U.S. patent application number 10/402499 was filed with the patent office on 2003-10-02 for instrument guidance system for spinal and other surgery.
This patent application is currently assigned to Neutar L.L.C., a Maine corporation. Invention is credited to Franck, Joel I., Franklin, Ronald J., Haer, Frederick C..
Application Number | 20030187351 10/402499 |
Document ID | / |
Family ID | 28457898 |
Filed Date | 2003-10-02 |
United States Patent
Application |
20030187351 |
Kind Code |
A1 |
Franck, Joel I. ; et
al. |
October 2, 2003 |
Instrument guidance system for spinal and other surgery
Abstract
A method and apparatus for positioning a surgical instrument
during stereotactic surgery on a body, for example, during spinal
surgery or general surgery. A mounting device is attached to a bone
structure of the body, for example, by attaching a rail to the
spine for spinal surgery, or a mounting plate and a rod attached to
the mounting plate. In spinal surgery, the rail is attached to the
spine by clamping the rail to two spinous processes and adjusting
the separation of the two spinous processes to match the separation
of the two processes in three-dimensional scanned image, thereby
matching a curvature of the spine with a corresponding curvature of
the spine in the image. Multiple of fiducial points are located on
the body in relation to the mounting device. An adjustable guidance
fixture that includes an instrument guide for guiding the surgical
instrument along a constrained trajectory relative to the
instrument guide is attached to the mounting device. A location and
orientation of the instrument guide is tracked and a position of
the constrained trajectory in the three-dimensional image is
computed. The guidance fixture is adjusted relative to the mounting
device using a first constrained motion followed by a second
constrained motion, so that the constrained trajectory of the
instrument guide passes through the target.
Inventors: |
Franck, Joel I.; (Durham,
ME) ; Haer, Frederick C.; (Brunswick, ME) ;
Franklin, Ronald J.; (Bowdoinham, ME) |
Correspondence
Address: |
FISH & RICHARDSON PC
225 FRANKLIN ST
BOSTON
MA
02110
US
|
Assignee: |
Neutar L.L.C., a Maine
corporation
|
Family ID: |
28457898 |
Appl. No.: |
10/402499 |
Filed: |
March 28, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10402499 |
Mar 28, 2003 |
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09317676 |
May 24, 1999 |
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6546277 |
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09317676 |
May 24, 1999 |
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09063658 |
Apr 21, 1998 |
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09317676 |
May 24, 1999 |
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09063930 |
Apr 21, 1998 |
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6273896 |
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60096384 |
Aug 12, 1998 |
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Current U.S.
Class: |
600/429 |
Current CPC
Class: |
A61B 2034/2057 20160201;
A61B 90/10 20160201; A61B 2034/107 20160201; A61B 2034/2072
20160201; A61B 2090/3979 20160201; A61B 90/11 20160201; A61B 34/20
20160201; A61B 2090/3983 20160201; A61B 2034/2068 20160201; A61B
2034/2055 20160201; A61B 2090/3945 20160201; A61B 2090/363
20160201 |
Class at
Publication: |
600/429 |
International
Class: |
A61B 005/05 |
Claims
What is claimed is:
1. An apparatus for stereotactic surgery on a spine comprising: a
guidance fixture including an instrument guide for moving a
surgical instrument along a constrained trajectory; a mounting
device including a longitudinal rail and a plurality of clamps for
securing the longitudinal rail to the spine; an adjustment
mechanism for adjusting a location and an orientation of the
constrained trajectory relative to the mounting device; and a
signaling device for providing signals related to the location and
the orientation of the constrained trajectory.
2. An apparatus for stereotactic surgery on a body, comprising: a
guidance fixture, including (a) an instrument guide for moving a
surgical instrument along a constrained trajectory relative to the
instrument guide, (b) an adjustable portion supporting the
instrument guide, including a base having a central axis and an
adjustment mechanism coupled between the base and the instrument
guide, wherein a configuration of the adjustment mechanism
determines an orientation of the instrument guide relative to the
central axis of the base, and (c) a signaling device for providing
a signal representation of the configuration of the adjustment
mechanism; and a mounting device coupled to the guidance fixture
for attaching the guidance fixture to the body, the mounting device
including an attachment portion for rigid attachment to a bone
structure of the body.
3. The apparatus of claim 2 wherein the attachment portion of the
mounting device includes a first clamp for attaching the mounting
device to a first point on a spine, and the mounting device further
includes a longitudinal rail.
4. The apparatus of claim 3 wherein the attachment portion includes
a second clamp for attaching the mounting device to a second point
on the spine.
5. The apparatus for claim 3 wherein the mounting device further
includes a transverse rail coupled between the longitudinal rail
and the guidance fixture and an adjustable coupler coupling the
longitudinal rail and the transverse rail.
6. The apparatus of claim 2 wherein the mounting device further
includes a tracking device which when the mounting device attached
to the body is rigidly coupled to the body, the tracking device
providing a signal representation of a position of the body.
7. The apparatus of claim 6 wherein the tracking device includes a
plurality of tracking markers and the signal representation of the
position of the body includes a plurality of signals propagating
from corresponding tracking markers.
8. The apparatus of claim 7 wherein the signals propagating from
the tracking markers are electromagnetic signals.
9. The apparatus of claim 8 wherein the tracking markers are light
emitting diodes and the signals propagating from the tracking
markers are optical signals.
10. The apparatus of claim 7 wherein the signals propagating from
the tracking markers are acoustic signals.
11. The apparatus of claim 2 wherein the mounting device further
includes and an adjustable portion coupling the attachment portion
to the guidance fixture.
12. The apparatus of claim 2 wherein the attachment portion
includes a mounting plate for attaching the mounting device
directly to a bone structure of the body.
13. The apparatus of claim 12 wherein the mounting device further
includes a rod removably attached to the mounting base.
14. A method for stereotactic spinal surgery comprising: attaching
a longitudinal rail to a spine; registering the longitudinal rail,
including locating a plurality of anatomical fiducial points on the
spine in relation to the longitudinal rail; providing an adjustable
guidance fixture that includes an instrument guide for guiding the
surgical instrument along a constrained trajectory relative to the
instrument guide; attaching the adjustable guidance fixture to the
longitudinal rail; tracking a location and an orientation of the
instrument guide relative to the longitudinal rail; and adjusting
the orientation of the instrument guide such the constrained
trajectory passes through a target in the body.
15. The method of claim 14 further comprising driving the surgical
instrument along the constrained trajectory toward the target.
16. The method of claim 14 wherein attaching the longitudinal rail
to the spine includes attaching said rail to a first spinous
process.
17. The method of claim 16 wherein attaching the rail to a first
spinous process includes clamping said rail to said spinous
process.
18. The method of claim 17 wherein attaching the longitudinal rail
to the spine further includes attaching said rail to a second
spinous process.
19. The method of claim 18 wherein attaching the longitudinal rail
to the spine further includes adjusting the separation of the first
and the second spinous processes to match a desired curvature of
the spine.
20. The method of claim 19 wherein attaching the longitudinal rail
to the spine further includes verifying locations a plurality of
anatomical fiducial points on the spine in relation to the
longitudinal rail.
21. The method of claim 14 further comprising attaching a tracking
device to the rail, and locating the anatomical points in relation
to the rail includes locating the tracking device and the
anatomical points using a remote sensing device.
22. The method of claim 14 wherein including locating a plurality
of anatomical fiducial points on the spine in relation to the
longitudinal rail includes: tracking a location of the longitudinal
rail with using a remote sensing device; tracking a location of a
probe positioned at each of the fiducial points using the remote
sensing device; and comparing the location of the probe and the
location of the longitudinal rail at each of the fiducial
points.
23. The method of claim 22 further comprising attaching a tracking
device to the rail, and wherein tracking a location of the
longitudinal rail using the remote sensing device includes locating
the tracking device using the remote sensing device.
24. The method of claim 14 wherein the adjustable guidance fixture
includes a base coupled to the instrument guide, said guidance
fixture enabling a plurality of constrained adjustments of the
instrument guide relative to the base.
25. The method of claim 23 wherein adjusting the orientation of the
instrument guide includes using a first constrained motion of the
constrained adjustments and then adjusting the guidance fixture
using a second constrained motion of the constrained adjustments,
so that the constrained trajectory of the instrument guide passes
through the target.
26. The method of claim 25 wherein in adjusting the guidance
fixture, the first of the constrained adjustments includes a
rotation of the instrument guide about a central axis of the base,
and the second of the constrained adjustments includes a pivoting
of the instrument guide to adjust an angle of the instrument guide
and the central axis.
27. The method of claim 14 further comprising: providing a
three-dimensional image of the spine; computing a position of the
constrained trajectory in the three-dimensional image based on the
tracked location and orientation of the instrument guide;
displaying a planar section of the three-dimensional image of the
body in conjunction with a representation of the constrained
trajectory.
28. The method of claim 27 wherein the displayed planar section
containing the target on the spine and the method further, and
adjusting the orientation of the instrument guide includes:
adjusting the guidance fixture using a first constrained motion
until the constrained trajectory of the instrument guide lies in a
plane corresponding to the displayed planar section; and adjusting
the guidance fixture using a second constrained motion, such that
the orientation continues to lie in the plane corresponding to the
displayed planar section, until the constrained trajectory passes
through the target point.
29. The method of claim 27 further comprising: driving the surgical
instrument along the constrained trajectory toward the target,
including tracking a location of the surgical instrument and
displaying the location of the surgical instrument in conjunction
with the scanned image.
Description
RELATED APPLICATIONS
[0001] This is a divisional application of U.S. application
"INSTRUMENT GUIDANCE SYSTEM FOR SPINAL AND OTHER SURGERY," Ser. No.
09/317,676, filed May 24, 1999, which is a continuation-in-part
application of U.S. application "INSTRUMENT GUIDANCE FOR
STEREOTACTIC SURGERY," Ser. No. 09/063,658 filed Apr. 21, 1998 and
a continuation-in-part of U.S. application "REMOVABLE FRAMES FOR
STEREOTACTIC LOCALIZATION," Ser. No. 09/063,930 filed Apr. 21,
1998, and also claims the benefit of U.S. Provisional application
serial No. 60/096,384, filed Aug. 12, 1998.
BACKGROUND
[0002] This invention relates to instrument guidance for
stereotactic surgery.
[0003] Stereotactic localization is a method for locating a target
within a three-dimensional object. This method is used in the
medical arts and sciences to locate a target in the human body, in
particular in the brain or spine, for medical and surgical
treatment. Stereotactic surgery has a history dating back to the
turn of the century, when the Horsely-Clark Apparatus was described
as a mechanical frame system in which an animal was immobilized.
This frame system permitted reproducible targeting within the
animal's brain for physiological experiments. This and similar
technology found application in 1948 in the work of Wycis and
Speigel. In their work, a frame was attached to a human skull. The
frame permitted targeting of sites within the human brain for
neurosurgical treatment. A detailed survey of the field of
stereotactic surgery can be found in Textbook of Stereotactic and
Functional Neurosurgery, P. L. Gildenberg and R. R. Tasker (eds.),
McGraw-Hill, June 1997 (ISBN: 0070236046).
[0004] One approach to stereotactic surgery involves the following
steps. Fiducial scanning markers are attached to the body in one of
a variety of manners, including using an attachable frame or
attaching the markers to the skin with an adhesive. A scan is then
taken of a body, for example of the head, to produce a
three-dimensional image of the body. Scanning can be done using a
variety of techniques including CT, MRI, PET, and SPECT. Images of
the fiducial scanning markers that are located around the body are
then located in the three-dimensional image at fiducial image
points. Points of interest, such as the location of a tumor, are
located in the three-dimensional image with reference to these
fiducial image points. The body and the image are registered by
matching the locations of the scanning markers and the coordinates
of the fiducial image points. In an approach to stereotactic brain
surgery, a three-dimensional frame is screwed to the patient's
skull prior to scanning the head. This frame serves as a mechanical
reference mechanism that supports scanning fiducial markers at
fiducial points around the body. The frame remains attached to the
patient's skull from before scanning until after surgery is
complete. Prior to surgery, a mechanical guide assembly is attached
to the frame. The relative location in the image of the point of
interest with respect to the fiducial image points is determined,
and this relationship is used to adjust the mechanical guide
assembly with respect to the fiducial points on the frame. Using
the adjusted mechanical guide assembly, a surgical instrument is
then guided to a location in the body that corresponds to the point
of interest in the image.
