JPS59183400A - X ray intensifying screen - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an X-ray intensifying screen for use with a photographic film element on which an X-ray image is recorded;
and particularly relates to screens with improved image properties. Still more particularly, the present invention relates to an X-ray screen with controllable speed and to radiographs exhibiting good image clarity and reduced noise.

Luminescent phosphor (luminescent ph) in the binder
X-ray intensifying screens prepared by total encapsulation (osphor) and coated on a suitable support are well known in the art. These X-ray screens absorb X-rays and generate energy in the form of light, which in turn causes the photographic film combined with it to light. The phosphors used in these screens are generally 6
Types: (1) Broadband emitters (e.g. cawo4
), (2) narrow band emitters (e.g. Baycz:Bu)
and (6) line emitters (e.g. La0Br; Tm
). X produced using these phosphors
Ray screens are used in conjunction with radiographic silver film to record X-ray images. Potentially Harmful
The use of x-ray screens is particularly useful in the medical x-ray field since there is a critical need to reduce patient exposure to radiation. Screen is overall fishing line speed (sensitivity)
, and therefore requires less x-ray power for satisfactory image production.

One way to increase speed is to increase the thickness of the phosphor coating. As the speed is increased, however, there is usually a decrease in image sharpness and therefore a decrease in the amount of medical information that can be generated from this thread.

Typically, the speed of an X-ray screen is reduced by reducing the thickness of the phosphor layer or by adding broadband absorbers (eg, dyes or pigments) to the X-ray screen construction. Although these prior art screen speed controls provide the desired high sharpness, they also increase noise and mottling in the final radiographs produced therefrom.

Radiographic noise is a "grain" or mottled pattern that results from the electrostatic nature of the imaging process. The source of noise is the dispersion of the scintillation effect of individual phosphor crystals. Crystals with lower efficiency are less efficient at forming images. Those that can contribute only minimally to the process but have high efficiency lead to an increase in density. Fluctuations in developed density appear as noise. By narrowing the dispersion of scintillation efficiency, radiographic noise is reduced. As discussed above, the addition of dyes or pigments to the screen structure effectively widens the dispersion of the synnarration efficiency and thus increases the overall noise. .

X-ray screen constructions usually consist of a phosphor-containing layer coated on a suitable support. Underlayer coated between phosphor and support
It is also advantageous to use reflective or absorbent layers (for example reflective or absorbent layers) and to include a protective opanicoat for the phosphor layer.

It is an object of the present invention to provide an improved X-ray screen made entirely of phosphors exhibiting narrow band or line emission.

Another object of the present invention is to provide an entire X-ray screen that can be used with photographic film to achieve controlled speed, good image sharpness and low noise and mottling.

These and other purposes are sequentially (1) a support, (
2) an optional underlayer, (6) a narrow or line band phosphor-coated layer dispersed in a binder, in an X-ray intensifying screen, layers (2), (3);
Alternatively, this improvement is achieved by incorporating in (4) a small amount of a non-fluorescent ultraviolet (UV) light absorber having an absorption maximum below 400 nm. X-ray screens made according to the present invention used with photographic film provide clear images with lower noise and mottling than screens made without absorbers.

Although the use of stone absorbers in X-ray screens is not new per se (see U.S. Pat. No. 3,743,1833), the use of specifically narrow-band or line-band phosphors to improve these highly efficient It has not been shown to significantly improve the image sharpness of materials with good quality.

There are a number of commercially available optical absorbers that exhibit absorption maxima below 400 nm. All work within the scope of this invention. These include the following:

B) 2,2'-dihydroxy-5-alkoxy ~
400-Nizophenone C) 2'-(2'-hydroxy-3'-alkyl
~400 phenyl) penztriazole D) p-methoxybenzylidene malonic acid di ~660
Methyl ester is carboxylated bibridge water nylacetate product] Polymer ALB, product of Sandoz Co., USA] G) Oxalic acid anilide derivative [Zando Ball @~630
VSU, a product of Santo Corporation, USA] These absorbents can be dissolved in any convenient organic solvent (e.g. acetone) and added to the layer (3) or (3) in an amount depending on the desired effect and the layer to which they are added. It can be added to (4).

