JPS6051694B2 - intensifying screen - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in intensifying paper used for radiation, e.g., X-ray photography.

As shown in Fig. 1, this kind of ambiguous paper is constructed by coating phosphor B on a support base A. It is placed over a film C, and phosphor B absorbs the irradiated X-rays. By emitting fluorescence and exposing the film C to light, it is useful for improving the sensitivity and contrast of the image formed on the film C.

(D in the figure is a protective film.) However, on the other hand, the use of an intensifying screen poses a problem in that the sharpness of the image decreases. Further, one possible measure for improving image sharpness is to make the phosphor layer of the intensifying screen thinner, but there is a problem that if the phosphor layer is made too thin, the necessary sensitivity will be lost.

Based on the above-mentioned circumstances, the present invention provides an intensifying screen that can effectively improve sharpness while having the necessary sensitivity.

The present invention will be explained below. The basic idea of the intensifying screen according to the present invention is to change the light transmittance in the phosphor layer.

That is, it is set so that the light transmittance of the phosphor on the support side is lowered, and the light transmittance of the side from which the light emitted from the phosphor layer is taken out (film side) is relatively higher. For this reason, in the present invention, a different color (that is, a color that absorbs the light emitted from the phosphor) is arranged in the phosphor layer so that the concentration is higher on the support side, thereby increasing the light transmittance inside the phosphor layer. of,
It should be higher towards the film side and lower towards the support stand.

As a result, the light intensity distribution after the phosphor emits light is relatively larger toward the film side and smaller toward the support base, and the ratio of image formation due to light emission deep in the phosphor layer (on the support base side), which causes blurring, is small. It becomes. This effect further improves the sharpness of the final image. Figure 2 shows a specific example based on these points, where 1 is a support made of paper or plastic, and 2 is a support made of calcium tungstate (C).
3 is a protective film made of cellulose acetate or the like.

The colored part 4 is formed of a red pigment, and this colored part 4
There is a high concentration area 4a on the support side of the phosphor layer 2, and a medium concentration area 4b and a low concentration area 4 from this side toward the protective film side.
It is formed by decreasing the concentration continuously or stepwise from c. In this intensifying screen, as shown in the diagram in Figure 3, the light transmittance T of the phosphor layer decreases from the protective film side of the phosphor to the support stand side, and conversely, the light absorption rate α increases. I'm going to go there. As described above, in the intensifying screen of the present invention, by changing the light transmittance and light absorption rate of the phosphor layer, the light emission of the phosphor layer near the film is more effectively linked to image formation. It is possible to minimize the influence on the image due to light emission near the support stand, which causes blurring of the image.

Therefore, if the thickness of the phosphor layer is the same, when comparing the sharpness, the one having the colored portion has better sharpness.

However, when compared in terms of sensitivity, those with colored areas are slightly lower. However, the degree of improvement in sharpness is greater than the degree of decrease in sensitivity. From these relationships, when comparing the sharpness when the sensitivity is set to the same state, the sharpness is superior in a wide range with the colored portion. It is especially advantageous in areas with relatively low sensitivity. This relationship will be explained in FIGS. 4 to 6.

Figure 4 is a diagram showing the relationship between the thickness (relative thickness) of the phosphor layer and sharpness, Figure 5 is a diagram showing the relationship between the thickness of the phosphor layer and sensitivity, and Figure 6 is a diagram showing the relationship between the thickness of the phosphor layer and sensitivity. FIG. 3 is a diagram showing the relationship between sensitivity and sharpness. In each figure, a curve X represents an intensifying screen without a colored portion, and a curve Y represents an intensifying screen having a colored portion. As shown in Fig. 4, the thickness t (relative thickness 100
shall be.

If the sharpness of an intensifying screen having a phosphor layer ( ) is 100, the sharpness of an intensifying screen having a colored portion is improved to about 110 because blurring of the image due to light emission near the support is reduced. When the relative thickness of the phosphor layer is reduced to 50, the sharpness improves, and in an intensifying screen without a colored part, the sharpness is 1.
An intensifying screen having one colored area provides a sharpness of 125. Sharpness can be obtained in the same way with a thicker phosphor layer. Also, as shown in Figure 5, the thickness of the phosphor is 100 mm!
If the sensitivity of an intensifying screen without a colored part is 100, then the sensitivity of an intensifying screen with a colored part decreases to about 80.

When the thickness of the phosphor is 50 mm, an intensifying screen without colored parts has a sensitivity of about 50, whereas an intensifying screen with colored parts has a sensitivity of about 40, which is 3. Based on these relationships, if we plot the sensitivity on the horizontal axis and the sharpness on the vertical axis as shown in the diagram in Figure 6, we can see that in regions with low relative sensitivity, for the same sensitivity, the intensifying screen with colored parts is better. It can be seen that the sharpness is excellent.

