X-ray or gamma ray systems or devices – Beam control – Antiscatter grid
Reexamination Certificate
1999-12-13
2001-06-26
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Beam control
Antiscatter grid
Reexamination Certificate
active
06252938
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for making focused and unfocused grids and collimators which are movable to avoid grid shadows on an imager, and which are adaptable for use in a wide range of electromagnetic radiation applications, such as x-ray and gamma-ray imaging devices and the like. More particularly, the present invention relates to a method and apparatus for making focused and unfocused grids, such as air core grids, that can be constructed with a very high aspect ratio, which is defined as the ratio between the height of each absorbing grid wall and the thickness of the absorbing grid wall, and that are capable of permitting large primary radiation transmission therethrough.
2. Description of the Related Art
Anti-scatter grids and collimators can be used to eliminate the scattering of radiation to unintended and undesirable directions. Radiation with wavelengths shorter than or equal to soft x-rays can penetrate materials. The radiation decay length in the material decreases as the atomic number of the grid material increases or as the wavelength of the radiation increases. These grid walls, also called the septa and lamellae, can be used to reduce scattered radiation in ultraviolet, x-ray and gamma ray systems, for example. The grids can also be used as collimators, x-ray masks, and so on.
For scatter reduction applications, the grid walls preferably should be two-dimensional to eliminate scatter from all directions. For many applications, the x-ray source is a point source close to the imager. An anti-scatter grid preferably should also be focused. Methods for fabricating and assembling focused and unfocused two-dimensional grids are described in U.S. Pat. No. 5,949,850, entitled “A Method and Apparatus for Making Large Area Two-dimensional Grids”, referenced above.
When an anti-scatter grid is stationary during the acquisition of the image, the shadow of the anti-scatter grid will be cast on the imager, such as film or electronic digital detector, along with the image of the object. It is undesirable to have the grid shadow show artificial patterns.
The typical solution to eliminating the non-uniform shadow of the grid is to move the grid during the exposure. The ideal anti-scatter grid with motion will produce uniform exposure on the imager in the absence of any objects being imaged.
One-dimensional grids, also known as linear grids and composed of highly absorbing strips and highly transmitting interspaces which are parallel in their longitudinal direction, can be moved in a steady manner in one direction or in an oscillatory manner in the plane of the grid in the direction perpendicular to the parallel strips of highly absorbing lamellae. For two-dimensional grids, the motion can either be in one direction or oscillatory in the plane of the grid, but the grid shape needs to be chosen based on specific criteria.
The following discussion pertains to a two-dimensional grid with regular square patterns in the x-y plane, with the grid walls lined up in the x-direction and y-direction. If the grid is moving at a uniform speed in the x-direction, the film will show unexposed stripes along the x-direction, which also repeat periodically in the y-direction. The width of the unexposed strips is the same or essentially the same as the thickness of the grid walls. This grid pattern and the associated motion are unacceptable.
If the grid is moving at a uniform speed in the plane of the grid, but at a 45 degree angle from the x-axis, the image on the film or imager is significantly improved. However, strips of slightly overexposed film parallel to the direction of the motion at the intersection of the grid walls will still be present. As the grid moves in the x-direction at a uniform speed, the grid walls block the x-rays everywhere, except at the wall intersection, for the fraction of the time
2d/D,
where d is the thickness of the grid walls and D is the periodicity of the grid walls. At the wall intersection, the grid walls blocks the x-rays for the fraction of the time
2d/D<t≦d/D,
depending on the location. Thus, stripes of slightly overexposed x-ray film are produced.
Methods for attempting to eliminate the overexposed strips discussed above are disclosed in U.S. Pat. Nos. 5,606,589, 5,729,585 and 5,814,235 to Pellegrino et al., the entire contents of each patent being incorporated herein by reference. These methods attempt to eliminate the overexposed strips by rotating the grid by an angle A, where A=atan(n/m), and m and n are integers. However, these methods are unacceptable or not ideal for many applications.
Accordingly, a need exists for a method and apparatus for eliminating the overexposed strips associated with two-dimensional focused or unfocused grid intersections.
SUMMARY OF THE INVENTION
An object of the present invention, therefore, is to provide a method and apparatus for manufacturing a focused or unfocused grid which is configured to minimize overexposure at its wall intersections when the grid is moved during imaging.
Another object of the present invention is to provide a method and apparatus for moving a focused or unfocused grid so that no perceptible areas of variable density are cast by the grid onto the film or other two-dimensional electronic detectors.
A further object of the present invention is to provide a method and apparatus for assembling sections of a two-dimensional, focused or unfocused grid.
Still another object of the present invention is to provide a method and apparatus for joining stacked layers of two-dimensional focused or unfocused grids.
These and other objects of the present invention are substantially achieved by providing a grid, adaptable for use with electromagnetic energy emitting devices, comprising at least metal layer, formed by electroplating. The grid comprises top and bottom surfaces, and a plurality of solid integrated walls. Each of the solid integrated walls extends from the top to bottom surface and having a plurality of side surfaces. The side surfaces of the solid integrated walls are arranged to define a plurality of openings extending entirely through the layer. For some applications, all the walls are 90° with respect to the top and bottom surfaces. For some other applications, at least some of the walls extend at an angle other than 90° with respect to the top and bottom surfaces such that the directions in which the walls extend all converge at a point in space at a predetermined distance from the front surface of the at least one layer.
These and other objects of the present invention are also substantially achieved by providing a grid, adaptable for use with electromagnetic energy emitting devices. The grid comprises at least one solid metal layer, formed by electroplating. The solid metal layer comprises top and bottom surfaces, and a plurality of solid integrated, intersecting walls, each of which extending from the top to bottom surface and having a plurality of side surfaces. The side surfaces of the walls are arranged to define a plurality of openings extending entirely through the layer, and at least some of the side surfaces have projections extending into respective ones of the openings.
REFERENCES:
patent: 5970118 (1999-10-01), Skokolov
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Dr. P. Bley, “The Liga Process for Fabrication of Three-Dimensional Microscale Structures,”Interdisciplinary Sci. Rev.., vol. 18, pp. 267-272 (1993).
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“IBM Team Develops Ultrathick Negative Res
Church Craig E.
Creatv MicroTech, Inc.
Roylance, Abrams, Berdo and Goodman LLP
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