Patent Publication Number: US-11039736-B2

Title: System for controlling an instrument using shape sensors

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 15/660,828, filed Jul. 26, 2017, which is a continuation application of U.S. patent application Ser. No. 14/303,270, filed Jun. 12, 2014 (now U.S. Pat. No. 9,737,198), which is a continuation application of U.S. patent application Ser. No. 12/524,249 (filed Dec. 11, 2009), now U.S. Pat. No. 8,784,303, which is a national stage application of International Application No. PCT/US2008/052365 (filed Jan. 29, 2008), which claims the benefit of priority of U.S. Provisional Patent Application No. 60/898,200, filed (Jan. 29, 2007), all of which are incorporated herein by reference in their entirety. 
    
    
     INCORPORATION BY REFERENCE 
     All patents, patent publications and patent applications mentioned in this application are incorporated herein, in their entirety, by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates, generally, to articulating instruments or snake-like robots. More particularly, the present invention relates to sensing the shape of articulating instruments or snake-like robots. 
     BACKGROUND OF THE INVENTION 
     Endoscopes, colonoscopes and other controllable instruments have found widespread medical and industrial uses. As the complexity of the movement or use of such instruments increases, there is a need to more precisely control, locate within the body or identify the shape of the controllable instrument. A number of different types of shape sensing devices are available. 
     While shape sensing devices are available, challenges remain in the integration of shape sensing devices into controllable instruments. Challenges remain in systems capable of coordinated use of the shape information for control or operation of the controllable instrument or procedures that would benefit from shape information. Embodiments of the inventive systems and controllable instruments described herein address these and other challenges. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention provides an instrument having an elongate body, comprising a steerable distal portion and a plurality of articulating segments. The instrument can be modified to incorporate a shape sensor to indicate the shape of at least a portion of the instrument. In one embodiment, the shape sensor is an optical shape sensor. In other embodiments, the shape sensor can be a resistance changing flexible band, a bend sensor, a potentiometer, or a magnetic sensor, for example. 
     Another aspect of the invention provides a system that closes the control loop between the control signals used to direct the movement of an instrument and the shape indicating signal for the shape of all or a portion of the instrument. The system can comprise a user input device, a controller, an instrument having articulating segments, and a shape sensor, for example. The controller is configured to direct the movement of the instrument in response to a control signal from the user input device and a shape signal from the shape sensor. 
     Yet another aspect of the invention provides a method of controlling an instrument having an elongate body. The method includes the steps of inputting a control signal to a controller to change the shape of an instrument; sensing the shape of a portion of the instrument with a shape sensor; outputting a shape signal corresponding to the shape of the portion of the instrument from the shape sensor to the controller; and directing the movement of the instrument in response to the control signal and the shape signal. 
     One aspect of the invention provides a system for sensing the shape of an instrument. The system comprises an instrument having an elongate body, a shape sensor extending along a portion of the elongate body in a spiral pattern, and an indicator on each end of the shape sensor to maintain the axial orientation of the ends of the shape sensor. The spiral pattern can comprise an integral number of full spiral turns from one end of the elongate body to the other end. In one embodiment, the shape sensor is an optical shape sensor. The axial orientation of the shape sensor can be maintained in a variety of ways, including, but not limited to, physical or visual markers on the shape sensor, clipping the shape sensor to the elongate body, or integrating the shape sensor into the elongate body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which: 
         FIG. 1  illustrates a steerable endoscope in accordance with one embodiment of the present invention. 
         FIGS. 2A-2C  depict embodiments of vertebrae-type links in accordance with an embodiment of the present invention. 
         FIG. 3  illustrates a system that closes the control loop between control signals used to direct the movement of a controllable instrument and a shape indicating signal for the shape of all or a portion of the controllable instrument in accordance with an embodiment of the present invention. 
         FIG. 4  illustrates an articulating segment having an optical shape sensing fiber along its length in accordance with an embodiment of the present invention. 
         FIG. 5  illustrates an articulating segment utilizing a resistance changing flex sensor to sense the shape of the articulating segment in accordance with an embodiment of the present invention. 
         FIG. 6  illustrates an articulating segment utilizing a bend sensor to sense the shape of the articulating segment in accordance with an embodiment of the present invention. 
