Patent Publication Number: US-2011049373-A1

Title: Radiological image reader

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a radiological image reader that reads radiological images from a medium having a radiological image forming surface including a photostimulable phosphor. 
     A radiological image reader that reads radiological images from an imaging plate irradiates a radiological image forming surface of the imaging plate with the excitation light emitted from a light source and detects the photostimulated luminescence light emitted from an irradiation point of the excitation light by a photodetector. The radiological image forming surface is scanned by the irradiation point of the excitation light. The radiological image forming surface is scanned by an irradiation point in a plurality of modes. 
     In the radiological image reader of Japanese Patent Application Laid-Open No. 61-267451, a transport mechanism linearly moves an imaging plate supported on a flat surface, and then an excitation light optical system linearly moves an irradiation point in a direction perpendicular to a linear movement direction of the imaging plate. In the radiological image reader of Japanese Patent Application Laid-Open No. 61-267451, however, the distance between the light source and the irradiation point cannot be maintained constant, and an angle of incidence of the excitation light with respect to the radiological image forming surface cannot be maintained constant, whereby radiological images cannot be read in a uniform manner. 
     In the radiological image reader in FIG. 2 of Japanese Patent Application Laid-Open No. 06-160998, a transport mechanism linearly moves an imaging plate supported on a cylindrical surface in an axis direction, and a rotation mechanism rotates an excitation light optical system around the axis. The radiological image reader of Japanese Patent Application Laid-Open No. 06-160998 has a problem that the imaging plate is susceptible to damage because it is curved. Moreover, in the radiological image reader of Japanese Patent Application Laid-Open No. 06-160998, mounting of the imaging plate is time consuming, which makes it difficult to continuously read radiological images from a large number of imaging plates. Note that there is also known a radiological image reader that rotates a cylindrical surface in place of rotating an excitation light optical system. 
     In the radiological image reader of Japanese Patent Publication No. 06-97328, a rotation mechanism rotates an imaging plate supported on a flat surface, and a transport mechanism linearly moves an excitation light optical system in a radial direction. In the radiological image reader of Japanese Patent Publication No. 06-97328, mounting of the imaging plate is time consuming, and thus it is difficult to continuously read radiological images from a large number of imaging plates. 
     In the radiological image reader of Japanese Patent No. 2580183, a transport mechanism linearly moves an imaging plate supported on a flat surface, and an excitation light optical system circularly moves an irradiation point on a running plane on which a radiological image forming surface of the imaging plate runs. 
     According to the radiological image reader of Japanese Patent No. 2580183, the above-mentioned problems are solved. However, a hole is formed in a mirror that reflects the photostimulated luminescence light and guides the reflected light to a photodetector, and thus the photostimulated luminescence light is not efficiently guided from the irradiation point to the photodetector, which results in insufficient sensitivity in reading of radiological images. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a radiological image reader capable of improving the sensitivity of reading a radiological image. 
     The present invention is directed to a radiological image reader that reads a radiological image from a medium having a radiological image forming surface including a photostimulable phosphor. 
     According to a first aspect of the present invention, a radiological image reader includes a holder, a light source, a scanning mechanism, a photodetector and a relative movement mechanism. The holder holds the medium in a flat manner. The light source emits excitation light. The scanning mechanism causes an optical path of the excitation light emitted from the light source to rotate around a rotation axis that is perpendicular to a scanning plane and is apart from the light source, and causes an irradiation point at which the excitation light emitted from the light source is irradiated to circularly move on the scanning plane. The scanning plane includes a radiological image forming surface of the medium held by the holder. The photodetector is provided-on the rotation axis and detects photostimulated luminescence light emitted from the irradiation point. The relative movement mechanism causes the holder to move in a direction perpendicular to the rotation axis, relative to the scanning mechanism. 
     Accordingly, an angle of incidence of the excitation light to the radiological image forming surface is maintained constant, and a radiological image is read in a uniform manner. In addition, the medium is not curved, which suppresses damage to the medium. Further, incidence of the photostimulated luminescence light to the photodetector is not impeded, which improves the sensitivity of reading a radiological image. Moreover, the light source becomes apart from the rotation axis, which facilitates power feeding to the light source. 
     According to a second aspect of the present invention, in the first aspect, the scanning mechanism includes an excitation light optical system and a rotation mechanism. The excitation light optical system guides the excitation light to an irradiation point apart from the rotation axis. The rotation mechanism causes at least part of the excitation light optical system to rotate around the rotation axis. The excitation light optical system includes a first bending optical element. The first bending optical element is provided on the rotation axis and bends the excitation light that has reached from a direction in which the rotation axis extends toward the direction inclined with respect to the rotation axis. The rotation mechanism causes the first bending optical element to rotate around the rotation axis. 
     Accordingly, it is not required to rotate the light source, which facilitates power feeding to the light source. 
     According to a third aspect of the present invention, in the second aspect, the excitation light optical system further includes a second bending optical element. The second bending optical element is secured separately from the rotation mechanism on the rotation axis and guides the excitation light from the direction inclined with respect to the rotation axis to the first bending optical element by bending the excitation light toward the direction in which the rotation axis extends. 
     Accordingly, the light source is easily separated from the rotation axis, which increases a degree of freedom in structure of the radiological image reader. 
     According to a fourth aspect of the present invention, in the second aspect, the radiological image reader further includes a photostimulated luminescence light optical system. The photostimulated luminescence light optical system guides the photostimulated luminescence light emitted from the irradiation point to the photodetector. 
     Accordingly, the photostimulated luminescence light emitted from the irradiation point is efficiently guided to the photodetector, which improves the sensitivity of reading a radiological image. 
     According to a fifth aspect of the present invention, in the fourth aspect, part of an optical path of the excitation light optical system and part of an optical path of the photostimulated luminescence light optical system pass through a common light guide part. 
     Accordingly, at least part of the excitation light optical system and part of the photostimulated luminescence light optical system rotate in synchronization with each other, and the photostimulated luminescence light emitted from the irradiation point is efficiently guided to the photodetector, leading to an improvement in reading of an radiological image. 
     According to a sixth aspect of the present invention, in the fifth aspect, the photostimulated luminescence light optical system is part of a structure provided between the photodetector and the scanning plane. A light guide part is formed in the structure. The light guide part has the light inlet for photostimulated luminescence light on a surface opposed to the scanning plane and a light outlet for photostimulated luminescence light on a surface opposed to the photodetector. The excitation light optical system guides the excitation light from the light source to the scanning plane via the light guide part. 
     Accordingly, the optical path of the excitation light and the optical path of the photostimulated luminescence light coexist inside the light guide part, and thus the radiological image reader is miniaturized. 
     According to a seventh aspect of the present invention, in the sixth aspect, an optical axis of the photostimulated luminescence light optical system passes through the irradiation point. 
     Accordingly, the photostimulated luminescence light emitted from the irradiation point is efficiently guided to the photodetector, which improves the sensitivity of reading a radiological image. 
     According to an eighth aspect of the present invention, in the fifth aspect, the photostimulated luminescence light optical system is part of a structure provided between the photodetector and the scanning plane. The rotation mechanism causes the structure to rotate around the rotation axis. 
     Accordingly, the structure is made simple to be easily rotated, which facilitates the rotation of the photostimulated luminescence light optical system. 
     According to a ninth aspect of the present invention, in the eighth aspect, the structure is a hollow body. A hollow light guide part as the light guide part is formed in the hollow body. The hollow light guide part has a light inlet for photostimulated luminescence light that is opposed to the scanning plane and a light outlet for photostimulated luminescence light that is opposed to the photodetector. 
     Accordingly, the photostimulated luminescence light is efficiently guided from the light inlet to the light outlet, which improves the sensitivity of reading a radiological image. 
     According to a tenth aspect of the present invention, in the eighth aspect, the structure includes a solid light guide part as the light guide part. The solid light guide part has a light inlet for photostimulated luminescence light that is opposed to the scanning plane and a light outlet for photostimulated luminescence light that is opposed to the photodetector. 
     Accordingly, the photostimulated luminescence light is efficiently guided from the light inlet to the light outlet, which improves the sensitivity of reading a radiological image. 
     Desirably, in the ninth or tenth aspect, the light guide part has a shape selected from the group consisting of an oval spherical shape, a cylindrical shape and a conical shape. 
     Desirably, in the ninth or tenth aspect, the structure includes a lens that is provided to the light inlet and guides the photostimulated luminescence light to an inside of the light guide part. 
     According to an eleventh aspect of the present invention, in the ninth or tenth aspect, the light inlet is formed apart from the rotation axis, and the light outlet is formed on the rotation axis. 
     Accordingly, the photostimulated luminescence light is guided to the light outlet formed on the rotation axis, and the photodetector is easily provided on the rotation axis, which simplifies the photostimulated luminescence light optical system. 
     According to a twelfth aspect of the present invention, in the fourth aspect, the photostimulated luminescence light optical system is part of a structure provided between the photodetector and the scanning plane to be secured separately from the rotation mechanism. A light guide part is formed in the structure. The light guide part has a light inlet for photostimulated luminescence light on a surface opposed to the scanning plane and a light outlet for photostimulated luminescence light on a surface opposed to the photodetector. A surface of the light guide part is a concave reflecting mirror that has rotational symmetry with the rotation axis and collects the photostimulated luminescence light entering from the light inlet to the light outlet. 
     Accordingly, the structure is secured, which simplifies the radiological image reader. 
     According to a thirteenth aspect of the present invention, in the eighth aspect, the radiological image reader further includes a blower mechanism guiding air toward the scanning plane. 
     Accordingly, the medium is pressed against the holder, which suppresses positional deviation of the medium. 
     According to a fourteenth aspect, in the eighth aspect, the radiological image reader further includes an optical filter. The optical filter is interposed between the photodetector and the structure. The optical filter has a higher transmittance of a wavelength of the photostimulated luminescence light than a transmittance of a wavelength of the excitation light. 
     Accordingly, the excitation light less affects the photodetector, which improves the sensitivity of reading a radiological image. 
     According to a fifteenth aspect of the present invention, in the first aspect, the radiological image reader further includes a housing and a dust collecting mechanism. The housing accommodates the light source, the scanning mechanism and the photodetector. The dust collecting mechanism collects dust inside the housing. 
     Accordingly, dust inside the housing decreases, and dust is prevented from adhering to the medium, which improves the accuracy of reading a radiological image. 
     According to a sixteenth aspect of the present invention, in the first aspect, the relative movement mechanism moves the medium relative to the scanning mechanism in a linear manner. 
     Accordingly, the transport mechanism is simplified. 
     According to a seventeenth aspect of the present invention, in the first aspect, the scanning mechanism is secured, and the relative movement mechanism moves the holder. 
     Accordingly, a large number of media are continuously read with ease. Further, the length from the light source to the irradiation point is maintained constant, whereby a radiological image is read in a uniform manner. 
     According to an eighteenth aspect of the present invention, in the first aspect, the holder is secured, and the relative movement mechanism moves the scanning mechanism. 
     Accordingly, a footprint does not increase extremely even in a case where a large number of media are read. 
     According to a nineteenth aspect of the present invention, in the eighteenth aspect, the relative movement mechanism moves the light source integrally with the scanning mechanism. 
