Radiation image converting apparatus

Abstract: The invention relates to a radiation image converting apparatus (2) which employs an accelerated phosphorescence fluorescent plate (22) which is rigid or low in flexibility. The apparatus (2) comprises a lead-containing sheet (35) formed as a single flexible sheet or as a chain of rigid plates, and a moving mechanism (32, 33, 34) for moving the lead-containing sheet (35) to a position behind the fluorescent plate (22) prior to photographing, and retracting it from that position prior to reading.

Description: The present invention relates to a radiation image converting apparatus which employs an accelerated phosphorescence fluorescent screen. In recent years, systems wherein a radiation image is recorded on an X-ray film or the like and the film on which a radiation image is recorded is used as it is for observation, diagnosis or the like have been and are being gradually replaced by another system. In the newer system, radiation which has passed through an object to be photographed is incident upon an accelerated phosphorescence fluorescent material formed as a sheet or panel to accumulate and record a radiation image thereon; this image is photoelectrically read to obtain an image signal, upon which image processing is subsequently performed to obtain a reproduction image. The basic construction of such a system is disclosed in detail in U.S. Patent No. 3,859,527. Here, the expression "accelerated phosphorescence fluorescent material" signifies a fluorescent material which temporarily stores, when it is subjected to radiation such as X-rays, α rays, β rays or γ rays, part of the energy of the radiation. Thereafter, if excitation light such as infrared rays, visible rays or ultraviolet rays is shone onto the material during the storage period, the accumulated energy is radiated as accelerated phosphorescence light. The type of radiation energy which is readily accumulated, the wavelength of excitation light suitable to produce phosphorescence, the wavelength of the emitted accelerated phosphorescence light, and so forth, vary according to the type of fluorescent material. The amount of accelerated phosphorescence light emitted from the fluorescent material following irradiation of excitation light increases in proportion, over a wide range of energy, to the energy of radiation originally incident on the material. Furthermore, the ratio between the amount of emitted light and the original irradiation energy can be varied by adjusting the amount of excitation light. Accordingly, a radiation image which is not influenced by a variation in amount of exposure radiation can be obtained. Moreover, in a system for obtaining an X-ray image of a human body, the exposure dose to a human body during X-ray photography can be reduced. A radiation image converting apparatus may include a photographing and recording section including an accelerated phosphorescence fluorescent plate (below, fluorescent plate) wherein an accelerated phosphorescence fluorescent material is formed in a panel and is rigid or has low flexibility, and a reading unit for shining excitation light onto the plate and for receiving accelerated phosphorescence light emitted from the plate to obtain an image signal. This apparatus has the problem that when radiation such as X-rays is incident on the fluorescent plate, part of the radiation passes through the plate and is scattered within the apparatus so as to be reintroduced into the plate; consequently, the sharpness of the image recorded on the plate is deteriorated, so that a visible image reproduced from an image signal obtained by reading the image is unclear. The present inventors realised that a possible solution to this problem might be the provision, similarly as in conventional X-ray apparatus, of a lead plate on the rear face of the fluorescent plate. This would absorb radiation which had passed through the fluorescent plate, thus stopping it from scattering inside the apparatus. In the case of a conventional apparatus which employs an X-ray film, there is no problem if such a lead plate is provided because the X-ray film is taken out after completion of photography to be developed. However, when an accelerated phosphorescence fluorescent plate is employed, it is necessary, after completion of photography, to dispose the fluorescent plate and the reading unit close to each other to effect reading of the radiation image recorded on the plate. Therefore, if a lead plate is disposed behind the fluorescent plate, it is difficult to place the fluorescent plate and reading unit sufficiently close to each other. This is a serious obstacle to miniaturizing the apparatus and simplifying its structure. Thus, it is desirable to provide a radiation image converting apparatus which prevents radiation which has passed through the fluorescent plate from being scattered back onto the plate, and which facilitates miniaturization of the equipment and simplification