Patent Grant
11776706
X-ray backscatter imaging has been used for detecting concealed contraband, such as drugs, explosives, and weapons, since the late 1980s. Unlike traditional transmission x-ray imaging, which creates images by detecting the x-rays penetrating through an object, backscatter imaging uses reflected or scattered x-rays to create the image.
In example embodiment assemblies, a disk chopper wheel need not be enclosed in a full shielded housing. Instead, embodiments incorporate a novel, open-geometry disk chopper wheel that includes one or more scatter plates especially configured to limit x-ray leakage and greatly reduce the weight of the chopper disk assembly relative to prior art systems. Embodiments are designed with one or more scatter plates on a source side of the disk chopper wheel, and embodiments may also optionally include one or more scatter plates on an exit side of the disk chopper wheel. The scatter plates are designed to absorb x-rays that are scattered off the chopper wheel, either in the forward or backward directions. A shielded structure may also be added to enclose a fan beam entering the chopper wheel assembly in a region between an x-ray source (e.g., x-ray tube) and the disk assembly.
In one embodiment, an x-ray chopper wheel assembly includes a disk chopper wheel configured to rotate about a rotation axis thereof. The rotation axis is perpendicular to a rotation plane of the disk chopper wheel, and the disk chopper wheel has a solid cross-sectional area in the rotation plane and is configured to absorb x-ray radiation received from an x-ray source at a source side of the disk chopper wheel (an input side at which radiation from an x-ray source is initially incident). The disk chopper wheel also defines one or more radial slit openings configured to pass x-ray radiation from the source side of the disk chopper wheel to an output side of the disk chopper wheel
The x-ray chopper wheel assembly also includes a source-side scatter plate having a solid cross-sectional area in a plane parallel to the rotation plane of the disk chopper wheel. The source-side scatter plate is configured to absorb x-ray radiation and defines an open slot therein configured to pass x-ray radiation. The solid cross-sectional area of the source-side scatter plate is substantially smaller than the solid cross-sectional area of the disk chopper wheel. The assembly further includes a support structure configured to secure the source-side scatter plate substantially parallel to the rotation plane of the disk chopper wheel with a source-side gap between the source-side scatter plate and the source side of the disk chopper wheel.
The solid cross-sectional area of the source-side scatter plate in the plane parallel to the rotation plane of the disk chopper wheel may be less than 75%, less than 50%, less than 25%, or less than 10% of the cross-sectional area of the disk chopper wheel. The source-side gap may be in a range of approximately 0.5 mm to approximately 1.0 mm. The source-side scatter plate may be formed from tungsten or another high-Z material. The source-side scatter plate may have a thickness on the order of 1.0 mm. The cross-sectional area of the source-side scatter plate may be in a range of about 100% to about 5,000% larger or in a range of about 500% to about 10,000% larger than an open cross-sectional area of one of the one or more radial slit openings in the rotation plane of the disk chopper wheel.
The source-side scatter plate may have a plate width in a direction parallel to a radial direction of the disk chopper wheel, and this plate width may be in a range of about 10% to about 70% greater than a slit length of one of the one or more radial slit openings in the radial direction of the disk chopper wheel. The source-side scatter plate may be formed of pure or alloyed lead, tin, iron, or tungsten.
The assembly may further include an output-side scatter plate, which may have a solid cross-sectional area in a plane parallel to the rotation plane of the disk chopper wheel, with the output-side scatter plate configured to absorb x-ray radiation. The output-side scatter plate may define an open slot therein configured to pass x-ray radiation, and the solid cross-sectional area of the output-side scatter plate in the plane parallel to the rotation plane of the disk chopper wheel may be substantially smaller than the solid cross-sectional area of the disk.
The support structure may be further configured to secure the output-side scatter plate substantially parallel to the rotation plane of the disk chopper wheel with an output-side gap between the output-side scatter plate and the disk chopper wheel. The support structure may be further configured to secure the disk chopper wheel at the rotation axis thereof.
