Patent Publication Number: US-2023148897-A1

Title: Steerable flexible needle with embedded shape sensing

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/599,015 filed Feb. 15, 2012 and U.S. Provisional Application No. 61/594,959 filed Feb. 3, 2012, which are incorporated by reference herein in their entirety. 
    
    
     BACKGROUND 
     Aspects of this disclosure are related to shape sensing in a minimally invasive surgical instrument, and more particularly to the incorporation of shape sensing capabilities into a flexible needle. 
     Minimally invasive surgical procedures typically rely on some sort of instrument position monitoring to ensure proper access to, and behavior at, the target surgical location. Conventional minimally invasive surgical instruments are generally either formed from generally rigid, elongate elements (e.g., laparoscopic or robotic systems) or highly flexible systems designed to follow a predetermined anatomic path (e.g., angioplasty balloon catheters). In either case, position monitoring typically involves localized tracking. 
     For example, the overall shape of an instrument formed from rigid bodies can be determined via monitoring of just the extrema (e.g., the joints and ends) of those elements. For example, the shape of a rigid three-linkage robotic arm having two rotational joints (single degree of freedom for each joint) can be modeled using measurements from just the two rotational joints. 
     For catheter-based procedures, it is generally the catheter tip position that is critical, with the length of the catheter simply residing within a vessel in the body. For example, in an angioplasty procedure, the guidewire and/or balloon catheter tip must be positioned at the arterial blockage, and so the guidewire/balloon catheter tip is monitored (typically via direct visualization). The remaining guidewire/catheter length is not actively monitored, except in an incidental sense to the extent the remaining length is shown during fluoroscopic visualization of the tip advancement. 
     However, increasingly more complex minimally invasive surgical systems can require enhanced instrument position monitoring for safe and effective use. For example, the development of flexible, steerable needles provides an opportunity for procedures such as biopsy and/or therapeutic treatment, such as ablation treatments or radioactive seeds placement, at internal locations that would be problematic to access via a straight path—e.g., if it would be undesirable to puncture any intervening anatomy. Flexible, steerable needles can be delivered to the target site by direct penetration into the tissue, such as for example in the case of transcutaneous biopsy needles for the liver or other internal organs. Flexible, steerable needles can be delivered to the target site making use of the channel of an endoscope or a catheter, such as for example in the case of transluminal lung or stomach biopsy. 
     As used herein, steerable needles refer to a broad category of flexible needles with control inputs at the base (i.e., outside the body of the patient) and distal regions meant for piercing or puncturing target tissue. Depending on the shape and mechanical properties of the needle, interaction forces between the needle and the patient anatomy (i.e., the target tissue and/or any intervening anatomy between the surgical entry point and the target tissue) can cause the needle to deflect, such that steering can be provided by simply applying rotation to the base of the needle. Alternatively or additionally, a steerable needle can include active actuators to provide shaping and directionality. Steerable needles generally have a high axial stiffness and a tip shape that allows them to puncture or penetrate tissue with minimal axial compression, as compared to catheter-type devices that have a low axial stiffness and are not suited to penetrate or puncture. 
     Note that the term “flexible” in association with a steerable needle should be broadly construed. In essence, it means the needle can be bent without harm. For example, a flexible steerable needle may include a series of closely spaced components that are similar to “vertebrae” in a snake-like arrangement. In such an arrangement, each component is a short link in a kinematic chain, and movable mechanical constraints (e.g., pin hinge, cup and ball, and the like) between each link may allow one (e.g., pitch) or two (e.g., pitch and yaw) degrees of freedom (DOF) of relative movement between the links. As another example, a flexible steerable needle may be continuous, such as a closed bendable tube (e.g., nitinol, polymer, and the like) or other bendable piece (e.g., kerf-cut tube, helical coil, and the like). 
     At the same time, the use of a flexible needle in a minimally invasive fashion can be significantly more complicated than conventional robotic or laparoscopic procedures. Not only is the variability in the actual shape of a steerable needle much greater than that of a linkage of rigid elements, but the needle flexibility can greatly increase susceptibility to deviation from a target trajectory due to variations in tissue characteristics (e.g., scar tissue, or otherwise denser than expected tissue, may result in greater than expected curvature of the flexible needle). 
     Accordingly, it is desirable to provide a steerable needle system that can be effectively used in minimally invasive surgical procedures. 
     SUMMARY 
     By incorporating a shape sensor into a flexible needle, the shape and/or surgical trajectory of such a needle can be effectively monitored and controlled to enable efficient and effective procedure performance. 
