Visual light calibrator for an x-ray backscattering imaging system

An x-ray backscattering imaging system creating a backscatter image representing a structure is disclosed. The system includes a drum rotatable about an axis of rotation at a rotational speed, a radioactive source, a container, at least one collimator, at least one light emitting element, and a plurality of backscatter detectors. The radioactive source is connected to the drum and generates x-ray beams. The container houses the radioactive source and is constructed of a material that substantially blocks the x-ray beams generated by the radioactive source. The collimator is defined by the container and has a length and an aperture, where the collimator filters a stream of x-rays generated by the radioactive source such that the x-ray beams traveling substantially parallel with respect to the length of the collimator pass through the aperture. The light emitting element generates visible light and is positioned to direct the visible light into the collimator.

FIELD

The disclosed system relates to a calibrator for an x-ray backscattering imaging system and, more particularly, to an x-ray backscattering imaging system including a light emitting element for generating visible light parallel to and coincident with a stream of x-rays.

BACKGROUND

It is often necessary to inspect internal components of various types of objects, such as buildings, automobiles, containers, aircraft, or maritime vessels. Inspection of such structures and facilities by partial or complete disassembly of the structures to visually inspect internal components of interest may be impracticable. One technique for inspecting such components utilizes x-ray backscattering imaging systems. X-ray backscattering imaging systems provide an inspection process in which x-rays are reflected backwards from within the object or component of interest and recorded by a detector or detectors. X-ray backscattering imaging systems do not need to be powerful enough to transmit x-rays entirely through the component of interest and the surrounding components. Rather, partial penetration to a depth of interest is all that is required.

One specific type of backscattering imaging system includes a rotating drum, one or more collimators, and a radioactive source. Each collimator filters a stream of x-rays generated by the radioactive source. As the drum of the backscattering imaging system rotates during operation, the x-rays that are substantially parallel with respect to a corresponding collimator exit the collimator through a corresponding aperture. The x-rays that exit the aperture may be referred to as x-ray beams. The x-ray beams are then directed upon an object to be inspected by the backscattering imaging system.

The x-ray beams are aligned with one another in order to create a bright and uniform beam. If the backscattering imaging system includes multiple collimators, then x-ray flux exiting each of the apertures needs to be of an equal size and amount. Furthermore, multiple collimators may produce images with vertical streaking. The vertical streaking is caused by differences in the alignments of apertures in the backscattering imaging system, which results in diminished and inconsistent flux output from the apertures. An operator may attempt to align the apertures by a manual trial and error process, but such efforts are typically time consuming and usually only provide moderate improvement in the image quality. In another approach, intensity variations between apertures may be partially compensated using automated averaging during the calibration process. However, this approach is only partially effective and may not substantially eliminate the vertical streaking in the images.

SUMMARY

In one aspect, an x-ray backscattering imaging system creating a backscatter image representing a structure is disclosed. The system includes a drum rotatable about an axis of rotation at a rotational speed, a radioactive source, a container, at least one collimator, at least one light emitting element, and a plurality of backscatter detectors. The radioactive source is connected to the drum and generates x-ray beams. The container houses the radioactive source and is constructed of a material that substantially blocks the x-ray beams generated by the radioactive source. The collimator is defined by the container and has a length and an aperture, where the collimator filters a stream of x-rays generated by the radioactive source such that the x-ray beams traveling substantially parallel with respect to the length of the collimator pass through the aperture. The light emitting element generates visible light and is positioned to direct the visible light into the collimator. The collimator filters a stream of visible light generated by the light emitting element such that the visible light traveling substantially parallel with respect to the length of the collimator passes through the aperture, and the visible light passing through the aperture is coincident and substantially parallel with respect to the x-ray beams that pass through the aperture. The backscatter detectors are for detecting backscattering radiation created as the x-rays generated by the radioactive source scatter back from the structure.