The support structure may include an inner portion configured to secure the disk chopper wheel at the rotation axis thereof, with one or more radial spokes extending from the inner portion and configured to secure the source-side scatter plate. The support structure may further include a source-side portion and an output-side portion, with the source-side and output-side portions configured to be connected together and to secure the disk chopper wheel therebetween. The support structure may be formed of aluminum. The support structure may be configured to be mounted within a handheld x-ray scanner or within a fixed-mount or mobile x-ray scanning system.
The x-ray chopper wheel assembly may further include a shield structure configured to enclose the x-ray radiation in a region of travel between the x-ray source and the source-side scatter plate.
The x-ray source may be configured to output x-rays having an end-point energy in a range of about 120 kiloelectron volts (keV) to about 450 keV.
The source-side scatter plate may be configured to output a fan beam of x-rays through the open slot therein, and the assembly may be configured to output a pencil beam of x-rays. The disk chopper wheel and source-side scatter plate may be arranged relative to each other to substantially confine x-ray radiation scattered therefrom. Substantial confinement may also be achieved based on an arrangement of the disk chopper wheel and source-side scatter plate with the optional output-side scatter plate.
The substantial confinement may limit leakage of scattered radiation to no more than 50% leakage of the radiation that is scattered or to a dose of no more than 5 milli-Rem per hour at a distance of 5 cm away from an outer surface of the assembly, whichever is greater. The substantial confinement may limit leakage of scattered radiation to no more than 10% of scattered radiation or to a dose of no more than 0.5 milli-Rem per hour at a distance of 5 cm away from the outer surface of the assembly, whichever is greater.
The foregoing will be apparent from the following more particular description of example embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments.
A description of example embodiments follows.
An x-ray tube has been used to generate x-rays that are collimated into a fan beam by a slot in an attenuating plate. The fan beam is then typically “chopped” into a pencil beam by a rotating “chopper wheel” with slits therein. As the chopper wheel rotates, the wheel slits rotate across the fan beam, causing the x-ray pencil beam to scan over an object being imaged.
For backscatter imaging, the intensity of the x-rays scattered in the backward direction is then recorded by one or more large area backscatter detectors as a function of the position of the illuminating, scanning pencil x-ray beam. By moving the object through the plane in which the x-ray pencil beam scans, either on a conveyor or under the object's own power, a two-dimensional backscatter image of the object is produced. Chopper wheels usually include three basic types: a rotating disk, a rotating wheel, or a rotating hoop rotated through the fan beam.
Existing x-ray backscatter imaging systems that implement a rotating disk chopper wheel also include a chopper wheel enclosure that completely contains the disk chopper wheel in a shielded housing, as described in relation to
The shielded housing typically includes an aluminum box, for example, that is lined internally with sufficient lead to absorb any x-rays that are incident directly upon it, as well as any x-rays that have scattered from the chopper disk. An entry slot is typically provided for the incident fan beam of x-rays emitted from the x-ray tube to enter the shielded housing. An exit slot is also provided in the housing to allow the sweeping pencil beam, created by the rotating disk chopper wheel, to exit the housing.
For a 120 kiloelectron Volt (keV) to 160 keV backscatter x-ray system designed for scanning baggage, for example, the shielding is typically between ⅛ inches thick and ¼ inch thick. For a chopper disk that is 18 inches in diameter, for example, the lead shielding in such a disk housing can, therefore, weigh between about 40 pounds and 80 pounds. Moreover, for a system with a 4 inch diameter disk, the shielding in such a system can weigh between about 3 pounds and about 6 pounds. It would be advantageous to have a way to reduce these relatively high weights. A reduction in weight and cost would be advantageous for all types of rotating disk x-ray scanning systems, including forward and backward scattering systems and fixed-mount and mobile x-ray scanning systems. Moreover, reducing the weight of the chopper disk and related assembly would be especially advantageous to the feasibility of developing and deploying handheld x-ray scanning systems. However, any possible weight-reduced system should also include a way to maintain the degree of x-ray scattering confinement and related safety of use that existing shielded housings provide.