Layer (1) is the support. A number of elements can be used, such as paper or metal foil, such as aluminum. Preferably, a polymeric hydrophobic organic polymer support is used. Suitable polymeric supports include cellulose derivatives such as cellulose acetate, cellulose propionate, cellulose acetate butyrate and ethylcellulose;
Polyethylene, polyvinyl chloride, poly(vinyl chloride/vinyl acetate), polyvinylidene chloride,
Polyvinyl acetate, polyacrylonitrile, polystyrene and polyisobutylene, and polyesters such as polyethylene terephthalate and US r.
, 465,319, which can be obtained by the method described in the specification of No. 465,319. Polyethylene terephthalate film is particularly useful because of its dimensional stability. % useful supports include U.S. Pat. No. 2,779,
Biaxially oriented polyethylene terephthalate coated with nine layers of a vinylidene chloride/methyl acrylate/itaconic acid copolymer basecoat as described in No. 684. The thickness of the support is approximately 0.0025 to 0.06 inches (0.0
064 to 0.0762'y++). 0.01 inches (0.02543) is preferred.

Furthermore, the support may contain dyes or finely divided pigments such as titanium oxide, lithopone, magnesium carbonate, aluminum oxide, carbon black and colored pigments such as tartrazine (C
IA 640), Victoria Green WB Base (C
IA 800), and Nubian Resin Black (C
IA 864) can be included as an opacifier or as a light absorber or can be coated with it.

The dyes and pigments described above are particularly useful in reflective layers to alter light generation or block unwanted wavelengths. Additionally, the base support can be metallized to provide a reflective effect.

EXAMPLE A phosphorous ethylene terephthalate base can be coated with a thin layer of aluminum. It is preferred to apply on the support a reflective layer comprising anatase grade 'rto2 dispersed in chlorosulfonated ethylene C, Hypal 20, a Duhon product. Many other reflective pigments can also be used in the reflective layer. These include, inter alia, potassium titanate as described in US Pat. No. 3,895,157.

There are many phosphors that emit narrow or line emission bands. These include the yttrium tank v-) % I/CY(
Nb) TaO4, lanthanum oxyparide (especially La
Among others, barium fluorohalide (Bayct: Ku) as described in US Pat. No. 4,076,897 is used. These phosphors are usually milled in a solvent/binder mixture for several hours and coated onto the reflective layer referred to above.

A large number of binders can be used in the active layer (6) of the present invention. Although it is preferred to use polyvinyl butyral resins, there is also a group of suitable polymers used in the prior art that can be used herein. For example, polyurethane elastomeric binders are particularly effective because of their adhesion to the aforementioned conventional supports. However, polyurethane is subject to degradation by UV light. Many conventional phosphors produce substantial amounts of UV light. This can further be reflected back into the active layer by the support. Therefore, measures must be taken to prevent this decomposition (
(See US Pat. No. 5,745,853). Therefore, the use of binders other than polyurethane is preferred.

A protective overcoat prepared according to the teachings of the prior art can be applied over the phosphor layer. These top coats are made of cellulose nitrate or acetate or poly(methyl methacrylate), poly(imbutyl methacrylate)
and vinyl chloride/vinyl acetate copolymer resin mixtures (see U.S. Pat. No. 2,907,882). Overcoats similar to those described in US Pat. No. 3,895,157 are particularly effective. The overcoat layer can be about 0.0001 to 0.005 inches (0.0003 to 0.015 cm) thick.

It is preferred to use all of the fluoroacrylate overcoats described in US Patent Application No. 420,487.

X prepared as described in the examples above and below
Line screens are obviously useful in medical radiography, for example. The addition of trv light absorbers makes it possible to control the speed of the screen in a predictable manner.

That is, when exposed in combination with radiographic film,
These screens provide excellent image clarity and importantly reduce noise and mottling.

This makes it possible to determine more information from the image. This is a significant and unexpected finding compared to the prior art which teaches that a reduction in phosphor layer thickness improves image sharpness only with a simultaneous increase in noise and mottle.

The invention will now be illustrated by the following examples, of which example 2 is considered the best mode.

Example 1 Support (1), reflective layer (2), activated phosphor J*
Three X-ray intensifying screens were manufactured, including (3) and an overcoat layer (4). In this example, UV
The light absorber was placed in N(4). A reflective suspension was prepared by sand milling the following component mixture for about 4 hours.

Ingredients 1-% Anatase TiO228.4 n-butyl acetate 65.1 Mixed petroleum naphtha (initial p, 247'F) 2
3.5 Dioctyl sodium sulfococtalate 1
．． 1 ester polymeric organosilicone fluid (2% by weight in Tol20,6) The milled suspension was filtered through a filtration media with an average 30 micron pore size. This suspension was degassed and then a base layer of vinylidene chloride/methyl acrylate/itaconic acid copolymer prepared as described in U.S. Pat. No. 2,69B,240. Coated onto a biaxially oriented polyethylene terephthalate film sheet. A reflective layer was obtained giving a TiO2 coating weight of approximately 0.029 f/inch.

