondence between two-dimensional points in N imaging planes and their image points is known, then there are:
；
let the above formula be abbreviated ap=0, wherein:
equation ap=0 includesA total of 6 unknowns, since only the ratio between the unknowns is valid, do not require +. >The solution of this equation is matrix +.>A feature vector corresponding to the minimum feature value of (a).
Solving for vector P such that ap=0, let:
；
according toCalculating the internal and external parameters of the hyperspectral camera 8:
at least 5 known plane point-pixel point correspondence is required from equation (3) to solve for the internal and external parameters of the hyperspectral camera 8. The larger the number of known correspondences, the smaller the solution error.
For each feature point, the actual coordinates thereof can be measuredAt the same time the coordinates of its projection point can be found from the annular hyperspectral projection map +.>From actual coordinates/>And the coordinates of its projection points +.>An equation can be listed +.>
The N feature points may list N or more forms of equations, and writing the N equations as a matrix form is equation (3).
In the formula (3) of the present invention,is a vector related to the internal and external parameters of the camera, and the calibration of the camera is equivalent to finding the vector for satisfying equation (3)>The solving method is as specified in the description between the formula (3) to the formula (4).
The internal and external parameters of the hyperspectral camera 8 are calibrated by using the calibration object shown in fig. 5. Note that the connection line of the bottom end of the ith (i=0, 1, …, n) thin rod and the center of the bottom plate Is->，/>And->The included angle is->The method comprises the steps of carrying out a first treatment on the surface of the The bottom end of the ith slender rod is positioned at the outer edge of the (i+1) th ringThe top view of the calibration object is shown in fig. 6.
Fig. 7b shows a flow of a method for calculating internal and external parameters of a hyperspectral camera according to an embodiment of the present invention.
As shown in fig. 7b, the method for calculating the internal and external parameters of the hyperspectral camera 8 includes the following steps:
and 21, moving the rotation center of the base plate of the calibration object to a rotation shaft of the sample to be tested, and shooting a calibration annular hyperspectral projection graph of the calibration object in the process of rotating the calibration object for one circle.
In the specific implementation process, firstly, a calibration object is placed on an object carrying rotary table, so that the calibration object rotates at a constant speed; the calibration object comprises a bottom plate and thin rods vertically fixed on the bottom plate, rings with different alternate colors are formed on the bottom plate, textures with different alternate colors are formed on the thin rods, connecting lines of the bottom ends of the thin rods and the central point of the bottom plate are distributed at equal angles, the distances between the bottom ends of the thin rods and the central point of the bottom plate are sequentially increased, and detailed description can refer to related description corresponding to fig. 5 and 6 in the first embodiment and is not repeated here. The specific operation steps are as follows:
(1) The top surface of the carrying rotary table 4 is adjusted to be completely horizontal by adopting a level gauge, at the moment, the rotating shaft of the sample to be measured is in the vertical direction, and a calibration object is placed on the leveled carrying rotary table 4.
(2) The work station 11 sends an instruction to rotate the loading turntable 4 at a constant speed.
And secondly, moving the center of the bottom plate of the calibration object to the rotation axis of the sample to be tested to coincide. The specific operation steps are as follows:
(1) And fixing a visible light camera right above the calibration object.
(2) The base plate 15-1 of the calibration object is photographed by a visible light camera.
(3) The console terminal of the workstation 11 displays in real time the circle at the center of the base plate 15-1 photographed by the visible light camera.
(4) The centroid of the circle is calculated to obtain the center point position of the bottom plate 15-1.
(5) Tracking the movement track of the central point of the bottom plate 15-1, and translating the calibration object along the X or Y direction to minimize the drift amount of the central point of the bottom plate 15-1, wherein the central point of the bottom plate 15-1 is positioned on the rotating shaft of the sample 5 to be tested, and all the thin rods 15-2 fixed on the bottom plate 15-1 are parallel to the rotating shaft of the sample 5 to be tested.
(6) After the center point of the base plate 15-1 is moved onto the rotation axis of the sample 5 to be measured, the visible light camera is evacuated.
Thirdly, shooting a calibration annular hyperspectral projection graph of the calibration object in the process of rotating the calibration object for one circle.
And step 22, calculating the internal and external parameters of the hyperspectral camera according to the corresponding relation between the actual coordinates of the characteristic points on the calibration object and the projected pixel coordinates based on the calibrated annular hyperspectral projection graph.
In the implementation process, characteristic points of the calibration object are established based on the boundary of the alternate rings on the base plate and the texture edge of the thin rod. The specific operation steps are as follows:
(1) And measuring the radius of the outer edge of each ring on the bottom plate to obtain a first group of characteristic point plane coordinates.