In another aspect, a method of calibrating an x-ray backscattering imaging system is disclosed. The method comprises rotating a drum about an axis of rotation at a rotational speed, where a container is connected to the drum and houses a radioactive source that generates x-ray beams. The method further includes directing visible light generated by a light emitting element into a collimator defined by the container. The collimator includes a length and an aperture. The method includes filtering a stream of visible light generated by the light emitting element by the collimator. The method further includes allowing the visible light traveling substantially parallel with respect to the length of the collimator to pass through the aperture. The visible light passing through the aperture is coincident and substantially parallel with respect to the x-ray beams that pass through the aperture. The method also includes directing the visible light exiting the aperture of the collimator upon a surface to create a light spot. Finally, the method also includes adjusting at least one of a size, shape, and location of the aperture of the collimator based on the light spot.

Other objects and advantages of the disclosed method and system will be apparent from the following description, the accompanying drawings and the appended claims.

DETAILED DESCRIPTION

As shown inFIG. 1, the disclosed x-ray backscattering imaging system10according to an aspect of the disclosure is used to inspect an object or structure18. In one approach, the structure18may be a multilayer object such as, for example, a building. The x-ray backscattering imaging system10may include a two-dimensional optical detector22(shown inFIG. 5), an on-board positioning system30, a front shield32, an exterior shield36, a rotating drum40(shown inFIG. 2A), a radioactive source42(shown inFIG. 2A), a handle44, at least one light emitting element56(shown inFIG. 2B), and one or more backscatter detectors58. The x-ray backscattering imaging system10includes a calibration feature that utilizes visible light generated by the light emitting element56shown inFIG. 2Bto align, shape, and size x-ray beams generated by the radioactive source42, and is explained in greater detail below.

Turning back toFIG. 1, in one embodiment, the x-ray backscattering imaging system10is relatively lightweight and portable. Accordingly, an operator may move the backscattering imaging system10in a generally horizontal direction with respect to the structure18in order to inspect one or more areas of the structure18. The on-board positioning system30tracks the resulting horizontal displacement of the backscattering imaging system10. The on-board positioning system30is any type of device for detecting and measuring the horizontal displacement of the x-ray backscattering imaging system10in a horizontal direction with respect to the structure18. For example, the on-board positioning system30may be an inertial measuring unit (IMU), a global positioning system (GPS), at least one acoustic distance sensor, an optical encoder configured to read an exterior surface20of the structure18, one or more encoder wheels that roll against the exterior surface20of the structure18, or one or more linear encoders.

Referring toFIG. 2A, in one approach the radioactive source42may be a gamma source that emits gamma radiation. Some examples of gamma sources include, but are not limited to, Cesium-137, Cobalt-60, and Iridium-192. Some other types of radioactive elements that may be used include, for example, alpha sources, beta sources, or neutron sources. The radioactive source42and the visible light element56are both housed within a container62. In one embodiment, the radioactive source42may be relatively small and lightweight, thereby enabling the disclosed x-ray backscattering imaging system10to be portable and easily held by a user. The container62is constructed of a material that substantially blocks the x-ray beams generated by the radioactive source42from exiting the container62such as, for example, lead or tungsten. The container62defines a cavity54that contains the radioactive source42.

In the embodiment as shown inFIG. 2A, the container62defines a collimator64located along an outermost edge or face66of the container62.FIG. 2Bis an enlarged view of the collimator64shown inFIG. 2A. In the non-limiting embodiment as shown, the light emitting element56is positioned within the collimator64. The light emitting element56is configured to generate visible light that is seen by the human eye, which typically includes wavelengths from about 390 nanometers to about 700 nanometers. In the embodiment as shown inFIG. 2B, the light emitting element56is a light emitting diode (LED) or an organic LED (OLED). However, in another embodiment shown inFIG. 9, the light emitting element56is a diode laser, which is explained in greater detail below.

