Patent Publication Number: US-2023149108-A1

Title: Systems and methods of continuous registration for image-guided surgery

Description:
RELATED APPLICATIONS 
     This patent application claims priority to and the benefit of the filing date of U.S. Provisional Patent Application 62/416,393, entitled “Systems and Methods of Continuous Registration For Image-Guided Surgery,” filed Nov. 2, 2016, which is incorporated by reference herein in its entirety. 
    
    
     FIELD 
     The present disclosure is directed to systems and methods for conducting an image-guided procedure, and more particularly to systems and methods for registering a model of patient anatomy to one or more instruments being used in a medical procedure. 
     BACKGROUND 
     Minimally invasive medical techniques are intended to reduce the amount of tissue that is damaged during medical procedures, thereby reducing patient recovery time, discomfort, and deleterious side effects. Such minimally invasive techniques may be performed through natural orifices in a patient anatomy or through one or more surgical incisions. Through these natural orifices or incisions clinicians may insert minimally invasive medical instruments (including surgical, diagnostic, therapeutic, or biopsy instruments) to reach a target tissue location. To assist with reaching the target tissue location, the location and movement of the medical instruments may be correlated with pre-operative or intra-operative images of the patient anatomy. With the image-guided instruments correlated to the images, the instruments may navigate natural or surgically created passageways in anatomic systems such as the lungs, the colon, the intestines, the kidneys, the heart, the circulatory system, or the like. Systems and methods for performing registered models for use during image-guided surgery with minimal clinical disturbances are needed. 
     SUMMARY 
     The embodiments of the invention are best summarized by the claims that follow the description. 
     However, an exemplary method of registering a model of one or more anatomic passageways of a patient to a patient space may include accessing a set of model points in a model space of the model of one or more anatomic passageways of the patient, collecting a first set of measured points along a length of a catheter inserted into the one or more anatomic passageways of the patient, the measured points determined by a shape of the catheter in the patient space, and assigning points of the first set of measured points to a plurality of first subsets of measured points. The exemplary method may further include registering the first subsets of measured points with the set of model points to produce a first plurality of registration candidates, comparing the registration candidates to identify an optimal subset associated with an optimal registration of the first plurality of registration candidates, and displaying a visual representation of the optimal registration in a user interface provided by a display. The optimal registration translates the set of model points and at least one subset of the first set of measured points into a common space. 
     Another exemplary method of registering a model of one or more anatomic passageways of a patient to a patient space, may include accessing a set of model points of the model of one or more anatomic passageways of a patient, collecting a set of measured points along a length of a catheter inserted into the one or more anatomic passageways of the patient, the measured points determined by a shape of the catheter in the patient space, and registering subsets of the set of measured points with the set of model points to produce a plurality of registration candidates. The exemplary method may further include selecting a registration candidate of the plurality of registration candidates for use in performing a medical procedure and applying the selected registration candidate to the set of model points of the model to register the model to the patient space. 
     An exemplary medical imaging system may include a movement detector, a flexible catheter having a proximal end coupled to an instrument carriage that is moveable along an insertion stage, and a point gathering instrument extending along a length of the flexible catheter. The exemplary system may further include a tracking system that is configured to register a set of measured points collected by the point gathering instrument to a model of one or more anatomic passageways. The tracking system may access a set of model points in a model space and collect the set of measured points along the length of the flexible catheter inserted into the one or more anatomic passageways of a patient, the measured points being determined by a shape of the catheter in a patient space. The tracking system may also assign the set of measured points into subsets according to a periodic physiological function monitored by the movement detector, select a first registration candidate from a plurality of registration candidates based on the subsets of measured points, and apply the selected first registration candidate to the set of model points of the model to register the model to the patient space. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory in nature and are intended to provide an understanding of the present disclosure without limiting the scope of the present disclosure. In that regard, additional aspects, features, and advantages of the present disclosure will be apparent to one skilled in the art from the following detailed description. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         FIG.  1    is a simplified diagram of a teleoperated medical system, in accordance with embodiments of the present disclosure. 
         FIG.  2 A  is a simplified diagram of a medical instrument system utilizing aspects of the present disclosure. 
         FIG.  2 B  is a simplified diagram of a medical instrument with an extended medical tool according to some embodiments. 
         FIGS.  3 A and  3 B  are side views of a patient coordinate space including a medical instrument mounted on an insertion assembly according to some embodiments of the present disclosure. 
         FIG.  4 A,  4 B,  4 C, and  4 D  illustrates the distal end of the medical instrument system of  FIGS.  2 ,  3 A,  3 B , during insertion within a human lung. 
         FIG.  5    is a flowchart illustrating a method used to provide guidance in an image-guided surgical procedure according to an embodiment of the present disclosure. 
         FIGS.  6 A,  6 B, and  6 C  illustrate steps in segmentation process that generates a model of a human lung for registration according to an embodiment of the present disclosure. 
         FIG.  7    illustrates a flowchart of a portion of an image-guided surgical procedure according to an embodiment of the present disclosure. 
         FIGS.  8 A and  8 B  illustrate a phase-based binning process and an amplitude-based binning process for collecting measured points within patient anatomy according to an embodiment of the present disclosure. 
         FIG.  9    illustrates phase-based and amplitude-based binning of measured points within patient anatomy according to an embodiment of the present disclosure. 
         FIGS.  10 A,  10 B,  10 C, and  10 D  illustrate insertion depth-based binning of measured points within patient anatomy according to an embodiment of the present disclosure. 
         FIGS.  11 A and  11 B  illustrate registration between a centerline model of patient anatomy and a set of measured points according to an embodiment of the present disclosure. 
         FIGS.  12 A and  12 B  illustrate registration between a centerline model of patient anatomy and a set of measured points according to another embodiment of the present disclosure. 
         FIG.  13 A and  13 B  illustrates a display stage of a registration technique according to an embodiment of the present disclosure. 
     
    
    
     Embodiments of the present disclosure and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures, wherein showings therein are for purposes of illustrating embodiments of the present disclosure and not for purposes of limiting the same. 
     DETAILED DESCRIPTION 
     In the following description, specific details are set forth describing some embodiments consistent with the present disclosure. Numerous specific details are set forth in order to provide a thorough understanding of the embodiments. It will be apparent, however, to one skilled in the art that some embodiments may be practiced without some or all of these specific details. The specific embodiments disclosed herein are meant to be illustrative but not limiting. One skilled in the art may realize other elements that, although not specifically described here, are within the scope and the spirit of this disclosure. In addition, to avoid unnecessary repetition, one or more features shown and described in association with one embodiment may be incorporated into other embodiments unless specifically described otherwise or if the one or more features would make an embodiment non-functional. 
     In some instances well known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the embodiments. 
     This disclosure describes various instruments and portions of instruments in terms of their state in three-dimensional space. As used herein, the term “position” refers to the location of an object or a portion of an object in a three-dimensional space (e.g., three degrees of translational freedom along Cartesian x-, y-, and z-coordinates). As used herein, the term “orientation” refers to the rotational placement of an object or a portion of an object (three degrees of rotational freedom—e.g., roll, pitch, and yaw). As used herein, the term “pose” refers to the position of an object or a portion of an object in at least one degree of translational freedom and to the orientation of that object or portion of the object in at least one degree of rotational freedom (up to six total degrees of freedom). As used herein, the term “shape” refers to a set of poses, positions, or orientations measured along an object. 
       FIG.  1    is a simplified diagram of a teleoperated medical system  100  according to some embodiments. In some embodiments, teleoperated medical system  100  may be suitable for use in, for example, surgical, diagnostic, therapeutic, or biopsy procedures. As shown in  FIG.  1   , medical system  100  generally includes a teleoperational manipulator assembly  102  for operating a medical instrument  104  in performing various procedures on a patient P. Teleoperational manipulator assembly  102  is mounted to or near an operating table T. An operator input system called a master assembly  106  allows an operator  0  (e.g., a surgeon, a clinician, or a physician) as illustrated in  FIG.  1    to view the interventional site and to control teleoperational manipulator assembly  102 . 
