System and method for controlling image contrast in an X-ray system

Abstract

An X-ray inspection system for scanning an object and providing a corresponding contrast-controlled scanned image is provided. The system includes an X-ray source configured to generate an X-ray beam for irradiating the object, wherein the X-ray source is coupled to at least a first beam filter having a first thickness and a second beam filter having a second thickness, the second thickness being greater than the first thickness; a detector array; a processing unit; a user interface configured to receive user input indicating a desired contrast level in an image; and a controller configured to adjust a position of at least one of the first or second beam filters based on the user input indicating the desired contrast level in at least one image.

Description

Technical Field

[0001] The present invention relates to an apparatus and method for controlling image contrast in a transmission or backscatter X-ray inspection system. Background Art

[0002] X-ray inspection systems typically include a beam filter for filtering the inspection X-ray beam before it irradiates the object being inspected. The beam filter limits the total dose of the X-ray beam by limiting the flux and lowest energy portion of the X-ray beam spectrum. This is desirable in certain applications, such as medical applications where energies below 30 keV are generally expected to be absorbed by the patient's soft tissue. Similarly, in a backscatter X-ray inspection system used to inspect cargo, the lowest radiation energies may be absorbed in the cargo being irradiated. Some of the scattered radiation, which produces low-energy radiation, may be absorbed by the housing of the inspection system. These low-energy photons are considered to contribute to the dose but do not provide any benefit in exchange, so even in the absence of specific dose limitations, the principle of ALARA (the dose should be as low as possible) motivates the removal of low-energy radiation.

[0003] The application of beam filters and reduction of low energy beam spectral components can also suppress certain portions of the image data that would only show the exterior of the imaged object, thereby providing an image with a clearer view of the interior of the object.

[0004] In a backscatter X-ray inspection system, the shape of the beam spectrum affects the quality of the image obtained. Therefore, controlling the beam spectrum shape of a backscatter X-ray inspection system can optimize the system's ability to highlight organic (or non-organic) threats in the image, especially with reference to threats located behind steel shielding.

[0005] U.S. Patent No. 9,014,339 discloses "(a) scanning apparatus for scanning a light beam in a one-dimensional scan, the apparatus comprising: a. a radiation source for generating a fan-shaped radiation beam, the radiation beam emanating effectively from a source axis and characterized by a width; b. an angle selector, fixed during scanning, for limiting the range of the scan; and c. a multi-aperture unit rotatable about a central axis such that a flux of the light beam incident on a target is the same per revolution for different fields of view of the light beam on the target, wherein the multi-aperture unit comprises an inner multi-aperture hoop characterized by a hoop axis, the inner multi-aperture hoop being made of a material that is opaque to the light beam, and wherein the inner multi-aperture hoop comprises aperture rings spaced laterally along the hoop axis in such a manner that axial movement of the multi-aperture hoop positions the aperture rings in the light beam, the light beam being collimated by corresponding aperture angles in the angle selector."

[0006] U.S. Patent No. 9,291,582 discloses “an adjustable collimator for shaping a particle beam, the particle beam being characterized by dynamically sweeping a radial direction of propagation radially relative to an aperture ring rotating about an axis of rotation and serving to interrupt the beam, the swept direction of propagation being transverse to the axis of rotation of the aperture ring, the collimator comprising: a. a shielding element being substantially opaque to passage of particles in the dynamically swept direction of propagation; and b. a gap in the shielding element adapted to pass particles in the dynamically swept direction of propagation, the gap being characterized by a length taken along a long dimension and a jaw spacing taken along a narrow dimension, both the long dimension and the jaw spacing being transverse to the dynamically swept direction of propagation, wherein at least one of the length of the gap and the jaw spacing is adjusted.”

[0007] The prior art patents mentioned above disclose using beam filters to reduce dose, change the energy distribution of the beam and promote dual energy backscattering. However, the cited art does not disclose using beam filters to control the contrast value of the scanned image.

[0008] A system and method for controlling the contrast value of a scanned image using a beam filter is needed to improve the detectability of threat materials hidden behind metal obscurations and enable an operator to adjust the image to optimize the image display according to his or her specific preferences. Enabling the operator to control the contrast of the image can improve his or her ability to detect threats, identify contraband, and / or increase scanning throughput. Summary of the Invention

[0009] The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools, and methods, which are intended to be exemplary and illustrative, not limiting in scope.This application discloses many embodiments.

[0010] In some embodiments, the present specification is directed to an X-ray inspection system for scanning an object, the system comprising: an X-ray source configured to generate an X-ray beam for irradiating the object, wherein the X-ray beam irradiating the object defines a field of view, and wherein the X-ray source is coupled to at least a first beam filter having a first thickness and a second beam filter having a second thickness greater than the first thickness; a detector array adapted to receive radiation from the X-ray beam, the radiation being transmitted through or scattered from the object, and generating data representing at least one image; a processing unit configured to receive the data representing the at least one image and to generate at least one image for display based on the data representing the at least one image; a user interface configured to receive user input indicating a desired contrast level in the at least one image; and a controller configured to adjust a position of at least one of the first beam filter or the second beam filter based on the user input indicating the desired contrast level in the at least one image.

[0011] Optionally, the desired contrast level includes at least one of a first contrast level, a second contrast level, a third contrast level, and a fourth contrast level, and wherein the first contrast level is smaller than the second contrast level, the second contrast level is smaller than the third contrast level, and the third contrast level is smaller than the fourth contrast level.

[0012] Optionally, when the user interface receives user input of the first contrast level, the controller is configured to cause the first beam filter and the second beam filter to be out of the field of view of the X-ray source.

[0013] Optionally, when the user interface receives user input of the second contrast level, the controller is configured to bring the first beam filter into the field of view of the X-ray source and bring the second beam filter out of the field of view of the X-ray source.

[0014] Optionally, when the user interface receives user input of a third contrast level, the controller is configured to remove the first beam filter from the field of view of the X-ray source and locate the second beam filter in the field of view of the X-ray source.

[0015] Optionally, when the user interface receives user input of a fourth contrast level, the controller is configured to position the first beam filter in the field of view of the X-ray source and the second beam filter in the field of view of the X-ray source.

[0016] Optionally, the first beam filter and the second beam filter comprise a metal material having a high atomic number.

[0017] Optionally, the first filter and the second filter include at least one of bronze, tin, tungsten, pure copper (copper), and a copper matrix embedded with tungsten particles.

[0018] Optionally, the first beam filter and the second beam filter include a first layer made of tungsten or lead and a second layer made of steel or pure copper configured to absorb fluorescent light emitted by the first layer.

[0019] Optionally, the system further comprises a shield coupled to the first beam filter and the second beam filter, the shield being configured to reduce radiation leakage.

[0020] Optionally, the system further comprises a pencil beam forming aperture placed in front of the X-ray source, wherein the first beam filter is located between the X-ray source and the pencil beam forming aperture, and wherein image contrast is increased by increasing the distance between the pencil beam forming aperture and the first beam filter and decreasing the distance between the first beam filter and the X-ray source.

[0021] Optionally, the system further comprises a third beam filter.

[0022] Optionally, the first beam filter, the second beam filter and the third beam filter respectively include a 0.5 mm thick pure copper material, a 1.0 mm thick pure copper material and a 2.0 mm thick pure copper material.

[0023] Optionally, the processing unit is further configured to modify one or more nonlinear transfer functions, the nonlinear transfer functions being adapted to process the data representing the at least one image based on a desired contrast level. Optionally, the nonlinear transfer function comprises at least one of a gamma function or an S-curve function.

[0024] Optionally, the processing unit is further configured to implement at least one of the first set of program instructions and the second set of program instructions based on a desired contrast level. Optionally, the processing unit is further configured to implement the first set of program instructions based on at least one of the first contrast level and the second contrast level, and wherein the first set of program instructions includes one or more contrast enhancement functions. Optionally, the processing unit is further configured to implement the second set of program instructions based on at least one of the third contrast level or the fourth contrast level, and wherein the second set of program instructions includes one or more edge enhancement functions.

[0025] In some embodiments, the present specification is directed to a method for scanning an object using an X-ray inspection system, the method comprising: irradiating the object with an X-ray beam generated by an X-ray source, wherein the X-ray beam irradiating the object defines a field of view, and wherein the X-ray source is coupled to at least a first beam filter having a first thickness and a second beam filter having a second thickness greater than the first thickness; detecting radiation from the X-ray beam that is transmitted through the object or scattered from the object and generating data representing at least one image; generating at least one image for display based on the data representing the at least one image; receiving user input indicating a desired contrast level in the at least one image; and controlling a position of at least one of the first beam filter and the second beam filter based on the user input indicating the desired contrast level in the at least one image.

[0026] Optionally, receiving user input indicating a desired contrast level includes receiving at least one of a first contrast level, a second contrast level, a third contrast level, and a fourth contrast level, and wherein the first contrast level is less than the second contrast level, the second contrast level is less than the third contrast level, and the third contrast level is less than the fourth contrast level.

[0027] Optionally, controlling the position of at least one of the first beam filter and the second beam filter comprises positioning the first beam filter and the second beam filter out of a field of view of the X-ray source if user input indicating a first contrast level is received.

[0028] Optionally, controlling the position of at least one of the first beam filter and the second beam filter includes positioning the first beam filter in the field of view of the X-ray source and the second beam filter out of the field of view of the X-ray source if user input indicating a second contrast level is received.

[0029] Optionally, controlling the position of at least one of the first beam filter or the second beam filter comprises positioning the first beam filter out of the field of view of the X-ray source and positioning the second beam filter in the field of view of the X-ray source.

[0030] Optionally, controlling the position of at least one of the first beam filter or the second beam filter comprises positioning both the first beam filter and the second beam filter within the field of view of the X-ray source if user input indicating a fourth contrast level is received.

[0031] Optionally, the first beam filter and the second beam filter comprise a metal material having a high atomic number.

[0032] Optionally, the first filter and the second filter include at least one of bronze, tin, tungsten, pure copper, or a copper matrix embedded with tungsten particles.

[0033] Optionally, the first beam filter and the second beam filter include a first layer made of tungsten or lead and a second layer made of steel or copper configured to absorb fluorescent light emitted by the first layer.

[0034] Optionally, generating the at least one image for display based on the data representing the at least one image comprises modifying one or more non-linear transfer functions adapted to process the data representing the at least one image based on a desired contrast level.

[0035] Optionally, the one or more nonlinear transfer functions include at least one of a gamma function and an S-curve function.

[0036] Optionally, generating the at least one image for display based on the data representing the at least one image comprises implementing at least one of the first set of program instructions or the second set of program instructions based on a desired contrast level.

[0037] Optionally, the method further comprises implementing a first set of programming instructions based on at least one of the first contrast level or the second contrast level, wherein the first set of programming instructions comprises one or more contrast enhancement functions.

[0038] Optionally, the method further comprises implementing a second set of programming instructions based on at least one of the third contrast level or the fourth contrast level, and wherein the second set of programming instructions comprises one or more edge enhancement functions.

