JP2015038461A - Scintillator panel and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scintillator panel capable of improving reliability and total characteristics including an afterimage characteristic on a scintillator layer.SOLUTION: A scintillator panel 10 includes: a support substrate 11 which transmits X-ray 16; and a scintillator layer 13 which is in contact with the support substrate 11 to convert the X-ray 16 coming from the outside into light. The scintillator layer 13 is a fluorescent body which contains CsI as a halogenide and Tl as an activator. The density of the activator in the fluorescent body is 1.6 mass%-2.0 mass%; and the density distribution of the activator in the plane in a thickness direction is ±15% or less.

Description

  Embodiments described herein relate generally to a scintillator panel that converts radiation into light and a method for manufacturing the scintillator panel.

  As a new-generation X-ray diagnostic image detector, an X-ray detector, which is a planar radiation detector using an active matrix or a solid-state imaging device such as a CCD and a CMOS, has attracted attention. By irradiating the X-ray detector with X-rays, an X-ray image or a real-time X-ray image is output as a digital signal.

  The X-ray detector includes a scintillator panel having a scintillator layer that converts radiation into light, and a photoelectric conversion substrate that converts light converted by the scintillator panel into an electrical signal. The light converted in the scintillator layer by incident X-rays reaches the photoelectric conversion substrate and is converted into electric charge. This electric charge is read out as an output signal and converted into a digital image signal by a predetermined signal processing circuit or the like. Is done.

  In addition, when CsI, which is a halide, is used for the scintillator layer, since CsI alone cannot convert incident X-rays into visible light, excitation of light with respect to incident X-rays is performed in the same manner as general phosphors. An activator is contained in order to activate.

  In the X-ray detector, since the peak wavelength of the light receiving sensitivity of the photoelectric conversion substrate exists in the visible light region of 400 nm to 700 nm, when CsI is used for the scintillator layer, the light excited by the incident X-rays Tl having a wavelength of around 550 nm is used as an activator.

  When the scintillator layer is a phosphor containing Tl as an activator in CsI, which is a halide, the concentration and concentration of the activator Tl is similar to that of a phosphor containing a general activator. It will be greatly affected by the distribution.

  In a scintillator panel having a scintillator layer containing an activator, if the concentration and concentration distribution of the activator are not optimized, the characteristics of the scintillator layer will be deteriorated, and the sensitivity related to the light emission characteristics of the scintillator layer (light emission) Efficiency) and afterimage (a phenomenon in which the subject image of the X-ray image before the (n-1) -th X-ray image remains in the n-th X-ray image).

  For example, in diagnosis using an X-ray image, the imaging conditions vary greatly depending on the subject {incident X-ray dose: approximately 0.0087 mGy to 0.87 mGy (since X-ray transmittance varies depending on the region)}, (n -1) There may be a large difference in the dose of incident X-rays between the X-ray image and the n-th X-ray image, and the dose difference between incident X-rays between the (n-1) -th and n-th X-ray images. Is (n-1)> n, the light emission characteristic of the scintillator layer in the non-subject portion of the (n-1) th X-ray image is changed by the large energy of incident X-rays, and the nth X-ray image Up to this, an afterimage occurs due to the remaining effect.

  This afterimage characteristic is an important characteristic in diagnosis using an X-ray image as compared with sensitivity (light emission efficiency) and resolution (MTF) which are characteristics of other scintillator layers.

  Conventionally, for the purpose of improving sensitivity (luminous efficiency) and resolution (MTF), there has been a proposal to define the concentration and concentration distribution of the activator of the scintillator layer.

JP 2007-232636 A

  Conventionally, many improvements in the characteristics of the scintillator layer are related to sensitivity (light emission efficiency) and resolution (MTF), and few are related to an improvement in overall characteristics including afterimage characteristics.

  The problem to be solved by the present invention is to provide a scintillator panel capable of improving the overall characteristics including the afterimage characteristics of the scintillator layer and improving the reliability, and a method for manufacturing the scintillator panel.

