U.S. patent application number 17/699690 was filed with the patent office on 2022-06-30 for tracking marker support structure and surface registration methods employing the same for performing navigated surgical procedures.
The applicant listed for this patent is 7D SURGICAL ULC. Invention is credited to Michael Leung, Adrian Mariampillai, Peter SIEGLER, Beau Anthony Standish, Victor X.D. Yang.
Application Number | 20220202507 17/699690 |
Document ID | / |
Family ID | |
Filed Date | 2022-06-30 |
United States Patent
Application |
20220202507 |
Kind Code |
A1 |
SIEGLER; Peter ; et
al. |
June 30, 2022 |
TRACKING MARKER SUPPORT STRUCTURE AND SURFACE REGISTRATION METHODS
EMPLOYING THE SAME FOR PERFORMING NAVIGATED SURGICAL PROCEDURES
Abstract
Devices and methods are provide for facilitating registration
and calibration of surface imaging systems. Tracking marker support
structures are described that include one or more fiducial
reference markers, where the tracking marker support structures are
configured to be removably and securely attached to a skeletal
region of a patient. Methods are provided in which a tracking
marker support structure is attached to a skeletal region in a
pre-selected orientation, thereby establishing an intraoperative
reference direction associated with the intraoperative position of
the patient, which is employed for guiding the initial registration
between intraoperatively acquired surface data and volumetric image
data. In other example embodiments, the tracking marker support
structure may be employed for assessing the validity of a
calibration transformation between a tracking system and a surface
imaging system. Example methods are also provided to detect whether
or not a tracking marker support structure has moved from its
initial position during a procedure.
Inventors: |
SIEGLER; Peter; (TORONTO,
CA) ; Leung; Michael; (Markham, CA) ;
Mariampillai; Adrian; (Toronto, CA) ; Standish; Beau
Anthony; (Toronto, CA) ; Yang; Victor X.D.;
(Toronto, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
7D SURGICAL ULC |
Toronto |
|
CA |
|
|
Appl. No.: |
17/699690 |
Filed: |
March 21, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16601623 |
Oct 15, 2019 |
11291509 |
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17699690 |
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15513862 |
Mar 23, 2017 |
10463434 |
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PCT/CA2015/050939 |
Sep 23, 2015 |
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16601623 |
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62054784 |
Sep 24, 2014 |
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International
Class: |
A61B 34/20 20060101
A61B034/20; A61B 17/28 20060101 A61B017/28; A61B 5/00 20060101
A61B005/00; A61B 5/11 20060101 A61B005/11; A61B 90/00 20060101
A61B090/00; A61B 17/88 20060101 A61B017/88 |
Claims
1. A surgical tool comprising: a functional distal portion; a
plurality of tracking markers fixed in position and orientation
relative to said functional distal portion, said plurality of
tracking markers being configured to be detectable by an optical
tracking system; and a geometrical marker fixed in position and
orientation relative to said functional distal portion, said
geometrical marker being configured to be detectable by a surface
detection system; said geometrical marker comprising a plurality of
planar surfaces, wherein at least two of the planar surfaces are
oriented at oblique angles relative to one another, thereby
facilitating detection of said geometrical marker by the surface
detection system over a range of relative orientations between said
surgical tool and the surface detection system.
2. The surgical tool according to claim 1 wherein said geometrical
marker is a first geometrical marker, said surgical tool further
comprising a second geometrical marker.
3. The surgical tool according to claim 2 wherein said first
geometrical marker and said second geometrical marker have
different shapes.
4. The surgical tool according to claim 2 wherein said first
geometrical marker extends from a first planar base surface and
said second geometrical marker extends from a second planar base
surface, wherein said first planar base surface is angled relative
to said second planar base surface.
5. The surgical tool according to claim 1 wherein said geometrical
marker resides closer to said functional distal portion than said
plurality of tracking markers.
6. The surgical tool according to claim 1 wherein said geometrical
marker has a truncated pyramidal shape.
7. The surgical tool according to claim 1 wherein said functional
distal portion comprises a clamp.
8. A system comprising: the surgical tool according to claim 1; the
surface detection system; the tracking system; and processing and
control circuitry operatively coupled to said surface detection
system and said tracking system, said processing circuitry
comprising at least one processor and associated memory, said
memory comprising instructions executable by said at least one
processor for performing operations comprising: employing the
tracking system to determine a first position and orientation of
the surgical tool in a frame of reference of said tracking system;
employing the surface detection system to acquire surface data, and
processing the surface data and reference surface data
characterizing said geometrical marker to determine a second
position and orientation of the surgical tool in a frame of
reference of said surface detection system; and employing the first
position and orientation and the second position and orientation to
determine a calibration transformation between the frame of
reference of said tracking system and the frame of reference of
said surface detection system.
9. The system according to claim 8 wherein said processing and
control circuitry is further configured to compare the calibration
transformation to a previously determined calibration
transformation to determine whether or not the previously
determined calibration transformation is valid.
10. The system according to claim 9 said processing and control
circuitry is further configured to employ the first position and
orientation and the previously determined calibration
transformation to segment the surface data within a subregion
corresponding to an estimated location of the geometrical marker,
thereby obtaining segmented surface data, and wherein the segmented
surface data and the reference surface data are processed to
determine the second position and orientation.
11. The system according to claim 8 wherein said geometrical marker
is a first geometrical marker, said surgical tool further
comprising a second geometrical marker.
12. The system according to claim 11 wherein said first geometrical
marker and said second geometrical marker have different
shapes.
13. The system according to claim 11 wherein said first geometrical
marker extends from a first planar base surface and said second
geometrical marker extends from a second planar base surface,
wherein said first planar base surface is angled relative to said
second planar base surface.
14. The system according to claim 8 wherein said geometrical marker
resides closer to said functional distal portion than said
plurality of tracking markers.
15. The system according to claim 8 wherein said geometrical marker
has a truncated pyramidal shape.
16. The system according to claim 9 wherein said surgical tool
comprises a clamp.
17. A method of determining a calibration transformation between a
frame of reference of a tracking system and a frame of reference of
a surface detection system, the method comprising: providing a
surgical tool according to claim 1; employing the tracking system
to determine a first position and orientation of the surgical tool
in a frame of reference of said tracking system; employing the
surface detection system to acquire surface data, and processing
the surface data and reference surface data characterizing said
geometrical marker to determine a second position and orientation
of the surgical tool in a frame of reference of said surface
detection system; and employing the first position and orientation
and the second position and orientation to determine the
calibration transformation.
18. The method according to claim 17 further comprising comparing
the calibration transformation to a previously determined
calibration transformation to determine whether or not the
previously determined calibration transformation is valid.
19. The method according to claim 17 wherein the first position and
orientation and the previously determined calibration
transformation are employed to segment the surface data within a
subregion corresponding to an estimated location of the geometrical
marker, thereby obtaining segmented surface data, and wherein the
segmented surface data and the reference surface data are processed
to determine the second position and orientation.
20. The method according to claim 17 wherein said geometrical
marker resides closer to said functional distal portion than said
plurality of tracking markers.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional
Application No. 62/054,784, titled "TRACKING MARKER SUPPORT
STRUCTURE AND SURFACE REGISTRATION METHODS EMPLOYING THE SAME FOR
PERFORMING NAVIGATED SURGICAL PROCEDURES" and filed on Sep. 24,
2014, the entire contents of which is incorporated herein by
reference.
BACKGROUND
[0002] Surgical guidance enables surgeons to localize the position
of surgical instruments relative to the human body without having
complete visual access during surgery. Surgical guidance is
routinely used in surgeries that involve anatomical locations such
as the spine, brain, hip or other organs.
[0003] In general, surgical guidance consists of two steps: The
first step includes the acquisition of a three dimensional (3D)
data set of a relevant anatomical region of the body. This step may
involve single or multiple imaging modalities such as computed
tomography (CT), magnetic resonance tomography (MRT), positron
emission tomography (PET) and ultrasound (US). The 3D data set may
be acquired before and/or during the surgical procedure. In the
second step, the spatial position of the body and the spatial
relation of the surgical instruments to the position of the
anatomical region are tracked during the surgery. The spatial
position of this anatomical region is then mapped to its 3D data
set using specific image registration techniques. After
registration, the spatial position of the surgical instruments as
they are being used by the surgeon can be displayed relative to the
previously acquired 3D data set of the anatomical region. Surgical
guidance systems usually incorporate the use of a reference
structure which is affixed to the patient in order to track patient
motion and breathing so that tool tracking remains accurate during
the procedure.
[0004] In some applications, optical-based systems are used for
tracking spatial positions of tools and the reference frame during
the surgery. These systems are based on two cameras that detect the
positions of at least three markers attached to the tracked
surgical instruments and require line-of-sight from the cameras to
the markers (for example, mounted with LEDs, or mounted with
reflective probes). This necessitates the careful positioning of
the cameras and design of tracked instruments so that line-of-sight
is maintained during a surgical procedure.
SUMMARY
[0005] Devices and methods are provided for facilitating
registration and calibration of surface imaging systems. Tracking
marker support structures are described that include one or more
fiducial reference markers, where the tracking marker support
structures are configured to be removably and securely attached to
a skeletal region of a patient. Methods are provided in which a
tracking marker support structure is attached to a skeletal region
in a pre-selected orientation, thereby establishing an
intraoperative reference direction associated with the
intraoperative position of the patient, which is employed for
guiding the initial registration between intraoperatively acquired
surface data and volumetric image data. In other example
embodiments, the tracking marker support structure may be employed
for assessing the validity of a calibration transformation between
a tracking system and a surface imaging system. Example methods are
also provided to detect whether or not a tracking marker support
structure has moved from its initial position during a
procedure.
[0006] Accordingly, in a first aspect, there is provided a method
of intraoperatively registering surface data with volumetric image
data, the method comprising:
[0007] detecting, with a tracking system, signals associated with
fiducial markers located on a tracking marker support structure,
wherein the tracking marker support structure is removably attached
to a skeletal feature of a subject in a pre-selected orientation
relative to the skeletal feature;
[0008] processing the signals and employing the pre-selected
orientation to determine an intraoperative reference direction
associated with an intraoperative position and orientation of the
subject;
[0009] intraoperatively acquiring the surface data from a surgical
region of interest; and
[0010] employing the intraoperative reference direction when
registering the surface data to the volumetric image data.