     As used herein, steerable needles refer to a broad category of flexible needles with control inputs at the base (i.e., outside the body of the patient) and distal regions meant for piercing or puncturing target tissue. The control inputs allow the needle to be guided along a desired surgical trajectory to a target location within the patient. In some embodiments, the needle may include a tip geometry that imparts a directional motion as the tip passes through tissue, such that the control inputs can simply be a handle(s) or other control to axially rotate the needle. In other embodiments, the needle may include wires, cables, or any other actuation mechanism to allow for more direct control over the shape and direction of travel of the needle. In such embodiments, the control inputs would be configured to provide the appropriate manipulation or actuation energy to the actuation mechanism(s) of the needle. 
     Depending on the shape and mechanical properties of the needle, interaction forces between the needle and the patient anatomy (i.e., the target tissue and/or any intervening anatomy between the surgical entry point and the target tissue) can cause the needle to deflect and move along curved trajectories. The shape and/or direction of these trajectories can be influenced through the control inputs. Steerable needles can be used in minimally invasive clinical procedures for diagnosis and treatment of difficult to reach targets, e.g., in prostate biopsy and brachytherapy. 
     In some embodiments, a steerable needle can be a highly flexible (e.g., nitinol) needle with an asymmetric beveled tip and control inputs for insertion and shaft rotation. As it is inserted into tissue, the needle moves approximately along a circular path in the direction of the bevel. Rotating the needle shaft causes the bevel direction to change, thereby causing the needle shape and/or trajectory direction to change as the needle is moved through the patient anatomy. In other embodiments, a steerable needle can be a highly flexible (e.g., nitinol) needle with a pre-bent tip section and control inputs for insertion and shaft rotation. In this case, the needle moves along an approximately circular trajectory in the direction of the pre-bent tip (the lowest-energy state of the needle), wherein shape and/or trajectory direction changes can be effected via needle shaft rotation. In yet other embodiments, a steerable needle can be a highly flexible needle with an asymmetric tip (either beveled or pre-bent) that is controlled from the base by shaft insertion, shaft rotation, and bending at the entry point to control shape and/or trajectory direction. In various other embodiments, a steerable needle can be a concentric-tube device in which several flexible pre-bent tubes are assembled concentrically. The external control inputs determine the relative orientation and sliding amount of the different flexible tubes. The tip position and orientation can be changed by sliding and rotating the pre-bent tubes using the control inputs, thereby enabling control over shape and/or trajectory direction in use. 
     In some embodiments, a steerable needle can be fitted with a shape sensor(s) that measures the continuous shape of the needle. The sensor can be placed in a separate lumen in the wall of the needle, tacked in place (optionally in grooves) on the inside or outside of the needle wall, be removably inserted into the lumen of the needle (e.g., as part of a stylet), or otherwise coupled to the flexible needle along at least a portion of its length. The use of the interior lumen of the needle beneficially avoids the requirement of extra wall thickness or size. 
     The information obtained from the shape sensor can be used in various ways. For example, from the measured shape the total insertion depth into the tissue as well as the tip position and orientation can be determined. These variables can be used in a servo-loop to precisely control the needle insertion and orientation—instead of measuring just the proximal insertion and rotation amounts on the control inputs and assuming perfect transfer to the tip, the shape sensor can be used to directly measure the distal insertion and rotation, independent from the torsional and axial flexibility of the needle and the effects of friction and normal forces between the needle and the tissue. 
     In another embodiment, the measured tip position and orientation (as computed from the shape information) can be used in planning algorithms that compute feasible paths from the current needle position to the target location. The shape sensor can be used to measure the needle pose in place of or in addition to (potentially imprecise and noise) imaging techniques. 
     In another embodiment, the shape sensor can be used to identify unknown model parameters in the biomechanical model of the tissue, as used in the planning software. For example, the bend radius of the trajectory of a steerable needle depends on the properties of the needle as well as the local properties of the surrounding tissue. These properties are hard to predict, but the shape sensor can be used to measure current actual bend radius of the trajectory to update model parameters. 
     In another embodiment, where one of the control inputs is bending the needle base near the entry point of the tissue, the shape sensor information, in conjunction with the needle material properties, can be used to estimate and locally update the kinematic mapping between needle base motions and needle tip motions. This mapping can be used to control the base of the needle for desired tip motion. 
     In another embodiment, the shape measurements can be used to detect undesired motions of the needle shaft, such as buckling and large deviations from the expected or allowed path. In conjunction with a mechanical model of the needle, the measured needle shape can also be used to estimate forces applied along the needle shaft. This could be used to identify points where high force is being applied to tissue. 
