U.S. patent application number 15/183936 was filed with the patent office on 2016-10-06 for systems and methods for reducing measurement error in optical fiber shape sensors.
The applicant listed for this patent is Intuitive Surgical Operations, Inc.. Invention is credited to Stephen J. Blumenkranz, Caitlin Q. Donhowe, Vincent Duindam.
Application Number | 20160287344 15/183936 |
Document ID | / |
Family ID | 49775045 |
Filed Date | 2016-10-06 |
United States Patent
Application |
20160287344 |
Kind Code |
A1 |
Donhowe; Caitlin Q. ; et
al. |
October 6, 2016 |
SYSTEMS AND METHODS FOR REDUCING MEASUREMENT ERROR IN OPTICAL FIBER
SHAPE SENSORS
Abstract
A shape sensing apparatus comprises an instrument including an
elongated shaft with a neutral axis. The shape sensor also includes
a first shape sensor with an elongated optical fiber extending
within the elongated shaft at a first radial distance from the
neutral axis. The apparatus also includes a shape sensor
compensation device extending within the elongated shaft and
including a temperature sensor. The apparatus also comprises a
tracking system for receiving shape data from the first shape
sensor and compensating data from the shape sensor compensation
device for use in calculating a bend measurement for the
instrument.
Inventors: |
Donhowe; Caitlin Q.;
(Sunnyvale, CA) ; Blumenkranz; Stephen J.;
(Redwood City, CA) ; Duindam; Vincent; (Mountain
View, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Intuitive Surgical Operations, Inc. |
Sunnyvale |
CA |
US |
|
|
Family ID: |
49775045 |
Appl. No.: |
15/183936 |
Filed: |
June 16, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13925965 |
Jun 25, 2013 |
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15183936 |
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61663951 |
Jun 25, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/00 20130101; A61B
34/30 20160201; A61B 34/37 20160201; A61B 2034/2061 20160201; A61B
1/00165 20130101; A61B 2018/00791 20130101; A61B 1/00167 20130101;
A61B 90/06 20160201; A61B 2090/3614 20160201; A61B 2034/301
20160201; A61B 34/20 20160201 |
International
Class: |
A61B 34/20 20060101
A61B034/20; A61B 34/37 20060101 A61B034/37 |
Claims
1-26. (canceled)
27. A shape sensing apparatus comprising: an instrument including
an elongated shaft with a neutral axis; a first shape sensor
including an elongated optical fiber extending within the elongated
shaft at a first radial distance from the neutral axis; a shape
sensor compensation device extending within the elongated shaft,
the shape sensor compensation device including a temperature
sensor; and a tracking system adapted to receive shape data from
the first shape sensor and compensating data from the shape sensor
compensation device for calculating a bend measurement for the
instrument.
28. The apparatus of claim 27, wherein the shape sensor
compensation device is located at a second radial distance from the
neutral axis.
29. The apparatus of claim 27, wherein the shape sensor
compensation device is located between the neutral axis and the
first radial distance.
30. The apparatus of claim 27, wherein the temperature sensor and
the first shape sensor are enclosed in insulation.
31. The apparatus of claim 27, wherein the shape sensor
compensation device includes a plurality of shape sensors that
together with the first shape sensor, are arranged at angular
intervals about the neutral axis at the first radial distance.
32. The apparatus of claim 27, wherein the first shape sensor
includes a plurality of optical cores, each of which includes a
fiber Bragg grating.
33. A method of operating a shape sensing apparatus comprising:
providing an instrument including an elongated shaft defining a
neutral axis; receiving shape data from a first shape sensor, the
first shape sensor including an elongated optical fiber extending
within the elongated shaft at a first radial distance from the
neutral axis; receiving compensation data from a shape sensor
compensation device extending within the elongated shaft, wherein
the shape sensor compensation device includes a temperature sensor;
and generating an instrument bend measurement based upon the
received shape data and the compensation data.
34. The method of claim 33, wherein the temperature sensor includes
a fiber optic temperature sensor.
35. The method of claim 33, wherein receiving compensation data
includes receiving temperature data from the temperature
sensor.
36. The method of claim 35, wherein generating the instrument bend
measurement comprises adjusting the shape data based on the
temperature data and a set of predetermined temperature
characterization data for the first shape sensor.
37. The method of claim 33, wherein the shape sensor compensation
device is located at a second radial distance from the neutral
axis.
38. The method of claim 33, wherein the shape sensor compensation
device is located between the neutral axis and the first radial
distance.
39. The method of claim 33, wherein the step of receiving
compensation data includes receiving axial load data from a second
shape sensor which includes a second elongated optical fiber
extending within the elongated shaft at a second radial distance
from the neutral axis and wherein a displacement angle between the
first and second shape sensor about the neutral axis is
approximately 180.degree. and the first and second radial distances
are approximately equal.
40. The method of claim 33, wherein the shape sensor compensation
device includes a plurality of shape sensors that together with the
first shape sensor, form a ring about the neutral axis at the first
radial distance and wherein receiving compensation data further
includes receiving the compensation data from one of the plurality
of shape sensors located on a common bending plane with the first
shape sensor.
