Patent Document

CROSS REFERENCE TO RELATED PATENTS  
       [0001]     This application claims the benefit of U.S. provisional application No. 60/630,797 filed Nov. 24, 2004, which is herein incorporated in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates generally to methods and apparatus for computed tomography (CT), and more particularly to methods and apparatus that provide for a field replaceable CT digital module.  
         [0003]     Modular radiation detector arrays typically include a collimator, a scintillator array or package, and a photo diode assembly. The collimator, scintillator package “pack”, and diode assembly are precision aligned and attached together to form a detector module. A number of modules are mounted on rails to form the detector array, and pins are fabricated in the pack to enable precise positioning of the pack onto the rails.  
         [0004]     The accurate positioning of the collimator, scintillator package, and diode assembly to attach and optically couple them together can be problematic. Additionally, the accurate positioning of the modules relative to one another to form the detector array can be problematic. Because of the X-ray to light conversion process, it is useful that the analog area of a CT module be sealed against all light sources. Further, in order to allow installation and removal of the digital module, a card guide is required to properly align the module for installation and extraction for a CT system. Moreover, the analog portion of the module is subject to Electromagnetic interference (EMI) and requires EMI protection.  
         [0005]     One problem with installing a digital module is that the analog module with a pin-in-pack alignment feature is typically moved in the detector Z direction, such that the analog module does not make contact with the collimator rails, before aligning the pin in pack. The digital module is then typically moved in the detector Y direction to bring the analog module into position so that the pin in pack feature engages the collimator combs without damaging a collimator plate. This complex motion has traditionally precluded replacement of modules in the field. The current practice is to use non-field serviceable analog detector modules that, on occasion, experience a failure in the field. When such failure occurs, the entire detector is removed from the CT system, returned to the factory for disassembly and repair. This current practice is costly and time-consuming.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0006]     In one aspect, a method of installing an electronic board is provided. The method includes inserting the board into a guide in a first direction. The board is then translated in a second direction different from the first direction. Upon inserting the board a gasket is sealed to prevent light, dust, or electromagnetic interference from passing through the gasket. A lock is then engaged to maintain the electronic board in a substantially fixed position.  
         [0007]     In another aspect, an electronic board assembly is provided. The assembly includes a guide configured to receive the electronic board in both a first and second direction. A gasket is provided to prevent the passing of light, dust, or electromagnetic interference when the electronic board is inserted into the guide. The assembly further includes a lock to maintain the electronic board in a substantially fixed position after insertion into the guide.  
         [0008]     In a further aspect, a medical system is provided. The medical system includes a guide and an electronic board configured to be inserted into the guide. A gasket is provided to prevent the passing of light, dust, or electromagnetic interference when the electronic board is inserted into the guide. The assembly further includes a lock to maintain the electronic board in a substantially fixed position after insertion into the guide. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a pictorial view of a CT imaging system embodiment.  
         [0010]      FIG. 2  is a block schematic diagram of the system illustrated in  FIG. 1 .  
         [0011]      FIG. 3  illustrates a set of rails with a 3 zone heater attached.  
         [0012]      FIG. 4  illustrates a digital module card cage with EMI screen, a back plate, end plates, and card guides.  
         [0013]      FIG. 5  illustrates a digital module an analog front end, a board guide, heat sink, digital cable, T-slot block, and A/D boards.  
         [0014]      FIG. 6  illustrates a board guide with light seal gasket, a compression clip, and a card guide.  
         [0015]      FIG. 7  illustrates module insertion steps and clip installation.  
         [0016]      FIG. 8  illustrates digital module positioning in a card guide and a card cage.  
         [0017]      FIG. 9  illustrates digital module positioning and alignment of the front end of the module.  
         [0018]      FIG. 10  illustrates a light seal and EMI cover plate positioned over modules after they have been installed into the rails.  
         [0019]      FIG. 11  illustrates a first concept of a card guide with Z motion guides, flow block, and light seal.  
         [0020]      FIG. 12  illustrates a second concept with a master card guide alignment plate and a Wedge Lok clamp.  
         [0021]      FIG. 13  illustrates a third concept with a top card guide with retention feature for connecting the digital connector.  
