Abstract:
Methods and apparatus for directing radiation to and from a sample to be scanned. In one example, first radiation propagating along a first axis is reflected off of the first axis so as to impinge on the sample. In response to the first radiation, the sample emits second radiation, which is directed to a detector. In one aspect, the second radiation is received directly from the sample by a reflector, which reflects the second radiation such that it travels substantially through air to impinge on the detector. In another aspect, the second radiation is directed such that it travels toward the detector in a direction having a significant vector component parallel to the first axis. In yet another aspect, a detection surface of the detector is oriented essentially perpendicular to the first axis and adapted to detect at least some of the second radiation traveling in a direction non-parallel to the first axis.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation (CON) of U.S. Ser. No. 09/928,291, filed Aug. 2, 2001 now U.S. Pat. No. 6,624,438, which is a continuation-in-part (CIP) of U.S. Ser. No. 09/253,983, filed Nov. 18, 1998, now U.S. Pat. No. 6,291,831 each of which applications is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to an axially oriented optical system and more particularly to a system using a radial rotating light beam for scanning a medium mounted on a fixed cylindrical member. 
     BACKGROUND 
     Previously, scanners of X-ray exposed phosphor plates performed their function on a flat-bed or the external surface of a rotating drum. These systems have problems that increase the cost and reduce the quality of the X-ray image. The undesirable results obtained with a flat-bed or rotating drum system are caused by the continuous changing of the angles and distances of the light beam paths used for stimulating the phosphor of the X-ray exposed phosphor plates. Also, the collection of the stimulated light is performed with a different path and angle for each position on the phosphor plate, thereby requiring complicated, expensive compensation with a resultant reduction in quality. Additionally, the complications with attendant increases in cost are exacerbated when existing systems for supporting the phosphor plates do not maintain a fixed positioning during the scanning procedure. 
     Apparatus for radiation image read-out are known and are described, for example, in U.S. Pat. Nos. 4,886,968 and 5,396,081. 
     An optical system for an internal drum readout apparatus using a radial rotating light beam, which provides for minimizing distortion together with a reduction of cost and complexity cannot be found in the art. 
     Neither the prior art devices nor contemplated solutions for their deficiencies are capable of resulting in a digitizer apparatus providing a combination of reduction in cost with an increase in accuracy and quality. 
     SUMMARY 
     In view of the aforementioned drawbacks of the conventional scanner systems, this invention provides a scanning system with a novel on-axis optical system to minimize distortion and avoid complex compensation introduced by currently used arrangements, while at the same time achieving cost reduction. 
     In addition, a light beam scanning system for digitizing X-ray exposed phosphor plates for storage and/or image display is provided. 
     There is thus provided, in accordance with a preferred embodiment of the present invention, a scanning apparatus, which includes a medium attached to a surface of a fixed, hollow cylindrical segment, the fixed, hollow cylindrical segment having a first longitudinal axis, a rotational radial laser beam rotating around the first longitudinal axis and arranged to scan said medium, and a light sensitive detector having a light acceptance direction along a second axis coinciding with the first longitudinal axis of the cylindrical segment. 
     Further, in accordance with a preferred embodiment of the present invention, the apparatus further includes at least one reflector for directing the beam towards the medium. The apparatus further includes transport apparatus for rotating and translating the laser beam. 
     Further, in accordance with a preferred embodiment of the present invention, the medium is a phosphor plate. 
     Further, in accordance with a preferred embodiment of the present invention, the reflecting unit may be a slanted mirror fixedly mounted for movement with the transport apparatus. A hole may be formed in the center of the slanted mirror for directing the laser beam therethrough. Furthermore, in accordance with a preferred embodiment of the present invention, the slanted mirror forms an angle in the range of 30-60 degrees relative to the longitudinal axis. The slanted mirror may be concave. 
     Further, in accordance with a preferred embodiment of the present invention, the apparatus further includes a rotating shaft, the laser beam being attached to the rotating shaft, wherein power is directed via slip rings attached to the rotating shaft. 
     Further, in accordance with a preferred embodiment of the present invention, the apparatus further includes a hollow shaft providing a beam path from the light source to the hole, and a mirror fixedly mounted in the hole for movement with the transport and rotated with the shaft for presentation of the beam along a radial from the axis to the medium. 