[0005] In another form of stereotactic surgery, known generally as
"image-guided" stereotactic surgery, rather than relying on
mechanical adjustment of a guide assembly, visual feedback is
provided to a surgeon by displaying a composite image formed from
the scanned three-dimensional image and a synthesized image of a
hand-held surgical instrument. The surgeon guides the hand-held
instrument into the body using the visual feedback. In this form of
surgery, a frame is attached to the patient and a scan is taken as
described above. After scanning, the head and frame are secured in
a fixed position, for example, fixed to an operating table. In
order to display the image of the surgical instrument in a proper
relationship to the scanned image, the position and orientation of
the instrument is sensed using a localization apparatus that
remains in a fixed position relative to the body. The localization
apparatus can be coupled to the surgical instrument using an
articulated mechanical arm on which the surgical instrument is
attached. Sensors in the joints of the arm provide signals that are
used to determine the location and orientation of the instrument
relative to a fixed base of the mechanical arm. Some more recent
systems do not use mechanical coupling between the surgical
instrument and the localization apparatus and instead rely on
remote sensing of small localized energy emitters (e.g., sources or
transducers of energy) fixed to the instrument. For example, a
camera array is used to locate light-emitting diodes (LEDs) that
are attached to the instrument. The locations of the LED images in
the camera images are used to determine the three-dimensional
physical locations of the LEDs relative to the camera array. The
locations of multiple LEDs attached to the instrument are then used
to determine the location and orientation of the instrument.
Another example of remote sensing uses sound generators and a
microphone array and relies on the relative time of arrival of
acoustical signals to determine the three-dimensional locations of
the sound generators.
[0006] Before a synthesized image of the instrument can be combined
with the scanned image in a proper relationship, some form of
registration is required. For example, the tip of the surgical
instrument can be placed at each of several fiducial markers for
which corresponding images have been located in the
three-dimensional scanned image. Registration of the synthesized
image of the instrument and the scanned image can thereby be
established.
[0007] In a variant of image-guided stereotactic surgery, generally
known as "dynamic referencing," the head and frame are secured in a
fixed position, as in the image-guided approach. However, unlike
other image-guided techniques, the sensors (e.g., cameras) of the
localization apparatus are not at a fixed location. In order to
compensate for the motion of the sensors, energy emitters are fixed
to the frame as well as to the instrument. At any point in time,
the location and orientation of the frame relative to the sensors
as well as the location and orientation of the instrument relative
to the sensors are both determined, and the differences in their
locations and orientations are used to compute the location and
orientation of the instrument relative to the frame. This computed
location of the instrument is then used to display the synthesized
image of the surgical instrument in an appropriate relationship to
the scanned image.
[0008] Still another approach to stereotactic surgery, generally
known as "frameless image-guided" stereotactic surgery, does not
rely on attaching a frame to the body before scanning. Instead,
adhesive fiducial scanning markers are applied to the scalp, or
small screws are inserted into the skull, and the patient is
scanned as in the techniques described above. During surgery, the
patient is immobilized and locked in place using a head clamp or a
frame. The image-guided stereotactic approach described above is
then followed, including the registration procedure described above
to establish the locations of the fiducial scanning markers
relative to the instrument.
[0009] In image-guided techniques, a surgeon can rely on a variety
of views of a three dimensional scanned image. These views can
include a three-dimensional surface view with an adjustable point
of view (e.g., a perspective view with surface shading). In
addition, planar (i.e., two-dimensional) views of the image can be
displayed. In particular, three two-dimension "slices" through
orthogonal planes of the image are typically displayed, with the
orientations of the planes being sagittal (dividing a head into a
left and a right part), coronal (dividing a head into a front and a
back part), and axial (dividing a head into an upper and lower
part). As the orientations of the planes are predetermined, the
particular planes that are displayed can be determined by the point
of intersection of the three planes. A point, such as the tip of a
probe, can be displayed in a three-dimensional surface view as a
point in a appropriate geometric relationship. The point can be
displayed in a planer view by orthogonally projecting the point
onto the associated plane. A line can be displayed in a planar view
as an orthogonal projection onto the associated plane, or as the
point of intersection of the line and the associated plane. Note
that if a first point, such as a surgical entry point is used to
determine which planes are displayed, a second point, such as a
surgical target point, does not in general fall in any of the
displayed planes.
[0010] Planar views of a three-dimensional scan can also use
alternative orientations than the standard sagittal, coronal, and
axial orientations described above, allowing two points to lie in
two orthogonal planes, and one of the two points to additionally
lie in a third orthogonal plane. In particular, a "navigational"
view can be determined according to two points in an image, such as
an entry point at the surface of a body and a target point within
the body. The line joining the entry point and the target point is
chosen as the intersection of two orthogonal planes, navigation
planes 1 and 2. The orientation of navigational planes 1 and 2 is
arbitrary (that is, the two planes can be rotated together around
their intersecting line). A third plane, orthogonal to navigation
planes 1 and 2, provides a "bird's eye" view looking from the entry
point to the target point. This bird's eye plane is typically
chosen to pass through the target point. (Such a navigational view
is shown in FIG. 14a). Using a navigational view, the orientation
of a surgical instrument is typically shown as a line projected
orthogonally onto the two navigational planes, and as the point of
intersection of the line and the bird's eye plane. Manipulating an
instrument using such a navigational view for feedback requires
considerable practice and is not intuitive for many people.
[0011] Image-guided frameless stereotaxy has also been applied to
spine surgery. A reference frame is attached to an exposed spinous
process during open spine surgery, and a probe is used to register
the patient's spine with scanned image of the spine. Anatomical
landmarks are used as fiducial points which are located in the
scanned image. Visual feedback is provided to manually guide
placement of instruments, such as insertion of pedicle screws into
the spinal structures.
SUMMARY
[0012] In one aspect, in general, the invention is a method for
positioning a surgical instrument during stereotactic surgery on a
body, for example, during spinal surgery or general surgery. In
this method, the body has been previously scanned to produce a
three-dimensional image of the body which includes a target. A
mounting device is attached to a bone structure of the body, for
example, by attaching a rail to the spine, or a mounting plate to
the pelvis and attaching a rod to the mounting plate. Multiple of
fiducial points are located on the body in relation to the mounting
device. For example, the fiducial points are anatomical points
which are located using a remote sensing device that is used to
track the mounting device and a probe that is placed at the
fiducial points. The method also includes providing an adjustable
guidance fixture that includes an instrument guide for guiding the
surgical instrument along a constrained trajectory relative to the
instrument guide. A location and orientation of the instrument
guide is tracked and a position of the constrained trajectory in
the three-dimensional image is computed. The guidance fixture is
adjusted relative to the mounting device using a first constrained
motion followed by a second constrained motion, so that the
constrained trajectory of the instrument guide passes through the
target. The method further includes driving the surgical instrument
along the constrained trajectory toward the target, and
subsequently removing the mounting device from the bone
structure.
[0013] The method can include one or more of the following
features.
[0014] The rail is attached to the spine by clamping the rail to
two spinous processes and adjusting the separation of the two
spinous processes to match the separation of the two processes in
three-dimensional scanned image, thereby matching a curvature of
the spine with a corresponding curvature of the spine in the
image.
[0015] Locating the fiducial points in relation to the rail
includes tracking a location and orientation of the rail using a
remote sensing device and also tracking a location of a point on a
probe using the remote sensing device. The point on the probe is
positioned at the fiducial points. When the fiducial points are
anatomical points of one vertebral segment, this facilitates
poly-segmental tracking via unisegmental mapping registration
[0016] The tracked location and orientation of the rail is compared
to the tracked location of the point on the probe to determine the
location of the fiducial points in relation to the rail.
[0017] In another aspect, in general, the invention is a method for
positioning a surgical instrument during stereotactic spinal
surgery, the spine having been previously scanned to produce a
three-dimensional image of the spine which includes a target on the
spine. A longitudinal rail is attached to the spine. Attaching the
rail to the spine can include clamping the longitudinal rail to two
spinous processes and adjusting the separation of the two spinous
processes to match a separation of the two processes in the
three-dimensional image, thereby maintaining a fixed geometric
relationship between the longitudal rail and a portion of the spine
between the two spinous processes and matching a curvature of that
portion spine with a corresponding curvature of that portion of the
spine in the three-dimensional image. Multiple anatomical fiducial
points are located on the spine in relation to the longitudinal
rail. Locating these points includes tracking a location of the
longitudinal rail with using a remote sensing device, tracking a
location of a probe positioned at each of the fiducial points using
the remote sensing device, and comparing the location of the probe
and the location of the longitudinal rail at each of the fiducial
points. An adjustable guidance fixture that includes an instrument
guide for guiding the surgical instrument along a constrained
trajectory relative to the instrument guide is attached to the
rail. A location and orientation of the instrument guide is tracked
and a position of the constrained trajectory in the
three-dimensional image is computed. A planar section of the
three-dimensional image of the body in conjunction with a
representation of the constrained trajectory, the planar section
containing the target on the spine. The guidance fixture is
adjusted using a first constrained motion until the constrained
trajectory of the instrument guide lies in a plane corresponding to
the displayed planar section and using a second constrained motion,
such that the orientation continues to lie in the plane
corresponding to the displayed planar section, until the
constrained trajectory passes through the target point. The
surgical instrument is driven along the constrained trajectory
toward the target, including tracking a location of the surgical
instrument and displaying the location of the surgical instrument
in conjunction with the scanned image.
[0018] In another aspect, in general, the invention is an apparatus
for stereotactic surgery on a spine. The apparatus includes a
guidance fixture that includes an instrument guide for moving a
surgical instrument along a constrained trajectory. The apparatus
also includes a mounting device that includes a longitudinal rail
and multiple clamps for securing the longitudinal rail to the
spine, and an adjustment mechanism for adjusting the location and
orientation of the constrained trajectory relative to the mounting
device. The apparatus also includes a signaling device for
providing signals related to a location and orientation of the
constrained trajectory.
[0019] In another aspect, in general, the invention is an apparatus
for stereotactic surgery on a body. The apparatus includes a
guidance fixture that includes (a) an instrument guide for moving a
surgical instrument along a constrained trajectory relative to the
instrument guide, (b) an adjustable portion supporting the
instrument guide, including a base having a central axis and an
adjustment mechanism coupled between the base and the instrument
guide, wherein a configuration of the adjustment mechanism
determines an orientation of the instrument guide relative to the
central axis of the base, and (c) a signaling device for providing
a signal representation of the configuration of the adjustment
mechanism. The apparatus also includes a mounting device coupled to
the guidance fixture for attaching the guidance fixture to the
body, the mounting device including an attachment portion for rigid
attachment to a bone structure of the body.
[0020] The invention can include one or more of the following
features.
[0021] The attachment portion of the mounting device includes a
first clamp for attaching the mounting device to a first point on a
spine, and the mounting device further includes a longitudinal
rail.
[0022] The attachment portion includes a second clamp for attaching
the mounting device to a second point on the spine.
[0023] The mounting device further includes a transverse rail
coupled between the longitudinal rail and the guidance fixture and
an adjustable coupler coupling the longitudinal rail and the
transverse rail.
[0024] The mounting device further includes a tracking device which
when the mounting device attached to the body is rigidly coupled to
the body, the tracking device provides a signal representation of a
position of the body.
[0025] The tracking device includes multiple tracking markers, for
example energy reflectors or emitters, and the signal
representation of the position of the body includes multiple
signals, such as electromagnetic, optical, or acoustic signals,
propagating from corresponding tracking markers.
[0026] The mounting device further includes an adjustable portion
coupling the attachment portion to the guidance fixture.
[0027] The attachment portion includes a mounting plate for
attaching the mounting device directly to a bone structure of the
body.
[0028] The mounting device further includes a rod removably
attached to the mounting base.
[0029] An advantage of the invention is that it permits accurate
stereotactic surgery on various parts of the body, and in
particular, allows accurate stereotactic surgery on the spine.
Attaching the guidance fixture to a mounting device that is
attached to a bone structure, such as a rail attached to a spine,
provides a way of holding the guidance fixture in a fixed
relationship to a target in the body.
[0030] An advantage of using a spinal rail is that by using two
clamps, the spine can be maintained in a fixed curvature and the
curvature can be adjusted to match the curvature at the time that a
scan was taken. In this way, a single spinal segment can be
registered with scanned image and thereby achieve registration for
a series of spinal segments. This reduces the amount of time taken
in surgery that would be needed to repeatedly re-register each
spinal segment.
[0031] Other features and advantages are apparent from the
following description and from the claims.
DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a flowchart of a stereotactic brain surgery
procedure;
[0033] FIG. 2 is a head with threaded inserts implanted including a
cross-sectionial view of the skull and a threaded insert;
[0034] FIG. 3 is a head with a scanning MIRRF attached including a
detailed exploded view of the attachment of the MIRRF to the
implanted threaded inserts;
[0035] FIG. 4 illustrates scanning of a head on which a scanning
MIRRF is attached;
[0036] FIG. 5 is a head with a tracking MIRRF attached and a
cranial probe being tracked using a camera array;
[0037] FIG. 6 is a dataflow diagram for computation of a composite
image including a synthesized image of a probe;
[0038] FIG. 7 illustrates locating a planned entry point using the
tracked cranial probe and a computer display;
[0039] FIG. 8 is a display of a virtual burr hole and accessible
cone of orientations;
[0040] FIG. 9 is a head with a tracking MIRRF and a guidance
fixture attached being tracked using a camera array;
[0041] FIG. 10 is a view of a base platter and an adjustable base
of a guidance fixture;
[0042] FIG. 11 is an exploded view of the adjustable base of a
guidance fixture;
[0043] FIG. 12 is a dataflow diagram for computation of a composite
image including a synthesized image of a surgical instrument;
[0044] FIG. 13 is a detailed flowchart of trajectory replanning and
fixture alignment;
[0045] FIGS. 14a-c illustrate a navigational view display and
corresponding planar segments through a body;
[0046] FIGS. 15a-f illustrate a "field of view" display and
corresponding conical section through a body;
[0047] FIG. 16 is a guidance fixture including an adjustable base
and an instrument drive attached to a base platter;
[0048] FIGS. 17a-b show a burr hole ring used to secure an
instrument using a flexible membrane;
[0049] FIG. 17c is a retractor in a guidance fixture;
[0050] FIG. 18 is a calibration jig;
[0051] FIG. 19 is a phantom jig and a guidance fixture and a
tracking MIRRF attached to the jig;
[0052] FIG. 20 is an arc shaped MIRRF attached to a head including
a view of a threaded insert and mounting bolt;
[0053] FIG. 20a is a MIRRF attached to a subcutaneous insert;
[0054] FIG. 21 is a scanning marker and a tracking marker attached
to a threaded insert;
[0055] FIG. 22 is a guidance fixture and a tracking MIRRF attached
to a conventional stereotactic frame;
[0056] FIG. 23 is a tracking MIRRF attached directly to a guidance
fixture;
[0057] FIGS. 24a-b illustrate an instrumented guidance
fixtures;
[0058] FIGS. 25a-b illustrate an actuated guidance fixture;
[0059] FIG. 26 illustrates a remotely controlled guidance
fixture;
[0060] FIG. 27 illustrates a teleoperator configuration;
[0061] FIG. 28 illustrates locating a mounting base using a
mechanical arm;
[0062] FIGS. 29a-d illustrate a head-mounted mechanical arm;
[0063] FIG. 30 is a flowchart of a spinal surgery procedure;
[0064] FIGS. 31a-b illustrate a guidance fixture attached to spinal
rails for spinal surgery;
[0065] FIGS. 32a-b illustrate a guidance fixture attached to the
pelvis for general surgery; and
[0066] FIG. 33 is a head-mounted camera array.
DESCRIPTION
[0067] Brain Surgery
[0068] Referring to FIG. 1, an aspect of the invention relates to
stereotactic brain surgery. This approach to brain surgery involves
a series of steps, shown in FIG. 1, from start 100 prior to
scanning through finish 199 after the surgical phase of a procedure
is completed. There are generally two phases to the approach. The
first phase involves creating a three-dimensional image of the head
(steps 105, 110, 115, 120), planning a surgical trajectory based on
the image (step 125), and validating the guidance fixture (step
130) that will be used during the surgical procedure. The second
phase involves the remaining steps (steps 135 through 195) that are
used to carry out the actual surgical procedure. The steps of the
first phase can be carried out quite some time before those of the
second phase. For example, creating the three-dimensional image of
the head can be done on one day, and the steps used to carry out
the actual surgery can be done on a subsequent day. Also, the steps
of the second phase may be repeated, for example on several
different days, illustrated by transition 192 between steps 195 and
135.
[0069] Pre-Operative Phase
[0070] One to three days prior to surgery, the patient is seen in a
post anesthesia care unit (PACU) or other suitable location.
Referring to FIG. 1, the first step of the procedure is to attach
anchors to which scanning, registration, and tracking markers will
be subsequently attached (step 105). Referring to FIG. 2, the
anchors include two threaded inserts 220 that are surgically
implanted into the patient's skull 210 using a template (described
below). The template precisely determines the separation and
parallel orientation of inserts 220.
[0071] Referring to FIG. 3, a rigid cross-shaped device, a scanning
"miniature removable reference frame" (scanning MIRRF) 310, is next
attached to threaded inserts 220 using screws 320 (FIG. 1, step
110). A retention plate 330 is used to aid precise reattachment of
scanning MIRRF 310 to the skull. Retention plate 330 is also used
as the template during insertion of threaded inserts 220. Scanning
MIRRF 310 includes four fiducial scanning markers 340 that will be
visible in the scanned image. Scanning MIRRF 310 is made from a
material that is chosen to interfere as little as possible with the
type of scan that will be performed. For example, for MRI and CT
scans, the chosen material can be polycarbonate, which results in
scanning MIRRF 310 being almost invisible in the scanned image.
Fiducial scanning markers 340 are mounted in spherical cavities in
scanning MIRRF 310. The design of the cavities is such that the
"press-in" marker inserts can be removed for cleaning. The
star-shaped design of scanning MIRRF 310 is such that, when
attached, the elongated part of the star extends behind or in front
of the ear so that mounting screws 320 are located toward the top
of the skull where soft tissue thickness is minimal and skull
thickness is maximal. This minimal tissue thickness allows threaded
inserts 220 to be implanted easily under local anesthetic by making
a small incision. As an alternative to attaching a single MIRRF as
shown in FIG. 3, multiple MIRRFs can be attached in a similar
manner to increase the number or separation of the scanning
markers.
[0072] Referring to FIG. 4, MRI or CT scanner 400 is used to obtain
a three-dimensional digitized image 410 of the head, for example,
as a series of two-dimensional "slices" (step 115 in FIG. 1). In
addition, a model or map of the surface of the skull can be made
allowing, for instance, subsequent three-dimensional surface
display of the skull. The fiducial scanning markers 340 produce
fiducial images 420 at in image 410. Fiducial coordinates 421 of
fiducial images 420 in the coordinate system of image 410 are
determined, for example, by manually positioning a cursor at
fiducial images 420 on a computer display. Image 410, along with
the fiducial coordinates 421, are stored on a computer readable
storage medium 430 for use during the subsequent surgical phase of
the approach. Typically the image is stored as a series of
two-dimensional images, each corresponding to a horizontal "slice"
of the head.
[0073] After scanning, scanning MIRRF 310 is removed (FIG. 1, step
120), and threaded inserts 220 are left in place. Antibiotic
ointment can be applied and the patient is either discharged or
sent to the operating room.
[0074] Also after scanning, a surgeon determines the location of a
target point within the brain and an entry point through the skull
(FIG. 1, step 125). A planned surgical trajectory is then
determined as the line joining the entry point and the target
point. The surgeon plans the trajectory using a computer display of
image 410 which provides, for example, a three-dimensional surface
view, and sagittal, coronal, and axial planar views. This allows
the surgeon, for example, to plan a trajectory that avoids critical
structures in the brain. The target and entry points, and the
trajectory are stored along with the image on storage medium
430.
[0075] Other than an optional fixture validation (FIG. 1, step
130), all the preoperative steps are complete at this point.
[0076] Surgical Phase
[0077] Referring to FIG. 5, the surgical phase of the procedure
begins by attaching a tracking MIRRF 510 to threaded inserts 220
(not shown) that remained implanted in the patient's skull after
scanning MIRRF 310 was previously removed. Tracking MIRRF 510 has a
very similar structure to scanning MIRRF 310. Tracking MIRRF 510
includes fiducial divots 540 at the centers of locations
corresponding to fiducial markers 340 (shown in FIGS. 3 and 4).
Four tracking LEDs 550 are also attached to tracking MIRRF 510.
Since tracking MIRRF 510 is rigid, the geometric relationship
between tracking LEDs 550 and fiducial divots 540 is fixed and can
be determined beforehand and verified in a subsequent verification
step, or can be unknown and determined in a subsequent registration
step. Preferably, tracking MIRRF 510 is made of a material that is
lightweight and can be autoclaved, such as Radel.
[0078] After attaching tracking MIRRF 510 to the patient's skull,
the patient can be comfortably placed in an awake, possibly lightly
sedated, state in an operating room chair, which is similar to a
dental chair. The patient is allowed to recline in an essentially
unrestrained manner in the operating room chair in a semi-sitting
position. Alternatively, at the surgeon's prerogative and if
appropriate, general anesthesia can be administered to the
patient.
[0079] Referring still to FIG. 5, a camera array 560 provides
time-varying digitized images 586 to a localization application 588
executing on a computer workstation 580. The patient can be free to
move relative to camera array 560 and relative to the operating
room chair, and camera array 560 can be free to move relative to
the patient and relative to the operating room chair. Camera array
560 includes three CCD cameras 562 positioned in a fixed
configuration relative to one another. Alternatively, two cameras,
which are sufficient for three dimensional localization, or more
than three cameras, which may provide greater accuracy, can be
used. Each camera 562 in camera array 560 produces one time-varying
image. Each tracking LED 550 on tracking MIRRF 510 is powered and
emits infra-red illumination which is seen as a bright point in
each of time-varying digitized images 586. Based on the relative
coordinates of the bright points in images 586 from each camera 562
of camera array 560 localization application 588 computes the
position (i.e., the coordinates) of tracking LEDs 550 in the
coordinate system of camera array 560. Using the positions of
multiple tracking LEDs 550, the location and orientation of
tracking MIRRF 510 can be computed by localization application 588.
Tracking of MIRRF coordinates 510 is illustrated schematically by
line 564.
[0080] A cranial probe 570, including three probe LEDs 572 attached
along its length, is also tracked using camera array 560 and
localization application 588. Based on the coordinates of the
images of probe LEDs 572 in images 586 and probe geometry 584,
localization application 588 computes the position and orientation
of probe 570 in the coordinate system of camera array 560.
[0081] Registration
[0082] Using cranial probe 570, the surgeon then carries out a
registration step (FIG. 1, step 140). In this registration step,
the surgeon first locates the fiducial points in the image. Then he
touches the tip of probe 570 to each of fiducial divots 540 in
tracking MIRRF 510 in turn, indicating to localization application
588 when he is touching each of the divots. Localization
application 588 then computes a three-dimensional conformal
registration (map) between image 410 and the coordinate system of
tracking MIRRF 510.
[0083] Note that if the geometric relationship of tracking LEDs 550
and fiducial divots 540 is known to localization application 588,
for example using a previously calibrated MIRRF, the coordinates of
the fiducial divots can be computed from the coordinates of the
tracking LEDs, which in turn can be computed from the locations of
the fiducial images in the camera images. The step of touching the
divots can be omitted in this case, or used to verify the computed
coordinates of fiducial divots.
[0084] Having computed the conformal mapping, localization
application 588 continuously combines image 410 and a synthesized
image of probe 570 to form a composite image 599 that combines the
scanned image with the synthesized image of the probe. Composite
image 599 is shown on a computer display 610 which includes a
three-dimensional surface display.
[0085] Referring to FIG. 6, the registration and image composition
functions performed by localization application 588 involves a
series of data processing stages. As shown in FIG. 5, time-varying
digitized images 586 are provided to localization application 588
from camera array 560. Referring to FIG. 6, time-varying digitized
images 586 are input to MIRRF tracking 591, a processing stage of
localization application 588, which tracks tracking LEDs 550 on
tracking MIRRF 510 and produces "MIRRF/cam" 593, an orientation and
location of tracking MIRRF 510 in the coordinate system of camera
array 560. At the same time, probe tracking 590 tracks probe 570
and produces "probe/cam" 592, an orientation and location of probe
570 in the coordinate system of camera array 560. Probe tracking
590 makes use of probe geometry 584 which specifies the geometric
relationship between the tip of the probe 570 and probe LEDs 572.
The next stage of localization application 588, relative
positioning 594 inputs MIRRF/cam 593 and probe/cam 592 and produces
"probe/MIRRF" 595, the position and orientation of probe 570 in the
coordinate system of tracking MIRRF 510. When the surgeon touches
fiducial divots 540, registration 581 takes the location
information from probe/MIRRF 595 and records it in "fids/MIRRF"
582, the coordinates of fiducial divots 540 in the coordinate
system of tracking MIRRF 510. Fiducial coordinates 421, the
coordinates of fiducial images 420 in the coordinate system of
image 410, are provided to localization application 588, along with
image 410, from storage medium 430. Mapping 587 includes matching
of corresponding coordinates in fids/MIRRF 582 and fiducial
coordinates 421 and forming a conformal map 589 between the
coordinate system of image 410 and the coordinate system of
tracking MIRRF 510. Conformal map 589 includes the quantities
required to transform any three-dimensional coordinate in the
coordinate system of tracking MIRRF 510 into a three-dimensional
coordinate in the coordinate system of image 410. These quantities
correspond, in general, to a rotation, scaling, and translation of
points in the coordinate system of tracking MIRRF 510 to determine
the corresponding points in the coordinate system of image 410.
