JPH11194198A - Fluorescence plate and method for combining fluorescence plate and imaging element and forming radiation image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluorescence plate obtainable of higher sensitivity image than conventional ones without degrading image quality for the fluorescence plate used together with a CCD imaging element for radiation image formation, combination of the fluorescence plate obtainable of higher sensitivity radiation image and the image element and a method for forming the radiation image by using the combination. SOLUTION: Fluorescence plate constituted by providing on a support body a fluorescence layer wherein fluorescent particles emitting more light with wavelength over 590 nm than light with wavelength less than 590 nm when excited by radiation are dispersed in a combining agent resin; Combination of the fluorescence plate and imaging element consisting of CCD having spectral sensitivity in red and infrared range; Radiation having penetrated a subject is irradiated to the fluorescence plate and the emission is detected with the CCD imaging element to form a radiation image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorescent plate which emits red or infrared light upon irradiation with radiation and is used for capturing an X-ray image, and the fluorescent plate and a charge coupled device (Charge Coupled Device).
Hereinafter, the present invention relates to a combination with an image pickup device comprising a “CCD”) and a radiation image forming method using the combination.

[0002]

2. Description of the Related Art Conventionally, as a method of detecting and imaging an X-ray image, there is a method of absorbing radiation such as X-rays transmitted through a subject with an intensifying screen, converting the radiation into light, and directly contacting the intensifying screen. There are known a direct photographing method using an intensifying screen and a film system in which an image is taken on a film, and an indirect photographing method in which an X-ray transmitted through a subject is absorbed by a fluorescent plate and an image projected on the fluorescent plate is captured on a film by a mirror camera or the like. .

As another method for detecting and capturing an X-ray image, a method using an X-ray image intensifier without using a fluorescent plate is known. In addition, an X-ray transmitted through a subject is converted into light by a fluorescent plate. Japanese Patent Laid-Open No. Hei 4-287580 discloses a method of photographing the image by a CCD image pickup device. A method of converting an X-ray transmitted through a subject into light by a fluorescent plate, receiving the X-ray by the CCD image pickup device, digitizing each pixel, and photographing. Is described in JP-A-8-147456 and the like.

In each of these systems, a fluorescent plate that always absorbs radiation transmitted through a subject and converts it into a visible radiation image is used. Conventionally, the fluorescent plate used here is supported as a basic structure. Body and a phosphor layer provided on the support, and the phosphor layer is composed of phosphor particles that emit blue or green light, mainly green light upon irradiation, and a binder that disperses and supports the phosphor particles. ing. The phosphor particles emit blue or green light when irradiated with radiation such as X-rays, and emit light having an intensity corresponding to the radiation absorption difference of the subject, thereby rendering an optical image.

In indirect photographing represented by a mirror camera system, an X-ray photographed image of a subject can be obtained by drawing a light image from a fluorescent plate on a film through a lens. In the method of combining a fluorescent plate and a CCD image pickup device, a method of detecting a light image from the fluorescent plate through a lens and detecting the light image with the CCD image pickup device or a method of detecting a light image from an optical fiber bundle through an image fiber is used.
An X-ray photographed image can be obtained by a method of detecting with an imaging element.

[0006]

However, the above-mentioned system in which the fluorescent plate and the CCD image pickup device are combined has a problem that the sensitivity of the system is still low. In order to increase the sensitivity, the system is used for the fluorescent film of the fluorescent plate. It is possible to increase the sensitivity somewhat by increasing the amount of the phosphor, but in this case, although the sensitivity is slightly increased, there is a disadvantage that the image quality, particularly sharpness, is reduced. Was.

Accordingly, the present invention is to provide a fluorescent plate which is used together with a CCD image pickup device for forming a radiation image and which can obtain an image with higher sensitivity than the conventional fluorescent plate without deteriorating the image quality. Aim.

Another object of the present invention is to provide a combination of a fluorescent plate and an image pickup device which can obtain a radiation image with higher sensitivity than the conventional combination.

Still another object of the present invention is to provide a radiographic image forming method capable of obtaining a radiographic image with higher sensitivity while suppressing a decrease in image quality as compared with the conventional method.

