Patent Application: US-2262008-A

Abstract:
methods and apparatus provide continuous guidance of endoscopy during a live procedure . a data - set based on 3d image data is pre - computed including reference information representative of a predefined route through a body organ to a final destination . a plurality of live real endoscopic images are displayed as an operator maneuvers an endoscope within the body organ . a registration and tracking algorithm registers the data - set to one or more of the re images and continuously maintains the registration as the endoscope is locally maneuvered . additional information related to the final destination is then presented enabling the endoscope operator to decide on a final maneuver for the procedure . the reference information may include 3d organ surfaces , 3d routes through an organ system , or 3d regions of interest , as well as a virtual endoscopic image generated from the precomputed data - set . the preferred method includes the step of superimposing one or both of the 3d routes and rois on one or both of the re and ve images . the 3d organ surfaces and routes may correspond to the surfaces and paths of a tracheobronchial airway tree extracted , for example , from 3d mdct images of the chest .

Description:
this invention resides in a system - level approach to guidance of endoscopy , including a complete paradigm for real - time image - based guidance providing a physician with continuously - updated navigational and guidance information . at least three novel embodiments for guidance of endoscopy are disclosed . additional elements such as global surface rendering , local cross - sectional views , and pertinent distances provide additional utility to the physician . phantom results were generated using bronchoscopy performed on a rapid prototype model of a human tracheobronchial airway tree . the system has also been tested in ongoing live human tests . ten such tests have been performed thus far and focus on bronchoscopic intervention of pulmonary patients using 3d chest ct . this disclosure presents generally applicable methods , but focuses on the chest and bronchoscopy . in this domain , phase i centers around acquisition and analysis of an mdct image , where the rois may be lymph nodes , suspect cancer nodules , diffuse infiltrates , airway stent locations , or any other clinically - significant locations . 8 , 10 at least three integrated system - level approaches for real - time image - based guidance of endoscopy are described . these approaches present novel guidance strategies and are possible because of fast ct - video registration engines that we have previously proposed . 36 , 37 the high speed of these registration engines allows continuous registration of the video at a real - time video frame rate . the approach has general applicability to colonoscopy for the colon , sinoscopy for the sinuses and angioscopy for the vasculature . phantom and live patient results are also presented . our approach for continuous guidance of endoscopy relies on multiple inputs , as depicted in fig1 . the first of these inputs is the live real endoscopic ( re ) video of the anatomy of interest , provided by the endoscope during the endoscopic procedure . the quantity i re θ j ( i , j ) denotes the ( i , j ) th pixel of the j th 2d re video frame captured from the re camera &# 39 ; s unknown viewpoint θ f =( x , y , z , α , β , γ ) where ( x , y , z ) denotes the 3d spatial location and ( α , β , γ ) denotes the euler angles specifying the orientation of the re camera with respect to the radiological image &# 39 ; s 3d coordinate axes . the remaining inputs are derived from the 3d image of the anatomy of interest , which is acquired during the preoperative planning phase in advance of the procedure . these inputs include 3d surfaces depicting the interior surface of the hollow organ , the rois depicted as 3d regions defined within the scan data , and precomputed 3d paths p k through the hollow organ to reach these rois . each path consists of a set of 6d viewpoints known as viewing sites . the l th viewing site of the k th path , denoted by p k ( l ), is comprised of ( x , y , z ) location and orientation parametrized by the euler angles ( α , β , γ ). we work primarily with bronchoscopy , where the endoscopic device is a bronchoscope , and where the 3d surfaces and paths correspond to the surfaces and central axes of the tracheobronchial airway tree , as extracted from a 3d mdct image of the chest . the rois in this domain may be lymph nodes , suspect tumors , narrowed airways , or any other diagnostically relevant regions visible in the 3d mdct image . the guidance system comprises a computer displaying the live real endoscopic ( re ) video side - by - side sometimes with a depiction of the interior surface data . the camera parameters — e . g ., field of view ( fov )— used