[0011] In another aspect, there is provided a method of assessing
the validity of a previously determined calibration transformation
between a surface imaging system and a tracking system, the method
comprising:
[0012] detecting, with the tracking system, signals associated with
fiducial markers located on a tracking marker support structure,
wherein the tracking marker support structure is removably attached
to a patient, and acquiring surface data using the surface imaging
system, wherein the surface data is obtained from a spatial region
that includes at least a portion of the tracking marker support
structure;
[0013] processing the signals to determine a position and
orientation of the tracking marker support structure;
[0014] determining, based on the intraoperative position and
orientation of the tracking marker support structure, and based on
the previously determined calibration transformation between a
reference frame of the surface imaging system and a reference frame
of the tracking system, a spatial subregion, in the reference frame
of the surface imaging system, that is associated with the tracking
marker support structure;
[0015] segmenting the surface data within the spatial subregion to
obtain a segmented surface associated with the tracking marker
support structure;
[0016] registering the segmented surface to reference surface data
characterizing the surface of the tracking marker support
structure, thereby obtaining a spatially registered reference
surface; and
[0017] employing the spatially registered reference surface to
assess the validity of the previously acquired calibration
transformation.
[0018] In another aspect, there is provided a device for
positioning fiducial markers relative to an exposed vertebrae, the
device comprises:
[0019] a pair of forceps having a longitudinal axis associated
therewith;
[0020] a pair of clamping jaws located near a distal region of the
forceps, wherein the clamping jaws are configured to contact
opposing sides of a spinous process when a force is applied to the
forceps;
[0021] a locking mechanism operably connected to the forceps for
removably maintaining the forceps in a clamped configuration;
and
[0022] a tracking frame having a proximal end connected to the
forceps at a location remote from clamping jaws, wherein the
tracking frame supports, near a distal region thereof, the fiducial
markers;
[0023] wherein the forceps extend from the clamping jaws such that
when the clamping jaws are clamped to the spinous process, the
longitudinal axis associated with the forceps is angled relative to
the Anterior-Posterior a normal direction that is associated with
the subject, wherein the normal direction lies in the sagittal
plane and is perpendicular to the Inferior-Superior direction of
the spine, such that a skeletal region adjacent to the skeletal
feature is unobstructed by the forceps, thereby permitting overhead
surface data acquisition of the skeletal region; and
[0024] wherein at least a portion of the tracking frame is angled
relative the longitudinal axis of the forceps, such that contact is
avoided between the fiducial markers and a user gripping the
forceps.
[0025] In another aspect, there is provided a device for fixing
fiducial markers relative to an exposed vertebrae, the device
comprises:
[0026] a pair of forceps having a longitudinal axis;
[0027] a pair of clamping jaws located near a distal region of the
forceps, wherein the clamping jaws are configured to contact
opposing sides of a spinous process of the exposed vertebrae when a
force is applied to the forceps;
[0028] a locking mechanism operably connected to the forceps for
removably maintaining the forceps in a clamped configuration;
and
[0029] a tracking frame having a proximal end connected to the
forceps at a location remote from clamping jaws, wherein the
tracking frame supports, near a distal region thereof, the fiducial
markers;
[0030] wherein the clamping jaws are characterized by a normal axis
that is perpendicular to the Inferior-Superior direction of the
spine when the clamping jaws are clamped to the spinous
process;
[0031] wherein the longitudinal axis of the forceps is angled
relative to the normal axis of the clamping jaws, and such that a
skeletal region adjacent to the skeletal feature is unobstructed by
the forceps; and
[0032] wherein at least a portion of the tracking frame is angled
relative the longitudinal axis of the forceps, such that contact is
avoided between the fiducial markers and a user gripping the
forceps.
[0033] In another aspect, there is provided a device for fixing
fiducial markers relative to an exposed vertebrae, the device
comprises:
[0034] a pair of forceps having a longitudinal axis;
[0035] a pair of clamping jaws located near a distal region of the
forceps;
[0036] a tracking frame having a proximal end connected to the
forceps at a location remote from clamping jaws, wherein the
tracking frame supports, near a distal region thereof, the fiducial
markers;
[0037] a locking mechanism operably connected to the forceps for
removably maintaining the forceps in a clamped configuration;
[0038] wherein the clamping jaws are shaped to uniquely contact
opposing sides of a skeletal feature, such that the fiducial
markers are oriented in a pre-selected orientation relative to the
skeletal feature.
[0039] In another aspect, there is provided a clamping device for
clamping to a spinous process, the device comprises:
[0040] a pair of forceps having a longitudinal axis;
[0041] a pair of clamping jaws located near a distal region of the
forceps;
[0042] a locking mechanism operably connected to the forceps for
removably maintaining the forceps in a clamped configuration;
[0043] wherein each clamping jaw comprises a clamping surface
having two co-planar outer flat surfaces and an inwardly directed
surface connecting the two outer flat surfaces, such that the
clamping jaws are configured for clamping to a wide range of
spinous process geometries, and wherein the outer flat surfaces and
the inwardly directed surface each comprise spikes.
[0044] In another aspect, there is provided a method of detecting a
change in the position and orientation of a tracking marker support
structure relative to a patient to which the tracking marker
support structure is attached, the method comprising:
[0045] detecting, with a tracking system, signals associated with
the fiducial markers located on the tracking marker support
structure, and acquiring surface data from a surgical region of
interest using a surface imaging system;
[0046] determining the current position and orientation of the
tracking marker support structure based on the signals;
[0047] obtaining previously measured surface data from the surgical
region of interest and an associated previously determined position
and orientation of the tracking marker support structure;
[0048] registering the surface data with previously acquired
surface data to obtain an intraoperative transformation;
[0049] comparing the intraoperative transformation to the shift
between the current position and orientation of the tracking marker
support structure and the previously determined position and
orientation of the tracking marker support structure and
determining a change in the position and orientation of the
tracking marker support structure relative to the patient.
[0050] In another aspect, there is provided a method of segmenting
surface data to remove surface artifacts associated with an
instrument having fiducial markers attached thereto, the method
comprising:
[0051] intraoperatively acquiring the surface data from a surgical
region of interest using a surface imaging system;
[0052] detecting, with a tracking system, signals associated with
the fiducial markers located on the instrument,
[0053] processing the signals to determine an intraoperative
position and orientation of the instrument;
[0054] employing the intraoperative position and orientation of the
instrument, and employing a calibration transformation between a
reference frame associated with the tracking system and a reference
frame associated with the surface imaging system, to determine a
suitable position and orientation of a cropping mask for removal of
the surface artifacts associated with the instrument; and
[0055] segmenting the surface data to remove the surface artifacts
within the region associated with the cropping mask.
BRIEF DESCRIPTION OF DRAWINGS
[0056] Embodiments will now be described, by way of example only,
with reference to the drawings, in which:
[0057] FIG. 1A shows a schematic of an example surgical guidance
system that includes an overhead integrated tracking system that
employs structured light surface detection for image registration
and optical tracking of medical instruments and medical devices
with marker attachments.
[0058] FIG. 1B is a block diagram illustrating an example system
configuration, including various example components of a control
and processing unit.
[0059] FIG. 2 shows an example block diagram showing the components
of a tracking marker support structure.
[0060] FIGS. 3A and 3B provide an (A) isometric and (B) top view of
an example embodiment of a tracking marker support structure.
[0061] FIGS. 4 and 5 provide side and top views, respectively, of
the use of an example tracking marker support structure for
clamping the tracking marker support structure in a pre-configured
orientation.
[0062] FIGS. 6A and 6B illustrate an example embodiment of a
tracking marker support structure that employs a spring locking
mechanism, where FIG. 6B provides a detailed view of the spring
locking mechanism.
[0063] FIGS. 7A and 7B illustrate an example embodiment of a
tracking marker support structure that employs a thumb-screw
mechanism, where FIG. 7B provides a detailed view of the
thumb-screw mechanism.
[0064] FIGS. 8A and 8B illustrate an alternative example embodiment
of a tracking marker support structure that employs a thumb-screw
mechanism, where FIG. 8B provides a detailed view of the
thumb-screw mechanism.
[0065] FIGS. 9A-I show different example implementations of
clamping jaws employed by the gripping mechanism.
[0066] FIGS. 10A-H shows additional example implementations of
clamping jaws based on curved plates.
[0067] FIG. 11A is a flow chart illustrating an example method of
employing a tracking marker support structure to support the
registration of intraoperatively acquired surface data to
volumetric (e.g. pre-operatively acquired) image data.
[0068] FIG. 11B is a flow chart illustrating an example method of
employing a tracking marker support structure to support the
registration of intraoperatively acquired surface data to
volumetric image data for multiple vertebral levels.
[0069] FIG. 12A illustrates an example screenshot that can be
employed for obtaining information regarding the intraoperative
position of a patient.
[0070] FIG. 12B-I illustrate the use of different cropping masks
which may be employed for the segmentation of a surface within a
spatial region or within a prescribed distance associated with the
position of attachment of the tracking marker support
structure.
[0071] FIG. 13A illustrates an example method of employing a
tracking marker support structure for the intraoperative assessment
of the validity of a previously determined calibration
transformation between a tracking system and a surface imaging
system.
[0072] FIGS. 13B and 13C illustrate the use of cropping masks for
the segmentation of a surface associated with the tracking marker
support structure when performing active calibration.
[0073] FIGS. 14A to 14E illustrate an active calibration process,
in which a tracking marker support structure is employed to verify
the calibration transformation between the tracking system and the
surface imaging system.
[0074] FIG. 15 illustrates an example implementation of a tracking
marker support structure that incorporates an additional surface
with characteristic structures that provide additional
non-symmetric surfaces useful for the registration process.
[0075] FIG. 16 itemizes the characteristic features, and associated
design constraints, of an example tracking marker support
structure.
[0076] FIG. 17 shows a generalized profile of an example tracking
marker support structure used for navigation of spinal procedures,
identifying a set of characteristic geometrical parameters.
[0077] FIG. 18 provides example values for the dimensions of the
characteristic geometrical parameters identified in FIG. 17.
[0078] FIGS. 19A to 19D illustrate an example implementation of a
tracking marker support structure based on the feature set shown in
FIG. 16 and pertaining to cranial and/or maxillofacial surgical
applications.
[0079] FIG. 19E shows a generalized profile of an example tracking
marker support structure used for navigation of cranial and/or
maxillofacial surgical procedures, identifying a set of
characteristic geometrical parameters.
