Computed Tomography (CT) security inspection system with enhanced X-ray shielding
阅读说明：本技术 具有增强的x射线屏蔽的计算机断层扫描（ct）安全检查系统 (Computed Tomography (CT) security inspection system with enhanced X-ray shielding ) 是由 B.M.戈登 O.约翰逊 于 2018-11-19 设计创作，主要内容包括：用于在X射线安全检查系统中扫描物体的方法,其中X射线安全检查系统包括装备有辐射屏蔽帘的进入隧道、X射线部分以及装备有辐射屏蔽帘的离开隧道,所述方法包括：使物体以第一速度速率并且连续物体之间具有第一分离程度而穿过进入隧道；使物体以第二速度速率并且连续物体之间具有第二分离程度而穿过X射线部分；以及使物体以第三速度速率并且连续物体之间具有第三分离程度而穿过离开隧道；其中第二速度速率小于第一速度速率和第三速度速率,并且其中连续物体之间的第二分离程度小于连续物体之间的第一分离程度和连续物体之间的第三分离程度。(Method for scanning an object in an X-ray security inspection system, wherein the X-ray security inspection system comprises an entrance tunnel equipped with a radiation shielding curtain, an X-ray section and an exit tunnel equipped with a radiation shielding curtain, the method comprising: passing the objects into the tunnel at a first velocity rate and with a first degree of separation between successive objects; passing the objects through the X-ray portion at a second velocity rate and with a second degree of separation between successive objects; and passing the objects through the exit tunnel at a third speed rate with a third degree of separation between successive objects; wherein the second velocity rate is less than the first velocity rate and the third velocity rate, and wherein the second degree of separation between the successive objects is less than the first degree of separation between the successive objects and the third degree of separation between the successive objects.)
1. A method for scanning an object in an X-ray security inspection system, wherein the X-ray security inspection system comprises an entrance tunnel equipped with a radiation shielding curtain, an X-ray section, and an exit tunnel equipped with a radiation shielding curtain, the method comprising:
passing the objects into the tunnel at a first velocity rate and with a first degree of separation between successive objects;
passing the objects through the X-ray portion at a second velocity rate and with a second degree of separation between successive objects; and
passing the objects through the exit tunnel at a third speed rate and with a third degree of separation between successive objects;
wherein the second velocity rate is less than the first velocity rate and the third velocity rate, and wherein the second degree of separation between the successive objects is less than the first degree of separation between the successive objects and the third degree of separation between the successive objects.
2. The method of claim 1, wherein the X-ray security inspection system comprises a CT security inspection system.
3. The method of claim 1, wherein the second speed rate is a maximum speed that permits acceptable scan results.
4. The method of claim 3, wherein the second velocity rate is 15cm or less per second.
5. The method of claim 1, wherein the first and third velocity rates are maximum velocities that permit an appropriate number of radiation shielding curtains to fall back between successive objects to their "fully down" positions.
6. The method of claim 1, wherein the first and third velocity rates are 22-27cm per second or greater.
7. The method of claim 1, wherein the first and third speed rates are the same.
8. The method of claim 1, wherein the first and third velocity rates are different from each other.
9. The method of claim 1, wherein the radiation shielding curtain comprises a lead-containing curtain.
10. An apparatus for scanning an object, the apparatus comprising:
an X-ray security inspection system, wherein the X-ray security inspection system comprises an entrance tunnel equipped with a radiation shielding curtain, an X-ray section, and an exit tunnel equipped with a radiation shielding curtain;
means for passing the objects into the tunnel at a first velocity rate and with a first degree of separation between successive objects;
means for passing the objects through the X-ray portion at a second velocity rate and with a second degree of separation between successive objects; and
means for passing the objects through the exit tunnel at a third speed rate and with a third degree of separation between successive objects;
wherein the second velocity rate is less than the first velocity rate and the third velocity rate, and wherein the second degree of separation between the successive objects is less than the first degree of separation between the successive objects and the third degree of separation between the successive objects.
