Image reconstruction method for security check CT

文档序号：484866 发布日期：2022-01-04 浏览：7次中文

阅读说明：本技术 一种安检ct的图像重建方法 (Image reconstruction method for security check CT ) 是由魏增辉孙翠丽李保磊莫阳丁洁赵雷刘宇吴凯徐圆飞于 2021-09-29 设计创作，主要内容包括：本发明涉及一种安检CT的图像重建方法,属于安检CT成像技术领域,解决了现有技术中确定物体进入或离开安检CT的方法,得到的物体扫描位置不准确,重建数据量大,并且难以保证扫描物体的完整性的问题。方法包括：采集不包含物体的探测器空扫数据；当接收到物体触发信号时,采集探测器的完整数据；基于所述空扫数据和完整数据得到边缘排投影数据；基于所述边缘排投影数据得到物体进入角度和物体离开角度；基于物体的进入和离开角度,获取物体不同位置的断层数据,进而重建出物体图像。通过该方法重建图像,能够降低重建数据量,并且能够保证物体图像的完整性。(The invention relates to an image reconstruction method of a security check CT (computed tomography), belongs to the technical field of security check CT imaging, and solves the problems that the scanning position of an obtained object is inaccurate, the reconstruction data volume is large, and the integrity of the scanned object is difficult to ensure in the method for determining the entrance or exit of the object into or out of the security check CT in the prior art. The method comprises the following steps: acquiring detector empty scan data which does not contain an object; when an object trigger signal is received, acquiring complete data of a detector; obtaining edge row projection data based on the null scan data and the complete data; obtaining an object entrance angle and an object exit angle based on the edge row projection data; and acquiring the fault data of different positions of the object based on the entering and leaving angles of the object, and further reconstructing an object image. The method is used for reconstructing the image, the reconstruction data volume can be reduced, and the integrity of the object image can be ensured.)

1. An image reconstruction method of a security check CT is characterized by comprising the following steps:

acquiring detector empty scan data which does not contain an object;

when an object trigger signal is received, acquiring complete data of a detector;

obtaining edge row projection data based on the null scan data and the complete data;

obtaining an object entrance angle and an object exit angle based on the edge row projection data;

and acquiring the fault data of different positions of the object based on the object entrance angle and the object exit angle, and further reconstructing an object image.

2. The image reconstruction method for security inspection CT according to claim 1, wherein the acquiring the complete data of the detector when the object trigger signal is received comprises:

when the received signal is a trigger signal when the object enters the security check CT, starting to acquire complete data when the object enters the security check CT;

when the received signal is a trigger signal when the object leaves the security check CT, starting to acquire complete data of the object leaving the security check CT;

the complete data is the data of the detector acquired by the detector rotating along a set rotation interval angle from an initial acquisition angle; and rotating the detector by the set angle to serve as an acquisition period.

3. The image reconstruction method for security inspection CT according to claim 2, wherein the edge row projection data includes a start row projection data and an end row projection data, and the obtaining of the edge row projection data based on the null scan data and the complete data specifically includes:

if the data is complete data when an object enters, extracting initial row data in the complete data, and extracting initial row data of a corresponding acquisition angle in the sweep data; after subtracting the complete data initial row data from the initial row data corresponding to the blank scanning data, calculating the average value of the data of each detection unit in the initial row corresponding to each acquisition angle to obtain initial row projection data;

if the data is complete data when the object leaves, extracting finishing row data in the complete data, and extracting finishing row data of a corresponding acquisition angle in the sweep data; after the complete data end row data is subtracted from the corresponding end row data of the air scanning data, calculating the average value of the data of each detection unit in the end row corresponding to each acquisition angle to obtain the projection data of the end row;

the edge row which receives the attenuation signal of the object firstly in the detector when the object enters the security check CT is taken as a starting row, and the edge row which receives the attenuation signal of the object last in the detector when the object leaves the security check CT is taken as an ending row; the null scan data is data of the detector acquired by rotating the detector for one circle along a set rotation interval angle when no object exists in the security check CT.