[0086] Referring still to FIG. 6, the next stage of localization
application 588, probe mapping 596, takes the continually updated
probe coordinates, probe/MIRRF 595, and conformal map 589, and
computes probe/image 597, the coordinates of probe 570 in the
coordinate system of image 410. Then, image composition 598
combines image 410 and a synthesized image of probe 570 to form
composite image 599.
[0087] Composite image 599 typically includes a three-dimensional
surface view and three orthogonal planar views. The orthogonal
planar views can correspond to the three standard orientations,
sagittal, coronal, and axial planes, for instance passing through
the planned target point. More typically, three planar views of a
navigational view that is determined by the planned entry and
target points are included in composite image 599. The tip of the
probe is displayed as an orthogonal projection onto the planes of
the planar views, and as a point in an appropriate geometric
relationship in the three-dimensional surface view. The orientation
of the probe can be displayed using a line passing through the tip
of the probe and displayed as a orthogonal projection onto
navigational planes 1 and 2 of the navigational view, and as a
point of intersection on the bird's eye view of the navigational
view.
[0088] If the geometric relationships of the fiducial points,
fids/MIRRF 582, the coordinates of fiducial divots 540 does not
match the geometric relationships of fiducial coordinates 421, then
an error in placing probe 570 during the registration procedure may
have occurred. If such an error is detected, conformal mapping 589
is not computed, a warning is provided to the surgeon, and the
surgeon must perform the registration procedure again. Furthermore,
if the geometric relationships between fiducial divots 540 is known
through prior measurement or calibration, registration errors and
errors locating fiducial points 420 in image 410 can also be
detected.
[0089] Referring to FIG. 7, a cranial probe 570 is used to
determine an actual entry point. A computer display 610 shows
composite image 599, which includes a three-dimensional surface
view and three planar views of a navigational view determined by
the planned entry and target points.
[0090] Referring to FIG. 8, a virtual burr hole 640 is displayed in
the planar views of navigational view at the probe location 642 of
cranial probe 570. In addition, the range of adjustable
orientations of a guidance fixture that would be attached at probe
location 642 is displayed as a cone 644, and the extent of effects
of x-y adjustment of the guidance fixture is displayed as a second
cone 646. Display of cones 644 and 646 allows the surgeon to verify
that planned target point 650 is accessible in the range of
adjustments of a guidance fixture attached at probe location
642.
[0091] When the surgeon has located an entry point 620 on the
skull, he marks the entry point as the desired center point of
attachment of a guidance fixture that will be used during the
surgical phase of the procedure.
[0092] The patient then has a small area of the head shaved and
draped off. A 2 to 4 cm linear incision is made over entry point
620 after local anesthesia is administered. The location of entry
point 620 is then reconfirmed using cranial probe 570 after the
incision is made. An approximately 1 cm burr hole (not shown in
FIG. 7) is then drilled through the skull at entry point 620 (FIG.
1, step 150). The surgeon opens the dura under the burr hole and
visually inspects the area to determine that no critical
structures, such as a blood vessel, are located directly under the
burr hole. If the location of the burr hole is found to be
unacceptable, a new entry point can be planned and return to the
step of locating the entry point (FIG. 1, step 145).
[0093] Attaching the Guidance Fixture
[0094] Referring to FIG. 9, having drilled the burr hole, the
surgeon next attaches a guidance fixture 710 to the skull (FIG. 1,
step 155). (Note that an optional instrument drive can also
included in the guidance fixture but is not shown in FIG. 9.) As is
described more fully below, guidance fixture 710 includes a base
platter 720 on which platter LEDs 730 are attached. Base platter
720 is attached to an adjustable base 715, which is in turn
attached to the skull. The orientation of a line normal to base
platter 720 is adjustable within a cone forming a solid angle of
approximately 45 degrees. After attaching guidance fixture 710 the
surgeon adjusts the orientation of base platter 720 (FIG. 1, step
170; note that optional steps 160 and 165 are described below). A
surgical instrument 740, including an instrument LED 742 fixed
relative to the instrument, passes through guidance fixture 710.
Surgical instrument 740 is constrained to follow a fixed trajectory
perpendicular to and through a central opening through adjusted
base platter 720. Workstation 580 tracks the location and
orientation of base platter 720, and the displacement of surgical
instrument 740, indicated schematically by lines 564 and 750
respectively, and computes the position of surgical instrument 740
in the coordinate system of image 410. Workstation 580 continually
displays on display 610 a composite image 750 including a
navigational view of image 410 showing the position and orientation
of surgical instrument 740. The surgeon uses the visual feedback on
display 610 to position surgical instrument 740 along the
constrained trajectory. Note that during this time, the patient is
not necessarily immobilized. Both the patient and camera array 560
can move and, as long as platter LEDs 730 and instrument LED 742
are visible to camera array 560 at an appropriate distance and
orientation, workstation 580 call maintain a continuously updated
display.
[0095] Referring to FIG. 10, guidance fixture 710 includes base
platter 720 and adjustable base 715. In use, base platter 720 is
attached to an entry column 850 (through an x-y positioning table
1150, described fully below) which is held in adjustable base 715.
The orientation of entry column 850 can be adjusted relative to
skull 210 using separate rotation and pivoting motions, as
described below. Referring also to the exploded view of adjustable
base 715 shown in FIG. 11, guidance base 715 includes a mounting
base 820, which is rigidly attached to the skull during an
operation using screws through mounting holes 822. Mounting holes
822 pass through mounting tabs 723 as well as through the inside of
the mounting base 820. Mounting tabs 823 are pliable to allow them
to conform to the skull. As mounting base 820 may be distorted in
being mounted to the skull, it can be designed to be disposable.
Mounting base 820 has a cylindrical opening which accepts a
rotating collar 830. A rotation locking screw 824 in mounting base
820, when tightened, locks rotating collar 830 in place and
prevents its movement within the mounting base. Entry column 850 is
held within rotating collar 830 by a pivoting collar 840. Pivoting
collar 840 slides in an arc-shaped pivoting guide 841 within
rotating collar 830. When rotated, a pivoting locking knob 846
prevents pivoting/collar 840 from sliding by drawing a collar clamp
842 against pivoting collar 840 using a threaded rod 920. When
rotated, a pivoting adjustment knob 844 slides pivoting collar 840
along pivoting guide 841.
[0096] Referring again to FIG. 11, mounting base 820 includes
mounting holes 822 drilled through mounting tabs 723 (one tab is
not visible on the side opposite the visible one), as well as
through the inside of mounting base 820. Mounting base 820 includes
a threaded hole 922 within which rotation locking screw 824 turns.
Rotation locking screw 824 mates with a recessed channel 923 in
rotating collar 830, thereby preventing rotation of rotating collar
830 and also preventing rotating collar 830 from lifting off
mounting base 820.
[0097] Entry column 850 includes a cylindrical portion 913 and a
spherical portion 914 at one end. Spherical portion 914 mates with
a spherical socket 916 in the bottom of rotating collar 830. When
mated, entry column 850 can pivot within rotating collar 830. Entry
column 850 also has opposing groves 910 which mate with protrusions
912 on the inside of the circular opening in pivoting collar 840.
Entry column 850 passes through the circular opening, and
protrusions 912 mate with groves 910. When assembled, the mated
groves and protrusions hold the spherical portion 914 of entry
column 850 against spherical socket 916 in the bottom of rotating
collar 830.
[0098] The position of pivoting collar 840 within pivoting guide
841 is adjusted by turning pivoting adjustment knob 844 and
tightened in place by rotating pivoting tightening knob 846.
Pivoting adjustment knob 844 attaches to a pivoting adjustment rod
930 which passes through collar clamp 842 and the main portion of
pivoting collar 840 to a rack and pinion mechanism. A pinion 931 is
attached to the end pivoting adjustment rod 930. Pinion 931 mates
with an arc-shaped rack 932 which attaches to rotating collar 830
using three screws 934. Rotation of pivoting adjustment knob 844
rotates pivoting adjustment rod 930 and pinion 931, which then
slides pivoting collar 840 in pivoting guide 841. Rotating pivoting
locking knob 846 locks pivoting collar 840 rigidly to rotating
collar 830. Tightening both rotation locking screw 824 and pivoting
locking knob 846 fixes the orientation of entry column 850 relative
to mounting base 820.
[0099] Referring to FIG. 10, the procedure for attaching and
adjusting guidance fixture 710 (FIG. 1, steps 155 through 170) is
carried out as follows. Mounting base 820 is attached in a
temporary fashion over burr hole 625. While attaching the base,
mounting tabs 723 are conformed to the shape of the skull 210 and
secured to the skull an orientation generally directed towards the
target using three or more titanium bone screws 724 passing through
mounting holes 822 through mounting tabs 723 and through the
interior of the mounting base.
[0100] After mounting base 820 is attached to skull 210, the
remainder of guidance base 715 is attached to mounting base 820. In
particular, rotating collar 830, with entry column 850 already
attached, and adjusted to be centered (oriented along the central
axis of guidance base 715) is inserted in mounting base 820 and
rotation locking screw 824 is tightened to mate with recessed
channel 923.
[0101] After guidance base 715 is attached to skull 210, the
remainder of guidance fixture 710 is attached to guidance base 715.
In FIG. 10, the drive assembly, which is already attached to base
platter 720 at the time base platter 720 is attached to guidance
base 715 is not shown. Base platter 720 is attached to entry column
850 via an x-y positioning table 1150 (described below). During the
alignment phase in which the orientation of guidance base 715 is
adjusted, x-y positioning table 1150 remains centered.
[0102] During a surgical procedure, surgical instrument 740 is
passed through a central opening 721 of base platter 720 and
through entry column 850 into the brain. During the alignment phase
in which x-y table 1150 is centered, a line along the trajectory
surgical instrument 740 would follow passes along the central axis
of entry column 850. Adjusting the orientation of guidance base 715
adjusts this trajectory. In all orientations, the trajectory passes
through a single point on the central axis of guidance base 715
near the surface of the skull. If the guidance base is exactly
mounted over the planned entry point, this single point is the
planned entry point. More typically, the point is slightly
displaced from the planned entry point due to mounting
inaccuracies.
[0103] Referring again to FIG. 9, platter LEDs 730 on base platter
720 are sensed by camera array 560, and the location and
orientation of base platter 720 in the coordinate system of image
410 is computed by localization application 588 executing on
computer workstation 580. Localization application 588 computes the
location and orientation of base platter 720 using the known
geometry of the base platter relative to platter LEDs 730.
[0104] Referring to FIG. 12, localization application 588 computes
composite image 750 (FIG. 9) in a series of data transformations.
Time-varying digitized images 586 are passed to MIRRF tracking 591
as well as platter tracking 7010 and instrument tracking 7012.
MIRRF tracking 591 produces "MIRRF/cam" 592, the position and
orientation of tracking MIRRF 510 in the coordinate system of
camera array 560. Platter tracking 7010 produces "platter/cam"
7020, the position and orientation of base platter 720. The
instrument trajectory is at a known location and orientation
relative to platter LEDs 730 on base platter 720, therefore the
location and orientation of the instrument trajectory in the
coordinate system of camera array 560 is also known. Instrument
tracking 7012 produces instrument/cam 7022, the location of
instrument LED 742 in the coordinate system of camera array 560.
Platter localization 7030 uses conformal map 589, MIRRF/cam 593,
and platter/cam 7020 to compute platter/image 7040, the location
and orientation of base platter 720 in the coordinate system of
image 410. Note that once guidance fixture 710 is attached and
aligned, then base platter 720 no longer moves relative to the
skull (other than due to adjustment of x-y table 1150) and
therefore, platter/image 7040 can be fixed rather than continuously
recomputed. Instrument depth measurement 7032 combines platter/cam
7020 and instrument/cam 7022 to compute instrument/platter 7042,
the depth of penetration of the surgical instrument relative to the
plane of base platter 720. Instrument depth measurement 7032 makes
use of the known displacement of the tip of the instrument from
instrument LED 742. Instrument localization 7050 takes
platter/image 7040 and instrument/platter 7042 and computes
instrument/image 7060, the location and orientation of the surgical
instrument in the coordinate system of image 410. Finally, image
composition 7070 combines image 410 with a synthesized image of the
surgical instrument to generate a composite image 750.
[0105] Referring to FIG. 13, before aligning guidance fixture 710,
the surgical trajectory is optionally replanned to go through the
center of the actual mounted position of the guidance fixture,
rather than the planned entry point (FIG. 1, step 165).