41. A medical instrument system comprising: an instrument including
an elongated shaft with a neutral axis; a first shape sensor
including an elongated optical fiber extending within the elongated
shaft at a first radial distance from the neutral axis; and a shape
sensor compensation device extending within the elongated shaft,
wherein the shape sensor compensation device includes a temperature
sensor; a tracking system adapted to receive shape data from the
first shape sensor and compensating data from the shape sensor
compensation device for calculating a bend measurement for the
instrument; and a display system adapted to display a virtual image
of the instrument using the bend measurement.
42. The medical instrument system of claim 41, wherein the
instrument includes an end effector for manipulating tissue in
response to a teleoperation command.
43. The medical instrument system of claim 41, wherein the
temperature sensor includes an optical fiber.
44. The medical instrument system of claim 41, wherein the shape
sensor compensation device is located at a second radial distance
from the neutral axis.
45. The medical instrument system of claim 41, wherein the shape
sensor compensation device is located between the neutral axis and
the first radial distance.
46. The medical instrument system of claim 41, wherein the shape
sensor compensation device includes a plurality of shape sensors
that together with the first shape sensor, are arranged at angular
intervals about the neutral axis at the first radial distance.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application 61/663,951 filed Jun. 25, 2012, which is incorporated
by reference herein in its entirety.
FIELD
[0002] The present disclosure is directed to systems and methods
for reducing measurement error in a shape sensing optical fiber,
and more particularly to systems and methods for reducing
measurement error in shape sensing optical fibers used in surgical
instruments.
BACKGROUND
[0003] Minimally invasive medical techniques are intended to reduce
the amount of tissue that is damaged during diagnostic or surgical
procedures, thereby reducing patient recovery time, discomfort, and
deleterious side effects. Such minimally invasive techniques may be
performed through natural orifices in a patient anatomy or through
one or more surgical incisions. Through these natural orifices or
incisions clinicians may insert surgical instruments to reach a
target tissue location. To reach the target tissue location, the
minimally invasive surgical instruments may navigate natural or
surgically created passageways in anatomical systems such as the
lungs, the colon, the intestines, the kidneys, the heart, the
circulatory system, or the like. Navigational assist systems help
the clinician route the surgical instruments and avoid damage to
the anatomy. These systems can incorporate the use of shape sensors
to more accurately describe the shape, position, orientation, and
pose of the surgical instrument in real space or with respect to
pre-procedural or concurrent images. The accuracy and precision of
these shape sensors may be compromised by many factors including
temperature variations, the location of the shape sensor within the
instrument, and axial loading on the sensor. Improved systems and
methods are needed for increasing the accuracy and precision of
navigational assist systems, including minimizing the effects of
factors that compromise shape sensor accuracy.
SUMMARY
[0004] The embodiments of the invention are summarized by the
claims that follow below.
[0005] In one embodiment, a shape sensing apparatus comprises an
instrument including an elongated shaft with a neutral axis. The
shape sensing apparatus also includes a first shape sensor with an
elongated optical fiber generally parallel to and at a first radial
distance from the neutral axis of the elongated shaft. The
apparatus also includes a shape sensor compensation device
extending within the elongated shaft parallel to the neutral axis.
The apparatus also comprises a tracking system for receiving shape
data from the first shape sensor and compensating data from the
shape sensor compensation device for use in calculating a bend
measurement for the instrument.
[0006] In another embodiment, a shape sensing method comprises
providing an instrument including an elongated shaft defining a
neutral axis. The method also comprises receiving shape data from a
first shape sensor. The first shape sensor includes an elongated
optical fiber extending within the elongated shaft parallel to and
at a first radial distance from the neutral axis. The method also
comprises receiving compensation data from a shape sensor
compensation device aligned with the elongated shaft parallel to
the neutral axis. The method also comprises generating an
instrument bend measurement based upon the received shape data and
the compensation data.
[0007] In another embodiment, a medical instrument system comprises
a surgical instrument with an elongated shaft having a neutral
axis. The system also includes a first shape sensor including an
elongated optical fiber extending within the elongated shaft
parallel to and at a first radial distance from the neutral axis.
The system further includes a shape sensor compensation device
extending within the elongated shaft parallel to the neutral axis.
The system further includes a tracking system adapted to receive
shape data from the first shape sensor and compensating data from
the shape sensor compensation device for calculating a bend
measurement for the instrument. The system further includes a
display system for displaying a virtual image of the surgical
instrument using the bend measurement.
BRIEF DESCRIPTIONS OF THE DRAWINGS
[0008] Aspects of the present disclosure are best understood from
the following detailed description when read with the accompanying
figures. It is emphasized that, in accordance with the standard
practice in the industry, various features are not drawn to scale.
In fact, the dimensions of the various features may be arbitrarily
increased or reduced for clarity of discussion. In addition, the
present disclosure may repeat reference numerals and/or letters in
the various examples. This repetition is for the purpose of
simplicity and clarity and does not in itself dictate a
relationship between the various embodiments and/or configurations
discussed.
[0009] FIG. 1 is a robotic surgical system, in accordance with
embodiments of the present disclosure.
