Abstract:
An imaging apparatus and related method comprising a detector located a distance from a source and positioned to receive a beam of radiation in a trajectory; a detector positioner that translates the detector to an alternate position in a direction that is substantially normal to the trajectory; and a beam positioner that alters the trajectory of the radiation beam to direct the beam onto the detector located at the alternate position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 14/223,361 filed on Mar. 24, 2014, which is a continuation of U.S. patent application Ser. No. 12/684,430 filed on Jan. 8, 2010, now U.S. Pat. No. 8,678,647 issued on Feb. 16, 2010, which is a continuation of U.S. patent application Ser. No. 11/522,794 filed on Sep. 18, 2006, now U.S. Pat. No. 7,661,882 issued on Feb. 16, 2010, which is a continuation of U.S. patent application Ser. No. 10/392,365 filed on Mar. 18, 2003, now U.S. Pat. No. 7,108,421 issued on Sep. 19, 2006, which claims benefit of U.S. Patent Application No. 60/366,062 filed on Mar. 19, 2002. The entire disclosures of each of the above applications are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a system for imaging a subject, and particularly to a system for detecting image radiation. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     In conventional computerized tomography for both medical and industrial applications, an x-ray fan beam and a linear array detector are employed to achieve two-dimensional axial imaging. The quality of these two-dimensional (2D) images is high, although only a single slice of an object can be imaged at a time. To acquire a three-dimensional (3D) data set, a series of 2D images are sequentially obtained in what is known as the “stack of slices” technique. One drawback to this method is that acquiring the 3D data set one slice at a time is an inherently slow process. There are other problems with this conventional tomographic technique, such as motion artifacts arising from the fact that the slices cannot be imaged simultaneously, and excessive exposure to x-ray radiation due to overlap of the x-ray projection areas. 
     Another technique for 3D computerized tomography is cone-beam x-ray imaging. In a system employing cone-beam geometry, an x-ray source projects a cone-shaped beam of x-ray radiation through the target object and onto a 2D area detector area. The target object is scanned, preferably over a 360-degree range, either by moving the x-ray source and detector in a scanning circle around the stationary object, or by rotating the object while the source and detector remain stationary. In either case, it is the relative movement between the source and object which accomplishes the scanning. Compared to the 2D “stack of slices” approach for 3D imaging, the cone-beam geometry is able to achieve 3D images in a much shorter time, while minimizing exposure to radiation. One example of a cone beam x-ray system for acquiring 3D volumetric image data using a flat panel image receptor is discussed in U.S. Pat. No. 6,041,097 to Roos, et al. 
     A significant limitation of existing cone-beam reconstruction techniques occurs, however, when the object being imaged is larger than the field-of-view of the detector, which is a quite common situation in both industrial and medical imaging applications. In this situation, some measured projections contain information from both the field of view of interest and from other regions of the object outside the field of view. The resulting image of the field of view of interest is therefore corrupted by data resulting from overlying material. 
     Several approaches have been proposed for imaging objects larger than the field-of-view of the imaging system. U.S. Pat. No. 5,032,990 to Eberhard et al., for example, discusses a technique for 2D imaging of an object which is so wide that a linear array detector is not wide enough to span the object or part which is to be viewed. The method involves successively scanning the object and acquiring partial data sets at a plurality of relative positions of the object, x-ray source, and detector array. U.S. Pat. No. 5,187,659 to Eberhard et al. discusses a technique for avoiding corrupted data when performing 3D CT on an object larger than the field of view. This technique involves scanning the object with multiple scanning trajectories, using one or more x-ray sources and detectors which rotate in different trajectories relative to the target object. Yet another technique is discussed in U.S. Pat. No. 5,319,693 to Ebarhard et al. This patent discusses simulating a relatively large area detector using a relatively small area detector by either moving the actual area detector relative to the source, or moving the object relative to the area detector. All of these techniques are characterized by complex relative movements between one or more x-ray sources, detectors, and the object being imaged. Furthermore, in each of these techniques, the target object is exposed to excessive x-ray radiation from regions of overlapping projections. 
