Patent Description:
The present invention relates to the field of radiation imaging, and more particularly, to a spiral Computed Tomography (CT) device.

With the development of the world economy and international trade, transportation of containers has been more and more widely applied in various countries' economies. At the same time, security inspection of the containers has also become more important. Especially after the "<NUM>" incident in <NUM>, countries around the world have strengthened security inspection against terrorist attacks, drug trafficking, smuggling, etc., and have enhanced inspection standards. Among the several common inspection methods in the field of security inspection, X-ray transmission technology has advantages such as strong penetration ability, short measurement time and high resolution, and therefore is often used for inspection of cargos in containers in airports, customs etc. However, with the improvement of social needs and the development of technology, CT technology has also been introduced into the field of social public security from initial medical diagnosis and industrial non-destructive testing.

After the development for many years, the CT technology has gradually evolved from scanning using a thin X-ray beam, a small fan beam, or a large fan beam to scanning using spiral CT. The difference from the initial normal CT technology is in that, during scanning with the spiral CT, both a scanning bracket and an object to be detected are continuously moved, an X-ray source is spirally rotated relative to the object, and detectors continuously collect projection data, so as to obtain a three-dimensional image of the object to be detected, which may greatly shorten time for scanning. In addition, a resolution capability of the CT technology itself for densities and atomic numbers may further improve effects of material recognition during inspection.

In <NUM>, the Elscint company firstly introduced dual-slice spiral CT technology. Then, other companies have also developed multi-slice spiral CT technology. In this multi-slice spiral CT technology, a structure of multiple rows of detectors is used to obtain projection data in multiple slices simultaneously during scanning in a circle, thereby increasing a detection area, obtaining a high-quality three-dimensional reconstructed image, and also improving the scanning efficiency of the system. The conventional multi-slice spiral CT has been widely used in the medical field etc., but cannot be well applied to inspection of large objects such as air containers etc. Specifically, in consideration of inconsistency among dosages of fan-shaped X-ray beams, fan angles of the X-ray beams must be kept below a certain upper limit value. Therefore, in a case where a volume of a large object such as an air container etc. is much greater than that of an object to be detected in the medial field, a larger inspection space is required by the same multi-slice spiral CT device in order to realize detection of the air container. In addition, a penetration power of an X-ray source is also a factor which must be considered, and complex structures of the X-ray source and detectors as well as stability problems caused by load-carrying also cannot be ignored.

Therefore, there is a need for a spiral CT device capable of performing inspection of a large object with good performance.

The International Application No. <CIT> discloses a rotate CT scanner which is related art to the present invention. In the rotate CT scanner source-detector units are mounted on a gantry displaced from each other in the Z direction and the detector units are arranged to acquire data from large volumes of a subject in a single rotation so that the scanner can provide time coherent images of large <CIT> relates to a spiral CT scanner.

In order to solve the above problems existing in the conventional art, the present disclosure proposes a spiral CT device.

According to an aspect of the present disclosure, there is proposed a spiral CT device according to claim <NUM>.

In one embodiment, the inspection station is movable in the first direction and/or in a direction perpendicular to the first direction.

In one embodiment, the first direction is a vertical direction.

In one embodiment, the rotation supporting apparatus is a slip ring, the plurality of X-ray sources and the plurality of X-ray receiving apparatuses are disposed on a circumference of the slip ring, and one of the X-ray sources and a corresponding one of the X-ray receiving apparatuses are located on opposite sides of the circumference with respect to a center thereof.

In one embodiment, in the detection state, a center of the circumference of the slip ring coincides with a center of the inspection space.

In one embodiment, the rotational supporting apparatus is a bracket.

According to the invention, the X-ray sources are X-ray accelerators.

According to the invention, the X-ray sources provide fan-shaped X-ray beams.

According to the invention, the plurality of X-ray sources are closely disposed on the rotational supporting apparatus, and the fan-shaped X-ray beams provided by the plurality of X-ray sources cover the inspection space with a minimum degree of overlapping.

In one embodiment, the X-ray receiving apparatuses each comprise a plurality of rows of detectors.

In one embodiment, the spiral CT device further comprises a processor. The processor is connected to the plurality of X-ray receiving apparatuses and configured to process the collected X-rays and reconstruct a three-dimensional image of the object to be inspected,
wherein the three-dimensional image is reconstructed by the processor using a linear interpolation method.

In one embodiment, when two adjacent ones of the plurality of X-ray receiving apparatuses have an overlapped coverage, data in the overlapping region is processed using a compressive sensing technique.