  The scintillator panel of this embodiment includes a support substrate that transmits radiation, and a scintillator layer that contacts the support substrate and converts radiation incident from the outside into light, and the scintillator layer has Ts on CsI that is a halide. A phosphor contained as an activator, and the concentration of the activator in the phosphor is 1.6 mass% to 2.0 mass%, and the concentration distribution of the activator in the in-plane direction and the film thickness direction is within ± 15%. .

It is sectional drawing of the 1st structural example of the scintillator panel which shows one Embodiment. It is sectional drawing of the 2nd structural example of a scintillator panel same as the above. It is sectional drawing of the 3rd structural example of a scintillator panel same as the above. It is sectional drawing of the 4th structural example of a scintillator panel same as the above. It is sectional drawing of the imaging device using a scintillator panel same as the above. It is a graph which shows the correlation with Tl density | concentration of the scintillator layer of a scintillator panel same as the above, and a sensitivity ratio. It is a graph which shows the correlation with Tl density | concentration of a scintillator layer same as the above, and MTF ratio. It is a graph which shows the correlation with Tl density | concentration and a residual image ratio of a scintillator layer same as the above. It is a graph which shows the correlation with the lamination period of a scintillator layer, and a sensitivity ratio same as the above. It is a graph which shows the correlation with the lamination period of a scintillator layer, and MTF ratio same as the above. It is a graph which shows the correlation with the lamination period of a scintillator layer, and an afterimage ratio same as the above. It is a schematic diagram which shows the formation method of a scintillator layer same as the above. It is an X-ray image image | photographed on specific imaging conditions using the scintillator panel same as the above, (a) is an X-ray image in case of Tl density | concentration: 0.1 mass%, (b) is Tl density | concentration: 1.0 mass%. (C) is an X-ray image when Tl concentration is 1.2 mass%, (d) is an X-ray image when Tl concentration is 1.6 mass%, and (e) is Tl concentration: It is an X-ray image in the case of 2.0 mass%. It is a table | surface which shows each characteristic in Tl density | concentration: 0.1 mass%, 1.0 mass%, 1.2 mass%, 1.6 mass%, and 2.0 mass% in a scintillator panel same as the above.

  Hereinafter, an embodiment will be described with reference to FIGS. 1 to 14.

  1 to 4 show first to fourth structural examples of the basic configuration of the scintillator panel 10.

  First, a first structural example of the scintillator panel 10 will be described with reference to FIG. The scintillator panel 10 includes a support substrate 11 that transmits X-rays as radiation. A reflection layer 12 that reflects light is formed on the support substrate 11, and the radiation is converted into visible light on the reflection layer 12. A scintillator layer 13 is formed, and a protective layer 14 that seals the scintillator layer 13 is laminated on the scintillator layer 13.

  The support substrate 11 is made of a substance that has a light element as a main component rather than a transition metal element and has a good X-ray transmittance.

  The reflective layer 12 is made of a highly reflective metal material such as Al, Ni, Cu, Pd, or Ag, and reflects the light generated in the scintillator layer 13 in the opposite direction to the support substrate 11 to increase the light utilization efficiency. .

  The scintillator layer 13 is formed by a vapor deposition method such as a vacuum deposition method, a sputtering method, or a CVD method, for example, a halogen compound such as cesium iodide (CsI), which is a high-intensity fluorescent material, or an oxide such as gadolinium sulfate (GOS). A phosphor such as a system compound is deposited on the support substrate 11 in a columnar shape to form a film. The scintillator layer 13 is formed in a columnar crystal structure in which a plurality of strip-shaped columnar crystals 13a are formed in the surface direction of the support substrate 11.

  Then, in the scintillator panel 10 configured in this way, X-rays 16 as radiation incident on the scintillator layer 13 from the support substrate 11 side are converted into visible light 17 by the columnar crystals 13a of the scintillator layer 13, and supported. Visible light 17 is emitted from the surface of the scintillator layer 13 opposite to the substrate 11 (the surface of the protective layer 14).

