CN110428478B - Alternating light source fan beam X-ray CT sampling method and device - Google Patents
Alternating light source fan beam X-ray CT sampling method and device Download PDFInfo
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Abstract
The invention discloses a method and a device for sampling an alternative light source fan beam X-ray CT, wherein the method comprises the following steps: in the process of one-circle rotation scanning of the scanning system, controlling a plurality of X-ray light sources to be periodically and alternately switched in turn, so that only one X-ray light source at each rotation angle is in an X-ray emitting state to acquire projection data of each light source; taking the parallel beam CT data space as a reference space, and mapping the projection data of each light source to the reference space so as to analyze the distribution condition of the acquired data; and reconstructing the projection data subsets corresponding to each light source to obtain a final reconstructed image. In the method, a plurality of light sources with similar positions alternately generate X rays to replace the original fixed position single light source in the scanning process, so that the scanning data are distributed in the parallel beam CT data space more uniformly, the information content of the scanning data is improved, and a high-quality reconstructed image is finally obtained.
Description
Technical Field
The invention relates to the technical field of radiation imaging, in particular to a method and a device for sampling an X-ray CT with an alternative light source fan beam.
Background
An X-ray CT imaging system is widely used in the fields of medical treatment, security inspection, industrial inspection, and the like, for fluoroscopic imaging of an object by using the characteristic that X-rays are attenuated in the object when passing through the object. In 1972, Hounsfield designed the first parallel beam CT, which only used one light source and one detector, and the detector and the light source moved tangentially along a circular scanning track during each angle data acquisition process as shown in fig. 1(a), which realizes the standard parallel beam CT data acquisition mode, but the scanning time is several hours. In subsequent developments, the CT data acquisition modality and system architecture were optimized step by step. In the second generation of parallel beam CT with small fan angle, a plurality of detectors are used to replace the original single detector on the basis of the first generation of parallel beam CT as shown in fig. 1(b), the detector and the light source still move tangentially along the scanning circular track in the data acquisition process at each angle, and because the plurality of detectors acquire data simultaneously, the step length of each tangential translation can be increased remarkably, thereby reducing the time consumption in the scanning process. The third generation of fan beam CT further increases the number of detectors of the detector array, the detector array can completely cover the scanning field of view as shown in fig. 1(c), the light source only rotates on the rail during the scanning process, the tangential translational motion of the detector and the light source is not needed during the data acquisition process at each angle, the fan angle projection data at the angle can be obtained by one-time data acquisition, and the magnitude of the fan beam CT is reduced during the scanning. Siemens 2005 introduced the first dual-source CT, which had two independent fan-beam CT X-ray sources and detectors, with the two sources located on the same rotating circular track and 90 degrees out of phase as shown in fig. 1(d), and during CT scanning, the two fan-beam CT systems collected data simultaneously, further shortening the CT scanning time. Dual source CT has important applications in fast imaging scenarios such as cardiac imaging. When the CT scanning mode and the system structure are gradually upgraded, the scanning data is also converted into fan beam CT data from parallel beam CT data. Each data acquired by fan beam CT may be equivalent to one data point of the parallel beam CT data space. In the ideal continuous acquisition case, fan beam CT data can be fully equivalent to parallel beam CT. However, in practical applications, data acquisition is discrete, and after fan-beam CT data is equivalent to parallel-beam CT, the fan-beam CT data is no longer uniformly distributed in the parallel-beam CT data space, and at this time, the imaging quality is lost to a certain extent compared with the parallel-beam CT.
Disclosure of Invention
The invention provides an alternating light source fan beam X-ray CT sampling method and device, which are used for solving the technical problems that in a part of subspace of a parallel beam CT data space, fan beam data is densely distributed and information redundancy occurs, while in the other part of subspace, the fan beam data is sparsely distributed and the quality of a reconstructed CT image is influenced to a certain extent due to insufficient acquired information.