[0039] In some embodiments, the present specification is directed to a method for controlling the contrast of a scanned image obtained by using an X-ray inspection system, the method comprising: irradiating an object with an X-ray beam generated by an X-ray source, wherein the X-ray beam irradiating the object defines a field of view, and wherein the X-ray source is coupled to at least a first beam filter having a first thickness and a second beam filter having a second thickness greater than the first thickness; detecting radiation from the X-ray beam that is transmitted through or scattered from the object and generating data representing at least one image; generating at least one scanned image for display based on the data representing the at least one image; receiving user input indicating a desired contrast level in the scanned image as one of a first contrast level, a second contrast level, a third contrast level, and a fourth contrast level, and wherein the first contrast level is less than the second contrast level, the second contrast level is less than the third contrast level, and the third contrast level is less than the fourth contrast level; and changing a position of at least one of the first beam filter and the second beam filter relative to the field of view of the X-ray source based on the user input indicating the desired contrast level in the scanned image.

[0040] Optionally, changing the position of at least one of the first beam filter and the second beam filter comprises positioning the first beam filter and the second beam filter out of a field of view of the X-ray source if user input indicating a first contrast level is received.

[0041] Optionally, controlling the position of at least one of the first beam filter and the second beam filter includes positioning the first beam filter in the field of view of the X-ray source and the second beam filter out of the field of view of the X-ray source if user input indicating a second contrast level is received.

[0042] Optionally, controlling the position of at least one of the first beam filter or the second beam filter comprises positioning the first beam filter out of the field of view of the X-ray source and positioning the second beam filter in the field of view of the X-ray source.

[0043] Optionally, controlling the position of at least one of the first beam filter or the second beam filter comprises positioning both the first beam filter and the second beam filter within the field of view of the X-ray source if user input indicating a fourth contrast level is received.

[0044] In some embodiments, the present specification is directed to a method for combining scanned images to obtain an image with improved detection quality, the scanned image being obtained by using an X-ray inspection system, the method comprising: irradiating an object with an X-ray beam generated by an X-ray source, wherein the X-ray beam irradiating the object defines a field of view, and wherein the X-ray source is coupled to at least a first beam filter having a first thickness and a second beam filter having a second thickness greater than the first thickness; obtaining a first scanned image of the object using the first beam filter; obtaining a second scanned image of the object using the second beam filter; determining one or more areas containing edges in the second image by using the first image as a guide; applying an edge enhancement algorithm only to the determined areas containing edges in the second image; and applying a smoothing algorithm to all areas of the second image except the determined areas containing edges to reduce noise in the second image to obtain an image with improved detection quality.

[0045] Optionally, the first image is a high resolution image.

[0046] Optionally, the second image is a high contrast image.

[0047] Optionally, determining one or more regions containing edges in the second image by using the first image as a guide includes: determining one or more regions containing edges in the first image.

[0048] Optionally, applying the edge enhancement algorithm only to the determined area containing edges in the second image includes: not applying the edge enhancement algorithm to areas without edges in the second image to prevent the edge enhancement algorithm from enhancing noise in the areas without edges in the second image.

[0049] Optionally, the method further includes determining a potential threat located in the second image; and applying a graphical indicator to the first image based on the determined potential threat located in the second image to guide an operator in analyzing the threat area.

[0050] The above and other embodiments of the present specification will be described in more depth in the drawings and detailed description provided below. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] These and other features and advantages of the present specification will be further understood as they become better appreciated by reference to the detailed description when considered in conjunction with the accompanying drawings:

[0052] Figure 1A is a diagram illustrating a system for integrating a variable beam filter with a mechanical beam shutter of an X-ray source according to an embodiment of the present specification;

[0053] Figure 1Bis a side view illustrating a system for integrating a variable beam filter with a mechanical beam shutter of an X-ray source according to another embodiment of the present specification;

[0054] Figure 1C Shown as Figure 1B A top view of the shutter and filter mechanism is shown;

[0055] Figure 1D shows a top view of an X-ray source coupled with a shutter and multiple filters according to an embodiment of the present specification;

[0056] Figure 2A shows the effect of applying a beam filter on a backscattered X-ray image of a car containing several organic threats and metallic projectiles;

[0057] Figure 2B Shows the application of comparison on a backscattered X-ray image of a car containing several organic threats and metal projectiles. Figure 2A The effect of a stronger beam filter is shown;

[0058] Figure 3A An image of a laboratory test setup used to study organic and metallic image features behind a metal plate;

[0059] Figure 3B Shows the use Figure 3A X-ray images obtained by the device shown in FIG, wherein organic and metallic image features are Figure 3A The metal plate shown in is visible behind;

[0060] Figure 3C shows the results obtained by using four different beam filtering conditions. Figure 3A Radiation image of the device;

[0061] Figure 3D The results obtained by using different filter thickness, beam power and scanning speed are shown. Figure 3A Radiation image of the device;

[0062] Figure 3E A graph showing the relationship between X-ray doses corresponding to beam filters of different thicknesses;

[0063] Figure 4 is a diagram of an imaging module coupled to a turntable according to an embodiment of the present specification;

[0064] Figure 5A is a diagram of an exemplary beam filtering system configuration for obtaining at least three beam spectra according to an embodiment of the present specification;

[0065] Figure 5Bis a diagram of an exemplary beam filtering system configuration for obtaining multiple beam spectra according to an embodiment of the present specification;

[0066] Figure 5C is a diagram of an exemplary beam filtering system configuration that employs multiple filter rings around an X-ray source to obtain multiple beam spectra according to an embodiment of the present specification;

[0067] Figure 5D is a diagram of a top view of an exemplary beam filtering system configuration according to an embodiment of the present specification, the configuration employing multiple filters linearly arranged in front of a source to obtain multiple beam spectra;

[0068] Figure 6A is a diagram of a contrast beam filter employed in an X-ray collimation system according to an embodiment of the present specification;

[0069] Figure 6B is a diagram illustrating a contrast beam filter used in an X-ray collimation system according to another embodiment of the present specification;

[0070] Figure 6C Another embodiment according to the present specification is shown. Figure 6B The contrast beam filter inspection system shown in FIG is used in conjunction with a scatter shield;

[0071] Figure 7A is a side cross-sectional view of a pencil beam collimation system using a beam filter according to an embodiment of the present specification;

[0072] Figure 7B Is to use Figure 7A A top cross-sectional view of the pencil beam collimation system of the filter shown;

[0073] Figure 8A depicts an exemplary graphical user interface for enabling an operator to adjust the contrast of an image according to an embodiment of the present specification;

[0074] Figure 8B is a flow chart illustrating a method for automatically determining a signal-to-noise ratio in response to a user selecting a beam filter thickness and a scan speed for an inspection system according to an embodiment of the present description;

[0075] Figure 8C is a flow chart illustrating a method for automatically determining an image contrast value in response to a user selecting a signal-to-noise ratio and a scan speed for an inspection system according to an embodiment of the present description;

[0076] Figure 8D is a flow chart illustrating a method for automatically determining a maximum scan speed in response to a user selecting a signal-to-noise ratio and image contrast values for an inspection system according to an embodiment of the present description;

[0077] Figure 8E is a table showing correlations among beam filter thickness, scanning speed, and signal-to-noise ratio values according to an embodiment of the present specification;

[0078] Figure 9A is a graph illustrating a transfer function that may be used to process a backscattered X-ray image according to an embodiment of the present specification;

[0079] Figure 9B is a backscattered image processed by using a linear function according to an embodiment of the present specification;

[0080] Figure 9C The embodiment of the present specification shows the method of processing the image by using the gamma transfer function. Figure 9B Backscatter image of

[0081] Figure 9D The embodiment of the present invention is shown by using an S-curve transfer function to process Figure 9B Backscatter image of

[0082] Figure 10 is a table illustrating filter chains for different beam filter configurations that may employ a variable filter system according to an embodiment of the present specification;

[0083] Figure 11 shows image display adjustments made to a scanned image that has been processed using one or more beam filters according to an embodiment of the present specification;

[0084] Figure 12 is a flowchart illustrating a method of controlling a contrast value of a scanned image obtained from a backscatter X-ray inspection system according to an embodiment of the present specification;

[0085] Figure 13 is a flowchart illustrating a method of combining scanned images to obtain an image with improved detection quality according to an embodiment of the present specification. DETAILED DESCRIPTION

[0086] The present disclosure provides a method for controlling backscatter image quality based on the degree of beam filtering provided in an X-ray inspection system. In an embodiment, the present disclosure provides a backscatter inspection system in which a plurality of beam filters of varying thicknesses are deployed at different locations to filter an X-ray beam configured to illuminate an object, thereby producing a scanned image having varying contrast values depending on the thickness and location of the beam filters used.

[0087] limited:

[0088] The terms "image penetration" and "penetration contrast" refer to the contrast characteristics between an image target and its surroundings, where the target is located behind an obscurant in the radiation image.

[0089] The term "image contrast" or "contrast" refers to the level of brightness or color of pixels in an image such that the objects represented by the pixels are visually distinguishable from one another. Thus, modifying contrast means increasing, decreasing, or otherwise changing the value of the brightness or color level of one or more pixels in an image, thereby affecting how those pixels are visually distinguishable from one another.

[0090] The term "signal-to-noise ratio (SNR)" is defined as (mean signal / pixel) / (standard deviation).

[0091] The term "flux" is defined as a measure of the number of X-ray photons in a radiation image used to form the image.

[0092] The term "spectral hardness" is defined as a bremsstrahlung spectrum that is filtered to preferentially attenuate lower energy components.

[0093] When an element is referred to as being “on,” “connected to” or “coupled to” another element, it can be directly on, connected to or coupled to the other element, or one or more intervening elements may be present, unless otherwise specified.

[0094] In various embodiments, a "computing device / controller" includes an input / output interface, at least one communication interface, and a system memory. In various embodiments, the computing device / controller includes conventional computer components such as a processor, necessary non-transient memory or storage devices such as RAM (random access memory) and a disk drive, a monitor or display, and one or more user input devices such as a keyboard and a mouse. In an embodiment, the user input device allows the user to input commands such as clicking a button on a mouse or keyboard or alternatively by touching in an embodiment where the display is touch-enabled. The computing device / controller may also include software that supports wireless or wired communication over a network (e.g., HTTP, TCP / IP, and RTP / RTSP protocols). These components communicate with a central processing unit (CPU) to enable the operation of the computing device / controller. In various embodiments, the computing device / controller may be a traditional stand-alone computer, mobile phone, tablet computer, or laptop computer. In some embodiments, the functionality of the computing device / controller may be distributed across multiple computer systems and architectures.

[0095] In some embodiments, execution of multiple program instructions or code sequences causes or results in a CPU of a computing device / controller performing various functions and processes. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the processes of the systems and methods described herein. Thus, the described systems and methods are not limited to any specific combination of hardware and software.

[0096] The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting.The singular forms "a," "an," and "the" are intended to include the plural forms as well.