  FIG. 2 shows a second structural example of the scintillator panel 10. The first structure example of the scintillator panel 10 shown in FIG. 1 is the same as the other structure except that the reflective layer 12 is not provided.

  FIG. 3 shows a third structural example of the scintillator panel 10. In the first structural example of the scintillator panel 10 shown in FIG. 1, the scintillator layer 13 does not form the columnar crystal 13a, and the other configurations are the same.

  FIG. 4 shows a fourth structural example of the scintillator panel 10. In the second structural example of the scintillator panel 10 shown in FIG. 2, the other structures are the same except that the scintillator layer 13 does not form the columnar crystal 13a.

  FIG. 5 shows a CCD-DR type photographing apparatus 20 using the scintillator panel 10. The imaging device 20 has a housing 21, the scintillator panel 10 is installed at one end of the housing 21, a mirror-like reflector 22 and an optical lens 23 are installed inside the housing 21, A light receiving element 24 such as a CCD is installed at the end. X-rays 16 emitted from an X-ray generation source (X-ray tube) 25 enter the scintillator panel 10, and visible light 17 converted by the scintillator layer 13 is emitted from the surface of the scintillator layer 13. An X-ray image is projected on the surface of the scintillator layer 13, the X-ray image is reflected by the reflecting plate 22, condensed by the optical lens 23 and irradiated to the light receiving element 24, and the X-ray image is electrically converted by the light receiving element 24. Convert to signal and output.

  In the scintillator panel 10 having the structure shown in FIGS. 1 to 4, the scintillator layer 13 is a phosphor containing Tl as an activator in CsI, which is a halide, and the following (1) (2) ( It has the characteristics of 3).

  (1): The concentration of the activator in the phosphor is 1.6 mass% to 2.0 mass%, and the concentration distribution of the activator in the in-plane direction and the film thickness direction of the phosphor is within ± 15%.

  (2): The concentration distribution of the activator in the in-plane direction and the film thickness direction of the phosphor is within ± 15% and the uniformity is maintained at least in the region of the unit film thickness of 200 nm or less.

  (3): The scintillator layer 13 is formed by a vacuum deposition method using two evaporation sources of CsI and TlI, and preferably has a structure of a strip-like columnar crystal 13a.

  Here, in the scintillator panel 10 of the first structural example shown in FIG. 1, the film thickness of the scintillator layer 13 is 350 μm, the activator is Tl, and the correlation between the Tl concentration in the scintillator layer 13 and each characteristic is tested. 6 to 8, and the laminating period of the scintillator layer 13 when the Tl concentration in the scintillator layer 13 is constant {the forming period of the unit film thickness (formed film thickness per substrate rotation)} and each The results of testing the correlation of characteristics are shown in FIGS.

  FIG. 6 shows the correlation between the Tl concentration in the scintillator layer 13 and the sensitivity ratio. The test conditions are incident X-ray: 70 kV-0.0087 mGy, sensitivity ratio: a ratio based on the sensitivity when the Tl concentration in the scintillator layer 13 is 0.1 mass%, and the scintillator layer formation conditions ( (Except for the Tl concentration in the scintillator layer 13). As shown in FIG. 6, the sensitivity was most improved when the Tl concentration in the scintillator layer 13 was in the vicinity of 1.4 mass% to 1.8 mass%.

  FIG. 7 shows the correlation between the Tl concentration in the scintillator layer 13 and the MTF ratio as the resolution. Test conditions are incident X-ray: 70 kV-0.0087 mGy, MTF ratio: ratio based on MTF (at 2 Lp / mm) when the Tl concentration in the scintillator layer 13 is 0.1 mass%, and each test sample The scintillator layer forming conditions (except for the Tl concentration in the scintillator layer 13) are the same. Then, as shown in FIG. 7, the Tl concentration in the scintillator layer 13 was substantially constant up to around 2.0 mass%.

