Closed X-ray chopper wheel

Abstract

A chopper wheel assembly includes a collimator configured to narrow an X-ray beam. The chopper wheel has a plane configured to face the collimator direction, and a housing configured to receive the chopper wheel. The chopper wheel includes a central axis, a plurality of slits in the plane, a first protrusion extending from the plane in the collimator direction, and a second protrusion extending from the plane in the collimator direction. The slits extend radially outward relative to the central axis. The first protrusion is located radially outside the plurality of slits, and the second protrusion is located radially inside the plurality of slits. Each protrusion is arranged around the central axis for 360 degrees. The housing includes an inner wall which, when the chopper wheel is received in the housing, includes a first groove configured to receive the first protrusion and a second groove configured to receive the second protrusion.

Description

Background of the Invention

[0001] 1. Field of the Invention

[0002] The present invention generally relates to x-ray backscatter instruments. More particularly, at least one embodiment relates to an x-ray backscatter instrument having an enclosed chopper wheel.

[0003] 2. Related technical discussions

[0004] Backscatter X-ray imaging is often used in security screening to detect contraband located in hidden areas, such as behind solid metal panels in the body of a car or truck. Generally, this method involves an instrument that directs a relatively narrow beam of X-rays at a solid surface. The X-ray energy passes through the surface and reflects or scatters off any items on the far side of the surface. The instrument creates an image of the item using the X-rays reflected or scattered from the item.

[0005] X-ray backscatter instruments include shielding to improve the safety of the instrument operator and those near the instrument while in use. Early X-ray backscatter instruments were typically large, heavy units that were mounted in a fixed location or moved on a wheeled cart. However, today’s instruments are often available in a portable, handheld format. These handheld instruments present additional challenges for shielding because the operator is in close proximity to the instrument while it is generating X-ray energy.

[0006] Typically, an X-ray backscatter instrument includes an X-ray source, a collimator for narrowing the X-ray beam generated by the X-ray source, and a chopper wheel housed in a housing. These are light source components that focus the X-rays generated by an electron tube into a beam that can be used for scanning. The housing is made of a material known to provide X-ray shielding. When the instrument generates X-ray energy, a drive motor is coupled to the chopper wheel to rotate the chopper wheel. The chopper wheel includes a set of slits for generating a smaller "pencil beam" of X-ray energy from the X-ray energy received by the collimator. Typically, four slits are positioned around the chopper wheel at ninety degree intervals.

[0007] In practice, it is impractical to construct an X-ray backscatter instrument with sufficient shielding to completely eliminate X-ray energy escaping from the instrument. Instead, the instrument should be designed to comply with OSHA regulations, which permit an operator to use an X-ray instrument provided that the operator is not exposed to more than an established safety threshold of X-ray energy in a given period of time. In some cases, regulations permit operations with exposures greater than the stated threshold, but only if the individual has completed certified radiation training.

[0008] Referring now to FIG. 1, which shows a cross-section of a chopper wheel assembly 100 according to the prior art. The assembly 100 includes a collimator 120, a chopper wheel 122, a housing 124, and a motor 126 including a hub 132. The chopper wheel 122 includes a source-side surface 128. The housing 124 includes an inner surface 130, a source-side X-ray opening 134, and a target-side X-ray opening 136. The motor 126 is connected to the chopper wheel 122 at the hub 132. The cross-sectional view shows the rotational angle of the chopper wheel at which none of four slits (not shown) are positioned adjacent to the source-side X-ray opening 134 and the target-side X-ray opening 136.

[0009] In operation, X-ray energy is provided by an X-ray source (not shown) located to the left of the chopper wheel assembly 100. The X-ray energy is directed to the collimator 120, which is used to narrow the X-rays directed to the chopper wheel 122. The beam reaches the chopper wheel 122 through the source-side opening 134. The chopper wheel 122 rotates at a speed such that during a known time period of each rotation of the device, one of the slits is at least partially aligned with the source-side opening 134 while being aligned with the target-side opening 136. When the slit is at least partially aligned with the openings 134, 136, the collimated beam enters the source-side opening 134, passes through the slit, and exits the housing 124 through the target-side opening 136.

