JP2001324598A - Storage phosphor screen having thick outermost layer, and using method therefof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recording and reproducing an image produced by transmitting a radiation having high resolution, in particular in a relatively high frequency, and to provide a storage phosphor screen used in the method. SOLUTION: This photostimulable phosphor screen contains a photostimulable phosphor and the transparent outermost layer having a thickness d larger than 150 μm, and this method is a method for reading the radiation image preserved in the photostimulable storage phosphor screen having the thick transparent outermost layer for reading stimulated light through the outermost layer by stimulating the screen through the outermost layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a storage phosphor screen and a method for recording and reproducing X-ray images by use thereof.

[0002]

BACKGROUND OF THE INVENTION A known use of storage phosphors is in the formation of X-ray images. U.S. Pat. No. 3,859,527 discloses a method for forming an X-ray image using a photostimulable phosphor introduced into a panel. The panel is exposed to a pattern of conditioned incident x-ray light and the resulting phosphor temporarily stores the energy contained within the x-ray emission pattern. At some interval after exposure, visible or infrared light scans the panel to stimulate the emission of stored energy as light, which is detected and sequentially converted to electrical signals, which are processed. A visible image can be formed. For this purpose, the phosphor must preserve as much incident X-ray energy as possible and emit as little stored energy as possible before being stimulated by the scanning beam. This is called "digital radiography" or "computerized radiography"("computed
radiography ").

[0003] With any radiographic system that uses a phosphor screen, and thus also in a digital radiographic system, the quality of the image formed is highly dependent on the structure of the phosphor screen.

Several methods and / or means have been proposed for providing storage phosphor screens that combine high speed with high resolution and low noise-and / or methods of using them. For example, US-A-4 585
At 944, on each side of the screen where the stimulating lines enter the screen, the product of the average thickness (d _av ) and the refractive index of the layers for each layer present is 1.14 of the wavelength of the stimulating lines. It is disclosed to provide a storage phosphor screen carrying one or more layers having a d _av of greater than 05 times. The disclosure shows that the thickness of the adhesive layer should also satisfy the above conditions, especially if the transparent protective layer is adhered to the phosphor layer by an adhesive layer. .

For example, EP-A-233 497 includes:
A radiation image storage panel comprising a phosphor layer containing a stimulable phosphor, wherein one surface of the phosphor layer has a stimulus wavelength of the stimulable phosphor and a zero.
A multilayer optical filter having a transmittance of no less than 70% for light at an angle of incidence in the range of ５5 degrees and having a reflectance of no less than 60% for the stimulus wavelength and light at an angle of incidence no less than 30 degrees. A panel characterized by being equipped is disclosed.

[0006] EP-A-440 853 discloses a fluorescent storage screen for storing an X-ray latent image which is read by stimulation with radiation that provides a stimulus having a first wavelength, wherein the storage screen comprises a first storage screen. A stimulable phosphor whose X-ray image, which is responsive to the radiation of wavelength, is potentially stored and emits radiation of a second wavelength, and reflection of the radiation having at least the first wavelength. A screen comprising at least one optical layer coating the surface of the stimulable phosphor layer which is highly transmissive for the radiation having at least the first wavelength. It has been disclosed.

[0007] US-A-5 877 508 discloses a radiation image storage panel comprising a substrate and a stimulable phosphor layer, which is overlaid on a substrate of material, It transmits light emitted by the stimulable phosphor layer and absorbs and / or absorbs light having a wavelength that falls within the stimulation wavelength range for the stimulable phosphor layer.
Or a panel for diffusing is disclosed. The stimulus lines are shown to impinge on the screen on the opposite side of the surface and the emitted light is captured on its side, where the stimulating lines impinge on the opposite side of the first side. It does not interfere with the reading of the stimulated light on that side of the screen, because light having a wavelength falling within the stimulating wavelength range is thus prevented from passing or propagating through the substrate, and thereby preserves the radiation image The signal-to-noise ratio of the image signal detected from the panel is prevented from being lowered.

In EP-A-021 174, the carrier, the phosphor layer or the protective layer, if at least one of them comprises a colorant absorbing the stimulating light, And that the sharpness of the image formed by the storage phosphor screen comprising the protective film can be enhanced.