     Accordingly, the length from the light source to the irradiation point is maintained constant, whereby a radiological image is read in a uniform manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a reader according to a first preferred embodiment; 
         FIG. 2  is a perspective view of an internal mechanism of the reader according to the first preferred embodiment; 
         FIG. 3  is a top view showing a track of an irradiation point and a radiological image forming surface on a scanning plane; 
         FIG. 4  is a cross-sectional view of a rotary structure according to a second preferred embodiment; 
         FIG. 5  is a cross-sectional view of a rotary structure according to a third preferred embodiment; 
         FIG. 6  is a cross-sectional view of another rotary structure according to the third preferred embodiment; 
         FIG. 7  is a cross-sectional view of a rotary structure according to a fourth preferred embodiment; 
         FIG. 8  is a cross-sectional view of a rotary structure according to a fifth preferred embodiment; 
         FIG. 9  is a cross-sectional view of a rotation mechanism and a rotary structure according to a sixth preferred embodiment; 
         FIG. 10  is a cross-sectional view of another rotation mechanism and another rotary structure according to the sixth preferred embodiment; 
         FIG. 11  is a cross-sectional view of a rotation mechanism and a rotary structure according to a seventh preferred embodiment; 
         FIG. 12  is a cross-sectional view of a reading mechanism according to an eighth preferred embodiment; 
         FIG. 13  is a bottom view of a fixed structure according to the eighth preferred embodiment; 
         FIG. 14  is a cross-sectional view of a transport mechanism according to a ninth preferred embodiment; 
         FIG. 15  is a bottom view of the transport mechanism according to the ninth preferred embodiment; 
         FIG. 16  is a cross-sectional view of a transport mechanism according to a tenth preferred embodiment; 
         FIG. 17  is a top view showing an arrangement of imaging plates according to an eleventh preferred embodiment; 
         FIG. 18  is a cross-sectional view of a reader according to a twelfth preferred embodiment; 
         FIG. 19  is a perspective view of the reader according to the twelfth preferred embodiment; and 
         FIG. 20  is a cross-sectional view of a reader according to a thirteenth preferred embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Preferred Embodiment 
     A first preferred embodiment relates to a radiological image reader  1002  that reads radiological images from a radiological image forming surface S of an imaging plate IP. 
     (Imaging Plate IP) 
     The imaging plate IP is a medium having the radiological image forming surface S including a photostimulable phosphor. When the radiological image forming surface S is irradiated with radial rays such as X-rays, a radiological image is drawn as a latent image on the radiological image forming surface S. The reader  1002  reads the radiological image from the radiological image forming surface S and generates image data of the radiological image. 
     (Outline of Reader  1002 ) 
       FIG. 1  is a schematic view of the reader  1002 , which is a cross-sectional view of the reader  1002 .  FIG. 2  is a schematic view of an internal mechanism  1004  of the reader  1002 , which is a perspective view of the internal mechanism  1004 . 
     As shown in  FIGS. 1 and 2 , the reader  1002  includes a reading mechanism  1007  that reads radiological images from the radiological image forming surface S, a belt  1080  that holds the imaging plate IP, a belt drive mechanism  1082  that causes the belt  1080  to go therearound, a controller  1030  that controls the reader  1002 , a dust collecting mechanism  1032  that collects dust, an erase beam light source  1024  that emits an erase beam, a frame  1026  that supports components, and a housing  1028  that accommodates those described above. 
     The imaging plate IP inserted into an inlet  1094  formed in the housing  1028  and carried into the reader  1002  is held in an outgoing portion of the belt  1080 . The imaging plate IP held in the outgoing portion of the belt  1080  is transported to a direction A and passes below the reading mechanism  1007 . The reading mechanism  1007  reads a radiological image drawn on the radiological image forming surface S of the imaging plate IP that passes therebelow. 
     (Outline of Reading Mechanism  1007 ) 
     The reading mechanism  1007  includes an excitation light source  1008  that emits excitation light EL, a photodetector  1010  that detects photostimulated luminescence light PL, an optical filter  1012  that prevents the excitation light EL from entering the photodetector  1010 , a fixed mirror  1014  that reflects the excitation light EL that has reached from a horizontal direction toward a direction in which a rotation axis RA extends and guides the reflected light, a rotating mirror  1016  that reflects the excitation light EL that has reached from the direction in which the rotation axis RA extends toward a direction inclined with respect to the rotation axis RA and guides the reflected light, a rotary structure  1018  that guides the photostimulated luminescence light PL emitted from an irradiation point P toward the photodetector  1010 , a bearing  1020  that supports the rotary structure  1080 , and a rotation mechanism  1022  that rotates the rotary structure  1018  around the rotation axis RA. 
     The excitation light source  1008  irradiates the fixed mirror  1014  with the excitation light EL, and thus the rotation axis RA is positioned at a position apart from the excitation light source  1008 . 
     The excitation light EL is guided by the fixed mirror  1014  and the rotating mirror  1016  through bending of light, specifically, reflection. 
     In the present application, changing of an advancing direction of light through, for example, reflection, refraction, or both, reflection and refraction is expressed by bending. 
     (Relationship between Rotation Axis RA and Scanning Plane SP) 
     The rotation axis RA is perpendicular to the scanning plane SP including the radiological image forming surface S of the imaging plate IP held by the belt  1080 . The imaging plate IP is transported to the direction perpendicular to the rotation axis RA, and the radiological image forming surface S moves on the scanning plane SP. 
     (Relationship between Track TR of Irradiation Point P and Movement of Radiological Image Forming Surface S) 
       FIG. 3  is a top view showing a track TR of the irradiation point P and the radiological image forming surface S on the scanning plane SP. 
     As shown in  FIG. 1 , in particular, in  FIG. 3 , the reading mechanism  1007  causes the irradiation point P which is irradiated with the excitation light EL emitted from the excitation light source  1008  to circularly move on the scanning plane SP. The reader  1002  causes the radiological image forming surface S to sequentially pass through across positions of arcs A 1  and A 2  each occupying part of the track TR of the irradiation point P. As a result, the radiological image forming surface S is repeatedly scanned by the irradiation point P that moves on the arcs A 1  and A 2 . The reading mechanism  1007  detects the photostimulated luminescence light PL emitted from the irradiation point P which scans the radiological image forming surface S. 
     (Scanning Mechanism  1036 ) 
     The scanning mechanism  1036  that is part of the reading mechanism  1007  and causes the irradiation point P to circularly move includes an excitation light optical system  1034  and the rotation mechanism  1022 . The excitation light optical system  1034  includes the fixed mirror  1014  and the rotating mirror  1016  and guides the excitation light EL toward the irradiation point P apart from the rotation axis RA. The rotation mechanism  1022  causes the rotating mirror  1016  constituting part of the excitation light optical system  1034  to rotate around the rotation axis RA together with the rotary structure  1018 . Owing to the scanning mechanism  1036 , the distance of an optical path from the excitation light source  1008  to the irradiation point P is maintained constant, and the angle of incidence of the excitation light EL with respect to the radiological image forming surface S is maintained constant, with the result that radiological images are read in a uniform manner. 
     (Excitation Light Optical System  1034 ) 
     The excitation light optical system  1034  may include an optical element other than the fixed mirror  1014  and the rotating mirror  1016 . For example, the excitation light optical system  1034  may include a mirror that bends the excitation light EL further and guides the bent light, a lens that collects or converges the excitation light EL, or the like. A prism or the like may be used as a bending optical element that bends the excitation light EL and guides the bent light. 
     In a case where a prism is used, the excitation light EL is guided through reflection, refraction or the like. 
     In the example shown in  FIG. 1 , the excitation light optical system  1034  that guides the excitation light EL to the imaging plate IP is formed of a light guide part that bends light. 
     In the present invention, the optical elements that bend and guide light are expressed by terms for a bending optical element. 
     The fixed mirror  1014  and the rotating mirror  1016  are examples of the bending optical elements. 
     The bending optical element is an example of a component constituting the light guide part that bends light. 
     Examples of the component of the light guide part that bends the light, which is employed in the present application, include a bending optical element, a reflection optical system, a refraction optical system, a reflection and refraction optical system and a reflecting mirror, and any of them may be used. 
     For example, in order to guide the excitation light EL emitted from the excitation light source  1008  toward the direction in which the rotation axis RA extends, a curved or bent hollow waveguide (not shown) or an optical fiber (not shown) such as a quartz fiber may be arranged in place of using the fixed mirror  1014 . In order to guide the excitation light EL that has reached from the direction in which the rotation axis RA extends toward the direction inclined with respect to the rotation axis RA, a curved or bent hollow waveguide (not shown) or an optical fiber (not shown) such as a quartz fiber may be arranged in place of using the rotating mirror  1016 . 
     In the description below, terms for reflection are used for bending of light in many cases, but not limited to reflection, components capable of bending light are appropriately used. 
     (Rotating Mirror  1016 ) 
     The rotating mirror  1016  bends the excitation light EL that has reached from the direction in which the rotation axis RA extends toward the direction inclined with respect to the rotation axis RA. The excitation light EL that has bent by the rotating mirror  1016  is guided to the irradiation point P apart from the rotation axis RA. 
     The rotating mirror  1016  is provided on the rotation axis RA. The rotating mirror  1016  is fixed to the rotary structure  1018  within the rotary structure  1018 . Owing to the rotating mirror  1016 , the optical path of the excitation light EL is not required to be rotated before reaching the rotating mirror  1016 , and thus the excitation light source  1008  needs not to be moved. Accordingly, as shown  FIG. 1 , the excitation light source  1008  can be fixed to and disposed in the frame  1026  apart from the rotation mechanism  1022  and the rotary structure  1018 , which facilitates power feeding to the excitation light source  1008 . 
     The rotating mirror  1016  integrated with the rotary structure  1018  rotates around the rotation axis RA in synchronization with the rotary structure  1018 , and thus the optical path of the excitation light EL that ranges from the rotating mirror  1016  to the scanning plane SP rotates around the rotation axis RA, and the irradiation point P circularly moves on the scanning plane SP. When the rotary structure  1018  and the rotating mirror  1016  are rotated in synchronization with each other, a position at which the photostimulated luminescence light PL is obtained in a light guide part  1046  described below can be maintained constant. Accordingly, the photostimulated luminescence light PL emitted from the irradiation point P is efficiently guided to the photodetector  1010 , which improves the sensitivity of reading a radiological image. 
     The inclination of a reflecting surface of the rotating mirror  1016  with respect to a horizontal direction affects the distance between the rotation axis RA and the irradiation point P, that is, a diameter 2r of the track TR of the irradiation point P (see  FIG. 3 ). The reflecting surface of the rotating mirror  1016  is inclined with respect to the horizontal direction such that the diameter 2r of the track TR is at least larger than a width w of the radiological image forming surface S (see  FIG. 3 ). Accordingly, the entire radiological image forming surface S is scanned by the irradiation point P. The “width w of the radiological image forming surface S” is a dimension of the radiological image forming surface S in the direction perpendicular to a transport direction of the imaging plate IP. 
     The rotating mirror  1016  is provided on the rotation axis RA and thus does not move even when rotating around the rotation axis RA. Further, the reflecting surface of the rotating mirror  1016  is merely required to reflect the excitation light EL that has reached by passing through the rotation axis RA. Therefore, it suffices that the reflecting surface of the rotating mirror  1016  is slightly larger than a cross-section of a beam of the excitation light EL. 
     (Fixed Mirror  1014 ) 
     The fixed mirror  1014  bends the excitation light EL that has reached from the horizontal direction toward the direction in which the rotation axis RA extends and guides the bent light to the rotating mirror  1016 . The direction of the excitation light EL that reaches the fixed mirror  1014  is not required to be horizontal, and is only required to be a direction inclined with respect to the direction in which the rotation axis RA extends. The excitation light source  1008  is made apart from the rotation axis RA thanks to the fixed mirror  1014 , and thus power feeding to the excitation light source  1008  is facilitated, which increases a degree of freedom in structure of the reader  1002 . 
     The fixed mirror  1014  is provided on the rotation axis RA. The fixed mirror  1014  is fixed to the frame  1026  separately from the rotation mechanism  1022  outside the rotary structure  1018 . When the fixed mirror  1014  is provided outside the rotary structure  1018 , the excitation light EL is guided to the fixed mirror  1014  without being interfered by the rotary structure  1018 . The direction inclined with respect to the direction in which the rotation axis RA extend may be a direction perpendicular to the direction in which the rotation axis RA. 
