JP2010060414A - Scintillator plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scintillator plate with a scintillator layer which is excellent in sharpness and adhesiveness to its substrate. <P>SOLUTION: In the scintillator plate with the scintillator layer consisting of deposition crystals on a substrate, the average roughness (Ra) of the central line on the contact surface of the substrate contacting the scintillator layer is 0.001≤Ra≤0.1 μm and the maximum roughness (Rt) of the contacting surface and the average roughness (Ra) have a relation of 5≤Rt/Ra≤150. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a scintillator plate used when a radiographic image of a subject is formed.

  Conventionally, radiographic images such as X-ray images have been widely used for diagnosis of medical conditions in the medical field. In particular, radiographic images using intensifying screen-film systems have been developed as an imaging system that combines high reliability and excellent cost performance as a result of high sensitivity and high image quality in the long history. Used in the medical field.

  However, these pieces of image information are so-called analog image information, and free image processing and instantaneous electric transmission cannot be performed like the digital image information that has been developed in recent years.

  In recent years, digital radiographic image detection apparatuses represented by computed radiography (CR), flat panel type radiation detectors (FPD) and the like have appeared. In these, since a digital radiographic image can be directly obtained and an image can be directly displayed on an image display device such as a cathode ray tube or a liquid crystal panel, image formation on a photographic film is not necessarily required. As a result, these digital X-ray image detection devices reduce the need for image formation by the silver halide photography method, and greatly improve the convenience of diagnosis work in hospitals and clinics.

  Computed radiography (CR) is currently accepted in the medical field as one of the digital technologies for X-ray images. However, the image quality level of the screen / film system has not been reached due to insufficient sharpness and insufficient spatial resolution. Further, as new digital X-ray imaging techniques, for example, the magazine Physics Today, November 1997, page 24, John Laurans' paper “Amorphous Semiconductor User in Digital X-ray Imaging”, magazine SPIE Vol. 32, 1997. A flat-plate X-ray detector using a thin film transistor (TFT) described in a paper by El Antonuk on “Development of a High Resolution, Active Matrix, Flat-Panel Imager with Enhanced Fill Factor”, etc. Has been developed.

  The flat panel X-ray detector (FPD) is characterized in that the device is smaller than the CR and the image quality at a high dose is excellent. However, on the other hand, due to the electrical noise of the TFT and the circuit itself, the signal-to-noise ratio has been reduced in low-dose imaging, and the image quality level has not been reached.

  A scintillator plate made of an X-ray phosphor having the property of emitting light by radiation is used to convert the radiation into visible light. However, in order to improve the S / N ratio in low-dose imaging, the light emission efficiency is high. It will be necessary to use scintillator plates. In general, the light emission efficiency of the scintillator plate is determined by the thickness of the phosphor layer and the X-ray absorption coefficient of the phosphor. The thicker the phosphor layer, the more scattered the emitted light in the phosphor layer. Occurs and sharpness decreases. Therefore, when the sharpness necessary for the image quality is determined, the film thickness is determined.

  Among them, cesium iodide (CsI) has a relatively high rate of change from X-rays to visible light, and phosphors can be easily formed into a columnar crystal structure by vapor deposition. And the thickness of the phosphor layer could be increased (see Patent Document 1).

  In addition, it is known that cesium iodide contains an element called an activator such as thallium, sodium, or rubidium in order to improve luminous efficiency.

The above scintillator is manufactured by vapor deposition, but it is known that the surface of the base material is roughened or the surface is roughened by plasma treatment or the like in order to improve the adhesion between the base material and the scintillator. ing. However, this method has a problem of poor crystallinity and insufficient sharpness. Moreover, the technique which improves adhesiveness and corrosivity is disclosed by using an aluminum support body and making surface roughness Ra of an anodized layer 0.01-0.3 micrometer (refer patent document 2).
JP-A-63-215987 JP 2007-292755 A

  However, even if the above-described conventional technique is used, it has been difficult to realize a scintillator plate that forms columnar crystals with good crystallinity and at the same time has excellent adhesion to a substrate.

  An object of the present invention is to provide a scintillator plate that has a scintillator layer that has excellent adhesion to a substrate and that has excellent sharpness.

