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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a radiation image recording and read-out system
for exposing a stimulable phosphor to a radiation to have a radiation
image stored therein, scanning the stimulable phosphor with a stimulating
ray to cause the stimulable phosphor carrying the radiation image to emit
light in the pattern of the radiation image stored therein, reading out
the emitted light to obtain an electric signal, and reproducing a visible
image by use of the obtained electric signal. More particularly, this
invention relates to a radiation image recording and read-out system in
which the stimulable phosphor is circulated and reused to record radiation
images.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays,
.alpha.-rays, .beta.-rays, .gamma.-rays or ultraviolet rays, they store a
part of the energy of the radiation. Then, when the phosphor which has
been exposed to the radiation is exposed to a stimulating ray 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
referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473 and 4,315,318, U.S.
patent application Ser. No. 220,780, U.S. Pat. No. 4,387,428, Japanese
Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to
use the stimulable phosphor for recording a radiation image of the human
body for medical diagnosis. Specifically, the stimulable phosphor is first
exposed to a radiation to have a radiation image stored therein, and is
then scanned with a stimulating ray which causes it to emit light in the
pattern of the stored image. The light emitted from the stimulable
phosphor upon stimulation thereof is photoelectrically detected and
converted to an electric image signal, which is processed as desired to
reproduce a visible image of a quality suitable for viewing and diagnostic
purposes. The final visible image may be reproduced in the form of a hard
copy or may be displayed on a cathode ray tube (CRT). The stimulable
phosphor sheet used in this method may be in any of various forms such as
a panel, drum or the like, which are herein generally referred to as
sheets. In this radiation image recording and reproducing method, the
stimulable phosphor sheet is used to temporarily store the radiation image
in order to reproduce the final visible image therefrom on a final
recording medium. For economical reasons, therefore, it is desirable that
the stimulable phosphor sheet be used repeatedly.
In order to reuse the stimulable phosphor sheet, the radiation energy
remaining on the stimulable phosphor sheet after it is scanned with a
stimulating ray to read out the radiation image stored thereon should be
eliminated or erased by the method described, for example, in Japanese
Unexamined Patent Publication No. 56(1981)-11392 or 56(1981)-12599.
Practically, it is possible to save manpower by supplying the stimulable
phosphor sheet to an image erasing apparatus by use of a conveying means
such as a belt conveyor after the radiation image is read out from the
stimulable phosphor sheet, and returning the stimulable phosphor sheet to
the image recording section by use of a similar conveying means after the
radiation image remaining on the stimulable phosphor sheet is erased.
In general, however, it is not easy to design and manufacture a conveying
means which can convey a sheet material like the stimulable phosphor sheet
without any failure due to clogging, sheets caught at an intermediate
point, or the like. Further, the stimulable phosphor sheet must be
conveyed in the intact form without being scratched or flawed. This also
makes it difficult to design and manufacture the conveying means.
Furthermore, it sometimes happens that some phosphor sheets are processed
for reproducing the radiation images therefrom immediately after the
radiation images are recorded thereon, and some are processed later
together with the others. As a result, the sequence of using the phosphor
sheets is disordered, and the new and old phosphor sheets are sent in the
mixed form to the image recording section. In this case, it is impossible
to obtain reproduced images of a uniform quality since the quality of the
reproduced images differs between the new and old phosphor sheets. Thus,
it is desired to replace the old phosphor sheets with new ones when
necessary. For this purpose, it is necessary to inspect the quality of
images reproduced from the respective phosphor sheets or to control the
number of repetitions of the recording operations for the respective
phosphor sheets, thereby to determine whether to replace the phosphor
sheets with new ones or to reuse them for further recording operations.
However, it is very troublesome to conduct quality control for individual
phosphor sheets.