The collimator64defines a length L and an aperture opening A. The collimator64collimates the radiation generated by the radioactive source42. Specifically, the collimator64filters a stream of x-rays generated by the radioactive source42such that only the x-rays traveling substantially parallel with respect to the length L of the collimator64are allowed to pass through and exit the aperture A. Similarly, the collimator64also collimates the visible light generated by the light emitting element56. The visible light also travels in a path along the length L of the collimator64and exits the aperture A. The visible light that passes through the aperture A is coincident to and substantially parallel with respect to the x-ray beams that also pass through the aperture A.

Referring generally to bothFIGS. 2B and 4, the visible light exiting the aperture A of the collimator64is directed upon a surface72of the optical detector22to create a silhouette or light spot68. The light spot68is representative of the x-rays that also exit the aperture A of the collimator64. The light spot68created by the visible light exiting the aperture A of the collimator64is representative of the x-rays generated by the radioactive source42. Specifically, the light spot68is representative of the size, shape, and location of the x-rays beams generated by the radioactive source42. Thus, an operator calibrates the x-ray beam based on the visible light spot68, which is described in greater detail below. Those of ordinary skill in the art will readily appreciate that a distance measured between the optical detector22and the aperture A of the collimator64is increased or decreased in order to change the size of the light spot68viewed upon the surface72of the optical detector22.

In the embodiment as shown inFIGS. 2A and 2B, the light emitting element56is positioned within the collimator64so as to intersect with the x-ray beams generated by the radioactive source42. This position of the light emitting element56is possible because LEDs and OLEDs are transparent to radiation, and therefore do not block the x-rays when the radioactive source42generates the x-rays. In one embodiment, the LED is removable so that a replacement LED may be installed in the event the original LED is no longer able to generate visible light.

The light emitting element56is positioned to direct visible light into the collimator64. In the embodiment as shown inFIG. 2B, the light emitting element56is positioned between a proximate end50and a distal end52of the collimator64. However, it is to be appreciated that the light emitting element56may be placed at any position along the length L within the collimator64. For example, in one approach the light emitting element56may be positioned within the collimator64directly adjacent to the aperture A, which may result in brighter, more well-defined beams of visible light. In another embodiment, the light emitting element56may be positioned within the cavity54of the container62in a location that is directly adjacent to an opening46at the proximate end50of the collimator64.

As seen inFIG. 2B, a shutter48may be placed at the opening46located at the proximate end50of the collimator64. Similar to the container62, the shutter48is also constructed of a relatively dense material to substantially shield or stop the radiation generated from the radioactive source42. During calibration of the x-ray backscattering imaging system10, the shutter48is positioned at the opening46to block the x-rays generated by the radioactive source42from entering the collimator64. Instead, the visible light element56is activated and generates visible light that exits the aperture A of the collimator64to create the light spot68(FIG. 4). Therefore, the size, shape, and location of the light spot68is adjustable, without subjecting an operator to the radiation generated by the radioactive source42.

Once calibration is complete, the operator deactivates the light emitting element56and then actuates the shutter48in a direction away from the opening46in order to allow for x-rays to exit the collimator64. Specifically, in the embodiment as shown inFIG. 2B, the shutter48is actuated in a sideways direction70, and away from the opening46of the collimator64. The shutter48may be actuated by a motor (not illustrated) such as a nanomotor.

Turning back toFIG. 2A, the container62may be connected to the drum40. The drum40may be housed or encased within the exterior shield36, and is rotatable about an axis of rotation A-A at a rotational speed. In the non-limiting example as shown, the exterior shield36includes a generally cylindrical profile. In the embodiment as shown inFIG. 2A, the container62may be located along an outermost surface74of the drum40. However, in an alternative approach, the container62is housed within the drum40as well, which is illustrated inFIG. 7and described in greater detail below.

The x-rays generated by the radioactive source42or the visible light generated by the light emitting element56travel through a scanning window80, which is an opening defined by the exterior shield36. The exterior shield36is constructed of a relatively dense material having a high atomic number that may substantially shield or stop the radiation generated from the radioactive source42such as, for example, titanium or lead. The scanning window80may be constructed of a material that allows for x-rays X and visible light exiting the collimator64to pass through. The scanning window80may also be used to filter out lower energy x-rays exiting the collimator64. In one non-limiting example, the scanning window80may be constructed of a relatively thin sheet of aluminium or copper having a thickness ranging from about one-tenth of a millimeter to about five millimeters. In another approach, the scanning window80may be an open void within the exterior shield36.

