Radiant energy – Source with recording detector – Using a stimulable phosphor
Reexamination Certificate
2002-04-03
2004-08-31
Sung, Christine (Department: 2878)
Radiant energy
Source with recording detector
Using a stimulable phosphor
C250S581000
Reexamination Certificate
active
06784449
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a radiation image recording/read-out method, a radiation image recording/read-out apparatus and a stimulable phosphor sheet, and more particularly to a radiation image recording/read-out method and a radiation image recording/read-out apparatus in which a radiation image is recorded from one side of a stimulable phosphor sheet and the radiation image recorded on the stimulable phosphor sheet is read out from the other side of the stimulable phosphor sheet, and a stimulable phosphor sheet suitable for the method and the apparatus.
2. Description of the Related Art
When certain kinds of phosphor are exposed to radiation such as X-rays, &agr;-rays, &bgr;-rays, electron-beams, ultraviolet rays and the like, they store a part of energy of the radiation. Then when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted from the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is generally referred to as “a stimulable phosphor”. In this specification, the light emitted from the stimulable phosphor upon stimulation thereof will be referred to as “stimulated emission”. There has been known a radiation image recording and reproducing system in which a stimulating light beam such as a laser beam is projected onto a stimulable phosphor sheet (a sheet provided with a layer of the stimulable phosphor) which has been exposed to radiation passing through an object such as a human body to have a radiation image of the object stored on the stimulable phosphor sheet, and the stimulated emission emitted from the stimulable phosphor sheet is photoelectrically detected, thereby obtaining an image signal (a radiation image signal). A radiation image of the object is reproduced as a visible image on the basis of the radiation image signal on a recording medium such as a photographic film or a display such as a CRT. See, for instance, Japanese Unexamined Patent Publications Nos. 55(1980)-12429, 56(1981)-11395 and 56(1981)-11397.
The stimulable phosphor sheet employed in such radiation image recording and read-out generally has a layered structure comprising a stimulable phosphor layer and a support layer which supports the stimulable phosphor layer. Projection of the radiation, projection of the stimulating light beam and detection of the stimulated emission are generally performed from the stimulable phosphor layer side. There have been known various apparatuses for recording on and/or read-out from the stimulable phosphor sheet, e.g., a radiation image recording apparatus which records radiation image information on the stimulable phosphor sheet, a radiation image read-out apparatus which reads out radiation image information recorded on the stimulable phosphor sheet, and a radiation image recording/read-out apparatus which is formed by integrating a radiation image recording apparatus and a radiation image read-out apparatus in a unit and includes a built-in stimulable phosphor sheet (will be referred to as “a built-in radiation image recording/read-out apparatus”, hereinbelow).
In the built-in radiation image recording/read-out apparatus, there has been a demand that for miniaturizing the apparatus by arranging the apparatus so that a latent image of the object is recorded by projecting a radiation from the support layer side and the latent image is read out by projecting the stimulating light beam onto the stimulable phosphor sheet from the stimulable phosphor layer side and detecting the stimulated emission from the stimulable phosphor layer side.
That is, in the system where recording of the image and read-out of the image are performed from the same side of the stimulable phosphor sheet (this system will be referred to as “the same-side recording/read-out system”, hereinbelow), there is required a conveyor system for conveying the stimulable phosphor sheet to the read-out system and turning the stimulable phosphor sheet over to oppose the same side of the stimulable phosphor sheet to the read-out system after recording of the image, which increases the overall size of the apparatus. To the contrast, in the system where recording of the radiation image and read-out of the image are performed from opposite sides of the stimulable phosphor sheet (this system will be referred to as “the opposite-side recording/read-out system”, hereinbelow), the radiation image can be read out from the stimulable phosphor sheet without moving the stimulable phosphor sheet (or by moving by a very small distance) or turning over the same, which is advantageous to reduce the overall size of the apparatus.
However, in the opposite-side recording/read-out system, there has been a problem that the image quality of the radiation image obtained is bad as compared with that obtained by the same-side recording/read-out system.
That is, when the radiation is projected onto the stimulable phosphor sheet through the support layer, the latent image is formed in a part of the stimulable phosphor layer nearer to the support layer, and accordingly, when the stimulating light is projected onto the stimulable phosphor layer from the stimulable phosphor layer side, scattering and absorption of the stimulating light occur in the stimulable phosphor layer before the stimulating light reaches the part of the stimulable phosphor layer in which the latent image is formed, whereby the stimulating light is diverged and weakened. At the same time, the stimulated emission emitted from the part of the stimulable phosphor layer in which the latent image is formed is scattered and absorbed by the stimulable phosphor layer before it is radiated from the stimulable phosphor layer, whereby the area from which the stimulated emission is assumed to be emitted is broadened and the stimulated emission as radiated from the stimulable phosphor sheet is weakened. As a result, since noise is generated in the detected stimulated emission by scattered light (e.g., scattered stimulated emission, scattered stimulated emission emitted from surrounding stimulable phosphor stimulated by scattered stimulating light) and the stimulated emission is weakened, the image quality of the radiation image obtained by the opposite-side recording/read-out system is bad as compared with that obtained by the same-side recording/read-out system.
The stimulable phosphor sheets which have been conventionally employed are structured so that the radiation is projected from the stimulable phosphor layer side, and the power density of the stimulating light projected onto the stimulable phosphor sheet is generally about 4.5J/m
2
.
The image quality of the radiation image is generally evaluated on the basis of the sharpness (MTF) and the grainness (as the amount of stimulated emission increases, the grainness is improved and as the stimulated emission emitting area is widened, the sharpness of the image deteriorates), and the higher the sharpness (MTF) or the grainness is, the better, the image quality is evaluated to be.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary object of the present invention is to provide a radiation image recording/read-out method and a radiation image recording/read-out apparatus which makes it feasible to reduce the overall size of the apparatus without deteriorating image quality of the radiation image obtained, and to provide a stimulable phosphor sheet suitable for the method and the apparatus.
In accordance with a first aspect of the present invention, there is provided a radiation image recording/read-out method comprising the steps of projecting radiation onto a stimulable phosphor sheet, having a reflective layer which is not longer than 5 &mgr;m in scattering length and is interposed between a stimulable phosphor layer and a support layer, from the support layer side of the stimulable phosphor sheet, projecting stimulating light onto the stimulable phosphor sheet, which has been exposed to the radiation, from
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