SCINTILLATOR PANEL AND RADIATION IMAGE SENSOR

Abstract: The surfaces of an amorphous carbon substrate 10 of a scintillator panel 1 have undergone sandblasting, and an Al film 12 serving as a reflecting film is formed on one surface. A columnar scintillator 14 for converting incident radiation into visible light is formed on the surface of the Al film 12.

Description: Technical Field The present invention relates to a scintillator panel and radiation image sensor used for medical X-ray photography and the like. Background Art Conventionally, X-ray photosensitive films have been used for medical and industrial X-ray photography. However, radiation imaging systems using radiation detectors have come into widespread use owing to advantages in convenience and retention of photographic results. In such a radiation imaging system, pixel data based on 2D radiation is acquired as an electrical signal by the radiation detector, and the signal is processed by the processor and displayed on the monitor. As a conventional, typical radiation detector, a radiation detector having a structure in which an image sensing element is stuck to a scintillator panel having a scintillator formed on a substrate made of aluminum, glass, molten quartz, or the like is available. In this radiation detector, the scintillator converts radiations incident from the substrate side into light, and the image sensing element detects the light (see Japanese Patent Publication A radiation detector for medical purposes, especially for dental examination, uses low-energy X-rays. If, therefore, an aluminium substrate is used, quite a few X-ray components are absorbed by the substrate. In a radiation detector using low-energy X-rays, therefore, the substrate of the scintillator panel is required to have high radiation transmittance. Another X-ray detector is known from US5585638 having a converter to convert X-rays to visible light, an imager (scintillator) for converting that light into electrical signals and an automatic exposure control X-ray detector in which various layers of semiconductive material are divided into a plurality of conductive elements defining a plurality of regions each adjacent one of the plurality of conductive elements. The measurement of the intensity of X-rays striking the different regions is measured. It is an object of the present invention to provide a scintillator panel in which the optical output is increased. Disclosure of Invention According to the present invention there is provided a scintillator panel characterised by: a substrate made of amorphous carbon; a scintillator deposited on said substrate; and a protective film entirely covering said scintillator panel. In one embodiment in accordance with the present invention there is provided a reflecting film between the substrate and the scintillator. Preferably, the reflecting film is a metal. In an alternative form the reflecting film is a thin transparent film having a refractive index lower than the refractive index of said scintillator. Preferably, the thin transparent film is a film made of a material containing a substance selected from the group consisting of LiF, MgF 2 , CaF 2 , SiO 2 , Al 2 O 3 , MgO, NaCl, KBr, KCl, and AgCl. Therefore, in accordance with the present invention there is provided a radiation image sensor characterized by comprising an image sensing element and a scintillator panel as defined in the present invention, wherein said image sensing element opposes the output of said scintillator of said scintillator panel. According to one embodiment of this radiation image sensor, the scintillator panel has the substrate made of amorphous carbon as a major constituent resulting in high radiation transmittance, so that the amount of light reaching the image sensing element can be increased. Brief Description of Drawings Fig. 1 is a sectional view of a scintillator panel according to the first embodiment; Fig. 2 is a sectional view of a radiation image sensor according to the first embodiment; Fig. 3A is a view showing the step in manufacturing the scintillator panel according to the first embodiment; Fig. 3B is a view showing the step in manufacturing the scintillator panel according to the first embodiment; Fig. 3C is a view showing the step in manufacturing the scintillator panel according to the first embodiment; Fig. 3D is a view showing the step in manufacturing the scintillator panel according to the first embodiment; Fig. 4 is a sectional view of a scintillator panel according to the second embodiment; Fig. 5 is a sectional view of a radiation image sensor according to the second embodiment; Fig. 6 is a sectional view of a scintillator panel according to the third embodiment; Fig. 7 is a sectional view of a radiation image sensor according to the third embodiment; Fig. 8 is a