     In another embodiment, the shape sensor can be used in conjunction with imaging techniques to improve registration of the needle relative to preoperative data. The base, or some other portion of the shape sensor, can be registered to the image coordinate space by attaching an image-able fiducial to a portion of the fiber, or docking a fixed reference point on the fiber to a visible fiducial feature on the patient, or similar. The intraoperative imaging would provide a means to adapt needle trajectory in response to tissue motion or deformation. The measured shape of the needle could be used to assist in detecting and localizing the needle in intraoperative images, such that its position/orientation with respect to anatomical targets could be measured. 
     In another embodiment, the shape sensor can be used, in conjunction with a driving mechanism, to provide input in order to manually or automatically control an actuator that steers the flexible needle during a medical procedure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a block diagram of a minimally invasive surgical system that includes a steerable needle incorporating shape sensing. 
         FIG.  1 B  is a block diagram of a shape sensor processing system that can be part of the minimally invasive surgical system of  FIG.  1 A . 
         FIGS.  2 A- 2 B  are diagrams of steerable needle types usable with the minimally invasive surgical system of  FIG.  1 A . 
         FIGS.  3 A- 3 F  are various steerable needle/shape sensor combinations usable with the minimally invasive surgical system of  FIG.  1 A . 
         FIGS.  4 - 7    are operational flow diagrams for a minimally invasive surgical system incorporating a steerable needle with shape sensor. 
     
    
    
     DETAILED DESCRIPTION 
     By incorporating a shape sensor into a flexible needle, the shape and/or surgical trajectory of such a needle can be effectively monitored and controlled to enable efficient and effective procedure performance. 
     The embodiments below will describe 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, 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    shows an exemplary minimally invasive surgical system  100  that includes a steerable needle  110  that can be manipulated during a surgical procedure by an actuator  130 . As used herein, steerable needles refer to a broad category of flexible needles with control inputs (i.e., actuator  130 ) at the base (i.e., outside the body of the patient) and distal regions meant for piercing or puncturing target tissue. Such needles can be used for diagnosis and/or treatment of difficult to access targets in a patient, such as in prostate biopsy, lung biopsy, liver biopsy, and brachytherapy, among others. Note that in various embodiments, system  100  can include any number of steerable needles, as indicated by optional steerable needle  110 - 2  (along with any actuation, control, sensing, and/or processing elements required for the additional needles  110 ). 
     Actuator  130  can manipulate needle  110 , for example, by steering needle  110  along a desired surgical trajectory to a target location within the patient, changing the shape of needle  110 , and/or changing the orientation of needle  110 . As described in greater detail below, in some embodiments, the needle may include a tip geometry that imparts a directional motion as the tip passes through tissue, such that the control inputs can simply be a handle(s) or other control to axially rotate the needle. In other embodiments, the needle may include wires, cables, or any other actuation mechanism to allow for more direct control over the shape and direction of travel of the needle. In such embodiments, the control inputs would be configured to provide the appropriate manipulation or actuation signals/energy to the actuation mechanism(s) of the needle. 
     System  100  further includes a continuous shape sensor  120  that is substantially aligned with at least a portion of steerable needle  110 . Regardless of the specific steering mechanism provided for needle  110 , usability of system  100  in a minimally invasive surgical procedure is enhanced by the inclusion of shape sensor  120 . As described in greater detail below, the data read by shape sensor  120  is acquired and converted into usable shape information by a processor  140 . The shape information can then be used to guide further manipulation of needle  110 . A shape sensor is an elongate sensor that provides shape measurement over the length of the sensor. In contrast to a discrete position sensor, a shape sensor enables shape measurement via a single sensor. Note that a shape sensor may include a single continuous sensing region or multiple sensing regions distributed over the length of the sensor, so long as the data from the shape sensor as a whole can be used to determine the measured shape. The integrated nature of a shape sensor can be particularly useful in delivering accurate shape measurement of needle  110 . This in turn can enable more precise control and/or enhanced error correction to ensure that needle  110  accurately traverses a desired surgical trajectory. 
     Note that although shape sensor  120  is depicted and described as a single shape sensor for explanatory purposes, in various embodiments shape sensor  120  can include multiple shape sensors, where each shape sensor measures the shape of a continuous portion of the overall length of needle  110 . Also, in various other embodiments, needle  110  can include multiple parallel shape sensors, as indicated by optional additional shape sensor(s)  120 - 2 . Such multiple shape sensors can be used, for example, to provide for greater shape modeling precision or to compensate for temperature or other sensor-affecting factors. Various other usages will be readily apparent. 
     Shape sensor  120  can be coupled to needle  110  in a variety of ways. For example,  FIG.  3 A  shows shape sensor  120  housed in a lumen  112 A in a wall  110 W of needle  110 . Wall  110 W further defines an interior needle lumen  111  for surgical use (e.g., material delivery or biopsy). In various embodiments, an optional securing feature  121 A (e.g., a slot, ridge, threads, shoulder, or any other feature) can be provided on needle  110  (e.g., at the distal end region or anywhere along lumen  112 A) to assist in securing, aligning, and/or orienting sensor  120  with needle  110 . In such embodiments, shape sensor  120  can itself include a corresponding mating feature(s). 
