Abstract:
An optical system for an internal drum readout apparatus is disclosed. The optical system includes a hollow cylindrical segment defining a central axis, a support structure configured and adapted to translate along the central axis, a mirror mounted on the support structure for translational movement therewith and for rotational spinning around the central axis, a light source mounted to the support structure for providing a beam capable of being directed along the central axis which in turn is directed against the medium thereby producing a stimulated light, a detector coaxially aligned with the central axis, the detector being configured and adapted to absorb stimulated light direct toward and reflected off of the angled mirror, and a shroud mounted on the support structure for blocking stimulated light not directed toward the angled mirror, wherein the stimulated light not directed toward the angled mirror would otherwise degrade the medium prematurely.

Description:
BACKGROUND  
         [0001]    1. Technical Field  
           [0002]    The present disclosure is directed to an axially oriented optical system and method of using the same, and more particularly, the present disclosure is directed to an apparatus for improving the computed radiography image generated by the axially oriented optical system and the method for using the same. The present disclosure is also directed to a method of using the optical system disclosed herein.  
           [0003]    2. Background of Related Art  
           [0004]    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 plate. 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 and expensive compensation measures. 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.  
           [0005]    Accordingly, many, if not all, of these deficiencies have been overcome in U.S. Pat. No. 6,291,831 to Koren, the entire disclosure of which is herein incorporated by reference. As seen in FIG. 1, the Koren Patent discloses a scanning apparatus  10  including a fixed, hollow cylindrical segment  12  having a central, longitudinal axis  16 , the interior of which forms a concave surface for intimate contact with a medium for recording and/or readout  14  (e.g., a phosphor plate), a support structure forming a transport (not shown) for translational movement along the axis, a light source  18  (e.g. laser) mounted on the transport for movement therewith and for providing a beam capable of being directed along the axis, and a slanted mirror  26 , angled 45° with respect to the axis and mounted on the transport for translational movement therewith and for rotational spinning around the axis.  
           [0006]    According to the Koren Patent, the scanning operation involves the mounting of laser  18  and slanted mirror  26  in such a manner so that slanted mirror  26  bends a beam of light 90° and is capable of rotating the beam of light. Accordingly, the beam of light can then be manipulated to form a rotating spot on phosphor plate  14  which follows a path of a portion of a circle on phosphor plate  14 . The transport  38 , including optic system  10  having light source  18  and spinning mirror  26 , and its subsequent movement to traverse phosphor plate  14  is coordinated with the rotative movement of the spot such that when the spot reaches the end of phosphor plate  14 , transport  38  is moved the distance of one pixel in order for the next scan to be conducted. According to the Koren Patent, readout of a previously X-ray exposed phosphor plate is obtained a 635 nm laser  18  stimulating the crystal layer of phosphor plate  14  causing it to radiate light at 390 nm as the beam spot on the phosphor plate  14  makes its scan. The rotating mirror  26  receives the emitted light around its outer periphery for reflection onto a Schott type filter  24  which is transparent to 390 nm light and absorbent to 635 nm light. The light passing through filter  24  is applied to detector photomultiplier tube  20 , which converts the light to an electrical signal that is amplified and gated to represent one pixel on the circular scan and converted to a digital number representing the brightness of the pixel.  
           [0007]    In view of the aforementioned improvements and benefits of the Koren Patent over the prior art device, a need exists for an improved scanning apparatus which further reduces distortion, cost and the overall complexity of the operation while simultaneously improving the accuracy and quality of the resulting scan.  