Further, in a movable X-ray diagnostic station such as a traveling X-ray
diagnostic station in the form of a vehicle like a bus which is provided
with the radiation image recording and read-out system and travels for
recording radiation images for the purpose of collective medical
examination, the amount of the recording materials capable of being loaded
on the movable radiographic station is limited. Therefore, it is desired
to load the stimulable phosphor sheets which can be used repeatedly on the
movable radiographic station, once store the radiation images of the
objects on the phosphor sheets, transfer the electric image signals read
out from the phosphor sheets into a recording medium having a large
storage capacity, such as a magnetic tape, circulate and reuse the
phosphor sheets for further recording and read-out operations, thereby to
obtain the radiation image signals of many objects. In this case, it is
not necessary to load a number of stimulable phosphor sheets or panels
having a relatively large size (for example, having a size of a
conventional X-ray film cassette).
Particularly, when the elements of the system, e.g. the circulatable and
reusable recording materials formed of a stimulable phosphor, the image
recording section for exposing each recording material to a radiation
passing through the object, the image read-out section for reading out the
radiation image stored in the recording material, and the erasing means
for erasing the radiation energy remaining on the recording material after
the read-out step to again record another radiation image thereon, are
combined into one unit, the system can easily be loaded on the movable
radiographic station for traveling to conduct medical examination and can
also be easily installed in a hospital or the like. This is very
advantageous in practical use.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide a radiation image
recording and read-out system in which the stimulable phosphor for
recording a radiation image therein can be circulated and reused to
repeatedly form reproduced visible images having a uniform quality.
Another object of the present invention is to provide a radiation image
recording and read-out system which is easy to design, manufacture,
control and move.
The specific object of the present invention is to provide a radiation
image recording and read-out system which is small in size, light in
weight, and suitable for installation in a movable radiographic station, a
hospital, or the like.
The radiation image recording and read-out system in accordance with the
present invention comprises at least one recording material comprised of a
stimulable phosphor layer and fixed on a supporting material, an image
recording section for exposing said recording material to a radiation
passing through an object to have a radiation transmission image of the
object stored on said recording material, an image read-out section
provided with a photoelectric read-out means for scanning said recording
material with a stimulating ray which causes it to emit light and reading
out the emitted light to obtain an electric image signal, a means for
moving said recording material with respect to said recording section and
said image read-out section, and an erasing means for eliminating the
radiation energy remaining on said recording material after the read-out
step.
In the present invention, the electric image signal obtained in the image
read-out section may then be once stored on a recording medium such as a
magnetic tape or a magnetic disk, displayed on a CRT or the like to
immediately observe the radiation image, or permanently recorded as a hard
copy on a photographic material or the like by use of a reproducing
apparatus. The reproducing apparatus may be directly coupled with the
system in accordance with the present invention, installed separately from
the system for conducting reproduction via a memory, or placed at a remote
position for conduction reproduction through radio communication. In the
case mentioned last, it is possible, for example, to reproduce the
radiation image recorded in the movable X-ray diagnostic station by use of
a radio signal receiver in a hospital, and informing the results of
diagnosis conducted by the radiologist to the movable X-ray diagnostic
station through radio communication.
In the radiation image recording and read-out system in accordance with the
present invention, the recording materials formed of stimulable phosphor
layers for recording radiation images therein are circulated and reused in
the form fixed on a supporting material. Since the recording materials are
circulated and reused in good order unlike the phosphor sheets which are
used in the discrete form, it is possible to always obtain reproduced
images of a uniform, stable quality without any risk of the recording
materials damaged. Further, the system is easy to conduct quality control
since, when the stimulable phosphor layers are deteriorated, all layers
can be replaced by new ones. Since the recording materials are built in
the system, it is easy to handle them and to operate the system.
Furthermore, since the system has a simple construction, it is easy to
design and manufacture, small in size and light in weight. Accordingly,
the system in accordance with the present invention is very suitable for
installation in a movable radiographic station, a hospital, or the like.
This is very advantageous in practical use.
The stimulable phosphor referred to in this invention means a phosphor
which is able to store radiation energy upon exposure thereof to such
radiation as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays or
ultraviolet rays, and then emits light in proportion to the stored energy
of the radiation upon stimulation with a stimulating ray such as a visible
ray.