An embodiment of the invention provides an alternating light source fan beam X-ray CT sampling method, which comprises the following steps:
in the process of one-circle rotation scanning of the scanning system, controlling a plurality of X-ray light sources to be periodically and alternately switched in turn, so that only one X-ray light source at each rotation angle is in an X-ray emitting state to acquire projection data of each light source;
taking the parallel beam CT data space as a reference space, and mapping the projection data of each light source to the reference space so as to analyze the distribution condition of the acquired data; and
and reconstructing the projection data corresponding to each light source to obtain a final reconstructed image.
Another embodiment of the present invention provides an alternating light source fan beam X-ray CT sampling apparatus, including:
the acquisition module is used for controlling the plurality of X-ray light sources to be periodically and alternately switched in turn in the process of one-circle rotation scanning of the scanning system, so that only one X-ray light source at each rotation angle is in an X-ray emitting state to acquire projection data of each light source;
the mapping module is used for mapping the projection data of each light source to a reference space by taking a parallel beam CT data space as the reference space so as to analyze the distribution condition of the acquired data; and
and the reconstruction module is used for reconstructing the projection data corresponding to each light source to obtain a final reconstructed image.
The technical scheme of the invention at least realizes the following beneficial technical effects:
in the scanning process, a plurality of light sources with similar positions alternately generate X rays to replace the original fixed position single light source, so that the scanning data are distributed more uniformly in the parallel beam CT data space, more reasonable data are acquired and distributed, the information quantity of the scanning data is improved, the physical information quantity is increased, and finally a high-quality reconstructed image is obtained.
Additional aspects and advantages 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.
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The foregoing and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic diagram of a CT scanning system structure/scanning mode of each generation, wherein (a) is a schematic diagram of a parallel beam CT scanning mode, (b) is a schematic diagram of a small fan angle parallel beam CT scanning mode, (c) is a schematic diagram of a fan beam CT scanning mode, and (d) is a schematic diagram of a dual-source fan beam CT scanning mode;
FIG. 2 is a flow chart of an alternate light source fan beam X-ray CT sampling method according to one embodiment of the present invention;
FIG. 3 is a schematic view of an alternate light source fan beam CT system according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of an alternate light source CT system according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of data distribution acquired by an alternate light source CT system in accordance with an embodiment of the present invention;
fig. 6 is a schematic view of another alternative light source CT system according to the present invention, wherein (a) is an isosceles triangle arranged alternative light source system, (b) is an inclined line arranged alternative light source system, and (c) is a general arrangement alternative light source system;
fig. 7 is a schematic structural diagram of an alternative light source fan-beam X-ray CT sampling apparatus according to an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
The method and the device for sampling the alternating light source fan beam X-ray CT are described below with reference to the attached drawings, wherein the method is provided based on the application background of the fan beam CT, can be applied to other common three-dimensional CT system structures such as cone beam CT, spiral CT and the like, enables the distribution of three-dimensional acquisition data to be more reasonable, and is also applied to a plurality of fields such as nondestructive testing, medical diagnosis, safety inspection and the like.
Currently, fan beam CT is widely used in clinical medicine and industrial inspection because the data distribution acquired by fan beam CT itself is less uniform than parallel beam CT. In the molecular space of the space part of the parallel beam CT data, the fan beam data are densely distributed, and information redundancy occurs; in the other part of the subspace, the fan beam data is sparsely distributed, and the quality of the reconstructed CT image is influenced to a certain extent due to insufficient acquisition information. Therefore, the invention provides a design idea of a fan-beam CT system with alternative light sources, in the scanning process, a plurality of light sources with similar positions alternately generate X rays to replace the original fixed-position single light source, so that the scanning data is distributed more uniformly in the parallel-beam CT data space, the information content of the scanning data is improved, and a high-quality reconstructed image is finally obtained.
FIG. 2 is a flow chart of an alternate light source fan beam X-ray CT sampling method according to an embodiment of the present invention.
