Radiant energy – Source with recording detector – Using a stimulable phosphor
Reexamination Certificate
2002-09-24
2004-09-28
Hannaher, Constantine (Department: 2878)
Radiant energy
Source with recording detector
Using a stimulable phosphor
C250S581000
Reexamination Certificate
active
06797977
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a radiation image read-out method and apparatus. This invention particularly relates to a radiation image read-out method and apparatus, wherein a radiation image having been stored on a stimulable phosphor sheet is read out with a line sensor comprising a plurality of photoelectric conversion devices, which are arrayed in a straight line.
2. Description of the Related Art
It has been proposed to use stimulable phosphors in radiation image recording and reproducing systems for computed radiography (CR). Specifically, radiation carrying image information of an object, such as a human body, is irradiated to a stimulable phosphor sheet, which comprises, for example, a substrate and a layer of the stimulable phosphor overlaid on the substrate. In this manner, a radiation image of the object is recorded on the stimulable phosphor sheet. Thereafter, with radiation image read-out apparatuses, stimulating rays, such as a laser beam, are irradiated to the stimulable phosphor sheet, on which the radiation image of the object has been stored. The stimulating rays cause the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted by the stimulable phosphor sheet is photoelectrically detected and converted into an electric image signal.
Novel radiation image read-out apparatuses for use in the radiation image recording and reproducing systems utilizing the stimulable phosphor sheets described above have been proposed in, for example, Japanese Unexamined Patent Publication Nos. 60(1985)-111568, 60(1985)-236354, and 1(1989)-101540. In the proposed radiation image read-out apparatuses, from the point of view of keeping the emitted light detection time short, reducing the size of the apparatus, and keeping the cost low, a line light source for irradiating linear stimulating rays onto a stimulable phosphor sheet is utilized as a stimulating ray source, and a line sensor comprising a plurality of photoelectric conversion devices arrayed along the length direction of a linear area of the stimulable phosphor sheet, onto which linear area the stimulating rays are irradiated by the line light source, is utilized in order to detect the light emitted by the stimulable phosphor sheet. (The length direction of the linear area of the stimulable phosphor sheet will hereinbelow be referred to as the main scanning direction.) Also, the proposed radiation image read-out apparatuses comprise scanning means for moving the stimulable phosphor sheet with respect to the line light source and the line sensor and in a direction, which is approximately normal to the length direction of the linear area of the stimulable phosphor sheet. (The direction, which is approximately normal to the length direction of the linear area of the stimulable phosphor sheet, will hereinbelow be referred to as the sub-scanning direction.)
However, in the radiation image read-out apparatuses described above, when the linear stimulating rays are irradiated to the stimulable phosphor sheet, the light emitted from the exposed area of the stimulable phosphor sheet takes on the form of a spread light having predetermined spread (of approximately 600 &mgr;m in the sub-scanning direction) due to scattering of the stimulating rays within the stimulable phosphor sheet and diffusion of the light emitted by the stimulable phosphor sheet. Also, in cases where a charge coupled device (CCD) is utilized as each of the photoelectric conversion devices for receiving the light emitted by the stimulable phosphor sheet, it is not always possible to set the width of the CCD, which width is taken in the sub-scanning direction, to be large. Practically, the width of the CCD, which width is taken in the sub-scanning direction, is capable of being set to be at most approximately 100 &mgr;m. The width of the CCD, which width is taken in the sub-scanning direction, is thus smaller than the width of the spread light described above. Therefore, the CCD cannot receive all of the light emitted from the corresponding site of the exposed area of the stimulable phosphor sheet, and the light collecting efficiency cannot be kept high. Also, such that sufficient radiation absorption may be obtained, it is necessary for the stimulable phosphor layer of the stimulable phosphor sheet to have a certain value of thickness. Therefore, even though the width of the linear stimulating rays impinging upon the linear area of the stimulable phosphor sheet, which width is taken in the sub-scanning direction, is narrow, the scattering of the stimulating rays within the stimulable phosphor sheet and the diffusion of the light emitted by the stimulable phosphor sheet occur inevitably, and it is not always possible to set the width of the spread light described above to be smaller than the width of the CCD. Further, in cases where an image of the spread light described above is formed on the photoelectric conversion device by use of a contracting optical system comprising a lens, the light collecting efficiency cannot be kept high. Furthermore, a technique has been proposed, wherein a tapered fiber is located on the light receiving surface of the CCD, and the spread light described above is thereby contracted, such that the light collecting efficiency may not become low. However, the proposed technique has the problems in that the tapered fiber is expensive, and limitation is imposed upon an aperture ratio.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide a radiation image read-out method wherein, in cases where light emitted from an area of a stimulable phosphor sheet exposed to stimulating rays has predetermined spread, and a width of each of photoelectric conversion devices for receiving the emitted light, which width is taken in a sub-scanning direction, is smaller than the width of the spread light, which width is taken in the sub-scanning direction, an efficiency with which the emitted light is collected is capable of being enhanced, and an image signal having a high signal-to-noise ratio is capable of being obtained.
Another object of the present invention is to provide an apparatus for carrying out the radiation image read-out method.
The present invention provides a radiation image read-out method, comprising the steps of:
i) linearly irradiating stimulating rays onto an area of a surface of a stimulable phosphor sheet, on which a radiation image has been stored, with stimulating ray irradiating means, such that the stimulating rays are linear along a main scanning direction on the surface of the stimulable phosphor sheet, the stimulating rays causing the stimulable phosphor sheet to emit light in proportion to an amount of energy stored thereon during its exposure to radiation,
ii) receiving the light, which is emitted from the linear area of the surface of the stimulable phosphor sheet exposed to the linear stimulating rays, with a line sensor via a light collecting optical system, the line sensor comprising a plurality of photoelectric conversion devices arrayed in a straight line along the main scanning direction, the received light being subjected to photoelectric conversion performed by the line sensor,
iii) moving the stimulable phosphor sheet with respect to the stimulating ray irradiating means and the line sensor and in a sub-scanning direction, and
iv) successively reading outputs of the line sensor in accordance with the movement,
wherein an optical guide member is located between the light collecting optical system and the line sensor, the optical guide member having a reflection surface for reflecting the emitted light components of the emitted light, which emitted light components have been radiated out from the light collecting optical system and have spread over a range wider than a width of each of the photoelectric conversion devices, the width being taken in the sub-scanning direction, such that the photoelectric conversion devices are capable of receiving th
Fuji Photo Film Co. , Ltd.
Hannaher Constantine
Moran Timothy J.
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