4. The image reconstruction method for security inspection CT according to claim 3, wherein the object entry angle is obtained based on the projection data of the starting row, specifically:

if all the data in the current initial row projection data are smaller than a preset first threshold value, the corresponding complete data have no object, and the initial row projection data of the complete data of the next acquisition cycle are obtained when the object enters the security check CT for judging again;

if the number of data smaller than a preset second threshold in the current initial row of projection data is smaller than a preset third threshold, the corresponding complete data has an object at an initial acquisition angle, and the initial acquisition angle is used as an object entry angle;

otherwise, extracting the projection data of the initial row according to a preset first threshold and a preset second threshold, and performing linear fitting on the extracted data to obtain a flat area so as to obtain the entry angle of the object.

5. The image reconstruction method for security inspection CT according to claim 3, wherein the object departure angle is obtained based on the end row projection data, specifically:

if the number of data smaller than the preset second threshold in the current finished row projection data is smaller than a preset third threshold, objects exist in the corresponding complete data at all acquisition angles, and the finished row projection data of the complete data of the next acquisition period when the objects leave the security check CT are obtained for judging again;

if all the data in the projection data of the current finishing row are smaller than a preset first threshold value, the corresponding complete data have no object, and the initial acquisition angle of the complete data is taken as an object leaving angle;

otherwise, extracting the projection data of the initial row according to a preset first threshold and a preset second threshold, and performing piecewise linear fitting on the basis of the extracted data to obtain a flat area so as to obtain the departure angle of the object.

6. The image reconstruction method of the security check CT according to claim 4 or 5, wherein the extracting of the projection data of the starting row or the projection data of the ending row according to the preset first threshold and the second threshold specifically includes:

7. The image reconstruction method for security inspection CT according to claim 6, wherein when the projection data of the initial row or the projection data of the final row are extracted, a plurality of projection data are added forward based on the first projection data and a plurality of projection data are added backward based on the last projection data as the extracted data.

8. The image reconstruction method for security inspection CT according to claim 7, wherein the obtaining of the flat region by piecewise linear fitting based on the extracted data is specifically:

based on the extracted data h₁The fitted straight line g (t) is expressed as:

wherein the content of the first and second substances,

T＝(t₀,…,t_k)，0＝t₀≤…≤t_k＝n；

the set of endpoints T and slope α are constrained according to:

wherein α ═ α (α)₀,…,α_k-2)；

Obtaining a fitted linear equation by using a least square method, and further obtaining the slope of each linear segment and sets K and B of end points on two sides after fitting;

9. The image reconstruction method for safety check CT according to claim 8,

when the initial row of projection data is extracted based on the preset first threshold and the second threshold to obtain the object entrance angle, then

If the extracted data does not have a flat area, each acquisition angle in the corresponding complete data has an object or has an abnormality, and the initial acquisition angle of the complete data is taken as an object entry angle;

otherwise, the slope of the straight line segment connected to the end of the flat region is compared to a sixth threshold: if the value is larger than the sixth threshold value, taking the acquisition angle corresponding to the tail end position of the flat area in the complete data as an object entrance angle; otherwise, acquiring complete data of the next acquisition cycle when the object enters the security check CT and judging again.

10. The image reconstruction method for safety check CT according to claim 8,

when the departure angle of the object is obtained by extracting the projection data of the initial row based on the preset first threshold and the second threshold, then

If no flat area exists in the extracted data, the corresponding complete data has an object at each acquisition angle, and the complete data of the next acquisition cycle is obtained to judge again when the object leaves the security check CT;

if the extracted data are all flat areas, the corresponding complete data have no object or are abnormal, and the initial acquisition angle of the corresponding complete data is used as the object leaving angle;

Technical Field

The invention relates to the technical field of security check CT imaging, in particular to an image reconstruction method of security check CT.