With the spiral CT device according to the present disclosure, large objects may be inspected while ensuring a small system size, a short inspection time, and a high inspection quality. Thereby, the problems in the conventional techniques described above are solved, thereby satisfying the needs of airports for inspection of large cargos.

The specific embodiments of the present disclosure will be described in detail below. It should be noted that the embodiments herein are used for illustration only, without limiting the present disclosure. In the description below, a number of specific details are explained to provide better understanding of the present disclosure. In other instances, well known circuits, materials or methods are not described specifically so as not to obscure the present disclosure.

The present disclosure will be described in detail below with reference to the accompanying drawings.

Firstly, <FIG> illustrates a structural diagram of a spiral CT device <NUM> according to an embodiment of the present disclosure. As shown, the spiral CT device <NUM> illustrated comprises an inspection station <NUM>, a rotational supporting apparatus <NUM>, two X-ray sources <NUM>-<NUM> and <NUM>-<NUM> (collectively referred to as <NUM> hereinafter), and two X-ray receiving apparatuses <NUM>-<NUM> and <NUM>-<NUM> (collectively referred to as <NUM> hereinafter). It is to be illustrated that, for convenience of description, only two X-ray sources <NUM> and two X-ray receiving apparatuses <NUM> are exemplarily shown in <FIG>. It should be understood that in other embodiments of the present disclosure, more or less X-ray sources <NUM> and X-ray receiving apparatuses <NUM> may be included.

The inspection station <NUM> is configured to carry an object to be inspected. The inspection station <NUM> defines an inspection space which is located above the inspection station and is used for accommodating the object to be inspected. In one embodiment, the inspection space <NUM> may be physically defined by a physical component (for example, a wall panel built on the inspection station <NUM>) or defined by other technical means (for example, infrared detection) in an auxiliary manner. Alternatively, the inspection space <NUM> may also be defined without any physical components, but instead it is agreed that there is a space of a particular size above the inspection station <NUM>.

In one embodiment, the inspection station <NUM> is movable in a first direction and/or in a direction perpendicular to the first direction. The movement in the first direction makes it convenient to place the object to be inspected. For example, the inspection station <NUM> is firstly brought down to a suitable height, and after the object to be inspected is placed on the inspection station <NUM>, the inspection station <NUM> is raised to a height suitable for CT measurement. The movement in the direction perpendicular to the first direction makes it convenient to perform the spiral CT inspection, and a speed of the horizontal movement may be determined by a rotation period and a measurement length.

In one embodiment, the first direction is a vertical direction (as shown in <FIG>).

In a detection state, the inspection station <NUM> is rotatable in the direction (as indicated by the horizontal direction in <FIG>) perpendicular to the first direction, so that the inspection station <NUM> cooperatively rotates with the rotational supporting apparatus <NUM> described below to realize helical scanning of the object to be inspected.

The rotational supporting apparatus <NUM> is shown as a ring in <FIG>. It may be seen that the rotational supporting apparatus <NUM> is shown as a slip ring in <FIG>. However, it should be understood that in other embodiments of the.

The X-ray sources <NUM> are located on the rotational supporting apparatus <NUM> and are configured to transmit X-rays to pass through the inspection space <NUM>.

The X-ray sources <NUM> are X-ray accelerators for providing high-energy X-ray beams.

The X-ray sources <NUM> provide fan-shaped X-ray beams.

The X-ray sources <NUM>-<NUM> and <NUM>-<NUM> are closely disposed on the rotational supporting apparatus, and the fan-shaped X-ray beams provided by the X-ray sources cover the inspection space <NUM> with a minimal degree of overlapping. In this way, a size of the system may be better reduced.

A case where the two X-ray sources <NUM>-<NUM> and <NUM>-<NUM> are closely disposed is exemplarily shown in <FIG>. A distance SO from a target point of one of the X-ray source(s) <NUM> to a central point of the inspection space <NUM> (i.e., a rotational radius of the target point of the X-ray source <NUM>) is: <MAT> where R is a radius of a circular region shown in <FIG>, θ is a fan angle of an X-ray beam of the X-ray source <NUM>, and n is a number of the X-ray source(s) <NUM> used. By taking θ = θmax = <NUM>° as an example, when a single X-ray source <NUM> is used, SO<NUM>S = R/sin(<NUM>°); and when two X-ray sources <NUM> which are closely disposed are used under the same conditions, SO<NUM>S = R/sin(<NUM>°). Thus, SO<NUM>S/SO<NUM>S = <NUM>, that is, the rotational radius of the target point when two X-ray sources <NUM> are used is <NUM>/<NUM> times the rotational radius of the target point in a case where a single X-ray source <NUM> is used. Therefore, when a plurality of X-ray sources are used, the rotational radius SO of the target point of each of the X-ray sources is effectively decreased, thereby reducing the size of the system.