     To date, there does not exist a radiation system for imaging large field-of-view objects in a simple and straightforward manner while minimizing the target object&#39;s exposure to radiation. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     The present invention relates to radiation-based imaging, including 3D computerized tomography (CT) and 2D planar x-ray imaging. In particular this invention relates to methods and systems for minimizing the amount of missing data and, at the same time, avoiding corrupted and resulting artifacts in image reconstruction when a cone-beam configuration is used to image a portion of an object that is larger than the field of view. 
     An imaging apparatus according to one aspect comprises a source that projects a beam of radiation in a first trajectory; a detector located a distance from the source and positioned to receive the beam of radiation in the first trajectory; an imaging area between the source and the detector, the radiation beam from the source passing through a portion of the imaging area before it is received at the detector; a detector positioner that translates the detector to a second position in a first direction that is substantially normal to the first trajectory; and a beam positioner that alters the trajectory of the radiation beam to direct the beam onto the detector located at the second position. The radiation source can be an x-ray cone-beam source, and the detector can be a two-dimensional flat-panel detector array. 
     By translating a detector of limited size along a line or arc opposite the radiation source, and obtaining object images at multiple positions along the translation path, an effectively large field-of-view may be achieved. In one embodiment, a detector positioner for translating the detector comprises a positioner frame that supports the detector and defines a translation path, and a motor that drives the detector as it translates within the positioner frame. A positioning feedback system, which can include a linear encoder tape and a read head, can be used to precisely locate and position the detector within the positioner frame. Other position encoder systems could also be used as the positioning feedback system, such as a rotary encoder and a friction wheel. 
     A radiation source, such as an x-ray source, includes a beam positioning mechanism for changing the trajectory of the emitted radiation beam from a fixed focal spot. This enables the beam to scan across an imaging region, and follow the path of a moving target, such as a translating detector array. In one aspect, the beam positioning mechanism of the present invention enables safer and more efficient dose utilization, as the beam positioner permits the beam to sequentially scan through limited regions of the target object, so that only the region within the field-of-view of the translating detector at any given time need be exposed to harmful radiation. 
     In one embodiment, a tilting beam positioning mechanism includes a frame which houses the radiation source, and a motorized system connected to both the frame and the source, where the motorized system pivots or tilts the source relative to the frame to alter the trajectory of the radiation beam projected from the source. In a preferred embodiment, the source is pivoted about the focal spot of the projected radiation beam. The motorized tilting system could include, for example, a linear actuator connected at one end to the fixed frame and at the other end to the source, where the length of the actuator controls the angle of tilt of the source, or a motorized pulley system for tilting the source. In another embodiment, a movable collimator is driven by a motor for changing the trajectory of the output beam. 
     In still another aspect, the invention includes means for rotating the source and translatable detector relative to an object to obtain images at different projection angles over a partial of full 360-degree scan. In one embodiment, the source and detector are housed in a gantry, such as a substantially O-shaped gantry ring, and are rotatable around the inside of the gantry ring. The source and detector can be mounted to a motorized rotor which rotates around the gantry on a rail and bearing system. In another embodiment, the source and translatable detector remain fixed on a support, such as a table, while the object rotates on a turntable or rotatable stage. 
     The invention also relates to a method of imaging an object comprising projecting a beam of radiation in a first trajectory, the beam traveling through a first region of the object and onto a detector located at a first position; translating the detector to a second position in a direction that is substantially normal to the first trajectory; and altering the trajectory of the beam so that the beam travels through a second region of the object and onto the detector located at the second position. Preferably, the beam of radiation comprises a cone-beam or fan-beam of x-ray radiation, and the detected radiation is used to produce two-dimensional planar or three-dimensional computerized tomographic (CT) object images. 
