JP2012058170A - Scintillator panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scintillator panel of a radiation image detection device that has sufficient sharpness and secures high light emission efficiency.SOLUTION: The scintillator panel is used for the radiation image detection device constituted by arranging a plurality of scintillators which convert radiation into visible light and a plurality of optical detection elements on a substrate, one to one, and has a scintillator layer which is divided into a plurality of sections corresponding to the optical detection elements, and has the scintillators arranged in the sections, the scintillators in the sections being larger in mean thickness at center parts than at peripheral parts.

Description

  The present invention relates to a scintillator panel of a radiographic image detection apparatus used for medical or industrial radiographic imaging.

  Conventionally, a radiographic imaging apparatus such as an X-ray image has been widely used for diagnosis of a medical condition in a medical field. In particular, radiographic imaging devices using intensifying screens and X-ray films have been used in medical sites around the world as a result of high sensitivity and high image quality in a long history.

  In recent years, digital radiographic image detectors such as flat panel detectors (FPDs) have also appeared, and radiographic images are acquired as digital information and image processing is performed freely. Information can be sent immediately.

  The radiation image detection device has a scintillator panel that converts radiation into fluorescence. The scintillator panel receives radiation that has passed through the subject, and instantaneously emits fluorescence from the phosphor (scintillator) with an intensity corresponding to the radiation dose, and has a configuration in which a phosphor layer is provided on the substrate. Then, the light emitted from the scintillator is detected by the detection pixel of the photoelectric conversion layer and converted into an electric signal.

  In order to increase the electrical signal detected by the detection pixel, it is desirable that the scintillator panel has high light emission efficiency, and the light emission efficiency increases as the thickness of the scintillator layer increases. Since the scintillator emits isotropically, as the thickness increases, scattered light is generated inside the scintillator layer, and thus the emitted light also spreads in the lateral direction perpendicular to the thickness direction of the scintillator layer and affects the surrounding pixels. This causes a problem of so-called crosstalk that sharpness is lowered.

  In order to improve diagnosis, it is preferable to obtain an image with high sharpness. There have been coating-type scintillator panels coated with phosphor particles and vapor-deposited scintillator panels in which columnar phosphor crystals are deposited on a substrate. In any case, sufficient sharpness is achieved by scattered light generated inside the scintillator layer. Sex is not obtained.

  As a means for solving such a problem, in the radiation detector disclosed in Patent Document 1, the scintillator layer of the scintillator panel has a partition structure corresponding to the detection pixel section of the photoelectric conversion layer.

  In the radiation detector disclosed in Patent Document 2, a light guide is provided in the partition structure of the scintillator layer, and the generated light is guided to the detection pixel.

JP 2004-340737 A JP-A-5-188148

  However, in the radiation detectors described in Patent Documents 1 and 2, the countermeasure for the lateral leakage of light at the joint between the photoelectric conversion layer and the scintillator layer is not sufficient, and the achievement level for the sharpness improvement effect is It was insufficient.

  In view of such a problem, the present invention has an object to obtain a scintillator panel that can obtain sufficient sharpness and can ensure high luminous efficiency.

  The above object is achieved by the invention described below.

1. A scintillator panel used in a radiological image detection apparatus in which a plurality of scintillators that convert radiation into visible light and a plurality of light detection elements are arranged in a one-to-one correspondence on a substrate,
The scintillator layer is divided into a plurality of sections corresponding to the light detection elements, and a scintillator is disposed in the sections,
The scintillator panel in the compartment is characterized in that the average thickness of the central part is thicker than the average thickness of the peripheral part.

2. When the scintillator in the section is a rectangular shape when viewed from the radiation irradiation side, the scintillator in one section is divided into nine sections in total by dividing the scintillator in one section into three parts vertically and horizontally when viewed from the top surface. In addition, when the average thickness of the central portion is wc and the average thickness of the other peripheral portions is we,
1.1 <wc / we <2.0
2. The scintillator panel according to 1, wherein the relational expression is satisfied.