11. The apparatus of claim 10, wherein the X-ray security inspection system comprises a CT security inspection system.
12. The apparatus of claim 10, wherein the second speed rate is a maximum speed that permits acceptable scan results.
13. The apparatus of claim 12, wherein the second velocity rate is 15cm or less per second.
14. The apparatus of claim 10, wherein the first and third velocity rates are maximum velocities that permit an appropriate number of radiation shielding curtains to fall back between successive objects to their "fully down" positions.
15. The method of claim 10, wherein the first and third velocity rates are 22-27cm per second or greater.
16. The method of claim 10, wherein the first and third speed rates are the same.
17. The method of claim 10, wherein the first and third velocity rates are different from each other.
18. The apparatus of claim 10, wherein the means for passing the object into the tunnel comprises a first conveyor belt.
19. The apparatus of claim 10 wherein the means for passing the object through the X-ray portion comprises a second conveyor.
20. The apparatus of claim 10 wherein the means for passing the objects out of the tunnel comprises a third conveyor belt.
21. The apparatus of claim 10 wherein the means for passing the object into the tunnel comprises a series of powered rollers.
22. The apparatus of claim 10 wherein the means for passing the object through the X-ray portion comprises a series of powered rollers.
23. The apparatus of claim 10 wherein the means for passing the object out of the tunnel comprises a series of powered rollers.
24. The apparatus of claim 10, wherein the radiation shielding curtain comprises a lead-containing curtain.
Technical Field
The present invention relates generally to X-ray security inspection systems and, more particularly, to a Computed Tomography (CT) security inspection system with enhanced X-ray shielding.
Background
X-ray security inspection systems are widely used at airports and other security sensitive locations to scan luggage and other containers for explosives and other contraband. These X-ray security inspection systems typically have one (or several) fixed (i.e., stationary) X-ray sources that operate at low power (e.g., 2 mA) at approximately 160,000 volts (i.e., 160 kV). The bags or containers (usually loaded in trays) are moved on a conveyor past the fixed X-ray source(s).
When X-rays impinge upon a bag or other container passing the X-ray source(s) on the conveyor, an appropriate amount of scattered X-rays are emitted from the bag or other container undergoing closer inspection. Some of these scattered X-rays are reflected in the direction of the entry or exit segment of the conveyor belt that is moving the bag or container past the stationary X-ray source(s). To avoid exposure of X-rays to persons who may be near the entrance of the X-ray security inspection system (i.e., the "entrance tunnel" containing the entrance segment of the conveyor belt) or near the exit of the X-ray security inspection system (i.e., the "exit tunnel" containing the exit segment of the conveyor belt), a plurality of lead-containing curtains (e.g., 3 to 6 curtains) have heretofore been placed in each tunnel (i.e., in each of the entrance and exit tunnels).
In these older X-ray security inspection systems, typical throughput rates for trays (sometimes also referred to as bins) containing bags or other containers have typically been in the range of 200 (or up to 300) trays per hour. Thus, at these low transit rates through the trays entering and exiting the tunnel in which the lead-containing curtains are located, the trays can move through the relatively low number of curtains with sufficient spacing between the trays and thus sufficient time between the trays containing the bags or other containers being scanned for the curtains to be pushed up, and then fall back down.
So, in general, with older X-ray security inspection systems involving a combination of low X-ray power and low pallet throughput, a modest amount of a lead-containing curtain can adequately attenuate the appropriate amount of scattered X-rays emitted into the entering and exiting tunnels from the bags or other containers carried by the pallet.
However, over the past few years, it has become apparent to those responsible for airport security that the effectiveness of these older X-ray security inspection systems is very inadequate. In response, companies began designing Computed Tomography (CT) security inspection systems. Such CT security inspection systems are intended to have throughput rates of approximately 600 trays per hour (i.e., 600 bags or other containers per hour). These CT security inspection systems, which make many X-ray projections (e.g., 1000 or more projections per rotation of the CT machine), must use higher power (typically 5-8mA at 160 kV) X-rays, and also use approximately 24 rows of projections simultaneously. As a result, the power of scattered X-rays from CT security inspection systems is almost 100 times higher than the power of scattered X-rays from older X-ray security inspection systems, and it has become clear that practical solutions need to be found to reduce the scattered X-rays emanating from the tunnel into and out of CT security inspection systems.