[0010] The size of the slit is relatively small when compared to the total surface area of the solid regions of the chopper wheel 122. As a result, for most of each rotation of the chopper wheel 122, the solid regions of the chopper wheel 122 are located between the source-side opening 134 and the target-side opening 136. When the solid region of the chopper wheel 122 rotates in front of the source-side opening 134, X-ray energy is scattered from a portion of the chopper wheel 122. The X-rays are scattered in an isotropic manner from the inner surface 130 into the region between the source-side surface 128 and the inner surface 130. Thus, the scattered X-ray energy can propagate in a range from a direction perpendicular to the source-side surface 128 to a direction substantially parallel to the source-side surface 128. That is, the X-ray energy can radially outwardly propagate in the region between the planar source-side surface 128 and the planar inner surface 130, such that the energy is directed to the outer radius of the housing.

[0011] Tungsten and tungsten alloys are common shielding materials because they have a high density, good machinability, and desirable X-ray shielding properties due to the relatively high atomic number of tungsten. However, tungsten is an expensive specialty metal. Nevertheless, existing methods typically fabricate the housing 124 from tungsten or tungsten alloys because they can effectively shield a large amount of X-ray energy scattered from the chopper wheel. SUMMARY OF THE INVENTION

[0012] Accordingly, there is a need to provide an apparatus, system, and method for a closed chopper wheel design that reduces the scattered X-ray energy reaching the chopper wheel housing to allow more common materials to provide the chopper wheel housing. According to some embodiments, the chopper wheel and associated housing include structural features providing a labyrinth design that increases the X-ray energy attenuation of X-rays scattered from the chopper wheel before the X-ray energy reaches the housing of the chopper wheel. In some embodiments, protrusions located at radially inner and outer positions on the chopper wheel are received by grooves in the chopper wheel housing. In one embodiment, the chopper wheel and integral protrusions are made of tungsten or a tungsten alloy. According to the embodiment, the chopper wheel provides unitary attenuation such that the housing is made of brass or another material having an atomic number lower than tungsten while still substantially reducing the X-ray energy transmitted outside the housing.

[0013] According to one aspect, there is provided a chopper wheel assembly configured to be used with an X-ray energy source. The chopper wheel assembly includes a collimator configured to narrow an X-ray beam generated by the X-ray energy source; a chopper wheel having a plane configured to face the direction of the collimator; and a housing including a hollow interior region configured to receive the chopper wheel. According to one embodiment, the chopper wheel includes a central axis, a plurality of slits in the plane, a first protrusion extending from the plane in the direction of the collimator, and a second protrusion extending from the plane in the direction of the collimator. In a further embodiment, the slits extend radially outwardly relative to the central axis, the first protrusion is located radially outside the plurality of slits and is provided to surround the central axis 360 degrees, and the second protrusion is located radially inside the plurality of slits and is provided to surround the central axis 360 degrees. Additionally, the housing includes an inner wall facing the chopper wheel and away from the direction of the collimator, and when the chopper wheel is received in the housing, the inner wall includes a first groove configured to receive the first protrusion and a second groove configured to receive the second protrusion.

[0014] According to another aspect, a handheld backscatter X-ray imaging system includes an outer housing having a plurality of handles, a display screen located within the outer housing and viewable with the system held by the plurality of handles, an X-ray energy source configured to generate an X-ray beam, a collimator configured to narrow the X-ray beam, and a chopper wheel having a configuration facing the direction of the collimator. According to one embodiment, the display screen is configured to display X-ray images and the X-ray energy source is located within the outer housing. According to another embodiment, the chopper wheel includes a central axis, a plurality of slits radially extending outward relative to the central axis through the chopper wheel, a first protrusion extending from a surface in the direction of the collimator, and a second protrusion extending from a plane in the direction of the collimator, the first protrusion being located radially outside the plurality of slits and disposed 360 degrees around the central axis, the second protrusion being located radially inside the plurality of slits and disposed 360 degrees around the central axis. According to an alternative embodiment, the handheld backscatter X-ray imaging system includes an outer housing that provides only one handle, for example, in a housing having an outer shape similar to a radar gun.