       FIG.  3 B  shows another embodiment of needle  110  in which shape sensor  120  is attached to the outer surface of wall  110 W. In some embodiments, wall  110 W can include an optional outer groove  112 B that can help to capture and/or align sensor  120  with needle  110 . In various other embodiments, an optional securing feature  121 B (e.g., a slot, ridge, threads, shoulder, or any other feature) can be provided on needle  110  (e.g., at the distal end region or anywhere along groove  112 B) to assist in securing, aligning, and/or orienting sensor  120  with needle  110 . In such embodiments, shape sensor  120  can itself include a corresponding mating feature(s). 
       FIG.  3 C  shows another embodiment of needle  110  in which shape sensor  120  is attached to the inner surface of wall  110 W. In some embodiments, wall  110 W can include an optional inner groove  112 C that can help to capture and/or align sensor  120  with needle  110 . In various other embodiments, an optional securing feature  121 C (e.g., a slot, ridge, threads, shoulder, or any other feature) can be provided on needle  110  (e.g., at the distal end region or anywhere along groove  112 C) to assist in securing, aligning, and/or orienting sensor  120  with needle  110 . In such embodiments, shape sensor  120  can itself include a corresponding mating feature(s). 
     Note that in various other embodiments, multiple shape sensors  120  can be incorporated into needle  110 . For example, and shown in  FIG.  1 A , an optional second shape sensor  120 - 2  can be affixed to needle  110  to provide additional shape measurement data for enhanced accuracy, error correction, temperature compensation, etc. Note that while both sensors are depicted as being positioned within inner lumen  111  of needle  110  for exemplary purposes, in various other embodiments, both shape sensors  120  can be on the outer surface of needle  110 , or within wall  110 W, or in any combination of inner surface, outer surface, and in-wall placements. Note further that any number of shape sensors  120  can be present, and in any relative arrangement along needle  110 . 
       FIG.  3 D  shows another embodiment of needle  110  in which shape sensor  120  is positioned within needle lumen  111 . This configuration allows shape measurements of needle  110  to be taken during insertion and navigation until the surgical target location is reached. Shape sensor  120  can then be removed, as shape and position information is no longer required, and the surgical procedure can be performed using the (now clear) needle lumen  111 . In various embodiments, shape sensor  120  can be replaced within needle lumen  111  prior to removal of needle  110  from the patient. In some embodiments, shape sensor  120  can be part of a flexible stylet or guidewire sized to fit within needle lumen  111 . The placement of shape sensor  120  within needle lumen  111  beneficially avoids impact to needle wall  110 W and can allow for the use of larger diameter and potentially more accurate shape sensors  120 . 
     Note further that the tip design for steerable needle  110  can take any form or shape as required for the particular procedural requirements of a surgical procedure. In some embodiments, needle  110  can include a bevel tip (e.g., Baker needle tip), as shown in  FIGS.  3 A- 3 D . In various other embodiments, alternative tip geometries can be used. For example,  FIG.  3 E  shows needle  110  with a rounded tip (e.g., Tuohy needle tip), and  FIG.  3 F  shows needle  110  with a solid tip (e.g., Sprotte needle tip). Various other tip designs will be readily apparent. 
     As further shown in  FIG.  3 F , in some embodiments needle  110  can include optional additional sensors  315  to provide further usage information. For example, sensor  315  can be a position sensor (e.g., EM sensor, accelerometer, etc.) providing localized position data that can be used with the shape data from shape sensor  120  to model the in-situ pose and/or shape of needle  110 . Although depicted in the solid distal tip  311  of needle  110  in  FIG.  3 F  for exemplary purposes, in various other embodiments, additional sensor(s)  315  can be located anywhere on needle  110 , regardless of specific needle configuration. 
     Likewise, various mechanisms can be used to steer needle  110 . For example, depending on the shape and mechanical properties of needle  110 , interaction forces between needle  110  and the patient anatomy (i.e., the target tissue and/or any intervening anatomy between the surgical entry point and the target tissue) can cause needle  110  to deflect as it is advanced through that patient anatomy. The mechanism may be actuated, manually or automatically, using information from the shape sensor as input. 