[0009] EP-A-158 862 discloses a phosphor screen when the protective layer is adhered to the phosphor layer by an adhesive layer containing a colorant absorbing the stimulating light. It has been disclosed that the sharpness of the can be further enhanced.

While the use of storage phosphor screens in accordance with these disclosures does offer the possibility of producing sharp X-ray images, there remains a need in X-ray imaging to further enhance image sharpness. I do.

[0011]

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of recording and reproducing images produced by transmitting high resolution radiation, especially at relatively high frequencies.

Another object of the present invention is to provide a storage phosphor screen for use in a method for recording and reproducing images produced by transmitting radiation having a high resolution, especially at relatively high frequencies. It is to provide.

It is an object of the present invention to:-stimulate a photostimulable phosphor screen to emit stimulated light; and-collect the stimulated light. Photostimulable storage phosphor. Reading a radiation image stored in a screen, wherein the phosphor screen has a transparent outermost layer having a thickness, d, greater than 150 μm; and the stimulating and collecting This is achieved by providing a method characterized in that both are performed through the transparent outermost layer.

Another object of the invention is achieved by providing a stimulable phosphor screen having a transparent outermost layer having a thickness, d, greater than 150 μm.

[0015] Preferably, the thickness of the outermost layer is 150 <
It is such that d < 4000 μm.

[0016] More preferably, the outermost layer comprises a colorant that absorbs stimulating light.

[0017] Other advantages and embodiments of the present invention will become apparent from the following description.

[0018]

DETAILED DESCRIPTION OF THE INVENTION As used herein, the term "penetrating radiation" refers to ia radiation generated from a radioisotope (eg, a Co60 source), generated by any type of x-ray generator. Radiation, high-energy radiation generators (eg, Betatron) and high-energy particles, such as radiation from samples labeled with radioisotopes, such as in autoradiography. Used to do things.

The sharpness of the image produced by stimulating the screen in a storage phosphor screen to absorb the transmitted radiation imagewise and to release the stored energy is particularly high at relatively high spatial frequencies. (Ie>
Where the stimulation of the energy stored in the storage screen and the reading of the stimulated light take place through a thick outermost layer, ie a transparent layer having a thickness, d, greater than 150 μm. It has been found that it can be enhanced in this time. Preferably, the thickness is such that 150 μm <d < 4000 μm. More preferably, the thick outermost layer is 150 μm
<D < 2500 μm.
Even when the stimulation of the stored energy and the reading of the amount of stimulated light are performed through a thick (180 μm thick) non-colored layer, an advantageous effect on the sharpness in the region of relatively high frequencies is seen. If the square wave response is higher than the spatial frequency of 4 lp / mm, pass through the thick layer at frequencies below 4 lp / mm when compared to stimulation and reading through a thin (10 μm thick) uncolored transparent layer. Square wave response during stimulation and reading is lower.

[0020] Preferably, the thick outermost layer through which the stimulation of the energy stored in the screen and the reading of the stimulated light takes place is a colorant which selectively absorbs the stimulating light (ie, the stimulated light). (A colorant that does not absorb light or absorbs very little). In the method of the present invention, especially when the color of the thick outermost layer through which the screen is stimulated is adjusted such that there is an absorption of light that gives the same stimulus as the colored thinner (10 μm) outermost layer, When examining parts in the image having a spatial frequency higher than mm, the dose of transmitted radiation required to form the image remains the same, but the sharpness of the final image is higher. This means that the method can be stimulated and read by EP-A-0217.
The same was true when compared to the method performed through a lightly colored protective layer as described in No. 4. If the stimulation of the energy stored in the screen and the reading of the stimulated light take place through the thick outermost layer, the SWR (square wave response) at low frequencies will cause the stimulation and reading to be as described in EP-A-021 174. The degree of coloration could be selected to be as high as when performed through the thin colored protective layer described, and at higher frequencies the SWR was relatively high. When using a screen with a thick outermost layer that selectively absorbs the stimulating light, the intensity of the light used to stimulate the screen, adapts the stimulating light intensity to the absorbance with respect to the speed of the system Advantageously. If laser light having a wavelength greater than 510 nm is used to stimulate the screen in the method according to the invention, the thick outermost layer in the screen for use in the invention should be at least 65% in the region where it is smaller than 480 nm. A very good compromise between speed and increase in sharpness when colored to show a transmittance spectrum with a transmittance of at most 65% in the region above 510 nm Was found. In systems where the use of relatively high laser power to stimulate the screen does not limit the feasibility of the method, coloring the outermost layer to show at most 35% transmission in the region where it is greater than 510 nm Can be.