In order to ensure that the system collects a sufficient amount of data and condition where rays which are emitted by an /th X-ray source and received by an mth detector at an rth projection angle interact with the object to be inspected, and generally refers to a length of a line of intersection between a corresponding pixel and the X-rays.

For a sparse image, the image to be reconstructed may firstly be converted into a gradient image, and then an I<NUM> mode of the gradient image is minimized. In this way, the image reconstruction process is transformed into a nonlinear optimization problem under constraint conditions, which may be solved by the iterative reconstruction algorithm, the gradient descent method or the convex set mapping method etc..

<FIG> illustrates a flowchart of a method <NUM> for reconstructing a three-dimensional image from projection data obtained by a CT device according to the present disclosure. This method <NUM> is not encompassed by the wording of the claims but is considered as useful for understanding the invention. The CT device is not limited to the spiral CT device described in the embodiments of the present disclosure (as described above with reference to <FIG>) as long as the CT device comprises a plurality of pairs of X-ray sources and X-ray receiving apparatuses. Hereinafter, for the convenience of description, when the method <NUM> is described in detail, the spiral CT device shown in <FIG> will be taken as an example.

Specifically, the method <NUM> starts at step S210, in which corresponding projection data is obtained by each pair of X-ray source and X-ray receiving apparatus among the plurality of pairs of X-ray sources and X-ray receiving apparatuses. Then, in step S220, the projection data obtained by each pair of X-ray source and X-ray receiving apparatus is interpolated. Finally, in step S230, a three-dimensional image is reconstructed based on the interpolated projection data using image reconstruction algorithms. Here, in step S230, for two pairs of X-ray sources and X-ray receiving apparatuses having an overlapped projection portion, an image reconstruction algorithm for data corresponding to the overlapped projection portion in the interpolated projection data obtained using the two pairs of X-ray sources and X-ray receiving apparatuses is different from direction in which the inspection station horizontally moves) interpolation, for example, a <NUM>-degree or <NUM>-degree linear interpolation method, needs to be used. By taking the most commonly-used <NUM>-degree linear interpolation method as an example, assuming that an interpolation position is Zimg, a data collection position is Z(α), and a position from the sampling point by <NUM>° is Z(α+π), then projection data obtained after the <NUM>-degree linear interpolation is: <MAT> where p(n,m) is data collected by an mth detector crystal at an nth projection angle, and p(n+ Np,π,m) is projection data from p(n,m) by <NUM>°. Interpolation coefficients ω<NUM> and ω<NUM> are as follows respectively: <MAT> <MAT>.

After linear interpolation of the projection data, a three-dimensional image is reconstructed using an image reconstruction algorithm, for example, reconstruction methods such as the Filtered Back Projection (FBP) reconstruction method, or the iterative Ordered Subset maximum Expectation Method (OSEM) or the Algebraic Reconstruction Technique (ART) in combination with the FBP algorithm etc..

In one embodiment, when two adjacent ones (for example, the X-ray receiving apparatuses <NUM>-<NUM> and <NUM>-<NUM> in <FIG>) of the X-ray receiving apparatuses <NUM> have an overlapped coverage, data in the overlapping region is processed using a compressive sensing technique.

