JPH05150388A - Radiation image information reader - Google Patents

Abstract

PURPOSE:To finely reduce a beam diameter and to irradiate an accumulative phosphor plate with stimulating light in proximity thereto at the time of reading out information from the accumulative phosphor plate CONSTITUTION:One end of an optical fiber 5 consisting of a core part and a clad part enclosing the circumference thereof and has 1 to 50mum core diameter of the device for scanning the accumulative phosphor plate with the stimulating light, detecting the fluorescence from the accumulative phosphor plate by a photodetector and reading the radiation image recorded thereon is disposed to face a stimulating light source 4 for the laser beam having a diameter larger than 50mum and a photoirradiation port at the other end and a photodetecting light transmission port of the photodetector 9 are disposed to face the accumulative phosphor plate 3 in proximity thereto. The laser beam from the light source 4 is converged to the prescribed diameter by the optical fiber 5 and is transferred at extremely high efficiency to irradiate the accumulative phosphor plate 3 with a very small spot diameter. Consequently, noises are suppressed from the accumulative phosphor plate 3 and the reading out is executed with the high resolution.

Description

Detailed Description of the Invention

[0001]

The present invention relates to radiation image information recorded in a stimulable phosphor by irradiating the stimulable phosphor with excitation light and measuring the light emitted from the stimulable phosphor. The present invention relates to a reading device for reading.

[0002]

2. Description of the Related Art Conventionally, so-called radiography using a silver salt has been used to obtain a radiographic image, but in recent years, a radiographic image without using a silver salt has been reproduced due to problems such as depletion of silver resources on a global scale. There has been a demand for ways to do it. As an alternative to the radiographic method described above, the radiation that has passed through the subject is absorbed by the phosphor, and then this phosphor is excited with a certain energy and the radiation energy accumulated by this phosphor is emitted as fluorescence. In fact, a method of detecting this fluorescence and reproducing an image has been considered. As a specific method, a method of converting a radiation image by using a thermoluminescent phosphor as a phosphor and heat energy as excitation energy has been proposed (see British Patent No. 1462769). This conversion method uses a panel in which a thermoluminescent phosphor layer is formed on a support, irradiates the thermoluminescent phosphor layer of this panel with radiation that has passed through the subject, and absorbs this to respond to the intensity of the radiation. The accumulated radiation energy is accumulated, and then the accumulated radiation energy is taken out as a light signal by heating the thermoluminescent phosphor layer, and an image is obtained by the intensity of the light. However, heating causes the drawback that the panel must be heat resistant. A radiation image conversion method using an electromagnetic wave selected from visible rays and infrared rays as the excitation energy has also been proposed (see US Pat. No. 3,859,527). This method does not require heat resistance of the panel as compared with the above-mentioned method using heat energy, but has the following drawbacks. (A) The amount of decay of energy stored in the phosphor is large depending on the wavelength of the excitation light, which greatly affects the duration of the recorded image. (B) The excitation speed of the phosphor changes depending on the wavelength of the excitation light, which causes a difference in the image reading speed. (C) There is a drawback in that the contrast of an image is significantly lowered when reflected light of excitation light or other ambient light enters the detector because the light emission due to excitation of the phosphor is weak.

In order to solve such a problem, the stimulable phosphor material is scanned with excitation light, and the emitted light from each point is detected by a photodetector, whereby the stimulable phosphor material is recorded. In a method of reading a radiation image, a stimulable phosphor material is excited by using light having a wavelength range of 600 nm to 700 nm as the excitation light, and the luminescent light of the stimulable phosphor material has a wavelength range of 300 nm to 500 nm. A novel radiation image reading system in which light is received by a photodetector has been proposed (Japanese Patent Laid-Open Nos. 55-12429 and 5-12429).
5-15025)).