[0010] FIG. 2 illustrates a surgical instrument system utilizing
aspects of the present disclosure
[0011] FIGS. 3 and 4 are cross-sectional views of a surgical
instrument including an optical fiber shape sensor according to one
embodiment of the present disclosure.
[0012] FIGS. 5 and 6 are cross-sectional views of a surgical
instrument including an optical fiber shape sensor and a shape
sensor compensation device according to another embodiment of the
present disclosure.
[0013] FIG. 7 is a cross-sectional view of a surgical instrument
including an optical fiber shape sensor and a shape sensor
compensation device according other embodiments of the present
disclosure.
[0014] FIGS. 8 and 9 are cross-sectional views of a surgical
instrument including an optical fiber shape sensor and a shape
sensor compensation device according to another embodiment of the
present disclosure.
[0015] FIG. 10 is a cross-sectional view of a surgical instrument
including an optical fiber shape sensor and a shape sensor
compensation device according to another embodiment of the present
disclosure.
[0016] FIGS. 11 and 12 illustrate the surgical instrument of FIG.
10 bent in different planes.
[0017] FIG. 13 is a flowchart describing a method according to an
embodiment of the disclosure.
DETAILED DESCRIPTION
[0018] In the following detailed description of the embodiments of
the invention, numerous specific details are set forth in order to
provide a thorough understanding of the disclosed embodiments.
However, it will be obvious to one skilled in the art that the
embodiments of this disclosure may be practiced without these
specific details. In other instances well known methods,
procedures, components, and circuits have not been described in
detail so as not to unnecessarily obscure aspects of the
embodiments of the invention.
[0019] 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.
[0020] Referring to FIG. 1 of the drawings, a robotic surgical
system is generally indicated by the reference numeral 100. As
shown in FIG. 1, the robotic system 100 generally includes a
surgical manipulator assembly 102 for operating a surgical
instrument 104 in performing various procedures on the patient P.
The assembly 102 is mounted to or near an operating table O. A
master assembly 106 allows the surgeon S to view the surgical site
and to control the manipulator assembly 102.
[0021] In alternative embodiments, the robotic system may include
more than one manipulator assembly. The exact number of manipulator
assemblies will depend on the surgical procedure and the space
constraints within the operating room among other factors.
[0022] The master assembly 106 may be located at a surgeon's
console C which is usually located in the same room as operating
table O. However, it should be understood that the surgeon S can be
located in a different room or a completely different building from
the patient P. Master assembly 106 generally includes an optional
support 108 and one or more control device(s) 112 for controlling
the manipulator assemblies 102. The control device(s) 112 may
include any number of a variety of input devices, such as
joysticks, trackballs, gloves, trigger-guns, hand-operated
controllers, voice recognition devices or the like. In some
embodiments, the control device(s) 112 will be provided with the
same degrees of freedom as the associated surgical instruments 104
to provide the surgeon with telepresence, or the perception that
the control device(s) 112 are integral with the instruments 104 so
that the surgeon has a strong sense of directly controlling
instruments 104. In some embodiments, the control devices 112 are
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, or the like).
[0023] A visualization system 110 may include a viewing scope
assembly (described in greater detail below) such that a concurrent
or real-time image of the surgical site is provided to surgeon
console C. The concurrent image may be, for example, a two or three
dimensional image captured by an endoscope positioned within the
surgical site. In this embodiment, the visualization system 100
includes endoscopic components that may be integrally or removably
coupled to the surgical instrument 104. However in alternative
embodiments, a separate endoscope, attached to a separate
manipulator assembly may be used with the surgical instrument to
image the surgical site. The visualization system 110 may be
implemented as hardware, firmware, software or a combination
thereof which interact with or are otherwise executed by one or
more computer processors, which may include the processors of a
control system 116 (described below).
[0024] A display system 111 may display an image of the surgical
site and surgical instruments captured by the visualization system
110. The display 111 and the master control devices 112 may be
oriented such that the relative positions of the imaging device in
the scope assembly and the surgical instruments are similar to the
relative positions of the surgeon's eyes and hands so the operator
can manipulate the surgical 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 an operator that is
physically manipulating the surgical instruments 104.
[0025] Alternatively or additionally, monitor 111 may present
images of the surgical site recorded and/or modeled preoperatively
using imaging technology such as, computerized tomography (CT),
magnetic resonance imaging (MRI), fluoroscopy, thermography,
ultrasound, optical coherence tomography (OCT), thermal imaging,
impedence imaging, laser imaging, or nanotube X-ray imaging. In
some embodiments, the monitor 111 may display a virtual
navigational image in which the actual location of the surgical
instrument is dynamically referenced with preoperative images to
present the surgeon S with a virtual image of the surgical site at
the location of the tip of the surgical instrument. An image of the
tip of the surgical instrument or other graphical or alphanumeric
indicators may be superimposed on the virtual image to assist the
surgeon controlling the surgical instrument.