     Master assembly  106  may be located at a physician&#39;s console which is usually located in the same room as operating table T, such as at the side of a surgical table on which patient P is located. However, it should be understood that operator  0  can be located in a different room or a completely different building from patient P. Master assembly  106  generally includes one or more control devices for controlling teleoperational manipulator assembly  102 . The control devices may include any number of a variety of input devices, such as joysticks, trackballs, data gloves, trigger-guns, hand-operated controllers, voice recognition devices, body motion or presence sensors, and/or the like. To provide operator O a strong sense of directly controlling instruments  104  the control devices may be provided with the same degrees of freedom as the associated medical instrument  104 . In this manner, the control devices provide operator O with telepresence or the perception that the control devices are integral with medical instruments  104 . 
     In some embodiments, the control devices may have more or fewer degrees of freedom than the associated medical instrument  104  and still provide operator O with telepresence. In some embodiments, the control devices may optionally be manual input devices which move with six degrees of freedom, and which may also include an actuatable handle for actuating instruments (for example, for closing grasping jaws, applying an electrical potential to an electrode, delivering a medicinal treatment, and/or the like). 
     Teleoperational manipulator assembly  102  supports medical instrument  104  and may include a kinematic structure of one or more non-servo controlled links (e.g., one or more links that may be manually positioned and locked in place, generally referred to as a set-up structure) and a teleoperational manipulator. Teleoperational manipulator assembly  102  may optionally include a plurality of actuators or motors that drive inputs on medical instrument  104  in response to commands from the control system (e.g., a control system  112 ). The actuators may optionally include drive systems that when coupled to medical instrument  104  may advance medical instrument  104  into a naturally or surgically created anatomic orifice. Other drive systems may move the distal end of medical instrument  104  in multiple degrees of freedom, which may include three degrees of linear motion (e.g., linear motion along the X, Y, Z Cartesian axes) and in three degrees of rotational motion (e.g., rotation about the X, Y, Z Cartesian axes). Additionally, the actuators can be used to actuate an articulable end effector of medical instrument  104  for grasping tissue in the jaws of a biopsy device and/or the like. Actuator position sensors such as resolvers, encoders, potentiometers, and other mechanisms may provide sensor data to medical system  100  describing the rotation and orientation of the motor shafts. This position sensor data may be used to determine motion of the objects manipulated by the actuators. 
     Teleoperated medical system  100  may include a sensor system  108  with one or more sub-systems for receiving information about the instruments of teleoperational manipulator assembly  102 . Such sub-systems may include a position/location sensor system (e.g., an electromagnetic (EM) sensor system); a shape sensor system for determining the position, orientation, speed, velocity, pose, and/or shape of a distal end and/or of one or more segments along a flexible body that may make up medical instrument  104 ; and/or a visualization system for capturing images from the distal end of medical instrument  104 . 
     Teleoperated medical system  100  also includes a display system  110  for displaying an image or representation of the surgical site and medical instrument  104  generated by sub-systems of sensor system  108 . Display system  110  and master assembly  106  may be oriented so operator O can control medical instrument  104  and master assembly  106  with the perception of telepresence. 
     In some embodiments, medical instrument  104  may have a visualization system (discussed in more detail below), which may include a viewing scope assembly that records a concurrent or real-time image of a surgical site and provides the image to the operator or operator O through one or more displays of medical system  100 , such as one or more displays of display system  110 . The concurrent image may be, for example, a two or three dimensional image captured by an endoscope positioned within the surgical site. In some embodiments, the visualization system includes endoscopic components that may be integrally or removably coupled to medical instrument  104 . However in some embodiments, a separate endoscope, attached to a separate manipulator assembly may be used with medical instrument  104  to image the surgical site. In some examples, the endoscope may include one or more mechanisms for cleaning one or more lenses of the endoscope when the one or more lenses become partially and/or fully obscured by fluids and/or other materials encountered by the endoscope. In some examples, the one or more cleaning mechanisms may optionally include an air and/or other gas delivery system that is usable to emit a puff of air and/or other gasses to blow the one or more lenses clean. Examples of the one or more cleaning mechanisms are discussed in more detail in International Publication No. WO/2016/025465 (filed Aug. 11, 2016) (disclosing “Systems and Methods for Cleaning an Endoscopic Instrument”), which is incorporated by reference herein in its entirety. The visualization system may be implemented as hardware, firmware, software or a combination thereof which interact with or are otherwise executed by one or more computer processors, which may include the processors of a control system  112 . The processors of the control system  112  may execute instructions corresponding to methods and operators described herein. 
     Display system  110  may also display an image of the surgical site and medical instruments captured by the visualization system. In some examples, teleoperated medical system  100  may configure medical instrument  104  and controls of master assembly  106  such that the relative positions of the medical instruments are similar to the relative positions of the eyes and hands of operator  0 . In this manner operator  0  can manipulate medical instrument  104  and the hand control as if viewing the workspace in substantially true presence. By true presence, it is meant that the presentation of an image is a true perspective image simulating the viewpoint of a physician that is physically manipulating medical instrument  104 . 
     In some examples, display system  110  may present images of a surgical site recorded pre-operatively or intra-operatively using image data from imaging technology such as, computed tomography (CT), magnetic resonance imaging (MM), fluoroscopy, thermography, ultrasound, optical coherence tomography (OCT), thermal imaging, impedance imaging, laser imaging, nanotube X-ray imaging, and/or the like. The pre-operative or intra-operative image data may be presented as two-dimensional, three-dimensional, or four-dimensional (including e.g., time based or velocity based information) images and/or as images from models created from the pre-operative or intra-operative image data sets. 
     In some embodiments, often for purposes of imaged guided surgical procedures, display system  110  may display a virtual navigational image in which the actual location of medical instrument  104  is registered (i.e., dynamically referenced) with the preoperative or concurrent images/model. This may be done to present the operator  0  with a virtual image of the internal surgical site from a viewpoint of medical instrument  104 . In some examples, the viewpoint may be from a tip of medical instrument  104 . An image of the tip of medical instrument  104  and/or other graphical or alphanumeric indicators may be superimposed on the virtual image to assist operator O controlling medical instrument  104 . In some examples, medical instrument  104  may not be visible in the virtual image. 
     In some embodiments, display system  110  may display a virtual navigational image in which the actual location of medical instrument  104  is registered with preoperative or concurrent images to present the operator  0  with a virtual image of medical instrument  104  within the surgical site from an external viewpoint. An image of a portion of medical instrument  104  or other graphical or alphanumeric indicators may be superimposed on the virtual image to assist operator O in the control of medical instrument  104 . As described herein, visual representations of data points may be rendered to display system  110 . For example, measured data points, moved data points, registered data points, and other data points described herein may be displayed on display system  110  in a visual representation. The data points may be visually represented in a user interface by a plurality of points or dots on display system  110  or as a rendered model, such as a mesh or wire model created based on the set of data points. In some examples, the data points may be color coded according to the data they represent. In some embodiments, a visual representation may be refreshed in display system  110  after each processing operation has been implemented to alter the data points. In some embodiments, a virtual navigational image may be presented in the display  110  that depicts a model of an anatomical passageway from a perspective of an instrument being inserted along or through a corresponding actual anatomical passageway. 
