RADIATION IMAGE READ-OUT METHOD AND APPARATUS

Abstract: A stimulable phosphor sheet having a stimulable phos­ phor layer on one surface and a magnetic material layer on the opposite surface is employed in a radiation image read-out system. A magnet for attracting the magnetic material layer of the stimulable phosphor sheet is positioned on or within the peripheral surface of a drum. The stimulable phosphor sheet carrying a radiation image stored therein is closely contacted with the peripheral surface of the drum by magnetic attraction, and the drum is rotated to move the stimulable phosphor sheet. At the same time, the stimulable phosphor sheet is scanned with a light beam at right angles to the moving direc­ tion of the stimulable phosphor sheet.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a radiation image readout method in a radiation image recording and read-out system using a stimulable phosphor sheet, and an apparatus for carrying out the method. rition of the Prior Art A radiation image recording and read-out system using a stimulable phosphor is disclosed, for example, in U.S. Patent iios. 4,258,264 and 4,315,318, and Japanese Unexamined Patent Publication No. 56(1981)-11395. The method was also described at meetings of the radiation society, in "Nikkan Kogyo Shinbun (Daily Industrial Newspaper), June 23, 1981 edition, page 16, and elsewhere, and attracted attention in various fields. The aforesaid system provides various radiation images useful for viewing, particularly for diagnostic purposes, which could not be obtained by the conventional radiography using a silver halide photographic material. Moreover, the system can further provide improved diagnostic effects when combined with an up-to-date medical image recording technique such as computed tomography (CT) or introduction of radio-isotope into human bodies. Therefore1 the system is very effective for viewing purposes, particularly for medical diagnosis. The aforesaid system generally comprise the steps of (i) recording (recording and storing a radiation image in a stimulation phosphor), (ii) read-out (converting the stored image into an image signal, and sometimes storing the readout image signal), and (iii) reproducing (converting the image signal into a visible image, i.e. displaying the visible image on a display device such as a cathode ray tube or permanently recording the visible image on a recording medium such as photographic film). The present invention is concerned with the read-out step in the aforesaid system. The read-out of the radiation image stored in the stimulable phosphor is conducted by exposing the stimulable phosphor carrying radiation energy stored therein to stimulating rays which cause the stimulable phosphor to emit light in proportion to the radiation energy, and photoelectrically detecting the emitted light Desirably, a sheet or a plate provided with a stimulable phosphor layer (hereinafter referred to as the recording material) is two-dimensionally scanned with a light bean such as a laser beam, and the light emitted from the recording material upon stimulation thereof is sequentially detected by use of a photodetector such as photomultiplier to obtain an image signal. In this case, the two-dimensional scanning is conducted by scanning the recording material provided with the stimulable phosphor layer with the light beam in the main scanning direction and the sub-scanning direction. For this purpose, the recording material is moved in one direction, and an optical scanning system for scanning the recording material at right angles to the moving direction of the recording material is used. Alternatively, the recording material is maintained statiorar:, and an optical scanning system for scanning the recording material both in the main scanning direction and in the sub-scanning direction is used. The former method using the optical scanning system for scanning only in one direction is employed in many cases since the optical scanning system is far more inexpensive than the optical scanning system for scanning in two directions. However, in the former method, it is an important requirement to move the recording material in one direction at a stable speed. Namely, when the recording material is moved at a predetermined speed in one direction for the sub-scanning and, at the same time, scanned with a light beam for the main scanning at right angles to the sub-scanning direction, unless the recording material is moved very accurately at a predetermined, constant speed, nonuniformity occurs in the read-out operation and makes it impossible to obtain a visible image having a uniform image density at the subsequent reproducing step. Therefore, a high accuracy is required in the sub-scanning, necessitating a holding means and a moving mechanism for the recording material, both of which must be of high-accuracy and, consequently, are of expensive