[0026] As shown in FIG. 1, a control system 116 includes at least
one processor and typically a plurality of processors for effecting
control between the surgical manipulator assembly 102, the master
assembly 106, and the image and display system 110. The control
system 116 also includes software programming instructions to
implement some or all of the methods described herein. While
control system 116 is shown as a single block in the simplified
schematic of FIG. 1, the system may comprise a number of data
processing circuits (e.g., on the surgical manipulator assembly 102
and/or on the master assembly 106), with at least a portion of the
processing optionally being performed adjacent an input device, a
portion being performed adjacent a manipulator, and the like. Any
of a wide variety of centralized or distributed data processing
architectures may be employed. Similarly, the programming code may
be implemented as a number of separate programs or subroutines, or
may be integrated into a number of other aspects of the robotic
systems described herein. In one embodiment, control system 116 may
support wireless communication protocols such as Bluetooth, IrDA,
HomeRF, IEEE 802.11, DECT, and Wireless Telemetry.
[0027] In some embodiments, control system 116 may include servo
controllers to provide force and torque feedback from the surgical
instruments 104 to the hand-operated control device 112. Any
suitable conventional or specialized servo controller may be used.
A servo controller may be separate from, or integral with
manipulator assemblies 102. In some embodiments, the servo
controller and manipulator assembly are provided as part of a
robotic arm cart positioned adjacent to the patient's body. The
servo controller transmits signals instructing the manipulator
assemblies to move instruments which extend into an internal
surgical site within the patient body via openings in the body.
[0028] Each of the manipulator assemblies 102 that support a
surgical instrument 104 and may comprise a series of manually
articulatable linkages, generally referred to as set-up joints, and
a robotic manipulator. The robotic manipulator assemblies 102 may
be driven by a series of actuators (e.g., motors). These motors
actively move the robotic manipulators in response to commands from
the control system 116. The motors are further coupled to the
surgical instrument so as to advance the surgical instrument into a
naturally or surgically created anatomical orifice and to move the
distal end of the surgical instrument in multiple degrees of
freedom that may include three degrees of linear motion (e.g., X,Y,
Z linear motion) and three degrees of rotational motion (e.g.,
roll, pitch, yaw). Additionally, the motors can be used to actuate
an articulatable end effector of the instrument for grasping
tissues in the jaws of a biopsy device or the like.
[0029] FIG. 2 illustrates a shape sensing apparatus 118 which
includes the surgical instrument system 104 and its interfacing
systems. The surgical instrument system 104 includes a steerable
instrument 120 coupled by an interface 122 to manipulator assembly
102 and visualization system 110. The instrument 120 has a flexible
body 124, a steerable tip 126 at its distal end 128, and the
interface 122 at its proximal end 130. The body 124 houses cables,
linkages, or other steering controls (not shown) that extend
between the interface 122 and the tip 126 to controllably bend or
turn the tip as shown for example by the dotted line versions of
the bent tip 126, and in some embodiments control an optional end
effector 132. The end effector is a working distal part that is
manipulable for a medical function, e.g., for effecting a
predetermined treatment of a target tissue. For instance, some end
effectors have a single working member such as a scalpel, a blade,
or an electrode. Other end effectors such as the embodiment of FIG.
2, have a pair or plurality of working members such as forceps,
graspers, scissors, or clip appliers, for example. Examples of
electrically activated end effectors include electrosurgical
electrodes, transducers, sensors, and the like. End effectors may
also include conduits to convey fluids, gases or solids to perform,
for example, suction, insufflation, irrigation, treatments
requiring fluid delivery, accessory introduction, biopsy extraction
and the like). In other embodiments, flexible body 124 can define
one or more lumens through which surgical instruments can be
deployed and used at a target surgical location.
[0030] The instrument 120 can also include an image capture element
134 which may include a stereoscopic or monoscopic camera disposed
at the distal end 128 for capturing images that are transmitted to
and processed by the visualization system 110 for display by the
display system 111. Alternatively, the image capture element 134
may be a coherent fiber-optic bundle that couples to an imaging and
processing system on the proximal end of the instrument 120, such
as a fiberscope. The image capture element 134 may be single or
multi-spectral for capturing image data in the visible or
infrared/ultraviolet spectrum.
[0031] A tracking system 136 interfaces with a sensor system 138
for determining the shape (and optionally, pose) of the distal end
128 and or one or more segments 137 along the instrument 120.
Although only an exemplary set of segments 137 are depicted in FIG.
2, the entire length of the instrument 120, between the distal end
128 and the proximal end 130 and including the tip 126 may be
effectively divided into segments, the shape (and location, pose,
and/or position) of which may be determined by the sensor system
138. The tracking system 136 may be implemented as hardware,
firmware, software or a combination thereof which interact with or
are otherwise executed by one or more computer processors, which
may include the processors of a control system 116.
[0032] The sensor system 138 includes an optical fiber 140 aligned
with the flexible body 124 (e.g., provided within an interior
channel (not shown) or mounted externally). The tracking system 136
is coupled to a proximal end of the optical fiber 140. In this
embodiment, the fiber 140 has a diameter of approximately 200
.mu.m. In other embodiments, the dimensions may be larger or
smaller.