     Also, in accordance with a preferred embodiment of the present invention, the apparatus further includes a Fresnel lens mounted within the hollow cylindrical segment and proximate to the concave interior of the hollow cylindrical segment. The Fresnel lens has a longitudinal axis perpendicular to the longitudinal axis of the hollow cylindrical segment and the Fresnel lens has a hole formed in the center thereof to allow the beam and the receiving light emanating from the medium to pass through undisturbed. 
     Further, in accordance with a preferred embodiment of the present invention, the light emanating from the medium is refracted by the Fresnel lens the refracted light being reflected by the slanted mirror through the detector. 
     In addition, in accordance with a preferred embodiment of the present invention, there is also provided a scanning method. The method includes: 
     attaching a medium to a surface of a fixed, hollow cylindrical segment, having a first longitudinal axis; 
     arranging a rotational radial laser to rotate around the first longitudinal axis beam to scan the medium; and 
     detecting the rays reflected from the medium along a second axis, said second axis coinciding with the first longitudinal axis. 
     These and other advantages, features and objects will become more apparent from the following description taken in connection with the illustrative embodiments in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An axially oriented optical system in accordance with the present invention will be described infra with respect to the accompanying drawings, which are not drawn to scale, of which: 
     FIG. 1 is a schematic representation of one embodiment or arrangement of the optical system of this invention; 
     FIG. 2 is a schematic representation of an alternative arrangement of the optical system of this invention; 
     FIG. 3 is a schematic view of the embodiment of FIG. 2 with a rotative drive and encoding system that is applicable to all embodiments; 
     FIGS. 4A and 4B are schematic representations of a phosphor plate or film with a representation of the scan pattern thereon and a representation of a system for axial movement of the optical system, respectively; 
     FIG. 5 is a block diagram of the control system for the operation of the optical system of this invention; 
     FIG. 6 is an isometric view of the optical system of a scanning apparatus constructed and operative in accordance with a further embodiment of the invention; 
     FIG. 7 is a schematic representation of the arrangement of the optical system of FIG. 6; 
     FIG. 8 is a detailed schematic representation of the Fresnel lens arrangement used in the embodiment of FIG.  6  and 
     FIG. 9 which is a schematic representation of an alternative arrangement of the optical system of this invention. 
    
    
     DETAILED DESCRIPTION 
     Reference is now made to FIG. 1, which illustrates an embodiment of the present invention in which a system for scanning a medium mounted on a fixed cylindrical member is shown The scanning apparatus  10  comprises a hollow cylinder  12  on the internal face of which is mounted a scanning medium  14 . The light beam for scanning is rotated, as will be described hereinbelow, against the fixed hollow cylinder  12 . 
     FIG. 1 shows a portion or segment of hollow cylinder  12  for shaping a medium, such as a phosphor plate  14 , on the internal face of the cylinder for a scanning procedure. The longitudinal, central axis  16  of the portion of the cylinder  12  forms the main axis of the optical system of the scanning apparatus  10 . Thus, when the phosphor plate  14  is located against and conforms to the internal cylindrical shape of the hollow, cylinder segment  12 , the axis of the phosphor plate  14  is collinear with axis  16 . As is usual with apparatus of this type, the phosphor plate is required to be enclosed to eliminate light other than that required for its function. Since the enclosure is not part of the inventive concept of this invention, it is not shown in the interest of clarity. 
     The optical system of the scanning apparatus  10  includes a focused laser light source  18  having its peak wavelength at a suitable level (preferably approximately 635 nm) in order to stimulate the phosphor plate  14  and a light sensitive detector  20 , for example, a photomultiplier tube for converting the stimulated light with a peak wavelength of 390 nm emitted from the phosphor plate  14  into electric signals. The laser beam is directed, as shown by the arrowed line, at a small mirror  22  located and affixed at the center of the detector  20 , for example, by gluing it to a filter  24  of the Schott type that blocks the laser beam wavelength and allows only passage of the 390 nm stimulated light emitted from the phosphor plate  14 . The small mirror  22  directs the laser light source beam 90 degrees along the axis  16  of the cylinder segment  12  to the center of a rotating mirror  26 , whose rotation is about the axis  16 , and is angled with respect to axis  16  to direct the laser beam along the radius from axis  16  to the phosphor plate  14  on the interior of cylinder  12 . Of course, if small lasers were used, they could be mounted on the filter  24  in place of small mirror  22 . The optimal angle of the rotating mirror  26  depends on the type of mirror being used. For example, for a flat rotating mirror shown in the embodiment of FIG. 1, having the dual function of reflecting both the stimulating light and stimulated light, the angle should be preferably be 45 degrees. 
