Patent Publication Number: US-2023145993-A1

Title: Apparatuses and Methods for Registering a Real-Time Image Feed From an Imaging Device to a Steerable Catheter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of U.S. Ser. No. 16/682,132, filed on Nov. 13, 2019, which in turn is a continuation of U.S. Ser. No. 15/208,534, filed on Jul. 12, 2016, which in turn is a continuation of U.S. Ser. No. 14/259,362, filed on Apr. 23, 2014. All of these applications are hereby incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     The invention relates generally to medical devices and particularly to apparatuses and methods associated with a range of image guided medical procedures for detecting, sampling, staging and/or treating target tissues in the lungs of a patient. 
     Image guided surgery (IGS), also known as image guided intervention (IGI), enhances a physician&#39;s ability to locate instruments within anatomy during a medical procedure. IGS can include 2-dimensional (2D), 3-dimensional (3D), and 4-dimensional (4D) applications. The fourth dimension of IGS can include multiple parameters either individually or together such as time, motion, electrical signals, pressure, airflow, blood flow, respiration, heartbeat, and other patient measured parameters. 
     Although significant improvements have been made in these fields, a need remains for improved medical devices and procedures for visualizing, accessing, locating, real-time confirming while sampling and manipulating a target tissue. 
     SUMMARY OF THE INVENTION 
     Among the various aspects of the present invention may be noted apparatuses for use in and methods associated with medical procedures; such apparatuses and methods, for example, may include apparatuses and methods that enhance a physician&#39;s ability to confirm the location of a target tissue within a patient during a medical procedure, such as image guided surgery (IGS) or image guided intervention (IGI) and such apparatuses and methods may further include apparatuses and methods that facilitate visualizing, accessing, locating, and manipulating the targeted tissue. 
     Briefly, therefore, one aspect of the present invention is a method of confirming the location of a target tissue within a patient using a navigation system. The navigation system comprises a localization device, a display, and a pre-acquired image dataset of an airway of the patient. The navigation system is adapted to display images from the image dataset and to provide location information of a medical device within the patient in relation to a patient tracking device comprising a plurality of localization elements. The method comprises affixing the patient tracking device to an external surface of the patient, tracking the location of the patient tracking device using the navigation system, displaying an image from the image dataset on the display, wherein the displayed image is registered to the patient tracking device, and determining an initial location of the target tissue in the image dataset and navigating a steerable catheter through the airway of the patient to a position proximate the initial location. The steerable catheter has a proximal end portion and a distal end portion terminating in a tip, a working channel extending there between, and a localization element disposed proximate the distal end portion thereof. The method further comprises tracking the location of the localization element of the steerable catheter in the airway using the navigation system, generating information regarding the presence of the target tissue using a tissue sensing device inserted into the working channel of the steerable catheter, and determining a confirmed location of the target tissue using the generated information regarding the presence of the target tissue and the tracked location of the localization element. The method further comprises recording the confirmed location of the target tissue and, displaying the confirmed location of the target tissue on the display of the navigation system in an image from the image dataset. 
     Another aspect of the present invention is a method of navigating a percutaneous needle to a target tissue within a patient using a navigation system. The navigation system comprises a localization device, a display, and a pre-acquired image dataset of an airway of the patient. The navigation system is adapted to display images from the image dataset and to provide location information of a medical device within the patient in relation to a patient tracking device comprising a plurality of localization elements. The method comprises affixing the patient tracking device to an external surface of the patient, tracking the location of the patient tracking device using the navigation system to monitor the respiratory state of the patient, and displaying an image from the image dataset on the display as a function of the monitored respiratory state, wherein the displayed image is registered to the patient tracking device. The method further comprises determining an initial location of the target tissue in the image dataset and navigating a steerable catheter through the airway of the patient to a position proximate the initial location. The steerable catheter has a proximal end portion and a distal end portion terminating in a tip, a working channel extending there between, and a localization element disposed proximate the distal end portion thereof. The method further comprises tracking the location of the localization element of the steerable catheter in the airway using the navigation system, generating one or more images of the target tissue using an imaging device inserted into the working channel of the steerable catheter, and determining a confirmed location of the target tissue in relation to the patient tracking device using the generated images and the tracked location of the localization element. The method further comprises recording the confirmed location of the target tissue, the recording comprising four-dimensional data comprising a three-dimensional location of the confirmed target tissue in relation to the patient tracking device and the respiratory state of the patient at the time the location of the target tissue was confirmed and applying the confirmed location of the target tissue to an image from the image dataset depicting the airway at the respiratory state of the patient at the time the location of the target tissue was confirmed. The method further comprises displaying the confirmed location of the target tissue on the display of the navigation system in an image from the image dataset, the displayed image depicting the airway at the respiratory state of the patient at the time the location of the target tissue was confirmed. Furthermore, the method comprises displaying a trajectory of a percutaneous device from an entry point on the patient&#39;s body to the confirmed location on the display of the navigation system, wherein the percutaneous device includes a localization element, inserting the percutaneous device into the patient and navigating the percutaneous device to the confirmed location, and intercepting the target tissue at the confirmed location. 
     Another aspect of the present invention is a method of navigating a medical device to the confirmed location of the target tissue using indicia indicating the confirmed location of the target tissue and/or indicia indicating the location of the medical device. Thus the method may include displaying the confirmed location of the target tissue on the display of the navigation system without requiring that an image of the image dataset be displayed. This method of navigating a medical device to the confirmed location of the target tissue does not require re-registering one or more image datasets to the patient so long as the patient tracking device affixed to the patient does not move or the patient does not move relative to an electromagnetic field generator of the navigation system. Therefore, this method does not require displaying a hybrid “Inspiration-Expiration” 3D airway model, one or more images from one or more image datasets, a navigation pathway, and/or a real-time image feed from a bronchoscopic video camera, in order to permit a physician or other healthcare professional in navigating a medical device to the confirmed location of the target tissue. 
     Another aspect of the present invention is directed to a method of registering a real-time image feed from an imaging device inserted into a steerable catheter using a navigation system comprising a display. The steerable catheter comprises an elongate flexible shaft having a proximal end portion, a distal end portion terminating in a tip, a working channel extending therebetween, and handle attached to the proximal end portion of the flexible shaft. The method comprises inserting the imaging device into the working channel of the steerable catheter, generating a real-time image feed of one or more reference points, wherein the orientation of the reference points is known, orienting the handle of the steerable catheter to a neutral position, displaying the real-time image feed on the display, and registering the real-time image feed to the steerable catheter by rotating the displayed image so that the reference points in the real-time image feed are matched to the known orientation of the reference points. 
     Another aspect of the present invention is directed to a method of enhancing registration of the real-time image feed of a bronchoscopic video camera by correcting image distortion in the real time image feed. For example, bronchoscopic video cameras typically include fish-eye lenses which increase the field of view of the bronchoscopic video camera thus providing the physician or other healthcare professional with a larger view of the airway of the patient. However, the fish-eye lenses introduce barrel distortion into the real-time image feed. Due to this barrel distortion, the interpretation of the real-time image feed may be compromised. Correcting for this image distortion in the real-time image feed provides a more accurate depiction of the airway of the patient, thus permitting an enhanced registration of the real-time image feed. 
     Yet another aspect of the present invention is directed to the construction and use of a hybrid “Inspiration-Expiration” 3D airway model. The hybrid “Inspiration-Expiration” 3D airway model may be used to reduce or eliminate errors in registration. Constructing the hybrid “Inspiration-Expiration” 3D airway model comprises calculating a population of deformation vector fields, wherein the deformation vector field(s) comprise vectors from one or more voxels in inspiration images or in an inspiration 3D airway model to one or more corresponding voxels in expiration images or in an expiration 3D airway model. After the deformation vector field is calculated, the inspiration images and/or the inspiration 3D airway model may be deformed to the expiration state of the patient using the deformation vector field. Accordingly, the voxels in the inspiration images and/or inspiration 3D airway model are deformed to match the location, shape, and orientation of the airways of the patient at expiration. This results in the hybrid “Inspiration-Expiration” 3D airway model, wherein the hybrid “Inspiration-Expiration” 3D airway model contains the structural information of the airways of patient depicted in the inspiration images and/or inspiration 3D airway model. However, this structural information is now more closely matched to the location, shape, and orientation of the airways of the patient depicted in the expiration images and/or expiration 3D airway model. Accordingly, the deformation vectors represent a change in location of the structure of the airway and a change in shape of the structure of the airway from inspiration to expiration. 
     Yet another aspect of the present invention is directed to a method of injecting dye into a target tissue using a needle inserted into the working channel of a steerable catheter or using a needle inserted into the working channel of a percutaneous needle. Thus, when sampling the target tissue using a medical device inserted into the steerable catheter or percutaneous needle, the presence of dye in the sample provides an indication that the correct target tissue was sampled. This may be helpful, for example, in lung resections where there is significant movement of the lungs of the patient. For example, during lung resections there may be a gap between the chest wall and the lung and the physician or other healthcare profession may use a rigid scope to enter into the patient. Because the target tissue was previously dyed using a needle inserted into the working channel of steerable catheter or using a needle inserted into the working channel of the percutaneous needle, the physician or other healthcare professional may be able to visually see the dye. This may assist the physician or healthcare professional in sampling and/or treating the correct target tissue. 
     Yet another aspect of the present invention is directed to a method of simulating and/or displaying a variety of image views using a navigation system based on the position and orientation (POSE) of a localization element in a steerable catheter, percutaneous device, and/or some other medical device. For example, the navigation system may be able to simulate and/or display axial images, coronal images, oblique images, orthogonal image slices, oblique or off-axis image slices, volume rendered images, segmented images, fused modality images, maximum intensity projection (MIPS) images, video, and video enhanced images. To simulate these views, the navigation system may modify one or more images from an image dataset using known image manipulation techniques. The images in the image dataset may be fluoroscopic images, ultrasound images, to computed tomography (CT) images, fused computed tomography-positron emission tomography (CT/PET) images, magnetic resonance imaging (MRI) images, etc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The details of the present invention, both as to its construction and operation can best be understood with reference to the accompanying drawings, in which like numerals refer to like parts, and in which: 
         FIG.  1    left perspective view of a patient tracking device on a patient according to an embodiment of the invention; 
         FIG.  2    is a schematic illustration of an image analysis system according to an embodiment of the invention; 
         FIG.  3    is a schematic illustration of a navigation system according to an embodiment of the invention; 
         FIG.  4    is a graphical representation illustrating the function of the patient tracking device according to an embodiment of the invention; 
         FIG.  5 A  is an illustration of a patient being imaged using an imaging device according to an embodiment of the invention; 
         FIG.  5 B  is an illustration of a patient being imaged using an imaging device according to an embodiment of the invention; 
         FIG.  5 C  is a schematic illustration of an image dataset according to an embodiment of the invention; 
         FIG.  6 A  is a schematic illustration of an inspiration 3D airway model according to an embodiment of the invention; 
         FIG.  6 B  is a schematic illustration of an expiration 3D airway model according to an embodiment of the invention; 
         FIG.  6 C  is a schematic illustration of a hybrid “Inspiration-Expiration” 3D airway model according to an embodiment of the invention; 
         FIG.  7    is a front perspective view of a hybrid “Inspiration-Expiration” 3D airway model according to an embodiment of the invention; 
         FIG.  8    is a schematic illustrating vector distances of the patient tracking device according to an embodiment of the invention; 
         FIG.  9 A  is a schematic illustrating vector distances from a localization element on the patient tracking device according to an embodiment of the invention; 
         FIG.  9 B  is a schematic illustrating vector distances from an image dataset according to an embodiment of the invention; 
         FIG.  10    is a flowchart illustrating a method according to an embodiment of the invention; 
         FIG.  11    is a left side view of a steerable catheter according to an embodiment of the invention; 
         FIG.  11 A  is a left partial section view of a steerable catheter according to an embodiment of the invention; 
         FIG.  12 A  is a left partial cut away view of a steerable catheter according to an embodiment of the invention; 
         FIG.  12 B  is a left partial cut away view of a steerable catheter according to an embodiment of the invention; 
         FIG.  13    is a left side view of a percutaneous needle according to an embodiment of the invention; 
         FIG.  13 A  is a left partial cut away view of a percutaneous needle according to an embodiment of the invention; 
         FIG.  14    illustrates a population of images which may be displayed on a display of a navigation system according to an embodiment of the invention; 
         FIG.  15    is a flowchart illustrating a method of registering the real-time image feed from a bronchoscopic video camera to a steerable catheter according to an embodiment of the invention; 
         FIG.  16    is a left perspective view of a steerable catheter in a jig for registering the real-time image feed from a bronchoscopic video camera to a steerable catheter according to an embodiment of the present invention; 
         FIG.  16 A  is a front view of a steerable catheter in a jig for registering the real-time image feed from a bronchoscopic video camera to a steerable catheter according to an embodiment of the present invention; 
         FIG.  16 B  is an image from a real-time image feed from a non-registered bronchoscopic video camera in a steerable catheter according to an embodiment of the present invention; 
         FIG.  16 C  is an image from a real-time image feed from a registered bronchoscopic video camera in a steerable catheter according to an embodiment of the present invention; 
         FIG.  17    is a flowchart illustrating a method of registering the real-time image feed from a bronchoscopic video camera to a steerable catheter according to an embodiment of the invention; 
         FIG.  17 A  is a flowchart illustrating additional steps of a method of registering the real-time image feed from a bronchoscopic video camera to a steerable catheter according to an embodiment of the invention; 
         FIG.  18 A  is an image of an expected orientation of anatomical features in the airway of the patient according to an embodiment of the invention; 
         FIG.  18 B  is an image from a real-time image feed from a non-registered bronchoscopic video camera in a steerable catheter according to an embodiment of the present invention; 
         FIG.  18 C  is an image from a real-time image feed from a registered bronchoscopic video camera in a steerable catheter according to an embodiment of the present invention; 
         FIG.  19    is a section view of steerable catheter illustrating registering the real-time image feed from a bronchoscopic video camera to a steerable catheter and to a localization element of the steerable catheter according to an embodiment of the invention; 
         FIG.  20 A  is a flowchart illustrating a portion of a method of confirming the location of a target tissue according to an embodiment of the invention; 
         FIG.  20 B  is a flowchart illustrating a portion of a method of confirming the location of a target tissue according to an embodiment of the invention; 
         FIG.  20 C  is a flowchart illustrating a portion of a method of confirming the location of a target tissue according to an embodiment of the invention; 
         FIG.  20 D  is a flowchart illustrating a portion of a method of confirming the location of a target tissue according to an embodiment of the invention; 
         FIG.  20 E  is a flowchart illustrating a portion of a method of confirming the location of a target tissue according to an embodiment of the invention; 
         FIG.  21    is an image from an endobronchial ultrasound device according to an embodiment of the invention; 
         FIG.  22    illustrates a population of images which may be displayed on a display of a navigation system according to an embodiment of the invention; 
         FIG.  22 A  illustrates an enlarged view of an image which may be displayed on a display of a navigation system according to an embodiment of the invention; and 
         FIG.  23    illustrates a population of images which may be displayed on a display of a navigation system according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The accompanying Figures and this description depict and describe embodiments of a navigation system (and related methods and devices) in accordance with the present invention, and features and components thereof. It should also be noted that any references herein to front and back, right and left, top and bottom and upper and lower are intended for convenience of description, not to limit the present invention or its components to any one positional or spatial orientation. 
     Those of skill in the art will appreciate that in the detailed description below, certain well known components and assembly techniques have been omitted so that the present methods, apparatuses, and systems are not obscured in unnecessary detail. 
     With larger volumes of patients expected to obtain lung cancer screening, obtaining definitive diagnoses may avoid numerous unneeded lung resections as about only 4% of patients from lung cancer screening are typically found to have a malignancy. However, peripheral target tissues (e.g., nodule, lesion, lymph node, tumor, etc.) that are smaller than 2 cm in size still present a difficult problem to solve. Typical bronchoscopes that are designed mainly for central airway inspection will be limited to the extent they can travel due to their large diameters before becoming wedged in the airway of the patient. Thus, to affect the 5 and 10 year survival rate of patient&#39;s that have target tissues which may be less than 2 cm in size, the apparatuses and methods as described herein allow for enhanced target tissue analysis for staging, intercepting target tissues in the periphery of the lungs that may not be accessible via airways, obtaining larger and higher quality tissue samples for testing, and provide a streamlined patient flow. Accordingly, the apparatuses and methods described herein enable a physician or other healthcare professional to initially determine the location of a target tissue and to confirm the location of the target tissue. In one embodiment, a hybrid “Inspiration-Expiration” 3D model may be used to provide patient specific 4D respiratory models which address peripheral respiratory motion. In certain patients, portions of the lungs including the upper lobes may move, on average, 15 mm between inspiration and expiration. Using a steerable catheter with an imaging device, such as a radial endobronchial ultrasound (EBUS) device inserted therein, a physician or other healthcare professional can determine a confirmed location of the target tissue. Additionally, apparatuses and methods described herein enable a physician or other healthcare professional to transition to a percutaneous approach to the target tissue, if needed. If the physician or other healthcare professional is unable to reach the target tissue for any reason, including but not limited to, the target tissue being below the surface of the airway (i.e., sub-surface target tissue), no airway proximate the target tissue, the pathway to the target tissue is very tortuous, or larger or additional tissue sample from a core biopsy is desired, the physician or other healthcare professional may insert navigated percutaneous needles to the confirmed location of the target tissue. Thus it will be understood that the apparatuses and methods described herein may be used to intercept target tissue(s) in the airway, on the wall of the airway, in the wall of the airway, and/or beyond the wall of the airway. That is, the apparatuses and methods described herein may be used to intercept target tissue(s) not only inside the airway, but may intercept target tissue(s) and other anatomical structures inside and/or beyond the wall of the airway. Thus in certain embodiments, sub-surface target tissue(s) may be intercepted. 