3. The scintillator in the section has a circular shape when viewed from the radiation irradiation side, and the average thickness inside a concentric circle having a radius of one third when the scintillator of one section is viewed from the top is wc, When the average thickness on the outside is we,
1.1 <wc / we <2.0
2. The scintillator panel according to 1, wherein the relational expression is satisfied.

  According to the present invention, by making the average thickness of the central part of the scintillator in the section of the scintillator panel thicker than the average thickness of the peripheral part, light leaks in the lateral direction at the junction between the photoelectric conversion layer and the scintillator layer. Therefore, it is possible to obtain a radiological image detection apparatus that can obtain sufficient sharpness and can ensure high luminous efficiency.

It is sectional drawing of the radiographic image detection apparatus 1 which concerns on this embodiment. FIG. 2 is an enlarged cross-sectional view of FIG. 1, showing a scintillator layer 121 and a photoelectric conversion layer 13. FIG. 3 is an enlarged perspective view of one section of scintillator 121 s arranged in the scintillator layer 121 shown in FIG. 2. 4A is an outline view of the scintillator 121s viewed from above, and FIG. 4B is a cross-sectional view taken along line AA in FIG. 4A. It is an example of the scintillator 121s of a reverse regular square thrust trapezoid shape. It is an example of the scintillator 121s of a reverse regular square thrust trapezoid shape. It is an example of scintillator 121s of truncated cone shape. It is an example of scintillator 121s of truncated cone shape. It is an example of the scintillator layer 121 using scintillator 121s of various shapes. It is an example of the scintillator layer 121 using scintillator 121s of various shapes. It is an example of the scintillator layer 121 using the quadrangular prism-shaped scintillator 121s which concerns on a comparative example.

  Although the present invention will be described based on an embodiment, the present invention is not limited to the embodiment.

  FIG. 1 is a cross-sectional view of a radiation image detection apparatus 1 according to the present embodiment. The radiation image detection apparatus 1 is provided in a housing 11 so as to be in pressure contact with the scintillator panel 12 that receives radiation transmitted through a subject and instantaneously emits fluorescence at an intensity corresponding to the dose. A plurality of light receiving elements 13 s (see FIG. 2) that photoelectrically convert light from the panel 12 are two-dimensionally arranged, and a protective cover 14 that protects the scintillator panel 12 is provided. In FIG. 1 and subsequent figures, the z direction is a direction opposite to the irradiation direction of the radiation 7, and the x direction and the y direction indicate the arrangement direction of the light receiving elements.

  The scintillator panel 12 has a configuration in which a cushion layer 123 is disposed on the back surface of the substrate 122 on which the scintillator layer 121 is formed.

  The substrate 122 is made of a material that transmits radiation. The substrate 122 preferably has flexibility so that the scintillator panel 12 can be uniformly brought into contact with the surface of the photoelectric conversion layer 13. For example, a flexible polyimide film having a thickness of 125 μm can be used. In addition to the polyimide film, a cellulose acetate film, a polyester film, a polyethylene terephthalate film, a polyethylene naphthalate film, a polyamide film, a triacetate film, a polycarbonate film, or the like can be used. As thickness, 50-500 micrometers is preferable.

  The cushion layer 123 is for bringing the scintillator panel 12 into pressure contact with the photoelectric conversion layer 13 with an appropriate pressure. For example, a silicon-based or urethane-based foam material with little X-ray absorption can be used.

  The protective film 125 is for moisture-proofing the scintillator layer 121 and suppressing deterioration of the scintillator layer 121, and is composed of a film with low moisture permeability. For example, a polyethylene terephthalate film (PET) can be used. Besides PET, a polyester film, a polymethacrylate film, a nitrocellulose film, a cellulose acetate film, a polypropylene film, a polyethylene naphthalate film, or the like can be used.

  The photoelectric conversion layer 13 is composed of a plurality of light receiving elements 13s (see FIG. 2) arranged two-dimensionally. For example, it can be constituted by a photodiode + a thin film transistor (TFT). The signal charge photoelectrically converted by the photodiode is read out using the TFT. In addition, CMOS, CCD, etc. can be used as the light receiving element 13s.