     The light source  18 , filter  24  with small mirror  22  and detector  20  remain fixed against rotation, while angled or slanted mirror  26  and its shaft  28  are rotated together. At the point of stimulation of the phosphor plate  14 , the stimulated light at 390 nm is directed, as shown by the arrowed beam lines, back toward the slanted, rotating mirror  26  for passage through the filter  24  to the detector  20  for conversion to an electronic signal for digitalization, as will later be described. 
     The optical items  18  through  28  are to be moved in translation so that the beam from the light source traverses the fixed phosphor plate  14 , for example, in the direction of the arrows below the figure while the focused beam either creates arcs of circles or, if desired, a helix during the traverse. 
     FIG. 2 illustrates a further embodiment of the present invention. FIG. 2 schematically represents an alternative arrangement whereby the light source  18  lies on axis  16  of shaft  28 , which is collinear with the hollow cylinder portion  12 , which forms the support for phosphor plate  14 . In this application the shaft is hollow to allow the passage of the beam therethrough, and the angled rotating mirror  26  has a hole  30  at its center for allowing the passage of the beam to small mirror  22 , which is mounted within the hole. Mirror  22  need not be the exact shape as illustrated. For example, it could be a penta prism or other optic arrangement that will perform the same result as the small mirror  22 . 
     In this embodiment, the angle of the rotating mirror  26  may be adjusted to suit the s type of mirror being used. For instance, if rotating mirror is flat, the mirror may be angled at any suitable angle depending on the size of the mirror and preferably is within the range of 30-60 degrees. Alternatively, rotating mirror  26  may be an alternative shape, such as concave. 
     FIG. 3A illustrates the embodiment of FIG. 2 with the addition of a conventional motor mechanism comprising rotor  32 , mounted for rotation with shaft  28 , and a fixed stator  34 . In the embodiments of FIGS. 1,  2  and  3  the filter  24  and detector  20  do not rotate. A conventional on-axis optical encoder system  36  is also mounted with respect to the motor for providing feedback pulses to stabilize rotation speed and for determining the beam positioning. 
     Reference is now made to FIG. 3B which illustrates a further embodiment of the present invention, which is similar to the embodiments of FIGS. 2 and 3A, except that mirror  26  is omitted. In this embodiment, the beam passes through the hollow shaft  28  to the small mirror  22 , which is mounted, as shown in FIG. 3A, at the end of the chamfered hollow shaft. The beam is reflected (B 1 ) at right angles towards the scanning medium  14 . Some of the stimulated light, illustrated by the angle between beams B 2  and B 3 , is directed back towards the detector  20  (via filter  24 ). By altering the size of the detector the amount of collected light may be varied. 
     In a further alternative embodiment, at least one reflector may be optionally added, as illustrated, for exemplary purposes only, by curved reflectors  152 . As will be appreciated by persons knowledgeable in the art, the shape, size and number of reflectors may be altered so as to direct the desired pre-determined amount of light towards detector  20 . 
     FIGS. 4A and 4B are illustrations of a phosphor plate film  14  and the mechanism for traversing the film, respectively, during scanning whereby the rotation of the optical system  10  produces a scan path indicated by the parallel lines of FIG.  4 A. 
     It is an advantage of the present invention that by using a fixed cylinder, the scanning medium can be mechanically fed, in contrast to scanning systems using rotating drums which require the manual attachment of the scanning medium to the face of the drum. 
     FIG. 4A additionally utilizes the parallel lines for depicting a chosen distance, in this case 100 micron spacing, from the previous scan. FIG. 4B illustrates the film  14  of FIG. 4A in its position in the apparatus with the hollow, cylindrical portion  12  removed for clarity. The parallel lines of the film  14  in FIG. 4B are illustrative only of the cylindrical shape of the film  14  when it is within the cylinder  12 . 
