JPH0551221B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of the Invention) The present invention irradiates excitation light onto a stimulable phosphor sheet on which radiographic image information is stored and recorded, thereby photoelectrically converting stimulated luminescence light emitted from the stimulable phosphor sheet. The present invention relates to a radiation image information reading device that detects and reads the radiation image information, and particularly relates to a radiation image information reading device that uses a multilayer film filter to improve the utilization efficiency of the excitation light. (Technical Background and Prior Art of the Invention) Certain phosphors are exposed to radiation (X-rays, α-rays, β-rays,
When irradiated with γ-rays, electron beams, ultraviolet rays, etc., a part of this radiation energy is accumulated in the phosphor, and when this phosphor is irradiated with excitation light such as visible light, the phosphor changes depending on the accumulated energy. is known to exhibit stimulated luminescence, and phosphors exhibiting this property are called stimulable phosphors (stimulable phosphors). Using this stimulable phosphor, radiation image information of a subject such as a human body is temporarily recorded on a stimulable phosphor sheet, and this stimulable phosphor sheet is two-dimensionally scanned with excitation light such as a laser beam. The resulting stimulated luminescent light is photoelectrically read by a photodetector to obtain an image signal, and based on this image signal, it is applied to a recording material such as a photographic light-sensitive material or a display device such as a CRT. The applicant has already proposed a radiation image information recording and reproducing system that outputs a radiation image of a subject as a visible image. (Unexamined Japanese Patent Publication No. 55-12429
No. 56-11395, etc. ) This system has the practical advantage of being able to record images over a much wider range of radiation exposure compared to conventional radiographic systems using silver halide photography. In other words, in stimulable phosphors, it is recognized that the amount of emitted light that is stimulated and emitted by excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range. Even if the amount of radiation exposure varies considerably depending on the conditions, the amount of stimulated luminescence light emitted from the stimulable phosphor sheet is read by the photoelectric conversion means by setting the reading gain to an appropriate value and converted into an electrical signal. However, by using this electrical signal to output a radiation image as a visible image to a recording material such as a photographic light-sensitive material or a display device such as a CRT, it is possible to obtain a radiation image that is not affected by fluctuations in radiation exposure. can. By the way, in the above-mentioned radiation image information recording and reproducing system, a problem has conventionally been recognized that the utilization efficiency of excitation light is low. That is, most of the excitation light such as laser light is reflected on the surface of the stimulable phosphor sheet and cannot be effectively used to excite the stimulable phosphor. Therefore,
Particularly when reading with high sensitivity is desired, a high-output excitation light source is required, and its power consumption is also disadvantageous. (Object of the Invention) The present invention has been made in view of the above circumstances, and provides radiation image information that sufficiently increases the utilization efficiency of excitation light and thus enables high-sensitivity reading with a low-output excitation light source. The purpose of this invention is to provide a reading device. (Structure of the Invention) As described above, the radiation image information reading device of the present invention scans excitation light two-dimensionally on a stimulable phosphor sheet, and detects the stimulated luminescence light emitted by the excitation light on a photodetector. In the radiation image information reading device, the photodetector is disposed on the side of the sheet opposite to the excitation light irradiation surface, and the excitation light is placed near the stimulable phosphor sheet A multilayer filter is disposed in the optical path so that the reflectance of the excitation light increases as the angle of incidence increases, while a multilayer filter that reflects stimulated luminescence light well regardless of the angle of incidence thereof. be. The above-mentioned multilayer film filter is made by sequentially stacking several to several dozen layers of two or more types of materials with different optical refractive indexes on a substrate with a thickness of about 1/4 of the wavelength of light by vacuum evaporation or other methods. It is what it is. In this case, by appropriately setting the optical refractive index and film thickness of each substance,
Various properties can be obtained. Note that as the low refractive index material, for example, SiO ₂ , MgF ₂ , etc. are used, while as the high refractive index material, for example, TiO ₂ , ZrO ₂ , ZnS, etc. are used. Also, arranging the multilayer film filter close to the stimulable phosphor sheet means both arranging it in contact with the sheet and arranging it with a minute gap between it and the stimulable phosphor sheet. shall be included. (Function) When the multilayer filter as described above is placed in the excitation light optical path in close proximity to the storage layer phosphor sheet, the angle of incidence must be made sufficiently small (usually as much as possible).