         FIG. 7  illustrates a flowchart illustrating steps taken to control an instrument having an elongate body in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  depicts an instrument  10 , in accordance with an embodiment of the present invention. Instrument  10  has elongate body  12  with steerable distal portion  14 , automatically controlled proximal portion  16 , and flexible and passively manipulated proximal portion  18 . Automatically controlled proximal portion  16  may also be flexible and passively manipulated, although it is preferred to provide automatically controlled proximal portion  16 . Elongate body  12  can have only steerable distal portion  14  and automatically controlled portion  16 . As described below and as schematically illustrated in  FIG. 3 , the instrument  10  and the associated control system or controller may be modified to incorporate a shape sensor and control the instrument based at least in part on a shape indicating signal provided by one or more shape sensors on or associated with the instrument  10 . Fiber optic imaging bundle  20  and illumination fiber(s)  22  may extend through elongate body  12  to steerable distal portion  14 , or video camera  24  (e.g., CCD or CMOS camera) may be positioned at the distal end of steerable distal portion  14 . A user views live or delayed video feed from video camera  24  via a video cable (e.g., wire or optical fiber, not shown) or through wireless transmission of the video signal. Typically, instrument  10  will also include one or more access lumens, working channels, light channels, air and water channels, vacuum channels, and a host of other well known complements useful for both medical and industrial endoscopy. These channels and other amenities are shown generically as working channel  26 . In particular these amenities may include multiple tool channels in order to provide access for tools to a surgical site by passing the instrument through a natural orifice proximate to a surgical target site, as in natural orifice transluminal (or transgastric) endoscopic surgery (NOTES). Various details of the use of a controllable instrument and methods for using a controllable instrument in a transluminal or NOTES procedure are further described in U.S. patent application Ser. No. 11/522,305 titled “Methods and Apparatus for Performing Transluminal and Other Procedures,” filed on Sep. 14, 2006 and commonly assigned to the assignee of the present application. The systems, instruments and devices described in “Methods and Apparatus for Performing Transluminal and Other Procedures” may be modified as described herein to provide shape sensing capabilities and/or control to the systems, instruments and methods described therein. 
     Preferably, automatically controlled proximal portion  16  comprises a plurality of articulating segments  28 , which are controlled via computer and/or electronic controller  30 . Such an automatically controlled endoscope is described in further detail in commonly assigned U.S. patent application Ser. No. 10/229,577, now U.S. Pat. No. 6,858,005, titled “Tendon-Driven Endoscope and Methods of Insertion,” filed on Aug. 27, 2002, and U.S. patent application Ser. No. 11/750,988 titled “Methods and Apparatus for Displaying Three-Dimensional Orientation of a Steerable Distal Tip of an Endoscope,” filed on May 18, 2007, both commonly assigned to the assignee of the present application. Preferably, the distal end of a tendon is mechanically connected to each articulating segment  28  or steerable distal portion  14 , with the proximal end of the tendon mechanically connected to actuators to move articulating segments  28  or steerable distal portion  14 . The actuators driving the tendons may include a variety of different types of mechanisms capable of applying a force to a tendon, e.g., electromechanical motors, pneumatic and hydraulic cylinders, pneumatic and hydraulic motors, solenoids, shape memory alloy wires, electronic rotary actuators or other devices or methods as known in the art. If shape memory alloy wires are used, they can be configured into several wire bundles attached at a proximal end of each of the tendons within the actuator. The actuators driving the tendons may be positioned inside instrument  10 , or, alternatively, the actuators may be positioned outside instrument  10 . 
     Segment articulation may be accomplished by applying energy, e.g., electrical current, electrical voltage, heat, etc., to each of the bundles to actuate a linear motion in the wire bundles which in turn actuate the tendon movement. The linear translation of the actuators within the controller may be configured to move over a relatively short distance to accomplish effective articulation depending upon the desired degree of segment movement and articulation. In one embodiment, knobs attached to rack and pinion gearing can be used to actuate the tendons attached to steerable distal portion  14 . An axial motion transducer  32  (also called a depth referencing device or datum) may be provided for measuring the axial motion, i.e., the depth change, of elongate body  12  as it is advanced and withdrawn. As elongate body  12  of instrument  10  slides through axial motion transducer  32 , it indicates the axial position of the elongate body  12  with respect to a fixed point of reference. Axial motion transducer  32  is more fully described in U.S. patent application Ser. No. 11/522,305 titled “Methods and Apparatus for Performing Transluminal and Other Procedures,” filed on Sep. 14, 2006. Additionally, an optical sensor may be used to determine the axial position of the instrument, either alone or in combination with an optical shape sensor as more fully described below. In either case, the depth information combined with the shape information can be used to construct a three-dimensional image of the elongate body as it is inserted or withdrawn. Additionally, information from such a system may be used to provide, the shape of the pathway followed by the sensor from a reference point (i.e., the datum). Additionally, information from such a system may be used as input to a control system to: (i) Drive the instrument to a location under the control of a user; (ii) Provide recommended steering commands to a user to manipulate the instrument to a desired location or orientation (iii) Automatically control the instrument to conform to inputs from a user, a predetermined pathway (surgical planning) or inputs from an imaging system or display. 
