Abstract:
A system and method are provided for control of a navigation system for deploying a medical device within a subject, and for enhancement of a display image of anatomical features for viewing the projected location and movement of medical devices, and projected locations of a variety of anatomical features and other spatial markers in the operating region. The display of the X-ray imaging system information is augmented in a manner such that a physician can more easily become oriented in three dimensions with the use of a single-plane X-ray display. The projection of points and geometrical shapes within the subject body onto a known imaging plane can be obtained using associated imaging parameters and projective geometry.

Description:
FIELD OF THE INVENTION 
     This invention relates to a system and methods for interventional medicine, and more specifically to computer assisted navigation and imaging of medical devices within a subject body. 
     BACKGROUND OF THE INVENTION 
     Interventional medicine is the collection of medical procedures in which access to the site of treatment is made through one of the subject&#39;s blood vessels, body cavities or lumens. For example, angioplasty of a coronary artery is most often performed using a catheter which enters the patient&#39;s arterial system through a puncture of the femoral artery in the groin area. Other interventional medical procedures include the assessment and treatment of tissues on the inner surface of the heart (endocardial surfaces) accessed via peripheral veins or arteries, treatment of vascular defects such as cerebral aneurysms, removal of embolic clots and debris from vessels, treatment of tumors via vascular access, endoscopy of the intestinal tract, etc. 
     Interventional medicine technologies have been applied to manipulation of instruments which contact tissues during surgical procedures, making these procedures more precise, repeatable and less dependent of the device manipulation skills of the physician. Some presently available interventional medical systems for directing the distal tip of a medical device from the proximal end of the medical device use computer-assisted navigation and a display means for providing a visual display of the medical device along with anatomical images obtained from a separate imaging apparatus. Such systems can provide a visual display of blood vessels and tissues, obtained from a Fluoroscopy (X-ray) imaging system for example, and can display a projection of the medical device being navigated to a target destination using a computer that controls the orientation of the distal tip of the medical device. 
     In some cases, it may be difficult for a physician to become oriented in a three dimensional setting using a display of a single-plane X-ray image projection. Enhancement or augmentation of the single-plane X-ray image may be required to aid the physician in visualizing the orientation of the medical device and blood vessels. A method is therefore desired for enhancing a display image of the anatomical surfaces and the orientation of a medical device in real time to improve navigation through the blood vessels and tissues. 
     SUMMARY OF THE INVENTION 
     According to the principles of the present invention, a system and method are provided for control of a navigation system for deploying a medical device within a subject, and for enhancement of a display image of anatomical features for viewing the current location and orientation of a medical device moving through the subject body. The display of the X-ray imaging system information is augmented in a manner such that a physician can more easily become oriented in three dimensions with the use of a single-plane X-ray display. A typical X-ray imaging system comprises a source for emitting a beam through a three dimensional space and onto a plane, where a point within a subject body in the three dimensional space is projected onto the plane. The projection of a point within the subject body onto the imaging plane can be obtained using an orthographic projection matrix derived from the point-to-image plane distance and the source-to-image plane distance. Thus, a point location within the subject body having known coordinates, properly registered to the frame of reference of the X-ray system, can be projected onto the X-ray image plane of the live X-ray image in the same manner. 
     In accordance with one aspect of the invention, a method of projection can be used to graphically overlay a representation of the actual medical device location and orientation onto the X-ray image. One or more desired target points within the subject can also be projected onto the X-ray image, as well as one or more reference markers on the subject to track patient movement. A graphical representation of a virtual medical device can be overlaid to show a visual reference of a predicted new location and orientation of the actual medical device that corresponds to a desired navigational configuration. A mathematical model of the medical device can be used to define the configuration of the virtual medical device, which can model the behavior of the device corresponding to a change in navigation control variables to predict deflection and rotation of the medical device. A desired direction for steering the medical device within the plane of the X-ray image can be graphically represented, and surface shapes within the subject may also be rendered and graphically represented on the X-ray image display. All the graphically overlaid information is also updated in real time as the X-ray imaging system is rotated or moved, to augment the image display and enhance visualization of the orientation of a medical device in a three dimensional space using a single-plane X-ray image displayed on the control system. 
     It is thus an object of the invention to provide a system and method for augmenting the displayed anatomical image of a subject with graphically overlaid objects to provide enhanced visualization of medical devices, anatomical locations, shapes, markers, and other objects and annotations in a three dimensional space for aiding in the orientation and navigation of the medical device through the subject body. 
     It is a further object of the invention to provide a system and method for enabling virtual representation of the medical device, for providing a visual reference of a predicted orientation and location of the medical device corresponding to a desired configuration or movement to a desired target. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an automated system for navigating a medical device through the lumens and cavities in the operating regions in a patient in accordance with the principles of this invention; 
         FIG. 2  is an illustration of the projection geometry for projecting a location point onto an imaging plane in accordance with the principles of the present invention; 