     Teleoperated medical system  100  may also include control system  112 . Control system  112  includes at least one memory and at least one computer processor (not shown) for effecting control between medical instrument  104 , master assembly  106 , sensor system  108 , and display system  110 . Control system  112  also includes programmed instructions (e.g., a non-transitory machine-readable medium storing the instructions) to implement some or all of the methods described in accordance with aspects disclosed herein, including instructions for providing information to display system  110 . While control system  112  is shown as a single block in the simplified schematic of  FIG.  1   , the system may include two or more data processing circuits with one portion of the processing optionally being performed on or adjacent to teleoperational manipulator assembly  102 , another portion of the processing being performed at master assembly  106 , and/or the like. The processors of control system  112  may execute instructions comprising instruction corresponding to processes disclosed herein and described in more detail below. Any of a wide variety of centralized or distributed data processing architectures may be employed. Similarly, the programmed instructions may be implemented as a number of separate programs or subroutines, or they may be integrated into a number of other aspects of the teleoperational systems described herein. In one embodiment, control system  112  supports wireless communication protocols such as Bluetooth, IrDA, HomeRF, IEEE 802.11, DECT, and Wireless Telemetry. 
     In some embodiments, control system  112  may receive force and/or torque feedback from medical instrument  104 . Responsive to the feedback, control system  112  may transmit signals to master assembly  106 . In some examples, control system  112  may transmit signals instructing one or more actuators of teleoperational manipulator assembly  102  to move medical instrument  104 . Medical instrument  104  may extend into an internal surgical site within the body of patient P via openings in the body of patient P. Any suitable conventional and/or specialized actuators may be used. In some examples, the one or more actuators may be separate from, or integrated with, teleoperational manipulator assembly  102 . In some embodiments, the one or more actuators and teleoperational manipulator assembly  102  are provided as part of a teleoperational cart positioned adjacent to patient P and operating table T. 
     Control system  112  may optionally further include a virtual visualization system to provide navigation assistance to operator O when controlling medical instrument  104  during an image-guided surgical procedure. Virtual navigation using the virtual visualization system may be based upon reference to an acquired preoperative or intraoperative dataset of anatomic passageways. The virtual visualization system processes images of the surgical site imaged using imaging technology such as computerized tomography (CT), magnetic resonance imaging (MRI), fluoroscopy, thermography, ultrasound, optical coherence tomography (OCT), thermal imaging, impedance imaging, laser imaging, nanotube X-ray imaging, and/or the like. Software, which may be used in combination with manual inputs, is used to convert the recorded images into segmented two dimensional or three dimensional composite representation of a partial or an entire anatomic organ or anatomic region. An image data set is associated with the composite representation. The composite representation and the image data set describe the various locations and shapes of the passageways and their connectivity. The images used to generate the composite representation may be recorded preoperatively or intra-operatively during a clinical procedure. In some embodiments, a virtual visualization system may use standard representations (i.e., not patient specific) or hybrids of a standard representation and patient specific data. The composite representation and any virtual images generated by the composite representation may represent the static posture of a deformable anatomic region during one or more phases of motion (e.g., during an inspiration/expiration cycle of a lung). 
     During a virtual navigation procedure, sensor system  108  may be used to compute an approximate location of medical instrument  104  with respect to the anatomy of patient P. The location can be used to produce both macro-level (external) tracking images of the anatomy of patient P and virtual internal images of the anatomy of patient P. The system may implement one or more electromagnetic (EM) sensor, fiber optic sensors, and/or other sensors to register and display a medical implement together with preoperatively recorded surgical images, such as those from a virtual visualization system, are known. For example U.S. Patent Application No. 13/107,562 (filed May 13, 2011) (disclosing “Medical System Providing Dynamic Registration of a Model of an Anatomic Structure for Image-Guided Surgery”) which is incorporated by reference herein in its entirety, discloses one such system. Teleoperated medical system  100  may further include optional operations and support systems (not shown) such as illumination systems, steering control systems, irrigation systems, and/or suction systems. In some embodiments, teleoperated medical system  100  may include more than one teleoperational manipulator assembly and/or more than one master assembly. The exact number of teleoperational manipulator assemblies will depend on the surgical procedure and the space constraints within the operating room, among other factors. Master assembly  106  may be collocated or they may be positioned in separate locations. Multiple master assemblies allow more than one operator to control one or more teleoperational manipulator assemblies in various combinations. 
       FIG.  2 A  is a simplified diagram of a medical instrument system  200  according to some embodiments. In some embodiments, medical instrument system  200  may be used as medical instrument  104  in an image-guided medical procedure performed with teleoperated medical system  100 . In some examples, medical instrument system  200  may be used for non-teleoperational exploratory procedures or in procedures involving traditional manually operated medical instruments, such as endoscopy. Optionally medical instrument system  200  may be used to gather (i.e., measure) a set of data points corresponding to locations within anatomic passageways of a patient, such as patient P. 
     Medical instrument system  200  includes elongate device  202 , such as a flexible catheter, coupled to a drive unit  204 . Elongate device  202  includes a flexible body  216  having proximal end  217  and distal end or tip portion  218 . In some embodiments, flexible body  216  has an approximately 3 mm outer diameter. Other flexible body outer diameters may be larger or smaller. 
     Medical instrument system  200  further includes a tracking system  230  for determining the position, orientation, speed, velocity, pose, and/or shape of distal end  218  and/or of one or more segments  224  along flexible body  216  using one or more sensors and/or imaging devices as described in further detail below. The entire length of flexible body  216 , between distal end  218  and proximal end  217 , may be effectively divided into segments  224 . If medical instrument system  200  is consistent with medical instrument  104  of a teleoperated medical system  100 , tracking system  230 . Tracking system  230  may optionally be implemented as hardware, firmware, software or a combination thereof which interact with or are otherwise executed by one or more computer processors, which may include the processors of control system  112  in  FIG.  1   . 
     Tracking system  230  may optionally track distal end  218  and/or one or more of the segments  224  using a shape sensor  222 . Shape sensor  222  may optionally include an optical fiber aligned with flexible body  216  (e.g., provided within an interior channel (not shown) or mounted externally). In one embodiment, the optical fiber has a diameter of approximately 200 μm. In other embodiments, the dimensions may be larger or smaller. The optical fiber of shape sensor  222  forms a fiber optic bend sensor for determining the shape of flexible body  216 . In one alternative, optical fibers including Fiber Bragg Gratings (FBGs) are used to provide strain measurements in structures in one or more dimensions. The optical fiber of the shape sensor system  222  may enable the simultaneous collection of a set of measured points that describe the positions of various portions of the shape sensor  222  along the length of the flexible catheter body  216  at a single point in time. Various systems and methods for monitoring the shape and relative position of an optical fiber in three dimensions are described in U.S. patent application Ser. No. 11/180,389 (filed Jul. 13, 2005) (disclosing “Fiber optic position and shape sensing device and method relating thereto”); U.S. patent application Ser. No. 12/047,056 (filed on Jul. 16, 2004) (disclosing “Fiber-optic shape and relative position sensing”); and U.S. Pat. No. 6,389,187 (filed on Jun. 17, 1998) (disclosing “Optical Fibre Bend Sensor”), which are all incorporated by reference herein in their entireties. 
     Sensors in some embodiments may employ other suitable strain sensing techniques, such as Rayleigh scattering, Raman scattering, Brillouin scattering, and fluorescence scattering. In some embodiments, the shape of the elongate device may be determined using other techniques. For example, a history of the distal end pose of flexible body  216  can be used to reconstruct the shape of flexible body  216  over the interval of time. In some embodiments, tracking system  230  may optionally and/or additionally track distal end  218  using a position sensor system  220 . Position sensor system  220  may be a component of an EM sensor system with positional sensor system  220  including one or more conductive coils that may be subjected to an externally generated electromagnetic field. Each coil of EM sensor system  220  then produces an induced electrical signal having characteristics that depend on the position and orientation of the coil relative to the externally generated electromagnetic field. In some embodiments, position sensor system  220  may be configured and positioned to measure six degrees of freedom, e.g., three position coordinates X, Y, Z and three orientation angles indicating pitch, yaw, and roll of a base point or five degrees of freedom, e.g., three position coordinates X, Y, Z and two orientation angles indicating pitch and yaw of a base point. Further description of a position sensor system is provided in U.S. Pat. No. 6,380,732 (filed Aug. 11, 1999) (disclosing “Six-Degree of Freedom Tracking System Having a Passive Transponder on the Object Being Tracked”), which is incorporated by reference herein in its entirety. In some embodiments, the shape sensor  222  may also function as the position sensor because the shape of the sensor  222  together with information about the location of the base of the shape sensor  222  (in the fixed coordinate system of the patient, referred to as “patient space”) allows the location of various points along the shape sensor, including the distal tip, to be calculated. 
