Abstract:
An imaging system includes a source and a detector that can be quickly and easily moved out of the way after scanning. During scanning, the actual paths that the source and detector travel are tracked, such as by an associated surgical navigation system tracking system. The actual locations of the source and detector during each x-ray image are used in the image reconstruction algorithm. Since the actual locations are used in the algorithm, the locations do not have to be as precisely controlled. In one embodiment, the source and detector are mounted proximate outer ends of first and second c-arm sections. The first and second c-arm sections are extendable to form a complete c-arm and retractable to a collapsed position when not in use. In the disclosed embodiment, the c-arm sections are mounted to a base or carriage under the patient support surface (such as the surgical table).

Description:
[0001]     This application claims priority to U.S. Provisional Application Ser. No. 60/493,195, filed Aug. 7, 2003. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     Image guided surgery is becoming more common, especially in the areas of inter-cranial surgery. Systems are utilized to take data gathered from pre-operative scans by MRI, CT scanners, ultrasounds, or the like. The data is used to generate a three-dimensional image to guide a surgeon during an operation. Often this includes some method for tracking an instrument location with respect to the image displayed by the system. Generally, the image is registered relative to locators attached to the patient. Then, the position and orientation of the surgical instruments is registered and tracked relative to the image and the patient so that the location and orientation of the instruments relative to the image is continuously displayed while the surgeon performs the surgery.  
         [0003]     The problem with using the pre-operative image is that the object selected may have shifted between the time the pre-operative image was taken and the time of surgery. This is especially true once surgery has begun and the shape of the intercranial cavity changes as the surgeon gains access. Changes in the pre-operative image and the actual surgical subject introduce variations into the surgical process. In matters like intercranial surgery the tolerance for variations is low, thus even small changes between the image and actual subject may cause problems and make the surgery less effective. To solve this problem additional images may be taken during surgery to update the previously received information. However, selecting the area to be scanned, setting up the intra-surgery scanner, and performing the scan require movement of bulky equipment and surgery must be stopped to set up the equipment properly and perform the scan. In addition it is difficult to move the equipment to the desired area to be scanned thus increasing the time and effort required to update the image properly. Thus, because of the time and effort required, intraoperative scans are generally not used.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention provides an imaging system that is particularly advantageous for intraoperative use, although it may be used anywhere that space and easy setup is important. Generally, the imaging system includes a source and a detector that can be quickly and easily moved out of the way after scanning. Since much of the bulk of the known CT scanners comes from the structure that moves the source and detector along precisely controlled, predetermined paths, one way that the imaging system of the present invention reduces its size is by eliminating the requirement for such precisely controlled, predetermined paths. Instead, the actual paths that the source and detector travel are tracked, such as by the surgical navigation system tracking system. The actual locations of the source and detector during each x-ray image are used in the image reconstruction algorithm. Since the actual locations are used in the algorithm, the locations do not have to be as precisely controlled.  
         [0005]     In one embodiment, the source and detector are mounted on opposite ends of a collapsible c-arm. The source is mounted at an outer end of a first c-arm section and the detector is mounted at an outer end of a second c-arm section. The first and second c-arm sections are extendable to form a complete c-arm and retractable to a collapsed position when not in use. In the disclosed embodiment, the c-arm sections are mounted to a base or carriage under the patient support surface (such as the surgical table). The carriage includes a motor for driving the c-arm rotatably about the patient support surface. The carriage is also movable longitudinally under the patient support surface, so that any desired portion of the patient can be scanned. Other embodiments and variations are also disclosed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     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:  
         [0007]      FIG. 1  is an end view of imaging system according to a first embodiment of the present invention, showing the c-arm in a first position.  
         [0008]      FIG. 2  shows the c-arm in a second position.  
         [0009]      FIG. 3  shows the c-arm in a collapsed position.  
         [0010]      FIG. 4  is a side view of the imaging system of  FIG. 1  in use.  
         [0011]      FIG. 5  is an end view of an imaging system according to a second embodiment of the present invention.  
         [0012]      FIG. 6  is a sectional view through the carriage of a third embodiment of the present invention.  
         [0013]      FIG. 7  is an end view of a fourth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     A first embodiment of an intraoperative imaging system  20  according to the present invention is shown in  FIGS. 1-4 . The imaging system  20  is particularly useful for image-guided surgery or other applications where intra-operative imaging would be desired. Although applicable for other types of imaging systems, the present invention will be described with respect to an intra-operative CT scanning system  20  for illustrative purposes. Referring to  FIG. 1 , the CT scanning system  20  includes a source  22  and detector  24  mounted at outer ends of a first c-arm section  26  and a second c-arm section  28 , respectively. The source  22  may be a cone-beam x-ray source  22 . The detector  24  may be a flat panel detector  24  having a converter for converting x-rays into light which is detected by an array of photodetectors.  