     Additionally, the apparatuses and methods described herein provide easy to understand localization information to the physician or other healthcare professional, as well as display the preferred entry site and trajectory views of the percutaneous needle that are aligned to the target tissue. Once aligned, the physician or other healthcare professional may direct the percutaneous needle along the trajectory to the target tissue while viewing a display of the location of the tip of percutaneous needle on a navigation system as described herein. The physician or other healthcare professional may then intercept the target tissue in a variety of ways, including, but not limited to, performing a standard core biopsy, an aspiration, and/or delivering therapy using a variety of medical devices inserted through the percutaneous needle. 
     As shown in  FIG.  1   , an apparatus according to an embodiment of the invention includes patient tracking device (PTD)  20  comprising two or more markers  22  and two or more localization elements  24  proximate markers  22 . Markers  22  are visible in images captured by an imaging device and the position and orientation (POSE) of localization elements  24  may be tracked by a localization device in an image analysis system and/or a navigation system. PTD  20  comprises a population of separate pads  26 ,  28 ,  30 , each of which may include one or more markers  22  and localization elements  24  proximate markers  22 . First and second pads  26 ,  28  may each include one marker  22  and one localization element  24 . Third pad  30  may include four markers  22  and four localization elements  24  located proximate the periphery of third pad  30 . Additionally, wires  32 ,  34 ,  36  are used to connect localization elements  24  in each of first, second, and third pads  26 ,  28 ,  30  to image analysis system  50  (see  FIG.  2   ) and/or navigation system  70  (see  FIG.  3   ). In alternative embodiments, localization elements  24  may be wirelessly connected to navigation system  70 .  FIG.  1    illustrates PTD  20  having six markers  22  and six localization elements  24 , but any number of two or more markers  22  and localization elements  24  can be used. Patient tracking device (PTD)  20  can be coupled to a dynamic body such as, for example, a selected dynamic portion of the anatomy of a patient  10 . 
     Markers  22  are constructed of a material that can be viewed on an image, such as, for example, X-ray images or CT images. In certain embodiments, markers  22  can be, for example, radiopaque such that they are visible via fluoroscopic imaging. In other embodiments, for example, markers  22  may be echogenic such that they are visible via ultrasonic imaging. In yet other embodiments, markers  22  may be both radiopaque and echogenic. In certain embodiments, for example, localization elements  24  comprise six (6) degree of freedom (6DOF) electromagnetic coil sensors. In other embodiments, localization elements  24  comprise five (5) degree of freedom (5DOF) electromagnetic coil sensors. In other embodiments, localization elements  24  comprise other localization devices such as radiopaque markers that are visible via fluoroscopic imaging and echogenic patterns that are visible via ultrasonic imaging. In yet other embodiments, localization elements  24  can be, for example, infrared light emitting diodes, and/or optical passive reflective markers. Localization elements  24  can also be, or be integrated with, one or more fiber optic localization (FDL) devices. 
     While PTD  20  is shown comprising a population of separate pads containing markers  22  and localization elements  24 , in certain embodiments, PTD  20  may comprise one pad containing markers  22  and localization elements  24 . In another embodiment, for example, PTD  20  may include markers  22  but not localization elements  24 . In another embodiment, for example, PTD  20  may include localization elements  24  but not markers  22 . In various embodiments, markers  22  and localization elements  24  can be the same device. In certain embodiments, for example, localization elements  24  may function or serve as markers  22 . PTD  20  can be a variety of different shapes and sizes. For example, in one embodiment PTD  20  is substantially planar, such as in the form of a pad that can be disposed at a variety of locations on a patient&#39;s  10  body. PTD  20  can be coupled to patient  10  with adhesive, straps, hook and pile, snaps, or any other suitable coupling method. In another embodiment the PTD can be a catheter type device with a pigtail or anchoring mechanism that allows it to be attached to an internal organ or along a vessel. 
     As described more fully elsewhere herein, an image analysis system is configured to receive image data associated with the dynamic body generated during a pre-surgical or pre-procedural first time interval. The image data can include an indication of a position of each of markers  22  for multiple instants in time during the first time interval. Then a navigation system can also receive position data associated with localization elements  24  during a second time interval in which a surgical procedure or other medical procedure is being performed. The navigation system can use the position data received from localization elements  24  to determine a distance between the localization elements  24  for a given instant in time during the second time interval. The navigation system can also use the image data to determine the distance between markers  22  for a given instant in time during the first time interval. The navigation system can then find a match between an image where the distance between markers  22  at a given instant in time during the first time interval is the same or substantially the same as the distance between localization elements  24  associated with those markers  22  at a given instant in time during the medical procedure, or second time interval. Additionally, the navigation system can determine a sequence of motion of the markers and match this sequence of motion to the recorded motion of the markers over the complete procedure or significant period of time. Distance alone between the markers may not be sufficient to match the patient space to image space in many instances, the system may also determine the direction the markers are moving and the range and speed of this motion to find the appropriate sequence of motion for a complex signal or sequence of motion by the patient. 
     A physician or other healthcare professional can use the images selected by the navigation system during a medical procedure performed during the second time interval. For example, when a medical procedure is performed on a targeted anatomy of a patient, such as a heart or lung, the physician may not be able to utilize an imaging device during the medical procedure to guide him to the targeted area within the patient. Accordingly, PTD  20  can be positioned or coupled to the patient proximate the targeted anatomy prior to the medical procedure, and pre-procedural images can be taken of the targeted area during a first time interval. Markers  22  of PTD  20  can be viewed with the image data, which can include an indication of the position of markers  22  during a given path of motion of the targeted anatomy (e.g., the heart) during the first time interval. Such motion can be due, for example, to inspiration (i.e., inhaling) and expiration (i.e., exhaling) of the patient, or due to the heart beating. During a medical procedure, performed during a second time interval, such as a procedure on a heart or lung, the navigation system receives data from localization elements  24  associated with a position of localization elements  24  at a given instant in time during the medical procedure (or second time interval). The distance between selected pairs of markers  22  can be determined from the image data and the distance, range, acceleration, and speed between corresponding selected pairs of localization elements  24  can be determined based on the position and orientation (POSE) data for given instants in time. Accordingly, the range of motion and speed of markers  22  can be calculated. 
     Because localization elements  24  are proximate the location of markers  22 , the distance between a selected pair of localization elements  24  can be used to determine an intra-procedural distance between the pair of corresponding markers  22 . An image from the pre-procedural image data taken during the first time interval can then be selected where the distance between the pair of selected markers  22  in that image corresponds with or closely approximates the same distance determined using localization elements  24  at a given instant in time during the second time interval. This process can be done continuously during the medical procedure, producing simulated real-time, intra-procedural images illustrating the orientation and shape of the targeted anatomy as a catheter, sheath, needle, forceps, guidewire, fiducial delivery devices, therapy device, or similar medical device(s) is/are navigated to the targeted anatomy. Thus, during the medical procedure, the physician can view selected image(s) of the targeted anatomy that correspond to and simulate real-time movement of the anatomy. In addition, during a medical procedure being performed during the second time interval, such as navigating a catheter or other medical device or component thereof to a targeted anatomy, the location(s) of a localization element (e.g., an electromagnetic coil sensor) coupled to the catheter during the second time interval can be superimposed on an image of a catheter. The superimposed image(s) of the catheter can then be superimposed on the selected image(s) from the first time interval, providing simulated real-time images of the catheter location relative to the targeted anatomy. This process and other related methods are described in U.S. Pat. No. 7,398,116, entitled Methods, Apparatuses, and Systems Useful in Conducting Image Guided Interventions, filed Aug. 26, 2003, which is hereby incorporated by reference. 
     Referring now to  FIGS.  2  and  3   , two systems which may be used during image guided surgery are described in detail. The first system illustrated in  FIG.  2   , is image analysis system  50 . Image analysis system  50  is used during generation of a population of images of patient  10  during a first time interval, prior to a medical procedure being performed on patient  10 . The second system, illustrated in  FIG.  3   , is navigation system  70 . Navigation system  70  is used during a medical procedure performed on patient  10  during a second time interval. As will be described, imaging system  50  and navigation system  70  may include, in various embodiments, substantially similar or identical components. Accordingly, image analysis system  50  and navigation system  70  may be able to carry out substantially similar or identical functions. In certain embodiments, image analysis system  50  and navigation system  70  and may comprise a single system. In certain embodiments, for example, image analysis system  50  may also function or serve as a navigation system. In certain embodiments, for example, navigation system  70  may also function or serve as an image analysis system. 
     As shown in  FIG.  2   , image analysis system  50  comprises a processor  52  having memory component  54 , input/output (I/O) component  58 , and optional localization device  56 . Image analysis system  50  may also optionally include display  60 , electromagnetic field generator  62 , and/or user interface device(s)  64  (e.g., keyboard, mouse). 
     Image analysis system  50  further includes and/or is in data communication with imaging device  40 . Imaging device  40  can be, for example, a computed tomography (CT) device (e.g., respiratory-gated CT device, ECG-gated CT device), a magnetic resonance imaging (MRI) device (e.g., respiratory-gated MRI device, ECG-gated MRI device), an X-ray device, a 2D or 3D fluoroscopic imaging device, and 2D, 3D or 4D ultrasound imaging devices, or any other suitable medical imaging device. In one embodiment, for example, imaging device  40  is a computed tomography-positron emission tomography (CT/PET) device that produces a fused computed tomography-positron emission tomography (CT/PET) image dataset. In the case of a two-dimensional imaging device, a population of two-dimensional images may be acquired and then assembled into volumetric data (e.g., three-dimensional (3D) image dataset) as is well known in the art using a two-dimensional to three-dimensional conversion. Pre-procedurally during a first time interval, imaging device  40  can be used to generate a population of images of patient  10  while PTD  20  is coupled to patient  10 ; wherein the population of images depict the anatomy of patient  10 . The anatomy, may include, but is not limited to, the lungs, heart, liver, kidneys, and/or other organs of patient  10 . The population of images can be compiled into an image dataset. As stated above, some or all markers  22  of PTD  20  are visible on the population of images and provide an indication of a position of some or all of markers  22  during the first time interval. The position of markers  22  at given instants in time through a path of motion of patient  10  can be illustrated with the images. 
     Processor  52  of image analysis system  50  includes a processor-readable medium storing code representing instructions to cause the processor  52  to perform a process. Processor  52  can be, for example, a commercially available personal computer, or a less complex computing or processing device that is dedicated to performing one or more specific tasks. For example, processor  52  can be a terminal dedicated to providing an interactive graphical user interface (GUI) on optional display  60 . Processor  52 , according to one or more embodiments of the invention, can be a commercially available microprocessor. Alternatively, processor  52  can be an application-specific integrated circuit (ASIC) or a combination of ASICs, which are designed to achieve one or more specific functions, or enable one or more specific devices or applications. In yet another embodiment, processor  52  can be an analog or digital circuit, or a combination of multiple circuits. 
     Additionally, processor  52  can include memory component  54 . Memory component  54  can include one or more types of memory. For example, memory component  54  can include a read only memory (ROM) component and a random access memory (RAM) component. Memory component  54  can also include other types of memory that are suitable for storing data in a form retrievable by processor  52 . For example, electronically programmable read only memory (EPROM), erasable electronically programmable read only memory (EEPROM), flash memory, as well as other suitable forms of memory can be included within the memory component. Processor  52  can also include a variety of other components, such as for example, coprocessors, graphic processors, etc., depending upon the desired functionality of the code. 
     Processor  52  can store data in memory component  54  or retrieve data previously stored in memory component  54 . The components of processor  52  can communicate with devices external to processor  52  by way of input/output (I/O) component  58 . According to one or more embodiments of the invention, I/O component  58  includes a variety of suitable communication interfaces. For example, I/O component  58  can include, for example, wired connections, such as standard serial ports, parallel ports, universal serial bus (USB) ports, S-video ports, local area network (LAN) ports, small computer system interface (SCSI) ports, and so forth. Additionally, I/O component  58  can include, for example, wireless connections, such as infrared ports, optical ports, Bluetooth® wireless ports, wireless LAN ports, or the like. Embodiments of image analysis system  50  which include display  60 , electromagnetic field generator  62 , and/or user interface device(s)  64 , such components communicate with processor  52  via I/O component  58 . 
     Processor  52  can be connected to a network, which may be any form of interconnecting network including an intranet, such as a local or wide area network, or an extranet, such as the World Wide Web or the Internet. The network can be physically implemented on a wireless or wired network, on leased or dedicated lines, including a virtual private network (VPN). 
     As stated above, processor  52  receives the population of images from imaging device  40 . Processor  52  identifies the position of selected markers  22  within the image data or voxel space using various segmentation techniques, such as Hounsfield unit thresholding, convolution, connected component, or other combinatory image processing and segmentation techniques. Processor  52  determines a distance and direction between the position of any two markers  22  during multiple instants in time during the first time interval, and stores the image data, as well as the position and distance data, within memory component  54 . Multiple images can be produced providing a visual image at multiple instants in time through the path of motion of the dynamic body. 
     As stated above, processor  52  can optionally include a receiving device or localization device  56  for tracking the location of localization elements  24  of PTD  20 , as described more fully elsewhere herein. By tracking localization elements  24  associated with PTD  20  when the population of images are generated by imaging device  40 , the population of images may be gated. That is, image analysis system  50  determines the respiratory phase at which the population of images were generated and this information may be stored in an image dataset and/or in another data store in memory component  54 . 
     In general, image analysis system  50  may comprise any tracking system typically employed in image guided surgery, including but not limited to, an electromagnetic tracking system. An example of a suitable electromagnetic tracking subsystem is the AURORA electromagnetic tracking system, commercially available from Northern Digital Inc. (Waterloo, Ontario Canada). In one embodiment, image analysis system  50  may include an electromagnetic tracking system, typically comprising an electromagnetic (EM) field generator  62  that emits a series of electromagnetic fields designed to engulf patient  10 , and localization elements  24  coupled to PTD  20 . In certain embodiments, for example, localization elements  24  are electromagnetic coils that receive an induced voltage from electromagnetic (EM) field generator  62 , wherein the induced voltage is monitored and translated by localization device  56  into a coordinate position of localization elements  24 . In certain embodiments, localization elements  24  are electrically coupled to twisted pair conductors to provide electromagnetic shielding of the conductors. This shielding prevents voltage induction along the conductors when exposed to the magnetic flux produced by the electromagnetic field generator. 
     Accordingly, localization device  56  can be, for example, an analog to digital converter that measures voltages induced onto localization elements  24  in the field generated by EM field generator  62 ; creates a digital voltage reading; and maps that voltage reading to a metric positional measurement based on a characterized volume of voltages to millimeters from electromagnetic field generator  62 . Position data associated with localization elements  24  can be transmitted or sent to localization device  56  continuously during imaging of patient  10  during the first time interval. Thus, the position of localization elements  24  can be captured at given instants in time during the first time interval. Because localization elements  24  are proximate markers  22 , localization device  56  uses the position data of localization elements  24  to deduce coordinates or positions associated with markers  22  during the first time interval. The distance, range, acceleration, and speed between one or more selected pairs of localization elements  24  (and corresponding markers  22 ) is then determined and various algorithms are used to analyze and compare the distance between selected elements  24  at given instants in time, to the distances between and orientation among corresponding markers  22  observed in a population of pre-procedural images. 
     As shown in  FIG.  3   , navigation system  70  comprises a processor  72  having memory component  74 , input/output (I/O) component  78 , and localization device  76 . Navigation system  70  also includes display  80 , electromagnetic field generator  82 , and/or user interface device(s)  84  (e.g., keyboard, mouse). In certain embodiments, navigation system  50  further includes and/or is in data communication with imaging device  40  (see  FIG.  2   ). 
