CN115937349A - Luggage CT reconstruction region determination method - Google Patents

Abstract

The invention relates to a method for determining a luggage CT reconstruction area, belongs to security system detection, and solves the problem of computer computing resource waste caused by a large-area blank area in the CT reconstruction area in the prior art. The method comprises the following steps: step 1: in projection data for reconstructing tomographic data M, projection data having a rotation angle from s to s + M-1, denoted by p, is extracted ₁ (ii) a Step 2: to p is p ₁ The projection data of (2) is preprocessed to obtain p ₂ (ii) a And step 3: to p ₂ Processing is carried out, and a reconstruction region is determined; wherein m is the angle number required for reconstructing a single fault; wherein s is the starting angle. The size of the image reconstruction area is determined in a self-adaptive mode according to the actual size of the detected package.

Description

Luggage CT reconstruction region determination method

Technical Field

The invention relates to the technical field of security system detection, in particular to a method for determining a CT reconstruction region of a luggage.

Background

Among X-ray-based explosive inspection technologies, X-ray computed tomography imaging (CT) technology has been highly regarded in the field of security inspection because of its own unique advantages. The X-ray CT security inspection technology is characterized in that a tomographic image of a scanned object is obtained by reconstructing CT data, and identification of dangerous goods in the scanned object is realized by analyzing feature data in the tomographic image.

In a security CT apparatus, there is usually a detection channel, the size of the detection channel determines the size of the largest package that the system can detect, and in order to be suitable for the maximum package reconstruction, the CT reconstruction image area usually covers the area of the largest package that can be detected. In the actual inspection process, the size of the actual inspection parcel is usually far smaller than the maximum parcel size, so that a large-area blank area exists in the system reconstruction area, and the computing resources of a computer are greatly wasted.

Disclosure of Invention

In view of the above analysis, an embodiment of the present invention is directed to provide a method for determining a baggage CT reconstruction region, so as to solve the problem of computer resource waste caused by a large empty region in the existing CT reconstruction region.

In one aspect, an embodiment of the present invention provides a method for determining a baggage CT reconstruction region, including:

step 1: among projection data for reconstructing tomographic data M, projection data having a rotation angle from s to s + M-1, denoted by p, is extracted ₁ ；

Step 2: to p ₁ The projection data of (2) is preprocessed to obtain p ₂ ；

And 3, step 3: to p is p ₂ Processing is carried out, and a reconstruction region is determined;

wherein m is the angle number required for reconstructing a single fault;

wherein s is the starting angle.

Further, in the step 2, the preprocessing comprises dark field correction, bright field correction and log correction;

the dark field correction adopts a method of subtracting dark field data from acquired data to correct the image of the CT detector;

the bright field correction adopts a two-point correction method, and on the premise of assuming that the pixels of the CT detector are all in linear response, the coefficient for correction is obtained by a method of solving the ratio of two points of a set point value and bright field corrected data;

wherein, assuming that the X-photons are monoenergetic, the change of the X-ray intensity obeys the Lambert-Beers law, and the Log correction expresses the result of logarithmic operation of the ratio of the incident ray intensity to the emergent ray intensity as the line integral of the attenuation coefficient on the X-ray path as the projection measured value required in the CT reconstruction.

Further, the step 3 comprises:

s311: using a parallel beam rebinning algorithm to reburn p ₂ Data rearrangement to parallel beams P ^p ；

S312: from P, based on the relation of the source and the CT detector in the starting angle s ^p In which one or more angle data p are obtained with the ray direction perpendicular to the height direction _i ；

S313: based on angle data p _i Determining the geometric relation between the rays emitted by the multiple virtual ray sources and a reconstruction region;

s314: based on the determined geometric relationship, p _i Processing the data to obtain a reconstructed height h ₁ ；

Wherein i is a positive integer, p _i Is p ₃ 、p ₄ ……p _i Indicating different angle data.

Further, in step S311, the virtual detector projection data after rearrangement is represented as P ^p (θ, t, b) satisfies:

wherein θ represents the rotation angle after rearrangement;

t is the intra-row distance of the parallel rays;

b is the row pitch;

r is a focal length;

P ^f to rearrange the original data.