     In some embodiments, tracking system  230  may alternately and/or additionally rely on historical pose, position, or orientation data stored for a known point of an instrument system along a cycle of alternating motion, such as breathing. This stored data may be used to develop shape information about flexible body  216 . In some examples, a series of positional sensors (not shown), such as electromagnetic (EM) sensors similar to the sensors in position sensor  220  may be positioned along flexible body  216  and then used for shape sensing. In some examples, a history of data from one or more of these sensors taken during a procedure may be used to represent the shape of elongate device  202 , particularly if an anatomic passageway is generally static. The tracking system  230  may include the position sensor system  220  and a shape sensor system  222  for determining the position, orientation, speed, pose, and/or shape of the distal end  218  and of one or more segments  224  along the instrument  200 . The tracking system  230  may be implemented as hardware, firmware, software or a combination thereof which interact with or are otherwise executed by one or more computer processors, which may include the processors of a control system  116 . 
     Flexible body  216  includes a channel  221  sized and shaped to receive a medical instrument  226 .  FIG.  2 B  is a simplified diagram of flexible body  216  with medical instrument  226  extended according to some embodiments. In some embodiments, medical instrument  226  may be used for procedures such as surgery, biopsy, ablation, illumination, irrigation, or suction. Medical instrument  226  can be deployed through channel  221  of flexible body  216  and used at a target location within the anatomy. Medical instrument  226  may include, for example, image capture probes, biopsy instruments, laser ablation fibers, and/or other surgical, diagnostic, or therapeutic tools. Medical tools may include end effectors having a single working member such as a scalpel, a blunt blade, an optical fiber, an electrode, and/or the like. Other end effectors may include, for example, forceps, graspers, scissors, clip appliers, and/or the like. Other end effectors may further include electrically activated end effectors such as electrosurgical electrodes, transducers, sensors, and/or the like. In various embodiments, medical instrument  226  is a biopsy instrument, which may be used to remove sample tissue or a sampling of cells from a target anatomic location. Medical instrument  226  may be used with an image capture probe also within flexible body  216 . In various embodiments, medical instrument  226  may be an image capture probe that includes a distal portion with a stereoscopic or monoscopic camera at or near distal end  218  of flexible body  216  for capturing images (including video images) that are processed by a visualization system  231  for display and/or provided to tracking system  230  to support tracking of distal end  218  and/or one or more of the segments  224 . The image capture probe may include a cable coupled to the camera for transmitting the captured image data. In some examples, the image capture instrument may be a fiber-optic bundle, such as a fiberscope, that couples to visualization system  231 . The image capture instrument may be single or multi-spectral, for example capturing image data in one or more of the visible, infrared, and/or ultraviolet spectrums. Alternatively, medical instrument  226  may itself be the image capture probe. Medical instrument  226  may be advanced from the opening of channel  221  to perform the procedure and then retracted back into the channel when the procedure is complete. Medical instrument  226  may be removed from proximal end  217  of flexible body  216  or from another optional instrument port (not shown) along flexible body  216 . 
     Medical instrument  226  may additionally house cables, linkages, or other actuation controls (not shown) that extend between its proximal and distal ends to controllably the bend distal end of medical instrument  226 . Steerable instruments are described in detail in U.S. Pat. No. 7,316,681 (filed on Oct. 4, 2005) (disclosing “Articulated Surgical Instrument for Performing Minimally Invasive Surgery with Enhanced Dexterity and Sensitivity”) and U.S. patent application Ser. No. 12/286,644 (filed Sep. 30, 2008) (disclosing “Passive Preload and Capstan Drive for Surgical Instruments”), which are incorporated by reference herein in their entireties. 
     Flexible body  216  may also house cables, linkages, or other steering controls (not shown) that extend between drive unit  204  and distal end  218  to controllably bend distal end  218  as shown, for example, by broken dashed line depictions  219  of distal end  218 . In some examples, at least four cables are used to provide independent “up-down” steering to control a pitch of distal end  218  and “left-right” steering to control a yaw of distal end  281 . Steerable elongate devices are described in detail in U.S. patent application Ser. No. 13/274,208 (filed Oct. 14, 2011) (disclosing “Catheter with Removable Vision Probe”), which is incorporated by reference herein in its entirety. In embodiments in which medical instrument system  200  is actuated by a teleoperational assembly, drive unit  204  may include drive inputs that removably couple to and receive power from drive elements, such as actuators, of the teleoperational assembly. In some embodiments, medical instrument system  200  may include gripping features, manual actuators, or other components for manually controlling the motion of medical instrument system  200 . Elongate device  202  may be steerable or, alternatively, the system may be non-steerable with no integrated mechanism for operator control of the bending of distal end  218 . In some examples, one or more lumens, through which medical instruments can be deployed and used at a target surgical location, are defined in the walls of flexible body  216 . 
     In some embodiments, medical instrument system  200  may include a flexible bronchial instrument, such as a bronchoscope or bronchial catheter, for use in examination, diagnosis, biopsy, or treatment of a lung. Medical instrument system  200  is also suited for navigation and treatment of other tissues, via natural or surgically created connected passageways, in any of a variety of anatomic systems, including the colon, the intestines, the kidneys and kidney calices, the brain, the heart, the circulatory system including vasculature, and/or the like. 
     The information from tracking system  230  may be sent to a navigation system  232  where it is combined with information from visualization system  231  and/or the preoperatively obtained models to provide the physician or other operator with real-time position information. In some examples, the real-time position information may be displayed on display system  110  of  FIG.  1    for use in the control of medical instrument system  200 . In some examples, control system  116  of  FIG.  1    may utilize the position information as feedback for positioning medical instrument system  200 . Various systems for using fiber optic sensors to register and display a surgical instrument with surgical images are provided in U.S. patent application Ser. No. 13/107,562, filed May 13, 2011, disclosing, “Medical System Providing Dynamic Registration of a Model of an Anatomic Structure for Image-Guided Surgery,” which is incorporated by reference herein in its entirety. 
     In some examples, medical instrument system  200  may be teleoperated within medical system  100  of  FIG.  1   . In some embodiments, teleoperational manipulator assembly  102  of  FIG.  1    may be replaced by direct operator control. In some examples, the direct operator control may include various handles and operator interfaces for hand-held operation of the instrument. 
       FIGS.  3 A and  3 B  are simplified diagrams of side views of a patient coordinate space including a medical instrument mounted on an insertion assembly according to some embodiments. As shown in  FIGS.  3 A and  3 B , a surgical environment  300  includes a patient P is positioned on the table T of  FIG.  1   . Patient P may be stationary within the surgical environment in the sense that gross patient movement is limited by sedation, restraint, and/or other means. Cyclic anatomic motion including respiration and cardiac motion of patient P may continue, unless patient is asked to hold his or her breath to temporarily suspend respiratory motion. Accordingly, in some embodiments, data may be gathered at a specific, phase in respiration, and tagged and identified with that phase. In some embodiments, the phase during which data is collected may be inferred from physiological information collected from patient P. Within surgical environment  300 , a point gathering instrument  304  is coupled to an instrument carriage  306 . In some embodiments, point gathering instrument  304  may use EM sensors, shape-sensors, and/or other sensor modalities. Instrument carriage  306  is mounted to an insertion stage  308  fixed within surgical environment  300 . Alternatively, insertion stage  308  may be movable but have a known location (e.g., via a tracking sensor or other tracking device) within surgical environment  300 . Instrument carriage  306  may be a component of a teleoperational manipulator assembly (e.g., teleoperational manipulator assembly  102 ) that couples to point gathering instrument  304  to control insertion motion (i.e., motion along the A axis) and, optionally, motion of a distal end  318  of an elongate device  310  in multiple directions including yaw, pitch, and roll. Instrument carriage  306  or insertion stage  308  may include actuators, such as servomotors, (not shown) that control motion of instrument carriage  306  along insertion stage  308 . 
