Radiant energy – Invisible radiation responsive nonelectric signalling – Luminescent device
Reexamination Certificate
2000-10-26
2002-09-17
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiation responsive nonelectric signalling
Luminescent device
C250S484300
Reexamination Certificate
active
06452192
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a radiation image storage panel. This invention particularly relates to a radiation image storage panel comprising a stimulable phosphor layer and a light reflecting layer, which contains a light reflecting substance and is overlaid on one surface of the stimulable phosphor layer.
2. Description of the Related Art
In lieu of conventional radiography, radiation image recording and reproducing techniques utilizing a stimulable phosphor have heretofore been used in practice. The radiation image recording and reproducing techniques utilizes a radiation image storage panel (referred to also as the stimulable phosphor sheet) provided with a stimulable phosphor. With the radiation image recording and reproducing techniques, the stimulable phosphor of the radiation image storage panel is caused to absorb radiation, which carries image information of an object or which has been radiated out from a sample, and thereafter the stimulable phosphor is exposed to an electromagnetic wave (stimulating rays), such as visible light or infrared rays, which causes the stimulable phosphor to produce the fluorescence (i.e., to emit light) in proportion to the amount of energy stored thereon during its exposure to the radiation. The produced fluorescence (the emitted light) is photoelectrically detected to obtain an electric signal. The electric signal is then processed, and the processed electric signal is utilized for reproducing a visible image on a recording material.
The radiation image recording and reproducing techniques have the advantages in that a radiation image containing a large amount of information can be obtained with a markedly lower dose of radiation than in the conventional radiography. Therefore, the radiation image recording and reproducing techniques are efficient particularly for direct medical radiography, such as the X-ray image recording for medical diagnosis.
The radiation image storage panel utilized for the radiation image recording and reproducing techniques has a basic structure comprising a substrate and a stimulable phosphor layer overlaid on one surface of the substrate. In cases where the stimulable phosphor layer has self-supporting properties, the radiation image storage panel need not necessarily be provided with the substrate. Ordinarily, the stimulable phosphor layer is constituted of a layer, which comprises a binder and a stimulable phosphor dispersed in the binder. Alternatively, the stimulable phosphor layer may be constituted of a stimulable phosphor evaporated layer, a stimulable phosphor sintered layer, or the like. The stimulable phosphor has the properties such that, when the stimulable phosphor is caused to absorb radiation, such as X-rays, and is then exposed to an electromagnetic wave (stimulating rays), such as visible light or infrared rays, the stimulable phosphor emits light in proportion to the amount of energy stored thereon during its exposure to the radiation. Therefore, when the radiation image storage panel is exposed to the radiation, which carries image information of an object or which has been radiated out from a sample, the stimulable phosphor layer of the radiation image storage panel absorbs the radiation in proportion to the dose of radiation, and a radiation image of the object or the sample is stored as an image of energy from the radiation on the radiation image storage panel. The radiation image storage panel is then exposed to the stimulating rays, and the image having been stored on the radiation image storage panel can be detected as the light emitted by the radiation image storage panel. The emitted light is detected photoelectrically to obtain an image signal, the image signal is processed, and the thus obtained processed image signal can then be utilized for reproducing the radiation image of the object or the sample as a visible image.
As described above, the radiation image recording and reproducing techniques are the advantageous image forming techniques. As in the cases of an intensifying screen employed in the conventional radiography, it is desired that the radiation image storage panel utilized for the radiation image recording and reproducing techniques has a high sensitivity and can yield an image of good image quality (with respect to sharpness, graininess, and the like).
As a technique for enhancing the sensitivity of the radiation image storage panel, a technique, wherein a light reflecting layer is formed on a substrate by, for example, applying a coating composition, which contains an appropriate binder and a white pigment dispersed in the binder, onto the substrate, and a stimulable phosphor layer is then formed on the light reflecting layer, has heretofore been known. The radiation image storage panel provided with the light reflecting layer, which is constituted of a white pigment, is disclosed in, for example, Japanese Unexamined Patent Publication No. 56(1981)-12600. In Japanese Unexamined Patent Publication No. 56(1981)-12600, as white pigments, titanium dioxide, white lead, zinc sulfide, aluminum oxide, and magnesium oxide are exemplified.
As for a stimulable phosphor employed in the radiation image storage panel, a bivalent europium activated alkaline earth metal (particularly, barium) fluorohalide phosphor has heretofore been known as a preferable phosphor for a high luminance of emitted light, and the like. The emission spectrum of the bivalent europium activated alkaline earth metal fluorohalide phosphor is a band spectrum ranging from the near ultraviolet region to the blue region and has a light emission peak in the vicinity of 390 nm. In cases where a stimulable phosphor, which emits light of the near ultraviolet region besides the visible region, is employed in the radiation image storage panel (the bivalent europium activated alkaline earth metal fluorohalide phosphor described above emits light of the near ultraviolet region with an intensity higher than the intensity of light of the visible region), if a light reflecting layer constituted of one of the white pigments exemplified in Japanese Unexamined Patent Publication No. 56(1981)-12600, which white pigments are other than magnesium oxide, is formed between the substrate and the stimulable phosphor layer in order to enhance the sensitivity of the radiation image storage panel, the problems described below will occur. Specifically, the white pigments exemplified in Japanese Unexamined Patent Publication No. 56(1981)-12600, which white pigments are other than magnesium oxide, exhibit a high reflectivity with respect to light of the visible region and a markedly low reflectivity with respect to light of the near ultraviolet region (i.e., the reflection spectra of the white pigments do not extend to the near ultraviolet region). Therefore, the light reflecting layer constituted of one of the aforesaid white pigments cannot have sufficiently high light reflection characteristics. Accordingly, in cases where the radiation image storage panel is provided with the light reflecting layer constituted of one of the aforesaid white pigments, the sensitivity of the radiation image storage panel cannot always be enhanced sufficiently.
Therefore, research has heretofore been conducted to make an improvement of the radiation image storage panel from the aspect of the material for the light reflecting layer constituted of a white pigment. For example, in Japanese Unexamined Patent Publication No. 59(1984)-162500, it has been disclosed that an alkaline earth metal fluorohalide represented by the formula M
II
FX, in which M
II
is at least one of Ba, Sr, and Ca, and X is at least one of Cl and Br, may be utilized as a white pigment.
Also, a radiation image storage panel provided with a light reflecting layer, in which an oxide of a metallic element radiating out secondary X-rays having energy of 38 keV to 60 keV is employed as a pigment, is proposed in, for example, Japanese Unexamined Patent Publication No. 6(1994)-174898. With the proposed radiation image storage panel, in ca
Fuji Photo Film Co. , Ltd.
Gabor Otilia
Hannaher Constantine
Sughrue & Mion, PLLC
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