[0106] Aligning the Guidance Fixture
[0107] The surgeon aligns guidance fixture 710 using visual
feedback. Referring to FIGS. 14a-c, a navigational view indicating
the trajectory of the surgical instrument is used. Referring to
FIG. 14a, navigational planes 1020 and 1022 correspond to
navigational planar views 1030 and 1032 respectively. Navigational
planes 1020 and 1022 are orthogonal and their intersection forms a
line passing through an entry point 1010 and a target point 1012.
Bird's eye plane 1024, the third plane of the navigation view, is
orthogonal to planes 1020 and 1024 and passes through target point
1012.
[0108] Referring to FIG. 14b-c, navigational planes 1020 and 1024
are shown schematically, along with a line 1040 corresponding to
the orientation of guidance fixture 710. The goal of the alignment
procedure is to make line 1040 coincident with the intersection of
planes 1020 and 1022. The alignment procedure is carried out in a
series of two motions each of which is constrained to one degree of
freedom. Initially, line 1040 is not generally coincident with
either navigational plane. Prior to beginning the alignment
procedure, the orientation of line 1040 is displayed as orthogonal
projections, lines 1041 and 1042, on planes 1020 and 1022,
respectively.
[0109] In the first alignment motion, rotating collar 830 is
rotated within mounting base 820 (FIGS. 10 and 11). Referring to
FIG. 14b, this rotation causes line 1040 to sweep out a portion of
a cone, indicated diagrammatically by dashed arrow 1050. After
rotation through an angle .phi..sub.1, orientation line 1040 is in
the direction of line 1043, which is coincident with plane 1022.
During the rotation, the orthogonal projection line 1041 of line
1040 in plane 1020 forms a smaller and smaller angle .theta..sub.1
with the desired orientation in plane 1020, while the angle
.theta..sub.2 between the orthogonal projection line 1042 in plane
1022 and the desired orientation in plane 1022 increases,
ultimately to .phi..sub.2 when line 1040 is coincident with plane
1022.
[0110] Referring to FIG. 14c, the second alignment motion reduces
the angle .phi..sub.2 while maintaining the coincidence of the
orientation line and plane 1022. This motion corresponds to sliding
pivoting collar 840 within rotating collar 830 (FIGS. 8 and 9).
Alignment is achieved when angle .phi..sub.2 is zero, that is, the
orientation line 1040 is coincident with the intersection of planes
1020 and 1022.
[0111] At this point, after tightening the locking knobs on
guidance fixture 710, base platter 720 is firmly fixed to the
skull, in an orientation and location that constrains a surgical
instrument passing through it to pass along the replanned
trajectory to the planned target point in the head.
[0112] In addition to, or as an alternative to, using a
navigational view to provide visual feedback during the alignment
procedure, a "field of view" display can be provided. Referring to
FIGS. 15a-f, the field of view display uses a representation of a
cross-section of a cone extending below the entry point. Referring
to FIG. 15a, the central axis of a cone 1061 is coincident with the
central axis of the mounting base of a guidance fixture mounted at
an entry point 1010. That is, the central axis of the cone is
generally perpendicular to the surface of the skull at the entry
point. The angle of the cone corresponds to the range of possible
alignments of a guidance fixture mounted at the entry point. In
this embodiment, this is a 45 degree angle. The cross-section is
normal to the central axis of the cone, and passes through a target
point 1012. Referring to FIG. 15b, the corresponding display shows
a circular section 1070 of the scanned image. The center 1011 and
the target point 1012 are indicated. Also indicated are two
orthogonal axes. An axis 1072 corresponds to the achievable
orientations of the guidance fixture as its pivoting collar is
moved in the rotating collar. Another axis 1074 is orthogonal to
axis 1072. Motion of the rotating collar rotates the orientation of
axes 1072 and 1074. These axes can be thought of as intersections
of the navigational planes with the bird's eye plane of a
navigational view, although here, the intersecting lines rotate
with the rotation of the guidance fixture while in the navigational
view, the navigation planes remain fixed as the guidance fixture is
rotated. Referring to FIG. 15c, after an appropriate rotation, axis
1072 passes through target point 1012. FIG. 15d shows the display
after this rotation. Motion of the pivoting collar is indicated by
a line 1076, parallel to axis 1074. If the pivoting collar is
centered, then line 1076 is aligned with axis 1074, as is shown in
FIG. 15d. When the guidance fixture is aligned with the target
point, line 1076 passes through target point 1064, as does axis
1072. FIG. 15f, corresponding to FIG. 15e, shows the display after
alignment is achieved. This circular field of view display provides
intuitive visual feedback to the surgeon who is aligning the
guidance fixture. Furthermore, displacement of the x-y table can
also be shown in such a field of view display, by indicating the
intersection of the resulting instrument trajectory on the circular
display.
[0113] Inserting the Surgical Instrument
[0114] Referring to FIG. 16, an instrument drive 1110 is attached
to base platter 720 prior to attaching the combination of
instrument drive 1110, base platter 720, and x-y table 1150 to
guidance base 715. In FIG. 16, instrument drive 1110 is shown
partially mounted onto a drive post 1120. Prior to attachment to
guidance base 715, drive post 1120 is fully inserted into
instrument drive 1110 so that instrument drive 1110 is in contact
with base platter 720. Base platter 720 can be displaced relative
to guidance base 715 in a plane orthogonal to entry column 850
using two perpendicular adjustment screws 1060, and 1062 turned by
x-y table adjustment knobs 1061, and 1063. Note that prior to
alignment (FIG. 1, step 170) the x-y table is adjusted so that
central opening 721 in base platter 720 is centered over entry
column 850.
[0115] Instrument drive 1110 includes a drive platform 1130 that
moves within a drive mechanism 1125 along a threaded rod 1132.
Threaded rod 1132 is oriented parallel to drive post 1120 and
perpendicular to base platter 720. In this embodiment, rotation of
threaded rod 1132, which causes displacement of drive platform
1130, is manual using a mechanism that is not shown. Alternative
embodiments can use an electronic stepper motor or a manual
hydraulic drive to rotate threaded rod 1132 and thereby displace
drive platform 1130.
[0116] In operation, a surgical instrument, such as a
micro-electrode, is passed into the brain through a guidance tube.
After alignment of guidance fixture 710, the guidance tube is
manually inserted into the brain through central opening 721 in
base platter 720. The guidance tube is then secured in clamp 1135
that is fixed relative to drive mechanism 1125. The instrument is
passed into the guidance tube and is secured in a clamp 1133, which
is fixed relative to drive platform 1130.
[0117] Instrument LED 742 is attached to drive platform 1130. The
displacement of the end of the surgical instrument from instrument
LED 742 is known to localization application 588 which executes on
workstation 580. By tracking the position of instrument LED 742, as
well as platter LEDs 730, the position of the end of a surgical
instrument on workstation 580 and displayed on display 610 (FIG. 9)
to the surgeon. The surgeon then uses this visual feedback in
adjusting the depth of the instrument.
[0118] Surgical Instruments
[0119] Various types of surgical probes or instruments can be
attached to drive mechanism 1110 shown in FIG. 16. One type of
instrument is an electrode, such as a recording micro-electrode or
a stimulating electrode or lesioning electrode. The electrode is
introduced into a rigid insertion (guidance) tube that is attached
to drive mechanism, 1110. Another type of instrument is a
hypothermia cold probe.
[0120] In cases of movement disorder or pain surgery, a chronically
implanted stimulating electrode can be placed utilizing an
insertion tube. The lead, being of a smaller diameter than the
insertion tube, can be slipped through the insertion tube upon
removal of the drive and guide assembly, to allow fixation of the
chronically implanted electrode into the brain. The electrode is
secured to the skull using a compression-fitting. A chronically
implanted recording electrode can similarly be placed during
epilepsy surgery to monitor abnormal activity within the deep brain
utilizing similar techniques.
[0121] When an instrument is to be implanted chronically, it is
important that the instrument is not disturbed during the process
of securing it to the skull. For instance, after a chronically
implanted recording electrode has been accurately positioned using
the guidance fixture, the guidance fixture must be removed before
the lead of the electrode can be secured. However, the electrode
can be dislodged during this process prior to securing the
lead.
[0122] In order to prevent dislodging of the electrode while
removing the guidance fixture, a flexible membrane is used to
constrain the motion of the electrode in the burr hole. Referring
to FIG. 17a, a circular burr hole ring 1240 is inserted into burr
hole 625 after the surgeon drills the burr hole prior to attaching
mounting base 820 over the burr hole. Burr hole ring 1240 has a
thin elastic membrane 1242 across the bottom of the ring.
Therefore, an instrument that passes through the burr hole must
pass through membrane 1242 to enter the brain. Elastic membrane
1242 is made of a material such as Silastic (silicone rubber) that
is biocompatible and non-permeable. The membrane is self-sealing in
that if it is punctured by an instrument that is then withdrawn,
the membrane remains non-permeable.
[0123] After attaching guidance fixture 710 to its mounting base
820, the fixture is aligned to direct an electrode 1250 toward the
target point 1012. Electrode 1250 passes through an insertion tube
1254. Insertion tube 1254 is driven through membrane 1242
puncturing the membrane, then the electrode is driven to target
point 1012. Alternatively, a separate pointed punch can be driven
through the membrane to make a hole through which the insertion
tube is subsequently inserted.
[0124] After electrode 1250 is properly positioned at the target
point, guidance fixture 710 is removed, and insertion tube 1254 is
removed.
[0125] Referring to FIG. 17b, electrode 1250 remains secured by
elastic membrane 1242, preventing the electrode from being
dislodged while the guidance fixture is being removed and the while
the burr hole, which still has burr hole ring 1240 inserted, is
exposed. A burr hole cap 1244 is then secured in burr hole ring
1240. The lead of electrode 1250 is clamped in a channel between
the burr hole ring and cap, thereby preventing tension on the lead
from dislodging the electrode.
[0126] A similar approach is used to secure other chronically
implanted instruments, such as a shunt tube. Membrane 1242 is first
punctured, for instance using a punch, using an insertion tube, or
using the instrument itself. The instrument is inserted using the
guidance fixture. After the guidance fixture is removed, an
appropriate cap are secured to the burr hole ring 1240.
[0127] Note that a burr hole ring 1240 with membrane 1242 is
applicable for securing instruments inserted into the brain using
other methods than guided using a guidance fixture. For instance,
the same burr hole ring and cap can be used when inserting an
instrument freehand or using a conventional stereotactic frame.
[0128] In cases of hydrocephalus or other situations where chronic
drainage of intracranial cavities is necessary, a shunt tube, such
as a ventricular shunt, can be applied through the insertion tube
into the target such as the ventricles of the brain. The shunt tube
will have a stylet and be slipped into the insertion tube.
[0129] The insertion tube structure and its retention ring will
have varying diameters, depending on the diameters of the various
objects that can be placed in the insertion tube, such as the shunt
tube, in this application, or micro-electrodes, in the prior
application. The insertion tube, therefore, will be connected to
the drive mechanism using varying sized retention rings. Referring
to FIG. 16, the retention rings would be fit at points 1133 or 1135
on drive mechanism 1110. The shunt will be directed towards the
target established by the software mechanism alluded to above. The
shunt tube will then be secured to the skull via mechanisms
described in prior art, or using an elastic membrane described
above.
[0130] Alternatively, a biopsy probe can be inserted into the
insertion tube by first placing a biopsy tube with a
trocar/obturator through the insertion tube. The mechanism would
then be directed down towards the appropriate target using the
drive mechanism. The obturator would be removed, and a cutting
blade will then be inserted into the biopsy tube.
[0131] In applications in which a radioactive seed for
brachytherapy, a targeting nodule with a radio sensitizing,
chemotherapeutic agent for external beam radiation, or a sustained
release polymer drug or microdialysis capsule for local drug
administration, are required for placement in a deep brain target,
a different insertion tube can be connected to the drive mechanism
1110. A delivery catheter can be placed through the insertion tube.
The whole mechanism can be directed towards the deep target using
the software system as alluded to above. An insertion plunger can
be used to insert the object of delivery and the system is then be
removed after insertion of the object. A micro-endoscope can also
be inserted through the insertion tube mechanism described above
and deep brain structures can be visualized prior to excision or
lesioning.
[0132] X-Y Table
[0133] In certain surgical procedures, it is desirable to drive a
surgical instrument along several parallel tracks. This is
facilitated using x-y table 1150 (FIG. 16). Before an instrument is
driven toward the target, an offset is adjusted using adjustment
knobs 1061, and 1063. These knobs include markings that allow
precise adjustment.
[0134] An example of a procedure using penetration of an instrument
along parallel tracks involves mapping the electrical activity of a
region of the brain. The surgical instrument in this case is a thin
electrode that is repeatedly inserted to points on a two- or
three-dimensional grid. At each point, electrical activity is
monitored.