to present this surface data match those extracted by calibration of the endoscopic device . thus , this depiction constitutes a virtual endoscopic ( ve ) camera . the ve camera can therefore synthesize ve images i ve θ v at arbitrary virtual viewpoint θ v within the ct volume . let { circumflex over ( θ )} f denote the registered ve viewpoint that represents the best estimate of the re camera &# 39 ; s unknown viewpoint ( i . e ., { circumflex over ( θ )} f ≈ θ f ) and therefore i ve { circumflex over ( θ )} f denotes the registered ve view . the portions of the 3d path and rois visible within the ve camera &# 39 ; s fov can be projected to form a layer image i p θ v and appear superimposed on the ve view as depicted in fig2 and others . we denote this blending process by the ⊕ operator and define the superimposed ve view as i ve + p θ v ≡ i ve θ v ⊕ i p θ v . the ve camera can be moved independently of the endoscope , allowing the extracted anatomy to be freely navigated and explored . in fig2 , the bottom two panes statically display the re view from a previous time instant s , while the top two panes dynamically display the current live re video view i re θ f ⊕ i p { circumflex over ( θ )} f and registered ve view i ve + p { circumflex over ( θ )} f . each view has the 3d paths and roi overlaid . this saved view is useful for keeping an overview of the local area when performing biopsies . the above inputs and system provide the basis for three endoscopic guidance strategies . strategy i centers around registrations performed at discrete decision points ( e . g ., bifurcations of the airway tree ). each registration presents the physician with the correct path on which to continue in order to reach the roi and , if close enough , presents the location of the roi itself . in contrast , continuous registration / tracking is at the core of strategy ii and allows the registered ve view i ve + p { circumflex over ( θ )} f to be displayed synchronously with the live re video i re θ f . in order to simplify the view presented to the physician , strategy iii refines upon strategy ii by presenting only the 3d paths and rois fused onto the re video ( i re θ f ⊕ i p { circumflex over ( θ )} f ), dispensing altogether with the ve view . the three strategies are integrated ; each strategy builds upon the previous one and any combination of these strategies may be used for guidance to a particular roi . the methods are presented below along with a more concrete step - by - step example for the case of bronchoscopy . the goal of strategy i is to provide guidance at key decision points ( e . g , bifurcation points ) along the path to each roi . as such , this method centers on discrete registration / tracking events at each of these decision points . the method proceeds as follows : 1 . a ve view i ve + p θ v0 , displaying the 3d path and rois , is presented at an initial reference location θ v 0 = p k ( l 0 ) along the path to the current roi ( e . g ., main carina for bronchoscopy ). 2 . the physician moves the endoscope so it is within the vicinity of the ve view . 3 . a combined registration / tracking may optionally be invoked , thereby making the virtual 3d space registered to the current viewpoint of the endoscope ( i . e ., the viewpoint of the re camera is estimated and the ve camera matches this viewpoint : θ v ={ circumflex over ( θ )} f ). at this point , the precomputed 3d path and rois may also be superimposed on the re video frame ( i re θ f ⊕ i p { circumflex over ( θ )} f ). the physician may then maneuver and handle the endoscope locally , with the 3d path and rois properly adjusting their positions on the superimposed view to account for the local scope movement . additionally , an instantaneous snapshot of the current registered views may be saved and displayed alongside the continuously - updating ve i ve + p { circumflex over ( θ )} f and re i re θ f ⊕ i p { circumflex over ( θ )} f views to provide , for example , an overview of the biopsy site before moving close to the surface to perform the biopsy . an example of this saved view is displayed in fig2 . as with each of the three strategies , the 3d path and rois i p { circumflex over ( θ )} f may be toggled at any point to allow unobscured observation of the re video i re θ f . alternately , display of the roi may be automatically suppressed if the endoscope has not reached the local vicinity of the destination . 4 . the registration / tracking operation is temporarily halted and the ve camera is moved further along the desired path ( θ v i ← p k ( l i )), closer to the 3d roi . 5 . steps 2 - 4 are repeated until the endoscope is within the local vicinity of the destination . the roi ( if previously suppressed ) can now appear in order to provide an unambiguous signal that the target location ( e . g ., the proper local airway branch ) has been reached . 