However, according to the above method, information accumulated in a stimulable phosphor plate (hereinafter abbreviated as a fluorescent plate) made of a stimulable phosphor having a radiation image (hereinafter simply abbreviated as a fluorescent substance) is converted into visible light. Alternatively, the following method is also disclosed as a so-called radiation image information reading device (hereinafter abbreviated as reading device) for reading electromagnetic waves such as infrared rays as excitation light. (1) A large half mirror inclined at 45 ° is arranged at a position away from the fluorescent plate, the excitation light passes through this half mirror and is incident on the fluorescent plate, and the emitted light is laterally reflected by the half mirror and collected. A method of collecting with an optical lens and reading with a photodetector. (2) Alternatively, the photodetector and the fluorescent plate are opposed to each other, a reflective optical element such as a mirror or a prism is arranged between them, and the reflective optical element is irradiated with excitation light, and the reflected light is incident on the fluorescent plate.
The excitation light and the emitted light are separated by a method in which the emitted light is directly collected or collected by a lens or the like and read by a photodetector, and the defect of the point (c) is eliminated. However, these methods still have the following drawbacks because the emitted light has a large difference of 1/10 ^{2 to} 1/10 ⁶ with respect to the excitation light. In the method (1), the excitation light is attenuated and scattered by the half mirror, which becomes a factor that determines the resolution of the image. The beam diameter of the excitation light cannot be made sufficiently small, and good reproduced image quality cannot be obtained. Further, a part of the scattered light enters the photodetector and becomes a noise, so that redevelopment of clear image quality cannot be obtained. In the method (2), the diameter of the beam cannot be made sufficiently small to irradiate the excitation light from a position distant from the reflective optical element, and there is a reflective optical element between the photodetector and the fluorescent plate. Therefore, the reflective optical element blocks the emitted light, and the photodetector cannot sufficiently receive the emitted light, or scattered light of the excitation light is reflected by a holder or the like that holds the reflective optical element. There was a defect that it entered the photodetector and became noise. Further, in any of the above methods (1) and (2), the irradiation light and the photodetector cannot be brought sufficiently close to the fluorescence solution because the irradiation and the light reception are performed via the half mirror and the reflection optical element. Irradiation light having a large beam diameter and sufficient received light cannot be obtained, so there is a limit to improvement of image quality. In addition, in order to read out the information stored in the fluorescent plate, it is necessary to scan the fluorescent plate at high speed with excitation light having a small spot diameter. Therefore, in the method (1), the excitation light source must be moved. Therefore, it is not preferable to apply the present method and apparatus which require fine precision. Further, in the method (2), the beam diameter of the excitation light changes due to the distance between the excitation light source and the reflective optical element changing from moment to moment depending on the read position, and it is very difficult to adjust this to a constant value. So, depending on the reader,
Not applicable.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to make the beam diameter of excitation light sufficiently small and set it to an arbitrary value. It is an object of the present invention to provide a reading device in which irradiation light having a good beam intensity and received light having a sufficient light amount can be obtained, and further this light is irradiated in the vicinity of a fluorescent plate to suppress noise due to scattering of irradiation light. ..

[0006]

In order to solve such a problem, in the present invention, a stimulable phosphor plate is scanned with excitation light, and fluorescence from the stimulable phosphor plate is detected by a photodetector. In a device for reading a radiation image recorded on the laser, a laser having a core part and a clad part surrounding the core part, and one end of the optical fiber having a core diameter of 1 to 50 μm having a diameter larger than 50 μm The light irradiation port at the other end and the light receiving / guiding port of the photodetector are arranged so as to face the light-exciting light source and face and be close to the stimulable phosphor plate.

[0007]

[Operation] A laser beam with high coherency is narrowed down to an excitation light with a small spot diameter by an optical fiber with a small transmission loss, and it is transmitted with a minimum loss to irradiate the phosphor plate, so an extremely small spot It is possible to sufficiently excite the phosphor plate with light having a diameter, suppress noise, and read information with high resolution.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will now be described based on the illustrated embodiments. The reading apparatus according to the present invention is generally an apparatus for reading the information recorded on the fluorescent plate by radiographic image capturing in the radiographic image reading method shown in the flow chart of FIG.

In FIG. 2, a perforation 6a is formed in a phosphor plate 3 consisting of a phosphor layer 1 and a support layer 2 obtained by radiographic image capturing, in the approximate center of a light source 4 for generating excitation light and a reflective optical element 6. Through the optical fiber 5 whose opening surface is arranged so as to face the fluorescent plate 3 substantially perpendicularly, the excitation light irradiates the fluorescent plate 3, and the light of the fluorescent plate 3 emitted by this excitation light is collected by the reflection optical element 6 and condensed. Lens 7,
It is incident on the photodetector 9 through the filter 8 and the amount of light is detected. By using the optical fiber 5 as described above, the excitation light can be applied to the fluorescent plate 3 with a good spot diameter without scattering and attenuation of the excitation light by the half mirror as described in (1) above.