         [0022]      FIG. 14  illustrates a fourth concept with a front seal plate and EMI and light seal with a Wedge Lok clamp.  
         [0023]      FIG. 15  illustrates a Wedge Lok clamp for use with the digital module. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     There are herein provided radiation detection methods and apparatus useful for imaging systems such as, for example, but not limited to a Computed Tomography (CT) System. The apparatus and methods are illustrated with reference to the figures wherein similar numbers indicate the same elements in all figures. Such figures are intended to be illustrative rather than limiting and are included herewith to facilitate explanation of an exemplary embodiment of the herein described apparatus and methods.  
         [0025]     In some known CT imaging system configurations, a radiation source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as an “imaging plane”. The radiation beam passes through an object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated radiation beam received at the detector array is dependent upon the attenuation of a radiation beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.  
         [0026]     In third generation CT systems, the radiation source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged such that an angle at which the radiation beam intersects the object constantly changes. A group of radiation attenuation measurements, i.e., projection data, from the detector array at one gantry angle is referred to as a “view”. A “scan” of the object includes a set of views made at different gantry angles, or view angles, during one revolution of the radiation source and detector.  
         [0027]     In an axial scan, the projection data is processed to reconstruct an image that corresponds to a two dimensional slice taken through the object. One method for reconstructing an image from a set of projection data is referred to in the art as the filtered back projection technique. This process converts the attenuation measurements from a scan into integers called “CT numbers” or “Hounsfield units”, which are used to control the brightness of a corresponding pixel on a display device.  
         [0028]     To reduce the total scan time, a “helical” scan may be performed. To perform a “helical” scan, the patient is moved while the data for the prescribed number of slices is acquired. Such a system generates a single helix from a fan beam helical scan. The helix mapped out by the fan beam yields projection data from which images in each prescribed slice may be reconstructed.  
         [0029]     As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.  
         [0030]     Also as used herein, the phrase “reconstructing an image” is not intended to exclude embodiments of the present invention in which data representing an image is generated but a viewable image is not. Therefore, as used herein the term, “image,” broadly refers to both viewable images and data representing a viewable image. However, many embodiments generate (or are configured to generate) at least one viewable image.  
         [0031]      FIG. 1  is a pictorial view of a CT imaging system  10 .  FIG. 2  is a block schematic diagram of system  10  illustrated in  FIG. 1 . In the exemplary embodiment, a computed tomography (CT) imaging system  10  is shown as including a gantry  12  representative of a “third generation” CT imaging system. Gantry  12  has a radiation source  14  that projects a cone beam  16  of X-rays toward a detector array  18  on the opposite side of gantry  12 .  
         [0032]     Detector array  18  is formed by a plurality of detector rows (not shown in  FIGS. 1 and 2 ) including a plurality of detector elements  20  which together sense the projected X-ray beams that pass through an object, such as a medical patient  22 . Each detector element  20  produces an electrical signal that represents the intensity of an impinging radiation beam and hence the attenuation of the beam as it passes through object or patient  22 . An imaging system  10  having a multislice detector  18  is capable of providing a plurality of images representative of a volume of object  22 . Each image of the plurality of images corresponds to a separate “slice” of the volume. The “thickness” or aperture of the slice is dependent upon the thickness of the detector rows.  
         [0033]     During a scan to acquire radiation projection data, gantry  12  and the components mounted thereon rotate about a center of rotation  24 .  FIG. 2  shows only a single row of detector elements  20  (i.e., a detector row). However, multislice detector array  18  includes a plurality of parallel detector rows of detector elements  20  such that projection data corresponding to a plurality of quasi-parallel or parallel slices can be acquired simultaneously during a scan.  
         [0034]     Rotation of gantry  12  and the operation of radiation source  14  are governed by a control mechanism  26  of CT system  10 . Control mechanism  26  includes a radiation controller  28  that provides power and timing signals to radiation source  14  and a gantry motor controller  30  that controls the rotational speed and position of gantry  12 . A data acquisition system (DAS)  32  in control mechanism  26  samples analog data from detector elements  20  and converts the data to digital signals for subsequent processing. An image reconstructor  34  receives sampled and digitized radiation data from DAS  32  and performs high-speed image reconstruction. The reconstructed image is applied as an input to a computer  36  which stores the image in a mass storage device  38 .  