     Processor  72  of navigation system  70  includes a processor-readable medium storing code representing instructions to cause the processor  72  to perform a process. Processor  72  can be, for example, a commercially available personal computer, or a less complex computing or processing device that is dedicated to performing one or more specific tasks. For example, processor  72  can be a terminal dedicated to providing an interactive graphical user interface (GUI) on optional display  80 . Processor  72 , according to one or more embodiments of the invention, can be a commercially available microprocessor. Alternatively, processor  72  can be an application-specific integrated circuit (ASIC) or a combination of ASICs, which are designed to achieve one or more specific functions, or enable one or more specific devices or applications. In yet another embodiment, processor  72  can be an analog or digital circuit, or a combination of multiple circuits. 
     Additionally, processor  72  can include memory component  74 . Memory component  74  can include one or more types of memory. For example, memory component  74  can include a read only memory (ROM) component and a random access memory (RAM) component. Memory component  74  can also include other types of memory that are suitable for storing data in a form retrievable by processor  72 . For example, electronically programmable read only memory (EPROM), erasable electronically programmable read only memory (EEPROM), flash memory, as well as other suitable forms of memory can be included within the memory component. Processor  72  can also include a variety of other components, such as for example, coprocessors, graphic processors, etc., depending upon the desired functionality of the code. 
     Processor  72  can store data in memory component  74  or retrieve data previously stored in memory component  74 . The components of processor  72  can communicate with devices external to processor  72  by way of input/output (I/O) component  78 . According to one or more embodiments of the invention, I/O component  78  includes a variety of suitable communication interfaces. For example, I/O component  78  can include, for example, wired connections, such as standard serial ports, parallel ports, universal serial bus (USB) ports, S-video ports, local area network (LAN) ports, small computer system interface (SCSI) ports, and so forth. Additionally, I/O component  78  can include, for example, wireless connections, such as infrared ports, optical ports, Bluetooth® wireless ports, wireless LAN ports, or the like. Additionally, display  80 , electromagnetic field generator  82 , and/or user interface device(s)  84 , communicate with processor  72  via I/O component  78 . 
     Processor  72  can be connected to a network, which may be any form of interconnecting network including an intranet, such as a local or wide area network, or an extranet, such as the World Wide Web or the Internet. The network can be physically implemented on a wireless or wired network, on leased or dedicated lines, including a virtual private network (VPN). 
     In general, navigation system  70  may comprise any tracking system typically employed in image guided surgery, including but not limited to, an electromagnetic tracking system. An example of a suitable electromagnetic tracking subsystem is the AURORA electromagnetic tracking system, commercially available from Northern Digital Inc. (Waterloo, Ontario Canada). In one embodiment, navigation system  70  may include an electromagnetic tracking system, typically comprising an electromagnetic (EM) field generator  82  that emits a series of electromagnetic fields designed to engulf patient  10 , and localization elements  24  coupled to PTD  20 . In certain embodiments, for example, localization elements  24  are electromagnetic coils that receive an induced voltage from electromagnetic (EM) field generator  82 , wherein the induced voltage is monitored and translated by localization device  76  into a coordinate position of localization elements  24 . In certain embodiments, localization elements  24  are electrically coupled to twisted pair conductors to provide electromagnetic shielding of the conductors. This shielding prevents voltage induction along the conductors when exposed to the magnetic flux produced by the electromagnetic field generator. 
     Accordingly, localization device  76  may be, for example, an analog to digital converter that measures voltages induced onto localization elements  24  in the field generated by EM field generator  82 ; creates a digital voltage reading; and maps that voltage reading to a metric positional measurement based on a characterized volume of voltages to millimeters from electromagnetic field generator  82 . Position data associated with localization elements  24  may be transmitted or sent to localization device  76  continuously during the medical procedure performed during the second time interval. Thus, the position of localization elements  24  may be captured at given instants in time during the second time interval. Because localization elements  24  are proximate markers  22 , localization device  76  uses the position data of localization elements  24  to deduce coordinates or positions associated with markers  22  during the second time interval. The distance, range, acceleration, and speed between one or more selected pairs of localization elements  24  (and corresponding markers  22 ) is then determined and various algorithms are used to analyze and compare the distance between selected elements  24  at given instants in time, to the distances between and orientation among corresponding markers  22  observed in a population of pre-procedural images. 
     Because localization elements  24  of PTD  20  may be tracked continuously during the first and/or second time intervals, a sequence of motion of PTD  20  that represents the motion of an organ of patient  10  or the patient&#39;s  10  respiratory cycle may be collected. As patient  10  inhales and exhales, the individual localization elements  24  of PTD  20  will move relative to one another. That is, as patient  10  inhales, the distance between some or all of localization elements  24  of PTD  20  may increase. Conversely, as patient  10  exhales, the distance between some or all of localization elements  24  of PTD  20  may decrease. The sequence of motion of localization elements  24  is tracked by image analysis system  50  and/or navigation system  70  and image analysis system  50  and/or navigation system  70  derives a respiratory signal based on the positions of localization elements  24  during the respiratory cycle of patient  10 . The sequence of motion may then be analyzed to find unique similar points within the image dataset and images within the image dataset may be grouped. 
     According to one particular embodiment, the respiratory signal derived from PTD  20  is used to gate the localization information of a medical device in the airway of patient  10 . In other embodiments, the respiratory signal derived from PTD  20  is used during the first time interval to gate the population of images generated by imaging device  40 . Using PTD  20  to derive a respiratory signal may assist in determining multiple airway models, for example, by performing a best fit of the real-time patient airway model to the image dataset to derive the optimal registration and gated period in the patient&#39;s respiratory cycle. Additionally or alternatively, the respiratory signal may be derived from devices other than PTD  20  that are known in the art for measuring the respiratory cycle of a patient. In certain embodiments, for example, a device that records the resistance between two locations on the patient may be used to measure the respiratory cycle. For example, such device a is similar to a variable potentiometer in that the resistance of the patient changes between two fixed points as the patient inhales and exhales. Thus, the resistance may be measured to create a respiratory signal. In other embodiments, a spirometer may be used to measure the respiratory cycle. In yet other embodiments, a cardiac signal may be used to gate the localization information of a medical device in the airway of patient  10 . It will be understood that any type of device for generating a cardiac signal may be used, including, but not limited to an ECG device, PTD  20 , etc. 
       FIG.  4    is a schematic illustration indicating how markers  22  of PTD  20  can move and change orientation and shape during movement of patient  10 . The graph is one example of how the lung volume can change during inhalation (inspiration) and exhalation (expiration) of patient  10 . The corresponding changes in shape and orientation of PTD  20  during inhalation and exhalation are also illustrated. The six markers  22  shown in  FIG.  1    are schematically represented and labeled a, b, c, d, e, and f. As described above, a population of images of PTD  20  may be taken during a first time interval. The population of images include an indication of relative position of one or more markers  22 ; that is, one or more markers  22  are visible in the images, and the position of each marker  22  is then observed over a period of time. A distance between any two markers  22  may then be determined for any given instant of time during the first time interval. For example, a distance X between markers a and b is illustrated, and a distance Y between markers b and f is illustrated. These distances may be determined for any given instant in time during the first time interval from an associated image that illustrates the position and orientation of markers  22 . As illustrated, during expiration of patient  10  at times indicated as A and C, the distance X is smaller than during inspiration of patient  10 , at the time indicated as B. Likewise, the distance Y is greater during inspiration than during expiration. The distance between any pair of markers  22  may be determined and used in the processes described herein. Thus, the above embodiments are merely examples of possible pair selections. For example, a distance between a position of marker e and a position of marker b may be determined. In addition, multiple pairs or only one pair may be selected for a given procedure. 
       FIGS.  5 A and  5 B  illustrate the generation of a population of images during a first time interval using imaging device  40 , PTD  20 , and optionally electromagnetic field generator  62  of image analysis system  50 . In  FIG.  5 A , patient  10  inhales and patient  10  is scanned using imaging device  40  which generates a population of images  402  of the anatomy of patient  10  and markers  22  at inspiration. As shown, patient  10  may place their arms above their head as they inhale, and this may be considered a total lung capacity (TLC) scan. In  FIG.  5 B , patient  10  exhales and patient  10  is scanned using imaging device  40  which generates a population of images  404  of the anatomy of patient  10  and markers  22  at expiration. As shown, patient  10  may place their arms below their head, and this may be considered a functional residual capacity (FRC) scan. The Functional Residual Capacity is the lung volume at the end of a normal expiration, when the muscles of respiration are completely relaxed. At FRC (and typically at FRC only), the tendency of the lungs to collapse is exactly balanced by the tendency of the chest wall to expand. In various embodiments, the population of images  402 ,  404  may be two-dimensional (2D) images. In other embodiments, for example, the population of images  402 ,  404  may be three-dimensional (3D) images. Additionally, the population of images  402 ,  404  may be respiratory gated by tracking the location of localization elements  24  of PTD  20  by image analysis system  50  and/or navigation system  70  using EM field generator  62 ,  82  during image generation. In other embodiments, for example, the population of images  402 ,  404  may be gated using any type of device known for generating a physiological signal for gating. 
     In various embodiments, for example, instead of patient  10  holding an inspiration or expiration state, a cine loop of images may be generated in conjunction with the patient&#39;s respiratory cycle information from PTD  20 . Thus the cine loop comprises a population of images generated from inspiration to expiration where the population of images are gated to the respiratory cycle of patient  10  using PTD  20 . This can serve to limit registration point selection, in order to be consistent with the patient&#39;s respiratory cycle that a 3D dataset such as CT, MR, or PET has acquired. This technique advantageously maximizes registration accuracy, a major flaw in conventional systems in the prior art. 
     As described above, imaging device  40  is in data communication with image analysis system  50  and/or navigation system  70  and sends, transfers, copies and/or provides the population of images  402 ,  404  taken during the first time interval associated with patient  10  to image analysis system  50  and/or navigation system  70 . As shown in  FIG.  5 C , image analysis system  50  and/or navigation system  70  compiles the population of images  402  at inspiration into a 3D image data subset  406  of the anatomy of patient  10  and markers  22  at inspiration (referred to herein as inspiration 3D image data subset  406 ). Additionally, image analysis system  50  and/or navigation system  70  compiles the population of images  404  at expiration into a 3D image data subset  408  of the anatomy of patient  10  at expiration (referred to herein as expiration 3D image data subset  408 ). The inspiration 3D image data subset  406  and the expiration 3D image data subset  408  are then stored in an image dataset  400  in memory component  54 ,  74  of image analysis system  50  and/or navigation system  70 . 
     Additionally, acquiring a population of images at both inspiration and expiration may assist navigation of a steerable catheter during a second time interval. Referring now to  FIGS.  6 A- 6 C , in addition to segmenting the markers  22  of PTD  20  from the population of images  402 ,  404  generated during the first time interval, processor  52  of image analysis workstation  50  generates three-dimensional models of the airway of patient  10  by segmenting the 3D image data subsets  406 ,  408 . In various embodiments, segmentation of the airway may be accomplished using an iterative region growing technique wherein a seed voxel in the airway is selected as an initialization parameter. Voxels neighboring the seed voxel are then evaluated to determine whether they are a part of the airway, form the wall surrounding the airway, or form other tissue. Following segmentation, a surface mesh of the airway may be generated to produce a surface skeleton. The surface of the airway may then be rendered. 
     As shown in  FIG.  6 A , a three-dimensional model of the airway of patient  10  at inspiration (“inspiration 3D airway model  410 ”) is generated by segmenting the inspiration 3D image data subset  406 .  FIG.  6 A  shows an Inspiration/arms-up pathway registration; this is, generally speaking, the preferred image scan acquisition state for automatic segmentation of the tracheo-bronchial tree. Processor  52  may also segment one or more target tissues  420  (e.g., lesions, lymph nodes, blood vessels, tumors, etc.) which may be navigated to during a second time interval using a variety of medical devices as described more fully elsewhere herein. The segmentation of the target tissue(s)  420  may be refined to define different characteristics of the target tissue, such as, for example, density of the target tissue. Additional image data formats may also be loaded into processor  52 , such as, for example, PET or MR and processor  52  may be able to map the CT, PET, and/or MR data to one another. 
     As shown at  FIG.  6 B , a three-dimensional model of the airway of patient  10  at expiration (“expiration 3D airway model  412 ”) is generated by segmenting the expiration 3D image data subset  408 . As discussed above, a variety of segmentation algorithms known in the art may be used to generate the inspiration and expiration 3D airway models  410 ,  412 .  FIG.  6 B  shows, in contrast to  FIG.  6 A , an FRC/arms-down segmentation. Because the patient&#39;s  10  lungs are more full of air at inspiration than at expiration, the inspiration 3D airway model  410  includes more structure than the expiration 3D airway model  412 . Accordingly, as shown in  FIG.  6 B , expiration 3D airway model  412  includes fewer structure(s) and the structure(s) are in different locations and/or orientations than at inspiration. However during a procedure such as directing a navigated steerable catheter to a target tissue within the airway of patient  10  (e.g., during a second time interval), the breathing cycle of patient  10  may be closer to tidal breathing. That is, patient  10  usually never reaches full inspiration during the procedure and thus if the segmentation of the airways of patient  10  at inspiration is used for navigation purposes, there will be significant error in the registration of the segmented airway to patient  10 . 
     In certain embodiments, a hybrid “Inspiration-Expiration” 3D airway model  414  is constructed as shown in  FIG.  6 C  using the inspiration 3D airway model  410  and the expiration 3D airway model  412 . The hybrid “Inspiration-Expiration” 3D airway model  414  may be used to reduce or eliminate the errors in registration. To construct the hybrid “Inspiration-Expiration” 3D airway model  414 , a population of deformation vector fields is calculated by processor  52 ,  72  of image analysis system  50  and/or navigation system  70 . The deformation vector field comprises vectors from one or more voxels in the inspiration 3D airway model  410  to one or more corresponding voxels in the expiration 3D airway model  412 . After the deformation vector field is calculated, the inspiration 3D airway model  410  is deformed to the expiration state of patient  10  using the deformation vector field. Accordingly, the voxels in the inspiration 3D airway model  410  are deformed to match the location, shape, and orientation of the airways of patient  10  at expiration. This results in the hybrid “Inspiration-Expiration” 3D airway model  414 , wherein the hybrid “Inspiration-Expiration” 3D airway model  414  contains all of the structural information of the airways of patient  10  depicted in inspiration 3D airway model  410 . However, this structural information is now more closely matched to the location, shape, and orientation of the airways of patient  10  depicted in expiration 3D airway model  412 . Accordingly, the deformation vectors represent not only a change in location of the structure of the airway but a change in shape of the structure of the airway from inspiration to expiration. 
       FIG.  7   , illustrates a 3D representation of hybrid “Inspiration-Expiration” 3D airway model  414  which includes a target tissue  420  segmented by processor  52 ,  72 . This 3D representation of hybrid “Inspiration-Expiration” 3D airway model  414  may include surface information. Hybrid “Inspiration-Expiration” 3D airway model  414  may additionally include navigation pathway  416 . Image analysis system  50  and/or navigation system  70  may calculate navigation pathway  416  from the entry of the airway to the location of target tissue  420 . In certain embodiments, navigation pathway  416  may be an optimal endobronchial path to a target tissue. For example, navigation pathway  416  may represent the closest distance and/or closest angle to the target tissue. A physician or other healthcare professional may follow navigation pathway  416  during an image guided intervention to reach the location of target tissue  420 . 
     Although target tissue  420  locations and navigation pathway(s)  416  may be automatically calculated by image analysis system  50  and/or navigation system  70 , a physician or other healthcare professional may manually adjust target tissue  420  locations and/or navigation pathway(s)  416 . 
     In general, the embodiments described herein have applicability in “Inspiration to Expiration”-type CT scan fusion. According to various methods, the user navigates on the expiration 3D image data subset  408  for optimal accuracy, while using the inspiration 3D image data subset  406  to obtain maximum airway segmentation. In one embodiment, for example, a user could complete planning and pathway segmentation on the inspiration 3D image data subset  406  of patient  10 . Preferably, a deformation vector field is created between at least two datasets (e.g., from inspiration 3D image data subset  406  to expiration 3D image data subset  408 ). The deformation or vector field may then be applied to the segmented vessels and/or airways and navigation pathway  416  and target tissue  420  locations. In these and other embodiments, the deformation or vector field may also be applied to multiple image datasets or in a progressive way to create a moving underlying image dataset that matches the respiratory or cardiac motion of patient  10 . 
     By way of example, in certain embodiments, “Inspiration to Expiration” CT fusion using the lung lobe centroid and vector change to modify an airway model may also be applicable. In accordance with various embodiments, this technique is used to translate and scale each airway based on the lung lobe change between inspiration images and expiration images. The lung is constructed of multiple lobes and these lobes are commonly analyzed for volume, shape, and translation change. Each lobe changes in a very different way during the patient&#39;s breathing cycle. Using this information to scale and translate the airways that are located in each lobe, it is possible to adapt for airway movement. This scaled airway model may then be linked to the 4D tracking of the patient as described herein. 