     For example, in various embodiments, needle  110  can be made from a highly flexible material (e.g., nitinol) and have an asymmetric bevel tip or pre-bent tip, such as shown in  FIG.  1 A . When inserted into tissue, the bevel tip will cause needle  110  to move in a curved trajectory in the direction of the bevel. Steerability is provided by rotating needle  110  axially to cause the bevel direction, and hence the needle trajectory, to change. In such cases, actuator  130  can be anything from a knob(s), handle(s), or other manual interface, to active drivers such as a servo motor, or combinations of manual and automated actuators. 
     In various other embodiments, needle  110  can be steered via more active mechanisms. For example,  FIG.  2 A  shows an embodiment of needle  110  formed from multiple coaxial curved needle segments  210 A,  210 B,  210 C, and  210 D. Note that while four needle segments  210  are depicted for exemplary purposes, in various other embodiments needle  110  can include any number of segments. In use, actuator  130  can control the relative rotation and extension of segments  210 A- 210 D, thereby determining the shape and orientation of needle  110 .  FIG.  2 B  shows another embodiment of needle  110  in which one or more control cables  215  are provided to which tension and/or extension forces can be applied to cause desired bending of needle  110 . Cable(s) can be controlled via mechanical tensioners, motor actuators, or any other mechanism. For example, in some embodiments, cable(s)  215  can include material that responds to thermal changes, such as nitinol wire(s) configured to contract in response to electrical current-induced heating (such as described in “A Nitinol Wire Actuated Stewart Platform”, by Dunlop et al. (Proc. 2002 Australasian Conference on Robotics and Automation, Nov. 27-29, 2002), herein incorporated by reference in its entirety). Various other steering mechanisms will be readily apparent. 
     Regardless of the specific steering mechanism used with flexible needle  110 , the usability of system  100  in a minimally invasive surgical procedure is enhanced by the inclusion of shape sensor  120  and the shape information provided therefrom. Furthermore, such benefit accrues regardless of the particular mode of control applied to needle  110 . Specifically, in various embodiments, system  100  can be a purely manual system (e.g., an endoscopic instrument), in which actuator  130  is directly controlled by an optional manual controller  150 , as shown in  FIG.  1 A . In some embodiments, optional manual controller  150  can be actuator  130  (e.g., a knob, handle, or grip for rotating needle  110 ), and in other embodiments optional manual controller can be a handle(s), trigger(s), lever(s), grip(s), and/or any other user interface for providing control inputs to actuator  130 , either via direct mechanical attachment or linkage, via electrical/electronic control, or any combination of the above. In various other embodiments, system  100  can be a robotic system in which control over needle  110  is provided via a console or other remote interface of an optional robotic platform  160 . In yet other embodiments, system  100  can incorporate elements of both direct control and robotic control (e.g., robotic system with manual override) and therefore include both optional manual controller  150  and optional robotic platform  160 . 
     In robotically-assisted or telerobotic surgery, the surgeon typically operates a control device to control the motion of surgical instruments at the surgical site from a location that may be remote from the patient (e.g., across the operating room, in a different room or a completely different building from the patient) or immediately adjacent to the patient. Thus in some embodiments, robotic platform  160  can include one or more manually-operated input devices, such as joysticks, exoskeletal gloves or the like, which are coupled (directly or indirectly) to actuator  130  with servo motors or other drive mechanisms for steering needle  110  to the surgical site. During a procedure, robotic platform  160  can, in some embodiments, provide mechanical articulation and control of a variety of surgical instruments in addition to needle  110 , such as tissue graspers, electrosurgical cautery probes, retractors, staplers, vessel sealers, endoscopes, scalpels, ultrasonic shears, suction/irrigation instruments, and the like, that each perform various functions for the surgeon, e.g., grasping a blood vessel, or dissecting, cauterizing or coagulating tissue. 
     Shape sensor  120  can be any type of shape sensor capable of measuring the curvature of flexible needle  110  during surgical use. For example, in various embodiments, shape sensor  120  can include a fiber optic shape sensor, such as described with respect to the systems and methods for monitoring the shape and relative position of a optical fiber in three dimensions described in U.S. patent application Ser. No. 11/180,389, filed on Jul. 13, 2005; U.S. provisional patent application Ser. No. 60/588,336, filed on Jul. 16, 2004, and U.S. Pat. No. 6,389,187, filed on Jun. 17, 1998, the disclosures of which are incorporated herein in their entireties. In some embodiments, an optical fiber in shape sensor  120  can comprise one or more cores (either single- and/or multi-mode) contained within a single cladding. Multi-core constructions can be configured to provide sufficient distance and cladding separating the cores such that the light in each core does not interact significantly with the light carried in other cores. In other embodiments, shape sensor  120  can include any number of optical fibers with the same or varying numbers of cores. In other embodiments, one or more of the cores in the optical fiber can be used for illumination and/or ablation. 
     In certain embodiments, shape sensor  120  can be a fiber optic bend sensor that includes a backscatter mechanism such as fiber Bragg gratings (FBGs), such as in product from Luna Innovations, Inc. (Blacksburg, Va.). In such embodiments, an array of FBGs can be provided within each core that comprises a series of modulations of the core&#39;s refractive index so as to generate a spatial periodicity in the refraction index. The spacing may be chosen so that the partial reflections from each index change add coherently for a narrow band of wavelengths, and therefore reflect only this narrow band of wavelengths while passing through a much broader band. During fabrication of the FBGs, the modulations are spaced by a known distance, thereby causing reflection of a known band of wavelengths. However, when a strain is induced on the fiber core, the spacing of the modulations will change, depending on the amount of strain in the core. 
     To measure strain, light is sent down the fiber, and the reflected wavelength is a function of the strain on the fiber and its temperature. This FBG technology is commercially available from a variety of sources, such as Smart Fibres Ltd. of Bracknell, England. When applied to a multicore fiber, bending of the optical fiber induces strain on the cores that can be measured by monitoring the wavelength shifts in each core. By having two or more cores disposed off-axis in the fiber, bending of the fiber induces different strains on each of the cores. These strains are a function of the local degree of bending of the fiber. Regions of the cores containing FBGs, if located at points where the fiber is bent, can thereby be used to determine the amount of bending at those points. These data, combined with the known spacings of the FBG regions, can be used to reconstruct the shape of the fiber. 
     Note, however, that while the use of FBGs are described above for exemplary purposes, any mechanism for creating backscatter could be used in shape sensor  120 , such as Rayleigh scattering, Raman scattering, Fluorescence scattering, and Brillouin scattering, among others. Typically, fiber optic shape sensors operate via optical time domain reflectometry (OTDR) or via optical frequency domain reflectometry (OFDR). The Kerr effect can also be used in shape sensor  120 . 
     Note further that in various other embodiments, any flexible, elongate sensor or combination of sensors can be used as shape sensor  120 . In various embodiments, shape sensor  120  can include a bend-enhanced fiber (BEF) sensor, such as ShapeTape from Measurand Inc. (Fredericton, New Brunswick, Canada), flexible piezoresistive sensor arrays or wire strain detectors (such as described in “ULTRA-SENSITIVE SHAPE SENSOR TEST STRUCTURES BASED ON PIEZO-RESISTIVE DOPED NANOCRYSTALLINE SILICON”, Alpuim et al. (NanoSpain2008, Apr. 14-18, 2008), herein incorporated by reference in its entirety, and in “Electromechanical analysis of a piezoresistive pressure microsensor for low-pressure biomedical applications”, Herrera-May et al. (REVISTA MEXICANA DE FI&#39;SICA 55 (1) 14-24 February 2009), herein incorporated by reference in its entirety), a nitinol wire for resistive strain measurement, an unaltered polarization-maintaining (PM) optical fiber, and/or any other shape sensing technologies. 
     Processor  140  detects the shape and position of steerable needle  110  and processes that information to assist in surgical procedures. Processor  140  is configured to interface with the specific type of sensor(s) in shape sensor  120  (e.g., providing interferometry and/or reflectometry capabilities for use with optical fiber sensors, or providing a voltage and/or current meter for use with resistance-based sensors).  FIG.  1 B  shows an exemplary embodiment of processor  140  for processing the measurement data from a fiber optic shape sensor  120 . In view of this disclosure, instructions and modules used in any one of, or any combination of operations described with respect to processor  140  can be implemented in a wide variety of software and/or hardware architectures, such as software code modules running on dedicated processors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other logic implementation, alone or in any combination. 
     Processor  140  in  FIG.  1 B  includes an interrogator  141 , an input/output module  142 , a processor module  143 , and a shape data processing module  144 . Interrogator  141  interrogates the optical fiber of shape sensor  120  and provides shape information to input/output module  142 . Processor module  143  then processes the information from input/output module  142  using a shape data processing module  144  (e.g., stored in memory within processor  140 ). The generated shape information for needle  110  can then be used to model the in-situ pose and/or shape of needle  110 . In some embodiments, known reference frame data (e.g., the position and orientation of actuator  130 /proximal end region of needle  110 ) can be combined with the shape information for needle  110  to determine the in-situ pose and/or shape. In various other embodiments, positional measurements taken of needle  110  (e.g., via additional sensors on needle  110  or through visualization tracking) can be used with the shape data from shape sensor  120  to determine the in-situ pose and/or shape. More detailed description of an exemplary pose-determination process is provided in copending and commonly assigned U.S. patent application Ser. Nos. 12/164,829, and 12/618,082, both of which are incorporated herein by reference in their entireties. 
     Note that in various embodiments, processor  140  (or system  100 ) can include optional additional processing modules to make use of the shape data provided by shape sensor  120 . In some embodiments, an optional path planning module  145  can be included to identify an appropriate trajectory (or multiple trajectory options) for either fully- or semi-automated control or for providing guidance for manual control over system  100 . In various other embodiments, if automated or semi-automated control is provided by system  100 , an optional control planning module  146  can be included to generate the appropriate control signals for actuator  130 , for example based on the output of path planning module  145 . 
     In various other embodiments, an optional error detection module  147  can be included to compare measured shape, pose, and/or position data against expected values (e.g., desired values or values predicted from a mathematical model). For example, in some embodiments, the measured data can be compared against model data to validate and/or update the model data. In other embodiments, the measured data can be compared to target data (e.g., comparing actual trajectory of needle  110  to a desired trajectory) to avoid excessive deviation from a desired behavior. In some embodiments, such error detection can provide notification to the surgeon via visual, aural, or tactile cues or reports. In various other embodiments, deviations can be presented graphically (e.g., on a video monitor, overlaying actual trajectory onto desired trajectory). In such embodiments, an optional graphics module  148  can also be included in processor  140  to provide the necessary graphical representation of the measurements of shape sensor  120 . In other embodiments, graphics module  148  can be included simply to provide a visual representation of the shape data measured by shape sensor  120 . 
     As noted above, a surgical procedure can be beneficially enhanced by measuring the shape of a steerable needle and then controlling the needle (e.g., adjusting the shape of the needle, changing the orientation of the needle (e.g., axial rotation), advancing/retracting the needle, etc.) based on that measured shape. Note that while the descriptions herein refer to the use of a steerable flexible needle with shape sensor in surgical applications for exemplary purposes, in various embodiments, the same methods and procedures can be use in animals (e.g., veterinary use), cadavers, artificial anatomic replicas, and/or computer simulations of surgical procedures. 
       FIG.  4    shows an exemplary flow diagram for the use of shape sensing in such a procedure. In a Shape Measurement step  410 , the shape of a steerable flexible needle (such as needle  110  described above) is measured. The measurement can be performed using any type of shape sensor capable of providing real time shape information for the flexible needle (such as shape sensor  120  described above). Then, in a Shape Modeling step  420 , the measured data is used to model the actual shape of the flexible needle. 
     Note that depending on the requirements of the surgical system and procedure itself, the specific level of shape modeling in step  420  can vary. For example, in some embodiments, step  420  may simply involve determining the standalone shape of the needle—for example to determine if the needle has reached a desired deployed state. In some other embodiments, step  420  can involve determining the shape of the needle along with its orientation (e.g., using additional reference frame information from the proximal (attachment) region of the needle to the actuator (such as actuator  130 , above), or from additional sensor data (such as sensor  315  above)). For example,  FIG.  5    shows an embodiment of the flow diagram of  FIG.  4    that includes an optional Pose Modeling step  522 . 
     The continuous shape modeling of step  420  can provide a significant procedural advantage over approaches limited to the use of catheters having a single position sensor (or several discrete sensors at particular locations), which can only estimate shape and orientation by assuming perfect mechanical transfer between the inputs and the measured locations. The actual shape measurements of step  420  can allow total insertion depth of the needle to be accurately determined, along with distal tip position and orientation. This determination can be made regardless of the torsional and axial flexibility of the needle and any effects of friction and normal forces between the needle and the patient tissue, which would otherwise need to be precisely modeled to produce similar results using a discrete sensor system—an unwieldy and likely unmanageable approach for most surgical applications. 
     In some embodiments, step  420  can include the identification or refinement of model parameters in a biomechanical model of the tissue and/or kinematic model of the needle system, as indicated by optional Adjust Model Parameters step  523  in  FIG.  5   . For example, the actual behavior of the needle (e.g., bend radius) as it traverses a patient tissue or anatomical structure can be used to derive tissue density, changes in material (e.g., diseased or degenerative tissue regions exhibiting unexpected material properties, such as tumors, cysts, osteoporosis, etc.), or other difficult to predict and model anatomical aspects. In other embodiments, the actual needle trajectory can be used to estimate and update kinematic mapping between the actuator inputs and the actual needle movement (e.g., the tip and/or the shaft of the needle), thereby improving the responsiveness and accuracy of the needle control. In other embodiments, the actual needle trajectory can be used to calculate loading of the needle, at discrete locations or along its entire length, since the curvature(s) of the needle will be dependent at least in part on the local forces applied to the needle. 
     In some other embodiments, the pose information determinable in step  420  can be beneficially used to indicate or visualize the actual placement of the needle within a patient or the actual surgical trajectory being followed by the needle, as in an optional Path Modeling step  430 . For example, step  430  can include using the needle shape information determined in step  420  to determine one or more target trajectories for the continuing advance of the needle (e.g., based on needle properties, anatomical model properties, needle behavior up to current location, supplemental anatomical information (e.g., visualization, enhanced material properties based on actuation force required by needle, etc.), and/or any other path-affecting information), as indicated by an optional Path Planning step  531  in  FIG.  5   . 
     In various other embodiments, steps  420  and/or  430  can include comparing the actual needle shape and/or trajectory with an expected or desired shape/trajectory. Any deviation from the desired shape/trajectory can be identified and/or used to provide feedback to the surgeon as to potential corrective actions, depending on the magnitude of the deviation. For example,  FIG.  6    shows a flow diagram in which step  420  includes an optional Detect Shape Deviation step  621  in which the measured shape is compared to an expected shape. The deviation can then be assessed in an Exceeds Threshold? step  622 , where if the deviation is greater than some preset limit, a notification is provided in an Error State step  623 . This notification can take any form, including a visual warning, an audible warning, an error message, a tactile indication, warning icon, and/or system freeze/recovery action, among others. In some embodiments, step  623  can result in procedure abort or restart, due to excessive needle deformation. In various other embodiments, if the shape deviation is less than a maximum deviation, a determination is made in an optional Correction Required? step  624 , wherein if the deviation is small enough, no adjustment to the needle shape is made, and the process simply continues. However, if the deviation is determined to require correction, such correction can be calculated in a Determine Adjustment step  625 . This adjustment can be provided to the surgeon as instructions, graphical representation, or any other means for conveying the information to the surgeon, or can be provided automatically to the system to cause automatic correction of the needle shape (e.g., providing appropriate control signals to the needle actuator). 
     In another example,  FIG.  7    shows a flow diagram in which step  430  includes an optional Detect Path Deviation step  731  in which the measured needle trajectory is compared to an expected trajectory (e.g., a pre-operatively determined trajectory or an intraoperatively modeled trajectory). The deviation can then be assessed in an Exceeds Threshold? step  732 , where if the deviation is greater than some preset limit, a notification is provided in an Error State step  733 . This notification can take any form, including a visual warning, an audible warning, an error message, a tactile indication, warning icon, and/or system freeze/recovery action, among others. In some embodiments, step  733  can result in procedure abort or restart, due to excessive trajectory deviation. In various other embodiments, if the trajectory deviation is less than a maximum deviation, a determination is made in an optional Correction Required? step  624 , wherein if the deviation is small enough, no adjustment to the needle shape and/or actuation control inputs is made, and the process simply continues. However, if the deviation is determined to require correction, such correction can be calculated in a Determine Adjustment step  625 . This adjustment can be provided to the surgeon as instructions, graphical representation, or any other means for conveying the information to the surgeon, or can be provided automatically to the system to cause automatic correction of the needle trajectory (e.g., providing appropriate control signals to the needle actuator). 
     In some other embodiments, the shape and/or position of the needle can also be adjusted in an optional Needle Control step  440 . For example, the shape and/or path information derived from step  420  and optional step  430 , respectively, can be used to determine the appropriate advancement/retraction and/or shape adjustment for the needle. For instance, if steps  420  and/or  420  indicate that the needle shape is sub-optimal for completion of the desired procedure, the needle can be adjusted towards a more optimized shape in step  440  (e.g., by actively changing the needle shape, by changing the needle orientation to cause the desired shape change during advancement/retraction, and/or by performing any other shape-affecting action). Similarly, if steps  420  and/or  430  indicate that the trajectory of the needle is sub-optimal for completion of the desire procedure, the needle can be adjusted towards a more optimized path in step  440  (e.g., by changing needle shape, by changing the needle orientation (e.g., rotation), retracting the needle, and/or any other trajectory-impacting action). In various embodiments, this shape and/or trajectory adjustment can be performed manually, in response to surgeon cues (e.g., visual indication of deviation, sounds, or tactile indications when a deviation from the desired path is detected), automatically, or any combination of the above. In some embodiments, the specific controls applied to the needle actuator can be determined based on the shape sensor data, as indicated by an optional Control Planning step  532  in  FIG.  5   . 
     All examples and illustrative references are non-limiting and should not be used to limit the claims to specific implementations and embodiments described herein and their equivalents. The headings are solely for formatting and should not be used to limit the subject matter in any way, because text under one heading may cross reference or apply to text under one or more headings. Finally, in view of this disclosure, particular features described in relation to one aspect or embodiment may be applied to other disclosed aspects or embodiments of the disclosure, even though not specifically shown in the drawings or described in the text.