Three-dimensional focused anti-scatter grid and method for manufacturing thereof

Abstract

A device for, and method of manufacture of, a focused anti-scatter grid for improving the image contrast of x-ray images produced in medical, veterinary or industrial applications. The grid comprising a series of modular units so juxtaposed with each other as to form a series of focused channels for the passage of the focused imaging x-rays. The modules comprise a series of focusing ribbons of a heavy metal or a series of mating solid arcuate forms, formed of a polymer and having on at least one side surface a layer of heavy metal.

What is claimed is: 
     
         1 . A focused grid comprising: a plurality of modules, each module comprising alternating radiation transparent materials and radiation-absorbent materials, the modules being so assembled such that adjacently positioned modules are so juxtaposed one with each other to form focused channels; and a frame onto which the plurality of modules are mounted and secured in the desired juxtaposition. 
     
     
         2 . The focused grid of  claim 1  where the modules are substantially identical to each other and comprise thin, heavy metal ribbons, spaced one from another, wherein the frame supports the plurality of thin, heavy metal ribbons so separated and juxtaposed as to define channels through the air space defined by and between the ribbons, the channels focusing any radiation passing through them along a single focus line, the focus line contains the locus of an x-ray source, the channels comprising primarily only air. 
     
     
         3 . The focused anti-scatter grid according to  claim 2  wherein the frame comprises at least two opposed brackets that each incorporate a plurality of holders to support the heavy metal ribbons in planes orthogonal to the long axis of the brackets, and that are each inclined relative to each other so as to converge to a single focus line in a plane parallel to the surface of the frame that contains the locus of an x-ray source; the ribbons at one end of the brackets being inclined at an opposite angle to the ribbons at the opposite end of the brackets. 
     
     
         4 . The focused anti-scatter grid according to  claim 3 , wherein each of the brackets define a slit for holding the ribbons at the inclined angle relative to each other, and the planes of the ribbons are arrayed so as to describe a fixed angle from the focus line, with respect to the planes bisecting adjacent slits in which the adjacent ribbons are held. 
     
     
         5 . The focused anti-scatter grid according to  claim 4  wherein the inclined angle of the ribbons reverse relative to a central line of the anti-scatter grid, along the focus of the x-radiation, is reversed on the two sides of the central line. 
     
     
         6 . The focused anti-scatter grid according to  claim 4 , wherein the ratio of the depth of the ribbons to the spacing between the ribbons is in the range of from 3:1 to 20:1. 
     
     
         7 . The focused anti-scatter grid according to  claim 3 , wherein the thin, heavy metal ribbons are formed from a heavy metal selected from the group consisting of lead, bismuth, tungsten, tantalum or alloys thereof, and which have a thickness of between 10 microns and 1000 microns. 
     
     
         8 . The focused anti-scatter grid according to  claim 6 , wherein the ribbons in a grid set are of equal length, and are held in tension by the frame, to maintain the planarity of their outer surfaces and straightness and alignment to the focus of the x-radiation. 
     
     
         9 . The focused anti-scatter grid of  claim 8  comprising a frame which incorporates two transversely aligned sets of ribbons so as to form a crossed linear focused grid, both sets of ribbons being so arrayed as to have focus lines which lie in the same plane, with the convergence at the location of the x-ray source. 
     
     
         10 . The focused grid of  claim 2  where the spacing between the ribbons is in the range of from 0.2 mm to 1 cm. 
     
     
         11 . The focused grid of  claim 1  where the modules are formed of arc-shaped molded polymer material covered along at least one side surface with a heavy metal layer, the polymer material being sufficiently rigid to maintain its arc shape in use; the modules being each substantially identical to each other so that when a plurality of the modules are mated together, the mated modules form a spherical section, and focused channels for the passage of x-radiation are formed through the polymer material, between the heavy metal layers of adjacently positioned modules. 
     
     
         12 . The focused grid of  claim 11  where each of the modules has a pair of side surfaces and at least one side surface has a contour adapted to mating with a side surface of another such module. 
     
     
         13 . The focused grid of  claim 12  where the at least one mating surface comprises a corrugated surface formed with V-shaped or undulating grooves. 
     
     
         14 . The focused grid of  claim 12  where the heavy metal is selected from the group consisting of lead, bismuth, tungsten and tantalum, and alloys thereof. 
     
     
         15 . The focused grid of  claim 14  where the heavy metal alloy is a low melting alloy combining Bismuth and at least one of Lead, Strontium, Cadmium and Indium. 
     
     
         16 . The focused grid of  claim 11  where the polymer material is a substantially rigid, foamed polymer composed mainly of the low atomic number elements Hydrogen, Carbon, Oxygen or Nitrogen, and having a density of less than 1.2 grams per cubic centimeter, so as to be substantially radiation-transparent. 
     
     
         17 . The focused grid of  claim 16  where the rigid polymer is selected from ABS, Urethane, acrylic or polycarbonate polymers. 
     