         FIG. 3  is an illustration of an anatomical image display comprising images of the actual medical device, graphically overlaid images of a virtual medical device configuration and a series of target locations according to the principles of the present invention; 
         FIG. 4A  is a schematic diagram of a navigation system and imaging system combination, in which the navigation system determines the where objects in the operating region should appear based upon information from the imaging system; 
         FIG. 4B  is a schematic diagram of a navigation system and imaging system combination, in which the imaging system determines where objects in the operating region should appear based upon position information from the navigation system; 
         FIG. 5  is a view of the screen of a magnetic navigation system, with imported images from an imaging system in accordance with the principles of this invention; 
         FIG. 6A  is an x-ray image of an anatomic model of a human heart along an axis 26° on the LAO side, showing objects overlaid on the image in accordance with the principles of operation; 
         FIG. 6B  is an x-ray image of the anatomic model of the human heart along an axis 26° on the RAO side; 
         FIG. 7A  is an x-ray image of an anatomic model of a human heart along an axis 25° on the LAO side, showing objects overlaid on the image in accordance with the principles of operation; 
         FIG. 7B  is an x-ray image of the anatomic model of the human heart along an axis 27° on the RAO side; 
         FIG. 8A  is an x-ray image of an anatomic model of a human heart along an axis 25° on the LAO side, showing objects overlaid on the image in accordance with the principles of operation; 
         FIG. 8B  is an x-ray image of the anatomic model of the human heart along an axis 8° on the RAO side; 
         FIG. 8C  is an x-ray image of the anatomic model of the human heart along an axis 27° on the RAO side; 
         FIG. 9A  is an x-ray image of an anatomic model of a human heart along an axis 25° on the LAO side, showing objects overlaid on the image in accordance with the principles of operation; 
         FIG. 9B  is an x-ray image of an anatomic model of a human heart along an axis 16° on the LAO side; 
         FIG. 9C  is an x-ray image of an anatomic model of a human heart along an axis 6° on the LAO side; 
         FIG. 9D  is an x-ray image of an anatomic model of a human heart along an axis 17° on the RAO side; 
         FIG. 9E  is an x-ray image of an anatomic model of a human heart along an axis 27° on the RAO side. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An automated system for navigating a medical device through the lumens and cavities in an operating region in a patient in accordance with the principles of this invention is indicated generally as  20  in  FIG. 1 . The system  20  comprises an elongate medical device  22 , having a proximal end and a distal end adapted to be introduced into the operating region in a subject. The system  20  also comprises an imaging system  30  for displaying an image of the operating region on a display  32 , including a representation of the distal end of the medical device  22  in the operating region. 
     The system also includes a navigation system for manipulating the distal end of the medical device  22 . In this preferred embodiment the navigating system is a magnetic navigation system  50 . Of course, the navigation system could alternatively be a piezoelectric or electrostrictive system or a mechanical control system with pull wires or servo motors, or other suitable system for orienting the distal tip of the medical device. The magnetic navigation system  50  orients the distal end of the medical device  22  in a selected direction through the interaction of magnetic fields associated with the medical device  22  inside the operating region and at least one external source magnet outside the subject&#39;s body. The catheter may then be advanced in the selected direction, to reach the target destination through the successive reorientation stepwise process and advancement. 
     A preferred embodiment of the present invention describes a method for a navigation system associated with an elongate flexible catheter or medical device and an X-ray imaging system, for providing a suitable projection of a graphic overlay of the medical device and target locations within the subject body. The control or actuation means used to steer or navigate the medical device with a computer controlled navigation system may be any of a variety of method known to those skilled in the art, such as mechanical, magnetic, electrostrictive, hydraulic, or others. One preferred embodiment is one where an externally applied magnetic field is used to steer the device, while device advancement and retraction is mechanically driven. Such a navigation system is typically used in conjunction with an X-ray system such as a Fluoroscopy Imaging system, with a mutually known registration between the systems. Other anatomical features such as curves, ridge lines, ablation lines, surface portions, landmark locations, marker locations as reference, and so on, possibly including data from preoperative or intraoperative three dimensional images, can be overlaid on the live X-ray display. Past device configurations can also be displayed as a reference so that any changes in configuration such as patient shift can be monitored during the course of the procedure. 
     Likewise reconstructed features such as blood vessels reconstructed from contrast agent injection and subsequent imaging and image processing, or other path reconstructions as defined by a user to produce a three dimensional path could be overlaid on the live X-ray display. 
     A typical X-ray imaging system comprises a source for emitting a beam through a three dimensional space and onto an imaging plane, where a point within a subject body in the three dimensional space is projected onto the plane. In a preferred embodiment, the X-ray imaging system is preferably a Fluoroscopy imaging system capable of providing images on at least two separate planes, which together can provide the three dimensional coordinates for a location displayed in the two separate planes.  FIG. 2  shows a geometric illustration of an X-ray source point of origin  60  for emitting a beam towards the subject and the imaging plane  62 . The projection of {right arrow over (x)}, a point  64  in a three dimensional space, onto the imaging plane  62  as a perspective projection {right arrow over (x)} p , can be obtained using an orthographic projection matrix. The orthographic projection matrix can be derived from h the point-to-image plane distance  72 , and d the source-to-image plane distance  70 , or distance to the center {right arrow over (x)} c  of the plane  62 . A vector {right arrow over (q)} from a point in space {right arrow over (x)} to the center of the plane {right arrow over (x)} c  may be defined as {right arrow over (q)}=({right arrow over (x)}−{right arrow over (x)} c ):. The source-to-image distance  70  is defined as d. The orthographic projection of {right arrow over (q)} onto the imaging plane  72  is:
 