Specifically, by taking the case shown in <FIG> as an example, if a plurality of rows of detectors are used as the X-ray receiving apparatuses <NUM>, since the X-ray sources <NUM> have a certain size, two target points may not completely coincide. In order to completely cover the object to be inspected with the rays, it may inevitably enable partial overlapping of the X-ray receiving apparatuses <NUM>-<NUM> and <NUM>-<NUM> (as shown in <FIG>). Conventional image reconstruction algorithms (for example, the FBP) cannot be used for overlapping data in this partial overlapping region. This is because firstly, when the X-rays are absorbed, an exponential decay law is followed, and the overlapping projection data may be regarded as a sum of a plurality of exponential functions, and cannot be expanded "in a non-destructive manner" to a linear function with a limited length; and secondly, if the object to be inspected is discretized, the overlapping projection data makes the imaging system underdetermined, which results in failure in acquisition of a correct solution. In this regard, certain processing, such as the compressive sensing technique described above, is required to be used. Under conditions that data sparsity is satisfied and random sampling is implemented, image quality may be recovered using a sampling frequency much less than an Nyquist sampling frequency. Since the original image is sparse, the projection data may be expressed as: <MAT> where Nb and Nr are a number of detector crystals in the overlapping region and a projection angle of scanning in a circle, respectively; f is a two-dimensional image matrix, vector M<NUM>,<NUM> is a system matrix corresponding to a first or second X-ray source, and element Ml,m,r (/=<NUM>,<NUM>; m=<NUM>,<NUM>,. , Nb; r=<NUM>,<NUM>,. , Nr) indicates a condition where rays which are emitted by an lth X-ray source and received by an mth detector at an rth projection angle interact with the object to be inspected, and generally refers to a length of a line of intersection between a corresponding pixel and the X-rays.

<FIG> illustrates a flowchart of a method <NUM> for reconstructing a three-dimensional image from projection data obtained by a CT device according to an embodiment of the present disclosure. The CT device is not limited to the spiral CT device described in the embodiments of the present disclosure (as described above with reference to <FIG>) as long as the CT device comprises a plurality of pairs of X-ray sources and X-ray receiving apparatuses. Hereinafter, for the convenience of description, when the method <NUM> is described in detail, the spiral CT device shown in <FIG> will be taken as an example.

Specifically, the method <NUM> starts at step S210, in which corresponding projection data is obtained by each pair of X-ray source and X-ray receiving apparatus among the plurality of pairs of X-ray sources and X-ray receiving apparatuses. Then, in step S220, the projection data obtained by each pair of X-ray source and X-ray receiving apparatus is interpolated. Finally, in step S230, a three-dimensional image is reconstructed based on the interpolated projection data using image reconstruction algorithms. Here, in step S230, for two pairs of X-ray sources and X-ray receiving apparatuses having an overlapped projection portion, an image reconstruction algorithm for data corresponding to the overlapped projection portion in the interpolated projection data obtained using the two pairs of X-ray sources and X-ray receiving apparatuses is different from an image reconstruction algorithm for data corresponding to remaining portions except for the overlapped projection portion in the interpolated projection data.

In step S210, corresponding projection data is obtained by each pair of X-ray source and X-ray receiving apparatus among the plurality of pairs of X-ray sources and X-ray receiving apparatuses. By taking the spiral CT structure <NUM> shown in <FIG> as an example, the X-ray sources <NUM>-<NUM> and <NUM>-<NUM> emit X-rays respectively, and the X-ray receiving apparatuses <NUM>-<NUM> and <NUM>-<NUM> receive the X-rays passing through the object to be inspected respectively, to obtain corresponding projection data respectively. Preferably, as in the case shown in <FIG>, the two X-ray sources <NUM>-<NUM> and <NUM>-<NUM> have a coverage including the entire inspection space (this is true not only in a dimension corresponding to the paper sheets, but also in various slices distributed in a direction perpendicular to the paper sheets). Thereby, the reproduction of the three-dimensional image of the object to be inspected may be realized using data obtained using the X-ray sources <NUM>-<NUM> and <NUM>-<NUM> and the X-ray receiving apparatuses <NUM>-<NUM> and <NUM>-<NUM>.

In step S220, the projection data obtained using each pair of X-ray source and X-ray receiving apparatus is interpolated. In an example, the interpolation step is implemented using linear interpolation. Still By taking the spiral CT device shown in <FIG> as an example, since projection data in a slice depending on any of the scanning axes is incomplete, it is necessary to fill blank regions between existing data using the existing data through interpolation to avoid volume artifacts from occurring during reconstruction. In the above description, the exemplary interpolation method has been described in the description of <FIG>, and details thereof will not be described herein again.

The projection data enriched by interpolation will be used for reconstruction in a next step.

In step S230, a three-dimensional image is reconstructed based on the interpolated projection data using image reconstruction algorithms. Here, the image reconstruction algorithms may be conventional image reconstruction algorithms, for example, the FBP. However, it is necessary to consider that the projection of two pairs of adjacent X-ray sources and X-ray receiving apparatuses is likely to overlap, and the conventional image reconstruction algorithms are no longer applicable for the overlapping region, that is, an algorithm (for example, the compressive sensing technique) different from the conventional image reconstruction algorithms is required to be used for the overlapping region. The exemplary algorithm for the overlapping region has been described above with respect to <FIG> and will not be described again here.

