Radiant energy – Source with recording detector – Using a stimulable phosphor
Reexamination Certificate
2002-07-30
2004-06-29
Wells, Nikita (Department: 2881)
Radiant energy
Source with recording detector
Using a stimulable phosphor
C250S581000, C250S582000, C250S583000, C250S585000, C250S586000, C250S588000
Reexamination Certificate
active
06756602
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of and apparatus for reading out a radiation image, and more particularly to a method of and apparatus for reading out a radiation image where an image read-out means is moved back and forth relatively to a stimulable phosphor sheet.
2. Description of the Related Art
When certain kinds of phosphor are exposed to a radiation such as X-rays, &agr;-rays, &bgr;-rays, &ggr;-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 light 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 stimulable phosphor sheet (a sheet provided with a layer of the stimulable phosphor) is exposed to a radiation passing through an object such as a human body to have a radiation image of the object stored on the stimulable phosphor sheet as a latent image, stimulating light such as a laser beam is projected onto 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) representing a radiation image of the object. See, for instance, Japanese Unexamined Patent Publication Nos. 55(1980)-12429, 56(1981)-11395 and 56(1981)-11397.
This system is advantageous over the conventional radiograph system using silver halide photographic film in that a radiation image can be recorded over a much wider range of exposure to a radiation. That is, it has been found that the amount of radiation energy stored in the stimulable phosphor sheet as a latent radiation image and the amount of stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light are proportional to each other over a very wide range. Accordingly, even if the exposure of the stimulable phosphor sheet to the radiation is greatly increased or reduced under various image taking conditions, an image recorded on the stimulable phosphor sheet can be accurately reproduced by accurately converting the amount of stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light to an electric image signal.
In apparatuses for reading out an image from the stimulable phosphor sheet (apparatuses for projecting stimulating light and photoelectrically detecting the stimulated emission, the image read-out means comprising a stimulating light projecting means for projecting stimulating light onto a stimulable phosphor sheet on which a radiation image has been recorded and a photoelectric convertor means which photoelectrically converts the stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light to an electric signal is moved back and forth relatively to the stimulable phosphor sheet and the radiation image is read out generally only during the forward movement of the photoelectric convertor means relatively to the stimulable phosphor sheet.
Further, a radiation image recorded on the stimulable phosphor sheet can be erased by exposing the stimulable phosphor sheet to erasing light and the erased stimulable phosphor sheet can be reused to record and reproducing a radiation image. The residual radiation image still held by a stimulable phosphor sheet after an image is read out from the stimulable phosphor sheet by projecting stimulating light onto the stimulable phosphor sheet is generally erased by projecting a predetermined amount of erasing light onto the stimulable phosphor sheet sufficient to release radiation energy still held by the stimulable phosphor sheet as a latent radiation image to such an extent that the stimulable phosphor sheet becomes reusable irrespective of the magnitude of the residual radiation energy.
However, when the radiation image is read out only during the forward movement of the photoelectric convertor means relatively to the stimulable phosphor sheet, the time required for the photoelectric convertor means to return to the original position from the end of the forward movement thereof becomes a dead time during which no operation useful to obtain a radiation image is performed, which elongates the cycle time for reading out radiation images from the stimulable phosphor sheets and deteriorates the working efficiency of the radiation image read-out apparatus.
Further projecting the erasing light onto the stimulable phosphor sheet in an amount sufficient to release the residual radiation energy can lead to waste of power. That is, the erasing light can be projected onto the stimulable phosphor sheet in an amount more than necessary to release the residual radiation energy when the residual radiation energy is relatively small. Further, projecting the erasing light in an amount more than necessary shortens the service life of the erasing light source.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary object of the present invention is to provide a method of and apparatus for reading out a radiation image which can improve the working efficiency in reading out a radiation image from a stimulable phosphor sheet.
Another object of the present invention is to provided a method of and apparatus for reading out a radiation image which can improve the energy efficiency in erasing a stimulable phosphor sheet by projecting erasing light onto the stimulable phosphor sheet.
In accordance with the present invention, a stimulable phosphor sheet bearing thereon a radiation image is moved back and forth in first and second directions opposite to each other relatively to an image read-out means in order to two-dimensionally expose the stimulable phosphor sheet to stimulating light, and stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light is detected during both the forward movement (movement in the first direction) and the backward movement (movement in the direction) of the stimulable phosphor sheet to obtain first and second image signals on the basis of the stimulated emission detected during the respective movements of the stimulable phosphor sheet, and the second image signal is used in various ways, thereby effectively using the backward movement of the stimulable phosphor sheet relatively to the image read-out means.
That is, in accordance with a first aspect of the present invention, there is provided a radiation image read-out method in which stimulating light is projected onto a stimulable phosphor sheet, bearing thereon a radiation image, along a main scanning line by an image read-out means while one of the stimulable phosphor sheet and the image read-out means is being moved in a sub-scanning direction intersecting the main scanning direction relatively to the other and stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light is detected by the image read-out means and is photoelectrically converted to an electric image signal thereby, wherein the improvement comprises the steps of
moving back and forth one of the stimulable phosphor sheet and the image read-out means in the sub-scanning direction relatively to the other,
detecting stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light during both the forward movement and the backward movement of said one of the stimulable phosphor sheet and the image read-out means to obtain first and second image signals on the basis of the stimulated emission detected during the respective movements of said one of the stimulable phosphor sheet and the image read-out means, and
obtaining an image
El-Shammaa Mary
Fuji Photo Film Co. , Ltd.
Wells Nikita
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