Patent Publication Number: US-2009225954-A1

Title: X-Ray Collimators, and Related Systems and Methods Involving Such Collimators

Description:
BACKGROUND 
     1. Technical Field 
     The disclosure generally relates to non-destructive inspection of components. 
     2. Description of the Related Art 
     Computed tomography (CT) involves the use of X-rays that are passed through a target. Based on the amount of X-ray energy detected at a detector located downstream of the target, information about the target can be calculated. By way of example, representations of target shape and density in three dimensions can be determined. 
     SUMMARY 
     X-ray collimators, and related systems and methods involving such collimators are provided. In this regard, an exemplary embodiment of an X-ray collimator comprises: a first member having channels located on a surface thereof; and a second member having protrusions located on a surface thereof; the first member and the second member being oriented such that the protrusions extend into the channels to define collimator apertures, each of the collimator apertures being defined by a portion of the first member and a portion of the second member. 
     An exemplary embodiment of an X-ray system comprises: an X-ray source; and an X-ray collimator having a first member and a second member, the first member having channels located on a surface thereof, the second member having protrusions located on a surface thereof, the first member and the second member being oriented such that the protrusions extend into the channels to define collimator apertures, each of the collimator apertures being defined by a portion of the first member and a portion of the second member, each of the collimator apertures being aligned with the X-ray source. 
     An exemplary embodiment of a method involving an X-ray collimator comprises: providing a first member having channels located on a surface thereof; providing a second member having protrusions located on a surface thereof; and orienting the first member and the second member such that the protrusions extend into the channels to define X-ray collimator apertures. 
     Other systems, methods, features and/or advantages of this disclosure will be or may become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features and/or advantages be included within this description and be within the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a schematic diagram depicting an exemplary embodiment of a system involving an X-ray collimator. 
         FIG. 2  is a schematic diagram depicting the embodiment of the X-ray collimator of  FIG. 1 , showing detail of the collimator members. 
         FIG. 3  is a schematic diagram depicting surface detail of the collimator members of an embodiment of an X-ray collimator. 
         FIG. 4  is a schematic diagram depicting the collimator members of  FIG. 3  in an assembled orientation. 
         FIG. 5  is a flowchart depicting an exemplary embodiment of a method involving an X-ray collimator. 
     
    
    
     DETAILED DESCRIPTION  
     X-ray collimators, and related systems and methods involving such collimators are provided, several exemplary embodiments of which will be described in detail. In this regard, collimators can be used, for example, in X-ray systems that are configured to perform non-destructive inspection of components. In such a system, X-rays are passed through a component and attenuation of the X-rays is measured by a set of detectors. A collimator is located upstream of the detectors to reduce the number of unwanted (e.g., scattered) X-rays reaching the detectors that can result in inaccurate measurements of X-ray attenuation. In some embodiments, such a collimator includes two members, with one of the members exhibiting channels and the other of the members exhibiting corresponding protrusions. The members are oriented so that the protrusions are received within the channels to form collimator apertures that are configured for enabling passage of X-rays. In some embodiments, the members are formed of tungsten, on which small surface features are conventionally considered difficult to form. 
       FIG. 1  is a schematic diagram depicting an exemplary embodiment of a system involving an X-ray collimator. As shown in  FIG. 1 , system  100  includes an X-ray source  102 , a collimator  104 , a turntable  106  on which a target  108  is positioned, a detector array  110 , an image processor  112 , and a display/analysis system  114 . In operation, X-ray source  102  (e.g., a point source) is operative to emit X-rays. In this embodiment, the X-rays are emitted as a fan-shaped beam  115 . 
     Collimator  104  is located downstream of source  102  and is formed of X-ray absorbing materials. In the embodiment of  FIG. 1 , tungsten is used although, in other embodiments, various other materials can be used such as brass or lead, for example. Details about an exemplary embodiment of a collimator will be described later with respect to  FIG. 2 . 