It should be understood that the method <NUM> may further comprise other conventional steps included in conventional three-dimensional image reconstruction methods, such as image noise reduction and smoothing, image correction, artifact region reconstruction, etc..

For example, <FIG> illustrates a specific exemplary flowchart of a three-dimensional image reconstruction method <NUM> implemented based on the spiral CT device illustrated in <FIG>. Of course, it should be understood that various steps in <FIG> and an order of the steps are merely exemplary, and in other examples, other processing steps may be added or existing processing steps may be deleted, and the steps in <FIG> may further be exchanged.

The exemplary three-dimensional image reconstruction flow illustrated in <FIG> starts at data collection in step <NUM> and performs preliminary image reconstruction <NUM> through the interpolation <NUM> as described above. Next, the overlapping region processing step <NUM> is performed as described above. It should be illustrated that although the preliminary reconstruction <NUM> and the overlapping region processing <NUM> are illustrated here as two separate steps, they may also be implemented as a single step, i.e., different processing is implemented for different portions (for example, like step S230 of method <NUM> in <FIG>).

Then, the reconstruction flow further proceeds to image noise reduction and smoothing processing in step <NUM> to improve a signal to noise ratio.

In step <NUM>, image correction is performed. The image correction comprises processes such as geometric correction, scatter correction, beam correction, detector gain correction, and metal artifact correction etc. In addition to the correction methods commonly used in X-ray inspection systems, the metal artifact correction is not negligible in inspection of containers. The most critical step in the metal artifact correction is to segment out a metal artifact region, that is, to determine a boundary of the metal artifact region, using the threshold method, clustering method, edge detection method, average method or region growth method etc..

In step <NUM>, the metal artifact region is reconstructed. Here, forward projection of the segmented region is performed to determine a position of a metal track in projection. Interpolation, for example, commonly-used linear interpolation, cubic spline interpolation, or fourth-order polynomial interpolation etc., is then performed to avoid, for example, striped artifacts, comet-like artifacts, etc..

In step <NUM>, a contrast enhancement process is performed on the preliminarily reconstructed image.

Finally, in step <NUM>, a three-dimensional result is displayed in a form of a three-dimensional image or a two-dimensional cross-sectional view at a specific position etc..

Claim 1:
A spiral Computed Tomography, CT, device for inspection of large cargos, comprising:
an inspection station (<NUM>) operable to carry an object to be inspected on a carrying surface thereof, wherein an inspection space (<NUM>) is defined above the carrying surface, a normal direction for the carrying surface is a first direction, and the inspection station (<NUM>) is operable to move along a second direction perpendicular to the first direction to cause the object to be inspected to pass through the inspection space (<NUM>);
a rotational supporting apparatus (<NUM>) disposed around the inspection space in a plane perpendicular to the second direction and operable to rotate around the inspection space (<NUM>); characterized in that the spiral CT device further comprises
a plurality of X-ray accelerators (<NUM>-<NUM>, <NUM>-<NUM>) located on the rotational supporting apparatus (<NUM>) and configured to transmit X-rays to pass through the inspection space (<NUM>); and
a plurality of X-ray receiving apparatuses (<NUM>-<NUM>, <NUM>-<NUM>) in one-to-one correspondence to the plurality of X-ray accelerators, the plurality of X-ray receiving apparatuses (<NUM>-<NUM>, <NUM>-<NUM>) being located on the rotational supporting apparatus (<NUM>) and opposing to the plurality of X-ray accelerators (<NUM>-<NUM>, <NUM>-<NUM>) respectively, the plurality of X-ray receiving apparatuses (<NUM>-<NUM>, <NUM>-<NUM>) being configured to collect the X-rays passing through the inspection space (<NUM>),
wherein the plurality of X-ray accelerators (<NUM>-<NUM>, <NUM>-<NUM>) and the plurality of X-ray receiving apparatuses (<NUM>-<NUM>, <NUM>-<NUM>) are operable to rotate with the rotational supporting apparatus (<NUM>);
wherein the plurality of X-ray accelerators (<NUM>-<NUM>, <NUM>-<NUM>) are closely disposed on the rotational supporting apparatus (<NUM>), and fan-shaped X-ray beams provided by the plurality of X-ray accelerators (<NUM>-<NUM>, <NUM>-<NUM>) cover the inspection space (<NUM>) with a minimum degree of overlapping.