Further, in step S313, in p _i Under the angle, the geometrical relationship satisfies:

the rays emitted by the plurality of virtual ray sources are parallel to each other and consistent with the horizontal direction of the reconstruction area, and finally are incident on the virtual detector.

Further, the step S314 includes:

s3141: based on the determined geometric relationship, for p _i Processing the data to obtain a binary image N;

s3142: accumulating the binary image N along the direction of the ray to obtain a one-dimensional vector S;

s3143: in the one-dimensional vector S, the last position which is smaller than the value t and the previous positions of which are all smaller than the value t is recorded as h ₁ Obtaining a reconstruction height h ₁ ；

Wherein t is a positive integer, and the value range is as follows: t is less than 5.

Further, the step S3141 includes:

s31411: based on the determined geometric relationship, p _i The data in the image acquisition device are back projected to a reconstruction area according to the direction of the ray to obtain a two-dimensional image;

s31412: carrying out mean value filtering on the obtained two-dimensional image to eliminate the influence of noise so as to obtain an image M;

s31413: comparing the M with the value b to obtain a binary image N;

where b is a positive number, representing system noise.

Further, the step 3 comprises:

s321: processing data under each angle to obtain an overlapping area U;

s322: taking the data obtained after the comparison of the overlap region U and the value l as a final reconstruction region;

wherein l = m-q;

m is the number of angles used to determine the overlap region U;

q is a non-negative integer for appropriately enlarging the reconstruction region, and has a value in the range of 0-20cm.

Further, the step S321 includes:

s3211: comparing the data of the first angle with the value s, and converting the data into binary data G;

s3212: searching the first non-zero position of the edge positions of the two ends of the binary data G, wherein the position connecting line of the corresponding detector unit and the ray source is a phase tangent line, and setting a pixel point between the phase tangent lines in the reconstruction region as 1 and setting the pixel point as U;

s3213: processing the data at the second angle based on the steps S3211 and S3212, and adding the pixel points located in the reconstruction region between the phase tangents at the angle to U after setting 1;

s3214: based on the steps S3211-S3213, processing the data at each angle to obtain an overlapping area U;

where s is background noise.

Further, m is the projection angle degree acquired when the rotation angle of the CT detector is larger than 180 degrees.

Compared with the prior art, the invention can realize at least one of the following beneficial effects:

1. in the invention, projection data with a rotation angle from s to s + M < -1 > is extracted from projection data used for reconstructing fault data M for processing, and the reconstruction height h is obtained based on the determination of the geometric relationship between rays emitted by a plurality of virtual ray sources and a reconstruction region ₁ And then only the area where the object is located is reconstructed, so that the size of the image reconstruction area is determined in a self-adaptive manner according to the actual size of the detected package, a blank area with a large area in the system reconstruction area is avoided, and the waste of computing resources of a computer is avoided.

2. Through processing data of different angles, the first non-zero position of the edge positions at two ends of binary data G is obtained and searched, and then the position connecting line of a corresponding detector unit and a ray source is obtained, namely, tangent lines are obtained, pixel points located in a reconstruction region between the tangent lines under all angles are placed 1 and added with U to obtain a final reconstruction region, therefore, an external convex polygon of an object is formed through a plurality of tangent rays, the reconstruction region of the object can be obtained, the size of the image reconstruction region is determined according to the actual size of a detected package in a self-adaptive mode, a blank region with a large area in the system reconstruction region is avoided, and further the waste of computing resources of a computer is avoided.

In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.

Drawings

The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.

FIG. 1 is a flowchart of a baggage CT reconstruction region determination method according to the present invention;

FIG. 2 shows a graph of p in the present invention ₃ Under the angle, a schematic diagram of the geometrical relationship among multiple virtual ray sources, rays, a reconstruction region and a virtual detector exists;

FIG. 3 is a schematic diagram showing the positional relationship among the CT source, the reconstruction region, the scanned object, and the CT detector at a certain angle according to the present invention;

FIG. 4 is a schematic diagram of the CT source and the CT detector of FIG. 3 after being rotated by a certain angle;

FIG. 5 is a schematic view of the overlapping region of two tangent rays at two angles according to the present invention, which encompasses the scanned object;

FIG. 6 is a schematic diagram of the positional relationship between the reconstruction region and the channel region, between the determination line and the conveyor belt line in the present invention;

fig. 7 is a schematic diagram of a CT structure of the baggage of the present invention.