of its structure. US-A-3 859 527 discloses an apparatus according to the preamble of accompanying claim 1. In this apparatus, the radiation-absorbing member is a mask interposed between an infrared or heat source and the fluorescent plate, used to define an area of the plate to be stimulated by the infrared or heat source. The mask and source are moved together to scan over the fluorescent plate. EP-A-0 142 706 discloses a similar kind of apparatus in which a radiation-absorbing member (shielding plate) has an adjustable size for defining an aperture through which a recording plate is exposed to X-rays. US-A-4 158 143 discloses irradiation equipment including an arrangement of carrier plates for varying an aperture of an emergent X-ray beam. According to the invention, there is provided a radiation image converting apparatus which includes a reading unit for irradiating excitation light upon an accelerated phosphorescence fluorescent plate on which a radiation image is accumulated and recorded and for receiving accelerated phosphorescence light emitted from said fluorescent plate to produce an image signal carrying the radiation image, and a radiation-absorbing means for absorbing radiation; characterized in that said apparatus further includes a photographing and recording unit including said accelerated phosphorescence fluorescent plate on which a radiation image is to be accumulated and recorded; in that said radiation-absorbing means contains lead and is positionable by a mechanism of the apparatus into a position behind said plate to absorb radiation which has been irradiated upon said fluorescent plate and passed through said fluorescent plate; and in that said mechanism is operative, prior to said radiation image being accumulated and recorded onto said fluorescent plate, to move said radiation-absorbing means to said position behind said fluorescent plate, and further operative, prior to reading the radiation image by said reading unit to produce said image signal, to move said radiation-absorbing member from said position to another position withdrawn from said position. The mechanism need only be constructed such that it can reconfigure the apparatus between a configuration in which the radiation-absorbing means, e.g. sheet, is behind the fluorescent plate and another configuration in which the means is retracted therefrom, and is not limited to any particular mechanism. For example, when the radiation-absorbing means is a flexible lead-containing sheet, the mechanism may be constructed such that it winds up the lead-containing sheet (e.g. on a roller) or moves the sheet, without winding, to anywhere it does not create an obstacle. Although the positional relationship between the fluorescent plate and the reading unit is not limited to a particular one, the reading unit may for example be disposed, in said position, behind the radiation absorbing member such that it shines, in said another position, excitation light onto the rear face of the fluorescent plate and detects phosphorescence from the rear face. Instead of a lead-containing sheet, the radiation-absorbing means may be constituted by a radiation-absorbing plate composed of a plurality of lead-containing plates combined or connected in such a manner as to be flexible at least in a predetermined direction. In this instance, the mechanism is constructed such that it moves the radiation-absorbing plate between a position behind the fluorescent plate and a position retracted therefrom. In embodiments of the invention, since the radiation-absorbing means is disposed, during photographing, behind the fluorescent plate, radiation which has passed through the fluorescent plate is absorbed, and consequently prevented from re-entering the fluorescent plate and deteriorating the sharpness of a radiation image. However, since the radiation-absorbing means is retracted prior to reading, the fluorescent plate and the reading unit can be readily disposed close to each other without the radiation-absorbing means creating an obstacle. Since the radiation-absorbing means can be flexible, a mechanism for moving it may be simpler than that needed to move a rigid lead plate of the type employed in a conventional X-ray film system. Thus, miniaturization of the equipment and simplification of its structure can be realized. Since the radiation-absorbing member is preferably flexible, it may be wound up in order to retract it from the position behind the fluorescent plate. In this case, only a small space is required in which to retract the radiation-absorbing member, thus further contributing to miniaturization. Further, when the reading unit is provided at the rear face of the fluorescent plate, reading can be performed while the fluorescent plate is kept fixed or makes a simple parallel movement or the like, which contributes to further simplification of the mechanism and further reduction in size of the equipment. Reference is made, by way of example, to