     In the embodiment depicted in  FIG. 1 , handle  34  is connected to illumination source  36  by illumination cable  38  that is connected to or continuous with illumination fibers  22 . Handle  34  is connected to electronic controller  30  by way of controller cable  40 . User input device  42  (e.g., a joy stick) is connected to electronic controller  30  by way of second cable  44  or directly to handle  34 . Controller  30  controls the movement of the segmented automatically controlled proximal portion  16 . 
     In one embodiment, articulating segments  28  of instrument  10  can be constructed from a plurality of links  200  as shown in  FIGS. 2A-2C .  FIG. 2A  shows an end view of a single link  200 . Each link  200  can define a central aperture or working channel  202  that can collectively form the internal lumen as previously described. As shown in  FIG. 2B , the links  200  may have two pairs of hinges  204  and  206 . The first pair of hinges  204  can project perpendicularly from a first face of link  200  and a second pair of hinges  206  located 90 degrees around the circumference from the first pair, projecting perpendicularly away from the face of link  200  on a second face of the vertebra opposite to the first face. In the embodiment shown in  FIG. 2C , each articulating segment  28  can comprise four links  200 , although any number of links may be used including just one link. The ultimate number of links  200  used is primarily defined by the purpose for which articulating segments  28  or instrument  10  will be used. Each link  200 , in this embodiment, can move with one degree of freedom relative to an adjacent link. Multiple links provide a segment  28  with two degrees of freedom. Further details of the articulating segments can be found in U.S. patent application Ser. No. 11/871,104 titled “System for Managing Bowden Cables in Articulating Instruments,” filed on Oct. 11, 2007 and commonly assigned to the assignee of the present application. 
       FIG. 3  illustrates an exemplary system  300  and method that closes the control loop between the control signals used to direct the movement of the instrument and a shape indicating signal for the shape of all or a portion of a controllable instrument. The following description of system  300  includes references to instrument  10  of  FIG. 1 , since the system  300  is implemented utilizing an instrument such as instrument  10 . In order to determine the shape of elongate body  12 , instrument  10  can further include shape sensor  302  in contact with elongate body  12 . For example, the shape sensor can be an optical sensing fiber or fiber bundle extending along the length of the elongate body. Embodiments of the present invention build upon the concept of measuring the shape of the optical fiber and using those measurements to determine curvature and/or relative position of an instrument to which the optical fiber is associated. In some embodiments, shape sensing is accomplished by creating a linear array of high spatial resolution fiber optic bend sensors. In general, by assuming each element is sufficiently small, by knowing the curvature of the structure at each individual element the overall shape is reconstructed through an integration process. Additional types of shape sensors and their orientation on or within instrument  10  will be discussed below in more detail. 