As shown in fig. 2, the alternating light source fan beam X-ray CT sampling method includes the steps of:
in step S101, during one rotation of the scanning system, the plurality of X-ray light sources are controlled to periodically and alternately switch in turn, so that only one X-ray light source is in an X-ray emitting state for each rotation angle, so as to obtain projection data of each light source.
Wherein, the fan beam CT system of alternative light source has a plurality of X ray sources that the position is close, and in the rotary scanning process, a plurality of X ray sources are the emission X ray in turn, replace original single X ray light source to obtain the CT data collection that distribute more rationally, and then promote and rebuild imaging image quality.
For example, as shown in FIG. 3, the scanning system contains multiple X-ray sources that are closely located, while the detector array is identical to the fan beam CT. In the process of one-circle rotation scanning, all the light sources are periodically and alternately switched in sequence, and only one light source in each rotation angle is in an X-ray emitting state. T is needed if the scanning system rotates for one circlerSampling N in one weekaThe period of switching from one light source to the next is adjusted to Tr/NaSecond, scanning was performed using different light sources at adjacent angles. If there is N in totalsA light source, the projection data obtained by the first light source is
The projection data obtained by the second light source is
Due to different scanning anglesAnd the positions of the light sources are not completely the same, so that the condition that the local distribution of the collected data is too dense can be avoided to a certain extent.
During system construction, there are various easy-to-implement ways to construct an alternating light source CT system, such as using one X-ray machine and emitting X-ray split light to the X-ray machine, so that X-rays are emitted from several nearby positions. When one branch ray is used, the lead layer is used for shielding other branches, and the alternate switching of the light source is realized by adjusting the shielding condition of the lead layer.
In step S102, the parallel beam CT data space is used as a reference space, and the projection data of each light source is mapped to the reference space to analyze the distribution of the acquired data.
In an embodiment of the present invention, the reference space is a two-dimensional space, and each point in the two-dimensional space corresponds to a data acquisition ray, and two dimensions of the data acquisition ray are an angle of the ray and a vertical distance from an origin to the ray, respectively, so that each ray path can be uniquely mapped as a point of the reference space during scanning.
Specifically, parallel-beam CT scanning directly generated by Radon transform is a fundamental method of tomographic image scanning, and a parallel-beam CT data space is used as a reference space (simply referred to as a reference space) for analyzing distribution of sample data. The reference space is a two-dimensional space, each point in the space corresponds to a data acquisition ray, and the two dimensions of the reference space are the angle Theta of the ray and the vertical distance T from the origin to the ray. Each ray path may be uniquely mapped to a point in the reference space during a fan beam scan or other tomographic scan. When the alternating light source CT is designed, whether an alternating light source system is reasonable or not can be analyzed, firstly, through program simulation verification, the inclination angles theta and the distances t from the origin of all collected rays in alternating light source scanning are calculated, so that the projected rays are completely mapped to a reference space, the distribution condition of data points in the reference space is analyzed, and if sampling points are uniformly distributed in a region of interest (FOV) (namely | t | is in the radius of the FOV), the alternating source CT design scheme is reasonable.
In step S103, the projection data corresponding to each light source is reconstructed to obtain a final reconstructed image.
The scanning mode of the alternating light source CT increases the physical information quantity of the acquired data, and the physical information in the original projection data is converted into visual image information by a reconstruction algorithm. Both parallel beam CT and fan beam CT scans have standard precision reconstruction methods such as Filtered Back Projection (FBP) analytical reconstruction. For fan beam CT with alternating light sources, a corresponding exact reconstruction formula can be derived for each specific light source layout.
The general and general reconstruction method comprises the following steps:
(1) the accurate analytic reconstruction method comprises the following steps: and respectively carrying out analytic reconstruction on the data acquired by each light source to obtain sparse angle reconstruction images, and then superposing the sparse angle reconstruction images to obtain accurate reconstruction images.