     The fixed mirror  1014  is provided between a lower surface  1042  of the rotary structure  1018  and the scanning plane SP. Accordingly, the photodetector  1010  and the fixed mirror  1014  are separated from each other by the rotary structure  1018 , which prevents the stray light of the excitation light EL from entering the photodetector  1010 . Further, the excitation light EL is not shielded by the imaging plate IP. 
     Inclination of the reflecting surface of the fixed mirror  1014  with respect to the horizontal direction depends on the direction from which the excitation light EL comes. In the example of  FIG. 1 , the reflecting surface of the fixed mirror  1014  is inclined with respect to the horizontal direction so as to bend the excitation light EL that has come toward the direction in which the rotation axis RA extends. 
     (Excitation Light Source  1008 ) 
     Specifically, a wavelength of the excitation light EL emitted from the excitation light source  1008  is determined in accordance with a wavelength of the light with which the imaging plate IP is effectively excited. For example, as to an imaging plate IP that is currently on the market, the light having a wavelength of 500 to 800 nm can be used in many cases, and any light source can be used as the excitation light source  1008  as long as it emits the light having the above-mentioned wavelength band. 
     The excitation light source  1008  is desirably a laser light source. This results in a thinner beam of the excitation light EL and a smaller irradiation point P, which improves the accuracy of reading radiological images. Further, the excitation light source  1008  is desirably a semiconductor laser light source. Accordingly, the reader  1002  is miniaturized. 
     In the reader  1002 , the excitation light source  1008  is not required to be rotated, and thus the excitation light source  1008  is separated from the rotation mechanism  1022  and fixed to the frame  1026 . As a result, power feeding to the excitation light source  1008  is facilitated. Further, the excitation light source  1008  is made apart from the rotation axis RA due to the presence of the fixed mirror  1014 , which facilitates power feeding to the excitation light source  1008 . 
     (Photodetector  1010 ) 
     The photodetector  1010  detects the photostimulated luminescence light PL that has been emitted from the irradiation point P and arrived via the rotary structure  1018 . The photodetector  1010  generates a signal corresponding to the strength of the detected photostimulated luminescence light PL. 
     The photodetector  1010  is desirably a photomultiplier, a photodiode or the like. 
     The photostimulated luminescence light PL is the light having a wavelength of 350 to 450 nm in many cases, and a detector that detects the light of the above-mentioned wavelength band is preferably used as the photodetector  1010 , which may be appropriately selected in accordance with a wavelength of the photostimulated luminescence light emitted from the imaging plate IP. 
     In the reader  1002 , the photodetector  1010  is not required to be rotated, and thus the photodetector  1010  is separated from the rotation mechanism  1022  and fixed to the frame  1026 . As a result, power is easily fed to the photodetector  1010  and a signal from the photodetector  1010  is easily obtained. The photodetector  1010  is opposed to a light outlet  1050  of the rotary structure  1018  with the optical filter  1012  being sandwiched therebetween. 
     The photodetector  1010  is provided on the rotation axis RA. This is enabled by making the excitation light source  1008  apart from the rotation axis RA and separating the excitation light source  1008  from the photodetector  1010  by the rotary structure  1018 . As a result, the excitation light optical system  1034  that guides the excitation light EL to the irradiation point P does not prevent the photostimulated luminescence light PL from entering the photodetector  1010 , which improves the sensitivity of reading a radiological image. 
     (Optical Filter  1012 ) 
     In the optical filter  1012 , the transmittance at a wavelength of the photostimulated luminescence light PL is higher than the transmittance at a wavelength of the excitation light EL. Accordingly, the excitation light EL less affects the photodetector  1010 , leading to an improvement in the sensitivity of reading a radiological image. 
     A wavelength dependence of the transmittance of the optical filter  1012  is determined in accordance with a type of a photostimulable phosphor to be used. In a case where barium fluoride halide containing europium as an activator is used as a photostimulable phosphor, a photostimulable phosphor is irradiated with red excitation light EL, and near-ultraviolet photostimulated luminescence light PL is detected, for example, a blue filter is used as the optical filter  1012 . 
     The optical filter  1012  has a plate-like shape. 
     The optical filter  1012  is interposed between the photodetector  1010  and the light outlet  1050  of the rotary structure  1018 . The optical filter  1012  is fixed to the frame  1026 . The optical filter  1012  may be attached to an upper surface  1044  of the rotary structure.  1018  so that the light outlet  1050  of the rotary structure  1018  is covered with the optical filter  1012 . The optical filter  1012  may be attached to a lower surface of the photodetector  1010  so that a light receiving part of the photodetector  1010  is covered with the optical filter  1012 . 
     (Photostimulated Luminescence Light Optical System  1040 ) 
     The photostimulated luminescence light optical system  1040  that guides the photostimulated luminescence light PL emitted from the irradiation point P on the scanning plane SP to the photodetector  1010  is part of the rotary structure  1018 . The rotary structure  1018  is configured so as to be easily rotated, and thus the photostimulated luminescence light optical system  1040  is easily rotated by making the photostimulated luminescence light optical system  1040  part of the rotary structure  1018 . 
     (Rotary Structure  1018 ) 
     An outer shape of the rotary structure  1018  is approximately cylindrical. A cylinder axis of the rotary structure  1018  is positioned at the same position as the rotation axis RA. 
     The rotary structure  1018  is provided between the photodetector  1010  and the scanning plane SP. The lower surface  1042  of the rotary structure  1018  is opposed to the scanning plane SP and is parallel to the scanning plane SP. The upper surface  1044  of the rotary structure  1018  is opposed to the photodetector  1010 . 
     (Light Guide Part  1046 ) 
     The rotary structure  1018  is a hollow body in which a hollow light guide part  1046  that guides the photostimulated luminescence light PL from the irradiation point P to the photodetector  1010  is formed. The light guide part  1046  has, on the lower surface  1042  of the rotary structure  1018  that is opposed to the scanning plane SP, the light inlet  1048  for the photostimulated luminescence light PL that is opposed to the scanning plane SP in a similar manner, and has on the upper surface  1044  of the rotary structure  1018  that is opposed to the photodetector  1010 , the light outlet  1050  for the photostimulated luminescence light PL that is opposed to the photodetector  1010  in a similar manner. A surface (which represents an inner surface of the hollow in the rotary structure  1018  according to the first preferred embodiment)  1052  of the light guide part  1046  has an oval spherical surface shape. That is, the light guide part  1046  has an oval spherical body shape. The surface  1052  of the light guide part  1046  is subjected to mirror finishing for efficiently reflecting the photostimulated luminescence light PL. A reflecting film for reflecting the photostimulated luminescence light PL may be formed on the surface  1052  of the light guide part  1046 . The surface  1052  serves as the reflecting surface in a case of mirror finishing and a case of forming a reflecting film. The photostimulated luminescence light PL entering from the light inlet  1048  is reflected on the surface  1052  of the light guide part  1046 , and is guided to the photodetector  1010  via the light outlet  1050 . The photostimulated luminescence light PL is efficiently guided from the light inlet  1048  to the light outlet  1050  by the light guide part  1046 , and thus the sensitivity of reading a radiological image is improved. 
     An optical axis of the light guide part  1046  that serves as the photostimulated luminescence light optical system  1040  desirably passes through the irradiation point P. Accordingly, the photostimulated luminescence light PL emitted from the irradiation point P is efficiently guided to the photodetector  1010 , which improves the sensitivity of reading a radiological image. In the case where the surface  1052  of the light guide part  1046  forms an oval spherical surface, the optical axis of the light guide part  1046  coincides with a long axis of an oval sphere body having the oval spherical surface. Therefore, the surface  1052  of the light guide part  1046  has rotation symmetry of optical axis. 
     The light inlet  1048  is made apart from the rotation axis RA, and the light outlet  1050  is formed on the rotation axis RA. Accordingly, the photodetector  1010  is disposed on the rotation axis. RA separately from the rotation mechanism  1022  and the rotary structure  1018 , which makes it easy to feed power to the photodetector  1010  and obtain a signal from the photodetector  1010 . Further, the photostimulated luminescence light optical system  1040  is simplified. 
     (Light Guide Part  1054 ) 
     A hollow light guide part  1054  that guides the excitation light EL from the fixed mirror  1014  to the rotating mirror  1016  is also formed in the rotary structure  1018 . The light guide part  1054  has a light inlet  1056  for the excitation light EL on the lower surface  1042  of the rotary structure  1018  and a confluence  1058  at which the light guide part  1054  joins the light guide part  1046  on the surface  1052  of the light guide part  1046 . The light guide part  1054  is provided on the rotation axis RA. The light guide part  1054  extends in the rotation axis RA direction. The rotating mirror  1016  is provided to the confluence  1058 . The excitation light EL entering from the light inlet  1056  reaches the rotating mirror  1016  by passing through the light guide part  1054 , is reflected by the rotating mirror  1016 , and then passes through the light guide part  1046  to be guided to the scanning plane SP via the light inlet  1048 . Accordingly, the excitation light optical system  1034  guides the excitation light EL from the excitation light source  1008  to the scanning plane SP via the light guide part  1046 . That is, part of the optical path of the excitation light optical system  1034  and part of the optical path of the photostimulated luminescence light optical system  1040  pass through the common light guide part  1054 . This contributes to causing the optical path of the excitation light EL and the optical path of the phosphoresecent light PL to coexist inside the rotary structure  1018  for miniaturizing the reader  1002 . 
     The light guide part  1054  may be hollow or formed by a solid body, and may be appropriately formed of, for example, a resin such as an acrylic resin and one having excellent transmittance efficiency such as glass. The light guide part  1054  may be formed of a solid body including a single material, or may be formed of a solid body including a plurality of materials, such as an optical fiber formed by collecting a plurality of optical fibers. 
     (Other Items of Rotary Structure  1018 ) 
     A belt groove  1062  over which a belt  1068  of the rotation mechanism  1022  is hung is formed on a side surface  1060  of the rotary structure  1018 . The width of the belt groove  1062  is slightly larger than the width of the belt  1068 . The belt groove  1062  extends in a circumferential direction of the rotary structure  1018 . In place of forming the belt groove  1062  on the side surface  1060  of the rotary structure  1018 , a pulley may be provided to the side surface  1060  of the rotary structure  1018 . 
     A bearing groove  1078  to which an inner ring  1076  of the bearing  1020  is fixed is formed on the side surface  1060  of the rotary structure  1018 . 
     A desirable material of the rotary structure  1018  is a resin that is easily formed, though not limited thereto. 
     (Rotation Mechanism  1022 ) 
     The rotation mechanism  1022  includes a motor  1064  that generates a driving force for rotation, a pulley  1066  that adjusts a ratio of rotation, and the belt  1068  that transmits a driving force of the motor  1064  to the rotary structure  1018 . A motor-housing  1070  of the motor  1064  is fixed to the frame  1026 . The pulley  1066  is fixed to a shaft  1072  of the motor  1064 . The belt  1068  is hung over the pulley  1066  and the belt groove  1062 . 
     (Bearing  1020 ) 
     The bearing  1020  supports the rotary structure  1018  in a state where the rotary structure  1018  is capable of being rotated around the rotation axis RA. An outer ring  1074  of the bearing  1020  is fixed to the frame  1026 , and the inner ring  1076  of the bearing  1020  is fixed to the bearing groove  1078  of the rotary structure  1018 . 
     While  FIG. 1  shows the case where the bearing  1020  is a roller bearing, the rotary structure  1018  may be supported by a sliding bearing, a fluid dynamic bearing or the like. 
