X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2001-05-30
2003-02-11
Dunn, Drew A. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S098800, C250S367000, C250S370110
Reexamination Certificate
active
06519313
ABSTRACT:
BACKGROUND OF INVENTION
This invention relates generally to high-Z inter-scintillator materials and a method of manufacturing such inter-scintillator reflectors, where the high-Z inter-scintillator material acts as a high density x-ray absorber.
Solid state detectors for computed tomography (CT) imaging use scintillators to convert x-rays into scintillation radiation which itself is converted to an electrical signal with a photodiode. Detector arrays are typically comprised of scintillator pixels separated by an inter-scintillator material used to pipe the scintillation radiation towards the diode. The materials used as the inter-scintillator material are typically highly reflecting at the scintillation radiation wavelengths emitted by the scintillator in order to collect a large fraction of the scintillation radiation at the diode.
Appropriate inter-scintillator materials include high refractive index solid materials such as TiO
2
formed in a castable low index medium such as an epoxy.
One drawback of such a system is the darkening of the inter-scintillator material when it is struck by a dose of x-rays commonly used in CT imaging. A typical dose over the life of the detector is 1 Mrad. This darkening results in lower reflectivity and less efficient collection of the scintillation radiation, and thus a lowering of the sensitivity of the x-ray detector.
Furthermore, the darkening is often not uniform over the entrance face of the detector. This lack of uniformity in darkening can result in image degradation if the detector is not properly calibrated. In addition to the inter-scintillator material itself, the diode below the reflector is also sensitive to radiation and must be protected from the x-ray beam.
Current CT detectors use a collimator assembly to protect the inter-scintillator material from damage by x-rays. This assembly consists of tall tungsten plates aligned perpendicular to the plane of the x-ray fan beam. This assembly is primarily used to minimize scattered x-rays from reaching the scintillator, but is also used to protect the inter-scintillator material between pixels from the x-rays. For multi-slice CT, where the detector is segmented in the direction parallel to the fan beam, wires are used to protect the reflector and diodes. These wires are strung between the deep plates in grooves machined in the plates.
The manufacturing of such a two dimensional collimator with plates and wires is complex. The separate construction of the collimator with protective wires and the scintillator/reflector body requires accurate alignment of these devices during construction of the complete detector. This alignment cannot be done optically since the inter-scintillator material between the scintillator pixels is obscured by reflector material covering the top of the pixels (“surface reflector”). Therefore, either x-ray alignment or rigorous dimensional tolerances must be used to ensure that the reflector material is aligned with the protective wires.
SUMMARY OF INVENTION
In view of the foregoing, it would be desirable to provide a scintillator pack including a scintillator pixel array, and an x-ray absorbing layer in the inter-scintillator regions that avoids or reduces the above mentioned problems. The x-ray absorbing layer eliminates the requirement of protective tungsten cross-wires over the inter-scintillator regions. Thus quality and reproducibility are improved, while costs are reduced.
In accordance with one aspect of the present invention, there is provided a scintillator pack. The scintillator pack comprises an array of scintillator pixels and an x-ray absorbing layer formed in inter-scintillator regions between the scintillator pixels. The x-ray absorbing layer comprises a high density x-ray absorbing material.
In accordance with another aspect of the present invention there is provided an x-ray device. The x-ray device comprises an x-ray source, a scintillator pack, and a scintillation radiation detector. The scintillator pack has an array of scintillator pixels where a pixel of the array emits scintillation radiation upon an x-ray from the x-ray source being absorbed by the pixel. The scintillator pack also includes an x-ray absorbing layer, comprising a high density x-ray absorbing material, formed in inter-scintillator regions between the scintillator pixels. The scintillation radiation detector is optically coupled to the scintillator pack for detecting scintillation radiation.
In accordance with another aspect of the present invention there is provided an x-ray detection device. The x-ray detection device comprises a scintillator pack and a scintillation radiation detector. The scintillator pack has an array of scintillator pixels where a pixel of the array emits scintillation radiation upon an x-ray being absorbed by the pixel. The scintillator pack also includes an x-ray absorbing layer, comprising a high density x-ray absorbing material, formed in inter-scintillator regions between the scintillator pixels. The scintillation radiation detector is optically coupled to the scintillator pack for detecting scintillation radiation.
In accordance with another aspect of the present invention there is provided a method of forming a scintillator pack. According to this aspect of the invention the method comprises providing an array of scintillator pixels, and forming an x-ray absorbing layer in inter-scintillator regions between the scintillator pixels, where the x-ray absorbing layer is of a high density x-ray absorbing material.
According to this aspect of the invention the x-ray absorbing layer may be formed by disposing a melted eutectic alloy of a metal into the inter-scintillator regions between the scintillator pixels.
According to this aspect of the invention the x-ray absorbing layer may alternatively be formed by disposing a glass melt into the inter-scintillator regions between the scintillator pixels, and cooling the glass melt to form a glass in the inter-scintillator regions.
According to this aspect of the invention the x-ray absorbing layer may alternatively be formed by providing a high density x-ray absorbing powder, dispersing the powder within a liquid matrix to form a precursor mix, disposing the precursor mix within the inter-scintillator regions, and solidifying the precursor mix to form a solid layer.
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Duclos Steven Jude
Venkataramani Venkat Subramaniam
Dunn Drew A.
General Electric Company
Ho Allen C.
Johnson Noreen C.
Vo Toan
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