Disclosed herein are embodiment x-ray chopper wheel assemblies that can provide scanning x-ray pencil beams while shielding and attenuating scattered x-rays to safe levels without the weight of existing shielded housings. Embodiments can provide radiation safety levels comparable to existing, full-shielded disk housings such as those described in connection with
As illustrated in
The chopper wheel assembly 100 of
The disk chopper wheel 101 is configured to rotate with a rotation 24 about a rotation axis that is perpendicular to a rotation plane of the disk chopper wheel. These details are further illustrated and described in connection with the specific embodiment shown in
The disk chopper wheel 101 has a solid cross-sectional area in the rotation plane, as further illustrated in
The source-side scatter plate 103 has a solid cross-sectional area in a plane that is parallel to the rotation plane of the disk chopper wheel, as further illustrated in connection with
Advantageously, in embodiments described herein, such as those in
The source-side scatter plate 103 may be formed of tungsten, another material having a high Z (atomic number), or an alloy of one of these materials, etc. The source-side scatter plate may have a thickness in certain embodiments on the order of 1.0 mm, for example. Thickness of the scatter plate is further illustrated in connection with
The cross-sectional area of the source-side scatter plate 103 may be in a range of about 100% to about 5,000% larger than an open cross-sectional area of one of the radial slit openings 121 in the disk chopper wheel, for example. An open cross-sectional area of one of the radial slit openings is further illustrated in connection with
While the assembly 100 of
The support structure 102 that secures the source-side scatter plate 103 may be advantageously formed of aluminum or another lightweight material. This is because the support structure 102 need not be relied upon for x-ray shielding or scattering confinement. Instead, the source-side scatter plate 103 (and in other embodiments, the output-side scatter plate) perform this function. Again, the limited size of the source-side scatter plate relative to the disk chopper wheel, together with the ability of other components such as the chopper wheel mount 105 and support structure 102 to be formed of lightweight materials, enable dramatically lower weight for various types of x-ray scanning systems, such as the handheld scanner 155 of
Embodiment x-ray assemblies may be used in systems using a wide range of x-ray energies. An x-ray source such as the x-ray tube 14 may be configured to output x-rays having an end-point energy in a range of about 120 kiloelectron volts (keV) to about 450 keV, for example. Furthermore, in other embodiments, this energy range may be between about 120 keV and about 160 keV, for example. In particular, handheld scanning systems, such as that of the scanner 155 of
In particular, in the embodiment of
A significant disadvantage of the arrangement of
A significant advantage of the embodiments illustrated in
The assembly 400 further includes a source-side scatter plate 403 that has a solid cross-sectional area in a plane parallel to the rotation plane of the wheel. This cross-sectional area is illustrated in
The source-side scatter plate 403 is secured by a support structure 402a-b that secures the source-side scatter plate substantially parallel to the rotation plane of the disk chopper wheel with a source-side gap between the source-side scatter plate and the source side of the disk chopper wheel, as further illustrated in
The output-side scatter plate 404 has a solid cross-sectional area in a plane parallel to the rotation plane of the disk chopper wheel, as illustrated in
In the embodiment assembly 400, the support structure 402a-b is further configured to secure the disk chopper wheel 401 at the rotation axis 440. Advantageously, therefore, the support structure 402a-b performs both the functions of securing the chopper wheel and the functions of securing the source-side and output-side scatter plates 403 and 404, respectively. Further, in the embodiment assembly 400, it will be noted that the support structure includes the two portions 402a and 402b on the source side and output side of the chopper wheel, respectively. This provides a particularly robust and stable configuration that performs many needed support functions. However, in other embodiments, such as in the assembly 100 illustrated in
Further in the embodiment assembly 400 in
The support structure 402a-b is formed of aluminum, advantageously, for lighter weight. In other embodiments, other materials may be used. Nonetheless, aluminum may be advantageously used because of cost, sufficient rigidity and strength, and because the source-side and output-side scatter plates provide the desired shielding, while the support structure need not be relied upon for x-ray shielding.
The assembly 400 further includes an optional shield structure 405 that is configured to enclose the x-ray radiation in a region of travel between the x-ray source (e.g., x-ray tube, not shown in
As also illustrated in greater detail in
As illustrated in
The output-side scatter plate 404 similarly has a thickness 570 and an output-side gap 552 between the scatter plate 404 and the output side 578 of the disk chopper wheel.
