WO2017223350A1

WO2017223350A1 - Removing light energy from a fiber cladding

Info

Publication number: WO2017223350A1
Application number: PCT/US2017/038816
Authority: WO
Inventors: Eric E. Sanborn; Mark Froggatt; Jeffrey T. Lacroix
Original assignee: Intuitive Surgical Operations Inc
Current assignee: Intuitive Surgical Operations Inc
Priority date: 2016-06-23
Filing date: 2017-06-22
Publication date: 2017-12-28
Anticipated expiration: 2018-12-23

Abstract

A system comprises a coupling member for coupling a first optical fiber member to a second optical fiber member, the second optical fiber member including a sensing region and a medical instrument into which a distal end of the second optical fiber member extends. The system also comprises a cladding light remover positioned between the coupling member and the sensing region. The cladding light remover includes a tubular member with a substantially linear lumen portion and a curved lumen portion. The second optical fiber member extends through the tubular member to remove light energy traveling in a cladding of the second optical fiber member.

Description

REMOVING LIGHT ENERGY FROM A FIBER CLADDING

RELATED APPLICATION

This application claims the benefit of priority of U.S. Provisional Application 62/353,842, filed June 23, 2016, which is herein incorporated by reference in its entirety.

FIELD

The present disclosure is directed to systems and methods for removing light energy from an optical fiber cladding.

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 harmful 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. One such minimally invasive technique is to use a flexible and/or steerable catheter that may be inserted into anatomic passageways and navigated toward a region of interest within the patient anatomy. Medical tools, such as sensor instruments, are deployed through the catheter to determine the shape of the medical tool during a procedure and to determine the position and orientation of a portion of the catheter such as the distal end. Sensor instruments that incorporate an optical fiber shape sensor may experience sensor noise that adversely affects the measurements obtained by the sensor instruments. Systems and method are needed for improving the signal to noise ratio in sensor instruments.

SUMMARY

The embodiments of the invention are best summarized by the claims that follow the description.

Consistent with some embodiments, a system comprises a coupling member for coupling a first optical fiber member to a second optical fiber member, the second optical fiber member including a sensing region and a medical instrument into which a distal end of the second optical fiber member extends. The system also comprises a cladding light remover positioned between the coupling member and the sensing region. The cladding light remover includes a tubular member with a substantially linear lumen portion and a curved lumen portion. The second optical fiber member extends through the tubular member to remove light energy traveling in a cladding of the second optical fiber member.

Consistent with some embodiments, a system comprises a coupling member for coupling a first optical fiber member to a second optical fiber member. The second optical fiber member includes a sensing region. The system also includes an instrument into which a distal end of the second optical fiber member extends. The system also includes a cladding light remover between the coupling member and the sensing region. The cladding light remover includes a first tube having a first lumen extending between a first end and a second end and a second tube having a second lumen sized to receive the first tube and hold the first tube in a curved shape. The second optical fiber member extends through the cladding light remover to remove light energy traveling in a cladding of the second optical fiber member.

Consistent with some embodiments, a method comprises launching light energy into a cladding of an optical fiber sensor. The optical fiber sensor has a distal end coupled to a termination element. The method also comprises passing the optical fiber sensor through a curved lumen within a cladding light remover to remove the light energy from the cladding of the optical fiber sensor. The optical fiber sensor forms a first localized bend as it enters the curved lumen and forms a second localized bend as it exits the curved lumen.

Consistent with some embodiments, an optical fiber coupling apparatus comprises a coupling section for coupling a first optical fiber member to a second optical fiber member. The second optical fiber member including a coated region and an uncoated region. The apparatus also comprises a fastening member fastened to the uncoated region and a tubular body adjacent to the fastening member through which a portion of the uncoated region of and the coated region of the second optical fiber extends. An adhesive material fills the tubular body around the uncoated region. The adhesive material has a higher index of refraction than a fiber coating of the coated region of the second optical fiber.

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 according to some embodiments.