     (Transport Mechanism  1006 ) 
     A transport mechanism  1006  includes the belt  1080  that holds the imaging plate IP in a flat manner and the belt drive mechanism  1082  that causes the belt  1080  to go therearound. 
     The belt  1080  has a larger width compared with the imaging plate IP and has no end. 
     The belt drive mechanism  1082  includes rollers  1084 ,  1086 ,  1088  and  1090 . The roller  1084  positioned at one end of the belt drive mechanism  1082  is on an upstream side of a transport direction with respect to the track TR of the irradiation point P, whereas the roller  1090  positioned at the other end of the belt drive mechanism  1082  is on a downstream side of the transport direction with respect to the track TR of the irradiation point P. The number of rollers provided between the roller  1084  and the roller  1090  may be increased or reduced. 
     The respective rollers  1084 ,  1086 ,  1088  and  1090  are capable of rotating around the rotation axis extending in the direction that is parallel to the scanning plane SP and is perpendicular to the transport direction. The roller  1084  or the roller  1090  is applied with the driving force for rotation. 
     The belt  1080  is hung over the rollers  1084 ,  1086 ,  1088  and  1090  and is caused to go therearound. An upper surface of the outgoing portion of the belt  1080  that travels from the roller  1084  toward the roller  1090  and is opposed to the lower surface  1042  of the rotary structure  1018  becomes a holding surface  1092  on which the imaging plate IP whose radiological image forming surface S faces upward is placed. 
     The holding surface  1092  is part of the belt  1080  being a component of the transport mechanism  1006  that transports the imaging plate IP and also is a holder that holds the imaging plate IP. 
     The outgoing portion of the belt  1080  holds the imaging plate IP in a flat manner and is linearly moved relative to the fixed reading mechanism  1007  by the belt drive mechanism  1082 . Accordingly, the holding surface  1092  is moved in the direction perpendicular to the rotation axis RA with respect to the scanning mechanism  1036 , and the imaging plate IP placed on the holding surface  1092  is linearly transported in the direction perpendicular to the rotation axis RA with respect to the fixed scanning mechanism  1036 . The imaging plate IP is linearly moved relative to the scanning mechanism  1036 . When the imaging plate IP is held in a flat manner, the imaging plate IP is not curved, which prevents the imaging plate IP from being damaged. In addition, when the imaging plate IP is linearly transported, the transport mechanism  1006  is simplified. 
     The transport mechanism  1006  is an example of a relative movement mechanism that moves a holder formed of the holding surface  1092  in the direction perpendicular to the rotation axis RA relative to the scanning mechanism  1036 . 
     In the relative movement mechanism, the holder may move with respect to the scanning mechanism, the scanning mechanism may move with respect to the holder, or the holder and the scanning mechanism may move. In any case, the holder moves relative to the scanning mechanism. 
     (Dust Collecting Mechanism  1032 ) 
     The dust collecting mechanism  1032  collects dust inside the housing  1028 . As a result, dust inside the housing  1028  decreases, and thus dust is prevented from adhering to the imaging plate IP, which improves the accuracy of reading a radiological image. 
     The dust collecting mechanism  1032  is achieved by, for example, mounting an exhaust fan to which a dust collecting filter is attached onto an exhaust port of the housing  1028 . 
     (Erase Beam Light Source  1024 ) 
     The erase beam light source  1024  irradiates the imaging plate IP after the radiological image is read with an erase beam for erasing a radiological image. 
     The erase beam light source  1024  is provided on the downstream side of the transport direction with respect to the track TR of the irradiation point P and above the scanning plane SP. The erase beam light source  1024  irradiates the scanning plane SP with an erase beam toward the scanning plane SP. Accordingly, reading of a radiological image to erase of a radiological image is completed inside the reader  1002 . 
     (Controller  1030 ) 
     The controller  1030  feeds power to the excitation light source  1008  and the erase beam light source  1024  to control lighting of the excitation light source  1008  and the erase beam light source  1024 . 
     In addition, the controller  1030  feeds power to the transport mechanism  1006  to control transportation of the imaging plate IP by the transport mechanism  1006 . 
     Moreover, the controller  1030  feeds power to the photodetector  1010  to control the photodetector  1010 , and obtains a signal generated by the photodetector  1010  to produce image data. The image data may be produced by a device outside the housing  1028 . 
     2 Second Preferred Embodiment 
     A second preferred embodiment relates to a rotary structure  2018  employed in place of the rotary structure  1018  according to the first preferred embodiment. 
       FIG. 4  is a schematic view of the rotary structure  2018  according to the second preferred embodiment, which is a cross-sectional view of the rotary structure  2018 . 
     An outer shape of the rotary structure  2018  is approximately cylindrical as in the rotary structure  1018  according to the first preferred embodiment. A cylinder axis of the rotary structure  2018  coincides with the rotation axis RA. 
     The rotary structure  2018  is provided between the photodetector  1010  and the scanning plane SP. A lower surface  2042  of the rotary structure  2018  is opposed to the scanning plane SP and is parallel to the scanning plane SP. An upper surface  2044  of the rotary structure  2018  is opposed to the photodetector  1010 . 
     (Light Guide Part  2046 ) 
     The rotary structure  2018  is formed of a solid body in which a light guide part  2046  of translucent body is provided inside a translucent body accommodating part formation  2100 , in place of the hollow light guide part  1046  according to the first preferred embodiment. The light guide part  2046  has, on the lower surface  2042  of the rotary structure  2018 , a light inlet  2048  for the photostimulated luminescence light PL that is opposed to the scanning plane SP, and has on the upper surface  2044  of the rotary structure  2018 , a light outlet  2050  for the photostimulated luminescence light PL that is opposed to the photodetector  1010 . 
     A surface (which represents an outer surface of the translucent body in the rotary structure  2018  according to the second preferred embodiment)  2052  of the light guide part  2046  has an oval spherical surface shape. That is, the light guide part  2046  has an oval spherical body shape. A refractive index of the light guide part  2046  is determined such that the surface  2052  of the light guide part  2046 , that is, an interface between the light guide part  2046  and an outside thereof is a total reflection surface for the photostimulated luminescence light PL when viewed from the inside of the light guide part  2046 . A reflecting film for reflecting the photostimulated luminescence light PL may be formed on the surface  2052  of the light guide part  2046 . The photostimulated luminescence light PL entering from the light inlet  2048  is reflected on the surface  2052  of the light guide part  2046 , and is guided to the photodetector  1010  via the light outlet  2050 . The photostimulated luminescence light PL is efficiently guided from the light inlet  2048  to the light outlet  2050  by the light guide part  2046 , and thus the sensitivity of reading a radiological image is improved. 
     An optical axis of the light guide part  2046  desirably passes through the irradiation point P. Accordingly, the photostimulated luminescence light PL emitted from the irradiation point P is efficiently guided to the photodetector  1010 , which improves the sensitivity of reading a radiological image. In the case where the surface  2052  of the light guide part  2046  forms an oval spherical surface, the optical axis of the light guide part  2046  coincides with a long axis of an oval sphere body having the oval spherical surface. Therefore, the surface  2052  of the light guide part  2046  has rotation symmetry of optical axis. 
     The light inlet  2048  is made apart from the rotation axis RA, and the light outlet  2050  is formed on the rotation axis RA. Accordingly, the photodetector  1010  is disposed on the rotation axis RA separately from the rotation mechanism  1022  and the rotary structure  2018 , which makes it easy to feed power to the photodetector  1010  and obtain a signal from the photodetector  1010 . Further, the photostimulated luminescence light optical system  2040  is simplified. 
     (Light Guide Part  2054 ) 
     A light guide part  2054  formed of translucent body that guides the excitation light EL from the fixed mirror  1014  to the rotating mirror  1016  is also formed in the rotary structure  2018 . The light guide part  2054  has a light inlet  2056  for the excitation light EL on the lower surface  2042  of the rotary structure  2018  and a confluence  2058  at which the light guide part  2054  joins the light guide part  2046  on the surface  2052  of the light guide part  2046 . The light guide part  2054  extends in the rotation axis RA direction. The light guide part  2054  is provided on the rotation axis RA. The rotating mirror  1016  is provided to the confluence  2058 . The excitation light EL entering from the light inlet  2056  reaches the rotating mirror  1016  by passing through the light guide part  2054 , is reflected by the rotating mirror  1016 , and then passes through the light guide part  2046  to be guided to the scanning plane SP via the light inlet  2048 . 
     A whole of the light guide part  2054  and the light guide part  2046  may be formed of an integrated solid body of translucent body, but a part thereof may be formed of an integrated solid body of translucent body. 
     (Other Items of Rotary Structure  2018 ) 
     A belt groove  2062  and a bearing groove  2078  similarly to the belt groove  1062  and the bearing groove  1078  according to the first preferred embodiment are formed on a side surface  2060  of the rotary structure  2018 . 
     There may also be employed a rotary structure in which the translucent body accommodating part formation  2100  that is filled with the light guide parts  2046  and  2054  is omitted, which makes support thereof difficult. 
     A desirable material of the rotary structure  2018  is a resin that is easily formed, though not limited thereto. In particular, an acrylic resin or the like is desirable for a material of the light guide part  2046 , but one having an excellent transmittance efficiency such as glass may be appropriately used. The light guide part  2046  may be formed of a solid body including a single material, or may be formed of a solid body including a plurality of materials, such as an optical fiber formed by collecting a plurality of optical fibers. 
     As in the light guide part  1054  according to the first preferred embodiment, the light guide part  2054  may be formed hollow or formed by a solid body. 
     3 Third Preferred Embodiment 
     A third preferred embodiment relates to a rotary structure  3018  that is employed in place of the rotary structure  1018  of the first preferred embodiment. 
       FIG. 5  is a schematic view of the rotary structure  3018  according to the third preferred embodiment, which is a cross-sectional view of the rotary structure  3018 . 
     An outer shape of the rotary structure  3018  is approximately cylindrical. A cylinder axis of the rotary structure  3018  is positioned at the same position as the rotation axis RA. 
     The rotary structure  3018  is provided between the photodetector  1010  and the scanning plane SP. A lower surface  3042  of the rotary structure  3018  is opposed to the scanning plane SP and is parallel to the scanning plane SP. An upper surface  3044  of the rotary structure  3018  is opposed to the photodetector  1010 . 
     As shown in  FIG. 5 , the rotary structure  3018  includes a hollow formation  3100  and a lens  3200  that guides the photostimulated luminescence light PL toward an inside of a light guide part  3046 . 
     (Light Guide Part  3046 ) 
     The hollow formation  3100  is a hollow body in which a hollow light guide part  3046  that guides the photostimulated luminescence light PL from the irradiation point P to the photodetector  1010  is formed. As in the rotary structure  2018  according to the second preferred embodiment, a light guide part that is formed of a translucent body and is solid may be formed in place of the hollow light guide part  3046 . In the case of the solid guide light part, a desirable material thereof is an acrylic resin or the like, and one having an excellent transmittance efficiency such as glass may be appropriately used. The light guide part  3046  may be formed of a solid body including a single material, or may be formed of a solid body including a plurality of materials, such as an optical fiber formed by collecting a plurality of optical fibers. A SELFOC lens may be used. In the case of the solid light guide part, the lens  3200  may be omitted. 
     As in the light guide part  1054  according to the first preferred embodiment, the light guide part  3054  may be formed hollow or formed by a solid body. 
     A whole of the light guide part  3054  and the light guide part  3046  may be formed of an integrated solid body of translucent body, but a part thereof may be formed of an integrated solid body of translucent body. 