[0033] The optical fiber 140 forms a fiber optic bend sensor for
determining the shape of the instrument 120. In one alternative,
optical fibers including Fiber Bragg Gratings (FBG) are used to
provide strain measurements in structures in one or more
dimensions. Various systems and methods for monitoring the shape
and relative position of a optical fiber in three dimensions are
described in U.S. patent application publication no. 2006/0013523,
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 other alternatives,
sensors employing other strain sensing techniques such as Rayleigh
scattering, Raman scattering, Brillouin scattering, and
Fluorescence scattering may be suitable. In other alternative
embodiments, the shape of the instrument 120 may be determined
using other techniques. For example, if the history of instrument
tip's pose is stored for an interval of time that is smaller than
the period for refreshing the navigation display or for alternating
motion (e.g., inhalation and exhalation), the pose history can be
used to reconstruct the shape of the device over the interval of
time. As another example, historical pose, position, or orientation
data may be stored for a known point of an instrument along a cycle
of alternating motion, such as breathing. This stored data may be
used to develop shape information about the instrument.
Alternatively, a series of positional sensors, such as
electromagnetic (EM) sensors, positioned along the instrument can
be used for shape sensing. Alternatively, a history of data from a
positional sensor, such as an EM sensor, on the instrument during a
procedure may be used to represent the shape of the instrument,
particularly if an anatomical passageway is generally static.
Alternatively, a wireless device with position or orientation
controlled by an external magnetic field may be used for shape
sensing. The history of its position may be used to determine a
shape for the navigated passageways.
[0034] The optical fiber 140 is used to monitor the shape of at
least a portion of the instrument 120. More specifically, light
passing through the optical fiber 140 is processed by the tracking
system 126 for detecting the shape of the surgical instrument 120
and for utilizing that information to assist in surgical
procedures. The tracking system 136 may include a detection system
for generating and detecting the light used for determining the
shape of the instrument 120. This information, in turn, in can be
used to determine other related variables, such as velocity and
acceleration of the parts of a surgical instrument. By obtaining
accurate measurements of one or more of these variables in real
time, the controller can improve the accuracy of the robotic
surgical system and compensate for errors introduced in driving the
component parts. The sensing may be limited only to the degrees of
freedom that are actuated by the robotic system, or may be applied
to both passive (e.g., unactuated bending of the rigid members
between joints) and active (e.g., actuated movement of the
instrument) degrees of freedom.
[0035] The information from the tracking system 136 may be sent to
the navigation system 142 where it is combined with information
from the visualization system 110 and/or the preoperatively taken
images to provide the surgeon or other operator with real-time
position information on the display system 111 for use in the
control of the instrument 120. The control system 116 may utilize
the position information as feedback for positioning the instrument
120. Various systems for using fiber optic sensors to register and
display a surgical instrument with surgical images are provided in
U.S. patent application Ser. No. 13/107,562, entitled "Medical
System Providing Dynamic Registration of a Model of an Anatomical
Structure for Image-Guided Surgery," which is incorporated by
reference herein in its entirety.
[0036] In the embodiment of FIG. 2, the instrument 104 is
teleoperated within the robotic surgical system 100. In an
alternative embodiment, the manipulator assembly may be replaced by
direct operator control. In the direct operation alternative,
various handles and operator interfaces may be included for
hand-held operation of the instrument.
[0037] FIGS. 3 and 4 are cross-sectional views of the surgical
instrument 120 including the optical fiber shape sensor 140
according to one embodiment of the present disclosure. To simplify
the illustration, details of the steering components and visual
imaging system have been omitted. The illustration is not drawn to
scale. In this embodiment, the optical fiber 140 comprises four
cores 144a-144d contained within a single cladding 146. Each core
may be single-mode with 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, the number of cores may vary or each core may be
contained in a separate optical fiber. In the embodiments of FIGS.
3 and 4, the fiber cores are arranged with 90.degree. spacing about
the center of the fiber 140. In other embodiments, four cores may
be arranged with one core in the center of the fiber and three
cores spaced at 120.degree. intervals about the center.
[0038] In some embodiments, an array of FBG's is provided within
each core. Each FBG comprises a series of modulations of the core'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 FBG's, 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. Alternatively, backscatter or other optical
phenomena that vary with bending of the optical fiber can be used
to determine strain within each core.
[0039] Thus, to measure strain, light is sent down the fiber, and
characteristics of the returning light are measured. For example,
FBG's produce a reflected wavelength that 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. Use of FBG technology in
position sensors for robotic surgery is described in U.S. Pat. No.
7,930,065 which is incorporated by reference herein in its
entirety.
[0040] The shape sensor may provide shape data to the tracking
system in the form of strain data. Additionally, strain data may be
supplemented with data related to light response, temperature
errors, twist errors, or other data that may contribute to
determining shape.
[0041] 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 bend radius of the fiber, the radial position
of the core with respect to the fiber centerline and the angular
position of the core about the core centerline with respect to the
plane of fiber bending. For example, strain induced wavelength
shifts in regions of the cores containing FBG's 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. Such a system has been described by Luna
Innovations. Inc. of Blacksburg, Va.