FIG. 2A is a simplified diagram of a medical instrument system according to some embodiments.

FIG. 2B is a simplified diagram of a medical instrument with an extended medical tool according to some embodiments.

FIG. 3 is a cross sectional view of an optical fiber according to some embodiments.

FIG. 4 is a schematic illustration of an optical fiber sensing system according to some embodiments.

FIG. 5 is a side view of a sensor instrument according to some embodiments.

FIG. 6 is a cladding light remover according to some embodiments. FIG. 7 illustrates cladding light launch and removal according to some embodiments.

FIG. 8A illustrates a connector including a cladding light remover according to some embodiments.

FIG. 8B illustrates a detailed view of a portion of the connector of FIG.

8 A.

FIG. 9 is a flowchart illustrating a method for removing light from a cladding layer of an optical fiber sensor.

FIG. 10A illustrates a connector including a cladding light removal portion according to some embodiments.

FIG. 10B illustrates in greater detail the cladding light removal portion of FIG. 10A.

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 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 O. A master assembly 106 allows a clinician or surgeon S to view the interventional site and to control teleoperational manipulator assembly 102.

Master assembly 106 may be located at a surgeon's console which is usually located in the same room as operating table O, such as at the side of a surgical table on which patient P is located. However, it should be understood that surgeon S 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 surgeon S 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 surgeon S 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 surgeon S 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 surgeon S 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 clinician or surgeon S 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. 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 control system 112 may execute instructions comprising instruction corresponding to processes disclosed herein and described in more detail below.

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 surgeon S. In this manner surgeon S 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 surgeon 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 (MRI), 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 clinician or surgeon S 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 surgeon S controlling medical instrument 104. In some examples, medical instrument 104 may not be visible in the virtual image.

In some embodiments, display system 1 10 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 clinician or surgeon S 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 surgeon S in the control of medical instrument 104. As described herein, visual representations of data points may be rendered to display system 1 10. For example, measured data points, moved data points, registered data points, and other data points described herein may be displayed on display system 1 10 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 1 10 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 data points.

Teleoperated medical system 100 may also include control system 112. Control system 1 12 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 1 10. Control system 1 12 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 1 12 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. 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 O.

Control system 1 12 may optionally further include a virtual visualization system to provide navigation assistance to surgeon S 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. 2A 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.

Medical instrument system 200 includes catheter system 202 coupled to a drive unit 204. Catheter system 202 includes a flexible body 216 having proximal end 217 and distal end 218 (also called "tip portion 218")· In some embodiments, flexible body 216 has an approximately 3 mm outer diameter and an approximately 2mm inner diameter surrounding a working channel. Other flexible body outer diameters may be larger or smaller. As shown in FIG. 2B, a working channel 221 may extend through the flexible body 216. Catheter system 202 may optionally include shape sensor 222 for determining the position, orientation, speed, velocity, pose, and/or shape of the catheter tip at distal end 218 and/or of one or more segments 224 along flexible body 216. The sensor 222 may extend through the working channel 221 or may extend through a separate and dedicated sensor lumen. 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 a medical instrument 104 of a teleoperated medical system 100, shape sensor 222 may be a component of sensor system 108. If medical instrument system 200 is manually operated or otherwise used for non-teleoperational procedures, shape sensor 222 may be coupled to a tracking system 230 that interrogates shape sensor 222 and processes received shape data.

Shape sensor 222 may optionally include an optical fiber aligned with flexible body 216 (e.g., provided within an interior channel of the catheter wall (not shown) or mounted externally). In one embodiment, the optical fiber has a diameter of approximately 200 μπι. 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 catheter system 202. In one alternative, optical fibers including Fiber Bragg Gratings (FBGs) are used to provide strain or temperature measurements in structures in one or more dimensions.