First, the problem appears to be solved by simply adding more leaded curtains at the entry and exit tunnels of the CT security inspection system. However, this is not the case. To understand the importance of the problem, it is considered necessary to reduce the level of scattered X-rays emanating from the entrance and exit tunnels to 1/30,000, rather than the previous requirement of approximately 1/300, because CT security inspection systems produce nearly one hundred times as many scattered X-rays as older X-ray security inspection systems. It is noted that a curtain with a lead equivalent of 0.5mm lead thickness attenuates scattered X-rays to 1/5.5. For four curtains, the factor is raised to the fourth power, which results in an attenuation of approximately 915:1, which is much more attenuated than is sufficient for older X-ray security inspection systems. That is, only four curtains of 0.5mm lead equivalent are spent shielding the older X-ray security inspection system sufficiently from entering and exiting the tunnel, but at least six such curtains are spent "fully down" to produce the 30,000:1 attenuation required by the CT security inspection system. Additionally, at the high throughput speeds of CT security inspection systems, where the tray is almost always disposed under (and displaces) some curtains, it takes more than six installed curtains to provide at least six "full down" curtains at any given time. However, if this larger number of leaded curtains is installed at the entry and exit tunnels of the CT security inspection system, the leaded curtains must be closer to each other (since the length of the entry and exit tunnels is generally severely constrained by the available space of the CT security inspection system), and this leads to a double problem: (i) must push the tray harder to lift more curtains, and (ii) the curtains do not reach "full down" until after the entire tray has passed the curtains slightly more than at least an additional distance of around 30cm (which is a function of the height of the tray and the bag or container etc. loaded in the tray). Therefore, simply adding more curtains does not work at all for the higher throughput rates of CT security inspection systems.
See fig. 1-5, which illustrate how a lead-containing curtain does not reach "full down" at the higher throughput rates of CT security inspection systems.
More particularly, fig. 1-5 illustrate an exemplary prior art CT
At a throughput rate of 600 trays per hour (i.e., one tray per six seconds), and with the
Another approach proposed for attenuating X-rays exiting the entry and exit tunnels of a CT security inspection system is to make the entry and exit tunnels longer so that the lead-containing curtains can be spaced farther apart. In theory, this approach may give curtain time to reach "full down" between successive pallets, but in practice it requires entry and exit tunnels that are excessively longer than generally allowed by the space constraints present at airports and other security sensitive locations.
Another approach to attenuating X-rays exiting a tunnel and entering a CT security inspection system is described in U.S. patent application publication No. US 2016/0372223A 1. The method of U.S. patent application publication No. US2016/0372223 a1 uses a rotating curtain between successive trays. However, in practice, this method does not work because the rotating curtain needs to be precisely synchronized with the tray movement in order to quickly drop between the upcoming trays. In addition, this approach does not work at the higher expected throughput rates of newer CT security inspection systems because it is difficult to have enough curtains fully down between trays to provide the required level of X-ray attenuation.
Still another proposed method is to provide multiple curtains on a roller that moves rapidly up and down between successive trays. In addition to the engineering complexity and power requirements required to move the curtain up and down fast enough, such an approach is prohibitively expensive, adding a significant cost per entry and exit tunnel.
Yet another proposed approach is to build a complex tool that will open the entry tunnel for a short period of time, push the tray quickly to scan, reverse the process at the exit tunnel, and then repeat the process for the next tray. While theoretically possible, the difficulty, reliability and power required by such complex systems has been found to be impractical.