After drying this layer at about 70-75''F, an active phosphor layer was applied over the reflective layer. The phosphor was prepared from the following composition by milling for about 12 hours.

Ingredients j・PolyLa0Br:
Tm 58.3 Polyvinyl butyral (granular, intrinsic viscosity 0.81)
5.6n-butyl acetate
16,8n-Proper Tools
16.8 Polymeric organosilicone fluids
0.8 Clycerol Monolaurate 1,4 Over the dried phosphor layer an overcoat layer from the following solution was applied.

Cellulose heptatate (contains 6.5 acetyl)
155.8%)
92.4 Urea-formanogen human resin
0.9UV light absorber 0.043
Manufactured several screens. Screen ■ contains UV light absorber (4), screen ■ contains UV light absorber (B)
and screen m contained UV light absorber (C) at the level indicated above. As a control, a screen containing no UV light absorber was produced.

The screen referred to above was passed through a 2 m aluminum filter with high speed medical X-ray film at 8 (] K
Tested by vi exposure to an X-ray machine at Vp, 2 mAe. Place a step wedge and resolution target between the X-ray source and the film/screen (
(closely attached to this). Each exposed film was then developed in a conventional X-ray development system, fixed and washed.

The following results were obtained.

Control 1.71 8.3
0.014 screen l (tinubi 0.98
8.0 0.011n■328) Screen■(cyan) 1.05 7.7
0.012-bu@UV-5411) (Note) (1) In all cases, the velocity is the value obtained by exposure to De5-hon H1-plusum (its velocity = 1.00
).

(2) The smaller the number, the lower the markings (see U.S. Percentage No. 4,028,550 Specification No. 4a).

That is, the addition of UV light absorbers into the coating layer (4) can significantly reduce the mottling produced on the screen and improve the overall image quality of the exposed film. Powerful.

Example 2 Do the same as in Example 1, but with UV light absorption (B
) i 0.121! t% phosphor (LaOBr: Tm
) level was added to the active phosphor layer (3). The following results were obtained.

Control 1.76 8.8 0.017 Invention
1.05 8.9 0.014UV light absorber growth) 1
- When the monophoton layer (9) was added, the resolution was clearly increased and the mottling was significantly reduced.

Example 6 Efficiency of the Invention When UV Light Absorber is Added to the Reflective Layer In order to fully test the effectiveness of the invention when UV light absorber (B) is added directly to the reflective suspension, Example 1 is repeated but UV light absorber (B) is added directly to the reflective suspension at 0.18X. Screens were prepared by adding at the % TiO2 level.

The following results were obtained.

Control 1.45 8.6 0
．． 012 Invention 0.82 B, 6 0
．． 010 Example 4 UV light absorbers may also be used in combination with light absorbing underlayers.

To test this effect, an activated phosphor suspension (see 9Ql 1) containing 0.56% by weight of total UV light absorber (B) 'k sufficient carbon to produce an optical density of 8.0 or higher. was coated onto a polyethylene terephthalate film support (one opaque) containing the following. This simulates the application of an absorbent underlayer (as opposed to a reflective underlayer in the previous example). When this screen was used to expose a high speed X-ray film as taught in Example 1, the following results were obtained.

Control 1.00 10.4
0.014 Invention 0.65 10.4
[1,012 Example 5 Three screens were manufactured with the following constructions to compare prior art screens and screens manufactured according to the teachings of the present invention.

Support (1) - Same as Example 1 Reflective layer (2) - Same as Example 1 Phosphor layer (3) - Same as Example 1, but with different coating weights and additives (see table below) Overcoat Layer (4) - In the same screen I as in Example 1, the phosphor layer was coated at a thickness of 0.022 inches and the beam absorber (B) was coated at a thickness of 0.022 inches.
52 kg was added to the phosphor. Screen ■ contained no additives and was coated in a 0.012 inch layer. Screen M is a monoazo dye Solvent Yellow 6 dye (C process A,
11160:1) was contained in 1.7 ml of a 1-ti solution. Results were obtained when these screens were used to expose high speed medical X-ray film samples as described in Example 1.

■0 Invention 22 0.93 9.3 0.0
11H0 No dye 12 0.93 1[1,
40,015II1. 1.7+++/plow inspection armpit 22
0.79 11.1 0.013 When coated with a thinner coating weight than the screen of the present invention, the dye-loaded screen (prior art element) had slightly sharper resolution but only about 40 The ax was expensive. When dye was added to a screen of comparable thickness, the screen was about 20% higher in mottling. Thus, screens incorporating the present invention greatly improve the signal/mottle ratio and thereby produce an overall improved image of the exposed x-ray film.