FIG. 3 is a cross sectional view of an optical fiber 300 according to some embodiments. The optical fiber 300 includes a plurality of fiber cores 302 through which light energy is propagated. The fiber cores 302 are surrounded by cladding layer 304. The cladding layer 304 is surrounded by a coating or buffer layer 306 that protects the cladding. In this embodiment, the optical fiber 300 is a multi-core (three core) fiber, but in alternative embodiments, a single core or a different number of cores may be used. The index of refraction of the cladding layer 304 is lower than the core(s) which results in total internal light reflection, guiding the light through the core even when the optical fiber is bent at least moderately.

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 No. 11/180,389 (filed July 13, 2005) (disclosing "Fiber optic position and shape sensing device and method relating thereto"); U.S. Patent Application No. 12/047,056 (filed on Jul. 16, 2004) (disclosing "Fiber-optic shape and relative position sensing"); and U.S. Patent 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 catheter may be determined using other techniques. For example, a history of the distal end pose of catheter system 202 can be used to reconstruct the shape of flexible body 216 over the interval of time. As another example, historical pose, position, or orientation data may be 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, such as electromagnetic (EM) sensors, positioned along flexible body 216 can be used for shape sensing. In some examples, a history of data from a positional sensor, such as an EM sensor, on the instrument system during a procedure may be used to represent the shape of the instrument, particularly if an anatomic passageway is generally static. In some examples, a wireless device with position or orientation controlled by an external magnetic field may be used for shape sensing. The history of the position of the wireless device may be used to determine a shape for the navigated passageways.

In some embodiments, medical instrument system 200 may, optionally, include 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 an example EM sensor system implementing a position 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, the example EM sensor system implementing the 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 an EM sensor system is provided in U.S. Patent No. 6,380,732 (filed August 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, shape sensor 222 may also function as the position sensor because the shape of shape sensor 222 together with information about the location of the base of shape sensor 222 (in the fixed coordinate system of patient P) allows the location of various points along shape sensor 222, including distal end 218, to be calculated.

In some embodiments, tracking system 230 may optionally include position sensor system 220 and shape sensor 222 for determining the position, orientation, speed, pose, and/or shape of distal end 218 and of one or more segments 224 of medical instrument system 200. 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.

Flexible body 216 includes a channel 221 sized and shaped to receive a medical instrument 226. In one example, the working channel 221 may have a diameter of approximately 2 mm. 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 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. 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.

Medical instrument 226 may additionally house cables, linkages, or other actuation controls (not shown) that extend between proximal end 217and distal end 218 of medical instrument 226 to controllably bend distal end 218 of medical instrument 226. Steerable instruments are described in detail in U.S. Patent 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 No. 12/286,644 (filed Sept. 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 catheters are described in detail in U.S. Patent Application 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. Catheter system 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 surgeon 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 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.

FIG. 2B is a simplified diagram of a medical instrument with an extended medical tool 226 according to some embodiments. In some embodiments, extended medical tool 226 may be used for procedures such as surgery, biopsy, ablation, illumination, irrigation, or suction. Medical tool 226 can be deployed through working channel 221 of flexible body 216 and used at a target location within the anatomy. If, for example, medical tool 226 is a biopsy instrument, it may be used to remove sample tissue or a sampling of cells from a target anatomic location. Medical tool 226 may be used with an image capture probe also within flexible body 216. Alternatively, medical tool 226 may itself be the image capture probe. Medical tool 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 tool 226 may be removed from proximal end 217 of flexible body 216 or from another optional instrument port (not shown) along flexible body 216.

Fiber optic sensor systems used with the medical instrument system 200 or in other sensing applications determine the shape of the optical fiber (and therefore the shape of the catheter) by interrogating light energy signals reflected along the optical fiber. If the signals become noisy, the accuracy of the shape sensor information becomes compromised. Coupling devices such as fiber optic connectors or fanout devices create discontinuities that may reduce the efficiency of light transfer. For example, at a connector, light energy exits the core of one fiber and enters the core of a mating connector's fiber. The light transfer is not 100% efficient. For example, some of the light reflects back in the direction that in came, and some light is launched into the cladding of the mating fiber rather than into the mating fiber core. In standard optical fiber, such as the type used in telecommunications systems, light in the cladding propagates in the cladding until it reaches the interface between the cladding and the coating. Because standard telecommunication fiber uses an acrylate or polyimide coating that has a higher index of refraction than the cladding, the light in the cladding is stripped out or removed from the cladding by the coating so that it cannot be reintroduced to the core(s) and adversely impact the system performance as noise.