[0080] FIG. 19F provides example values for the dimensions of the
characteristic geometrical parameters identified in FIG. 19E.
[0081] FIG. 20 shows a flow chart illustrating an example method in
which a surface imaging based surgical guidance system is used to
detect whether or not the tracking marker support structure has
been bumped or moved intraoperatively from its initial
position.
[0082] FIG. 21 is a flow chart illustrating such an example method
of performing selective surface segmentation based on known
properties of tools or instruments that may be present within the
field of view of a surface imaging system.
[0083] FIGS. 22A-22D illustrate an example implementation of a
tracking marker support structure based on the feature set shown in
FIG. 16 and pertaining to cranial based surgical procedures.
[0084] FIG. 22E shows a generalized profile of an example tracking
marker support structure used for navigation of cranial based
surgical procedures, identifying a set of characteristic
geometrical parameters.
[0085] FIG. 22F provides example values for the dimensions of the
characteristic geometrical parameters identified in FIG. 22D.
DETAILED DESCRIPTION
[0086] Various embodiments and aspects of the disclosure will be
described with reference to details discussed below. The following
description and drawings are illustrative of the disclosure and are
not to be construed as limiting the disclosure. Numerous specific
details are described to provide a thorough understanding of
various embodiments of the present disclosure. However, in certain
instances, well-known or conventional details are not described in
order to provide a concise discussion of embodiments of the present
disclosure.
[0087] As used herein, the terms "comprises" and "comprising" are
to be construed as being inclusive and open ended, and not
exclusive. Specifically, when used in the specification and claims,
the terms "comprises" and "comprising" and variations thereof mean
the specified features, steps or components are included. These
terms are not to be interpreted to exclude the presence of other
features, steps or components.
[0088] As used herein, the term "exemplary" means "serving as an
example, instance, or illustration," and should not be construed as
preferred or advantageous over other configurations disclosed
herein.
[0089] As used herein, the terms "about" and "approximately" are
meant to cover variations that may exist in the upper and lower
limits of the ranges of values, such as variations in properties,
parameters, and dimensions. Unless otherwise specified, the terms
"about" and "approximately" mean plus or minus 25 percent or
less.
[0090] It is to be understood that unless otherwise specified, any
specified range or group is as a shorthand way of referring to each
and every member of a range or group individually, as well as each
and every possible sub-range or sub-group encompassed therein and
similarly with respect to any sub-ranges or sub-groups therein.
Unless otherwise specified, the present disclosure relates to and
explicitly incorporates each and every specific member and
combination of sub-ranges or sub-groups.
[0091] As used herein, the term "on the order of", when used in
conjunction with a quantity or parameter, refers to a range
spanning approximately one tenth to ten times the stated quantity
or parameter.
[0092] Unless defined otherwise, all technical and scientific terms
used herein are intended to have the same meaning as commonly
understood to one of ordinary skill in the art. Unless otherwise
indicated, such as through context, as used herein, the following
terms are intended to have the following meanings:
[0093] As used herein, the term "position" refers to the location
(e.g. x,y,z) of an object and its orientation (e.g. relative to one
or more rotational axes) in three dimensions (3D) within a
coordinate system.
[0094] As used herein, the term "tracking system" refers to a
system that allows the detection of the position of an object in
three dimensions. An example of a tracking system is an optical
tracking system operating with visual or infrared light that may
employ stereo cameras to detect the positions of passive optical
markers (e.g. reflective spheres) and/or active optical markers
(e.g. light emitting diodes (LEDs)). Other non-limiting examples of
tracking systems include electromagnetic tracking systems and
surface imaging tracking systems.
[0095] As used herein, the term "marker" refers to a locating
indicator that may be affixed or otherwise connected to a flexible
or rigid handheld implement, patient, subject, instrument, tool, or
other component of a surgical system or surgical field, and which
is detectable by a tracking system for use in determining a
position. A marker may be active or passive, and may be detectable
using an optical or electromagnetic detector. An example optical
passive marker is a reflective sphere, or portion thereof, and an
example active optical marker is an LED. Another example of a
marker is a glyph, which may contain sufficient spatial and/or
geometrical co-planar features for determining a three-dimensional
position and orientation. For example, a glyph marker may include
at least three corner features, where the three corner features
define a plane.
[0096] As used herein, the term "surface imaging system" refers to
a system that detects the topology of a 3D surface (e.g. acquires a
set of surface data describing the surface topology) within a field
of view. Examples of surface imaging techniques include structured
light illumination, laser range finding, and photogrammetry.
[0097] As used herein, the term "calibration transformation" refers
to a transformation that relates the coordinate system of a surface
imaging system to that of a tracking system. The term "last
calibration transformation" refers to the last valid or correct
calibration transformation of the system. The last calibration can
be determined either during the last service maintenance or by the
system itself using a validation step.
[0098] As used herein, the term "tracking marker support structure"
refers to a rigid structure including one or more fiducial or
reference markers for intraoperative tracking, that configured to
be securely attached to a subject (e.g. vertebra or the head), for
example, to facilitate a registration process.
[0099] FIG. 1A shows an illustration of an example of a surgical
guidance system for tracking the intraoperative position of a
medical instrument relative to patient anatomy during a spinal
surgery. Patient 10 is shown in the prone (face down) position,
with spine 15 exposed. Although the present example system employs
a combination of an optical tracking system and a structured light
surface imaging system, it will be understood that other types of
tracking systems (i.e. non-optical) may be employed, and that other
types of surface imaging systems (i.e. other than employing
structured light) may be employed.
[0100] The optical tracking subsystem is used to detect the
position of medical instrument 40. In the example embodiment shown
in FIG. 1, the optical tracking subsystem includes stereo cameras
with integrated infrared lighting 25 and attachment of highly
reflective markers 65 to medical instrument 40. Due to their high
reflectivity to infrared light, markers 65 can be easily localized
in each image of the two cameras 25. These image positions are used
to calculate the 3D position of each marker 65 by geometrical
triangulation. If at least three markers 65 are rigidly attached to
medical instrument 40, it is possible to compute its position (the
six degrees of freedom--6-DOF). It is to be understood that in some
embodiments, less than three markers may be employed for position
tracking. For example, a single marker may be provided for position
tracking, provided that the single marker includes sufficient
spatial structure and/or content. An example of such a single
marker is a glyph including co-planar spatial features such as
corner or edge features.
[0101] In the example illustrations provided herein, markers 65 for
the optical tracking system are shown as reflective spheres, which
are commonly used for passive optical tracking. However, any other
type of markers, or marker attributes, can be used depending on the
used tracking system such as, but not limited to LEDs, which do not
require integration of additional lighting, reflective spheres,
glyphs, varying marker color, varying marker size, varying marker
shape.
[0102] The structured light imaging subsystem shown in the example
embodiment is used to generate surface datasets. It includes at
least one illumination device 30 and at least one camera 35. The
illumination device(s) 30 project temporally and/or spatially
modulated light onto the surface to be imaged, while the camera(s)
35 capture images of the illuminated surface. This active
illumination enables robust and efficient identification of pixel
correspondences between calibrated camera-projector (a projector
may be thought of as an inverse camera) or calibrated camera-camera
system. The correspondence (disparity) data can then be transformed
into real-space coordinate data in the coordinate system of the
calibrated camera(s) 35 and/or projector(s) 30 by geometrical
triangulation. During surgery, the structured light imaging system
is positioned such that 3D surface of the surgical site (e.g. the
bony surfaces of the exposed spine 15) is acquired. The created
virtual representation of the 3D surface is then registered to
volumetric image data (e.g. CT, MRI, US, PET, etc.) by processing
unit 50, using, for example, methods described in International
Patent Application No. PCT/CA2011/050257. The volumetric image data
may be pre-operatively acquired, but is not necessarily
pre-operatively acquired. For example, in some applications, the
volumetric image data may also be intra-operatively acquired.
[0103] FIG. 1B provides a block diagram illustrating an example
implementation of a system for surface imaging. Volumetric data 95
is provided to control and processing unit 50 for registration to
intraoperatively acquired surface data. Surface imaging system 92
scans object 1000, and surface topology data is provided to control
and processing unit 50, which is registered with volumetric image
data 95. Tracking system 94 is employed to track the positions and
orientations of surgical instruments, and of a tracking marker
support structure, as described below. A calibration transformation
is determined between the reference frames of the surface imaging
system 92 and the tracking system 94.
[0104] Surface imaging system 92 may be any suitable system for
detecting, measuring, imaging, or otherwise determining the surface
topology of one or more objects using optical radiation or sound
waves (e.g. ultrasound). Non-limiting examples of suitable optical
devices include laser range finders, photogrammetry systems, and
structured light imaging systems, which project surface topology
detection light onto a region of interest, and detect surface
topology light that is scattered or reflected from the region of
interest. The detected optical signals can be used to generate
surface topology datasets consisting of point clouds or meshes.
Other examples using sound waves for determining surface topology
can include ultrasonography.
[0105] FIG. 1B also provides an example implementation of control
and processing unit 50, which includes one or more processors 70
(for example, a CPU/microprocessor or a graphical processing unit,
or a combination of a central processing unit or graphical
processing unit), bus 72, memory 74, which may include random
access memory (RAM) and/or read only memory (ROM), one or more
internal storage devices 76 (e.g. a hard disk drive, compact disk
drive or internal flash memory), a power supply 84, one more
communications interfaces 80, external storage 86, a display 78 and
various input/output devices and/or interfaces 82 (e.g., a
receiver, a transmitter, a speaker, a display, an imaging sensor,
such as those used in a digital still camera or digital video
camera, a clock, an output port, a user input device, such as a
keyboard, a keypad, a mouse, a position tracked stylus, a position
tracked probe, a foot switch, and/or a microphone for capturing
speech commands).
[0106] Control and processing unit 50 may be programmed with
programs, subroutines, applications or modules, which include
executable instructions, which when executed by the processor,
causes the system to perform one or more methods described in the
disclosure. Such instructions may be stored, for example, in memory
74 and/or internal storage 76. In particular, in the example
embodiment shown, registration module 88 includes executable
instructions for generating performing image registration. For
example, registration module 88 may include executable instructions
for performing the methods disclosed herein, such as the methods
illustrated in FIGS. 11A, 11B, 13A, 20 and 21.
[0107] Although only one of each component is illustrated in FIG.