[0010]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have proposed a method of combining a fluorescent plate and a CCD image pickup device for use in forming a radiation image by combining a fluorescent plate and a CCD image pickup device, As a result of intensive studies, the above-mentioned object of the present invention has been achieved by adopting a specific combination different from the conventional ones in terms of the emission characteristics of the fluorescent plate and the spectral sensitivity characteristics of the CCD image sensor used in combination with the fluorescent plate. I found that I could do it.

According to the present invention, (1) a phosphor particle which emits more light in a wavelength range of 590 nm or more than that in a wavelength range of less than 590 nm when excited by radiation is contained in a binder resin. A phosphor plate comprising a phosphor layer dispersed on a support; (2) light emission when excited by radiation, in which the amount of light emitted in the wavelength region of 590 nm or more is larger than the amount of light emitted in the wavelength region of less than 590 nm. A phosphor plate comprising a support on which a phosphor layer in which phosphor particles are dispersed in a binder resin is provided, and a charge-coupled device (CC) having a spectral sensitivity in a red or infrared region.
(3) a combination of a phosphor plate and an image pickup device comprising: (3) the phosphor particles described above in (2), wherein the phosphor particles have a peak wavelength of an emission spectrum in a wavelength region of 590 nm or more; (4) the phosphor particles are Gd ₂ O ₂ S: Eu and Gd
A combination of the phosphor plate and the image pickup device according to any one of (2) to (3), wherein the combination is at least one of ₂ O ₃ : Eu; and (5) a surface of the phosphor layer of the phosphor plate. The combination of the fluorescent plate and the imaging device according to any one of the above (2) to (4), wherein a protective film is provided; (6) irradiating the fluorescent plate with radiation transmitted through an object; In the radiation image forming method of forming a radiographic image by detecting the light emission of the fluorescent plate with an imaging device including a charge-coupled device (CCD), the amount of light emitted from the fluorescent plate is 590 n
The amount of light emitted in the wavelength region of 590 nm or more is larger than the amount of light emitted in the wavelength region of less than m, and the imaging device including the charge-coupled device (CCD) has a spectral sensitivity in the red or infrared region. Radiation imaging method.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

As a general method for producing the phosphor plate of the present invention, a predetermined amount of a phosphor and a binder are mixed, and an organic solvent is added thereto to prepare a phosphor coating solution having an appropriate viscosity. There is a method of forming a phosphor layer by applying a liquid on a support with a knife coater, a roll coater, or the like, followed by drying. Examples of the binder include nitrified cotton, cellulose acetate, polyvinyl butyral, linear polyester, and vinyl chloride-vinyl acetate copolymer.

As the organic solvent used for preparing the phosphor coating solution, for example, ethanol, isopropyl alcohol, butanol, methyl ethyl ketone, methyl isobutyl ketone, butyl acetate, ethyl acetate, toluene, xylene and the like are used.

The amount of the binder in the obtained phosphor layer is as follows:
The solid content is preferably 1 to 10 parts by weight, more preferably 1 to 6 parts by weight, based on 100 parts by weight of the phosphor.

As the phosphor used in the phosphor plate of the present invention, for example, Gd ₂ O ₂ S: Eu, Gd ₂ O ₃ : Eu,
(Zn, Cd) S: Ag, CdS: Ag, CaS: E
u, MgS: Mn phosphors are used. Among these phosphors, Gd ₂ O ₂ S: Eu and Gd ₂ O ₃ : Eu are particularly preferred in terms of sensitivity when used as a phosphor plate. More preferably, it is used as a phosphor layer. Each of these phosphors is an X-ray phosphor that emits in the red or infrared region and has a peak wavelength of an emission spectrum of 590 nm or more on the long wavelength side when excited by radiation.
When excited by radiation such as X-rays, the emission spectrum has a peak wavelength of 590 nm or more from the red region to 1000 nm.
There is no particular limitation as long as the phosphor is in the infrared wavelength range.

The fluorescent plate thus obtained may be used as it is. However, like a conventional fluorescent plate, polyethylene phthalate is used as a protective film on the surface of the fluorescent layer in order to improve its mechanical durability. A film is formed by laminating a plastic thin film such as polycarbonate, or dissolving a resin such as cellulose acetate butyrate, cellulose acetate, polyvinyl butyral in a solvent, applying a thin film on the phosphor layer surface, and drying. It is desirable to form a protective film on the upper surface of the phosphor layer by the method described above.