     Schematically illustrated in FIG. 4B is the means for effecting the axial path spacing of the optical system as disclosed in FIGS. 2 and 3. A support structure or transport  38 , as seen in FIG. 4B is provided with bearings, not shown, for those parts of the optical system  10 , which are required to be rotated, as is conventional in the field of mechanical design. The means for movement of the optical system of this invention along its axis  16  can be selected from a variety of options, only one of which is illustrated. The support structure  38  has a pair of rods  40  for stabilization, guidance and maintenance of direction of the transport  38  in a straight line. A threaded member  42 , fixed with respect to any axial movement, is engaged with mating threads in the support structure  38  for its axial movement in order to obtain the traversing for scanning of the focused spot with respect to the film  14 . A linear stepping motor  44 , schematically shown, provides the rotation of the threaded member to accurately space the separate scans across film  14 . Although the light source  18  is only schematically depicted, it is shown as attached to the support structure  38 . 
     FIG. 5 is a block diagram illustrating the control of the apparatus thus far described. The DC motor  32 ,  34  the encoder  36  and the 45 degree angled mirror  26  are connected for simultaneous rotary operation as shown in FIG. 3, since they all are on the same shaft  28 . The DC motor has a rotation motor control  46 , which in turn is connected for cooperation with encoder  36 . The stepper motor  44  of FIG. 4B has a linear stepper control  50 , which is also connected with the output from encoder  36 . The output from the detector, photomultiplier (PMT)  20  and that of encoder  36  provide input to the analog processing unit  48 , which provides its output to an analog to digital converter  52  for connection with a PC computer  54 . 
     Operation 
     Operation of the apparatus of this invention as a readout device involves the presentation of an X-ray exposed phosphor plate or film  14  to the interior of a fixed portion of a hollow cylinder  12  to which the phosphor plate is pressed firmly to conform to the circular configuration of the cylindrical portion without any motion ensuing while the scanning or reading is being effected. Apparatus for this purpose is well known. 
     The scanning operation involves the mounting of a light source such as a 635 nm laser  18  and a spinning mirror surface  26  that is angled at a suitable angle (depending on the type of rotating mirror used, as described hereinabove with respect to FIGS. 1-4) with respect to its axis of rotation  16 , which is collinear with the central axis of the film  14  and its support  12 . In order to bend the light beam 90 degrees and to rotate it with the mirror, the beam has to be reflected from the center of rotation of the mirror  26 . The beam then forms a rotating spot on the film that follows a path of a portion of a circle on the phosphor plate  14 . When the laser beam starts from between the rotating mirror  26  and the filter  24 , no hole in the rotating mirror  26  is required. Whereas the laser  18 , when it is behind the rotating mirror  26 , requires a hole in its center with a small mirror  22  therein to supply the directing of the beam perpendicular to a spot on the film. 
     The support structure or transport  38  contains an optical system which includes light source  18 , spinning mirror  26  and small mirror  22 , when required, and its movement to traverse the phosphor plate  14  is coordinated with the rotative movement of the spot such that, when the spot reaches the end of the film  14 , the cart then moves the distance of one pixel for the next scan. The spot is chosen to be, for example, 100 micron in diameter thereby forming a circular line 100 micron wide; therefore the transport  38  moves the optic system a distance of 100 micron for the next scan. 
     More specifically as a readout device, using phosphor plates, the following operation is effected. 
     Readout of a previously X-ray exposed phosphor plate is obtained by the 635 nm laser  18  stimulating the crystal layer of the phosphor plate causing it to radiate light at 390 nm as the beam spot on the film makes its scan. The rotating mirror  26  receive the emitted light around its outer periphery for reflection onto the Schott type filter  24  which is transparent to 390 nm while absorbing 635 nm light. The light passing through filter  24  is applied to detector photomultiplier tube  20 , which converts the light to an electric signal that is amplified, gated to represent one pixel on the circular scan and converted to a digital number representing the brightness of the pixel. The filter  24  and detector  20  are also mounted on the transport  38 . 
     The encoder  36  stabilizes the motor  32 ,  34  by feed back pulses which also control the gating of the output of the detector photomultiplier  20  to define time samples equivalent to 100 micro-meters in distance. The pulses are also used for defining, at any point in time during the scan, the angular position of rotating mirror  26  and the angle of the stimulated emission from the phosphor plate in order to activate the stepper motor for the next parallel scan. If a helical scan is required, the change would be within the skill of an ordinary technician. 
     Since the paths of the stimulating light and the stimulated light for all points are identical, and since the hitting and emitting angles for all scan points are perpendicular and identical, and since the scanning speed is constant and easy to maintain, there is no need for correction algorithms or compensation. Digitization resulting from the scanning action results in the ability to replicate and/or store the data from the film. 