         [0015]     The first and second c-arm sections  26 ,  28  are slidably connected to one another, such that first c-arm section  26  slides telescopes within the second c-arm section  28 . The first and second c-arm sections  26 ,  28  can be extended to the position shown in  FIG. 1 , where they form a complete c-arm  30 , thereby positioning the centers of the source  22  and detector  24  180 degrees apart.  
         [0016]     The c-arm  30  is also preferably slidably mounted within a carriage  32 , such that the c-arm  30  can be rotated approximately slightly more than 180 degrees generally about an axis x, substantially centered within the c-arm  30  and positioned substantially between the source  22  and detector  24 . The carriage  32  is also slidably mounted on rails  36  such that the carriage  32  and c-arm  30  can translate along the x-axis. One or more motors  37  control the position and motion of the carriage  32  on the rails  36 . The carriage  32  and/or the rails  36  may be part of (or simply placed below) an operating table  38 . The carriage  32  preferably includes a motor  39  engaging the c-arm  30  to drive the c-arm  30  about the x-axis in a controlled manner.  
         [0017]     The patient and/or the table  38  may include fiducials or locators  40  that are detectable on the CT images, so that the position and orientation of the surgeon&#39;s tools  43  can subsequently be determined relative to the three-dimensional image by an image-guided surgery tracking system  44  according to known image-guided surgery techniques. Several types of suitable tracking systems  44  are known.  
         [0018]     The tracking system  44  may include sensors  46 , which may be CCDs that optically detect the locators  40 , RF receivers that receive wireless signals from the locators  40  or lasers that measure distance to each of the locators  40 . Other known types of tracking systems  44  could also be utilized. The present invention is independent of the specific type of tracking system  44  used. Additionally, the c-arm sections  26 ,  28  may include locators  40  such that their position and orientation can be determined relative to the image-guided surgery tracking system  44  and relative to the table  38 .  
         [0019]     If the c-arm sections  26 ,  28  include locators  40 , the ability of the c-arm  30  to keep the source  22  and detector  24  at precisely fixed locations relative to one another becomes less important. Since the tracking system  44  determines the location of the c-arm sections  26 ,  28  (and thus, the source  22  and detector  24 ), at each position at which an x-ray image is taken, these coordinates can be used in the reconstruction algorithm, in which the multiple x-ray images are used to construct a 3D image of the scanned area. The data in each x-ray image may be corrected or otherwise offset prior to reconstruction in order to take into account the true position of the source  22  and detector  24 , which may not travel along a perfect arc at precise, equal intervals due to the fact that they are mounted on a c-arm  30 , especially a c-arm  30  that is formed in sections. Alternatively, the locations of the source  22  and detector  24  at which each x-ray image was taken may be factored directly into the reconstruction algorithm, i.e. rather than trying to “correct” the data back to ideal source and detector locations prior to reconstruction, using the actual locations of the source and detector in the reconstruction algorithm. Also, for the same reasons, it is not important that the c-arm  30  actually rotate about a single axis, but it should generally rotate about the area of interest in the patient to be scanned, which may be an area in or near the interior of the arc of the c-arm  30 .  
         [0020]     A computer  50  has a processor, memory and storage and is suitably programmed to perform the functions described herein. The computer  50  may include a keyboard  52   a  and a mouse  52   b  as user input devices and a display  54 . The computer  50  controls the function and operation of the devices in the manner described herein. The computer  50  also receives the x-ray images from the detector  22  and reconstructs a 3D image from the x-ray images using suitable techniques. The computer  50  controls the motor  39  to move the c-arm  30  through the carriage  32  about the x-axis while the x-ray images are taken at selected intervals. The computer  50  also receives the data from the tracking system  44  and corrects or offsets the data received from the detector  24  by the data indicating the positions of the data  22  and detector  22  in the reconstruction algorithm.  
         [0021]     The c-arm  30  is rotated about the x-axis by the motor  39  in the carriage  32  as controlled by the computer  50 . The c-arm  30  is rotatable about the x-axis approximately a little greater than 180 degrees to the position shown in  FIG. 2 , such that a complete scan of the patient can be taken.  
