JP2007208420A - Condensing optical system and image reading apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a condensing optical system, such as a light guide capable of preventing adhesion of dust to itself, due to static electricity using a simple configuration, and to provide an image reading apparatus capable of obtaining an image, without longitudinal stripes or the like, and with superior S/N and high quality. <P>SOLUTION: In the condensing optical system, a light incident face 21a of the condensing optical system is formed with a transparent film 25, having charging characteristic that is opposite to the charging characteristic of the type of material configuring the face. The transparent film 25 is made of Nylon or a type of a material having charging characteristic, equivalent to that of Nylon. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a condensing optical system and an image reading apparatus used for a radiographic image reading apparatus or the like.

  Radiation images such as X-ray images are often used in fields such as disease diagnosis. The X-ray image is obtained by irradiating the phosphor layer (phosphor screen) with X-rays that have passed through the subject, thereby generating visible light, and then using this visible light as when taking a normal photograph. Thus, a so-called radiographic method in which a silver halide photographic light-sensitive material (hereinafter also simply referred to as “photosensitive material”) is irradiated and then subjected to development processing to obtain a visible silver image is widely used.

  However, in recent years, a new method for taking out an image directly from a phosphor layer has been proposed in place of an image forming method using a photosensitive material having a silver halide salt. In this method, the radiation transmitted through the subject is absorbed by the phosphor, and then the phosphor is excited by light or thermal energy, for example, so that the radiation energy accumulated by the phosphor is absorbed as fluorescence. There is a method of emitting and detecting this fluorescence and imaging.

  Specifically, for example, a radiation image conversion method using a stimulable phosphor as described in Patent Documents 1 and 2 below is known. This method uses a radiation image conversion sheet or plate (hereinafter also simply referred to as “plate”) containing a stimulable phosphor, and the radiation transmitted through the subject to the stimulable phosphor layer of this plate. The radiation energy corresponding to the radiation transmission density of each part of the subject is accumulated, and then the photostimulable phosphor is raster scanned with excitation light such as laser light in the visible to near infrared region, Radiation energy accumulated in the fluorescent material is emitted as stimulated emission light. A signal based on the intensity of the stimulated emission light is converted into an electric signal by a photoelectric conversion element such as a CCD or a photomultiplier tube, and then this signal is displayed as a visible image on a display device such as a film or a CRT.

  According to the radiographic image recording / reproducing method described above, a radiographic image with a much smaller exposure dose and abundant information can be obtained as compared with a radiographic method using a combination of a conventional radiographic film and an intensifying screen. Has the advantage of being able to. As described above, a stimulable phosphor is a phosphor that exhibits stimulated emission when irradiated with radiation and then irradiated with excitation light, and practically has a wavelength corresponding to the excitation spectrum of the stimulable phosphor. Generally, phosphors exhibiting stimulated emission in the wavelength range of 300 to 500 nm by excitation light in the range of 550 to 750 nm are used.

  Plates using these photostimulable phosphors release accumulated energy by scanning excitation light after accumulating radiation image information, so that radiation images can be accumulated again after scanning and can be used repeatedly. Is possible. Normally, the accumulated information remains on the plate only by the excitation light scanning and appears as noise at the next photographing, so the accumulated information is erased by a halogen lamp or the like. In other words, the conventional radiographic method consumes a radiographic film for each imaging, whereas this radiographic image conversion method allows the plate to be used repeatedly, which is advantageous in terms of resource protection and economic efficiency. is there.

  This system using a photostimulable phosphor plate is called a computed radiography (hereinafter also referred to as “CR”), and is widely used today. This radiographic image reading apparatus using CR is roughly divided into two types: a dedicated type with a built-in plate and a cassette type in which a cassette in which a plate is stored is inserted into the apparatus, and the plate is pulled out from the cassette in the apparatus to perform reading. Is done. These devices are widely used in the medical field today because of the economy that can be used repeatedly and the convenience of handling images as digital data.

  FIG. 4 schematically shows a main part of a conventional CR condensing optical system. When a laser beam from a semiconductor laser is irradiated onto a radiation image conversion plate on which a radiation image is recorded while being scanned, The stimulated emission light generated on the image plane is directly and / or reflected by the condensing mirror, is incident on the tip of the light guide, is condensed, and is photoelectrically converted by the photoelectric conversion element. Laser scanning on the image plane is the main scanning, the direction is the main scanning direction (perpendicular to the paper surface in FIG. 4), the movement of the plate in the direction perpendicular thereto is sub-scanning, and the direction is the sub-scanning direction (see FIG. 4 in the vertical direction), two-dimensional image reading can be performed by moving the plate or the optical system itself in the sub-scanning direction with respect to the main scanning of the laser beam.