     In addition to shape sensor  302 , system  300  of  FIG. 3  also includes user input device  42 , controller  30 , actuator  304 , and articulating segments  28 . As previously described, user input device  42  is in communication with controller  30  and is configured to provide a control signal to change the shape of at least one of the articulating segments  28 . Controller  30  is in communication with actuator  304  to direct the movement of articulating segments  28  and, thus, control the shape of elongate body  12 . In particular, a user inputs a control signal into user input device  42  (i.e., such as a joystick or a computer) which then transmits the control signal to the controller  30 . The user may control the instrument  10  or indicate desired motions in several exemplary ways. In one embodiment, the user steers the steerable distal portion  14  with user input device  42  and identifies the direction instrument  10  needs to proceed. Instrument  10  is then advanced and the segments following steerable distal portion  14  take on the shape of the segment before it. This follow-the-leader shape determination, in general, works by proximately adjacent segments taking on the shape of an adjacent distal segment as instrument  10  is advanced distally. The determination as to the degree a segment has conformed to the shape of another segment and the determination of the shape of one or more segments are determined at least in part by a shape sensor. The follow-the-leader shape determination works the same whether advancing distally or withdrawing proximally. Alternatively, in another embodiment, the user can enter any desired shape of the elongate body (i.e., such as into a computer, interacting with a visual display or graphical user interface), irrespective of the steerable distal portion and even without advancement or withdrawal of elongate body  12 . In other words, the controller, with or without input from a user, can manipulate the elongate body  12  into any desired shape. The determination as to whether or to what degree the elongate body  12  has moved into the desired shape depends at least in part on a shape indicating signal produced by a shape sensor in communication with the elongate body  12  and the controller  30 . 
     As the shape of instrument  10  changes in response to the control signal from user input device  42 , shape sensor  302  provides a shape signal corresponding to the shape of at least one of articulating segments  28 . For example, if shape sensor  302  runs along the entire length of elongate body  12 , then the shape signal can correspond to the shape of the entire length of elongate body  12 . However, for applications where instrument  10  is inserted into a patient, it can be understood that shape sensor  302  need not run along the entire length of elongate body  12 , but rather, only be sufficiently long to indicate the shape of the portion of elongate body  12  inserted into a patient (i.e., the portion of elongate body  12  out of sight from the user). 
     Shape sensor  302  is configured to provide a shape signal corresponding to the shape of at least one of the articulating segments  28 . Controller  30 , being in communication with both user input device  42  and shape sensor  302 , can direct the movement of at least one of the articulating segments  28  in response to the control signal from user input device  42  and the shape signal from shape sensor  302 . It can be appreciated that an articulating instrument or snake-like robot as described above may not always achieve the shape intended by the user. For example, an actuator may fail, or the tendons responsible for moving articulating segments  28  may bind, stretch, slip, or break, causing articulating segments  28  to fail to achieve the shape intended by the user. As such, controller  30  can direct the movement of instrument  10  in response to the shape signal from shape sensor  302  to compensate for any errors within instrument  10  so that instrument  10  can automatically achieve the shape intended by the user. 
     In one embodiment, a user may guide or steer instrument  10  with user input device  42  while monitoring the actual shape of elongate body  12 , as sensed by shape sensor  302 . For example, system  300  can further include a video display (not shown in  FIG. 3 ) configured to receive the shape signal from shape sensor  302  and display an output representing the shape of a portion of elongate body  12 . Thus, the user can guide, steer or direct movement or alteration of the shape of the instrument  10  by monitoring the shape of elongate body  12  as it is displayed on the video display. Since controller  30  directs the movement of elongate body  12  in response to the control signal from user input device  42  and the shape signal from shape sensor  302 , system  300  provides a closed-loop feedback control system for controlling instrument  10  in response to the actual shape of the elongate body  12 . 
     In yet another embodiment of system  300 , the user can input a desired shape onto an interactive display such as a graphical user interface display or the like and controller  30  can direct instrument  10  to automatically achieve the desired shape. This is accomplished in a similar fashion as described above, as controller  30  directs the movement of elongate body  12  in response to the shape signal from shape sensor  302  until the shape of elongate body  12  matches the desired shape from the user. 
     System  300  can be implemented in a variety of surgical procedures. For example, a surgical opening can be created in a patient into which instrument  10  can be inserted and controlled using the system as described above. The surgical opening can also be a natural body orifice, or an opening created after first passing at least a portion of the elongate body through a natural or created opening in the body. In a NOTES procedure, for example, elongate body  12  can be inserted into a patient&#39;s stomach through the nose or mouth and then through the esophagus. In this example, once elongate body  12  is within the stomach, a surgical opening can be incised in the stomach wall to provide entry for elongate body  12  into the peritoneal or abdominal cavity. Thus, the system  300  can accurately sense, measure, determined and/or control the shape of elongate body  12  when it is inside a patient, including all or a portion of elongate body  12  beyond the surgical opening, beyond a natural body orifice or both. 
