Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
2000-02-08
2002-05-21
Dang, Hung Xuan (Department: 2873)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S370140
Reexamination Certificate
active
06392237
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for obtaining radiation image data. More specifically, the present invention relates to a method and an apparatus for simultaneously obtaining a plurality of radiation image data sets to be used in energy subtraction processing employing a one-shot method, by using a solid-state radiation detector comprising a plurality of radiation detection layers.
2. Description of the Related Art
In radiation photography aimed at medical diagnoses, radiation image reading and recording apparatuses using films for radiation photography or stimulable phosphor sheets have been known.
Recently, various kinds of solid-state radiation detectors (whose main part comprises semiconductors) for outputting image signals representing radiation image information by detecting radiation have been proposed and put into practice. Various types of solid-state radiation detectors have been proposed as the radiation detectors to be used in the radiation image reading and recording apparatuses.
For example, with respect to an electric charge generation process in which radiation is converted into an electric charge, solid-state radiation detectors of different types, such as optical conversion type detectors (see Japanese Unexamined Patent Publication Nos. 59(1984)-211263 and 2(1990)-164067, PCT International Publication No. WO92/06501, and SPIE Vol. 1443 Medical Imaging V; Image Physics (1991), p.108-119, for example) and direct conversion type detectors (MATERIAL PARAMETERS IN THICK HYDROGENATED AMORPHOUS SILICON RADIATION DETECTORS, Lawrence Berkeley Laboratory. University of California, Berkeley, Calif. 94720 Xerox Parc. Palo Alto. Calif. 94304, Metal/Amorphous Silicon Multilayer Radiation Detectors, IEEE TRANSACTIONS ON NUCLEAR SCIENCE. VOL. 36. NO.2. APRIL 1989, and Japanese Unexamined Patent Publication No. 1(1989)-216290, for example) have been known. In an optical conversion type detector, light emitted from phosphor by exposing the phosphor to radiation is detected by a photoelectric conversion device and a signal electric charge thereby obtained is stored in a capacitor of the device. The stored electric charge is then converted into an image signal (electric signal) and the signal is output. In a direct conversion type detector, a signal electric charge generated within a radiation conductive material by exposing the material to radiation is collected by an electric charge collecting electrode and stored in a capacitor. The stored electric charge is then converted into an electric signal and the signal is output.
With respect to an electric charge reading process in which a stored electric charge is read out, solid-state radiation detectors of other types, such as TFT reading type detectors which read the charge by scanning TFT's (Thin Film Transistors) connected to capacitors and optical reading type detectors in which a charge is read by irradiating reading light (an electromagnetic wave for reading) thereon have been known.
Fuji Photo Film Co., Ltd. has proposed solid-state radiation detectors of improved direct conversion type (see Japanese Patent Application Nos. 10(1998)-232824 and 10(1998)-271374). A radiation detector of improved direct conversion type means a radiation detector employing both the direct conversion method and the optical reading method. The radiation detector of improved direct conversion type comprises a first conductive layer which is transparent to radiation for recording, a photoconductive layer for recording exhibiting photoconductivity (or, more accurately radiation conductivity,) when receiving the radiation for recording which has passed through the first conductive layer, an electric charge transport layer which acts approximately as an insulator to an electric charge having the same polarity as an electric charge charged in the first conductive layer while acting approximately as a conductor to an electric charge having the reversed polarity, a photoconductive layer for reading exhibiting photoconductivity (or, more accurately electromagnetic wave conductivity,) when receiving an electromagnetic wave for reading, and a second conductive layer which is transparent to the electromagnetic wave for reading, with these layers being stacked in this order. A signal electric charge (latent image electric charge) representing image information is stored at the interface (capacitor) between the photoconductive layer for recording and the electric charge transport layer. The first and the second conductive layers function as electrodes. The photoconductive layer for recording, the electric charge transport layer, and the photoconductive layer for reading comprise the main part of the solid-state detector of this type.
As methods of reading the signal electric charge in the improved direct conversion method, the following methods are known. For example, the second conductive layer (hereinafter called reading electrode) has a flat shape, and the signal electric charge is detected by scanning the reading electrode with spot-like reading light such as a laser beam. Alternatively, a stripe electrode in a comb-like shape is used as the reading electrode and a linear light source elongated along the direction almost orthogonal to the longitudinal direction of the stripe electrode scans the stripe electrode longitudinally to detect the signal charge.
Meanwhile, in reading and recording of radiation images using stimulable phosphor sheets or the like, processing called energy subtraction processing is also known (see Japanese Unexamined Patent Publication Nos. 59(1984)-83486, 60(1985)-225541, and 3(1991)-109679, and Japanese Patent No. 2627086, for example). In the energy subtraction processing, radiations having different energy distributions are irradiated onto a subject. By using a characteristic that a specific organ of the subject (such as an internal organ, a bone, and a blood vessel) absorbs characteristic radiation energy, 2 image signals describing a specific organ in different manners are obtained. After appropriate weighting has been carried out on the 2 image signals, subtraction between the 2 signals is carried out to obtain a radiation image emphasizing or extracting the specific portion of the subject in the radiation image.
In the subtraction processing, a plural-shot method (described in Japanese Unexamined Patent Publication No. 60(1985)-225541, for example) and a one-shot method (described in Japanese Unexamined Patent Publication No. 59(1984)-83486, for example) have been known. In the plural-shot method (2-shot method if the number of shoots is 2), photographing using radiation having energy which is different for each time is carried out a plurality of times. Based on image signals obtained by reading radiation images as a result of photographing, the subtraction processing is carried out. In the one-shot method, a plurality of recording sheets (2 recording sheets, for example) between which a filter is sandwiched are exposed to radiation having passed through a subject and radiation images each representing a high to low energy component of the radiation are recorded simultaneously by photographing at one time.
Since the plural-shot method has a time lag between each photographing, a subject moves during the photographing. As a result, a false image (motion artifact) caused by disagreement due to the motion between visible images reproduced based on image signals after subtraction processing is created and the quality of the visible images is lowered substantially. On the other hand, the one-shot method is advantageous in terms of not creating false images due to the subject motion, since a plurality of images are photographed at once.
For reading and recording radiation images using a solid-state radiation detector, Fuji Photo Film Co., Ltd. has proposed a solid-state radiation detector suitable for the energy subtraction processing using the one-shot method (see Japanese Unexamined Patent Publication No. 7(1995)-84056).
The radiation detector
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