the accompanying drawings in which:- Fig. 1 is a schematic illustration showing a system for obtaining an X-ray image of a human body; Fig. 2 is a schematic perspective view of the internal structure of an X-ray image converting apparatus showing a first preferred embodiment of the present invention; Fig. 3 is an enlarged perspective view showing a moving mechanism for an accelerated phosphorescence fluorescent plate of the X-ray image converting apparatus of Fig. 2; Fig. 4 is a perspective view, partly broken, of part of another X-ray image converting apparatus showing a second preferred embodiment of the present invention; Figs. 5(A) and 5(B) are an enlarged perspective view and a sectional view, respectively, of a sheet moving mechanism of the X-ray image converting apparatus shown in Fig. 4; Figs. 6(A) and 6(B) are a side elevational view and a perspective view, respectively, of part of a further X-ray image converting apparatus showing a third preferred embodiment of the present invention; and Figs. 7(A) and 7(B) are a side elevational view and a perspective view, respectively, of part of a still further X-ray image converting apparatus showing a fourth preferred embodiment of the present invention. Referring first to Fig. 1 there is shown an entire system for obtaining an X-ray image of a human body including an X-ray image converting apparatus to which the present invention is applied. An object 3 for photographing will be disposed in front of a photographing and recording section 21 of an X-ray image converting apparatus 2 between an X-ray generating apparatus 1 and the X-ray image converting apparatus 2. In this condition, X-rays 4 are emitted from the X-ray generating apparatus 1, and those of the X-rays 4 which have passed through the object 3 for photographing are irradiated upon an accelerated phosphorescence fluorescent plate 22 provided in the photographing and recording section 21 so that an X-ray image of the object 3 for photographing is accumulated and recorded on the accelerated phosphorescence fluorescent plate 22. A reading unit 40 is provided in the X-ray image converting apparatus 2, and in the reading unit 40, the accelerated phosphorescence fluorescent plate 22 after photographing is scanned by a laser beam 41 which serves as excitation light, whereupon accelerated phosphorescence light emitted from each scanning point is photoelectrically read and A/D (analog to digital) converted so that a digital image signal S is produced. The image signal S is inputted to an image processing apparatus 5, in which various image processes such as a frequency emphasizing process are performed for the image signal S, whereafter the image signal S is inputted to an image display unit 6 such as a CRT image display unit so that a visible image based on the image signal is reproduced and displayed on the image display unit 6. Referring to Fig. 2, there is shown general construction of the internal structure of an X-ray image converting apparatus according to a first preferred embodiment of the present invention. A fixing plate 24 to which an accelerated phosphorescence fluorescent plate 22 is fixed is provided in the photographing and recording section 21 of the X-ray image converting apparatus 2. The fixing plate 24 is driven by a motor 25 so that, it is moved, under the guidance of a slide 26, in the direction indicated by an arrow mark A in Fig. 2 when photographing is to be performed but in the opposite direction indicated by another arrow mark B in Fig. 2 to a position adjacent a pair of wires 31 when reading is to be performed. Fig. 3 shows details of a mechanism for moving the accelerated phosphorescence fluorescent plate 22. Referring also to Fig. 3, an external thread is formed on a shaft 27 of the motor 25, and the fixing plate 24 to which the accelerated phosphorescence fluorescent plate 22 is fixed is fixed to a fixing base 28. The fixing base 28 has a projection or rib 28a formed thereon for being received for sliding movement in an elongated groove 26a of the slide 26 and further has a hole 28b formed as a female thread therein with which the shaft 27 of the motor 25 is held in threaded engagement. Thus, when the motor 25 is rotated in one or the other direction, the fixing base 28 is moved in the direction indicated by the arrow mark A or B. Referring back to Fig. 2, a lead containing sheet 35 is provided in the X-ray image converting apparatus 2 such that it is moved between a first position in which it is wound up on a roller 34 which is driven by a motor 32 by way of a belt 33 and a second position in which it is stretched along the rear face side of the accelerated phosphorescent fluorescent plate 22. The lead containing sheet 35 is a flexible sheet which sufficiently contains therein lead which absorbs X-rays, and an upper end face of the lead containing sheet 35 is connected to a wire not shown attached to the roller 34 while a lower end face of the lead containing sheet 35 is