In the present invention, in order to improve the signal-to-noise ratio of
the image signal obtained, it is desirable to make the wavelength
distribution of the stimulating ray different from and far apart from the
wavelength distribution of the light emitted from the stimulable phosphor.
Therefore, it is preferable that the stimulating ray and the stimulable
phosphor be selected to satisfy this requirement. Preferably, the
stimulable phosphor should emit light having a wavelength within the range
between 300 nm and 500 nm, and the wavelength of the stimulating ray
should be within the range between 450 nm and 700 nm.
As the stimulable phosphor capable of emitting light having a wavelength
within the range between 300 nm and 500 nm, for example, rare earth
element activated alkaline earth metal fluorohalide phosphor is preferred.
One example of this phosphor is, as shown in Japanese Unexamined Patent
Publication No. 55(1980)-12143, a phosphor represented by the formula
(Ba.sub.1-x-y,Mg.sub.x,Ca.sub.y)FX:aEu.sup.2+ wherein X is at least one of
Cl and Br, x and y are numbers satisfying 0<x+y.ltoreq.0.6 and xy.noteq.0,
and a is a number satisfying 10.sup.-6 .ltoreq.a.ltoreq.5.times.10.sup.-2.
Another example of this phosphor is, as shown in Japanese Unexamined
Patent Publication No. 55(1980)-12145, a phosphor represented by the
formula (Ba.sub.1-x,M.sup.II.sub.x)FX:yA wherein M.sup.II is at least one
of Mg, Ca, Sr, Zn and Cd, X is at least one of Cl, Br and I, A is at least
one of Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb and Er, x is a number satisfying
0.ltoreq.x.ltoreq.0.6, and y is a number satisfying 0.ltoreq.y.ltoreq.0.2.
Further, as the stimulable phosphor can be used ZnS:Cu,Pb; BaQ.xAl.sub.2
O.sub.3 :Eu wherein 0.8.ltoreq.x.ltoreq.10; and M.sup.II O.xSiO.sub.2 : A
wherein M.sup.II is Mg, Ca, Sr, Zn, Cd or Ba, A is Ce, Tb, Eu, Tm, Pb, Tl,
Bi or Mn, and x is a number satisfying 0.5.ltoreq.x.ltoreq.2.5, as shown
in Japanese Unexamined patent Publication No. 55(1980)-12142. Furthermore,
as the stimulable phosphor can be used LnOX:xA wherein Ln is at least one
of La, Y, Gd and Lu, X is at least one of Cl and Br, A is at least one of
Ce and Tb, x is a number satisfying 0.ltoreq.x.ltoreq.0.1, as shown in
Japanese Unexamined Patent Publication No. 55(1980)-12144. Among the above
enumerated phosphors, the rare earth element activated alkaline earth
metal fluorohalide phosphor is the most preferable, among which barium
fluorohalides are the most preferable in view of the high intensity of
emission of light.
Further, barium fluorohalide phosphors added with a metal fluoride as
disclosed in Japanese Unexamined Patent Publication Nos. 56(1981)-2385 and
56(1981)-2386, or barium fluorohalide phosphors added with at least one of
a metal chloride, a metal bromide and a metal iodide as disclosed in
Japanese Patent Application No. 54(1979)-150873 are also preferable
because of their improved light emitting characteristics.
It is also desirable to color the stimulable phosphor layer constituting
the recording material made of the above phosphor by use of pigments or
dyes to improve the sharpness of the image obtained thereby as disclosed
in U.S. patent application Ser. No. 156,520, U.S. Pat. No. 4,394,581.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view showing the first embodiment of the radiation
image recording and read-out system in accordance with the present
invention,
FIG. 2 is a schematic view showing the second embodiment of the system in
accordance with the present invention,
FIG. 3 is a schematic view showing the third embodiment of the system in
accordance with the present invention,
FIGS. 4A and 4B are schematic diagrams showing the fourth embodiment of the
system in accordance with the present invention,
FIG. 5 is a schematic view showing the fifth embodiment of the system in
accordance with the present invention,
FIG. 6 is an enlarged view showing a part of the system shown in FIG. 5,
FIG. 7 is a schematic view showing the sixth embodiment of the system in
accordance with the present invention,
FIG. 8 is a schematic view showing the seventh embodiment of the system in
accordance with the present invention,
FIG. 9 is a schematic view showing the eighth embodiment of the system in
accordance with the present invention, and
FIG. 10 is a schematic view showing the ninth embodiment of the system in
accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will hereinbelow be described in further detail with
reference to the accompanying drawings.
