Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-11-29
2002-05-07
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S208100, C250S227200, C250S370110
Reexamination Certificate
active
06384400
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to radiation imaging, and more particularly, to radiation imaging via the conversion of radiation into visible light impinging on a light sensitive imaging array.
Radiation imagers typically include a scintillator coupled to a light sensitive imaging array. Radiation absorbed in the scintillator, such as a fiber optic scintillator, result in the emission of optical photons which in turn pass into the light sensitive imaging array. The light sensitive imaging array, such as a plurality of photodiodes, generates an electrical signal corresponding to the incident optical photon flux. Each of the photodiodes is coupled to circuitry to allow charge collected on the photodiode to be read.
Fiber optic scintillators or fiber optic scintillating plates are formed from an array of scintillating glass fibers disposed substantially parallel to one another. The core of each of the glass fibers is doped with a scintillating material so that the glass fibers scintillate when excited by radiation such as x-rays. The surface of each of the glass fibers is clad with a non-scintillating, lower optical index glass material.
Light generated in the scintillator in response to absorption of radiation in the core of a scintillating glass fiber is emitted isotropically. The portion of the light emitted at an angle less than the optical critical angle for the fiber is reflected and guided within the glass fiber and preferably made to exit from a surface of the fiber optic scintillator directed towards the light sensitive imaging array. The portion of the light emitted at an angle greater than the optical critical angle for the fiber exits the side of the glass fiber and thus may impinge on and be detected elsewhere by the light sensitive imaging array. This latter portion of the light or so called “optical cross-talk” results in image quality degradation.
While fiber optic scintillators are generally suitable for medical imaging, for example, using x-rays having energies of about 50 KeV to about 80 KeV, such fiber optic scintillators have a number of drawbacks for use in industrial imaging applications such as nondestructive testing of parts using x-rays having high energies, e.g., about 100 KeV or greater.
For example, increasing the density of the scintillating glass fibers, in order to stop and absorb high energy x-rays, undesirably results in a reduction of the brightness or luminance of the scintillator. In particular, high-density glass fibers doped with a scintillating material typically exhibit a poorer conversion of absorbed radiation into optical photons compared to low-density glass fibers.
In addition, increasing the thickness of the scintillator in order to stop and absorb the high energy x-ray s also undesirably results in increased optical cross-talk which degrades the resulting detected image.
Non-scintillating, black or colored glass fibers, so called “extramural absorber” (EMA) fibers have been used, e.g., interspersed among the plurality of scintillating glass fibers, for the purpose of absorbing stray light before the light reaches the bottom surface of the fiber optic scintillator. However, while EMA fibers reduce optical cross-talk and thus improve the resolution of the scintillator, the image brightness or luminance is also reduced as fewer optical photons reach the image plane at the bottom of the fiber optic scintillator.
Therefore, there is a need for a high resolution and high luminous scintillator for use in medical imaging and in industrial imaging using high energy radiation.
SUMMARY OF THE INVENTION
The present invention provides a scintillator having a first plurality of radiation absorbing elements comprising a scintillating material for converting radiation into light, and a second plurality of radiation absorbing elements interspersed among the first plurality of radiation absorbing elements. The first plurality of radiation absorbing elements has a first radiation absorption efficiency, and the second plurality of radiation absorbing elements has a second radiation absorption efficiency which is greater than the first radiation absorption efficiency.
In another aspect of the invention, a radiation imager is provided having a light sensitive imaging array, and a scintillator, as noted above, disposed adjacent to the light sensitive imaging array.
In still another aspect of the invention, a method for forming a scintillator includes providing a bundle, comprising a first plurality of radiation absorbing elements having a scintillating material for converting radiation into light and a second plurality of radiation absorbing elements, as noted above, interspersed among the first plurality of radiation absorbing elements, drawing the bundle to reduce the cross-section of the first plurality of radiation absorbing elements and the second plurality of radiation absorbing elements, cutting the drawn bundle into a plurality of sections, and assembling the plurality of sections to form a scintillator having an array of parallel first and second radiation absorbing elements.
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Albagli Douglas
DeJule Michael Clement
Han Sung Su
Possin George Edward
General Electric Company
Hale Lester R.
Johnson Noreen C.
Le Que T.
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