[0097] This specification is directed to multiple embodiments. The following disclosure is provided to enable one of ordinary skill in the art to practice the specification. The language used in this specification should not be interpreted as a general negation of any one specific embodiment or used to limit the claims beyond the meaning of the terms used therein. The general principles defined herein can be applied to other embodiments and applications without departing from the spirit and scope of the specification. In addition, the terms and expressions used are for the purpose of describing exemplary embodiments and should not be considered restrictive. Therefore, this specification will be given the widest scope to include numerous alternatives, modifications and equivalents consistent with the disclosed principles and features. For the sake of clarity, details related to technical materials known in the technical field related to the specification are not described in detail so as not to unnecessarily obscure this specification.

[0098] In the description and claims of this application, each word "comprises," "includes," and "has" and forms thereof are not necessarily limited to the members of the list with which these words are associated. It should be noted here that any feature or component described in conjunction with a particular embodiment can be used and implemented with any other embodiment unless expressly stated otherwise.

[0099] In an embodiment, the present description provides a system for varying the thickness of a beam filter applied to an X-ray beam. Figure 1A is a diagram illustrating a system for integrating a variable beam filter with a mechanical beam shutter of an X-ray source according to an embodiment of the present specification. As shown, an X-ray source 150 is coupled to a shutter 152, which can cover the source 150 if desired. Shutter 152 is coupled to a first beam filter 154 and a second beam filter 156. By using two beam filters, at least three different beam spectral shapes can be generated, one using each filter 154, 156, and one using neither filter. In alternative embodiments, beam filters of different designs using a sliding mechanism can also be used to obtain a desired number of beam filters and corresponding beam spectral shapes.

[0100] Figure 1B1 is a side view showing a system for integrating a variable beam filter with a mechanical beam shutter of an X-ray source according to another embodiment of the present specification. In an embodiment, an X-ray beam is generated by using an X-ray source 160 and a beam forming aperture 161. Figure 1B As shown, an X-ray source 160 is coupled to a shutter 162 that can be slid over to cover the beam forming aperture 161 if desired. The shutter 162 is coupled to a beam filter 164 and a beam filter 166. Figure 1B In the embodiment shown, the shutter 162 and filters 164, 166 are configured to move parallel to the axis of the X-ray source 160, covering the beam forming aperture 161 and being used to obtain different filter configurations. Figure 1B In the exemplary configuration shown, aperture 161 is covered by beam filter 166. Aperture 161 and beam filter 166 are in the same plane. To achieve a different filter configuration, beam filter 166 is moved out of the plane of aperture 161, while beam filter 164 is moved into the plane of aperture 161, thereby being configured to cover aperture 161.

[0101] Figure 1C illustrate Figure 1B A top view of the shutter and filter mechanism is shown. During operation, Figure 1C As shown, the filter 166 is translated and positioned in front of the beam forming aperture 161 to produce a filtered X-ray beam 168, while the shutter 162 and filter 164 are slid to a position offset from and not in front of the beam forming aperture 161, as shown. Dashed line 170 depicts the position of the shutter 162 and filters 164, 166 in an open position, wherein in the open position, the shutter 162 and filters 164, 166 do not cover the beam forming aperture 161. In embodiments, an unlimited number of filters may be used Figure 1B In the design shown, there is no limit on the number of filters that can be used because of the viewing angle of the light source. Figure 1D A top view of an X-ray source 180 coupled with a shutter and multiple filters, according to an embodiment of the present disclosure, is shown. As shown, any of the filters 182a, 182b, ..., 182n or the shutter 184 can be translated to cover a beam-forming aperture 181 coupled to the X-ray source 180 to achieve desired beam filtering. As shown, when one of the filters 182a, 182b, ..., 182n is positioned in front of the beam-forming aperture 181, a filtered X-ray fan beam 188 is obtained.

[0102] refer to Figure 1AIn various embodiments, minimum beam filtering is used to enhance the lowest energy components of the beam spectrum by, for example, applying filtering by the first filter 154. By using minimum beam filtering, aesthetically pleasing high signal-to-noise ratio images can be obtained. In addition, minimum beam filtering results in maximized contrast between low atomic number materials (e.g., plastic) and high atomic number materials (e.g., steel), as well as maximized spatial resolution, particularly for features outside the target. This enhances the detectability of organic threats that may be hidden behind thin obscurants, such as, but not limited to, cloth-covered trucks. Minimum beam filtering can also produce better contrast, resulting in better detection of thin organic threats against thick or opaque organic backgrounds. The contrast of thin organic targets against thick organic backgrounds also benefits from a softer beam spectrum. This form of contrast is referred to as "layer contrast" in the ANSI-N42.46 Standardized Test for Image Quality of Cargo Backscatter X-ray Inspection Systems.

[0103] In various embodiments, additional beam filtering, such as by applying second filter 156, is applied to maximize the contrast between organic and metallic objects in the radiation image for targets behind metallic obscurations, such as within a vehicle. Low-energy components of the X-ray beam spectrum have a low probability of penetrating the obscuration, but a high probability of interacting near the obscuration surface, and are therefore used only to generate an image of the obscuration. Application of the beam filter reduces the low-energy components, thereby suppressing image data that only displays the exterior of the imaged object, thereby enhancing the view of the interior of the object.

[0104] Figure 2A Shown is the effect of applying a beam filter on a backscattered X-ray image of a car containing multiple organic threats and metallic projectiles. Figure 2B Shows the application of the comparison method on a backscattered X-ray image of a car containing multiple organic threats and metal projectiles. Figure 2A The effect of a stronger beam filter is shown. Figure 2A and Figure 2B The car 200 includes a trunk 202 containing two large explosive simulant canisters 204, and 155mm artillery shells 206 (seen as black objects in the figure) near the bottom of the canisters 204. The rear door 208 contains several simulated drug packages 210 within the door panel. The front door 212 contains a smaller simulated drug package 214. Another simulated drug package 216 is located in the front wheel well 218. Figure 2A The beam filter used in Figure 2B The beam filter used in Figure 2A As can be seen in FIG, the headlights 222 and the plastic side trim 224 appear brighter compared to the metal body of the car 200, which appears darker in the image. Figure 2B In the beam filtration ratio Figure 2A, so all organic threats inside the car appear brighter relative to their surroundings. Figure 2A In the example, the shell 206 is only seen as a shadow in the organic material tank 204 in the trunk 202. Figure 2B has better visual contrast because the organic background 204 is better than Figure 2A It looks brighter.

[0105] The contrast between metallic objects and air also increases with increasing beam filtering. Figure 2A As can be seen in FIG, the trunk 202 and hood 220 of the car 200 are almost integrated into the background, however Figure 2B In the example, the transition from the steel object to the background is clearly defined. Figure 2B Thus, if the shell 206 is presented against a black background, it will appear brighter in the Figure 2B is detectable in Figure 2A It will be difficult to detect.

[0106] Figure 3A An image of a laboratory test setup used to study organic and metallic image features behind a metal plate. Figure 3B Shows the use Figure 3A X-ray images obtained by the device shown in FIG, wherein organic and metallic image features are Figure 3A The metal plate shown is visible behind. Figure 3A and Figure 3B Shown is a lab test setup with various image targets, including an image quality indicator for resolution, a step wedge for penetration, and several real-world image targets designed to simulate the physical conditions of a threat or contraband concealed in a vehicle. Figure 3A and Figure 3B Apparatus 300 includes a metal safe 302 containing a handgun 304, a first metal plate 306, and simulated objects 308 containing drugs, explosives, and cash hidden behind the plate; a second metal plate 310, and a simulated pipe bomb 312 hidden behind the plate. A sugar bag 314, serving as a simulated object for all types of organic threats, including drugs and explosives, is also placed behind plate 310. Plate 310 is made of 0.048-inch (1.2 mm) thick steel, simulating the trunk of a car that might represent a VBIED or smuggling scenario. Plates 306, 310, and metal safe 302 are 1 to 2 mm thick and made of steel. Test apparatus 300 is positioned on a conveyor belt (not shown) in front of an imaging module (not shown). The imaging module contains a 220 keV X-ray source and imaging hardware similar to commercial backscatter imaging products designed for inspecting cars and trucks.

[0107] Figure 3Cshows the results obtained by using four different beam filter conditions Figure 3A radiated images of the device. Image 350 was obtained using a 0.8 mm Beryllium vacuum window on the X-ray source used to image the device 300. Therefore, image 350 was obtained by using a negligible or zero beam filter. Images 360, 370, and 380 were obtained using 0.5 mm, 1.0 mm, and 2.0 mm thick copper beam filters, respectively. Figure 3C As can be seen in FIG, the visibility of the sugar bag 314 gradually increases from the unfiltered image 350 to the maximum filtered image 380, indicating that the visual detection capability of organic threats improves with increasing thickness of the applied beam filter.

[0108] In an embodiment, image 350 has a flux of 125% and a signal-to-noise ratio (SNR) of 37.1 or 112% at a radiation dose of 10.11R or 124%; image 360 has a flux of 78% and a signal-to-noise ratio (SNR) of 29.4 or 88% at a radiation dose of 6.1uR or 74%; image 370 has a flux of 57% and a signal-to-noise ratio (SNR) of 25 or 75% at a radiation dose of 4.7uR or 58%; and image 380 has a flux of 37% and a signal-to-noise ratio (SNR) of 20.1 or 60% at a radiation dose of 3.1uR or 37%. Thus, while the low-filter image 350 is more aesthetically pleasing with its darker background and sharper edges, the higher-filter images 360, 370, and 380 provide better visual detection of a threat item hidden behind 1 mm of steel at a significantly lower radiation dose. Adding 2 mm of copper beam filtering (image 380) shifts the average energy of the beam from 73 keV in image 350 to 120 keV in image 380, while reducing the X-ray dose by a factor of 3 and the SNR by a factor of 1.8. This SNR reduction is equivalent to a 3-4x reduction in photon flux.

[0109] like Figure 3C As shown, image 360 with a 0.5mm beam filter provides a significant increase in visual detectability and increases the average energy of the primary beam spectrum by -30%, from 73 keV in image 350 to 95 keV in image 360. Subsequent images 370 and 380 each provide a higher level of detectability and increase the average energy by 12% to 13%, from 95 keV in image 360 to 106 keV in image 370 to 120 keV in image 380. Each increase in average energy allows a relatively larger portion of the primary X-ray beam to penetrate the steel shielding and generate a scattered signal from the target behind the shielding. Therefore, it is clear that for a given threat, a larger relative signal from the target of interest provides a larger signal and greater contrast relative to the surrounding environment. Figure 3CImage studies have empirically shown that the benefits of removing the total flux from the beam to obtain a harder beam from which lower energy photons have been removed outweigh the costs (in terms of SNR and aesthetic image smoothness).