The above object of the present invention can be achieved by the following constitution.
1. In a scintillator plate having a scintillator layer made of vapor-deposited crystals on a substrate, the center line average roughness (Ra) of the contact surface of the substrate that contacts the scintillator layer is 0.001 ≦ Ra ≦ 0.1 μm A scintillator plate, wherein the contact surface has a maximum roughness (Rt) and Ra has a relationship of 5 ≦ Rt / Ra ≦ 150.
2. 2. The scintillator plate according to 1, wherein the deposited crystal is a columnar crystal.
3. The scintillator plate according to 1 or 2, wherein the deposited crystal contains cesium iodide and an activator.

  By the above means of the present invention, a columnar crystal having better crystallinity than before can be obtained, and a high-performance scintillator plate having a scintillator layer having excellent sharpness and excellent adhesion to a substrate can be provided.

  In the scintillator plate having a scintillator layer made of vapor-deposited crystals on a base material, the present invention has a center line average roughness (Ra) of a contact surface of the base material in contact with the scintillator layer of 0.001 ≦ Ra ≦ 0. The maximum roughness (Rt) of the contact surface and the Ra have a relationship of 5 ≦ Rt / Ra ≦ 150.

  In the present invention, in particular, by having a specific relationship between the center line roughness Ra of the surface of the substrate and the maximum roughness Rt, high performance with excellent sharpness and excellent adhesion to the substrate. Scintillator plates are obtained.

  In the present invention, the center line average roughness (Ra) of the contact surface of the substrate that contacts the scintillator layer is 0.001 ≦ Ra ≦ 0.1 μm, and the maximum roughness (Rt) of the contact surface. And the Ra has a relationship of 5 ≦ Rt / Ra ≦ 150.

  The contact surface of the substrate that contacts the scintillator layer is a surface on which the deposited crystal according to the present invention is deposited.

  The center line average roughness Ra of the contact surface is required to be 0.001 to 0.1 μm, and particularly preferably 0.005 to 0.05 μm.

  If Ra is less than 0.001 μm, the adhesiveness is insufficient, and if Ra exceeds 0.1 μm, the crystallinity of the columnar crystals deteriorates and the sharpness becomes insufficient.

  Further, within the range of Ra, in the present invention, it is necessary that Ra and the maximum roughness (Rt) have a relationship of 5 ≦ Rt / Ra ≦ 150, and in particular 10 ≦ Rt / Ra ≦ 100. Preferably there is.

  When Rt / Ra is less than 5, the adhesiveness is insufficient, and when Rt / Ra exceeds 150, the crystallinity of the columnar crystal is deteriorated and the sharpness is insufficient.

  The maximum roughness (Rt) and centerline average roughness (Ra) in the present invention are defined by the following JIS surface roughness (B0601). The maximum roughness (Rt) is the roughness curve extracted by the reference length L, and when the extracted part is sandwiched between two straight lines parallel to the center line, the distance between the two straight lines is measured in the direction of the vertical magnification of the roughness curve. Then, this value is expressed in micrometers (μm). The centerline average roughness (Ra) is a portion of the measured length L extracted from the roughness curve in the direction of the centerline, the centerline of this extracted portion is the X axis, the direction of the vertical magnification is the Y axis, and the roughness curve Is represented by y = f (x), the value obtained by the following equation is expressed in micrometers (μm).

  As a method for measuring Rt and Ra, the humidity is adjusted for 24 hours under the condition that the measurement samples are not superimposed on each other in an environment of 25 ° C. and 65% RH, and then measured in the environment. The non-overlapping conditions shown here are, for example, a method of winding with the substrate edge portion raised, a method of stacking paper between the substrate and the substrate, a frame made of cardboard, etc. One of the methods to fix.

  Examples of the measuring apparatus that can be used include a RSTPLUS non-contact three-dimensional micro surface shape measuring system manufactured by WYKO.

  In order to set Rt and Ra of the contact surface in contact with the scintillator layer of the base material within the scope of the present invention, for example, a thin film surface layer containing two kinds of matting agents having different average particle diameters is formed on the surface of the base material. Applying a thin film containing two types of matting agents with different average particle diameters by adjusting the average particle size and addition amount of two types of matting agents, or manufacturing a support used as a substrate by a coextrusion method It can be easily adjusted by adjusting the average particle size and addition amount of the two kinds of matting agents, or by adjusting the processing method when performing the sandblasting treatment on the surface of the substrate on which the scintillator layer is formed. it can.

  In the present invention, it is preferable to use organic or inorganic powder as a matting agent in order to control the surface roughness.

