Radiation image recording and read-out method and apparatus

Details Radiation image recording and read-out method and apparatus Radiation image recording and read-out method and apparatus

1999-08-18

2001-05-08

Kim, Robert H. (Department: 2882)

X-ray or gamma ray systems or devices

Beam control

Antiscatter grid

C378S098200, C250S580000, C250S584000

Reexamination Certificate

active

06229877

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a radiation image recording and read-out method and apparatus. This invention particularly relates to prevention of deterioration in image quality due to scattered radiation.
2. Description of the Prior Art
Operations for recording radiation images are carried out in various fields. For example, radiation images to be used for medical purposes are recorded as in X-ray image recording for medical diagnoses. Also, radiation images to be used for industrial purposes are recorded as in radiation image recording for non-destructive inspection of substances. In order to carry out such operations for recording radiation images, there has heretofore been utilized the so-called “radiography” in which radiation films and intensifying screens are combined with each other. With the radiography, when radiation, such as X-rays, carrying image information of an object impinges upon the intensifying screen, a fluorescent material contained in the intensifying screen absorbs energy from the radiation and produces fluorescence (i.e. instantaneously emitted light). Therefore, the radiation film, which is superposed upon the intensifying screen in close contact therewith, is exposed to the fluorescence produced by the fluorescent material, and a radiation image is thereby formed on the radiation film. In this manner, the radiation image can be directly obtained as a visible image on the radiation film.
The applicant proposed radiation image read-out apparatuses, which are referred to as the computed radiography (CR) apparatuses. With the proposed CR apparatuses, a stimulable phosphor sheet, on which a radiation image has been stored, is exposed to stimulating rays, such as a laser beam, which cause it to emit light in proportion to the amount of energy stored thereon during its exposure to radiation. The light emitted by the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal. The image signal having been obtained from the CR apparatuses is utilized for reproducing and displaying a visible image on a cathode ray tube (CRT) display device or for reproducing a visible image on film by a laser printer (LP), or the like. The reproduced image is utilized for making a diagnosis, e.g. for investigating the presence or absence of a diseased part or an injury or for ascertaining the characteristics of the diseased part or the injury.
However, in order for a radiation image to be obtained by utilizing radiation film, when the radiation image is to be visualized directly, it is necessary for sensitivity regions of the radiation film and the intensifying screen to be set so as to coincide with each other during the image recording operation. Also, it is necessary for a developing process to be carried out on the radiation film. Therefore, the problems occur in that considerable time and labor are required to obtain the radiation image by utilizing the radiation film.
Further, with the apparatuses for photoelectrically reading out a radiation image from radiation film or a stimulable phosphor sheet, the radiation image must be converted into an electric image signal, and image processing must be performed on the image signal such that a visible image having desired image density and contrast may be obtained. For such purposes, it is necessary for the scanning for reading out the radiation image to be performed by utilizing image read-out means. Therefore, operations for obtaining a visible radiation image cannot be kept simple, and considerable time is required to obtain the visible radiation image.
Such that the problems encountered with the conventional techniques may be solved, apparatuses utilizing semiconductor devices (referred to as the solid-state radiation detectors), which detect radiation and convert it into an electric signal, have been proposed. As the solid-state radiation detectors, various types of radiation detectors have been proposed. One of typical solid-state radiation detectors comprises two-dimensional image read-out means and a fluorescent material layer (i.e., a scintillator) overlaid upon the two-dimensional image read-out means. The two-dimensional image read-out means comprises an insulating substrate and a plurality of photoelectric conversion devices, which are formed in a two-dimensional pattern on the insulating substrate and each of which corresponds to one pixel. When the scintillator is exposed to radiation carrying image information, it converts the radiation into visible light carrying the image information. (The solid-state radiation detector having such a constitution will hereinbelow be referred to as the “photo conversion type of solid-state radiation detector.”) Another typical solid-state radiation detector comprises two-dimensional image read-out means and a radio-conductive material overlaid upon the two-dimensional image read-out means. The two-dimensional image read-out means comprises an insulating substrate and a plurality of charge collecting electrodes, which are formed in a two-dimensional pattern on the insulating substrate and each of which corresponds to one pixel. When the radio-conductive material is exposed to radiation carrying image information, it generates electric charges carrying the image information. (The solid-state radiation detector having such a constitution will hereinbelow be referred to as the “direct conversion type of solid-state radiation detector.”)
The photo conversion types of solid-state radiation detectors are described in, for example, Japanese Unexamined Patent Publication Nos. 59(1984)-211263 and 2(1990)-164067, PCT International Publication No. WO92/06501, and “Signal, Noise, and Read Out Considerations in the Development of Amorphous Silicon Photodiode Arrays for Radiotherapy 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.
Examples of the direct conversion types of solid-state radiation detectors include the following:
(i) A solid-state radiation detector having a thickness approximately 10 times as large as the ordinary thickness, the thickness being taken in the direction along which radiation is transmitted. The solid-state radiation detector is described in, for example, “Material Parameters in Thick Hydrogenated Amorphous Silicon Radiation Detectors,” Lawrence Berkeley Laboratory, University of California, Berkeley, Calif. 94720 Xerox Parc. Palo Alto. Calif. 94304.
(ii) A solid-state radiation detector comprising two or more layers overlaid via a metal plate with respect to the direction along which radiation is transmitted. The solid-state radiation detector is described in, for example, “Metal/Amorphous Silicon Multilayer Radiation Detectors, IEE TRANSACTIONS ON NUCLEAR SCIENCE, Vol. 36, No. 2, April 1989.
(iii) A solid-state radiation detector utilizing CdTe, or the like. The solid-state radiation detector is proposed in, for example, Japanese Unexamined Patent Publication No. 1(1989)-216290.
Also, in Japanese Patent Application No. 9(1997)-222114, the applicant proposed a solid-state radiation detector improved over the direct conversion type of solid-state radiation detector. (The proposed solid-state radiation detector will hereinbelow be referred to as the “improved direct conversion type of solid-state radiation detector.”)
The improved direct conversion type of solid-state radiation detector comprises:
i) a first electrical conductor layer having permeability to recording radiation,
ii) a recording photo-conductive layer, which exhibits photo-conductivity when it is exposed to the recording radiation having passed through the first electrical conductor layer,
iii) a charge transporting layer, which acts approximately as an insulator with respect to electric charges having a polarity identical with the polarity of electric charges occurring in the first electrical conductor layer, and which acts approximately as a conductor with respect

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