     In one aspect, the invention is able to image objects larger than the field-of-view of the detector in a simple and straightforward manner by utilizing a detector positioner that translates the detector array to multiple positions, thus providing an effectively large field-of-view using only a single detector array having a relatively small size. In addition, a beam positioner permits the trajectory of the beam to follow the path of the translating detector, which advantageously enables safer and more efficient dose utilization, as only the region of the target object that is within the field-of-view of the detector at any given time needs to be exposed to harmful radiation. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIGS. 1A-C  are schematic diagrams showing an x-ray scanning system with a translating detector array according to one embodiment of the invention; 
         FIGS. 2A-D  are side and perspective views illustrating the x-ray source and detector of the system of  FIG. 1 ; 
         FIG. 3  illustrates the wide field-of-view achievable with the translating detector system of the present invention; 
         FIG. 4  is a schematic diagram showing a data collection matrix of an x-ray scanner system according to one embodiment of the invention; 
         FIG. 5  is an exploded view of an x-ray detector positioning stage according to one embodiment; 
         FIGS. 6A-C  shows the x-ray detector positioning stage translating to three positions; 
         FIG. 7  is an exploded view of an x-ray source and source positioning stage according to one embodiment of the invention; 
         FIG. 8  is a perspective view of an assembled x-ray source and positioning stage; 
         FIGS. 9A-C  shows an x-ray source tilted to three positions by a linear actuator, according to one embodiment of the invention; 
         FIG. 10  shows a motorized belt and pulley system for tilting an x-ray source to multiple positions, according to another embodiment; 
         FIG. 11  shows a motorized sliding collimator for directing an x-ray beam to multiple detector positions, according to yet another embodiment; 
         FIG. 12  is a perspective view of a rotor assembly for rotating an x-ray source and detector within a gantry; 
         FIG. 13  is a cutaway side view showing the rotor assembly within a gantry ring; 
         FIG. 14  is a schematic illustration of a mobile cart and gantry assembly for tomographic and planar imaging of large field-of-view objects according to one embodiment; 
         FIG. 15  illustrates a table-top x-ray assembly with rotatable stage for tomographic and planar imaging of large field-of-view objects according to yet another embodiment; and 
         FIG. 16  shows a detector that is translated along a line. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
       FIGS. 1A-C  schematically illustrate an x-ray scanning system with a translating detector array according to one embodiment of the invention. The scanning system shown in  FIGS. 1A-C  includes gantry  11 , which in this embodiment comprises a generally circular, or “O-shaped,” housing having a central opening into which an object being imaged is placed. The gantry  11  contains an x-ray source  13  (such as a rotating anode pulsed x-ray source) that projects a beam of x-ray radiation  15  into the central opening of the gantry, through the object being imaged, and onto a detector array  14  (such as a flat panel digital detector array) located on the opposite side of the gantry. The x-rays received at the detector  14  can then be used to produce a 2D planar or 3D tomographic object reconstruction images using well-known techniques. 
     The detector  14  is translated to multiple positions along a line or arc in a direction that is generally normal to the trajectory of beam  15 . This permits the detector to capture images of objects that are wider than the field-of-view of the detector array.  FIGS. 1A-1C  show the large field-of-view imaging area when the detector is translated to three positions along an arc opposite the x-ray source. This is more clearly illustrated in  FIGS. 2A-C , which are side views of the source and detector as the detector translates to three different positions.  FIG. 2D  is a perspective view showing the resultant large imaging field-of-view by combining the data obtained at all three source and detector positions. As shown in  FIGS. 2A-C , as the detector moves to each subsequent position, the last column of detector pixels  41  is positioned adjacent to the location of the leading column of pixels  42  from the prior detector position, thereby providing a large “effective” detector having a wide field-of-view, as shown in  FIG. 2D . The image obtained is a combination of the three images abutted against one another, resulting in a large field-of-view using only a single detector array having a relatively small size. The detector  14  being translated along a line is illustrated in  FIG. 16 . 