     In various aspects, the systems and methods described herein involve modifying inspiration images generated by imaging device  40  (e.g., CT, CT/PET, MRI, etc.) to the expiration cycle for navigation. It is well understood that the patient&#39;s airways are contained within multiple lobes of the lung. It is also understood that airways significantly change between inspiration and expiration. In certain embodiments, to increase the accuracy of the map for navigation, it may be beneficial to include the detail of the inspiration images, coupled with the ability to navigate it accurately during expiration. For many patients, the expiration state may be the most repeatable point in a patient&#39;s breath cycle. In preferred embodiments, this modification may be carried out in accordance with the following steps: 
     1) Generate a population of images of patient  10  at both inspiration and expiration using imaging device  40 ; 
     2) Segment the airways in both the inspiration and expiration images; 
     3) Segment the lung lobes in both the inspiration and expiration images (as the lung lobes are identifiable in both the inspiration and expiration images with a high degree of accuracy); 
     4) Determine a volume difference for each lung lobe between inspiration and expiration, use this change to shrink the airway size from the inspiration to the expiration cycle. Preferably, this is done for each individual lobe, as the percentage change will typically be different for each lobe. 
     5) Determine the centroid for each lung lobe and the vector change in motion from the main carina in both inspiration images and expiration images. This vector may then be used to shift the airways that are associated with each lung lobe. A centroid for the airway may be calculated based on the segmented branches. For each airway branch in the segmentation, it includes a tag that associates it with the respective lung lobe. The central airway including the main carina and initial airway branches for each lobe that is linked according to the expiration scan location of these points. Next, a plane may be defined using the main carina and initial airway branch exits to determine the vector change for each lobe. 
     Among the lobes to modify, for example: 
     left inferior lobe—the bottom lobe of the lung on the left side of patient  10 ; 
     left superior lobe—the top lobe of the lung on the left side of patient  10 . 
     right inferior lobe—the bottom lobe of the lung on the right side of patient  10 ; 
     right middle lobe—the middle lobe of the lung on the right side of patient  10 ; 
     right superior lobe—the top lobe of the lung on the right side of patient  10 . 
     Exemplary calculations are as follows: 
     Inspiration Airway—Left Inferior Lobe (LIL)×70% (reduction in volume Inspiration to Expiration calculated)=ExAirwayLIL; 
     Determine Expiration Central Airway points (Main Carina and Initial Airway branches) based upon segmentation; 
     Shift ExAirwayLIL by vector distance (3 cm, 45 degrees up and back from main carina) that LIL centroid moved from inspiration to expiration. 
     Preferably, this process is repeated for each lobe. In certain embodiments, the completion of 5 lobes will result in a hybrid “Inspiration-Expiration” 3D airway model for patient  10 . 
     In various embodiments, the target location for the patient may be selected in the expiration images and applied to the hybrid “Inspiration-Expiration” 3D airway model  414 . Alternatively, it may be selected in the inspiration images and adjusted based on the same or similar criteria as the inspiration airways. In either case, it may be adjusted individually or linked to the airway via a 3D network and moved in the same transformation. 
     A deformation field may also be included in the analysis in various other embodiments described herein. For example, the deformation field may be applied to fuse 3D fluoroscopic images to CT images to compensate for different patient orientations, patient position, respiration, deformation induced by the catheter or other instrument, and/or other changes or perturbations that occur due to therapy delivery or resection or ablation of tissue. 
     Following the generation of hybrid “Inspiration-Expiration” 3D airway model  414 , during a second time interval, a medical procedure is then performed on patient  10  with PTD  20  coupled to patient  10  at the same location as during the first time interval when the population of pre-procedural images were taken. Preferably, the second time interval immediately follows the first time interval. However, in certain embodiments, second time interval may occur several hours, days, weeks or months after the first time interval. After hybrid “Inspiration-Expiration” 3D airway model  414  is generated and one or more target tissues  420  are identified and one or more navigation pathways  416  are calculated, this information is transferred from image analysis system  50  to navigation system  70 . This transfer may be done according to the DICOM (Digital Imaging and Communications in Medicine) standard as known in the art. It will be understood that the transfer may be done using any method and according to any standard without departing from the scope of the invention. For example, this transfer may be accomplished between image analysis system  50  to navigation system  70  using a variety of methods, including, but not limited to, a wired connection, a wireless connection, via CD, via a USB device, etc. 
     It should be noted that image dataset  400  may be supplemented, replaced or fused with an additional image dataset. In one embodiment, for example, during the second time interval an additional population of images may be taken. In other embodiments, for example, after the second time interval an additional population of images may be taken. By generating one or more additional image datasets, potential changed physical parameters of patient such as patient  10  movement, anatomical changes due to resection, ablation, general anesthesia, pneumothorax, and/or other organ shift may be accounted for during the procedure. Accordingly, images from CT-Fluoro, fluoroscopic, ultrasound or 3D fluoroscopy may be imported into image analysis system  50  and/or navigation system  70 . 
     Using the respiratory signal derived from PTD  20 , navigation system  70  selects an image from the population of pre-procedural images  402 ,  404  taken during the first time interval that indicates a distance or is grouped in a similar sequence of motion between corresponding markers  22  at a given instant in time, that most closely approximates or matches the distance or similar sequence of motion between the selected localization elements  24 . The process of comparing the distances is described in more detail below. Thus, navigation system  70  displays images corresponding to the actual movement of the targeted anatomy during the medical procedure being performed during the second time interval. The images illustrate the orientation and shape of the targeted anatomy during a path of motion of the anatomy, for example, during inhaling and exhaling. 
       FIG.  8    illustrates an example set of distances or vectors d 1  through d 6  between a set of markers  22 , labeled m 1  through m 9  that are disposed at spaced locations on PTD  20 . As described above, a population of pre-procedural images is taken of a patient  10  to which PTD  20  is coupled during a first time interval. The distances between markers  22  are determined for multiple instants in time through the path of motion of the dynamic body (e.g., the respiratory cycle of the patient). Then, during a medical procedure, performed during a second time interval, localization elements  24  (not shown in  FIG.  8   ) proximate the location of markers  22  provide position data for localization elements  24  to localization device  76  (not shown in  FIG.  8   ). Navigation system  70  uses the position data to determine distances or vectors between localization elements  24  for multiple instants in time during the medical procedure or second time interval. 
       FIG.  9 A  shows an example of distance or vector data from localization device  76 . Vectors a 1  through a 6  represent distance data for one instant in time and vectors n 1  through n 6  for another instant in time, during a time interval from a to n. As previously described, the vector data may be used to select an image from the population of pre-procedural images that includes distances between the markers m 1  through m 9  that correspond to or closely approximate the distances a 1  through a 6  for time a, for example, between the localization elements. The same process may be performed for the vectors n 1  through n 6  captured during time n. 
     One method of selecting the appropriate image from the population of pre-procedural images  402 ,  404  is to execute an algorithm that sums all of the distances a 1  through a 6  and then search for and match this sum to an image containing a sum of all of the distances d 1  through d 6  obtained pre-procedurally from the image data that is equal to the sum of the distances a 1  through a 6 . When the difference between these sums is equal to zero, the relative position and orientation of the anatomy or dynamic body D during the medical procedure will substantially match the position and orientation of the anatomy in the particular image. The image associated with distances d 1  through d 6  that match or closely approximate the distances a 1  through a 6  may then be selected and displayed. For example,  FIG.  9 B  illustrates examples of pre-procedural images, Image a and Image n, of a dynamic body D that correspond to the distances a 1  through a 6  and n 1  through n 6 , respectively. An example of an algorithm for determining a match is as follows: 
     Does Σa i =Σd i  (i=1 to 6 in this example) OR 
     Does Σ(a i −d i )=0 (i=1 to 6 in this example). 
     If yes to either of these, then the image is a match to the vector or distance data obtained during the medical procedure. 
       FIG.  10    is a flowchart illustrating a method according to an embodiment of the invention. A method  100  includes at step  102  generating image data during a pre-procedural or first time interval. As discussed above, a population of images are generated of a dynamic body, such as patient  10 , using imaging device  40  (e.g., CT Scan, MRI, etc.). The image data is associated with one or more images generated of PTD  20  coupled to a dynamic body, where PTD  20  includes two or more markers  22 . In other words, the image data of the dynamic body is correlated with image data related to PTD  20 . The one or more images may be generated using a variety of different imaging devices as described previously. The image data include an indication of a position of a first marker and an indication of a position of a second marker, as illustrated at step  104 . The image data include position data for multiple positions of the markers during a range or path of motion of the dynamic body over a selected time interval. As described above, the image data include position data associated with multiple markers, however, only two are described here for simplicity. A distance between the position of the first marker and the position of the second marker is determined for multiple instants in time during the first time interval, at step  106 . As also described above, the determination may include determining the distance based on the observable distance between the markers on a given image. The image data, including all of the images received during the first time interval, the position, and the distance data is recorded in a memory component at step  108 . 
     Then at step  110 , during a second time interval, while performing a medical procedure on patient  10  with PTD  20  positioned on patient  10  at substantially the same location, position data is received for a first localization element and a second localization element. Localization elements  24  of PTD  20  are proximate markers  22 , such that the position data associated with localization elements  24  is used to determine the relative position of markers  22  in real-time during the medical procedure. The position data of localization elements  24  are recorded in a memory component at step  112 . 
     A distance between the first and second localization elements is determined at step  114 . Although only two localization elements  24  are described, as with the markers, position data associated with more than two localization elements may be received and the distances between the additional localization elements may be determined. 
     The next step is to determine which image from the population of images taken during the first time interval represents the relative position and/or orientation of the dynamic body at a given instant in time during the second time interval or during the medical procedure. To determine this, at step  116 , the distance between the positions of the first and second localization elements at a given instant in time during the second time interval determined in step  114  are compared to the distance(s) determined in step  106  between the positions of the first and second markers obtained with the image data during the first time interval. 
     An image is selected from the first time interval that best represents the same position and orientation of the dynamic body at a given instant in time during the medical procedure. To do this, the difference between the distance between a given pair of localization elements during the second time interval is used to select the image that contains the same distance between the same given pair of markers from the image data received during the first time interval. This is accomplished, for example, by executing an algorithm to perform the calculations. When there are multiple pairs of markers and localization elements, the algorithm may sum the distances between all of the selected pairs of elements for a given instant in time during the second time interval and sum the distances between all of the associated selected pairs of markers for each instant in time during the first time interval when the pre-procedural image data was received. 
     When an image is found that provides the sum of distances for the selected pairs of markers that is substantially the same as the sum of the distances between the localization elements during the second time interval, then that image is selected at step  118 . The selected image is then displayed at step  120 . The physician or other healthcare professional may then observe the image during the medical procedure. Thus, during the medical procedure, the above process may be continuously executed such that multiple images are displayed and images corresponding to real-time positions of the dynamic body may be viewed. 
     In addition to tracking the location of PTD  20 , navigation system  70  (see  FIG.  3   ) may also track any type of device which includes one or more localization elements. The localization elements in the medical devices may be substantially similar or identical to localization elements  24  of PTD  20 . The devices preferably include medical devices, including, but not limited to, steerable catheters, needles, stents, ablation probes, biopsy devices, guide wires, forceps devices, brushes, stylets, pointer probes, radioactive seeds, implants, endoscopes, energy delivery devices, therapy delivery devices, delivery of energy activated substances (e.g., porfimer sodium) and energy devices, radiofrequency (RF) energy devices, cryotherapy devices, laser devices, microwave devices, diffuse infrared laser devices, etc. In certain embodiments, the location of these devices are tracked in relation to PTD  20 . In other embodiments, for example, these devices are tracked in relation to electromagnetic field generator  62 ,  82 . It is also envisioned that at least some of these medical devices may be wireless or have wireless communications links. It is also envisioned that the medical devices may encompass medical devices which are used for exploratory purposes, testing purposes or other types of medical procedures. 
     One embodiment of a medical device which may be tracked by navigation system  70  is illustrated in  FIGS.  11  and  11 A . In one embodiment of the present invention, a navigated surgical catheter that is steerable  600  (referred herein to as “steerable catheter”) may be used to gain access to, manipulate, remove, sample or otherwise treat tissue within the body including, but not limited to, for example, heart or lung tissue. Steerable catheter  600  comprises an elongate flexible shaft  602  having a proximal end portion  604 , a distal end portion  606  terminating in tip  607 , and one or more working channels  608  extending from proximal end portion  604  to tip  607 . As shown in  FIG.  11 A , one or more localization elements  610  that are detectable by navigation system  70  are disposed proximate the distal end portion  606  of elongate flexible shaft  602 . Accordingly, the position and orientation (POSE) of localization elements  610  are tracked by localization device  76  of navigation system  70 . The one or more localization elements  610  are connected by wire  611  to navigation system  70 ; in alternative embodiments, the one or more localization elements  610  may be wirelessly connected to navigation system  70 . In certain embodiments, localization elements  610  comprise six (6) degree of freedom (6DOF) electromagnetic coil sensors. In other embodiments, localization elements  610  comprise five (5) degree of freedom (5DOF) electromagnetic coil sensors. In other embodiments, localization elements  610  comprise other localization devices such as radiopaque markers that are visible via fluoroscopic imaging and echogenic patterns that are visible via ultrasonic imaging. In yet other embodiments, localization elements  610  may be, for example, infrared light emitting diodes, and/or optical passive reflective markers. Localization elements  610  may also be, or be integrated with, one or more fiber optic localization (FDL) devices. Accordingly, in certain embodiments, localization elements  610  may be substantially similar or identical to localization elements  24  of PTD  20 . In other embodiments the steerable catheter may be non-navigated, such that it does not include any localization elements. 
     Steerable catheter  600  further comprises handle  612  attached to the proximal end portion  604  of elongate flexible shaft  602 . Handle  612  of steerable catheter  600  includes steering actuator  614  wherein distal end portion  606  is moved “up” and “down” relative to proximal end portion  604  by manipulating steering actuator  614  “up” and “down,” respectively. Additionally, distal end portion  606  is moved “left” and “right” relative to proximal end portion  604  by rotating handle  612  “left” and “right,” respectively, about handle longitudinal axis  613 . It will be understood that steering actuator  614  and handle  612  are connected to a steering mechanism (not shown) on the inside of steerable catheter  600  which is connected to distal end portion  606  of elongate flexible shaft  602  for causing the deflection in distal end portion  606 . Port  616 , disposed on handle  612 , provides access to working channel(s)  608  in elongate flexible shaft  602  of steerable catheter  600 , such that a medical device may be inserted into working channel(s)  608  through port  616 . 
     As shown in  FIGS.  12 A and  12 B , any number of medical devices or therapies may be inserted into working channel(s)  608  and/or extended out of tip  607  to deliver the medical devices or therapies to a target tissue. The medical devices may include, but are not limited to, imaging devices  633 , tissue sensing devices  632 , biopsy devices, therapy devices, steerable catheters, endoscopes, bronchoscopes, percutaneous devices, percutaneous needles, pointer probes, implants, stents, guide wires, stylets, etc. In certain embodiments, imaging devices  633  include, but are not limited to, bronchoscopic video cameras  630 , endobronchial ultrasound (EBUS) devices  634 , optical coherence tomography (OCT) devices, probe based Confocal Laser Endomicroscopy (pCLE) devices, or any known imaging device insertable into working channel  608  of steerable catheter  600 . Tissue sensing device  632  may be any type of device which may be used to determine the presence of a target tissue in patient  10 . In certain embodiments, tissue sensing device  632  may include, but is not limited to, imaging device  633 , a cell analysis device, a cancer detecting device, an exhaled breath condensate analyzer, a physiological characteristic sensor, a chemical analysis device, an aromatic hydrocarbon detection device, vacuum collection device, etc. The sensitivity of certain of the tissue sampling devices, such as aromatic hydrocarbon detection devices are dependent upon the density of the sample collected. Thus, by navigating steerable catheter  600  near the desired target tissue a sample of higher density may be captured and analyzed. Additionally, a vacuum collection device may be navigated using steerable catheter  600  to near the desired target tissue and/or an airway branch within one or two segments of the desired target tissue, and an air sample may be captured. In certain embodiments, therapy devices include, but are not limited to, ablation probes, energy delivery devices, radioactive seeds, delivery of energy activated substances (e.g., porfimer sodium) and energy devices, radiofrequency (RF) energy devices, cryotherapy devices, laser devices, microwave devices, diffuse infrared laser devices, fluids, drugs, combinations thereof, or the like). In certain embodiments, biopsy devices include, but are not limited to, needles, forceps devices, brushes, etc., In certain embodiments, steerable catheter  600  may also include a suction capability. 