Patent Document 3 below discloses a group consisting of a siloxane-based antistatic agent, a resin-based olefin, a resin-based polyester, and a UV curable hard coat agent at one end of the light-collecting guide and in the vicinity thereof in order to prevent electrostatic charge in the light-condensing guide. A radiation image reading apparatus coated with one or more selected antistatic agents is disclosed.
US Pat. No. 3,859,527 Japanese Patent Laid-Open No. 55-12144 Japanese Patent Publication No. 3636796

  However, when the light guide made of the acrylic or olefin resin is disposed so as to face the scanning line, dust or the like may adhere to the tip portion of the light guide as shown in FIG. The scanning light is blocked and appears as vertical stripes in the read image, which may impair the image quality. If the light guide is arranged sufficiently separated from the scanning line, the scanning light is not blocked even if dust adheres to it, but if this is done, the problem that the light collection efficiency is reduced and the SN ratio of the image is liable to occur.

  In contrast, Patent Document 3 proposes that an antistatic agent be coated on the tip of the light guide. However, the antistatic agent basically reduces the surface resistance and reduces the charge generated on the surface. It is formed for the purpose of escaping quickly, and when the dust is more strongly charged, there is a limit to its effect, for example, the dust may adhere to the surface even with a small residual charge.

  In view of the above-described problems of the prior art, the present invention has no condensing optical system and vertical streak that can prevent dust from adhering to a condensing optical system such as a light guide due to static electricity with a simple configuration. An object of the present invention is to provide an image reading apparatus capable of obtaining a high-quality image with a good ratio.

  In order to achieve the above object, as a result of intensive studies by the present inventors, when the material and charging characteristics of the target dust can be specified, a measure of releasing the charge is insufficient, and the light guide This is based on the finding that it is effective to generate a repulsive force between the light guide and the dust by making the charging codes of both the dust and the dust coincide with each other.

  For example, in a hospital where a radiological image reader is installed, hair (wool) and cotton generated from blankets and duvets are the main dust materials, and according to the charged column of the substance, hair (wool) and cotton are positive. If, for example, a material that tends to be negatively charged due to light transmittance characteristics, such as acrylic resin or olefin resin, must be used as the light guide, the surface of the light guide is charged positively. By modifying so as to be easy to do, a positive charge similar to that of dust is generated, and a repulsive force opposite to attracting dust is generated. In this way, the substance that modifies the surface of the light guide so as to be easily charged positively needs to be translucent in order to be used for the condensing optical system in addition to the property of being easily charged positively. As described above, in the present invention, a translucent film having charging characteristics similar to the charging characteristics of dust generated in the use environment is formed on the surface of the condensing optical system facing the scanning lines on the plate.

  That is, the condensing optical system according to the present invention is characterized in that a light-transmitting film having a charging characteristic opposite to the charging characteristic of the material constituting the surface is formed on the light incident surface of the condensing optical system.

  According to this condensing optical system, a material that is easily negatively charged, such as an acrylic resin or an olefin resin, is used for the condensing optical system, and dust in the usage environment is easily positively charged. For example, wool When cotton or cotton is the main material, dust tends to adhere to the surface of the condensing optical system, so charging opposite to the charging characteristics of the material constituting the condensing optical system surface (which tends to be negatively charged) By forming a translucent film having characteristics (easily positively charged) on the surface of the condensing optical system and making the surface of the condensing optical system have the same charging characteristics as dust, Rebounds on the surface and does not adhere to the surface of the condensing optical system. In this manner, dust can be prevented from adhering to a condensing optical system such as a light guide due to static electricity with a simple configuration.

  In the condensing optical system, the translucent film is preferably made of nylon or a material having a charging characteristic equivalent to that of nylon. Nylon is a preferred material formed on the surface of the condensing optical system facing the scanning line on the recording medium because it has a charging characteristic that is easily charged positively and is film-like and translucent.