[0110] like Figure 3C As shown, in addition to enhancing the detectability of organic sugar 314 behind plate 310, the thin plastic (organic) plate on the handle and the metal side of the pistol 304 inside the safe 302 gradually become more visible as the thickness of the beam filter increases. Furthermore, while the shapes of the simulants 308 of drugs, explosives, and cash hidden behind plate 306 are gradually obscured by the reduced flux with greater filter thickness in images 360, 370, and 380, the apparent brightness of the simulants 308 is enhanced by increasing beam filter thickness, and some smaller simulants 308 that were barely detectable or completely invisible in the unfiltered image 350 become more visible after the beam filter is applied, as can be seen in images 360, 370, and 380.

[0111] from Figure 3C It is clear that the spatial resolution of the unfiltered image 350 is superior to the images 360, 370, and 380 obtained after applying the beam filter. In different scenarios, either spatial resolution or contrast may be more desirable. However, for enhancing the visibility of objects near the edge of the detectability, such as the metal slide of the pistol 304 or the simulant object 308, spatial resolution provides little value for detection, while the increased contrast provided by the beam filter is crucial.

[0112] For quantitative measurement of relative image signal, each of images 350, 360, 370, and 380 is scaled to have the same minimum and maximum pixel values. The average signal from a group of pixels in a generally uniform region of interest at the location of one of the organic threats (e.g., sugar bag 314) located behind the steel shield (e.g., plate 310) in each scaled image is then compared.

[0113] Figure 3D The results obtained by using different filter thickness, beam power and scanning speed are shown. Figure 3A Radiation image of the device. Figure 3A 、 Figure 3B 、 Figure 3C and Figure 3D, image 395 was obtained using a 0.8 mm beryllium vacuum window on the X-ray source used to image device 300. Thus, image 395 was obtained using negligible or zero beam filtering. Image 397 was obtained using a 2.0 mm thick copper beam filter. In addition, the beam power used to obtain image 397 was three times that used to obtain image 395. As shown, 3D image 397 is more grainy than image 395. However, the contrast advantage of the 2 mm copper beam filter is comparable to that of image 395. Figure 3C 380 is the same as that shown in . Furthermore, the detectability of the sugar bag 314 and the drug, explosive, and cash simulants 308 is significantly improved in image 397 compared to image 395. Thus, even with different power adjustments, the contrast excitation beam filter of the present disclosure provides enhanced detection capabilities for organic threat materials hidden behind steel plates.

[0114] Scan speed has been observed to have the same effect on dose and image quality as changing beam power. Changing the scan speed by 1 / 2x is equivalent to increasing the beam power by 2x, so by reducing the scan speed, the same image quality as in Image 397 can be achieved. In various embodiments, multiple beam filters of varying thicknesses can be employed with varying scan speeds to provide the same dose in each case to obtain high-contrast images, such as Image 397.

[0115] In an embodiment, the variable beam filter of the present specification can be combined with a mobile backscatter vehicle inspection system, which is typically an imaging module built into a panel van or a small truck. The drive speed, that is, the horizontal scanning speed, is controlled by the truck's accelerator pedal. In order to achieve high-quality low-speed scanning, some mobile backscatter vehicle inspection systems use a mechanical scanning drive. As an example, the AS&E Mobile Search Backscatter truck has two scanning speeds, 3 inches / second (about 1 / 4 km / h) and 6 inches / second (about 0.5 km / h), both of which are controlled by a motorized high-friction drum that engages one of the truck's tires to rotate the wheel and drive the vehicle. In an embodiment, a thick filter is used in combination with the inspection system's mechanical scanning drive to obtain a low scanning speed, thereby providing radiation images with improved contrast and threat visibility.

[0116] In embodiments, where cargo dose constraints apply to the inspection system, mechanical control of the selected beam filter is coordinated with control of the selected scan speed to maintain a constant dose in the inspection system. In various embodiments, the relationship between beam filter thickness and dose reduction is non-linear and non-trivial, but can be calculated using known methods. Figure 3Eis a graph showing the relationship between X-ray dose corresponding to beam filters of varying thickness. The Y-axis 3012 of plot 3010 depicts the dose relative to a baseline intrinsic filter and the X-axis 3014 depicts the filter thickness. As shown in plot 3010, the X-ray dose decreases as the filter thickness increases. In embodiments, where cargo dose limitations do not apply, the system operator can select a beam filter for a desired contrast level and separately select a scan speed for a desired flux level in exchange for scan time. In various embodiments, due to the low scan speeds facilitated by the mechanical scan drive, the contrast level achieved at any signal-to-noise ratio is greater than that achieved at the Figure 3C The contrast level demonstrated in image 380 shown in FIG. 3 is at 220 keV using a 2 mm copper filter.

[0117] In embodiments where the system operator selects high contrast, high scan speed, and high signal-to-noise ratio, system power may be limited, resulting in a tradeoff between high contrast and scan speed and low power. Therefore, in one embodiment, the system automatically performs a trade-off analysis to determine the highest possible contrast for the desired, input scan speed and signal-to-noise ratio, and scans at the highest possible contrast, which may be lower than the desired contrast level input by the operator. In another embodiment, the system automatically performs a trade-off analysis to determine the highest possible signal-to-noise ratio for the desired input scan speed and contrast, and runs the scan at the highest possible signal-to-noise ratio, which may be lower than the desired signal-to-noise ratio input by the operator. In another embodiment, the system automatically performs a trade-off analysis to determine the fastest possible scan speed for the desired, input signal-to-noise ratio and contrast, and runs the scan at a desired scan speed that may be lower than the highest possible scan speed input by the operator.

[0118] In various embodiments, scanning speeds for typical cargo inspection systems range from approximately 1 kilometer per hour (km / h) to 10 km / h. For example, for inspection systems that may be transported on rails, for scanning systems where the target vehicle is dragged past the imager using a car wash-type mechanism, and in some embodiments, for vehicle-mounted scanning systems with a scanning drive, a minimum scanning speed ranging from approximately 0.1 km / h to 0.3 km / h may be achieved. In another example, for vehicle-based scanning systems where the speed is controlled by the driver (using an accelerator pedal or other device), and for stationary scanning systems that require the target vehicle to drive past the stationary scanning system, scanning speeds below approximately 1 km / h to 2 km / h are generally difficult to control and achieve. In various embodiments, a maximum scanning speed of 10 km / h may be achieved, as scanning speeds above 10 km / h result in poor image quality and reduced safety. However, in some embodiments, there is no limit on the maximum permissible scanning speed. Therefore, in one embodiment, the trade-off analysis performed by the system is bounded by a minimum scanning speed of 0.5 km / hr, more preferably 1 km / hr, and by a maximum scanning speed of 20 km / hr, preferably 10 km / hr.

[0119] In various embodiments, the scanning system delivers a radiation dose to the cargo in the range of between 1 μR / scan (microRems / scan) and 25 μR / scan. In embodiments, a minimum dose value of 1 μR / scan may be delivered to the scanned object, since doses below 1 μR / scan result in poor image quality. As is well known, the relationship between dose and image quality depends on multiple parameters, such as, but not limited to, detector size and / or beam size. In some embodiments, there is no lower limit to the allowed dose. The maximum dose to a scanned vehicle with a person still inside the vehicle is typically limited by local laws or generally accepted safety standards, and in some embodiments, it does not exceed 10 μR / scan or does not exceed 25 μR / scan. The maximum dose threshold may be the same even for unmanned vehicles, since humans may be present in the vehicle as smuggled cargo.

[0120] The SNR metric is based on various parameters of the imaging system and the method used to measure the SNR value. In the embodiments of this specification, a typical SNR value corresponds to Figure 3C Baseline image 370 shown in . Figure 3CThe image 380 shown in FIG has an SNR value of approximately 0.84x relative to the baseline image 370. In an embodiment, the minimum acceptable SNR value is approximately in the range of one-half (1 / 2)x or one-third (1 / 3)x of the SNR value relative to the baseline image 370. In an embodiment, the minimum acceptable SNR value is approximately in the range of one-quarter (1 / 4) to one-tenth (1 / 10) of the image throughput. In an embodiment, there is no maximum acceptable SNR value because the value of the SNR is limited by the capabilities of the scanning system with respect to parameters such as, but not limited to, cost, weight, and scan time. Therefore, in an embodiment, the trade-off analysis performed by the system is limited to a minimum acceptable SNR in the range of 1 / 4 to 1 / 10 of the image throughput.

[0121] In an embodiment, the mechanical scan drive is replaced by a turntable that carries the imaging modules of the inspection system and rotates about a vertical axis, thereby causing a fan beam of X-rays to be horizontally scanned over the target. Figure 4 4 is a diagram of an imaging module coupled to a turntable according to an embodiment of the present specification. Inspection system 400 includes an imaging module 402 fixedly positioned on a turntable 404, which in turn is supported by a base 406. Imaging module 402 includes at least an X-ray source 408 coupled to a shutter 410, which can cover source 408 if desired. Shutter 410 is coupled to a first beam filter 412 and a second beam filter 414. The operation of shutter 410 and filters 412, 414 is similar to that described above with respect to Figure 1A 、 Figure 1B 、 Figure 1C and Figure 1D The turntable 404 can be rotated to position the imaging module 402 so that the filtered fan beam 416 of X-rays is emitted in a desired direction. Figure 4 As shown, the beam 416 is scanned in the vertical direction. In an embodiment, the variable beam filter of the present disclosure can be coordinated with the rotation speed of the turntable to achieve the same radiation quality as described above.

[0122] The following U.S. Patent Nos., among other features, describe cargo scanning systems commonly owned by applicant or applicant's parent company, and are incorporated herein by reference in their entireties: 6,542,580; 6,542,580; 6,658,087; 7,099,434; 7,218,704; 7,322,745; 7,369,643; 7,400,701; 7,486,768; 7,517,149; 7,519,148; 7,593,506; 7,720,195; 7,783,004; 7,817,776; 7,860,213 ;7,876,880;7,963,695;7,991,113;7,995,707;7,995,705;8,054,937;8,059,781;8,170,177;8,194,822;8,275,091;8,345,819;8,356,937;8,385,501;8,433,036;8,437,448;8,457,275;8,503,605;8,579,506;8,644,453;8,668,386;8,687,765;8,7 74,357; 8,781,067; 8,824,632; 8,837,670; 8,840,303; 8,903,046; 8,908,831; 8,929,509; 8,971,485; 9,020,096; 9,025,731; 9,036,779; 9,052,403; 9,052,264; 9,057,679; 9,121,958; 9,158,027; 9,223,049; 9,223,052; 9,274,065; 9,279,901; 9,285,4 98; 9,429,530; 9,541,540; 9,562,866; 9,632,205; 9,688,517; 9,791,590; 9,817,151; 9,823,201; 9,835,756; 9,958,569; 10,007,021; 10,007,019; 10,098,214; 10,228,487; 10,302,807; 10,317,566; 10,408,967; 10,422,919; 10,585,207; and 10,591,629.