connected to one ends of the wires 31. The other ends of the wires 31 are attached to a pair of wire winding rollers 37 (only one is shown in Fig._ 2) which are driven by another motor 36. The reading unit 40 is provided just behind the wires 31. The reading unit 40 includes a housing 41 in which a pair of holes having a pair of slide bars 42 being fitted and a female threaded hole which is held in threaded engagement with a shaft 44 connected to a shaft of a motor 43 and having a male thread provided thereon are formed. Thus, when the motor 43 is rotated, the reading unit 40 is moved in an upward or downward direction, that is, in the direction indicated by an arrow mark C or D. A scanning optical system for repetitively scanning a laser beam on the accelerated phosphorescence fluorescent plate 22 in the direction indicated by an arrow mark X in Fig. 2 and a light receiving optical system for receiving accelerated phosphorescence light emitted from the accelerated phosphorescence fluorescent plate 22 upon scanning of a laser beam and converting the received accelerated phosphorescence light into an electric signal are provided in the reading unit 40. The scanning optical system is constituted from a laser light source 46, a rotary polygonal mirror 47, an f lens 48 and so forth all placed on a receiving table 45 while the light receiving optical system is constituted from a reflecting mirror 49, a light converging member 50 formed from a large number of optical fibers, a photomultiplier 51 and so forth. The reading unit 40 further includes therein an erasing lamp 52 for causing X-ray energy remaining in the accelerated phosphorescence fluorescent plate 22 after completion of reading to be discharged to put the accelerated phosphorescence fluorescent plate 22 into a re-usable condition. In operation, the accelerated phosphorescence fluorescent plate 22 is moved in the direction of the arrow mark A by rotation of the motor 25, and the lead containing sheet 35 is moved into the position wherein it is developed along the rear face side of the accelerated phosphorescence fluorescent plate 22 by rotation of the motor 27. The reading unit 40 then is in a condition wherein it is positioned at its limit position in the direction of the arrow mark C by rotation of the motor 43 so that an uppermost portion of the accelerated phosphorescence fluorescent plate 22 may be scanned by the reading unit 40. In this condition, X-ray photographing is performed in such a manner as seen from Fig. 1. After completion of the X-ray photographing, the motor 25 is rotated so that the accelerated phosphorescence fluorescent plate 22 is moved in the direction of the arrow mark B, and the motor 32 is rotated so that the lead containing sheet 35 is moved away from the position behind the accelerated phosphorescence fluorescent plate 22 and wound up onto the roller 34. After then, reading is performed in the following manner. In particular, a laser beam not shown emitted from the laser light source 46 is reflected and diverted by the rotary polygonal mirror 47 and then irradiated, after passing through the f lens 48, upon the accelerated phosphorescence fluorescent plate 22. Consequently, the accelerated phosphorescence fluorescent plate 22 is horizontally scanned repetitively in the X direction by the laser beam. During such repetitive horizontal scanning, the motor 43 is driven to move the reading unit 40 downwardly in the direction indicated by an arrow mark D in Fig. 2, whereupon the accelerated phosphorescence fluorescent plate 22 is vertically scanned in the direction indicated by an arrow mark Y. From each scanning point on the accelerated phosphorescence fluorescent plate 22, accelerated phosphorescence light of an amount corresponding to an amount of X-ray energy accumulated and recorded at the point is emitted, and the accelerated phosphorescence light is introduced directly or after reflection by the reflecting mirror 49 into the light converging member 50. Consequently, the accelerated phosphorescence light is thereafter guided by the light converging member 50 so that it is introduced into the photomultiplier 51, in which it is photoelectrically converted into an analog image signal. The analog image signal is logarithmically amplified by a logarithmic amplifier not shown and then converted into a digital image signal by an A/D (analog to digital) converter not shown either, whereafter it is transmitted to the image processing apparatus 5 (refer to Fig. 1). After the accelerated phosphorescence fluorescent plate 22 is scanned to its lowermost portion in this manner thereby to complete reading of the X-ray image, the erasing lamp 52 is lit and the motor 43 is reversed so that the reading unit 40 is moved to its uppermost position in the direction indicated by an arrow mark C in Fig. 2. Consequently, X-ray energy which may otherwise remain in the accelerated phosphorescence fluorescent plate 22 is discharged so that the accelerated