  The protective cover 14 protects the scintillator panel 12 from external impacts and the like, and also serves to compress the cushion layer 123 and press the scintillator panel 12 to the photoelectric conversion layer 13 with an appropriate pressure. For example, it is composed of a carbon plate with little X-ray absorption. In addition, an aluminum plate can be used as the protective cover 14.

  FIG. 2 is a cross-sectional view showing the scintillator layer 121 and the photoelectric conversion layer 13. The scintillator layer 121 is divided into a plurality of sections by a partition member 121b, and a scintillator 121s (also referred to as “phosphor”) is disposed in each section. The photoelectric conversion layer 13 and the scintillator layer 121 are joined via a joint sa. The light receiving element 13s constituting the photoelectric conversion layer 13 and the surface on which the scintillator 121s is formed are opposed to each other. The light receiving element 13s and the scintillator 121s in each section are arranged in a one-to-one correspondence, and the center part of the scintillator 121s (the center part in the xy plane, the same applies hereinafter) and the center part of the light receiving element 13s. The scintillator 121s converts the radiation 7 (see FIG. 1) from the scintillator panel 12 side into visible light. The converted visible light is detected by the light receiving element 13s, and the scintillator 121s is partitioned into a plurality of sections by the partition member 121b, and the partition member 121b is configured to reflect or absorb visible light. With this configuration, it is possible to prevent visible light generated in the scintillator from spreading in the lateral direction and being detected by the adjacent light receiving element 13s, thereby improving sharpness.

[Scintillator]
The material of the scintillator 121s applicable to the present invention may be any known material, but can be arbitrarily selected according to the required characteristics of the scintillator 121s. _{Specifically, CsI, Gd 2 O 2 S} , Lu 2 O 2 S, Y 2 O 2 S, LaCl 3, LaBr 3, LaI 3, CeBr 3, CeI 3, LuSiO 5, Ba (Br, F, I ) And the like, but are not limited thereto.

The activator material applicable to the present invention may be any known material, but can be arbitrarily selected according to required characteristics such as emission wavelength. Specific examples include compounds such as In, Tl, Li, K, Rb, Na, Eu, Cu, Ce, Zn, Ti, Gd, Tb, and Pr. In particular, CsI: Tl, LaBr ₃ : Ce, CeBr ₃ , Gd ₂ O ₂ S: Tb, Gd ₂ O ₂ S: Pr, Ce, and F can be preferably used from the viewpoint of X-ray absorption and emission luminance.

  Any existing method may be used to manufacture the scintillator 121s. Transparency can be improved by making it a single crystal by vapor deposition or pulling, reducing the gap by pressing or sintering the powder, or filling the powder with a material having a refractive index close to that of the scintillator 121s. it can. In particular, in order to improve the light emission luminance, it is a preferable embodiment that the scintillator 121s has an average visible light (light in a wavelength range of 360 to 830 nm) average transmittance of 80% or more. The thickness of the scintillator layer 121 is preferably in the range of 100 to 3000 μm from the viewpoint of sensitivity and the like.

  As a substrate material of the partition member 121b, a glass substrate, a carbon substrate, a glass paste substrate, a gypsum substrate, or the like can be used.

  A method for creating the scintillator layer 121 having a partition wall structure can be selected from the following methods. The partition wall member 121b having the partition wall structure may be formed first, and then the gap between the partition wall members may be filled with the scintillator 121s. The layer of the scintillator 121s may be formed first, and then the groove may be formed to form the partition wall member 121b. May be embedded.

  Examples of the former method for forming the barrier rib structure include a transfer method, a sand blast method, a laser processing method, a machining method, a photoresist method, a chemical etching method, and a LIGA method. Examples of a method for forming the scintillator 121s in the gap of the partition wall structure include a powder filling method, a melt filling method, a vapor deposition method, and a thickness method.

  Examples of the method for forming the groove on the scintillator 121s in the latter method include a transfer method, a sand blast method, a machining method, a photoresist method, a chemical etching method, a LIGA method, a wire method, a dicing method, and the like.