For some optical fiber applications, including medical sensing, coatings with indices of refraction lower than acrylate or polyimide coatings, may be beneficial. For example, some low index coating materials may be transparent to ultraviolet light used to write Fiber Bragg Gratings in a post processing operation after the fiber has been drawn. Examples of such low index coating materials include silicone which has an index of refraction lower than the fused silica used in the fiber cladding. Silicone is also particularly suitable for medical applications because it is biocompatible and adheres well to glass. When low index coatings are used, the light launched into the cladding continues to travel in the cladding along the length of the fiber without being substantially removed by the coating. Light traveling in cladding may be known as the cladding mode. Light energy travelling in the cladding propagates at a different rate than light energy propagating in the core. If the cladding light is not removed by the coating, it may be coupled back into the core at a later fiber discontinuity such as a connector or a termination member. In other examples, using fiber with a lower numerical aperture like standard telecommunication fiber, light may be launched into the cladding simply by bending the fiber, without the light passing through a fiber discontinuity. The re-coupled light results in the addition of a time shifted signal that mixes with the light signal traveling in the core to cause system noise that may make interpretation of the light reflected by the Fiber Bragg Gratings difficult and inaccurate. For medical sensing systems that are interested in the shape of a distal tip of an optical fiber, the consequences to the reintroduced cladding light are particularly harmful because a termination member is typically located at or near the distal tip of the sensing fiber. At this location the termination member may reintroduce cladding light where it has the greatest disruption on the main signal. Systems and methods for removing the cladding mode before it can be reintroduced to the core are described herein.

FIG. 4 an optical fiber sensing system 400. The sensing system 400 may be a component of a sensor system 108 and tracking system 230. The sensing system 400 includes an interrogation system 402 that includes electronics and optical equipment for passing light energy through the system and decoding light energy reflected through the system. The interrogation system 402 is coupled to an optical fiber 403 or to multiple optical fibers.

A coupling member 404 connects the optical fiber 403 to an optical fiber 405. The optical fiber 405 has a low index of refraction coating. The coupling member 404 may be, for example, an optical fiber connector that connects light traveling in the core of one fiber to the core of a mating fiber. In another example, the coupling member 404 may be a fanout device that receives light from multiple single core fibers and facilitates the transfer of light to one multi- core fiber. The fanout device may be a fused tapered device. Coupling member 404 may not be entirely efficient in transferring light between cores and causes some of the light from the entering fiber to become launched into the cladding of the exiting fiber(s) rather than the core(s). Thus, the optical fiber 405, distal of the coupling member 404, has light propagating in the cladding. If not removed, the time shifted light energy from the cladding may be reintroduced to the optical fiber core at a fiber terminator 408. The fiber terminator 408 is distal of a sensed region 407 of the instrument through which a sensing region of the multicore fiber 405 extends. Reintroduction of the cladding mode for reflection into the sensing region provides distortion in the signals reflected from the sensing region. To prevent this cladding mode reintroduction, an in-line cladding light remover 406 is located distal of the coupling member and proximal of the sensing region to strip the cladding mode and prevent its reintroduction to the core. As described in greater detail below, the in-line cladding light remover 406 provides a localized bend in the optical fiber 405 (with a low index of refraction coating) that allows the cladding mode to overcome the total internal reflection and exit the cladding into the coating where it becomes removed. The light remover 406 removes the cladding mode via one or more in-line bends, without the creating a full loop in the fiber 405.