  FIG. 8 shows the correlation between the Tl concentration in the scintillator layer 13 and the afterimage ratio. The test condition is that the dose difference between the incident X-rays of the (n-1) th and n-th X-ray images is (n-1)> n, and the incident X-ray is 70 kV in the (n-1) th X-ray image. -0.87 mGy, subject: lead plate (thickness 3 mm), X-ray image acquisition interval: 60 sec, incident X-ray: 70 kV-0.0087 mGy, subject: none, X-ray image acquisition interval for the nth X-ray image : 60 sec. Furthermore, the afterimage ratio is a ratio based on the afterimage when the Tl concentration in the scintillator layer 13 is 0.1 mass%, and the scintillator layer forming conditions (excluding the Tl concentration in the scintillator layer 13) of each test sample are the same. It is. As shown in FIG. 8, the afterimage was at the minimum level when the Tl concentration in the scintillator layer 13 was around 1.6 mass%. Further, in the region where the afterimage ratio is 0.5 (preferably 0.4) or less and the Tl concentration in the scintillator layer 13 is 1.6 mass% ± 0.4 mass%, no afterimage was confirmed.

  FIG. 9 shows the correlation between the lamination period of the scintillator layer 13 and the sensitivity ratio. The test conditions are incident X-ray: 70 kV-0.0087 mGy, Tl concentration in the scintillator layer 13: 0.1 mass%, sensitivity ratio: ratio based on the sensitivity when the lamination period of the scintillator layer 13 is 200 nm, The scintillator layer forming conditions (except for the Tl concentration in the scintillator layer 13) of each test sample are the same.

  FIG. 10 shows the correlation between the lamination period of the scintillator layer 13 and the MTF ratio. Test conditions are based on incident X-ray: 70 kV-0.0087 mGy, Tl concentration in scintillator layer 13: 0.1 mass%, MTF ratio: MTF (at 2 Lp / mm) when the laminating period of scintillator layer 13 is 200 nm. The scintillator layer formation conditions (excluding the Tl concentration in the scintillator layer 13) of each test sample are the same.

  FIG. 11 shows the correlation between the lamination period of the scintillator layer 13 and the afterimage ratio. The test condition is that the dose difference between the incident X-rays of the (n-1) th and n-th X-ray images is (n-1)> n, and the incident X-ray is 70 kV in the (n-1) th X-ray image. -0.87 mGy, subject: lead plate (thickness 3 mm), X-ray image acquisition interval: 60 sec, incident X-ray: 70 kV-0.0087 mGy, subject: none, X-ray image acquisition interval for the nth X-ray image : 60 sec. Further, the Tl concentration in the scintillator layer 13 is 0.1 mass%, the afterimage ratio is a ratio based on the afterimage when the stacking period of the scintillator layer 13 is 200 nm, and the scintillator layer forming conditions (scintillator layer 13 for each test sample) Except for the Tl concentration in it).

  As shown in FIGS. 9 to 11, each characteristic tends to deteriorate in the region where the lamination period of the scintillator layer 13 is 200 nm or more.

  This is because the peak wavelength of the emission wavelength of the scintillator layer 13 is around 550 nm, but the refractive index of CsI which is the base material of the scintillator layer 13 is 1.8, and therefore the emission wavelength propagating in the scintillator layer 13 If the peak wavelength of λ1 is λ1, it can be considered that λ1 = 550 nm / 1.8 = 306 nm from the relationship between the refractive index and the wavelength. Therefore, when the stacking period of the scintillator layer 13 is larger than λ1, This is because the possibility of being affected by the deterioration of the optical characteristics (scattering, attenuation, etc.) due to the variation in crystallinity and the variation in the Tl concentration in the scintillator layer 13 is matched.

  Further, as shown in FIGS. 6 to 8, in the region where the Tl concentration in the scintillator layer 13 is 1.2 mass% to 2.0 mass%, each characteristic is close to a stable state, so the Tl concentration in the scintillator layer 13 is Even if fluctuates (about ± 15%), the fluctuation of each characteristic is small.