construction. As the mechanism for moving the recording material in the sub-scanning direction, various methods have heretofore ben known. For example, a flexible sheet-like recording material is closely contacted with the peripheral surface of a drum by use of clamping devices or pinch rolls, and the drum is rotated to move the recording material. In another method, a suction box is installed at a part in the inside of a drum to make a sheet-like recording material adhere to a part of the peripheral surface of the drum corresponding to said part by suction force, and the drum is rotated to move the recording material. Alternatively, a suction box is positioned inside of an endless belt, and a plate-like recording material is placed on the belt and carried. In these methods, clamping devices or a suction box is necessary to hold the recording material in close contact with the drum or the belt. In addition, use of the suction box is disadvantageous from the practical viewpoint since the blower for generating the suction force generates noise and vibrations. Vibrations of the blower present a very real problem particularly in a read-out apparatus which is required to achieve feed of the recording material at a high accuracy and which incorporates a precise optical scanning system. SUMMARY OF THE INVENTION The primary object of the present invention is to provide a radiation image read-out method in which a simplified mechanism is employed for fixing a recording material to a drum and read-out can be conducted economically. Another object of the present invention is to provide a radiation image read-out method which eliminates problems with regard to noise and vibrations due to the mechanism for fixing a recording material to a drum. The specific object of he present invention is to provide a radiation image read-out method in which a scanning and read-out system can be positioned very near to the surface of a recording material. A further object of the present invention is to provide an apparatus for carrying out the above method. The present invention is characterized by the use of magnetic attraction as the means for closely contacting the stimulable phosphor sheet with the peripheral surface of the drum. In the present invention, a flexible stimulable phosphor sheet provided with a stimulable phosphor layer on one surface and a magnetic material layer on the opposite surface is employed, and a magnet for magnetically attracting the magnetic material layer of the stimulable phosphor sheet is positioned on or within the peripheral surface of the drum. The stimulable phosphor sheet is adhered to the peripheral surface of the drum by magnetic attraction7 and the drum is rotated to move the stimulable phosphor sheet. At the same time, the stimulable phosphor sheet is scanned with a light beam at right angles to the moving direction of the stimulable phosphor sheet. In the present invention, since adhesion of the stimulable phosphor sheet to the peripheral surface of the drum is effected by magnetic attraction, it is unnecessary to use clamp devices or a suction box, the construction of the read-out apparatus is simplified, and the problems with regard to noise and vibrations are solved. Further, since no mechanism projecting towards the surface of the stimulable phosphor sheet, such as a clamp device or pinch roll is needed, a scanning light source and a light condenser can be positioned near to the surface of the stimulable phosphor sheet as in the case of the conventional method using the suction box. Namely, the present invention has the advantage that noise and vibrations do not occur as they do in the case of the conventional method using clamping devices or pinch rolls, and also the advantage that the scanning and read-out system can be positioned near to the surface of the stimulable phosphor sheet as in the case of the conventional method using the suction box. The present invention is further advantageous in that the construction of the scanning and read-out system is simplified compared with the scanning and read-out system according to these conventional methods. Another advantage of the present invention is that read-out can be conducted economically. The magnet employed in the present invention may be a permanent magnet or an electromagnet. An electromagnet is advantageous in that the stimulable phosphor sheet can be easily loaded on and unloaded from the drum. The magnet may extend over the entire peripheral surface of a drum-like sheet holding body, or may extend only partially on the peripheral surface of the drum-Like sheet holding body so that the magnet can attract both the forward and rearward ends cf the stimulable phosphor sheet. Alternatively, the magnet may be positioned at one position inside of a cylindrical drum, for example, over the range of about a quarter of the entire circumference of the drum. By the