(2) The rearrangement analysis reconstruction method comprises the following steps: and mapping the alternate light source CT data to a parallel beam CT data space, obtaining the parallel beam CT data by an interpolation method, and then carrying out parallel beam CT analysis reconstruction.
(3) The iterative reconstruction method comprises the following steps: in scanning, although the light source positions are different at different angles, a fixed system matrix can be calculated for a specific system, and a statistical iterative algorithm is adopted to reconstruct an image.
(4) The neural network reconstruction method comprises the following steps: and aiming at a specific system structure, training and reconstructing the neural network in a supervised or unsupervised mode, and completing reconstruction by using the trained neural network.
It should be noted that the alternating light source CT system is easy to implement in terms of hardware construction and reconstruction algorithm.
The following further describes an implementation method and advantages of alternating light source fan beam CT in conjunction with an embodiment of a three-light source alternating light source CT system.
It should be noted that, although three light sources are used for switching alternately in this embodiment, the alternating light source fan-beam CT system of the present invention is not limited to three light sources, and the light source distribution position is not limited to the light source distribution in this embodiment.
First, an alternate source fan beam CT system configuration is implemented, as shown in FIG. 4, with a rotation center perpendicular to the equidistant detector array at a distance dod＝400mm，The vertical foot is positioned at the center of the equidistant detector, and the total length l of the detectord1200mm, for a total of 20 detectors, each 60mm in size. The system has three light sources, wherein the light source 1 is located on an extension of the rotation center to the perpendicular of the detector array, and the radial distance d from the light source 1 to the rotation center os_d1400 mm. The light sources 2 and 3 are respectively positioned at two sides of a connecting line of the light source 1 and the rotation center, and the projection of the light sources on the connecting line of the light source 1 and the rotation center is a distance d from the rotation centeros_d2＝dos_d3400mm, i.e. the projection of the light sources 2, 3 on the line connecting the light source 1 and the center of rotation coincides with the light source 1. And the vertical distance d of the light sources 2, 3 to the connection lineos_t2，dos_t3Is adjustable. When the system scans the in-plane fault layer, the light source and the detector rotate around the rotation center for one circle clockwise, and N is obtainedaAttenuation data at 30 angles. Wherein data at an angle β 1,4, 7.., 28 is obtained from X-rays generated by the light source 1, data at an angle β 2,5, 8.. 29 is obtained from X-rays generated by the light source 2, and data at an angle β 3,6, 9.., 30 is obtained from X-rays generated by the light source 3. In this embodiment, a larger detector size and angular interval are used for drawing the sampling point distribution diagram clearly. In practical situations, smaller detectors are typically employed and read detector data information at more angles.
Secondly, the influence of the alternating light source scanning on the distribution of the acquired data is analyzed, and specifically, the alternating light source CT acquired data is mapped to the parallel beam CT data for spatial analysis. In this embodiment, let dos_t2And dos_t3Remain equal and gradually increase from 0mm to 120 mm. FIG. 5 plots the difference dos_tIn case of alternating light source CT data distribution, where dos_tAs a control, 0mm is equivalent to a normally bright, classical fan beam CT as source 1. From fig. 5, it can be observed that when using a standard fan-beam CT scan, the corresponding t of each detector is equal at different rotation angles. The fan beam CT scan is therefore sparsely sampled in the t dimension. When gradually increasing dos_tWhen the angle reaches 30mm, because the relative position of the X-ray light source is changed alternately under different rotation angles, the t corresponding to each detector under different angles is atThe two sides of the original position are slightly staggered, so that the sampling rate of the T dimension is increased, and the CT data acquisition of the alternative light source is reasonable. When d is further increasedos_tWhen the distance reaches 120mm, although the data sampling points are still uniformly distributed, the light source is excessively offset at the moment, the T-dimension sampling points are diffused towards two sides, and the sampling in the central area is gradually sparse.