Further, in FIG. 3, the fluorescent plate 3 obtained by radiographic image capturing is arranged substantially at the center of the light source 4, the light source 4 and the photodetector 9 so that the opening surface faces substantially perpendicular to the fluorescent plate 3. An optical fiber 5 is arranged, and excitation light is emitted to the fluorescent plate 3 through the optical fiber 5. The light of the fluorescent plate 3 emitted by this excitation light is detected by a photodetector (a filter may be used if necessary) 9. By thus using the optical fiber 5 on the irradiation side, there is no need to use a reflective optical element unlike the method described in (2) above, so that excitation light can be irradiated with a good spot diameter and the light emitted from the fluorescent plate 3 can be emitted. Is significantly less reflected and scattered by the reflection optical element and its holder before entering the photodetector, and the beam diameter for determining the resolution of the image can be made sufficiently small.
A good image quality can be obtained, a part of scattered light does not enter the detector, a clear image quality can be obtained, and the photodetector 9 can be extremely close to the fluorescent screen 3. Therefore, the spread of the beam diameter due to the diffraction phenomenon of excitation light can be significantly reduced, the fluorescent plate and the detector can be brought close to each other, and the reflective optical element does not block the emitted light sufficiently, so that the emitted light is sufficiently Light could be received by the photodetector 9. Furthermore, by utilizing the flexibility of the optical fiber 5, the excitation light source 4 is fixed, and the irradiation light of the optical fiber is moved on the fluorescent plate 3, so that the optical path on the irradiation side is made constant and constant excitation is performed. The light could be easily scanned onto the fluorescent plate 3.

The optical fiber 5 used in the present invention is a thin wire that transmits the light incident from one end to the opening at the other end while repeating the total internal reflection, and a fiber generally used for optical communication is used. As shown in the cross section,
It is composed of a core 10 portion that transports light and a glad 11 that is provided so as to totally reflect light that passes through the core portion 10 that has a large number of perimeters. Such an optical fiber 5 includes, for example, quartz glass, quartz glass, core polymer, flood type, multi-component glass type, all-plastic type, etc., depending on the material. Any of the optical fibers described above can be used in the present invention. However, in particular, an optical fiber whose core 10 is made of silica glass is preferable because optical transmission with less loss is performed as shown in FIG. 5 showing the wavelength of the transmitted light and its transmission loss characteristics. Further, as is apparent from FIG. 5, since the wavelength range used as excitation light in the present invention is limited to visible light to infrared light, light transfer can be performed with very little loss, which is sufficient for image reading from the stimulable fluorescent plate. It was possible to perform various excitations.

Preferably, the excitation light has a function as a heat ray in the infrared rays of 800 nm or more, so that it is not preferable because the fluorescent plate 3 is heated during the scanning for reading.
When the thickness is 0 nm or less, the transmission loss of the optical fiber increases, which is not preferable. Therefore, 600n as excitation light
A wavelength range of m to 800 nm is preferred in the present invention. Further, it is more preferable that the excitation light is visible light having a wavelength of 700 nm or less, because the excitation light can be seen with the naked eye when adjusting the optical system device.

The core diameter of the optical fiber 5 (hereinafter referred to as the core diameter) r can be freely selected from about 1 μm to several hundreds μm or more. However, when the fluorescent plate is irradiated with the excitation light through the optical fiber 5, the resolution of the obtained radiographic image is reduced when the spot diameter is 300 μm or more, so the core diameter r is preferably 300 μm or less, and When the core diameter r is 1 μm or less, the amount of information read from the fluorescent plate becomes remarkably large, and further information cannot be reproduced during processing and reproduction (film, cathode ray tube, etc.), which is not preferable.

On the other hand, the excitation light has a high coherency,
A good image can be obtained by using a laser beam having a high radiation density, a narrow spectrum width, and a light pulse having a short peak value and a short lighting time. If this laser light is used as excitation light and the optical fiber 5 is used, the following advantageous effects as a radiation image information reading device can be obtained.

With a conventional laser beam, for example, a laser beam such as a He--Ne laser (633 nm), it was difficult to reduce the spot diameter to 50 μmφ or less, but in the present invention, as shown in FIG. Even if a large laser beam is irradiated, the light incident on the optical fiber 5 is determined by the diameter r of the core 10, so that the spot diameter of the excitation light to be obtained can be obtained very easily. Further, in order to improve the efficiency of the laser light, as shown in FIG. 7, the laser light emitted from the laser (laser diode or the like) 4'is used as a cylindrical lens 10 or a focusing fiber lens 13.
It is also possible to focus the light with a lens diameter such as the above and make it enter the core diameter r of the optical fiber 5. Since the laser light has high coherency and the like as described above, when a single mode optical fiber is used, the distance between the irradiation aperture of this optical fiber and the fluorescent plate does not matter much, but in the present invention, the spot diameter is more clear. Further, in order to obtain a more uniform excitation light distribution, a better read image was obtained by setting the distance between the irradiation aperture and the fluorescent plate according to the following formula.