As seen inFIG. 2A, the scanning window80may be formed as an angle A around the exterior shield36. In one approach, the angle A may range from about ten degrees to about one hundred and twenty degrees with respect to the axis of rotation A-A of the drum40. The specific dimensions of the angle A may depend on a desired height of the backscatter image generated by the x-ray backscattering imaging system10. For example, a smaller angle A results in a shorter backscatter image, while a larger angle A results in a taller backscatter image.

As the drum40rotates during operation of the x-ray backscattering imaging system10, the x-rays X or the visible light exiting the collimator64selectively pass through the scanning window80within the exterior shield36at a specific frequency, and are directed towards the structure18(FIG. 1). Turning back toFIG. 1, the front shield32may be used in the event x-rays are exiting the collimator64. The front shield32shields or blocks backscattering radiation84created as the x-rays X generated by the x-ray backscattering imaging system10scatter back from the structure18. The shield32is constructed of any type of relatively dense material that may substantially shield or stop the radiation generated from the radioactive source42. The shield32defines an aperture or opening86. Referring to bothFIGS. 1 and 2A, the x-rays exiting the scanning window80within the exterior shield36pass through the opening86of the shield32and towards the structure18.

FIG. 3is a front view of the x-ray backscattering imaging system10, where the handle44, the drum40, and the backscatter detectors58are illustrated (the front shield32has been removed inFIG. 3). As seen inFIG. 3, the scanning window80may include a horizontal length L1. The horizontal length L1of the scanning window80should be sized to be at least as wide as the aperture opening diameter D1of the collimator64(shown inFIG. 2B). Continuing to refer toFIG. 3, the handle44may be rotatably attached to the drum40. Specifically, the handle44may include a rod87located along the axis of rotation A-A of the drum40. In the example as illustrated inFIG. 3, a backscatter detector58is located on opposing sides98of the drum40. The backscatter detectors58detect backscattering radiation84created as the x-rays generated by the radioactive source42scatter back from the structure18. The backscatter detectors58generate a signal based on the backscattering radiation84detected. The backscatter detectors58may be, for example, solid state detectors or scintillators.

FIG. 4is a schematic illustration of the collimator64, collimated light76generated by the light emitting element56, and the two-dimensional optical detector22. The two-dimensional optical detector22may also be referred to as a position sensitive device, and refers to a component that is based on a silicon p-i-n diode. The optical detector22is temporarily placed in front of the exterior surface20of the structure18to be inspected by the backscattering imaging system10. As seen inFIG. 4, the collimated light76exits the aperture A of the collimator64, and is directed upon the surface72of the optical detector22to create the light spot68. The surface72of the optical detector22includes a plurality of pixels78arranged in a grid pattern. The optical detector22creates a voltage at each pixel78that is illuminated by the light spot68. The voltage is used to determine the size, shape, and location of the light spot68.

Turning back toFIG. 3, the x-ray backscattering imaging system10also includes a controller90in signal communication with a display94. The controller90is in signal communication with backscatter detectors58, the optical detector22, and the on-board positioning system30. The controller90refers to, or is part of, an application specific integrated circuit (ASIC), an electronic circuit, a combinational logic circuit, a field programmable gate array (FPGA), a processor (shared, dedicated, or group) that executes code, or a combination of some or all of the above, such as in a system-on-chip.

