JPH0711676B2 - Radiation image information reader - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention emits excitation light to a stimulable phosphor sheet on which radiation image information is stored and recorded, and thereby emitted from the stimulable phosphor sheet. The present invention relates to a radiation image information reading device that photoelectrically detects stimulated emission light to read the radiation image information, and more particularly relates to a radiation image information reading device that improves the utilization efficiency of the excitation light by using a multilayer film filter. It is a thing.

(Technical background of the invention and prior art) When a certain kind of fluorescent material is irradiated with radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.), a part of this radiation energy is fluorescent. It is known that when the fluorescent substance is accumulated in the body, and the fluorescent substance is irradiated with excitation light such as visible light, the fluorescent substance emits stimulated luminescence according to the accumulated energy, and exhibits such a property. The phosphor is called a stimulable phosphor (stimulable phosphor).

Using this stimulable phosphor, the radiation image information of a subject such as a human body is once recorded on a sheet of the stimulable phosphor, and the stimulable phosphor sheet is two-dimensionally excited by excitation light such as laser light. Scanning to produce stimulated emission light, the resulting stimulated emission light is photoelectrically read by a photodetector to obtain an image signal, and based on this image signal, a recording material such as a photographic light-sensitive material, a CRT, etc. The applicant has already proposed a radiation image information recording / reproducing system that causes a display device to output a radiation image of a subject as a visible image. (JP-A-55-12429, JP-A-56-11395, etc.) This system is practical because it can record an image over an extremely wide radiation exposure area as compared with a conventional radiographic system using silver salt photography. Have advantages. That is, in the stimulable phosphor, it has been recognized that the amount of emitted light stimulated by excitation after storage is proportional to the amount of radiation exposure over a very wide range,
Therefore, even if the radiation exposure amount fluctuates considerably due to various photographing conditions, the amount of stimulated emission light emitted from the stimulable phosphor sheet is read by the photoelectric conversion means by setting the reading gain to an appropriate value. By converting it into an electric signal, and using this electric signal to output a radiation image as a visible image on a recording material such as a photographic light-sensitive material or a display device such as a CRT, a radiation image that is not affected by fluctuations in radiation exposure dose can be obtained. Obtainable.

By the way, in the above-mentioned radiation image information recording / reproducing system, a problem that the utilization efficiency of excitation light is low has been conventionally recognized. That is, most of the excitation light such as laser light is reflected on the surface of the accumulative phosphor sheet,
It cannot be effectively used to excite the storage phosphor.
Therefore, particularly when reading with high sensitivity, a large output pumping light source is required, and the power consumption thereof becomes large.

(Object of the Invention) The present invention has been made in view of the above circumstances, and the radiation image information reading that sufficiently enhances the utilization efficiency of excitation light and thus enables high-sensitivity reading with a small-output excitation light source. The purpose is to provide a device.

(Structure of the Invention) In the radiation image information reading apparatus of the present invention, the excitation light is made to enter the main surface of the stimulable phosphor sheet at an incident angle of 0 [deg.] To perform the main scanning, and the main scanning direction is substantially perpendicular to the sheet. In a radiation image information reading device in which the sheet is conveyed in different directions and sub-scanning is performed, and the photostimulated luminescence light emitted thereby is photoelectrically read by a photodetector, wherein the stimulable phosphor sheet excitation It is arranged on the light incident side substantially parallel to the sheet, and takes a small value that allows the excitation light to pass satisfactorily when the reflectance with respect to the excitation light is about 0 °. On the other hand, a multilayer filter that allows the stimulated emission light to pass satisfactorily regardless of the incident angle, and the multilayer filter is brought into close contact with the stimulable phosphor sheet at least at the excitation light incident portion, With over preparative is characterized in that there was Heike and filter feed means for feeding in the direction of secondary scanning.

The above-mentioned multi-layered film filter has two or more kinds of substances with different light refraction indexes by vacuum deposition etc.
It is formed by sequentially laminating several layers to several tens of layers with a thickness of about 4. In this case, various characteristics can be obtained by appropriately setting the photorefractive index and the film thickness of each substance. Note that, as the low refractive index substance, for example, SiO ₂ , MgF ₂ or the like is used, while as the high refractive index substance, for example, TiO ₂ , ZrO ₂ , ZnS or the like is used.