As the coloring agent, either an organic coloring agent or an inorganic coloring agent can be used for coloring the thick outermost layer used in the present invention. Mixtures of colorants can also be used. By simple trial and error, it is possible to produce a colored, thick outermost layer that meets the spectral conditions indicated immediately above. For example, organic colorants having a solid color ranging from blue to green that can be used in the radiation image storage panel of the present invention include Zapon Fast.
Blue 3G (ZAPON FAST BLUE 3G) (Hoechst)
AG), Estrol Brill Blue N-
3RL (ESTROL BRILL BLUE N-3RL) (manufactured by Sumitomo Chemical Co., Ltd.), Sumiacryl Blue F-GSL (SUMIA
CRYL BLUE F-GSL) (manufactured by Sumitomo Chemical Co., Ltd.), D
・ D & C BLUE NO.1 (National Aniline Company Limited)
Aniline Co., Ltd.)), Spirit Blue
(SPIRIT BLUE) (manufactured by Hodogaya Chemical Co., Ltd.),
Oil Blue No. 603 (Oil Blue No. 603) (manufactured by Orient Company Limited), Kiton Blue A (Ciba Geigy)
igy) produced by AG), Eisen Katilon Blue G
LH (AIZEN CATHILON BLUE GLH) (manufactured by Hodogaya Chemical Co., Ltd.), Lake Blue AFH (LAKE BLUE
AFH) (manufactured by Kyowa Sangyo Co., Ltd.), RODALIN BLUE 6GX (manufactured by Kyowa Sangyo Co., Ltd.), PRIMOCYANINE 6GX (PRIMOCYANINE 6GX)
(Manufactured by Inahata Sangyo Co., Ltd.)
Green 6BH (BRILLACID GREEN 6BH) (manufactured by Hodogaya Chemical Co., Ltd.), cyanine blue BNRS (C
YANINE BLUE BNRS) (manufactured by Tokyo Ink Co., Ltd.) and LINOL BLUE SL (manufactured by Tokyo Ink Co., Ltd.). For example, inorganic colorants having a solid color in the blue to green range that can be used in the radiation image storage panel of the present invention include ultramarine blue, cobalt blue, cerulean blue, chromium oxide, TiO ₂ -ZnO. -Co
O-NiO pigments and the like are included.

[0022] Blue colored plastic films, such as those used as carriers for medical X-ray films, are also very well suited as outermost layers of the storage phosphor screen used in the method of the present invention. .

In a preferred embodiment of the invention, the thick outermost layer of the storage phosphor screen used in the invention is, for example, a Schott filter BG24a.
(Product name), Shot filter BG26 (Product name)
And an optical blue filter.

[0024] The thick outermost layer of the screen for use in the method of the present invention may advantageously be selected to have a refractive index equal to or greater than the refractive index of the phosphor layer.

The storage phosphor (also referred to as photostimulable phosphor) added into the screen having a thick outermost layer for use in the method of the present invention may be any storage phosphor known in the art. Can be phosphor. It is of the formula: (Ba _1-x M ^II _x ) FX: yA [where M ^II is M
g, one or more of Ca, Sr, Zn and Cd, X is one or more of Br, Cl or I, A is Eu, Tb, Ce, Tm, Dy, P
at least one member of the group consisting of r, Ho, Nd, Yb and Er, and x is in the range of 0 < x < 0.6 and y is in the range of 0 < y < 0.2] And the wavelength of the stimulating line can be 50 or less.
Not less than 0 nm.

Any stimulable phosphor of alkaline earth metal fluorohalide is useful in the present invention. Representative examples of such stimulable phosphors are set forth below, but barium fluorohalides useful in the present invention are not limited to these examples.