1B, any number of each component can be included in the control and
processing unit 50. For example, a computer typically contains a
number of different data storage media. Furthermore, although bus
72 is depicted as a single connection between all of the
components, it will be appreciated that the bus 72 may represent
one or more circuits, devices or communication channels which link
two or more of the components. For example, in personal computers,
bus 72 often includes or is a motherboard. Control and processing
unit 50 may include many more or less components than those
shown.
[0108] In one embodiment, control and processing unit 50 may be, or
include, a general purpose computer or any other hardware
equivalents. Control and processing unit 50 may also be implemented
as one or more physical devices that are coupled to processor 70
through one of more communications channels or interfaces. For
example, control and processing unit 50 can be implemented using
application specific integrated circuits (ASICs). Alternatively,
control and processing unit 50 can be implemented as a combination
of hardware and software, where the software is loaded into the
processor from the memory or over a network connection. For
example, connections between various components and/or modules in
FIG. 1A, which enable communications of signals or data between
various systems, may be a direct connection such as a bus or
physical cable (e.g. for delivering an electrical or optical
signal), such a LAN or WAN connections, or may be a wireless
connection, for example, as an optical transmission modality, or
wireless transmission modality such as Wifi, NFC or
Zigbee.RTM..
[0109] While some embodiments have been described in the context of
fully functioning computers and computer systems, those skilled in
the art will appreciate that various embodiments are capable of
being distributed as a program product in a variety of forms and
are capable of being applied regardless of the particular type of
machine or computer readable media used to actually effect the
distribution.
[0110] A computer readable medium can be used to store software and
data which when executed by a data processing system causes the
system to perform various methods. The executable software and data
can be stored in various places including for example ROM, volatile
RAM, non-volatile memory and/or cache. Portions of this software
and/or data can be stored in any one of these storage devices. In
general, a machine readable medium includes any mechanism that
provides (i.e., stores and/or transmits) information in a form
accessible by a machine (e.g., a computer, network device, personal
digital assistant, manufacturing tool, any device with a set of one
or more processors, etc.).
[0111] Examples of computer-readable media include but are not
limited to recordable and non-recordable type media such as
volatile and non-volatile memory devices, read only memory (ROM),
random access memory (RAM), flash memory devices, floppy and other
removable disks, magnetic disk storage media, optical storage media
(e.g., compact discs (CDs), digital versatile disks (DVDs), etc.),
among others. The instructions can be embodied in digital and
analog communication links for electrical, optical, acoustical or
other forms of propagated signals, such as carrier waves, infrared
signals, digital signals, and the like. As used herein, the phrases
"computer readable material" and "computer readable storage medium"
refers to all computer-readable media, except for a transitory
propagating signal per se.
[0112] Some aspects of the present disclosure can be embodied, at
least in part, in software. That is, the techniques can be carried
out in a computer system or other data processing system in
response to its processor, such as a microprocessor, executing
sequences of instructions contained in a memory, such as ROM,
volatile RAM, non-volatile memory, cache, magnetic and optical
disks, or a remote storage device. Further, the instructions can be
downloaded into a computing device over a data network in a form of
compiled and linked version. Alternatively, the logic to perform
the processes as discussed above could be implemented in additional
computer and/or machine readable media, such as discrete hardware
components as large-scale integrated circuits (LSI's),
application-specific integrated circuits (ASIC's), or firmware such
as electrically erasable programmable read-only memory (EEPROM's)
and field-programmable gate arrays (FPGAs).
[0113] In order to combine the tracking data with the surface data
for surgical navigation, a calibration procedure is required, which
relates the coordinate system of the tracking system to that of the
surface imaging system. If the relative position of the tracking
system and the surface imaging system is fixed, this calibration
may be performed by obtaining the position of at-least 3 points
from a calibration object from both systems, and aligning these
points to obtain the calibration transformation, as described in
International Patent Application No. PCT/CA2011/050257.
[0114] In an alternative embodiment, as disclosed in International
Patent Application No. PCT/CA2011/050257, the surface imaging
device may have fiducial markers attached to it, which may be
tracked by the tracking system. In this configuration, a
calibration procedure can be used to obtain the calibration
transformation from the coordinate system of the surface system to
the attached fiducial markers. The calibration transformation
between the coordinate system of the tracking system and the
surface imaging system is then continuously updated as the position
of surface imaging device is changed.
[0115] After calibration, the calibration transformation between
the coordinate system of the tracking system and the surface
imaging system is known. Registering the surface datasets and
volumetric image data is therefore equivalent to identifying the
position of the volumetric image data in the coordinate system of
the tracking system. As a result, any medical instrument 40, which
is afterwards tracked with the tracking subsystem, can be presented
to the surgeon as an overlay 55 of the surgical instrument 40 on
the registered 3D image data on a display 60 or other visualization
devices.
[0116] A number of factors can affect the ongoing validity of the
calibration transformation. For example, if the system were to
undergo a significant mechanical impact, the relative positioning
of the surface imaging system and the tracking system may shift
slightly. In another example, the transformation may be dependent
on the ambient temperature in which it is operating and thus only
valid within a specified range of ambient temperatures. In both of
these examples it would be advantageous to validate the accuracy of
the calibration transformation and/or generate a new calibration
transformation at the time of use without impacting the surgical
workflow.
[0117] While much of the discussion which follows assumes the use
of a system having two subsystems (tracking and surface imaging),
it is noted that alternative system configurations may be employed
to perform simultaneous tool tracking and acquisition of anatomical
surfaces using an integrated system, for example by identification
of surface topology on tools, as described in International Patent
Application No. PCT/CA2011/050257. In another example system
configuration, a system can utilize a common pair of cameras for
tool tracking (e.g. via glyphs or reflective spheres) and surface
imaging (e.g. in either the visible or IR). Using the same camera
systems for both tool tracking and surface imaging eliminates the
need for the calibration between the two systems described
above.
[0118] To compensate for patient or system motion, it is also
advantageous to use a tracked device attached to the patient's
anatomy (e.g. to a skeletal feature of the patient's anatomy).
Accordingly, as shown in FIG. 1, the position of a tracking marker
support structure 45 is recorded by the tracking system at the same
time (i.e. within a time duration that is sufficiently small to
preclude errors associated with patient motion) as when the surface
dataset is acquired. The surface dataset is transformed to the
coordinate system of tracking system (using the previously acquired
calibration transformation), and then registered to the volumetric
image data. Subsequent tracking of surgical instruments relative to
the volumetric image data can be performed relative to the tracked
tracking marker support structure, with compensation for patient or
system motion, without the need for continuous acquisition of
surface data.
[0119] During a surgical procedure, it is generally preferred that
tracking marker support structure 45 should not block the
line-of-sight on the surgical target for the surgeon. The risk of
possible obstructions of the surgeon's movement should be minimized
especially when other tracked medical instruments are in the
surgical field, where the tracking attachments could shadow each
other. It would also be beneficial for the surgeon to be able to
securely attach and to remove the tracking marker support structure
with relative ease. This is particularly important for spine
surgery, where normally more than one vertebra are instrumented and
the risk of misplacing by accidentally touching the tracking marker
support structure by the surgeon is high. Furthermore, in order to
minimize costs, a re-useable and sterilizable tracking marker
support structure 45 is preferred. This can be achieved by use of
appropriate materials like for example stainless steel, tungsten
carbide or titanium.
[0120] For surgical guidance using a combination of a tracking
system and a surface imaging system (as illustrated in the example
system shown in FIG. 1), it will be understood that in order to
acquire surface image data, tracking marker support structure 45
should not block the line-of-sight on the surgical target for the
structured light system. To achieve registration with the
volumetric image data, the surface imaging system should cover the
anatomical site of interest in a way that the characteristic
anatomy is represented in the acquired surface data. For example in
a navigated spine procedure, it will aid registration if the
acquired surface captures the surfaces of the lamina and the
spinous process in order to optimize the registration for a
particular level of the spine (vertebrae). However, a tracking
marker support structure can obstruct the visibility of the boney
surfaces to the surface imaging system.
[0121] Attaching the tracking marker support structure to an
adjacent vertebral level can avoid obstruction of the
line-of-sight, but this can reduce the accuracy of the navigation,
since the spine is flexible and the relative positions of the
vertebras can change between the acquisition of the preoperative
images and when the patient is on the operating table. Therefore,
it is beneficial to have a tracking marker support structure that
can be securely attached to the vertebrae that is being operated
on, while minimally obstructing the line-of-sight of the surface
imaging system to the relevant structures of that vertebrae.
[0122] FIG. 2 schematically illustrates an example tracking marker
support structure 45 used for surgical guidance combing a tracking
system and a surface imaging system for performing navigated spinal
surgery. Example tracking marker support structure 45 is shown
including removably attachable gripping mechanism 110, which firmly
and removably attaches to the vertebrae of interest and avoids or
reduces the obscuring of the relevant surfaces--the top of the
spinous process and the laminas--from the line-of-sight of the
surface system and the surgeon. Tracking marker support structure
45 is also shown including locking mechanism 120, which ensures
that the tracking marker support structure 45 remains securely
attached to the vertebrae and can be readily attached and removed.
Tracking marker support structure 45 is also shown having tracking
frame 130 that includes fiducial/tracking markers, which are
tracked by tracking system 94. As noted above, tracking frame 130
should not interfere with the surgeon's use of tools in the
vicinity of the vertebrae to which tracking marker support
structure 45 is attached.
[0123] FIG. 3A shows an example implementation of a tracking marker
support structure 200 which meets the above criteria for a
combination of tracking and surface imaging. This tracking marker
support structure 200 is based on a bone clamp design. It employs
forceps (which may be referred to as a pair of forceps) comprising
two members 205 that define longitudinal axis 201 and pivot around
a pin 210, such that jaws 215 with spikes are rotated to grip the
spinous process.
[0124] As shown in FIG. 3B, a locking mechanism is operably
connected to the forceps. In the present example implementation,
the locking mechanism includes a series of interlocking teeth 220
cooperates with two handles 225 on the other end of the members 205
to allow the surgeon to tighten and to lock tracking marker support
structure 200 in place.
[0125] As shown in FIG. 3A, marker attachment 230 is provided that
includes tracking (fiducial) markers near a distal region thereof,
where a proximal end of marker attachment 230 is mechanically
coupled (e.g. attached, connected, or integrally formed) the
forceps at a location that is remote from the location of clamping
jaws 215, in order to allow the tracking system to track the
position of the tracking marker support structure. In the present
example implementation, the tracking frame is mechanically coupled
to one of the interlocking teeth 220, but it will be understood
that marker attachment 230 may be mechanically coupled to other
portions of the forceps, such as to one of the handles, or to one
of longitudinal members 205. In this example embodiment, three
passive reflective spheres are used as markers 240 for tracking the
position of the tracking marker support structure. However, as
noted above, it will be understood that other configurations and
types of fiducial markers may be employed.