     Turntable  106  is a representative apparatus used for positioning a target, in this case, target  108 . In operation, turntable  106  is movable to expose various portions of the target to the X-rays emitted by source  102 . In this embodiment, turntable can be used to rotate the target both clockwise and counterclockwise, as well as to raise and lower the target. Altering of a horizontal position of the target in this embodiment is accomplished to expose different heights (e.g., horizontal planes) of the target to the fan-shaped beam. Notably, the elevation of the beam is fixed in this embodiment. 
     Detector array  110  is positioned downstream of the turntable. The detector array is operative to output signals corresponding to an amount of X-rays detected. In this embodiment, the array is a linear array, although various other configurations can be used in other embodiments. 
     Image processor  112  receives information corresponding to the amount of X-rays detected by the detector array and uses the information to compute image data corresponding to the target. The image data is provided to display/analysis system  114  to enable user interaction with the information acquired by the detector array. 
       FIG. 2  is a schematic diagram depicting collimator  104  of  FIG. 1 , showing detail of the collimator members. In particular, collimator  104  includes members (e.g., plates)  120 ,  122 , with the members being separated in  FIG. 2  by rotating member  120  about axis  124  to expose the sides of the members that normally contact each other when assembled. Specifically, when so assembled, side  126  of member  120  contacts side  128  of member  122 . 
     Side  128  of member  122  incorporates a set of channels (e.g., channels  130 ,  132 ) that extend radially outwardly from a center  134 , which is located at a point outside the periphery of member  122 . Center  134  corresponds to a location at which the X-ray source  102  is to be positioned during operation. In contrast, side  126  of member  120  incorporates a set of protrusions (e.g., protrusions  136 ,  138 ) that are oriented so that each of the protrusions can be received by a corresponding one of the channels when the members are assembled. By way of example, in the assembled configuration, protrusion  136  extends into channel  130 , and protrusion  138  extends into channel  132 . 
     Relative positions of the channels and protrusions is shown in greater detail in  FIGS. 3 and 4 , which schematically depict members  120  and  122  in unassembled and assembled configurations, respectively. As shown in  FIG. 3 , each of the channels is defined by a floor and sidewalls extending from the floor. For instance, channel  132  is defined by a floor  133  and sidewalls  135 ,  137 . Each protrusion is defined by an endwall and sidewalls extending from the endwall. For instance, protrusion  138  is defined by endwall  139  and sidewalls  141 ,  143 . 
     Each of the channels exhibits a width X 1 , with the spacing between adjacent channels being X 2 . In contrast, each of the protrusions exhibits a width X 2 , with the spacing between adjacent protrusions being X 1 . As shown in the assembled configuration of  FIG. 4 , each of the protrusions extends into a corresponding one of the channels, with the endwall of each protrusion being positioned adjacent to (e.g., contacting) a floor of a corresponding channel. 
     The aforementioned sizing and spacing results in the formation of collimator apertures (e.g., apertures  140 ,  142 ), each of which exhibits a width of (X 1 −X 2 )/2. By way of example, a width X 1  of 2.0 mm and a width X 2  of 1.6 mm results in collimator apertures of 0.2 mm ((2.0−1.6)/2), with the spacing between adjacent apertures being 1.8 mm (center to center). Thus, in this embodiment, the collimator apertures exhibit widths that are an order of magnitude smaller that the channels used to form the apertures. 
     Formation of a collimator may be accomplished by providing a blank stock of metal (e.g., tungsten) that is sized for thickness, width and length. Slots are then rough cut using a cutting tool (e.g., a 2 mm carbide cutter) to form the final depth and rough width of slots. A final pass of the cutting tool is then used to finish the vertical edges of the slots. Notably, cutting tool offsets can be adjusted during cutting to accommodate variations attributable to cutter wear. By way of example, cutting tool offsets can be adjusted after approximately each 10 inches (254 mm) of cut in order to maintain the slot dimensions within specification. The slotted block than can be cut in half, such as by using a 0.75 inch (19 mm) wide slot located at the center of the block. Collimator channels are formed by mating the two halves of the block. In some embodiments, alignment features, such as dowel pins can be used to ensure proper and maintained alignment of the two halves. 