In conclusion, the tangential offset can convert the sampling rate of the acquired data in Theta dimension into the sampling rate in T dimension, and the reasonable tangential offset enables the acquired data to be distributed more uniformly in the reference space. In a real system, the optimal dos_tThe number of detectors and the radius of the region of interest are determined together according to the number of scanning angles.
And finally, reconstructing the image, wherein in the embodiment, an accurate analytic reconstruction method is adopted, the acquired data subsets corresponding to the three light sources are respectively analyzed and reconstructed, and then the three images are superposed to obtain a final reconstructed image.
It should be noted that, as shown in fig. 6, in addition to the above tangential light source distribution embodiment, for different system structures and geometric parameters, the alternating light source fan beam CT may also have other implementation methods to obtain better effects.
According to the alternating light source fan beam X-ray CT sampling method provided by the embodiment of the invention, the light sources are rapidly and alternately switched in the scanning process, more reasonable data are collected and distributed, so that the physical information quantity is increased, a high-quality reconstructed image is finally obtained, a parallel beam CT data space is used as a reference space, data obtained by other scanning modes are mapped to the reference space, and the reasonability of the scanning mode and the system structure is further analyzed.
In order to realize the embodiment, the invention also provides an alternating light source fan beam X-ray CT sampling device.
FIG. 7 is a schematic structural diagram of an alternative light source fan-beam X-ray CT sampling apparatus according to an embodiment of the present invention.
As shown in fig. 7, the alternating light source fan beam X-ray CT sampling apparatus 10 includes: an acquisition module 100, a mapping module 200 and a reconstruction module 300.
The acquiring module 100 is configured to control the multiple X-ray light sources to periodically and alternately switch in turn during a rotational scanning process of the scanning system, so that only one X-ray light source at each rotation angle is in an X-ray emitting state, so as to acquire projection data of each light source.
In one embodiment of the present invention, during one rotation of the scanning system, the method includes:
an X-ray machine is used to emit X-ray beam, so that X-ray is emitted from several similar positions meeting the preset condition.
When any branch ray is used, the lead layer is used for shielding other branches, and the alternate switching of the light source is realized by adjusting the shielding condition of the lead layer.
And the mapping module 200 is configured to map the projection data of each light source to a reference space, using the parallel beam CT data space as the reference space, so as to analyze the distribution of the acquired data.
The reference space is a two-dimensional space, each point in the two-dimensional space corresponds to one data acquisition ray, and the two dimensions of the data acquisition ray are the angle of the ray and the vertical distance from the original point to the ray, so that each ray path can be uniquely mapped to be one point of the reference space during scanning.
And a reconstruction module 300, configured to reconstruct the projection data corresponding to each light source to obtain a final reconstructed image.
In an embodiment of the present invention, the performing the analytical reconstruction on the projection data subsets corresponding to each light source respectively includes:
respectively carrying out analytic reconstruction on the projection data of each light source to obtain sparse angle reconstruction images, and overlapping the sparse angle reconstruction images to obtain final reconstruction images; or
Mapping the alternate light source CT data to a parallel beam CT data space, obtaining parallel beam CT data through an interpolation method, and performing parallel beam CT analysis reconstruction; or
In the scanning process, a fixed system matrix is calculated for a scanning system, and a statistical iteration algorithm is adopted for image reconstruction; or
And training a reconstructed neural network in a supervised or unsupervised mode according to a specific system structure, and reconstructing by using the trained neural network.
It should be noted that the above explanation of the embodiment of the alternating light source fan beam X-ray CT sampling method is also applicable to the apparatus, and is not repeated herein.
