X-ray or gamma ray systems or devices – Beam control – Antiscatter grid
Reexamination Certificate
2002-07-08
2003-07-15
Dunn, Drew A. (Department: 2882)
X-ray or gamma ray systems or devices
Beam control
Antiscatter grid
C414S788100, C414S792200, C901S017000
Reexamination Certificate
active
06594342
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to radiography, and more particularly, to an anti-scatter grid for improving radiographic images, and a method and an apparatus for forming an anti-scatter grid.
In medical imaging systems, x-ray radiation that reaches a photosensitive film or detector includes both attenuated primary radiation, which forms the useful image, and scattered radiation, which degrades the image. Often, an anti-scatter grid is inserted between the patient and the photosensitive film or detector to attenuate the scattered radiation while transmitting most of the primary radiation.
One type of anti-scatter grid includes alternating strips of lead foil and interspace material such as a solid polymer material or a solid polymer and fiber composite material. The strips of the lead foil are typically stacked aligned toward the x-ray source to minimize attenuation of the primary radiation. A drawback with using a solid interspace material is that the interspace material exhibits attenuation and scatter of the radiation, which affects the quality of the radiographic image.
Another drawback with this type of anti-scatter grid is that conventional manufacturing processes consist of tediously laminating the individual strips of the lead foil and the solid interspace material, i.e., laboriously gluing together alternating layers of the strips of lead foil and the interspace material until thousands of such alternating layers comprise a stack. Furthermore, to fabricate a focused anti-scatter grid, the individual layers must be placed in a precise manner so as to position them at a slight angle to each other such that each layer is fixedly focused to a convergent point, i.e., to the radiation source.
After the composite of strips of lead foil and the interspace material is assembled into a stack, the stack is then cut and carefully machined along its major faces to the required grid thickness that may be as thin as only 0.5 millimeters. The fragile composite, for example, 40 centimeters by 40 centimeters by 0.5 millimeter, is difficult to handle. If the stack has survived the machining and handling processes, the stack is then laminated with a protective cover along its machined surfaces to reinforce the fragile layered assembly and provide enough mechanical strength for use in the field.
Another type of anti-scatter grid, so called “air cross grid,” has a large plurality of open air passages extending through the grid panel. The grid panel is made by laminating a plurality of thin metal foil sheets photo-etched to create through openings defined by partition segments. The etched sheets are aligned and bonded to form the laminated grid panel. Such an anti-scatter grid is labor intensive and expensive to fabricate, and depending on the size of the partition segments subject to damage during manufacture and use.
There is a need for a structurally robust anti-scatter grid capable of increasing the resolution and contrast of radiographic images. There is also a need for an apparatus and a method for forming an anti-scatter grid having a plurality of radiation absorbing strips aligned with a radiation source.
SUMMARY OF THE INVENTION
The present invention provides, in one aspect, an anti-scatter grid for use in radiography in which the anti-scatter grid includes a plurality of generally radiation absorbing elements, a plurality of generally non-radiation absorbing elements for passage of primary radiation through said anti-scatter grid spaced between said plurality of generally radiation absorbing elements, and wherein said plurality of generally non-radiation absorbing elements comprises a plurality of voids.
In another aspect, an apparatus for forming an anti-scatter grid for radiography includes an arm having a first end portion and a second end portion. The first end portion of the arm is pivotable about an axis so that the second portion is movable through an arc. The second end portion has a surface alignable with the axis and the surface is operable to align a plurality of spaced-apart radiation absorbing elements with the axis.
In yet another aspect, a method for forming an anti-scatter grid for radiography includes providing a surface alignable with an axis and moveable along an arc around the axis, providing a plurality of generally radiation absorbing elements, and using the surface to dispose the plurality of generally radiation absorbing elements in spaced-apart relation and to angle the plurality of radiation absorbing elements to align with the axis.
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“Mammography Grid Performance,” Rezentes et al., Radiology, vol. 210, No. 1, Jan. 1999, pp. 227-232.
Dunn Drew A.
General Electric Company
Patnode Patrick K.
Thompson John F.
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