     The light guide part  3046  has, on the lower surface  3042  of the rotary structure  3018 , a light inlet  3048  for the photostimulated luminescence light PL that is opposed to the scanning plane SP, and has on the upper surface  3044  of the rotary structure  3018 , a light outlet  3050  for the photostimulated luminescence light PL that is opposed to the photodetector  1010 . A surface (which represents an inner surface of the hollow in the rotary structure  3018  according to the third preferred embodiment)  3052  of the light guide part  3046  has a cylindrical surface shape. That is, the light guide part  3046  is cylindrical in shape. Strictly speaking, the cylinder in this case has a shape obtained by obliquely cutting the top and bottom of the cylinder. 
     The surface  3052  of the light guide part  3046  may form an oval spherical surface as in the rotary structure  1018  according to the first preferred embodiment. The photostimulated luminescence light PL entering from the light inlet  3048  is collected by the lens  3200  and is guided to the photodetector  1010  via the light outlet  3050 . The photostimulated luminescence light PL is efficiently guided from the light inlet  3048  to the light outlet  3050  by the light guide part  3046 , and thus the sensitivity of reading a radiological image is, improved. 
     The light inlet  3048  is made apart from the rotation axis RA, and the light outlet  3050  is formed on the rotation axis RA. Accordingly, the photodetector  1010  is disposed on the rotation axis RA separately from the rotation mechanism  1022  and the rotary structure  3018 , which makes it easy to feed power to the photodetector  1010  and obtain a signal from the photodetector  1010 . Further, a photostimulated luminescence light optical system  3040  is simplified. 
     (Light Guide Part  3054 ) 
     A hollow light guide part  3054  that guides the excitation light EL from the fixed mirror  1014  to the rotating mirror  1016  is also formed in the rotary structure  3018 . The light guide part  3054  has a light inlet  3056  for the excitation light EL on the lower surface  3042  of the rotary structure  3018  and a confluence  3058  at which the light guide part  3054  joins the light guide part  3046  on the inner surface  3052  of the light guide part  3046 . The light guide part  3054  extends in the rotation axis RA direction. The light guide part  3054  is provided on the rotation axis RA. The rotating mirror  1016  is provided to the confluence  3058 . The excitation light EL entering from the light inlet  3056  reaches the rotating mirror  1016  by passing through the light guide part  3054 , is reflected by the rotating mirror  1016 , and then passes through the light guide part  3046  to be guided to the scanning plane SP via the light inlet  3048 . 
     In the example shown in  FIG. 5 , the surface  3052  of the light guide part  3046  is a cylindrical surface of approximately a cylinder, strictly speaking, a cylindrical inner surface that is an inside of the cylinder. The cross-sectional shape of the light guide part  3046  becomes particularly large in the vicinity of the confluence  3058  due to the positioning of the rotating mirror  1016  and joining of a path of the excitation light EL in the vicinity of the confluence  3058 . Alternatively, the cross-sectional shape of the light guide part  3046  may be uniform between the light inlet  3048  and the light outlet  3050  and may be preferably a true circle. In addition the light guide part  3046  may have a linear long axis. In this case, the configuration easily processed by drilling is obtained. 
     Further, the shape may be one obtained by adding a portion of an oval spherical surface to part of a cylinder, and a shape capable of obtaining excellent light guiding efficiency is appropriately selected. 
     The long axis of the light guide part  3046  may be linear, and may be bent to such an extent that light is not prevented from advancing. 
     The lens  3200  constituting the photostimulated luminescence light optical system  3040  is fixed to the light inlet  3048  of the rotary structure  3018 . An optical axis of the lens  3200  passes through the irradiation point P. Accordingly, the photostimulated luminescence light PL emitted from the irradiation point P is efficiently guided to the photodetector  1010 , which improves the sensitivity of reading a radiological image. 
     (Other Items of Rotary Structure  3018 ) 
     A belt groove  3062  and a bearing groove  3078  similarly to the belt groove  1062  and the bearing groove  1078  according to the first preferred embodiment are formed on a side surface  3060  of the rotary structure  3018 . 
       FIG. 6  is a schematic view of a rotary structure  3018   a  that is a modification of the rotary structure  3018  according to the third preferred embodiment shown in  FIG. 5 , which is a cross-sectional view of the rotary structure  3018   a.    
     A basic structure of the rotary structure  3018   a  is similar to that of the rotary structure  3018 , and thus only features thereof are described. 
     In the rotary structure  3018  of  FIG. 5 , the light guide part  3054  and the light guide part  3046  join each other at the confluence  3058 , and the excitation light EL that has passed through the light guide part  3054  and been reflected by the rotating mirror  1016  passes through the light guide part  3046  to be guided to the scanning plane SP. On the other hand, in the rotary structure  3018   a  of  FIG. 6 , there is further provided a light guide part for excitation light EL passage  3054   a  that causes the excitation light EL that has been reflected by the rotating mirror  1016  to pass through toward the scanning plane SP. In addition, there is provided a light guide part for photostimulated luminescence light PL passage  3046   a  that guides the photostimulated luminescence light PL from the irradiation point P shown in  FIG. 1  to the photodetector  1010 , in place of the light guide part  3046  of the rotary structure  3018  of  FIG. 5 . Those are features of the rotary structure  3018   a.    
     A surface  3052   a  of the light guide part  3046   a  is subjected to mirror finishing for efficiently reflecting the photostimulated luminescence light PL. 
     While the light guide part  3046   a  is hollow, as in the rotary structure  2018  according to the second preferred embodiment, a solid light guide part formed of translucent body may be formed in place of the hollow light guide part  3046   a.  This is similar to the light guide part  3046  of the rotary structure  3018  of  FIG. 5 . 
     A solid light guide part may be buried in part of the hollow light guide part  3046   a.    
     The excitation light EL is reflected by the fixed mirror  1014  to pass through the light guide part  3054 , and is reflected, by the rotating mirror  1016  to pass through the light guide part  3054   a,  to be guided to the scanning plane SP. 
     The photostimulated luminescence light PL from the irradiation point P passes through the light guide part  3046   a  via the light inlet  3048   a,  and is guided to the photodetector  1010  via the light outlet  3050   a.    
     A surface (which represents an inner surface of the hollow in the rotary structure  3018   a  according to the third preferred embodiment)  3052   a  of the light guide part  3046   a  forms a cylindrical surface of a cylinder having a linear long axis and a uniform cross-sectional shape, preferably, having a circular shape of a true circle. Strictly speaking, the surface  3052   a  forms a cylindrical inner surface inside the cylinder. That is, the light guide part  3046   a  is cylindrical in shape. Further, strictly speaking, the cylinder in this case has a shape obtained by obliquely cutting the top and bottom of the cylinder. 
     In the case where the solid light guide part is formed in place of the hollow light guide part  3046   a,  a lower surface of the rotary structure  3018  and the light inlet  3048   a  are not necessarily required to be configured to form the same surface, and an upper surface of the rotary structure  3018   a  and the light outlet  3050   a  are not necessarily required to be configured to form the same surface. For example, when the solid body having a shape of a true cylinder whose top and bottom are not obliquely cut is used in place of the hollow light guide part  3046   a  or used so as to be buried in part of the light guide part  3046   a,  processing thereof is made much easier. 
     While a whole of the light guide part  3054   a  and the light guide part  3046   a  may be formed of an integrated solid body of translucent body, a part thereof maybe formed of an integrated solid body of translucent body. 
     A surface (inner surface of a hollow)  3054   b  of the light guide part  3054   a  forms a cylindrical surface of a cylinder having a linear long axis and a uniform cross-sectional shape, preferably, having a circle shape of a true circle. Strictly speaking, the surface  3054   b  forms a cylindrical inner surface inside the cylinder. 
     The long axes of the light guide part  3046   a  and the light guide part  3054   a  may be linear, and may be bent to such an extent that light is not prevented from advancing. 
     The light guide part  3046   a  and the light guide part  3054   a  may join together in the middle inside the rotary structure  3018   a,  as shown in  FIG. 6 . Alternatively, the light guide part  3046   a  and the light guide part  3054   a  may be configured so as not to join together and have an independent path individually. 
     Inside the light guide part  3046   a,  the lens that collects the photostimulated luminescence light PL after the photostimulated luminescence light PL passes through the light inlet  3048   a  is omitted. In this case, a cross-section of the cylinder formed by the cylindrical inner surface  3052   a  is set to have an area approximately equal to that of the detecting surface of the detecting surface of the photodetector  1010  to approximately twice, and accordingly light can be guided efficiently. 
     In the case where the surface  3052   a  of the light guide part  3046   a  has a conical shape in which a cross-sectional shape in the light inlet  3048   a  is larger than a cross-sectional shape in the light outlet  3050   a,  the light guide part  3046   a  is conical in shape. Strictly speaking, the cone in this case has a shape obtained by obliquely cutting the top and bottom of the cone. 
     4 Fourth Preferred Embodiment 
     A fourth preferred embodiment relates to a rotary structure  4018  that is employed in place of the rotary structure  1018  according to the first preferred embodiment. 
       FIG. 7  is a schematic view of the rotary structure  4018  according to the fourth preferred embodiment, which is a cross-sectional view of the rotary structure  4018 . 
     As shown in  FIG. 7 , the rotary structure  4018  has a similar structure to that of the rotary structure  1018  according to the first preferred embodiment. Note that in the rotary structure  4018 , an air communication hole  4200  is formed as a blower mechanism that guides air toward the scanning plane SP. The air communication hole  4200  has an air outlet  4204  on a lower surface  4042  of the rotary structure  4018  and an air inlet  4202  on an upper surface  4044  of the rotary structure  4018 . The air outlet  4204  is farther from the rotation axis RA than the air inlet  4202 . Accordingly, when the rotary structure  4018  rotates, air is sucked from the air inlet  4202 , and the air passes through the air communication hole  4200  to be blown from the air outlet  4204 . As a result, the imaging plate IP is pressed against the holding surface  1092 , which prevents the imaging plate IP from becoming misaligned. 
     Note that an air communication hole similar to the air communication hole  4200  may be formed in the rotary structure  2018  according to the second preferred embodiment or the rotary structure  3018  according to the third preferred embodiment. 
     5 Fifth Preferred Embodiment 
     A fifth preferred embodiment relates to a rotary structure  5018  that is employed in place of the rotary structure  1018  according to the first preferred embodiment. 
       FIG. 8  is a schematic view of the rotary structure  5018  according to the fifth preferred embodiment, which is a cross-sectional view of the rotary structure  5018 . 
     As shown in  FIG. 8 , the rotary structure  5018  has a similar structure to that of the rotary structure  1018  according to the first preferred embodiment. Note that a fan blade  5200  is formed as a blower mechanism that guides air toward the scanning plane SP in the rotary structure  5018 . Accordingly, air is blown toward the scanning plane SP by the fan blade  5200  when the rotary structure  5018  rotates, whereby the imaging plate IP is pressed against the holding surface  1092 , which prevents the imaging plate IP from becoming misaligned. 
     Note that a fan blade similar to the fan blade  5200  may be formed in the rotary structure  2018  according to the second preferred embodiment, the rotary structure  3018  according to the third preferred embodiment and the rotary structure  4018  according to the fourth preferred embodiment. Further, an air communication hole similar to the air communication hole  4200  according to the fourth preferred embodiment may be formed in the rotary structure  2018  according to the second preferred embodiment in which a fan blade is formed and the rotary structure  3018  according to the third preferred embodiment in which a fan blade is formed. 
     6 Sixth Preferred Embodiment 
     A sixth preferred embodiment relates to a rotary structure  6018  and a rotation mechanism  6022  and a rotary structure  6018   a  and a rotation mechanism  6022   a  that are employed in place of the rotary structure  1018  and the rotation mechanism  1022  according to the first preferred embodiment. 
       FIG. 9  is a schematic view of the rotation mechanism  6022  and the rotary structure  6018  according to the sixth preferred embodiment, which is a cross-sectional view of the rotation mechanism  6022  and the rotary structure  6018 . 