[0015] According to yet another aspect, a method is provided for generating attenuated X-ray energy during operation of a backscatter imaging system configured to generate a collimated beam of X-ray energy. According to one embodiment, the method provides a chopper wheel including an inner edge and an outer edge, the chopper wheel being configured to rotate in a plane to periodically interrupt an X-ray energy collimated beam oriented substantially perpendicular to the plane, creating an interruption in the scattered X-ray energy in a direction including substantially parallel to the plane of the chopper wheel; enclosing the chopper wheel within a housing with a gap left between the chopper wheel and an inner surface of the housing, the gap being substantially parallel to the plane of the chopper wheel; including a first protrusion at the outer edge of the chopper wheel that extends into the gap in a direction perpendicular to the plane, and including a second protrusion at the inner edge of the chopper wheel that extends into the gap in a direction perpendicular to the plane. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in each figure is represented by the same numeral. For clarity, not every component is labeled in every figure. In the drawings:

[0017] FIG. 1 shows elements included in an X-ray backscatter instrument according to the prior art;

[0018] Figure 2 An isometric view of a chopper wheel assembly according to one embodiment is shown;

[0019] Figure 3 An isometric view of a chopper wheel assembly according to one embodiment is shown;Figure 2 Exploded view of the chopper wheel assembly;

[0020] Figure 4 Shows a Figure 2 Cross-sectional view of the chopper wheel assembly according to one embodiment, the cross-section being in a vertical plane passing through the center of the chopper wheel assembly; and

[0021] Figure 5 Shows a Figure 4 Cross-sectional view of the removal of the chopper wheel according to one embodiment. DETAILED DESCRIPTION

[0022] The present invention is not limited to the application of the construction and arrangement details of the components shown in the following description or drawings. The present invention can be implemented or practiced in other embodiments and in various ways. In addition, the wording and terms used herein are for the purpose of description and should not be considered limiting. The use of "including", "comprising", "having", "containing", "involving" and their variants herein is intended to include the items listed hereinafter and their equivalents as well as additional items.

[0023] Now refer to Figure 2 , which shows a chopper wheel assembly 200 according to some embodiments. The chopper wheel assembly 200 includes a housing 240, a drive motor 245, and a pre-collimator 247. The housing 240 includes a source-side housing 249 and a target-side housing 251. The pre-collimator 247 includes a source-side opening 253. The chopper wheel is located within the housing 240, as described below and Figure 3 shown. In some embodiments, the chopper wheel assembly 200 is included in a handheld backscatter instrument. The instrument also includes an X-ray source, including an X-ray anode. In operation, the output of the X-ray source is directed to the source-side opening 253, where X-ray energy enters the pre-collimator 247 and is then directed into the housing 240.

[0024] According to the illustrated embodiment, the housing 240 is assembled by fastening the source-side housing 249 to the target-side housing 251 using fasteners, such as screws, bolts, or other fastening hardware. The housing 240 can be made of any of a variety of metals that are at least somewhat effective in blocking X-ray energy to provide shielding. According to some embodiments, the housing 240 is made of brass. Advantages of using brass compared to tungsten include lower cost and lighter weight. As described in more detail below, various embodiments of the chopper wheel assembly 200 include adding to the chopper wheel to increase the overall effectiveness of the shielding without the need to manufacture the housing 240 from a more expensive and higher atomic number material, such as tungsten.

[0025] According to the illustrated embodiment, the pre - collimator 247 is connected to the outer surface of the source - side housing 249. The pre - collimator also needs to be made of a material that provides shielding. According to various embodiments, the pre - collimator 247 is made of tungsten or a tungsten alloy.

[0026] According to some embodiments, the motor 245 is a brushless DC motor. In one embodiment, the motor is a Maxon EC32 FL.

