JPH0527096A - X-ray image conversion sheet and read-out thereof - Google Patents

Abstract

PURPOSE:To prevent the interference of light and obtain the superior image by forming fine unevenness on the surface of the accelerated fluorescent body film of a protecting film or inputting the laser beam in inclination by a prescribed angle, when the data of an X-ray image sheet is read out. CONSTITUTION:An accelerated fluorescent body layer 2 consisting of an accelerated flurescent body, resin binder, solvent and plasticizers is formed on a supporting body 3, and a glass plate protecting film 1 is attached on the accelerated flurescent body layer 2 through a spacer 7. Frosted glass treatment 4 is applied onto the undersurface of the protecting film 1, and an image conversion sheet 10 is formed by setting the protecting film 1 on the fluorescent body layer 2 side. When an image is picked up by using the sheet 10, no interference fringe is observed, and the superior image can be obtained. Further, in image read-out, if the film thickness of the protecting film 1 is set to (d), and the refractive index is set to (n), the interference fringe can be removed by radiating the laser beam having a beam radius of (r), in an angle theta shown by the equation I, and the distinct image can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray image conversion sheet and its reading method. A new digital radiography system (X-ray image conversion system) has been developed and used in place of the conventional medical X-ray photograph (screen film). An imaging plate (image conversion sheet) coated with a stimulable phosphor is used for the sensor portion of the system.

BaBr ₂ : Eu, which is a stimulable phosphor, is a phosphor having two functions of X-ray detection and memory.
When this phosphor is irradiated with X-rays or ultraviolet rays, Eu, which is the emission center, is excited and emits blue light (photoluminescence). At the same time, some electrons in Eu are excited and trapped in the color center. The color center is a Br ⁻ lattice defect,
The defect is positively charged. Since the electrons are negatively charged, they are trapped in the color center. This is the memory function.

Next, when the photostimulable phosphor is irradiated with a laser beam of red or infrared wavelength, the electrons trapped in the color center are excited and emit blue light when returning to the Eu orbit. This is stimulated emission. This stimulated emission intensity is proportional to the intensity of X-rays. This stimulated emission is converted into an electric signal by a photomultiplier tube. An X-ray photograph is obtained by image-processing this electric signal. The imaging plate can erase the memory by illuminating with white light and can be used any number of times. The basic principle is described in detail in US Pat. No. 3,859,527. A digital X-ray image device using such an X-ray image conversion sheet has an X-ray dose of 1/2 to 1/20 as compared with a conventional X-ray film (screen film),
An image with good contrast can be obtained.

[0004]

2. Description of the Related Art Conventionally, a flat and smooth glass plate, PET or polyester resin film has been used as a protective film for an image conversion sheet. Further, when reading data, a laser beam was scanned using a galvano mirror, a polygon mirror, a holographic or the like. At the central portion of the scan, the laser light is incident on the X-ray image conversion sheet at a substantially right angle.

[0005]

In the case of the conventional smooth protective film, when the X-ray is irradiated, the excitation light interferes due to the reflection on the surface of the protective film, and the interference fringes appear in the image, which deteriorates the image quality. There was a problem of letting it. Further, when the laser light is incident almost vertically at the central portion of the scan, the laser light slightly deviates from the vertical before and after that. At that time, interference occurs in the protective film in the X-ray image conversion sheet or the adhesive layer between the protective film and the phosphor layer.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to prevent the above interference. In order to prevent interference caused by the smooth surface of the protective film, the first aspect of the present invention is characterized in that minute irregularities are formed on the stimulable phosphor side surface of the protective film. It is possible to easily form fine irregularities by forming the protective film from glass and subjecting the surface of the phosphor layer side to frosted glass. Further, a resin layer having a rough surface may be formed on the surface of the protective film on the stimulable phosphor side.