Reference numerals are as follows:

1-a CT radiation source; 2-CT slip ring; 3-a CT detector; 4-an object; 5, a conveyor belt; 6-conveyer belt motor; 7-a motion control computer; 8-slip ring motor; 9-a data processing computer; 10-a reconstruction region; 11-a virtual ray source; 12-rays; 13-a virtual probe; 14-a channel region; 15-determining a line; 16-a conveyor line; 17-ray I; 18-ray II; 19-ray III; 20-ray IV.

Detailed Description

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention and not to limit the scope of the invention.

In order to solve the above problems, the present invention provides a method for determining a baggage CT reconstruction region, comprising the steps of:

step 1: in projection data for reconstructing tomographic data M, projection data having a rotation angle from s to s + M-1, denoted by p, is extracted ₁ ；

Step 2: to p is p ₁ The projection data of (2) is preprocessed to obtain p ₂ ；

And 3, step 3: to p is p ₂ Processing is carried out, and a reconstruction region is determined;

wherein m is the angle number required for reconstructing a single fault;

wherein s is the starting angle.

Wherein, in step 2, the preprocessing comprises dark field correction, bright field correction and log correction.

Wherein, step 3 includes:

s311: using a parallel beam rebinning algorithm to reburn p ₂ Data rearrangement to parallel beams P ^p ；

S312: from P, based on the relation of the source and the CT detector in the starting angle s ^p In which one or more angle data p are obtained with the ray direction perpendicular to the height direction _i ；

S313: based on angle data p _i Determining the geometric relation between the rays emitted by the multiple virtual ray sources and a reconstruction region;

s314: based on the determined geometric relationship, p _i Processing the data to obtain a reconstructed height h ₁ ；

Wherein i is a positive integer, p _i Is p ₃ 、p ₄ ……p _i Indicating different angle data.

Compared with the prior art, the method extracts the projection data with the rotation angle from s to s + M < -1 > from the projection data for reconstructing the fault data M for processing, and obtains the reconstruction height h based on the determination of the geometric relationship between the rays emitted by the multiple virtual ray sources and the reconstruction region ₁ Therefore, the size of the image reconstruction area is determined in a self-adaptive mode according to the actual size of the detected package, a large-area blank area in the system reconstruction area is avoided, and waste of computing resources of a computer is avoided.

Specifically, in step 1, the security check CT system includes a CT detector 3, and the CT detector 3 is used to acquire reconstructed tomographic data M, where M is a projection angle acquired when the rotation angle of the CT detector is greater than 180 °.

Specifically, in step 2, the preprocessing includes dark field correction, bright field correction, and log correction.

The dark field correction adopts a method of subtracting dark field data from acquired data to correct the image of the CT detector so as to solve the problem of inconsistency among different detection units due to the difference of dark current responses of a plurality of detection units of the CT detector under the environment without ray irradiation, namely the dark field; the dark field correction usually employs a method of subtracting the dark field data from the acquired data.

The method comprises the steps of bright field correction, namely gain correction, wherein the gain correction adopts a two-point correction method, and under the premise that the pixels of the CT detector are linear response, the gain coefficient for correction is obtained by a method of solving the ratio of two points of a set point value and data after gain correction, so that the problem of inconsistency among different detection units due to ray response inconsistency caused by ray distribution difference and inconsistency among rear-end electronic modules under the irradiation of rays is solved.

The computed tomography reconstruction depends on the measurement results of X-ray beams at different angles, the change of the X-ray intensity is assumed to be single energy, and the change of the X-ray intensity follows the Lambert-beer law, namely the ray shows the law of exponential attenuation, and at the moment, the Log correction expresses the result of logarithmic operation of the ratio of the incident ray intensity to the emergent ray intensity as the linear integral of the attenuation coefficient on the X-ray path, and the linear integral is used as a projection measurement value required in CT reconstruction.

Specifically, in step S311, the virtual detector projection data after rearrangement is represented as P ^p (θ,t,b)；

Wherein, P ^p (θ, t, b) satisfies:

/>

wherein θ represents the rotation angle after rearrangement;

t is the intra-row distance of the parallel rays;

b is a row pitch;

r is a focal length;

P ^f to rearrange the original data.