     
         18 . A method for manufacturing the focused grid of  claim 1 , the method comprising: forming a plurality of modules, each module comprising a strip of radiation-absorbent material with a relatively radiation-transparent material adjacent the strips of radiation-absorbent material, and assembling the modules in a frame such that adjacently positioned modules are so juxtaposed one with each other to form focused channels, thus forming the grid of alternating layers of radiation-transparent material and radiation-absorbent strips, such that adjacently positioned modules are so juxtaposed one with each other to form focused channels; the plurality of modules are so mounted and secured on the frame so as to maintain the desired angularity between the planes of the radiation-absorbent strips. 
     
     
         19 . The method for manufacturing the focused grid in accordance with  claim 18 , wherein the strips of radiation-absorbent material are formed in an arcuate shape, and further comprising forming a plurality of substantially identical arc-shaped, polymer modules covered along at least one side surface with a strip of radiation-absorbent material of heavy metal, and joining the plurality of heavy metal layer covered modules to each other so that when a plurality of the modules are mated together, the mated modules form a spherical section, each arc-shaped molded polymer module being separated from its adjacent such polymer module by a strip of radiation-absorbent material, so as to form the radiation transparent channels defined by the focusing heavy metal layers. 
     
     
         20 . The method for manufacturing the focused grid in accordance with  claim 19 , wherein the heavy metal strip is coated onto the polymer module. 
     
     
         21 . The method for manufacturing the focused grid in accordance with  claim 18 , wherein the radiation transparent material between the strips is primarily air and the strips of radiation-absorbent material are ribbons of a heavy metal held under tension in a frame. 
     
     
         22 . The focused anti-scatter grid according to  claim 1  further comprising:
 an open rectangular frame containing two brackets on two opposing sides of the grid, each bracket incorporating a plurality of narrow slits where the planes of the slits are orthogonal to the long axis of the brackets and are each inclined in the direction along the slit, to converge to a single line (focus line) in a plane parallel to the surface of the frame that contains the locus of the x-ray source; 
 the planes of the slits are not parallel but are arrayed along the brackets so that the plane bisecting the slit describes a fixed angle from the focus line, with respect to the planes bisecting adjacent slits; the planes of the slits on one bracket are precisely aligned with the slits on the opposing bracket; 
 the depths of the slits in the brackets along the planes extending to the focus line are sufficient so that the ratio of the depth to the spacing between slits is between 3:1 and 20:1; 
 thin, heavy metal ribbons extend through the slits in each bracket to the opposing bracket, and have a width corresponding to the depth of slits, and thickness in the range of from 10 microns and 1000 microns; 
 the width of the slits is formed to exceed the thickness of the ribbons by 50-100%; and 
 the two brackets extend substantially parallel to each other so that all ribbons in a grid are of equal length, sufficient to exceed the spacing between corresponding brackets across the open frame. 
 
     
     
         23 . The focused anti-scatter grid according to  claim 22  wherein the brackets are constructed in pairs where one bracket is fixed to the outer open frame and the opposing bracket is loaded under spring tension to ensure that the ribbons between them are aligned to the focus. 
     
     
         24 . A focused grid of  claim 22 , further comprising a frame comprising two pairs of vertically arranged brackets forming a crossed linear grid, the upper pair of brackets orthogonal to the lower pair; the ribbons extending between both pairs of brackets converge to orthogonal focus lines which lie in the same plane with the convergence at the location of the x-ray source. 
     
     
         25 . The focused grid of  claim 22  where the metal foil ribbons are constructed of copper, steel or alloys thereof with an over-coating of tin or antimony for use in mammographic applications. 
     
     
         26 . The focused grid of  claim 22  where the heavy metal foil ribbons are made of a material with poor tensile strength, selected from the group consisting of lead, tin, antimony bismuth and alloys thereof and further comprises a surface coating or adhered layers of a high tensile strength polymer, where the foil ribbon is strengthened on one or both surfaces of the ribbon; each ribbon having an opening at each end to hold a rigid rod to provide fixation and centering to the ribbons under tension. 
     
     
         27 . The focused grid of  claim 3  wherein the length of the brackets and the distance between the brackets can be in the range of three centimeters to 4 meters, and depends upon the application intended. 
     
     
         28 . The focused grid of  claim 4  where the bracket slits are machined to achieve focus distance ranging from a few tens of cm to 2 m or more. 
     
     
         29 . The focused grid of  claim 4  where the spacing between bracket slits is in the range of from two tenths of a mm to at least 5 cm, depending on the application required. 
     
     
         30 . The focused grid of  claim 4  where the bracket slits are machined to locate the focus point along an orthogonal to the surface of the grid frame through the center of the grid frame opening. 
     
     
         31 . The focused grid of  claim 4  where the bracket slits are machined to locate the focus point along an orthogonal to the surface of the grid frame that is through the midpoint of one inner edge of the grid frame.