     The source  13  preferably includes a beam positioning mechanism for changing the trajectory of the beam  15  from a stationary focal spot  40 , so that the beam follows the detector as the detector translates, as shown in  FIGS. 1A-C . This permits safer and more efficient dose utilization, as generally only the region of the target object that is within the field-of-view of the detector at any given time will be exposed to potentially harmful radiation. 
     Preferably, the translational movement of the detector and the trajectory of the x-ray beam can be automatically coordinated and controlled by a computerized motor control system. 
       FIG. 3  illustrates the large field-of-view obtainable using the translating detector array of the present invention, as compared to the field-of-view of the same array in a conventional static configuration. The small and large circles represent varying diameters of the region centered on the axis of the imaging area that is within the field-of-view of the detector for the non-translatable and translatable arrays, respectively. The diameter of this imaging region is approximately half the width of the detector, since the beam diverges in the shape of a cone as it projects from the focal spot of the source onto the detector array. As shown in  FIG. 3 , the diameter of this imaging region can be greatly increased by translating the detector array and scanning the x-ray beam to multiple positions along a line or arc on the gantry. 
     In one aspect, the x-ray source  13  and translatable detector  14  are rotatable around the interior of the gantry, preferably on a motorized rotor, to obtain large field-of-view x-ray images from multiple projection angles over a partial or full 360-degree rotation. Collection of multiple projections throughout a full 360-degree rotation results in sufficient data for three-dimensional cone-beam tomographic reconstruction of the target object. 
     As shown in the matrix diagram of  FIG. 4 , there are at least two methods for obtaining large field-of-view images over a partial or full 360-degree rotational scan of the target object. In the first method, for each rotational angle of the source and detector within the gantry, the detector is translated to two or more positions, capturing x-ray images at each detector position. This is shown in the top row of the matrix diagram of  FIG. 4 , where the x-ray source and detector stage are maintained at Rotor Angle  0 , while the detector translates on the stage to Detector Positions  1 - 3 . The rotor carrying the x-ray source and detector stage then rotate to a second position on the gantry, Rotor Angle  1 , and the detector again translates to the three detector positions. This process repeats as the x-ray source and detector stage rotate through N rotor positions on the gantry to obtain large field-of-view object images over a full 360-degree scan. 
     In a second method, for each position of the translating detector, the source and detector stage perform a partial of full 360-degree rotation around the target object. This is shown in the leftmost column of the matrix diagram of  FIG. 4 , where detector is maintained at Detector Position  1 , while the source and detector stage rotate within the gantry to Rotor Angles  0  through N. Then, as shown in the center column of  FIG. 4 , the detector is translated to Detector Position  2 , and the source and detector stage are again rotated to Rotor Angles  0  through N. This process is repeated for each position of the translating detector array, with the source and detector stage performing a partial or full scan around the target object for each detector position. 
     Turning now to  FIG. 5 , an x-ray detector positioner  100  according to one embodiment of the invention is shown in exploded form. The positioning stage comprises a detector carriage  101  for holding the detector, a friction drive  102  which attaches to the detector carriage, and a positioner frame  103  upon which the detector carriage is movably mounted, The positioner frame includes two parallel side walls  104 , a base  105 , and a series of lateral frames  106  extending between the side walls. The interior of the side walls  104  include three main concentric surfaces extending the length of the frame. On top of each side wall  104  is a flat surface upon which a friction wheel  109  is driven, in the center is a v-groove rail on which a pair of v-groove rollers  110  ride, and on the bottom is another flat surface upon which a linear encoder tape is affixed. 
     In the embodiment shown, the concentric radii of the components of the curved side rails vary as a function of a circumscribed circle centered at the focal spot of an x-ray source. The central ray or line that connects the focal spot to the center pixel of the detector array is essentially perpendicular to the flat face of the detector array. By moving the translating detector components along the defined curved side rails, the face of the detector translates tangentially to the circle circumscribed by connecting the ray or line that connects the focal spot to the center pixel of the detector array. Other embodiments include a circle with infinite radius, in which case the curved side rails become straightened along a flat plane or line. 
