Abstract:
A CT scanning system provides the ability to scan a patient&#39;s lower extremities while the patent is upright, i.e. either standing on the foot, or at least putting some load on the foot, or with the ankle at a given angle. The CT scanning system provides a generally horizontal upper support surface on which the patient&#39;s foot is supported. A gantry supporting an x-ray source and x-ray detector are rotated about a z-axis through the support surface. With the CT scanning system, the patient&#39;s lower extremities can be scanned while under load.

Description:
REFERENCE TO RELATED APPLICATION 
   This application claims priority to U.S. Provisional Application Ser. No. 60/676,734, which was filed on May 2, 2005. 

   BACKGROUND OF THE INVENTION 
   Diagnosing foot and ankle injuries and problems can be difficult. A large number of small, overlapping bones in the foot and ankle sometimes obscure the visualization of fractures or other problems from traditional X-rays. As a result, doctors often order CT scans of the foot and ankle. However, current CT scanners are too large, expensive and complicated to be located in the doctor&#39;s office. Therefore, the patient must go to a different location for the CT scan and then return to the doctor for analysis. Immediate diagnosis and treatment are often delayed by days. 
   Additionally, the current CT scanners require the patient to lie down, since they are designed to scan the whole body. The current CT scanner cannot take a CT scan of the foot and ankle under load (i.e., while the patient is standing). For patients that only experience foot or ankle pain when standing, or for whom walking or standing aggravates their foot or ankle pain, it may be desirable to be able to visualize the foot and ankle under load, since many of the bones and tissue in the foot and ankle may shift and move to a different position under load. 
   SUMMARY OF THE INVENTION 
   A CT scanning system provides the ability to scan a patient&#39;s lower extremities while the patent is upright, i.e. either standing on the foot, or at least putting some load on the foot, or with the ankle at a given angle. The CT scanning system provides a generally horizontal upper support surface on which the patient&#39;s foot is supported. A gantry supporting an x-ray source and x-ray detector are rotated about a z-axis through the support surface. With the CT scanning system, the patient&#39;s lower extremities can be scanned while under load. Other features and advantages of the CT scanning system are described below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages of the present invention can be understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
       FIG. 1  is a schematic sectional view of a CT scanning system according to one embodiment of the present invention. 
       FIG. 2  illustrates a patient using the CT scanning system of  FIG. 1  in a standing position. 
       FIG. 3  illustrates a patient using the CT scanning system in a non-weight bearing position. 
       FIG. 4  is a schematic sectional view of the CT scanner and patient&#39;s leg of  FIG. 3 . 
       FIG. 5  illustrates the CT scanner with an alternate support for the patient&#39;s leg. 
       FIG. 6  illustrates an alternate CT scanner. 
       FIG. 7  is a plan view of the CT scanner of  FIG. 6 . 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   A CT scanning system  10  according to one embodiment of the present invention is shown schematically in  FIG. 1 . The CT scanning system  10  includes an X-ray source  12  mounted opposite an X-ray detector  14  on a gantry  16 . The X-ray source  12  is preferably a cone-beam X-ray source and the detector  14  is preferably a flat panel detector. The flat panel detector  14  would have a converter for converting X-rays into visible light and an array of photo detectors behind the converter. Any suitable X-ray source  12  and detector  14  could be utilized, as the invention is independent of the specific technology used for the CT scanning system  10 . Although not shown, a collimator and other known CT components could also be utilized. 
   The gantry  16  is rotated about an axis Z by a motor  18  controlled by a computer  20 . The computer also controls the X-ray source  12  and receives X-ray images from the detector  14 . The computer  20  also includes the CT reconstruction algorithm that converts a plurality of X-ray images received by the detector  14  into a three-dimensional CT image stored in computer  20 . The computer  20  then selectively displays the CT image on a display  22 . 
   The gantry  16 , source  12 , detector  14  and motor  18  are mounted in a housing  26 . The housing  26  includes a hollow base  28  that contains the gantry  16 . The housing  26  further includes an annular upper portion  30  having an annular inner wall  32  and an annular outer wall  34 . The source  12  and detector  14  are mounted to rotate about the axis Z between the inner annular wall  32  and the outer annular wall  34 . The base  28  includes an upper surface  35  upon which may be supported an optional pedestal  36 . The pedestal  36  would be transparent to X-rays. 
   In use, the patient stands with one foot  40  on the pedestal  36  (or optionally on the upper surface  35  of the base  28 ) such that the foot  40 , ankle  42  and a portion of the lower leg  44  are within the field of view of the source  12  and detector  14 . This is shown more clearly in  FIG. 2 , where the patient P has one leg  44  in the housing  26  and the other leg on an optional outside support surface  48 , such as a bench. In this manner, the patient&#39;s foot  40 , ankle  42  and lower leg  44  can be scanned by the CT scanning system  10  while the patient P is placing weight on the foot  40 , ankle  42  and lower leg  44 . 