phosphorescence fluorescent plate 22 is put into a re-usable condition. Such sequence of operations as described above will be repeated to repeat photographing and reading. Here, since X-ray photographing is performed while the lead containing sheet 35 is developed along the rear face of the accelerated phosphorescence fluorescent plate 22, X-rays having passed through the accelerated phosphorescence fluorescent plate 22 are absorbed by the lead containing sheet 35. Consequently, it is prevented that, for example, such X-rays are scattered by the reading unit 40 and so forth and introduced into the accelerated phosphorescence fluorescent plate 22 again. Accordingly, an X-ray image of a high sharpness which is little influenced by backscattered radiations is accumulated and recorded on the accelerated phosphorescence fluorescent plate 22. Further, since the lead containing sheet 35 is wound up onto the roller 34 when reading is to be performed, it will not disturb the reading operation, and the reading operation can be performed only by parallelly moving the accelerated phosphorescence fluorescent plate 22 in the direction indicated by the arrow mark B in Fig. 2. Due to the construction wherein the lead containing sheet 35 is moved between the first position behind the accelerated phosphorescence fluorescent plate 22 and the second position retracted from behind the accelerated phosphorescence fluorescent plate 22 (the position on or adjacent the roller 34 in the arrangement shown in Fig. 2), the mechanism for moving the accelerated phosphorescence fluorescent plate 22 can be simplified and the overall size of the apparatus can be reduced comparing with an alternative arrangement wherein, for example, a rigid lead plate is disposed on the rear face of the accelerated phosphorescence fluorescent plate 22 and, when reading is to be performed, either the lead plate or the accelerated phosphorescence fluorescent plate 22 is moved away from its position. It is to be noted that, while, in the embodiment described above, the lead containing sheet 35 is wound up onto the roller 34, it need not be wound up in this manner, but may be retracted along an upper wall, a rear wall or the like of the inside of the housing of the apparatus while it remains in a developed condition. Referring now to Fig. 4, there is shown part of another X-ray image converting apparatus according to a second preferred embodiment of the present invention. The X-ray image converting apparatus shown includes a lead containing sheet 102 provided along a rear face of an accelerated phosphorescence fluorescent plate 101. The lead containing 102 is moved in the direction indicated by an arrow mark E or F under the guidance of a pair of guide rails 104 by rotation of a pair of motors 103. A moving mechanism for the lead containing sheet 102 is shown in more detail in an enlarged perspective view of Fig. 5(A) and also in Fig. 5(B) which is a sectional view taken along line Z-Z' of Fig. 5(A). Referring also to Figs. 5(A) and 5(B), a feeding portion 102a for which antislipping working has been performed is provided on each of an upper edge portion and a lower edge portion of the lead containing sheet 102. Meanwhile, a roller 105 for which antislipping working has been performed is mounted on each of the motors 103 and is held in contact with a corresponding one of the feeding portions 102a of the lead containing sheet 102 at a window portion 104a at which the corresponding guide rail 104 is cut away. A contacting guide plate 106 is provided on the rear side of each of the guide rails 104 remote from the corresponding roller 105 across the feeding portion 102a so that the feeding portion 102a of the lead containing sheet 102 is held between the roller 105 and the contacting guide plate 106. Further, a free rotation roller 107 is provided in each of the guide rails 104 such that it contacts with an end face of the lead containing sheet 102 as seen from Fig. 5(B) so that the frictional resistance of the lead containing sheet 102 upon movement is reduced. Thus, the lead containing sheet 102 is driven by the motors 103 to move, prior to photographing, to a position behind the rear face of the accelerated phosphorescence fluorescent plate 101 under the guidance of the guide rails 104 but to move, prior to reading, to another position retracted from the position behind the rear face of the accelerated phosphorescence fluorescent plate 101. Figs. 6(A) and 6(B) show a radiation absorbing plate of a further radiation image converting apparatus according to a third preferred embodiment of the present invention. Referring to Figs. 6(A) and 6(B), the radiation absorbing plate shown is composed of a plurality of lead containing plates 600 connected to each other by means of connecting screws 601 such that each adjacent ones thereof are partially overlapped with each other as seen in Fig. 6(A) so that the lead containing plates 600 may have a flexibility as a whole. An