Specifically, the outer edge radius of each ring on the base plate 15-1 is measuredObtaining a first group of characteristic point plane coordinates +.>。
(2) And measuring the height of the edge of each fine rod texture relative to the bottom plate to obtain a second group of characteristic point plane coordinates.
Specifically, the method comprises the following operation steps:
A. the height of the edge of the texture of each thin rod 15-2 relative to the base plate 15-1 is measured, and the height of the jth texture edge of the ith thin rod 15-2 relative to the base plate 15-1 is recorded asObtaining a second group of characteristic point plane coordinates
。
B. Obtaining the coordinates of the edges of the rings of the base 15-1 from the annular hyperspectral projection map
And the first group of characteristic point projection pixel coordinates are marked as first group of characteristic point projection pixel coordinates, and the first group of characteristic point projection pixel coordinates correspond to the first group of characteristic point plane coordinates.
C. The coordinates imaged by the edges of the textures of the thin rods 15-2 are obtained from the annular hyperspectral projection map
And the second group of characteristic point projection pixel coordinates are marked as second group of characteristic point projection pixel coordinates, and the second group of characteristic point projection pixel coordinates correspond to the second group of characteristic point plane coordinates.
Secondly, calculating internal and external parameters of the hyperspectral camera based on a calibrated annular hyperspectral projection graph according to the corresponding relation between the plane coordinates of the characteristic points and the coordinates of the projection pixels on the calibrated object; the internal and external parameters of the hyperspectral camera comprise equivalent focal length, principal point coordinates, rotation angles from a world coordinate system to a camera coordinate system and translation components from the world coordinate system to the camera coordinate system.
Specifically, the internal and external parameters of the hyperspectral camera 8 can be solved according to the corresponding relation between the first group of feature point projection pixel coordinates and the first group of feature point plane coordinates, the corresponding relation between the second group of feature point projection pixel coordinates and the second group of feature point plane coordinates, and the formulas (3) and (4)。
In step 702, when the object carrying turntable with the sample to be measured is rotated at equal intervals, the micro focal spot source emits X-rays, so that the X-rays penetrate the sample to be measured and reach the flat panel detector assembly 1.
In step 703, the flat panel detector assembly receives the X-rays to collect a plurality of X-ray projections of the sample to be measured at different rotation angles within a rotation range, the hyperspectral camera shoots an annular hyperspectral projection of the sample to be measured within the rotation range, and the flat panel detector assembly 1 and the hyperspectral camera respectively transmit the collected plurality of X-ray projections and the shot annular hyperspectral projection to the workstation.
Step 704, the workstation generates a 4D model of the sample to be tested according to the received multiple X-ray projection images and the annular hyperspectral projection image of the sample to be tested.
In this step, first, the workstation 11 may generate a CT three-dimensional model through a plurality of X-ray projection images of the sample 5 to be measured, and then, according to the correspondence between the spatial points in the CT three-dimensional model and the pixel points in the annular hyperspectral projection image, output the coordinates of the three-dimensional points and the spectral information together to obtain a 4D (spatial three-dimensional-spectral) model of the sample 5 to be measured. The specific operation steps are as follows:
(1) Adopting FDK algorithm, reconstructing according to the sequence of multiple X-ray projection images of the sample 5 to be detected to obtain fault images of each height of the sample 5 to be detected, performing foreground segmentation on all fault images, and regarding the first stepThe foreground point (i, j) in the Zhang Duanceng graph can obtain a three-dimensional point coordinate (i, j, k), and the set of the three-dimensional point coordinates corresponding to the foreground points of all the tomograms is the CT three-dimensional model of the sample 5 to be detected. />
(2) The workstation 11 registers according to the CT three-dimensional model of the sample to be detected generated in the step (1) and the captured annular hyperspectral projection image of the sample to be detected, and generates a 4D model of the sample to be detected.
In step (2), the specific registration method of the CT three-dimensional model and the annular hyperspectral projection map is as follows:
traversing the annular hyperspectral projection graph of the sample 5 to be detected, and for any column on the annular hyperspectral projection graphAccording to the coordinates->Judging that hyperspectral camera 8 shoots v-th frame imageThe intersection I of the time imaging plane with the sample 5 to be measured, for the firstWhen the point is a foreground point, carrying out back projection calculation on the point according to a formula (1) to judge the back projection light ray and the distance I of the point (u, v)>The nearest intersection point is the spatial point corresponding to the pixel point (u, v).
The method for judging the intersection part I of the imaging plane and the sample 5 to be tested when the hyperspectral camera 8 shoots the v-th frame image is as follows:
A. when the sample 5 to be measured is photographed, a vertical thin rod is placed on the object carrying rotary table 4 along with the sample 5 to be measured.