  Another condensing optical system according to the present invention is characterized in that a light-transmitting film made of nylon or a material having a charging characteristic equivalent to this is formed on the light incident surface of the condensing optical system.

  According to this condensing optical system, a material that is easily negatively charged, such as an acrylic resin or an olefin resin, is used for the condensing optical system, and dust in the usage environment is easily positively charged. For example, wool When the main material is cotton or cotton, dust easily adheres to the surface of the condensing optical system. By forming the surface of the condensing optical system to have the same charging characteristics as dust, the dust repels on the surface of the condensing optical system and does not adhere to the surface of the condensing optical system. In this manner, dust can be prevented from adhering to a condensing optical system such as a light guide due to static electricity with a simple configuration.

  In each of the condensing optical systems, the material constituting the surface of the condensing optical system is preferably a translucent acrylic resin or olefin resin.

  The condensing optical system includes a light guide disposed so as to face a scanning line on the recording medium, and forms the translucent film on a surface of the light guide on the scanning line side. Can be configured.

  The translucent film may be formed by adhering a film of the material by heat treatment or an ultraviolet curable adhesive. Since an air layer is not formed between the surface of the condensing optical system and the translucent film by bonding the translucent film, it is possible to suppress light reflection loss at the interface with the air.

  And a scanning optical system for irradiating the recording medium with a light beam in order to read image information from the recording medium on which the image is recorded, and emitting light or reflected light from the recording medium. Is preferably guided to the photoelectric conversion element, and the translucent film is preferably formed on the surface of the condensing optical system facing the scanning line on the recording medium. As a result, the above-described condensing optical system can be applied to an optical system for image reading, and dust can be prevented from adhering to the condensing optical system, so that the read image has no vertical stripes and has a good SN ratio. Images can be obtained.

  An image reading apparatus according to the present invention includes the above-described condensing optical system, and reads image information from the recording medium. According to this image reading apparatus, as described above, dust is collected on the surface of the condensing optical system for guiding the emitted light / reflected light from the recording medium to the photoelectric conversion element, which faces the scanning line on the recording medium. Since it does not adhere, it is possible to obtain a high-quality image with no vertical streak in the read image and a good SN ratio.

  Note that the thickness of the above-described translucent film is desirably 1 μm or more and 3 mm or less. When the translucent film has a thickness of 1 μm or more, the strength is sufficient, and when the thickness is 3 mm or less, the light transmittance in the blue region does not decrease so much and the SN ratio does not decrease.

  Further, the material having the same charging characteristics as nylon is a material that is more easily charged positively than iron in the charging train, such as rayon or cellophane, but is not limited thereto.

  According to the condensing optical system of the present invention, it is possible to prevent dust from adhering to the condensing optical system such as a light guide due to static electricity with a simple configuration. In addition, according to the image reading apparatus of the present invention, it is possible to obtain a high-quality image having no vertical streak or the like and a good SN ratio.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view schematically showing a condensing optical system for CR image reading according to the present embodiment. FIG. 2 is a side view showing a main part of the condensing optical system of FIG. FIG. 3 is a diagram showing a charge train in which various substances are arranged in the order in which they are easily charged.

  In the condensing optical system shown in FIG. 1, laser light emitted from a semiconductor laser 11 as an excitation light source driven by a laser drive circuit 19 becomes parallel light by a collimator lens 12 and enters a beam splitter 13 formed by a parallel plane plate. . The laser beam that has passed through the beam splitter 13 enters the cylindrical lens 14 and forms a linear image on the polygon mirror 15 that rotates in the rotation direction a. This is to prevent the influence of the tilt angle of the polygon mirror 15 by optically equalizing the polygon mirror surface and the image surface of the radiation image conversion plate P together with the cylindrical mirror 17 described later. It is a method.

  The laser beam reflected by the polygon mirror 15 reaches the image plane through the fθ lens 16 and the cylindrical mirror 17, and the polygon mirror 15 rotates to perform main scanning on the image plane in order to perform two-dimensional image reading. While performing the main scanning of the laser beam in the direction m, the plate (or the optical system itself) is moved in the sub-scanning direction n with respect to the main scanning of the laser beam.

  In addition, a part of the light from the beam splitter 13 is incident on the monitor detector 18 and feedback control is performed so that the light output of the semiconductor laser 11 is constant.

  The above-described semiconductor laser 11 to cylindrical mirror 17 constitute a scanning optical system.

