Patent Number: 
Section: description

FIG. 4 is a top view of a first layer of an X-ray absorbing grid in accordance with the present invention. In FIG. 4 a first grid layer L1 includes a plurality of cells 10. Each cell 10 has a center 12 and a perimeter 14. Perimeter 14 is formed of a material that absorbs X-rays. Thus, X-rays impacting perimeter 14 will be absorbed and will not be reflected onto the X-ray receptor. This allows a clearer X-ray image to be created. The number of cells 10 included in a layer varies according to the particular application. A hexagonal perimeter 14 is shown in the figures. However, any shape, preferably a polygon, is possible for perimeter 14. A shape with a plurality of straight sides is preferred in order to facilitate assembly of a plurality of cells 10. Regardless of the number of sides perimeter 14 has, the shape provides for multidimensional scatter reduction. That is, a single layer L1 will absorb scatter in two, orthogonal dimensions. In practice, X-rays are typically emitted from a point source. Like other forms of electromagnetic radiation, X-rays emitted from a point source are propagated in a plurality of directions. That is, the emitted X-rays contain a plurality of nonparallel vectors originating from the source. For purposes of illustration, only a single plane of emitted X-rays will be discussed. FIG. 6 shows a side view of a grid comprising a plurality of layers L1, L2, L3, L4, L(Nxe2x88x921), and L(N). A radiation source 20 emits X-rays 22 in a multitude of nonparallel directions, including angled X-rays 24 that are angled relative the X-ray receptor and central X-rays 26 that are substantially perpendicular to the X-ray receptor. Perimeters 14 are large enough to allow a large majority of the angled primary rays 24 to pass through without contacting perimeter 14 (and therefore without being absorbed). Similarly, the height of perimeter 14 is such that primary rays are not absorbed. As the angled X-rays 24 propagate from source 20, they spread away from central X-ray 26 in the direction of propagation. To increase the effectiveness of the grid, a plurality of layers can be used. This allows an increased surface area of X-ray absorbing material to combat scattered X-rays. Due to the spread of the angled primary X-rays 24, however, the cells of the respective layers must be shifted. Otherwise the result would be to effectively create a single cell of relatively great height, which would result in the absorption of primary X-rays. By using multiple layers, scatter reduction can be improved. For each successive layer, the cell size is varied. This allows rays passing through a first layer cell to also pass through a second layer cell. It will also be understood that because of the spread of X-rays 24, the height of the cells of lower layers can be greater than the height of the cells of the first layer while still allowing all primary rays 22 to pass through the grid. A magnification factor (M) for each layer of the grid can be calculated according to the following formula: M=F+(xxe2x88x921)*h/F, where F is the distance from the radiation source to the first layer, x is the layer in question, and h is the height of a single layer. By increasing the size of the cells by the multiplication factor associated with the particular layer, a grid allowing for both maximum passage of primary rays and maximum absorption of scatter rays can be fabricated. Thus, the radius of a circle circumscribed about a cell of the second layer (d2) equals the radius of a circle circumscribed about a cell of the first layer (d1) times the magnification factor. That is, d2=d1*M, or d2=d1*F+h/F. This increase in cell size is illustrated in FIGS. 4 and 5. With respect to FIG. 4, first layer L1 is shown. Layer L1 includes individual cells 30, 32, and 34. Cell 32 is located a distance xe2x80x9caxe2x80x9d away from cell 30, and cell 34 is located a distance xe2x80x9cbxe2x80x9d away from cell 30. Taking the center of cell 30 as the origin (0,0), it is seen that the center of cell 32 is located at (a,0) and the center of cell 34 is located at (0,b). With respect to FIG. 5, a second layer L2 is shown. Layer L2 includes individual cells 30xe2x80x2, 32xe2x80x2, and 34xe2x80x2, which correspond to cells 30, 32, and 34, respectively. Due to magnification, the cells of layer L2 are increased by the magnification factor M. Thus, taking the center of cell 30xe2x80x2 as the origin (0,0), the center of cell 32xe2x80x2 is located at (M*a,0) and the center of cell 34xe2x80x2 is located at (0,M*b). FIG. 7 is a partial side view of two layers in accordance with the present invention. Each layer of the grid has a substrate 50 and a plurality of cells 10. For convenience, only a partial view of each layer is shown. Substrate 50 has a first surface 51 and a second surface 52. Layer L1 has a cell 60 located on the first surface 51 and a cell 62 located on the second surface 52. Cell 60 is offset from cell 62. The advantages of offsetting the cells are discussed above. Layer L2 has a cell 64 on the first surface of the substrate and a cell 66 on the second surface of the substrate, cells 64 and 66 being offset. As shown by dashed lines in FIG. 7, cell 64 on the first surface of the second layer L2 is substantially aligned with cell 62 on the second surface of the first layer L1. Substrate 50 can be formed of any material that is substantially transparent to X-rays. Possible materials for substrate 50 include glass, aluminum, fiberglass reinforced plastic (epoxy or polyamide), and carbon reinforced plastic. Basically, any low atomic number material can be used. As stated previously, cells 10 are formed of a material that absorbs X-rays. Possible materials for cells 10 include heavy metals such as lead, nickel, cobalt, iron, tungsten, tantalum, and alloys thereof. Basically, any high atomic number material can be used. A layer can be included between the cells 10 and substrate 50 to facilitate adhesion of the cells 10 to the substrate 50. One possible adhesion facilitating material is copper. FIG. 8 is a partial side view of two layers in accordance with the present invention. For convenience, only a partial view of each layer is shown. Similar to the embodiment of FIG. 7, each layer has a substrate 50 and a plurality of cells 10. Each substrate 50 has first and second surfaces with a cell located on each surface. Unlike the embodiment of FIG. 7, cells on respective surfaces of a layer are substantially aligned rather than being offset. That is, cell 70 and cell 72 are substantially aligned, and cell 74 and cell 76 are substantially aligned. However, as shown by dashed lines, the cells of subsequent layers are offset. That is, cells 70 and 72 are offset from cells 74 and 76. Adjacent layers may be coupled in any convenient manner. For example, the first layer L1 may merely be positioned above the second layer L2. A layer of supporting material may optionally be placed intermediate adjacent layers. Although only a single plane of emitted X-rays was illustrated in the above discussion, it will readily be appreciated that the same analysis applies to the entire gamut of emitted X-rays. The cells can be of any shape that permits close packing arrays. Preferred shapes include a triangle, a trapezoid, a rhombus, a pentagon, a hexagon, a heptagon, or an octagon. While the preferred embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not of limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.