Specifically, in step S312, based on the relationship between the source and the CT detector in the starting angle S, p can be selected ^p To obtain a reconstructed height h by processing the single or multiple angle data ₁ ；

Wherein one or more of said angle data, and data p ₃ And p ₄ Different in positional relationship, or close to p ₃ And p ₄ Location.

Exemplarily from p ^p Two angle data p of ray direction perpendicular to height direction are obtained ₃ And p ₄ 。

Specifically, in step S313, p is _i Under the angle, the geometrical relationship satisfies:

the rays emitted by the plurality of virtual ray sources are parallel to each other and consistent with the horizontal direction of the reconstruction area, and finally are incident on the virtual detector.

Illustratively, as shown in FIG. 2, at p ₃ Under the angle, the rays emitted by the plurality of virtual ray sources 11 are parallel to each other,coinciding with the horizontal direction of the reconstruction region 10, is finally incident on a virtual detector 13.

Wherein, in p ₃ Similar geometrical relationships also exist for positions differing by 180 degrees, i.e. p ₄ Under angles, similar geometric relationships exist.

Specifically, step S314 includes:

s3141: based on the determined geometric relationship, for p _i Processing the data to obtain a binary image N;

s3142: accumulating the binary image N along the direction of the ray to obtain a one-dimensional vector S;

s3143: in the one-dimensional vector S, the last position which is smaller than the value t and the previous positions of which are all smaller than the value t is recorded as h ₁ Obtaining a reconstruction height h ₁ ；

Wherein t is a positive integer, and the value range is as follows: t is less than 5.

Wherein step S3141 includes:

s31411: based on the determined geometric relationship, p _i The data in the image acquisition device are back projected to a reconstruction area according to the direction of the ray to obtain a two-dimensional image;

s31412: carrying out mean filtering on the obtained two-dimensional image to eliminate the influence of noise so as to obtain an image M;

s31413: comparing M with the value b to obtain a binary image N;

wherein b represents the system noise, and the image is converted into binarization through numerical comparison so as to further eliminate the influence of the system noise, which is generally a small positive number and is particularly relevant to the CT system.

Wherein, the reconstruction height h is obtained ₁ Then, the height h of the rebuilt ₁ Carrying out redundancy increasing treatment to obtain the final reconstruction height h ₂ So as to improve the accuracy of the reconstruction result.

Wherein the final reconstruction height is h ₂ Satisfies the following conditions:

h ₂ ＝h ₁ +ss

wherein ss is redundancy and is 0-20cm.

As shown in fig. 7, the security check CT apparatus includes: the CT scanning device comprises a CT ray source 1, a CT slip ring 2, a CT detector 3, an object 4, a conveyor belt 5, a conveyor belt motor 6, a motion control computer 7, a slip ring motor 8 and a data processing computer 9. Wherein the height range of the reconstruction is the area between the height of the drive belt and h 2. As shown in fig. 3, the area of the object represented by the passage area 14 is only reconstructed by the above-described method in the area between the conveyor line 16 and the determination line 15. Therefore, in the actual inspection process, the reconstruction height is determined, and the detection area is determined, so that the size of the actual inspection parcel is the same as the parcel size, a large-area blank area in the system reconstruction area is avoided, and the computing resource of a computer is greatly wasted.

Further, the following case is not applicable to the processing in step 3 described above, and is as follows:

at an angle, the position relationship among the CT source 1, the reconstruction region 10, the scanned object 4, and the CT detector 3 is shown in fig. 3, wherein the ray 12 passes through the object 4 via the CT source 1 and is received by the CT detector 3, and the ray i 17 and the ray ii 18 are tangent to the outer edge of the object 4.

As shown in fig. 4, similarly, after the CT radiation source 1 and the CT detector 3 are rotated by a certain angle, the radiation rays iii 19 and iv 20 are tangent to the outer edge of the object 4.

As shown in fig. 5, the two angles of tangential rays form an overlap region 10 that encompasses the scanned object 4.

Similarly, as more angles are added, more and more tangent rays form a convex polygon circumscribing the object 4, and then the reconstruction region of the object is obtained. The specific method is as follows.