EP-A 345 903 includes the formula Ba _1-x
Sr _x F _2-ab Br _a X _b : zA wherein X is Cl and I
At least one member selected from the group consisting of: x is in the range of 0.10 < x < 0.55, and a is 0.70 <
a < 0.96, b is in the range of 0 < b < 0.15, z is in the range of 10 ⁻⁷ <z < 0.15, and A is Eu ²⁺ , Or Eu ³⁺ , Y, Tb, C
e, Tm, Dy, Pr, Ho, Nd, Yb, Er, L
Eu in combination with one or more co-dopants selected from the group consisting of a, Gd and Lu
²⁺ , and wherein fluorine is stoichiometrically present in the phosphor at more atomic percent than bromine alone or bromine combined with chlorine and / or iodine]. An optical body is disclosed.

US Pat. No. 4,261,854 includes the formula BaFX:
xCe, yA where 0 <x < 2 · 10 ⁻¹ and 0 < y <
Phosphor is disclosed having a 5.10 ^-3.

In US Pat. No. 4,336,154, the formula (Ba _1-x
M ²⁺ _x ) F ₂ .aBaX ₂ : yEuzB [wherein 0.5 < a <
1.25, 0 < x < 1, 10 ^-6 < y < 2.10 ^-1 , 0 <z
< 2 · 10 ⁻¹ ] is disclosed.

EP-A 704 511 includes the formula Ba
_{1-xy "-zr Sr x Pb} y" Cs 2 rEuzF 2-ab Br a I
_b [where 0 < x < 0.30, 10 ^-4 <y ″ <10 ^-3 , 1
^{0 -7 <z <0.15,0 <r} <0.05,0.75 <a +
A stimulable barium fluorohalide having b < 1.00, 0.05 <b <0.20] is disclosed.

EP-A-835 920 includes the formula Ba
_1-xyp-3q-z Sr _x M ²⁺ _y M ¹⁺ _2p M ³⁺ _2q F _2-ab Br
_a I _b : _z Eu [where M ¹⁺ is at least one alkali metal selected from the group consisting of Li, Na, K, Rb and Cs, and M ²⁺ is composed of Ca, Mg and Pb At least one divalent metal selected from the group
³⁺ is Al, Ga, In, Tl, Sb, Bi, Y, La,
Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, E
at least one trivalent metal selected from the group consisting of r, Tm, Yb and Lu, wherein 0 < x < 0.30, 0
<Y <0.10,0 <p <0.3,0 <q <0.1,0.0
5 < a < 0.76, 0.20 < b < 0.90, a + b <1.
Stimulable phosphors having 00 and 10 ⁻⁶ < z < 0.2 are disclosed.

Not only barium fluorohalide-preserved phosphors but also, for example, EP-A-304 121, EP
Halosilicate phosphors as disclosed in -A-382 295 and EP-A-522 619 can also be used in the present invention.

In screens having a thick outermost layer for use in the method of the present invention, an alkali metal halide phosphor can also be added. Such phosphors are disclosed, for example, in US Pat. No. 5,736,069, in which the formula: M ¹⁺ X. _a M ²⁺ X ′ ₂ BM
³⁺ X ″ ₃ : cZ [wherein M ¹⁺ is Li, Na, K, Cs
And is at least one member selected from the group consisting of Rb, M ²⁺ is Be, Mg, Ca, Sr, Ba, Zn, C
d, at least one member selected from the group consisting of Cu, Pb and Ni, and M ³⁺ is Sc, Y, La, Ce, P
r, Nd, Pm, Sm, Eu, Gd, Tb, Dy, H
at least one member selected from the group consisting of o, Er, Tm, Yb, Lu, Al, Bi, In and Ga;
Z is at least one member selected from the group Ga ¹⁺ , Ge ²⁺ , Sn ²⁺ , Sb ³⁺ and As ³⁺ , X, X ′ and X ″ can be the same or different and each Represents a halogen atom selected from the group consisting of F, Br, Cl and I, and 0 < a < 1, 0 < b < 1 and 0 <
c < 0.2] is disclosed.