According to the alternating light source fan-beam X-ray CT sampling device provided by the embodiment of the invention, the light sources are rapidly and alternately switched in the scanning process, more reasonable data are collected and distributed, so that the physical information quantity is increased, a high-quality reconstructed image is finally obtained, a parallel beam CT data space is used as a reference space, data obtained by other scanning modes are mapped to the reference space, and the reasonability of the scanning mode and the system structure is further analyzed.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (6)
1. An alternating light source fan beam X-ray CT sampling method, characterized by comprising the following steps:
in the process of one-circle rotation scanning of the scanning system, controlling a plurality of X-ray light sources to be periodically and alternately switched in turn, so that only one X-ray light source at each rotation angle is in an X-ray emitting state to acquire projection data of each light source;
taking the parallel beam CT data space as a reference space, and mapping the projection data of each light source to the reference space so as to analyze the distribution condition of the acquired data; and
reconstructing the projection data corresponding to each light source to obtain a final reconstructed image;
wherein the reconstructing the projection data corresponding to each light source includes:
respectively carrying out analytic reconstruction on the projection data of each light source to obtain sparse angle reconstruction images, and overlapping the sparse angle reconstruction images to obtain the final reconstruction image; or
Mapping the alternate light source CT data to a parallel beam CT data space, obtaining parallel beam CT data through an interpolation method, and performing parallel beam CT analysis reconstruction; or
In the scanning process, a fixed system matrix is calculated for the scanning system, and a statistical iteration algorithm is adopted for image reconstruction; or
Training a reconstructed neural network in a supervised or unsupervised mode according to a specific system structure, and reconstructing by using the trained neural network;
the reference space is a two-dimensional space, each point in the two-dimensional space corresponds to a data acquisition ray, and two dimensions of the data acquisition ray are the angle of the ray and the vertical distance from the origin to the ray, so that each ray path can be uniquely mapped to be one point of the reference space during scanning.
2. The method according to claim 1, wherein during one rotation of the scanning system, the method comprises:
an X-ray machine is used to emit X-ray beam, so that X-ray is emitted from several similar positions meeting the preset condition.
3. The method according to claim 1, wherein during one rotation of the scanning system, the method comprises:
when any branch ray is used, the lead layer is used for shielding other branches, and the alternate switching of the light source is realized by adjusting the shielding condition of the lead layer.
4. An alternating light source fan beam X-ray CT sampling apparatus, comprising:
the acquisition module is used for controlling the plurality of X-ray light sources to be periodically and alternately switched in turn in the process of one-circle rotation scanning of the scanning system, so that only one X-ray light source at each rotation angle is in an X-ray emitting state to acquire projection data of each light source;
the mapping module is used for mapping the projection data of each light source to a reference space by taking a parallel beam CT data space as the reference space so as to analyze the distribution condition of the acquired data; and
the reconstruction module is used for reconstructing the projection data corresponding to each light source to obtain a final reconstructed image;
wherein, in the reconstruction module, reconstructing the projection data corresponding to each light source includes:
respectively carrying out analytic reconstruction on the projection data of each light source to obtain sparse angle reconstruction images, and overlapping the sparse angle reconstruction images to obtain the final reconstruction image; or
Mapping the alternate light source CT data to a parallel beam CT data space, obtaining parallel beam CT data through an interpolation method, and performing parallel beam CT analysis reconstruction; or
In the scanning process, a fixed system matrix is calculated for the scanning system, and a statistical iteration algorithm is adopted for image reconstruction; or
Training a reconstructed neural network in a supervised or unsupervised mode according to a specific system structure, and reconstructing by using the trained neural network;
the reference space is a two-dimensional space, each point in the two-dimensional space corresponds to a data acquisition ray, and two dimensions of the data acquisition ray are the angle of the ray and the vertical distance from the origin to the ray, so that each ray path can be uniquely mapped to be one point of the reference space during scanning.
5. The apparatus of claim 4, wherein during one rotation of the scanning system, the apparatus comprises:
an X-ray machine is used to emit X-ray beam, so that X-ray is emitted from several similar positions meeting the preset condition.
6. The apparatus of claim 4, wherein during one rotation of the scanning system, the apparatus comprises:
when any branch ray is used, the lead layer is used for shielding other branches, and the alternate switching of the light source is realized by adjusting the shielding condition of the lead layer.
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