(Function) When the multilayer filter as described above is arranged in close contact with the stimulable phosphor sheet at the excitation light incident portion, the incident angle is made sufficiently small (as much as possible, it is 0%).
The excitation light, which is incident on the stimulable phosphor sheet (close to 0 °), passes well through the multilayer filter and reaches the sheet. Then, the excitation light that reaches the sheet and diffusely reflects there returns to the multilayer filter side at various angles, but at this time, a large amount of the excitation light that enters the multilayer filter at a large incident angle is reflected by the filter,
It will be folded back to the side of the accumulative phosphor sheet.
That is, the excitation light reflected on the stimulable phosphor sheet is, so to speak, trapped between the sheet and the multilayer filter, so that the excitation light is effectively used for exciting the stimulable phosphor. become.

On the other hand, the stimulated emission light emitted from the stimulable phosphor sheet by irradiation of the excitation light is also emitted from the sheet at various angles, and this stimulated emission light passes through the multilayer filter having the above-mentioned characteristics. Since it transmits well, the stimulated emission light can be efficiently detected by the photodetector.

(Embodiment) Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings.

1 and 2 show a first embodiment device of the present invention. For example, as shown in FIG. 1, a stimulable phosphor sheet 10 in which transmission radiation image information of a subject is stored and recorded by irradiating a subject such as a human body with radiation such as X-rays, is shown in FIG. Sheet transport means
By 11, the sheet is conveyed in the arrow Y direction for sub scanning. Further, the laser beam 13 as the excitation light emitted from the laser light source 12 is deflected by the galvanometer mirror 14 that reciprocally swings, passes through a multilayer film filter 30 described later,
The main scanning is performed on the accumulative phosphor sheet 10 in the arrow X direction substantially perpendicular to the sub-scanning direction Y. In this way, from the location of the sheet 10 irradiated with the laser beam 13, stimulated emission light 15 having a light amount corresponding to the radiation image information accumulated and recorded is emitted. The stimulated emission light 15 passes through the multilayer filter 30 and is condensed by a condenser 16 and photoelectrically detected by a photomultiplier (photomultiplier tube) 17 as a photodetector. The light collector 16 is made by molding a light guide material such as an acrylic plate, and the linear incident end face 16a extends along the beam scanning line on the stimulable phosphor sheet 10. The exit end face, which is arranged in the
The light receiving surface of the photomultiplier 17 is coupled to 16b. The stimulated emission light 15 that has entered the light collector 16 from the incident end face 16a proceeds by repeating total reflection inside the light collector 16 and is emitted from the emission end face 16b to be received by the photomultiplier 17, The photomultiplier 17 detects the amount of stimulated emission light 15 that carries the radiation image information. A condenser mirror 31 is arranged near the surface of the stimulable phosphor sheet 10 along the main scanning line on the sheet 10 (see FIG. 2) and does not face directly to the condenser 16 side. The stimulated emission light 15 is also reflected by the mirror 31 and efficiently collected on the side of the condenser 16.

The analog output signal (read image signal) S of the photomultiplier 17 is amplified by the logarithmic amplifier 20 and digitized by the A / D converter 21 with a predetermined recording scale factor. The digital read image signal Sd thus obtained
Is input to an image reproducing device 23 such as a CRT or an optical scanning recording device through the image processing device 22, and the radiation image accumulated and recorded in the stimulable phosphor sheet 10 is reproduced in the image reproducing device 23. .

