Abstract:
A C-arm system is disclosed herein. The C-arm system includes a support assembly, and a C-extension connected to the support assembly. The C-extension is selectively rotatable relative to the support assembly in both a clockwise and a counterclockwise direction. The C-arm system also includes a C-gantry connected to the C-extension. The C-gantry is adapted to retain an x-ray source and an x-ray detector. The C-gantry is selectively rotatable relative to the C-extension in both a clockwise and a counterclockwise direction. The C-extension is operable to extend the range of C-gantry rotation in both clockwise and counter clockwise directions. A corresponding method for operating a C-arm system is also provided.

Description:
FIELD OF THE INVENTION 
     This disclosure relates generally to a method and apparatus for a C-arm system having an extendable range of motion. 
     BACKGROUND OF THE INVENTION 
     C-arm equipment is commonly implemented for purposes such as surgical planning, co-registration, image fusion, navigation, implant fitting, surgical validation, etc. During these procedures, it is frequently desirable to observe the patient from several different orientations and is often preferable to do so without the need to reposition the patient. C-arm systems have been developed to meet these needs and are now well known in the medical and surgical arts. C-arm systems can be small enough and mobile enough to be present in an operating or exam situation without requiring the physician or technician to repeatedly move and without requiring the patient to change positions to obtain a suitable image. As an example, a gap defined by the C-arm gantry allows the device to laterally access a patient such that patient images are obtainable without physically moving the patient. 
     An x-ray source and an x-ray detector are generally mounted on opposing ends of the C-arm gantry such that x-rays emitted by the source are incident on and detectable by the x-ray detector. The source and the detector are positioned such that when an object (e.g., a human extremity) is interposed therebetween and is irradiated with x-rays, the detector produces data representative of characteristics of the interposed object. The data produced is frequently displayed on a monitor or electronically stored. 
     The C-arm gantry defines an axis of rotation about which the source and detector are rotatable. By positioning this axis of rotation at or near an object, and by rotating the source and detector around the object in an orbital motion, images of the object taken at a plurality of different orientations can be obtained. These images can be combined to generate a comprehensive three-dimensional image of the object. The process of combining images to produce a comprehensive three-dimensional image is commonly performed with reconstructive software. 
     The term “redundancy” refers to the process of obtaining data that is representative of a single portion of an object from multiple different orientations. Increasing the degree of data redundancy correspondingly increases image quality by reducing artifacts. “Artifacts” are distortions in an image that may be generated, for example, by reconstructive software in response to insufficient input data. One problem with conventional C-arm systems is that the gap defined by the C-arm gantry limits the range of orbital motion of the x-ray source and the x-ray detector. This limitation on the range of orbital motion correspondingly limits the degree of data redundancy obtainable, and therefore also limits image quality by increasing artifacts. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The above-mentioned shortcomings, disadvantages and problems are addressed herein which will be understood by reading and understanding the following specification. 
     In an embodiment, a C-arm system includes a support assembly, and a C-extension connected to the support assembly. The C-extension is selectively rotatable relative to the support assembly in both a clockwise and a counterclockwise direction. The C-arm system also includes a C-gantry connected to the C-extension. The C-gantry is adapted to retain an x-ray source and an x-ray detector. The C-gantry is selectively rotatable relative to the C-extension in both a clockwise and a counterclockwise direction. The C-extension is operable to extend the range of C-gantry rotation in both clockwise and counter clockwise directions. 
     In another embodiment, a C-arm system includes a support assembly defining a support assembly groove, and a C-extension having a first ridge and a second ridge. The C-extension is connected to the support assembly such that the first ridge is disposed at least partially within the support assembly groove. The C-extension is selectively rotatable relative to the support assembly in both clockwise and counterclockwise directions. The C-arm system also includes a C-gantry defining a gantry groove. The C-gantry is connected to the C-extension such that the second ridge is disposed at least partially within the gantry groove. The C-gantry is adapted to retain an x-ray source and an x-ray detector. The C-gantry is selectively rotatable relative to the C-extension in both clockwise and counterclockwise directions. The C-system also includes a first motor operatively connected to the C-extension, a second motor operatively connected to the C-gantry, and a controller operatively connected to the first and second motors such that C-extension rotation and C-gantry rotation can be independently induced in a selectable manner. The C-extension is operable to extend the range of C-gantry rotation in both clockwise and counter clockwise directions. 