As the powder used in the present invention, a powder having a Mohs hardness of 5 or more is preferably used. As the powder, a known inorganic powder or organic powder can be appropriately selected and used. Examples of the inorganic powder include titanium oxide, boron nitride, SnO ₂ , SiO ₂ , Cr ₂ O ₃ , α-Al ₂ O ₃ , α-Fe ₂ O ₃ , α-FeOOH, SiC, cerium oxide, corundum, artificial Examples thereof include diamond, garnet, garnet, mica, silica, silicon nitride, silicon carbide and the like.

  Examples of the organic powder include powders such as polymethyl methacrylate, polystyrene, and Teflon (registered trademark).

Among these, inorganic powders such as SiO ₂ , titanium oxide, barium sulfate, α-Al ₂ O ₃ , α-Fe ₂ O ₃ , α-FeOOH, Cr ₂ O ₃ , mica, etc. are preferable. SiO ₂ and α-Al ₂ O ₃ are preferable, and SiO ₂ is particularly preferable.

  The organic or inorganic powder preferably has an average particle size of 0.5 to 10 μm, more preferably 1.0 to 8.0 μm.

  Since the typical CsI scintillator shown below has very good crystallinity, a straight columnar structure is formed from a crystal nucleus to which vapor deposition vapor is attached. By setting the center line average roughness of the substrate to Ra ≦ 0.1 μm, a scintillator with good crystallinity can be formed from the root. When the surface is rougher than 0.1 μm, the crystallinity is disturbed and the crystal is fused at the root, which causes a reduction in sharpness.

(Base material)
The base material according to the present invention may have at least a substrate and may be provided with a reflective layer and an intermediate layer described below on the substrate, if necessary. The above-described method in which Ra and Rt of the contact surface according to the present invention are in the above ranges may be performed only on the substrate, or may be performed on a substrate provided with a reflective layer and an intermediate layer.

  That is, for example, when an intermediate layer is provided, a layer containing a matting agent is provided on the substrate before providing the intermediate layer, and then a method of providing the intermediate layer, or a layer containing the matting agent after providing the intermediate layer on the substrate. The method of providing can be taken.

(substrate)
The substrate is a plate-like film that can carry a scintillator layer, and can transmit 10% or more of radiation such as X-rays with respect to the incident dose.

  The substrate is preferably a flexible polymer film having a thickness of 50 to 500 μm. Examples thereof include polymer films (plastic films) such as cellulose acetate film, polyester film, polyethylene terephthalate film, polyamide film, polyimide film, triacetate film, polycarbonate film, and carbon fiber reinforced resin sheet.

Here, the “substrate having flexibility” means a substrate having an elastic modulus (E120) at 120 ° C. of 1000 to 6000 N / mm ² , and a polymer film containing polyimide or polyethylene naphthalate as the substrate. Is preferred.

  Note that the “elastic modulus” means the slope of the stress with respect to the strain amount in a region where the strain indicated by the standard line of the sample conforming to JIS-C2318 and the corresponding stress have a linear relationship using a tensile tester. Is what we asked for. This is a value called Young's modulus, and this Young's modulus is defined as elastic modulus.

Substrate used in the present invention, the elastic modulus at the 120 ° C. as described above (E120) is preferably a ^{1000N / mm 2 ~6000N / mm 2} . More preferably ^{1200N / mm 2 ~5000N / mm 2} .

Specifically, polyethylene naphthalate ^{(E120 = 4100N / mm 2)} , polyethylene terephthalate ^{(E120 = 1500N / mm 2)} , polybutylene naphthalate ^{(E120 = 1600N / mm 2)} , polycarbonate (E120 = 1700N / ^mm 2) , syndiotactic polystyrene ^{(E120 = 2200N / mm 2)} , polyetherimide ^{(E120 = 1900N / mm 2)} , polyarylate ^{(E120 = 1700N / mm 2)} , polysulfone ^{(E120 = 1800N / mm 2)} , polyethersulfone Examples thereof include a polymer film made of (E120 = 1700 N / mm ² ).

  These may be used singly or may be laminated or mixed. Among them, as a particularly preferable polymer film, a polymer film containing polyimide or polyethylene naphthalate is preferable as described above.

(Scintillator layer)
The scintillator layer according to the present invention is a layer containing a phosphor that emits fluorescence when irradiated with radiation, and is made of vapor-deposited crystals.