[Average thickness of scintillator 121s]
(First example, regular square frustum shape)
FIG. 3 is an enlarged perspective view of one section of the scintillator 121s arranged in the scintillator layer 121 shown in FIG. 4 is a view showing the same scintillator 121s as in FIG. 3, FIG. 4 (a) is an outline view in a top view shape, and FIG. 4 (b) is a cross-sectional view taken along line AA in FIG. 4 (a).

  The scintillator 121s shown in FIGS. 3 and 4 is an example of a regular quadrangular pyramid in which the upper side of the regular quadrangular pyramid is cut by a plane parallel to the bottom surface. The length of the bottom side is 3L, the length of the top side is 2/3 of 2/3, and the total thickness (height) is h. In the example shown in the figure, the scintillator 121s of each section has a narrow opening area (xy plane) on the radiation irradiation surface side and a wide opening area on the light receiving element side (light receiving element 13s side). Further, the side surface of the scintillator 121s in each section is inclined outward from the irradiation surface side toward the light receiving element side when viewed from the central axis side. Further, as shown in the sectional view of FIG. 4B, the side surface is linear.

  As shown in FIG. 4 (a), the top view, that is, the case where the bottom surface is divided into 9 sections in total by dividing the bottom face into 3 parts in the vertical and horizontal directions (xy direction), and the entire other peripheral part. The average thickness (the thickness in the z direction) of (total of e1 to e8) will be described.

  The average thickness is a volume per unit area, and can be calculated by dividing the volume V by the area S in a top view. Since the central portion c is a quadrangular prism, it can be easily understood that the average thickness wc = h.

Next, the volume Ve in the entire peripheral part other than the central part c is calculated. The total volume V of the regular square thrust base is V = 1/3 × ((3L) ² × (3L × 2L) + (2L) ² ) × h = 19/3 × L ² × h. Since the volume of the quadrangular prism in the central portion c is Vc = L ² × h, the volume of the entire peripheral portion excluding the central portion c is Ve = V−Vc = 16/3 × L ² × h.

Since the area Se in the top view of the entire peripheral portion excluding the central portion c is 8L ² (= 3L ² −L ² ), the average thickness we = Ve / Se = 2 / 3h of the peripheral portion. Therefore, the average thickness wc of the central part is thicker than the average thickness we of the peripheral part. Further, the ratio between the two is wc / we = 3/2, and it can be seen that the following formula (1) is also satisfied.
1.1 <wc / we <2.0 Formula (1)
(Modification, inverted square pyramid shape)
FIGS. 5 and 6 are diagrams corresponding to FIGS. 3 and 4, respectively, and the examples shown in these drawings are examples of a reverse regular quadrangle-shaped scintillator 121 s in which the directions in the z direction are reversed. In the example shown in the figure, the scintillator 121s of each section has a large opening area on the radiation irradiation surface side and a small opening area on the light receiving element side. Further, the side surface of the scintillator 121s in each section is inclined inward from the irradiation surface side toward the light receiving element side when viewed from the central axis side. Further, as shown in the sectional view of FIG. 6B, the side surface is linear.

  The same result is obtained in the scintillator 121s having such a shape, and the average thickness wc of the central portion c is h, and the average thickness we = 2 / 3h of the peripheral portion. Therefore, the average thickness wc of the central part is thicker than the average thickness we of the peripheral part. The ratio between the two is wc / we = 3/2, which also satisfies the formula (1).

(Second example, truncated cone shape)
FIG. 7 is a diagram corresponding to FIG. 3 and FIG. 4, respectively, and FIG. 7 is an example of a truncated cone-shaped scintillator 121s. It is a truncated cone shape obtained by cutting the upper part of the cone with a plane parallel to the bottom surface. The radius of the bottom circle is 3r, the radius of the top circle is 2r, and the total thickness (height) is h. In the example shown in the figure, the scintillator 121s of each section has a narrow opening area on the radiation irradiation surface side and a wide opening area on the light receiving element side. Further, the side surface of the scintillator 121s in each section is inclined outward from the irradiation surface side toward the light receiving element side when viewed from the central axis side. Further, as shown in the sectional view of FIG. 8B, the side surface is linear.

  As shown in FIG. 8B, when the top view, that is, the case where the bottom circle is divided into two concentric circles with a radius of 1/3, the central portion c on the inner side of the concentric circle and the peripheral portion e on the outer side is taken. Each average thickness (z-direction thickness) will be described.