6 . an additional graphical icon is introduced to confirm that the biopsy site of interest is within the current field of view . previous works have used transparency - based rendering to fuse an roi onto a rendered anatomical region such as an airway lumen , but this results in ambiguity in the actual location of the roi . with the added feature of the icon — an arrow in the case of fig2 and 6 — this ambiguity is eliminated . an example of this method is shown in fig6 in the results : ( rows 1 - 3 ) show steps 1 - 4 for the first two decision points . at each of these locations , the roi is initially suppressed to avoid distraction . upon arriving at the local vicinity of the destination ( rows 4 , 5 ), the 3d roi and graphical icon appear to unambiguously display the location of the biopsy site . at this point , a saved registration view may be invoked ( see fig2 ) to further increase the physician &# 39 ; s confidence in choosing a biopsy location . strategy i presents a framework for discrete registrations along a path to an roi . with the previously - proposed registration / tracking methods , 36 , 38 these discrete registration events are not only nearly instantaneous , allowing this process to be time - efficient , but also continuously update in real - time to reflect local changes in the viewpoint of the endoscope . this is a major improvement over prior guidance methods , such as those in the references that incorporated discrete static registrations on buffered video frames . 28 - 35 because registration / tracking methods are already fast enough to allow the ve view to be continuously synchronized with the video , we propose a variant of strategy i that incorporates continuous registration as an alternative to the discrete registration in step 3 . in this alternate strategy , after the initial registration is done ( steps 1 and 2 above ), registration can be performed continuously on the incoming video : the physician freely moves the endoscope , and the ve view continuously updates , assisting the physician to move the endoscope along the proper path to the roi . as with strategy i , display of the rois can be suppressed until within the local vicinity of the destination , and the 3d paths and rois can be toggled to provide the physician with additional guidance information or with unobscured visualization of the re video . this alternate framework defines strategy ii . 1 . a ve view i ve + p θ v0 , is presented at an initial reference location θ v 0 = p k ( l 0 ) along the path to the current roi . 2 . the physician moves the endoscope so it is within the vicinity of the ve view i ve + p θv 0 . 3 . continuous registration / tracking is activated , thereby making the virtual 3d space registered to the current position of the endoscope ( i . e ., θ v f ={ circumflex over ( θ )} f ∀ f ). at this point , the 3d path and rois ( if not suppressed ) may optionally be superimposed on the re video i re θ f ⊕ i p { circumflex over ( θ )} f as shown in fig3 . during continuous registration , the ve view ( right ) moves synchronously with the re video ( left ). likewise , the 3d roi and paths can be superimposed in real - time on the re video to provide guidance information . distances to the roi center and surface are shown in white . in addition , hovering the cursor above the roi displays distances to the airway and roi surfaces at that particular point . 4 . as the physician moves the endoscope along the proper path to the roi , the ve view i ve + p { circumflex over ( θ )} f and re view i re θ f ⊕ i p { circumflex over ( θ )} f , both including 3d paths and rois ( if not suppressed ), continuously updates until either the roi is reached or an unsatisfactory registration result is produced . 5 . in the case of an unsatisfactory registration result , continuous registration / tracking is deactivated , the ve view returns to the last known good location along the path ( θ v ← p k ( l n )) and navigation proceeds as normal from step 2 . 6 . when the endoscope is within the local vicinity of the destination , the roi ( if previously suppressed ) now appears superimposed in real - time on the ve and re views in order to provide an unambiguous signal that the target location ( e . g , the proper local airway branch ) has been reached . 