 {right arrow over (y)} =( I−nn   T ) {right arrow over (q)}  or
 
 {right arrow over (y)}=A{right arrow over (q)}=A ( {right arrow over (x)}−{right arrow over (x)}   c )
 
where nn T  is the 3×3 outer product constructed from the normal {right arrow over (n)} to the X-ray image plane, I is the 3×3 identity matrix, and (I−nn T ) is the orthographic projection matrix. From  FIG. 2 , it can be seen that:
 
                                  x   →     P     -       x   →     C            d     =            y   →            (     d   -   h     )         ,       where   ⁢           ⁢   h     =     (       q   →     ·     n   →       )               (   1   )                   Since   ⁢           ⁢     (         x   →     P     -       x   →     C       )       =                x   →     P     -       x   →     C            ·       y   →            y   →                ,           (   2   )               
Equation (1) may be rewritten as:
 
                     (         x   →     P     -       x   →     C       )     =           ⅆ               (     ⅆ     -   h       )       ⁢     y   →       =         ⅆ               (       ⅆ     -     n   →         ·     (       x   →     -       x   →     C       )       )       ⁢     A   ⁡     (         x   →     P     -       x   →     C       )                   (   3   )               
Equation (3) above defines the perspective projection {right arrow over (x)} p  of point {right arrow over (x)} onto the imaging plane, so {right arrow over (x)} p  may be rewritten in the form:
 
     
       
         
           
             
               
                 
                   
                       
                   