     As known in the art, an optical sensing fiber can comprise high-density linear arrays of fiber Bragg gratings (FBGs) in the cores of a multicore fiber, as described in “Sensing Shape”,  SPIE&#39;s OEMagazine , pp. 18-21 September 2005. There are multiple ways to measure the shape of a fiber, and, thereby, the shape of the instrument with which it is aligned. One method comprises shining a swept wave length laser down the fiber bundle and measuring the reflected light from the fiber bundle. Bends in the fiber bundle change the reflection properties of the FBGs, thereby the FBGs act as local strain gauges. The challenge comes in accurately reading the many FBG arrays to determine the shape of the fiber bundle. 
     One technique of reading the FBG arrays is the energy leakage technique that strips the cladding along specific regions of the fiber bundle. The bend in relation to the stripped cladding causes the amount of light transmitted through the fiber to increase or decrease in relation to the magnitude and of the bend. One limitation of the technique is that one fiber is required for each direction desired to be measured. 
     Another technique is cross-coupling of a multi-core fiber, as described in U.S. Pat. No. 6,888,623 titled “Fiber Optic Sensor for Precision 3-D Position Measurement,” issued on May 3, 2005. The cross coupling is a function of the shape of the fiber, and by analyzing the energy in each core, it is possible to determine the shape of the fiber. 
     In wavelength division multiplexing (WDM) Bragg gratings are written at various locations along a multicore fiber with different nominal center wavelengths. Each grating can be addressed independently by choosing the wavelength of light that is shone into the system to be close to the center wavelength of the grating. Strain (i.e., bend) in the fiber near the grating will shift the center wavelength of the grating slightly, which can be measured by the shifts in the reflected spectra. A limitation of this technology is that the number of gratings that can be addressed is limited by the total range of wavelengths that the input light source can be scanned, and the minimum difference in nominal center wavelength, as governed by the amount of shift expected in the wavelengths due to strain in the multicore cable, U.S. Pat. No. 7,317,849 titled “Optical Fiber Sensor and Method,” issued on Jan. 8, 2008, further describes this technique. 
     Optical time domain reflectometry (OTDR) can be used as one solution to the limitations of the WDM technique. This solution allows many simultaneous measurements by writing many gratings at the same nominal center wavelength and using time delay of the reflectance to separate the spatial location of the gratings. The location of reflections in a fiber optic cable is determined by measuring the time-of-flight of light from a launch point into a fiber to receipt of a reflection back to the approximate point of launch. In principle, this technique could be used to isolate the same-center-wavelength gratings, however in practice, the position resolution available by this technique is often coarse. 
     In another more preferred technique OTDR uses multicore fiber where all gratings are written at roughly the same nominal wavelength, and the location of the grating is determined in the frequency domain by forming a resonant cavity between the reflection of the gratings and a high reflector at the proximal end of the fiber. This technique requires only one multicore fiber to produce a shape sensor, allows many gratings to be written at the same nominal center wavelength, and permits long fibers. Luna Innovations (www.lunainnovations.com) is an organization that is producing shape sensors built on this technique. 
     As used herein in, optical shape sensor includes any known optical shape sensor. Details of construction, operation and use of exemplary optical sensors may be found in, without limitation, U.S. Pat. No. 6,376,830 titled “System and Method for Measuring the Transfer Function of a Guided Wave Device,” issued on Apr. 23, 2002, U.S. Pat. No. 6,426,496 titled “High Precision Wavelength Monitor for Tunable Laser Systems,” issued on Jul. 30, 2002, U.S. Pat. No. 6,856,400 titled “Apparatus and Method for the Complete Characterization of Optical Devices Including Loss, Birefringence and Dispersion Effects” issued on Feb. 15, 2005, U.S. Pat. No. 7,113,659 titled “Efficient Distributed Sensor Fiber,” issued on Sep. 26, 2006, and U.S. Pat. No. 7,099,015 titled “Fiber Optic Sensing Device for Measuring a Physical Parameter,” issued on Aug. 29, 2006. 
     When shape sensor  302  comprises an optical shape sensor, the axial orientation of the shape sensor from the proximal end through to the distal end must be aligned relative to the instrument  10 , as one method to increase the accuracy of the shape signal produced to correspond to the shape of the elongate body. As described above, working channel  26  runs down the center of instrument  10 . In one embodiment, the working channel is moved to an off-center position and the shape sensor is positioned to occupy the space formerly used by the working channel. Alternatively, the shape sensor  302  may be placed off-center in instrument  10 . However, all central shape sensor positions may create difficulties in maintaining the axial orientation of shape sensor  302 , because as instrument  10  bends the shape sensor can be compressed or stretched and is subject to breaking. 