         [0022]     In use, the imaging system  20  may initially be stored below the operating table  38  prior to use as shown in  FIG. 3 . In  FIG. 3 , the c-arm sections  26 ,  28  are retracted to a position below the table  38  out of the way of the surgeons and assistants. When a pre-operative or intra-operative image is desired, the c-arm sections  26 ,  28  are extended to the position shown in  FIGS. 1-2  and the imaging process is initiated, depending on the type of image desired. If a CT scan is required, the carriage  32  is moved along the rails to the desired portion of the patient&#39;s body, as shown in  FIG. 4 . The source  32  and detector  24  are then activated to produce a plurality of x-ray images of the desired portion of the patient&#39;s body. The c-arm  30  is rotated about the x-axis by computer-controlled motors in the carriage  32  as the source  32  and detector  34  take x-ray images at spaced intervals sufficient to create or update a three-dimensional image of the portion of the patient&#39;s body. The tracking system  44  repeatedly determines the positions of the source  22  and detector  24 , which are correlated to the x-ray images sent by the detector  24  to the computer  50 . The computer-controlled motors  37  may also move the carriage  32  along the rails  36  during rotation of the c-arm  30 , in order to produce a “rectified helical” scan (not a true helix, since the c-arm does not perform a complete orbit, but rotatably oscillates between the positions of  FIGS. 1 and 2 ).  
         [0023]     After scanning, the computer  50  reconstructs the 3D image of the portion of the patient based upon the x-ray images and positions of the source  22  and detector  24  at which each image was taken. The reconstructed image is then displayed on the display  54 . The c-arm  30  is collapsed again and moved out of the way under the table  38  so that surgery can begin (in the case of a preoperative scan) or continue (in the case of an intraoperative scan). Those of skill in the art would be able to develop the reconstruction algorithms described herein based upon the particular implementation chosen.  
         [0024]     A second embodiment of the system  20   a  is shown in  FIG. 5 . In  FIG. 5 , the c-arm section  28   a  is slidably mounted along the inner arc surface of the c-arm section  26   a . The c-arm sections  26   a ,  28   a  are shown in the collapsed position in  FIG. 5 . Otherwise, the operation is as described above.  
         [0025]     A third embodiment is shown in  FIG. 6 , which is a section view through the carriage  32   b . In this embodiment, the c-arm sections  26   b ,  28   b  are separately supported in the carriage  32   b , with separate motors  39   b  driving each about the axis during scanning. Although the source  22  and detector  24  are offset slightly along the x-axis, they can be tilted slightly to accommodate this offset.  
         [0026]     An imaging system  70  according to a fourth embodiment of the present invention is shown in  FIG. 7 . The imaging system  70  comprises a pair of c-arm halves  72  each having a rail  74  mounted on its inner circumference. Each c-arm half  72  is mounted on a movable base  76 , such that they can be moved together for scanning and away from one another after scanning. At least one of the bases  76  is mounted to the rail  36  (also shown in  FIG. 4 ) and includes the motor  37  for translating the system  70  along the rail  36  as described above. The c-arm halves  72  and rails  74  are attachable to one another to form an outer ring from c-arm halves  72  and an annular inner rail from rails  74 . The source  22  is mounted to a computer-controlled carriage  78  having a motor  79 . The detector  24  is mounted to a separate, independently controlled, motorized carriage  80  having a motor  81 . The carriages  78 ,  80  each include a plurality of the locators  40  (described above) for use with the tracking system  12 , in the manner described above. In operation, after the c-arm halves  72  and rails  74  are connected, the computer  50  ( FIG. 1 ) controls the motors  79 ,  81  to move the source  22  and detector  24  about the x-axis. Although an effort is made to keep the source  22  and detector  24  180 degrees apart, the carriages  78 ,  80  are independent, so precision will not be achieved. As described above, the locators  40  and the tracking system  12  ( FIG. 1 ) can be used to match each x-ray image with the actual locations of the source  22  and detector  24  and either “correct” for the location or otherwise take into account the actual locations of the source  22  and detector  24  when reconstructing the 3D image. As in the embodiments above, the c-arm halves  72  and bases  76  are moved along the x-axis as controlled by the computer  50 .  
         [0027]     Other variations of the present invention include a c-arm having three or more c-arm sections that are slidably mounted relative to one another, or three or more c-arm sections that are telescoping mounted relative to one another. This would further reduce the collapsed dimensions of the c-arm.  
         [0028]     Alternatively, the source  32  and detector  34  can each be mounted on a four-bar linkage designed to approximate arcs. It is not necessary that the source  32  and detector  34  move along perfect circles—only that their positions be known. Computer-controlled motors or other actuators can be used to move the source  32  and detector  34  along the arcs while taking images at known positions and orientations. The positions and orientations of the source and detector are also determined by the tracking system such that the images can be corrected based upon the actual positions of the source and detector at each of the plurality of rotational positions about the patient.  
         [0029]     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. Alphanumeric identifiers in method steps are for the purpose of ease of reference in dependent claims and are not intended to signify a required sequence of performance, and unless otherwise explicitly stated, such sequence should not be inferred.