rotation of the drum-like sheet holding body, the stimulable phosphor sheet may be moved either in the sub-scanning direction of the two-dimensional scanning or in the main scanning direction thereof. Namely, when the whole area of the stimulable phosphor sheet is closely contacted with and held on the peripheral surface of the drum, twodimensional scanning can be conducted by rotating the drum at a high speed and moving a light beam on the stimulable phosphor sheet at a low speed in a direction parallel to the rotation axis of the drum. In this case, the rotating direction of the drum is the main scanning direction, and the axial direction of the drum is the sub-scanning direction. When the forward and rearward ends of the stimulable phosphor sheet are magnetically attracted to the peripheral surface of the drum and the middle portion of the stimulable phosphor sheet is closely contacted with the peripheral surface of the drum by the sheet tension, two-dimensional scanning should preferably be conducted by rotating the drum at a low speed for effecting the sub-scanning and moving a light beam on the stimulable phosphor sheet at a high speed in the axial direction of the drum by use of a main scanning optical system. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view showing an embodiment of the apparatus for carrying out the radiation image read-out method in accordance with the present invention, and Figure 2 is a perspective view showing another embodiment of the apparatus for carrying out the radiation image read-out method in accordance with the present invention. DESCRIPTION OF THS PREFERRED EMBODIMENTS The present invention will hereinbelow be described in further detail with reference to the accompanying drawings. In Figure 1, a magnet layer 3 is laid over and attached to the peripheral surface of a drum 2 rotatably supported around a rotation axis 1, and a stimulable phosphor sheet 4 comprising a magnetic material layer 4a and a stimulable phosphor layer 4b is closely contacted with the magnet layer 3 by magnetic attraction. The drum 2 is rotated at a high speed in the direction of the arrow A around the rotation axis 1. At the same time, the stimulable phosphor sheet 4 is exposed to a light spot 5 emitted from light source 6 via a lens 7. The light source 6 and the lens 7 are moved in the direction of the arrow B parallel to the rotation axis 1 of the drum, thereby to two-dimensional scan the stimulable phosphor sheet 4 with the light beam. Namely, main scanning is effected in the rotating direction of the drum 2 indicated by the arrow A, and sub-scanning is effected in the rotation axis direction of the drum 2 indicated by the arrow B. Instead of moving the light source 6 and the lens 7, they may be maintained stationary and the drum 2 may be slid in the direction of the rotation axis 1 thereof in order to conduct the sub-scanning in the direction indicated by the arrow B. The stimulable phosphor sheet 4 is provided w-ith the magnetic material layer 4a and the stimulable phosphor layer 4b. In the stimulable phosphor layer 4b, an image of a radiation passing through an object is stored in advance. When the stimulable phosphor sheet 4 is exposed to the light spot 5, the exposed portion thereof emits light, and the emitted light is detected and converted into an image signal by a photodetector 8. The image signal is obtained in time sequence according to the two-dimensional scanning, and used for the image processing and reproducing. Specifically, the stimulable phosphor sheet 4 has the magnetic material layer 4a coated on the rear surface of a substrate (not shown) and comprising a binder and magnetic particles dispersed in the binder, and the stimulable phosphor layer 4b coated on the front surface of the substrate. Alternatively, the substrate may be omitted, and the magnetic material layer 4a may serve as the substrate. The magnet layer 3 is constituted by a ferromagnetic material layer laid over the peripheral surface of the cylindrical drum 2, and may be either a permanent magnet or an electromagnet wherein soft iron is magnetized by use of a magnetic field when necessary. When an electromagnet is employed as the magnet 3, a coil may be installed within the drum 2, and the magnet 3 may be magnetized by exciting the coil. The electromagnet is advantageous in that the stimulable phosphor sheet 4 can be handled easily when loading it on the drum 2 or unloading it from the drum 2 and, therefore, the loading and unloading operations are facilitated. When the drum 2 having the construction as described above is used, the stimulable phosphor sheet 4 is closely contacted with the surface of the magnet layer 3 fcrmei on the peripheral surface of the drum 2 by magnetic attraction, and it is unnecessary to use a special means for clamping the stimulable phosphor sheet 4 or fixing it by suction force generated by a blower or the