     Elongate device  310  is coupled to an instrument body  312 . Instrument body  312  is coupled and fixed relative to instrument carriage  306 . In some embodiments, an optical fiber shape sensor  314  is fixed at a proximal point  316  on instrument body  312 . In some embodiments, proximal point  316  of optical fiber shape sensor  314  may be movable along with instrument body  312  but the location of proximal point  316  may be known (e.g., via a tracking sensor or other tracking device). Shape sensor  314  measures a shape from proximal point  316  to another point such as distal end  318  of elongate device  310 . Point gathering instrument  304  may be substantially similar to medical instrument system  200 . 
     A position measuring device  320  provides information about the position of instrument body  312  as it moves on insertion stage  308  along an insertion axis A. Position measuring device  320  may include resolvers, encoders, potentiometers, and/or other sensors that determine the rotation and/or orientation of the actuators controlling the motion of instrument carriage  306  and consequently the motion of instrument body  312 . In some embodiments, insertion stage  308  is linear. In some embodiments, insertion stage  308  may be curved or have a combination of curved and linear sections. 
       FIG.  3 A  shows instrument body  312  and instrument carriage  306  in a retracted position along insertion stage  308 . In this retracted position, proximal point  316  is at a position L 0  on axis A. In this position along insertion stage  308  an A component of the location of proximal point  316  may be set to a zero and/or another reference value to provide a base reference to describe the position of instrument carriage  306 , and thus proximal point  316 , on insertion stage  308 . With this retracted position of instrument body  312  and instrument carriage  306 , distal end  318  of elongate device  310  may be positioned just inside an entry orifice of patient P. Also in this position, position measuring device  320  may be set to a zero and/or the another reference value (e.g., I=0). In  FIG.  3 B , instrument body  312  and instrument carriage  306  have advanced along the track, which may be linear or curved, of insertion stage  308  and distal end  318  of elongate device  310  has advanced into patient P. In this advanced position, the proximal point  316  is at a position L 1  on the axis A. In some examples, encoder and/or other position data from one or more actuators controlling movement of instrument carriage  306  along insertion stage  308  and/or one or more position sensors associated with instrument carriage  306  and/or insertion stage  308  is used to determine the position Lx of proximal point  316  relative to position L 0 . In some examples, position Lx may further be used as an indicator of the distance or insertion depth to which distal end  318  of elongate device  310  is inserted into the passageways of the anatomy of patient P. During insertion and while inserted within the anatomy of the patient P, the shape sensor  314  may be used to collect measured data points within the anatomy of the patient P. 
     Embodiments of the point gathering instrument  304  may collect measured points using any number of modalities, including EM sensing and shape-sensing. As the measurement points are collected from within the anatomic passageways of a patient, the points are stored in a data storage device, such as a memory. The set of measured points may be stored in a database that includes at least some, but may include all, of the measured points obtained during the procedure or immediately before the procedure. The set of measured points may be binned, sorted, or filtered, to produce subsets of measured points that are related in some way, such as being obtained during a common phase or portion of a phase of a periodic physiological motion, such as respiration. As stored in memory, each of the points may be represented by data comprising coordinates of the point, a timestamp, and a relative sensor position or individual sensor ID (when multiple sensors distributed along a length of the point gathering instrument  304  are used to determine the location of several points simultaneously). The binned subsets of measured points may be stored in separate data structures and/or in separate portions of memory. In some embodiments, data representing each point may also include a respiratory phase marker that indicates the respiratory phase of the patient in which the point was collected. A patient movement tracker  322  may be used to monitor and detect movement of the patient P. This movement may include gross movements as well as periodic physiological movements, such as respiration. Accordingly, the movement tracker  322  may serve as a physiological phase detector. The movement tracker  322  may be an optical tracking system or any other suitable system. In other embodiments, respiration may be monitored by a ventilator or by any other technique. 
       FIGS.  4 A,  4 B,  4 C, and  4 D  illustrate the advancement of the catheter  310  of  FIGS.  3 A and  3 B  through anatomic passageways  402  of the lungs  400  of the patient P of  FIGS.  1  and  3   . These passageways  402  include the trachea and the bronchial tubes. As the catheter  310  is advanced as the carriage  306  moves along the insertion stage  308 , the surgeon S may steer the distal end  318  of the catheter  310  to navigate through the anatomic passageways  402 . In navigating through the anatomic passageways  402 , the catheter  310  assumes a shape that may be “read” by the shape sensor  314  extending within the catheter  310 . As described herein, measured points obtained using the flexible catheter  310  may be assigned to one or more bins based on a variety of factors. For example, the measured points may be assigned to bins that correspond to portions of a periodic physiological motion, such as respiration. The measured points may also be assigned to bins that correspond to an insertion depth of the catheter  310 , such that points measured within the trachea, or a particular generation of the bronchial passageways, may be pooled or included in a single bin even as the distal end  318  of the catheter  310  advances through the anatomic passageways  402 . 
       FIG.  5    is a flowchart illustrating a general method  500  for use in an image-guided surgical procedure. At a process  502 , pre-operative or intra-operative image data is obtained from imaging technology such as, computed tomography (CT), magnetic resonance imaging (MRI), fluoroscopy, thermography, ultrasound, optical coherence tomography (OCT), thermal imaging, impedance imaging, laser imaging, or nanotube X-ray imaging. The pre-operative or intra-operative image data may correspond to two-dimensional, three-dimensional, or four-dimensi 1 onal (including e.g., time based or velocity based information) images. For example, the image data may represent the human lungs  400  of  FIGS.  4 A-D . At a process  504 , a computer system either operating alone or in combination with manual input is used to convert the recorded images into a segmented two-dimensional or three-dimensional composite representation or model of a partial or an entire anatomic organ or anatomic region. For example,  FIG.  6 A  illustrates a segmented model  600  of the lungs  400  of  FIGS.  4 A-D . Due to naturally occurring limitations or to limitations set by an operator, the segmented model  600  may not include all of the passageways present within the human lungs, but includes some passageways  601 . For example, relatively narrow and/or distal passageways of the lungs may not be fully included in the segmented model  600 . The segmented model  600  may be a three-dimensional model, such as a mesh model or another suitable model, that includes the walls defining the interior lumens or passageways of the lungs. In general, the model provides a mechanism or means for distinguishing between points within a region of anatomy and points outside the region of anatomy. The composite representation and the image data set describe the various locations and shapes of the passageways and their connectivity and may omit undesired portions of the anatomy included in the pre-operative or intra-operative image data. In some embodiments, the model  600  may include specifically desired features, such as a suspected tumor or other tissue portion of interest. 
     During the segmentation process the images are partitioned into segments or elements (e.g., pixels or voxels) that share certain characteristics or computed properties such as color, density, intensity, and texture. This segmentation process results in a two- or three-dimensional reconstruction that forms a model of the target anatomy based on the obtained image, like the model  600 . To represent the model, the segmentation process may delineate sets of voxels representing the target anatomy and then apply a function, such as marching cube function, to generate a 3D surface that encloses the voxels. The model may be made by generating a mesh, volume, or voxel map. This model may be shown in the display  110  to aid the surgeon S in visualizing the anatomy, such as the interior passageways of the lungs. 