  The activator which concerns on this invention is an element which can raise luminous efficiency by containing in fluorescent substance. Examples of the activator include thallium, sodium, rubidium and the like, and thallium is particularly preferably used. In order to make it contain in cesium iodide, it can carry out by the method of heating the vapor deposition raw material containing a cesium iodide and a thallium compound, and vapor-depositing on the said base material, for example.

  The vapor-deposited crystal according to the present invention is a crystal formed by heating a vapor deposition source containing a phosphor matrix and a compound containing an activator and vapor-depositing it on a substrate.

  Moreover, as a density | concentration of the activator in vapor deposition crystal, the range of 0.001-50 mol% is preferable from the surface of luminous efficiency with respect to a fluorescent substance base material, and the range of 0.1-20 mol% is especially preferable. preferable. The deposited crystal is preferably a columnar crystal.

  In addition, it is preferable that the thickness of a scintillator layer (phosphor layer) is 100-800 micrometers, and it is more preferable that it is 120-700 micrometers from the point from which the characteristic of a brightness | luminance and sharpness is acquired with sufficient balance.

(Reflective layer)
In the present invention, a reflective layer may be provided between the substrate and the scintillator layer.

  The reflective layer is a layer that can reflect the electromagnetic wave radiated in the direction of the fluorescent substrate emitted from the scintillator layer.

  A metal thin film is preferably used as the reflective layer. As the metal thin film, a film made of a material containing a substance in the group consisting of Al, Ag, Cr, Cu, Ni, Ti, Mg, Rh, Pt and Au is preferably used. Further, two or more metal thin films may be formed such as forming an Au film on the Cr film.

  Among the above, the aspect using an aluminum-containing film is a preferable aspect as the reflective layer.

  The thickness of the reflective layer is preferably 0.005 to 0.3 μm, more preferably 0.01 to 0.2 μm, from the viewpoint of the emission light extraction efficiency.

(Middle layer)
In the present invention, an intermediate layer may be further provided between the reflective layer and the scintillator layer.

  Examples of the intermediate layer include polyester resins, polyacrylic acid copolymers, polyacrylamide or derivatives and partial hydrolysates thereof, vinyl polymers such as polyvinyl acetate, polyacrylonitrile, and polyacrylic acid esters, and copolymers thereof. And a layer containing a resin such as natural products such as rosin and shellac and derivatives thereof.

(Scintillator plate)
A scintillator plate according to the present invention will be described with reference to FIG.

  FIG. 1 is a cross-sectional view of an example of a scintillator plate according to the present invention.

  A scintillator plate 10 according to the present invention includes a scintillator layer 2 on a substrate 8 as shown in FIG. 1, and when the scintillator layer 2 is irradiated with radiation, the scintillator absorbs the energy of the incident radiation. Thus, an electromagnetic wave having a wavelength of 300 nm to 800 nm, that is, an electromagnetic wave (light) ranging from ultraviolet light to infrared light centering on visible light is emitted.

  The base material 8 has the reflective layer 4 and the intermediate layer 3 on the substrate 1.

  Hereinafter, a method for forming the scintillator layer 2 on the substrate 8 will be described.

The scintillator layer 2 is formed by a vapor deposition method. In the vapor deposition method, the substrate 8 is placed in a known vapor deposition apparatus, and after the raw material of the scintillator layer 2 containing, for example, a phosphor base material (for example, cesium iodide) and an activator is filled in the vapor deposition source, At the same time as evacuating, an inert gas such as nitrogen is introduced from the inlet to create a vacuum of about 1.333 Pa to 1.33 × 10 ⁻³ Pa, and then the raw material is heated by a method such as resistance heating or electron beam The scintillator layer 2 is formed on the base material 8 by evaporating and depositing vapor deposited crystals of the phosphor base material on the surface of the substrate 1.

  Next, with reference to FIG. 2, the vapor deposition apparatus 20 is demonstrated as an example of the vapor deposition apparatus used when performing a vapor deposition method.