B. Positioning the slender rod in the tomogram, and recording the connection line between the centroid of the slender rod cross section and the central point of the tomogram as。
C. Positioning thin rods in a ring hyperspectral projection view, and marking the thin rods as。
D. Assume that the sample 5 to be measured is observed from the top view as clockwise rotation, and assume that the hyperspectral camera 8 takes the image of the v-th frame and takes the image of the v-th frame The rotation angle of the sample 5 to be measured in the frame image is +.>Record->Rotate counterclockwise along the center of the tomogram +.>The resulting straight line is l for annular highlightsColumn v of the spectrum projection graph, which corresponds to I, is the set of the intersection part of the straight line l and the foreground point in all the tomograms.
Therefore, the sample 4D reconstruction method realized by the sample 4D reconstruction system based on micro CT-hyperspectral dual-mode imaging can finish synchronous acquisition of a plurality of X-ray projection images of different rotation angles of the sample to be detected and an annular hyperspectral projection image of the sample to be detected through the flat panel detector assembly 1 and the hyperspectral camera 8 within one circle of rotation time of the sample to be detected.
Compared with the prior art, the X-ray projection image and the hyperspectral projection image can be obtained only by independently shooting the sample to be detected at least twice by using the CT equipment and the hyperspectral equipment, and the invention can simultaneously obtain a plurality of X-ray projection images and annular hyperspectral projection images of different rotation angles of the sample to be detected 5 through one operation, thereby not only greatly improving the operation efficiency, but also effectively improving the phenotype data dimension which can be obtained based on CT imaging and hyperspectral imaging by high-efficiency registration of the annular hyperspectral projection images and CT three-dimensional models generated based on the plurality of X-ray projection images.
It should be appreciated that various forms of the flows shown above may be used to reorder, add, or delete steps. For example, the steps described in the present disclosure may be performed in parallel, sequentially, or in a different order, provided that the desired results of the technical solutions of the present disclosure are achieved, and are not limited herein.
The above embodiments do not limit the scope of the present invention. It will be apparent to those skilled in the art that various modifications, combinations, sub-combinations and alternatives are possible, depending on design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of the present invention.

Claims (10)

1. A sample 4D reconstruction method based on micro CT-hyperspectral dual mode imaging, comprising:
the work station sends a control instruction to the PLC controller so that the object carrying rotary table with the sample to be tested is rotated according to a preset time interval;
the micro focal spot ray source emits X-rays so that the X-rays penetrate through the sample to be detected to reach the flat panel detector component;
the flat panel detector component receives the X-rays to acquire a plurality of X-ray projection images of the sample to be detected at different rotation angles within a rotation range, and the hyperspectral camera shoots an annular hyperspectral projection image of the sample to be detected within the rotation range;
The flat panel detector assembly and the hyperspectral camera respectively transmit the collected multiple X-ray projection images and the photographed annular hyperspectral projection images to a workstation;
and the workstation generates a 4D model of the sample to be tested according to the received X-ray projection images and the annular hyperspectral projection images of the sample to be tested.
2. The method for 4D reconstruction of a sample based on micro-CT-hyperspectral dual mode imaging as claimed in claim 1 wherein prior to the step of emitting X-rays from the micro focal spot source, the method further comprises:
positioning a rotation axis of the sample to be detected by adopting a plumb line on a reference object, so that the plumb line coincides with the rotation axis;
the orientation of the hyperspectral camera is adjusted such that the slit of the hyperspectral camera is aligned with the rotation axis.
3. A method of reconstructing a sample 4D based on micro-CT-hyperspectral dual mode imaging as recited in claim 2 wherein the step of coinciding the plumb line with the rotational axis by positioning the rotational axis with the plumb line on the reference comprises:
fixing a visible light camera right above the characteristic pattern of the reference object, shooting the characteristic pattern of the reference object through the visible light camera, and calculating the center point position of the characteristic pattern of the reference object;
And translating the reference object along the horizontal direction, so that the center point drift amount of the characteristic pattern of the reference object is minimized, and the plumb line on the reference object is coincident with the rotation axis.
4. A method of sample 4D reconstruction based on micro-CT-hyperspectral dual mode imaging as claimed in claim 2 or 3 wherein after the step of adjusting the orientation of the hyperspectral camera the method further comprises:
moving the rotation center of a bottom plate of a calibration object to the rotating shaft, and shooting a calibration annular hyperspectral projection graph of the calibration object in the process of rotating the calibration object once;
and calculating the internal and external parameters of the hyperspectral camera according to the corresponding relation between the actual coordinates of the characteristic points on the calibration object and the projected pixel coordinates based on the calibrated annular hyperspectral projection graph.