Yet another approach may be to significantly accelerate the speed of the conveyor belt through the system for a given desired throughput rate. This method will allow the trays to pass through the system faster, with more space between successive trays, so that the lead-containing curtains entering and leaving the tunnel will have time to fall down between successive trays. However, to achieve the same image quality at this higher throughput speed, a proportionally higher power X-ray source is required, or alternatively, a significantly greater number of detector rows, or both, and it is required to accelerate the rotational speed of the gantry carrying the X-ray source of the CT scanner. Thus, this approach adds significant cost and increases the power requirements of the system (which is generally not available at airports and other security sensitive locations where CT security inspection systems must be installed).
Accordingly, there is a need for new and improved Computed Tomography (CT) security inspection systems with increased X-ray shielding.
Disclosure of Invention
The present invention includes the provision and use of a new and improved Computed Tomography (CT) security inspection system with enhanced X-ray shielding.
In a preferred form of the present invention, there is provided a method for scanning an object in an X-ray security inspection system, wherein the X-ray security inspection system comprises an entrance tunnel equipped with a radiation shielding curtain, an X-ray section, and an exit tunnel equipped with a radiation shielding curtain, the method comprising:
passing the objects into the tunnel at a first velocity rate and with a first degree of separation between successive objects;
passing the objects through the X-ray portion at a second velocity rate and with a second degree of separation between successive objects; and
passing the objects through the exit tunnel at a third speed rate and with a third degree of separation between successive objects;
wherein the second velocity rate is less than the first velocity rate and the third velocity rate, and wherein the second degree of separation between the successive objects is less than the first degree of separation between the successive objects and the third degree of separation between the successive objects.
In another preferred form of the invention, there is provided apparatus for scanning an object, the apparatus comprising:
an X-ray security inspection system, wherein the X-ray security inspection system comprises an entrance tunnel equipped with a radiation shield, an X-ray section, and an exit tunnel equipped with a curtain of radiation shield;
means for passing the objects into the tunnel at a first velocity rate and with a first degree of separation between successive objects;
means for passing the objects through the X-ray portion at a second velocity rate and with a second degree of separation between successive objects; and
means for passing the objects through the exit tunnel at a third speed rate and with a third degree of separation between successive objects;
wherein the second velocity rate is less than the first velocity rate and the third velocity rate, and wherein the second degree of separation between the successive objects is less than the first degree of separation between the successive objects and the third degree of separation between the successive objects.
Drawings
These and other objects and features of this invention will be more fully disclosed in or made apparent from the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings, in which like numbers refer to like parts, and in which:
1-5 are schematic diagrams illustrating how prior art CT security inspection systems do not allow a sufficient amount of a lead-containing curtain to reach its "fully down" position in entering and exiting a tunnel to provide adequate X-ray shielding; and
6-11 are schematic diagrams illustrating how the present invention enables a sufficient amount of a lead-containing curtain to reach its "fully down" position in entering and exiting a tunnel to provide adequate X-ray shielding for a CT security inspection system.
Detailed Description
The present invention includes the provision and use of a new and improved Computed Tomography (CT) security inspection system with enhanced X-ray shielding.
More particularly, to further understand the X-ray shielding problems associated with prior art Computed Tomography (CT) security inspection systems, and to fully understand the new solution to this problem provided by the present invention, it should first be recognized that the standard pallet length in the united states is approximately 60cm (approximately two feet) and in europe is approximately 70 cm. As a practical example, it is generally desirable to have CT security inspection systems operate at 600 trays per hour. This is one tray every six seconds. Then, at 600 trays per hour, the distance between successive trays will be as follows for various conveyor speeds.
Conveyor speed
Tray spacing (6 seconds per tray)
Average spacing between trays in the United states
Average spacing between europeans
At 15cm per second
90cm
30cm
20cm
At 17.5cm per second
105cm
45cm
35cm
At 20cm per second
120cm
60cm
50cm
At 22.5cm per second
135cm
75cm
65cm
At 25cm per second
150cm
90cm
75cm
At 27.5cm per second
165cm
105cm
90cm
It should also be appreciated that in a practical sense, conveyor speed is limited by a combination of factors, i.e., X-ray power, CT rotational speed, detector coverage in the direction of conveyor motion, and system pitch (which is defined as the ratio of the advance of the tray under scrutiny per revolution of the gantry containing the X-ray source divided by the effective length of the detector in the direction of conveyor motion). In practice, X-ray power is generally limited by the power available at secure locations in airports; the rotational speed is generally limited by the permitted g-forces of the equipment and the power available to rotate the gantry; detector length is limited by cost; and the pitch is limited by the quality of the resulting image.