[0126] For clamping, the surgeon holds the tracking marker support
structure 200 with one hand 300 as indicated in FIG. 4. For
example, the surgeon may place the thumb 310 and the middle finger
320 through the two handles 225. The index finger 330 may be
employed to push against pivot pin 210, which helps to further
stabilize the clamp 200 inside the surgeon's hand 300.
[0127] As can be clearly seen in FIG. 3A and in FIG. 4, marker
attachment 230 is angled, relative to longitudinal axis 201, in a
direction toward the patient anatomy, thereby ensuring that the
surgeon's hand 300 will not contact marker attachment 230 or the
markers 240 during clamping. This is a useful feature of the
tracking marker support structure 200 because the surgeon's hand
300 might be covered by blood or other liquids, which could block
the markers 240 and cause interference with the tracking
system.
[0128] To attach or detach the tracking marker support structure
200 to the spinous process, the surgeon will adjust the clamping
force of the interlocking teeth 220 using the handles 225 and
therefore the grip of the jaws 215 onto the interlocked bone. This
locking mechanism can allow the surgeon to change the position of
the tracking marker support structure 200 between two spinous
processes in a short duration, for example, less than 10
seconds.
[0129] As shown in FIGS. 4 and 5, the members 205 of the forceps
extend from the clamping jaws 215 such that when the clamping jaws
are clamped to the spinous process 410 of the vertebra of interest
440, the longitudinal axis 201 associated with the forceps is
angled relative to the Anterior-Posterior (AP) direction 202 that
is associated with the subject, wherein the normal direction lies
in the sagittal plane and is perpendicular to the Superior-Inferior
(SI) 203 direction of the spine, such that a skeletal region 420 or
430 adjacent to the skeletal feature is unobstructed by the
forceps, thereby permitting overhead surface data acquisition of
the skeletal region.
[0130] In the example embodiment shown in FIGS. 3A and 4, clamping
jaws 215 are characterized by a normal axis 204 that is configured
to be perpendicular to the SI direction 203 of the spine when the
clamping jaws 215 are clamped to the spinous process 410. The jaws
215 are therefore configured to uniquely clamp to the spinous
process 410 in a pre-selected orientation, such that the normal
axis 204 of the clamping jaws 215 coincides with the AP direction
202. Accordingly, the attachment of tracking marker support
structure 200 to the patient establishes a reference direction that
is associated with the intraoperative orientation of the patient.
As described below, this reference direction can be employed to
guide the initial registration process between a surface that is
intraoperatively acquired by a surface imaging system and
volumetric imaging data.
[0131] FIG. 5 shows the example tracking marker support structure
200 securely attached to the spinous process 410 of a vertebrae
400. In this configuration, tracking marker support structure 200
is not blocking the view of the surgeon onto the spinous process
410 and the left or the right lamina 420 and 430 respectively, and
maintains a clear imaging field for the surface imaging system. In
addition, the marker attachment 230 with the markers 240 is clearly
visible to the tracking component of the combined navigation
system.
[0132] It will be understood that the locking mechanism shown in
FIG. 2 is but one example of a suitable locking mechanism, and that
a wide variety of alternative locking mechanisms may be employed.
For example, FIG. 6A, illustrates an example embodiment of a
tracking marker support structure 500 that employs a spring locking
mechanism 510. An extension spring 520 pushes the two members 205
together, which tightens the jaws 215 on the opposite side of the
pivot pin 210. The marker attachment 230 with the markers 240 is
connected to one of the members 205. As shown in a more detailed
view in FIG. 6B, extension spring 520 has a guidance wire or pin
530 that is received within extension spring 520. Guidance wire 530
is connected to one spring stopper 540 on one of the members 205
and passes through a hole or aperture in second spring stopper 550
on the other member 205. Another stopper 560 on the guidance wire
530 restricts the range possible movement of members 205. In order
to attach the tracking marker support structure 500 to a spinous
process, the surgeon opens the clamp by pushing apart the handles
225 and holds the reference close to the desired position on the
spinous process. When the handles 225 are released, the extension
spring 520 is automatically clamping the tracking marker support
structure 500 onto the spinous process.
[0133] FIG. 7A shows another example implementation of a tracking
marker support structure 600, which may be used for combined
tracking and structured light imaging. Again, two longitudinal
members, 630 and 640 respectively, with jaws 215 for clamping onto
the bone are connected via a pivot pin 210. In the present example
embodiment, the marker attachment 230 with the markers 240 is a
rigid extension of one of the members 630 beyond the pivot pin 210.
A thumb-screw mechanism 610 is used to tighten or loosen the grip
of the clamp onto the bone and to lock jaws 215 in place. The
mechanism is shown in more detail in FIG. 7B. A threaded spindle
660 is positioned between two cylinder holders 670, which are
connected to the two members 630 and 640 of the clamp by a
rotational axis 680. The surgeon can attach or detach the tracking
marker support structure 600 using the rotation wheel 690 on the
spindle 660. The thread on the spindle 660 is self-locking so that
the attachment of the tracking marker support structure 600 is
secure when the rotation wheel 690 is not used.
[0134] In an alternative example implementation, instead of
positioning the thumb-screw mechanism 610 and the clamping jaws 215
on the same side of the pivot pin 210, they can be on opposite
sides. For example, in the embodiment shown in FIG. 8A, the marker
attachment 230 with the markers 240 of tracking marker support
structure 700 is connected directly to the pivot pin 210 and
integrates the rotation wheel 650 of the thumb-screw mechanism 710
using a slit 720 (for detailed view see FIG. 8B).
[0135] The three example locking mechanisms described above
(interlocking teeth, extension spring and thumb-screw) allow an
easy, fast and secure attachment of the tracking marker support
structure to the spinous process. However, as noted above, persons
skilled in the art will understand that similar locking mechanisms
may be employed.
[0136] FIGS. 9A-I show different jaw 215 designs for the gripping
mechanism 110 (see FIG. 2), which could be used, for example, to
attach the tracking marker support structure to a spinous process.
FIG. 9A and show a rectangular plate configuration for gripping
flat surfaces such as those found in the lumbar and lower thoracic
region of the spine. The surface is carrying a number of coned
spikes, which increase the grip when the jaw is pressed onto the
bone. The number and position of spikes may vary for the specific
design. The connection to the member 205 is on the short side of
the rectangular plate. However, it will be understood that this
connection could be also be made on the long side of the
rectangular plate, for example, as shown in FIGS. 9C and D, if the
tracking marker support structure should be employed for shorter
spinous processes.
[0137] In other embodiments, the jaws may be configured to include
two or more fingers. For example, FIGS. 9E and F show an example
two finger configuration which is more suitable for rough bone
surfaces. FIGS. 9G to I show an alternative example two finger
configuration with four sloped spikes.
[0138] FIGS. 10A-H shows additional example jaw 215 designs based
on curved plates. An example angled bracket gripping plate, as
shown in FIGS. 10A and B are more suitable for gripping the rounded
spinous processes located in the upper thoracic and cervical
regions of the spine.
[0139] FIGS. 10C and D show a curved bracket also useful for the
upper thoracic and cervical regions of the spine.
[0140] FIGS. 10E to H show a number of gripping plate
configurations which are capable of achieving good grip in any
region of the spine due to the combination of a flat plate region
and curved or angled structures. More specifically, the example
gripping plate (jaw) configurations shown in FIG. 10F and FIG. 10H
each include co-planar flat surfaces 805 and 810, and also include
an inwardly directed surface connecting the two outer flat surfaces
805 and 810, such that the clamping jaws are configured for
clamping to a wide range of spinous process geometries. In FIG.
10E, the inwardly directed surface 820 is formed from two planar
surface segments. FIG. 10H illustrates an alternative
implementation in which the inwardly directed surface 830 is a
curved surface. The outer flat surfaces 805 and 810 and the
inwardly directed surfaces 815 and 820 each comprise spikes.
[0141] It will be understood that the clamping jaw configurations
shown in FIGS. 9A-I and FIGS. 10A-H may be provided with any type
of surgical clamping device, irrespective of whether or not the
clamping device includes a tracking frame. Furthermore, those
skilled in the art will understand that a wide variety of
alternative jaw (gripping plate) geometries and configurations may
be employed in addition to the example implementations shown in
FIGS. 9A-I and FIGS. 10A-H.
[0142] In the example embodiments provided below, examples of the
use of a tracking marker support structure during surgical guidance
are described. It will be understood, however, that the use of the
tracking marker support structure, and the methods below, while
being explained within the example context of spinal surgical
procedures, may be adapted to, and employed in, a wide range of
other surgical procedures. Examples of additional surgical
procedures that may benefit from the use of the present devices and
methods disclosed herein are provided below.
[0143] In the present non-limiting example, at the beginning of a
navigated posterior approach spine surgery, the patient is placed
in a prone (face-down) configuration on the operating table (see
FIG. 1) and anesthesia is administered. The surgeon approaches the
spine of the patient from the back and exposes the boney surface of
the vertebrae of interest by retracting soft tissue components.
[0144] Preparing the patient, the navigated portion of the surgery
begins, which is illustrated in the example flow chart shown in
FIG. 11A. In step 1010, the tracking marker support structure 45 is
securely attached to the spinous process of the vertebrae to be
navigated. In step 1020, the surface imaging system (such as a
structured light system) acquires a surface scan of the vertebrae,
and the tracking system is employed to record the position of the
tracking marker support structure 45 using triangulation of the
markers (e.g. passive optical fiducial markers 240 shown in FIG.
3A).
[0145] In step 1030, surgical guidance system may be provided with
registration support information that may be to facilitate and/or
improve the efficiency or accuracy of the registration of the
acquired surface to the volumetric (e.g. pre-operatively acquired)
image data (as described in further detail below). In step 1040,
the registration process utilizes the acquired surfaces of the
visible lamina and/or spinous process regions and the registration
support information to register the volumetric image data (e.g.
from a CT scan).