[0027] Now refer to Figure 3 which shows a Figure 2 exploded view of the chopper wheel assembly 200. The exploded view shows the chopper wheel 241, the hub 243, and the linear collimator 255 located in the housing 240 when the chopper wheel assembly 200 is fully assembled. The chopper wheel 241 has an integral annular shape defined by an inner circumference 246 and an outer circumference 248. The inner circumference 246 defines an opening 250 having a diameter D1 (as Figure 4 shown) in the central region of the chopper wheel 248. The hub 243 includes a solid disk - like shape and a central opening 252. The outer diameter of the hub 243 is sized such that the hub 243 is located within the opening 250 and is connected to the chopper wheel 241 at the inner circumference 246. The central opening 252 is sized to receive the shaft included in the motor 245. In operation, the motor 245 drives the hub 243 to rotate the hub 243 and the chopper wheel 241.

[0028] The linear collimator 255 is used to further shape the X - ray energy beam after the X - ray energy beam enters the housing 240 and before it reaches the chopper wheel 241. According to the illustrated embodiment, the linear collimator 255 is fixed within an opening in the source - side housing 249 such that it is aligned with the pre - collimator 247. According to another embodiment, the linear collimator 255 is connected to the inner surface of the source - side housing 249. The linear collimator 255 also needs to be made of a material that provides shielding. According to various embodiments, the linear collimator 255 is made of tungsten or a tungsten alloy.

[0029] A plurality of slits 242 are located within the chopper wheel 241. According to the illustrated embodiment, the slits 242 are spaced at 90 - degree intervals and extend radially for most of the distance between the inner circumference 246 and the outer circumference 248 of the chopper wheel 241.

[0030] The chopper wheel includes internal protrusions 254 and external protrusions 256 extending from the chopper wheel 241. Each protrusion 254, 256 extends axially from the surface in the direction of the source - side housing 249. In the illustrated embodiment, the internal protrusions 254 are located near the inner circumference 246 of the chopper wheel 241, and the external protrusions 256 are located near the outer circumference 248 of the chopper wheel 241, each being disposed 360 degrees around the axis of the chopper wheel 241.

[0031] Referring now to Figure 4 , a cross-sectional view of a chopper wheel assembly 200 according to one embodiment is shown. Figure 4 A first diameter D1 and a second diameter D2 are shown. According to the embodiment shown, the second diameter D2 is the outer diameter of the chopper wheel 241. The cross-sectional view shows a flat surface 258 on the source side of the chopper wheel 241. The inner protrusions 254 and the outer protrusions 256 extend substantially perpendicular to the flat surface 258 in the direction of the source-side housing 249. The inner protrusions 254 define the inner edge of the chopper wheel 241, and the outer protrusions 256 define the outer edge of the chopper wheel 241.

[0032] Figure 4 The inner surface 260 of the source-side housing 249 is also shown. The inner surface 260 is provided with an inner groove 262 and an outer groove 264. According to the embodiment shown, the grooves 262, 264 have a circular shape extending 360 degrees around the axis A. The inner groove 262 is located at a first radius relative to the axis A. The outer groove 264 is located at a second radius relative to the axis A, and the second radius is greater than the first radius. The inner groove 262 is positioned such that it aligns with the inner protrusions 254. Similarly, the outer groove 264 is positioned such that it aligns with the outer protrusions 256. That is, the inner protrusions 254 are located at the same radius as the inner groove 262, and the outer protrusions 256 are located at the same radius as the outer groove 264.

[0033] The housing 240 also includes a source-side opening 266 and a target-side opening 268. According to the embodiment shown, the pre-collimator 247 is aligned in the source-side opening 266, and the line collimator 255 is aligned with the target-side opening 268. As Figure 4 shown, the chopper wheel is at the point where it rotates about the axis A such that none of the plurality of slits 242 are in the plane of the cross-section. At this stage of the chopper wheel rotation, the path of the X-ray energy is blocked between the pre-collimator 247 and the line collimator 255, that is, blocked between the source-side opening 266 and the target-side opening 268.