The controller90generates the backscatter image representing an interior and/or an opposing side of the structure18(FIG. 1) upon the display94. The backscatter image is based on a position signal received from the on-board positioning system30. The position signal indicates horizontal position information relating to the location of the x-ray backscattering imaging system10relative to the structure18as the x-ray backscattering imaging system10is moved in a horizontal direction. The controller90correlates the movement of the x-ray backscattering imaging system10(FIG. 1) in the horizontal direction as well as a vertical scan movement of the radioactive source42with a density of the x-ray backscatter84detected by the backscatter detectors58. Referring toFIGS. 1, 2A, and 3, the vertical scan movement of the radioactive source42may be defined based on an angle of the x-rays X exiting the collimator64as well as a distance the x-rays X exiting the collimator64may travel before being backscattered by the structure18. The controller90determines the backscatter image based on the horizontal movement of the x-ray backscattering imaging system10relative to the structure18, the vertical scan movement of the radioactive source42, and the density of the x-ray backscatter84detected by the backscatter detectors58.

In one embodiment, the size, shape, and location of the light spot68is adjusted automatically by the controller90of the x-ray backscattering imaging system10. Referring toFIGS. 2A, 3, and 4, an operator may pre-select or program a shape, size, and location of the light spot68, where the pre-selected light spot is referred to as the reference light spot. The controller90includes a feedback control system, which identifies the difference between the actual size of the light spot68(which is indicated by the voltage generated by the optical detector22) and the reference light spot. The controller90adjusts the location of the aperture A using an alignment system180, which is illustrated inFIG. 5and is described in greater detail below. The controller90also adjusts the size of the light spot68using a sizing mechanism190, which is illustrated inFIG. 6and is described in greater detail below. The controller90continues to adjust the alignment system180and the sizing mechanism190until the size, shape, and location of the light spot68(FIG. 4) substantially matches the size, shape, and location of the reference light spot.

In the event the x-ray backscattering imaging system10includes more than one collimator (seen inFIG. 8), then the controller90adjusts each aperture of each collimator in a similar fashion. Specifically, each additional aperture is adjusted by comparing a corresponding light spot to either the reference light spot, or to an initial light spot68generated by the x-ray backscattering imaging system10.

Referring toFIGS. 1, 2A, 2B, 3 and 4, in another embodiment, an operator manually adjusts at least one of a size, shape, and location of the aperture A of the collimator64based on the light spot. Specifically, the optical detector22shown inFIG. 4is optional and may be omitted in some embodiments. Instead, the visible light passing through the aperture A of the collimator64is directed upon an exterior surface20of the structure18(FIG. 1) and creates a light spot68(the light spot68is not shown inFIG. 1). Accordingly, the light spot68is viewed directly upon the exterior surface20of the structure18. The operator adjusts the size, shape, and location of the light spot68manually using an external computer (not illustrated) that is connected to the x-ray backscattering imaging system10. The external computer may be, for example, a desktop computer, a tablet computer, or a smartphone that includes imaging software and a display. The operator may view previous images of the light spot68upon the display of the external computer, while dynamically adjusting the size, shape, and location of the aperture A. Adjustment of the size, shape, and location of the aperture A is described below and is shown inFIGS. 5 and 6.

In one embodiment, the operator changes the location of the aperture A using the alignment system180illustrated inFIG. 5. A beam170enters the collimator164, is collimated, and then passes through the aperture A. It is to be appreciated that the beam170is either an x-ray beam or visible light. After passing through the aperture A, the beam170is directed upon the surface72of the optical detector22.

The alignment system180includes at least one motor182,184,186, where a specific motor translates the aperture A along a selected axis of a three-dimensional Cartesian coordinate system. The three-dimensional Cartesian coordinate system expresses a location of a point in space using an x-coordinate, a y-coordinate, and a z-coordinate. In the embodiment as shown inFIG. 5, the alignment system180includes a first motor182, a second motor184, and a third motor186. The motors182,184, and186may be, for example, nanomotors and are in signal communication with the controller90.

The first motor182is configured to translate the aperture A along an x-axis of the three-dimensional Cartesian coordinate system. The second motor184is configured to translate the aperture A along a y-axis that is perpendicular to the x-axis. The third motor186is configured to translate the aperture A along a z-axis, which is perpendicular to both the x-axis and the y-axis. Referring toFIGS. 4 and 5, controller90instructs the alignment system180to translate the aperture A along at least one axis of the three-dimensional Cartesian coordinate system based on a location of the light spot68on the surface72of the optical detector22.