     In another embodiment, a method for operating a C-arm system includes providing a C-extension that is selectively rotatable in a clockwise or counter clockwise direction, and providing a C-gantry that is connected to the C-extension. The C-gantry is selectively rotatable in a clockwise or counter clockwise direction. The method for operating a C-arm system also includes controlling a first motor operatively connected to the C-extension in order to induce a selectable amount of C-extension rotation, and controlling a second motor operatively connected to the C-gantry in order to induce a selectable amount of C-gantry rotation. Independently controlling the first motor and the second motor increases the C-gantry range of rotation in both the clockwise direction and the counter clockwise direction. 
     Various other features, objects, and advantages of the invention will be made apparent to those skilled in the art from the accompanying drawings and detailed description thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a C-arm system in accordance with an embodiment; 
         FIG. 2  is a schematic diagram illustrating the C-arm system of  FIG. 1  rotated to the over scan end limit; 
         FIG. 3  is a schematic sectional diagram illustrating the C-arm system of  FIG. 1  rotated to the under scan end limit; and 
         FIG. 4  is a cross-sectional diagram illustrating the C-arm system of  FIG. 1  in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments that may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, and it is to be understood that other embodiments may be utilized and that logical, mechanical, electrical and other changes may be made without departing from the scope of the embodiments. The following detailed description is, therefore, not to be taken as limiting the scope of the invention. 
     Referring to  FIG. 1 , a C-arm system  10  is shown in the home position in accordance with an embodiment. The term “C-arm” generally refers to the shape of a conventional C-arm gantry (sometimes referred to as the C-gantry), however, it should be appreciated that, for purposes of this disclosure, terms such as C-arm, C-gantry and C-extension may encompass other shapes and orientations. The “home position” is that shown in  FIG. 1  wherein the x-ray source  18  is at the bottom most or six o&#39;clock position and the x-ray detector  20  is at the upper most or twelve o&#39;clock position. 
     The C-arm system  10  includes a C-arm gantry or C-gantry  12 , a C-arm extension or C-extension  14 , and a support assembly  16 . The support assembly  16  rotatably supports the C-extension  14  and/or the C-gantry  12  while remaining stationary relative thereto. The C-gantry  12  and the C-extension  14  are independently rotatable. The x-ray source  18  and the x-ray detector  20  are rigidly attached to opposing end portions of the C-gantry  12  such that these components are collectively rotatable as a single unit. The x-ray source  18  emits x-rays (not shown) that are detectable by the x-ray detector  20 . The x-ray source  18  and the x-ray detector  20  are configured such that when an object is interposed therebetween and is irradiated with x-rays, the x-ray detector  20  produces data representative of characteristics of the interposed object. This representative data can be implemented in a known manner to generate an image of the interposed object. 
     For illustrative purposes, this disclosure will hereinafter be described in accordance with an embodiment wherein C-extension  14  rotation is induced by a first motor  22  operatively connected thereto, and C-gantry  12  rotation is induced by a second motor  24  operatively connected thereto. It should be appreciated, however, that C-gantry  12  and C-extension  14  rotation may be induced in any known manner such as, for example, by a single motor operatively connected to both components, or by other types of power sources. A controller  26  is operatively connected to both the first and second motors  22 ,  24 . The controller  26  is adapted to operate one or both of the first and second motors  22 ,  24  and thereby selectively rotate the C-gantry  12  and/or the C-extension  14  as will be described in detail hereinafter. 
     The C-gantry  12  defines a gap  28  and an axis of rotation  30 . The C-arm system  10  is configured to laterally access a stationary object (not shown) such as a human patient. More precisely, the gap  28  accommodates the stationary object as the C-arm system  10  is translated into position such that the axis of rotation  30  generally coincides with the object&#39;s region of interest (e.g., a human extremity). Thereafter, the x-ray source  18  and the x-ray detector  20  are rotatable around the axis of rotation  30  to obtain a comprehensive three-dimensional image of the region of interest. 