Next, the operation of the above-described multilayer filter 30 will be described in detail. The multilayer filter 30 is, for example,
A short-pass filter having a spectral transmittance characteristic as shown in FIG. 3, a glass substrate 30A as shown in FIG. 2, and a multilayer film 30B as described above layered on the surface thereof.
Consists of. The multilayer filter 30 is formed to have substantially the same size as that of the stimulable phosphor sheet 10, and is placed on the sheet 10 in a close contact manner as follows. That is, the filter feeding means 40 is arranged above the sheet conveying means 11. The filter feeding means 40 is a movable table 32 which is movable in the sub-scanning direction Y and its reverse direction.
A motor 35 for moving in the above-mentioned direction via the rack 33 and the pinion 34, four air suction cups 36 mounted downward on the moving table 32, and the air suction cups 36 are moved up and down, respectively. Air cylinder 37
It consists of Each of the air suction cups 36 is connected to a negative pressure source such as a vacuum pump via an air pipe 38,
Air suction from the cup 36 is controlled by a control means such as a control valve (not shown). Moving table 32
Indicates that the accumulative phosphor sheet 10 is fed to the sheet feeding position (the position on the right end side in FIG. 1) on the sheet conveying means 11 and waits on the feeding position. There is. At this time, air is sucked from the air suction cups 36, and the multilayer filter 30 is suction-held in the cups 36 in a substantially horizontal state. When the stimulable phosphor sheet 10 is fed onto the sheet conveying means 11, the motor 35 is driven and the moving table 32 starts moving at the same speed as the sheet conveying means 11. At the same time, the air cylinder 37 is actuated to lower the air suction cup 36 by a predetermined distance, and the multilayer filter 30 held by them is superposed on the stimulable phosphor sheet 10. The multilayer filter 30 is held in close contact with the stimulable phosphor sheet 10 by a light pressing force of the air cylinder 37. Therefore, when the above-mentioned radiation image information reading is performed, the laser beam 13 transmitted through the multilayer film filter 30 is incident on the stimulable phosphor sheet 10.

When the reading is completed, the air cylinder 37 is actuated in the opposite direction to the previous one, and the air suction cup 36 moves up by a predetermined distance.
Thereby, the multilayer filter 30 is separated from the read-out accumulative phosphor sheet 10. At the same time, the motor 35 is rotated in the reverse direction, and the moving table 32 is returned to the above-mentioned sheet feeding position. By repeating the above operation, on the accumulative phosphor sheet 10 subjected to the radiation image information reading,
The multilayer filter 30 is always placed in close contact.
In the present embodiment, the stimulable phosphor layer 10B formed on the support (for example, carbon-filled PET: polyethylene terephthalate) 10A of the stimulable phosphor sheet 10 is formed.
In addition, the multilayer filter 30 is arranged so that the multilayer film 30B is in direct contact with it.

The multilayer filter 30 hardly absorbs light, and therefore the reflectance obtained is the value obtained by subtracting the transmittance shown in FIG. 3 described above from 1 (100%). In this embodiment, as the laser beam 13 which is the excitation light, a beam having a wavelength of 633 nm emitted from a He—Ne laser is used. As shown in FIG. 3, the light transmittance of the multilayer filter 30 with respect to the laser beam 13 is about 90%, 20% and 5% when the incident angle is 0 °, 30 ° and 45 °, respectively. As the angle increases, it sharply decreases (that is, the reflectance increases). On the other hand, the stimulable phosphor sheet 10 which is subjected to radiation image information reading in the apparatus of the present embodiment is 360 to 420 nm (mainly 390 nm) by the excitation of the laser beam 13.
It emits stimulated emission light 15 having the wavelength of. As shown in FIG. 3, the multi-layer film filter 30 emits light in this wavelength range,
It transmits satisfactorily with a transmittance of around 90% regardless of its incident angle. The incident angle dependence of the transmittance of the light of 390 nm and 633 nm is shown in FIG. 8 for easy understanding.

The laser beam 13 as the excitation light is as shown in FIG.
The light is made incident on the stimulable phosphor sheet 10 at an incident angle close to 0 °. Therefore, this laser beam 13 has a transmittance of 90%.
%, Passes through the multilayer filter 30 well, reaches the stimulable phosphor sheet 10, and reaches the stimulable phosphor 10 as described above.
Excite B. The laser beam 13 is reflected to some extent on the surface of the phosphor layer 10B of the stimulable phosphor sheet 10 and returns to the multilayer filter 30 side. Since this reflection is irregular reflection, the reflected light 13a enters the multilayer filter 30 at various incident angles. Of the reflected light 13a, the light that enters the multilayer film filter 30 at a large incident angle is reflected at a high reflectance by the filter 30 having the above-described characteristics, and again the accumulative phosphor sheet 10 side. Then, the stimulable phosphor 10B is excited again. That is, in this device,
The laser beam 13, which is the excitation light, is trapped between the multilayer filter 30 and the stimulable phosphor sheet 10,
It can be effectively used for exciting the stimulable phosphor 10B.