like. Therefore, the photodetectr 8 can be positioned near to the surface of the stimulable phosphor sheet 4, and read-out can be conducted in the absence of noise or vibrations due to a blower or the like. Further, the speed in the main scanning direction indicated by the arrow A can be stabilized by rotating the drum 2 at a high speed, and the sub-scanning can be conducted simply by moving the light source 6 and the lens 7 at a low speed with respect to the drum 2 Accordingly, the scanning system may have a simple construction and can be manufactured at a low cost. Even when the stimulable phosphor sheet 4 has a somewhat high rigidity or involves curling, it can be closely contacted with the surface of the magnet 3 formed around the drum 2 by increasing the magnetic attraction. Further, in the embodiment of Figure 1, the manner of operation need not be changed even when the size of the stimulable phosphor sheet 4 is changed. Accordingly, the apparatus is very easy to handle compared with a conventional apparatus using a clamping means wherein the positions of the clamps must be changed according to the size of the stimulable phosphor sheet. Figure 2 shows another embodiment of the apparatus for carrying out the radiation image read-out method in accordance with the present invention. In Figure 2, a hollow drum 12 rotatable around a rotation axis 17 is employed, and a magnet 13 is positioned, for example, within a peripheral surface 12a of the drum 12 over the range of about a quarter of the entire circumference of the drum 12. The magnet 13 may be either a permanent magnet or an electromagnet as in the embodiment shown in Figure 1. However, the magnet 13 is fixed in a predetermined position, and the drum 12 is rotated with the inner surface thereof sliding on the outer surface of the magnet 13 or slightly spaced apart from the outer surface of the magnet 13. The magnet 13 is secured to a fixed shaft 10 extending along the rotation axis 11 of the drum 12. The peripheral surface 12a of the drum 12 is made of a material permeable to magnetic current, and the end portion of the peripheral surface 12a is rotatably supported on the end portion of the shaft 10 by a supporting member having spokes 10a, 10b and 10c. When a stimulable phosphor sheet 14 provided with a magnetic material layer 14a on the rear side and a stimulable phosphor layer 14b on the front side is fed onto the peripheral surface 12a of the drum 12, the stimulable phosphor sheet 14 is magnetically attracted to and closely contacted with the portion of the peripheral surface 12a of the drum 12 within which the magnet 13 is positioned. As the drum 12 is rotated, the stimulable phosphor sheet 14 is moved in the sub-scanning direction indicated by the arrow AL. At the same time, the stimulable phosphor sheet 14 is exposed to a laser beam emitted from a laser beam source 16 and deflected in the main scanning direction B' by a scanning mirror 17 In this manner, the stimulable phosphor sheet 14 is scanned with the laser beam in two directions. When exposed to the laser beam, the stimulable phosphor sheet 14 emits light upon stimulaticn thereof, and the emitted light is condensed in a photodetectcr 18, such as photomultiplier, via a light guiding sheet 18a for condensing the light, thereby to obtain an image signal in time sequence. The light guiding sheet 1 8a is a total reflection type light guiding sheet having, at one end, a light input face extending in the main scanning direction B' near to the surface of the stimulable phosphor sheet 14 and, at the other end, a light output face opposed to a light receiving face of the photodetector 18. The light guiding sheet 18a is made, for example, of shaped acrylic resin or the like In the embodiment of Figure 2, since the magnet 13 is installed only at a part of the peripheral surface 12a of the drum 12, only a part of the stimulable phosphor sheet 14 fed onto the drum 12 is magnetically attracted and closely contacted with said part of the peripheral surface 12a, and the other portion of the stimulable phosphor sheet 14 is naturally separated from the peripheral surface 12a because of the absence of the action of magnetic attraction. Therefore, the stimulable phosphor sheet 14 can be easily unloaded from the drum 12. Also in the embodiment of Figure 2, since the stimulable phosphor sheet 14 is closely contacted with the drum 12, the stimulable phosphor sheet 14 is moved at a stable speed in the direction A' as the drum 12 is rotated, and the sub-scanning can thereby be conducted. Further, since no clamp is used, the light guiding sheet 18a can be positioned near to the surface of the stimulable phosphor sheet 14, and special operations are not necessary even when the size of the stimulable phosphor sheet 14 is changed In addition, since a suction means such as blower is not used, problems with regard to noise and vibrations do not occur.