The excitation light incident on the stimulable phosphor sheet (at an angle close to 0°) passes through the multilayer filter well and reaches the sheet. The excitation light that reaches the stimulable phosphor sheet and is diffusely reflected there returns to the multilayer filter at various angles, but at this time, the excitation light that enters the multilayer filter at a large angle of incidence is absorbed in large quantities by the filter. It is reflected and folded back toward the stimulable phosphor sheet. In other words, the excitation light reflected on the stimulable phosphor sheet is trapped between the sheet and the multilayer filter, so that the excitation light is effectively used to excite the stimulable phosphor. . On the other hand, by providing the multilayer film filter, the stimulated luminescence light emitted from the stimulable phosphor sheet by irradiation with the excitation light can be detected in the direction opposite to that of photodetection, that is, the multilayer film filter is provided. It is also possible to prevent loss of stimulated luminescent light due to undetected luminescent light emitted to the side. In other words, the stimulated luminescence light emitted in the direction opposite to the direction of photodetection is well reflected by the multilayer film filter regardless of its incident angle, so this stimulated luminescence light can be made to enter the photodetector, and the luminescence can be detected. Exhaustive light can be detected more efficiently than before. (Embodiments) Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings. 1 and 2 show a first embodiment of the present invention. For example, a stimulable phosphor sheet 10 that accumulates and records transmitted radiation image information of a subject such as a human body by irradiating radiation such as X-rays through the subject is formed by two pairs of nip rollers as shown in FIG. The sheet is transported in the direction of arrow Y for sub-scanning by a sheet transporting means 11 such as . The laser beam 13 as excitation light emitted from the laser light source 12 is deflected by a galvanometer mirror 14 that swings back and forth, passes through a multilayer filter 30 (described later), and passes on the stimulable phosphor sheet 10 as described above. Main scanning is performed in the direction of arrow X, which is substantially perpendicular to the sub-scanning direction Y. From the part of the sheet 10 irradiated with the laser beam 13 in this way, stimulated luminescence light 1 is emitted with an amount of light corresponding to the radiographic image information stored and recorded.
5 is emitted. This stimulated luminescence light 15 is collected by a light collector 16 disposed on the opposite side of the excitation light irradiation surface of the sheet 10, and is collected by a photomultiplier (photomultiplier tube) 17 as a photodetector. Detected photoelectrically by The light condenser 16 is made by molding a light guide material such as an acrylic plate, and has a linear incident end surface 16a extending along the beam scanning line on the stimulable phosphor sheet 10. The light-receiving surface of the photomultiplier 17 is coupled to the annularly formed output end surface 16b. From the incident end surface 16a to the light condenser 16
The stimulated luminescent light 15 that has entered the interior of the condenser 16 travels through repeated total reflection and reaches the output end surface 16b.
The photomultiplier 17 detects the amount of stimulated luminescent light 15 that is emitted from the photomultiplier 17 and carries the radiation image information. The analog output signal (read image signal) S of the photomultiplier 17 is amplified by a logarithmic amplifier 20 and digitized by an A/D converter 21 at a predetermined recording scale factor. The digital read image signal Sd obtained in this way is inputted through the image processing device 22 to an image reproducing device 23 such as a CRT or an optical scanning recording device, and in the image reproducing device 23, the stimulable phosphor sheet 10 is stored and recorded. The radiation image that was being displayed will be played back. Next, the operation of the multilayer filter 30 described above will be explained in detail. The multilayer filter 30 is, for example, a bandpass filter having spectral transmittance characteristics as shown in FIG. 3 when the angle of incidence to the filter is 0°, and a glass substrate as shown in FIG. 30A, and a multilayer film 30B as described above formed on the surface thereof. In addition, in this embodiment, the stimulable phosphor sheet 1
0 is a stimulable phosphor layer 10 on a transparent support 10A.
B is formed, and the multilayer film filter 30
is the multilayer film 3 on the stimulable phosphor layer 10B.
0B are placed in direct contact with each other. Further, the laser beam 13 is made to enter the multilayer film filter 30 in a substantially perpendicular direction, that is, with an incident angle of approximately 0°. Note that the transparent support 10A of the stimulable phosphor sheet 10 does not need to be provided.