       FIG. 5  is a flowchart depicting an exemplary embodiment of a method involving an X-ray collimator. As shown in  FIG. 5 , the method may be construed as beginning at block  150 , in which a first member having channels is provided. In block  152 , a second member having protrusions is provided. In block  154 , the first member and the second member are oriented so that the protrusions extend into the channels to form an X-ray collimator having collimator apertures. In some embodiments, each of the channels of the first member exhibits a width that is at least approximately twice as wide as a width of each of the collimator apertures. In block  156 , the collimator is used to direct X-rays at a target, such as for performing non-destructive inspection of the target to determine one or more of various characteristics. By way of example, the characteristics can include, but are not limited to, interior shape and density of the target. In some embodiments, the target can be a gas turbine engine component, such as a turbine blade. 
     It should be noted that a computing device can be used to implement various functionality, such as that attributable to the image processor  112  and/or display/analysis system  114  depicted in  FIG. 1 . In terms of hardware architecture, such a computing device can include a processor, memory, and one or more input and/or output (I/O) device interface(s) that are communicatively coupled via a local interface. The local interface can include, for example but not limited to, one or more buses and/or other wired or wireless connections. The local interface may have additional elements, which are omitted for simplicity, such as controllers, buffers (caches), drivers, repeaters, and receivers to enable communications. Further, the local interface may include address, control, and/or data connections to enable appropriate communications among the aforementioned components. 
     The processor may be a hardware device for executing software, particularly software stored in memory. The processor can be a custom made or commercially available processor, a central processing unit (CPU), an auxiliary processor among several processors associated with the computing device, a semiconductor based microprocessor (in the form of a microchip or chip set) or generally any device for executing software instructions. 
     The memory can include any one or combination of volatile memory elements (e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM, VRAM, etc.)) and/or nonvolatile memory elements (e.g., ROM, hard drive, tape, CD-ROM, etc.). Moreover, the memory may incorporate electronic, magnetic, optical, and/or other types of storage media. Note that the memory can also have a distributed architecture, where various components are situated remotely from one another, but can be accessed by the processor. 
     The software in the memory may include one or more separate programs, each of which includes an ordered listing of executable instructions for implementing logical functions. A system component embodied as software may also be construed as a source program, executable program (object code), script, or any other entity comprising a set of instructions to be performed. When constructed as a source program, the program is translated via a compiler, assembler, interpreter, or the like, which may or may not be included within the memory. 
     The Input/Output devices that may be coupled to system I/O Interface(s) may include input devices, for example but not limited to, a keyboard, mouse, scanner, microphone, camera, proximity device, etc. Further, the Input/Output devices may also include output devices, for example but not limited to, a printer, display, etc. Finally, the Input/Output devices may further include devices that communicate both as inputs and outputs, for instance but not limited to, a modulator/demodulator (modem; for accessing another device, system, or network), a radio frequency (RF) or other transceiver, a telephonic interface, a bridge, a router, etc. 
     When the computing device is in operation, the processor can be configured to execute software stored within the memory, to communicate data to and from the memory, and to generally control operations of the computing device pursuant to the software. Software in memory, in whole or in part, is read by the processor, perhaps buffered within the processor, and then executed. 
     It should be emphasized that the above-described embodiments are merely possible examples of implementations set forth for a clear understanding of the principles of this disclosure. Many variations and modifications may be made to the above-described embodiments without departing substantially from the spirit and principles of the disclosure. By way of example, although channels are depicted as being associated with one member of a collimator while protrusions are depicted as being associated with another, some embodiments can include combinations of channels and protrusions one each member. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the accompanying claims.