  The average thickness can be calculated by dividing the volume V by the area S as viewed from above. Since the central portion c is a cylinder, the average thickness wc of the central portion c is wc = h.

Next, the volume V in the peripheral part e other than the central part c is calculated. The volume of the circular platform V = 1/3 × π × ((3r) ² × (3r × 2r) + (2r) ² ) × h = 19/3 × π × r ² × h. Since the volume of the cylinder of the central portion c is π × r ² × h, the volume Ve of the peripheral portion e excluding the central portion c is Ve = 16/3 × π × r ² × h.

Since the area Se in the top view excluding the central portion c is 8πr ² (= 9πr ² −πr ² ), the average thickness we = Ve / Se = 2 / 3h in the peripheral portion. Therefore, the average thickness wc of the central part is thicker than the average thickness we of the peripheral part. The ratio of the two is wc / we = 3/2, which satisfies the above-described formula (1).

(Other examples)
9 and 10 are examples of the scintillator layer 121 using scintillators 121s having various shapes. The scintillator 121s shown in FIGS. 9 and 10 is a rotating body (a three-dimensional figure obtained by a locus when a plane is rotated once around a central axis extending in the z direction).

  9 (a) to 9 (d), the opening area on the radiation irradiation side (upward in FIG. 9) is the smallest, and gradually spreads downward and comes into contact with the photoelectric conversion layer 13. In this shape, the opening area is the largest. Further, the side surface of the scintillator 121s in each section is inclined outward from the irradiation surface side toward the light receiving element side when viewed from the central axis side. FIG. 9A is an example using a bell-shaped scintillator 121s, and as shown in the cross-sectional view, the side surface is bent inward in an arc shape on the irradiation surface side and then passes through the inflection point to the light receiving element side. It extends on a straight line. FIGS. 9B and 9C are examples using a trumpet-shaped scintillator 121s. In the examples of FIGS. 9B and 9C, the side surfaces are irradiated as shown in the cross-sectional views. On the surface side, it extends in parallel with the central axis and gradually bends outward in an arc shape while gradually increasing the inclination angle (so that it spreads outward). FIG. 9D shows an example of a conical scintillator 121s. This is an example in which the side surface extends in a straight line. However, in FIG. 9C and FIG. 9D, the opening area on the irradiation surface side is very narrow compared to other examples.

  FIGS. 10A and 10B are shapes in which the direction in the z direction is opposite to FIGS. 9A and 9B, respectively. The opening area (xy plane) on the radiation irradiation surface side (upward in the figure) is the largest, gradually narrowing downward, and the opening area is narrowest on the light receiving element side. .

  FIG. 10C shows an example of a scissor-shaped scintillator 121s, which has a shape in which the middle abdomen is the widest and narrower in the vertical direction.

  In the present embodiment, by setting the average thickness wc of the central portion of the scintillator 121s to be thicker than the average thickness we of the peripheral portion, the amount of light emitted from the scintillator 121s of each section by radiation irradiation is Can be more than the periphery. For this reason, most of the emitted light is poured into the corresponding light receiving element 13s, so that leakage of light from the joint sa in the lateral direction can be reduced, and sufficient sharpness can be obtained. A radiological image detection apparatus that can ensure high luminous efficiency can be obtained.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, the embodiment of this invention is not limited to this. Six types of scintillator layers 121 of Samples 1 to 6 were formed according to the following method, and the radiation image detection apparatus 1 was manufactured using each scintillator layer 121.

(Photoelectric conversion layer 13)
As the photoelectric conversion layer 13, a CMOS flat panel (Rado Icon X-ray CMOS camera system Shadow_Box 4KEV) was used. The arrangement pitch (pixel pitch) of the light receiving elements 13s is 48 μm. The photoelectric conversion layer 13 is common to the samples 1 to 6.