     There are a number of techniques that may be employed to ensure that the shape sensor is positioned to minimize damage and provide accurate signals representing the shape of all or a portion of the elongate body. Referring to  FIG. 4 , optical shape sensor  402  extends along a portion of the flexible elongate body in a spiral pattern, comprising a single full spiral turn along a single articulating segment  28 . In other embodiments, optical shape sensor  402  can extend in a spiral pattern for an integral number of full spiral turns, so long as the axial orientation of the shape sensor from the proximal end through to the distal end of the shape sensor relative to the instrument is maintained, as needed by the specific technical requirements of a particular optical shape sensor. Optical shape sensor can extend in a spiral pattern along only a single articulating segment  28 , as shown in  FIG. 4 , or can extend in a spiral pattern along multiple articulating segments of the elongate body, including along the entire length of the elongate body. In one embodiment, when the shape sensor spirals along multiple articulating segments, the shape sensor spirals for an integral number of full spiral turns for each articulating segment. This maintains the axial orientation along each articulating segment  28 , and collectively, therefore, along the elongate body. 
     The spiraling of optical shape sensor  402  along a portion of the flexible elongate body adds a naturally occurring twist to the optical shape sensor, which disrupts the axial orientation of the shape sensor as it runs along the flexible elongate body. As such, a counter twist must be induced in the optical shape sensor to remove the natural twist caused by the spiraling path along the elongate body and maintain the axial orientation of the shape sensor from the proximal end through to the distal end relative to the elongate body. 
     As further shown in  FIG. 4 , optical shape sensor  402  can include at least one indicator  404  on at least the proximal and distal ends of the shape sensor. The indicators  404  can be aligned throughout articulating segment  28  to maintain the axial orientation of the shape sensor proximal end and the shape sensor distal relative to the articulating segment  28 . In the embodiment of  FIG. 4 , indicators  404  are physical indicators, such as tabs extending from the shape sensor. These tabs can be fitted into clips  406 , which holds optical shape sensor  402  in place on each end of articulating segment  28  and maintains the axial orientation of the proximal end of the shape sensor relative to the distal end of the shape sensor. In this configuration, however, as described above, if the shape sensor is spiraled along articulating segment, the axial orientation of the shape sensor from the proximal end through to the distal end must still be aligned relative to the articulating segment, such as by inducing a counter twist in the shape sensor. In another embodiment, the physical indicators can be grooves designed to mate with the ends of the articulating segments. In yet another embodiment, indicators  404  can be a visual marker on the shape sensor itself, such as a colored or dotted line that runs the length of the shape sensor, for example. It should be understood that the shape sensor is illustrated on the elongate body for purposes of describing the relative position of the sensor to the elongate body or segment thereof. In some embodiments, the shape sensor is integrated into the elongate body, a sleeve that fits over or is joined to the elongate body or on, within, or about one or more of the articulating segments. 
     Shape sensor  302  described above is not limited to being an optical shape sensor. Retelling to  FIG. 5 , alternatively, resistance changing flexible bands can be implemented in elongate body  12 . As known in the art, resistance changing flexible bands change resistance when stretched. One example of resistance changing flexible bands are Stretch Sensors™, available from Images SI Inc. (http://www.imagesco.com/sensors/stretch-sensor.html). As shown in  FIG. 5 , flexible band sensors  502  can extend along the length of articulating segment  28  of elongate body  12 . Pairs of flexible band sensors  502  can run along first and second pairs of hinges  204  and  206  for each bending plane (x- plane and y-plane) of articulating segment  28 . In this embodiment, the flexible band sensors will experience a resistance gain and a resistance decrease during articulation. The resistance delta between of the flexible band sensors  502  can be determined or measured and used to determine the shape of each articulating segment  28 . Thus, the flexible band sensors  502  can provide a shape signal to controller  30 , as described above, corresponding to the shape of at least a portion of elongate body  12 . 