end of the radiation absorbing plate which is composed of the plurality of lead containing plates 600 connected to each other in this manner is connected to a roller 603 as shown in Fig. 6(B). When a motor 604 is energized to rotate the roller 603 in the direction indicated by an arrow mark G in Fig. 6(B), the lead containing plates 600 are wound up by the roller 603 so that they are retracted from the position behind an accelerated phosphorescence fluorescent plate (not shown). On the contrary when the motor 604 is energized reversely to rotate the roller 603 in the reverse direction indicated by an arrow mark H in Fig. 6(B), the lead containing plates 600 are introduced behind the rear face of the accelerated phosphorescence fluorescent plate. Figs. 7(A) and 7(B) show a radiation absorbing plate of a still further radiation image converting apparatus according to a fourth preferred embodiment of the present invention. Referring to Figs. 7(A) and 7(B), the radiation absorbing plate shown is composed of a plurality of lead containing plates 700 attached to a flexible belt 703 each by way of a connecting plate 701 such that each adjacent ones of the lead containing plates 700 are partially overlapped with each other as seen in Fig. 7(A). A plurality of lateral grooves 704 are formed at a predetermined pitch on a rear face of the belt 703. The radiation absorbing plate constructed in such a manner as described just above extends between a pair of rollers 705 (only one is shown in Fig. 7(B)). Each of the rollers 705 has a plurality of lateral protrusions or ribs 706 formed on an outer periphery thereof for fitting with the lateral grooves 704 of the belt 703. When one of the rollers 705 is rotated in the direction indicated by an arrow mark I in Fig. 7(B) by a motor 707, the lead containing plates 700 are transported by the belt 703 to a position retracted from their position behind an accelerated phosphorescence fluorescent plate (not shown). On the contrary when the motor 707 is energized reversely to rotate the roller 705 in the reverse direction indicated by an arrow mark J in Fig. 7(B), the lead containing plates 700 are moved to the position behind the rear face of the accelerated phosphorescence fluorescent plate. As seen from the radiation image converting apparatus of the third and fourth embodiments described above, such a lead containing sheet as is employed in the radiation image converting apparatus of the first and second embodiments may be replaced by a radiation absorbing plate which is composed of a plurality of rigid lead containing plates combined with each other such that they may have a flexibility as a whole. Further, such a plurality of lead containing plates combined with each other may either be wound up or be moved or shifted without being wound up. While several examples of a lead containing radiation absorbing plate and a moving mechanism for the same are described above, a lead containing sheet or a radiation absorbing plate and a mechanism for the same are not limited to those described above but may naturally be constructed in various manners. Further, while the structures for moving an accelerated phosphorescence fluorescent plate in the forward and backward directions are described with reference to Figs. 2 and 3, an alternative structure wherein an accelerated phosphorescence fluorescent plate is kept fixed may be employed, or even if an accelerated phosphorescence fluorescent plate is moved, the manner in which it is moved is not limited to that of Figs. 2 and 3. Further, the radiation image converting apparatus shown in Fig. 2 has the structure wherein reading is performed from the rear face side of the accelerated phosphorescence fluorescent plate 22, and while the system wherein reading is performed from the rear face side of the accelerated phosphorescence fluorescent plate 22 is preferable from the point of view of achievement of simplification in structure of the equipment and miniaturization of the entire equipment, the present invention is not limited to the specific system, but an alternative system may be employed wherein, for example, an accelerated phosphorescence fluorescent plate is tilted down to the rear face side while a reading unit is in an upwardly retracted condition and a laser beam is emitted downwardly from the reading unit so that the front surface side of the accelerated phosphorescence fluorescent plate is scanned by the laser beam and then accelerated phosphorescence light emitted from the front surface side of the accelerated phosphorescence fluorescent plate is received. Further, in this instance, if a mirror is disposed at a position below the accelerated phosphorescence fluorescent plate in the tilted down condition so that also accelerated phosphorescence light emitted from the rear face side of the accelerated phosphorescence fluorescent plate upon scanning may be converged, photoelectric conversion can be achieved at a higher S/N ratio.