FIG. 5 illustrates a sensor system 500 (e.g., sensor 222) including a connector body 502 that connects with a connector body 503. An optical fiber 505 extends within the connector body 503 to connect with an optical fiber 507 extending within connector body 502. In this example, the optical fiber 507 may have a low index of refraction coating surrounding the fiber cladding. The discontinuity at the connection of fibers 505, 507 may cause light energy from fiber 505 to enter the cladding of fiber 507. As previously described, the low index of refraction coating of fiber 507 may inhibit the stripping of the light propagating in the cladding, as compared to a high index of refraction coating. The connector 502 includes a protective boot 504. For mechanical protection, a furcation tube 512 may be coupled at a proximal end to the connector body 502 and at a distal end to an in-line cladding light remover 518. An axis Al extends centrally through the furcation tube. A catheter 520 extends from the cladding light remover 518. The fiber 507 extends through the furcation tube, the cladding light remover 518, and the catheter 520 to a termination device 522 such as a termination tube that houses the distal tip of the fiber 507.

FIG. 6 illustrates a cross-sectional view of the in-line cladding light remover 518. The light remover 518 includes a rigid tubular body 550 through which extends a channel 552 having a diameter Dl . The channel 552 is centered along a generally linear axis Al . The body is crimped to the furcation tube 512 by a crimp ring 553. The tubular body 550 may serve as an adapter for coupling the tubular body 550 to the catheter system 202 and may include threads 562 or other connection systems for coupling to the catheter system. A tube 556 extends within the channel 552. The tube 556 has a channel 557 extending between a distal end 560 and a proximal end 558. In this example, the tube 556 is formed from a pre -bent section of low friction tubing. The tube 556 has an outer diameter D2, and the channel 557 has a diameter slightly larger than the fiber 507. The tube 556 is affixed within the channel 552 by an adhesive 554 but could also be molded or formed in place in a similar geometry. When unconstrained by the channel 552, the pre -bent tube 556 has a smaller radius of curvature than it does inside the rigid tube body 550 because the channel 552 forces the tube 556 into a shallower curve with a larger radius of curvature. The channel 557 thus has a curved path within the straight channel 552. The proximal end 558 of the tube 556 abuts the furcation tube 512 so that the relatively linear channel 555 of the furcation tube joins to the curved channel 557. The distal end of the tube 556 may also be constrained relatively linearly, compared to the curved channel 557, by structures extending immediately adjacent to the distal exit of the fiber.

The fiber 507 extends through the channel 555, in generally parallel alignment with the axis Al . And, the fiber 507 continues through the channel

557. At the proximal end 558 of the tube 556, a localized bend is formed in the fiber 507 by directing the fiber away from the axis Al and along the curved channel 557. At the distal end 560 of the tube 556, a localized bend is formed in the fiber 507 by directing the fiber toward the axis Al (or generally parallel to axis Al) by structures or lumens immediately adjacent to the distal exit of the fiber. At the bend areas located at distal end 558 and proximal end 560, the fiber is not subjected to damaging forces or tensions that could negatively impact the sensing. At the localized bend areas at distal end 558 and proximal end 560, the cladding mode is stripped from the cladding so that it cannot be later reintroduced at the termination device 522.

In various alternatives, the lumen of the tube 556 may have a series of inline curves, a serpentine curve, or other curved shapes that create one or more localized bends in the optical fiber without looping the fiber. In various alternatives, the pre-bent tube may be eliminated and the outer tubular body 550 may be cast or machined to include an integral curved channel that creates one or more localized bends in the passing through optical fiber.

FIG. 7 illustrates light propagation at a localized bend area substantially similar to areas located at distal end 558 and proximal end 560. In this example, an optical fiber 600 is coupled to an optical fiber 602 at a connection location

604. The optical fiber 600 includes a core 608. The optical fiber 602 includes a core 610 surrounded by a cladding 612 which is surrounded by a covering 614. Covering 614 may be a coating of material or some material applied in some other manner. At the connection location 604, the discontinuity in the fibers causes light energy 620 to propagate into the cladding 612. The light energy 620 travels within the cladding 612 until it reaches the localized bend at bend area 622 (e.g. bend areas that may be located at distal end 558 or proximal end 560). At the bend area 622, the light energy 620 is stripped from the cladding 612 and removed through the covering 614.