     The friction drive  102  consists of a servomotor, gear head, belt drive, axle, and friction wheels  109 . The friction drive is mounted to the detector carriage  101  by brackets  107 . The friction wheels  109  are preferably spring-loaded and biased against the flat top surface of the side walls  104 . The rollers  110  are mounted to brackets  107 , and pressed into the central v-grooves of the positioner side walls  104 . The v-groove rollers  110  precisely locate the detector carriage  101  as well as allow loading from any direction, thus enabling the accurate positioning of the translated detector array independent of gantry angle or position. The friction wheel  109  minimizes the backlash in the positioning system. In addition, a read head  108  is located on a detector carriage bracket  107  for reading the encoder tape affixed to the bottom flat surface of the positioner side wall  104 . The read head  108  provides position feedback information to the servomotor for precise positioning of the detector carriage along the concentric axis of travel. The x-ray detector positioner  100  can also include bearings  29  attached to side walls  104  for rotating the entire detector assembly around the interior of a gantry, as described in further detail below. 
     Referring to  FIGS. 6A-C , the assembled detector positioner  100  is shown translating the detector carriage  101  to multiple positions along an arc. In operation, the detector carriage  101  and friction drive assembly  102  are precisely moved by the servomotor along the concentric axis of the positioning frame and accurately positioned by the linear encoder system. Three positions are shown in  FIGS. 6A-C , although the detector carriage  101  may be precisely positioned at any point along the arc defined by the positioner frame  103 . The compact nature of the friction drive  102  allows for maximum translation of the detector carriage  101  while the drive  102  remains completely enclosed within the positioner frame  103 , and allows the distal ends of the detector carriage to extend beyond the edge of the positioner frame (as shown in  FIGS. 6A and 6C ) to further increase the “effective” field-of-view obtainable with the detector. 
     As discussed above, the imaging system of the present invention preferably includes a radiation source with a beam positioning mechanism for changing the trajectory of the radiation emitted from a fixed focal spot, so that the beam may scan across multiple positions. One embodiment of an x-ray source stage  200  with a beam positioning mechanism is shown in  FIG. 7 . The stage comprises an outer wall frame  201  (shown in exploded form) which encloses the x-ray source  13 , a swiveling x-ray source mount  202 , and a servomotor linear actuator  203 . The x-ray source is supported on the bottom by source mount  202  and from the sides by a pair of bushing mounts  206 . The bushing mounts  206  are connected to the outer wall frame  201  by precision dowel pins  204  that are press-fit into bushings  205 . The dowel pins  204  permit the bushing mounts  206 , and thus the x-ray source  13  and source mount  202 , to pivot with respect to the outer wall frame  201  pivoting motion. This pivoting motion is preferably centered at the focal spot of the x-ray source. 
     The precision servomotor linear actuator  203  is attached at one end to the outer wall frame  201 , and at the other end to the swiveling x-ray source mount  202 . By varying the length of the motorized linear actuator  203 , the source mount  202  and x-ray source  13  can be pivoted about dowel pins  204  to tilt the x-ray source about its focal spot in a controlled manner. The fully assembled x-ray source stage is shown in  FIG. 8 . 
     The operation of the x-ray source and tilting beam positioning mechanism is shown in  FIGS. 9A-9C . As the linear actuator moves from a fully retracted position ( FIG. 9A ) to a fully extended position ( FIG. 9C ) the x-ray source pivots about its focal spot, thus altering the trajectory of the emitted radiation beam. In this embodiment, the pivot point represents the center of a circle with a radius defined by the distance from the focal spot to the center pixel of the detector array. The pivot angle is computed by determining the angle defined by the line connecting the focal spot of the x-ray detector and the center pixel of the detector array. A computerized motion control system can be used to synchronize the x-ray source tilt angle with the position of a translating detector array so that the x-ray beam remains centered on the detector even as the detector translates to different positions. 