[0146] Once the registration is complete, the system can present an
overlaid image, as shown in step 1050, of any tracked tool relative
to the registered volumetric image data for navigation of the
surgical procedure on the vertebrae (e.g. insertion of pedicle
screws). The tracking marker support structure allows the surgical
guidance system to detect, and compensate for, any movement (due to
respiration, patient movement, or system movement) of the vertebrae
during the navigation, without requiring acquisition and
registration of additional surface data to the volumetric image
data. In step 1060, the surgeon removes the tracking marker support
structure from the vertebrae and optionally restarts the process on
the next vertebrae if desired. This process may thus be repeated
one or more times to address one or more vertebral levels.
[0147] FIG. 11B illustrates an example method for performing
registration when the aforementioned process is repeated for an
additional vertebral level. In this example method, the method of
clamping and registering to a 1.sup.st spinous process shown in
FIG. 10A is repeated. However, after removal of tracking marker
support structure 1060, the tracking marker support is re-clamped
to a 2.sup.nd spinous process 1015. In step 1025 a second surface
scan and position is recorded by the surface imaging system and
tracking system respectively. Position data from the tracking
system acquired in step 1020 from the 1.sup.st vertebral body is
combined with position data acquired in step 1025 from the 2.sup.nd
vertebral body to calculate additional registration support data
1035. Examples of such data include estimates of axial direction of
the spine (can be used as an initial condition for the registration
1040) and the approximate spacing between vertebral bodies (which
can be used to specify cropping region for the registration
procedure 1040). It is noted that even if the tracking marker
support is not moved to an adjacent level, it is still possible to
estimate the mean distance between vertebral bodies since standard
practice ensures the surgeon always specifies (through a user
interface element) the level on which they have placed the
clamp.
[0148] In one example implementation of the process illustrated in
FIGS. 11A and 11B, the surgeon or system operator may be queried to
provide the registration support information. For example, in step
1030, the surgeon or system operator may be requested to indicate a
set of matched point pairs on the pre-operative scan and the
patient's body as initial information to guide the registration
process (for example, three point pairs may be requested and
provided). The points can be selected, for example, on the
patient's body using a tracked tool touching the patient's anatomy,
or virtually on the acquired surface (touch-less registration).
Typical point selection for spine surgery may include 1 point on
each of the left and right lamina and top of the spinous process
(or the ligament which runs over it).
[0149] In another embodiment, a set of different registration
support information could be provided and employed in step 1030.
For example, one piece of registration support information could be
information specifying a particular anatomical direction in the
acquired surface, for example the head-foot (superior-inferior)
direction.
[0150] This information can be obtained by querying the surgeon or
operator, or for example, by inferring this direction through the
positioning of the system relative to the patient. For example, if
the system is positioned near the head of the operating table then
the head-foot direction can be estimated with sufficient accuracy
for registration. FIG. 12A shows an example of graphical user
interface, where the surgeon or system operator can specify the
orientation of the system at the start of the surgery. This
information can be used together with the known patient positioning
during the pre-operative imaging (which is normally stored inside
the data header) as registration support information (i.e. a priori
information) to support the registration process.
[0151] In addition or alternatively, the surgeon or system operator
can be queried to enter the procedure specific information (e.g.
surgery type, patient positioning, surgical approach or incision
orientation) at the start of the surgery using a graphical user
interface similar to the one shown in FIG. 12A. For example, a
patient undergoing a posterior approach spine surgery will be in a
prone (face down) position on the operating table, which allows to
infer the anterior-posterior direction in the acquired surface
(since the system is always located above the patient). This
information could alternatively be obtained based on a
pre-determined surgical plan.
[0152] Another form of registration support information could be
one matched point pair selected on the pre-operative scan and the
patient's body or acquired surface. A convenient point for a
matched point pair could be the top of the spinous process of the
vertebrae of interest. Instead of asking the surgeon or system
operator to select the point on the spinous process, the known
attachment point of the tracking marker support structure can be
used. Assuming that the attachment point of the clamp is always to
the spinous process, the location of the spinous process on the
patient can be approximated using the tracked tracking marker
support structure position from the tracking system.
[0153] In several of the embodiments described herein, the tracking
marker support structure is configured to be attached a given
skeletal feature in a known relative orientation. The skeletal
feature may be a skeletal projection, such as a spinous process.
Such a skeletal feature has, associated therewith, a known
anatomical direction in the sagittal plane. For example, in the
example application of spinal surgical procedures, the tracking
marker support structures described herein are configured to clamp
to the spinous process such that the tracking marker support
structure is attached to the patient anatomy in a fixed position
and orientation relative to the point of attachment. For example,
the tracking marker support structure shown in FIG. 5 is configured
to clamp onto the spinous process in a pre-selected orientation
that automatically determines the inferior-superior direction of
the spine.
[0154] This known orientation of the tracking marker support
structure, relative to the patient anatomy, allows for the
determination of an intraoperative reference direction associated
with the intraoperative position and orientation of the patient.
This intraoperative reference direction may then be used,
optionally with additional registration support information (such
as one or more matched point pairs), as an input to the
registration process, in order to improve the efficiency and/or
accuracy of the registration process. As noted above, as the
volumetric image data typically has orientation information in a
header file, and therefore, determining an intraoperative reference
direction associated with the intraoperative patient orientation,
and thus the intraoperative orientation of the acquired surface,
can be beneficial in increasing the efficiency and/or accuracy of
the registration process.
[0155] For example, the intraoperative position and orientation of
the patient (or at least of the local anatomical region of
interest) can be determined based on the measured position of the
tracking marker support structure, due to the known orientation of
the tracking marker support structure relative to the skeletal
feature, and the calibration transformation between the reference
frame of the surface imaging device and the reference frame of the
tracking system.
[0156] A full set of registration support information that is
sufficient for the registration process may require a combination
of the above mentioned types of registration support information.
As noted above, in some embodiments, the registration support
information may include information associated with the position
and/or orientation of the tracking marker support structure, such
as the position of attachment (that is associated with a known
anatomical feature), and/or the orientation of the tracking marker
support structure relative to the orientation of the known
anatomical feature.
[0157] The surface imaging system has generally a field of view
that is much larger than the exposed vertebrae of interest in order
to enable the surgeon to operate on multiple vertebrae levels
without having to reposition the system each time. The additional
surface regions outside the immediate vicinity of the vertebrae of
interest generally do not help with the registration. Indeed, these
additional surface regions can be detrimental, potentially causing
an incorrect registration, if the spine in the operating room is
not in the same position as during the pre-operative imaging or if
soft tissue surfaces at the surgical incision borders are
scanned.
[0158] In one example embodiment, the tracking marker support
structure 45 is used to provide a spatial reference to determine
where to segment the acquired surface, so that only the immediate
surroundings of the vertebrae of interest is kept for
registration.
[0159] Before this segmentation is performed, the spatial position
of the tracking marker support structure 45 from the tracking
system is first transformed into the coordinate system of the
surface imaging system using the known calibration transformation
between the two systems. The segmentation is then performed by
cropping the surface data using a suitable mask within spatial
region or within a prescribed distance associated with the position
of attachment of the tracking marker support structure. For
example, a spherical mask surrounding the point of attachment may
be employed to determine the spatial region over where the acquired
surface is to be cropped as per the segmentation process.
[0160] This segmentation creates a partial surface covering mainly
the vertebrae of interest for the registration. Other masking
geometries can be used for the cropping of the surface data.
Examples are rectangular boxes, cylindrical discs or other types of
prisms with the main axis aligned to the spine, where the alignment
can be determined from the position of the clamping axis of the
tracking marker support structure, which is aligned with the
spinous process.
[0161] Examples of such cropping structures are shown in FIG.
12B-12G and include spherical, cigar shaped and patient specific
cropping masks. In these examples it is useful to define the marker
support structure tracking point 206 at the intersection of jaws
215 and members 210 on the member connecting rigidly to marker
attachment 230.
[0162] In FIGS. 12B and 12C, a spherical cropping region 208 is
shown centered on marker support structure tracking point 206. In
FIGS. 12D and 12E, a cigar shaped cropping mask 208 not centered on
maker support structure tracking point 206 is shown. In FIGS. 12F
and 12G, a patient specific cropping mask generated from CT scan
data is shown. Lastly, in FIGS. 12H and 12I a simple box cropping
region centered on marker support structure tracking point 206 is
shown.
[0163] These cropping masks may be used independently or in
conjunction with one another at different stages of the
registration process. For example, at an early stage of the
registration process a large spherical region may be used to align
multiple vertebral bodies in the surface data to volumetric images.
In a second stage a cigar shaped cropping region may be used to
refine the registration of the specific vertebral level. Finally,
in a third stage a tight patient specific cropping mask generated
from the preoperative CT scan of the particular level (through the
use of registration support information) can be used to further
refine the registration.
[0164] As mentioned before, the calibration of the surface imaging
system to tracking system enables surface imaging based surgical
guidance. However, the validity of the calibration transformation
can be compromised, if the relative position between the tracking
system and surfacing imaging system changed, for instance, due to
physical impact.
[0165] In one example embodiment, the tracking marker support
structure 45 is employed to compute a real-time calibration
transformation between the tracking system and the surface imaging
system, for example, to assess the validity of the previously
determined calibration transformation. As described below, this can
be achieved by performing surface detection to determine the
position and orientation of the tracking marker support structure
in the reference frame of the surface imaging system, and comparing
this position with the position of the tracking marker support
structure that is determined by the tracking system based on the
detection of signals from the markers, where the comparison employs
the last calibration transformation (the previously determined
calibration transformation). The validity of the last calibration
transformation can therefore be assessed by determining whether or
not the computed position and orientation are within a prescribed
tolerance.
[0166] This method may be performed at any time before or during a
surgical procedure, such as at each time registration is performed,
and optionally each time a tracking marker support structure is
attached to a new skeletal feature of a patient. For example, in
the case of a spinal surgical procedure, the method may be
performed or repeated when the tracking marker support structure
(or an additional tracking marker support structure) is attached to
a new vertebral level.
[0167] This method will be referred to herein as "active
calibration" and an example process diagram is illustrated in FIG.
13A. The method includes some additional steps when compared to the
process shown in FIG. 11 after attachment 1010 of the tracking
marker support structure to the spinous process and acquisition of
a surface of the surgical field 1020.