The method for reconstructing the region comprises the following steps:

step 1-2: same as the step 1-2;

and step 3: processing the data at each angle to obtain an overlapping area U;

specifically, the method comprises the following steps:

s31: comparing the data of the first angle with the value s, and converting the data into binary data G;

where s is background noise.

S32: searching the first non-zero position of the edge positions of the two ends of the binary data G, wherein the position connecting line of the corresponding detector unit and the ray source is a phase tangent line, and setting a pixel point between the phase tangent lines in the reconstruction region as 1 and setting the pixel point as U;

s33: processing the data under the second angle based on the steps S31 and S32, and adding the pixel points positioned in the reconstruction area between the tangent lines under the second angle to U after setting 1;

s34: based on steps S31 to S33, the data at each angle is processed to obtain an overlap area U.

And 4, step 4: and taking the data after the comparison of the overlap area U and the value l as a final reconstruction area.

Wherein l = m-q.

m is the number of angles used to determine the overlap region U;

q is a non-negative integer used to properly enlarge the reconstruction region, and has a value range of 0-20cm.

Compared with the prior art, the method extracts the projection data with the rotation angle from s to s + M < -1 > from the projection data for reconstructing the fault data M for processing, and obtains the reconstruction height h based on the determination of the geometric relationship between the rays emitted by the multiple virtual ray sources and the reconstruction region ₁ Therefore, the size of the image reconstruction area is determined in a self-adaptive mode according to the actual size of the detected package, a large-area blank area in the system reconstruction area is avoided, and waste of computing resources of a computer is avoided.

Through processing data of different angles, the first non-zero position of the edge positions at two ends of binary data G is obtained and searched, and then the position connecting line of a corresponding detector unit and a ray source is obtained, namely, tangent lines are obtained, pixel points located in a reconstruction region between the tangent lines under all angles are placed 1 and added with U to obtain a final reconstruction region, therefore, an external convex polygon of an object is formed through a plurality of tangent rays, the reconstruction region of the object can be obtained, the size of the image reconstruction region is determined according to the actual size of a detected package in a self-adaptive mode, a blank region with a large area in the system reconstruction region is avoided, and further the waste of computing resources of a computer is avoided.

Example 1:

a baggage CT reconstruction region determining method, as shown in fig. 1, includes:

step 1: in projection data for reconstructing tomographic data M, projection data having a rotation angle from s to s + M-1, denoted by p, is extracted ₁ 。

Wherein m is the projection angle degree acquired when the rotation angle of the CT detector is more than 180 degrees.

Wherein s is the starting angle.

As shown in fig. 4, the security inspection CT includes a CT radiation source 1, a CT slip ring 2, a CT detector 3, an object 4, a conveyor belt 5, a conveyor belt motor 6, a motion control computer 7, a slip ring motor 8, and a data processing computer 9; an object (luggage) 4 is placed on a conveyor belt 5, and is driven by a conveyor belt motor 6 to keep constant-speed travel along with the conveyor belt 5, and then enters a CT scanning area for scanning; the slip ring motor 8 controls the CT slip ring 2 to rotate at a constant speed, the CT ray source 1 sends an X-ray beam to transmit the object 4, the CT detector 3 receives an attenuation signal transmitted through the object 4 and continuously transmits the received signal into the data processing computer 9, and therefore data collected by the CT detector 3 form projection data of the fault data M.

The safety check CT system further comprises a light barrier module, so that the time for acquiring data is set according to the trigger signal of the light barrier device, and the integrity of acquired object data is guaranteed.

The light barrier device comprises a light barrier sending module and a light barrier receiving module, the light barrier sending module and the light barrier receiving module are respectively arranged at two ends of one side of the entrance of the security check channel, and the collection of data of the detector is controlled through the light barrier device. When an object enters a security check CT, when the light barrier receiving module cannot receive the pulse signal of the light barrier sending module, namely the light barrier device is changed from a smooth state to a blocking state, the light barrier is triggered to generate a trigger signal for the object to enter the security check CT, and complete data for the object to enter the security check CT are obtained; when the object leaves the security check CT, the light barrier receiving module receives the pulse signal of the light barrier sending module again, namely the light barrier device is changed from a blocking state to a smooth state, the light barrier is triggered to generate a trigger signal that the object leaves the security check CT, and complete data that the object leaves the security check CT is obtained.