In FIG. 1, an endless conveyor 1, e.g. a belt conveyor or a chain conveyor,
is used as the supporting material for supporting the three stimulable
phosphor sheets. These stimulable phosphor sheets 2 are fixed in equally
spaced relation on the conveyor 1. The conveyor 1 provided with the
phosphor sheets 2 is engaged with a driving roller 3 and a driven roller
4, and moved in the direction of the arrow by the driving roller 3 which
is rotated by a drive unit (not shown). In the vicinity of the driven
roller 4 is positioned a radiation source 5 to face the conveyor 1. The
radiation source 5 may be an X-ray source or the like, and projects a
radiation transmission image of an object 6 positioned between the
phosphor sheet 2 and the radiation source 5 onto the phosphor sheet 2. In
the vicinity of the driving roller 3 are positioned a stimulating ray
source 7 for emitting a stimulating ray such as a laser beam, a light
deflector 8 formed of a galvanometer mirror or the like for deflecting the
stimulating ray emitted from the stimulating ray source 7 in the width
direction of the conveyor 1, and a photodetector 9 for reading out the
light emitted from the phosphor sheet 2 upon stimulation thereof by the
stimulating ray. The photodetector 9 may be formed of a head-on type
photomultiplier, a photoelectric amplification channel plate or the like.
The photodetector 9 detects the light emitted from the phosphor sheets 2
upon stimulation thereof and guided by a light transfer means 10. An
erasing light source 11 is positioned to face the conveyor 1 on the side
opposite to the radiation source 5, the stimulating ray source 7 and the
photodetector 9. The erasing light source 11 emits light having a
wavelength within the stimulation wavelength range of the phosphor sheets
2 irradiated onto the phosphor sheets 2 to cause them to emit the
radiation energy stored thereon. The erasing light source 11 may be
formed, e.g., of a tungsten-filament lamp, halogen lamp, infrared lamp, or
laser source as described in Japanese Unexamined Patent Publication No.
56(1981)-11392. Since the radiation energy stored on the phosphor sheets 2
can also be eliminated by heating them as disclosed, for example, in
Japanese Unexamined Patent Publication No. 56(1981)-12599, the erasing
light source 11 may be replaced by a heating means. A cylindrical cleaning
roller 12 is opposed to the driven roller 4 with the conveyor 1
intervening therebetween. The cleaning roller 12 is rotated
counterclockwise in the diagram by a drive unit (not shown), and removes
dust from the surfaces of the phosphor sheets 2 moving in contact with the
cleaning roller 12. If necessary, the cleaning roller 12 may be of an
electrostatic attraction type which collects dust and the like by an
electrostatic force.
The light transfer means 10 may be of a material and a construction as
disclosed in U.S. Pat. No. 4,346,295, U.S. patent application Ser. No.
168,805, U.S. Pat. No. 4,369,367, Japanese Unexamined Patent Publication
No. 56(1981)-11395, and may be used by the method disclosed therein.