The source-side gap 550 may be in a range of approximately 0.5 mm to approximately 1.0 mm, for example. As this gap increases, leakage of scattered x-rays also increases, as illustrated in
As used herein, the source-side scatter plate 403 may be considered to be “substantially parallel” to the rotation plane of the chopper wheel when the source-side scatter plate and rotation plane of the disk chopper wheel are sufficiently parallel such that the chopper wheel may freely rotate without contacting the scatter plate 403. In a similar manner, the output-side scatter plate 404 may be considered to be “substantially parallel” to the chopper wheel 401 when the chopper wheel may freely rotate without risk of contact with the scatter plate 404. Where there is some degree of slight angle between either of the scatter plates and the rotation plane of the chopper wheel, the gap 550 or gap 552 may be considered to be the average distance between the plate 403 and the source side 576 of the disk chopper wheel or the average distance between the scatter plate 404 and the output side 578 of the disk chopper wheel.
In general, as the plate width increases, leakage of scattered x-rays decreases for a given gap. In general, greater scatter plate width relative to slit length of radial slits in the chopper wheel leads to greater confinement and less leakage of x-rays. The relationship is further illustrated in
Plate width is preferably greater than the lengths of radial slits in the chopper wheel, and the scatter plates all preferably fully overlap in cross section with the radial slits in the scatter plate, in order to enhance shielding. Nonetheless, it is also preferable for scatter plate width to be a small as possible in order to minimize total assembly weight. Accordingly, in example embodiments, as described above, the plate widths 588 and 589 may be in a range of about 10% to about 70% greater than a slit length of one of the radial slit openings. Furthermore, plate widths may be in other example ranges, such as about 5% to about 100%, about 10% to about 80%, about 20% to about 70%, about 30% to about 60%, or about 40% to about 50% greater than the slit length, depending on the plate gaps 550 and 552 and the desired maximum radiation leakage. In the context of plate widths, “about” as used herein denotes a tolerance of +/−5%.
The chopper wheel has a total area 786, which is the total cross-sectional area of solid portions of the chopper wheel, including solid portions of the inner hub 449 and of the outer disk 448 and excluding the open areas constituting the radial slits and excluding any other holes or openings introduced into the chopper wheel, such as holes in the inner hub 449 illustrated in
As described in connection with
As used herein, a solid cross-sectional area of the source-side scatter plate is “substantially smaller” than the solid cross-sectional area of the disk chopper wheel of an embodiment assembly when either the source-side plate width 588 or the source-side plate length 885 of the source-side scatter plate is smaller than the diameter 783 of the disk chopper wheel. In various embodiments, both the width 588 and length 885 of the source-side scatter plate may be smaller than the diameter 783 of the disk chopper wheel.
In some embodiments, the solid cross-sectional area of the source-side scatter plate may be smaller than a corresponding full enclosure would need to be in an enclosure width or length to enclose the chopper wheel fully. Further, in various embodiments, the source-side scatter plate may be smaller in weight than a corresponding full-shield enclosure would need to be to provide a comparable level of x-ray shielding. In various example embodiments, the solid cross-sectional area of the source-side scatter plate may be less than 90%, less than 70%, less than 50%, less than 40%, less than 30%, less than 25%, less than 15%, or less than 10% of the cross-sectional area 786 of the disk chopper wheel. Nonetheless, it is preferable for the solid cross-sectional area of the source-side scatter plate to be less than 50%, less than 25%, or less than 10% of the cross-sectional area 786 of the disk chopper wheel in order to reduce assembly weight the most and obtain maximum benefits of embodiment assemblies over the existing assembly in
The teachings of all patents, published applications and references cited herein are incorporated by reference in their entirety.
While example embodiments have been particularly shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the embodiments encompassed by the appended claims.
This application is a continuation of U.S. application Ser. No. 16/935,787, filed Jul. 22, 2020, which is a continuation of U.S. application Ser. No. 15/946,425, filed Apr. 5, 2018, now U.S. Pat. No. 10,770,195, which claims the benefit of U.S. Provisional Application No. 62/482,064, filed on Apr. 5, 2017. The entire teachings of the above applications are incorporated herein by reference.
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| Parent | 16935787 | Jul 2020 | US |
| Child | 17454993 | US | |
| Parent | 15946425 | Apr 2018 | US |
| Child | 16935787 | US |