[0042] In this embodiment of FIGS. 3 and 4, the fiber 140 includes
the four optical cores 144a-144d disposed at equal radial distances
from and equal angular intervals about the axis of the fiber 140
such that in cross-section, opposing pairs of cores 144a-144c and
144b-144d form orthogonal axes. The sensing locations along the
four optical cores are aligned such that measurements from each
core are from substantially correlated axial regions along the
optical fiber. For example, in one embodiment, each core 144a-144d
includes an array of collinear FBG's that are disposed at known
positions along the lengths of each core 144a-144d such that the
FBG's 144a-d for all four cores 144a-144d are aligned at a
plurality of sensor segments 137, including the steerable tip 126.
In this embodiment, the fiber 140 is centered at a radial distance
D1 from a neutral axis 150 that extends longitudinally through the
instrument 120. In alternative embodiments, the fiber 140 may be
centered about the neutral axis 150 or located at a different
radial distance. In this embodiment, the fiber 140 may be offset
from the neutral axis to accommodate other components of the
instrument 120 such as cables or other steering components or
visualization components (not shown) that may be centered on or
clustered about the neutral axis 150. In this embodiment, the
neutral axis 150 extends generally along the central axis of the
instrument 120. The neutral axis is the axis of the instrument 120
along which no axial strains (due to tension or compression) occur
during bending.
[0043] A bending of the fiber 140 in one of the sensor segments 137
will lengthen at least one core 144a-144d with respect to the
opposing core 144a-144d Interrogation of this length differential
along the fiber enables the angle and radius of bending to be
extracted. This interrogation may be performed using the tracking
system 136. There are a variety of ways of multiplexing the FBG's
so that a single fiber core can carry many sensors and the readings
of each sensor can be distinguished. Some of the various ways are
described in U.S. patent application Ser. No. 13/049,012 which is
incorporated by reference herein in its entirety.
[0044] In alternative embodiments, fibers with fewer or more cores
may be used. Likewise, the fiber cores may be arranged in different
patterns, such as, a central core with (axial refers to the fiber
orientation, not the spacing) additional cores spaced at angular
intervals around the central core. In an alternative embodiment,
the instrument body may include an internal channel sized to
accommodate the optical fiber and separate it from the steering or
visualization components, which themselves may be accommodated
through separate channels. In one embodiment, a hollow utility
channel may provide access for removable devices including
removable surgical instruments, removable steering components,
removable visualization components or the like.
[0045] When a fiber optic shape sensor is positioned offset from
the neutral axis, the fiber is subject to axial tensile and
compressive forces during bending which strain all of the fiber
cores and may contribute to bending measurement error. Temperature
variations in the fiber optic shape sensor alter the cores' index
of refraction and create apparent strain that also may contribute
to bending measurement error. Temperature variations in the shape
sensor may result, for example, from patient body heat, friction,
heat generated by components of the steering system, or heat
generated by components of the visualization system. Both strain
and temperature effects appear as common-mode perturbations to the
fibers in the shape sensors. Given that the shape sensor provides
the bend information as a differential measurement, under ideal
circumstances the strain or temperature common-mode perturbations
may have only limited impact, if any. However, in practice, the
common-mode rejection ratio of the shape sensor is finite and, due
to constructional differences, for example, its fibers may react
differently to said common-mode perturbations. As a consequence, an
undesired differential bend signal may result and negatively affect
the accuracy of the bend measurement. Because the strain due to
axial forces may not be distinguishable from the apparent strain
induced by temperature variations, it may be difficult to determine
the magnitude of the bending measurement error due to axial forces
versus temperature. Thus, it may be difficult to correct or
compensate for the measurement error that results from axial forces
and temperature. The problem is compounded because adjusting
compensation to make the shape sensor insensitive to axial forces,
may make the sensor increasingly sensitive to temperature and vice
versa.
[0046] Knowledge about the temperature variations in the instrument
near the shape sensor may be used to identify the effects of
temperature on the bending measurements and may be used to separate
the measurement error caused by temperature from the error caused
by axial loading. Information about the effects of the axial forces
and the temperature may then be used to algorithmically compensate
the computed bending measurements for the instrument. FIGS. 5 and 6
are cross-sectional views of a surgical instrument including an
optical fiber shape sensor and a sensor compensation device
according to one embodiment of the present disclosure. In this
embodiment, an instrument 200 is similar to the instrument 120,
with the differences described below. The instrument 200 includes a
fiber 202, similar to the fiber 140 which is offset from the
neutral axis 204 of the instrument 200 by the distance D1. In this
embodiment, the instrument 200 includes a sensor compensation
device 206 which measures temperature and/or temperature variations
in the instrument 200. The temperature-measuring sensor
compensation device 206 is an optical fiber with at least one core.