   When the patient is in position, the motor  18  rotatably drives the gantry  16  at least partially about the patient&#39;s foot  40 , ankle  42  and lower leg  44 , while the detector  14  takes a plurality of x-ray images at a plurality of rotational positions. A three-dimensional CT image is then reconstructed from the plurality of x-ray images utilizing known techniques and algorithms. The doctor can then view and manipulate the three-dimensional CT image on the display  22 , including taking section views, slices, rotating the CT image, adjusting image properties (contrast, etc) and other known methods. 
   The CT scanning system  10  can also be used in a non-load bearing configuration as shown in  FIG. 3 . The patient P is seated on an adjacent surface  52 , such as a stool, with the patient&#39;s lower leg  44  inside the housing  26 . Referring to  FIG. 4 , the patient&#39;s foot  40  and ankle  42  may be suspended above the pedestal  36  and the upper surface  35  of the base  28  during the scanning. The patient can optionally be scanned in both the load bearing and non-load bearing configurations as the doctor can compare the CT images from both. 
     FIG. 5  illustrates an alternative support  136  that could be used with the CT scanning system  10  of  FIGS. 1-4 . The alternative support  136  includes a platform  137  pivotably mounted on a column  138 . A motor  139  controls the pivoting position of the platform  137 . The platform  137 , column  138  and any coupling (not shown) between the motor  139  and the platform  137  are transparent to X-rays. In use, the patient&#39;s foot  40  is supported on the platform  137 . The motor  139 , as controlled by the computer  20  ( FIGS. 1-4 ), then pivots the platform  137  to a plurality of positions  137 ,  137   a ,  137   b , so that a CT scan of the foot  40 , ankle  42  and lower leg  44  is taken in each of the plurality of positions. 
   In any of the embodiments and configurations of  FIGS. 1-5 , it may be necessary to ensure proper alignment of the foot  40 , ankle  42  and lower leg  44  between the source  12  and detector  14 . This can be done with one or more of several alternative ways. First, a laser line pointer between the source  12  and detector  14  can be used for proper placement. One or two scout scans (two-dimensional images) at perpendicular positions) can be taken to verify that the foot  40 , ankle  42  and lower leg  44  are in the field of view. A glove or sock into which the foot  40  is inserted can be attached to the pedestal  36  or platform  137  at the proper location. X-ray transparent velco straps can also secure the foot  40  at the proper location. Airbags inflated from the inner annular wall  32  can surround the foot  40  and hold it in the proper location. 
     FIG. 6  illustrates an alternate CT scanner system  70  including the source  12  and detector  14  which are configured and which operate as described above, although oriented to rotated about a horizontal axis. Alternatively, the source  12  and detector  14  could rotate about a tilted axis or even a vertical axis and still be used with the features of this embodiment. The source  12  and detector  14  are rotatable about a portion of a table  72  adjacent a seat  74  having a seat back  76 . A strap  78  may optionally help stabilize the patient on the table  72 . 
   The system  70  includes a platform  237  pivotably mounted on an arm  238 . The platform  237  can be selectively pivoted to a selected angle relative to the arm  238  and locked in place. A strap  236  may optionally help stabilize a patient&#39;s foot  40  on the platform  237 . A motor, hydraulic actuator or other loading device  239  controls the load applied to the platform  237  along the axis of the arm  238 . An indicator/selector  240  permits an operator to choose and verify the amount of force being applied by the loading device  239 . The platform  237 , arm  238  and any coupling (not shown) between the arm  238  and the platform  237  are transparent to X-rays. 
     FIG. 7  is a top view of the system  70  of  FIG. 6  (without the patient). Optionally, the seat  74  is movable laterally relative to the table  72 , so that the left foot/ankle or right foot/ankle can be scanned easily. Additionally/alternatively, the seat  74  is rotatable (and vertically adjustable) so that the arm or wrist can be placed on the table  72 . 
   In use, the patient&#39;s foot  40  is supported on the platform  237  and optionally secured to the platform  237  by the strap  236 . The patient sits on the table  72  with the seat back  76  firmly behind the patient. The strap  78  may further stabilize the position of the patient on the table  72 . The operator selects an angle of the platform  237  so that the ankle  42  can be imaged in a desired angle. The operator also selects a load to be applied to the foot  40  using the indicator/selector  240 . The loading device  239  applies a force via the arm  238  and the platform  237  to the foot  40 , ankle  42  and lower leg  44 . The source  12  and detector  14  then rotate and perform a CT scan of the foot  40 , ankle  42  and lower leg  44 , with the foot  40  at the desired angle and with the desired, controlled, constant load (if any) applied. 
   In accordance with the provisions of the patent statutes and jurisprudence, exemplary configurations described above are considered to represent a preferred embodiment of the invention. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.