  The locus of the laser beam on the surface of the plate P extends in the main scanning direction m and becomes a straight line, and is a collection for collecting the stimulated emission light from each part of the relatively long scanning line k in the linear form on the photoelectric conversion element. An optical optical system is required. This condensing optical system is provided with a light guide 21 for efficiently guiding light from a long scanning line k to a round or square photomultiplier tube 23 which is a photoelectric conversion element through the condensing tube 22. ing. The light guide 21 is disposed so that the incident surface 21a extends in the main scanning direction m and faces the scanning line k on the plate P.

  The light guide 21 is made of an acrylic resin or an olefin resin having a relatively high light transmittance with respect to light having a wavelength of 300 to 500 nm in order to efficiently transmit the stimulated emission light.

  If the photoelectric surface of the photoelectric conversion element has the same length as the scanning line k, the photoelectric conversion element may be disposed as it is facing the reading line as it is, but such a photoelectric conversion element is a special one. Since the size is large and the cost is high, usually, a photoelectric conversion element such as a photomultiplier tube having a round or square photoelectric conversion surface is used.

  The stimulated emission light from the scanning line k in FIG. 1 enters from the incident surface 21a of the light guide 21, and is guided to the photomultiplier tube 23 through the condenser tube 22, and the optical signal is converted into an electrical signal to be imaged. Reading can be done.

  As shown in FIG. 2, a translucent film 25 is formed on the incident surface 21a located on the tip side of the light guide 21 of the condensing optical system of FIG. The translucent film 25 is made of translucent film-like nylon, and is bonded with an ultraviolet curable adhesive so as to cover substantially the entire incident surface 21a. Nylon has a charging characteristic that is easily positively charged.

  The translucent film 25 may be other than nylon as long as it has a charging property equivalent to that of nylon, and may be, for example, rayon or cellophane. For example, the translucent film 25 made of nylon is formed by adhering a nylon film to the incident light surface of the light guide 21 by an ultraviolet curable adhesive or a heat treatment, so that the incident surface 21 a and the translucent film 25 are formed. It becomes the structure which does not interpose an air layer in between, the reflection loss of the signal light in the interface with air can be suppressed, and a high SN ratio can be maintained.

  The thickness of the translucent film 25 made of nylon is preferably 1 μm or more and 3 mm or less, and if it is thinner than 1 μm, the strength is insufficient, and if it is thicker than 3 mm, the transmittance in the blue region is lowered. The S / N ratio decreases.

  Although the image reading apparatus can be configured with the condensing optical system shown in FIGS. 1 and 2 as described above, in this image reading apparatus, the radiation image conversion plate in which the radiation transmitted through the subject is absorbed by the stimulable phosphor. By irradiating P with laser light while two-dimensionally scanning, the stimulated emission light b generated as shown in FIG. 2 is reflected directly and / or the reflected light c reflected by the condenser mirror 24 is reflected by the light guide 21. When the light enters the incident surface 21a through the translucent film 25, the light signal is guided to the photomultiplier tube 23 through the condenser tube 22, and the optical signal is converted into an electric signal on the photoelectric conversion surface. This digital signal is displayed as a visible image on a film-like recording material such as a silver halide photographic material or a display device such as a CRT / liquid crystal panel.

  Next, the effect of the translucent film | membrane 25 formed in the entrance plane 21a of the light guide 21 in the condensing optical system of FIG. 1, FIG. 2 is demonstrated with reference to FIG.

  Generally, static electricity is generated when different materials are rubbed together, and each material is charged positively or negatively. At this time, whether each substance is positively charged or negatively charged depends on what the two substances are. Whether or not a certain substance is easily charged negatively or easily charged positively is generally evaluated by a sequence of charged columns as shown in FIG.

  Although the order of the charged series may vary slightly depending on the researcher, the large order relation remains unchanged. For example, an acrylic resin or an olefin resin is easily negatively charged, and glass is easily positively charged. Here, the problem is fibrous dust generated from clothes, etc. Especially in hospitals where radiographic image readers are installed, the main dust is wool (wool) and cotton generated from blankets and duvets. It becomes the material of. Referring to the charge train in FIG. 3, it can be seen that these are easily charged positively. That is, the mechanism of dust adhering to the light guide is that dust, such as positively charged hair and cotton, is attracted to the light guide made of negatively charged acrylic resin by Coulomb force.