     Additionally or alternatively, the model may include a centerline model that includes a set of interconnected line segments or points extending through the centers of the modeled passageways.  FIG.  6 B  shows an exemplary centerline model  602  derived from the model  600  or directly from the imaging data. The centerline segmented model  602  may include a set of three-dimensional straight lines or a set of curved lines that correspond to the approximate center of the passageways contained in the segmented model  602 . The higher the resolution of the model, the more accurately the set of straight or curved lines will correspond to the center of the passageways. Representing the lungs with the centerline segmented model  602  may provide a smaller set of data that is more efficiently processed by one or more processors or processing cores than the data set of the segmented model  602 , which represents the walls of the passageways of model  600 . In this way the functioning of the control system  112  may be improved. 
     As shown in  FIG.  6 B , the centerline segmented model  602  includes several branch points, some of which are highlighted for visibility in  FIG.  6 B . The branch points A, B, C, D, and E are shown at each of several of the branch points. The branch point A may represent the point in the model at which the trachea divides into the left and right principal bronchi. The right principal bronchus may be identified in the centerline segment model  602  as being located between branch points A and B. Similarly, secondary bronchi are identified by the branch points B and C and between the branch points B and E. Another generation may be defined between branch points C and D. Each of these generations may be associated with a representation of the diameter of the lumen of the corresponding passageway. In some embodiments, the model  602  may include an average diameter value of each segmented generation. The average diameter value may be a patient-specific value or a more general value derived from multiple patients. 
     Where the model includes a centerline model including a set of interconnected line segments, those line segments may be converted to a cloud or set of points  604 , referred to as model points, which are represented by the dashed lines of  FIG.  6 C . By converting the line segments into points, a desired quantity of model points corresponding to the interconnected line segments can be selected manually or automatically to represent the centerline model  602  (and thereby the model  600 ) during a registration process. In data, each of the points of the set of model points  604  may include coordinates such as a set of XM, YM, and ZM, coordinates, or other coordinates that identify the location of each point in the three-dimensional model space. In some embodiments, each of the points may include a generation identifier that identifies which passageway generation the points are associated with and/or a diameter or radius value associated with that portion of the centerline segmented model  602 . In some embodiments, information describing the radius or diameter associated with a given point may be provided as part of a separate data set. 
     After the centerline segmented model  602  is generated and stored in data as the set of points  604  shown in  FIG.  6 C , the model points  604  may be retrieved from data storage for use in an image-guided surgical procedure. In order to use the centerline segmented model  602  and the model  600  in the image-guided surgical procedure, the model points  604  may be registered to associate the modeled passageways in the model  600  with the patient&#39;s actual anatomy as present in a surgical environment. 
     Returning to  FIG.  5   , at a process  506 , measured points may be obtained from patient anatomy that corresponds to the anatomical model, as shown in  FIGS.  3 A-B  and  4 A-D. At a process  508 , the anatomic model data is registered to the patient anatomy prior to and/or during the course of an image-guided surgical procedure on the patient. Generally, registration involves the matching of measured point to points of the model through the use of rigid and/or non-rigid transforms. Measured points may be generated using landmarks in the anatomy, electromagnetic coils scanned and tracked during the procedure, or a shape sensor system. The measured points may be generated for use in an iterative closest point (ICP) technique, or another point set registration methods may also be used in registration processes within the scope of this disclosure. 
     After the process  508  in which the anatomical model is registered to the patient anatomy so that medical instrument positioned with respect to the patient anatomy can b e represented with respect to the anatomical model, the collection of measured points from the patient anatomy may continue. As new measured points are added, the registration may be updated at a process  510 . The updating of the registration may be performed continuously throughout a surgical procedure. In this way, changes due to patient movements (both gross movements and periodic physiological movements) may be compensated for. Additionally, measured points may be assigned into various subsets of points by one or more criteria, and by which some subsets or a particular subset may be determined to be better than others in registering the patient anatomy to the anatomical model. Points may also be assigned a numeric weighting reflecting the partial probability that the point is correctly assigned to any subset of point. However, a subset that may have provided optimal registration for a first period of time may become suboptimal at a later period of time. Updating the registration to use whichever subset of measured points provides the optimal registration at the time, may ensure the best and most useful relationship between the model and the anatomy is maintained. When a statistically significant change in the quality of a registration occurs (e.g., there is a significant change in the error value associated with the registration), the subset of measured points associated with that registration may be emptied by deletion of all points or may have a weighting of measured points applied thereto. 
     Other registration methods for use with image-guided surgery often involve the use of technologies based on electromagnetic or impedance sensing. Metallic objects or certain electronic devices used in the surgical environment may create disturbances that impair the quality of the sensed data. Other methods of registration may obstruct the clinical workflow. Some embodiments of the systems and methods described herein perform registration based upon ICP, or another point set registration algorithm, and the calibrated movement of a point gathering instrument with a fiber optic shape sensor, thus eliminating or minimizing disruptions in the surgical environment. Other registration techniques may be used to register a set of measured points to a pre-operative model or a model obtained using another modality. In the embodiments described below, EM sensors on the patient and the instrument and optical tracking systems for the instrument may be eliminated. 
       FIG.  7    is a flowchart illustrating a method  700  used to provide guidance to a clinician in an image-guided surgical procedure on the patient P in the surgical environment  300 , according to some embodiments of the present disclosure. The method  700  is illustrated in  FIG.  7    as a set of blocks, steps, operations, or processes. Not all of the illustrated, enumerated operations may be performed in all embodiments of the method  700 . Additionally, some additional operations that are not expressly illustrated in  FIG.  7    may be included before, after, in between, or as part of the enumerated operations. Some embodiments of the method  700  may include machine-readable instructions corresponding to the operations of the method  700  and stored in a memory. These instructions may be executed by a processor like a processor of the control system  112 . 
     Thus, some embodiments of the method  700  may begin at an operation  702 , in which the set of measured points is collected along the length of a catheter or other medical instrument. For example, the catheter may be the point gathering instrument  304  of  FIGS.  3 A and  3 B , or the medical instrument system  200  of  FIG.  2   . The catheter may include a fiber optic shape sensor that may be used to generate a plurality of three-dimensional points representing the shape of the catheter. Three-dimensional points may be related to a patient space by having a proximal end of the fiber optic shape sensor and a known location or a detected location. 
     In practice, the distal end  318  of the catheter  310  may traverse the patient P&#39;s anatomic passageways (e.g., airways of the patient&#39;s lungs) recording, via data from the shape sensor  314 , location data for the distal end of the catheter and other points along the shape of the shape sensor. This location data may include, or be processed to obtain, a set of measured points as described herein. More specifically, the movement of the distal tip of the catheter  610  may be controlled via teleoperational, manual, or automated control (e.g., via master assembly  106 ) to survey a portion of the anatomic passageways. 
     For example, teleoperational control signals may cause the carriage  306  to move along the axis A, causing the distal end  318  of the catheter to advance or retract within the anatomic passageways. Also or alternatively, teleoperational control signals may cause actuation of control members extending within the surgical instrument to move the distal end  318  in a range of movements including yaw, pitch, and roll. As the catheter is moved within the plurality of passageways, shape sensor data (and/or other position data in other embodiments that do not include a shape sensor) is gathered for multiple locations of the distal tip. In some embodiments, the catheter may extend up to approximately three branches deep into the various passageways. In some embodiments, the catheter may be extended through or into approximately three or more branched generations on each side of the lung. The number of generations accessible with the catheter  310  may increase as the diameter of the flexible catheter  310  decreases and/or the flexibility of the flexible catheter  310  increases. 