     Various other embodiments of an x-ray beam positioner can be employed according to the invention. For example, as shown in  FIG. 10 , the x-ray source can be tilted to multiple positions by a motorized belt and pulley system. In another embodiment shown in  FIG. 11 , the trajectory of the x-ray beam is altered by a sliding collimator that is driven by a servomotor. 
     As shown in  FIG. 12 , the x-ray source stage  200  and x-ray detector positioner  100  can be joined together by a curved bracket assembly  301  to produce a C-shaped motorized rotor assembly  33 . The rigid bracket  301  maintains the source and detector opposed to one another, and the entire rotor assembly can be rotated inside an O-shaped x-ray gantry. The rotor assembly  33  can also include a motor  31  and drive wheel  32  attached at one end of the rotor for driving the rotor assembly around the interior of the gantry. 
       FIG. 13  is a cutaway side view of a gantry  11  which contains a C-shaped motorized rotor  33 . The interior side walls of the gantry include curved rails  27  extending in a continuous loop around the interior of the gantry. The drive wheel  32  of the rotor assembly  33  contacts the curved rail  27  of the gantry, and uses the rail to drive the rotor assembly around the interior of the gantry. A rotary incremental encoder can be used to precisely measure the angular position of the rotor assembly within the gantry. The incremental encoder can be driven by a friction wheel that rolls on a concentric rail located within the sidewall of the gantry. The rotor assembly  33  also includes bearings  29 , which mate with the curved rails  27  of the gantry to help guide the rotor assembly  33  as it rotates inside the gantry. The interior of the gantry ring  11  can include a slip ring that maintains electrical contact with the rotor assembly  33  to provide the power needed to operate the x-ray source, detector, detector positioner, and/or beam positioner, and also to rotate the entire assembly within the gantry frame. The slip ring can furthermore be used to transmit control signals to the rotor, and x-ray imaging data from the detector to a separate processing unit located outside the gantry. Any or all of the functions of the slip ring could be performed by other means, such as a flexible cable harness attached to the rotor, for example. 
     Although the rotor assembly of the preferred embodiment is a C-shaped rotor, it will be understood that other rotor configurations, such as O-shaped rotors, could also be employed. For example, a second curved bracket  301  could be attached to close the open end of the rotor, and provide a generally O-shaped rotor. In addition, the x-ray source and detector could rotate independently of one another using separate mechanized systems. 
     An x-ray scanning system  10  according to one aspect of the invention generally includes a gantry  11  secured to a support structure, which could be a mobile or stationary cart, a patient table, a wall, a floor, or a ceiling. As shown in  FIG. 14 , the gantry  11  is secured to a mobile cart  12  in a cantilevered fashion via a ring positioning unit  20 . In certain embodiments, the ring positioning unit  20  enables the gantry  11  to translate and/or rotate with respect to the support structure, including, for example, translational movement along at least one of the x-, y-, and z-axes, and/or rotation around at least one of the x- and y-axes. X-ray scanning devices with a cantilevered, multiple-degree-of-freedom movable gantry are described in commonly owned U.S. Provisional Applications 60/388,063, filed Jun. 11, 2002, and 60/405,098, filed Aug. 21, 2002, the entire teachings of which are incorporated herein by reference. 
     The mobile cart  12  of  FIG. 14  can optionally include a power supply, an x-ray power generator, and a computer system for controlling operation of the x-ray scanning device, including translational movement of the detector, and tilting movement of the x-ray source. The computer system can also perform various data processing functions, such as image processing, and storage of x-ray images. The mobile cart  12  preferably also includes a display system  60 , such as a flat panel display, for displaying images obtained by the x-ray scanner. The display can also include a user interface function, such as a touch-screen controller, that enables a user to interact with and control the functions of the scanning system. In certain embodiments, a user-controlled pendant or foot pedal can control the functions of the scanning system. It will be understood that one or more fixed units can also perform any of the functions of the mobile cart  12 . 