FIGs. 8A and 8B provide cross-sectional views of a connector 700 with a connector body 701 housing an in-line cladding light remover 702 and a boot portion 703. This example efficiently packages the source of the discontinuity and the cladding light remover in a common housing. The connector 700 connects a proximal end 704 of a fiber 706 at a connection location 707 to a mating fiber (e.g. fiber 505) which creates a discontinuity where the fibers are connected. The cladding light modes may be launched at the connection location (i.e., the discontinuity) into the cladding of the fiber 706. Including the cladding light remover 702 in the connector body 701 distal of the connection location 707 may eliminate the need for an external cladding light remover at a more distal location. The cladding light remover 702 may be located at any location along the path of the fiber 706 distal of the connection location 707 within the connector body 701. In this example, the cladding light remover 702 may function substantially similar to the cladding light remover 518. The cladding light remover 702 includes a pre-bent curved tube 710 extending within a channel 712 of the connector 700. The channel 712 is generally linear.

Alternatively, the channel 712 may be curved but having a radius of curvature greater than the radius of curvature of curved tube 710 so that the curved tube 710 is able to maintain a smaller radius of curvature than the channel 712. In other words, the diameter of the channel 712 is sized sufficiently larger than the curved tube 710 to allow the curved tube to maintain a tighter radius of curvature than the channel 712. The tube 710 is formed from a pre -bent section of low friction tubing and is affixed within the channel 712 by an adhesive. In various alternatives, the pre-bent tube may be eliminated and the outer channel may be cast or machined to include an integral curved channel that creates one or more localized bends in the passing through optical fiber.

In this example, the cladding of the fiber 706 propagates the cladding mode proximal of the light remover 702. At a location 714 where the fiber 706 enters the curved tube 710 from the straight channel 712, a localized bend is formed in the fiber 706 by directing the fiber away from the central axis of the channel 712 and along the curve of the lumen of tube 710. At the location 716 where the fiber 706 exits the curved tube 710 into the straight channel 712, a localized bend is formed in the fiber 706. Thus, locations 714, 716 may also be referred to as localized bend areas. At the localized bend areas 714, 716, the cladding mode is stripped from the cladding so that it cannot be later reintroduced into the core of the fiber 706. The proximal end of the connector body 708 may include strain relief devices, such as the boot portion 703 , to reduce or eliminate strain in the optical fiber.

FIG. 9 illustrates a method 800 for removing light energy from a cladding of an optical fiber sensor. The method 800 is illustrated as a set of operations or processes 802-808. Not all of the illustrated processes 802-808 may be performed in all embodiments of method 800. Additionally, one or more processes that are not expressly illustrated in FIG. 9 may be included before, after, in between, or as part of the processes 802-808. In some embodiments, one or more of the processes 802-808 are optional and may be omitted.

At a process 802, light energy is launched into a cladding of the optical fiber sensor. Light energy may be launched into a cladding mode, for example, by a fanout device and/or a connector as previously described. The optical fiber sensor has a distal end coupled to a termination element. In the absence of a cladding light remover, the cladding modes may be reintroduced to the fiber by other distally located discontinuities such as a connector or by the termination element. This time-shifted, reintroduced light may interfere with the accuracy of the sensor. At a process 804, a first localized bend is created in the optical fiber sensor as the fiber enters a curved channel. At a process 806, the optical fiber sensor is passed through the curved channel within a cladding light remover. At a process 808, a second localized bend is created in the optical fiber sensor as the fiber exits the curved channel. The localized bends remove the light energy from the cladding of the optical fiber sensor.