     In some embodiments, a calibration procedure may be performed prior to the collection of measured points using a position measuring device like the point gathering instrument  304  or another suitable device, a relative position and/or orientation of a sensor reference point along an insertion path. For example, the point gathering instrument  304  of  FIGS.  3 A and  3 B  may be used to determine a position and orientation of the point  316  as the carriage  306  moves from a retracted position with the point  316  at location L 0  to an advanced position with the point  316  at the location L 1 . The calibration procedure may determine the direction of the movement of the point  316  for each change in the position measuring device  320 . For example, the distal end  318  of the catheter  310  may be held in a fixed position while the instrument body is routed along the insertion stage  308 . The position and orientation data collected by the shape sensor from the fixed point  316  is correlated with the position measuring device data as the instrument body is routed along the insertion stage, thus calibrating movement of the point  316  along the axis A of the insertion stage  308 . 
     Optionally, in an operation  703 , a state input may be received by the control system  112 . For example, the state input may be a periodic physiological motion signal describing the respiration of patient P or heartbeats of patient P. Other periodic physiological motion signal may be received and used in other embodiments.  FIGS.  8 A and  8 B , discussed in more detail further below illustrate a single period of an exemplary periodic physiological motion signal  800 . The periodic physiological motion signal includes a period T shown along the x-axis and amplitude shown along the y-axis. The signal shown in  FIGS.  8 A and  8 B  is simplified to more clearly communicate certain aspects of the present disclosure. Other state inputs may include non-physiological inputs such as instrument velocity, force, applied strain, or orientation. Other state inputs may include a detected obstruction (e.g., due to fog or debris) of the camera. Other state inputs may include a tagged measured point that is designated as belonging at a particular anatomical location or within a particular anatomic passageway. Such a tagged point may serve as a “ground truth” point during a registration. 
     At an operation  704 , the measured points may be assigned to a plurality of subsets of measured points. In some embodiments, the operations  702  and  704  may be performed substantially simultaneously. In other embodiments, the operation  702  may include storing the set of measured points in a pool of points in memory and the operation  704  may include retrieving the set of measured points from memory and then assigning the retrieved points to the plurality of subsets. The assignment of measured points to subsets may be referred to herein as “binning.” The measured points may each be assigned to one of several bins. The bins may be data structures and/or specific portions of memory.  FIGS.  8 A and  8 B  illustrate some exemplary ways in which measured points may be assigned to particular bins. Assignment of each point to any bin may be binary (explicitly inside or outside a given bin) or it may contain a soft assignment to any bin represented by some fractional weighting. 
     As shown in  FIG.  8 A , the periodic physiological motion signal  800  may be used to bin collected measured points.  FIG.  8 A  illustrates time-based or period-based binning, in which the time at which a particular measured point is obtained indicates the bin to which the point should be assigned. It should be noted that, when a fiber optic shape sensor is used to collect the measured points that a plurality of points are collected at a single time. All of the points collected from the fiber optic shape sensor at that time may be assigned to the same bin or subset of points. For example, if points are collected from the fiber-optic sensor  314  at a time in between zero and 1/8 th  of T, the points may be assigned to bin A. If the points are collected at a time between 1/8 th  of T and 3/8 th  of T, the points may be assigned to bin B. If the points are collected at the time between 3/8 th  of T and 5/8 th  of T, the points may be assigned to bin C. If the points are collected at a time between 5/8 th  of T and 7/8 th  of T, the points may be assigned to bin D. If the points are collected at a time between 7/8 th  of T and T, the points may be assigned to bin A. Other embodiments of the operation  704  may assign collected points to a bin differently. For example, the measured points may be assigned to one of more than four bins. The bins may be associated with unequal portions of the period T. The cutoffs for the bins may occur at the peak and the trough of the signal  800 . 
     As shown in  FIG.  8 A , the periodic physiological motion signal  800  may be used to bin measured points according to the amplitude of the signal  800 .  FIG.  8 B  illustrates amplitude cutoffs that sort the measured points into three bins: bin E, bin F, and bin G. For example, points collected when the amplitude of the periodic physiological motion signal  800  is greater than half a peak value may be assigned to bin E. Points collected when the amplitude of the periodic physiological motion signal  800  is less than half a minimum value may be assigned to bin G. Points collected in between these amplitude values may be assigned to bin F. Other embodiments may include more bins or fewer bins. 
     Referring now to  FIG.  9   , shown therein is an exemplary illustration of operation  704  of the method  700 .  FIG.  9    depicts the catheter  310  of  FIGS.  3 A-B  and  4 A-D. A shape sensor disposed within the catheter  310  (i.e., the shape sensor  314 ) measures points during four discrete time portions (at times t 1 , t 2 , t 3 , and t 4 ) within a period T. The times t 1 , t 2 , t 3 , and t 4  correspond to different bins, like the bins A, B, C, and D as shown in  FIG.  9   . As shown in  FIG.  9   , the shape and position of the catheter  310  at t 4  is different from the shape and position of the catheter  310  at the times t 1 , t 2 , and t 3 . This difference is not due to insertion of the catheter  310  deeper into the anatomic passageways  402 , but instead may be due to the periodic physiological motion of the lung  400  during respiration by the patient P. 
     Referring now to  FIGS.  10 A,  10 B,  10 C, and  10 D , another embodiment of the operation  704  is shown. In assigning each of the measured points to one of a plurality of bins, the assignment may be made based on an insertion depth of the catheter used to measure the points. Accordingly, a depth value may be received based on the movement of the carriage  306  relative to the stage  308  from an encoder or another sensor. The cutoffs between depths may be determined preoperatively based upon the segmented centerline model  602  of  FIG.  6 B . Other depths may be used in other embodiments. As shown in  FIG.  10 A , the points collected at a specific time by the catheter  310  may be sorted or assigned into depth bins A and B. In  FIG.  10 B , the catheter  310  has been inserted more when the measured points are collected and so the points are assigned to three depth bins: depth bins A, B, and C. As shown in  FIGS.  10 C and  10 D , as the catheter  310  is inserted deeper into the anatomical passageways of a lung  400 , measured points are assigned to depth bins A, B, C, and D. As shown in  FIGS.  10 A-D , the more proximal depth bins may include more measured points because a portion of the catheter  310  has been in proximal depths for a longer period of time, during which points may be collected on a regular basis. In some embodiments the number of points in a bin may be capped such that as new points are measured, the oldest points are removed from the subset or pool of points associated with that bin. 
     Returning again to  FIG.  7    and the method  700 , at operation  705 , a set of model points from a model may be received by the control system  112 . For example, the set of model points may be a set of points representing a model of the lung  400 . The set of model points received at operation  705  may be similar to the model points  604  of  FIG.  6 C , which are a set of points derived from the centerline model  602 , which was based on the model  600 . The set of model points  604  may be used to register the model  600  to the set of measured points collected with the catheter  310 . 
     After the operation  704 , an initial seed transformation may be performed at operation  706  to roughly place the measured points in relation to the model points, such that subsequent iterative registration operations can be performed. The registration process may be seeded with known information about the displacement and orientation relationship between the patient surgical environment and the anatomic model. For example, landmarks associated with the main carinas in the lungs  400  may be identified in the anatomic model information. Corresponding locations may be included in the measured points as part of the work flow. At operation  707 , the control system  112  may register each subset of measured points to the set of model points. Registration may be accomplished using a point set registration algorithm such as an iterative closest point (ICP) technique as described in operations  708 - 714 , or by implementation of another registration algorithm. 
