Abstract:
An X-ray detector is manufactured bonding detector layers onto a main frame leaving a protruding edge portion extending beyond edge of the detector layers. The protruding edge portion of the main frame is then detached from the main frame along a detachment line adjacent the edge of the detector layers before a cover with a thin edge wall is applied to the detector stack.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to the field of mammography, and in particular to a mammography detector. 
       BACKGROUND OF THE INVENTION 
       [0002]    In mammography screening X-ray film has been replaced by digital detectors. A typical setup is shown in US patent publication no. 2104/0205060. The patient places her breasts on a horizontal plate containing the X-ray detector, which consists of an array of stacks of laminar components bonded together. The end wall of the detector is placed against the chest wall of the patient. In order to obtain as complete a reading as possible, it is important that the distance to the edge of the active portion of the detector be as small as possible so that as much of the patient&#39;s breast as possible lies over the active surface of the detector. It is also important to ensure that the detector can be manufactured economically using automated manufacturing techniques. 
         [0003]    The laminar components are manufactured by bonding them as individual layers together on a supporting frame. The supporting frame must extend beyond the end wall of the stack in order to provide a trench to collect excess adhesive as described in our co-pending application no. PCT/CA2014/000584, which is hereby incorporated by reference. This tends to result in the active area of the detector being displaced from the chest, an effect that results in reducing the effectiveness of the detector. 
       SUMMARY OF THE INVENTION 
       [0004]    According to the present invention there a method of making an X-ray detector comprising providing a main frame for supporting a detector stack, the main frame having a detachable protruding edge portion; bonding detector layers onto the main frame leaving the protruding edge portion extending beyond edge of the detector layers; detaching the protruding edge portion of the main frame along a detachment line adjacent the edge of the detector layers; and applying a cover with a thin edge wall to the detector stack. 
         [0005]    Typically, the base frame is made of aluminum, although it can be made of other materials, such as other metals, plastic or reinforced plastic. The protruding portion may be snapped off manually or automatically using robotic techniques. Alternatively, it may be removably attached to the main frame, for example, with screws. To facilitate removal it may be made of, or coated with, a release agent, such as Teflon™. 
         [0006]    In accordance with another aspect the invention an X-ray detector comprising a detector stack bonded onto a frame base portion, an edge of said base frame being located such that it is aligned with, or underhangs an edge of said stack; and a protective cover with a thin edge wall applied to the detector stack. 
         [0007]    Yet another aspect the invention provides a precursor assembly for making an X-ray detector, comprising a detector stack bonded onto a main frame, an edge of said base frame protruding beyond the edge of the detector stack; said protruding edge portion being detachable along a line that is aligned with, or underhangs an edge of said stack. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: 
           [0009]      FIG. 1  is a plan view of a main frame; 
           [0010]      FIG. 2  is a photograph showing a plan view of the main frame with the glass carrier in place; 
           [0011]      FIG. 3  is a cross section through a partly formed detector stack located on a main frame; 
           [0012]      FIG. 4  is a cross section through a completed detector including a protective cover; and 
           [0013]      FIG. 5  shows a completed stack with silicon tiles in place. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0014]    Referring now to  FIGS. 1 to 3 , an X-ray detector stack is manufactured by bonding an array of individual silicon tiles  6  onto a glass carrier  5 . 
         [0015]    The glass carrier  5  is located within a recess formed in a metal supporting main frame  1  containing rectangular openings or windows  2  to permit the passage of ultraviolet light to cure the adhesive for bonding the layers together. The main frame  1  is typically made of aluminum, but it can be made of other metals, or plastic or reinforced plastic. 
         [0016]    During manufacture, as shown in  FIGS. 2 and 3 , first the glass carrier  5  is bonded to the main frame  1  ( FIG. 2 ) with a suitable adhesive. The silicon tiles  6  are then bonded onto the glass carrier layer  5  in the form of an array, with the silicon tiles abutting each other. 
         [0017]    Next the fiber optic plate (FOP)  7 , which is coated on top with scintillator, such as Cesium Iodide (CsI), is bonded over all the tiles  6  and a protective foil (not shown) is laid on top of the scintillator coating on the fiber optic plate  7 . The fiber optic plate  7  comprises a bundle of micron-sized optical fibers, and in effect serves as a medium to convey the light and image with high efficiency and low distortion to the silicon sensor. Unlike a normal optical lens, no focusing distance is required. 
         [0018]    The layers  5  and  6  are bonded together and onto the main frame  1  using a suitable adhesive  9   a ,  9   b ,  9   c . The adhesive  9   b  between layers  5  and  6  can be cured by passing ultraviolet light through the windows  2 . 
         [0019]    The main frame  1  has a protruding edge portion  11 . As described in our co-pending application referred to above, a trench  10  is provided in the protruding portion  11  of the frame base portion la between the edge  20  of the layers of the stacks on the edge  21  of the base frame  1  to catch excess adhesive  9  flowing out from between the layers,  5 ,  6 ,  7  in each of the stacks  8  along the edge of the base frame. 
         [0020]    A problem arises in that the protruding portion  11  necessary to support the trench  10  inevitably extends the main frame  1  by an amount d beyond the edge  20  of the stack  8 , as a result of which the edge  20  of the stack is displaced from the chest wall  18  ( FIG. 4 ) when the detector is in use. 
         [0021]    In accordance with embodiments of the invention a pre-scribed scribe line  12 , forming a detachment line, is provided in the base frame  1  prior to placement of the layers of the detector stack  8 . This can be scribed mechanically or by any suitable means. The scribe line  12  is located in alignment with, or slightly inwardly of (i.e. underhangs), the edge  20  of the stacks  8 . 
         [0022]    After placement of the layers  5 ,  6 ,  7 , the protruding portion  11  of the base frame  1  is snapped off, either manually or using robotic techniques, so that the edges  20  of the stacks  8  align with the edge  21  of base frame  1  as shown in  FIG. 4 . The protruding edge portion  11  is snapped off as one of the last stages in the manufacturing process. As a result the active components of the device are protected during handling. 
         [0023]    A conventional carbon cover  15  is then placed over the detector. The cover can be held in place by screws or other fixing means, or could be molded in place. The wall  17  of the cover  15  can be made very thin, namely less than  1  mm, so that when the X-ray detector abuts the chest wall  18  with the breast  16  lying on the active surface of the detector, the distance between the active edge  20  of the stacks  8  and the chest wall is very small. 
         [0024]    In an alternative embodiment, the protruding portion  11  can be provided as a separate piece that is screwed to the main frame  1  by means of screws  4  as shown in  FIG. 1 . In this case the piece can be made of, or coated with, Teflon/Delrin etc, to facilitate removal when the piece is removed. This acts as a release agent. After assembly of the detector stack, the screws  4  are removed, and the separate piece can be peeled away, facilitated by the action of the release agent. In this case the detachment line is provided by the interface between the removable piece and the main part of the frame  1 . 
         [0025]    The described technique is suitable for large-scale manufacturing.