FIG. 10A illustrates a connector 900 including a cladding light removal portion 902 according to some embodiments. FIG. 10B illustrates the cladding light removal portion 902 in greater detail. In this embodiment, the connector 900 includes a fastener such as a ferrule 904 with a distal end inserted into a tubular ferrule holder 906. An optical fiber 908 is stripped of its low index coating 910 to fit tightly within the ferrule 904. The fiber 908 may be bonded to the ferrule to prevent longitudinal movement of the optical fiber relative to the ferrule 904. Traditionally, the fiber 908 is stripped of its coating 910 along the length of the ferrule until approximately the guide feature 911. In other words, traditionally the proximal beginning of the coating 910 is at or a short distance distally from the guide feature 911. In this embodiment, however, to provide for cladding light removal, the proximal beginning of the coating 910 is at a distance LI from the guidance feature 911 at the distal end of the ferrule 904. This bare length LI of the fiber 908 extending distally of the ferrule 904 is also stripped of the low index coating 910. A filling material 912 fills the area of the channel of holder 906 around the fiber 908 between the ferrule 904 and the coating 910.

The filling material 912 may be a high refractive index epoxy or other high index adhesive or bonding material that surrounds the uncoated portion of the fiber 908 and functions to remove cladding mode light energy from the fiber 908. The filling material 912 may have a higher refractive index than the cladding of the fiber 908 and the coating 910. In this embodiment, the distance

LI may be approximately 6 mm, but the distance LI may be smaller or longer. In some embodiments, the distance LI may be greater than approximately half the length of the ferrule 904. In other embodiments, the distance LI may be sufficiently long to remove at least a portion of the cladding mode light. One or more elements in embodiments of the invention (e.g., the processing of signals received from the input controls and/or control of the flexible catheter) 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 machine-readable storage media, including any media that can store information including an optical medium, semiconductor medium, and magnetic medium. Machine-readable storage media 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, 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 processors 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.

Claims

CLAIMS What is claimed is:

1. A system comprising:

a coupling member for coupling a first optical fiber member to a second optical fiber member, the second optical fiber member including a sensing region;

a medical instrument into which a distal end of the second optical fiber member extends; and

a cladding light remover positioned between the coupling member and the sensing region and including a tubular member with a substantially linear lumen portion and a curved lumen portion, wherein the second optical fiber member extends through the tubular member to remove light energy traveling in a cladding of the second optical fiber member.

2. The system of claim 1 further comprising a connector assembly including the coupling member, the connector assembly coupling a distal end of the first optical fiber member to a proximal end of the second optical fiber member at an optical fiber joint.

3. The system of claim 2 wherein the connector assembly further includes the cladding light remover positioned distal of the optical fiber joint.

4. The system of claim 1 , or of claim 2 or 3, further comprising a fanout assembly including the coupling member, wherein the first optical fiber member is a single core fiber and the second optical fiber member is a multi-core fiber.

5. The system of claim 1 , or of claim 2 or 3, wherein the second optical fiber member is a shape sensor adapted to determine a shape of the sensing region.

6. The system of claim 1 , or of claim 2 or 3, wherein the second optical fiber member is a temperature or strain sensor.

7. The system of claim 1 , or of claim 2 or 3, wherein the tubular member includes a first tubular portion including the substantially linear lumen portion adjacent at an interface to a second tubular portion including the curved lumen portion, wherein the light energy traveling in cladding of the second optical fiber member is removed at the interface.

8. The system of claim 7 wherein the second tubular portion includes a tubular body including a substantially linear channel and a curved tubular member extending within the substantially linear channel, the curved tubular member including the curved lumen portion extending therethrough.

9. The system of claim 8 wherein the curved tubular member is affixed within the substantially linear channel by an adhesive.

10. The system of claim 8 wherein the curved tubular member is formed of a polymer.

11. The system of claim 1 , or of claim 2 or 3, wherein the second optical fiber member includes a cladding surrounding at least one optical core and wherein prior to removal, the removed portion of light energy traveling in the second optical fiber member is traveling in the cladding.