         [0035]     Computer  36  also receives commands and scanning parameters from an operator via a console  40  that has a keyboard. An associated cathode ray tube display  42  allows the operator to observe the reconstructed image and other data from computer  36 . The operator supplied commands and parameters are used by computer  36  to provide control signals and information to DAS  32 , radiation controller  28 , and gantry motor controller  30 . In addition, computer  36  operates a table motor controller  44  which controls a motorized table  46  to position patient  22  in gantry  12 . Particularly, table  46  moves portions of patient  22  through gantry opening  48 .  
         [0036]     In one embodiment, computer  36  includes a device  50 , for example, a floppy disk drive, CD-ROM drive, DVD drive, magnetic optical disk (MOD) device, or any other digital device including a network connecting device such as an Ethernet device for reading instructions and/or data from a computer-readable medium  52 , such as a floppy disk, a CD-ROM, a DVD or an other digital source such as a network or the Internet, as well as yet to be developed digital means. In another embodiment, computer  36  executes instructions stored in firmware (not shown). Generally, a processor in at least one of DAS  32 , reconstructor  34 , and computer  36  shown in  FIG. 2  is programmed to execute the processes described below. Of course, the method is not limited to practice in CT system  10  and can be utilized in connection with many other types and variations of imaging systems. In one embodiment, Computer  36  is programmed to perform functions described herein, accordingly, as used herein, the term computer is not limited to just those integrated circuits referred to in the art as computers, but broadly refers to computers, processors, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, and other programmable circuits. Although the herein described methods are described in a medical setting, it is contemplated that the benefits of the invention accrue to non-medical imaging systems such as those systems typically employed in an industrial setting or a transportation setting, such as, for example, but not limited to, a baggage scanning CT system for an airport or other transportation center.  
         [0037]     One feature of the herein described methods and apparatus enable a digital module of a CT detector to be field serviced without requiring the replacement of the entire detector. Previously, if an analog module fails, the entire detector is removed and sent back to the factory for repair, which is costly and time consuming. The herein described method and apparatus allow for installation of a digital module for repair and trouble shooting that additionally provides a light seal for the analog module. Furthermore, the card guide facilitates accurate and repeatable installation and removal of the digital module without damaging the sensitive analog portion of the module. In one embodiment, an integrated light seal provides EMI shielding of the low level analog signals produced by the photodiode. Also, in one embodiment, the integrated light seal feature facilitates the prevention of dust and debris from entering the analog region of the detector.  
         [0038]     Alternative embodiments are illustrated for locking and retaining the module in place, and for compressing the light seal gasket to ensure a repeatable, reliable, and robust joint. The herein described methods and apparatus enable a low-skilled operation, facilitating field replacement and serviceability of modules.  
         [0039]      FIG. 3  illustrates collimator  100  with rails  102  separated by end blocks  104 . Collimator plates (not shown) are mounted and retained between the rails. Three-zone heater  106  is mounted on rail  102 , with temperature sensors  108  mounted within rails  102  to control and for feedback control of three-zone heater  106 .  
         [0040]      FIG. 4  illustrates digital module card cage  200 . Detector alignment plate  202  with end plates  204  supports card cage  206 . Card guides  208  are mounted to detector alignment plate  202 , and T-Slots  210  are positioned in card cage  206  and Card guides  208  and T-slots  210  are aligned and pitched one to the other to mount detector modules (not shown). Airways  212  are positioned in detector alignment plate  202  to facilitate air flow over modules when mounted in digital module card cage  200 . EMI screen  214  mounts to detector alignment plate  202 , positioned to provide EMI protection to modules when mounted in digital module card cage  200 .  
         [0041]      FIG. 5  illustrates digital module  300 . Analog module  302  converts X-Rays to an analog signal and outputs the signal through flex circuits  304 . Analog-Digital (AD) boards  308  convert the analog signals from flex circuits  304  to digital signals using integrated circuits (not shown) positioned under heat sinks  306 . Digital signals output through digital cable  310 . T-guide  312  is positioned on digital module  300  to engage with T-slot  210  when installed into digital module card cage  200 . AD board guide  400  is positioned on digital module  300  to engage card guides  208  when installed into digital module card cage  200 .  