     As illustrated in  FIG.  12 A , for example, in certain embodiments, imaging device  633  is a bronchoscopic video camera  630 . Bronchoscopic video camera  630  may be inserted into working channel  608  and/or extended out distal end portion  606  of navigated steerable catheter  600 . By inserting bronchoscopic video camera  630  into working channel  608  of steerable catheter  600 , steerable catheter  600  may be used like a typical steerable bronchoscope, as described more fully elsewhere herein. 
     As shown in  FIG.  12 B , tissue sensing device  632  may be an imaging device  633 , wherein imaging device  633  is an endobronchial ultrasound (EBUS) device  634 ; however, as described above, it will be understood that imaging device  633  may include, but is not limited to, bronchoscopic video camera  630 , an optical coherence tomography (OCT) device, a probe based Confocal Laser Endomicroscopy (pCLE) device, or any known imaging device insertable into working channel  608  of steerable catheter  600 . 
     In embodiments, where tissue sensing device  632  is imaging device  633 , imaging device  633  may be able to generate a population of images of the target tissue(s), wherein the target tissue(s) may be in the airway, on the wall of the airway, in the wall of the airway, and/or beyond the wall of the airway. That is, the imaging device(s) may be able to generate images of target tissue(s) not only inside the airway, but may generate images of target tissue(s) and other anatomical structures inside and/or beyond the wall of the airway. Thus in certain embodiments, sub-surface target tissue may be imaged using the imaging device(s). Accordingly, using endobronchial ultrasound (EBUS) device  634 , an optical coherence tomography (OCT) device, a probe based Confocal Laser Endomicroscopy (pCLE) device, etc. while tracking the position and orientation (POSE) of localization element  610  of steerable catheter  600 , as described herein, multiple 3D volumes of image data regarding target tissue(s) and other anatomical structures inside and/or beyond the wall of the airway may be collected and a larger 3D volume of collected data may be constructed. Knowing the 3D location and orientation of the multiple 3D volumes will allow the physician or other healthcare professional to view a more robust image of, for example, pre-cancerous changes of target tissue(s) in patient  10 . This data may also be correlated to pre-acquired or intra-procedurally acquired image dataset  400  to provide additional information. 
     Additionally, in certain embodiments wherein steerable catheter  600  includes multiple working channels  608 , multiple medical devices may be inserted into the multiple working channels  608 . For example, bronchoscopic video camera  630  may be inserted into one working channel and a medical device such as a needle, forceps device or a brush may be inserted into a second working channel. Accordingly, a real-time image feed from bronchoscopic video camera  630  may be used to view the operation of the medical device. Although a steerable catheter has been described, it will be understood that any type of steerable medical device may be used in accordance with the methods described herein, including, but not limited to, endoscopes, bronchoscopes, etc. without departing from the scope of the invention. 
     Another embodiment of a medical device which may be tracked by navigation system  70  is illustrated in  FIGS.  13  and  13 A . In one embodiment of the present invention, a percutaneous needle  650  may be used to gain access to, manipulate, remove, sample or otherwise treat target tissue within patient  10  including, but not limited to, for example, target tissue on and/or in the heart or lung. Percutaneous needle  650  comprises an elongate shaft or cannula  652  having a proximal end portion  654 , a distal end portion  656  terminating in tip  657 , and one or more working channels  658  may extend from proximal end portion  654  to tip  657 . Percutaneous needle  650  further includes handle  652  attached to the proximal end portion  654 . Port  667 , disposed on handle  652 , provides access to working channel(s)  658  in cannula  652  of percutaneous needle  650 , such that a medical device may be inserted into working channel(s)  658  through port  667 . Any number of medical devices or therapies, as described herein, may be inserted into working channel(s)  658  and/or extended out of tip  657  to deliver the medical devices or therapies (e.g., steerable catheters, needles, stents, ablation probes, biopsy devices, guide wires, forceps devices, brushes, stylets, pointer probes, radioactive seeds, implants, endoscopes, energy delivery devices, therapy delivery devices, delivery of energy activated substances (e.g., porfimer sodium) and energy devices, radiofrequency (RF) energy devices, cryotherapy devices, laser devices, microwave devices, diffuse infrared laser devices, fluids, drugs, combinations thereof, or the like) to a target tissue. 
     As shown in  FIG.  13 A , one or more localization elements  660  that are detectable by navigation system  70  are disposed proximate the distal end portion  656  of cannula  652 . Accordingly, the position and orientation (POSE) of localization elements  660  are tracked by localization device  76  of navigation system  70 . The one or more localization elements  660  are connected by wire  661  to navigation system  70 ; in alternative embodiments, the one or more localization elements  660  may be wirelessly connected to navigation system  70 . 
     In certain embodiments, localization elements  660  comprise six (6) degree of freedom (6DOF) electromagnetic coil sensors. In other embodiments, localization elements  660  comprise five (5) degree of freedom (5DOF) electromagnetic coil sensors. In other embodiments, localization elements  660  comprise other localization devices such as radiopaque markers that are visible via fluoroscopic imaging and echogenic patterns that are visible via ultrasonic imaging. In yet other embodiments, localization elements  660  may be, for example, infrared light emitting diodes, and/or optical passive reflective markers. Localization elements  660  may also be, or be integrated with, one or more fiber optic localization (FDL) devices. Accordingly, in certain embodiments, localization elements  660  may be substantially similar or identical to localization elements  24  of PTD  20  and/or localization elements  610  of steerable catheter  600 . 
     While localization element  660  is illustrated proximate distal end portion  656 , it will be understood that localization element  660  may be located in other locations of percutaneous needle  650  without departing from the scope of the invention. For example, in certain embodiments, localization element  660  may be disposed proximate the proximal end portion  654  and/or proximate handle  662 . Navigation system  70  may be able to determine the location of tip  657  in relation to the location of PTD  20  by knowing the location of localization element  660  in relation to tip  657 . For example, if localization element  660  is disposed at handle  662 , navigation system  770  may be able to determine the location of tip  657  in relation to the position of localization element  660  if the length between tip  657  and localization element  660  is input into navigation system  70 . 
     In other embodiments, percutaneous needle  650  is non-navigated, such that it does not include any localization elements. However, the location of percutaneous needle  650  may still be tracked by navigation system  70  if a medical device containing a localization element is inserted into working channel  658  of percutaneous needle  650 . 
     In various embodiments, any of the medical devices described herein that may be inserted into working channel(s)  608 ,  658  of steerable catheter  600  and/or percutaneous needle  650  may be tracked individually with an integrated localization element (e.g., an electromagnetic (EM) sensor). Accordingly, the medical devices may be tip tracked. Additionally, wherein the inserted medical device is an ablation probe, ablation models may be displayed to assist in optimal placement of the ablation probe for treatment. It will be understood that the medical devices may be delivered endobronchially, percutaneously, and/or endobronchially and percutaneously simultaneously. 
     Referring again to navigation system  70 , navigation system  70  may display on display  80  multiple images which may assist a physician or other healthcare professional in conducting the methods described herein. Image dataset  400  generated during the first time interval may be registered to patient  10  using PTD  20 . As described above, localization elements  24  of PTD  20  are proximate markers  22  and because one or more markers  22  of PTD  20  are visible in image dataset  400  and localization elements  24  corresponding to the one or more markers  22  are tracked by navigation system  70 , image dataset  400  may be registered to patient  10 . This registration may be manually accomplished or may be automatically accomplished by navigation system  70 . 
     In addition to or alternative to registration using PTD  20 , registration may be completed by different known techniques. First, point-to-point registration may be accomplished by identifying points in an image space and then touching the same points in patient space. These points are generally anatomical landmarks that are easily identifiable on the patient. Second, lumen registration may be accomplished by generating a point cloud within the airways of patient  10  and matching the shape of the generated point cloud to an inspiration 3D airway model  410 , an expiration 3D airway model  412 , and/or a hybrid “Inspiration-Expiration” 3D airway model  414 . Using four-dimensional tracking (4D) the point cloud may be generated at the appropriate respiration cycle to match inspiration 3D airway model  410 , an expiration 3D airway model  412 , and/or a hybrid “Inspiration-Expiration” 3D airway model  414 . Generation of a point cloud is more fully described in U.S. Ser. No. 13/773,984, entitled “Systems, Methods and Devices for Forming Respiratory-Gated Point Cloud for Four Dimensional Soft Tissue Navigation,” filed on Feb. 22, 2013, which is hereby incorporated by reference. Third, surface registration may involve the generation of a surface in patient  10  space by either selecting multiple points or scanning, and then accepting the best fit to that surface in image space by iteratively calculating with processor  72  until a surface match is identified. Fourth, repeat fixation devices entail repeatedly removing and replacing a device (i.e., dynamic reference frame, etc.) in known relation to patient  10  or image fiducials of patient  10 . Fifth, two-dimensional (2D) image datasets may be registered to three-dimensional (3D) image datasets wherein, the two dimensional image datasets may include, but are not limited to, fluoroscopic images, ultrasound images, etc. and the three-dimensional (3D) image datasets may include, but are not limited, to computed tomography (CT) images, fused computed tomography-positron emission tomography (CT/PET) images, magnetic resonance imaging (MRI) images. Sixth, automatic registration may be accomplished by first attaching a dynamic reference frame to patient  10  prior to acquiring image data. It is envisioned that other known registration procedures are also within the scope of the present invention, such as that disclosed in U.S. Pat. No. 6,470,207, entitled Navigational Guidance via Computer-Assisted Fluoroscopic Imaging”, filed on Mar. 23, 1999, which is hereby incorporated by reference. 
     After image dataset  400  is registered to patient  10 , navigation system  70  displays on display  80  a variety of images as illustrated in  FIG.  14   . For example, as shown in panel  700 , hybrid “Inspiration-Expiration” 3D airway model  414  may be displayed. Additionally, as shown in panel  700 , an indicia  718  (shown as a crosshair) of the location of steerable catheter  600  is displayed. In certain embodiments, for example, indicia  718  indicates the location of distal end portion  606  of steerable catheter  600 . In other embodiments, for example, indicia  718  indicates the location of localization element  610  of steerable catheter  600 . In yet other embodiments, for example, indicia  718  indicates the location of tip  607  of steerable catheter  600 . That is, navigation system  70  may be able to display an indicia indicating the location of a portion of steerable catheter  600  based on the tracked location of localization element  610 . For example, if localization element  610  is disposed 5 mm from tip  607  of steerable catheter  600 , the 5 mm distance may be taken into account by navigation system  70  and the indicia of tip  607  indicating the location of tip  607  may be displayed and not the location of localization element  610 . An indicia  720  (shown as a circle) of an initial target tissue location may also be displayed on display  80  by navigation system  70  as shown in panel  700 . Indicia  718 ,  720  are shown as a crosshair and circle, respectively; however it is envisioned that other indicia may be used to indicate the location of steerable catheter  600 , initial target tissue location, confirmed target tissue location, location of percutaneous needle  650 , and/or any other target tissue or medical device. For example, indicia may have different shapes, colors, sizes, line weights and/or styles, etc. without departing from the scope of the invention. 
     Furthermore, navigation system  70  may be able to simulate and display axial, coronal and oblique images based on the position and orientation (POSE) of localization element  610  of steerable catheter  600 , as shown in panels  702 ,  704 , and  706 . To simulate these views, navigation system  70  may modify one or more images from image dataset  400  using known image manipulation techniques. Additionally, navigation system  70  may simulate and/or display orthogonal image slices, oblique or off-axis image slices, volume rendered images, segmented images, fused modality images, maximum intensity projection (MIPS) images, video, and video enhanced images. As shown, indicia of  718  of steerable catheter  600  and/or an indicia  720  of an initial target tissue location may also be displayed, as shown in panels  702 ,  704 , and  706 . 
     In various embodiments as shown in panel  712 , navigation system  70  also simulates a virtual volumetric scene within the body of patient  10 , such as the airways of patient  10 , from a point of view of a medical device, such as steerable catheter  600 , as it is being navigated into and/or through patient  10 . This virtual volumetric scene is a computer-generated visualization of a bronchoscopy procedure and simulates what would be viewed by a bronchoscopic video camera inserted into the airways. To simulate the virtual volumetric scene, navigation system  70  modifies one or more images from image dataset  400  using known image manipulation techniques. For example, navigation system  70  may be able to simulate the virtual volumetric scene using inspiration 3D airway model  410 , expiration 3D airway model  412 , and/or hybrid “Inspiration-Expiration” 3D airway model  414 . Accordingly navigation system  70  renders an internal view of 3D airway model(s)  410 ,  412 , and/or  414  based on a virtual bronchoscope video camera position, for example, by applying certain surface properties (e.g., Lambertian), diffuse shading model(s), and perspective projection camera model(s). Virtual lighting and shading may be applied to the rendered view to further enhance the virtual volumetric scene. The field of view (FOV) may be changed to match the field of view of bronchoscopic video camera  630  (see  FIG.  12 A ). The point of view may be adjusted to match bronchoscopic video camera  630  or to display a virtual volumetric scene from different points along the airway or outside the airway. Navigation system  70  may also be able to display a navigation pathway  416  in the virtual volumetric scene. Accordingly, the virtual volumetric scene may allow a physician or other healthcare professional to review the navigation pathway  416  prior to inserting steerable catheter  600  and/or other medical device into patient  10 . Additionally, in certain embodiments, an indicia of the location of localization element  610  of steerable catheter  600  and/or an indicia of an initial target tissue location may also be displayed. 
     Additionally, in various embodiments as shown in panel  716 , navigation system  70  also displays a real-time image feed from bronchoscopic video camera  630  inserted into working channel  608  of steerable catheter  600 . The real-time image feed may be static images or moving video. The real-time image feed may assist the physician or other healthcare professional in navigating steerable catheter  600  to proximate the initial location of the target tissue. Thus by inserting bronchoscopic video camera  630  into working channel  608  of steerable catheter  600  (see  FIG.  12 A ), steerable catheter  600  may be used like a typical steerable bronchoscope. Typical steerable bronchoscopes are used to visually inspect the airways of a patient and have a fixed bronchoscopic video camera in addition to one or more working channels. Typical steerable bronchoscopes may have steering actuators and steering mechanisms that permit them to be steered much like steerable catheter  600 . Because the bronchoscopic video camera of a typical steerable bronchoscope is fixed during manufacture of the steerable bronchoscope, the “up” orientation of the image feed from the bronchoscopic video camera as displayed to the physician or other healthcare professional is aligned with the “up” direction of the steering actuator of the typical steerable bronchoscope. That is, the orientation of the real-time image feed from the typical steerable bronchoscope is registered to the orientation of the steering directions of the typical steerable bronchoscope. Accordingly, when the physician or other healthcare professional steers the typical steerable bronchoscope “up,” the image feed will move “up.” Additionally, steering the typical steerable bronchoscope “down,” “left,” and “right,” the image feed will move “down,” “left,” and “right,” respectively. 
     However, because the bronchoscopic video camera is fixed (i.e., non-removable) in the typical steerable bronchoscope, the outside diameter of the typical steerable bronchoscope must be large enough to also accommodate one or more working channels. Due to the large outside diameter of typical steerable bronchoscopes, certain portions of the airways may be unreachable by the steerable catheter because the diameter of the airway may be too small. Accordingly, it may be desirable to use steerable catheter  600  which may have a smaller outside diameter than the typical steerable bronchoscope. Bronchoscopic video camera  630  may be inserted working channel  608  of steerable catheter  600  and a real-time image feed is displayed to the physician or other healthcare professional. Using the real-time image feed, the physician or other healthcare professional may navigate steerable catheter  600  to very small diameter portions of the airway which were previously inaccessible by a typical steerable bronchoscope. Once the physician or other healthcare professional has reached the desired target tissue with steerable catheter  600 , the physician or other healthcare professional may remove bronchoscopic video camera  630  from working channel  608  of steerable catheter  600  and insert one or more other medical devices into working channel  608  as described more fully elsewhere herein. Additionally, because bronchoscopic video camera  630  is not fixed in steerable catheter  600 , the ratio(s) of the diameter(s) of working channel(s)  608  of steerable catheter  600  to the outside diameter of steerable catheter  600  may be much higher than the ratio(s) of the diameter(s) of working channel(s) of a typical steerable bronchoscope to the outside diameter of a typical steerable bronchoscope. 