Turning now toFIG. 6, in another embodiment the adjustable sizing mechanism190is provided for determining the size and the shape of the aperture A. The sizing mechanism190includes two flat, plate-shaped shutters192,194. The shutters192,194are positioned by a motor196such as, for example, a nanomotor. One of the shutters is a fixed shutter192, and a remaining shutter is a moveable shutter194. The motor196may be connected to drive, or include, a threaded shaft100that threads into a boss102that may be connected to the shutter194. The motor196may be mounted on a fixed support such as a fixed shaft104, which may be held in place by a boss106attached to the fixed shutter192. The moveable shutter194translates in a first direction D1along a surface112of a wall segment114towards the fixed shutter192in order to decrease the size of the aperture A. The decreased size of the aperture A is illustrated inFIG. 6in phantom or dashed lines. Similarly, the movable shutter194translates in a second direction D2away from the fixed shutter192in order to increase the size of the aperture A. The increased size of the aperture A is illustrated inFIG. 5in phantom or dashed lines as well. The controller90actuates the motor196in order to vary the size of the aperture A.

In the embodiment as shown, the two shutters192,194include a parallelogram-shaped profile, and are positioned to overlap one another. As a result of the shape and orientation of the shutters192,194, the aperture A includes a triangular-shaped profile. However, this embodiment is merely exemplary in nature. Indeed, the shutters192,194may include a number of shapes. Moreover, the aperture A is not limited to a triangular-shaped profile. For example, in another embodiment the shutters192,194are changed in order to create a circular-shaped, a rectangle-shaped, or an irregularly-shaped aperture as well. Specifically, the shutters192,194are capable of being replaced with an alternative set of shutters having a different profile in order to create an aperture having another profile. Referring to bothFIGS. 4 and 6, the controller90instructs the sizing mechanism190to either increase or decrease the size of the aperture A based on the size of the light spot68on the surface72of the optical detector22.

FIG. 7is an alternative illustration of an x-ray backscattering imaging system200. The x-ray backscattering imaging system200includes similar elements as the system10shown inFIGS. 1 and 2A, except that a container262is positioned at the axis of rotation A-A within a rotating wheel or drum240. Similar to illustrations as shown inFIG. 2A, the container262is also used to contain a radioactive source242therein, and a light emitting element256is placed within a collimator264. The radioactive source242may be a gamma source, an alpha source, a beta source, a neutron source, or an x-ray generator. An x-ray generator contains an x-ray tube (not illustrated) to produce x-rays. An x-ray tube is a vacuum tube that converts electrical power into x-rays. Specifically, the x-ray tube produces x-rays by accelerating electrons into a target based on a high positive voltage difference between the target and an electron source. In one particular embodiment, the x-ray tube may be used to produce Bremsstrahlung radiation. The drum240includes a plurality of spokes298, where the spokes298surround the container262.

In addition to a central container262, the embodiment shown inFIG. 7differs from the system10shown inFIGS. 1 and 2Ain that a selected one of the spokes298includes the collimator264. Continuing to refer toFIG. 7, the container262defines an interior opening202. A first, proximate end204of the collimator264is connected to the opening202of the container262. A second, distal end210of the collimator264terminates at an aperture A1P. The aperture A1P is located along an outermost surface174of the drum240. As seen inFIG. 7, an aperture opening diameter of the collimator264is denoted as D1P and a length and of the collimator264is denoted as L1P.

In the embodiment as shown, the light emitting element256is positioned between the opening202and the aperture A1P of the collimator64. However, it is to be appreciated that the light emitting element256may be placed at any position along the length L1P of the collimator264. In one embodiment, the light emitting element256is positioned within the collimator264directly adjacent to the aperture A1P. In another embodiment, the light emitting element256is positioned within the container262, and in a location directly adjacent to the opening202of the collimator264. Similar to the embodiment as shown inFIG. 2B, the container262also includes a shutter (not illustrated inFIG. 7) for selectively blocking radiation generated by the radioactive source242.