  Furthermore, from the correlation shown in FIGS. 6 to 8, the characteristic improvement effect (especially afterimage characteristics) of the scintillator layer 13 is the largest in the region where the Tl concentration in the scintillator layer 13 is 1.2 mass% to 2.0 mass%, and The optimum value is around 1.6 mass%. However, when the scintillator layer 13 is a phosphor containing Tl as an activator in CsI which is a halide, the following characteristics (a) (b) (c) is there.

  (a): CsI has high hygroscopicity and deliquesces by reacting with moisture in the atmosphere. However, since TlI has no hygroscopicity, the higher the Tl concentration in the scintillator layer 13, the higher the moisture resistance of the scintillator layer 13. Will improve.

  (b): Since the atomic weight of Tl is larger than Cs, the higher the Tl concentration in the scintillator layer 13 is, the more the DQE (X-ray absorption rate) of the scintillator layer 13 is improved. In addition, it is possible to obtain an X-ray image with a high S / N ratio.

  (c): Since the atomic weight of Tl is larger than Cs, the higher the Tl concentration in the scintillator layer 13 is, the higher the DQE (X-ray absorption rate) of the scintillator layer 13 is. Damage to the camera is reduced.

  Thus, the higher the Tl concentration in the scintillator layer 13, the more the effects (a) to (c) are obtained.

  For this reason, if the Tl concentration in the scintillator layer 13 is set to 1.6 mass% to 2.0 mass%, it is possible to improve the characteristics including the afterimage characteristics of the scintillator layer 13 and to improve the reliability of the scintillator panel 10.

  Furthermore, even if the Tl concentration in the scintillator layer 13 is in the region of 1.6 mass% to 2.0 mass%, each characteristic can be obtained if the Tl concentration distribution in the in-plane direction and the film thickness direction of the scintillator layer 13 is largely biased. Therefore, the Tl concentration distribution in the in-plane direction and the film thickness direction of the scintillator layer 13 is preferably within ± 15%. If this Tl concentration distribution is within a fluctuation range of about ± 15%, the fluctuation of each characteristic is small and the influence is small.

  Therefore, as in the characteristic (1), the Tl concentration in the scintillator layer 13 is 1.6 mass% to 2.0 mass%, and the Tl concentration distribution in the in-plane direction and the film thickness direction of the scintillator layer 13 is ± 15. % Is preferable.

  In addition, if there is a large deviation in the Tl concentration distribution in the in-plane direction and the film thickness direction of the scintillator layer 13 at least in the region of the unit film thickness 200 nm or less of the scintillator layer 13, each characteristic is likely to fluctuate greatly. As in the characteristic (2), it is preferable that the Tl concentration distribution in the in-plane direction and the film thickness direction of the scintillator layer 13 is within ± 15% even in a region where the unit film thickness is 200 nm or less.

  Here, a schematic diagram of a method of forming the scintillator layer 13 is shown in FIG. The support substrate 11 is disposed in the vacuum chamber 30, and the evaporation particles from the CsI evaporation source 31 and the evaporation particles from the TlI evaporation source 32 installed in the vacuum chamber 30 are rotated while the support substrate 11 is rotated. A film of the scintillator layer 13 is laminated and formed by a vacuum vapor deposition method for vapor deposition on the laminated surface of the support substrate 11.

  At this time, if the rotation period of the support substrate 11 and the evaporation of CsI and TlI are controlled, the in-plane direction and the film thickness direction Tl concentration distribution per stacking period of the scintillator layer 13 can be arbitrarily controlled. Therefore, when the scintillator layer 13 is formed, if the uniformity of the Tl concentration distribution in the in-plane direction and film thickness direction per stacking period of the scintillator layer 13 is ensured, the entire in-plane direction and film thickness direction of the scintillator layer 13 The uniformity of the Tl concentration distribution is also ensured.

