Patent Application
20080095320
A more complete appreciation of this invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:
Methods and apparatus for forming complex-shaped, 3-D internal structures in hard materials to fabricate x-ray collimators are described. For simplicity and illustrative purposes, the principles of the embodiments are described. Moreover, in the following detailed description, references are made to the accompanying figures, which illustrate specific embodiments. Electrical, mechanical, logical, and structural changes may be made to the embodiments without departing from the spirit and scope of the embodiments.
Embodiments of the invention include methods which utilize a laminated stack of thin sheets to construct an X-ray collimator. The laminated sheets may comprise Tungsten or other X-ray attenuating materials. The 3-dimensional structures required to collimate x-rays according to the desired collimation function may be formed by creating apertures in laminated sheets and stacking the layers to form the required 3-dimensional structures in the composite collimator structure.
The collimator layers may be created from as few as a single laminated layer. In one embodiment, a plurality of collimator layers are created from different sections of a single laminated sheet. The portions of the laminated sheet that outline each collimator layer and the collimator layer's corresponding apertures may be removed through a well-known photo-etching process, or through machine punching, laser-cutting, drilling, or any other material removal process. The individual collimator layers are removed from the laminated layer, and may then be stacked and aligned according to the process described previously.
In the case where the collimator fabrication process creates sharp edges at the meeting points between collimator layers, the edges may be honed or smoothed through extrude honing (i.e., by pushing an abrasive at pressure through the 3-dimensional structures of the composite collimator structures) (step 108). This process may be used to smooth or knock off sharp edges within the 3-dimensional hollow structures in the composite collimator structure.
Alternatively, the apertures of each photo-etched collimator layer may be honed prior to stacking and attaching the collimator layers (step 109).
Embodiments of the invention allow creation of intricate shapes in a thin (for example, 0.001-0.010 inch) laminated sheet made from an X-ray attenuating material such as, but not limited to, Tungsten (W). By varying the sizes and/or shapes of the apertures in each collimator layer, a complex 3-dimensional internal shape can be created by stacking several layers together. The advantages include low raw material cost (for example, the cost of a thin laminated sheet versus a block of material) and low formation cost (for example, forming the layers using process such as photo-etching, punching, or laser-cutting, which are known to be lower cost that EDM techniques. This enables production of a complex X-ray collimator at an overall cost that is much less expensive than traditionally fabricated collimators.
A collimator 206 is employed to restrict x-ray exposure to the locations occupied by the sensors 205 and the intervening areas of the object under inspection in order to limit overall x-ray exposure of the object and to improve the dynamic range of the images captured by the sensors 205. To this end, the collimator 206 generates respective fan beams 203 directed at each of the respective sensors 205.
A field block 208 may be positioned between the x-ray source 202 and the sensors 205 close to the array of sensors. The field block 208 may be an x-ray absorbing plate comprising a respective aperture located over each sensor 205. Each aperture is positioned to expose only the corresponding sensor to the source 202. Furthermore, the field block 208 is positioned a sufficient distance away from the sensor(s) (i.e., the imaging plane) so as to limit the field of view of the respective sensors mainly to that of the corresponding fan beam directed at it. The field block 208 is therefore configured to pass x-rays sourced directly by the x-ray source 202 to respective ones of the sensors 205 and to block detection of reflected or scatter x-rays by the respective sensors 205. In this system, the position of the object under inspection 204 is altered relative to the x-ray source 202, sensors 205, collimator 206, and field block 208, passing between the collimator 206 and field block 208.
The collimator 206 is positioned close to the x-ray source 202 and configured to collimate x-rays generated by the x-ray source into one or more fan beams directed at corresponding ones of the sensors 205.
In operation, an object 204 to be inspected (shown only in
In order to generate the fan beams 203, the collimator 206 must be configured to direct x-rays from the source 202 into beams 203.
As shown in the design 300, the collimator design includes twelve 3-dimensional apertures 310. The 3-dimensional structures of the apertures 310 are narrow pyramidal structures. Each pyramidal structure is hollow, having a respective aperture 310 at the top of the respective pyramid though which x-rays generated by an x-ray point source may enter, and an aperture 312 which forms the hollow base of the pyramidal structure through which the rays exit. The dimensions of the base aperture 312 of its pyramidal 3-dimensional collimator aperture 310 dictates the fan beam coverage at the image plane. The angle of the pyramid with respect to both the x-ray source and the image plane dictates the direction of the fan beam.
In one embodiment, the collimator design 300 may be implemented according to the steps of
After photo-etching, punching, laser-cutting, or otherwise, of the laminated sheet(s) 450 to produce the collimator layers 401, 402, 403, 404, 405, 406, 407, 408, 409, and 410, the collimator layers are stacked and attached such that corresponding 2-dimensional apertures of each layer are appropriately aligned to form the 3-dimensional internal structures according to the collimator design. For example, the collimator layers of
In one embodiment, the edges at the meeting points between collimator layers are honed or smoothed through extrude honing (i.e., by pushing an abrasive at pressure through the 3-dimensional structures of the composite collimator structures) or other appropriate honing technique.
In one embodiment, the apertures of each collimator layer are honed prior to stacking and attaching the collimator layers.
Collimators fabricated according to the collimator fabrication technique described herein may be produced at much less cost than EDM techniques. Furthermore, once the etching patterns for each of the collimator layers are captured in artwork, collimators can be produced in high volume much more quickly than can be done using EDM techniques.
Although embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