Further, a transparent protective film or the like may be formed on the upper surface of the stimulable phosphor layer 10B. The multilayer filter 30 absorbs almost no light, so the reflectance is obtained by subtracting the transmittance shown in FIG. 3 from 1 (100%). In this embodiment, a beam with a waveform of 633 nm emitted from a He--Ne laser is used as the laser beam 13 which is excitation light. As shown in FIG. 3, the light transmittance of the multilayer filter 30 for this laser beam 13 is approximately 90% when the incident angle is 0°, that is, when the laser beam is incident for excitation of the sheet 10. ing. Further, the light transmittance of the multilayer film filter 30 for light having wavelengths other than 630 to 650 nm and having an incident angle of 0° is approximately 0%. On the other hand, the stimulable phosphor sheet 10 subjected to radiation image information reading in the apparatus of this embodiment is excited by the laser beam 13, and has a wavelength of 360 to 420 nm.
It emits stimulated luminescence light 15 with a wavelength of (mainly 390 nm). FIG. 4 shows the incidence angle dependence of the transmittance of the above-mentioned 390 nm and 633 nm light by the multilayer film filter 30. As described above, the laser beam 13 serving as excitation light is made incident on the stimulable phosphor sheet 10 at an incident angle close to 0°. Therefore, this laser beam 13 passes through the multilayer filter 3 with a transmittance of about 90%.
0 passes through well, reaches the stimulable phosphor sheet 10, and excites the stimulable phosphor 10B as described above. This laser beam 13 is reflected to some extent by the surfaces of the stimulable phosphor sheet 10 and the phosphor layer 10B, and returns to the multilayer filter 30 side. This reflection is diffuse reflection, and the reflected light 13a enters the multilayer film filter 30 at various angles of incidence. Of the reflected light 13a, the light that enters the multilayer filter 30 at a large angle of incidence is reflected at a high reflectance by the filter 30 having the above-mentioned characteristics, and is reflected again into the stimulable phosphor sheet 1.
Returning to the 0 side, the stimulable phosphor 10B is excited. That is, in this device, the laser beam 13, which is excitation light, is confined between the multilayer filter 30 and the stimulable phosphor sheet 10,
This will be effectively utilized for excitation of the stimulable phosphor 10B. Further, the stimulated luminescence light 15 also enters the multilayer filter 30 at different angles, and the multilayer filter 30 is configured so that the stimulated luminescence light 15
, it always reflects nearly 100% regardless of the angle of incidence. Therefore, as shown in FIG. 2, most of the stimulated luminescence light 15 that has diverged toward the multilayer filter 30 is reflected by the multilayer filter 30.
The light enters the light condenser 16 disposed below the stimulable phosphor sheet 10 from its incident end face 16a. By using the above-mentioned multilayer film filter in this way, the device of this embodiment effectively utilizes the laser beam as excitation light to increase the amount of stimulated luminescence light, and also increases the amount of stimulated luminescence light. Detection can be performed efficiently and the sensitivity of the device can be significantly increased compared to conventional methods. Note that the multilayer film filter in the above embodiment has extremely favorable characteristics, such as reflecting nearly 100% of the incident stimulated luminescence light and transmitting the excitation light with a reduction of 90% when the incident angle is 0°. but,
In general, the light transmittance of excitation light is 70% or more when the incident angle is 0 to 5 degrees, the reflectance of excitation light is 60% or more when the incidence angle is 30 degrees or more, and stimulated luminescence. If the light reflectance is 60% or more, a preferable effect of increasing sensitivity can be achieved. In addition to the glass substrate described above, a transparent plastic sheet made of polyethylene terephthalate, polyethylene, polyvinylidene chloride, polyamide, or the like may be used as the substrate for supporting the multilayer film. The effects of the multilayer filter 30 will be described below with specific numerical values. [Example] Methyl ethyl ketone was added to a mixture of a photostimulable divalent europium-activated barium fluoride bromide phosphor (BaFBr: 0.001El ²⁺ ) and a linear polyester resin,
Further, nitrocellulose with a degree of nitrification of 11.5% was added to prepare a dispersion containing the phosphor in a dispersed state. After adding tricresyl phosphate, n-butanol and methyl ethyl ketone to this dispersion,
Stir and mix thoroughly using a propeller mixer.
A coating liquid was prepared in which the phosphor was uniformly dispersed, the mixing ratio of the binder and the phosphor was 1:10, and the viscosity was 25 to 35 PS (at 25°C). A transparent glass plate (support, thickness: 1 mm) was placed horizontally, and the coating solution was applied uniformly using a doctor blade. Then, the support with the coating film formed on the coating solution is placed in a dryer, and the temperature inside the dryer is adjusted.
The coating film was dried by gradually increasing the temperature from 25°C to 100°C. In this way, a layer thickness can be achieved on the support.
A phosphor layer of 250 μm was formed. On the other hand, a transparent glass plate (glass substrate, thickness: approximately 1 mm) heated to approximately 350°C was placed in a vacuum container.
