Patent Number: 
Section: claims

1. In a focused anti-scatter grid 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 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 each 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 planes of the slits on the opposing bracket;thin, heavy metal ribbons extend through the slits in each bracket to the opposing bracket, and have a height corresponding to the depth of the slits;the width of the slits is formed to exceed the thickness of the ribbons by 50-100%; andand the two brackets extend substantially parallel to each other so that all ribbons in the grid are of equal length, sufficient to exceed the spacing between corresponding brackets across the open frame so as to extend beyond each bracket, the improvement comprising: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 10:1;the ribbons each having a thickness in the range of from 10 microns to 1000 microns;the brackets being constructed in pairs where one bracket is fixed to the outer open frame and the opposing bracket is loaded under spring tension relative to the frame so as to ensure that the ribbons between them are aligned to the focus;the heavy metal foil ribbons being 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 layer of a high tensile strength polymer on at least one side surface of the heavy metal foil, so that the foil ribbon is strengthened; each ribbon and attached polymer layer having an opening at each end, on the far side of each bracket, to hold a rigid rod to provide fixation and centering to the ribbons under tension, the rigid rod extending through all of the ribbons adjacent each bracket; andthe bracket slits being machined to achieve focus distances of at least 20 cm and the spacing between bracket slits being in the range of at least 0.2 mm. 2. The focused grid of claim 1 where the spacing between the ribbons is in the range of from 0.2 mm to 1 cm. 3. The focused grid of claim 1 where the polymer material is a substantially rigid, polymer composed mainly of the low atomic number elements Hydrogen, Carbon, Oxygen or Nitrogen. 4. The focused grid of claim 3 where the rigid polymer is selected from ABS, Urethane, acrylic or polycarbonate polymers. 5. The focused grid of claim 3 where the rigid polymer is foamed so as to have a density of less than 1.2 grams per cubic centimeter, so as to be substantially radiation-transparent. 6. The focused grid of claim 1 wherein the length of the brackets and the distance between the brackets can be in the range of three centimeters to 4 meters.