This fiber extends through the instrument 120 generally parallel to
the neutral axis 204. The sensor compensation device 206 is
centered at a radial distance D2 from a neutral axis 204 of the
instrument 200. In this embodiment, the radial distance D2 is
smaller than the radial distance D1 and the sensor compensation
device 206 is between the neutral axis and the fiber 202. In
alternative embodiments, the sensor compensation device may be
positioned at a radial distance greater than D1. To accurately
determine the effects of temperature on the shape sensor 202, the
sensor compensation device may be located anywhere generally near
the sensor, within the instrument 200. Optical fiber-based
temperature measurement devices may determine temperature or
temperature variations in a variety of ways. For example, an
optical fiber may be constructed so that temperature modulates the
intensity, phase, polarization, wavelength or transit time of light
in the fiber. Alternatively, the optical fiber may have evanescent
wave loss that varies with temperature, or temperature may be
determined by scatter analysis. Knowledge of the temperature or
temperature variations within the instrument near the shape sensor
may allow for the separation of the effects of temperature and
axial forces and for the identification of their effect on bending
measurements for the overall instrument 200. Algorithmic
compensation techniques are used to remove the effects of
temperature and/or axial forces from the final bending
measurements. Alternative systems for measuring temperature within
the instrument may be also be suitable for use in correcting the
effects of temperature from final measurements. Alternative
temperature measurement systems may include the use of a plurality
of discrete single-point temperature sensors, such as
thermocouples, resistance-based temperature sensors, and silicon
diodes, at different locations along the instrument. The
measurements taken at the different locations may be
interpolated.
[0047] In some embodiments, compensation for temperature effects on
shape sensor 202 can be performed using predetermined
characterization data. This temperature characterization data can
be generated empirically via controlled application of a
temperature gradient(s) (either continuous or localized) to shape
sensor 202. By holding shape sensor 202 in a fixed configuration
(e.g., straight, or with a known curvature), applying the
predetermined temperature gradient (e.g., using individual or
continuous heating elements), and monitoring the change in sensor
output, the effects of temperature variations on sensor 202 can be
characterized. In some embodiments, a single temperature gradient
can be applied to shape sensor 202, while in other embodiments,
multiple temperature gradients can be applied to shape sensor 202.
In any event, the generated temperature characterization data can
be compiled in any format, such as a lookup table housing the
empirically-generated data, a mathematical model of the thermal
response, or a simple scaling factor as a function of temperature,
among others. This temperature characterization data can then be
provided as a discrete package (e.g., to be stored in or loaded
into a computer-readable memory), combined with other
sensor-related data (e.g., incorporated into an overall calibration
file for sensor 202), or can be integrated into the measurement
algorithms/software/hardware for reading the output of sensor 202
(e.g., an interrogator or other electronic system such as tracking
system 136).
[0048] In an alternative embodiment, the optical fiber temperature
sensor may be shrouded in an insulation material together with the
fiber shape sensor. The insulation may be used to reduce the effect
of external temperature changing sources.
[0049] FIG. 7 is a cross-sectional view of a surgical instrument
including an optical fiber shape sensor and a sensor compensation
device according to another embodiment of the present disclosure.
In this embodiment, an instrument 300 is similar to the instrument
120, with the differences described below. The instrument 300
includes a fiber shape sensor 302, similar to the fiber shape
sensor 140 which is offset from the neutral axis of the instrument
300 by the distance D1. In this embodiment, the instrument 300
includes a sensor compensation device 304 which reduces the
temperature variations across the transverse dimensions of the
fiber 302. The sensor compensation device 304 may be a highly
thermal conductive coating, layer, jacket, or tubing that serves to
distribute heat uniformly around and along the optical fiber sensor
302. The sensor compensation device 304 may alternatively be a
highly insulating coating, layer, jacket, or tubing that insulates
optical fiber sensor 302 from external temperature variations. By
maintaining a relatively constant temperature across the fiber
shape sensor 302, the sensor compensation device 302 reduces the
measurement error that may be caused by high temperatures or
temperature variations in the sensor.
[0050] Knowledge about the axial forces causing compression and
tension in the shape sensor may be used to identify the magnitude
and/or effects of axial forces on the bending measurements and may
also be used to separate the measurement error caused by axial
forces versus temperature. Information about effects of the axial
forces and the temperature may then be used to algorithmically
compensate the computed bending measurements for the instrument.
FIGS. 8 and 9 are cross-sectional views of a surgical instrument
including an optical fiber shape sensor and a sensor compensation
device according to another embodiment of the present disclosure.
In this embodiment, an instrument 400 is similar to the instrument
120, with the differences described below. The instrument 400
includes a fiber shape sensor 402, similar to the fiber shape
sensor 140 which is offset from the neutral axis 404 of the
instrument 400 by the distance D1. In this embodiment, the
instrument 400 includes an optical fiber sensor compensation device
406 which measures the same bend in the instrument 400 but with
different axial forces. The sensor compensation device 406 is an
optical fiber identical to or substantially similar to the shape
sensor fiber 402.
[0051] The sensor compensation device 406 is centered at a radial
distance D2 from a neutral axis 408 of the instrument 400, but is
positioned on the opposite side of the neutral axis (approximately
180.degree. angular displacement) from the shape sensor fiber 402.
In this embodiment, the radial distance D2 is the same as the
radial distance D1. In alternative embodiments, the fiber optic
sensor compensation device may be positioned within the instrument
at other distances from the neutral axis or at other angular
displacements from the shape sensor.
