Radiant energy – Source with recording detector – Using a stimulable phosphor
Reexamination Certificate
2001-06-14
2003-01-07
Hannaher, Constantine (Department: 2878)
Radiant energy
Source with recording detector
Using a stimulable phosphor
C250S586000, C250S584000
Reexamination Certificate
active
06504168
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.
2. Description of the Related Art
It has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a radiation image of an object, such as a human body, is recorded on a stimulable phosphor sheet, which comprises a substrate and a layer of the stimulable phosphor overlaid on the substrate. Stimulating rays, such as a laser beam, are deflected land caused to scan pixels in the radiation image, which has been stored on the stimulable phosphor sheet, one after another. 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 successively from the pixels in the radiation image having been stored on the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal by photoelectric read-out means. The stimulable phosphor sheet, from which the image signal has been detected, is then exposed to erasing light, and radiation energy remaining thereon is thereby released.
Also, a novel radiation image recording and reproducing system aiming at enhancement of a detection quantum efficiency in the formation of the radiation image, i.e., a radiation absorptivity, a light emission efficiency, an emitted light pickup efficiency, and the like, has been proposed in, for example, Japanese Patent Application No. 11(1999)-372978. With the proposed radiation image recording and reproducing system, the radiation absorbing functions and the energy storing functions of the conventional stimulable phosphor are separated from each other, and a phosphor having good radiation absorbing characteristics and a phosphor having good light emission response characteristics are utilized respectively for radiation absorption and radiation image storage. The phosphor having good radiation absorbing characteristics (i.e., the phosphor for radiation absorption) is caused to absorb the radiation and to emit light having wavelengths falling within an ultraviolet to visible region. Also, the phosphor having good light emission response characteristics (i.e., the phosphor for energy storage) is caused to absorb the light, which has been emitted by the phosphor having good radiation absorbing characteristics, and to store energy of the emitted light. The phosphor having good light emission response characteristics, on which the energy of the emitted light has been stored, is then exposed to light having wavelengths falling within a visible to infrared region, which light causes the phosphor having good light emission response characteristics to emit light in accordance with the stored energy. The light having thus been emitted by the phosphor having good light emission response characteristics is successively detected with photoelectric read-out means, and an image signal is thereby obtained.
The image signal, which has been obtained from the radiation image recording and reproducing systems described above, is then subjected to image processing, such as gradation processing and processing in the frequency domain, such that a visible radiation image, which has good image quality and can serve as an effective tool in, particularly, the efficient and accurate diagnosis of an illness, can be obtained. The image signal having been obtained from the image processing is utilized for reproducing a visible image for diagnosis (a final image) or the like, on film or on a high resolution cathode ray tube (CRT) display device. In cases where the stimulable phosphor sheet, from which the image signal has been detected, is then exposed to the erasing light, and energy remaining on the stimulable phosphor sheet is thereby released, the erased stimulable phosphor sheet is capable of being used again for the recording of a radiation image.
Novel radiation image read-out apparatuses for use in the radiation image recording and reproducing systems 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 as photoelectric read-out means. (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, each of the photoelectric conversion devices constituting the line sensor, e.g. a charge coupled device (CCD) image sensor or a metal oxide semiconductor (MOS) image sensor, has limitation on an electric charge amount capable of being accumulated, and saturation is reached in the electric charge amount. Therefore, the photoelectric conversion devices are not capable of detecting a light intensity higher than a certain level. Accordingly, the problems occur in that accurate detection results cannot be obtained with respect to an area (a high dose area) on the stimulable phosphor sheet, at which a large amount of energy carrying the radiation image information has been stored. Thus the range of the light intensity which the line sensor is capable of detecting, i.e. a dynamic range of the line sensor, is narrow.
Accordingly, there has heretofore been proposed a technique for widening the dynamic range of the line sensor, wherein a width of each photoelectric conversion device of the line sensor, which width is taken in the sub-scanning direction, is set to be equal to a fraction of the width of one pixel in the final image, which width is taken in the sub-scanning direction, addition processing is performed on image signal components having been obtained from an identical photoelectric conversion device during several times of read-out stages consecutive in the sub-scanning direction, which read-out stages are performed by the identical photoelectric conversion device, an image signal component representing one pixel in the final image is obtained from the addition processing, and the dynamic range of the line sensor is thereby kept wide.
However, with the proposed technique for widening the dynamic range of the line sensor, in order for the addition processing to be performed on the outputs having been obtained with respect to the sub-scanning direction, it is at least necessary that the outputs of all of pixel regions of the line sensor arrayed in the main scanning direction, which outputs have been obtained from one time of the read-out stage, be stored in a storage device. The line sensor comprises a large number of the pixel regions arrayed along the main scanning direction. Therefore, the proposed technique for widening the dynamic range of the line sensor has the problems in that a storage device (a line memory) having a large storage capacity becomes neces
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