Similar to the embodiments described above and shown inFIGS. 2A and 2B, the collimator264collimates the radiation generated by the radioactive source242. Specifically, the collimator264filters a stream of x-rays generated by the radioactive source242such that only the x-rays traveling substantially parallel with respect to the length L1P of the collimator264are allowed to pass through and exit the aperture A1P. Similarly, the collimator264also collimates the visible light generated by the light emitting element256. The visible light also travels in a path along the length L1P of the collimator264and exits the aperture A1P, and travels in a direction within the collimator264that is substantially parallel with respect to the x-rays. The x-rays generated by the radioactive source242travel through a scanning window280, which is an opening defined by an exterior shield236, and exit the x-ray backscattering imaging system200.

FIG. 8is an illustration of an x-ray backscattering imaging system300. The x-ray backscattering imaging system300includes similar elements as the system10shown inFIGS. 1 and 2A, except that a container362is positioned at the axis of rotation A-A of a drum340. Also, the drum340includes a plurality of spokes398that surround the container362, and each spoke398of a drum340defines a unique collimator364. The container362contains a radioactive source342therein. Similar to the embodiment as shown inFIG. 7, the radioactive source342may be a gamma source, an alpha source, a beta source, a neutron source, or an x-ray generator having an x-ray tube. In one particular embodiment, the x-ray tube may be used to produce Bremsstrahlung radiation. Each collimator364includes a first, proximate end304connected to a corresponding opening302defined by the container362. A second, distal end310of the collimator364terminates at a corresponding aperture A2P. Each aperture A2P is located along an outermost surface374of the drum340. A corresponding light emitting element356is provided for each collimator364. For example, in the embodiment as shown inFIG. 8there are eight light emitting elements356that are provided for a corresponding one of the collimators364. As seen inFIG. 8, each light emitting element356is positioned along a length L2P of a corresponding collimator364at the same location. That is, in other words, a distance measured between each light emitting element356and a corresponding aperture A2P is the same.

In the embodiment as shown inFIG. 8, each light emitting element356is positioned between a corresponding one of the openings302and a corresponding aperture A2P of one of the collimators364. However, it is to be appreciated that the light emitting element356may be placed at any position along the length L2P of each collimator364, as long as the distance Q for each light emitting element356is the same. In one embodiment, the light emitting elements356may be positioned by a corresponding collimator364in a location directly adjacent to a corresponding aperture A2P. In another embodiment, the light emitting elements356may be positioned within the container362, and in a location directly adjacent to a corresponding one of the openings302of the collimator364. Similar to the embodiment as shown inFIG. 2B, the container362may also include a plurality of shutters (not illustrated inFIG. 8) for selectively blocking radiation generated by the radioactive source342.

FIG. 9is an alternative embodiment of the light emitting element56and collimator64shown inFIG. 2A, where one or more laser diodes456are now the light emitting element. The laser diodes456may also be referred to as injection lasers or diode lasers, and are semiconductor devices that produce coherent radiation in the visible spectrum. In one embodiment, the laser diodes456may be visible VCSELs (Vertical Cavity Surface Emitting Lasers) that emit visible light in the red spectrum, standard laser diodes, a pumped semiconductor laser, or a gas laser such as a helium neon (HeNe) laser.FIG. 9illustrates an exemplary collimator464and a portion of a container462. The collimator464includes a first proximate end404and a second distal end406. The container462also contains a radioactive source that is not visible inFIG. 9. It is to be appreciated that the collimator464and the laser diodes456are capable of being used in any of the configurations of the x-ray backscattering imaging systems10,200, and300shown inFIGS. 2A-2B, 7 and 8.