In view of the foregoing limitations, in practice, conveyor speeds through CT machines are limited to approximately 15cm per second in order to achieve acceptable image quality. A conveyor speed of 15cm per second (with a system throughput of 600 trays per hour) yields a tray spacing of 90cm between the start of successive trays (i.e., one tray per 6 seconds on a conveyor belt moving 15cm per second yields a tray spacing of 90cm between the start of successive trays). This implies a spacing of 30cm (90 cm-60cm =30 cm) between the trays in the united states and 20cm (90 cm-70cm =20 cm) between the trays in europe. Initially, it may be desirable to provide sufficient X-ray shielding at the entry and exit tunnels by having enough curtains drop down in the spaces between the trays to provide sufficient X-ray shielding, but this has not proven to be the case because when the tray (and its contents) pushes the curtains upward, the curtains do not return to their "fully down" position until the tray has moved more than 30cm beyond the point where the curtains hang. See fig. 1-5 and the discussion above in the section entitled "background of the invention".
Thus, a value (equivalent tray length or ETL) can be defined that is equal to the length of the tray plus the additional distance required for the curtain to return to its "fully down" position. In practice, at a throughput rate of 600 trays per hour, the ETL is the sum of the tray length (e.g., 60 cm) plus a distance greater than 30cm, i.e., a distance greater than 90 cm.
In other words, in order for there to be sufficient clearance between successive trays for the lead-containing curtains to reach their "fully down" position between successive trays, the input conveyor must move significantly faster than 15cm per second when the trays are placed on the input conveyor at a rate of one tray per 6 seconds (i.e., at a throughput of 600 trays per hour).
This provides insight into the problems as a prior art CT security inspection system: at 600 trays per hour, running at a belt speed of 15cm per second, the lead-containing curtains never have sufficient time to return to their "fully down" position between the trays. In fact, even a single curtain, after being lifted upwards by a tray moving at 15cm, cannot return to its "fully down" position, since the rear tray engages the curtain just as it is about to reach its "fully down" position. Thus, in the case of prior art CT security inspection systems operating at 600 trays per hour, at conveyor speeds of 15cm per second, it is not possible to provide the necessary X-ray attenuation.
The present invention recognizes that for the reasons previously enumerated and discussed above, there is an upper limit to the rate at which trays can pass through the X-ray portion of the system for each system, and that the trays cannot pass into and out of the tunnel at a rate such that the spacing between successive trays is less than the Equivalent Tray Length (ETL). In other words, the present invention recognizes that trays cannot pass through the X-ray portion of the system faster than 15cm per second, and that the present invention recognizes that trays cannot pass into and out of the tunnel at a speed that provides a spacing between successive trays that is less than the Equivalent Tray Length (ETL), which is a distance greater than 90 cm.
The present invention solves these problems in a new manner by providing a high speed CT security inspection system that moves trays through an entrance and exit tunnel at a significantly faster rate than they move through the X-ray portion of the system, thereby providing sufficient scanned image quality while also achieving enhanced X-ray shielding. In a preferred form of the invention this is achieved by providing three separate conveyor belts (i.e. one through the entry tunnel, one through the exit tunnel and one through the X-ray section of the system) and operating the entry and exit conveyor belts at a higher speed rate than the speed rate of the conveyor belts through the X-ray section of the system.
