X-ray or gamma ray systems or devices – Electronic circuit – With display or signaling
Reexamination Certificate
2000-02-17
2003-03-25
Dunn, Drew A. (Department: 2882)
X-ray or gamma ray systems or devices
Electronic circuit
With display or signaling
C378S098200, C250S370090
Reexamination Certificate
active
06539076
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a method and apparatus for photographing a radiation image, and more particularly to a radiation-image photographing method and apparatus that obtains the radiation-image information of a subject by detecting radiation transmitted through the subject with a solid radiation detector.
2. Description of the Related Art
Today, in the field of radiation photography with the object of medical analysis and the like, a wide variety of radiation-image photographing apparatuses have been proposed and put to practical use (see U.S. Pat. Nos. 5,514,873 and 5,354,982, Japanese Unexamined Patent Publication No. 8(1996)-299316, etc.). In the radiation-image photographing apparatus, radiation transmitted through a subject is detected by a solid radiation detector (which has a semiconductor as a major part and will also be hereinafter referred to simply as a detector) in order to obtain an image signal representative of a radiation image related to the subject.
Also, various types of solid radiation detectors to be used in the radiation-image photographing apparatus have been proposed. For instance, with respect to the charge-generating process of converting radiation to an electric charge, there is a solid radiation detector of light conversion type (see Japanese Unexamined Patent Publication Nos. 59(1984)-211263 and 2(1990)-164067, PCT International Publication No. WO 92/06501, SPIE Vol. 1443, “Medical Image V,” Image Physics (1991), pp. 108-119, etc.). In this type of detector, a fluorescent substance is irradiated with radiation and emits fluorescent light. The fluorescent light is detected by a photoelectric conversion element (which is a solid detector). The resultant signal charge is temporarily stored in the electricity storage portion of the photoelectric conversion element, and the stored charge is converted to an image signal (electric signal) and is output. There is also a solid radiation detector of direct conversion type (see “MATERIAL PARAMETERS IN THICK HYDROGENATED AMORPHOUS SILICON RADIATION DETECTOR,” Lawrence Berkeley Laboratory and University of California, Berkeley, Calif. 94720 Xerox Parc, Palo Alto, Calif. 94304, “Metal/Amorphous Silicon Multilayer Radiation Detectors,” IEE TRANSACTION ON NUCLEAR SCIENCE, Vol. 36, NO. 2 April 1989, Japanese Unexamined Patent Publication No. 1 (1989)-216290, etc.). In this type of detector, a signal charge, produced in a radiation conductor irradiated with radiation, is collected by a charge collecting electrode and is temporarily stored in an electricity storage portion. The stored charge is converted to an electric signal and is output.
In addition, with respect to the charge-reading process of reading out a stored electric charge to the outside, there is a thin-film transistor (TFT) reading type which reads out an electric charge by scanning and driving a TFT connected to the electricity storage portion, an optical reading type which emits reading light (reading electromagnetic wave) to a detector and reads out an electric charge, and so on.
Furthermore, the applicant of this application has proposed an improved direct conversion type of solid radiation detector in Japanese Unexamined Patent Publication Nos. 10(1998)-232824 and 10(1998)-271374. The improved solid radiation detector is of a direct conversion and optical reading type and is formed by stacking (1) a recording photoconductive layer which exhibits photoconductivity by receiving the emission of recording radiation directly or indirectly, (2) a charge transfer layer which operates as substantially an electric conductor with respect to an electric charge of the same polarity as a latent image charge and also operates as substantially an insulator with respect to a transfer charge of the opposite polarity from the latent image charge, and (3) a reading photoconductive layer which exhibits photoconductivity by receiving the emission of a reading electromagnetic wave, in the recited order. In this improved type of detector, a signal charge (latent image charge) carrying image information is stored in the interface (electricity storage portion) between the recording photoconductive layer and the charge transfer layer. Also, electrodes (first and second conductive layers) are stacked on both sides of these 3 layers. The recording photoconductive layer, the charge transfer layer, and the reading photoconductive layer form the major part of the solid radiation detector in this type.
In photographing a radiation image, incidentally, a predetermined voltage is applied across the above-mentioned detector (which is, for example, a solid detector such as a photoelectric conversion element) to emit radiation, whereby an electric charge representing radiation-image information is stored in the electricity storage portion. On the other hand, after photographing, the application of voltage is stopped, or a standby voltage less than the above-mentioned predetermined voltage is applied. In this way, the electric charge stored in the electricity storage portion is held and the occurrence of dark current, which will be caused by continuing to apply the aforementioned predetermined voltage, is prevented.
In the case of using the optical reading type detector, there are cases where preexposure light is emitted to the reading electrode side to remove unnecessary electric charges stored in the electricity storage portion before the emission of recording light (which unnecessary electric charges include (1) a residual electric charge left without being read out after electric charges in the electricity storage portion have been read out, (2) dark current which occurs as voltage is applied to the device, and so on), as described in the above-mentioned Japanese Unexamined Patent Publication No. 10(1998)-271374.
Some of the direct conversion type detectors can perform recording immediately after dc voltage has been applied between both ends of the detector to form a predetermined electric field within the detector, as described in the above-mentioned Japanese Unexamined Patent Publication No. 10(1998)-271374, and others need to perform real recording after the detector has been pre-charged by primary exposure before recording, as described in “23027 Method and device for recording and transducing an electromagnetic energy pattern (Research Disclosure, June 1983)”, for example.
Furthermore, for instance, as described in Japanese Unexamined Patent Publication Nos. 61(1986)-244176 and 9(1997)-206293, some of the light conversion type detectors need to supply a predetermined electric charge to the electricity storage portion in advance to fully charge the electricity storage portion prior to photographing.
However, for example, the above-mentioned U.S. Pat. No. 5,514,873 discloses only that with respect to a housing having a solid radiation detector (radiation converter), memory, an energy source, and a radio transmitter, the supply of energy to the converter is performed from the outside by radio. There is no description of the application of voltage to the detector and the timing of emitting radiation. Therefore, what is disclosed in this reference alone can neither necessarily store an electric charge in the electricity storage portion with reliability nor prevent dark current.
Also, the above-mentioned U.S. Pat. No. 5,354,982 discloses that the voltage applied to the device is lowered after the generation of a latent image in order to hold the latent image, but has the disadvantage that if the application of voltage is continued, a signal-to-noise (S/N) ratio will be reduced by the storage of dark current.
Furthermore, the above-mentioned Japanese Unexamined Patent Publication No. 8(1996)-271374 discloses that the X-rays transmitted through the solid radiation detector are detected with an X-ray sensor provided behind the detector and, based on the result of detection, the amount of the transmitted X-rays is controlled. However, there is no description as to how the timing of emitting the X-rays is controlled. The
Dunn Drew A.
Fuji Photo Film Co. , Ltd.
Hobden Pamela R.
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