Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
1999-08-26
2002-04-30
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S367000, C250S370110, C250S385100
Reexamination Certificate
active
06380542
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a radiation image detecting system, and more particularly to an improvement of quality of a radiation image reproduced on the basis of image data output from 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)-164057, 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.
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.
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 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.
In a radiation image detecting system using such a solid radiation detector, a radiation image which is poor in quality can be reproduced if the radiation image is reproduced on the basis of digital image data obtained by digitizing image data as it is output from the solid radiation detector. This is because the level of the image signal components output from the individual solid radiation detecting elements varies according to the radiographing conditions and/or the individual difference of the solid radiation detector, and accordingly if the radiation image is reproduced on the basis of digital image data obtained by digitizing image data as it is output from the solid radiation detector, the density and the contrast of the image cannot be always good. In this specification, the term “solid radiation detecting element” means an element which includes said photoelectric conversion element or the charge collection electrode as a major part and forms a picture element.
Further since the amount of a latent image charge which each solid radiation detecting element can store is limited, the radiation image detecting system using the solid radiation detector is lower in signal saturation level and narrower in dynamic range as compared with the conventional radiation image information read-out system using radiographic film or a stimulable phosphor sheet. Accordingly, even in the common working range, some picture elements can be saturated, the radiation image taken by the radiation image detecting system using the solid radiation detector is lower in quality than that taken by the conventional radiation image information read-out system using radiographic film or the like.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary object of the present invention is to provide a radiation image detecting system using a solid radiation detector which can output image data which is improved in image quality.
In accordance with the present invention, there is provided a radiation image detecting system comprising
a radiation detecting means comprising a plurality of solid radiation detecting elements which are two-dimensionally arranged and convert radiations bearing thereon image information to an image signal,
an A/D convertor which converts the image signal as output from the radiation detecting means to a digital image signal,
a standardization characteristic determining means which analyzes the digital image signal and determines a characteristic of standardization processing which is to be carried out on the digital image signal, and
a standardization processing means which carries out standardization processing on the digital image signal according to the characteristic of standardization processing
Fuji Photo Film Co. Ltd
Hannaher Constantine
Israel Andrew
Sughrue & Mion, PLLC
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