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     For any given point {right arrow over (x)} in a three dimensional space, a corresponding perspective projection point {right arrow over (x)} p  on the X-ray image plane can be determined using equation (4) above. Thus, for any point location within the imaging volume, a corresponding graphic overlay object may be suitably projected onto the X-ray image display. Such graphic overlay objects that may be suitably projected onto a display as illustrated in  FIG. 3  may include objects such as the actual medical device  100  and target locations  102 ,  104 ,  106  and  108  within the operating region of the subject. Other objects that can be usefully overlaid on the live X-ray display include anatomical features such as curves, ridge lines, ablation lines, surface portions, landmark locations, marker locations used as reference, and so on, possibly including data from preoperative or intraoperative three dimensional images. Likewise, previously marked or identified device configurations can also be displayed as a reference so that any changes in configuration due to factors such as patient shift can be monitored during the course of the procedure. Additionally, reconstructed features such as blood vessels reconstructed from contrast agent injection and subsequent imaging and image processing, or other path reconstructions as defined by a user to produce a three dimensional path, or a variety of path-like or other features extracted from three dimensional image data could be overlaid on the live X-ray display. 
     As the Fluoroscopic imaging system is moved or rotated about the subject, the graphically overlaid objects may be continuously updated and displayed along with the continuously updated X-ray images to provide projection images in real time to improve visualization of the orientation of the medical device and target locations. 
     Other graphic overlay objects that can be suitably projected onto the display may include one or more reference markers  110  on the subject body to provide a reference for the movement of the medical device  100 . In the preferred embodiment, the medical device  100  is preferably deployed from the distal end of a relatively stiff sheath inserted within the subject body. The distal end of such a sheath functions as a base for the distal end of a medical device  100  deployed therefrom. One efficient method to mark the pivot or base of the medical device as a reference marker  110  is to position the tip of the medical device  110  at the intended base, for example at the distal tip of a sheath, and then record the current location of the tip as a reference marker, as illustrated in  FIG. 3  at  110 . Reference markers could also be used to indicate target locations for the tip of the medical device to access, and text or other graphic annotations could be used to distinguish and identify various locations. A pre-operative anatomical three-dimensional data set, of an endocardial surface for example, could also be graphically rendered and projected onto the display at  118 , after a suitable registration of the coordinates to the frame of reference of the X-ray is performed. Likewise, an intra-operative three-dimensional data set could also be graphically rendered and projected onto the image display. 
     In the preferred embodiment where a magnetic navigation system is employed for controlling the orientation of the distal tip of the medical device, a graphic annotation of the current magnetic field direction  116  could be projected onto the live Fluoroscopy Image display as a steering reference. Where a localization system for determining the position of the medical device in a frame of reference translatable to the displayed image of the Fluoroscopy system is also included, a graphical rendition of portions of the medical device as determined from the localization information obtained from the localization system can be overlaid on the X-ray image display. Rates of change of control variables such as the magnetic field, or the rate of movement of the medical device may also be determined and displayed on the X-ray image display. 
     A graphical representation of a virtual medical device  112  can be overlaid to show a visual reference the medical device  100  being rotated or moved before initiating actual movement of the medical device. A mathematical model of the medical device can be used to define the configuration of the virtual medical device  112 , which can model the behavior of the device relative to a desired navigation rotation to predict movement of the medical device  110 . Thus, a desired rotation or re-orientation of the tip of the medical device  110  may be evaluated through a visual representation of a virtual medical device  112  in advance of re-orientation of the actual medical device  110 . The model of the virtual medical device  112  can account for the deflective behavior of the medical device  110  relative to changes in navigation control variables such as the applied magnetic field direction, and can provide a representation of the resulting changes in configuration of the device. A graphic indication  114  of a direction for steering the medical device within the plane of the X-ray image may also be graphically overlaid onto the display for coordination with a joystick that is mapped to the X-ray plane. Likewise, a desired target such as location point  102  may be entered, and the model of the virtual medical device  112  configuration can be used to determine the appropriate change in navigation control variables to steer the tip of the medical device to the desired target destination  102 . 