The radiation image recording and read-out system shown in FIG. 1 is
operated as described below. The conveyor 1 is intermittently moved the
distance corresponding to one-third of the entire circumference thereof at
a time by the driving roller 3. The stopping position of the conveyor 1
are set so that one phosphor sheet 2 faces the radiation source 5 when the
conveyor 1 stops. When the conveyor 1 is stopped, the radiation source 5
is turned on to cause the phosphor sheet 2 facing the radiation source 5
to store the radiation transmission image of the object 6. After the
radiation image is recorded on the phosphor sheet 2, the conveyor 1 is
further moved the distance of one-third the conveyor circumference and
stopped. At this time, the phosphor sheet 2 carrying the radiation image
stored thereon is stopped in the position facing the light deflector 8 and
the photodetector 9, and scanned with the stimulating ray emitted from the
stimulating ray source 7. Scanning is conducted in the width direction of
the conveyor 1 (main scanning) by the light deflector 8, and also in the
length direction of the conveyor 1 (subsidiary scanning) by the movement
of a stage (not shown) carrying the stimulating ray source 7, the light
deflector 8, the photodetector 9 and the light transfer means 10 in the
length direction of the conveyor 1. The stage can be easily formed by use
of a known linear movement mechanism. Upon exposure to the stimulating
ray, the phosphor sheet 2 emits light in the pattern of the radiation
image stored thereon. The emitted light is inputted to the photodetector 9
via the light transfer means 10, and an electric signal corresponding to
the radiation image stored on the phosphor sheet 2 is outputted from the
photodetector 9. After the radiation image is read out in this way, the
conveyor 1 is further moved the distance of one-third the circumference
thereof and stopped. In this condition, the phosphor sheet 2 from which
the radiation image has been read out is opposed to the erasing light
source 11, and exposed to the erasing light emitted therefrom to eliminate
the radiation energy of the radiation image remaining on the phosphor
sheet 2 after the read-out step, the radiation emitted from radioactive
isotopes such as .sup.266 Ra and .sup.40 K existing in trace amounts in
the stimulable phosphor, and environmental radiations stored in the
stimulable phosphor. In this way, the phosphor sheet 2 is recovered to the
condition usable for recording a further radiation image. Thereafter, the
conveyor 1 is moved the distance of one-third the conveyor circumference
until the erased phosphor sheet 2 faces the radiation source 5. Midway
during this movement, dust on the surface of the phosphor sheet 2 is
removed by the cleaning roller 12. The phosphor sheet 2 free from any
radiation energy and dust is reused to record a radiation image at the
radiation source 5.
As described above, the stimulable phosphor sheets 2 are circulated and
reused through the erasing step conducted by the erasing light source 11
and the cleaning step effected by the cleaning roller 12. One phosphor
sheet 2 passes through the image recording, image read-out and image
erasing steps while the conveyor 1 rotates one turn. It is, of course,
possible to simultaneously conduct these three steps for the three
phosphor sheets 2, respectively, when the conveyor 1 is stopped. In this
case, it is possible to improve the image processing speed.
In the embodiment shown in FIG. 1, since the phosphor sheets 2 are fixed on
the endless conveyor 1 and reused through the circulation of the conveyor
1, there is no risk of the stimulable phosphor being damaged unlike the
method in which discrete phosphor sheets are conveyed one by one. Further,
since the mechanism for circulating the phosphor sheets 2 can be formed of
a simple conveyor mechanism, the system is easy to design and manufacture.
Also, since the three phosphor sheets 2 are always used in the
predetermined sequence, the quality of the reproduced images does not
fluctuate among the phosphor sheets.
The electric image signal obtained from the photodetector 9 may immediately
be sent to a reproducing apparatus to reproduce the radiation image as a
hard copy or display it on a CRT, or may be digitized and temporarily
stored on a high-density recording medium such as a magnetic tape,
magnetic disk or optical disk to later reproduce the radiation image
therefrom. When the system in accordance with the present invention is
loaded on a traveling X-ray diagnostic station or the like for obtaining
radiation images for medical diagnosis, it is possible to reduce the
number of equipment to be loaded on the traveling station by conducting
the read-out and storing of the electric image signals on the high-density
recording medium at the site of recording and read-out operation, and
bringing the recording medium to a medical center or the like for
reproducing the radiation images. The electric image signals may also be
simultaneously inputted to the reproducing apparatus and the recording
medium. Namely, when the system is used in a hospital, the electric image
signals may be transferred from the recording and read-out station to the
recording medium for storage station where the image signals are
temporarily stored in a recording midium and, at the same time, they may
be transferred to the reproducing apparatus, e.g. a CRT, in the diagnostic
room in order to immediately use them for diagnosis.