  The vapor deposition apparatus 20 includes a vacuum pump 21 and a vacuum container 22 that is evacuated by the operation of the vacuum pump 21. Inside the vacuum vessel 22, a resistance heating crucible 23 is provided as a vapor deposition source, and a base material 8 configured to be rotatable by a rotating mechanism 24 is provided above the resistance heating crucible 23 via a substrate holder 25. is set up. A slit for adjusting the vapor flow of the phosphor evaporating from the resistance heating crucible 23 is provided between the resistance heating crucible 23 and the substrate 8 as necessary. In addition, the base material 8 is installed and used in the substrate holder 25 when using the vapor deposition apparatus 20.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

According to the following method, the scintillator plates 101-125 for the examples and comparative examples were produced.
(Preparation of base material)
A 125 μm thick polyimide resin sheet was used as a substrate, and a reflective layer (0.10 μm) was formed on the substrate by sputtering aluminum. In that case, the base materials 1-25 which have the roughness of Table 1 were obtained by adjusting the surface roughness by the side of a board | substrate vapor deposition surface.
(Preparation of scintillator layer)
Tl as an additive was mixed with cesium iodide (CsI) to obtain a vapor deposition material. Tl produced a deposition material of 0.3 mol% with respect to CsI. The evaporation material was filled in a resistance heating crucible, and the substrate 1 was placed on a rotating support holder, and the distance between the substrate 1 and the two evaporation sources was adjusted to 400 mm.

  Subsequently, after the inside of the vapor deposition apparatus was once evacuated, Ar gas was introduced and the degree of vacuum was adjusted to 0.1 Pa, and then the temperature of the substrate 1 was maintained at 200 ° C. while rotating the substrate holder 25 at a speed of 10 rpm. Next, the resistance heating crucible containing the vapor deposition material is heated to deposit the scintillator phosphor. When the film thickness of the scintillator layer (phosphor layer) reached 300 μm, vapor deposition was terminated and a scintillator plate sample 101 was obtained.

The scintillator plate samples 102 to 125 were obtained in the same manner as the scintillator plate sample 101 except that the base material shown in Table 1 was used instead of the base material 1.
"Evaluation of crystallinity of columnar crystals"
A tomographic photograph using a transmission electron microscope of the phosphor layer was taken, and the best level of crystallinity of the columnar crystals was set to 5.0, the worst level was set to 1.0, and visually observed at a rank of 0.5. Thus, the state of fusion of the base portion of the columnar crystal and the state of occurrence of abnormal crystal growth were observed and evaluated, and this was used as one of the indices for sharpness evaluation.
"Evaluation of MTF"
X-rays with a tube voltage of 80 kVp were irradiated to the radiation incident side of the FPD through a lead MTF chart, and image data was detected and recorded on a hard disk. Thereafter, the recording on the hard disk was analyzed by a computer, and the modulation transfer function MTF (MTF value at a spatial frequency of 1 cycle / mm) of the X-ray image recorded on the hard disk was taken as one of the indicators of sharpness evaluation. In the table, the higher the MTF value, the better the sharpness. MTF is an abbreviation for Modulation Transfer Function. The sample 101 is represented as 100 and expressed as a relative value.
"Evaluation of adhesion"
A 1 cm square notch on the surface of the phosphor layer (CsI: Tl) was cut with a cutter, and a cellophane tape was applied thereon, followed by peeling. The area of the peeled portion was visually evaluated, and the level with the least peeling was set to 5.0, the level with the most peeling was set to 1.0, and the rank was evaluated in increments of 0.5.

  The results are shown in Table 1.

  As is clear from the results in Table 1, the base line average roughness (Ra) of the contact surface in contact with the scintillator layer is 0.001 ≦ Ra ≦ 0.1 μm and 5 ≦ Rt / Ra ≦ 150. Can be used to obtain a scintillator plate having a scintillator layer having excellent crystallinity, excellent sharpness, and excellent adhesion to a substrate.

Cross section of scintillator plate Schematic configuration diagram of vapor deposition equipment

Explanation of symbols

1 Substrate 2 Scintillator layer (phosphor layer)
3 Intermediate Layer 4 Reflective Layer 8 Base Material 10 Scintillator Plate 20 Vapor Deposition Device 21 Vacuum Pump 22 Vacuum Container 23 Resistance Heating Crucible 24 Rotating Mechanism 25 Substrate Holder

Claims (3)

In a scintillator plate having a scintillator layer made of vapor-deposited crystals on a substrate, the center line average roughness (Ra) of the contact surface of the substrate that contacts the scintillator layer is 0.001 ≦ Ra ≦ 0.1 μm A scintillator plate, wherein the contact surface has a maximum roughness (Rt) and Ra has a relationship of 5 ≦ Rt / Ra ≦ 150. The scintillator plate according to claim 1, wherein the deposited crystal is a columnar crystal. The scintillator plate according to claim 1 or 2, wherein the deposited crystal contains cesium iodide and an activator.

Images