[0168] For active calibration, as shown in FIG. 13A, the acquired
surface should include at least a portion of the tracking marker
support structure 45, where the portion that is included has
sufficient surface topology (i.e. includes one or more reference
structures or surface features) to allow for the determination of
the position and orientation of the tracking maker support
structure via surface imaging. This is generally easily facilitated
in the example case of a spinal surgical procedure because the
tracking marker support structure 45 is typically directly attached
to the vertebrae of interest.
[0169] Assuming that the previously determined calibration
transformation is still sufficiently accurate, the transformation
from the last calibration 1210 between the surface imaging system
and tracking system can be used to identify a subregion within
which to segment surface data associated with the tracking marker
support structure from the acquired surface based on position
tracked by the tracking system in step 1220.
[0170] Since the tracking marker support structure is normally an
isolated spatial structure, a simple cropping with a mask (e.g. a
spherical mask) around the position predicted with the last
calibration 1210 will likely be sufficient in step 1220. However,
other cropping masks can be envisioned based on the known shape of
the tracking marker support structure. FIGS. 13B and 13C depict
examples of a spherical 1270 and a more conformal cropping mask
1280 for the marker support structure shown previously in FIGS. 3A
and 3B.
[0171] Referring again to FIG. 13A, step 1230, the segmented
tracking marker support structure from the acquired surface is
registered to reference surface data characterizing the known
surface of the tracking marker support structure (for example, a
3D-model of the tracking marker support structure or, for example,
to a previously acquired surface of the tracking marker support
structure) based on the position and orientation as currently
measured by the tracking system, which yields in an active
calibration transformation at the time of the surface acquisition
1020.
[0172] The active calibration is compared to the last calibration
1210 in step 1240 and 1250. If the active and the last calibration
transformation lie within a specified tolerance, the last
calibration transformation is deemed valid and may be used for the
following registration (alternatively, the new calibration
transformation may be used for future imaging registration).
However, if the calibration transformations do not agree within the
specific tolerance, the last calibration transformation is deemed
invalid. The last calibration transformation may be automatically
replaced with the active calibration transformation in step 1260
(alternatively, a new calibration transformation may be performed
using a calibration reference device).
[0173] After this decision, the registration process continues at
step 1030, in which registration support information is received,
and at 1040 in which the acquired surface is registered with the
volumetric images (either using the last calibration
transformation--if valid--or with the updated active calibration
transformation). The calibration transformation (last or newly
updated) may then be used, as shown at 1050, for the tracking of
surgical tools. After the surgical procedure is complete, or when a
portion of the surgical procedure is complete (e.g. the portion
pertaining to the position of the anatomical feature to which the
tracking marker support structure is fixed, such as a given
vertebral level) and the tracking marker support structure may be
removed from the spinous process as shown at 1060.
[0174] It will be understood that steps 1230 and 1240 of FIG. 13A
may be performed according to several different methods. For
example, as described above, a new calibration transformation can
be calculated (the active transformation), and compared to the last
calibration transformation. In another example, the segmented
surface data, registered to the reference surface data, can be
used, with the last calibration transformation, to predict the
current position of the tracking marker support structure, in the
reference frame of the tracking system. This predicted position can
be compared to the position that is currently measured by the
tracking system. If the predicted and measured positions are within
a prescribed tolerance, the last calibration transformation may be
deemed to be valid. On the other hand, if the predicted and
measured positions are outside of the prescribed tolerance, the
last calibration transformation may be deemed to be invalid, and a
new calibration transformation may be computed that results in the
predicted position agreeing with the measured position. It will be
understood that the comparisons between the positions may be made
in the reference frame of the tracking system, or in the reference
frame of the surface imaging system, according to variations of the
aforementioned methods.
[0175] FIGS. 14A-E show an example of the data outputs from the
main steps of the process diagram illustrated in FIG. 13A. The
surface image acquired in step 1020 is shown in FIG. 14A. The
tracking marker support structure 1310 (showing some parts and the
corresponding shadows) is attached to a spinous process 1320, which
is going to be tracked after the registration. The tracking frame
1330 with the markers 1340 is clearly visible in the surface image
and is used in this example for the active calibration.
[0176] Using the marker positions acquired by the tracking system
and the last calibration transformation, a spatial subregion is
identified that is associated with the estimated position and
orientation of the tracking marker support structure, such that at
least a portion of the tracking marker support structure (in the
present case, the tracking frame 1330) may be segmented in step
1220 from the surface image as shown in FIG. 14B. The known
3D-model 1350 of the tracking frame is shown in FIG. 14C. If the
last calibration is invalid or corrupted, the calibration
transformation of the 3D-model 1350 to the surface image 1330 of
the tracking frame based on the tracking data results in a clear
misalignment as shown in FIG. 14C. FIG. 14E shows the result after
a registration of the data shown in FIG. 14D in step 1230. This
yields in a new calibration transformation which may be employed,
after the steps 1240 and 1250, as the active calibration
transformation in step 1260.
[0177] In one example implementation of the aforementioned active
calibration method, the system may provide a warning to the surgeon
or system operator in step 1260 (see FIG. 13), if in the
calibration test 1240 and 1250 the active and the last calibration
transformation are not identical within a specified tolerance. For
example, the user might be asked to provide input instruction
whether the registration should be continued using the last
calibration transformation, or using the active calibration, or
even aborted.
[0178] Although the active calibration method is described above
using a tracking marker support structure that is attached to an
anatomical structure of the patient (e.g. a spinous process), it
will be understood that in other example implementations, any other
tool or tracking marker support structure with known 3D-design can
be used for active calibration, provided that the tool is tracked
during the acquisition of the structural light and visible in the
acquired surface.
[0179] In other example embodiments, the shape of the tracking
frame (e.g. tracking frame 130 as shown in FIG. 2) can be designed
so that the surface imaging system will always acquire a reference
surface that is suitable (or optimal) for registration. For
example, reference surfaces that may be incorporated into the shape
of the tracking marker support structure include geometrical
features such as pyramids, cubes, steps or chamfers, or other such
features that ensure that the surface imaging system will acquire a
surface from multiple possible views (i.e. relative positions
between surface imaging system and tool).
[0180] For example, FIG. 15 illustrates an example implementation
of a tracking marker support structure 1400 that incorporates an
additional surface 1410 with characteristic structures 1420. These
characteristic structures provide additional non-symmetric surfaces
useful for the registration process. First, they enable the
registration to be unique, whereas simple planar or spherical
structures which have high degrees of symmetry may lead to
registration ambiguity. Second, they reduce the probability of
overexposure by the surface imaging system and/or ambient lighting
conditions on all characteristic structures simultaneously.
Furthermore, surface properties (roughness/reflectivity) of
characteristic structures can also be tuned in order to optimize
surface image acquisition based on surface imaging system
specification and ambient environmental condition in which surface
imaging system is meant to be used.
[0181] FIG. 16 itemizes characteristic features of the tracking
marker support structure and provides a description as to how to
select the parameter values for a given surgical application.
[0182] FIG. 17 shows a generalized profile 1500 of a tracking
marker support structure used for navigation of spinal procedures.
The profile includes the gripping jaws 215, the members 205, pin
210 connecting the members, and marker attachment 230. The arrow
1510 indicates the line-of-view of the combined tracking and a
surface imaging system onto the tracking marker support structure
during an example intended use with a patient lying in the prone
position.
[0183] FIG. 17 defines identifies a set of characteristic
geometrical parameters of the example tracking marker support
structure. Example values for these dimensions for the example
application of spinal surgical procedures are specified in FIG.
18.
[0184] Referring to FIG. 18, the length 1520 and width 1525 of the
gripping tips 215 are given by the typical dimensions of a spinous
process, to which the tracking marker support structure will be
clamped. It can be advantageous to maximize the overlap of the
clamping surface of the jaws with the spinous process in order to
counteract the torque and to ensure stable attachment of the clamp
to the spinous process. It will therefore be understood that a
suitable size of the jaws 215 may depend on the anatomical regions
of the spine (lumbar, thoracic and cervical) to which the device is
to be attached. It will also be understand that the suitable size
of the jaws may vary depending on the patient subgroups (for
example pediatric vs. geriatric vs. healthy adult).
[0185] Referring again to FIG. 17, in order to avoid blocking of
the line-of-sight 1510 of the surface imaging system onto the
lateral laminae, the thickness of the gripping jaws should be as
small as possible without compromising the mechanical integrity of
the material. The angle 1530 subtended between normal direction
1540 and a longitudinal axis associated with members 210 should be
greater than approximately 20.degree. (e.g. between 20.degree. and
40.degree.), so that the tracking markers are not positioned
directly above the surface of the spinous process.
[0186] It is also noted that pivot pin 210, which is located
between members 205, could potentially block the line-of-sight onto
the spinous process. Therefore, a minimal distance 1570 between
pivot point 210 and to jaws 215 (along a longitudinal axis
associated with members 205) can be beneficial, depending on the
angle 1530 of the members 205. On the other hand, the necessary
gripping force and mechanism as well as the spread of distal arms
when releasing the clamping mechanism will define the position of
the pivot pin 210.
[0187] As described above, the tracking marker support structure is
intended to track the motion of the patient, as characterized by
motion of the spinous process. Therefore, tracking marker support
structure should not contact any other structures in the surgical
cavity, which could transfer unwanted motion to the marker
attachment 230. However, the marker attachment 230 requires a
minimal profile size in order to achieve good tracking
characteristics and might be close or even bigger than the profile
of the surgical cavity. It is therefore advantageous that the
marker attachment lie outside the surgical cavity when the tracking
marker support structure is attached to the spinous process.
[0188] This can be achieved, for example, by positioning the marker
attachment 230 such that marker attachment 230 resides at a
perpendicular offset 1540 relative to of approximately 80 mm.
[0189] However, the overall size of the tracking marker support
structure should be as small as possible to avoid blocking the
surgeon's movement or the placement of other surgical instruments,
such as, for example, a surgical microscope. Therefore, the
perpendicular offset 1540 of the marker attachment relative to the
gripping tip 1530 should not be above approximately 120 mm.
[0190] Another relevant issue is the potential for collision,
shadowing or other interference between the tracking marker support
structure and other tracked surgical instruments. Tracked surgical
instruments commonly employ a set of fiducial markers that are
positioned within a spatial region having a radius of approximately
40-70 mm relative to the shaft of the tracked instrument.
[0191] To avoid shadowing of such tracked tools by the marker
attachment of the tracking marker support structure, the distance
between marker attachment and jaws should be approximately 70 mm or
more. This places the marker attachment at a distance that is
sufficiently far from the surgical region of interest to result in
spatial interference with tracked surgical tools. This distance
also ensures that the marker attachment 230 of the tracking marker
support structure will not obscure the line-of-sight for the
surgeon or the structural light system 1510 onto the vertebra.