Claims: CLAIMS 1. A radiation image read-out method comprising the steps of: i) closely contacting a stimulable phosphor sheet, which is provided with a stimulable phosphor layer carrying a radiation image stored therein on one surface and a magnetic material layer on the opposite surface, with at least a part of a surface of a drum-like sheet holding body by magnetic attraction, ii) moving said stimulable phosphor sheet in one direction by rotating said drum-like sheet holding body, iii) scanning the surface of said stimulable phosphor sheet with a light beam at right angles to said movement direction of said stimulable phosphor sheet by use of a light beam scanning system, thereby two-dimensionally scanning the surface of said stimulable phosphor sheet, iv) causing said stimulable phosphor sheet to release the radiation energy stored therein as light emission by said scanning with the light beam, and v) photoelectrically reading out the emitted light to obtain an image signal. 2. A radiation image read-out apparatus comprising: i) a drum-like sheet holding body rotatably supported, ii) a magnet positioned on the peripheral surface of said sheet holding body for holding a stimulable phosphor sheet, which is provided with a stimulable phosphor layer carrying a radiation image stored therein on one surface and a magnetic material layer on the opposite surface, on said sheet holding body by closely contacting at least both ¯ends of said stimulable phosphor sheet with said sheet holding body by magnetic attraction acting between said magnet and said magnetic material layer of said stimulable phosphor sheet, iii) an optical scanning system for causing stimulating rays to scan said stimulable phosphor sheet from above, which is closely contacted with and held on said sheet holding body, in a direction parallel to the rotation axis of said sheet holding body, iv) a drive means for rotating said sheet holding body around said rotation axis, and v) a photoelectric converter for receiving the light emitted from said stimulable phosphor sheet exposed to said stimulating rays and photoelectrically converting the emitted light into an electric signal. 3. An apparatus as defined in Claim 2 wherein said optical scanning system serves as a sub-scanning means, and said drive means serves as a main scanning means. 4. An apparatus as defined in Claim 2 wherein said optical scanning system serves as a main scanning means, and said drive means serves as a sub-scanning means. 5. A radiation image read-out apparatus comprising i) a hollow drum-like sheet holding body rotatably supported, ii) a magnet positioned within said sheet holding body in a fixed position along a part of the peripheral surface of said sheet holding body, iii) a means for feeding a stimulable phosphor sheet, which is provided with a stimulable phosphor layer carrying a radiation image stored therein on one surface and a magnetic material layer on the opposite surface, onto said part of the peripheral surface of said sheet holding body within which said magnet is positioned, iv) a main scanning optical system for causing stimulating rays to scan said stimulable phosphor sheet from above, which is closely contacted with said part of the peripheral surface of said sheet holding body by magnetic attraction acting between said magnet and said magnetic material layer of said stimulable phosphor sheet, in a direction parallel to the rotation axis of said sheet holding body, v) a sub-scanning means for rotating said sheet holding means around said rotation axis, and vi) a photoelectric converter for receiving the light emitted from said stimulable phosphor sheet exposed to said stimulating rays and photoelectrically converting the emitted light into an electric signal. 6. An apparatus as defined in Claim 5 wherein said photoelectric converter is provided with a total reflection type light guiding sheet having, at one end, a light input face extending in the main scanning direction near to the surface of said stimulable phosphor sheet and, at the other end, a light output face opposed to a light receiving face of said photoelectric converter.

Inventors: TAKANO, MASAO C/O FUJI PHOTO FILM CO., LTD., YAMAMOTO, TAKAAKI C/O FUJI PHOTO FILM CO., LTD.
Applicants: FUJI PHOTO FILM CO., LTD.
Application year: 1983
Main classification: H04N1
IPC codes: A61B6, G03B42, H04N1, G06T1, G01N23, G01T1