     Reference point A identifies a first terminal end of the C-extension  14 , and reference point B identifies a second terminal end of the C-extension  14 . Reference point A of the C-extension  14  is rotatable in a clockwise direction from the home position shown in  FIG. 1  to the position labeled reference point C. Therefore, the range of C-extension  14  rotation in the clockwise direction is defined by λ which is the angular displacement between reference points A and C. Reference point B of the C-extension  14  is rotatable in a counter clockwise direction from the home position shown in  FIG. 1  to the position labeled reference point D. Therefore, a maximum range of C-extension  14  rotation in the counter clockwise direction is defined by δ which is the angular displacement between reference points B and D. 
     Reference point E identifies a first terminal end of the C-gantry  12 , and reference point F identifies a second terminal end of the C-gantry  12 . Reference point E of the C-gantry  12  is rotatable in a clockwise direction from the home position shown in  FIG. 1  to the position labeled reference point G. If the C-extension  14  is held stationary, the range of C-gantry  12  rotation in the clockwise direction is defined by α which is the angular displacement between reference points E and G. Reference point F of the C-gantry  12  is rotatable in a counter clockwise direction from the home position shown in  FIG. 1  to the position labeled by reference point H. If the C-extension  14  is held stationary, the range of C-gantry  12  rotation in the counter clockwise direction is defined by β which is the angular displacement between reference points F and H. 
     Referring to  FIG. 2 , the C-arm system  10  is shown with the C-gantry  12  rotated to the over scan end limit (OS max ). For purposes of this disclosure, “over scan” is defined as the degree to which reference point E identifying a terminal end of the C-gantry  12  is rotated in the counter clockwise direction from its home position shown in  FIG. 1 . As previously indicated, if the C-extension  14  is held stationary, C-gantry  12  over scan is limited to β° of rotation. If, however, the C-extension  14  is rotated by its maximum counter clockwise amount δ°, the allowable C-gantry  12  over scan OS max  becomes (β+δ)° of rotation. Therefore, the implementation of the C-extension  14  increases the maximum C-gantry over scan OS max  by δ°. This increase in C-Gantry  12  over scan range also increases the maximum allowable degree of data redundancy which correspondingly increases x-ray image quality by reducing artifacts. 
     Referring to  FIG. 3 , the C-arm system  10  is shown with the C-gantry  12  rotated to the under scan end limit (US max ). For purposes of this disclosure, “under scan” is defined as the degree to which reference point F identifying a terminal end of the C-gantry  12  is rotated in the clockwise direction from its home position shown in  FIG. 1 . As previously indicated, if the C-extension  14  is held stationary, C-gantry  12  under scan is limited to α° of rotation. If, however, the C-extension  14  is rotated by the maximum clockwise amount λ°, the allowable C-gantry  12  under scan US max  becomes (α+λ)° of rotation. Therefore, the implementation of the C-extension  14  increases the maximum C-gantry under scan US max  by λ°. This increase in C-Gantry  12  under scan range also increases the maximum allowable degree of data redundancy which correspondingly increases x-ray image quality by reducing artifacts. 
     Advantageously, the C-extension  14  can extend the total range of C-gantry  12  rotation to 360° allowing for optimal x-ray image quality. As an example, a C-arm system has been developed wherein the reference characters α, β, λ and δ have approximate values of 95°, 110°, 75°, and 80°, respectively. Therefore, according to the exemplary embodiment, the maximum over scan OS max  previously defined as (β+δ)° is 190°, and the maximum under scan US max  previously defined as (α+λ)° is 170°. Total C-gantry  12  rotation, which is equal to the sum of the maximum over scan and the maximum under scan (OS max +US max ), is therefore 360°. The full 360° scan range of the exemplary C-arm system provides significantly greater x-ray image quality than conventional C-arm systems which have only 200°-220° of total rotation. 