That is, when the laser light is emitted into space, the light beam immediately spreads due to diffraction.
However, if the wavelength of light is λ and the light beam diameter is R, then R
Up to a distance of about ₂ / λ (so-called Fresnel region), the light beam has a property of traveling with almost no spread. Therefore, in the present invention, when the laser light is used as the excitation light, it is preferable that the distance between the irradiation opening and the fluorescent plate is R ₂ / λ or less.

On the other hand, the single mode optical fiber described above maintains the coherency of the laser beam, but the multimode optical fiber has no such effect. Therefore, the excitation light (including laser light and light from other light sources) diffuses at a certain angle from the irradiation opening of the optical fiber. In order to irradiate the fluorescent plate with a small spot diameter, an optical fiber having a core diameter smaller than that spot diameter is used, and by adjusting the angle of diffusion and the distance between the fluorescent plates, the fluorescent plate with a spot diameter larger than the core diameter is used. It can also be irradiated with excitation light.

However, since the adjustment of this distance is minute and the spot diameter greatly changes, it is desired to adjust the diffusion angle of the light emitted from the irradiation opening of the optical fiber. Especially when the single mode optical fiber is not used as described above, it is important to keep this diffusion angle within a certain angle. On the other hand, as shown in FIG. 8, the multimode optical fiber 5 '
It is preferable to use such an optical fiber because a substantially parallel irradiation can be performed to a certain extent by providing the lens 14 at the irradiation opening.

In particular, as shown in FIG. 9, an optical fiber having a converging slope 15 in the glad near the inspection opening of the multimode optical fiber 5'and having a glass lens (hemispherical lens) 14 in the core portion is provided. The diffusion angle can be reduced by using fibers.

In the radiographic image reading apparatus of the present invention, it is preferable that the excitation light is applied to the upper surface of the phosphor screen in the normal direction. Therefore, the irradiation opening of the optical fiber is provided in the normal direction. If the excitation light is largely deviated in the normal direction, since the fluorescent film 1 has a thickness as shown in FIG. 10, only the z portion of the information accumulated in the phosphor is read out as normal information. , The y portion that is read at the same time becomes noise, and the normal information of the x portion is not read.
For this reason, the irradiation opening of the optical fiber is preferably provided at a position where the excitation light can be irradiated in the normal direction.

[0021]

As described above, in the present invention, the stimulable phosphor plate is scanned with the excitation light, and the fluorescence from the stimulable phosphor plate is detected by the photodetector and recorded therein. An apparatus for reading a radiographic image includes a core portion and a clad portion surrounding the core portion, and has a core diameter of 1 to 50.
One end of an optical fiber of μm is opposed to an excitation light source of laser light having a diameter larger than 50 μm, and a light irradiation port of the other end and a light receiving and guiding port of a photodetector are opposed to and close to the stimulable phosphor plate. Since it is arranged so that the laser light from the excitation light source can be focused on the small spot diameter by the optical fiber to irradiate the stimulable phosphor plate, the light irradiation port of the optical fiber and the light receiving port of the photodetector can be used. Both of them can be brought as close as possible to the surface of the storage phosphor plate, and only the fluorescence from the excitation light irradiation position can be efficiently detected.

[Brief description of drawings]

FIG. 1 is a flowchart showing a radiation image reading work process using a radiation image reading apparatus of the present invention.

FIG. 2 is a side view showing an embodiment of the present invention.

FIG. 3 is a side view showing another embodiment of the present invention.

FIG. 4 is a view showing a cross section of an optical fiber used in the present invention.

FIG. 5 is a diagram showing transmission loss characteristics with respect to each wavelength of the silica core type optical fiber used in the present invention.

FIG. 6 is a side view showing a method of causing light to be incident on an optical fiber from a light source.

FIG. 7 is a side view showing another method of causing light to be incident on an optical fiber from a light source.

FIG. 8 is a diagram showing an example of a multimode optical fiber.

FIG. 9 is a side view showing the other side of the multimode optical fiber.

FIG. 10 is an explanatory diagram showing a relationship between oblique incidence of excitation light and light emission of a stimulable phosphor plate.

[Explanation of symbols]

 1 stimulable phosphor layer 3 stimulable phosphor plate 4 excitation light source 5 optical fiber 6 reflective optical element 9 photodetector 10 core of optical fiber

Claims (1)

[Claims] 1. An apparatus for scanning a stimulable phosphor plate with excitation light, detecting fluorescence from the stimulable phosphor plate by a photodetector, and reading a radiation image recorded therein.
An optical fiber having a core part and a clad part surrounding the core part, and having a core diameter of 1 to 50 μm, has one end facing an excitation light source for laser light having a diameter larger than 50 μm, and a light irradiation port at the other end. A radiation image information reading device in which a light receiving and guiding port of the photodetector is opposed to and close to the stimulable phosphor plate.