A storage phosphor screen having a thick outermost layer is coated on a carrier to form a storage phosphor layer loaded with a dispersion of the storage phosphor in a binder resin and then coated. The thick outermost layer can be prepared by applying an adhesive to the top of this phosphor layer. In this case, any carrier known in the art can be used, including polymeric carriers, plain papers, processed papers such as photographic papers, coated papers, art papers, barita papers, resin-coated papers, It can be sized paper, cardboard, metal, etc. as described in Belgian Patent No. 784,615. It is preferable to use a polymeric carrier such as a cellulose acetate film, a polyester film, a polyethylene terephthalate ethylene film, a polyamide film, a polyimide film, a triacetate film, and a polycarbonate film. It can be a black carrier, which can be a reflective carrier, for example, a polyester incorporating one or more white pigments.

Preservative Phosphor Binders A preservative phosphor screen having a thick transparent outermost layer is prepared by coating the dispersion in resin directly onto the thicker transparent outermost layer and the phosphor is prepared. It is also possible to coat the layer with a protective layer, which may be thin. In this case, the protective layer is preferably, for example, EP-A-510 753 and EP-A-
UV or E as disclosed in US Pat.
B is a protective layer cured by B.

The storage phosphor screen having a thick transparent outermost layer can also be a binderless screen in which the phosphor is deposited, for example, by vacuum evaporation.

The method of the present invention is particularly useful for recording and reproducing X-ray images, where it is most important that details having high frequencies, ie very fine details, can also be detected. Therefore, the method of the present invention is particularly useful in mammography and non-destructive inspection of materials. In the former test it is most important to detect very small calcifications, and in the latter test fine cracks as small as hair must be recorded and reproduced.

[0038]

EXAMPLES Screen Screen Comparative Example 1 (CE1) The storage phosphor screen used here is Ba _0.83
Sr _0.17 FBr: Eu phosphor (US-A-551
4 See Example 1 of 298) in a binder solution containing polyethyl acrylate dissolved in ethyl acetate.
The dispersion was dispersed to have a pigment / binder ratio of 7/3 weight / weight and the dispersion was coated on a 100 μm thick black sheet of poly (ethylene polytetraphthalate).
Manufactured by giving a coating weight of 0 g / m ² . The top of the phosphor layer of this screen has a 1% absorption with 0% absorption for light having a wavelength of 678 nm.
An unpigmented transparent protective layer of 0 μm was applied. Comparative Example 2 (CE2) The storage phosphor screen of Comparative Example 1 was used, except for the presence of a 10 μm thick protective layer containing a dye and having an absorption of 27.9% for light having a wavelength of 678 nm. . Comparative Example 3 (CE3) This example is identical to Comparative Example 1, except for the amount of phosphor on this screen which was now 450 g / m ² . Invention Example 1 (IE1) A shot blue-green filter BG24a having an absorption of 30.1% for light having a wavelength of 678 nm 12
The storage phosphor screen of Comparative Example 1 was used, except for the presence of a 50 μm thick protective layer. Invention Example 2 (IE2) Shot blue-green filter BG26 with an absorption of 33.4% for light having a wavelength of 678 nm 100
The storage phosphor screen of Comparative Example 1 was used except for the presence of a 0 μm thick protective layer. Invention Example 3 (IE3) PET colored with MACROLEX BLUE (trade name Bayer, Leverkusen, Germany) having an absorption of 16.7% for light having a wavelength of 678 nm The storage phosphor screen of Comparative Example 1 was used except for the presence of a 180 μm thick protective layer which was a film. Invention Example 4 (IE4) Using the storage phosphor screen of Comparative Example 1, except for the presence of a 180 μm thick protective layer which is a transparent PET film having 0% absorption for light having a wavelength of 678 nm. did. The amount of phosphor on this screen is 450
g / m ² . Imaging Example 1 Exposure to X-Ray Five screens (CE1, CE2, E1, E2 and E3) were subjected to an empty frequency of 0.2 for 64 seconds with no filtering on X-rays with 50 kVp without filtering.
Exposure was performed using a Funk raster with 5, 0.5, 1, 2, 3, 4, and 5 lp / mm. Image reading The storage phosphor screen was stimulated with a diode laser emitting 678 nm light. Laser output is 16.5m
W, the full width at half maximum (FWHM) of the laser spot is 40 μm, and the emitted light is a square pixel with a side of 5 μm.
The reading was 6.5 μm. The read time per pixel was adjusted to have a 66% read depth for each screen. An optical amplifier (PM) having a system gain factor of 7.4 (ie, the ratio of photons falling on a PMT cathode to the incident X-rays) and a swank factor of 0.588 (ie, Poisson excess noise factor)
Read using T). Both stimulation and reading were performed through the protective layer. Measurements The square wave response (SWR) of the image of the funk raster on each screen was measured, assuming the square wave response of the CE1 screen at 0.025 lp / mm as 1.00.

