Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-12-24
2004-11-09
Dye, Rena (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C250S484400, C250S588000
Reexamination Certificate
active
06815092
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a radiation image storage panel suitable for use in the radiation image recording and reproducing method utilizing a stimulable phosphor.
BACKGROUND OF THE INVENTION
In radiography the interior of objects is reproduced by means of penetrating radiation which is high energy radiation belonging to the class of X-rays, &ggr;-rays and high energy elementary particle radiation, e.g. &bgr;-rays, electron beam or neutron radiation. For the conversion of penetrating radiation into visible light and/or ultra-violet radiation luminescent substances are used called phosphors.
During the last decade as a method replacing conventional radiography, radiation image recording and reproducing methods were developed utilizing a stimulable phosphor. Use is made in that method from a radiation image storage panel comprising a support and a stimulable phosphor layer provided thereon, wherein the steps are performed of causing the stimulable phosphor of the panel to absorb radiation energy having passed through an object or having radiated from an object, sequentially exciting the stimulable phosphor with an electromagnetic wave such as visible light or infrared rays, also called “stimulating rays”, in order to release the radiation energy stored in the phosphor as light emission (thus by stimulated emission), photoelectrically detecting and storing in digital form the emitted light and reproducing the radiation image of the object as a visible image from the stored digital information. The panel thus treated is subjected to a step for erasing a radiation image remaining therein, in order to be available for the next recording and reproducing procedure, thus providing repeated use.
The method described above permits use of reduced irradiation doses, when compared with a conventional radiography using a combination of a radiographic film and radiographic intensifying screen, where remakes may more often occur, due to failure in choice of exposure amounts: digital processing permits further electronic corrections and can provide enhanced image characteristics. Further, the method is very advantageous from the viewpoints of conservation of resource and economic efficiency because the radiation image storage panel can be repeatedly used while the radiographic film is consumed for each radiographic process in the conventional radiography.
The radiation image storage panel employed in the above-described method has a basic structure comprising a support and a stimulable phosphor layer provided on one surface of the support. If the phosphor layer is self-supporting, the support may be omitted. The phosphor layer usually comprises a binder and stimulable phosphor particles dispersed therein, but it may consist of agglomerated phosphor with no binder. The phosphor layer containing no binder can be formed by deposition process (e.g. chemical vapour deposition) or firing process. Further, the layer comprising agglomerated phosphor soaked with a polymer is also known. A transparent film of polymer material is normally placed on the free surface (surface not facing the support) of the phosphor layer in order to protect the layer from chemical deterioration or physical shock. This surface protective film can be formed by various methods, for example, by applying a solution of resin (e.g., cellulose derivatives, polymethyl methacrylate, polyurethane acrylate), by fixing a transparent resin film (e.g., a glass plate, a film of organic polymer such as polyethylene terephthalate) with adhesive, or by depositing inorganic materials on the phosphor layer.
In order to improve the quality (e.g., sharpness, graininess) of the resultant visible image, a radiation image storage panel having a protective film of a particular haze is proposed in JP-A 62-247298. A storage panel having a new protective film with a multi-layered structure comprising a plastic film and a fluorocarbon resin layer containing light-scattering fine particles has been proposed in U.S. Pat. No. 5,925,473.
The radiation image storage panel is repeatedly used in the cyclic procedure comprising the steps of: exposing to a radiation (for recording of a radiation image), irradiating with stimulating rays (for reading of the recorded image), and exposing to erasing light (for erasing the remaining image). In this procedure, the storage panel is transferred from one step to another by means of conveying means such as belt and rollers in the radiation image recording and reproducing apparatus, and after a cycle of the steps is conducted, the storage panel is piled up on other storage panels and stored for next cycle. Stains and abrasions due to direct contact of the surface of the storage panel with conveying means (e.g., belt and rollers) in the apparatus are highly responsible for disturbing passage of the stimulating ray and/or the stimulated emission, and consequently depress the resultant image quality. For this reason, the surface of the panel has to have enough durability to resist the stains and abrasions. A smooth and durable protective layer is thus highly desired.
Otherwise the sharpness of resultant image, as a rule, is improved by thinning the protective film. A thin protective film, however, often cannot satisfactorily protect the panel from the stains and abrasions, and hence the storage panel with the thin protective film generally has unsatisfactory durability. In order to solve this problem, various protective films were proposed. For example, a material having both high transparency and enough strength (e.g., polyethylene terephthalate) can be employed, or some kinds of resins can be used in combination. Further, a protective film having a multi-layered structure is also known. Those known protective films have been developed in consideration of protection of the stimulable phosphor layer from chemical and physical deterioration (e.g., scratch resistance, stain resistance and abrasion resistance), as well as sharpness of the resultant image. However, although those protective films are improved to a certain extent, their properties should be more improved. The image quality, particularly sharpness, besides being determined mainly by the thickness of the phosphor layer and the packing density, strongly depends on optical scattering phenomena in the phosphor layer. Those scattering phenomena particularly depend on the crystal size distribution of the phosphor particles, their morphology and the choice and amount of binder present in the phosphor layer or layers, which again is decisive for the packing density attainable for the phosphor particles. As is further also well-known the sensitivity of the screen is determined by the chemical composition of the phosphor, its crystal structure and crystal size properties, the weight amount of phoshor coated in the phosphor layer and the thickness of the phosphor layer.
It is general knowledge that sharper images with less noise are obtained with phosphor particles having a smaller average particle size, but light emission efficiency declines with decreasing particle size. Optimisation of average particle size for a given application clearly requires a compromise between imaging speed and image sharpness desired. Moreover the wavelength of the stimulating rays, providing emission of energy stored in the stimulable phosphor particles is decisive for the sharpness obtained: although having longer wavelengths than the light emitted by the storage phosphors after having been stimulated, shorter wavelengths (in the green to red range) selected from the stimulation spectrum clearly lead to a better sharpness than red to infrared light. Apart therefrom scattering of fluorescent radiation generated by the screens is known to be decreased by incorporating dyes in the storage panels, such as in U.S. Pat. No. 5,905,014, wherein a radiation image storage panel is provided having a support, an intermediate layer and a phosphor layer comprising a binder and a stimulable phosphor dispersed therein, said panel being colored with a colorant so that the mean refl
Cabes Thomas
Van den Bergh Rudolf
AGFA-Gevaert
Dye Rena
Guy Joseph T.
Nexsen Pruet , LLC
Thompson Camie S
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