By alternately and repeatedly vacuum depositing TiO ₂ and SiO ₂ while controlling the film thickness of each layer, a multilayer film filter (bandpass filter) having the transparent and reflective properties shown in Figure 4 is formed on a glass plate. was formed with a total film thickness of approximately 2 μm (approximately 20 laminated layers). The above-mentioned stimulable phosphor sheet and multilayer film filter were assembled into the apparatus shown in FIG. [Comparative example] Eliminating the multilayer filter in the above example,
The rest was the same as in the above example. The above two devices were evaluated by performing the following sensitivity test. After irradiating the stimulable phosphor sheet with X-rays with a tube voltage of 80KVp, a He-Ne laser beam (wavelength: 633n) was applied to the stimulable phosphor sheet.
m) and the sensitivity was measured. The results obtained are shown in Table 1.

[Table] As is clear from the results shown in Table 1, the device of the present invention equipped with a multilayer filter has significantly improved sensitivity compared to the conventional device without a multilayer filter. did. In the example described above, the multilayer filter 30 is arranged so as to be in contact with the stimulable phosphor sheet 10, but as shown in FIG. They may be arranged with a minute gap between them. Generally, radiation image information is read by transporting the stimulable phosphor sheet for sub-scanning, so if the multilayer filter 30 is placed apart from the stimulable phosphor sheet 10 as described above,
This is preferable because wear of the stimulable phosphor sheet 10 and the multilayer filter 30 is prevented. In addition, the multilayer filter may be provided in the excitation light optical path close to the stimulable phosphor sheet, and in addition to the one that moves relative to the sheet as described above, for example, the multilayer filter may be placed over the entire scanning area of the sheet. The multilayer film filter may be temporarily brought into close contact with the sheet, and a filter feeding means may be provided together with the sub-scanning means for the sheet to feed the multilayer film filter together with the sheet in the sub-scanning direction. (Effects of the Invention) As explained in detail above, in the radiation image information reading device of the present invention, the use efficiency of excitation light is sufficiently increased by the action of the multilayer film filter placed in the excitation light optical path close to the stimulable phosphor sheet. At the same time, the detection efficiency of stimulated luminescence light can also be improved. Therefore, according to the apparatus of the present invention, it is possible to sufficiently increase the sensitivity of reading radiation image information by using a low-output excitation light source and reducing power consumption. Furthermore, since the device of the present invention has a multilayer film filter that produces the above-mentioned effects placed in the excitation light optical path, it is possible to eliminate the need to cover all stimulable phosphor sheets with expensive multilayer filters. The radiation image information reading system can be formed at a lower cost than the case where the radiation image information reading system is used.

[Brief explanation of drawings]

Fig. 1 is a schematic perspective view showing a device according to one embodiment of the present invention, Fig. 2 is a side view showing an enlarged main part of the device according to the above embodiment, and Fig. 3 is a transmission through a multilayer filter used in the device of the present invention. A graph showing the spectrum,
FIG. 4 is a graph showing the incidence angle dependence of the transmittance of the multilayer filter for excitation light and stimulated emission light, and FIG. 5 is a side view showing another embodiment of the device of the present invention. DESCRIPTION OF SYMBOLS 10...Stormable phosphor sheet, 11...Sheet conveying means, 12...Laser light source, 13...Laser beam, 14...Galvanometer mirror, 15...
... Stimulated luminescent light, 17... Photo multiplier, 30... Multilayer film filter, 30A... Glass substrate, 30B... Multilayer film.

Claims (1)

[Claims] 1. Scanning excitation light two-dimensionally on a stimulable phosphor sheet on which radiation image information is accumulated and recorded,
In the radiation image information reading device, the stimulated luminescence light emitted from the part of the sheet scanned by the excitation light is photoelectrically read by a photodetector arranged on the side of the sheet opposite to the excitation light irradiation surface. , a multilayer film filter is disposed in the excitation light optical path close to the sheet, the reflectance of the excitation light increases as the angle of incidence increases, and the multilayer filter reflects the stimulated luminescence light well regardless of its angle of incidence. A radiation image information reading device characterized in that: 2 The multilayer filter has an incident angle of 0 to 5°.
The light transmittance of the excitation light is 70% or more, and the reflectance of the excitation light with an incident angle of 30° or more is 60% or more,
The radiation image information reading device according to claim 1, wherein the reflectance of the stimulated luminescence light is 60% or more.