[0135] Surgical Retractor
[0136] Referring to FIG. 17c, when larger masses within the brain,
such as brain tumors, have to be removed with precision, the drive
mechanism has a localizing surgical retractor 1210 mounted in place
of the insertion tube, and base platter 1220 has a large central
opening through which the retractor passes. Retractor 1210 includes
three or more spatulas 1212 inserted through base platter 1220 and
the entry column. Each spatula 1212 includes a tracking LED 1214
attached to it. The relationship of the spatulas is controlled by a
screw assembly 1216 that allows the relative distance between the
spatulas to be modified. Relatively small movement at the screw
assembly results in a larger movement at the other ends of the
spatulas due to the pivoting of the spatulas within the retractor.
Tracking LEDs 1214 are tracked by the camera array and the
localization application computes the depth of spatulas 1212 and
their displacement from the central axis. Using the tracking
approach described above, surgical localizing retractor 1210 is
directed towards the brain target. Upon acquiring the target, screw
assembly 1216 is adjusted to expand localizing retractor 1210 to
allow visualization of the underlying brain. A variety of surgical
instruments can be attached to retractor 1210 in addition to using
the retractor with more conventional manual techniques. These
instruments can include an endoscope, an ultrasonic aspirator, an
electronic coagulation/evaporator/ablator, or a laser.
[0137] Fixture Validation
[0138] An optional fixture validation step (FIG. 1, step 130) can
be used to confirm that the position of the tip of the surgical
instrument is accurately tracked. Two types of validation can be
performed. Referring to FIG. 18, guidance fixture 710 is attached
to an upper mounting plate 1334 of a calibration jig 1330. Prior to
attaching guidance fixture 710 to calibration jig 1330, pivoting
locking knob 846 (FIG. 10) is loosened allowing pivoting collar 840
to pivot. After guidance fixture 710 is attached, pivoting collar
840 is centered and pivoting locking knob 846 is tightened. A
guidance tube 1340 is clamped into the guidance fixture, and a
surgical instrument 1342 is passed through the guidance tube.
Guidance tube 1340 protrudes below upper mounting plate 1334. A
ruler 1335 can then be used to measure the depth of penetration of
the guidance tube. Similarly, rule 1335 can be used to measure the
penetration of surgical instrument 1342.
[0139] Referring to FIG. 19, a validation (or "phantom") jig 1312
can also be used. Tracking MIRRF 510 is attached to validation jig
1312. Guidance fixture 710 is be mounted on validation jig 1312. A
phantom target point 1320 at a known position relative to
validation jig 1312, and therefore at a known position relative to
the fiducial points on tracking MIRRF 510, is chosen. The
localization application 588 is programmed with the phantom target
position. Using the procedure that will be used during the surgical
phase, the surgeon performs the registration and alignment steps
and then drives the instrument through guidance fixture 710. if the
tip of the instrument is coincident with the phantom target point,
then guidance fixture 710 is validated. If for some reason the
instrument is not coincident with the phantom target point, for
example, due to improper attachment of the instrument to the drive
assembly resulting in an incorrect depth calibration, the surgeon
readjusts the instrument and attempts the validation step
again.
[0140] Alternative Scanning, Registration, and Tracking
[0141] Other embodiments of the invention use alternative scanning,
registration, and tracking markers, and methods of scanning and
registration.
[0142] In the first embodiment, scanning MIRRF 310 and tracking
MIRRF 510 are star-shaped. Other alternative shapes of MIRRFs can
be used. Referring to FIG. 20, an arc-shaped MIRRF 1410 is attached
to threaded inserts 1420 using bolts 1430, and marking and locking
nuts 1432. Arc-shaped MIRRF 1410 includes scanning fiducial markers
1412. The fiducial markers are more widely spaced than in
star-shaped MIRRFs 310, and 510, resulting in a more accurate
tracing of the MIRRF. During insertion of threaded inserts 1420,
arc-shaped MIRRF 1410 acts as a template for accurate positioning
of the threaded inserts.
[0143] In embodiments described above, threaded inserts are
inserted into the skull to provide the fixed points of attachment
for MIRRFs. Alternative embodiments use of the types of anchors or
forms of mechanical attachment, for example, including protruding
posts that are attached to the skull. A MIRRF is then attached to
the posts.
[0144] Another alternative method of attachment uses subcutaneous
anchors. Referring to FIG. 20a, an insert 1420a in fixed in the
skull. Insert 1420a has a divot in its head, which provides an
accurate position reference. After insert 1420 is attached to the
skull, skin 211 is secured over the insert. At later times, these
divots are used to mate clamping posts 1430a on a MIRRF, which hold
the MIRRF in place. Since implanted divots are covered by the skin,
they can remain in place for an extended period of time.
[0145] Such a subcutaneous insert allows repeated reattachment of a
fixture, such as a scanning or tracking MIRRFs, or repeated
reattachment of a guidance fixture itself. An application of such
periodic reattachment is periodic microrecording from a particular
location in the brain, or repeated lesioning of particular brain
structures.
[0146] Subcutaneous inserts also allow other devices, including
stereotactic radiation devices, to be repeatedly reattached at
precisely the same location. These devices include the Gamma Knike,
Lineal Accelerator (LINAC), or a multi-collimated machine, such as
the PEACOCK device. This approach to reattachment provides greater
precision than is possible using bite plates or facial molds to
reposition the devices.
[0147] An alternative to use of a MIRRF is to attach markers
directly to anchors in the skull. Referring to FIG. 21, each such
anchor, shown as threaded insert 1440, can support a single
scanning marker 1444 on a post 1442, subsequently support a single
registration divot 1450 on a second post 1451, and then support a
single tracking marker, LED 1448, on a third post 1446. The
geometric relationship of the anchor to the scanning marker is the
same as the geometric relationship of the anchor to the tracking
marker thereby allowing a localization application to directly
track the fiducial points by tracking the location of the tracking
marker.
[0148] Using any of the MIRRF structures described, multiple MIRRFs
can be used to provide increased accuracy in registration and
tracking. For example, two star-shaped MIRRFs can be used, one on
each side of the head.
[0149] In other embodiments, alternative attachment methods can be
used to secure a guidance fixture to the skull. For instance, the
mounting base can be relatively small and have extended "legs"
extending radically and secured to the skin or skull with sharp
points. These legs provide stabilization that may not be achievable
using mounting screws through the smaller mounting base. The
mounting base can alternatively include an insert that fits into
the burr hole. This insert can also be threaded to allow direct
attachment of the mounting base to the burr hole.
[0150] In other embodiments, threaded inserts are used to attach,
and subsequently accurately reattach, conventional stereotactic
frames. This allows the conventional stereotactic frame to be
removed and then accurately reattached to the skull. Procedures,
such as fractionated multi-day stereotactic radiation treatments
could then be performed with the stereotactic frame being
reattached for each treatment.
[0151] Referring to FIG. 22, a modified guidance fixture 1510 is
used in combination with a conventional stereotactic frame 1520.
Guidance fixture 1510 includes an x-y positioning table with LEDs
1512 and an instrument drive with an LED 1514 for tracking the
depth of the surgical instrument. The guidance assembly is
positioned on frame 1520 to align with the planned surgical
trajectory. A tracking MIRRF 1530 is attached to frame 1520 to
allow dynamic tracking.
[0152] Rather than using a scanning MIRRF with scanning fiducial
markers, or scanning fiducial markers attached directly to anchors
embedded in the skull, alternative embodiments can use other
features for registration. In one alternative embodiment, paste-on
scanning markers are attached to the skin. During the registration
phase, the cranial probe is positioned at each of the paste-on
markers in turn, rather than at the fiducial points on a MIRRF.
Tracking LEDs are attached in a fixed position relative to the
skull in some other way than using a MIRRF, for example, using an
elastic headband. Rather than using pasted on fiducial markers,
another alternative embodiment uses accessible anatomical features.
These features are located in the scanned image, and the probe is
positioned at these features during the registration phase. Still
another alternative does not use discrete fiducial points, but
rather makes use of the surface shape of the skull in a "surface
merge" approach. The surface of the skull is located in the
three-dimensional image. During registration, the cranial probe
touches a large number of points on the skull. The locations of
these points is matched to the shape of the skull to determine the
conformal mapping from the physical coordinate system to the image
coordinate system.
[0153] In yet another embodiment, referring to FIG. 23, a tracking
MIRRF 1610 can be attached directly to the base of a guidance
fixture 710. Tracking MIRRF 1610 is only useful for tracking after
guidance fixture 710 has been attached to the skull. In this
approach, registration is based on fiducial points elsewhere on the
skull than tracking MIRRF 1610.
[0154] Locating the entry point, over which guidance fixture 710 is
attached can be accomplished using one of a variety of alternative
techniques. For example, the entry point may be known for some
standardized procedures. Alternatively, the entry point may be
determined by registration of the skull and the three-dimensional
image based on fiducial markers attached to the head, for example
using adhesive pads, anatomical markers, or a "surface merge"
technique as described above.
[0155] Once the guidance fixture and tracking MIRRF 1610 are
attached to the skull, LEDs 1620 on tracking MIRRF 1610 are used to
track the location of the skull, and thereby track the location of
the surgical instrument. A reregistration step (FIG. 1, step 160)
can be performed to determine the relative position of the fiducial
points to LEDs 1620.
[0156] Various mechanical adjustments of guidance fixture 710, if
performed when an guidance tube is inserted in the brain, would
potentially damage the brain tissue. The guidance fixture
optionally includes a feature that the various locking knobs and
x-y adjustment knobs are rotated using a removable knob (or key).
When not in use, this knob is stowed on the drive assembly.
Whenever the removable knob is removed from its stowed position,
the signal from an electrical sensor on the drive assembly that is
connected to the workstation causes a warning, for example on the
computer display, to be provided to the surgeon.
[0157] Instrumented and Actuated Guidance Fixtures
[0158] In general, the embodiments of the guidance fixture
described above rely on a surgeon manually adjusting the guidance
fixture and driving a surgical instrument into the body based on
visual feedback. The manual steps carried out by the surgeon
include adjusting the orientation of rotating collar 830 (FIG. 10)
with respect to mounting base 820, and adjusting pivoting collar
840 by turning adjustment knob 844. The surgeon also adjusts x-y
table 1150 (FIG. 10) by turning x-y table adjustment knobs 1061 and
1063 (FIG. 16). The visual feedback which is presented to the
surgeon on a computer display is computed using remote sensing of
the location and adjusted orientation of the fixture. As described
previously, the remote sensing of the guidance fixture is based on
determining the locations of tracking markers attached to the
fixture as well as of tracking markers attached to the head.
[0159] As an alternative to using a remote sensing approach for
determining the position and orientation of the guidance fixture
relative to the body to which the fixture is attached, an
instrumented guidance fixture can be used. In an instrumented
guidance fixture, the position and orientation or the guidance
fixture as well as the position of the surgical instrument relative
to the guidance fixture are determined using sensors which directly
encode the configuration of the fixture. The outputs of these
sensors are used to compute the image which is provided as feedback
to the surgeon. For instance, electrical rotary and linear encoders
are used to generate electrical signals that are passed from the
guidance fixture to the workstation that computes the visual
feedback that is presented to the surgeon.
[0160] Referring to FIG. 24a, an instrumented guidance fixture 2400
includes five electrical sensors, two that encode the angles of
rotation of rotating collar 830 and pivoting collar 840 (sensors
2410), two for the x and y displacements of x-y table 1150 (sensors
2412), and one for the displacement of instrument drive platform
1130 (sensor 2413).
[0161] Referring to FIG. 24b, a workstation 580 accepts and stores
sensor signals 2430 from sensors 2410-2413 (not shown in FIG. 24b)
on instrumented guidance fixture 2400. A fixture tracking
application 2432 executing on workstation 580 takes sensor signals
2430 and computes fixture/instrument location 2434, which includes
the location and orientation of the guidance fixture 2400 and of
the surgical instrument (if an instrument is inserted in the drive
of the fixture). These orientations and locations are computed in
the frame of reference of the base of guidance fixture 2400.
[0162] A display application 2436 combines fixture/instrument
location 2434 with a previously computed base location 2442, which
includes the location and orientation of the base of guidance
fixture 2400 in the frame of reference of the scanned image 410, to
compute the orientation and location of the guidance fixture and
the instrument in the frame of reference of the image. Display
application 2436 then combines this computed location and
orientation with image 410 to form composite image 2444, which
shows representations of the fixture and instrument in conjunction
with one or more views of the scanned image. Composite image 2444
is shown on display 610, which provides visual feedback to the
surgeon who manipulates the guidance fixture and the
instrument.
[0163] Note that the fixture tracking application 2432 executed on
workstation 580 relies on base location 2442, which includes
knowledge of the location and orientation of the base of guidance
fixture 2400 in the frame of reference of the head. Note also, that
once the base of guidance fixture 2400 is attached to the head,
base location 2442 remains fixed as long as the base remains firmly
attached. Therefore, workstation 580 does not require ongoing
updating of base location 2442 once it is initially
established.