More particularly, in a preferred form of the invention, the speed rate of entry into and exit from the conveyor belt is set high enough to provide sufficient spacing between successive trays to allow time for the lead containing curtains to return to their "fully down" position between successive trays, and the speed rate of the conveyor belt through the X-ray portion of the system is set low enough to enable the required image quality to be achieved. In addition, the speed rate(s) of entry and exit conveyor belts are coordinated with the speed rate of the conveyor belts through the X-ray portion of the system to provide a continuous flow of trays at a desired throughput rate.
By way of example and not limitation, where the throughput rate of the system is 600 trays per hour (i.e., one tray per six seconds), with an X-ray conveyor speed of 15cm per second (a typical speed to achieve the required image quality), one tray per six seconds passes along the X-ray conveyor, meaning that there is a 30cm spacing between trays on the X-ray conveyor (i.e., a belt speed of 15cm per second and one tray per six seconds equals 90cm between trays, and where each tray has a length of 60cm, which results in a 30cm spacing between trays).
Depending on the length allowed for entry and exit of the tunnel (nominally 3-5 feet), which determines the spacing between the lead containing curtains, the conveyor speed entering the tunnel and the conveyor speed exiting the tunnel may be in the vicinity of 22cm per second, meaning that there is a 72cm gap between the trays on the entry and exit conveyors (i.e., a belt speed of 22cm per second and one tray per six seconds equals 132cm between trays, and where each tray has a length of 60cm, which results in a spacing of 72cm between trays). This spacing allows the lead-containing curtains entering and exiting the tunnel to return to their "fully down" position between the trays.
Thus, with the present invention, the entrance and exit conveyors are run at a higher speed rate than the speed rate of the conveyors through the X-ray portion of the system, and the spacing between trays in the entrance and exit tunnels is greater than the spacing between trays in the scanning portion of the system.
Depending on the actual length of entry and exit from the tunnel, the distribution between the lead-containing curtains may be optimally spaced, as long as the lead equivalents have on average six 0.5mm lead equivalent curtains in their "fully down" position. As one example, if the total available tunnel length into and out of the tunnel is about 4 or 5 feet, there may be five or six 0.5mm lead equivalent curtains appropriately spaced in each tunnel.
An inventive solution to the problem is therefore to move the trays through the entry tunnel at a first speed rate (e.g. 22-27cm per second), then decelerate them so that they move through the X-ray scanning section at a second, slower speed rate (e.g. 15cm per second), and then move through the exit tunnel at a third speed rate (e.g. 22-27cm per second) which is higher than the second speed rate.
Note that the velocity rate of entry into the conveyor (and the spacing between successive trays on entry into the conveyor) may, but need not, be the same as the velocity rate of exit from the conveyor (and the spacing between successive trays on exit from the conveyor). In fact, they may have different speed rates (and different spacings between successive trays). What is needed is: (i) the throughput out of the carousel must be equal to the throughput into the carousel (and the throughput into and out of the carousel must be equal to the throughput of the scanning carousel); (ii) the speed rate of entry and exit from the conveyor must be high enough to permit a sufficient number of lead containing curtains to fall back between successive pallets to their "fully down" position; and (iii) the speed rate of the conveyor belt through the scanning section must be low enough to achieve sufficient image quality.
In one preferred form of the present invention, and referring now to FIGS. 6-11, a novel CT
In accordance with the present invention, the
If desired, the lead-containing curtain of the new CT security inspection system may be replaced with a radiation-shielding curtain utilizing other X-ray blocking materials (e.g., tungsten, barium, etc.).
Also, if desired, the
In addition to the foregoing, the present invention preferably incorporates features that make it easier for the tray (or other such entity under test) to lift the lead-containing curtain upward. These features may include one or more of the following: (i) vertically placing one or more flexible hinges on top or inside each lead-containing curtain, (ii) appropriately staggering the lead-containing curtains (or vertical subassemblies of lead-containing curtains), and (iii) optimally varying the combination and pattern of lead-containing curtains, such as their spacing or hierarchical distribution weights.
Modifications of the preferred embodiment
It will be appreciated that numerous additional changes in the details, materials, steps, and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art while still remaining within the principle and scope of the invention.