[0123] In one embodiment, the system operator selects a beam filter range such that the dose output can vary by a specific factor (e.g., 8 times from minimum to maximum beam filtering), and the controller can be configured to modulate the scan speed by the same factor (8 times). If the controller determines that the maximum scan speed and minimum beam filter provide an SNR acceptable to the operator, the controller can automatically determine that the minimum scan speed and maximum beam filter provide the same dose and a similar SNR. In embodiments, larger or smaller ranges for beam filter or scan speed parameters can be adjusted based on the system's usage. For example, in a scenario where there are no dose-cargo constraints, the minimum allowable scan speed can be arbitrarily low and the final dose arbitrarily high, even if continuing to add beam filters is not feasible for mechanical reasons and greater contrast can be utilized at a constant dose at the lowest scan speed.

[0124] Mechanical Design of Variable Beam Filter

[0125] Return Reference Figure 1A In one embodiment, the X-ray tube is positioned relative to the object being scanned after each of the first filter 154 and the second filter 156. Preferably, the first filter 154 includes a curved surface that is concentrically positioned relative to the X-ray tube 150 and can be moved through an arc to alternately be positioned within or not within the field of view 167 of the X-ray tube 150. Similarly, the second filter 156 includes a curved surface that is concentrically positioned relative to the X-ray tube 150 and can be moved through an arc to alternately be positioned within or not within the field of view 167 of the X-ray tube 150. The first filter 154 and the second filter 156 are also preferably positioned concentrically relative to each other so that they can be moved simultaneously through an arc to be simultaneously within or not within the field of view 167 of the X-ray tube 150.

[0126] Figure 5A FIG is a diagram of an exemplary beam filtering system configuration for obtaining at least three beam spectra according to an embodiment of the present specification. Figure 5A As shown, filters 502, 504, and 506 of different thicknesses are positioned radially or concentrically around a beam-forming aperture 513 of an X-ray source 500 such that each filter occupies a portion of an arc around the source 500, with a portion 508 of the arc remaining open in a rotating wheel configuration. Three types of filtered beam spectra with a field of view 510 can be obtained by positioning each of the three filters 502, 504, and 506 (one after the other) in front of the beam-forming aperture 513. This configuration does not use a shutter, such as Figure 1A As shown. Since there is no shutter, the arc-shaped opening portion 508 can be occupied by any one of the filters 502, 504 and 506 in a manner that allows the opening portion 508 to be positioned in front of the beam forming aperture 513 to obtain a fourth unfiltered beam spectrum. For example, referring to Figure 5A , an unfiltered beam can be obtained by sliding filter 506 to opening portion 508 and sliding filter 504 to the position previously occupied by filter 506, thereby opening the arcuate portion in front of beam forming aperture 513 (previously occupied by filter 504). Figure 5A The filter placement / configuration shown in yields a spectral field of view of approximately 90 degrees.

[0127] It will be appreciated that the described radial translation filter system defines a field of view for each filter level that is smaller than the angular range of the filter, where the angular range is defined by the angle formed by one end of the filter, the center of the X-ray source, and the other end of the filter, as shown in FIG. Figure 1A , shown as angle 192 relative to filter 2. In one embodiment, the field of view is on the order of 0.5 degrees to 5 degrees less than the angular range of the filter.

[0128] Figure 5B FIG is a diagram of an exemplary beam filtering system configuration for obtaining multiple beam spectra according to an embodiment of the present specification. Figure 5B As shown, by reducing Figure 5A In order to obtain a field of view 510 of beam spectra, multiple filters can be employed in an arc around the source 500 along with a mechanical shutter to increase the number of beam spectra that can be obtained using the system. Figure 5B In the embodiment shown, six filters 502, 504, 506, 512, 514, and 516 of different thickness are used, enabling the system operator to obtain six different beam spectra with a field of view 518 corresponding to each filter. Figure 5A As explained, the open portion 508 of the arc provides an unfiltered beam spectrum when brought in front of the beam forming aperture 513. Figure 5B A mechanical shutter 520 is also employed in the configuration shown. In various embodiments, the "open" position provides zero millimeters of filtering of any material (i.e., allows all components of the X-ray beam to pass through), while the shutter can be considered to provide infinite filtering (i.e., does not allow any components of the X-ray beam to pass through). Although Figure 5B Only six filters are shown in FIG, but it will be apparent to one skilled in the art that any number of filters may be employed by reducing the field of view / increasing the distance of the filter ring from the source.

[0129] Figure 5C is a diagram of an exemplary beam filtering system configuration according to an embodiment of the present specification, which employs multiple filter rings around an X-ray source to obtain multiple beam spectra. Figure 5CIn the configuration shown, two concentric filter rings have been positioned around the source 500. The inner ring includes two filters 532, 534 of different thicknesses, a shutter 536, and an opening section 538; while the outer ring includes three filters 542, 544, 546 of different thicknesses and an opening section 548. By positioning various combinations of the five filters and the two opening sections before beam formation, different characteristics of the filtered beam 540 of the source 500 aperture 513 can be obtained. Figure 5C In the exemplary filter combination shown, beam spectrum 540 is obtained by placing filters 532 (from the inner ring) and 544 (from the outer ring) in front of beam-forming aperture 513. In various embodiments, for a field of view of approximately 90 degrees, twelve filter combinations (including combinations in which no filter is placed in front of beam-forming aperture 513, i.e., combinations in which both openings 538 and 548 are located in front of beam-forming aperture 513) are provided. Figure 5C This is possible when shutter 536 is used in the configuration shown. If shutter 536 is not included, a total of 16 filter combinations will be available for Figure 5C In various embodiments, filters 532, 534 and 542, 544, 546 can be made of the same or different materials. In an embodiment, where a filter having a first thickness in an outer ring is placed before a filter having a second thickness in an inner ring, and both filters are made of the same material, the combined filtering effect will be the same as if the thickness of the individual filters were the sum of the first and second thicknesses.

[0130] Figure 5D is an illustration of a top view of an exemplary beam filtering system configuration employing multiple filters arranged linearly in front of a beam forming aperture of a source to obtain multiple beam spectra, according to an embodiment of the present specification. Figure 5D As shown, filters 582, 584 and shutter 586 are arranged in a first vertical row in front of source 501, and filters 588, 590 and 592 are arranged in a second vertical row of filters (582, 584) in front of source 501. Figure 1C As explained, filters 582, 584 and shutter 586 and Figure 5D The filters 588, 590, and 592 shown in FIG can be translated vertically to position any of the filters (or shutters) at the beam forming aperture 515 of the source 501 to obtain a filtered beam 594. Dashed line 596 depicts the position of the filters 582, 584 and shutter 586 in an open position, i.e., not covering the beam forming aperture 515, and dashed line 598 depicts the position of the filters 588, 590, and 592 in the open position. In an embodiment, in FIG Figure 5DA large number of filters can be used in the design shown, since the angular field of view of the source places no limit on the number of filters that can be positioned in front of the beam forming aperture 515. In various embodiments, when filters are employed in a concentric ring configuration, as with respect to Figures 5A to 5C As explained, the field of view of a filter placed in front of the pencil beam forming aperture of an X-ray source is approximately 2° to 4° smaller than the filter angle. This is because the width of the pencil beam is finite according to known mechanical and optical rules, and due to timing and data management, the field of view of the filter is less than 360 / N, where N is an integer value. Therefore, if the field of view is less than 360 / N, it can be reduced by using a filter such as Figures 5A to 5C The filter configuration shown is used to obtain N spectra.

[0131] In embodiments, an exemplary contrast beam filter that can produce high contrast images of organic threats and can be used to enhance the visibility of objects near the edge of detectability is made of a dense material with a high atomic number. More specifically, the contrast beam filter is made of a metal such as, but not limited to, bronze, tin, tungsten, or a copper matrix embedded with tungsten particles. In embodiments, if the filter is made of a material such as tungsten or lead, whose fluorescence energy is high enough to be detected in a backscatter detector (e.g., 60 keV for tungsten and 75 keV for lead), the filter is designed to absorb substantially all of the fluorescence energy. In embodiments, the filter is designed from a composite material or is designed to have a multi-layer design that employs a secondary shielding layer made of steel or copper to absorb fluorescence from the lead or tungsten. In embodiments, the thickness of the secondary shielding layer is designed to absorb a predetermined portion of the fluorescence. For example, a secondary shielding layer made of a 0.5 mm thick copper sheet can attenuate the fluorescence of tungsten to half of its initial value.

[0132] In an embodiment, the contrast beam filter of the present disclosure is used in conjunction with a beam collimation system designed to prevent scatter from leaving the system without passing through the beam filter. This is because any Compton or Rayleigh scatter that escapes the beam filter but still exits through the beam-forming aperture forms a "halo" around the primary X-ray pencil beam, which in turn degrades the spatial resolution of the acquired image. Figure 6A is a diagram of a contrasting beam filter employed in an X-ray collimation system according to an embodiment of the present specification. Figure 6B is a diagram of a contrast beam filter employed in an X-ray collimation system according to another embodiment of the present specification. Figure 6A and Figure 6BThe system shown in FIG. 6 includes a shutter 602 coupled to a filter 604 for filtering an X-ray beam 606. The X-ray beam 606 is generated using an X-ray tube 608 and a pencil beam forming aperture 610. The aperture 610 is provided on a hoop 612 mounted to a rotatable disk-shaped structure 614 that provides space for the X-ray tube 608. Figure 6A As shown, the X-ray tube 608 is not positioned on the axis 616 of the rotating disk 614. A motor 618 enables the disk 614 to rotate. To minimize unwanted scatter, the beam 606 is collimated into a fan beam by a second collimator 620 that fills the space between the X-ray tube housing 622 and the shielding ring 624. The exit opening 626 of the X-ray tube housing 622 also assists in fan beam collimation and is referred to as the first fan collimator 621. Figure 6A and 6B As shown, the shutter 602 and the variable beam filter 604 are located between the exit opening 626 and the collimator 620. The shutter 602 coupled with the filter 604 can slide to at least partially cover the exit opening 626 to attenuate the beam 606, as described above with reference to FIG. Figures 1A to 1D Explained.

[0133] Figure 6A The system shown in FIG provides radiation safety for the personnel operating the system and the personnel being scanned by the system when in operation. This is because all direct paths of the beam 606 from the focus 628 to the aperture 610 pass through the filter 604. Figure 6A In the system shown, thin filters are used, which allows the maximum number of filters to be used within the given available space.

[0134] However, the system allows scattered radiation 630 to exit the system through the aperture 610 without first being attenuated by the filter 604. This scattered radiation 630 may not pose a safety problem because the scattered radiation is a relatively small portion of the total dose. Furthermore, since the safety of people around the system depends on the total dose, by increasing the beam filtering in proportion to the dose, the safety parameters can be met. However, even if the system is safe for people, the scanned images produced by the system may not be contrast effective (as described above) due to the scattered radiation 630. Figure 6A As shown, scattered radiation 630 contributes to the formation of a halo around the primary beam envelope 606. As the primary beam 606 is attenuated by the added filter, this unattenuated scattered 630 halo becomes proportionally more intense, further reducing image efficiency. In addition to reducing spatial resolution, scattered 630 halo also leads to a reduction in all forms of contrast because it causes background fogging in the scanned image.