[0034] Referring now to Figure 5 , a cross-sectional view of the removal of the chopper wheel assembly 200 according to one embodiment is shown. Figure 5 The inner surface 260 located on the source-side inner wall of the housing 240 is shown. According to the embodiment shown, the inner surface 260 includes a generally planar region that rises as the radial distance from the axis A increases. In one embodiment, the grooves 262, 264 are machined into the planar region at each of the first radius and the second radius. As Figure 4As shown, the inner recess 262 and the outer recess 264 are sized and positioned to accommodate the inner protrusion 254 and the outer protrusion 256 in the fully assembled chopper wheel assembly 200.

[0035] Referring again to Figure 4 , the gap 270 extends in an overall radially upward direction from near the axis A to the outer edge of the housing 240. However, when the chopper wheel assembly 200 is assembled, the gap 270 extends axially and is adjacent to the inner protrusion 254 and the outer protrusion 256. This geometry effectively provides an obstacle throughout the radial path of the gap 270. In various embodiments, the protrusions 254, 256 are machined as an integral part of the chopper wheel 241. Thus, the protrusions 254, 256 are made of tungsten or a tungsten alloy. The position and the material of manufacture of the protrusions 254, 256 provide an additional 360-degree shielding around the axis A throughout the radial path of the gap 270. Additionally, the two included protrusions provide shielding at the inner and outer diameters of the chopper wheel 241. Thus, the flat surface 258 of the chopper wheel 241 is supported such that X-ray energy scattered from the surface 258 is attenuated whether it scatters radially inward or radially outward.

[0036] For example, in operation, X-ray energy is scattered from the flat surface 258 of the chopper wheel 241. Some of the scattered energy propagates substantially parallel to the flat surface 258, e.g., in the region defining the gap 270. The X-ray energy propagates without attenuation in a radially outward direction within the gap 270 until it hits the outer protrusion 256. Similarly, some X-ray energy propagates without attenuation in a radially inward direction within the gap 270 until it hits the inner protrusion 254. Thus, the embodiments described herein provide a labyrinth design that adds structure in the chopper wheel to further attenuate X-ray energy. In combination with the grooves provided in the housing, the scattered X-ray energy must pass through additional channels

[0037] Although the foregoing has been described in the context of a handheld instrument, those of ordinary skill in the art will understand, in view of the present disclosure, that embodiments of the chopper wheel and the chopper wheel housing can be used in any of a variety of X-ray instruments, regardless of their size and portability. For example, a chopper wheel assembly including a chopper wheel having protrusions 254, 256 and a housing including grooves 262, 264 can be included in a large X-ray instrument designed for use at a fixed location or on a movable platform.

[0038] Accordingly, several aspects of at least one embodiment of the present invention have been described herein, and it should be understood that various changes, modifications, and improvements can be readily made by those skilled in the art. Such changes, modifications, and improvements are intended to be part of the present invention and within the spirit and scope thereof. Accordingly, the foregoing description and drawings are by way of example only.

Claims

1. A chopper wheel assembly configured to be used with an X-ray energy source, the chopper wheel assembly comprising: A collimator configured to narrow an X-ray beam generated by the X-ray energy source; A chopper wheel having a planar surface configured to face the collimator direction, a central axis, a plurality of slits in the planar surface, the slits extending radially outward relative to the central axis, a first protrusion extending from the planar surface in the collimator direction, the first protrusion being located radially outside the plurality of slits and arranged to surround the central axis by 360 degrees, a second protrusion extending from the planar surface in the collimator direction, the second protrusion being located radially inside the plurality of slits and arranged to surround the central axis by 360 degrees; and A housing including a hollow inner region configured to receive the chopper wheel, the housing including an inner wall facing the chopper wheel and away from the collimator direction, when the chopper wheel is received in the housing, the inner wall including a first groove configured to receive the first protrusion and a second groove configured to receive the second protrusion.

2. The chopper wheel assembly according to claim 1, wherein the housing is made of a material having an atomic number lower than tungsten.

3. The chopper wheel assembly according to claim 1, wherein the housing includes brass.

4. The chopper wheel assembly according to claim 1, wherein the inner wall includes a substantially flat region, and wherein the first groove and the second groove are located in the flat region.