Claims: A radiation image converting apparatus which includes a reading unit (40) for irradiating excitation light upon an accelerated phosphorescence fluorescent plate (22,101) on which a radiation image is accumulated and recorded, and for receiving accelerated phosphorescence light emitted from said fluorescent plate to produce an image signal carrying the radiation image, and a radiation-absorbing means (35,102) for absorbing radiation; characterized in that said apparatus further includes a photographing and recording unit including said accelerated phosphorescence fluorescent plate on which a radiation image is to be accumulated and recorded; in that said radiation-absorbing means (35,102) contains lead and is positionable by a mechanism of the apparatus into a position behind said flourescent plate to absorb radiation which has been irradiated upon said fluorescent plate and passed through said fluorescent plate (22,101); and in that said mechanism is operative, prior to said radiation image being accumulated and recorded onto said fluorescent plate, to move said radiation-absorbing means to said position behind said fluorescent plate, and further operative, prior to reading the radiation image by said reading unit to produce said image signal, to move said radiation-absorbing member from said position to another position withdrawn from said position. An apparatus according to claim 1, wherein said radiation-absorbing means (35,102) is a flexible lead-containing sheet. An apparatus according to claim 1, wherein said radiation-absorbing means is composed of a plurality of lead-containing plates (600,700) combined in such a manner as to have flexibility at least in a predetermined direction. An apparatus according to claim 3, wherein said plurality of lead-containing plates (600) are connected to each other such that adjacent plates partially overlap each other. An apparatus according to claim 3, wherein said plurality of lead-containing plates (700) are attached to a flexible belt (703) each by way of a connecting plate (701), such that adjacent lead-containing plates (700) partially overlap each other. An apparatus according to any of claims 2 to 5, wherein said mechanism includes a winding roller (34,603,705) for winding said radiation-absorbing means (35) thereon to retract it from the position behind said fluorescent plate (22). An apparatus according to any preceding claim, wherein, in said position, said reading unit (40) is disposed behind said radiation-absorbing means (35) which is disposed behind said fluorescent plate (22), and said reading unit is operative to irradiate excitation light upon said fluorescent plate from the rear face side and to receive accelerated phosphorescence light emitted from the rear face side of said fluorescent plate when said radiation-absorbing means is in said another position.

Inventors: HARAKI TAKAHIRO, HIRANO HIDEYUKI, ISHIWATA KENJI, NAMIKI FUMIHIRO, TAKEDA SIRO, HIRANO, HIDEYUKI, ISHIWATA, KENJI, NAMIKI, FUMIHIRO, TAKEDA, SIRO, Haraki Takahiro, c/o Fujitsu Limited, Hirano, Hideyuki, c/o Fujitsu Limited, Ishiwata, Kenji, c/o Fujitsu Limited, Namiki, Fumihiro, c/o Fujitsu Limited, Takeda, Siro, c/o Fujitsu Limited
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1992
Main classification: G21K4
IPC codes: G21K4, A61B6, G01T1, B41J3, G03B42