     At an operation  708 , after the initial coarse seed transformation has been performed to initiate the registration process, the set of measured data points D gathered from within the patient P is matched to the anatomic model points  604 . For example, each of the measured data points D may be matched with the closest point in the set of anatomic model points  604 . In this embodiment, the anatomic model points  604  is a set of points along the centerlines generated from a three-dimensional anatomic model, like the segmented centerline model  602  is generated from the segmented model  600  of  FIGS.  6 A and  6 B . The registration algorithm identifies matches between closest points in the measured data points and in the set of anatomic model points  604 . A result may be seen in  FIG.  11 A , which shown the model points  604  with a set of measured points  1100  after an initial seeding or registration process has begun. As illustrated in  FIG.  11 A , the set of measured points  1100  includes four subsets of measured points including the subset  1102 A (represented by solid circles), the subset  1102 B (represented by plus signs), the subset  1102 C (represented by open circles), and the subset  1102 D (represented by x&#39;s). The subsets  1102 A,  1102 B,  1102 C, and  1102 D may be collectively referred to as subsets  1102 . 
     In various alternatives, matching between the model points  604  and each of the subsets  1102  may be accomplished by using brute force techniques, KD tree techniques, etc. Some matches may be discarded based on maximum distance threshold calculations, maximum angle threshold calculations, or other metrics employed to filter out matches that are not deemed to be reliable enough for inclusion in the model. The anatomic model points  604  may be represented by any of several different kinds of points, including centerline points, mesh points, and/or volume points. 
     Referring again to the method  700  of  FIG.  7   , at an operation  710 , the transformation needed to map each subset of subsets  1102  to the position and orientation of the matched anatomic model points  604  is determined. More specifically, an overall computed offset in position and orientation is determined for each of subsets  1102 . In some embodiments, the computed corrective transformation may be limited such that only a certain number of degrees of rotation or a certain number of millimeters of displacement may be applied in a single iteration of the process. For example, even if a rotation or reorientation of the anatomic model points  604  of 20° is computed, the medical system may limit the change in orientation to 10°, 5°, or less. Similarly, in some embodiments even if a displacement of 40 mm is computed, the control system  112  may limit the displacement available in a single iteration to 20 mm, 10 mm, 5 mm, or less. In some embodiments, the limits may change according to a number of iterations performed such that less movement is permitted in later iterations than in earlier iterations. 
     At an operation  712 , each subset  1102  may be transformed using a rigid or non-rigid transformation that applies the computed offset in displacement and orientation to specifically move each point in the particular subset  1102 . In an alternative embodiment, the modeled data points may be transformed by using a rigid or non-rigid transform that applies the computed offset in displacement and orientation to move each point in the set of model points  604  toward the subsets  1102 . Accordingly, some embodiments of the present disclosure may refer to registering measured points to model points and moving (including translating and/or changing the orientation of) the measured points to better align with the model points, bringing them into a common space or common frame of reference. These registrations may be understood as registration candidates. In order to register the model  600  with the measured points  1100 , bringing the model  600  into patient space, an optimal registration candidate may be identified and selected. 
     At an operation  714 , the registration error between each of the subsets  1102  and the matched anatomic model points  604  is evaluated. In some embodiments, the error may be computed as the cumulative error or distance between each measured point to its nearest model point after being transformed. Alternatively, there might be expressed as the change in orientation and displacement from a previously computed registration. This may include the calculation of error values, including error values for orientation and displacement for each of the subsets  1102 . In other words, error factors for orientation and displacement may be individually determined for each matched subset  1102 . If the error factors in aggregate are greater than a threshold value, additional iterations of operations  708 - 714  may be repeated until the overall position and orientation error factors falls below the threshold value. 
     At an operation  716 , the convergence of each of the subsets  1102  may be compared to determine which of the registration candidates is optimal for use in a procedure relying upon the model  600  of  FIG.  6 A . In other words, overall error values associated with the registration candidates of each of the subsets  1102 A,  1102 B,  1102 C, and  1102 D to the model points  604  may be compared. The registration candidate having the smallest overall error value may be used to bring the model points  604  into the patient space in which the points  1100  are collected. The association between the model points  604  may permit the model  600  to be expressed in the patient space. In some embodiments, after determining the convergence of each subset, the convergence value may be compared with a threshold and, if the convergence drops below the threshold or if the associated error exceeds the threshold, the points collected up until that point in the failing subset or subsets may be discarded. For example, when the patient P makes a gross movement, the error for the registrations associated with one or more of the subsets may include significant errors, making the registration unusable for image-guided surgery. Because the subset has been “contaminated” with bad data associated with the patient P&#39;s movement, the subset may be emptied and point collection make begin anew. 
     For example, at operation  718 , a visual representation of the optimal registration of the model points  604  (and thereby the model  600 ) may be displayed in a graphical user interface provided by the display  110  of  FIG.  1   . The visual representation may depict the medical instrument system  200  in relation to the model  600 . An exemplary visual representation is shown in  FIG.  13 A .  FIG.  13 A  illustrates a display  1300  displaying, in a user interface, a rendering of anatomic passageways of a human lung based upon anatomic model  600  of  FIG.  6 A . With the model space registered to the patient as described above in  FIG.  7   , the current shape of the catheter  310  and the location of the distal end  318  may be located and displayed concurrently with the rendering of the passageways  601 , which includes passageways  601 A and  601 B. The data points may be visually represented in a user interface by a plurality of points or dots on the display or as a rendered model, such as a mesh or wire model created based on the set of data points. In some embodiments, a visual representation may be refreshed in the display  110  after each processing operations has been implemented to alter the data points.  FIG.  13 B  illustrates another exemplary display  1350  of a visual representation that may be provided to the surgeon S to aid in guiding the surgery.  FIG.  13 B  shows an internal view of a portion of the model  600  from a perspective of the medical instrument  200 , and depicts rendered models of the passageways  601 A and  601 B. The model  600  may be rendered in two or three-dimensions to facilitate guidance of the surgery. 
     The principles and embodiments of the present disclosure may improve image guided surgery by improving registration between models of patient anatomy and medical instruments being manipulated within the patient anatomy during a surgical procedure. Multiple candidate registrations may be produced based on subsets of measured data points and the multiple registrations may be compared to determine an optimal registration to be applied to the model to bring it into the patient space. These multiple candidate registrations may be continuously updated and compared to each other and to threshold values to ensure that the highest fidelity registration at any given time as provided for use in image guided surgery. 
     In some embodiments, when a later registration replaces an earlier registration or an earlier registration is deemed replaceable by the control system  112  with a later registration, an alert may be provided to the clinician through a user interface to indicate that there is a change in registration (e.g., from one subset of measured points to another) or that there is a superior registration available. In some embodiments, the control system  112  may require clinician approval through the user interface before the superior registration is implemented. For example, when a superior registration is identified an alert may be rendered to the display  110  along with a button or other user interface element by which the clinician can approve or disapprove to the new registration. The new registration will then be implemented or not depending on the clinician&#39;s decision. 
     One or more elements in embodiments of the invention may be implemented in software to execute on a processor of a computer system such as control system  112 . When implemented in software, the elements of the embodiments of the invention are essentially the code segments to perform the necessary tasks. The program or code segments can be stored in a non-transitory processor readable storage medium or device, including any medium that can store information including an optical medium, semiconductor medium, and magnetic medium. Processor readable storage device examples include an electronic circuit; a semiconductor device, a semiconductor memory device, a read only memory (ROM), a flash memory, an erasable programmable read only memory (EPROM); a floppy diskette, a CD-ROM, an optical disk, a hard disk, or other storage device. The code segments may be downloaded via computer networks such as the Internet, Intranet, etc. As described herein, operations of accessing, collecting, assigning, detecting, initiating, registered, displaying, receiving, generating, determining, moving data points, segmenting, matching, etc. may be performed at least in part by the control system  112  or the processor thereof. 
     Note that the processes and displays presented may not inherently be related to any particular computer or other apparatus. The required structure for a variety of these systems will appear as elements in the claims. In addition, the embodiments of the invention are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the invention as described herein. 
     While certain exemplary embodiments of the invention have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that the embodiments of the invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.