[0135] Figure 6B Shows the modification to produce a high contrast scanned image. Figure 6A collimation system. Figure 6B As shown, the exit opening 626 of the X-ray tube housing 622 is narrowed and the beam filter 604 is widened so that the light beam 606 has no direct path to exit the opening 626 without passing through the filter 604. Because this results in less direct light beam 606 falling on the wall of the second sector collimator 620, the thickness of the collimator 620 can be reduced because there is less scatter to be shielded. Figure 6A Compared with the system, Figure 6B The scattering in the system is reduced (and not in Figure 6B ), resulting in Figure 6B The system produces more efficient high-contrast images.

[0136] In various embodiments, the scatter shield used in conjunction with the filters of the present description is designed to eliminate any signal noise / scatter. Figure 6C Another embodiment according to the present specification is shown. Figure 6B The contrast beam filter inspection system shown in FIG is used in conjunction with a scatter shield. Figure 6C As shown, a backscatter detector 630 can be employed in the system to detect radiation backscattered from the imaged object. In various embodiments, the backscatter detector 630 also inevitably detects radiation scattered by the filter 604 that is part of the sliding / rotating filter changing system 631. Shielding 632 made of a material such as, but not limited to, lead is provided around the X-ray tube housing 622 and the aperture 610. In various embodiments, additional shielding features are incorporated into the system to eliminate leakage around the mobile filter changer assembly 631 of the filter 604. Scattering of the primary beam 606 by the filter 604 and / or components of the filter changing hardware can produce radiation such as Figure 6C 634. Additional shielding 636 is provided around the system to eliminate leakage of X-rays along the scattering path 634. Because the hardware components of the system (e.g., the tray 614, which may be made of a metal such as aluminum or steel) do not provide the required shielding, in an embodiment, additional shielding 638 made of lead or tungsten is provided around the components to prevent radiation leakage, as any leakage captured by the backscatter detector would degrade the resulting scan image quality.

[0137] In an embodiment, to prevent isotropic scattering from the beam filter from escaping the X-ray inspection system, a contrast beam filter is located close to the X-ray source when used in the X-ray inspection system. The farther the beam forming aperture of the beam collimation system of the X-ray inspection system is from the origin of this scattering (i.e., the beam filter), the smaller the solid angle of the aperture relative to the origin is, and less scattering escapes the system. The same is true for any multiple scattering that finds a path around the beam filter. In order to maximize contrast by minimizing the effects of X-ray scattering, in one embodiment, the system implements a beam filter that is as close to the X-ray tube as possible and as far away from the pencil beam forming aperture 610 as possible. The beam filter can be located between the tube and the fan collimator, or due to space limitations, it can be located between the fan collimator and the pencil beam forming aperture 610. As shown in Figure 6, in one embodiment, the beam filter is positioned as close to the X-ray tube (608) and the first fan collimator (621) as possible, and as far away from the pencil beam aperture (610) as possible to maximize contrast.

[0138] Figure 7A is a top cross-sectional view of a pencil beam collimation system using a beam filter according to an embodiment of the present specification. Figure 7B Yes Figure 7A A side cross-sectional view of a pencil beam collimation system employing a filter is shown. Figure 7A 、 Figure 7B A single beam filter 702 is shown in FIG. 1 , however, single filter 702 may be part of a plurality of beam filters employed in the aforementioned rotating or translating beam filter changing system. As shown, a primary beam 704 emitted from an X-ray tube 706 is attenuated by filter 702 and collimated by a pencil beam forming collimator 708. Isotropic scatter 710 from beam filter 702 constitutes a source of photons that can escape collimator 708 through an aperture 712 of the X-ray tube. Scattered photons 710 collimated by aperture 712 form separate beam spots or "halos" 714 around a beam spot 716 formed by primary beam 704, as shown. Halos 714 reduce spatial resolution because scattered photons 710 sample a large area and effectively average the backscattered signal from that area. This signal, combined with the good image signal from the primary beam spot, reduces all forms of contrast in the scanned image obtained by the system.

[0139] The intensity of the halo 714 signal (proportional to the flux of scattered photons escaping through the aperture 712) is proportional to the distance (L) from the filter 702 to the aperture 712. filter The intensity of the main beam 704 is inversely proportional to the square of the distance (L) from the focus 718 of the X-ray tube 706 to the aperture 712. fs). In various embodiments, the distance (Δ) from the focal point 718 of the X-ray tube 706 to the filter 702 is:

[0140] △=L fs -L filter Formula 1

[0141] The image degradation caused by the halo 714 is proportional to the ratio of the bad flux from the scattered halo to the good flux from the main pencil beam 704 and can be defined as:

[0142] L fs 2 / L filter 2 =L fs 2 / (L fs -△) 2 Formula 2

[0143] Therefore, by positioning the beam filter 702 in close contact with the X-ray tube 706, minimal bloom 714 will be achieved. fs Increase to 0.4*L fs , then the scattered halo intensity will increase by 2.25 times; △ further increases to 0.6*L fs Relative to 0.1*L fs The effect of the halo 714 on spatial resolution is a function of both halo intensity and halo size, which is a function of the size of the aperture 712, the distance between the aperture 712 and the focal point 718, and the size of the beam filter 702, which will be larger than the focal point 718. These factors vary depending on the inspection system, but for a narrow primary beam 704 and a narrow collimated aperture 712, and a target distance > 10*L, the halo intensity increases by a factor of 5.1. fs , the ratio of the size of the halo 714 (in one dimension) to the size of the main beam spot 716 is proportional to:

[0144] L fs / L filter =L fs / (L fs -△) Formula 3

[0145] Formula 3 is the square root of Formula 2. This relationship between Formula 2 and Formula 3 shows that if ∆ is from 0.1*L fs Increase to 0.4*L fs , then the diameter of the scattered halo will increase by 1.5 times; and relative to 0.1*L fs △, further increase △ to 0.6*L fs This will increase the halo diameter by a factor of 2.25.

[0146] In an embodiment, the contrast beam filter of the present specification is used in conjunction with a shielding device designed to contain all scatter from the beam filter or related components so that the scattered radiation does not escape the beam collimation system and does not enter one or more detectors of the X-ray inspection system. The escaping scattered radiation (leakage) causes fogging in the backscattered image obtained from the detector, thereby reducing image contrast. In a typical backscatter X-ray imaging system, the backscatter detector is located near the X-ray source (rather than on the far side of the image target) and the detector subtends a much larger area than a typical transmission X-ray detector. The backscatter detector is sensitive to X-ray dose much lower than the dose considered safe, and any leakage or scattered dose that enters the detector will cause a signal offset, thereby reducing contrast. In order to enhance image contrast, the image SNR will be affected, so it becomes critical to eliminate all other noise sources or unwanted signals. Therefore, the scatter shield used in conjunction with the filter of the present specification is designed to eliminate any signal noise / scatter, such as reference Figure 6C Thus, any leakage from all other parts of the beam forming and collimation system of the X-ray inspection system, such as but not limited to: direct leakage and scattering from the source housing; scattering escaping through the gap between the source housing and the rotating chopper that forms the scanned pencil beam; and scattering through gaps that exist only to accommodate the mechanical structure that moves the beam filter in and out of the beam, is attenuated by the use of the described shielding design.

[0147] Software Design of Variable Beam Filter

[0148] Figure 8A Depicted is an exemplary graphical user interface for enabling an operator to adjust the contrast of an image, according to an embodiment of the present specification.

[0149] refer to Figure 8A In one embodiment, a graphical user interface 801 has a display portion 804 and a plurality of controls 802, one of which may be a contrast level input mechanism, a scan speed input mechanism, and a signal-to-noise ratio input mechanism, and may be an icon, button, toggle, switch, dialog box, or other input mechanism. In one embodiment, an operator may interact with the input mechanism 802 to increase or decrease the contrast level of a generated image.

[0150] In one embodiment, the system may have an initial default contrast level that corresponds to a plurality of other default settings in the X-ray inspection system, including a default filter configuration. Upon modifying the contrast level, a controller 811 coupled to the X-ray inspection system communicates data with the graphical user interface via a network 815, causing any default contrast settings in the X-ray inspection system, including the filter positions described above and certain other software settings described below, to be reconfigured to accommodate the new contrast setting.

[0151] In an embodiment, for safety purposes, the controller 811 may modify any default settings for the minimum user-selectable scan speed to limit the maximum dose per scan. In an embodiment, the controller 811 may modify any default settings for the maximum duty cycle to limit the amount of dose received by the operator or bystanders.

[0152] In an embodiment, the controller 811 can inhibit scanning for a predetermined period of time after the predetermined scan time is reached, and can also modify the maximum duty cycle. For example, the system can be configured to emit X-rays for 45 minutes within any 60-minute period. In an embodiment, the time during which scanning is inhibited is different for each beam filter used in the system; wherein the time during which scanning is inhibited is proportional to the dose and is calculated as a function of time and beam filter. This enables a user to operate the system for part of an hour using one filter and the remainder of the hour using a different filter, with the controller 811 taking into account the combined dose for the hour to determine when to apply the scanning inhibition.

[0153] In an embodiment, the controller 811 automatically determines one of the following in response to a user selecting at least two of the parameters: beam filter thickness, scanning speed, and signal-to-noise ratio. Figure 8B 850 is a flow chart illustrating a method for automatically determining a signal-to-noise ratio in response to a user selecting a beam filter thickness and a scanning speed for an inspection system, according to an embodiment of the present disclosure. In step 850, the user selects a beam filter thickness and a maximum scanning speed for the inspection system. In embodiments, as described above, the contrast of the scanned image depends on the selected beam filter thickness. In embodiments, a thick filter may produce a high-contrast scanned image.

[0154] Figure 8E is an exemplary table showing the correlation between beam filter thickness, scanning speed, and signal-to-noise ratio values according to an embodiment of the present specification. Table 840 includes a column 842 listing a plurality of beam filters, a column 844 listing a plurality of corresponding scanning speeds, and a column 846 listing a plurality of SNR values relative to a baseline system including a 1 mm copper filter and operating at a scanning speed of 1 km / h with variable parameters including, but not limited to, scanning distance and detector array size. For example, a user may select: 1) a 2 mm thick copper beam filter to obtain maximum penetration contrast, and 2) a maximum scanning speed of 10 km / h to allow for rapid inspection of vehicles in a queue. Referring to Table 840, the controller ( Figure 8A811 in column 846) automatically determines that the SNR value can drop to 0.26 times the baseline configuration value shown in column 846. In an embodiment, the pre-defined threshold value for the SNR can set the SNR to not drop below 0.32 times the baseline value (corresponding to one-tenth of the baseline flux). In such an embodiment, the user is informed that the selected beam thickness and scan speed will provide an extremely low SNR value below the predetermined threshold. In an embodiment, the controller can prompt the user to limit the scan speed to 3 km / h for use with a 2.0 mm copper filter (or a scan speed range between 3 km / h and 10 km / h). In an embodiment, the controller can prompt the user to limit the beam filter thickness to 1 mm copper at a scan speed of 10 km / h.

