Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
1999-08-26
2002-09-24
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S370110, C250S591000
Reexamination Certificate
active
06455857
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a radiation image detecting system, and more particularly to suppression of deterioration in image quality due to backscattering of radiations and/or protection of a latent image charge detecting circuit against the radiations in a radiation image detecting system.
2. Description of the Related Art
There has been known a radiation image information read-out system using radiographic film or a stimulable phosphor sheet in medical radiography.
Recently there has been proposed a radiation image detecting system employing a solid radiation detector including a semiconductor as a major part which detects radiations and converts the intensity of radiations to an electric signal. Though various types of solid radiation detectors have been proposed, the following solid radiation detectors are representative.
That is, a solid radiation detector comprising a two-dimensional image reader formed by two-dimensionally forming a plurality of photoelectric conversion elements (each forming a picture element) on an insulating substrate and a phosphor layer (scintillator) which is formed on the two-dimensional image reader and generates visible light bearing thereon image information when exposed to radiations bearing thereon image information. The solid radiation detector of this type will be referred to as “a photo-conversion type solid radiation detector”, hereinbelow.
A solid radiation detector comprising a two-dimensional image reader formed by two-dimensionally forming a plurality of charge collection electrodes (each forming a picture element) on an insulating substrate and a radiation-conductive material layer which is formed on the two-dimensional image reader and generates electric charges bearing thereon image information when exposed to radiations bearing thereon image information. The solid radiation detector of this type will be referred to as “a direct conversion type solid radiation detector”, hereinbelow.
The photo-conversion type solid radiation detectors are disclosed, for instance, in Japanese Unexamined Patent Publication Nos. 59(1984)-211263 and 2(1990)-164067, PCT International Publication No. WO92/06501, “Signal, noise, and read out considerations in the development of amorphous silicon photodiode arrays for radiography and diagnostic x-ray imaging”, L. E. Antonuk et. al., University of Michigan, R.A. street Xerox, PARC, SPIE vol. 1443, “Medical Imaging V”, Image Physics (1991), pp. 108-119, and the like.
In the photo-conversion type solid radiation detector, the photoelectric conversion elements have also function of storing detected electric charges, and the electric charges obtained by photoelectric conversion are stored in the photoelectric conversion elements as latent image charges.
As the direct conversion type solid radiation detector, the following have been proposed.
1) A solid radiation detector which is about ten times as large as normal solid radiation detectors in thickness as measured in the direction in which radiations are transmitted through the solid radiation detector. See “MATERIAL PARAMETERS IN THICK HYDROGENATED AMORPHOUS SILICON RADIATION DETECTORS”, Lawrence Berkeley Laboratory. University of California, Berkeley, Calif. 94720 Xerox Parc. Palo Alto. Calif. 94304.
2) Those comprising a plurality of solid radiation detectors laminated in the direction in which radiations are transmitted with metal plates intervening therebetween. See “Metal/Amorphous Silicon Multilayer Radiation Detectors”, IEE TRANSACTIONS ON-NUCLEAR SCIENCE. VOL. 36. NO.2 APRIL 1989.
3) Solid radiation detectors using CdTe and the like disclosed in Japanese Unexamined Patent Publication No. 1(1989)-216290.
In the direct conversion type solid radiation detector, a capacitor is connected to each of the charge collection electrodes and the electric charges collected by the charge collection electrodes are stored in the capacitors as latent image charges.
This applicant has proposed an improvement on the direct conversion type solid radiation detector as disclosed in Japanese Patent Application 9(1997)-222114. The solid radiation detector will be referred to as “an improved direct conversion type solid radiation detector”, hereinbelow.
The improved direct conversion type solid radiation detector comprises a first conductive layer which is transparent to recording radiations, a recording photoconductive layer which exhibits photoconductivity upon exposure to the recording radiations passing through the first conductive layer, a charge transfer layer which acts substantially as an insulator to electric charges of the same polarity as that in which the first conductive layer is charged and as a conductor to electric charges reverse to that in which the first conductive layer is charged, a read-out photoconductive layer which exhibits photoconductivity upon exposure to read-out electromagnetic waves, and a second conductive layer which is transparent to the read-out electromagnetic waves. These layers are superposed one on another in this order and latent image charges are collected on the interface between the recording photoconductive layer and the charge transfer layer.
As a system for reading out the latent image charges in the improved direct conversion type solid radiation detector, there may be employed a read-out system where the read-out electrode (the second conductive layer) is made like a flat plate and the latent image charges are read out by scanning the read-out electrode with a read-out light spot such as a laser beam, or a read-out system where the read-out electrode is made like a stripe electrode (comb tooth electrode) and the latent image charges are read out by scanning the stripe electrode with a line light beam, extending in a direction perpendicular to the longitudinal direction of the stripe electrode, in the longitudinal direction of the stripe electrode. Irrespective of whichever read-out system is employed, the solid radiation detector forms a two-dimensional image read-out system in which a plurality of detecting elements (each forming a picture element) formed by the charge transfer layer, the read-out photoconductive layer and the second conductive layer are two-dimensionally arranged.
In any one of the solid radiation detectors described above, a detecting circuit which converts the latent image charges to an image signal is connected to the solid radiation detector. The detecting circuit converts the latent image charges stored on the photoelectric conversion elements, the charge collection electrodes or the detecting elements to an image signal, and the image signal is output after subjected to a predetermined image processing, and is reproduced as a visible image by a reproducing system such as a CRT.
In radiography employing such a solid radiation detector, radiations which have passed through an object and bear thereon transmission radiation image information of the object are caused to impinge upon the solid radiation detector, and the radiations are converted to latent image charges bearing thereon the transmission radiation image information of the object in the solid radiation detector, and the latent image charges are stored in the solid radiation detector. Thereafter the latent image charges in the solid radiation detector is converted to an image signal by a detecting circuit and the image signal is output.
Not all the radiations impinging upon the solid radiation detector are converted to the latent image charges but a part of the radiations passes through the solid radiation detector and impinges upon substance behind the solid radiation detector. The radiations reflected by the substance behind the solid radiation detector reenter the solid radiation detector from rearward as backscattering radiations bearing thereon image information on the substance and are converted to latent image charges bearing image information on the substance.
As a result, the solid radiation detector stores both the latent image charges representing the image information on the substan
Fuli Photo Film Co., Ltd.
Gagliardi Albert
Hannaher Constantine
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