     As shown in  FIG. 9 , the rotary structure  6018  has a similar structure to that of the rotary structure  1018  according to the first preferred embodiment. Note that in place of the belt groove  1062 , a rotor groove  6062  to which a hollow rotor  6302  of the rotation mechanism  6022  is fixed is formed in the rotary structure  6018 . The width of the rotor groove  6062  is slightly larger than that of the hollow rotor  6302 . The rotor groove  6062  extends in a circumferential direction of the rotary structure  6018 . 
     The rotation mechanism  6022  includes a motor  6300 . The motor  6300  includes the hollow rotor  6302  and a stator  6304 . 
     The hollow rotor  6302  has a ring shape in which an axis hole having substantially the same shape as a cross-sectional shape of the rotary structure  6018  in cross section perpendicular to the rotation axis RA is formed. The rotary structure  6018  is inserted into the axis hole of the hollow rotor  6302 , whereby the hollow rotor  6302  is fixed to the rotor groove  6062  of the rotary structure  6018 . The hollow rotor  6302  includes a permanent magnet  6304   m,  which generates a magnetic field flux. 
     The stator  6304  is fixed to a frame  6026 . The stator  6304  includes a coil  6304   c  that generates a rotational magnetic flux. 
     A rotational magnetic flux generating surface of the stator  6304  on which a rotational magnetic flux is generated and a magnetic field flux generating surface of the hollow rotor  6302  on which a magnetic field flux is generated are opposed to each other with a gap therebetween. 
     A bearing  6300  fixed to the stator  6304  pivotally supports the hollow rotor  6302  in a rotatable manner. 
     In the rotation mechanism  1022  according to the first preferred embodiment, the motor  1064  is not directly connected to the rotary structure  1018 , and thus there is required a driving force transmission mechanism that transmits a driving force of the motor  1064  to the rotary structure  1018 , such as the belt  1068 . In contrast, in the rotation mechanism  6022  according to the sixth preferred embodiment, the motor  6300  is directly connected to the rotary structure  6018 , and thus a driving force transmission mechanism that transmits a driving force of the motor  6300  to the rotary structure  6018  is omitted. 
     In place of the motor  6300  of rotational magnetic field type in which the hollow rotor  6302  generates a magnetic field flux and the stator  6304  generates a rotational magnetic field, there may be employed a motor of rotary armature type in which the stator  6304  generates a magnetic field flux and the hollow rotor  6302  generates a rotational magnetic flux. Note that the motor  6300  of rotational magnetic field type has an advantage that the reader  1002  is simplified because it is not required to feed power to the hollow rotor  6302  fixed to the rotary structure  6018 . 
       FIG. 10  is a schematic view of the rotation mechanism  6022   a  and the rotary structure  6018   a  according to the sixth preferred embodiment, which is a cross-sectional view of the rotation mechanism  6022   a  and the rotary structure  6018   a.    
     Basic structures are similar to those of the rotation mechanism  6022  and the rotary structure  6018  of  FIG. 9 , and thus only features thereof are described. 
     As shown in  FIG. 10 , the rotary structure  6018   a  has a similar structure to that of the rotary structure  6018  of  FIG. 9 . Note that a rotor  6500  is fixed to the rotary structure  6018   a,  and the rotary structure  6018   a  is configured to rotate upon rotation of the rotor  6500 . 
     The rotation mechanism  6022   a  includes a motor  6300   a.  The motor  6300   a  includes a hollow rotor  6302   a  and a stator  6304   a.    
     The rotor  6500  is inserted into an axis hole of the hollow rotor  6302   a  and is fixed. The hollow rotor  6302   a  includes a permanent magnet  6302   b  and generates a magnetic field flux. 
     The stator  6304   a  is fixed to a frame  6026   a.  The stator  6304   a  includes a coil  6304   b  that generates a rotational magnetic flux. 
     A rotational magnetic flux generating surface of the stator  6304   a  on which a rotational magnetic flux is generated and a magnetic field flux generating surface of the hollow rotor  6302   a  on which a magnetic field flux is generated are opposed to each other with a gap therebetween. A bearing  6300   c  fixed to the stator  6304   a  pivotally supports the hollow rotor  6302   a  in a rotatable manner. 
     The rotor  6500  and the rotary structure  6018   a  are integrally rotated by driving of the motor  6300   a.    
     There may be used a motor including a coil and a permanent magnet in the hollow rotor  6302   a  and the stator  6304   a,  respectively, in place of the motor  6300   a  including the permanent magnet  6302   b  and the coil  6304   b  in the hollow rotor  6302   a  and the stator  6304   a,  respectively. 
     In an upper portion of the frame  6026   a,  a photodetector support frame  6026   b  that supports a photodetector  6010   a  is fixed to a surface facing the top of the rotary structure  6018   a  with a gap therebetween. The photodetector  6010   a  is fixed to the photodetector support frame  6026   b  and faces the top center portion of the rotary structure  6018   a  with an optical filter  6012   a  being sandwiched therebetween, which receives the photostimulated luminescence light PL. 
     A bearing  6020   a  equivalent to the bearing  1020  according to the first preferred embodiment is fixed to the frame  6026   a  and supports a side surface of the rotary structure  6018   a  to pivotally support the rotary structure  6018   a  in a rotatable manner. The bearing  6300   c  pivotally supports the hollow rotor  6302   a  in a rotatable manner, and hence the bearing  6020   a  may be omitted. 
     In the preferred embodiment of  FIG. 10 , an outer diameter of the rotor  6500  can be made smaller than an outer diameter of the rotary structure  6018   a,  and thus an inner diameter of the hollow rotor  6302   a  can be made smaller. Therefore, it is possible to drive the motor  6300   a  at higher r.p.m. compared with the preferred embodiment of  FIG. 9 . 
     7 Seventh Preferred Embodiment 
     A seventh preferred embodiment relates to a rotary structure  7018  and a rotation mechanism  7022  that are employed in place of the rotary structure  1018  and the rotation mechanism  1022  according to the first preferred embodiment. 
       FIG. 11  is a schematic view of the rotary structure  7018  and the rotation mechanism  7022  according to the seventh preferred embodiment, which is a cross-sectional view of the rotary structure  7018  and the rotation mechanism  7022 . 
     As shown in  FIG. 11 , the rotary structure  7018  has a similar structure to that of the rotary structure  1018  according to the first preferred embodiment. Note that in place of the belt groove  1062 , a gear groove  7062  is formed in the rotary structure  7018 . The gear groove  7062  has a width slightly larger than that of the gear  7402  of the rotation mechanism  7022  and extends in a circumferential direction of the rotary structure  7018 . 
     The rotation mechanism  7022  includes a motor  7064  that generates a driving force of rotation and gears  7400  and  7402  that adjust a ratio of rotation and transmit a driving force of the motor  7064  to the rotary structure  7018 . 
     A motor-housing  7070  of the motor  7064  is fixed to the frame  7026 . The gear  7400  is fixed to a shaft  7072  of the motor  7064 . The gear  7402  has a ring shape in which an axis hole having substantially the same shape as the cross-sectional shape of the rotary structure  7018  in cross section perpendicular to the rotation axis RA is formed. The rotary structure  7018  is inserted into the axis hole of the gear  7402 , and the gear  7402  is fixed to the gear groove  7062  of the rotary structure  7018 . The gear  7400  and the gear  7402  are meshed with each other. In the case where a side surface  7060  of the rotary structure  7018  is resistant to abrasion, in place of mounting the gear  7402  to the side surface  7060  of the rotary structure  7018 , part of the side surface  7060  of the rotary structure  7018  may be caused to have a gear shape. Alternatively, a roller may be fixed to the shaft  7072  of the motor  7064  in place of the gear  7400 , and a roller surface may abut against the side surface  7060  of the rotary structure  7018 . 
     8 Eighth Preferred Embodiment 
     An eighth preferred embodiment relates to a reading mechanism  8007  that is employed in place of the reading mechanism  1007  according to the first preferred embodiment. 
       FIG. 12  is a schematic view of the reading mechanism  8007  according to the eighth preferred embodiment, which is a cross-sectional view of the reading mechanism  8007 . 
     As shown in  FIG. 12 , the reading mechanism  8007  includes an excitation light source  8008  that emits the excitation light EL, a photodetector  8010  that detects the photostimulated luminescence light PL, an optical filter  8012  that prevents the excitation light EL from entering the photodetector  8010 , a fixed mirror  8014  that bends the excitation light EL that has arrived from the horizontal direction toward the direction in which the rotation axis RA extends, a rotating mirror  8016  that bends the excitation light EL that has arrived from the direction in which the rotation axis RA extends toward the direction inclined with respect to the rotation axis RA, a fixed structure  8018  that guides the photostimulated luminescence light PL emitted from the irradiation point P to the photodetector  8010 , and a rotation mechanism  8022  that causes the rotating mirror  8016  to rotate around the rotation axis RA. 
     (Scanning Mechanism  8036 ) 
     A scanning mechanism  8036  that is part of the reading mechanism  8007  and causes the irradiation point P to circularly move includes an excitation light optical system  8034  and the rotation mechanism  8022 . The excitation light optical system  8034  includes the fixed mirror  8014  and the rotating mirror  8016  and guides the excitation light EL toward the irradiation point P apart from the rotation axis RA. The rotation mechanism  8022  causes the rotating mirror  8016  constituting part of the excitation light optical system  8034  to rotate around the rotation axis RA. Owing to the scanning mechanism  8036 , the distance from the excitation light source  8008  to the irradiation point P is maintained constant, and the angle of incidence of the excitation light EL with respect to the radiological image forming surface S is maintained constant, with the result that radiological images are read in a uniform manner. 
     (Excitation Light Optical System  8034 ) 
     The excitation light optical system  8034  may include optical elements other than the fixed mirror  8014  and the rotating mirror  8016 . For example, the excitation light optical system  8034  may include, for example, a mirror that bends the excitation light EL further and a lens that converges the excitation light EL. For example, a prism may be used as a bending optical element that bends the excitation light EL, in place of the mirror. 
     (Rotating Mirror  8016 ) 
     The rotating mirror  8016  bends the excitation light EL that has arrived from the direction in which the rotation axis RA extends toward the direction inclined with respect to the rotation axis RA. The excitation light EL that has bent by the rotating mirror  8016  is guided to the irradiation point P apart from the rotation axis RA. 
     The rotating mirror  8016  is provided on the rotation axis RA. The rotating mirror  8016  is fixed to an upper end of a rotating tubular body  8500  of the rotation mechanism  8022  inside the fixed structure  8018 . Owing to the rotating mirror  8016 , the optical path of the excitation light EL is not required to be rotated before reaching the rotating mirror  8016 , and thus the excitation light source  8008  needs not to be moved, which facilitates power feeding to the excitation light source  8008 . 
     The rotating mirror  8016  fixed to the rotating tubular body  8500  rotates around the rotation axis RA, whereby an optical path of the excitation light EL ranging from the rotating mirror  8016  to the scanning plane SP rotates around the rotation axis RA, and the irradiation point P circularly moves on the scanning plane SP. 
     A reflecting surface of the rotating mirror  8016  is tilted with respect to the horizontal direction similarly to the rotating mirror  1016  according to the first preferred embodiment. 
     (Fixed Mirror  8014 ) 
     The fixed mirror  8014  bends the excitation light EL that has arrived from the horizontal direction toward the direction in which the rotation axis RA extends and guides the bent light to the rotating mirror  8016 . The direction of the excitation light EL that reaches the fixed mirror  8014  is not required to be horizontal, and is only required to be the direction inclined with respect to the direction in which the rotation axis RA extends. The excitation light source  8008  is made apart from the rotation axis RA thanks to the fixed mirror  8014 , and thus power feeding to the excitation light source  8008  is facilitated, which increases a degree of freedom in structure of the reading mechanism  8007 . 
