Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1997-11-26
2001-06-12
Yao, Sam Chuan (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S250000, C156S259000, C156S345420, C250S36100C
Reexamination Certificate
active
06245184
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to computed tomograph (CT) imaging and, more particularly, to detectors utilized in connection with CT systems.
BACKGROUND OF THE INVENTION
In at least some computed tomograph (CT) imaging system configurations, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the “imaging plane”. The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal spot. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator adjacent the collimator, and photodiodes adjacent the scintillator.
Multislice CT systems are used to obtain data for an increased number of slices during a scan. Known multislice systems typically include detectors generally known as 3-D detectors. With such 3-D detectors, a plurality of detector cells form separate channels arranged in columns and rows.
A scintillator for a 3-D detector may have scintillator elements with dimension of about 1×2×3 mm, with narrow gaps of only a few mils, for example, approximately 0.004 inches, between adjacent elements. As a result of the small size and the close proximity of the elements various problems arise. For example, a signal which impinges upon one scintillator element may be improperly reflected upward or to adjacent elements causing a loss of resolution.
Scintillators typically are cut using accurate dicing saws by-etching, or by laser cuting. Such cutting is necessary to provide the desired dimensions. The most common way to cut scintillators is with the outside diameter (OD) of a diamond saw. An OD saw has a diamond coating on the outside periphery of the blade to cut materials, such as ceramics. To maintain blade rigidity for accurate cuts, very high speeds are used, e.g., from 10,000 to 30,000 rpm. Cutting gaps, for example, a 4 mil gap, in a ceramic scintillator, however can be difficult if the aspect ratio of the gap is greater than about 10. Particularly, OD saws often produce inaccurate cuts for scintillators with aspect ratios greater than
10
. Additionally, if only one scintillator is cut at a time, many handling operations are required for each three dimensional array. These methods are time consuming and expensive.
It would be desirable to provide a method for increasing cutting accuracy of scintillators for a 3-D detector. It would also be desirable to provide such a method that minimizes the number of handling operations required to create the scintillators.
SUMMARY OF THE INVENTION
These and other objects may be attained by a method of fabricating scintillators which includes the step of accurately cutting many ceramic scintillators at one time. Using the present method, ceramic scintillators may be cut at fairly fast speeds even if the scintillators are several inches thick and have aspect ratios greater than
10
. More particularly, and in one embodiment, the scintillator elements are cut using an inside diameter (ID) saw. The ID saw has a blade having an inner circumference cutting edge with a diamond coating. Because the outer surface of the blade can be tensioned to a high stress, the blade is much more rigid than an OD blade. This tension enables accurate cuts even if the blade is making very deep cuts.
In one specific embodiment, a stack of scintillators is cut in a first direction with the ID diamond saw to create first bar stacks. After separating the first bar stacks into individual first bars, the first bars are mounted in a fixture with 4 mil gaps between the bars. After filling the gaps with a cast reflector material, the cast first bars are cut with the ID saw blade inner circumference cutting edge in a 90 degree direction relative to the first cut to form second bar stacks. After separating the second bar stacks into second bars, the second bars are then placed in a fixture with gaps between the second bars, a cast reflector material is placed in the gaps, and the bars are ground to final dimensions as a finished array.
The above-described method facilitates fabrication of scintillators with increased accuracy. In addition, cutting and casting several larger pieces of scintillation material minimizes the handling of small pixels or small arrays, therefore saving time.
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patent: 5866908 (1999-02-01), Novak
Riedner Robert J.
Schedler Matthew
Armstrong Teasdale LLP
Cabou Christian G.
General Electric Company
Yao Sam Chuan
LandOfFree
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