[0155] Return Reference Figure 8B At step 852, a signal-to-noise ratio or amplifier gain level is automatically determined using the selected beam filter thickness and maximum scan speed. In an embodiment, controller 811 is programmed to determine the signal-to-noise ratio using the user-selected beam filter thickness and maximum scan speed. At step 854, the automatically determined signal-to-noise ratio or amplifier gain level is presented to the user via graphical user interface 801. At step 856, a determination is made as to whether the automatically determined signal-to-noise ratio or amplifier gain level is greater than a predetermined threshold, where the threshold is a baseline value indicating a minimum level of acceptable signal-to-noise ratio or amplifier gain level. If the signal-to-noise ratio or amplifier gain level is less than the predetermined threshold, the user is notified of the same at step 858. At step 860, the user is presented with an option to modify the beam filter thickness and / or the maximum scan speed selected at step 850. In an embodiment, the user can modify the beam filter thickness and / or the maximum scan speed by accessing controls 802 using graphical user interface 801. At step 862, if the signal-to-noise ratio or amplifier gain level exceeds a predetermined threshold, the user is notified of the same and the inspection system operates with the selected beam filter thickness, maximum scan speed, and the determined signal-to-noise ratio or amplifier gain level.

[0156] Figure 8C is a flow chart illustrating a method for automatically determining an image contrast value in response to a signal-to-noise ratio and a scan speed selected by a user for an inspection system according to an embodiment of the present specification. In step 870, the user selects a signal-to-noise ratio and a maximum scan speed for the inspection system. In an embodiment, as described above, the contrast of the scanned image depends on the thickness of the selected beam filter. In an embodiment, a thick filter will result in a high contrast scanned image. For example, the user may select a higher signal-to-noise ratio value, such as 1.4 times the typical baseline value, to obtain a smooth, clear image, and a maximum scan speed of 1 km / h for moderate speed inspections of a small number of vehicles. Then, with reference to Figure 8E As shown in Table 840, the controller ( Figure 8A811 in) automatically provides that the only compatible available beam filter thickness is a 0.8 mm Beryllium beam window (effectively zero beam filtering), which will provide moderate penetration contrast (below typical baseline values). Based on the purpose of the scanning system, in embodiments, a predefined threshold for penetration contrast may be defined. For example, a scanning system operated by the military may need to detect organic IEDs in the trunk of a car. In such an embodiment, the controller may prompt the user to select a thicker beam filter, such as a copper filter with a thickness of 1.0 mm. Figure 8E As shown in FIG, a scanning speed of 1 km / h shown in column 842 corresponds to an SNR value of 1.45x shown in column 846, which is higher than the expected SNR with a 1 mm copper filter. In an embodiment, if the scanning system can provide such a speed, the controller determines a lower scanning speed (e.g., 0.5 km / h). If the scanning system cannot provide such a low speed, the user is prompted to select a lower SNR value.

[0157] In step 872, an image contrast value or beam filter thickness is automatically determined using the selected signal-to-noise ratio and maximum scan speed. In an embodiment, the controller 811 is programmed to determine the image contrast value using the user-selected signal-to-noise ratio and maximum scan speed. In step 874, the automatically determined image contrast value is presented to the user via the graphical user interface 801. In step 876, a determination is made as to whether the automatically determined image contrast value is greater than a predetermined threshold, where the threshold is a baseline value indicating a minimum level of acceptable image contrast. If the image contrast value is less than the predetermined threshold, the user is notified of the same value in step 878. In step 880, the user is presented with the option to modify the signal-to-noise ratio and / or maximum scan speed selected in step 870. In an embodiment, the user can modify the signal-to-noise ratio and / or the selected maximum scan speed by accessing the plurality of controls 802 using the graphical user interface 801. In step 882, if the image contrast value is greater than the predetermined threshold, the user is notified of this fact and the inspection system is operating with the selected signal-to-noise ratio, maximum scan speed, and determined image contrast value.

[0158] Figure 8Dis a flow chart illustrating a method for automatically determining a maximum scan speed in response to a user selecting a signal-to-noise ratio and image contrast value for a detection system according to an embodiment of the present specification. At step 890, the user selects a signal-to-noise ratio and image contrast value for the inspection system. In an embodiment, as described above, the contrast of the scanned image depends on the selected beam filter thickness. In an embodiment, a thick filter will result in a high contrast scanned image. For example, a user may select an SNR value of 0.8 times a typical baseline value to obtain an image that is roughly equivalent to an image with a typical image grain level and a high penetration contrast value to maximize ease of use and effectiveness in detecting organic anomalies such as illicit drugs hidden behind vehicle body panels. Then, reference is made to Figure 8E As shown in Table 840, the controller ( Figure 8A 811 in the figure automatically determines that the ideal beam filter is a copper filter with a thickness of 2.0 mm and a maximum compatible scanning speed of 1 km / h. In an embodiment, based on the user's requirements, a maximum scanning speed of 3 km / h has been predefined. To ensure a moderately high scanning throughput, the controller prompts the user to select a lower SNR value (e.g., 0.48 times the typical baseline value) or a lower level of penetration contrast.

[0159] At step 892, a maximum scanning speed is automatically determined using the selected signal-to-noise ratio and image contrast values. In one embodiment, the controller 811 is programmed to determine the maximum scanning speed using the signal-to-noise ratio and image contrast values selected by the user. At step 894, the automatically determined maximum scanning speed is presented to the user via the graphical user interface 801. At step 896, a determination is made as to whether the automatically determined maximum scanning speed is greater than a predetermined threshold, where the threshold is a baseline value indicating a minimum acceptable maximum scanning speed level. If the maximum scanning speed is less than the predetermined threshold, the user is notified of this fact at step 898. At step 8100, the user is presented with an option to modify the signal-to-noise ratio and / or image contrast value selected at step 890. In one embodiment, the user can modify the selected signal-to-noise ratio and / or image contrast value using the graphical user interface 801 and the plurality of controls 802. At step 8102, if the maximum scanning speed is greater than the predetermined threshold, the user is notified, and the examination system operates at the selected signal-to-noise ratio, image contrast value, and the determined maximum scanning speed.

[0160] In various embodiments, the nonlinear transfer functions used, such as "gamma" and "S-curve" transfer functions, may have to be configured when selecting different contrast levels because the ideal gamma or S-curve transfer function depends on the ratio of bright / dark pixels in the image. In embodiments where only one beam filter is used, only one set of parameters is required to apply the transfer function, whereas where 'n' number of beam filters are used, 'n' sets of parameters (i.e., one set for each filter) are required. In embodiments, the gamma function is defined by one parameter, while the S-curve is defined by multiple parameters. The selection of the gamma or S-curve transfer function is based on the desired characteristics or "look" of the scanned image.

[0161] In an embodiment, a processing unit of an inspection system employs a contrast-excited beam filtering system that receives data representing an image and executes an S-curve transfer function from a detector array to suppress unsightly fogging and / or noise in dark background regions of a backscattered radiation image. In operation, a controller accesses a memory storing a plurality of parameters specific to each filter. For example, if there are N beam filters, the memory preferably stores and the controller preferably has access to N sets of corresponding parameters, wherein each set of corresponding parameters defines at least one of the above-described gamma function or S-curve transfer function. The plurality of parameters are pre-selected based on the desired aesthetic appearance of a given filter type. For backscattered radiation images, different detection materials correspond to changes in signal levels, and such transfer functions should be reconfigured based on the new contrast levels. Adding beam filters of the present specification both increases signal and increases noise in the air region (due to reduced flux), increases the need to modify the S-curve transfer function, and increases the need to carefully optimize the shape of the S-curve for a particular imaging scenario.

[0162] Figure 9A is a graph illustrating a transfer function that may be used to process a backscattered X-ray image according to an embodiment of the present specification. Figure 9B is a backscattered image processed by using a linear function according to an embodiment of the present specification. Figure 9C The embodiment of the present specification shows the method of processing the image by using the gamma transfer function. Figure 9B Backscattered image. Figure 9D The embodiment of the present invention is shown by using an S-curve transfer function to process Figure 9B Backscatter image of . 9A to 9D The shape of the S-curves 918 and 922 is a function of the parameters "A" and "C", where parameter A controls the amplification of medium and high signals and parameter C controls the suppression of low signals. Figure 9A and Figure 9B, image 910 was obtained using a 1.0 mm thick copper beam filter, where only the linear function depicted by plot 912 was applied, corresponding to values of A of 1 and C of 0.0001, and thus plot 910 represents the raw, unprocessed scan data. Figure 9A and Figure 9C , when image 910 is processed by using a gamma function such as the "square root filter" shown in plot 914, image 916 is obtained. By comparing Figure 9B and 9C As can be seen, compared to the original image 910, the image 916 has higher brightness and relative contrast in the darker areas in exchange for reduced contrast in the lighter areas. Figure 9A and Figure 9D When image 910 is processed using the S-curve function depicted by plot 918 corresponding to an A value of 2.25 and a C value of 0.25, image 920 is obtained. The S-curve of plot 918 is compatible with the use of relatively thick beam filters and can be applied to images obtained by using thick filters to darken any foggy background areas in the image. Figure 9A It can be seen that the S-curve of graph 918 has a steeper slope in the middle range of the input signal, providing more contrast in that range, and a shallower slope in the low end range of the input signal, demonstrating more low signal suppression. Figure 9B 、 9C As can be seen from Figures 9D and 9D, compared to the original image 910 and the gamma-processed image 916, the image 920 has reduced fog 915 and enhanced medium- and high-signal organic threats 917. Figure 9A , plot 922 depicts an S-curve corresponding to an A value of 1.75 and a C value of 0.1. The S-curve of plot 922 is compatible with the use of relatively thin beam filters and can be applied to images obtained by brightening medium and high signal areas using thin filters, such as, for example, organic threat simulants hidden behind steel.

[0163] In various embodiments, due to the reduced contrast in the image, a plurality of contrast enhancement algorithms are developed for processing images obtained using minimum beam filtering as described above. In various embodiments, a plurality of edge enhancement algorithms are developed for processing images obtained using increased beam filtering as described above. In some embodiments, contrast enhancement is achieved by employing methods such as, but not limited to, histogram stretching or adaptive contrast using adaptive histogram equalization and / or contrast-limited adaptive histogram equalization. In embodiments, image edges are enhanced using methods such as, but not limited to, 'Unsharp Masking' or Sobel filters, in combination with noise reduction achieved using a non-local means filter.