According to the second aspect of the present invention, in order to eliminate interference caused by vertical irradiation of laser light during reading, a stimulable phosphor having a protective film with a film thickness d and a refractive index n is used.
When reading the data recorded on the line image conversion sheet with a laser beam, γsin θ <2d / tan θ1, where θ1 = 90−sin ⁻¹ (sin (90−θ) / n), 0 ° <
It is characterized by irradiating laser light at an incident angle θ satisfying θ <90 °. A semiconductor laser can be used as the laser light.

[0008]

By forming minute irregularities on the phosphor layer side of the protective film, light is scattered on this surface, and as a result, interference does not occur. If the distance between the scattering surface and the phosphor layer is small, there is almost no reduction in resolution due to scattering. Further, by eliminating the portion where the laser beam is incident on the X-ray image conversion sheet substantially perpendicularly, there is no interference in the X-ray image conversion sheet when the laser beam is incident. Further, if the condensing system is covered with the X-ray image conversion sheet so that the reflected light of the irradiation light to the photostimulable luminescent material does not escape to the outside, the condensing efficiency is increased and the sensitivity is improved.

[0009]

EXAMPLES Example 1 (FIG. 1) A support (protective film) 3, a phosphor layer 2, and a protective film 1 were laminated in the constitution of FIG. 1 and used. As the support 3, a glass plate having a thickness of 300 μm was used. A stimulable phosphor layer 2 composed of a stimulable phosphor, a resin binder, a solvent, and a plasticizer was formed thereon.
Examples of the stimulated phosphor include BaBr ₂ : Eu, BaCl ₂ : Eu, BaCl
Br: Eu or the like can be used. As the resin binder, acrylic resin, polyester resin, cellulose resin or the like can be used. A solvent that can dissolve the resin binder is used, and acetone, toluene, MEK, or the like can be used. Dibutyl phthalate was used as the plasticizer. These materials were mixed in a weight ratio of 100: 60: 30: 6, and a phosphor layer was formed by a doctor blade method. After that, the solvent is dried, and a glass plate (thickness 300 μm is formed on the phosphor layer through the spacer 7.
The protective film 1 of m) was adhered. Further, ground glass treatment 4 is performed on one surface (lower surface) of the glass plate 1 used as a protective film,
An image conversion sheet was prepared by using it as the phosphor layer side. When an image was taken using this X-ray image conversion sheet, interference fringes could not be observed. For comparison, when a glass plate without frosted glass treatment was used for the protective film, interference fringes with a maximum size of 10% could be observed.

Example 2 (FIG. 2) The following was used as a protective film. Glass plate (thickness 3
00 μm) 1) UV curable resin 5 is applied to the surface (bottom surface) of 150 μm by spin coating, and then adhered to frosted glass coated with a release agent, irradiated with UV rays, and then the frosted glass is peeled off to form a protective film. Was formed. As a result, the ground glass transfer processing surface 6 is formed on the lower surface of the resin layer 5. The other conditions are the same as in Example 1. When an image was taken using this X-ray image conversion sheet, interference fringes could not be observed as in Example 1. still,
In both embodiments, the voids 8 formed by the spacers 7 may be filled with a substance having a refractive index of 1.3 or less or 1.7 or more.

Example 3 (FIG. 1) A glass plate having a thickness of 0.55 mm as the protective film 1 and a thickness of the support 3
1.1 mm glass plate, BaBr ₂ : Eu as stimulable phosphor 2
²⁺ was used. Photostimulable phosphor 300g, hydrophobic silica 1
g, a binder (acrylic resin) 3 g, toluene 30 g, and methyl ethyl ketone 20 g were mixed with a propeller mixer for 10 hours. After defoaming the coating solution, it was applied on the protective film by a doctor blade method to a thickness of 300 μm. A glass having a thickness of 0.3 mm was adhered around the support using an epoxy resin. The support was bonded at a temperature of 40 ° C. in an atmosphere having a humidity of 10% or less to obtain an X-ray image conversion sheet 10. That X
The line image conversion sheet was irradiated with 0.1 mSv of X-ray, and scanning was performed using a semiconductor laser (wavelength 780 nm, 20 mW). The scanning surface was tilted at 80 ° with respect to the X-ray image conversion sheet. The stimulated luminescence emitted at that time was collected using an optical fiber 11 (FIG. 4). At that time, the optical fiber 11 is as shown in FIG.
I covered it as much as possible so as not to block the laser light. The collected light was measured for voltage at the time of electric signal using a photomultiplier tube. Further, the electric signal was image-processed to obtain an X-ray image.