12. The system of claim 1 , or of claim 2 or 3, wherein the instrument has a proximal end coupled to the coupling member.

13. A system comprising:

a coupling member for coupling a first optical fiber member to a second optical fiber member including a sensing region; and

a cladding light remover between the coupling member and the sensing region, the cladding light remover including

a first tube having a first lumen extending between a first end and a second end; and

a second tube having a second lumen sized to receive the first tube and hold the first tube in a curved shape, wherein the second optical fiber member extends through the cladding light remover to remove light energy traveling in a cladding of the second optical fiber member.

14. The system of claim 13 further comprising a connector assembly including the coupling member which couples a distal end of the first optical fiber member to a proximal end of the second optical fiber member at an optical fiber joint.

15. The system of claim 14 wherein the connector assembly further includes the cladding light remover positioned distal of the optical fiber joint.

16. The system of claim 13, or of claim 14 or 15, further comprising a fanout assembly including the coupling member, wherein the first optical fiber member is a single core fiber and the second optical fiber member is a multi-core fiber.

17. The system of claim 13, or of claim 14 or 15, wherein the light energy traveling in the cladding of the second optical fiber member is removed at the first and second ends of the first tube.

18. The system of claim 13, or of claim 14 or 15, wherein the first tube is affixed within the second lumen by an adhesive.

19. The system of claim 13, or of claim 14 or 15, wherein the first tube is formed of a polymer.

20. The system of claim 13, or of claim 14 or 15, wherein the second optical fiber member includes a plurality of optical cores surrounded by the cladding.

21. The system of claim 13, or of claim 14 or 15, further comprising an instrument into which a distal end of the second optical fiber member extends, wherein the instrument has a proximal end coupled to the coupling member.

22. A method comprising:

launching light energy into a cladding of an optical fiber sensor, the optical fiber sensor having a distal end coupled to a termination element; and passing the optical fiber sensor through a curved lumen within a cladding light remover to remove the light energy from the cladding of the optical fiber sensor, wherein the optical fiber sensor forms a first localized bend as it enters the curved lumen and forms a second localized bend as it exits the curved lumen.

23. The method of claim 22 further comprising coupling a proximal end of the optical fiber sensor at a connector and wherein the light energy is launched into the cladding at the connector.

24. The method of claim 22 wherein the termination element is within a medical instrument.

25. The method of claim 24 further comprising detecting a shape of the medical instrument using the optical fiber sensor.

26. The method of claim 24 further comprising detecting a strain or a temperature measurement using the optical fiber sensor.

27. The method of claim 22, or of any of claims 23 to 26, further comprising passing the optical fiber sensor though a first generally straight lumen immediately distal of the first localized bend and passing the optical fiber sensor through a second generally straight lumen immediately proximal of the second localized bend.

28. An optical fiber coupling apparatus comprising:

a coupling section for coupling a first optical fiber member to a second optical fiber member, the second optical fiber member including a coated region and an uncoated region;

a fastening member fastened to the uncoated region; and

a tubular body adjacent to the fastening member through which a portion of the uncoated region of and the coated region of the second optical fiber member extends, wherein an adhesive material fills the tubular body around the uncoated region, the adhesive material having a higher index of refraction than a fiber coating of the coated region of the second optical fiber member.

29. The optical fiber coupling apparatus of claim 28 further comprising a connector adapted to connect the optical fiber coupling apparatus to a medical instrument.

30. The optical fiber coupling apparatus of claim 29 wherein light energy is launched into a cladding of the second optical fiber member at the coupling section and is removed from the cladding of the second optical fiber member in the uncoated region surrounded by the adhesive material.

31. The optical fiber coupling apparatus of claim 28, or of claim 29 or 30, wherein the second optical fiber member is a shape sensor.

32. The optical fiber coupling apparatus of claim 28, or of claim 29 or 30, wherein the second optical fiber member is a temperature or strain sensor.