[0164] In various embodiments, backscattered and transmitted X-ray images are typically processed by a series of software image enhancement filters prior to display, wherein the filters have an associated "strength," or degree to which each filter acts on the image. In some embodiments, the filters are defined by multiple parameters that adjust the strength of different factors within the filters. In various embodiments, the selection of filters and the degree to which the selected filters are combined before being applied to the image to process the image are unique to each given system. Figure 10 1000 is a table illustrating filter chains for different beam filter configurations that may be employed with a variable filter system according to an embodiment of the present specification. Columns 1002, 1004, and 1006 of table 1000 provide the characteristics of image processing obtained by using no (or very thin) filters, medium filters, and thick filters, respectively. As shown in table 1000, for an exemplary 220 kV bremsstrahlung spectrum, a 0.8 mm thick beryllium or 0.5 mm thick copper filter would correspond to no (or very thin) filter, a 1.0 mm copper filter would correspond to a medium filter, and a 2.0 mm copper filter would correspond to a thick filter. Using no (or very thin) filter would provide high SNR and high spatial resolution, but would provide low contrast for any objects placed behind an obstruction in the processed image, while using a thick filter would provide high contrast for any objects placed behind the obstruction behind a blurry but low SNR, resulting in a haze in low signal areas of the processed image. The use of no filter (column 1002) provides little or no image smoothing, low S-curve signal suppression factor, high nonlinear transfer function contrast enhancement, and, if desired, high edge enhancement in the processed image. The use of a medium filter (column 1004) provides moderate image smoothing, S-curve signal suppression factor, and nonlinear transfer function contrast enhancement, and, if desired, moderate edge enhancement in the processed image. The use of a thick filter (column 1006) provides strong image smoothing, high S-curve signal suppression factor, low nonlinear transfer function contrast enhancement, and moderate edge enhancement in the processed image.

[0165] In various embodiments, an X-ray inspection system employing two or more variable contrast filters of the present description includes a corresponding number of default display parameters that are automatically selected based on the selection of the beam filter.

[0166] In various embodiments, after processing a scanned image using one or more beam filters, a user may perform image adjustments such as, but not limited to, "histogram stretching," which is known in the art and is similar to user adjustments to the brightness and contrast of a cathode ray tube (CRT) television. This type of image adjustment does not alter any physical properties of the image as beam filters do. User image adjustments result only in brightness and contrast adjustments to the image's final display parameters, representing only a linear scaling of the available image data.

[0167] Figure 11 Figure 1106 illustrates image display adjustments made to a scanned image that has been processed using one or more beam filters, according to an embodiment of the present specification. Image 1102 has been processed using a thin (0.8 mm) Be beam filter. Image adjustments, such as, but not limited to, "histogram stretching," are applied to image 1102 to obtain image 1104. The image adjustments applied to image 1102 are depicted in graph 1106. As described above, thin filters require a brighter mid-range signal than thick or medium filters. Therefore, as depicted in graph 1106, the default display window, depicted by graph 1108, is set to allow the brightest pixels to be saturated, as depicted by graph 1110, in exchange for making the remaining pixels appear brighter, relative to the full-scale display depicted by graph 1112. Graph 1108 depicts the region between the high and low signal limits of the displayed data, referred to as the display window. As can be seen when comparing image 1102 to image 1104, feature 1114 in image 1104 is saturated, while feature 1116 has been brightened.

[0168] Image 1120 has been processed using a thick (2 mm) Cu beam filter. Image adjustments such as, but not limited to, "histogram stretching" are applied to image 1120 to obtain image 1124. The image adjustments applied to image 1120 are depicted in graph 1126. As described above, even after processing with a thick filter, the resulting image may still have unsightly noise or fog in the background, so as depicted in graph 1126, a default display window, depicted by plot 1128, is set to allow low signal data to be "clipped," as depicted by plot 1130 for initial display. Plot 1128 depicts the area between the high and low signal limits of the displayed data and is referred to as the display window. Since clipping low signal data may make the entire image appear darker, a small portion of the brightest pixels may be allowed to saturate, as shown in graph 1126, in order to increase the overall image brightness so that in bright areas, the average brightness level is roughly similar to the brightness level of a full-size display 1132. Comparing image 1120 to image 1124 , it can be seen that feature 1134 in image 1124 has become darker.

[0169] Figure 12The present invention is a flow chart illustrating a method for controlling the contrast value of a scanned image obtained from a backscatter X-ray inspection system according to an embodiment of the present disclosure. The system includes a plurality of beam filters of increasing thickness, coupled to an X-ray source, for filtering the X-ray beam generated by the X-ray source before it is irradiated onto a subject. In step 1202, a beam filter is selected for filtering the X-ray beam based on a default contrast setting or based on a desired contrast level input by an operator. The contrast selection is based on the desired contrast value of the scanned image, and it should be understood that the contrast value increases in direct proportion to the increase in filter thickness.

[0170] At step 1204, the system's default settings are reconfigured to correspond to the selected filter. This reconfiguration of the default settings allows the system to adapt to any changes in the scanned image corresponding to changes in the beam filter. At step 1206, one or more nonlinear transfer functions of an image processing module coupled to the inspection system are optimized to obtain a scanned image having a desired contrast value. In one embodiment, the acquired scanned image is processed using at least one of a contrast enhancement algorithm and an edge enhancement algorithm based on the desired contrast value and the desired signal-to-noise ratio value of the image.

[0171] In various embodiments, information from two images of the same target, where each image is obtained using a beam filter of a different thickness, can be combined to obtain an image with improved detection quality. Figure 13 The flowchart illustrates a method for combining scanned images to obtain an image with improved inspection quality, according to an embodiment of the present disclosure. In step 1302, a first high-resolution scanned image of an object is obtained. In step 1304, a second high-contrast scanned image of the same object is obtained. In embodiments, the first high-resolution scanned image is obtained using an inspection system in which the incident X-ray beam is filtered using a thin / minimum filter; the second high-contrast scanned image is obtained using an inspection system in which the incident X-ray beam is filtered using a thick filter. In various embodiments, edges located in the first high-resolution image serve as a guide for enhancing edges located in the second high-contrast image. In step 1306, regions in the second image containing edges are identified using the first image as a guide. In step 1308, an edge enhancement routine is applied to regions known to contain edges in the second image, while leaving other regions untouched, thereby preventing the edge enhancement algorithm from enhancing noise in regions of the image without edges. In step 1310, once located, the edges serve as a guide for edge preservation in the second image, while a smoothing algorithm is applied to reduce noise in the second high-contrast image. In an embodiment, potential threats located in the second, high-contrast image may be used as a guide to apply a graphical bounding box or other indicator to the first, high-resolution / high-SNR image to direct the operator in analyzing the threat area.

[0172] The above examples are merely illustrative of the many applications of the systems and methods of the present disclosure. Although only a few embodiments of the present disclosure are described herein, it should be understood that the present disclosure may be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. Therefore, the present examples and embodiments are to be considered as illustrative rather than restrictive, and the disclosure may be modified within the scope of the appended claims.

Claims

1. An X-ray inspection system for scanning an object, the system comprising: an X-ray source configured to generate an X-ray beam for irradiating an object, wherein the X-ray beam irradiating the object defines a field of view, and wherein the X-ray source is coupled to at least a first beam filter having a first thickness and a second beam filter having a second thickness greater than the first thickness; a detector array adapted to receive radiation from the x-ray beam that is transmitted through or scattered from the object and to generate data representative of at least one image; a processing unit configured to receive the data representing at least one image and to generate the at least one image for display based on the data representing at least one image; a user interface configured to receive a first user input indicating a desired contrast level in the at least one image and a second user input indicating a desired scanning speed for the object; a controller configured to adjust a position of at least one of the first beam filter and the second beam filter based on user input indicating a desired contrast level in the at least one image, wherein the system is configured to determine a highest possible contrast level based on the desired scanning speed, and wherein the controller is configured to adjust the position to achieve the highest possible contrast level relative to the desired contrast level.

2. The X-ray inspection system according to claim 1, wherein: The desired contrast level includes at least one of a first contrast level, a second contrast level, a third contrast level, and a fourth contrast level, and wherein the first contrast level is less than the second contrast level, the second contrast level is less than the third contrast level, and the third contrast level is less than the fourth contrast level.

3. The X-ray inspection system according to claim 2, wherein: When the user interface receives user input of the first contrast level, the controller is configured to cause the first beam filter and the second beam filter to be out of the field of view of the X-ray source.

4. The X-ray inspection system according to claim 2, wherein: When the user interface receives user input of the second contrast level, the controller is configured to position the first beam filter within a field of view of the X-ray source and position the second beam filter out of a field of view of the X-ray source.

5. The X-ray inspection system according to claim 2, wherein: When the user interface receives user input of the third contrast level, the controller is configured to cause the first beam filter to be out of the field of view of the X-ray source and the second beam filter to be in the field of view of the X-ray source.

6. The X-ray inspection system according to claim 2, wherein: When the user interface receives the user input of the fourth contrast level, the controller is configured to position the first beam filter in the field of view of the X-ray source and the second beam filter in the field of view of the X-ray source.

7. The X-ray inspection system according to claim 1, wherein: The first beam filter and the second beam filter include a metal material having a high atomic number.

8. The X-ray inspection system according to claim 1, wherein: The first beam filter and the second beam filter include at least one of bronze, tin, tungsten, pure copper, and a copper matrix embedded with tungsten particles.

9. The X-ray inspection system according to claim 1, wherein: The first beam filter and the second beam filter include a first layer made of tungsten or lead and a second layer made of steel or pure copper configured to absorb fluorescent light emitted by the first layer.

10. The X-ray inspection system of claim 1, further comprising a shield coupled to the first beam filter and the second beam filter, the shield configured to reduce radiation leakage.

11. The X-ray inspection system of claim 1 , further comprising a pencil beam forming aperture placed in front of the X-ray source, wherein The first beam filter is located between the X-ray source and the pencil beam forming aperture, and wherein image contrast is increased by increasing the distance between the pencil beam forming aperture and the first beam filter and decreasing the distance between the first beam filter and the X-ray source.

12. The X-ray inspection system of claim 1, further comprising a third beam filter.

13. The X-ray inspection system according to claim 12, wherein: The first beam filter, the second beam filter and the third beam filter respectively include a 0.5 mm thick pure copper material, a 1.0 mm thick pure copper material and a 2.0 mm thick pure copper material.

14. The X-ray inspection system according to claim 1, wherein: The processing unit is further configured to modify one or more non-linear transfer functions adapted to process the data representing the at least one image based on a desired contrast level.

15. The X-ray inspection system according to claim 14, wherein: The nonlinear transfer function includes at least one of a gamma function and an S-curve function.

16. The X-ray inspection system according to claim 2, wherein: The processing unit is further configured to implement at least one of a first set of program instructions and a second set of program instructions based on the desired contrast level.

17. The X-ray inspection system of claim 16, wherein: The processing unit is further configured to implement the first set of program instructions based on at least one of the first contrast level and the second contrast level, and wherein the first set of program instructions includes one or more contrast enhancement functions.

18. The X-ray inspection system of claim 16, wherein: The processing unit is further configured to implement the second set of program instructions based on at least one of the third contrast level and the fourth contrast level, and wherein the second set of program instructions includes one or more edge enhancement functions.

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