Using this X-ray image conversion sheet 10, the inclination of the scanning surface with respect to the X-ray image conversion sheet is set to 80 °, 70 °, 60
The same experiment as in Example 3 was conducted by changing the temperature to 90 °, 90 °, and 85 °. The results are shown in Table 1. In addition, Experimental Examples 4 and 5
Corresponds to the prior art.

[0013]

[Table 1] The reading sensitivity is represented by the potential difference between both ends of the resistance when the photomultiplier tube is provided with a terminal resistance of 1 kΩ. In addition, ◯ indicates that no interference fringes were generated, × indicates that interference fringes were generated, and Δ indicates the middle thereof.

From these results, it can be seen that by making the angle θ between the X-ray image conversion sheet and the scanning surface smaller than 85 °, interference fringes of the laser light are eliminated and a clear image with high sensitivity can be obtained. Incidentally, it has been experimentally confirmed that in general, in the case of the definition as shown in FIG. 3, the laser should be incident at an incident angle θ that satisfies the following expression (1). γ sin θ <2d / tan θ ₁ (1) where θ ₁ = 90−sin ⁻¹ (1 / n sin (90−θ)) degree 0 ° <θ <90 ° γ: laser beam diameter, n: protection Refractive index d of film: thickness of protective film

[0015]

As described above, according to the present invention, the interference fringes are eliminated by treating the surface of the protective film so as to be rough. Further, upon reading, interference fringes disappear by making the laser incident at a predetermined incident angle.

[Brief description of drawings]

FIG. 1 is an illustrative view showing one embodiment of the present invention.

FIG. 2 is an illustrative view showing another embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between a laser incident angle, a protective film thickness, and a refractive index.

FIG. 4 is a diagram showing a condensing system of the present invention.

[Explanation of symbols]

1 ... Protective film 2 ... Phosphor layer 3 ... Support (protective film) 4: Ground glass treated surface 5 ... UV effect resin layer 6 ... Ground glass transfer surface

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masami Hasegawa             1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture             Within Fujitsu Limited (72) Inventor Soichiro Hidaka             1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture             Within Fujitsu Limited

Claims (6)

[Claims] 1. An X-ray image conversion sheet (10) using a stimulable phosphor (2) having a protective film (1), wherein fine irregularities are formed on the surface of the protective film on the stimulable phosphor side. Characteristic X-ray image conversion sheet. 2. The X-ray image conversion sheet according to claim 1, wherein the protective film is formed of glass, and the surface of the phosphor layer side thereof is treated with frosted glass. 3. The X-ray image conversion sheet according to claim 2, wherein a resin layer (5) having a rough surface is formed on the surface of the protective film on the stimulable phosphor side. 4. The X-ray image conversion sheet according to claim 3, wherein the surface of the resin layer is formed by pressure-transferring the frosted glass-treated surface (6) of the protective film. 5. The X-ray image conversion sheet according to claim 4, wherein the resin layer is formed of a flexible material that is not impregnated with the stimulable phosphor. 6. An incident angle satisfying the following formula when reading data recorded on an X-ray image conversion sheet using a stimulable phosphor having a protective film having a film thickness d and a refractive index n, which satisfies the following formula: Reading method of X-ray image conversion sheet characterized by irradiating laser light at θ: γsin θ <2d / tan θ1 where θ1 = 90−sin ⁻¹ (sin (90−θ) / n), 0 ° <
θ <90 °