     The fixed mirror  8014  is provided on the rotation axis RA. The fixed mirror  8014  is fixed to the frame  8026  separately from the rotation mechanism  8022  outside the rotary structure  8018 . As a result, the excitation light EL is guided to the fixed mirror  8014  without being interfered by the rotary structure  8018 . 
     The fixed mirror  8014  is preferably fixed at a position between a lower surface  8042  of the fixed structure  8018  and the scanning plane SP. Accordingly, the photodetector  8010  and the fixed mirror  8014  are separated from each other by the fixed structure  8018 , which prevents the stray light of the excitation light EL from entering the photodetector  8010 . Further, the excitation light EL is not interrupted by the imaging plate IP. 
     A reflecting surface of the fixed mirror  8014  is inclined with respect to the horizontal direction similarly to the fixed mirror  1014  according to the first preferred embodiment. 
     (Excitation Light Source  8008 , Photodetector  8010  and Optical Filter  8012 ) 
     Those similar to the excitation light source  1008 , the photodetector  1010  and the optical filter  1012  according to the first preferred embodiment are employed as the excitation light source  8008 , the photodetector  8010  and the optical filter  8012 . 
     (Photostimulated Luminescence Light Optical System  8040 ) 
     The photostimulated luminescence light optical system  8040  that guides the photostimulated luminescence light PL emitted from the irradiation point P on the scanning plane SP to the photodetector  8010  is part of the fixed structure  8018 . 
     (Fixed Structure  8018 ) 
     An outer shape of the fixed structure  8018  is approximately cylindrical. A cylinder axis of the fixed structure  8018  is positioned at the same position as the rotation axis RA. 
     The fixed structure  8018  is provided between the photodetector  8010  and the scanning plane SP. The lower surface  8042  of the fixed structure  8018  is opposed to the scanning plane SP and is parallel to the scanning plane SP. The upper surface  8044  of the fixed structure  8018  is opposed to the photodetector  8010 . The fixed structure  8018  is fixed to the frame  8026  separately from the rotation mechanism  8022 . 
     The fixed structure  8018  is a hollow body in which a hollow light guide part  8046  that guides the photostimulated luminescence light PL from the irradiation point P to the photodetector  8010  is formed. The light guide part  8046  has a light inlet  8048  for the photostimulated luminescence light PL on the lower surface  8042  of the fixed structure  8018  that is opposed to the scanning plane SP and a light outlet  8050  for the photostimulated luminescence light PL on the upper surface  8044  of the fixed structure  8018  that is opposed to the photodetector  8010 . The light guide part  8046  has a bell shape in which the distance between the rotation axis RA and a surface (which represents an inner surface of the hollow in the fixed structure  8018  according to the eighth preferred embodiment)  8052  increases from the upper surface  8044  to the lower surface  8042  of the fixed structure  8018 . The surface  8052  of the light guide part  8046  has rotation symmetry of the rotation axis RA. Accordingly, the photostimulated luminescence light PL emitted from the irradiation point P that circularly moves is guided to the photodetector  8010  even when the fixed structure  8018  is not rotated. The surface  8052  of the light guide part  8046  serves as a concave reflecting mirror that collects the photostimulated luminescence light PL entering from the light inlet  8048  to the light outlet  8050 . 
       FIG. 13  is a bottom view of the fixed structure  8018 . 
     As shown in  FIG. 13 , in the lower surface  8042  of the fixed structure  8018 , the light inlet  8048  that is interrupted at two spots and has an incomplete circular shape is formed. Two interrupted spots are provided at locations where the optical path of the excitation light EL during scanning of the radiological image forming surface S is not shielded. 
     (Rotation Mechanism  8022 ) 
     The rotation mechanism  8022  includes a motor  8508  that generates a driving force of rotation, gears  8502  and  8504  that adjust a ratio of rotation and transmit a driving force of the motor  8508  to the rotating tubular body  8500 , a bearing  8506  that supports the rotating tubular body  8500 , and the rotating tubular body  8500  that supports the rotating mirror  8016 . 
     A motor-housing  8510  of the motor  8508  is fixed to the frame  8026 . The gear  8502  is fixed to a shaft  8512  of the motor  8508 . An axis hole having substantially the same shape as the cross-sectional shape of the rotating tubular body  8500  in cross section perpendicular to the rotation axis RA is formed in the gear  8504 . The rotating tubular body  8500  is inserted into the axis hole of the gear  8504 , and the gear  8504  is connected to the rotating tubular body  8500 . The gear  8502  and the gear  8504  are meshed with each other. 
     The bearing  8506  supports the rotating tubular body  8500  in the state where the rotating tubular body  8500  is capable of rotating around the rotation axis RA. An outer ring  8516  of the bearing  8506  is fixed to the inner bottom surface of the light guide part  8046  of the fixed structure  8018 , and an inner ring  8514  of the bearing  8506  is fixed to the rotating tubular body  8500 . 
     While  FIG. 12  shows the case where the bearing  8506  is a roller bearing, the rotating tubular body  8500  may be supported by a sliding bearing or a fluid dynamic bearing. 
     The rotation mechanism  8022  rotates the rotating tubular body  8500  around the rotation axis RA. 
     The rotating tubular body  8500  extends in the rotation axis RA direction. The rotating tubular body  8500  is provided on the rotation axis RA. 
     (Optical Path of Excitation Light EL) 
     The excitation light EL emitted from the excitation light source  8008  is reflected by the fixed mirror  8014  and enters a lower end of the rotating tubular body  8500 . The excitation light EL that has entered the lower end of the rotating tubular body  8500  is emitted from the upper end of the rotating tubular body  8500 , is reflected by the rotating mirror  8016 , and is guided to the scanning plane SP. 
     (Blower Mechanism  8530  and Dust-Proof Filter  8352 ) 
     In the case where the reading mechanism  8007  according to the eighth preferred embodiment is employed, desirably, a blower mechanism  8530  that generates an air stream and a dust-proof filter  8352  that removes dust from the air stream are provided. The air stream generated by the blower mechanism  8530  flows into the light guide part  8046  via the dust-proof filter  8352 , is guided, and is finally blown toward the scanning plane SP from the light inlet  8048 . Accordingly, the imaging plate IP is pressed against the holding surface  1092 , which prevents the imaging plate IP from becoming misaligned. 
     9 Ninth Preferred Embodiment 
     A ninth preferred embodiment relates to a transport mechanism  9006  that is employed in place of the transport mechanism  1006  according to the first preferred embodiment. 
       FIGS. 14 and 15  are schematic views of the transport mechanism  9006  according to the ninth preferred embodiment.  FIG. 14  is a cross-sectional view of the transport mechanism  9006 , and  FIG. 15  is a top view of the transport mechanism  9006 . 
     As shown in  FIGS. 14 and 15 , the transport mechanism  9006  includes a stage (holding part)  9602  that holds the imaging plate IP in a flat manner and a stage drive mechanism  9603  that causes the stage  9602  to reciprocate. The stage drive mechanism  9603  includes a guide rod  9604  that guides the stage  9602  toward the transport direction, a ball screw  9606  that sends the stage  9602  toward the transport direction, a motor  9608  that rotates the ball screw  9606 , and a frame  9610  that supports those described above. 
     The stage  9602  has a flat holding surface  9612  larger than the imaging plate IP. 
     In the stage  9602 , a guide rod hole  9614  that has a hole shape whose diameter is slightly larger than that of a cross-sectional shape of the guide rod  9604  in cross section perpendicular to the transport direction. The guide rod  9604  is inserted into the guide rod hole  9614 . The stage  9602  slides with respect to the guide rod  9604 . Accordingly, the stage  9602  is guided in the transport direction. 
     A screw hole  9616  corresponding to a screw shape of the ball screw  9606  is formed in the stage  9602 . The ball screw  9606  is screwed with the screw hole  9616 . 
     The guide rod  9604  and the ball screw  9606  extend in the transport direction. Both ends of the guide rod  9604  are fixed to the frame  9610 . One end of the ball screw  9606  is supported by the frame  9610  in a rotatable manner, and the other end of the ball screw  9606  is connected to a rotor of the motor  9608 . A motor-housing of the motor  9608  is fixed to the frame  9610 . 
     When the motor  9608  rotates the ball screw  9606 , the stage  9602  linearly moves relative to the fixed scanning mechanism  1036 . Accordingly, the imaging plate IP is transported in the direction perpendicular to the rotation axis RA. 
     The transport mechanism  9006  is an example of a relative movement mechanism that causes the holder formed of the holding surface  9612  to move relative to the scanning mechanism in the direction perpendicular to the rotation axis RA. 
     10 Tenth Preferred Embodiment  
     A tenth preferred embodiment relates to a transport mechanism  10006  that is employed in place of the transport mechanism  1006  according to the first preferred embodiment. 
       FIG. 16  is a schematic view of the transport mechanism  10006  according to the tenth preferred embodiment, which is a cross-sectional view of the transport mechanism  10006 . 
     As shown in  FIG. 16 , the transport mechanism  10006  includes a stage (holding part)  10602  that holds the imaging plate IP in a flat manner and a stage drive mechanism  10603  that causes the stage  10602  to reciprocate. The stage drive mechanism  10603  includes a guide rod  10604  that guides the stage  10602  toward the transport direction, a rack  10700  and a pinion  10702  that send the stage  10602  toward the transport direction, a motor  10704  that rotates the pinion  10702 , and a frame  10610  that supports those described above. 
     The stage  10602  has a flat holding surface  10612  larger than the imaging plate IP. 
     The guide rod  10604  and the rack  10700  extend in the transport direction. Both ends of the guide rod  10604  and the rack  10700  are fixed to the frame  10610 . The pinion  10702  is connected to a shaft of the motor  10704 . A motor-housing of the motor  10704  is fixed to a lower surface of the stage  10602 . The rack  10700  and the pinion  10702  are meshed with each other. When the motor  10704  rotates the pinion  10702 , the stage  10602  linearly moves relative to the fixed scanning mechanism  1036 . Accordingly, the imaging plate IP is linearly transported toward the direction perpendicular to the rotation axis RA. 
     Even when the rack  10700  is omitted and a roller whose roller surface abuts against a bottom upper surface and the like of the frame  10610  is connected to the shaft of the motor  10704  in place of the pinion  10702 , the stage  10602  moves relative to the fixed scanning mechanism  1036  in a similar manner, and the imaging plate IP is linearly transported toward the direction perpendicular to the rotation axis RA. 
     The stage drive mechanism  10603  is an example of a relative movement mechanism that moves the holder formed of the stage  10602  to move relative to the scanning mechanism in the direction perpendicular to the rotation axis RA. 
     11 Eleventh Preferred Embodiment 
     An eleventh preferred embodiment relates to an arrangement of imaging plates 
     IP 1  to IP 4  that are employed in place of an arrangement of the imaging plate IP according to the first preferred embodiment. 
       FIG. 17  is a schematic view showing an arrangement of the imaging plates IP 1  to IP 4  according to the eleventh preferred embodiment, which is a top view showing the arrangement of the imaging plates IP 1  to IP 4  in transportation. 
     As shown in  FIG. 17 , on the holding surface  1092  of the belt  1080 , the large imaging plate IP 1  for panoramic radiography is placed, and three small imaging plates IP 2  to IP 4  for oral radiography are placed by being arranged in the direction perpendicular to the transport direction. As described above, it is acceptable to place the imaging plates IP 1  to IP 4  of different sizes together or to arrange a plurality of imaging plates IP 1  to IP 4  in the transport direction and the direction perpendicular to the transport direction. 