Background

Current security inspection systems are typically provided with one or more sets of light barrier devices (opposed photoelectric switches) disposed at different heights within the security inspection channel. The light barrier device comprises a light barrier sending module and a light barrier receiving module, the entrance or exit of an object is judged according to the state of the light barrier, if the light barrier enters the shielding state from no shielding, the security inspection system considers that the object enters, and therefore subsequent security inspection processing is started, for example, X-rays are started, and a detector starts to acquire images; and if the light barrier enters the non-shielding state from the shielding state, the object is determined to completely pass through the area where the light barrier is located.

However, because the shapes of the objects for security inspection are various, the light barrier arranged at a fixed height cannot determine whether there are any objects at other height positions, for example, the wheels of a flat wheeled luggage are higher than the light barrier arranged at the bottom of the security inspection passage, which may cause a delay in determining that an object enters or determine that an object leaves in advance, and may appear as a part lacking in the object on the security inspection reconstructed image, that is, the scanning is incomplete, and the package cutting phenomenon occurs. In order to solve the problem of packet cutting, a fixed advance amount and a fixed delay amount are usually set in the data acquisition process after a light barrier signal is received in the conventional security inspection system to avoid the packet cutting situation as much as possible, but the method inevitably increases the data processing amount for scanning a single article and cannot completely avoid the packet cutting.

Therefore, for a security inspection system based on X-ray Computed Tomography (CT) for acquiring internal structure information of a scanned object by reconstructing projection data of the object in multiple angles, the current method for determining whether the object enters or leaves the security inspection CT has the defects of inaccurate scanning position of the obtained object, large reconstruction data volume and difficulty in ensuring the integrity of the scanned object.

Disclosure of Invention

In view of the foregoing analysis, an embodiment of the present invention is directed to provide an image reconstruction method for a security check CT, so as to solve the problems that, in the existing method for determining whether an object enters or leaves the security check CT, the obtained scanning position of the object is inaccurate, the reconstructed data volume is large, and the integrity of the scanned object is difficult to ensure.

The embodiment of the invention provides an image reconstruction method of a security check CT, which comprises the following steps:

acquiring detector empty scan data which does not contain an object;

when an object trigger signal is received, acquiring complete data of a detector;

obtaining edge row projection data based on the null scan data and the complete data;

obtaining an object entrance angle and an object exit angle based on the edge row projection data;

and acquiring the fault data of different positions of the object based on the object entrance angle and the object exit angle, and further reconstructing an object image.

Further, when the object trigger signal is received, acquiring complete data of the detector comprises:

when the received signal is a trigger signal when the object enters the security check CT, starting to acquire complete data when the object enters the security check CT;

when the received signal is a trigger signal when the object leaves the security check CT, starting to acquire complete data of the object leaving the security check CT;

Further, the edge row projection data includes a start row projection data and an end row projection data, and the obtaining of the edge row projection data based on the null scan data and the complete data specifically includes:

Further, the object entry angle is obtained based on the initial row of projection data, specifically:

Further, the object departure angle is obtained based on the end row projection data, specifically:

Further, the extracting of the projection data of the starting row or the projection data of the ending row according to the preset first threshold and the second threshold specifically includes:

Further, when the projection data of the initial row or the projection data of the final row are extracted, a plurality of projection data are added forward based on the first projection data and a plurality of projection data are added backward based on the last projection data to be used as the extracted data.

Further, the step of performing piecewise linear fitting based on the extracted data to obtain a flat region specifically includes:

based on the extracted data h₁The fitted straight line g (t) is expressed as:

wherein the content of the first and second substances,

T＝(t₀,…,t_k)，0＝t₀≤…≤t_k＝n；

the set of endpoints T and slope α are constrained according to:

wherein α ═ α (α)₀,…,α_k-2)；

Obtaining a fitted linear equation by using a least square method, and further obtaining the slope of each linear segment and sets K and B of end points on two sides after fitting;

Further, when the object entry angle is acquired by extracting the projection data of the initial row based on the preset first threshold and the second threshold, then