The stimulated emission light 15 also has a multi-layer film filter at various angles.
Although it is incident on 30, the multilayer filter 30 satisfactorily transmits the stimulated emission light 15 regardless of the incident angle thereof as described above, so that the stimulated emission light 15 efficiently enters the light collector 16. Incident.

Here, the effect of the multilayer filter 30 described above will be described in detail with specific numerical values. As a comparative example, reading was performed using the following devices, and the reading sensitivity in each case was measured. The parts not specifically described in each example are the same as those in the apparatus shown in FIG.

A device without the multilayer filter 30.

An apparatus in which only the substrate glass 30A is provided instead of the multilayer filter 30.

An apparatus using a multilayer filter having the spectral transmittance shown in FIG. 4 instead of the multilayer filter 30.

Using the same multilayer filter as above, glass substrate 30
A device in which A is placed on the side of the stimulable phosphor sheet 10 (see FIG. 5).

The apparatus of the above embodiment.

The reading sensitivity in each case is shown in the table below. Note that this sensitivity is a relative sensitivity with the sensitivity of the conventional device as 100. Also, the sharpness of the scanned image CTF (Contrast Transfe
r Function) was also measured. CTF ₁ and CTF ₂ are CTFs for 1 line / mm and 2 lines / mm, respectively. For all measurements, 8 lines of 1-line scanning data were taken and the average value was used as the measured value.

As shown in this table, according to the device of the present invention (devices of, and), the reading sensitivity can be improved to about twice as high as that of the conventional device while keeping the same excitation light energy. When the device of the present invention is used, the sharpness of the read image is lower than that when the conventional device is used. This is because the excitation light once scattered on the stimulable phosphor sheet 10 is used again to excite the stimulable phosphor sheet 10, so to speak, the stimulable phosphor is excited by a partially blurred excitation light. Because, it is considered. This sharpness is determined, for example, by the stimulable phosphor sheet 10
Can be increased by thinning the fluorescent layer 10B, and when high sensitivity is required instead of particularly high sharpness, in order to improve the sharpness as described above. It does not matter if the above procedure is not performed.

In order to hold the multilayer filter 30 in close contact with the stimulable phosphor sheet 10, a light pressing force by the air cylinder 37 is used as described above, and the multilayer filter 30 and the stimulable phosphor sheet 10 are used. Both side end portions of the above may be passed through a nip roller to be sandwiched. Further, particularly when the multilayer filter 30 is relatively heavy, no means for pressing the filter 30 toward the stimulable phosphor sheet 10 is provided, and the multilayer filter is simply placed on the stimulable phosphor sheet 10. You may make it mount. In this case, the conveyance of the multilayer filter 30 in the sub-scanning direction at the time of reading can be performed by the sheet conveying means 11.

Next, another embodiment of the present invention will be described with reference to FIG. In the apparatus of this embodiment, as the multilayer filter, a filter obtained by forming the above-described multilayer film on a cylindrical glass substrate is used. This cylindrical multilayer film filter 60 is driven by a motor 62 via a roller 61.
It is rotated in the direction of arrow R at a peripheral speed equal to the conveying speed of the sheet conveying means 11. The galvanometer mirror 14, the condenser 16, the photomultiplier 17, and the condenser mirror 31 are arranged in the cylindrical multilayer film filter 60, and the laser light source 12
The laser beam 13 emitted from is reflected by the mirror 63 and enters the galvanometer mirror 14.

Also in the apparatus having the above configuration, when the radiation image information is read from the stimulable phosphor sheet 10, the laser beam 13 as excitation light is incident on the stimulable phosphor sheet 10 through the multilayer filter 60. Therefore, the same effect as described above can be obtained by the multilayer filter 60. Instead of the cylindrical multi-layer film filter 60, it is also possible to use an endless belt-shaped multi-layer film filter using a flexible transparent member as a filter substrate.

When using the cylindrical or endless belt type multilayer filter described above, it is not necessary to place the multilayer filter in close contact with the entire surface of the phosphor sheet, and it is possible to accumulate only in the excitation light incident part. Can be placed in close contact with the fluorescent sheet. Therefore, when the size of the stimulable phosphor sheet is large, the size of the expensive multilayer filter can be formed smaller than the sheet size, which is economical.