7 . an additional graphical icon is introduced to confirm that the biopsy site of interest is within the current field of view . previous works have used transparency - based rendering to fuse an roi onto a rendered anatomical region such as an airway lumen , but this results in ambiguity in the actual location of the roi , with the added feature of the icon — an arrow in the case of fig2 and 6 — this ambiguity is eliminated . during continuous registration / tracking in strategy ii , there is little information presented by the ve view i ve + p { circumflex over ( θ )} f that is not already present in the augmented re video with superimposed paths and rois i re θ f ⊕ i p { circumflex over ( θ )} f . hence , a variant of strategy ii is to dispense with this unnecessary ve view i ve + p { circumflex over ( θ )} f during continuous registration and present only the re video with continuously - updated paths and rois superimposed thereon i re θ f ⊕ i p { circumflex over ( θ )} f , as shown in fig4 . as with strategies i and ii , these 3d path and roi elements may be toggled on / off at any point to allow unobscured inspection of the organ surface in the re video i re θ f . in fig4 , three viewpoints are shown along the path to the roi . in strategy iii , the ve view is not displayed . only the live re view i re θ f ⊕ i p { circumflex over ( θ )} f is shown , with path and roi information i p { circumflex over ( θ )} f superimposed on each video frame i re θ f in real - time . in each case , a colored line indicates the proper path to the roi . an external rendering of the airway tree is shown next to the re video pane , indicating the position of the endoscope tip updating in real - time . 1 . a ve view i ve + p θv 0 is presented at an initial reference location θ v 0 = p k ( l 0 ) along the path to the current roi . 2 . the physician moves the endoscope so it is within the vicinity of the ve view i ve + p θv 0 . 3 . continuous registration / tracking is activated , thereby making the virtual 3d space registered to the current position of the endoscope ( i . e ., θ v f ={ circumflex over ( θ )} f ∀ f ). at this point , the ve view i ve + p θv is hidden , and the 3d paths and rois ( if not suppressed ) are superimposed on the re video i re θ f ⊕ i hu { circumflex over ( θ )} f . note that in this strategy , because there is no ve view , the 3d paths superimposed on the re video are critical to guidance . however , they can still be temporarily toggled off to provide unobscured inspection of the re video i re θ f . 4 . as the physician moves the endoscope along the proper path to the roi , the re view i re θ f ⊕ i p { circumflex over ( θ )} f , including the 3d paths and rois ( if not suppressed ) continuously updates until either the target location is reached or an unsatisfactory registration result is produced . 5 . in the case of an unsatisfactory registration result , continuous registration / tracking is deactivated , the ve view is restored and displays the last known good location along the path ( θ v ← p k ( l n )). navigation then proceeds as normal from step 2 . 6 . when the endoscope is within the local vicinity of the destination , the roi ( if previously suppressed ) now appears superimposed in real - time on the re view i re θ f ⊕ i p { circumflex over ( θ )} f in order to provide an unambiguous signal that the target location ( e . g ., the proper local airway branch ) has been reached . 7 . in order to eliminate the ambiguity in the location of the roi , an additional graphical icon ( e . g ., an arrow similar to those in fig2 and 6 ) may optionally be introduced and blended with the re view i re θ f ⊕ i p { circumflex over ( θ )} f to confirm that the biopsy site of interest is within the current field of view . the above three methods provide the basic strategies for guidance of endoscopy . at times prior to and during endoscopy , it is useful to provide the physician with additional information , which updates continuously or with each discrete registration . distances may be displayed , including : 1 ) the distance from the endoscope tip to the roi center ; and 2 ) minimum distance from endoscope tip to the roi surface . hovering the mouse over a point in the ve view i ve + p θv or registered re view also i re θ f ⊕ i p { circumflex over ( θ )} f provides additional distances specific to that point . these include : 1 ) the distance from endoscope tip to the organ surface ; and 2 ) the distance from the endoscope tip to the roi surface . our system provides a global 3d surface renderer to display a global exterior view of the organ ( e . g ., airway tree ) surface and rois , as well as the 3d paths . local cross - sectional slices of the 3d data along and perpendicular to the endoscope viewing direction enable the physician to determine what lies between the tip of the scope and the roi . this is useful for avoiding arteries and other organs when performing a biopsy . the methods were incorporated into a computer gui software package on a standard pc and have been tested with phantoms as well as live human subjects . for the phantom study , step - by - step results are presented for guidance to an roi . for live human testing , a screen capture is presented from one of the 10 subjects for which this method was successfully used . phantom results demonstrate that the guidance methods and system can be successfully used as a navigational aid to guide a physician to rois within a patient . the phantom used was a red abs plastic rapid prototype model and was created from the endoluminal airway surfaces extracted from an mdct scan of human patient 21405 . 