  Therefore, the characteristics (1) to (3) are given to the scintillator layer 13 made of a phosphor containing Tl as an activator in CsI which is a halide in consideration of the characteristics (a) to (c). By doing so, it is possible to improve the characteristics of the scintillator layer 13 including the afterimage characteristics and to improve the reliability of the scintillator panel 10.

  An embodiment of the scintillator panel 10 of the first structural example shown in FIG. 1 will be described. In this example, the film thickness of the scintillator layer 13 is 350 μm, the lamination period of the scintillator layer 13 is 150 nm, the concentration distribution of the activator in the in-plane direction and the film thickness direction of the scintillator layer 13 is ± 15%, and the activator is Tl. The concentration of the activator in the scintillator layer 13: Five samples of 0.1 mass%, 1.0 mass%, 1.2 mass%, 1.6 mass%, and 2.0 mass% are prepared.

  For these five samples, X-ray images (n-th) obtained by photographing a subject under specific photographing conditions and processing the photographed image under predetermined image processing conditions are shown in FIGS. ) (d) (e) and the characteristic results are shown in the table of FIG. In FIG. 14, the sensitivity ratio, MTF ratio, and afterimage ratio are values based on the case where the Tl concentration in the scintillator layer 13 is 0.1 mass%.

  The imaging condition is that the dose difference between the (n-1) th and nth X-ray images is (n-1)> n, and the (n-1) th X-ray image has an incident X-ray of 70 kV. -0.87 mGy, subject: lead plate (thickness 3 mm), X-ray image acquisition interval: 60 sec, incident X-ray: 70 kV-0.0087 mGy, subject: none, X-ray image acquisition interval for the nth X-ray image : 60 sec.

  The image processing conditions are: Flat Field Correction: Yes, Window Processing: Yes (Image histogram average value ± 10%).

  As shown in FIGS. 13 (a) and 13 (b), when the concentration of the activator is 0.1 mass% and 1.0 mass%, an afterimage is confirmed in a range surrounded by a broken line in FIG. 13 (c) ( d) As shown in (e), afterimages were not confirmed in the range surrounded by the broken line in the figure when the concentration of the activator was 1.2 mass%, 1.6 mass%, and 2.0 mass%.

  Therefore, if the features (1) to (3) defined in the present embodiment are added to the scintillator layer 13, the afterimage characteristics can be improved with good sensitivity and MTF, so that the performance of the scintillator panel 10 is improved. And improved reliability.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

10 Scintillator panel
11 Support substrate
13 Scintillator layer

Claims (5)

A support substrate that transmits radiation;
A scintillator layer that contacts the support substrate and converts radiation incident from the outside into light, and
The scintillator layer is a phosphor containing Tl as an activator in CsI which is a halide, and the concentration of the activator in the phosphor is 1.6 mass% to 2.0 mass%, and in-plane direction and film A scintillator panel, wherein the concentration distribution of the activator in the thickness direction is within ± 15%. 2. The scintillator panel according to claim 1, wherein the scintillator layer has a concentration distribution of the activator in an in-plane direction and a film thickness direction of ± 15% or less in a region having a unit film thickness of 200 nm or less. The scintillator panel according to claim 1 or 2, wherein the scintillator layer has a columnar crystal structure. The scintillator panel according to any one of claims 1 to 3, wherein the support substrate is made of a material whose main component is a light element rather than a transition metal element. A scintillator panel manufacturing method comprising: a support substrate that transmits radiation; and a scintillator layer that contacts the support substrate and converts radiation incident from the outside into light,
The scintillator layer is a phosphor containing Tl as an activator in CsI which is a halide,
CsI and Tl so that the concentration of the activator in the phosphor is 1.6 mass% to 2.0 mass% and the concentration distribution of the activator in the in-plane direction and the film thickness direction is within ± 15%. The scintillator layer is formed by a vapor phase growth method using as a material source. A method for manufacturing a scintillator panel.