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

the invention provides an image reconstruction method of security check CT,

1. the method has the advantages that the edge row projection data of the acquired detector data are processed, the exact angle of the object entering or leaving the security check CT is determined, the data used for image reconstruction completely contain the object, the data amount processed by the reconstructed image is minimum, and the integrity of the object is also guaranteed;

2. the acquired detector empty scanning data which does not contain the object is differed from the edge row data which contains the complete data of the object, so that the influence of factors such as a conveying belt, bad pixels and the like in a security inspection system is eliminated, the acquired data are more accurate, and the accuracy of subsequently determining the object entrance angle and the object exit angle is further ensured;

3. the entrance angle and the exit angle of the object are preliminarily judged by comparing the edge row projection data with the first threshold, the second threshold and the third threshold, so that the data processing process is accelerated, and the speed of reconstructing the security check CT image is increased;

4. the method comprises the steps of carrying out piecewise linear fitting on the edge row projection data, searching a flat area of the edge row projection data, and further determining the entrance angle and the exit angle of an object, so that the scanned position of the object obtained by the security check CT is more accurate, the image of the object reconstructed by the security check CT is ensured to be complete, and the data volume of reconstruction is reduced.

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 schematic flowchart of an image reconstruction method of a security check CT according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a security check CT.

Reference numerals:

1-a CT radiation source; 2-CT slip ring; 3-a CT detector; 4-an object; 5, driving a belt; 6-driving the belt motor; 7-a motion control computer; 8-slip ring motor; 9-data processing computer.

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.

The invention discloses an image reconstruction method of a security check CT, as shown in FIG. 1, comprising the following steps:

and S1, acquiring detector null scan data without the object.

Specifically, the security inspection channel does not contain an object, when the radiation source is turned on, bright field data collected by rotating for a circle along a set rotation interval angle is collected and serves as null scan data, and the detector comprises a plurality of rows of detection units.

Preferably, when the radiation source is turned off, dark field data not including the object is acquired, a gain coefficient of the detector is acquired based on the acquired bright field data and the dark field data, and the data is corrected to obtain corrected bright field data as null scan data. It can be understood that the bright field data is corrected according to the gain coefficient, so that ray response inconsistency caused by ray distribution difference and inconsistency between rear-end electronic modules under the irradiation of rays can be eliminated, inconsistency exists between different detection units of the detector, and the obtained blank scanning data is more accurate.

And S2, when the object trigger signal is received, acquiring complete data of the detector.

In practice, when the object trigger signal is received, the complete data of the detector is acquired, which includes:

when the received signal is a trigger signal when the object enters the security check CT, starting to acquire complete data when the object enters the security check CT;

when the received signal is a trigger signal when the object leaves the security check CT, starting to acquire complete data of the object leaving the security check CT;

Specifically, the rotation interval angle may be set according to actual needs, and may be set to 0.5 degrees, 1 degree, or the like.

Specifically, the setting angle can be set according to the requirement, and for example, 360 degrees can be selected, namely, one rotation of the detector. Preferably, the set angle is equal to or less than 360 degrees. It should be noted that the setting angle can be set to different, variable angles, or can be set to a fixed angle to meet different requirements.

Specifically, the initial acquisition angle may be an angle between a detector rotation center and a detector direction relative to the detector rotation center and an object direction along a rotation direction, and the acquisition of detector data corresponding to the initial acquisition angle and a rotation setting angle of the detector is complete data; and the rotation set angle of the detector is used as an acquisition period, and the scanning data of the whole object comprises complete data of a plurality of acquisition periods.

Specifically, the security check CT system comprises a light barrier device, 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 an entrance of the security check channel, and acquisition 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.

It should be noted that, a certain interval exists between the light barrier device and the detector in the security check CT, and the time for acquiring data can be set according to the trigger signal of the light barrier device, so as to ensure the integrity of the acquired object data; and the light barrier is triggered by the object entering to the period when the object leaves the trigger, and the detector always acquires data for image reconstruction.

Illustratively, the detector includes 36 rows of detection units, each row includes 700 detection units, the set angle is 360 degrees, that is, the detector rotates once, and the data amount of the complete data is 36 × 700 × 360 when the detector data is acquired every 1 degree interval.