sectional view of a scintillator panel according to the fourth embodiment; Fig. 9 is a sectional view of a radiation image sensor according to the fourth embodiment; and Fig. 10 is a view showing outputs from the radiation image sensors according to the first to fourth embodiments in comparison with outputs from the conventional radiation image sensor. Best Mode for Carrying Out the Invention The first embodiment of the present invention will be described below with reference to Figs. 1, 2, and 3A to 3D. Fig. 1 is a sectional view of a scintillator panel 1. Fig. 2 is a sectional view of a radiation image sensor 2. As shown in Fig. 1, the surfaces of an amorphous carbon (a-C) (glassy carbon or glass-like carbon) substrate 10 have undergone sandblasting, and an aluminium (Al) film 12 serving as a reflecting film is formed on one surface. A columnar scintillator 14 for converting incident radiation into visible light is formed on the surface of the Al film 12. Note that Tl-doped CsI is used for the scintillator 14. The scintillator 14 is covered with a polyparaxylylene film 16, together with the substrate 10. As shown in Fig. 2, the radiation image sensor 2 has a structure in which an image sensing element 18 is stuck to the distal end side of the scintillator 14. The steps in manufacturing the scintillator panel 1 will be described next with reference to Figs. 3A to 3D. Sandblasting is performed on the surfaces of the rectangular or circular a-c substrate 10 (thickness: 1 mm) by using glass beads (#800). Fine projections/recesses are formed on the surfaces of the substrate 10 by this sandblasting (see Fig. 3A). The Al film 12 serving as a reflecting film is then formed on one surface of the substrate 10 to a thickness of 100 nm by vacuum vapor deposition (see Fig. 3B). A Tl-doped columnar CsI crystal is grown on the surface of the Al film 12 by vapor deposition to form the scintillator 14 having a thickness of 250 µm (see Fig. 3C). CsI used to form this scintillator 14 has high hygroscopicity, and hence absorbs water vapor from the air and deliquesces if it is kept exposed to the air. In order to prevent this, the polyparaxylylene film 16 is formed by the CVD method. More specifically, the substrate 10 on which the scintillator 14 is formed is placed in a CVD apparatus, and the polyparaxylylene film 16 is formed to a thickness of 10 µm. With this process, the polyparaxylylene film 16 is formed on the entire surfaces of the scintillator 14 and substrate 10 (see Fig. 3D). Note that the formation of the fine projections/recesses on the surfaces of the substrate 10 by sandblasting can improve the adhesion characteristics between the polyparaxylylene film 16 and the substrate 10, thus preventing peeling of the polyparaxylylene film 16. The radiation image sensor 2 is manufactured by sticking the image sensing element (CCD) 18 to the distal end portion side of the scintillator 14 of the completed scintillator panel 1 such that the light-receiving portion opposes the distal end portion side (see Fig. 2). According to the radiation image sensor 2 of this embodiment, radiation incident from the substrate 10 side is converted into light by the scintillator 14 and detected by the image sensing element 18. In this case, since a-C substrate 10 has high radiation transmittance, the amount of radiation absorbed by the substrate 10 can be reduced. Hence, the amount of radiation reaching the scintillator 14 can be increased. In addition, since the Al film 12 as a reflecting film is formed, light incident on the light-receiving portion of the image sensing element 18 can be increased. This makes it possible to sharpen the image detected by the radiation image sensor. Fig. 10 shows outputs from the radiation image sensor 2 which are obtained when the radiation image sensor 2 detects the X-rays generated by applying 40 kV, 50 kV, and 60 kV as tube voltages to the half-wave rectifying X-ray tube, in comparison with outputs from the conventional radiation image sensor. More specifically, if the output obtained when the conventional radiation image sensor detects the X-ray generated by applying 40 kV as a tube voltage to the half-wave rectifying X-ray tube is assumed to be 100%, the output obtained when the X-ray is detected by the radiation image sensor 2 is 260%. If the output obtained when the conventional radiation image sensor detects the X-ray generated by applying 50 kV as a tube voltage to the half-wave rectifying X-ray tube is assumed to be 100%, the output obtained when the X-ray is detected by the radiation image sensor 2 is 230%. If the output obtained when the conventional radiation image sensor detects the X-ray generated by applying 60 kV as a tube voltage to the half-wave rectifying X-ray tube is assumed to be 100%, the output obtained when the X-ray is detected by