         SUMMARY  
         [0008]    The present disclosure provides a shroud for use in an optical scanning apparatus including a hollow cylindrical segment defining a central axis, the cylindrical segment forming a support surface for a medium to be scanned while the medium conforms to an inner surface of the cylindrical segment; a support structure for translational movement along the central axis; a light source mounted on the transport for movement therewith and for providing a beam capable of being directed along the central axis; a reflecting element for directing the beam toward the medium to produce a stimulated light; and a slanted mirror mounted to the transport for translational movement therewith and for rotational spinning around the central axis, the slanted mirror reflecting stimulated light toward a light detector. The shroud includes a base wall configured and adapted to be coupled to the transport, the base wall defining an outer terminal edge; and an annular side wall integrally formed along the outer terminal edge, the annular side wall extending in a direction toward the slanted mirror, wherein the base wall and the annular side wall block the stimulated light from traveling past the detector and stimulating the medium prior to the beam stimulating the medium. It is envisioned that the base wall is configured and dimensioned such that the outer terminal edge thereof is in close proximity with the inner surface of the cylinder segment. It is further envisioned that the shroud could include a wiper or lip extending along the outer surface of the annular wall.  
           [0009]    The present disclosure further relates to an optical system for an internal drum readout apparatus, including a hollow cylindrical segment defining a central axis, the cylindrical segment forming a support surface for a medium to be scanned while the medium conforms to an inner surface thereof, a support structure configured and adapted to translate along the central axis, a mirror mounted on the support structure for translational movement therewith and for rotational spinning around the central axis, the mirror angled with respect to the central axis, a light source mounted to the support structure for providing a beam capable of being directed along the central axis which in turn is directed against the medium thereby producing a stimulated light, a detector coaxially aligned with the central axis, the detector being configured and adapted to absorb stimulated light direct toward and reflected off of the angled mirror, and a shroud mounted on the support structure for blocking stimulated light which is not directed toward the angled mirror, wherein the stimulated light not directed toward the angled mirror would otherwise degrade the medium prematurely. It is envisioned that the shroud is configured and dimensioned to block stimulated light which is not directed toward the detector. It is further envisioned that the shroud is configured and dimensioned to block errant light from entering the detector.  
           [0010]    In one aspect of the present disclosure, the shroud includes a base wall defining an outer terminal edge and an annular wall integrally formed around the outer terminal edge of the base wall. The annular wall of the shroud preferably extends toward the angled mirror. It is contemplated that the annular wall is orthogonally oriented with respect to the base wall. It is envisioned the annular wall extends toward the angled mirror a distance sufficient to block errant light while still permitting transmission of the beam and the stimulated light. It is further envisioned that the optical system could include a wiper or lip extending along the outer surface of the annular wall, wherein the wiper reduces a gap between the outer surface of the annular wall and an inner surface of hollow cylindrical segment. It is envisioned that the wiper is constructed from a resilient polymeric material and/or a brush-like material.  
           [0011]    In another aspect of the present disclosure, the shroud includes a base wall extending radially outward and having an outer terminal edge in close proximity with an inner surface of the hollow cylindrical segment, wherein the base wall is constructed from a polymeric material. It is envisioned that the optical system could further include a wiper or lip extending radially outward from the outer terminal edge thereof, wherein the wiper is constructed from resilient polymeric material and/or a brush-like material.  
           [0012]    According to an embodiment of the present, the mirror is angled at about 45° relative to the central axis. In one embodiment, the mirror is angled to reflect the stimulated light toward the detector. In another embodiment, the mirror is angled to reflect the beam toward the medium.  
           [0013]    It is envisioned that the light source is proximal of the angled mirror and the detector includes a reflecting surface mounted thereto for directing the beam toward the angled mirror. The light source is distal of the angled mirror and the angled mirror includes a central opening through which the beam passes and a reflecting surface mounted to the angled mirror for directing the beam toward the medium.  
           [0014]    It is contemplated that the light source is a laser. It is further contemplated that the medium is a phosphor plate. The phosphor plate emits a stimulated light when excited by the beam which stimulated light corresponds to data recorded thereon.  
           [0015]    It is envisioned that the detector includes a filter which permits light having a specific wavelength therethrough.  
           [0016]    The present disclosure is also directed to a method of improving a computer radiography image in a scanning apparatus wherein the scanning apparatus includes a fixed hollow cylindrical segment having a central, longitudinal axis, the interior of which forms a concave surface for intimate contact with a medium for recording and/or readout; a support structure forming a transport for translational movement along the axis; a light source mounted on the transport for movement therewith and for providing a beam capable of being directed along the axis; a slanted mirror, angled 45° with respect to the axis and mounted on the transport for translational movement therewith and for rotational spinning around the axis, the mirror configured to reflect the stimulated light onto a collector tube.  
           [0017]    The method includes the steps of providing a shroud device for reducing the collection of stimulated light and errant light which is not directed toward the angled mirror and which would otherwise prematurely degrade the medium, and mounting the shroud device to the collector tube such that the annular wall extends towards the angled mirror.  
           [0018]    It is envisioned that according to the method disclosed herein, the shroud device includes a base wall extending radially outward and having an outer terminal edge in close proximity with an inner surface of the hollow cylindrical segment and an annular wall integrally formed around the outer terminal edge of the base wall.  
           [0019]    The method may further include the step of providing a wiper or lip on the outer surface of the annular wall to reduce a gap between the outer surface of the annular wall and an inner surface of the cylindrical segment.  
           [0020]    Other objects and features of the present disclosure will become apparent from consideration of the following description taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    By way of example only, preferred embodiments of the disclosure will be described with reference to the accompanying drawings, in which:  
         [0022]    [0022]FIG. 1A is a schematic representation of one embodiment of a prior art arrangement of an optical system as described above;  
         [0023]    [0023]FIG. 1B is a schematic representation of an alternative embodiment of a prior art arrangement of an optical system;  
         [0024]    [0024]FIG. 1C is a schematic representation of a prior art arrangement of FIG. 1A or  1 B including a rotative drive and encoding system;  
         [0025]    [0025]FIG. 2 is a perspective view a shroud in accordance with an embodiment of the present disclosure;  
         [0026]    [0026]FIG. 2A is a cross-sectional side elevational view of a shroud in accordance with an alternative embodiment of the present disclosure as taken through line  2 - 2  of FIG. 2;  
         [0027]    [0027]FIG. 2B is a cross-sectional side elevational view of a shroud in accordance with yet another embodiment of the present disclosure as taken through line  2 - 2  of FIG. 2;  
         [0028]    [0028]FIG. 2C is a cross-sectional side elevational view of a shroud in accordance with still another embodiment of the present disclosure as taken through line  2 - 2  of FIG. 2;  
         [0029]    [0029]FIG. 2D is a cross-sectional side elevational view of a shroud in accordance with a further embodiment of the present disclosure as taken through line  2 - 2  of FIG. 2;  
         [0030]    [0030]FIG. 3 is a plan view of the shroud of FIG. 2;  
         [0031]    [0031]FIG. 4 is a cross-sectional side elevational view of the shroud of FIG. 2 as taken through line  4 - 4  of FIG. 3;  
         [0032]    [0032]FIG. 5 is a plan view of a spacer in accordance with an embodiment of the present disclosure;  
         [0033]    [0033]FIG. 6 is a schematic representation of one embodiment of an optical system in accordance with the present disclosure, incorporating the shroud of FIG. 2 therein;  
         [0034]    [0034]FIG. 7 is a schematic representation of an alternative embodiment of an optical system in accordance with the present disclosure, incorporating the shrouds of FIG. 2 therein;  
         [0035]    [0035]FIG. 8 is a schematic view of the embodiment of FIG. 6 with a rotative drive and encoding system that is applicable to each of the embodiment shown herein;  
         [0036]    [0036]FIG. 9 is a perspective view of a representation of a system for axial movement of the optical system; and  
         [0037]    [0037]FIG. 10 is a block diagram of a control system for operation of the optical system of the present disclosure. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0038]    As described above, a prior art arrangement of an optical system is shown and described in FIG. 1A. As seen in FIG. 1B, an alternative embodiment of a prior art arrangement of an optical system is shown whereby the light source  18  lies on axis  16  of shaft  28  which is collinear with hollow cylinder portion  12 , which forms the support for phosphor plate  14 . Shaft  28  is hollow in order to permit the beam to pass therethrough and angled mirror  26  has been provided with a hole  30  at its center in order for the beam to pass onto a small mirror  22 , which is mounted within hole  30 . Accordingly, when the beam passes through shaft  28 , small mirror  22  redirects the beam towards phosphor plate  14 .  
         [0039]    In FIG. 1C, there is shown the prior art embodiment of FIG. 1B with the addition of a conventional motor mechanism including a rotor  32 , mounted for rotation with shaft  28 , and a fixed stator  34 . In the prior art embodiments of FIGS.  1 A- 1 C, filter  24  and detector  20  do not rotate. A conventional on-axis optical encoder system  36  is also mounted with respect to the motor mechanism for providing feedback pulses to stabilize rotation speed and for determining the beam positioning.  
         [0040]    In each of the prior art optical system embodiments shown in FIGS.  1 A- 1 C, the Computer Radiography (CR) image is degraded in at least one of two ways. The CR image can be degraded by the beam reflecting within hollow cylinder  12  and prematurely releasing X-ray energy stored in phosphor plate  14 . Additionally, reflected beams within the CR chamber can cause degradation of the CR image when errant rays enter photomultiplier tube  20 .  
         [0041]    Turning now to FIGS.  2 - 4 , a shroud for use with any of the prior art optical system embodiments shown in FIGS.  1 A- 1 C, is shown generally as  200 . Shroud  200  includes a ring-like planar base wall  202  and an annular side wall  210  extending therefrom. Base wall  202  includes an outer terminal edge  204  and an inner terminal edge  206  defining an aperture  208  formed in base wall  202 . Preferably, base wall  202  and aperture  208  are co-axial defining a central axis “A”. Aperture  208  is configured and dimensioned to permit the emitted light reflected from spinning mirror  126 , as will be described in greater detail below, to pass therethrough and onto a photomultiplier tube (PMT) or detector  120 .  
         [0042]    Annular wall  210  preferably extends from outer terminal edge  204  of base wall  202  and is substantially orthogonally oriented with respect to base wall  202 . However, as seen in FIG. 2B, it is contemplated that annular wall  210  can be oriented at an angle greater or less than 90° with respect to base wall  202 . Annular wall  210  extends substantially around an entire length of outer terminal edge  204 . Preferably, annular wall  210  extends approximately 270° about outer terminal edge  204 , terminating in terminal end walls  210   a ,  210   b  defining an opening  212 . Opening  212  is configured and dimensioned to receive an arm (not shown) of transport  138  (see FIG. 9).  
         [0043]    In designing shroud  200  it is preferable that shroud  200  is configured and dimensioned to block a maximum amount of air and/or light possible while simultaneously not interfering not interfering with the transmission of the beam of light directed toward phosphor plate  14  or the stimulated light emanating from phosphor plate  14  and directed toward spinning mirror  26  and onto photomultiplier tube  20 . Preferably, shroud  200  should be configured and dimensioned to extend radially outward a distance such that an outer terminal edge of shroud  200  is spaced a distance from the inner surface of cylinder portion  112  which is sufficient to permit phosphor plate  114  to pass between the outer terminal edge of shroud  200  and the inner surface of cylinder portion  112 .  
         [0044]    As seen in FIG. 2A, base wall  202  can be configured and dimensioned to extend radially outward a relatively greater distance such that outer terminal edge  204  is proximate the inner surface of cylinder portion  112  and wherein a wiper  220  is provided on the outer surface of annular wall  210  which wiper  220  is configured and dimensioned to substantially fill the gap between annular wall  210  and the inner surface of cylinder portion  112 . Alternatively, it is envisioned that base wall  202  extends radially outward a relatively smaller distance and wherein wiper  220  is configured and dimensioned to fill the relatively larger gap between annular wall  210  and the inner surface of cylinder portion  112 . Preferably, wiper  220  is constructed from a resilient polymeric material and/or a brush-like material. In this manner, wiper  220  can contact phosphor plate  114  and simple lightly graze over the surface thereof without damaging or otherwise interfering with the surface of phosphor plate  114 . Preferably, annular wall  210  extends proximally a distance sufficient to block as much errant light as possible without interfering with the transmission of the beam of the stimulated light released from phosphor plate  114 . In this manner, shroud  200  is effective in blocking substantially all of the light from traveling distally through cylinder portion  112  and/or from prematurely striking photomultiplier tube  120 .  
         [0045]    Turning now to FIGS. 2C and 2D, annular wall  210  is removed and base wall  202  is configured and dimensioned to extend radially outward such that terminal edge  204  is in close proximity with the inner surface of cylinder portion  112 . In FIG. 2C, base wall  202  is constructed from a polymeric material wherein base wall  202  is substantially rigid near the inner terminal edge (not shown) and becomes increasingly pliable and/or flexible in the radially outward direction. In this manner, outer terminal edge  204  will not damage phosphor plate  114  as it passes thereover. Alternatively, as seen in FIG. 2D, base wall  202  is constructed from a rigid material and a wiper  222  is affixed to outer terminal edge  222 . Preferably, wiper  222  is constructed from a resilient polymeric material and/or a brush-like material. In either embodiment, base wall  202  is effective in blocking substantially all of the air and/or light from traveling distally through cylinder portion  112 .  
         [0046]    As seen in FIG. 2B and as previously described, annular wall  210  is oriented at an angle greater than 90° with respect to base wall  202 . Preferably, angled annular wall  210  extends radially from terminal edge  204  of base wall  202  a distance such that the terminal edge of angled annular wall  210  grazes over phosphor plate  114 . It is contemplated that angled annular wall  210  can be integrally formed with base wall  202  or can be fixedly secured to base wall  202 . Preferably, angled annular wall  210  is constructed from a resilient polymeric material and/or a brush-like material in order to keep from damaging the surface of phosphor plate  114  and angled annular wall  210  slides thereover.  
         [0047]    Preferably, shroud  200  may be constructed from any suitable material for blocking errant light in a CR application environment. In an exemplary embodiment, shroud  200  is constructed from a rigid durable material, such as, for example, aluminum and the like. In a particular example, shroud  200  is constructed from 3003-H14 Aluminum having a thickness of about 0.050. Additionally, it is envisioned that shroud  200  is finished to be “hard anodized”, preferably colored black. Other coatings that minimize reflectance may also be used, such as dark surface finishes.  
         [0048]    It is envisioned that base wall  202  of shroud  200  includes a plurality of radially oriented, preferably, evenly spaced, mounting holes  214  formed therein. Mounting holes  214  permit attachment of shroud  200  to transport  138  (see FIG. 9). As seen in FIG. 3, base wall  202  of shroud  200  includes a series of cut-outs  216  formed between terminal end walls  210   a ,  210   b  of annular side wall  210 . Cut-outs  216  are configured and dimensioned to permit proper mounting of shroud  200  to transport  138 .  
         [0049]    As seen in FIG. 5, a spacer is generally shown as  250 . Spacer  250  is ring-like, having an outer terminal edge  252  and an inner terminal edge  254  defining an aperture  256 . Preferably, outer terminal edge  252  of spacer  250  has a diameter which is greater than the diameter of inner terminal edge  254 . Spacer  250  includes a plurality of mounting holes  258  formed therein. Preferably, mounting holes  258  of spacer  250  radially and axially align with mounting holes  214  of shroud  200 .  
         [0050]    Spacer  250  is typically used when shroud  200  is being mounted to an optical system  100  where aperture  208  is larger than necessary for mounting of shroud  200  to photomultiplier tube  120 . Accordingly, spacer  250  is operatively coupled to shroud  200  such that a center of spacer  250  is axially aligned with axis “A” and thereby reduces the size of aperture  208  of shroud  200  to the size of aperture  256  of spacer  250 .  
         [0051]    Turning now to FIGS.  6 - 9 , operation of optical systems  100 , in cooperation with shroud  200 , is shown. As seen in FIGS.  6 - 9 , shroud  200  is mounted to photomultiplier tube  120  in a manner such that axis “A” is aligned with an axis of rotation  116  of a spinning mirror surface  126  and such that annular wall  210  extends in the direction of spinning mirror  126 . Preferably, base wall  202  of shroud  200  is placed between a distal surface of photomultiplier tube  120  and filter  124 . In this manner annular wall  210  extends distally over filter  124 . Preferably, annular wall  210  extends an amount which is sufficient to extend past a distal surface of filter  124 .  
         [0052]    With shroud  200  in position, operation of optical apparatus  100  involves the presentation of an X-ray exposed phosphor plate or film  114  to the interior of a fixed portion of a hollow cylinder  112  to which phosphor plate  114  is pressed firmly in order for phosphor plate  114  to conform to the circular configuration of the cylindrical portion. Spinning mirror  126  is then mounted in optical system  100  such that a surface of spinning mirror  126  is angled at 45° with respect to its axis of rotation  116 .  
         [0053]    The scanning operation then involves the activation of a light source  118 , such as, for example, a 635 nm laser, thus creating a beam “X” which is co-linear with central axis  16  in order for beam “X” to be bent 90° by spinning mirror  126  and in order to form a rotating spot on phosphor plate  114  that follows a path of a portion of a circle.  
         [0054]    As seen in FIG. 6, when beam “X” emanates from between rotating mirror  126  and filter  124 , no hole in rotating mirror  126  is required. Preferably, light source  118  is positioned such that beam “X” is transmitted toward central axis  116  in a plane parallel to the surface of filter  124 . A small mirror  122  is positioned on the surface of filter  124 , along central axis  116 , for redirecting beam “X” toward spinning mirror  126 , preferably, along central axis  116 , which beam “X” is then redirected by spinning mirror  126  in a perpendicular direction onto phosphor plate  114 .  
         [0055]    As seen in FIGS. 7 and 8, when beam “X” emanates from behind rotating mirror  126 , along central axis  116 , a hole is required at the center of rotating mirror  126  and a small mirror  122  positioned within the hole and oriented in such a manner so as to redirect beam “X” in a perpendicular direction toward phosphor plate  114 .  
         [0056]    Returning to FIGS.  1 A- 1 C, during a readout of a previously X-ray exposed phosphor plate  14 , light source  18  transmits beam “X” onto phosphor plate  14  thereby stimulating a crystal layer of phosphor plate  14  causing it to radiate a light “Y” at 390 nm as beam “X” makes its scan across phosphor plate  14 . Radiant light “Y” is dispersed in all directions and can be generalized as being divided into at least two components, a first radiant component “Y 1   a ” which is directed toward spinning mirror  26  and a second radiant component “Y 1   b ” which is not directed toward spinning mirror  26 . In operation, second radiant component “Y 1   b ” of light “Y 1 ” directed away from spinning mirror  26  (e.g., longitudinally proximally down tube  12  and/or radially around tube  12 ) strikes a region of phosphor plate  14  which has not yet been stimulated. Second radiant component “Y 1   b ” can in turn prematurely stimulate the crystal layer of phosphor plate  14  causing it to release light prior to stimulation by beam “X”. As such, when beam “X” does stimulate the region of phosphor plate  14  which has been prematurely stimulated by second radiant component “Y 1   b ”, less light is radiated from the crystal layer as compared to if the crystal layer had not been previously excited. In addition, second radiant component “Y 1   b ” can strike filter  24  at an angle as compared to directly off of spinning mirror  26 , thereby causing errant image information to reach detector  20 .  
         [0057]    Meanwhile, first radiant component “Y 1   a ” of light “Y 1 ” strikes the surface of spinning mirror  26  resulting in first radiant component “Y 1   a ” being reflected in all directions and can be generalized as being divided into at least two components, a first reflected component “Y 2   a ” which is directed toward filter  24  and a second reflected component “Y 2   b ” which is not directed toward filter  24  (e.g., longitudinally proximally down tube  12  and/or radially around tube  12 ). First reflected component “Y 2   a ” travels toward filter  24 , passes through filter  24  and strikes photomultiplier tube  20  which in turn converts first reflected component “Y 2   a ” into an electrical signal that is amplified and gated to represent one pixel on the circular scan. However, second reflected component “Y 2   b ” can in turn prematurely stimulate the crystal layer of phosphor plate  14  causing it to release light prior to stimulation by beam “X”. As such, when beam “X” does stimulate the region of phosphor plate  14  which may have been prematurely stimulated by second reflected component “Y 2   b ”, less light is radiated from the crystal layer as compared to if the crystal layer had not been previously excited.  
         [0058]    As seen in FIGS.  6 - 8 , shroud  200  improves the CR image in at least one of two ways, namely, reducing the effects of second radiant light “Y 1   b ” on phosphor plate  114  and/or reducing the effects of second reflected light “Y 2   b ” on phosphor plate  114 . In one aspect, annular wall  210  and back wall  202  of shroud  200  reduce, if not eliminate, the amount of second radiant light “Y 1   b ” traveling past spinning mirror  126  and prematurely stimulating the crystal layer of phosphor plate  114  by blocking second radiant light “Y 1   b ” from ever traveling proximally down tube  112 . In addition, annular wall  210  and back wall  202  of shroud  200  reduce, if not eliminate, the amount of second reflected light “Y 2   b ” traveling past filter  114  and prematurely stimulating the crystal layer of phosphor plate  114  by blocking second radiant light “Y 2   b ” from ever traveling proximally down tube  112 .  
         [0059]    Preferably, shroud  200  is provided with a black finish, and more preferably, not polished. In this manner, shroud  200  more readily absorbs second radiant light “Y 1   b ” and second reflected light “Y 2   b ” thus reducing the possibility of second radiant light “Y 1   b ” being reflected and second reflected light “Y 2   b ” from being re-reflected against phosphor plate  114 .  
         [0060]    Schematically illustrated in FIG. 9 is a means for effecting the axial path spacing of optical system  100  having shroud  200  mounted thereto. While the means for movement of optical system  100  along axis  116  can be accomplished in a variety of ways, only one method is illustrated and ill be described. As shown in FIG. 9, a support structure  138  is provided having a pair of rods  140  for stabilizing, guiding and maintaining the direction of transport  138  in a straight line. A threaded member  142 , fixed with respect to any axial movement, is engaged with mating threads in support structure  138  for its axial movement in order to obtain the traversing for scanning of the focused spot with respect to phosphor plate  114 . A linear stepping motor  144  (schematically shown) provides the rotation of threaded member  142  to accurately space the separate scans across phosphor plate  114 .  
         [0061]    Turning now to FIG. 10, a block diagram illustrating the control of optical system  100 , having shroud  200  mounted thereto, is shown. As seen in FIG. 10, a DC motor  132 ,  134 , encoder  136  and spinning mirror  126  are connected for simultaneous rotary operation. Motor  132  has a rotation motor control  146 , which in turn is connected for cooperation with encoder  136 . A stepper motor  144  is provided having a linear stepper control  150 , which is also connected with the output from encoder  136 . The output from photomultiplier tube  120  and that of encoder  136  provide input to an analog processing unit  148 , which provides its output to an analog to digital converter  152  for connection with a PC computer  164 .  
         [0062]    While shroud  200  has been described as blocking radiant light “Ylb” not directed toward spinning mirror  26  and second reflected component “Y 2   b ” not directed toward filter  24 , it is envisioned that shroud  200  is effective in blocking any errant light from entering photomultiplier tube  120  from any external and/or internal light source.  
         [0063]    It will be understood that various modifications may be made to the embodiments disclosed herein. Therefore, the above description should not be construed as limiting, but merely as an exemplification of preferred embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.