And S3, obtaining edge row projection data based on the null scan data and the complete data.

In implementation, the edge row projection data includes a start row projection data and an end row projection data, and the obtaining of the edge row projection data based on the null scan data and the complete data specifically includes:

if the data is complete data when an object enters, extracting initial row data in the complete data, and extracting initial row data of a corresponding acquisition angle in the sweep data; and after subtracting the complete data initial row data from the initial row data corresponding to the blank scanning data, calculating the average value of the data of each detection unit in the initial row corresponding to each acquisition angle to obtain the initial row projection data.

If the data is complete data when the object leaves, extracting finishing row data in the complete data, and extracting finishing row data of a corresponding acquisition angle in the sweep data; after the complete data end row data is subtracted from the corresponding end row data of the air scanning data, calculating the average value of the data of each detection unit in the end row corresponding to each acquisition angle to obtain the projection data of the end row; it can be understood that the null scan data is detector data which does not contain an object and is acquired at each acquisition angle by the detector rotating for one circle, and corresponding acquisition angles can be found in the null scan data by all acquisition angles within the complete data set angle.

The edge row which receives the attenuation signal of the object first in the detector when the object enters the security check CT is taken as a starting row, and the edge row which receives the attenuation signal of the object last in the detector when the object leaves the security check CT is taken as an ending row.

It can be understood that after the data of the initial row corresponding to the blank scanning data subtracts the data of the complete data of the initial row or the data of the final row corresponding to the blank scanning data subtracts the data of the complete data of the final row, the two-dimensional data T of m × s is obtained, wherein m is the number of detector units of the single row of data, and s is the number of acquisition angles of the detector rotating by a set angle; and then calculating the average value of the data of each detection unit in the ending row corresponding to each acquisition angle to obtain a one-dimensional vector h with the length of s, namely the projection data of the starting row or the ending row. Further, the data with the value smaller than the set eighth threshold value in the two-dimensional data T is eliminated and then averaged, so that the weak signal is prevented from being submerged, wherein the eighth threshold value is set to be a smaller value larger than 0.

Preferably, after the data of the initial row of the blank scanning data is subtracted from the data of the initial row of the complete data or the data of the end row of the blank scanning data is subtracted from the data of the end row of the complete data, the data smaller than zero is set as zero, and the interference of error data is eliminated.

Preferably, after the gain coefficient and the dark field data acquired in step S1 are used to correct the acquired start line data or end line data, the corrected blank scan data is subjected to subsequent processing, so that interference can be further eliminated, and the accuracy of the data can be improved.

It can be understood that the acquired detector empty scanning data which do not contain the object and the edge row data which contain the complete data of the object are differentiated, so that the influence of factors such as a conveying belt, a bad pixel and the like in a security inspection system is eliminated, the acquired data are more accurate, and the accuracy of subsequently determining the entrance angle and the exit angle of the object is further ensured.

And S4, obtaining an object entrance angle and an object exit angle based on the edge row projection data.

During implementation, the object entrance angle is obtained based on the initial row projection data, which specifically comprises the following steps:

During implementation, the object departure angle is obtained based on the end row projection data, specifically:

Specifically, in consideration of the difference of data under the condition that a radiation source and a detector fluctuate, counting fluctuation of bright field data when no object exists to obtain a fluctuation threshold value, and setting a first threshold value and a second threshold value according to the fluctuation threshold value, wherein the first threshold value is a fractional multiple of the fluctuation threshold value, and preferably the fractional multiple is 0.8; the second threshold value is an integer multiple of the fluctuation, and preferably, the integer multiple is set to a value greater than 3 and less than 10. In addition, the third threshold value may be set to an integer less than 10.