Each laser diode456is provided with a lens470and a reflecting element472. The laser diodes456each generate a laser beam474traveling in a direction towards a corresponding lens470and reflector472. The lens470disperses the laser beam474generated by a corresponding laser diode456into a stream of dispersed visible light478. The lens470is positioned within the container462so as to direct the visible light478upon a mirrored surface480of a corresponding reflecting element472. In one approach, the reflecting elements472are micromirrors having an aluminum reflective coating. The visible light478is then directed towards a surface482within the container462. The surface482is oriented so as to direct the visible light478into the collimator464. The reflecting elements472are of sufficient size to re-direct the visible light478through the collimator464, where the visible light478completely fills the collimator464.

The visible light478travels along a length L3P of the collimator464and exits an aperture A3P located at the distal end406of the collimator464. The visible light478is directed upon a surface, such as the surface72of the optical detector22which is described above and illustrated inFIG. 4. The visible light478creates a light spot468upon the surface72of the optical detector22. Alternatively, in another embodiment, the visible light478creates the light spot468upon an exterior surface20of the structure18(shown inFIG. 1) that is being inspected.

FIG. 10is an exemplary process flow diagram illustrating a method500for creating the light spot68shown inFIG. 4. Referring generally toFIGS. 1, 2A, 2B, 3, 4, and 10the method500begins at block502. In block502, the drum40is rotated about the axis of rotation A-A at the rotational speed. As seen inFIGS. 2A and 2B, the container62is connected to the drum40and houses the radioactive source42that generates x-ray beams. Method500may then proceed to block504.

In block504, the visible light generated by the visible light element56is directed into the collimator64defined by the container62. As mentioned above and seen inFIG. 2A, the collimator64filters the stream of x-rays generated by the radioactive source42such that the x-ray beams traveling substantially parallel with respect to the length of the collimator64pass through the aperture A. Method500may then proceed to block506.

In block506, the method500includes filtering the stream of visible light generated by the light emitting element56by the collimator64. Method500may then proceed to block508.

In block508, the visible light traveling substantially parallel with respect to the length of the collimator64is allowed to pass through the aperture A. As mentioned above, the visible light passing through the aperture A is coincident and substantially parallel with respect to the x-ray beams that pass through the aperture A. Method500may then proceed to block510.

In block510, the visible light exiting the aperture A of the collimator is directed upon a surface to create the light spot68. Specifically, in the embodiment as shown inFIG. 4, the light spot68is directed upon the surface72of the optical detector22. However, as mentioned above, in one embodiment the optical detector22is optional. Instead, the light spot68is directed upon the exterior surface20of the structure18shown inFIG. 1. Method500may then proceed to block512.

In block512, the aperture A is adjusted based on the light spot68. Specifically, in one embodiment the size, shape, and location of the light spot68are adjusted automatically by the controller90of the x-ray backscattering imaging system10. In another embodiment, an operator may manually adjust the size, shape, and location of the light spot68. Method500may then terminate.

Referring generally toFIGS. 1-10, the disclosed x-ray backscattering imaging system includes a visual light calibration feature that allows for an operator to make adjustments to the size, shape, and location of a collimator's aperture. Accordingly, every time the x-ray backscattering imaging system is activated for use, a calibration procedure may be conducted to adjust the size, shape, and location of the aperture. The calibration of the aperture is completed using the visible light generated by the disclosed light emitting element. Once calibration is complete, the x-ray backscattering imaging system may inspect a structure by detecting backscattering radiation created as the x-rays generated by the radioactive source scatter back from the structure. Thus, an operator is able to calibrate the size, shape, and location of the x-rays, without being subjected to the radiation generated by the radioactive source. Furthermore, in the event more than one collimator is included, the disclosed system may substantially eliminate vertical streaking from an image. The disclosed system may also improve a signal-to-noise value and spatial resolution of the image, which also improves the overall quality of the image.

While the forms of apparatus and methods herein described constitute preferred aspects of this disclosure, it is to be understood that the disclosure is not limited to these precise forms of apparatus and methods, and the changes may be made therein without departing from the scope of the disclosure.