An image sensor such as a CCD used in combination with the fluorescent plate of the present invention has a spectral sensitivity in the red or infrared wavelength range, or has a spectral sensitivity in other wavelength ranges. An imaging element such as a CCD having a higher sensitivity to light having a wavelength of 590 nm or more in the red or infrared region than light having a wavelength in the green wavelength region is used.

In addition, the radiation image forming method of the present invention comprises a fluorescent plate which emits light mainly in the red or infrared region obtained as described above, and a fluorescent plate having a spectral sensitivity in the red or infrared region or a red to infrared region. In combination with an imaging device such as a CCD whose spectral sensitivity is higher than the spectral sensitivity in the blue or green region, the radiation transmitted through the subject is irradiated onto the fluorescent screen in exactly the same way as in the conventional method. The radiation image of the object formed in the image is detected by an image pickup device such as a CCD, and once subjected to photoelectric conversion and then to digital conversion. For example, this is displayed on a cathode ray tube or a light carrying the obtained radiation image. A radiographic image is formed by means such as converting it into a signal and reproducing it as a radiographic image on a photographic film. In this case, a fluorescent plate and a CCD for detecting a visible radiation image visualized on the phosphor layer
Combination with an image sensor such as a conventional fluorescent plate that draws a blue or green light emission radiation image on the phosphor layer by irradiation, and a conventional CCD image sensor that is also particularly sensitive to blue or green light emission The selection of the fluorescent plate and the imaging device such as a CCD and the combination thereof are various from the viewpoint of the emission color (emission spectrum wavelength) of the fluorescent plate and various characteristics such as the spectral sensitivity of the imaging device such as the CCD. Although it is conceivable, according to the study of the present inventors, surprisingly, a phosphor having a peak wavelength of an emission spectrum in a wavelength region of 590 nm or more is contained in the phosphor layer, and of the light emission amount from the phosphor plate, Where the amount of light emission of 590 nm or more is larger than the amount of light emission at a wavelength lower than 590 nm,
The fluorescent plate of the present invention may be used with a phosphor having a spectral sensitivity in the red or infrared wavelength range or a spectral sensitivity in these wavelength ranges greater than the spectral sensitivity in the blue or green wavelength range.
It has been found that when combined with an imaging device such as a CD, a radiation image can be formed with higher sensitivity than the conventional combination without lowering the image quality.

[0020]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples.

Example 1 The molar ratio of Eu / Gd was 0.1.
035 / 0.965, 95 parts by weight of Gd ₂ O ₂ S: Eu phosphor {phosphor (1)}, 5 parts by weight of polyvinyl butyral (binder), and about 1: 1 by weight of toluene, ethanol and methyl ethyl ketone. : 50 parts by weight of the mixture (organic solvent) mixed at a ratio of 1: 1 was sufficiently mixed to prepare a phosphor coating solution.

Next, this phosphor coating solution is placed on a 250 μm-thick polyethylene terephthalate film into which titanium dioxide has been kneaded, and the phosphor coating weight after drying is 95 mg.
/ cm ² with a knife coater,
This was dried to produce the fluorescent plate of Example 1 {Fluorescent plate (1)}.

[0023] (Examples 2 and 3) a phosphor coating weight after drying, respectively 80 mg / cm ² and 110 mg / cm ²
Fluorescent plates (2) and (3) of Examples 2 and 3 were respectively manufactured in the same manner as the fluorescent plate (1) of Example 1 except that the above conditions were satisfied.

(Examples 4 and 5) Fluorescent plate (1) of Example 1
Gd ₂ 0 ₂ S used to: instead of Eu phosphor (1), phosphor molar ratio of Eu / Gd is 0.045 / 0.955 (2) and the molar ratio of Eu / Gd 0. 025 /
0.975 phosphor (3) was manufactured, and each of the phosphor layers (2) and (3) was used in the phosphor layer (1). The phosphor plate (4) and the phosphor plate (5) of Example 4 and Example 5 were manufactured.

(Comparative Example 1) Gd ₂ O ₂ S: Tb phosphor instead of Gd ₂ O ₂ S: Eu phosphor {phosphor (1)} used for phosphor plate (1) of Example 1 A phosphor plate (R1) of Comparative Example 1 was manufactured in the same manner as the phosphor plate (1) of Example 1 except that (R1)｝ was used.