     Although the invention has been illustrated in the accompanying drawings and described in the foregoing specification in terms of preferred embodiments, the invention is not limited to these embodiments. It will be apparent to those skilled in this art that certain changes, modifications and substitutions can be made without departing from the true spirit and scope of the appended claims. For example, the laser light source  18  could be mounted on the filter  24  thereby eliminating the need for small mirror  22 . Furthermore, the teachings of this invention are applicable to other than a phosphor plate medium. 
     Reference is now made to FIGS. 6-8 which illustrate a further embodiment of the scanning apparatus, generally designated  100 , constructed and operative in accordance therewith. FIG. 6 shows a portion or segment of a hollow cylinder  102  (similar to hollow cylinder  12  described hereinabove). FIG. 7 is a schematic representation of the arrangement of the optical system  100  and FIG. 8 is a detailed representation of the optical arrangement. 
     The optical system  100  is similar to the optical system of scanning apparatus  10  described hereinabove with respect to FIGS. 1-5. Elements having similar functions as previous embodiments are similarly designated and will not be further described. 
     The optical system  100  comprises a hollow cylinder  102  for shaping the phosphor plate medium  14  (or similar) to be scanned on the internal face of the cylinder and the optical system shown in FIG.  3 . The optical system includes a light source  18  which lies on the axis  16  of a hollow shaft  28 . The hollow shaft, which is collinear with the hollow cylinder portion  102 , allows the beam to pass through The angled mirror  26  has a hole  30  at its center with a small mirror  22  mounted within the hole. 
     In addition, optical system  100  further comprises a Fresnel lens  104 , which is inserted on the coaxial cylinder  102 , as shown in FIG.  8 . The cylinder  102  is connected to the slanted mirror system and rotates with it, The Fresnel lens  104  is placed on the cylinder so that its longitudinal axis  106  is parallel with the central axis  16  of the laser beam. 
     As previously described with respect to the embodiments of FIGS. 1-5 (that is without the Fresnel lens  104 ), the light collection is based on a cone of stimulated light with its source at the impinging point  105  of the laser. The base of the cone is defined by the angled mirror  26  which is reflected into the detector photomultiplier (PMT) tube  20 . Alternatively, the stimulated light may be directly aimed to the PMT tube  20   
     In order to not to obstruct the bean of light and prevent distortions, a hole  108  is drilled through the center of the Fresnel lens  104 . The diameter of the hole  108  is configured so as to allow the same amount of stimulated light to pass through to the mirror and PMT as the previously described embodiments not having a lens, that is the lens  104  does obstruct the passage of any light. As best seen in FIG. 7, the impinging ray  110  is returned as rays  112  and  114 , which are reflected by mirror  26  as rays  116  and  118 , respectively, through filter  24  into PMT  20 . 
     The addition of the Fresnel lens  104  expands the angle of the cone from the impinging point  105  to the rim of the Fresnel lens  104 . As best seen in FIG. 8, the angle of stimulated light is increased from “A” to “A+2B”. Thus, additional rays, such  120  and  122 , arc refracted through the rim of the Fresnel lens  104  and then reflected by mirror  26  as rays  124  and  126 , respectively, through filter  24  into PMT  20 . 
     Thus, in this embodiment, an additional amount of light enters the PMT  20 , the amount of light being proportional to the expanded angle (“A+2B”). The Fresnel lens  104  concentrates (or bends) the light reflected into its “ring” to the mirror. In other words, the addition of the Fresnel lens  104  allows an increased amount (2B) of light to be collected thereby improving the light collection efficiency of the system. 
     It will be appreciated that the invention is not limited to the use of a Fresnel lens but may be used with any other type of light collecting device. 
     Reference is now made to FIG. 9, which is a schematic representation of a further embodiment of the present invention. This embodiment is similar to the embodiment of FIG.  2 . Elements having similar functions as previous embodiments are similarly designated and will not be further described. 
     In the embodiment of FIG. 9, the laser source is attached to the rotating shaft  28  via slip rings  132  (known in the art) enabling power to be fed to the light source (modulator)  18 . The laser beam is then directed through the hole  130  in mirror  26 . The rays are reflected through filter  24  into PMT  20 . 
     It will be further appreciated that the present invention is not limited by what has been described hereinabove and that numerous modifications, all of which fall within the scope of the present invention, exist. Rather the scope of the invention is defined by the claims, which follow: