Abstract:
An animal holder is provided with a specialized coupling that is releasably mountable to a number of different imaging machines such as X-ray, CAT, MRI and PET machines. Composite images created from combining images from such different machines are particularly clear due to the predetermined alignment of the animal holder within the center of the field of view of each machine.

Description:
GOVERNMENT RIGHTS 
     This invention was made with government support under contracts 1 R41 NS050141-01 and 3 R41 NS050141-0151 awarded by The National Institutes of Health (NIH). The government has certain rights in the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to apparatus for holding a specimen, such as a laboratory animal, in a fixed position during an imaging procedure such as X-ray, CAT and CT scans, MRI and PET imaging. The invention relates in particular to such apparatus which provide for the accurate repeatable positioning of a specimen time and again within the same imaging machine or within a number of different imaging machines. 
     2. Description of Prior Developments 
     In the field of medical research and patient treatment, it is often desirable to take a series of pictures or images of an anatomical feature, such as the brain, heart, knee or other organ or musculoskeletal feature over a period of time. Doctors and researchers need to review and study such features over time to understand the development, aging and changes normally associated with such features. Doctors and researchers also need to study such features as a function of the duration of a disease or pathological condition such as cancers and tumors. Doctors and researchers also need to review and monitor physiological changes in anatomical features as a function of time due to various treatments such as pharmacological and surgical treatments. 
     Different imaging machines are best suited for imaging different types of anatomical features. For example, bone is generally better imaged by X-ray machines and computerized axial tomography (CAT or CT) scanning machines, while soft tissue is generally better imaged by magnetic resonance imaging (MRI) machines. Imaging techniques such as bioluminescent, fluorescent and photon emission tomography (PET) generally provide better bio-functional data while MRI and CT imaging generally provide better structural and anatomical data. 
     As a result of the strengths and weaknesses of the various imaging techniques, researchers have come to rely on the use of a combination of images from different imaging machines to produce compound or superimposed images which integrate the best features from each imaging technique. This multiple image technique requires a specimen to be imaged on and moved between a series of different imaging machines. 
     In order to produce accurate and clear composite images, the specimen must be accurately and repeatably positioned within each imaging machine to allow for the accurate coregistration of the various images. This has proved to be a difficult, labor intensive and time consuming setup, adjustment and alignment process. 
     SUMMARY OF THE INVENTION 
     The present invention has been developed to assist doctors and researchers in accurately and repeatably imaging the same specimen, such as a laboratory mouse or rat, over an extended period of time, such as in longitudinal time course studies, using one or more imaging machines. In accordance with the invention, a specimen may be transported in-situ from one imaging machine to the next in such a predetermined position as to facilitate the coregistration of images from one or more of the imaging machines. 
     That is, the present invention minimizes the variability of animal or specimen placement within the field of view of any one or more of a series of different imaging machines. This is achieved by enabling the removal of the animal or specimen from one imaging machine and the subsequent placement of the animal or specimen in the same or different imaging machine in exactly the same relative position and location time after time. This is particularly advantageous for longitudinal time course studies, where the specimen is imaged at one point in time, removed from the imaging machine and at a later time placed back into the same machine in exactly the same position and imaged again. 
     The present invention also minimizes the variability of animal or specimen placement when the same animal or specimen is taken from one imaging machine to the next. Images from each of a series of imaging machines may be taken of the same animal or specimen in the same position as the image taken in the first imaging machine. An animal or specimen is loaded and locked into position in accordance with the invention, and moved to each imaging device within a single common holder. 
     This process, apparatus and technique not only eliminates multiple setups in multiple machines, it also eliminates multiple handlings of the animal or specimen. This is particularly advantageous in those cases where the animal or specimen is contagious. Moreover, this process, apparatus and technique improves specimen position repeatability and machine setup time and throughput. 
     As noted above, researchers typically superimpose images from different imaging machines to form a single coregistered or composite image, taking the best features from MRI, X-ray, PET and other machines to maximize the clarity and information provided within the images. The present invention provides for the creation of clear compound images from different imaging machines by accurately positioning a specimen or patient in the same relative position in each machine. This increases the quality and reliability of coregistration of the individual images. It also increases the speed and accuracy of specialized software used to create the compound images from the different images produced by the different machines. 
     The present invention provides two main sections or assemblies for accomplishing the accurate and repeatable positioning of laboratory specimens such as rats and mice within the“sweet spot” or field of view of each one of various imaging machines. The first main section is a spacing or positioning receiver section and the second section is a specimen or animal holding section. A specialized coupling is provided to accurately align and connect the specimen or animal holding system to the positioning receiver assembly which can be permanently or removably mounted to an imaging machine. 
     In accordance with the invention, the animal holding system is releasably coupled to the positioning receiver assembly. The animal holding system is mountable interchangeably on a positioning receiver assembly on one or more imaging machines. The positioning receiver assemblies are specially adapted to mount on each respective imaging machine in such a manner that when the animal holding system is coupled to the positioning receiver assembly, the animal holding system optimally positions the animal within the field of view on each respective imaging machine. 
     The specialized coupling between the animal holding assembly and the positioning receiver assembly includes a male component and a female component. Each positioning receiver assembly includes the female component portion of the coupling along with a control lever to engage, lock and release the animal holding system. The animal holding system includes a male component portion of the coupling. When the male coupling portion is inserted into the female receiver coupling portion and engaged and locked, a precision, reproducible alignment coupling and connection is formed. 
     The combination of the positioning receiver assembly and the animal holding system produces an animal management system. From time to time an additional assembly called a positioning assembly system may be required to facilitate the placement of the animal management system into an imaging machine. This is typically required on MRI machines due to their inherent design. Each positioning assembly system, and/or as the case may be, positioning receiver assembly can be kept mounted to its respective imaging machine so that the animal holding system can be coupled to the imaging machine directly via the positioning receiver assembly or indirectly via the positioning assembly system for an MRI machine, in a highly repeatable way. 
     The aforementioned objects features and advantages of the invention will in part, be pointed out with particularity, and will, in part, become obvious from the following more detailed description of the invention, taken in conjunction with the accompanying drawings, which form an integral part thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a perspective exploded view of a first embodiment of an animal management system, also called a specimen positioning system, constructed in accordance with a first embodiment of the invention and adapted for use in an MRI machine; 
         FIG. 2  is a perspective view of the animal management system of  FIG. 1  mounted in a positioning assembly system adapted for mounting within the bore of an MRI machine; 
         FIG. 3  is a perspective exploded view of a second embodiment of the invention showing an animal management system adapted for use in a CT or PET imaging machine; 
         FIG. 4  is a partial perspective view of the animal management system of  FIG. 3  mounted to a bracket adapted to be removably clamped or mounted on the outer face of a CT imaging machine and inserted within the bore of a CT imaging machine; and 
         FIG. 5  is a perspective view of a third embodiment of the invention showing the animal management system mounted to another CT machine. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described in conjunction with the drawings, beginning with  FIG. 1  which shows an animal management system or specimen positioning system  10  constructed in accordance with a first embodiment of the invention. The positioning system  10  is adapted for use in an MRI positioning assembly such as disclosed in US patent application publication number US 2005/0027190A1, filed Aug. 10, 2001, under application Ser. No. 10/631,226, and which is incorporated herein in its entirety by reference. 
     While the specimen positioning assembly in US 2005/0027190 provides for a unitary specimen positioning assembly, the present invention provides for an equivalent modular multicomponent positioning system. That is, the positioning system  10  of the present invention includes a detachable modular specimen holder or animal holding system  12  which is removably and selectively mountable on a positioning receiver assembly  14  which is adapted for mounting on an imaging machine. 
     A modular coupling  16  is provided between the animal holding system  12  and the positioning receiver assembly  14  for accurately and repeatably coupling the animal holding system  12  to the positioning receiver assembly  14  to form a positioning system  10 . Coupling  16  includes a male coupling portion  18  mounted on an outer end of the animal holding system  12  and a female coupling portion  20  mounted on an inner end of the positioning receiver assembly  14 . If desired, the male and female portions  18 ,  20  of coupling  16  can be reversed, as long as all other compatible systems  10  are similarly adapted. 
     Once the male coupling portion  18  is inserted within the female coupling portion  20 , a male keying member  22  projecting from a predetermine circumferential or clockwise position (such as 12 o&#39;clock) on the male coupling portion  18  is inserted and guided into a complementary keying slot  24  formed in a predetermined circumferential or clockwise position (such as 12 o&#39;clock) on the female coupling portion  20  so as to circumferentially align the animal holding system  12  with the positioning receiver assembly  14 . This clockwise alignment ensures proper, accurate and repeatable placement of a specimen held within the animal holding system  12  within a known, generally horizontal, axial plane within the field of view of an imaging machine, as discussed further below. 
     Once the male coupling portion  18  is fully inserted within the female coupling portion  20 , a cam ring  26  with internal circumferentially-extending cam ramps mounted within the female coupling portion  20  can be rotated by a cam lever or cam grip tab  28  to radially compress a circumferentially-spaced series of balls  29  loosely held within coupling portion  20  and thereby axially wedge and lock the male coupling portion  18  into a tight axial abutment against a radial registration surface on the female coupling portion  20 . At the same time, a frustoconical male plug portion  30  on the male coupling member  18  is tightly seated and centered within a complimentary frustoconical female socket portion  32  formed within the female coupling portion  20 . 
     This conical nesting centers the male coupling portion  18  within the female coupling portion  20  and thereby coaxially aligns the animal holding system  12  with the positioning receiver assembly  14 . At the same time, the tight axial abutment between the male and female coupling portions  18 ,  20  accurately axially locates and registers the animal holding system  12  with respect to the positioning receiver assembly  14 . 
     In order to release and separate the male coupling portion  18  from the female coupling portion  20 , an operator need only rotate or push the cam tab  28  in an opposite direction to that of the locking direction. The animal holding system  12  can then be easily removed and placed in another positioning receiver assembly  14  in a different type of imaging machine. Additional details of the quick-connect and quick disconnect coupling  16  are provided in U.S. patent application Ser. No. 11/346,851, filed Feb. 3, 2006, titled, Coupling Assembly for Animal Management Systems. 
     As further shown in  FIG. 1 , the animal holding system  12  further includes an interconnection panel  34  which includes various ports  36  for the passage of fluids such as anesthesia gasses, and various electrical connectors  38  for the connection of sensor lead wires from ECG sensors and respiratory sensors, for example, located within animal holding chamber  39 . The fluid ports  36  and electrical connectors  38  communicate with aligned passages formed through the male coupling portion  18  to which the panel  34  is connected. 
     A lead support tray or trough  40  receives and supports the electrical wires and fluid tubes exiting the outer end of the male coupling portion  18 . These wires and tubes extend from within the panel  34 , through channels or passages through the male coupling portion  18  and outwardly along the positioning receiver assembly  14 . They then pass through conduits  42  formed through the cylindrical base  44  of the positioning receiver assembly  14 . The tubes and electrical leads can then be respectively connected to external sources of fluids and to remote monitoring devices via an outer connector plate  45 . 
     The specimen or animal chamber  39  includes a cylindrical tube  46  connected and hermetically sealed to the interconnection panel  34 . Tube  46  may be made of clear or transparent plastic or glass. The inner end of tube  46  may terminate in a semihemispherical bulb in a manner similar to a common test tube. Alternatively, an end cap  48  can be threaded onto an inner threaded open end of tube  46  as shown in  FIG. 1 . In this case, a porous filter  50  is clamped or mounted to the inner end of tube  46  by end cap  48 . 
     In order to accurately position and restrain a specimen, such as a laboratory rat, within the animal holding system  12 , a live specimen alignment bed  52  is accurately positioned axially and circumferentially (clockwise) within tube  39 . The outer end of the alignment bed  52  is accurately and removably mounted to the interconnection panel  34  by a pair of eyelets  54  ( FIG. 3 ) which aligns with threaded bores in the interconnection panel  34 . Threaded fasteners such as plastic screws can be used to fix the alignment bed  52  to the interconnection panel  34  via eyelets  54 . 
     The alignment bed  52  is formed as a unitary integral support surface with a central longitudinal groove or channel  56  for accurately aligning and holding the body of an animal centrally within the tube  39 . Channel  56  extends closely parallel with the central axis  57  of tube  39 . Grooves or slots  58  are formed in alignment bed  52  for positioning and fixing in predetermined place the rear legs of an animal. Grooves or slots  60  are formed in alignment bed  52  for positioning and fixing in predetermined place the front legs of an animal. 
     A bite bar  62  is placed at the inner end of the alignment bed  52  to anchor an animal&#39;s teeth in a known axial position which corresponds to a position closely adjacent to the centerline of the field of view of each imaging machine into which the positioning system  10  is subsequently mounted. Ear bars and/or a head clamp (not shown) may also be provided to lock an animal&#39;s head in a predetermined axial location and radial orientation on the alignment bed  52 . 
     The positioning receiver assembly  14  in  FIG. 1  is specially configured to operate within a commercially available MRI machine. In this case, the positioning receiver assembly  14  is provided with a pair of diametrically-opposed axially-extending side rails  64 . Each side rail  64  has a V-shaped axial groove  66  which self-aligns within a positioning assembly by sliding over a pair of complementary cylindrical rods in the manner described in US patent application publication number US 2005/0027190A1, mentioned above. 
     While the specimen positioning assembly of US 2005/0027190A1 relies on a fixed exterior annular end plate to abut against a mounting plate on a positioning assembly on the exterior of an MRI machine to provide proper registration and alignment of the specimen positioning assembly within the MRI machine, the specimen positioning system  10  of  FIG. 1  has an axially-adjustable stop pad  70  which allows for axial adjustment of the positioning system  10  within the bore of an MRI machine. 
     Stop pad  70  is connected to a pair of slide rods  72  that are frictionally clamped between a lower double V-block  74  and an upper clamp bar  76 . A thumb screw  78  is turned to raise and lower the clamp bar  76  to adjust the clamping force on the slide rods  72  so as to set the axial position of the stop pad  70 , as desired. This allows a researcher to axially adjust and align a desired portion of an animal within the field of view of an imaging machine. A standard position for alignment of the brain of the specimen can be set at the fully extended (inward) position of the stop pad  80 . 
     The lower double V-block  74  is fixed to the outer connector plate  45  through which fluid and electrical leads can pass, as described above. An arch-shaped carrying handle  84  is connected to the outer connector plate  45  to allow an operator to carry the entire positioning system  10  as a unit, as desired, such as from one imaging machine to the next. 
     The positioning system  10  of  FIG. 1  is shown mounted within a mating positioning assembly system  90  in  FIG. 2 . The positioning assembly system  90  of  FIG. 2  is adapted to be mounted within the bore of an MRI machine of conventional construction in a manner similar to that described in US 2005/0027190 A1, noted above. 
     The positioning assembly system  90  of  FIG. 2  includes an elongated cylindrical tube  92  having a diameter closely matching that of the bore of an MRI machine within which the positioning assembly system is to be mounted. A series of axially-spaced mounting rings  94  is mounted within the tube  92  with plastic fasteners or adhesives. Each mounting ring  94  is formed with a pair of diametrically-opposed V-shaped notches  96  for accurately centering and mounting a pair of diametrically-opposed axially-aligned cylindrical guide rods  98 . 
     Guide rods  98  are fixed to each of the mounting rings  94  and to a front mounting plate  100  with plastic fasteners, such as plastic screws. Adhesives can also be used for this purpose. The cylindrical tube  92  is also attached to the front mounting plate  100  with adhesives or plastic brackets or retainers. 
     As further seen in  FIG. 2 , the positioning system  10  of  FIG. 1  is inserted into the positioning assembly system  90  by sliding the V-grooves  66  on side rails  64  over the diametrically-opposed cylindrical guide rods  98  until the stop pad  70  abuts the outer face  102  of the front mounting plate  100 . In actual practice, the tube  92  of the positioning assembly system  90  will be premounted within the bore of an MRI machine, similar to a shell in a cannon bore, and the inner face  104  of the front mounting plate  100  will be tightly fixed against an exterior alignment and registration surface of the MRI machine. 
     The front mounting plate  100  will be fixed to the alignment and registration surface of the MRI machine in a predetermined clockwise orientation, such that the cylindrical guide rods  98  are aligned within a horizontal plane passing through the central axis  105  of the tube  92  and through the coaxially aligned bore of the MRI machine. This relationship ensures that the side rails  64  on the positioning receiver assembly  14  will be similarly aligned along with any animal holding system  12  mounted on the positioning receiver assembly  14 . 
     The axial distance between the front face of the fully inwardly extended stop pad  70  and a predetermined imaging area  106  on the specimen alignment bed  52  is accurately dimensioned so that when the positioning system  10  is fully inserted within the positioning assembly system  90 , the imaging area  106  is centrally aligned within and around the centerline or center of the field of view  107  of the imaging machine, as well as along axis  105 . In this embodiment, positioning system  10  and positioning system  90  abut and register with one another to center and position the brain of a laboratory rat at the intersection of central axis  105  and centerline  107  of the imaging machine for optimal imaging of the brain. 
     As further seen in phantom in  FIG. 2 , a cylindrical tubular radio frequency coil or RF probe  109  is set a predetermined axial length from the mounting plate  100 . In this manner, when the positioning system  10  is inserted within the positioning system  90 , the axial location of the animal holding system  12 , which is also axially set and referenced off mounting plate  100 , is optimally positioned axially and coaxially within the RF probe  109 . Probe can be fixed to end wall  111  with plastic screws. 
     Once a specimen is imaged within an imaging machine fitted with the positioning assembly system  90  of  FIG. 2 , the positioning system  10  is withdrawn from the positioning assembly  90  and from the imaging machine by a simple axial pull on handle  84 . 
     The positioning system  10  simply slides in and out of the positioning assembly  90 , which may be permanently, semi-permanently or removably mounted to the imaging machine. Once the positioning system  10  is removed, the animal holding system  12  can be accessed and quickly released from the positioning receiver assembly  14 . This is done by unlocking and releasing the coupling  16  and axially sliding the male coupling portion  18  out of the female coupling portion  20 . 
     At this point, animal holding system  12  with a specimen still fixed within chamber  39  can be mounted to another positioning receiver assembly  14 , such as shown in  FIGS. 3 ,  4  and  5 . In  FIGS. 3 and 4 , the positioning receiver assembly  14  is adapted for mounting to a micro CT and/or to a micro PET imaging machine of conventional design. 
     The positioning receiver assembly  14  of  FIGS. 3 and 4  is in the form of a relatively simple bracket and plate configuration. A modular female coupling portion  20  is accurately and rigidly mounted in a predetermined axial and circumferential orientation to the front face of a vertical mounting bracket  110  fixed to a flat rectangular horizontal mounting plate  112 . 
     As in the previous example, the circumferential or clockwise orientation of the female coupling portion  20  is closely and accurately fixed so that when the male keying member  22  on the male coupling portion  18  on the animal holding system  12  is inserted in the keying slot  24  in the female coupling portion  20 , the animal holding system  12  will be fixed in a corresponding predetermined clockwise position with respect to the positioning receiver assembly  14 . As seen in  FIG. 4 , the female coupling portion  20  is rigidly fixed to the mounting bracket  110  by a set of mounting screws  114 . 
     Bracket  110  may include a mounting arch or collar  116  which surrounds a circular bore  118  ( FIG. 4 ) formed through the upper portion of bracket  110 . A lead support tray  40  extends through bore  118  for the support of fluid tubing and electrical sensor wires. In the example shown, bracket  110  is arranged substantially perpendicular to the mounting plate  112 . 
     A mounting flange  120  is fixed to the bottom of mounting plate  112  for aligning and mounting the positioning receiver assembly  14  to an external support assembly  121  for a CT or PET machine, as shown in  FIG. 4 . A V-shaped notch  122  ( FIG. 3 ) is formed in the center of the inner edge of mounting flange  120 . 
     As seen in  FIG. 4 , an end block  126  is fixed to a mounting pad  128  on an actuator assembly  130  adapted for mounting on the outer surface of a CT imaging machine. The positioning receiver assembly  14 , with the animal holder system  12  attached, is placed on the mounting pad  128  and pushed forwardly against end block  126 . A V-shaped key (not shown) projecting outwardly from the center of end block  126  keys into the V-shaped notch  122  on mounting flange  120  and properly centers the positioning receiver assembly  14  on mounting pad  128 . 
     At the same time, the front edge of mounting flange  120  is fully seated within a channel  124  in end block  126  to further align and position the positioning receiver assembly  14  on mounting pad  128 . A clasp or over-center snap-fit type connector or latch  132  then latches over a tab or tang  134  extending outwardly from the outer edge of the mounting flange  120  to anchor and lock the positioning receiver assembly in a predetermined position. In  FIG. 4 , the positioning receiver assembly  14  is shown positioned just above the mounting pad  128 , just prior to being anchored in position by clasp  132  and tang  134 . 
     The actuator assembly  130  is adapted to drive the mounting pad  128  and attached positioning receiver assembly  14  up and down as shown by arrows  136  and in and out of a magnet bore as shown by arrows  138 . The actuator assembly  130  can be controlled by a microcontroller or other digital indexing controller. 
     As further seen in  FIG. 4 , the actuator assembly  130  is mounted in a known predetermined orientation and position to an elongated pan-shaped bracket  140  having a large circular aperture  142  formed in its upper end portion. Bracket  140  is fixed to the front face  144  of a CT machine, such that the circular aperture  142  concentrically surrounds the circular entrance  146  to the machine bore  148  of the CT machine (not shown). 
     Since the dimensions and spatial locations of the machine bore  148 , bracket  140 , actuator assembly  130 , mounting pad  128 , positioning receiver assembly  14  and animal holding system  12  are mutually coordinated and predetermined, the imaging area  106  within the animal holding system  12  is preset and predetermined to coincide with the “sweet spot” or centerline  107  of the imaging machine, as in the previous example. 
       FIG. 5  shows yet another embodiment of the invention, wherein the specimen positioning system  10  is mounted on yet another different imaging machine, in this case a CT scanner  150 . The system  10  is supported on a linear drive table  152  connected to the front surface  154  of a CT machine. 
     A stepped L-shaped bracket assembly  156  fixed to and supporting the positioning receiver assembly  14  mounts the animal holding system  12  to the drive table  152  for controlled linear movement into and out of the bore  158  of the imaging machine. In this example, electrical leads  160  and fluid tubing  162  are shown exiting the lead support tray  40  extending from the female coupling portion  20 . 
     As in the prior examples, all dimensions of all components of the specimen positioning system  10  are registered, coordinated and matched with those on the respective imaging systems. In this case, they are registered with the drive table  152  and bore  158  so that the imaging area  106  will nominally be positioned within the sweet spot or centerline of the field of view within bore  158  upon controlled and coordinated actuation of drive table  152 . 
     It can now be appreciated that the present invention provides a working system which coordinates all specimen and accompanying coil placements within the field of view of each imaging system for proper referencing. This minimizes the guesswork of where a gradient coil is positioned, where an RF probe is positioned and where/how the animal or specimen is located in relation to the centerline of the field of view of the imaging system, as all components as well as the specimen are referenced from the same relative zero point. It becomes as simple as placing the animal onto the animal holder, interfacing and connecting the animal holder with a machine specific positioning receiver assembly  14 , and in the case of an MRI type imaging machine, interfacing the V-grooves and rails of the positioning assembly system  90 , and sliding the animal management system  10  into the magnet bore until a mechanical stop engages a reference surface. At this point, the specimen is properly located to be imaged. 
     When the animal management system  10  is not utilized in an MRI type system, all these attributes are still maintained via the positioning receiver assembly  14 . An operator simply loads an animal into a predetermined fixed position within the animal holder  12 , and then engages the animal holder  12  with the imaging machine via a specific positioning receiver assembly  14  mounted to the imaging machine. 
     These characteristics of the invention form the mechanical basis that properly positions the animal within the field of view of each imaging machine. If an operator is running a series of images on different machines (modalities) with the same animal, once the animal is placed onto the animal holder  12 , it is passed between and interfaced with the different machines via the machine specific positioning receivers  14 , which allow for the connection of the animal holder to the machine. 
     For example, a research protocol could begin with an MRI scan. When the MRI scan is done, the animal management system  10  is then removed from the bore of the MRI magnet. The animal holder  12  is then disengaged from the positioning receiver assembly  14  and moved to the next imaging modality and placed in the positioning receiver assembly  14  on the next imaging machine, such as a micro CT machine. Since each imaging machine has a machine specific positioning receiver assembly already on it, the researcher merely engages the coupling  16 , locks the animal holder into place via the locking lever  28 , and starts the next scanning session with the specimen automatically properly positioned for optimum imaging results. 
     There has been disclosed heretofore the best embodiment of the invention presently contemplated. Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.