Wherein, the object entering and leaving the security check CT refers to the object entering and leaving the scanning area of the security check CT detector.

The light barrier device and the detector in the security check CT have a certain interval, and the time for acquiring data is set according to the trigger signal of the light barrier device, so that the integrity of the acquired object data is guaranteed; during the period from the triggering of the light barrier by the object entering to the triggering of the object leaving, the detector always acquires data to acquire projection data of the tomographic data M.

Step 2: to p ₁ The projection data of (2) is preprocessed to obtain p ₂ ；

Specifically, the preprocessing includes dark field correction, bright field correction, and log correction.

The dark field correction adopts a method of subtracting dark field data from acquired data to correct the detector image so as to solve the problem of inconsistency among different detection units due to the difference of dark current responses of a plurality of detection units of the detector under the condition of no ray irradiation, namely dark field; the dark field correction usually employs a method of subtracting the dark field data from the acquired data.

The method comprises the steps of bright field correction, namely gain correction, wherein the gain correction adopts a two-point correction method, and under the premise that detector pixels are linear in response, a gain coefficient for correction is obtained by a method of solving the ratio of two points of a set point value and gain corrected data, so that the problem of inconsistency among different detection units due to ray response inconsistency caused by ray distribution difference and inconsistency among rear-end electronic modules under the irradiation of rays is solved.

The computed tomography reconstruction depends on the measurement results of X-ray beams at different angles, the change of the X-ray intensity is assumed to be single energy, and the change of the X-ray intensity follows the Lambert-beer law, namely the ray shows the law of exponential attenuation, and at the moment, the Log correction expresses the result of logarithmic operation of the ratio of the incident ray intensity to the emergent ray intensity as the linear integral of the attenuation coefficient on the X-ray path, and the linear integral is used as a projection measurement value required in CT reconstruction.

And 3, step 3: using a parallel beam rebinning algorithm to reburn p ₂ Data rearrangement to parallel beams P ^p The virtual detector projection data after rearrangement is represented as P ^p (θ,t,b)；

Wherein, P ^p (θ, t, b) satisfies:

wherein θ represents the rotation angle after rearrangement;

t is the intra-row distance of the parallel rays;

b is a row pitch;

r is a focal length;

P ^f to rearrange the original data.

And 4, step 4: from P, based on the relation of the source and the CT detector in the starting angle s ^p Two angle data p of ray direction perpendicular to height direction are obtained ₃ And p ₄ ；

And 5: based on two angle data p ₃ And p ₄ Determining the geometric relation between the rays emitted by the multiple virtual ray sources and a reconstruction region;

wherein, as shown in FIG. 2, at p ₃ At the angle, after being rearranged into parallel beams, the rays emitted by the multiple virtual ray sources 11 are parallel to each other, are consistent with the horizontal direction of the reconstruction region 10, and finally are incident on the virtual detector 13.

Wherein, in p ₃ Similar geometrical relationships also exist for positions differing by 180 degrees, i.e. p ₄ Under angles, similar geometric relationships exist.

Step 6: based on the determined geometric relationship, p ₃ And p ₄ Processing the data to obtain a binary image N;

specifically, the method comprises the following steps:

s61: based on the determined geometric relationship, p ₃ And p ₄ According to the direction of the ray 12, back-projecting the data in (1)Acquiring a two-dimensional image in the reconstruction region 10;

the back projection process is a process of erasing the collected data back according to the light direction, that is, the pixel values of the positions where the rays 12 pass through are all the data collected by the detector corresponding to the rays 12.

S62: the obtained two-dimensional image is subjected to mean filtering to eliminate the influence of noise, so as to obtain an image M.

S63: and comparing the M with the value b to obtain a binary image N.

Wherein b represents the system noise, and the image is converted into binarization through numerical comparison so as to further eliminate the influence of the system noise, which is generally a small positive number and is particularly relevant to the CT system.

And 7: accumulating the binary image N along the direction of the ray 12 to obtain a one-dimensional vector S;

and step 8: in the one-dimensional vector S, the last position which is smaller than the value t and the previous positions of which are all smaller than the value t is recorded as h ₁ Obtaining a reconstruction height h ₁ ；

Wherein t is a positive integer, and the value range is as follows: t is less than 5.