It can be understood that whether an object exists in the initial row of projection data or the final row of projection data is judged according to a first threshold, the projection data are both smaller than the first threshold, which indicates that the fluctuation of the numerical value in the projection data is smaller than that of the data without the object, the object does not exist in the projection data, at this time, if the object entry angle is sought, the acquired complete data of the next period is obtained to continue to seek the object entry angle, and if the object exit angle is sought, the initial acquisition angle at this time is taken as the object exit angle; judging whether an object exists in the initial row of projection data or the final row of projection data according to a second threshold and a third threshold, wherein the number of numerical values with smaller fluctuation is smaller than the third threshold, the object exists in each acquisition angle in the projection data, for example, the set angle is 360 degrees, namely the detector rotates for one circle, the number of the acquisition angles s is 720, if the projection data with smaller fluctuation exists in more than 710 acquisition angles, the object exists in the projection data from the initial acquisition angle, at the moment, if the object entry angle is found, the initial acquisition angle at the moment is taken as the object entry angle, and if the object exit angle is found, the acquired complete data of the next period continues to find the object exit angle. The entrance angle and the exit angle of the object are preliminarily judged by comparing the edge row projection data with the first threshold, the second threshold and the third threshold, so that the data processing process is accelerated, and the speed of reconstructing the security check CT image is improved.

In implementation, the starting row projection data or the ending row projection data are extracted according to a preset first threshold and a preset second threshold, wherein the first threshold is smaller than the second threshold; the method specifically comprises the following steps:

and determining the first projection data and the last projection data which are larger than a first threshold value and smaller than a second threshold value in the projection data of the starting row or the projection data of the ending row, and extracting data between the first projection data and the last projection data to serve as extraction data. That is, if the first projection data is the nth row projection data or the nth row projection data₁An acquisition angle x_n1The last projection data is the projection data of the initial row or the projection data of the final row is the nth₂An acquisition angle x_n2Then extract data h₁＝h(x_n1：x_n2) Where h denotes the start line projection data or the end line projection data.

Specifically, when the projection data of the starting line or the projection data of the ending line are extracted, a plurality of projection data are added forward based on the first projection data and a plurality of projection data are added backward based on the last projection data as the extracted data. That is, the data h is extracted₁＝h(x_w1：x_w2) Wherein w is₁＝max(n₁-z,0)，w₂＝min(n₂+ z, s-1), where z represents an increasing or decreasing number of projection data. Preferably, several projection data are added forward or backward, and 5-25 projection data can be selected.

During implementation, the step of performing piecewise linear fitting based on the extracted data to obtain the flat area specifically comprises the following steps:

based on the extracted data h₁The fitted straight line g (t) is expressed as:

wherein the content of the first and second substances,

T＝(t₀,…,t_k)，0＝t₀≤…≤t_k＝n；

in the formula, k represents the number of straight line segments fitted in the extracted data; n represents the total angle number of acquisition of the extracted data; t represents the set of endpoints of the fitted straight line segment, T_jRepresenting the angle corresponding to the jth endpoint in the endpoint set; g_j(t) a jth polyline representing a fitted straight line in the extracted data; alpha is alpha_jIndicates the jth broken line G_j(t) the corresponding coefficient; it should be noted that k is assumed here, and the number of line segments and the positions of end points are divided according to the line segment data that is fit for more cases when constraint optimization is performed.

The set of endpoints T and slope α are constrained according to:

wherein α ═ α (α)₀,…,α_k-2)；

Obtaining a fitted linear equation by using a least square method, and further obtaining the slope of each linear segment and sets K and B of end points on two sides after fitting;

and based on the slope of each straight line segment and the sets K and B of the end points on the two sides, taking continuous straight line segments meeting the condition that the absolute value of the slope is less than a fourth threshold or the length of the line segment is less than a fifth threshold in the fitted straight lines as flat areas. It can be understood that if the slope of the straight line is small, the change of the area is smooth; if the slope of the straight line is large, but the length of the line segment is short, it is considered as an existing disturbance, and it is also considered as a flat region. Preferably, the fourth threshold value may be set to a positive number smaller than 1. Preferably, the number of line segments in the continuous straight line segments is greater than the preset number of line segments, for example, the number of line segments is greater than or equal to 2, that is, the continuous straight line segments at least include 2 straight line segments; if there are a plurality of continuous straight line segments in the extracted data, this case is ignored and no processing is performed.