     The imaging display of the present invention may be further augmented by the use of gated location data, for example where the gating is performed with respect to ECG (electro cardiograph) data, so that the device location is always measured at the same phase of a periodic cycle of anatomical motion such as the cardiac cycle. In a preferred embodiment, this data is input into the navigation system together with the real-time location data in a manner such that the location data may be projected onto the X-ray image display. 
     It should be noted that the overlay of the medical device and various objects could be controlled by a user input from an input device such as a joystick, mouse, or hand-held localized stylus, or it could automatically be controlled by a computer. Alternatively, a joystick could also be used to control the direction or steering of the medical device within the subject body. Additional design considerations such as the above modifications may be incorporated without departing from the spirit and scope of the invention. More particularly, the system and method may be adapted to medical device guidance and actuation systems other than magnetic navigation systems, including electrostrictive, mechanical, hydraulic, or other actuation technologies. Likewise, a variety of medical devices such as catheters, cannulas, guidewires, microcatheters, endoscopes and others known to those skilled in the art can be remotely guided according to the principles taught herein. Accordingly, it is not intended that the invention be limited by the particular form described above, but by the appended claims. 
     Operation 
     In operation, the imaging system of the various embodiments of the present invention display an image of an operating region together with an overlay of representations of various objects in the operating region to facilitate the user&#39;s orientation within the image. For example these objects can include points that the user has identified or marked, or which have been identified or marked for the user. The objects can alternatively or additionally include shapes, for example closed loops identifying openings in the operating region. The objects can also be reconstructions of medical devices in the operating region, based upon mathematical models of the devices or position information from a localization system. The positions and shapes of the representations automatically change as the imaging plane changes when the imaging beam and imaging plate move about the operating region. Thus the user does not lose the points of reference and landmarks that he or she may have been using prior to the reorientation of the imaging system. This reorientation can occur frequently during medical procedures as the imaging system is moved to accommodate other equipment in the procedure room (e.g. a magnetic navigation system), or when the user desires a different imaging angle to better observe the procedure. 
     In one embodiment the imaging system consists of an imaging beam source, an imaging plate, an imaging processor, for processing the imaging data collected by the imaging plate, and a display for displaying the image from the processed imaging data. This imaging system can be used in conjunction with another system, such as a navigation system for orienting the a medical device in the operating region in the subject, or a medical localization system for determining the location of a medical device in the operating region in the subject. Whether using the navigation system or the localization system, the user can generally identify points of interest, for example anatomical land marks or points of physiological interest. Representations of these points can be displayed on the image of the operating region from the imaging system, to help the user visualize the operating region and the procedure. However, in addition to overlaying the representation on a static image from the imaging system, the overlay can be dynamically adjusted as the imaging plane changes so that the objects not only remain on the display, but the remain in the correct position and orientation relative to the displayed image and the displayed image changes. 
     The method can be implemented in several ways as illustrated by  FIGS. 4A and 4B . In one embodiment, shown schematically in  FIG. 4A , the navigation or localization system receives information about the location of the imaging beam source and the imaging receiver, and uses this information to determine where objects of known locations in the operating region should appear on the image generated by the imaging system. More specifically, the imaging system  100  can provide the navigation system (or localization system)  102  with information about the position/orientation of the imaging beam source  104  and the imaging receiver  106 . (This is represented by arrow  108 ). Using this information the navigation system (or localization system)  104  can determine where an object of known position in the operating region should appear in an image generated by the imaging system. This information can be communicated back to the imaging system  100  so that the selected objects can be overlaid in the proper location and orientation on the image generated by the imaging system, and displayed on the display  110 . (This is represented by arrow  112 ) 
     As the imaging beam source  104  and imaging receiver  106  move, the information provided by the imaging system to the navigation system (or the localization system), and the resulting information provided by the navigation system (or the localization system) to the imaging system is updated. (This is represented by arrow  114 ). So that representations of the selected objects can be overlaid on the images from the imaging system are updated as the imaging system moves about the operating region. 
     As shown in  FIG. 4B , the navigation system (or the localization system)  102  can provide the imaging system with the positions of objects in the operating region. The imaging system  100  can use this information to determine where the objects should appear in an image generated by the imaging system, using the known position of the imaging beam source  104  and imaging receiver  106 , and then overlay representations of the objects on the image generated by the imaging system on the display  110 . 