Each of the fluorescent plates (1) to (3), the fluorescent plate (4) and the fluorescent plate (5) of Examples 1 to 5 obtained as described above is irradiated with X-rays, and the fluorescent layers are removed. When the emission spectrum of the emission of
It emitted red or infrared light having main emission peaks at around 5 nm, 615 nm and 705 nm. Also,
The phosphor plate (R1) of Comparative Example 1 was measured for the emission spectrum upon X-ray excitation in the same manner.
It exhibited green to yellow-green emission having a main peak emission at around nm and 490 nm.

Each of the fluorescent plates (1) to (5) and the fluorescent plate (R1) has a spectral sensitivity peak wavelength of about 600 nm to 8 as illustrated in FIG.
The system sensitivity was measured in combination with a CCD image sensor near 50 nm. Table 1 shows the results.

As is clear from Table 1, when compared with the fluorescent plates having the same phosphor coating weight, when the fluorescent plate (1), the fluorescent plate (4) and the fluorescent plate (5) are combined, the conventional fluorescent plate (R1 ) Is clearly higher than when combined with

Further, from the comparison between the fluorescent plate (2) of Example 2 and the fluorescent plate (R1) of Comparative Example (1), it can be seen that the sharpness is high with the fluorescent plates having the same sensitivity.

In the table, "Sensitivity" indicates the sensitivity measurement as a system in which a fluorescent plate and a CCD image pickup device are combined. The X-ray-irradiated light from each fluorescent plate is received by the CCD image pickup device. The intensity of the electric signal output in proportion to the amount is defined as the sensitivity of the system based on each of the combinations, and the respective sensitivities are the same as those of the fluorescent plate (R
The relative values are shown when the sensitivity in the case of 1) is set to 100.

On the other hand, the "sharpness" was relatively judged by the naked eye from the screen drawn on the display.

[0032]

[Table 1]

[0033]

As described above in detail, the sensitivity of the radiation image forming system according to the present invention in which the fluorescent plate emitting light in the red and / or infrared region and the CCD image pickup device having the spectral sensitivity in the red and infrared regions are combined. Is a conventional fluorescent plate that emits blue or green light and a CC that has spectral sensitivity in the blue or green region.
A radiation image with higher sensitivity and less decrease in sharpness can be obtained as compared with a system in which a D imaging element is combined.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of the spectral sensitivity of a CCD used in the present invention.

FIG. 2 is a diagram illustrating an emission spectrum of a fluorescent plate (1) in Example 1 of the present invention.

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Claims (6)

[Claims] 1. A fluorescence obtained by dispersing, in a binder resin, phosphor particles that emit, when excited by radiation, a light emission amount in a wavelength region of 590 nm or more than that in a wavelength region of less than 590 nm. A fluorescent plate having a body layer provided on a support. 2. A fluorescent material comprising a binder resin and phosphor particles which emit, when excited by radiation, a light emission amount in a wavelength region of 590 nm or more than that in a wavelength region of less than 590 nm. A fluorescent plate having a body layer provided on a support,
A combination of a fluorescent plate composed of a charge-coupled device (CCD) having a spectral sensitivity in the red or infrared region and an imaging device. 3. The combination of a fluorescent plate and an image sensor according to claim 2, wherein said phosphor particles have a peak wavelength of an emission spectrum in a wavelength range of 590 nm or more. 4. A combination of a fluorescent plate and an image sensor according to claim 2, wherein said phosphor particles are at least one of Gd2 O2 S: Eu and Gd2 O3: Eu. . 5. The combination of a fluorescent plate and an image pickup device according to claim 2, wherein a protective film is provided on a surface of said phosphor layer of said fluorescent plate. 6. A radiation image forming method for irradiating a fluorescent plate with radiation transmitted through a subject and detecting a light emission from the fluorescent plate with an image pickup device comprising a charge-coupled device (CCD) to form a radiation image. Is larger in the wavelength range of 590 nm or more than in the wavelength range of less than 590 nm.
A method of forming a radiation image, wherein the imaging device comprising D) has a spectral sensitivity in a red or infrared region.