[0164] Referring still to FIG. 24b, one method of establishing base
location 2442 is illustrated. In this illustration, using an
approach similar to the registration approaches described
previously, a tracking MIRRF 510 is attached in a known location
relative to a scanning MIRRF that was attached during scanning.
Using a probe 570 that is tracked using camera array 560, the body
and image are first registered. In particular, the tip of probe 570
is first touched to known locations on MIRRF 510 such as divots at
the locations corresponding to locations of scanning markers. A
remote localization application 2440 compares the locations of the
tip of the probe with the coordinates of the scanning markers in
the image. This comparison is used establish a conformal mapping
between the body and image reference frames. Then the tip of the
probe is touched to a set of predetermined points on the base of
guidance fixture 2400. Remote localization application 2440 uses
the locations of the points on the base and the conformal map to
establish base location 2442.
[0165] Using this procedure, once the base has been fixed to the
head, and base location 2442 has been determined, there is no need
to further track MIRRF 510 with the camera array. The patient can
move around and, as long as workstation 580 receives the signals
from sensors 2410, display 610 can provide feedback to the surgeon.
Sensors 2410 can be coupled to workstation 580 in a number of ways,
including using wires 2420 carrying electrical sensor signals.
Alternatively, signals passing through optical fibers, or radio or
optical signals transmitted through the air from the patient to a
receiver attached to the workstation, can be used. In any of these
cases, the patient is free to move around, as long as the sensor
signals are passed to the workstation.
[0166] Separate from instrumentation of a guidance fixture, a
guidance fixture can be actuated as an alternative to requiring
that the guidance fixture be manually adjusted. Referring to FIG.
25a, an actuated guidance fixture 2500 includes a stepper motor
2513 that is couple to drive platform 1130. Rotation of stepper
motor 2513 raises or lowers the drive platform, thereby displacing
an attached instrument. The linear displacement of the drive
platform is directly related to the angular rotation of the stepper
motor. Actuated guidance fixture also includes motors 2510 and
2511, that rotate and pivot the guidance fixture, and two motors
2512 which adjust x-y table 1150.
[0167] Referring to FIG. 25b, in one version of remote actuation of
the guidance fixture, the surgeon provides manual input 2532 to a
controller 2530 by manipulating manual controls. Controller 2530
converts these manual inputs into control signals 2540 for driving
motors 2510-2513. The surgeon relies on visual feedback, as in the
previously described approaches, as he manipulates the manual
controls.
[0168] Alternative versions of actuated guidance fixture 2500 can
use different types of motors. For instance, hydraulic motors can
be used and the guidance fixture and the controller can be coupled
to the guidance fixture by hydraulic lines. This hydraulic approach
provides electrical isolation between the patient and the
workstation. Also, the entire guidance fixture and hydraulic motors
can be fabricated from materials that do not interfere with
scanning. This allows use of such an actuated fixture during
scanning, which is useful in certain operative procedures.
[0169] Control signals provided to actuators on the guidance
fixture can also be used to determine the configuration of the
fixture. For instance, in controlling a stepper motor, the number
of discrete "steps" commanded by a controller can be counted to
determine the angle of rotation of the motor. This computed angle
can be used in addition to, or even instead of, signals from
sensors on the fixture.
[0170] Referring to FIG. 26, a guidance fixture 2600 is both
instrumented with sensors 2410-2413 (not shown) and actuated with
motors 2510-2513 (not shown). Sensor signals 2430 are provided to a
workstation 580 from sensors 2410-2413. The workstation computes
motor control signals 2540 which are used to drive motors
2510-2513. In this arrangement, a control application 2650
executing on workstation 580 uses sensor signals 2430 as feedback
information and controls the guidance fixture by generating motor
control signals 2540. Control application 2650 also accepts base
location 2442 which allows it to compute the location and
orientation of the fixture in the frame of reference of the image
or the body.
[0171] Control application 2650 accepts commands 2620 from the
surgeon. These commands can range in complexity. An example of a
simple command might be to displace a surgical instrument to a
particular depth. A more complex command might be to align the
guidance fixture with a planned target location. In the latter
case, control application 2650 uses a stored target location 2610
and controls motors 2510-2513 to align the fixture. Even more
complex commands can be used to invoke entire preprogrammed
procedures. An example of such a preprogrammed procedure is to map
a region of the brain by repeatedly positioning the x-y table and
inserting and then withdrawing a recording electrode.
[0172] In addition to angular and position sensors, force sensors
can be incorporated into an instrumented guidance fixture.
Referring still to FIG. 26, control application 2650 can provide
feedback signals 2621, including force feedback signals, to the
surgeon.
[0173] Teleoperation
[0174] An actuated guidance fixture, such as actuated guidance
fixture 2500, or actuated and instrumented guidance fixture 2600,
described above, are applicable to telerobotic surgery in which the
surgeon is distant from the patient. A surgical nurse, physician's
associate, or some other assistant to the surgeon is in the some
location as the patient. This assistant performs some functions,
such as attaching the guidance fixture to the patient, but does not
perform the actual surgery.
[0175] Referring to FIG. 27, a three-dimensional image 410 is
produced by scanning a patient. Before scanning, the assistant has
attached scanning markers, such as the scanning MIRRF described
previously, to the patient. The image is sent to workstation 580
through a pair of transceivers 2710, 2712, one located near the
patient, and one near the surgeon. The transceivers can be coupled
by various types of channels, including a radio channel, or a data
network connection. The surgeon locates the scanning markers in the
image, and plans the surgical trajectory.
[0176] At the beginning of the surgical phase, the assistant
locates the entry point and attaches an instrumented and actuated
guidance fixture 2600 to the patient. After the fixture is
attached, signals from the sensors are transmitted to workstation
580 through transceivers 2710, 2712, and control signals are
transmitted back from workstation 580 through the transceivers to
the fixture. In addition, images from camera array 560 are
transmitted to the workstation. A registration step is carried out,
in this case using a probe which is tracked by camera array
560.
[0177] Once guidance fixture 2600 is attached and registered, the
surgeon controls the fixture remotely. Based on the sensor signals
from the guidance fixture, workstation 580 computes images which
are presented on display 610 as visual feedback to the surgeon. The
surgeon can interact with the workstation in a number of ways. in
FIG. 27, a manipulator 2750 is coupled to workstation 580. The
manipulator includes a "phantom" jig and a manipulator fixture that
is similar to the guidance fixture that is attached to the
patient's head. The surgeon adjusts the manipulator fixture which
provides control signals to a teleoperator application 2740
executing on workstation 580. Teleoperator application 2740
converts these control signal to motor control signals for guidance
fixture 2600 and transmits the motor control signals to the
guidance fixture. If the sensors on the guidance fixture include
force sensors, teleoperator application 2740 receives force signals
from guidance fixture 2600 which are used to control manipulator
2750 to provide for feedback to the surgeon.
[0178] During the surgery, the assistant is responsible to tasks
such as attaching the guidance fixture, exchanging instruments in
the guidance fixture, and surgical tasks such as opening the skull
and closing the skin.
[0179] Various alternative manipulators 2750 can be used to provide
a physical interface for the surgeon. For instance a joystick or a
three dimensional pointer (e.g., an instrumented glove) can be used
in conjunction with a head-mounted display in a virtual reality
based arrangement.
[0180] Alternative Registration
[0181] In the approaches described above, in general, registration
is performed using a remote sensing approach. The registration
procedure is used to determine a conformal map between a coordinate
system that is fixed relative to the body and the coordinate system
of the scanned image. Alternative registration procedures do not
rely on remote sensing. These registration procedures also include
steps for determining the location and orientation of an attached
base of a guidance fixture. If an instrumented guidance fixture is
used, remote sensing is not required after the registration
procedure is completed.
[0182] In one alternative approach illustrated in FIG. 28, initial
registration and location of the mounting base is performed by
securing the body in a fixed location relative to the base of an
articulated arm 2820. For example, a head can be secured using a
conventional head frame 2810. The angles in the joints 2822 of
articulated arm 2830 provide signals to workstation 580 which are
used to determine the location of the end of the arm relative to
the base.
[0183] The procedure for determining the location and orientation
of the base in the image coordinate system is as follows.
Articulated arm 2820 is coupled to workstation 580 and provides arm
signals 2850, which encode the joint angles of the arm, to the
workstation. A base localization application 2852, which executes
on workstation 580, determines the coordinates of the end point of
the arm in the reference frame of the base of the arm. In a first
phase of the procedure, the surgeon touches the end point of the
arm to each of a set of fiducial points 2832. Correspondingly,
fiducial point coordinates 421 are stored on workstation 580. Using
fiducial point coordinates 421 and the coordinates of the fiducial
points in the reference frame of the arm, base localization
application 2852 computes a conformal map between the image
coordinate system and the arm coordinate system.
[0184] The second phase of the procedure, the surgical phase,
involves three steps. First, the surgeon locates an entry point by
pointing with the end of the arm and viewing the display to select
an entry point. Next, the surgeon drills the burr hole at the entry
point and attaches the mounting base. Finally, the surgeon touches
the end of the arm to a set of predetermined points on a guidance
fixture mounting base that has already been attached to the head.
Using the locations of these points relative to the base of the arm
and the conformal map computed in the first step, base localization
application 2852 computes base location 2442.
[0185] In another alternative to registering the mounting base, a
miniaturized mechanical arm is attached directly to the body,
thereby not requiring the patient to be restrained during the
registration and base localization procedure. The procedure is
carried out as follows.
[0186] Referring to FIGS. 29a-b, a bone anchor 2910 is fixed in the
skull prior to scanning. Using scanning markers attached to bone
anchor 2910, the locations and orientations of the bone anchors in
the coordinate system of the image are determined after the scan is
obtained. The attached scanning markers are such that the
orientation as well as location of each bone anchor can be
determined. For instance, a small array of scanning markers can be
attached to each bone anchor, and the rotation of the array can be
constrained by the position of an index point 2912 on the bone
anchor.
[0187] A miniature arm 2920 is attached to bone anchor 2910. In
particular, an arm base 2922 is attached to bone anchor 2910. Base
2922 mates with index point 2912 thereby constraining its rotation
about the central axis of the bone anchor. Since the location and
orientation of the bone anchor was previously determined form the
scanned image, a conformal map between the reference frame of
miniature arm 2920 and the image reference frame is computed
without requiring any registration step. The surgeon can touch a
set of fiducial points to verify the accuracy of the conformal
map.
[0188] Referring to FIG. 29a, miniature arm 2920 includes an
instrumental joint 2923 through which a shaft 2924 passes. Joint
2923 allows four degrees of freedom. These degrees of freedom are
(a) rotation around a control axis of base 2922 (i.e., around the
central axis of bone anchor 2910), (b) elevation relative to the
base, (c) rotation of the shaft along its axis, and (d) extension
of the shaft. Joint 2923 includes sensors which generates signals
encoding these four motions. These signals are provided to
workstation 580 (not shown in FIGS. 29a-b). A pointer 2926 is
rigidly attached to shaft 2924, For any position of the tip of
pointer 2926, workstation 580 computes the coordinates of the tip
relative to arm base 2922. Using the conformal map, the workstation
then computes the coordinates of the tip of the arm in the
reference frame of the image.
[0189] Referring to FIG. 29b, miniature arm 2920 is used to locate
entry point 2930 and subsequently registering a mounting base
attached over the entry point.
[0190] Alternatively, referring to FIGS. 29c-d mounting base 2940
can be directly attached to shaft 2924. In this way, an entry point
is selected by moving the mounting base, and attaching the base to
the skull while it is still attached to shaft 2924.
[0191] After the instrumented guidance fixture is attached to the
mounting base, the arm is no longer required and can be removed
from the bone anchor.
[0192] Spinal and General Surgery
[0193] Another aspect of the invention relates to spinal and
general surgery. These approaches include several steps that are in
common with the approaches to brain surgery described above.
[0194] In spinal surgery, the approach is useful for complex spinal
procedures, such as implantation of vertebral pedicle fixation
screws for fusion. Clinical conditions in which this approach may
be useful include degenerative disc and bone disease, tumor,
trauma, congenital or developmental abnormalities, and
infection.
[0195] Referring to the flowchart in FIG. 30, in spinal surgery,
the procedure follows a similar sequence of steps as in the brain
surgery procedure shown in FIG. 1. Referring to FIGS. 31a-b, the
spine 1910 is scanned to produce a three-dimensional spinal image
(step 1810). Rather than attaching scanning markers to the body
prior to scanning, fiducial points are anatomical points of spinal
structure that can be located both on spine 1910 during surgery and
in the spinal image. Fiducial coordinates of these anatomical
points are determined in the same manner as fiducial coordinates of
images of scanning markers are found in the previously described
brain surgery procedures, for example by manually positioning a
cursor on a display of the spinal image (step 1815). One or more
target points are also located in the three-dimensional spinal
image (step 1820).