     As the positions of the imaging beam source and imaging receiver change, the imaging system can redetermine where the objects should appear in an image generated by the system in the new configuration, and overlay the representations of the object on the image generated by the imaging system, so that the representations of the objects are updated as the imaging system moves about the operating region. 
     An example of a display from a graphical user interface from a magnetic navigation system is shown in  FIG. 5 . The interface in  FIG. 5  allows the user to import images from an x-ray imaging system, and display them in windows in the display. The magnetic navigation system allows the user to identify points in the operating region and show these points on an overlay on the image from the imaging system. The overlay becomes “persistent” such that as the imaging system is moved about the operating region, and another image is made of the operating region, the overlay is adjusted in position and/or orientation so that it correctly shows the points on the new image. This is illustrated in  FIG. 5  in which two images from the operating region in different directions are depicted in side by side panes on the interface, and the overlaid objects are properly positioned and oriented in each, 
       FIG. 6A  shows an x-ray image of an anatomical model of a human heart taken in a direction 26° to the left anterior side. An object, and more specifically a representation of a ring  200  constructed from a plurality of points  202  is overlaid on the x-ray image.  FIG. 6B  shows an x-ray image of the anatomical model taken in a direction 26° to the right anterior side (i.e., rotated 52° from  FIG. 6A ). The representation of the ring  200  and constituent points  202  in  FIG. 6B  have been rotated from  FIG. 6A  in accordance with the principles of this invention, to remain in the proper orientation with respect to the image in the new imaging direction. 
       FIG. 7A  shows an x-ray image of an anatomical model of a human heart taken in a direction 25° to the left anterior side. Objects, and more specifically a plurality of annotations including an “E”  204 , an “F”  206 , and a “G”  208  are overlaid on the x-ray image.  FIG. 7B  shows an x-ray image of the anatomical model taken in a direction 27° to the right anterior side (i.e., rotated 52° from  FIG. 7A ). The representation of the annotations “E”  204 , “F”  206 , and “G”  208  in  FIG. 7B  have been rotated from  FIG. 7A  in accordance with the principles of this invention, to remain in the proper orientation with respect to the image in the new imaging direction. 
       FIG. 8A  shows an x-ray image of an anatomical model of a human heart taken in a direction 25° to the left anterior side. An object. and more specifically a catheter  210  is overlaid on the x-ray image. The representation of catheter  210  can be generated from localization data of one or more points on the corresponding real catheter in the operating region. Alternatively, the representation of the catheter  210  can be generated from a mathematical model of the actual catheter in the operating region (for example using the control variable from the navigation system). 
       FIG. 8B  shows an x-ray image of the anatomical model taken in a direction 8° to the right anterior side (i.e., rotated 33° from  FIG. 8A ). The representation of the catheter  210  in  FIG. 8B  has been rotated from  FIG. 8A  in accordance with the principles of this invention, to remain in the proper orientation with respect to the image in the new imaging direction.  FIG. 8C  shows an x-ray image of the anatomical model taken in a direction 27° to the right anterior side (i.e., rotated 19° from  FIG. 8B ). The representation of the catheter  210  in  FIG. 8C  has been rotated from  FIG. 8B  in accordance with the principles of this invention, to remain in the proper orientation with respect to the image in the new imaging direction. 
       FIG. 9A  shows an x-ray image of an anatomical model of a human heart taken in a direction 25° to the left anterior side. Objects, and more specifically representations of points  212 ,  214 , and  216  in the operating region are overlaid on the x-ray image.  FIG. 9B  shows an x-ray image of the anatomical model taken in a direction 16° to the right anterior side (i.e., rotated 9° from  FIG. 9A ). The representation of the points  212 ,  214  and  216  in  FIG. 8B  have been rotated from  FIG. 9A  in accordance with the principles of this invention, to remain in the proper orientation with respect to the image in the new imaging direction.  FIG. 9C  shows an x-ray image of the anatomical model taken in a direction 6° to the left anterior side (i.e., rotated 3° from  FIG. 9B ). The representation of the points  212 ,  214 , and  216  in  FIG. 9C  has been rotated from  FIG. 9B  in accordance with the principles of this invention, to remain in the proper orientation with respect to the image in the new imaging direction.  FIG. 9D  shows an x-ray image of the anatomical model taken in a direction 17° to the right anterior side (i.e., rotated 23° from  FIG. 9C ). The representation of the points  212 ,  214 , and  216  in  FIG. 9D  has been rotated from  FIG. 9C  in accordance with the principles of this invention, to remain in the proper orientation with respect to the image in the new imaging direction.  FIG. 9E  shows an x-ray image of the anatomical model taken in a direction 27° to the right anterior side (i.e., rotated 10° from  FIG. 9D ). The representation of the points  212 ,  214 , and  216  in  FIG. 9E  has been rotated from  FIG. 9D  in accordance with the principles of this invention, to remain in the proper orientation with respect to the image in the new imaging direction.