Example 6 CaWO4 is an example of a broadband emissive phosphor that is outside the scope of this invention. Six screens were manufactured using the following configuration.

The support (1) and the reflective layer (2) were the same as described in Example 1. The phosphor layer (3) is La0Br i of Example 1.
It contained Cawoak at the base of Tm. The oat sea coat layer (4) was the same as Example 1 except for the UV absorber.

Screen I contained no quaternary absorbent. Screen ■ contained 0.52% by weight of ■ light absorber) and Screen ■ contained 0.52% by weight of UV light absorber (based on original cellulose acetate).

Using all of these screens, the high-speed medical X taught in Example 1
A line film was exposed. The following results u, UV absorber (B
) 0.45 B, 6 0.008111
, UV absorber (AID, 51 B, 2 0. [
]08 These results show that, compared to Example 1, for example, there was no effect on the overall image quality when a UV light absorber was used in conjunction with a broadband emitting phosphor.

Example 7 Ba(Pb)804 (other broadband emitting phosphors)
Example 6 was repeated nine times by substituting . The following results were obtained.

l, without UV absorber 0.33 9.1
0.00911, UV absorber (B) 0.22
9.1 [1,009■, UV absorber (A)
0.21 9.0 0.008 Again, the UV light absorber did not significantly improve the image quality of the screen-exposed film with the broadband emitting Ba(Pb) 804 phosphor.

Example 8 In order to further test the effectiveness of UV light absorbers in other phosphor systems, Y(
Nb) T8.04 (narrow bunt light emitter) 16 units are used, and overcoat! (4) Middle KO, 521
A screen was manufactured using a known UV light absorber (B). The following results were obtained.

[, TJV absorbent included 0.57 9.1
[1,009 Image quality improvement was observed here.

example ? Still other phosphors with narrow emission bands are LoOC
It is A'Bi. A two-bridge screen with this phosphor was made according to the teachings of Example 1. Screen ■ was manufactured without a UV light absorber, while screen ■ contained 0.521 g of a quaternary absorber in the overcoat layer. This screen was exposed to high speed medical x&91 film. I used it and got the following results.

1. No UV absorber 0.90 10.8
0. []17n, UV absorber (B) 0.
71 12.2 [1,013 Examples 10 BaFCl as phosphor: Eu (narrow band emitter) was used and in the overcoat layer [UV light absorber (
Example 9 was repeated using B) in an amount of 1.04 m. The following results were observed.

n, UV absorber used 0.73 8.7
0.011 An improvement in image quality was observed here.

Example 11 Example 10 was repeated using La0Br:Tb (line phosphor) as the phosphor and UV light absorber (B) in the overcoat layer in a total amount of 0.52B.

The following results were observed.

n, using UV absorber 1.21 8.0
0.011 An improvement in image quality was observed here.

Claims (1)

Claims: 1) sequentially comprising (1) a support, an active layer comprising a phosphor exhibiting narrow or line band emission dispersed in a binder, and (6) an overcoat layer. and wherein layer (2) or (3) contains a small amount of a non-fluorescent ultraviolet (UV) light absorber having an absorption maximum below 400 nm. 2) The UV light absorber is 2-(2'-hydroxy-3'+
5'-Dialkylphenyl)benzotriazole, 2+
An X-ray intensifying screen according to claim 1, which is from the group consisting of 2'-dihydroxy-5-alkoxy-benzophenones and oxalic acid anilide derivatives. 5) The X-ray intensifying screen according to claim 1, wherein the phosphor is IaOBr:Tm. 4)! The X-ray intensifying screen according to claim 1, wherein the mixture is folivinyl butyral. 5) An X-ray intensifying screen according to claim 1, wherein the lower layer is inserted between the support (1) and the active layer (2). 6) An X-ray intensifying screen according to claim 1, wherein the support contains or is coated with an opacifying dye, a reflective dye or a finely divided pigment. 7) The X-ray intensifying screen according to claim 5, wherein the lower layer contains a small amount of a non-fluorescent stone absorber having an absorption maximum below 400 nm. 8) Sequentially (1) a film-forming polyester support, (2) an underlayer comprising 'rjoz dispersed in chlorosulfonated polyethylene, (3) a La0Br dispersed in z IJ vinyl butyral: (4) an overcoat consisting essentially of a fluoroacrylate polymer;
improved X-rays, characterized in that layer (2), (3) or (4) contains a small amount of a non-fluorescent IUV light absorber with an absorption maximum below 400 nm. intensifying screen.