5. The chopper wheel assembly according to claim 1, wherein the first protrusion defines an outer edge of the chopper wheel, and wherein the second protrusion defines an inner edge of the chopper wheel.

6. The chopper wheel assembly according to claim 5, further comprising a motor and a chopper wheel hub configured to be connected to the motor, wherein the chopper wheel defines a central opening, and wherein the hub is configured to be fixed within the central opening.

7. The chopper wheel assembly according to claim 5, wherein the inner wall includes a substantially flat region, and wherein the first groove and the second groove are located in the flat region.

8. A handheld backscatter X-ray imaging system, which comprises: An outer housing including a plurality of handles; A display screen located in the outer housing and visible when the system is held by the plurality of handles, the display screen being configured to display an X-ray image; An X-ray energy source configured to generate an X-ray beam, the X-ray energy source being located within the outer housing; A collimator configured to narrow the X-ray beam; and A chopper wheel having a surface configured to face the collimator direction, a central axis, a plurality of slits extending radially outward relative to the central axis through the chopper wheel, a first protrusion extending from the surface in the collimator direction, the first protrusion being located radially outside the plurality of slits and arranged to surround the central axis by 360 degrees, a second protrusion extending from the surface in the collimator direction, the second protrusion being located radially inside the plurality of slits and arranged to surround the central axis by 360 degrees.

9. The handheld backscatter X-ray imaging system according to claim 8, further comprising a chopper wheel housing located within the outer housing and configured to encapsulate the chopper wheel, wherein the chopper wheel housing is made of a material having an atomic number lower than tungsten.

10. The handheld backscatter X-ray imaging system according to claim 9, wherein the housing comprises brass.

11. The handheld backscatter X-ray imaging system according to claim 9, wherein the chopper wheel housing comprises a hollow interior region configured to receive the chopper wheel, the chopper wheel housing comprising an inner wall facing the chopper wheel and away from the collimator, and when the chopper wheel is received in the hollow interior region, the inner wall comprises a first groove configured to receive a first protrusion and a second groove configured to receive a second protrusion.

12. The handheld backscatter X-ray imaging system according to claim 11, wherein the inner wall comprises a substantially flat region, and wherein the first groove and the second groove are located in the flat region.

13. The handheld backscatter X-ray imaging system according to claim 8, wherein the first protrusion defines an outer edge of the chopper wheel, and wherein the second protrusion defines an inner edge of the chopper wheel.

14. The handheld backscatter X-ray imaging system according to claim 8, further comprising a motor and a chopper wheel hub configured to be connected to the motor, wherein the chopper wheel defines a central opening, and wherein the hub is configured to be fixed within the central opening.

15. A method of generating attenuated X-ray energy during operation of a backscatter imaging system configured to produce a collimated beam of X-ray energy, the method comprising: providing a chopper wheel including an inner edge and an outer edge, the chopper wheel configured to rotate in a plane to periodically interrupt a collimated beam of X-ray energy directed substantially perpendicular to the plane, the interruption producing scattered X-ray energy in a direction including substantially parallel to the plane of the chopper wheel; encapsulating the chopper wheel within a housing, leaving a gap between the chopper wheel and an inner surface of the housing, the gap being substantially parallel to the plane of the chopper wheel; including a first protrusion at the outer edge of the chopper wheel, the first protrusion extending into the gap in a direction perpendicular to the plane; and including a second protrusion at the inner edge of the chopper wheel, the second protrusion extending into the gap in a direction perpendicular to the plane.

16. The method according to claim 15, further comprising: including a first groove in the inner surface, the first groove being configured to receive the first protrusion when the chopper wheel rotates on the surface; and including a second groove in the inner surface, the second groove being configured to receive the second protrusion when the chopper wheel rotates on the surface.

17. The method according to claim 16, wherein the chopper wheel includes a central axis, and wherein the method comprising: setting the first protrusion 360 degrees around the central axis; and The second protrusion is arranged around the central axis by 360 degrees.

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