And step 9: to height h ₁ Carrying out redundancy increasing treatment to obtain the final reconstruction height h ₂ 。

Wherein the reconstruction height is h ₂ Satisfies the following conditions:

h ₂ ＝h ₁ +ss

wherein ss is redundancy and is 10cm.

Wherein, corresponding to the security check CT equipment, the reconstructed height ranges are the height of the transmission belt and h ₂ The area in between. As shown in fig. 3, the area of the object represented by the passage area 14 is only reconstructed by the above-described method in the area between the conveyor line 16 and the determination line 15. Therefore, in the actual inspection process, the reconstruction height is determined, and the detection area is determined, so that the size of the actual inspection parcel is the same as the parcel size, a large-area blank area in the system reconstruction area is avoided, and the computing resource of a computer is greatly wasted.

Specifically, the process of security check CT reconstructing three-dimensional data of an image is as follows: firstly, an object 4 is placed on a conveyor belt 5, and then, under the drive of a conveyor belt motor 6, the object moves at a constant speed along with the conveyor belt 5 and enters a CT scanning area for scanning; the slip ring motor 8 controls the CT slip ring 2 to rotate at a constant speed, the CT ray source 1 sends an X-ray beam to transmit the object 4, the CT detector 3 receives an attenuation signal transmitted through the object 4 and continuously transmits the received signal into the data processing computer 9.

The data processing computer 9 calculates a reconstruction region in the tomographic data according to the acquired data, reconstructs the determined reconstruction region by using a reconstruction algorithm, and finally three-dimensionally displays three-dimensional data formed by all the tomographic regions on a screen to reconstruct an image.

Example 2

A baggage CT reconstruction region determination method, which is different from embodiment 1 in that:

and step 3: processing data under each angle to obtain an overlapping area U;

specifically, the method comprises the following steps:

s31: comparing the data of the first angle with the value s, and converting the data into binary data G;

where s is background noise.

S32: searching the first non-zero position of the edge positions of the two ends of the binary data G, wherein the position connecting line of the corresponding detector unit and the ray source is a phase tangent line, and setting a pixel point between the phase tangent lines in the reconstruction region as 1 and setting the pixel point as U;

s33: processing the data under the second angle based on the steps S31 and S32, and adding the pixel points positioned in the reconstruction region between the phase tangents under the angle to U after setting 1;

s34: based on steps S31 to S33, the data at each angle is processed to obtain an overlap area U.

And 4, step 4: and taking the data after the comparison of the overlap area U and the value l as a final reconstruction area.

Wherein l = m-q.

m is the number of angles used to determine the overlap region U;

q is a non-negative integer for appropriately enlarging the reconstruction region, and has a value in the range of 0-20cm.

The method obtains the reconstruction region by processing data under different angles, and the method is applicable to the following conditions:

at an angle, the position relationship among the CT source 1, the reconstruction region 10, the scanned object 4, and the CT detector 3 is shown in fig. 3, wherein the ray 12 passes through the object 4 via the CT source 1 and is received by the CT detector 3, and the ray i 17 and the ray ii 18 are tangent to the outer edge of the object 4.

As shown in fig. 4, similarly, after the CT radiation source 1 and the CT detector 3 are rotated by a certain angle, the radiation rays iii 19 and iv 20 are tangent to the outer edge of the object 4.

As shown in fig. 5, the two angles of tangential rays form an overlap region 10 that encompasses the scanned object 4.

Similarly, as more angles are added, more and more tangent rays form a convex polygon circumscribing the object 4, and then the reconstruction region of the object is obtained. The specific method is as shown above.

Those skilled in the art will appreciate that all or part of the processes for implementing the methods of the embodiments described above can be implemented by a computer program, which can be stored in a computer-readable storage medium, for instructing the relevant hardware. The computer readable storage medium is a magnetic disk, an optical disk, a read-only memory or a random access memory, etc.

While the invention has been described with reference to specific preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.

Claims (10)

1. A method for determining a CT reconstruction region of a baggage, comprising:

step 1: in projection data for reconstructing tomographic data M, projections having a rotation angle from s to s + M-1 are extractedData, denoted as p ₁ ；

And 2, step: to p ₁ The projection data of (2) is preprocessed to obtain p ₂ ；

And step 3: to p ₂ Processing is carried out, and a reconstruction region is determined;

wherein m is the angle number required for reconstructing a single fault;

wherein s is the starting angle.