Table 1 shows the results.

[0040]

[Table 1]

For each of the images, the detection effect (DQE)
A simplified equation for calculating the DQE of a CR (computer radiography) system published by Lubinsky et al. SPIE Vol. 767 (1987) p; 167:

[0042]

(Equation 1)

[0043] wherein a alpha = X-ray absorption, in excess noise due epsilon / m = Poisson excess noise = optical depth defects, a G = gain factor = g.η _scan, g each absorption Is the average number of electrons stored for a given X-ray photon and η _scan is the DQE of the scanning step, MTF _(f)
Is the MTF of the system calculated from the SWR].

The results are shown in Table 2.

[0045]

[Table 2]

Imaging Example 2 Exposure to X-Ray Two screens (CE3 and E4) were filtered using a molybdenum tube with 30 μm molybdenum and 40 mm plexiglass windows to X-rays with 26 kVp without filtering. , Empty frequencies 0.25, 0.2
Exposure was performed using a funk raster with 5, 1, 2, 3, 4, and 5 lp / mm. Image reading The storage phosphor screen was stimulated with a diode laser emitting 678 nm light. Laser output is 16.5m
W, the full width at half maximum (FWHM) of the laser spot is 40 μm, and the emitted light is a square pixel with a side of 5 μm.
The reading was 6.5 μm. The read time per pixel was adjusted to have a 66% read depth for each screen. An optical amplifier (PMT) having a system gain factor of 2.3 (ie, the ratio of photons falling on the PMT cathode to incident X-rays) and a swank factor of 0.7 (ie, Poisson excess noise factor). Was read using. Both stimulation and reading were performed through the protective layer. Measurements The square wave response (SWR) of the image of the funk raster on each screen was measured, assuming the square wave response of the CE1 screen at 0.025 lp / mm as 1.00.

Table 3 shows the results.

[0048]

[Table 3]

For each of the images, the detection effect (DQE)
Was calculated as described above using a simplified formula for calculating the DQE of a CR (Computerized Radiography) system.

Table 4 shows the results.

[0051]

[Table 4]

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Peter Willems Belgium Bee 2640 Malt Cell Septes Trat 27 Agfa-Gevuert Na Mrose Fennoutjap

Claims (9)

[Claims] 1. Stimulating a photostimulable phosphor screen to emit stimulated light, and collecting the stimulated light stored in a photostimulable storage phosphor screen. Reading the applied radiation image, wherein the phosphor screen has a transparent outermost layer having a thickness, d, greater than 150 μm, and both the stimulating and the collecting are performed. The method is performed through the transparent outermost layer. 2. The thickness, d, is 150 μm <d < 400.
2. The method of claim 1 wherein the method is such that 0 .mu.m. 3. The transparent outermost layer is colored with a colorant which selectively absorbs stimulating radiation.
The method described in. 4. The method according to claim 1, wherein said stimulating is carried out using light having a wavelength greater than 600 nm and said thick outermost layer is a blue filter. 5. A photostimulable phosphor and 150.
A photostimulable phosphor screen comprising a transparent outermost layer having a thickness, d, greater than μm. 6. The thickness, d, is 150 μm <d < 400.
The stimulable phosphor screen of claim 5, wherein the screen is such that it is 0 µm. 7. The transparent outermost layer is colored with a colorant which selectively absorbs stimulating radiation.
A phosphor screen that can be stimulated according to claim 1. 8. The stimulable phosphor according to claim 5, wherein said stimulating is carried out using light having a wavelength of more than 600 nm and said thick outermost layer is a blue filter. screen. 9. The stimulable phosphor screen according to claim 5, wherein said screen further comprises a carrier.