[0052] When positioned at opposite but equal locations from the
neutral axis 408, a bend about the X-axis (bending in the YZ-plane)
will place one of the fibers 402, 406 into compression and the
other into tension. Thus the bend measurements derived from each of
the fibers 402, 406 would exhibit errors due to opposite axial
forces. The true value of the bend, at the neutral axis, would be a
value between the fiber bend measurements. Knowledge of the axial
force measurement error within the instrument may also allow for
the separation of the effects of temperature and axial forces and
for the identification of their respective effects on bending
measurements. Algorithmic compensation techniques are then used to
remove the effects of axial forces and/or temperature from the
final bending measurements. Although the fiber 402 is identified as
the shape sensor and fiber 406 is identified as the shape sensor
compensation device, it is understood that because the fibers are
operatively the same, either one can be considered the sensor and
the other the compensation device.
[0053] FIG. 10 is a cross-sectional view of a surgical instrument
including an optical fiber shape sensor and a shape sensor
compensation device according to another embodiment of the present
disclosure. In this embodiment, an instrument 500 is similar to the
instrument 400 of FIG. 8, but includes a plurality of radially
spaced optical fiber shape sensors 502-508, each of which is
identical to or substantially similar to shape sensor 140 of FIG.
1. In this embodiment, each shape sensor 502-508 serves as a sensor
compensation device to the oppositely positioned sensor. For
example, the axial load measurement error associated with shape
sensor 504 may be used to compensate the measurements derived from
shape sensor 508 and vice versa, to achieve a compensated bend
measurement for the neutral axis. Using a plurality of radially
spaced optical fiber shape sensors allows for axial force
compensation through different bending planes.
[0054] For example, FIGS. 11 and 12 illustrate the surgical
instrument 500 of FIG. 10 bent in the YZ and XZ planes,
respectively. In FIG. 11, the bend in the YZ plane puts shape
sensor 502 into compression and shape sensor 506 into tension. The
equal and opposite positions of the shape sensors 502, 506 about
the neutral axis will cause equal and opposite axial strains in the
sensors. Shape sensors 504, 508 would experience minimal or no
axial forces and should provide the same bending measurement. In
FIG. 12, the bend in the XZ plane puts shape sensor 504 into
compression and shape sensor 508 into tension. The equal and
opposite positions of the shape sensors 504, 508 about the neutral
axis will cause equal and opposite axial strains in the sensors.
Shape sensors 502, 506 would experience minimal or no axial forces.
and should provide the same bending measurement. Using a radial
array of shape sensors may more accurately reduce the measurement
errors due to axial strain for bending in a variety of different
planes.
[0055] For alternative embodiments in which the instrument is not
symmetric about a neutral axis, shape sensor placement about the
neutral axis may be calculated according to known methods so that
the effects of the axial forces are equal and opposite.
[0056] FIG. 13 is a flowchart providing a method 600 for using the
shape sensing apparatus. Prior to implementation of this method,
preoperative images (e.g., CT, MR, or the like) of the patient may
be captured. During the surgical procedure, the instrument may be
inserted into the patient through a natural or surgically created
opening. The display system may display endoscopic images from the
visualization system and may also display preoperative images
associated with the current location of the tip of the instrument.
As the instrument navigates natural or surgically created
passageways with the patient, the tracking system and the
navigation system are used to determine the bend of various
segments of the instrument and thus the overall shape of the
instrument. At 602, shape data is received from a fiber optic shape
sensor extending within the surgical instrument parallel to the
neutral axis of the surgical instrument. At 604, compensating data
is received from a sensor compensation device. For example,
temperature data may be received from a temperature sensor located
near the shape sensor or axial load shape data may be received from
another shape sensor located opposite the neutral axis of the
instrument from the shape sensor. Optionally, temperature sensor
information may be modified or otherwise combined with
predetermined temperature characterization data. At 606, a bend
measurement for the surgical instrument is calculated using the
data received from the shape sensor and the sensor compensation
device.
[0057] Although the shape sensors and sensor compensation devices
have been described herein with respect to teleoperated or hand
operated surgical systems, these sensors and sensor compensation
systems will find application in a variety of medical and
non-medical instruments in which accurate instrument bending
measurements would otherwise be compromised by temperature, sensor
location, or other physical conditions of the shape sensors.
[0058] One or more elements in embodiments of the invention may be
implemented in software to execute on a processor of a computer
system such as control system 108. 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 processor readable storage medium
or device that may have been downloaded by way of a computer data
signal embodied in a carrier wave over a transmission medium or a
communication link. The processor readable storage device may
include any medium that can store information including an optical
medium, semiconductor medium, and magnetic medium. Processor
readable storage device examples include an electronic circuit; a
semiconductor device, a semiconductor memory device, a read only
memory (ROM), a flash memory, an erasable programmable read only
memory (EPROM); a floppy diskette, a CD-ROM, an optical disk, a
hard disk, or other storage device, The code segments may be
downloaded via computer networks such as the Internet, Intranet,
etc.
[0059] Note that the processes and displays presented may not
inherently be related to any particular computer or other
apparatus. Various general-purpose systems may be used with
programs in accordance with the teachings herein, or it may prove
convenient to construct a more specialized apparatus to perform the
operations described. 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.
[0060] 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.
* * * * *