     The C-arm system  10  will hereinafter be described in accordance with an exemplary embodiment wherein the first and second motors  22 ,  24  (shown in  FIG. 1 ) are arc-shaped linear motors. As is known in the art, a “linear motor” is a type of electric motor configured to produce linear rather than rotational output. The arc-shape of the exemplary linear motors therefore produce generally linear output along the arc defining their shape. Referring now to  FIG. 4 , a cross sectional diagram illustrates the motors  22 ,  24  attached to the C-gantry  12 , the C-extension  14 , and the support assembly  16  in accordance with an exemplary embodiment. It should be appreciated that other motor configurations, and other C-gantry  12 , C-extension  14 , and support assembly  16  sectional configurations may alternatively be envisioned. 
     The support assembly  16  cross-section is generally rectangular and defines a reduced diameter portion referred to herein as the support assembly groove  32 . The C-gantry  12  cross-section is also generally rectangular and defines a reduced diameter portion referred to herein as the gantry groove  34 . The C-extension  14  cross-section is generally I-shaped, and is preferably positioned between and connected to the C-gantry  12  and the support assembly  16 . The C-extension  14  includes a first protrusion or ridge  36  that is adapted for engagement with the complementary support assembly groove  32  such that the C-extension  14  is supported by and piloted on the support assembly  16 . The C-extension  14  includes a second protrusion or ridge  38  that is adapted for engagement with the complementary gantry groove  34  such that the C-extension  14  is also supported by and piloted on the C-gantry  12 . While the cross-sectional geometry of the C-arm system  10  components has been described in accordance with an embodiment wherein adjacent components have complementary interlocking retention features (i.e., a groove and a ridge), it should be appreciated that the specific retention features may vary. As an example, according to one alternate embodiment, the C-extension may include first and second grooves (not shown) respectively engaged by a support assembly ridge (not shown) and a gantry ridge (not shown). 
     According to one embodiment, a first plurality of bearings  40  are disposed between the support assembly  16  and the C-extension  14  in order to minimize frictional losses caused by relative motion therebetween. More precisely, the first plurality of bearings  40  are disposed within the support assembly groove  32  and are engaged by the ridge  36  of the C-extension  14 . A second plurality of bearings  42  may be similarly disposed between the C-gantry  12  and the C-extension  14  in order to minimize frictional losses caused by relative motion therebetween. The bearings  40  and  42  may include any type of bearing devices such as, for example, ball bearings or roller bearings, any may also include any known device adapted to facilitate relative motion and minimize friction. 
     The arc-shaped linear motor  22  includes a translatable rotor  44  and a stator  46 . The rotor  44  of motor  22  is mounted to the C-extension  14 , and the stator  46  of motor  22  is mounted to the support assembly  16 . The linear motion of the rotor  44  is imparted to the C-extension  14  attached thereto such that the C-extension  14  is translated relative to the support assembly  16 . The curved geometry of the C-extension  14  converts this linear motion into rotation about the axis of rotation  30  (shown in  FIG. 1 ). The arc-shaped linear motor  24  includes a translatable rotor  48  and a stator  50 . The rotor  48  of motor  24  is mounted to the C-gantry  12 , and the stator  50  of motor  24  is mounted to the C-extension  14 . The linear motion of the rotor  48  is imparted to the C-gantry  12  attached thereto such that the C-gantry  12  is translated relative to the C-extension  14 . The curved geometry of the C-gantry  12  converts this linear motion into rotation about the axis of rotation  30 . 
     For some applications, it may be desirable to maintain relatively constant velocity of the x-ray source  18  and the x-ray detector  20  as they are rotated about the axis of rotation  30  (shown in  FIG. 1 ) on the C-gantry  12 . Such constant velocity can be maintained by implementing the controller  26  (shown in  FIG. 1 ) to coordinate the motors  22 ,  24  in a predefined manner. According to one embodiment, the motors  22 ,  24  can be operated sequentially such that the first motor  22  is operated to rotate the C-extension  14  in a first direction and at a first speed, and thereafter the second motor  24  is operated to rotate the C-gantry  12  in the first direction and at approximately the first speed. In this manner, the accumulated rotational speed otherwise produced by operating the motors simultaneously can be avoided. 
     While the invention has been described with reference to preferred embodiments, those skilled in the art will appreciate that certain substitutions, alterations and omissions may be made to the embodiments without departing from the spirit of the invention. Accordingly, the foregoing description is meant to be exemplary only, and should not limit the scope of the invention as set forth in the following claims.