Patent Number: 
Section: description

FIG. 1 is a schematic view of a radiographic imaging arrangement 10 including an x-ray source 12, such as an x-ray tube, that generates and emits x-radiation, or x-rays, toward an object 14. A portion of the x-rays are differentially absorbed by object 14 and a portion of the x-rays penetrate object 14 and travel along paths 16 as primary, or direct, radiation. Still another portion of the x-rays penetrates object 14 and is deflected from paths 16 as scattered radiation. The direct and scattered x-rays travel toward a photosensitive film 18, and the exposure of film 18 creates a radiograph, or x-ray, image. In an alternative embodiment, imaging arrangement 10 includes a digital system using a digital detector in lieu of photosensitive film 18. To increase the x-ray image contrast, radiograph imaging arrangement 10 includes an anti-scatter grid 20. Anti-scatter grid 20, in one embodiment, is a focused grid including a plurality of x-ray absorbent members 22 arranged in a geometric pattern that is focused, i.e., arranged approximately parallel to the direct x-ray beams emanating from x-ray source 12. Therefore, scattered radiation, or radiation that arrives at x-ray anti-scatter grid 20 at an angle different from its original path generated by x-ray source 12, impinges x-ray absorbing members 22 and the scattered radiation is substantially absorbed and prevented from reaching photosensitive film 18. Direct radiation passes through anti-scatter grid 20 between x-ray absorbent members 22 for exposure with photosensitive film 18 to generate a clear radiograph image. FIG. 2 is a perspective view of exemplary focused anti-scatter grid 20 fabricated from an injection molded engineered thermoplastic into an integral framework 30 of x-ray absorbent members 22. A plurality of flat sheets 32 of x-ray absorbent material are arranged generally parallel to a longitudinal axis 34 of anti-scatter grid 20, but generally inclined to one another to form a focused geometric grid 20 along a longitudinal dimension of grid 20. Each x-ray absorbent sheet 32 is connected at a respective top edge 36 and bottom edge 38 of each sheet 32 by a first cross member 40 and a second cross member 42 substantially parallel to first cross member 40. Framework cross members 40, 42 maintain absorbent sheets 32 in proper position relative to one another and strengthen or rigidify anti-scatter grid 20 for handling during x-ray procedures. Framework cross members 40, 42 are essentially x-ray transmissive. A plurality of inter-spaces 44 are formed between x-ray absorbent sheets 32 and each inter-space 44 receives a spacer material that is x-ray transmissive, i.e., substantially non-absorbent of x-ray radiation, so that direct radiation travels through inter-spaces 44 substantially unimpeded. Integral molding of x-ray anti-scatter framework 30 renders conventional fiber-like inter-space material structurally unnecessary so that, in one embodiment, inter-space material is air. In alternative embodiments, fiber-like inter-space material known in the art is arranged between x-ray absorbent sheets 32, and framework cross members 40, 42 may be removed when the assembly is complete. In one embodiment, x-ray anti-scatter grid 20 is injection molded from an engineered thermoplastic material loaded with high density particles for x-ray absorption, yet with a sufficiently high yield strength suitable for x-ray applications and suited for injection or compression molding using conventional equipment. Suitable high density particles for use in loading the thermoplastic material are known in the art, and include, for example, lead, but non toxic alternatives such as copper, tungsten, and the like may be appropriately selected to avoid toxicity issues. One such suitable thermoplastic material, for example, is an ECOMASS(trademark) compound that is commercially available from M.A. Hannah Engineered Materials of Norcross, Ga. ECOMASS(trademark) is a tungsten-thermoplastic mix that can be formulated to have a density equal to lead, which has been conventionally used to fabricate x-ray absorbent sheets, but with a greater yield strength than lead. Thus, a higher yield strength of anti-scatter grid 20 fabricated from ECOMASS(trademark) is not only more structurally sound than conventional anti-scatter grid materials but is pliable or flexible, as further described below, along one or more axes of the grid, such as longitudinal axis 34. In addition, by injection molding anti-scatter grid 20, tedious manufacturing processes conventional in the art may be avoided, and anti-scatter grid 20 may be manufactured more quickly and more reliably than a conventional focused grid. FIG. 3 is a partial perspective view of another embodiment of an anti-scatter grid 50, including two substantially perpendicular axes 52, 54 along which x-ray absorbent sheets 56 are arranged in a parallel fashion with respect to axes 52, 54, but inclined relative to one another to form a two-dimensional focused grid 50. In other words, anti-scatter grid 50 is focused in two directions. Thus, a focused mesh is created that defines inter-spaces 58 between x-ray absorbent sheets 56. A spacer material that is x-ray transmissive, i.e., substantially non-absorbent of x-ray radiation, is received in inter-spaces 58 so that radiation travels through inter-spaces 58 substantially unimpeded. Integral molding of x-ray absorbent sheets 56 renders conventional fiber-like inter-space material structurally unnecessary so that, in one embodiment, inter-space material is air. In alternative embodiments, fiber-like inter-space material known in the art is arranged between x-ray absorbent sheets 56. Anti-scatter grid 50 is integrally fabricated from an injection molded engineered thermoplastic, such as ECOMASS(trademark) into a framework of x-ray absorbing members or sheets 56. Using conventional equipment and conventional techniques, a high density, high yield strength mesh framework is formed into a focused cross grid while eliminating the manufacturing challenges of conventional cross grids. Because of the increased yield strength afforded by the engineered thermoplastic material, anti-scatter grid 50 is pliable and may be flexed about one or both of axes 52, 54 to adjust or vary a focal length of grid 50 in one or more directions. For example, by flexing grid 50 about both axes 52, 54 a substantially equal amount, a substantially spherical focused grid may be formed and used for a certain x-ray procedure. To accommodate a different procedure, grid 50 may be flexed in an opposite fashion and returned to its previous form. Thus, a wide variety of interim anti-scatter grid configurations may be realized in a single grid 50 to accommodate a large number of x-ray procedures. It is contemplated that a grid could be formed having different stiffness along pre-determined axes to allow easier flexing in one direction than in another, or to prohibit flexing in a given direction but allowing it in others to facilitate acquisition of desired focal lengths. FIG. 4 illustrates radiographic imaging arrangement 10 including a flexed anti-scatter grid 60, which may be a one dimensional focused anti-scatter grid, such as grid 20 (shown in FIG. 2), or a two dimensional focused anti-scatter grid, such as grid 50 (shown in FIG. 3) to adjust the focal length of imaging arrangement 10. When anti-scatter grid 60 is flexed, an orientation of absorbent sheets and inter-space material is altered, and hence the effective focal length of grid 60 is changed to accommodate different requirements of different x-ray procedures. Thus, unlike conventional focused anti-scatter grids, a cost-effective, easily manufactured and stronger anti-scatter grid is provided using non toxic materials. Elimination of fiber like inter-space material increases contrast of radiograph images, and the higher yield strength of engineered thermoplastics allows a more versatile grid capable of flexing between two or more interim positions to accommodate a variety of x-ray procedures. Due to elimination of conventional fiber-like inter-space material that absorbs a measurable portion of x-rays, a higher quality image is realized with a given radiation dose, or conversely, the radiation dose can be reduced while still achieving a high contrast image comparable to known anti-scatter grids. 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.