(Common conditions for samples 1 to 5)
A partition member 121b divided into a plurality of sections at a pitch of 48 μm was formed by a sandblasting process using a 100 mm □ carbon substrate. After the formation, a silver reflective layer was formed on the surface of the partition wall member 121b by plating, and then a transparent acrylic film was formed on the surface with a thickness of about 2 μm as a protective layer for the silver reflective film. Thereafter, CsI: TlI phosphor powder having an average particle diameter of 2 μm was filled in the gaps between the partition members 121b with a high pressure to form the scintillator layer 121. Finally, the surface was polished. Then, the scintillator panel 12 is formed by using the formed scintillator layer 121, and the scintillator panel 12 is aligned so that the center portions of the respective light receiving elements 13s and the scintillators 121s in each section coincide as shown in FIG. The radiation image detection apparatus 1 was produced by bonding the layer 121 and the photoelectric conversion layer 13 together.

(Shape of scintillator 121s of samples 1 to 5)
Sample 1 is a comparative example, and samples 2 to 5 are examples.

  Sample 1 has the shape of a regular quadrangular prism shown in FIG.

  Sample 2 has the shape of a regular quadrangular pyramid shown in FIG.

  Sample 3 has the bell shape shown in FIG.

  Sample 4 has a quadrangular pyramid shape shown in FIG.

  The sample 5 has a trumpet shape shown in FIG.

(Evaluation of sharpness)
X-rays with a tube voltage of 80 kVp are irradiated from the back surface (in the direction of arrow 7 in FIG. 1) of the radiation image detection device 1 of each embodiment through a lead MTF chart, and the image data is detected by the photoelectric conversion layer 13 and recorded on the hard disk. did. Thereafter, the recording on the hard disk was analyzed with a personal computer, and the modulation transfer function (MTF (Modulation Transfer Function)) of the X-ray image recorded on the hard disk was calculated. Two types of MTF charts having a spatial frequency of 1 cycle / mm and 5 cycles / mm were used. MTF was measured 50 times and the average value was used as the calculation result. The results are shown in Table 1. In the results in Table 1 below, the higher the MTF (%), the better the resolution.

(Evaluation of brightness)
In the image data obtained in the measurement of the sharpness, the luminance of the portion of the MTF chart that is not shielded by lead was measured. The average value of 50 locations was used as the luminance value, and the relative value was shown in Table 1 as the relative luminance with the luminance value of Sample 1 as the reference (100%).

  As is clear from Table 1, it can be seen that Samples 2 to 5 of Examples have high MTF values and excellent sharpness compared to Sample 1 of Comparative Example. Furthermore, it can be seen that Samples 2 to 4, which are more preferred examples satisfying Equation (1), have a higher relative luminance. In addition, as shown in Table 1, compared with the sample 1, the samples 2 to 5 have the same manufacturing cost, so that all evaluations are evaluated as ◯.

DESCRIPTION OF SYMBOLS 1 Radiation image detection apparatus 12 Scintillator panel 121 Scintillator layer 121s Scintillator 121b Partition member 122 Substrate 123 Cushion layer 125 Protective film 13 Photoelectric conversion layer 13s Light receiving element

Claims (3)

A scintillator panel used in a radiological image detection apparatus in which a plurality of scintillators that convert radiation into visible light and a plurality of light detection elements are arranged in a one-to-one correspondence on a substrate,
The scintillator layer is divided into a plurality of sections corresponding to the light detection elements, and a scintillator is disposed in the sections,
The scintillator panel in the compartment is characterized in that the average thickness of the central part is thicker than the average thickness of the peripheral part. When the scintillator in the section is a rectangular shape when viewed from the radiation irradiation side, the scintillator in one section is divided into nine sections in total by dividing the scintillator in one section into three parts vertically and horizontally when viewed from the top surface. In addition, when the average thickness of the central portion is wc and the average thickness of the other peripheral portions is we,
1.1 <wc / we <2.0
The scintillator panel according to claim 1, wherein the relational expression is satisfied. The scintillator in the section has a circular shape when viewed from the radiation irradiation side, and the average thickness inside a concentric circle having a radius of one third when the scintillator of one section is viewed from the top is wc, When the average thickness on the outside is we,
1.1 <wc / we <2.0
The scintillator panel according to claim 1, wherein the relational expression is satisfied.

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