It is possible and preferable for obtaining a radiation image having a high
diagnostic efficiency and accuracy to process the electric image signal in
order to intensify the image and change the contrast. In the present
invention, it is preferable to conduct the frequency processing as
disclosed in U.S. Pat. No. 4,315,318, U.S. patent application Ser. Nos.
105,240, and 220,780, U.S. Pat. No. 4,346,295, Japanese Unexamined Patent
Publication Nos. 56(1981)-75137, 56(1981)-75139 and 56(1981)-75141, and/or
the gradation processing as disclosed in U.S. Pat. Nos. 4,302,672,
4,276,473 and 4,310,886.
In the embodiment shown in FIG. 1, the subsidiary scanning of the
stimulable phosphor sheets 2 is conducted by moving the stimulating ray
source and read-out apparatus with respect to the stationary phosphor
sheets 2. However, it is also possible to maintain the stimulating ray
source and read-out apparatus stationary, and move the phosphor sheets 2
to conduct the subsidiary scanning. In order to move the phosphor sheets 2
for this purpose, it is possible to mount the phosphor sheets 2 on the
conveyor 1 via a stage, instead of directly fixing them thereon, move the
stage on the conveyor 1 when the conveyor 1 is being halted to read out
the radiation image, and return the stage to a predetermined position
after the read-out is over. Alternatively, the phosphor sheets may be
directly mounted on the conveyor 1, and the subsidiary scanning may be
conducted by moving the conveyor 1. In the latter case, the distance
between the image recording section and the image read-out section may be
made different from the intervals between the adjacent phosphor sheets 2,
and after the conveyor 1 has been moved to scan one phosphor sheet 2 in
the subsidiary direction, the conveyor 1 may be moved to a position to
locate the next phosphor sheet 2 at the image recording section. In this
case, the image recording and the image read-out are not conducted at the
same time. Further, in order to speed up the recording and read-out
operation by carrying out the image recording and the image read-out in
parallel with each other, it is possible to move the conveyor 1 to scan
one phosphor sheet 2 in the subsidiary scanning direction while a
radiation image is being recorded on the next phosphor sheet 2, which is
being moved together with the conveyor 1, by use of the slit exposure
method. It is also possible to use several conveyors that can
automatically transfer the phosphor sheets 2 therebetween, and operate the
conveyors in such a way that the phosphor sheets 2 are ultimately
circulated via these conveyors. In this case, when the read-out speed is
extremely lower than the recording speed, it becomes possible to increase
the read-out speed by installing a plurality of image read-out sections
for one image recording section, connecting the conveyors branched from
the image recording section to the respective image read-out sections, and
supplying the phosphor sheets 2 to the respective image read-out sections.
Further, when the phosphor sheets 2 are transferred among a plurality of
conveyors as described above, it is possible to connect two conveyors via
one stage for temporarily storing the phosphor sheets 2. This connection
method is convenient since deteriorated phosphor sheets can be removed
from the system or new phosphor sheets can be added thereto by use of this
stage without stopping the system.
In the first embodiment described above, since the stimulable phosphor
sheets 2 are fixed on the conveyor 1 in engagement with the rollers 3 and
4, the phosphor sheets 2 must be flexible. However, from the viewpoints of
durability of the stimulable phosphor and formation of radiation images of
high quality, it is desirable to avoid bending of the phosphor sheets.
FIG. 2 to 4B show the second to fourth embodiments in which the phosphor
sheets are fixed on rigid supporting materials formed to circulate the
phosphor sheets without bending them.