3a . the mdct scan was acquired by a 16 - detector siemens sensation - 16 scanner , and consists of 706 512 × 512 slices with resolution of δx = δy = 0 . 67 mm , δz = 0 . 5 mm . guidance was performed using an olympus bf type xp260f ultrathin bronchoscope with 2 . 8 mm distal tip diameter , and the bronchoscopic video was captured during the procedure by a matrox meteor - ii video capture card at 30 frames per second . the video generated by this bronchoscope is circular and fits within a 288 × 290 pixel bounding box . upon capture , the significant barrel distortion of the wide field - of - view ( fov ) lens is corrected for each frame in real - time using the model of zhang 39 and the distortion - corrected video is subsequently cropped to a rectangle measuring 292 × 313 pixels . preoperative planning and guidance were performed on a dell precision 650 workstation with a dual - core 3 . 0 ghz pentium processor , 4 gb ram and 512 mb ati radeon video card , running windows xp . all system software was built using visual c ++. net 2003 and developed in - house . prior to phase - i preoperative planning by a physician , the endoluminal airway tree surfaces and centerlines were automatically extracted from the mdct image . for this study , a spherical roi was then defined manually , with 2 . 4 mm diameter and touching , but external to the endoluminal airway surfaces . the roi — located between the right middle lobe takeoff and the right lower lobe — is displayed along with the endoluminal surfaces in fig5 . in clinical practice , this step would be performed by the physician . as a final automated preoperative planning step , the centerline path with closest approach to each roi was computed and stored . 40 in fig5 , global external 3d surface rendering displays the location of the roi used for phantom testing . the roi resides at the bifurcation point between the right lower lobe and right middle lobe bronchi . all phase - i analysis and phase - ii guidance is performed using an integrated software system developed within our lab . the system consists of several interactive tools to manipulate and visualize the preprocessed anatomical dataset ( raw 3d image , rois , endoluminal surfaces and centerlines , recorded snapshots and avi movies , etc .) these tools include : multiplanar reformatted ( mpr ) slicers , useful for viewing , measuring and defining rois within the raw data ; projection , sliding thin slab , oblique cross - section , shear - warp and volume renderers , useful for more complex visualization of the raw image data ; endoluminal and extraluminal 3d surface renderers , providing visualization of endoluminal airway surfaces from the interior and exterior ; and video match tools , providing the basis for guidance with the ability to register live endoscopic video with ct - derived endoluminal renderings . a more complete description of this system and its tools is provided by higgins et at . 34 during phase - i analysis , the endoscopist views the location of the roi on the transverse slicer as is standard practice , but is also presented with the extraluminal 3d surface renderer ( e . g ., fig5 ), which provides an anatomical overview of each roi &# 39 ; s location . the endoscopist also plays an endoluminal fly - through movie along the path to each roi , in order to preview the actual endoscopy . phase - ii begins by interfacing the virtual endoscopy system with the endoscope . the virtual endoscopy software is then invoked , displaying the extraluminal renderer and the ct - video matching tool , and the previously computed closest path is selected , which highlights this path in blue in both of these tools . at this point the video capture begins , providing the endoscopic video source for the ct - video matching tool to process and display . for the roi depicted in fig5 , each step along the path to the roi is shown in fig6 . in each case , a 3d surface rendering displays the location of the ve camera within the endoluminal airway tree , while the re video i re θ f is displayed side - by - side with the ve view i ve + p { circumflex over ( θ )} f . row 1 , left : the ve view is positioned near the main carina ; right : the endoscopist moves the re camera to near the main carina . row 2 , left : registration / tracking is invoked at the main carina . the paths now appear overlaid on the re view with i re θ f ⊕ i p { circumflex over ( θ )} f with the blue path highlighting the proper path to reach the roi ; right : the ve view i ve + p θ η is moved to the second generation bifurcation . row 3 , left : the endoscopist follows the path taken by the ve view to arrive at the same bifurcation ; right : a registration is performed , and the path again