  As described above, the action of the antistatic agent is to quickly release the generated charges by lowering the surface resistance value. However, as long as the dust is positively charged and the light guide is negatively charged, this effect is a matter of degree, and if the dust is strongly positively charged, such as during drying, the effect will fade. End up.

  As described above, when the material and charging characteristics of the target dust can be specified, it is effective not to take measures to escape the charge but to make both charging codes coincide to generate a repulsive force. If a material that tends to be negatively charged due to light transmittance characteristics must be used as a guide, this surface can be modified to be positively charged to generate a positive charge similar to dust. By generating a repulsive force opposite to attracting dust, the dust is prevented from adhering to the incident surface of the light guide.

  This material is easily positively charged and needs to be translucent for use in a condensing optical system, but this requirement can be satisfied by using, for example, nylon from the charging train of FIG. Further, as described above, any material satisfying the above conditions need not be limited to nylon, and any material having charging characteristics equivalent to nylon, such as rayon or cellophane, can be used. More specifically, the charging characteristic equivalent to that of nylon refers to a material that is more likely to be charged more positively than iron in the charging train.

  The case where the light guide made of acrylic resin as shown in FIGS. 1 and 2 is used as it is (comparative example), and the case where a light-transmitting film made of nylon film having a thickness of 15 μm is adhered to the incident surface by heat treatment (example). The number of vertical streaks due to dust adhesion was compared when images were acquired by bringing tens of thousands to hundreds of thousands of fibrous dusts mainly composed of hair into the CR image reading apparatus.

  In the case of no comparative translucent film, five vertical streaks were observed, whereas when the translucent film of the nylon film of the example was adhered, no vertical streak was observed. In addition, when the device was disassembled and the state of the tip of the light guide was observed, in the comparative example without the translucent film, hundreds of short dust adhered to the dust that generated vertical streaks. On the other hand, in the case of an example in which a translucent film made of nylon film was adhered, only a few short dusts were attached.

  As described above, the best mode for carrying out the present invention has been described. However, the present invention is not limited to these, and various modifications are possible within the scope of the technical idea of the present invention. For example, the condensing optical system of the present invention may be used not only for the image reading condensing optical system as shown in FIGS. 1 and 2, but also for other condensing optical systems. It is.

  Further, the image reading apparatus may be either a plate built-in dedicated type or a cassette type.

It is a perspective view which shows typically the condensing optical system for the image reading by this Embodiment. It is a side view which shows the principal part of the condensing optical system of FIG. It is a figure which shows the electrification row | line | column which arranged the various substances in order that it is easy to charge (refer Watanabe Electric Industry Co., Ltd. homepage). It is a side view which shows the principal part of the conventional condensing optical system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Semiconductor laser 15 Polygon mirror 21 Light guide 21a Incident surface 25 Translucent film P Radiation image conversion plate, plate b Photoluminescence light k Scan line m Main scanning direction n Sub scanning direction

Claims (8)

  A condensing optical system, wherein a light-transmitting film having a charging characteristic opposite to a charging characteristic of a material constituting the surface is formed on a light incident surface of the condensing optical system.   The condensing optical system according to claim 1, wherein the translucent film is made of nylon or a material having a charging characteristic equivalent to that of nylon.   A condensing optical system, wherein a light-transmitting film made of nylon or a material having a charging characteristic equivalent to this is formed on a light incident surface of the condensing optical system.   The condensing optical system according to claim 1, 2 or 3, wherein a material constituting the surface of the condensing optical system is an acrylic resin or an olefin resin.   The condensing optical system according to any one of claims 1 to 4, wherein the condensing optical system includes a light guide, and the light-transmitting film is formed on a light incident surface of the light guide.   6. The condensing optical system according to claim 1, wherein the translucent film is formed by adhering a film of the material by heat treatment or an ultraviolet curable adhesive. In order to read image information from a recording medium on which an image is recorded, a scanning optical system that irradiates the recording medium while scanning with a light beam is provided, and the condensing optical system photoelectrically emits light or reflected light from the recording medium. Configured to lead to the conversion element,
The condensing optical system according to claim 1, wherein the translucent film is formed on a surface of the condensing optical system facing a scanning line on the recording medium. An image reading apparatus comprising the condensing optical system according to claim 7 and reading image information from the recording medium.

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