Specifically, if the angle of the head end position of the flat area is m₁Angle of end position is m₂Then the corresponding positions of the two end points in the projection data of the initial row or the projection data of the final row, i.e. the corresponding positions in the complete data, are respectively the angle

In implementation, when the initial row of projection data is extracted based on the preset first threshold and the second threshold to obtain the entry angle of the object, the method comprises the following steps

if the extracted data are all flat areas, objects do not exist in the corresponding complete data, and the complete data of the next acquisition cycle are obtained for judging again when the objects enter the security check CT; preferably, the complete data can be used as bright-field data for the next acquisition cycle for gain correction.

Otherwise, the slope of the straight line segment connected to the end of the flat region is compared to a sixth threshold: if the value is larger than the sixth threshold value, taking the acquisition angle corresponding to the tail end position of the flat area in the complete data as an object entrance angle; otherwise, acquiring complete data of the next acquisition cycle when the object enters the security check CT and judging again. That is, after the projection data in the extracted data passes through a flat region, there is an upwardly inclined region indicating that the object enters the security CT imaging field of view at the acquisition angle.

Specifically, the sixth threshold value may be set to a value larger than the fourth threshold value.

otherwise, the slope of the straight line segment connecting the head end of the flat area is compared with a seventh threshold: if the value is smaller than the seventh threshold value, the corresponding acquisition angle of the head end position of the flat area in the complete data is used as the object leaving angle; otherwise, acquiring complete data of the next acquisition cycle when the object leaves the security check CT and judging again. That is, the extracted data of the end row of projection data is a flat region after a downward sloping region, indicating that the object leaves the security CT imaging field of view at this acquisition angle.

Specifically, the seventh threshold value may be set to a value smaller than the negative fourth threshold value.

The method has the advantages that segmented straight line fitting is carried out on the edge row projection data, the flat area of the edge row projection data is searched, the entering angle and the leaving angle of the object are further determined, the position of the object scanned by the security check CT is more accurate, the object image reconstructed by the security check CT is complete, and the data volume of reconstruction is reduced.

And S5, acquiring the tomographic data of the object at different positions based on the object entrance angle and the object exit angle, and further reconstructing an object image.

It can be understood that after the object entry angle and the object exit angle of the current object are obtained, the confirmation of the object entry angle and the object exit angle of the next object is started according to the light barrier signal.

Fig. 2 is a schematic structural diagram of a security check CT in this embodiment, where the security check 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.

The process of security check CT reconstruction image three-dimensional data is as follows: firstly, an object (luggage) 4 is placed on a conveyor belt 5, and then, the object (luggage) moves at a constant speed along with the conveyor belt 5 under the drive of a conveyor belt motor 6 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 determines the initial position and the end position of the object to be reconstructed according to the object entrance angle and the object exit angle obtained by calculation of collected data, then fault data of different positions of the object are obtained, and then three-dimensional data formed by all faults are displayed on a screen in a three-dimensional mode, and reconstruction of images is achieved.

Compared with the prior art, the image reconstruction method for the security check CT provided by the invention has the advantages that the edge row projection data of the acquired detector data are processed, the exact angle of the object entering or leaving the security check CT is determined, the data used for image reconstruction completely contain the object, the reconstruction speed is increased, the data volume of the subsequent fault is reduced, the data volume processed by the reconstructed image is minimized, and the integrity of the object is ensured.

Those skilled in the art will appreciate that all or part of the flow of the method implementing the above embodiments may be implemented by a computer program, which is stored in a computer readable storage medium, to instruct related hardware. The computer readable storage medium is a magnetic disk, an optical disk, a read-only memory or a random access memory.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.

14页详细技术资料下载

上一篇：一种医用注射器针头装配设备

下一篇：一种低功耗红外反射检测电路

Image reconstruction method for security check CT

相关技术

网友询问留言