[0192] Because of the potential for the marker attachment, which
may include addition surfaces 1410 and addition characteristic
structures 1420, to weigh significantly more than the rest of the
tracking marker support structure, a longer distance between marker
attachment and the gripping jaws increases the torque applied about
gripping jaws, which could damage the clamped tracking marker
support structure or require a gripping force which might break the
spinous process onto which it is being clamped.
[0193] As can be seen from FIG. 17, the horizontal distance D-1550
between marker attachment 230 and gripping jaws 215 and the
distance H-1540 of the marker attachment 230 relative to the
gripping tip 215 directly define the direction of the members 205
and therefore the angle .alpha. 1530 towards the gripping tip 215.
The combined tracking and surface imaging system is normally
positioned directly above the surgical cavity, which allows a
direct line-of-sight 1510 with minimal shadowing effects. Since the
marker attachment 230 should be perpendicular to optical axis 1510
to ensure optimal tracking, the angle of the marker attachment 1560
should be in the range between 70.degree. and 110.degree..
[0194] Although the angles shown in the examples provided herein
are shown as fixed angles, it will be understood that any or all
angles may be replaced by adjustable angles having lockable joints
which span the angular ranges specified or a subset of these
ranges. Likewise, although the lengths of various components and
members shown in the examples provided herein are shown being
fixed, it will be understood that any or all lengths may be
replaced by adjustable lengths (e.g. via telescopic members that
are slidably engaged) having two or more lockable configurations
that span the length ranges specified or a subset of these
ranges.
[0195] In will be understood that any or all angles, which are
shown as discontinuities in the profile in FIG. 17, may be replaced
by smooth arcs or other shapes, which cover the same angular and
distance range. For example, it will be understood that angles
described and claimed herein may refer to the local angles at the
point of attachment of one component to another, or to virtual
angles associated with the intersection of the longitudinal axes
associated with various components.
[0196] Other tracking marker support structures designs based on
the feature set described in FIG. 16 can be generated for different
anatomical locations. In fact, many of the realizations of tracking
marker support structure shown in the examples provided herein can
be employed in orthopedic shoulder surgery, where the tracking
marker support structure is clamped to the spine of the
scapula.
[0197] In other surgical applications, the tracking marker support
structure could be configured, for example, according to FIG. 16
and based on the local anatomy.
[0198] An example of a tracking marker support structure based on
the feature set shown in FIG. 16 and pertaining to cranial and/or
maxillofacial surgical applications is shown in FIG. 19A and FIG.
19B. In this example implementation, the tracking marker support
structure 1600 comprises a mouth guard like portion 1610 which is
clamped inside the mouth to either the upper (FIG. 19A) or lower
(FIG. 19B) part of the jaw/teeth, depending on whether the lower
member or the remainder of the skull is to be tracked. The tracking
frame 1620 protrudes from the mouth such that it is visible to the
navigation system and a screw based hinge mechanism 1630 is used to
lock the clamp in place. A detailed view of the back and the front
of the mouth guard and the screw based hinge mechanism is shown in
FIG. 19C and FIG. 19D respectively. To connect the tracking marker
support structure 1600, the mouth guard 1610 is pressed onto of the
line of teeth. By tightening the two screws 1640 of the hinge
mechanism 1630, the teeth is clamped between two fixation plates
1650 and the inner rim of the mouth guard 1660. Loosening the
screws 1640, the marker support structure 1600 is removed from the
teeth. This example provides another illustrative embodiment of a
tracking marker support structure that is configured to attach to
patient anatomy in a pre-selected orientation, which, as described
above, may be useful in providing registration support information
for use in performing registration of acquired surface data with
volumetric image data.
[0199] FIG. 19E shows a generalized profile of tracking marker
support structure suitable for cranial and/or maxillofacial
surgical applications. The profile's main features include marker
attachment 1620 and clamping jaws 1650. The arrow 1510 indicates
the line-of-view of the combined tracking and a surface imaging
system onto the tracking marker support structure during an example
intended use with a patient held in a stereotactic frame in a
supine position. Much of the same motivation for features,
dimensions and angles of generalized tracking marker support
structure 1500, which is suitable for spine surgery and shown in
FIG. 17, also directly carry over to this application. Examples
values for dimensions and angles are shown in FIG. 19F. FIG. 22A-D
shows an example of a tracking marker support structure 2100 for
neurosurgical applications. The tracking marker support structure
2100 is used after the soft tissue has been retracted from the
skull and one or more perforator holes have been made. The marker
support structure hook 2110 is inserted into one of the perforator
holes 2125 with hook 2110 positioned between the dura and the
skull. During insertion the hook is positioned pointing away from
the skull flap 2140 such that clamping is maintained after skull
flap removal and good visualization of the cortical surface is
maintained. The set screw 2105 is used to fix the tracking marker
support structure into place using jaw 2120. Next registration to
the skull surface is performed using the systems and methods
described above. Finally the skull flap 2140 is removed and the
navigated surgical procedure progresses in a standard fashion.
Alternatively the surface of the brain or other internal structure
could also be used for registration after skull flap 2140 has been
removed. FIG. 22E shows a generalized profile of tracking marker
support structure 2100 suitable for cranial procedures. Key
features include jaw 2325 and marker attachment 230. Examples
values for dimensions and angles for the generalized profile shown
in FIG. 22E are shown in FIG. 22F. Dimensions for hook width is
driven by the typical size of the perforator hole while the
distance between the jaw and the hook is driven by typical skull
thickness. Other distances ranges are specified primarily for not
obstructing the line-of-sight of the tracking system and the
surgeon's range of motion.
[0200] FIG. 20 shows a flow chart illustrating an example method in
which a surface imaging based surgical guidance system is used to
detect whether or not the tracking marker support structure has
been bumped or moved intraoperatively from its initial position.
The method involves intraoperatively reacquiring the surface data
for the anatomical region of interest, and recording the current
location of the tracking marker support structure as shown in step
1710. The new surface data is registered to the initially acquired
surface data in step 1720, in order to obtain an intraoperative
transformation within the reference frame of the surface imaging
system. The intraoperative transformation is then employed to
estimate the current position and orientation of the tracking
marker support structure in the reference frame of the tracking
system, based on the previously known position of the tracking
marker support structure, as shown at step 1730. If there has been
little or no movement of the tracking marker support structure
position relative to the patient, then the transformations
describing the tracking marker support structure motion and patient
surface motion between the two time points will lie within a
pre-selected threshold. In other words, the intraoperative
transformation can be compared to the difference between the
current and previous position and orientation of the tracking
marker support structure, in order to detect a change in the
position and orientation of the tracking marker support structure
relative to the patient.
[0201] This check is performed in step 1740 with the output 1750
either triggering a warning (e.g. alerting a user of the system)
and potentially stopping tracking 1760, if the transformations are
significantly different or allowing the tracking to continue if the
change in the relative position and orientation of the tracking
marker support structure lies within a pre-selected tolerance. This
procedure can be performed at any time after initial attachment of
the tracking marker support structure to the patient anatomy. For
example, the method may be performed at a pre-selected frequency,
or, for example, on demand as initiated by the surgeon or operator,
or for example, each time a new step in the surgical plan is to be
executed.
[0202] It will be understood that the verification procedure
described above and shown in FIG. 20 is equally valid if the
surface imaging subsystem is used to measure the new position of
the tracking marker support structure (for comparison with the
estimated position). It is also to be understood that the active
calibration procedure described in FIG. 13 can also be applied in
combination with the verification method in order to simultaneously
mitigate effects of relative motion between the surface imaging
subsystem and tracking subsystem.
[0203] In another embodiment, a method of data segmentation
pertaining to surface imaging surgical guidance system is
presented. In some applications, it may be advantageous to remove
surface data pertaining to instruments tracked by the tracking
system from the surface data acquired by the surface imaging
subsystem. This can be accomplished, for example, by using a known
shape or geometry (e.g. as provided by CAD/engineering design files
or a known 3D model) of tools being tracked by the tracking
subsystem.
[0204] In one example implementation, the method involves
intraoperatively acquiring the surface data using a surface imaging
system, the surface data including surface artifacts associated
with the surface of an instrument, detecting, with a tracking
system, signals associated with the fiducial markers located on the
instrument, and processing the signals to determine an
intraoperative position and orientation of the instrument. The
intraoperative position and orientation of the instrument may then
be used, along with the calibration transformation between the
reference frames associated with the tracking system and the
surface imaging system, to determine a suitable position and
orientation of a cropping mask for removal of the surface artifacts
associated with the instrument. The cropping mask, correctly
positioned relative to the surface data (e.g. where the cropping
mask has been transformed into the reference frame of the surface
imaging device), may then be employed to segment the surface data
to remove the surface artifacts within the region associated with
the cropping mask.
[0205] FIG. 21 is a flow chart illustrating such an example method
of performing selective surface segmentation based on known
properties of tools or instruments that may be present within the
field of view of a surface imaging system. First, in step 1810, a
tool-specific cropping region is generated based on the known
geometrical properties of the tool CAD file. As shown at step 1820,
the tool position and orientation is determined (e.g. measured with
the tracking system) when surface data of the anatomical region is
acquired. The cropping region is positioned and oriented based on
the detected position and orientation of the tool, as determined
based on data acquired from the tracking subsystem. This cropping
region may be initially specified within the frame of reference of
the tracking subsystem, and then shifted into the coordinate system
of the surface imaging subsystem using the transformation linking
the two subsystems, as shown at step 1830. Alternatively, the
position and orientation of the tool within the reference frame of
the surface imaging system, and the cropping region may be
generated within the reference frame of the surface imaging system.
The cropping region is then used to reject points within the
acquired surface data that lie within the cropping region, as shown
at step 1840. This method, or variations thereof, may be employed
to improve the quality and robustness of the registration process
between surfaced data and volumetric image data and/or surface data
acquired at two or more time points (where surgical tools may be in
two different locations).
[0206] The specific embodiments described above have been shown by
way of example, and it should be understood that these embodiments
may be susceptible to various modifications and alternative forms.
It should be further understood that the claims are not intended to
be limited to the particular forms disclosed, but rather to cover
all modifications, equivalents, and alternatives falling within the
spirit and scope of this disclosure.
* * * * *