     Note that in the case where a plurality of imaging plates IP 2  to IP 4  are arranged in the direction perpendicular to the transport direction, a diameter of the track TR is determined such that the entire radiological image forming surfaces of the arranged plurality of imaging plates IP 2  to IP 4  are scanned. 
     12 Twelfth Preferred Embodiment 
     A twelfth preferred embodiment relates to a radiological image reader  12002  that reads a radiological image from the radiological image forming surface S of the imaging plate IP. A main difference between the reader  1002  according to the first preferred embodiment and the radiological image reader  12002  according to the twelfth preferred embodiment resides in that the holder (belt  1080 ) is moved relative to the fixed reading mechanism  1007  in the reader  1002  according to the first preferred embodiment, whereas a reading mechanism  12007  is moved relative to a fixed holder (tray  12080 ) in the reader  12002  according to the twelfth preferred embodiment. By focusing attention on this difference, the reader  12002  according to the twelfth preferred embodiment is described. 
       FIGS. 18 and 19  are schematic views of the reader.  FIG. 18  is a cross-sectional view of the reader, and  FIG. 19  is a perspective view of the reader. 
     As shown in  FIGS. 18 and 19 , the reader  12002  includes the reading mechanism  12007  that reads a radiological image from the radiological image forming surface S, the tray  12080  that holds the imaging plate IP, an erase beam light source  12040  that emits an erase beam, a frame  12026  that accommodates the reading mechanism  12007  and the erase beam light source  12040 , a frame drive mechanism  12802  that causes the reading mechanism  12007  and the erase beam light source  12040  to reciprocate together with the frame  12026 , a tray drive mechanism  12804  that causes the tray  12080  to reciprocate, and a housing  12028  that accommodates those described above. 
     The imaging plate IP, which has been carried into the reader  12002  by a carrying-in/out mechanism  12806  including the tray  12080  and the tray drive mechanism  12804 , is held by the tray  12080  in a flat manner. The tray  12080  is a holder that holds the imaging plate IP. The reading mechanism  12007  is transported toward a direction B or BA, and passes above the imaging plate IP held by the tray  12080 , to thereby read a radiological image drawn on the radiological image forming surface S. 
     The reading mechanism  12007  is similar to the reading mechanism  1007  according to the first preferred embodiment except for that the components, which are equivalent to the components fixed to the frame  1026  that does not move in the reading mechanism  1007  according to the first preferred embodiment, are fixed to the frame  12026  that moves. The reader mechanism  12007  includes a scanning mechanism that causes the irradiation point P to circularly move. 
     The frame drive mechanism  12802  includes support pieces  12808 ,  12810 ,  12812  and  12814  that support the frame  12026 , a guide rod  12816  that guides the support pieces  12808  and  12810  toward the drive direction, a ball screw  12818  that sends the support pieces  12812  and  12814  toward the drive direction, and a motor  12820  that rotates the ball screw  12818 . 
     Formed in the support pieces  12808  and  12810  are guide rod holes having substantially the same hole shape as a cross-sectional shape of the guide rod  12816  in cross section perpendicular to the drive direction. The guide rod  12816  is inserted into the guide rod holes. The support pieces  12808  and  12810  are fixed to the frame  12026  and slide with respect to the guide rod  12816 . Accordingly, the frame  12026  and the reading mechanism  12007  and the erase beam light source  12040  that are fixed to the frame  12026  are guided in the drive direction. 
     Formed in the support pieces  12812  and  12814  are screw holes corresponding to the screw shape of the ball screw  12818 . The ball screw  12818  is screwed with the screw holes. 
     The guide rod  12816  and the ball screw  12818  extend in the drive direction. Both ends of the guide rod  12816  are fixed to the housing  12028 . While the support structure thereof is not specifically described, one end of the ball screw  12818  is supported by the housing  12028  in a rotatable manner, and the other end of the ball screw  12818  is connected to a rotor of the motor  12028 . The motor-housing of the motor  12820  is fixed to the housing  12028 . 
     When the motor  12820  rotates the ball screw  12818 , the frame  12026  and the reading mechanism  12007  and the erase beam light source  12040  that are fixed to the frame  12026  linearly move relative to the fixed tray  12080 . As a result, the reading mechanism  12007  and the erase beam light source  12040  are linearly transported in the direction perpendicular to the rotation axis RA. 
     The tray drive mechanism  12804  includes a roller  12822  that sends the tray  12080  in the drive direction and the motor  12820  that rotates the roller  12822 . 
     A roller surface of the roller  12822  abuts against a bottom surface of the tray  12080 . The roller  12822  is connected to a shaft of the motor  12820 . A motor-housing of the motor  12820  is fixed to the housing  12028 . 
     When the motor  12820  rotates the roller  12822 , the tray  12080  moves between an ejection position at which the tray  12080  is drawn from the housing  12028  and a loading position at which the tray  12080  is pushed into the housing  12028 . When the tray  12080  is at the ejection point, the imaging plate IP is placed on a holding surface  12824  of the tray  12080 , and the imaging plate IP placed on the holding surface  12824  of the tray  12080  is collected. When the tray  12080  is at the loading position, a radiological image drawn on the radiological image forming surface S of the imaging plate IP placed on the holding surface  12824  of the tray  12080  is read by the reading mechanism  12007 . 
     The erase beam light source  12040  is fixed to the frame  12026  and moves together with the reading mechanism  12007  along the drive direction by driving of the frame drive mechanism  12802 , to thereby perform erasing. 
     In the state where the tray  12080  is at the loading position and the imaging plate IP is carried into the reader  12002 , the tray  12080  and the imaging plate IP are fixed with respect to the housing  12028  and the reader  12002  main body. 
     The scanning mechanism equivalent to the scanning mechanism  1036  according to the first preferred embodiment is also part of the reading mechanism  12007 , and thus the scanning mechanism constituting the reading mechanism  12007  is also moved relative to the tray  12080  fixed to the housing  12028  and the reader  12002  main body at the loading position. The excitation light source is part of the reading mechanism  12007  as well, and thus the scanning mechanism and the excitation light source constituting the reading mechanism  12007  are integrally moved. 
     The frame drive mechanism  12802  is an example of a relative movement mechanism that causes the holder formed of the tray  12080  to move in the direction perpendicular to the rotation axis RA relative to the scanning mechanism constituting the reading mechanism  12007 . 
     13 Thirteenth Preferred Embodiment 
     A thirteenth preferred embodiment relates to a radiological image reader  13002  that reads a radiological image from the radiological image forming surface S of the imaging plate IP. A main difference between the reader  1002  according to the first preferred embodiment and the radiological image reader  13002  according to the thirteenth preferred embodiment resides in that the reader  1002  according to the first preferred embodiment causes the holder (belt  1080 ) to move relative to the fixed reading mechanism  1007 , whereas the reader  13002  according to the thirteenth preferred embodiment causes the holder (belt  13080 ) and the reading mechanism  13007  to move. The reader  13002  according to the thirteenth preferred embodiment is described below particularly by focusing attention on this difference. 
       FIG. 20  is a schematic view of the reader  13002 , which is a cross-sectional view of the reader  13002 . 
     As shown in  FIG. 20 , the reader  13002  includes the reading mechanism  13007  that reads a radiological image from the radiological image forming surface S, the belt  13080  that holds the imaging plate IP, a belt drive mechanism  13082  that causes the belt  13080  to go therearound, an erase beam light source  13024  that emits an erase beam, a frame  13026  that accommodates the reading mechanism  13007 , a frame drive mechanism  13802  that causes the reading mechanism  13007  to reciprocate together with the frame  13026 , and a housing  13028  that accommodates those described above. A transport mechanism  13006  according to the thirteenth preferred embodiment that includes the belt  13080  and the belt drive mechanism  13082  is similar to the transport mechanism  1006  according to the first preferred embodiment, which includes a scanning mechanism that causes the irradiation point P to circularly move. 
     The imaging plate IP that is inserted into an inlet  13094  formed in the housing  1028  and is carried into the reader.  12002  is held at an outgoing portion of the belt  13080 . The imaging plate. IP held at the outgoing portion of the belt  13080  is transported toward a direction A. The reading mechanism  13007  is transported toward a direction B. The imaging plate IP held by the belt  13080  and the reading mechanism  13007  cross each other within the reader  13002 , and the reading mechanism  13007  reads a radiological image drawn on the radiological image forming surface S. 
     (Outline of Reading Mechanism  13007 ) 
     The reading mechanism  13007  is similar to the reading mechanism  1007  according to the first preferred embodiment except for that the components, which are equivalent to the components fixed to the frame  1026  that does not move in the reading mechanism  1007  according to the first preferred embodiment, are fixed to the frame  13026  that moves. 
     The frame drive mechanism  13802  according to the thirteenth preferred embodiment is similar to the frame drive mechanism  12802  according to the twelfth preferred embodiment. 
     A holding surface of the imaging plate IP that is part of the belt  13080  is a component of the transport mechanism  13006  that transports the imaging plate IP and is also a holder that holds the imaging plate IP. 
     A holding surface of the belt  13080  moves in the direction perpendicular to the rotation axis RA with respect to the scanning mechanism of the reading mechanism  13007 , and the imaging plate IP placed on the holding surface is linearly transported in the direction perpendicular to the rotation axis RA with respect to the scanning mechanism of the reading mechanism  13007 . The imaging plate IP is linearly moved relative to the scanning mechanism of the reading mechanism  13007 . 
     Owing to driving of the frame drive mechanism  13802 , the reading mechanism  13007  linearly moves relative to the belt  13080 . Accordingly, the reading mechanism  13007  is linearly transported in the direction perpendicular to the rotation axis RA. 
     The scanning mechanism, equivalent to the scanning mechanism  1036  according to the first preferred embodiment is also part of the reading-mechanism  13007 , and thus the scanning mechanism constituting the reading mechanism  13007  is also moved relative to the holding surface of the belt  13080 . 
     The direction in which the reading mechanism  13007  moves by driving of the frame drive mechanism  13802  and the direction in which the holding surface of the belt  13080  moves by driving of the transport mechanism  13006  are opposite to each other. 
     The transport mechanism  13006  and the frame drive mechanism  13802  are examples of a relative movement mechanism that causes the holder formed of the holding surface of the belt  13080  to move in the direction perpendicular to the rotation axis RA relative to the scanning mechanism of the reading mechanism  13007 . 
     According to the reader  1002  of the first preferred embodiment that causes the holder (belt  1080 ) to move relative to the fixed reading mechanism  1007 , if the configuration is made such that the reading mechanism  1007  is transported for scanning after the imaging plate IP is placed on the belt  1080  and that the imaging plate IP that has undergone scanning is sent in the state of being placed on the belt  1080 , the space for placing the imaging plate IP is required in front of and behind the reading mechanism  1007 , leading to an increase in size of the belt  1080  by that amount. In contrast, according to the reader  13002  of this preferred embodiment employing the configuration of the reader  12002  according to the twelfth preferred embodiment that causes the reading mechanism  12007  to move relative to the fixed holder (tray  12080 ), the reading mechanism  13007  moves as well, and thus the imaging plate IP can be placed on the belt  13080  by retracting the reading mechanism  13007  in advance. As a result, the belt  13080  and the reading mechanism  13007  can be moved and the scanning can be performed, leading to a reduction in space on the belt  13080  side by that amount. That is, a footprint does not extremely increase. The reader  13002  according to the thirteenth preferred embodiment that moves the holder (belt  13080 ) and the reading mechanism  13007  is capable of making a footprint particularly small by taking advantages of those. 
     14 Others 
     While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention. In particular, it is naturally intended that items described in the first to thirteenth preferred embodiments are combined. In addition, it is also intended that the modified preferred embodiments according to the second to tenth preferred embodiments are employed in the reader  12002  according to the twelfth preferred embodiment or the reader  13002  according to the thirteenth preferred embodiment.