     While the removable nature of bronchoscopic video camera  630  provides the above mentioned benefits, because the bronchoscopic video camera  630  is not fixed in steerable catheter  600 , the “up” orientation of the image feed from bronchoscopic video camera  630  as displayed to the physician or other healthcare professional may not be aligned with the “up” direction of steering actuator  614  of steerable catheter  600 . That is, depending on how the physician or other healthcare professional inserts bronchoscopic video camera  630  into working channel  608  of steerable catheter, what appears as “up” in the real-time image feed from bronchoscopic video camera  630  may not correspond to an “up” steering input to steering actuator  614 . Accordingly, the real time image feed may be rotated relative to the expected steering direction. This may introduce uncertainty and or confusion to the physician or other healthcare professional. For example, the physician or other healthcare professional may see an airway on the left hand side of the displayed real-time image feed and may accordingly manipulate handle  612  of steerable catheter to cause distal end portion  606  of steerable catheter  600  to steer left. However, because the orientation of the real-time image feed is not aligned with the with steering actuator  614  of steerable catheter  600 , the airway that the physician or other healthcare professional thought was on the left hand side of the real-time image feed is not actually reachable by a left hand steering input to steerable catheter  600 . Accordingly, the orientation of the image feed from bronchoscopic video camera  630  as displayed to the physician or other healthcare professional may not be aligned with steering actuator  614  of steerable catheter  600 . Thus, to ensure that the physician or other healthcare professional is navigating down the desired airway, the “up” orientation of the real-time image feed from bronchoscopic video camera  630  as displayed to the physician or other healthcare professional should be aligned with the “up” direction of steering actuator  614  of steerable catheter  600 . 
     Referring now to  FIG.  15   , one method of registering the real-time image feed from a bronchoscopic video camera  630  to a steerable catheter  600  is described. At step  900 , bronchoscopic video camera  630  is inserted into working channel  608  of steerable catheter  600 . In certain embodiments, tip  631  (see  FIG.  12 A ) of bronchoscopic video camera  630  is positioned proximate or extended past tip  607  of steerable catheter  600 . At step  902 , a real-time image feed of one or more reference points is generated using bronchoscopic video camera  630 , wherein the orientation of the reference point(s) is known. That is, the physician or other healthcare professional may know or ascertain the orientation of the reference point(s) independently from the real-time image feed. At step  904 , the physician or other healthcare professional orients handle  612  of steerable catheter  600  to a neutral position. Preferably, handle  612  of steerable catheter  600  is considered to be in a neutral position when longitudinal axis  613  of handle  612  is substantially vertical, when no “up” or “down” steering input is applied to steerable catheter  600  by steering actuator  614 , and when no “left” or “right” steering input is applied to steerable catheter  600  by rotation of handle  612  about longitudinal axis  613 . When in the neutral position, it is not required that elongate flexible shaft  602  of steerable catheter  600  be straight. Elongate flexible shaft  602  may be flexed; however it is contemplated that no additional steering inputs are applied to steerable catheter  600 . 
     At step  906 , the real-time image feed of bronchoscopic video camera  630  is displayed on display  80  of navigation system  70 . At step  908 , the real-time image feed is registered to steerable catheter  600  by rotating the displayed real-time image feed so that the reference point(s) in the real-time image feed are matched to the known orientation of the reference point(s). In certain embodiments, the physician or healthcare professional manually rotates the real-time image feed on display  80  of navigation system  70  using user interface device  84  (e.g., keyboard, mouse). In other embodiments, for example, navigation system  70  may automatically rotate the real-time image feed on display  80  of navigation system  70 . 
     Optionally, the registration may be confirmed by steering steerable catheter  600  to cause a deflection of distal end portion  606  of elongate flexible shaft  602  in a direction and observing that the displayed real-time image feed moves in that same direction. For example, if physician or other healthcare professional manipulates steering actuator  614  to cause an “up” deflection in distal end portion  606  of elongate flexible shaft  602 , the displayed real-time image feed will also move “up.” Similarly, if the physician or other healthcare professional manipulates steering actuator  614  to cause a “down” deflection in distal end portion  606  of elongate flexible shaft  602 , the displayed real-time image feed will also move “down.” Additionally, if the physician or other healthcare professional rotates handle  612  “left” or “right” to cause a “left” or “right” deflection in distal end portion  606  of elongate flexible shaft  602 , the displayed real-time image feed will also move “left” or “right.” Accordingly, after the real-time image feed is registered to steerable catheter  600 , what is displayed as “up,” “down,” “left,” and/or “right,” corresponds to “up,” “down,” “left,” and “right” steering inputs to steerable catheter  600 . That is, the orientation of the displayed real-time image feed is matched to the steering mechanics of steerable catheter  600 . 
     As shown in  FIGS.  16  and  16 A- 16 C , a jig  802  may be used in conjunction with the method of registering the real-time image feed from a bronchoscopic video camera  630  to a steerable catheter  600  described in  FIG.  15   . As shown in  FIG.  16   , jig  802  may include receiver  803  into which distal end portion  606  of steerable catheter  600  may be placed. Jig  802  further includes three round objects  804  which serve as the reference points described above. Accordingly, when viewed along arrow A, round objects  804  are known to be oriented as shown in  FIG.  16 A . When placed in jig  802 , bronchoscopic video camera  630  is inserted into working channel  608  of steerable catheter  600  and handle  612  of steerable catheter  600  is oriented in a neutral position, as described above. Thus if the three round objects  804  are rotated a certain angle in the displayed real-time image feed from bronchoscopic video camera  630  as shown in  FIG.  16 B , the real-time image feed needs to be registered by rotating the displayed real-time image feed so that the three round objects  804  in the real-time image feed are matched to the known orientation of the three round objects  804  as shown in  FIG.  16 C . While reference points are illustrated as three round objects  804 , it will be understood that any shape object may be used as a reference point, including, but not limited to, a T-shaped object, a cross-shaped object, a square shaped object, etc. Additionally, while three reference points are illustrated, it will be understood that jig  802  may include one or more reference points. In other embodiments, for example, jig  802  may include a picture or pattern which serves as the one or more reference points. 
     Another embodiment of the method of registering the real-time image feed from a bronchoscopic video camera  630  to a steerable catheter  600  is shown in  FIG.  17   . At step  910 , bronchoscopic video camera  630  is inserted into working channel  608  of steerable catheter  600 . In certain embodiments, tip  631  (see  FIG.  12 A ) of bronchoscopic video camera  630  is positioned proximate or extended past tip  607  of steerable catheter  600 . At step  912 , steerable catheter  600  is inserted into the airway of patient  10 . At step  914 , a real-time image feed of one or more reference points is generated using bronchoscopic video camera  630 , the reference point(s) comprising anatomical feature(s) of the airway wherein the orientation of the anatomical feature(s) is known. In certain embodiments, the anatomical feature(s) may include the right main bronchus (RMB) and the left main bronchus (LMB). 
     As shown in  FIG.  18 A , it is generally understood that the RMB and the LMB of most patients are oriented at about a 3 o&#39;clock position and about a 9 o&#39;clock position respectively when viewed with a typical steerable bronchoscope. Referring again to  FIG.  17   , at step  916 , the physician or other healthcare professional orients handle  612  of steerable catheter  600  to a neutral position. Preferably, handle  612  of steerable catheter  600  is considered to be in a neutral position when longitudinal axis  613  of handle  612  is substantially vertical, when no “up” or “down” steering input is applied to steerable catheter  600  by steering actuator  614 , and when no “left” or “right” steering input is applied to steerable catheter  600  by rotation of handle  612  about longitudinal axis  613 . When in the neutral position, it is not required that elongate flexible shaft  602  of steerable catheter  600  be straight. Elongate flexible shaft  602  may be flexed; however it is contemplated that no additional steering inputs are applied to steerable catheter  600 . 
     At step  918 , the real-time image feed of bronchoscopic video camera  630  is displayed on display  80  of navigation system  70 . As shown in  FIG.  18 B , the displayed real-time image feed of bronchoscopic video camera  630  shows the RMB and LMB rotated such that the RMB appears at about a 2 o&#39;clock position and the LMB appears at about an 8 o&#39;clock position. At step  920 , the real-time image feed is registered to steerable catheter  600  by rotating the displayed real-time image feed so that the anatomical feature(s) in the real-time image feed are matched to the known orientation of the anatomical feature(s). Thus as shown in  FIG.  18 C , after registration, the displayed real-time image feed of bronchoscopic video camera  630  shows the RMB and LMB at about a 3 o&#39;clock position and at about a 9 o&#39;clock position, respectively. In certain embodiments, the physician or healthcare professional manually rotates the real-time image feed on display  80  of navigation system  70  using user interface device  84  (e.g., mouse). In other embodiments, for example, navigation system  70  may automatically rotate the real-time image feed on display  80  of navigation system  70 . The method may optionally continue according to steps illustrated in  FIG.  17 A  as described more fully elsewhere herein. 
     Optionally, the registration may be confirmed by steering steerable catheter  600  to cause a deflection of distal end portion  606  of elongate flexible shaft  602  in a direction and observing that the displayed real-time image feed moves in that same direction. For example, if physician or other healthcare professional manipulates steering actuator  614  to cause an “up” deflection in distal end portion  606  of elongate flexible shaft  602 , the displayed real-time image feed will also move “up.” Similarly, if the physician or other healthcare professional manipulates steering actuator  614  to cause a “down” deflection in distal end portion  606  of elongate flexible shaft  602 , the displayed real-time image feed will also move “down.” Additionally, if the physician or other healthcare professional rotates handle  612  “left” or “right” to cause a “left” or “right” deflection in distal end portion  606  of elongate flexible shaft  602 , the displayed real-time image feed will also move “left” or “right.” Accordingly, after the real-time image feed is registered to steerable catheter  600 , what is displayed as “up,” “down,” “left,” and “right,” corresponds to “up,” “down,” “left,” and “right” steering inputs to steerable catheter  600 . 
     In some embodiments, the registration of the real-time image feed to steerable catheter  600  may be enhanced by correcting image distortion in the real time image feed. For example, bronchoscopic video cameras typically include fish-eye lenses which increase the field of view of the bronchoscopic video camera thus providing the physician or other healthcare professional with a larger view of the airway of patient  10 . However, the fish-eye lenses introduce barrel distortion into the real-time image feed. Due to this barrel distortion, the interpretation of the real-time image feed may be compromised. Correcting for this image distortion in the real-time image feed provides a more accurate depiction of the airway of patient  10 , thus permitting an enhanced registration of the real-time image feed to steerable catheter  600 . 
     Referring again to  FIG.  14   , in yet other embodiments, the virtual volumetric scene displayed in panel  712  may be registered to the real-time image feed from a bronchoscopic video camera  630  displayed in panel  716 . However, as steerable catheter  600  is navigated through the airways of patient  10 , steerable catheter  600  may be positioned in such a way such that what appears “up” in the real-time image feed may not correspond to the physical “up” direction of patient  10 . That is, the physical “up” of patient  10  usually corresponds to the anterior direction of patient  10  as patient  10  is oriented during the procedure. Typically, patient  10  is in the supine position and thus, the physical “up” of the patient will correspond to an actual “up.” However, in certain situations, patient  10  may be in different orientations during the procedure, such as on their side or chest However, the virtual volumetric scene displayed in panel  712  is shown with the chest of patient  10  facing up. Accordingly, the real-time image feed as shown in panel  716  may not match the virtual volumetric scene displayed in panel  712 . To assist the physician or other healthcare professional in navigating down the correct airway, the virtual volumetric scene may be registered to the real-time image feed, wherein the real-time image feed has been registered to steerable catheter  600 . 
     In some embodiments, image correction is applied to the real-time image feed to assist in registering the virtual volumetric scene to the real-time image feed. To register the virtual volumetric scene as shown in panel  712  with the real-time image feed from bronchoscopic video camera  630  as shown in panel  716 , the lens distortion of the real-time image feed must be corrected or the same lens distortion must be applied to the virtual volumetric scene. 
     After correcting the real-time image feed for lens distortion, virtual volumetric scene is registered to the real-time image feed. An initial registration may be performed in a region of the airway that is easily locatable with steerable catheter  600 , such as the trachea for example. Thus the virtual volumetric scene as shown in panel  712  may be manually or automatically rotated to match one or more airway structure(s) (e.g., RMB and LMB) visible in both the virtual volumetric scene and the real-time image. In various embodiments, a matching algorithm may then be used to maintain registration of the virtual volumetric scene to the real-time image feed as steerable catheter  600  is navigated through the airway. Other registration methods known in the art may also be applied without departing from the scope of the invention. For example, the virtual volumetric scene may be registered to the real-time image feed using intensity based maximization of information mutual to the real-time image feed and the virtual volumetric scene instead of matching structures. In other embodiments, for example, surface normals of the real-time image feed may be calculated using a linear shape from shading algorithm based on the unique camera and/or lighting configurations of bronchoscopic video camera  630 . The virtual volumetric scene may then be registered to the real-time image feed by matching the calculated surface normal with surface normal of the virtual volumetric scene. Accordingly, the registration of the virtual volumetric scene to the real-time image feed may cause both the real-time image feed and the virtual volumetric scene to be displayed on display  80  with “up” as “up.” 
     In yet other embodiments, the registration of the virtual volumetric scene to the real-time image feed may be enhanced by registering the real-time image feed to localization element  610  of steerable catheter  600 . By registering the real-time image feed to localization element  610 , both the real-time image feed and/or the virtual volumetric scene may be shown in the “up” orientation on display  80  no matter what the position and orientation (POSE) of localization element  610  in steerable catheter  600  is as tracked by navigation system  70 . The physician or other healthcare professional may always expect that an “up” steering input on steering actuator  614  will always result in the displayed real-time image moving “up.” Thus, even if physician or other healthcare professional moves handle  612  of steerable catheter such that longitudinal axis  613  is not substantially vertical and thereby causes a rotation of distal end portion  606  of steerable catheter  600 , because the real-time image feed is registered to steerable catheter  600  and to localization element  610 , navigation system  70  may display real-time image feed and/or virtual volumetric scene with “up” as “up.” Accordingly, the physician or other healthcare professional may still be able to easily determine how to manipulate steering actuator  614  of steerable catheter  600  to navigate steerable catheter  600  along navigation pathway  416  displayed in panel  712 . 
     Referring now to  FIG.  17 A , a method of registering the real-time image feed from bronchoscopic video camera  630  to localization element  610  of steerable catheter  600  is described. Preferably, registration of the real-time image feed from bronchoscopic video camera  630  to localization element  610  of steerable catheter  600  is performed after the real-time image feed from bronchoscopic video camera  630  is registered to steerable catheter  600 . At step  922 , navigation system  70  tracks the location of localization element  610  of steerable catheter  600 . At step  924 , the orientation of the registered real-time image feed with respect to localization element  610  is determined. Referring now to  FIG.  19   , a section view of steerable catheter  600  is shown to aid in describing the registration of the real-time image feed from bronchoscopic video camera  630  to localization element  610  of steerable catheter  600 . For purposes of simplicity not all structure of steerable catheter  600 , localization element  610 , and bronchoscopic video camera  630  are illustrated. As shown in  FIG.  19   , O i  represents the un-registered orientation of the real-time image feed from bronchoscopic video camera  630 . O R  represents the orientation of the real-time image feed from bronchoscopic video camera  630  after the real-time image feed from bronchoscopic video camera  630  is registered to steerable catheter  600 . Thus during registration of the real-time image feed from bronchoscopic video camera  630  to steerable catheter  600 , the real-time image feed was rotated by angle Θ (see  FIGS.  15 ,  17    steps  908 ,  920  respectively). 
     Thus, referring again to  FIG.  17 A , determining the orientation of the registered real-time image feed with respect to localization element  610  at step  924 , comprises determining the angle β from O R  to the tracked location of localization element  610 . At step  926 , the determined orientation (e.g., angle β) is recorded to navigation system  70 . Accordingly, after the real-time image feed from bronchoscopic video camera  630  is registered to localization element  610  of steerable catheter  600 , the real-time image feed and/or the virtual volumetric scene may be shown in the “up” orientation on display  80  regardless of the position and orientation (POSE) of localization element  610  in steerable catheter  600  as tracked by navigation system  70 . Additionally, by registering the real-time image feed from bronchoscopic video camera  630  to localization element  610  of steerable catheter  600 , the registration of the virtual volumetric scene may be maintained to the real-time image feed as steerable catheter  600  is navigated in the airway of patient  10 . 
     In various embodiments as described above, registering the real-time image feed from a bronchoscopic video camera  630  to a steerable catheter  600  permits displaying one or more navigational aids over the real-time image feed from bronchoscopic video camera  630 , wherein the navigational aids are registered to the real-time image feed. In certain embodiments, the navigational aids may be determined using the hybrid “Inspiration-Expiration” 3D airway model  414 . For example, in certain embodiments, navigation system  70  may overlay navigation pathway  416  onto the real-time image feed from bronchoscopic video camera  630 . In other embodiments, for example, navigation system may also overlay directional cues such as arrows or other indicators on the real-time image feed from bronchoscopic video camera  630 . Integrating navigational aids, including but not limited to navigation pathway  416  and/or directional cues, with the real-time image feed may assist the physician or other healthcare professional in navigating steerable catheter  600  to the desired target tissue. Accordingly, in certain embodiments wherein navigational aids are overlaid onto real-time image feed, a virtual volumetric scene does not need to be displayed on display  80  of navigation system  70 . 