         [0042]      FIG. 6  illustrates AD board guide  400  and light seal compression clip  402 . AD board guide  400  has attached light seal gasket  404  onto guide base  412  with guide keys  406 . Card guide  408  has key cutouts  410  that mate with guide keys  406  when installed into digital module card cage  200 .  
         [0043]      FIG. 7  illustrates three motions for installation of board guide  400 , when attached to digital module  300 , into card guide  408 . Digital module  300  first is moved in direction  430  until guide keys  406  are positioned over key cutouts  410 . Once positioned, digital module  300  is engaged by moving in direction  440  and light seal gasket  404  is compressed and light seal compression clip  402  is inserted to retain digital module  300  in card guide  408 .  
         [0044]      FIG. 8  illustrates a perspective view of the same motion of digital module  300 , while also showing the end of digital module  300  with T-guide  312  engaging with T-slot  210 . Three steps are illustrated for retaining end portion  462  of digital module  300 . View  1  illustrates digital module  300  partially installed in direction  464  while engaging board guide  400  and T-guide  312  during motion in direction  464 . View  2  illustrates digital module  300  fully seated in digital module card cage  200 . View  3  illustrates wedge clamp  460  frictionally engaged between T-guide  312  and T-slot  210  to retain digital module  300 .  
         [0045]      FIG. 9  illustrates engagement of analog module  302  of digital module  300  in collimator  100 . Collimator fingers  482  have gaps for positioning of collimator plates (not shown). Alignment fingers  480  extend from selected collimator fingers as illustrated to engage pack alignment pins (not shown) protruding from analog module  302 . Once digital module  300  is installed, guide keys  406  engage with key cutouts  410 . The card guide alignment features prevent the pack from catching on detector rails until located over alignment pins, and provide rough alignments in X and Z dimensions for analog module  302 .  
         [0046]      FIG. 10  illustrates digital modules  300  installed into digital card cage  200 . Light seal cover plate  490  is attached to digital card cage  200  using fasteners  492  to prevent light leakage to analog modules  302  when inserted into digital card cage  200 .  
         [0047]      FIG. 11  illustrates a first concept for installation of digital module  300  inserted into digital card cage  200 . Z motion guide  502  is positioned on digital module  300  to control motion in the Z direction during installation. Flow block  504  is positioned to prevent air flow reaching analog modules  302 . Light seal gasket  404  prevents light leakage from reaching analog modules  302 .  
         [0048]      FIG. 12  illustrates a second concept for installation of digital module  300  inserted into digital card cage  200 . Master card guide alignment plate  510  has card guide  512  positioned to receive digital modules  300 , with air flow cutouts  514  positioned to allow flow over heat sinks  306 , with EMI and light seal  516  positioned to protect analog modules  302  from EMI and light exposure. Wedge Lok clamps  518  engage digital modules  300  to retain them during use from motion.  
         [0049]      FIG. 13  illustrates a third concept for installation of digital module  300  inserted into digital card cage  200 . Master plate  540  has slot  542  positioned to receive engagement features from digital module  300  to enable alternate designs of digital connector and cable  310 . Such design enables simpler connector routing and reduced board length.  
         [0050]      FIG. 14  illustrates a fourth concept for installation of digital module  300  inserted into digital card cage  200 . Card guide  600  is positioned to enable wedge clamp  602  to clamp digital module  300 .  
         [0051]      FIG. 15  illustrates Wedge-Lok card retainers for card retention.  
         [0052]     Technical effects of the herein described methods and apparatus provide for a two dimensional card motion control, and a keyed card guide board clip design that provides repeatable and accurate module motion to protect the analog modules and collimator from damage. Additional technical effects include the field replaceability of an integrated analog and digital DAS assembly, the repeatable lights sealing of an analog module, and for digital module locking and retaining that automatically crushes light seal gaskets to ensure light seal. Other technical effects are an integrated accessory clip that automatically crushes light seal gaskets to ensure light seal, and a light seal design that also performs dust and EMI shielding of the collimator and analog module.  
         [0053]     Exemplary embodiments are described above in detail. The assemblies and methods are not limited to the specific embodiments described herein, but rather, components of each assembly and/or method may be utilized independently and separately from other components described herein.  
         [0054]     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.

Technology Category: 1