appears on the re view i re θ f ⊕ i p { circumflex over ( θ )} f . row 4 , left : the ve view is moved to final bifurcation point ; right : endoscopist follows the ve motion . row 5 , left : a registration is performed , highlighting the location of the roi on the re view i re θ f ⊕ i p { circumflex over ( θ )} f ; right : continuous registration / tracking allows the 3d paths and roi to move synchronously with the re video view i re θ f ⊕ i p { circumflex over ( θ )} f as the physician moves the endoscope . initially , the ve view i ve + p θv and the re i re θ f view are unregistered . as in step 1 of strategy i , the ve view i ve + p θv 0 is moved to an easily identified initial location θ v 0 = p k ( l 0 ) ( just before the main carina in this case ), as depicted in the left half of row 1 . following step 2 , the physician moves the endoscope to the vicinity of the ve view , depicted in the right half of row 1 . per step 3 , a registration is performed , bringing the ve view i ve + p { circumflex over ( θ )} f and re video i re θ f into alignment ( θ v ←{ circumflex over ( θ )} f ). this allows the fusion of path and roi information i p { circumflex over ( θ )} f from from the ve view onto the re video data i re θ f to form a fused re view i re θ f ⊕ i p { circumflex over ( θ )} f . this is shown on the left half of fig6 , row 2 . because the correct path p k to reach the roi is computed a priori and is overlaid on the re video in blue , there is no ambiguity as to which direction to proceed . proceeding to step 4 , the ve camera is advanced along the path to the second bifurcation ( θ v ← θ v 1 ≡ p k ( l 1 )), beginning the second iteration of the process . again , the physician follows the motion of the ve camera , and a registration is performed , as shown in row 3 of fig6 . in row 4 , the ve camera is moved 1 bifurcation further down the path ( θ v ← θ v 2 ≡ p k ( l 2 )), and the physician again follows the motion of the virtual endoscope . at this point , the roi ( displayed in green ) is clearly visible in the ve view i ve + p θv 2 at the bifurcation point . row 5 shows the result of registration , with the re view i re θ f ⊕ i p { circumflex over ( θ )} f , including superimposed paths and rois shown alongside the registered ve view i ve + p { circumflex over ( θ )} f . in this case , registration was allowed to proceed continuously as the endoscope was moved in real - time around the local region . as the scope is moved closer to the bifurcation point ( right half of row 5 ), the location of the roi becomes very apparent with an icon indicating a possible approach to the roi . in addition to phantom studies , this system has also been tested in ongoing live human tests using strategies i and ii for portions of each case . ten such cases have been performed as of the submission of this paper and focus on bronchoscopic intervention of pulmonary patients using 3d chest ct . fig7 is a screen capture taken during human case 20349 . 3 . 9 , showing the layout of the overall virtual endoscopy system during a registration and just prior to a tbna procedure . the bottom left window displays a global rendering of the tracheobronchial tree and rois , with the position and orientation of the bronchoscope tip shown by the sphere and needle . the appropriate path to the selected roi is also shown . the ct - video matching tool resides in the top window and displays the live bronchoscopic video feed on the left and the registered ve view on the right . both views have the paths and rois transparently superimposed . the bottom center windows shows a cross - sectional view at the location of the endoscope tip , and is useful for determining what types of tissue lie beyond the airway walls that could potentially hinder biopsy . the window on the bottom right displays the transverse slice at the endoscope &# 39 ; s current location and is similar to the radiologic slices a physician is accustomed to examining in standard practice . this invention provides at least three integrated methods for continuous real - time image - based guidance of endoscopy . the methods build on each other and are not mutually exclusive ; any combination of the methods may be used for guidance during an endoscopic guidance procedure . the framework presented is the first such paradigm to incorporate real - time 3d radiologic images and endoscopic video registration . this enables real - time guidance that provides the physician with continuously - updated precise navigational information . the methods are a significant improvement over the current standard clinical workflow , which requires a physician to mentally reconstruct 3d structures from 2d transverse slices of the 3d scan data and later navigate to the rois with no guidance . the methods also improve upon past systems incorporating image - 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