In the embodiment described above, a short-pass filter having the spectral transmittance characteristic shown in FIG. 3 or 4 is used as the multilayer filter, but in the device of the present invention, a so-called band-pass filter is used. It is also possible to use a multilayer filter (a schematic spectral transmittance characteristic is shown in FIG. 7). That is, as a multilayer filter of such a band-pass filter type, the spectral transmittance characteristic that the reflectance for excitation light increases as the incident angle increases, while the stimulated emission light satisfactorily transmits regardless of the incident angle. If one having the above is used, the same effect as the above-described effect can be obtained. FIG. 9 shows an example of the incident angle dependence of the light transmittance of the multilayer filter which is the interference filter.

In the device of the present invention, as a multilayer filter, the excitation light transmittance is 70% or more, more preferably 80% or more (that is, the excitation light reflectance is 30% or less, more preferably 20% or less) within an incident angle of 5 °, and Excitation light reflectance is 60% or more, more preferably 70% or more at an incident angle of 30 ° or more, and stimulated emission light transmittance is 60% or more, more preferably 80% at an incident angle of 0 to 40 °.
It is preferable to use the above.

(Effects of the Invention) As described in detail above, in the radiation image information reading apparatus of the present invention, the utilization efficiency of the excitation light is improved by the action of the multilayer film filter closely attached to the stimulable phosphor sheet in the excitation light incident portion. It is possible to raise it sufficiently. Therefore, according to the device of the present invention, it is possible to use a small-output excitation light source, reduce power consumption, and sufficiently increase the sensitivity of reading radiation image information. Further, the device of the present invention is one in which a multilayer filter having the above-described effects is arranged in the optical path of the excitation light. Therefore, according to this device, all the accumulative phosphor sheets are covered with expensive multilayer filters. The radiation image information reading system can be formed at a lower cost than the case of wearing the radiation image information. Further, in the device of the present invention, since the multilayer filter is fed in the sub-scanning direction together with the stimulable phosphor sheet, the stimulable phosphor sheet and the multilayer filter may rub against each other and wear. To be prevented.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an apparatus according to one embodiment of the present invention, FIG. 2 is a side view showing a main part of the apparatus according to the above embodiment, and FIGS. 3 and 4 are multilayer films used in the apparatus according to the present invention. A graph showing an example of spectral transmittance characteristics of a filter for each incident angle of light, FIGS. 5 and 6 are side views showing another embodiment of the device of the present invention, and FIG. 7 is used for the device of the present invention. 8 is a graph showing the spectral transmittance characteristics of another multilayer filter, and FIGS. 8 and 9 show the incident angle dependence of the transmittance of the multilayer filter used in the device of the present invention for excitation light and stimulated emission light. It is a graph which shows an example. 10 …… Accumulative phosphor sheet, 11 …… Sheet conveying means 12 …… Laser light source, 13 …… Laser beam 14 …… Galvanometer mirror, 15 …… Stimulated emission light 17 …… Photomultiplier 30,60… … Multilayer membrane filter, 30A …… Glass substrate 30B …… Multilayer membrane, 32 …… Movement stand 33 …… Rack, 34 …… Pinion 35, 62 …… Motor, 36 …… Air suction cup 37 …… Air cylinder, 40 …… Filter feeding means 61 …… Roller

Claims (3)

[Claims] 1. An excitation light is incident on a stimulable phosphor sheet on which radiation image information is stored and recorded at an incident angle of 0 ° to perform main scanning, and in a direction substantially perpendicular to the main scanning direction. In a radiation image information reading device for photoelectrically reading, by a photodetector, stimulated emission light emitted from a portion of the sheet that has been scanned with the excitation light, by carrying out the sub-scan while conveying the sheet, and the accumulative phosphor. The sheet is arranged on the excitation light incident side of the sheet substantially in parallel with the sheet, and the incident angle is increased by taking a small value that allows the excitation light to be well transmitted when the reflectance for the excitation light is approximately 0 °. And a multilayer filter that allows the stimulated emission light to pass satisfactorily regardless of the incident angle of the stimulated emission light, and the multilayer filter is adhered to the sheet at least at the excitation light incident portion. Radiation image information reading apparatus characterized by a filter feeding means for feeding with said sheet in a direction of the sub-scan is provided. 2. The radiation image information reading apparatus according to claim 1, wherein the multilayer film filter is a short-pass filter. 3. The radiation image information reading apparatus according to claim 1, wherein the multilayer film filter is a bandpass filter.