     Although registering the real-time image feed from a bronchoscopic video camera  630  to a steerable catheter  600  has been described in detail herein, it will be understood that image feeds from other imaging devices  633  inserted into working channel  608  of steerable catheter  600  may be registered in similar manners. The imaging devices  633  may include, but are not limited to, endobronchial ultrasound (EBUS) device  634  (see  FIG.  12 B ), an optical coherence tomography device (OCT), and probe based Confocal Laser Endomicroscopy (pCLE). 
     Returning to  FIG.  14   , navigation system  70  may also display a graphical representation  708  of the respiratory cycle of patient  10  monitored using PTD  20 . In certain embodiments, one or more of the images and/or indicia displayed in panels  700 ,  702 ,  704 ,  706 ,  712  and  716  are displayed as a function of the monitored respiratory state. That is, images in image dataset  400  and/or generated from image dataset  400  are displayed on display  80  that depict the anatomy of patient  10  at the monitored respiratory state. For example, when the patient is at expiration as monitored by PTD  20 , images of the anatomy of the patient depicting the anatomy at expiration are displayed. Accordingly, when the patient is at inspiration as monitored by PTD  20 , images of the anatomy of patient  10  depicting the anatomy at inspiration are displayed. In other embodiments, one or more of the images displayed in panels  700 ,  702 ,  704 ,  706 ,  712  and  716  may not be displayed as a function of the monitored respiratory state. That is, images in image dataset  400  and/or generated from image dataset  400  are displayed on display  80  that depict the anatomy of patient  10  at one respiratory state. For example, when the patient is at expiration and inspiration as monitored by PTD  20 , images of the anatomy of patient  10  depicting the anatomy at expiration are displayed. In embodiments where images are not displayed according to the monitored respiratory state, an indication  710  of whether the displayed images match the monitored respiratory state may be shown (e.g., “Respiration Matched”, “Respiration out of Sync”). 
     Additionally, the display of indicia of the locations of the target tissue and/or indicia of the location of various medical devices may be synchronized or gated with an anatomical function, such as the cardiac or respiratory cycle, of patient  10 . That is, in certain embodiments, the indicia are displayed on display  80  as a function of the monitored respiratory state. In certain instances, the cardiac or respiratory cycle of patient  10  may cause the indicia to flutter or jitter within patient  10 . In these instances, the indicia will likewise flutter or jitter on the image(s) displayed on display  80 . 
     To eliminate the flutter of the indicia on the displayed image(s), the position and orientation (POSE) of localization elements  610 ,  660  is acquired at a repetitive point within each cycle of either the cardiac cycle or the respiratory cycle of patient  10 . To synchronize the acquisition of position data for localization elements  610 ,  660 , navigation system  70  may use a timing signal (e.g., respiratory phase signal) generated by PTD  20 ; however one skilled in the art will readily recognize other techniques for deriving a timing signal that correlate to at least one of the cardiac or respiratory cycle or other anatomical cycle of the patient. 
     As described above, the indicia indicate the location of steerable catheter  600  and percutaneous needle  650  based on the location of localization elements  610 ,  660  tracked by navigation system  70  as steerable catheter  600  and percutaneous needle  650  are navigated by the physician or other healthcare profession on and/or within patient  10 . Rather than display the indicia on a real-time basis, the display of the indicia may be periodically updated based on the timing signal from PTD  20 . In various embodiments, PTD  20  may be connected to navigation system  70 . Navigation system  70  may then track localization elements  610 ,  660  in response to a timing signal received from PTD  20 . The position of the indicia may then be updated on display  80 . It is readily understood that other techniques for synchronizing the display of an indicia based on the timing signal are within the scope of the present invention, thereby eliminating any flutter or jitter which may appear on the displayed image(s). It is also envisioned that a path (or projected path) of steerable catheter  600 , percutaneous needle  650 , and/or other medical devices may also be illustrated on the displayed image(s). 
     Utilizing the devices, systems, and/or methods described herein, a method of endobronchially confirming the location of a target in the lung of a patient and percutaneously intercepting the target at the confirmed location may be performed. In various embodiments, this method is performed during a second time interval after an image dataset  400  is generated during a first time interval. As illustrated in  FIGS.  20 A — 20 B, an embodiment of a method of endobronchially confirming the location of a target is illustrated. At step  1000 , PTD  20  is affixed to the external surface of a patient  10 . At step  1002 , the respiratory state of patient  10  may be monitored by tracking the location of PTD  20  using navigation system  70 . At step  1004 , navigation system  70  displays an image from image dataset  400  on display  80  as a function of the monitored respiratory state. The displayed image is selected from one or more images in image dataset  400  and/or is generated by navigation system  70  using one or more images in image dataset  400 . The displayed image is registered to PTD  20 . At step  1006 , an initial location of one or more target tissues in image dataset  400  is determined. This initial location of the target tissue is where it is believed that a target tissue is located within patient  10 . 
     In certain embodiments, for example, the initial location of the target tissue(s) is determined after image dataset  400  is generated during the first time interval. In certain embodiments, for example, the initial location of the target tissue(s) may be selected at the start of and/or during the second time interval. The initial location of the target tissue(s) may be determined automatically using nodule detection or segmentation algorithms carried out by processor  52  of image analysis system  50  and/or processor  72  of navigation system  70 . Additionally or alternatively, a physician or other healthcare professional manually identifies a target tissue on an image displayed on display  60  of image analysis system  50  and/or display  80  of navigation system  70 . The physician or other healthcare professional may then determine the initial location of the target tissue(s) by selecting the target tissue depicted on display(s)  50 ,  80  using user interface device(s)  64 ,  84  (e.g., by clicking on displayed target tissue with a mouse) or some other point selection tool. In other embodiments, the initial location of the target tissue may be determined by the physician or other healthcare professional using nodule segmentation tools and/or using nodule density information. An indicia  720  of the initial target tissue location may then be displayed on display  80  as shown in  FIG.  14   . 
     Returning to  FIG.  20 A , at step  1008 , a physician or other healthcare professional navigates steerable catheter  600  through the airway of patient  10  to a position proximate the initial location of the target tissue. Additionally, in certain embodiments, an imaging device  633  such as bronchoscopic video camera  630  (see  FIG.  12 A ) is inserted into working channel  608 , navigation system  70  displays on display  80  the real-time image feed of the inside of the airway of patient  10  generated by bronchoscopic video camera  630  as shown in panel  716  of  FIG.  14   . As described above the real-time image feed may be registered to steerable catheter  600 . In certain embodiments, navigation system  70  may overlay navigation pathway  416  onto the real-time image feed from bronchoscopic video camera  630 . In other embodiments, for example, navigation system may also overlay directional cues such as arrows or other indicators on the real-time image feed from bronchoscopic video camera  630 . Integrating navigational aids, including but not limited to navigation pathway  416  and/or directional cues, with the real-time image feed may assist the physician or other healthcare professional in navigating steerable catheter  600  to the desired target tissue. Accordingly, in certain embodiments wherein navigational aids are overlaid onto real-time image feed, a virtual volumetric scene does not need to be displayed on display  80  of navigation system  70 . 
     With reference again to  FIG.  20 A , as steerable catheter  600  is navigated through the airway of patient  10 , at step  1010 , navigation system  70  tracks the location of localization element  610  of steerable catheter  60 . As described above, an indicia of  718  of the location of steerable catheter  600  may also be displayed on display  80  as shown in panels  700 ,  702 ,  704 , and  706  of  FIG.  14   . 
     Referring now to  FIG.  20 B , the method continues at step  1012 , where information regarding the presence of the target tissue is generated using tissue sensing device  632  inserted into working channel  608  of steerable catheter  600 . In certain embodiments, tissue sensing device  632  may be imaging device  633  inserted into the airway of patient  10 , such as, for example, endobronchial ultrasound (EBUS) device  634  (see  FIG.  12 B ), an optical coherence tomography device (OCT), and/or probe based Confocal Laser Endomicroscopy (pCLE). Imaging device  633  may be extended out tip  607  of steerable catheter  600  and may generate a population of images of the target tissue. Where imaging device  637  is EBUS device  634 , EBUS device  634  may be a radial EBUS device or a linear EBUS device. Illustrated in  FIG.  21    is an exemplary image  721  of the target tissue generated by a radial EBUS device which may be displayed on display  80 . In other embodiments, tissue sensing device  632  may include, but is not limited to, a cell analysis device, a cancer detecting device, an exhaled breath condensate analyzer, a physiological characteristic sensor, a chemical analysis device, an aromatic hydrocarbon detection device, etc. 
     Returning to  FIG.  20 B , a confirmed location of the target is using the generated information regarding the presence of the target tissue and the tracked location of localization element  610  of steerable catheter  600 . For example, if tissue sensing device  632  is an imaging device  633  which generates a population of images of the target tissue, navigation system  70  tracks the extension (x), if any, of imaging device  633  in relation to localization element  610 . By tracking the extension (x) in relation to localization element  610  and the position and orientation (POSE) of localization element  610 , navigation system  70  knows the coordinates at which the population of images of the target tissue are generated and may thus determine the actual location and size of the target tissue within patient  10 . In certain embodiments, the confirmed location of the target tissue is determined in relation to the location of PTD  20 . In other embodiments, for example, the confirmed location of the target tissue is determined in relation to the location of electromagnetic (EM) field generator  82  of navigation system  70 . 
     At step  1016 , after the confirmed location of the target tissue is determined, the confirmed location of the target tissue is recorded. In one embodiment, for example, recording the confirmed location of the target tissue comprises recording a three-dimensional (3D) location of the confirmed target tissue in relation to PTD  20 . In another embodiment, for example, recording the confirmed location of the target tissue comprises recording a three-dimensional (3D) location of the confirmed target tissue in relation to electromagnetic (EM) field generator  82  of navigation system  70 . In one embodiment, for example, recording the confirmed location of the target tissue comprises recording four-dimensional data (4D) comprising a three-dimensional (3D) location of the confirmed target tissue in relation to PTD  20  and the respiratory state of patient  10  at the time the location of the target tissue was confirmed. In another embodiment, for example, recording the confirmed location of the target tissue comprises recording four-dimensional data (4D) comprising a three-dimensional (3D) location of the confirmed target tissue in relation to electromagnetic (EM) field generator  82  of navigation system  70  and the respiratory state of patient  10  at the time the location of the target tissue was confirmed. In yet another embodiment, for example, recording the confirmed location of the target tissue comprises recording four-dimensional (4D) data comprising a three-dimensional location (3D) of the confirmed target tissue in relation to PTD  20  and a cardiac state of the patient at the time the location of the target tissue was confirmed. In yet another embodiment, for example, recording the confirmed location of the target tissue comprises recording four-dimensional (4D) data comprising a three-dimensional location (3D) of the confirmed target tissue in relation to electromagnetic (EM) field generator  82  and a cardiac state of the patient at the time the location of the target tissue was confirmed. In various embodiments, this confirmed location of the target tissue may then be applied to one or more images from image dataset  400  depicting the airway at the respiratory state of patient  10  at the time the location of the target tissue was confirmed. This information is recorded in memory component  74  of navigation system  70 . 
     At step  1018 , the confirmed location of the target tissue is displayed on display  80  of navigation system  70  in one or more images from image dataset  400 . In certain embodiments, the displayed image(s) depict the airway of the patient at the respiratory state of patient  10  at the time the location of the target tissue was confirmed. As shown in  FIG.  22   , navigation system  70  may display an indicia  722  (shown as crosshair bounded by a square) of the confirmed location of the target tissue in a variety of images, including but not limited to, hybrid “Inspiration-Expiration” 3D airway model  414  in panel  700 , axial, coronal and oblique images in panels  702 ,  704  (shown enlarged in  FIG.  22 A ), and  706 , respectively, and virtual volumetric scene in panel  712 . Navigation system  70  may be able to display an indicia  720  (shown as circle in crosshair bounded by a circle) of the initial location of the target tissue, an indicia  722  of the confirmed location of the target tissue, and an indicia  718  (shown as crosshair) of steerable catheter  600 . The method may optionally continue according to steps illustrated in  FIGS.  20 C and  20 E  as described more fully elsewhere herein. 
     After the confirmed location of the target tissue is recorded, the physician or other healthcare professional can return to the confirmed location of the target tissue using a medical device, such as steerable catheter  600  or percutaneous needle  650 , without needing to re-register the patient. Accordingly, because, in certain embodiments, the confirmed location of the target tissue is recorded in relation to the location of patient tracking device  20 , the physician or other healthcare professional can navigate medical device to the confirmed location of the target tissue knowing the location of patient tracking device  20 . For example, in certain embodiments, the physician or other healthcare professional navigates to the confirmed location of the target tissue wherein navigation system  70  displays on display  80  only an indicia  722  of the confirmed location of the target tissue, an indicia  718  of steerable catheter  600 , and/or an indicia  734  of percutaneous needle  650  (see  FIG.  23   ). Using one or more of indicia  722 ,  718 ,  734 , physician or other healthcare professional navigates medical device to the confirmed location of the target tissue without needing navigation system  70  to display hybrid “Inspiration-Expiration” 3D airway model  414 , one or more images from image dataset  400 , navigation pathway  416 , and/or real time image feed from bronchoscopic video camera  630 . 
     Additionally, because, in certain embodiments, the confirmed location of the target tissue is recorded in relation to the location of electromagnetic (EM) field generator  82 , the physician or other healthcare professional can navigate medical device to the confirmed location of the target tissue if patient  10  has not moved relative to localization device  76 . For example, in certain embodiments, the physician or other healthcare professional navigates to the confirmed location of the target tissue wherein navigation system  70  displays on display  80  an indicia  722  of the confirmed location of the target tissue, an indicia  718  of steerable catheter  600 , and/or an indicia  734  of percutaneous needle  650 . Using one or more of indicia  722 ,  718 ,  734 , physician or other healthcare professional navigates medical device to the confirmed location of the target tissue without needing navigation system  70  to display hybrid “Inspiration-Expiration” 3D airway model, one or more images from image dataset  400 , navigation pathway  416 , and/or real time image feed from bronchoscopic video camera  630 . 
     Due to a variety of factors including, but not limited to, registration errors, shifting of patient location, changes in patient anatomy, the initial target location determined at step  1006  may not match the actual confirmed location of the target determined in step  1014 . Accordingly, without performing this confirmation step, a biopsy or medical therapy delivered to the initial target location may only partially intercept the actual target tissue or may be performed at an incorrect location such as healthy tissue. Insufficient and/or incorrect sampling or treatment of the target tissue and/or healthy tissue may lead to misdiagnoses and/or reduced treatment efficacy. Thus, by confirming the actual location of the target tissue in relation to PTD  20  and/or electromagnetic (EM) field generator  82 , intercepting (e.g., sampling, treating) the target tissue may be more accurately carried out in a variety of ways. Consequently, a physician or other healthcare professional may have a higher confidence that they are intercepting the target tissue. In certain embodiments, for example, the target tissue may be sampled using a variety of medical devices including, but not limited to, forceps devices, needles, brushes, etc. Treatment may also be endobronchially delivered to the confirmed location of the target tissue using a variety of medical devices including, but not limited to, ablation probes, radioactive seeds, implants, energy delivery devices, therapy delivery devices, delivery of energy activated substances (e.g., porfimer sodium) and energy devices, radiofrequency (RF) energy devices, cryotherapy devices, laser devices, microwave devices, diffuse infrared laser devices, fluids, drugs, combinations thereof, or the like. 
     In certain embodiments, the target tissue may not be reachable using endobronchial methods, accordingly, after the location of the target tissue is endobronchially confirmed, the target tissue may be percutaneously intercepted. The percutaneous interception may be carried out using a percutaneous device. Percutaneous device may preferably be percutaneous needle  650  described above. Because percutaneous needle  650  includes localization element  660 , the position and orientation (POSE) of tip  657  is tracked by navigation system  70 . Accordingly, navigation system  70  calculates and displays a trajectory of percutaneous needle  650  based on where percutaneous needle  650  is located and oriented by physician or other healthcare professional. However, in various embodiments, for example, percutaneous device may include, but is not limited to percutaneous needle  650 , a thoracic wedge resection device, a biopsy gun, a tracked core biopsy device, and/or any other medical device which may be used to percutaneously intercept a target tissue. The percutaneous devices preferably include a localization element so that the position and orientation (POSE) of the percutaneous devices may be tracked by navigation system  70 . 
     Referring now to  FIG.  20 C , at step  1020 , navigation system  70  displays on display  80  one or more trajectories from an entry point on the surface of patient  10  to the confirmed location of the target tissue. In certain embodiments, a displayed trajectory may be a suggested trajectory calculated by navigation system  70  wherein the suggested trajectory is the shortest distance from the confirmed location of the target tissue to the external surface of patient  10 . Navigation system  70  may utilize procedural position of patient  10  such as supine, prone, or laying on the left or right side to calculate the suggested trajectory. Accordingly, navigation system  70  may display a suggested trajectory that does not require altering the procedural position of patient  10 . For example, if the trajectory having the shortest distance from the confirmed location of the target tissue to the external surface of patient  10  requires entry through the back of patient  10 , but patient  10  is supine, an alternative suggested trajectory may be calculated and displayed which permits entry through the chest or side of patient  10 . 