     The O-shaped gantry can include a segment that at least partially detaches from the gantry ring to provide an opening or “break” in the gantry ring through which the object to be imaged may enter and exit the central imaging area of the gantry ring in a radial direction. An advantage of this type of device is the ability to manipulate the x-ray gantry around the target object, such as a patient, and then close the gantry around the object, causing minimal disruption to the object, in order to perform x-ray imaging. Examples of “breakable” gantry devices for x-ray imaging are described in commonly-owned U.S. patent application Ser. No. 10/319,407, filed Dec. 12, 2002, now U.S. Pat. No. 6,940,941, issued Sep. 6, 2005, the entire teachings of which are incorporated herein by reference. 
     It will also be understood that although the embodiments shown here include x-ray imaging devices having O-shaped gantries, other gantry configurations could be employed, including broken ring shaped gantries having less than full 360 degree rotational capability. 
     Referring to  FIG. 15 , a table-top version of the large field-of-view scanning device is depicted. In this embodiment, the connector bracket, gantry, and rotor friction drive have been replaced by a rigid table mount  302  and a turntable  303  located in the center of the field of view. The turntable rotates the object to be imaged in a complete 360-degree rotation to capture projection images from any direction. The detector and source positioning assemblies  100 ,  200  are rigidly mounted a fixed distance from one another. The turntable  303  can be rigidly mounted to the table at any point along the ray connecting the x-ray focal spot and the center of the detector positioning assembly. The data collection techniques for this embodiment are essentially the same as those described for the x-ray gantry, except that in this case, it is the rotation of the object relative to the source and detector, rather than the rotation of the source and detector relative to the object, which effects the x-ray scanning. 
     The x-ray imaging systems and methods described herein may be advantageously used for two-dimensional and/or three-dimensional x-ray scanning. Individual two-dimensional projections from set angles along the gantry rotation can be viewed, or multiple projections collected throughout a partial or full rotation may be reconstructed using cone or fan beam tomographic reconstruction techniques. This invention could be used for acquiring multi-planar x-ray images in a quasi-simultaneous manner, such as described in commonly-owned U.S. patent application No. 10/389,268 entitled “Systems and Methods for Quasi-Simultaneous Multi-Planar X-Ray Imaging,” , filed on Mar. 13, 2003, now U.S. Pat. No. 7,188,998, issued on Mar. 13, 2007, the entire teachings of which are incorporated herein by reference. Also, the images acquired at each detector position could be reprojected onto virtual equilinear or equiangular detector arrays prior to performing standard filtered backprojection tomographic reconstruction techniques, as described in commonly-owned U.S. Provisional Application No. 60/405,096, filed on Aug. 21, 2002. 
     The detector arrays described herein include two-dimensional flat panel solid-state detector arrays. It will be understood, however, that various detectors and detector arrays can be used in this invention, including any detector configurations used in typical diagnostic fan-beam or cone-beam imaging systems, such as C-arm fluoroscopes. A preferred detector is a two-dimensional thin-film transistor x-ray detector using scintillator amorphous-silicon technology. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. For instance, although the particular embodiments shown and described herein relate in general to computed tomography (CT) x-ray imaging applications, it will further be understood that the principles of the present invention may also be extended to other medical and non-medical imaging applications, including, for example, magnetic resonance imaging (MRI), positron emission tomography (PET), single photon emission computed tomography (SPECT), ultrasound imaging, and photographic imaging. 
     Also, while the embodiments shown and described here relate in general to medical imaging, it will be understood that the invention may be used for numerous other applications, including industrial applications, such as testing and analysis of materials, inspection of containers, and imaging of large objects. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.