In such areas, the use of the intensifying screen of the present invention is practically advantageous. In particular, intensifying screens that use a support base with a high light reflectance (for example, a white support base) have the disadvantage that although the sensitivity increases due to reflection from the support base, the image becomes blurred and the sharpness is poor. However, according to the present invention, these disadvantages of intensifying screens can be improved. Furthermore, appropriate sharpness can be obtained by controlling the colored portions. In addition, with an intensifying screen using a support with a high reflectance, the sensitivity may be sufficiently high for practical purposes, and the benefit of improved sharpness more than compensates for the slight decrease in sensitivity caused by the colored parts. . Note that the contrast of the image is slightly reduced due to the presence of colored parts; however,
This does not pose a practical problem.

This is because the contrast of the image is largely determined by the film properties and the phosphor material. The intensifying screen of the present invention is particularly suitable for diagnosing minute areas such as the chest, head, and bones, and is effective when used in combination with a large-capacity X-ray device.

Note that the intensifying screens that do not have the colored portions shown by curves X in Figures 4 to 6 correspond to high-sharp intensifying screens that are conventionally used for diagnosis of minute areas such as those described above. It is something to do. A typical example of the manufacturing method for obtaining the intensifying screen of the present invention will be described.

One method is to mix a pigment with a phosphor, a binder and a solvent, and apply this mixture onto a protective film. In this case, by using a low viscosity mixture, a difference in color density can be created by utilizing the difference in specific gravity between the phosphor pigment and the binder. Another method is to apply a mixture of a pigment, a solvent, and a binder to the support side portion of the phosphor layer that has been formed in advance (however, the support has not yet been provided at this stage).
There is something that penetrates into the phosphor layer. A specific example of the present invention will be explained.

A red pigment (Colortex #101 manufactured by Sanyo Chemical Co., Ltd.) was added to CawO4 phosphor (particle size 5.5μ) at 0% by weight, 0.0% by weight, and 0.1% by weight. Ral and butyl acetate to form a slurry with a viscosity of about 50 CpS.

Next, this slurry was applied onto a protective film made of polyester with a thickness of 10 μm, and the coating weight after drying was 25, 50, 75 mg.
/al and dried. Initial drying was performed at room temperature so that the red pigment in this phosphor layer was spread more densely on the side opposite to the protective film (on the support side) due to the difference in ratio. Table 1 shows the light reflectance of the protective film side and the support side of the phosphor layer thus obtained. As is clear from the table, the light reflectance of all the fluorescent layers to which red pigment was added is lower toward the support.

From this, it can be said that the fluorescent layer containing the red pigment has a structure in which the light absorption rate is higher toward the support side. Next, the above phosphor layer was attached to a support made of a polyester film having a thickness of 250 μm. The sensitivity and sharpness of the developed X-ray film were measured by superimposing the photosensitive paper on the X-ray film and performing X-ray photography using a conventional method.Relationship between the amount of phosphor applied and the relative sensitivity and phosphor coating weight versus sharpness (sensitivity of Toshiba DD intensifying screen and 2eP/7
077! (assuming the MTF value of 100%) is
The results were as shown in the graphs of FIGS. 7 to 9. As shown by the solid line in FIG. 7, the relative sensitivity decreases with the addition of the red colorant, but the relative sharpness improves, as shown by the solid line in FIG. 8.

As a result, as shown in the relationship between relative sensitivity and relative sharpness in Figure 9, the relative sharpness at a relative sensitivity of 100 (DD intensifying screen sensitivity) is approximately 2% with the addition of 0.0% red pigment; 0.1
It has been improved by adding a red pigment in a seed amount of % and not adding it in approximately 4%.

As explained above, the intensifying screen of the present invention is made by mixing a pigment with a phosphor to form a colored layer to change the light transmittance of the phosphor. By changing the light transmittance of the image, it is possible to increase the sharpness of the image while maintaining the necessary sensitivity, and it can be advantageously used in radiography, for example, X-ray photography.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing the basic structure of an intensifying screen, Fig. 2 is a sectional view showing an example of an intensifying screen according to the present invention, and Fig. 3 is a sectional view showing the light transmittance and light of the phosphor of the intensifying screen. A model diagram showing changes in absorption rate, Figure 4 is a diagram showing the relationship between the thickness of the phosphor layer and sharpness, and Figure 5 is a diagram showing the relationship between the thickness of the phosphor layer and sensitivity. FIG. 6 is a diagram showing the relationship between sensitivity and sharpness. FIG. 7 is a line diagram showing the relationship between the phosphor coating weight and relative sensitivity in a specific example of the present invention, and FIG. 8 is a line diagram 5 showing the relationship between the phosphor coating weight and relative sharpness in the same specific example. FIG. 9 is a diagram showing the relationship between relative sensitivity and relative sharpness in the same specific example. A... Support stand, B... Phosphor, C... Film, D... Protective film, 1... Support stand, 2... Phosphor layer, 3... Protective film, 4 ...Coloring section.

Claims (1)

[Claims] 1. An intensifying screen in which the phosphor layer is colored so that the degree of absorption of the phosphor's luminescence decreases toward the side from which the phosphor layer extracts the luminescence (film side).