the radiation image sensor 2 is 220%. The second embodiment of the present invention will be described next. Note that the same reference numerals denoting the parts of the scintillator panel 1 and radiation image sensor 2 as in the first embodiment denote the same parts in the second embodiment. Fig. 4 is a sectional view of a scintillator panel 3. Fig. 5 is a sectional view of a radiation image sensor 4. As shown in Fig. 4, the surfaces of a-C substrate 10 of the scintillator panel 3 have undergone sandblasting, and an Al film 12 serving as a reflecting film is formed on one surface. As a low-refractive-index member, an LiF film (thin transparent film) 22 having a refractive index (refractive index = 1.3) lower than that of a scintillator 14 is formed on the Al film 12. The columnar scintillator 14 for converting incident radiation into visible light is formed on the surface of the LiF film 22. Note that Tl-doped CsI (refractive index = 1.8) is used for the scintillator 14. The scintillator 14 is covered with a polyparaxylylene film 16, together with the substrate 10. As shown in Fig. 5, the radiation image sensor 4 has a structure in which an image sensing element 18 is stuck to the scintillator 14 side of the scintillator panel 3. The steps in manufacturing the scintillator panel 3 will be described next. First of all, sandblasting is performed on the surfaces of the rectangular or circular a-C substrate 10 (thickness: 1 mm) by us ing glass beads (#800), thereby forming fine projections/recesses on the surfaces of the substrate 10. The Al film 12 serving as a reflecting film is then formed on one surface of the substrate 10 to a thickness of 100 nm by vacuum vapor deposition, and the LiF film 22 as a low-refractive-index member is formed on the Al film 12 to a thickness of 100 nm by vacuum vapor deposition. A Tl-doped columnar CsI crystal is grown on the surface of the LiF film 22 by vapor deposition to form the scintillator 14 having a thickness of 250 µm. The polyparaxylylene film 16 is formed to a thickness of 10 µm by the CVD method. With this process, the polyparaxylylene film 16 is formed on the entire surfaces of the scintillator 14 and substrate 10. The radiation image sensor 4 is manufactured by sticking the image sensing element (CCD) 18 to the distal end portion of the scintillator 14 of the completed scintillator panel 3 such that the light-receiving portion opposes the distal end portion (see Fig. 5). According to the radiation image sensor 4 of this embodiment, radiation incident from the substrate 10 side is converted into light by the scintillator 14 and detected by the image sensing element 18. In this case, since a-C substrate 10 has high radiation transmittance, the amount of radiation absorbed by the substrate 10 can be reduced. Hence, the amount of radiation reaching the scintillator 14 can be increased. In addition, since the Al film 12 as a reflecting film and the LiF film 22 as a low-refractive-index member are formed, light incident on the light-receiving portion of the image sensing element 18 can be increased. This makes it possible to sharpen the image detected by the radiation image sensor. As shown in Fig. 10, if the output obtained when the conventional radiation image sensor detects the X-ray generated by applying 40 kV as a tube voltage to the half-wave rectifying X-ray tube is assumed to be 100%, the output obtained when the X-ray is detected by the radiation image sensor 4 is 300%. If the output obtained when the conventional radiation image sensor detects the X-ray generated by applying 50 kV as a tube voltage to the half-wave rectifying X-ray tube is assumed to be 100%, the output obtained when the X-ray is detected by the radiation image sensor 4 is 270%. If the output obtained when the conventional radiation image sensor detects the X-ray generated by applying 60 kV as a tube voltage to the half-wave rectifying X-ray tube is assumed to be 100%, the output obtained when the X-ray is detected by the radiation image sensor 4 is 260%. The third embodiment of the present invention will be described next. Note that the same reference numerals denoting the parts of the scintillator panels 1 and 3 and radiation image sensors 2 and 4 as in the first and second embodiments denote the same parts in the third embodiment. Fig. 6 is a sectional view of a scintillator panel 5. Fig. 7 is a sectional view of a radiation image sensor 6. As shown in Fig. 6, the surfaces of a-C substrate 10 of the scintillator panel 3 have undergone sandblasting, and an LiF film (thin transparent film) 22 is formed on one surface. A columnar scintillator 14 for converting incident radiation into visible light is formed on the surface of the LiF film 22. Note that Tl-doped CsI is used for the scintillator 14. The scintillator 14 is covered with a