In FIG. 2, four stimulable phosphor sheets 102 are fixed on the sides of a
quadrangular prism-like turret 101. The turret 101 is provided with a
shaft 101a on which a rotation member 101b such as a sprocket wheel is
fixed. The rotation member 101b receives the driving force of a drive unit
103 via a driving force transfer member 103a formed of a chain or the
like. The turret 101 is rotated at 90.degree. intervals in the direction
of the arrow by the drive unit 103. A radiation source 105 is opposed to
one side of the turret 101, and a stimulating ray source 107, a light
deflector 108, a photodetector 109 and a light transfer means 110 are
positioned in the vicinity of the side opposite to the aforesaid side. An
erasing light source 111 is positioned to face the side of the turret 101
adjacent to the aforesaid side facing the radiation source 105 on the side
upstream of turret rotation from the aforesaid side. The radiation source
105, the stimulating ray source 107 and the other parts positioned around
the turret 101 may be of the same types as those used in the first
embodiment shown in FIG. 1, and the means for supporting and circulating
the phosphor sheets employed in the system shown in FIG. 2 differs from
that in FIG. 1. In the same way as in FIG. 1, when the turret 101 is
stopped, the radiation source 105 is turned on to have the phosphor sheet
102 store a radiation transmission image of an object 106. After the
turret 101 is rotated 90.degree. twice, the phosphor sheet 102 carrying
the radiation image stored thereon is stopped at the position facing the
light deflector 108, the photodetector 109 and the like, and scanned with
the stimulating ray emitted from the stimulating ray source 107 to have
the phosphor sheet 102 emit light upon stimulation thereof. The light
emitted from the phosphor sheet 102 is photoelectrically read out by the
photodetector 109, which outputs an electric image signal corresponding to
the radiation image. In the system shown in FIG. 2, since it is difficult
to conduct the subsidiary scanning of the stimulating ray by the rotation
of the turret 101, the other subsidiary scanning methods described above
are employed. After the radiation image is read out from the phosphor
sheet 102, the turret 101 is rotated 90.degree. to position the phosphor
sheet 102 at the erasing light source 111, where the radiation energy
remaining on the phosphor sheet 102 is erased for reusing the sheet.
In FIG. 2, the phosphor sheet 102 is free of any process at one of the four
stages of the turret 101. The process-free stage is not limited to the
position shown in FIG. 2. Accordingly, it is also possible to form the
system in which three phosphor sheets are fixed on a triangular prism-like
turret. When it takes a long time to conduct the erasing step, two erasing
stages may be installed.
In the present invention, any number of stimulable phosphor sheets may be
fixed on the supporting material, and the erasing zone need not be
positioned independently from the zone for conducting the image recording
or the image read-out. For example, in the third embodiment shown in FIG.
3, a plate-like supporting material 201 rotatable at 180.degree. intervals
around a drive shaft 203 is used, and two phosphor sheets 202a and 202b
are mounted on both sides of the supporting material 201. A radiation
source 205 is opposed to the phosphor sheet 202a, while a stimulating ray
source 207, a light deflector 208, a photodetector 209, a light transfer
means 210, and an erasing light source 211 are opposed to the phosphor
sheet 202b. The supporting material 201 is rotated at 180.degree.
intervals via the drive shaft 203, and the image recording and the image
read-out are repeated for the phosphor sheets 202a and 202b. The erasing
light source 211 is turned off when the image read-out is conducted, and
is turned on after the image read-out is finished. After the erasing light
source 211 is turned off, the supporting material 201 is rotated to move
the phosphor sheets 202a and 202b. When the plate-like supporting material
201 is used, it is of course possible to fix the phosphor sheet on only
one side of thereof. In this case, however, the image recording and
read-out speed drops since the image recording and the image read-out
cannot be conducted simultaneously. In the embodiments of FIGS. 2 and 3, a
means for cleaning the phosphor sheets, such as the cleaning roller 12
shown in FIG. 1, is not installed. However, if necessary, it is possible
to use a self-traveling type cleaning roller which moves to clean the
surfaces of the phosphor sheets after the erasing step.
Instead of rotating the phosphor sheet supporting material as described
above, it may be moved in any other ways, for example, may be linearly
reciprocated. In the fourth embodiment shown in FIGS. 4A and 4B, a
plate-like supporting material 301 is placed on a rail 304 for
reciprocation therealong by use of a drive unit 303 for driving, for
example, a pinion gear which is engaged with a rack on the side of the
rail 304 to form a rack-pinion mechanism. Two phosphor sheets 302a and
302b are fixed on the supporting material 301. A radiation source 305 is
positioned on the side facing the center of the rail 304, where the
phosphor sheet 302a is | | |