[0196] During the surgical phase of the procedure, the patient is
positioned on an operating table and spine 1910 exposed. The
patient's position is adjusted so that the curvature of the
patient's spine 1910 matches the curvature in the spinal image in
as close a fashion as possible. For instance, the surgeon matches
an actual interspinous distance equal to the corresponding
interspinous distance in the scanned image.
[0197] A tracking MIRRF 1940 is attached to a spinous process 1912
by a spinous clamp 1932 and a clamping post 1934 (step 1825).
Spinous process 1912 is, in general, the most rostral of the
spinous processes to be studied during a posterior spinal surgical
approach. MIRRF 1940 has a similar shape to tracking MIRRF 510
(FIG. 5), although MIRRF 1940 can have a variety of shapes. MIRRF
1940 includes tracking LEDs 1942.
[0198] A longitudinal spinal rail 1930 is also attached to exposed
spine 1910 (step 1830). One end of spinal rail 1930 is attached to
spinous process 1912 by spinous clamp 1932. A second spinous clamp
1933 is used to secure the other end of spinal rail 1930 to another
spinous process 1913. Longitudinal spinal rail 1930 has distance
markers that are used to measure the separation of spinous clamps
1932 and 1933 to allow the surgeon to obtain an appropriate
correspondence to the patient.quadrature.s position and spine
curvature at the time of scanning (step 1835). Various sizes of
longitudinal spinal rails can be used depending on how many
segments of spine are to be operated upon.
[0199] A registration step is then carried out (step 1840). A probe
with probe LEDs attached to it is tracked using a camera array. In
a procedure similar to that described above for brain surgery, the
coordinates of the fiducial points in the reference frame of MIRRF
1940 are computed after positioning the probe at the fiducial
points. These are matched to the fiducial coordinates found in the
spinal image. Registration can be performed using fiducial points
on only one segment of spine 1910. Because the curvature of the
spine during surgery is adjusted using longitudinal spinal rail
1930 to match the curvature in the spinal image, the remaining
segments of spine 1910 between spinous processes 1912 and 1913 are
also accurately registered. Fiducial points on multiple segments of
spine 1910 can also be used for registration. If the geometric
relationship between the fiducial coordinates in the spinal image
does not match the geometric relationship of the coordinates of the
fiducial points in the reference frame of MIRRF 1940 (step 1845),
one possible source of error is inadequate matching of the
curvature of the spine to the curvature at the time of scanning. In
the case of inadequate matching of the curvature, the surgeon can
readjust longitudinal spinal rail 1930 (step 1835) and attempt the
registration step again until an adequate conformal mapping can be
computed.
[0200] A lateral spinal rail 1950 is then attached to longitudinal
spinal rail 1930 using a mobile rotatory joint 1952. Attached to
lateral spinal rail 1950 is a guidance fixture 1960. Guidance
fixture 1960 includes a planar base 1962 and tracking LEDs 1964 of
similar structure to guidance fixture 710 (FIG. 9). Guidance
fixture 1962 does not, in general, include a guidance tube. A
mounting base 1966 of guidance fixture 1960 clamps to lateral
spinal rail 1950.
[0201] Exemplary spinal surgical procedures involve insertion of a
pedicle screw and insertion of an intervertebral fixation cage into
spine 1910 for spinal stabilization and fusion. These surgical
procedures proceed as follows.
[0202] Guidance fixture 1960 is positioned over the targeted
position by sliding lateral spinal rail 1950 along longitudinal
spinal rail 1940 and securely tightening mobile rotatory joint
1952, and then securely tightening guidance fixture 1960 in
position on lateral spinal rail 1950 (step 1850). An example of a
targeted position is the left pedicle of the L1 vertebral body.
[0203] A trajectory from guidance fixture 1960 to the targeted
position is then replanned (step 1855). The replanned trajectory
can be checked to verify that it avoids critical neural structures.
Guidance fixture 1960 is then aligned using the two-step rotation
and pivoting procedure described above, using visual feedback in a
navigational view (step 1860).
[0204] If the surgical procedure involves pedicle screw fixation, a
drill is introduced through guidance fixture 1960 and a hole is
drilled through the pedicle into the vertebral body, without
violating any critical neural structure. The pedicle screw is then
introduced into the pedicle through the guidance fixture 1960 (step
1865). As with the instrument drive used for brain surgery, the
drill can include a tracking LED attached to it for tracking
insertion of the drill.
[0205] If the procedure involves another target on the spine (step
1870), mobile rotatory joint 1952 and guidance fixture 1960 are
then loosened, and lateral spinal rail 1950 and guidance fixture
1960 are slipped over to the next appropriate target and the above
procedure is repeated. In this fashion, rapid insertion of pedicle
screws is accomplished.
[0206] If the surgical procedure involves insertion of
intervertebral fixation cages guidance fixture 1960 is targeted
towards a disc space. The disc is removed through guidance fixture
1960 using a standard disc removal system. The fixation cage is
then inserted using guidance fixture 1960 into the intervertebral
space.
[0207] In the surgical procedure involves percutaneous spinal
fixation, incisions are made to expose spinous processes 1912, 1913
and longitudinal spinal rail 1930 and MIRRF 1940 are attached as
described above. After registration using one or both of the
exposed spinous processes, guidance fixture 1960 is attached and
aligned on a trajectory through the pedicle or the intervertebral
disc space. A small incision is made in the skin underneath
guidance fixture 1960. An insertion tube is then be placed through
guidance fixture 1960 so as to rapidly dissect through muscle and
direct along the trajectory path and directed towards the pedicle
or the intervertebral disc space. Using the techniques described
above, the pedicle screws or intervertebral fixation cages can then
be applied.
[0208] Related procedures can also be used for spinal cord surgery.
In spinal cord surgery, an electrode can be placed within the
spinal cord to make electrical measurements. Then, other surgical
instruments can be introduced into the spinal cord based on the
scanned image and the electrical measurements.
[0209] An alternative method of registration in spinal surgery uses
instrumented miniature arm 2920 (FIG. 29a) is attached to the
longitudinal spinal rail, rather than to a bone anchor 2910 as in
the case of brain surgery. In a registration step, the surgeon
positions the tip of arm 2924 at multiple anatomical point. Using
the configuration of the arm when touching the points, the
localization application executing on the workstation determines
the location and orientation of the arm relative to the spine. The
miniature arm is then used to orient the base of the guidance
fixture. Since the base of the arm is at the known location and
orientation relative to the spine, and the guidance fixture is at a
known location and orientation relative to the base of the arm, the
localization application can compute the location and orientation
of the guidance fixture relative to the spine. This location and
orientation is then displayed to the surgeon.
[0210] General Surgery
[0211] Another aspect of the invention relates to general surgery,
such as abdominal surgery. Referring to FIGS. 32a-b, the approach
is applicable, for example, for biopsy and draining of a liver cyst
2017. Referring to FIG. 32a, prior to scanning, a base plate 2010
is attached to the pelvis 2015, or another fixed bony structure,
utilizing a percutaneous technique using several screws. A scanning
MIRRF 2020 is attached to a column 2012 which is attached to base
plate 2010. A scan of the patient is taken. A target is located in
the scanned image within the body, in this example within the liver
2016. Column 2012 and scanning MIRRF 2020 are removed, and base
plate 2010 is left attached to the patient.
[0212] Referring to FIG. 32b, at the time of surgery, column 2012
is reattached to base plate 2010 and a tracking MIRRF 2022 of the
same geometry as scanning MIRRF 2020 is attached to column 2012.
Registration of the tracking MIRRF with the image is performed
using a surgical probe as in the brain surgery registration
procedure described above.
[0213] In an approach similar to that used for spinal surgery, a
guidance fixture 2030 is attached to column 2012 using a rod 2032
and a clamp. Using the trajectory replanning and two-step alignment
procedure described above, guidance fixture 2030 is aligned with
the planned target.
[0214] A small incision is made in the skin along the instrument
trajectory. A guidance tube 2035 is then inserted through guidance
fixture 2030 towards the target. A variety of general surgical
instruments, such as an optical fiber for endoscopic visualization,
an excision device, a vascular coagulator, a biopsy tube, or a
drainage tube, can be passed through the guidance tube. The depth
of penetration of the instrument is tracked using a workstation and
displayed to the surgeon.
[0215] As an alternative to attaching column 2012 to a base plate
attached to the pelvis, column 2012 can be attached to an inferior
rib 2018 near the liver on the right upper quadrant of the abdomen,
both anteriorly and posteriorly.
[0216] If a second surgical instruments is necessary, a secondary
guidance fixture can attached to column 2012 and aligned by the
same technique, and the second instrument passed through the
secondary guidance fixture and through a second incision. Multiple
instruments can be placed in this manner using multiple guidance
fixtures.
[0217] Head-Mounted Camera Array
[0218] In yet another alternative approach directed to stereotactic
brain surgery, a lightweight camera array is attached directly to
anchor screws mounted in the skull, as shown in FIG. 33. The camera
array is used to track the location and orientation of a guidance
fixture, probes, and instruments relative to the head. Since the
cameras move with the patient, the patient can be free to move
around without requiring separate tracking of the patient in order
to compute the relative displacement of instruments relative to the
patient.
[0219] Using this approach, two or more bone anchors 1700 are
attached to the skull. Scanning markers are attached to anchors
1700 and the patient is scanned producing a three-dimensional
image. Using techniques described above, the location and
orientation of each bone anchor is determined from the scanned
image.
[0220] At the time of surgery, carbon-fiber, acrylic or similar
removable posts 1710 are attached to each of the bone anchors 1700.
An array of cameras 1720, using CCD cameras with short focal-length
lens, are fixed to the posts, directed roughly towards the
skull.
[0221] Cameras 1720 serve the purpose of camera array 560 (FIG. 5)
in the approaches in which the patient is free to move relative to
the camera array. In this approach, although free to move around,
the patient is essentially fixed relative to the cameras. There is
therefore no need to track both the body and the guidance fixture
since the body doesn't move relative to the cameras. Moreover, the
locations and orientations of anchors 1700 in the image reference
frame are determined by locating the scanning markers that are
attached to these anchors prior to scanning. Since the geometry of
posts 1710 is also known, the locations of the camera in the
reference frame of the image are known. Essentially, the conformal
map between the image reference frame and the camera reference
frame can be pre-computed given the locations and orientations of
the bone anchors. The location of an LED in the camera reference
frame is determined from the digitalized images produced by cameras
1720 and then transformed to the image reference frame. In this way
the location and orientation of guidance fixture 710 is tracked
without requiring the surgeon to carry out explicit registration
steps.
[0222] As an alternative to mounting the cameras on posts 1710,
other types of mounting fixtures can be attached to anchors 1700.
For instance, a single fixture can be mounted to multiple anchors.
Also, a customized mounting fixture can be fabricated to position
the cameras in a known position relative to the anchors.
[0223] Alternative Embodiments
[0224] Alternative related embodiments can make use of known
geometric relationships of points on various devices. For instance,
the relationship between the tip of a probe and the location of
tracking LEDs can be calibrated and used by a localization
application to compute the location of tip using the computed
location the LEDs. Similarly, the relationship between the location
of fiducial points on a MIRRF and tracking LEDs call be calibrated,
thereby allowing a localization application to compute the
coordinates of fiducial points from the coordinates of the tracking
LEDs without using the registration procedure described above.
[0225] In the above embodiments, tracking LEDs are tracked using a
camera. Other alternative embodiments can use other
three-dimensional sensing and tracking approaches. Rather than
LEDs, other tracking markers that are active emitters of
electromagnetic or mechanical energy such as electronic sparks,
heat, magnetic energy, or sound can be used. Appropriate
three-dimensional tracking approaches, for example, using imaging
or triangulation techniques determine the three-dimensional
coordinates of the emitters. Alternatively, tracking markers that
are passive reflectors or transducers of externally applied
localizing energy, such as infrared light, sound, magnetism, can be
used.
[0226] The devices described above can be made of a variety of
materials. One alternative is to use a material, such as carbon
fiber, which does not interfere with MRI scanning. This allows use
of the devices during intraoperative MRI scanning. Also, use of
hydraulic drive mechanisms rather than electrical motors avoids
interference with MRI scanning.
[0227] In the surgical procedures described above, the patient is
not necessary immobilized. It may be desirable, however, to
immobilize the patient, for example by clamping the guidance
fixture to an operating table, at some times during the
surgery.
[0228] It is to be understood that the foregoing description is
intended to illustrate and not limit the scope of the invention,
which is defined by the scope of the appended claims. Other
aspects, advantages, and modifications are within the scope of the
following claims.
* * * * *