5. The method for reconstructing a sample 4D based on micro-CT-hyperspectral dual mode imaging as set forth in claim 4, wherein the step of moving the center of rotation of the base plate of the calibration object onto the rotation axis, during one rotation of the calibration object, capturing a calibration annular hyperspectral projection map of the calibration object comprises:
Placing a calibration object on the object carrying rotary table to enable the calibration object to rotate at a constant speed, wherein the calibration object comprises a bottom plate and thin rods vertically fixed on the bottom plate, rings with different colors at intervals are formed on the bottom plate, textures with different colors at intervals are formed on the thin rods, connecting lines of the bottom ends of the thin rods and the central point of the bottom plate are distributed at equal angles, and the distances between the bottom ends of the thin rods and the central point of the bottom plate are sequentially increased;
moving the center of the bottom plate of the calibration object to the rotation axis to coincide;
and shooting a calibration annular hyperspectral projection graph of the calibration object in the process of rotating the calibration object for one circle.
6. The method for reconstructing a sample 4D based on micro-CT-hyperspectral dual-mode imaging as set forth in claim 4, wherein the step of calculating internal and external parameters of the hyperspectral camera based on the calibrated annular hyperspectral projection map according to a correspondence between actual coordinates of feature points on the calibration object and projection pixel coordinates comprises:
establishing characteristic points of the calibration object based on the juncture of the alternate rings and the grain edges of the thin rods on the bottom plate;
based on the calibrated annular hyperspectral projection graph, calculating internal and external parameters of the hyperspectral camera according to the corresponding relation between the actual coordinates of the characteristic points of the calibrated object and the projected pixel coordinates; the internal and external parameters of the hyperspectral camera comprise equivalent focal length, principal point coordinates, rotation angles from a world coordinate system to a camera coordinate system and translation components from the world coordinate system to the camera coordinate system.
7. The method for reconstructing a sample 4D based on micro-CT-hyperspectral dual mode imaging as set forth in claim 6, wherein said step of establishing feature points of said calibration object based on a boundary of alternating circles on said base plate and a textured edge of a thin rod comprises:
measuring the radius of the outer edge of each ring on the bottom plate to obtain a first group of characteristic point plane coordinates;
and measuring the height of the edge of each fine rod texture relative to the bottom plate to obtain a second group of characteristic point plane coordinates.
8. The method for reconstructing a sample 4D based on micro-CT-hyperspectral dual mode imaging as set forth in claim 1, wherein the step of generating a 4D model of the sample to be measured from the plurality of X-ray projections and the annular hyperspectral projection of the sample to be measured received by the workstation comprises:
the workstation adopts an FDK algorithm, and a fault chart of each height of the sample to be detected is obtained according to the sequence reconstruction of a plurality of X-ray projection charts of the sample to be detected;
the workstation performs foreground segmentation on the fault diagrams of the sample to be detected at all heights to generate a CT three-dimensional model of the sample to be detected;
and the workstation performs registration according to the CT three-dimensional model of the sample to be detected and the annular hyperspectral projection graph to generate a 4D model of the sample to be detected.
9. A sample 4D reconstruction system based on micro-CT-hyperspectral dual mode imaging, the system comprising:
the object carrying rotary table is used for placing a sample to be tested and driving the sample to be tested to rotate;
a micro focal spot ray source for emitting X-rays to the sample to be measured;
the flat panel detector component is used for receiving the attenuated X-rays penetrating through the sample to be detected, and obtaining a plurality of X-ray projection images of different rotation angles of the sample to be detected after the sample to be detected rotates for one circle;
the hyperspectral camera is positioned on one side of the sample to be detected, a slit of the hyperspectral camera is aligned with a rotation axis of the sample to be detected, the hyperspectral camera is used for shooting the sample to be detected, and after the sample to be detected rotates for one circle, an annular hyperspectral projection graph of the sample to be detected is obtained;
the working station is used for controlling the start and stop of the object carrying rotary table, the acquisition of the ray projection diagram, the acquisition of the annular hyperspectral projection diagram, the reconstruction of a CT three-dimensional model and the completion of the reconstruction of a 4D model of the sample to be detected based on the CT three-dimensional model and the annular hyperspectral projection diagram;
And the PLC is used for realizing communication between the workstation and the servo motor and driver, and further controlling the start and stop of the object carrying rotary table.
10. The micro-CT-hyperspectral dual mode imaging based sample 4D reconstruction system as set forth in claim 9 wherein the workstation includes at least one processor; and a memory communicatively coupled to the at least one processor;
the memory stores instructions executable by the at least one processor to enable the at least one processor to perform the method of sample 4D reconstruction of any one of claims 1 to 8.
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