     In an alternative embodiment, shape sensor  302  can comprise a plurality of flex sensors, such as those made by FlexPoint (www.flexpoint.com) or SpectraSymbol (www.spectrasymbol.com). As shown in  FIG. 6 , flex sensors  602  and  604  (flex sensors  604  are provided along hinges  204  but obscured from view in  FIG. 6 ) can be attached to hinges  206  and  204  of each link  200 , respectively, to provide a signal to the controller  30  a signal indicative of the angle of articulation. Flex sensors  602  and  604  are flat and bend in one plane, but are essentially not bendable in the orthogonal plane. Thus, in this embodiment, flex sensors  602  and  604  are aligned so the bending plane of each pair of links  200  is approximately parallel with the bending plane of the flex sensor across each hinge. As described above, the flex sensors  602  and  604  can provide a shape signal to controller  30  corresponding to the shape of at least a portion of elongate body  12 . 
     In yet another embodiment, a potentiometer (POT) can be used to measure joint angles as yet another technique for determining the shape of all or a portion of the elongate body. Similar to the embodiments described above, A POT-purchase assembly can be provided at each hinge of the articulating segments  28 . In this embodiment, the POT has a wiper that brushes against a carbon film thereby changing the resistance output from the POT. The wiper is attached to a slotted piece, which is fixed on hinges  204  and  206  between adjacent links  200  of articulating segments  28 . Articulation of links  200  turns the slotted piece and causes the wiper to brush against the carbon film and change the resistance output of the POT as described. This resistance can be provided as a shape signal to controller  30 , as described above, corresponding to the shape of at least a portion of elongate body  12 . An alternative to a POT sensor is the use of an optical encoder, as will be appreciated by the skilled artisan. 
     Another alternative device and technique for shape sensing includes using magnetic sensors, or alternatively sensors that detect variations in magnetic fields generated by a transmitter. Ascension Technology Corporation (http://www.ascension-tech.com/) is developing sensors suited to the purposes described herein. U.S. patent application Ser. No. 11/242,048 titled “DC Magnetic-Based Position and Orientation Monitoring System for Tracking Medical Instruments,” filed on Oct. 4, 2005, also discloses this technology. The magnetic sensors can be placed at intervals along elongate body  12 , in accordance with an embodiment of the present invention. The spatial orientation of and movements detected by the magnetic sensors may be used to indicate, determine or measure the shape of all or a portion of the elongate body. In the same manner as described above, the magnetic sensors can provide a shape signal to controller  30  corresponding to the shape of at least a portion of elongate body  12 . 
       FIG. 7  shows a flowchart illustrating an exemplary method of controlling an instrument having an elongate body according to an embodiment of the present invention. Certain details and features have been left out of flowchart  700  that are apparent to a person of ordinary skill in the art. For example, a step may consist of one or more substeps or may involve specialized equipment or materials, as known in the art. 
     The following description of flowchart  700  includes references to instrument  10  of  FIG. 1  and system  300  of  FIG. 3 , since the method steps in flowchart  700  are implemented utilizing an instrument such as instrument  10 . At step  702  of flowchart  700 , a control signal is outputted to a controller to change the shape of an instrument having an elongate body. As described above, a user can input a control signal into user input device  42 , which can transmit the control signal to controller  30 , for example. In one embodiment, controller  30  is in communication with actuator  304  to direct the movement of elongate body  12 . 
     At step  704  of flowchart  700 , the shape of at least a portion of the elongate body is sensed with a shape sensor. As described above, shape sensor  302  provides a shape signal corresponding to the shape of at least one of articulating segments  28 . In one embodiment, shape sensor  302  runs along the entire length of elongate body  12  to provide a shape signal corresponding to the shape of the entire length of elongate body  12 . However, in another embodiment, instrument  10  is inserted into a patient so shape sensor  302  need not run along the entire length of elongate body  12 , but rather, only be sufficiently long to indicate the shape of the portion of elongate body  12  inserted into the patient. 
     At step  706  of flowchart  700 , the shape signal corresponding to the shape of the portion of the elongate body is outputted from the shape sensor to the controller. In one embodiment, the outputting step can further include the step outputting the shape signal to a video display to display an output representing the shape of the portion of the elongate body. As described above, system  300  can include a video display configured to receive the shape signal from shape sensor  302  and display an output representing the shape of a portion of elongate body  12 . Thus, the user can guide, steer or direct movement or alteration of the shape of the instrument  10  by monitoring the shape of elongate body  12  as it is displayed on the video display. 