     In certain embodiments, the suggested trajectory may be calculated that extends through the longest axis or longest diameter of the target tissue to ensure that the amount of target tissue sampled and/or treated is increased and/or maximized. Additionally, the patient  10  specific segmented target tissue may also have characteristics such as high density or spiculations that identify preferred regions to sample and/or treat. For example, in certain embodiments, the suggested trajectory may be calculated to extend through spiculations of the target tissue. In other embodiments, for example, a change in size of the target tissue may be seen between inspiration and expiration scans. In certain situations, this apparent change in size may be the result of infected tissue near the target tissue changing in size from inspiration to expiration. Typically, however, the target tissue will not change in size from inspiration to expiration, accordingly image analysis system  50  and/or navigation system  70  may be able to identify the target tissue based on a minimal or no change in density, size, location, and shape from inspiration to expiration. The suggested trajectory may thus be calculated to extend through such portions of the target tissue. 
     Additionally or alternatively, in certain embodiments, a displayed trajectory may be an actual trajectory calculated by navigation system  70  wherein the actual trajectory is the based on where percutaneous needle  650  is located and oriented by physician or other healthcare professional. Accordingly, in certain embodiments, navigation system  70  may be able to display on display  80  both a suggested trajectory and an actual trajectory of percutaneous needle  650 . Thus, a physician or other healthcare professional may move tip  657  of percutaneous needle  650  along the body of patient  10  and may orient percutaneous needle  650  so that the suggested trajectory and the actual trajectory displayed by navigation system  70  on display  80  are in alignment. Once the actual trajectory and the suggested trajectory are in alignment, the physician or other healthcare professional inserts percutaneous needle  650  into patient along the actual trajectory. In other embodiments, for example, no suggested trajectory may be displayed. 
       FIG.  23    illustrates one embodiment where navigation system  70  displays on display  80  suggested and actual trajectories from an entry point on the surface of patient  10  to the confirmed location of the target tissue. Panels  724  and  726  illustrate views that navigation system  70  may display. The displayed images may be selected from one or more images in image dataset  400  or may be generated by navigation system  70  using one or more images in image dataset  400 . Additionally, indicia  722  (shown as crosshair bounded by a square) of the confirmed location of the target tissue and suggested trajectory  730  from entry point  732  to the confirmed location of the target tissue are displayed on display  80 . Furthermore, an indicia  734  of the location of percutaneous needle  650  is displayed. In certain embodiments, for example, indicia  734  indicates the location of distal end portion  656  of percutaneous needle  650 . In other embodiments, for example, indicia  734  indicates the location of localization element  660  of percutaneous needle  650 . In yet other embodiments, for example, indicia  734  indicates the location of tip  657  of percutaneous needle  650 . An actual trajectory  736  of percutaneous needle  650  is also displayed on display  80  by navigation system  70  as shown in panels  724 ,  726 . As described more fully elsewhere herein, suggested trajectory  730  may avoid anatomical structures  740  such as, for example, bone, the heart, the liver, other organs, fissures, diseased tissue, such as chronic obstructive pulmonary disease (COPD) lung tissue, and blood vessels. Furthermore, as shown in panel  724 , navigation system  70  may be able to display a distance from tip  657  of percutaneous needle  650  to the confirmed location of the target tissue. 
     Referring again to  FIG.  20 C , at step  1022 , the physician or other healthcare professional inserts percutaneous needle  650  into the patient and navigates tip  657  proximate to the confirmed location of the target tissue. Then at step  1024 , the target tissue at the confirmed location is intercepted. In certain embodiments, for example, intercepting the target tissue at the confirmed location includes inserting a biopsy device into working channel  658  of percutaneous needle  650  and extending the biopsy device beyond tip  657  to sample the target tissue. In other embodiments, for example, intercepting the target tissue at the confirmed location includes inserting a therapy device into working channel  658  of percutaneous needle  650  and delivering therapy to the target tissue. In various embodiments, therapy device may be an ablation probe and navigation system  70  may be able to display on display  80  ablation models at the confirmed location of the target tissue. The ablation models may assist the physician or other healthcare professional in delivering the appropriate amount of treatment to the target tissue. The method may optionally continue according to steps illustrated in  FIG.  20 D  as described more fully elsewhere herein. 
     In various embodiments, the method as described in  FIGS.  20 A- 20 C  may further include the step of taking a population of images of at least a portion of percutaneous needle  650  at the confirmed location of the target tissue using imaging device  633  disposed in the airway of the patient. For example, as described above, imaging device  633  may be EBUS device  634  extended out tip  607  of steerable catheter  600 . The images may be used to confirm that tip  657  of percutaneous needle  650  was actually navigated to proximate the confirmed location of the target tissue. The image(s) of percutaneous needle  650  at the confirmed location of the target tissue may be recorded into a patient file as proof that the confirmed location of the target was reached. Additionally, imaging device  633  may be used to generate a population of images of the biopsy device sampling the target tissue and/or a population of images of the therapy device delivering therapy to the target tissue. The image(s) of biopsy device and therapy device sampling or delivering therapy to the target tissue may be recorded into a patient file as proof that the target tissue was sampled and/or treated. 
     Additional to or alternative to using imaging device  633  to evaluate whether percutaneous needle  650  has been navigated to proximate the confirmed location of the target tissue, a sensing device may be used to sense the presence of at least a portion of percutaneous needle  650  at the confirmed location of the target tissue. For example, the sensing device may include, but is not limited to, a heat sensor, magnetic sensor, electrical sensor, that may be extended out tip  607  of steerable catheter  600 . In certain embodiments, the sensing device may also be able to sense the presence of the biopsy device sampling the target tissue and/or the therapy device delivering therapy to the target tissue. For example, a heat sensor extended out tip  607  of steerable catheter  600  may be used to determine when the target tissue has been sufficiently treated. Additionally, navigating steerable catheter  600  down multiple airways adjacent to a target tissue and extending a heat sensor out tip  607  of steerable catheter  600  in each of the adjacent airways may be used to determine when a target tissue that is located between the adjacent airways has been treated. In certain embodiments, heat sensors may be placed in multiple airways adjacent to a target tissue using steerable catheter  600  and the multiple heat sensors may be used to determine when a target tissue that is located between the adjacent airways has been treated. 
     In various embodiments, the method as described in  FIGS.  20 A- 20 C  may further include the steps outlined in  FIG.  20 D . At step  1026 , using imaging device  633  disposed in the airway of patient  10 , a population of images are generated of one or more anatomical structures proximate the confirmed location of the target tissue. Anatomical structures may include, but are not limited to, bone, the heart, the liver, other organs, fissures, diseased tissue, such as, for example chronic obstructive pulmonary disease (COPD) lung tissue, and blood vessels. Accordingly, the anatomical structures may be any structure within the body of patient  10  that should be avoided, if possible, by percutaneous needle  650 . The imaging device, for example, may be EBUS device  634  extended out tip  607  of steerable catheter  600 . At step  1028 , a confirmed location of the anatomical structure(s) is determined in relation to the location of PTD  20  using the population of images and the tracked location of localization element  610  of steerable catheter  600 . For example, navigation system  70  tracks the extension (x), if any, of EBUS device  634  in relation to localization element  610 . By tracking the extension (x) in relation to localization element  610 , navigation system  70  knows the coordinates at which the population of images of the anatomical structure(s) are generated and may thus determine the actual location and size of the anatomical structure(s) within patient  10  with respect to PTD  20 . 
     At step  1030 , after the location of the anatomical structure(s) is determined, the confirmed location of the anatomical structure(s) is recorded. In one embodiment, for example, recording the confirmed location of the anatomical structure(s) comprises recording a three-dimensional (3D) location of the confirmed anatomical structure(s) in relation to PTD  20 . In another embodiment, for example, recording the confirmed location of the anatomical structure(s) comprises recording a three-dimensional (3D) location of the confirmed anatomical structure(s) in relation to electromagnetic (EM) field generator  82  of navigation system  70 . In one embodiment, for example, recording the confirmed location of the anatomical structure(s) comprises recording four-dimensional data (4D) comprising a three-dimensional (3D) location of the confirmed anatomical structure(s) in relation to PTD  20  and the respiratory state of patient  10  at the time the location of the anatomical structure(s) was confirmed. In another embodiment, for example, recording the confirmed location of the anatomical structure(s) comprises recording four-dimensional data (4D) comprising a three-dimensional (3D) location of the confirmed anatomical structure(s) in relation to electromagnetic (EM) field generator  82  of navigation system  70  and the respiratory state of patient  10  at the time the location of the anatomical structure(s) was confirmed. In yet another embodiment, for example, recording the confirmed location of the anatomical structure(s) comprises recording four-dimensional (4D) data comprising a three-dimensional location (3D) of the confirmed anatomical structure(s) in relation to PTD  20  and a cardiac state of the patient at the time the location of the anatomical structure(s) was confirmed. In yet another embodiment, for example, recording the confirmed location of the anatomical structure(s) comprises recording four-dimensional (4D) data comprising a three-dimensional location (3D) of the confirmed anatomical structure(s) in relation to electromagnetic (EM) field generator  82  and a cardiac state of the patient at the time the location of the anatomical structure(s) was confirmed. In various embodiments, this confirmed location of the anatomical structure(s) may then be applied to one or more images from image dataset  400  depicting the airway at the respiratory state of patient  10  at the time the location of the anatomical structure(s) was confirmed. This information is recorded in memory component  74  of navigation system  70 . 
     Optionally, at step  1032 , navigation system  70  calculates and displays a trajectory of a percutaneous device (e.g., percutaneous needle  650 ) from the confirmed location of the target tissue to a corresponding entry point on the body of patient  10 . This trajectory may avoid some or all of the anatomical structures. Accordingly, if a physician or other healthcare professional inserts percutaneous device, such as percutaneous needle  650 , following this trajectory, the percutaneous device may avoid some or all of the anatomical structures thereby preventing damage to the anatomical structure(s). 
     In various embodiments, in addition to calculating and/or displaying any of the trajectories described herein, navigation system  70  displays an extended trajectory of a medical device that may be inserted into working channel  658  of percutaneous needle  650  and extended past tip  657 . In certain embodiments, for example, the medical device may include, but is not limited to, an aspiration needle, a forceps device, a brush, or any type of biopsy device. In other embodiments, for example, the medical device may include, but is not limited to, an ablation probe, a radioactive seed placement device, a fiducial placement device, and/or any type of therapy device. The extended trajectory displays the potential extension of the medical device so that it may be confirmed that potential extension of the medical device will sample and/or treat the target tissue and will not hit one or more anatomical structures. The displayed extended trajectory may also aid in ensuring that a sufficient sample is taken and/or that the treatment may be properly placed in the target tissue. 
     In various embodiments, the method as described in  FIGS.  20 A- 20 B  may further include the steps outlined in  FIG.  20 E . In addition to or alternative to generating images of anatomical structures of patient  10  using imaging device  633  inserted into the airway of patient  10 , one or more atlas models are employed to assist the procedure during the second time interval. The atlas model(s) are three-dimensional models of human anatomy and therefore include a variety of anatomical structures. The anatomical structures may include, but are not limited to, bone, the heart, the liver, other organs, fissures, diseased tissue, such as, for example, chronic obstructive pulmonary disease (COPD) lung tissue, and blood vessels. Accordingly, the anatomical structures may be any structure within the body of patient  10  that should be avoided, if possible, by percutaneous device (e.g., percutaneous needle  650 ). Additionally, the atlas model(s) may include weighted information related to the acceptability of a planned trajectory or planned ablation procedure to determine the optimal plan. This weighted information may include, but is not limited to, information regarding which anatomical structure(s) cannot be crossed by a medical device, information regarding avoid anatomical structure(s) by at least a given distance, and information regarding the heat sink effect of anatomical structure(s) so that ablation location and amount may be adjusted. 
     Thus as shown in  FIG.  20 E  at step  1034 , one or more atlas models is matched to image dataset  400  of patient  10  wherein the matching may comprise deforming the atlas model(s) to the image dataset  400  and/or registering the atlas model(s) to patient  10 . At step  1036 , navigation system  70  identifies anatomical structure(s) to be avoided by the trajectory of the percutaneous device. At step  1038 , navigation system  70  may calculate and display a trajectory of the percutaneous device from the confirmed location of the target tissue to a corresponding entry point on the body of patient  10 . This trajectory may avoid some or all of the anatomical structures. Accordingly, if a physician or other healthcare professional inserts percutaneous device, such as percutaneous needle  650 , following this trajectory, percutaneous device may avoid some or all of the anatomical structures thereby preventing damage to the anatomical structure(s). Following the steps outlined in  FIG.  20 E , the method may optionally further include the steps illustrated in  FIG.  20 C . 
     In any of the embodiments of the methods described herein, a dye may be injected into the target tissue at the confirmed location using a needle inserted into working channel  608  of steerable catheter  600  or using a needle inserted into working channel  658  of percutaneous needle  650 . Thus, when sampling the target tissue using a medical device inserted into working channel  658  of percutaneous needle  650 , the presence of dye in the sample provides another indication that the correct target tissue was sampled. These additional steps may be helpful, for example, in lung resections where there is significant movement of the lungs of patient  10 . For example, during lung resections there may be a gap between the chest wall and the lung and the physician or other healthcare profession may use a rigid scope to enter into patient  10 . Because the confirmed target tissue was previously dyed using a needle inserted into working channel  608  of steerable catheter  600  or using a needle inserted into working channel  658  of percutaneous needle  650 , the physician or other healthcare professional may be able to visually see the dye. This may assist the physician or healthcare professional in sampling and/or treating the correct target tissue. 
     Additionally, in various embodiments of the methods described herein, after tip  607  of steerable catheter  600  has been navigated proximate confirmed location of target tissue a sample of air proximate the confirmed location of the target tissue may be taken. Then cells, scents or other potential indicators of cancer within the air sample may then be analyzed to determine if the target tissue is cancerous. In certain embodiments, a breath analysis device may be inserted into working channel  608  of steerable catheter  600  and this breath analysis device may sample the air in situ. In other embodiments, a vacuum of air may be drawn on working channel  608  from port  616  to sample the air proximate the confirmed location of the target tissue may be taken. The vacuum may be created by a syringe inserted into port  616  or by some other suction device known in the art. In yet other embodiments, a sample of air proximate an airway segment near the confirmed location of the target tissue may be taken instead of, or in addition to, the sample taken proximate the confirmed location of the target. 
     Furthermore, in any of the embodiments of the methods described herein, navigation system  70  may be able to control a robotic medical device having a percutaneous needle. Navigation system  70  may be able to cause robotic medical device to navigate a percutaneous needle to the calculated entry point on the surface of patient  10 . The percutaneous needle may then be inserted into patient  10  at the calculated entry point on the surface of patient  10  and the percutaneous needle may be extended to the confirmed location along the calculated trajectory. Thus, a robotic medical device may use information from navigation system  70  to perform any of the methods described herein. 
     The accompanying Figures and this description depict and describe certain embodiments of a navigation system (and related methods and devices) in accordance with the present invention, and features and components thereof. It should also be noted that any references herein to front and back, right and left, top and bottom and upper and lower are intended for convenience of description, not to limit the present invention or its components to any one positional or spatial orientation. 
     It is noted that the terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “contain” (and any form of contain, such as “contains” and “containing”), and “include” (and any form of include, such as “includes” and “including”) are open-ended linking verbs. Thus, a method, an apparatus, or a system that “comprises,” “has,” “contains,” or “includes” one or more items possesses at least those one or more items, but is not limited to possessing only those one or more items. Individual elements or steps of the present methods, apparatuses, and systems are to be treated in the same manner. 
     The terms “a” and “an” are defined as one or more than one. The term “another” is defined as at least a second or more. The term “coupled” encompasses both direct and indirect connections, and is not limited to mechanical connections. 
     Those of skill in the art will appreciate that in the detailed description above, certain well known components and assembly techniques have been omitted so that the present methods, apparatuses, and systems are not obscured in unnecessary detail. 
     While various embodiments of the invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the invention should not be limited by any of the above-described embodiments, but should be defined only in accordance with the following claims and their equivalents. 
     The previous description of the embodiments is provided to enable any person skilled in the art to make or use the invention. While the invention has been particularly shown and described with reference to embodiments thereof, it will be understood by those skilled in art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. For example, the patient tracking device, steerable catheter, percutaneous needle, and localization elements may be constructed from any suitable material, and may be a variety of different shapes and sizes, not necessarily specifically illustrated, while still remaining within the scope of the invention.