2. The method of claim 1, wherein: in the step 2, the preprocessing comprises dark field correction, bright field correction and log correction;

the dark field correction adopts a method of subtracting dark field data from acquired data to correct the image of the CT detector;

the bright field correction adopts a two-point correction method, and on the premise of assuming that the pixels of the CT detector are all in linear response, the coefficient for correction is obtained by a method of solving the ratio of two points of a set point value and bright field corrected data;

wherein, assuming that the X-photons are monoenergetic, the change of the X-ray intensity obeys the Lambert-Beers law, and the Log correction expresses the result of logarithmic operation of the ratio of the incident ray intensity to the emergent ray intensity as the line integral of the attenuation coefficient on the X-ray path as the projection measured value required in the CT reconstruction.

3. The method of claim 1, wherein step 3 comprises:

s311: using a parallel beam rebinning algorithm to reburn p ₂ Data rearrangement to parallel beams P ^p ；

S312: from P, based on the relation of the source and the CT detector in the starting angle s ^p In which one or more angle data p are obtained with the ray direction perpendicular to the height direction _i ；

S313: based on angle data p _i Determining the geometrical relationship between rays emitted by the multiple virtual ray sources and a reconstruction region;

s314: based on the determined geometric relationship, p _i Data of (1) toProcessing to obtain a reconstructed height h ₁ ；

Wherein i is a positive integer, p _i Is p ₃ 、p ₄ ……p _i Indicating different angle data.

4. The method according to claim 3, wherein in step S311, the virtual detector projection data after rebinning is represented as P ^p (θ, t, b) satisfies:

wherein θ represents the rotation angle after rearrangement;

t is the intra-row distance of the parallel rays;

b is the row pitch;

r is a focal length;

P ^f to rearrange the original data.

5. The method of claim 3, wherein: in step S313, in p _i Under the angle, the geometrical relationship satisfies:

the rays emitted by the plurality of virtual ray sources are parallel to each other and consistent with the horizontal direction of the reconstruction region, and finally the rays are incident on the virtual detector.

6. The method according to claim 3, wherein the step S314 comprises:

s3141: based on the determined geometric relationship, p _i Processing the data to obtain a binary image N;

s3142: accumulating the binary image N along the direction of the ray to obtain a one-dimensional vector S;

s3143: in the one-dimensional vector S, the last position which is smaller than the value t and the previous positions of which are all smaller than the value t is recorded as h ₁ Obtaining a reconstruction height h ₁ ；

Wherein t is a positive integer, and the value range is as follows: t is less than 5.

7. The method according to claim 6, wherein the step S3141 comprises:

s31411: based on the determined geometric relationship, p _i The data in the image acquisition device are back projected to a reconstruction area according to the direction of the ray to obtain a two-dimensional image;

s31412: carrying out mean value filtering on the obtained two-dimensional image to eliminate the influence of noise so as to obtain an image M;

s31413: comparing M with the value b to obtain a binary image N;

where b is a positive number, representing system noise.

8. The method of claim 1, wherein step 3 comprises:

s321: processing data under each angle to obtain an overlapping area U;

s322: taking the data obtained after the comparison of the overlapping area U and the value l as a final reconstruction area;

wherein l = m-q;

m is the number of angles used to determine the overlap region U;

q is a non-negative integer used to properly enlarge the reconstruction region, and has a value range of 0-20cm.

9. The method according to claim 8, wherein the step S321 comprises:

s3211: comparing the data of the first angle with the value s, and converting the data into binary data G;

s3212: searching the first non-zero position of the edge positions of the two ends of the binary data G, wherein the position connecting line of the corresponding detector unit and the ray source is a phase tangent line, and setting a pixel point between the phase tangent lines in the reconstruction region as 1 and setting the pixel point as U;

s3213: processing the data at the second angle based on the steps S3211 and S3212, and adding the pixel points located in the reconstruction region between the phase tangents at the angle to U after setting 1;

s3214: based on the steps S3211-S3213, processing the data at each angle to obtain an overlapping area U;

where s is background noise.

10. The method of claim 1, wherein: and m is the projection angle degree acquired when the rotation angle of the CT detector is greater than 180 degrees.

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