     At step  708  of flowchart  700 , the movement of the elongate body is directed in response to the control signal and the shape signal. As described above, controller  30 , being in communication with both user input device  42  and shape sensor  302 , can direct the movement of at least one of the articulating segments  28  in response to the control signal from user input device  42  and the shape signal from shape sensor  302  to provide a closed-loop feedback control system for controlling instrument  10 . 
     In other embodiments, the method can further include the step of creating a surgical opening in a patient. A surgical opening can be created in a patient into which instrument  10  can be inserted and controlled using the system described above. The surgical opening can also be a natural body orifice, or an opening created after first passing at least a portion of the elongate body through a natural or created opening in the body. Additionally, the method can further include the step of sensing the shape of least a portion of the elongate body beyond the surgical opening, and outputting the shape signal to a video display to display an output representing the shape of the portion of the elongate body beyond the surgical opening. 
     In addition to sensing the shape of the elongate body, optical sensors can be used to determine the depth of insertion of the elongate body from a particular pre-defined point. This information can also be used to construct the three dimensional shape of the elongate body, as previously described. Two or more shape sensors may be used to determine the depth of insertion of an instrument. Consider a pair of shape sensors. Each sensor is capable of providing x,y,z position within an x,y,z coordinate system. One sensor is placed at a fixed location and is used as a reference location. In one embodiment, the x,y,z tip position of the first sensor is used as the point of reference. The point of reference may be placed at, on or near a natural or surgically created opening in the body. The point of reference sensor may be positioned adjacent a surgically created opening created within the body after entering the body through a natural opening or a surgically created opening. The reference point may be positioned at or near a natural opening even if a surgical opening is created and utilized elsewhere. For example, the reference point may be at or near the mouth when an opening is created in the stomach or at another point in the alimentary canal. Additionally, the reference point opening may be created and the shape sensor and flexible instrument positioned and used in support of NOTES, as described in co-pending patent application Ser. No. 11/522,305 filed Sep. 14, 2006 titled “Methods and Apparatus Useful in Performing Transluminal and Other Procedures.” The second sensor is attached to an instrument. The instrument passes near the tip of the first sensor. The x, y, z position of the second instrument is known. Next, compare the x,y,z positions along the instrument until one matches or most nearly corresponds to the x,y,z position of the tip. The x,y,z position on the instrument is then used to determine the position of the instrument relative to the reference point or the depth that the instrument has been inserted beyond the reference point. Additionally, the shape of the second instrument is also known based on information from the second shape sensor. The path, organ or portion of the body traversed relative to the reference point may also be determined using the depth of insertion and the shape of the second shape sensor. Similar techniques may also be used while the instrument is being withdrawn or manipulated. 
     In an alternative embodiment, the techniques described herein may be used to measure the relative location of a shape sensor with respect to another position sensor that is not a shape sensor. For example, if the anus was placed in a known location on an operating room table, and the shape sensor&#39;s base is located in a known location with respect to an operating room table, depth of insertion could be determined entirely using a single shape sensor in the scope, and the second sensor is the “ruler” formed by the known relative locations of the anus and the base of the shape sensor. 
     It would be possible to discern velocity, acceleration and higher order derivatives from this arrangement as well. Use of multiple sensors could be used to provide redundancy, consistency/error checking, and lower error and lower signal noise through various stochastic estimation techniques (such as extended Kalman filters, Unscented Transform filters, Weiner filtering, H_infinity optimal estimation and the like). 
     As for additional details pertinent to the various embodiments described herein, materials and manufacturing techniques may be employed as within the level of those with skill in the relevant art. The same may hold true with respect to method-based aspects of the invention in terms of additional acts commonly or logically employed. There are additional system requirements needed to ensure the full integration and proper operation of a shape sensor with the elongate body and associated control system optical shape sensors, for example require a light source and a perfect components to ensure the light source is focused or provided to the optical sensor. These and other conventional components are also included as part of the system  300  as needed by the technical requirements of the particular shape sensor or sensors being used. 
     Also, it is contemplated that any optional feature of the inventive variations described may be set forth and claimed independently, or in combination with any one or more of the features described herein. Likewise, reference to a singular item, includes the possibility that there are plural of the same items present. More specifically, as used herein and in the appended claims, the singular forms “a,” “and,” “said,” and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation. Unless defined otherwise herein, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The breadth of the present invention is not to be limited by the subject specification, but rather only by the plain meaning of the claim terms employed. 
     It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.