Radiation image read-out method and apparatus

Details Radiation image read-out method and apparatus Radiation image read-out method and apparatus

2001-06-07

2003-09-16

Hannaher, Constantine (Department: 2878)

Radiant energy

Source with recording detector

Using a stimulable phosphor

C250S584000

Reexamination Certificate

active

06621094

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 and 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, alight 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 is caused to absorb the radiation and to emit light having wavelengths falling within a ultraviolet to visible region. Also, the phosphor having good light emission response characteristics 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, 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.)
FIG. 5
is an explanatory view showing spread of light emitted by a stimulable phosphor sheet. As illustrated in
FIG. 5
, in the cases of a transmission type of constitution, wherein a line light source and a line sensor are located on opposite surface sides of a stimulable phosphor sheet, a stimulable phosphor layer
50
a
of a stimulable phosphor sheet
50
′, on which a radiation image has been stored, is exposed to stimulating rays L having been produced by a stimulating ray source and is caused to emit light M in proportion to the amount of stored energy carrying radiation image information. Also, the emitted light M passes through a substrate
50
b
capable of transmitting the emitted light M and is projected onto each of photoelectric conversion devices
21
,
21
, . . . acting as light receiving devices. In such cases, for example, after the stimulating rays L impinge upon the stimulable phosphor sheet
50
′, the stimulating rays L are scattered within the stimulable phosphor sheet
50
′. Also, the emitted light M, which has been produced by the stimulable phosphor sheet
50
′ when the stimulable phosphor sheet
50
′ is exposed to the stimulating rays L, is scattered within the stimulable phosphor sheet
50
′ before the emitted light M is radiated out from the surface of the stimulable phosphor sheet
50
′. Due to such reasons, a width d
M
of the emitted light M becomes larger than a width d
L
of the stimulating rays L, and the emitted light M spreads inevitably.
The same problems as in the cases of the transmission type of constitution also occur in the cases of a reflection type of constitution, wherein the line light source and the line sensor are located on an identical surface side of a stimulable phosphor sheet.
As illustrated in
FIG. 5
, in cases where the emitted light M is collected by a line sensor, wherein a width d
P
of each photoelectric conversion device
21
, which width d
P
is taken in the direction normal to the main scanning direction, is smaller than the width d
M
of the emitted light M, which width d
M
is taken in the beam width direction of the emitted light M, the light collecting efficiency cannot be kept high due to leakage of the emitted light M, and therefore an image having good image quality cannot be obtained. Accordingly, how the spread of the emitted light M is ascertained and how the emitted light M is collected such that the amount of light, which does not impinge upon the photoelect

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