polyparaxylylene film 16, together with the substrate 10. As shown in Fig. 7, the radiation image sensor 6 has a structure in which an image sensing element 18 is stuck to the distal end portion side of the scintillator 14 of the scintillator panel 5. The steps in manufacturing the scintillator panel 5 will be described next. First of all, sandblasting is performed on the surfaces of the rectangular or circular a-C substrate 10 (thickness: 1mm) by using glass beads (#800), thereby forming fine projections/recesses on the surfaces of the substrate 10. The LiF film 22 as a low-refractive-index member is then formed on one surface of the substrate 10 to a thickness of 100 nm by vacuum vapor deposition. A Tl-doped columnar CsI crystal is grown on the surface of the LiF film 22 by vapor deposition to form the scintillator 14 having a thickness of 250 µm. The polyparaxylylene film 16 is formed to a thickness of 10 µm by the CVD method. With this process, the polyparaxylylene film 16 is formed on the entire surfaces of the scintillator 14 and substrate 10. The radiation image sensor 6 is manufactured by sticking the image sensing element (CCD) 18 to the distal end portion side of the scintillator 14 of the completed scintillator panel 5 such that the light-receiving portion opposes the distal end portion side (see Fig. 7). According to the radiation image sensor 6 of this embodiment, radiation incident from the substrate 10 side is converted into light by the scintillator 14 and detected by the image sensing element 18. In this case, since a-C substrate 10 has high radiation transmittance, the amount of radiation absorbed by the substrate 10 can be reduced. Hence, the amount of radiation reaching the scintillator 14 can be increased. In addition, since the LiF film 22 is formed as a low-refractive-index member, light satisfying the total reflection condition is reflected by the interface between the scintillator 14 and the LiF film 22, and the amount of light incident on the light-receiving portion of the image sensing element 18 can be increased. This makes it possible to sharpen the image detected by the radiation image sensor. As shown in Fig. 10, if the output obtained when the conventional radiation image sensor detects the X-ray generated by applying 40 kV as a tube voltage to the half-wave rectifying X-ray tube is assumed to be 100%, the output obtained when the X-ray is detected by the radiation image sensor 6 is 220%. If the output obtained when the conventional radiation image sensor detects the X-ray generated by applying 50 kV as a tube voltage to the half-wave rectifying X-ray tube is assumed to be 100%, the output obtained when the X-ray is detected by the radiation image sensor 6 is 200%. If the output obtained when the conventional radiation image sensor detects the X-ray generated by applying 60 kV as a tube voltage to the half-wave rectifying X-ray tube is assumed to be 100%, the output obtained when the X-ray is detected by the radiation image sensor 6 is 190%. The fourth embodiment of the present invention will be described next. Note that the same reference numerals denoting the parts of the scintillator panel 1 and radiation image sensor 2 as in the first embodiment denote the same parts in the fourth embodiment. Fig. 8 is a sectional view of a scintillator panel 7. Fig. 9 is a sectional view of a radiation image sensor 8. As shown in Fig. 8, one surface and side surfaces of a-C substrate 10 of the scintillator panel 7 have undergone sandblasting, and the other surface is mirror-polished. A columnar scintillator 14 for converting incident radiation into visible light is formed on the other surface of this substrate. Note that Tl-doped CsI is used for the scintillator 14. The scintillator 14 is covered with a polyparaxylylene film 16, together with the substrate 10. As shown in Fig. 9, the radiation image sensor 8 has a structure in which an image sensing element 18 is stuck to the scintillator 14 side of the scintillator panel 7. The steps in manufacturing the scintillator panel 7 will be described next. First of all, sandblasting is performed on the surfaces of the rectangular or circular a-C substrate 10 (thickness: 1 mm) by using glass beads (#800), thereby forming fine projections/recesses on the surfaces of the substrate 10. In addition, the other surface of the substrate 10 is mirror-polished. A Tl-doped columnar CsI crystal is grown on the other surface of the substrate 10 by vapor deposition to form the scintillator 14 having a thickness of 250 µm. The polyparaxylylene film 16 is formed to a thickness of 10 µm by the CVD method. With this process, the polyparaxylylene film 16 is formed on the entire surfaces of the scintillator 14 and substrate 10. The radiation image sensor 8 is manufactured by sticking the image sensing element (CCD) 18 to the distal end portion side of the scintillator 14 of the completed scintillator panel 7 such that the light-receiving portion opposes the distal end portion side (see Fig. 9). According to the radiation image sensor 8 of this embodiment, radiation incident from the substrate 10 side is converted into light by the scintillator 14 and detected by the image sensing element 18. In this case, since a-C substrate 10 has high radiation transmittance, the amount of radiation absorbed by the substrate 10 can be reduced. Hence, the amount of radiation reaching the scintillator 14 can be increased. This can increase the amount of light incident on the light-receiving portion of the image sensing element 18, thereby sharpening the image detected by the radiation image sensor 8. As shown in Fig. 10, if the output obtained when the conventional radiation image sensor detects the X-ray generated by applying 40 kV as a tube voltage to the half-wave rectifying X-ray tube is assumed to be 100%, the output obtained when the X-ray is detected by the radiation image sensor 8 is 150%. If the output obtained when the conventional radiation image sensor detects the X-ray generated by applying 50 kV as a tube voltage to the half-wave rectifying X-ray tube is assumed to be 100%, the output obtained when the X-ray is detected by the radiation image sensor 8 is 135%. If the output obtained when the conventional radiation image sensor detects the X-ray generated by applying 60 kV as a tube voltage to the half-wave rectifying X-ray tube is assumed to be 100%, the output obtained when the X-ray is detected by the radiation image sensor 8 is 130%. In each embodiment described above, the a-C substrate is used. However, a graphite substrate may be used. The graphite substrate has high radiation transmittance like the a-C substrate. In this case, therefore, the amount of radiation reaching the scintillator can be increased as in the case wherein the a-C substrate is used. In the above embodiments, a LiF film is used as a thin transparent film. However, a film made of a material containing selected from the group consisting LiF, MgF 2 , CaF 2 , SiO 2 , Al 2 O 3 , MgO, NaCl, KBr, KCl, and AgCl may be used. In each embodiment described above, CsI (Tl) is used as the scintillator 14. However, the present invention is not limited to this. For example, CsI (Na), NaI(Tl), LiI(Eu), or KI(Tl) may be used. In each embodiment described above, examples of the polyparaxylylene are polymonochloroparaxylylene, polydichloroparaxylylene, polytetrachloroparaxylylene, polyfluoroparaxylylene, polydimethylparaxylylene, and polydiethylparaxylylene. According to the scintillator panel of the present invention, since the substrate made of carbon as a major constituent has high radiation transmittance, the amount of radiation absorbed by the substrate can be decreased, and the amount of radiation reaching the scintillator can be increased. In addition, according to the radiation image sensor of the present invention, since the scintillator panel has the substrate made of carbon as a major constituent having high radiation transmittance, the amount of light reaching the image sensing element can be increased. Industrial Applicability As described above, the scintillator panel and radiation image sensor of the present invention are suited for medical X-ray photography and the like.

Claims: A scintillator panel, characterised by : a substrate (10) made of amorphous carbon; a scintillator (14) deposited on said substrate; and a protective film (16) entirely covering said scintillator panel. A scintillator panel according to claim 1, characterized by further comprising a reflecting film (12) formed between said substrate (10) and said scintillator (14). A scintillator panel according to claim 2, characterized in that said reflecting film (12) is a metal film. A scintillator panel according to claim 2, characterized in that said reflecting film (12) is a thin transparent film having a refractive index lower than a refractive index of said scintillator. A scintillator panel according to claim 4, characterized in that said thin transparent film (12) is a film made of a material containing a substance selected from the group consisting of LiF, MgF 2 , CaF 2 , SiO 2 , Al 2 O 3 , MgO, NaCl, KBr, KCl, and AgCl. A radiation image sensor characterized by comprising an image sensing element (2) and a scintillator panel (1) as defined in any one of claims 1 to 5, wherein said image sensing element (2) opposes the output of said scintillator (14) of said scintillator panel (1).

Inventors: HOMME TAKUYA, SATO HIROTO, TAKABAYASHI TOSHIO, HOMME, TAKUYA, SATO, HIROTO, TAKABAYASHI, TOSHIO
Applicants: HAMAMATSU PHOTONICS KK, HAMAMATSU PHOTONICS K.K.
Application year: 1999
Main classification: G01T1
IPC codes: G01T1, B32B9