U.S. patent application number 09/846640 was filed with the patent office on 2001-10-04 for instrument guidance for stereotactic surgery.
Invention is credited to Bucholz, Richard D., Carroll, Catalina J., Clayton, John B., Franck, Joel I., Frank, Kevin J., Franklin, Ronald J., Haer, Frederick C., Henderson, Jaimie, Smith, Kurt R..
Application Number | 20010027271 09/846640 |
Document ID | / |
Family ID | 22050645 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010027271 |
Kind Code |
A1 |
Franck, Joel I. ; et
al. |
October 4, 2001 |
Instrument guidance for stereotactic surgery
Abstract
A method and apparatus for positioning a surgical instrument
during stereotactic surgery using a guidance fixture. The guidance
fixture includes an upper portion, which includes an instrument
guide for moving the surgical instrument along a constrained
trajectory relative to the upper portion, and includes an
adjustable base supporting the upper portion, which includes a
mounting base and an adjustment mechanism. The adjustable base can
include a rotating collar attached to the mounting base and a
pivoting collar coupling the rotating collar to the upper portion.
A remote sensing device, such as a camera array sensing LEDs on the
fixture, is used to determine the orientation of the upper portion
of the guidance assembly in relation to the body.
Inventors: |
Franck, Joel I.; (Durham,
ME) ; Haer, Frederick C.; (Brunswick, ME) ;
Franklin, Ronald J.; (Bowdoinham, ME) ; Frank, Kevin
J.; (Lafayette, CO) ; Clayton, John B.;
(Superior, CO) ; Henderson, Jaimie; (St. Louis,
MO) ; Bucholz, Richard D.; (St. Louis, MO) ;
Smith, Kurt R.; (Eldorado Spring, CO) ; Carroll,
Catalina J.; (Memphis, TN) |
Correspondence
Address: |
G. ROGER LEE
Fish & Richardson P.C.
225 Franklin Street
Boston
MA
02110-2804
US
|
Family ID: |
22050645 |
Appl. No.: |
09/846640 |
Filed: |
May 1, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09846640 |
May 1, 2001 |
|
|
|
09063658 |
Apr 21, 1998 |
|
|
|
Current U.S.
Class: |
600/426 ;
606/130 |
Current CPC
Class: |
A61B 2034/2055 20160201;
A61B 2090/363 20160201; A61B 2034/2072 20160201; A61B 34/20
20160201; A61B 90/11 20160201; A61B 2034/2068 20160201; A61B
2034/107 20160201 |
Class at
Publication: |
600/426 ;
606/130 |
International
Class: |
A61B 006/00 |
Claims
What is claimed is:
1. A method for positioning a surgical instrument during
stereotactic surgery, comprising: providing a guidance fixture that
includes an upper portion, including an instrument guide for moving
the surgical instrument along a constrained trajectory relative to
the upper portion, and includes an adjustable base supporting the
upper portion, including a mounting base and an adjustment
mechanism; attaching the guidance fixture to a body, including
attaching the mounting base to the body; determining using a remote
sensing device the orientation of the upper portion of the guidance
fixture in relation to the body; displaying a representation of a
relationship of the constrained trajectory and a target point in
the body; and aligning the guidance fixture, including aligning the
orientation of the upper portion to achieve a desired relation
between the constrained trajectory and the target point, including
rotating the upper portion about a central axis of the mounting
base and pivoting the upper portion to adjust an angle between the
upper portion and the central axis.
2. The method of claim 1 wherein determining the orientation of the
upper portion includes: determining the locations of a first
plurality of tracking markers affixed to the upper portion;
determining the locations of a second plurality of tracking markers
affixed to the body; and computing the orientation using the
locations of the first and the second pluralities of tracking
markers.
3. The method of claim 1 further comprising: locking the adjustment
mechanism to fix the orientation of the upper portion in relation
to the body; determining a displacement of the surgical instrument
along the constrained trajectory; displaying a representation of a
location of the surgical instrument in relation to the body;
guiding the surgical instrument into the body along the constrained
trajectory.
4. The method of claim 3 wherein determining the displacement of
the surgical instrument includes: determining using a remote
sensing device a location of a tracking marker affixed in a fixed
relationship to the surgical instrument; determining the locations
of a plurality of tracking markers affixed to the guidance
assembly; and computing the displacement using the location of the
marker affixed in a fixed relationship to the surgical instrument
and the locations of the plurality of tracking markers affixed to
the guidance assembly.
5. A method for positioning a surgical instrument during
stereotactic surgery comprising: providing a guidance fixture that
includes an upper portion, including an instrument guide for moving
the surgical instrument along a constrained trajectory relative to
the upper portion, and includes an adjustable base supporting the
upper portion, including a mounting base and an adjustment
mechanism; attaching the guidance fixture to a body, including
attaching the mounting base to the body; determining using a remote
sensing device the orientation of the upper portion of the guidance
assembly in relation to the body; displaying a representation of a
relationship of the constrained trajectory and a target point in
the body; and aligning the guidance fixture, including aligning the
orientation of the upper portion to achieve a desired relation
between the constrained trajectory and the target point; attaching
at an attachment location on the body a scanning frame that
includes a plurality of scanning markers; scanning a
three-dimensional image of the body, including locating images of
the scanning markers in the three-dimensional image; attaching to
the body a tracking frame that includes a plurality of tracking
markers; and registering the body and the three-dimensional image,
including tracking the tracking markers in the tracking frame, and
locating points relative to the body which correspond to the
locations of the scanning markers.
6. The method of claim 5 wherein attaching the tracking frame
includes attaching the tracking frame in a predetermined location
in relation to the attachment location of the scanning frame.
7. The method of claim 5 wherein locating points relative to the
body which correspond to the locations of the scanning markers
includes: tracking the location of a point on a probe using the
remote sensing device; positioning the point on the probe at each
of the points on the body corresponding to the scanning
markers.
8. The method of claim 5 wherein locating points on the body
includes computing the locations of points relative to the body
which correspond to the locations of the scanning markers using a
known geometry relationship of the locations of the scanning
markers on the attached scanning frame and the locations of the
tracking markers on the attached tracking frame.
9. The method of claim 1 wherein displaying the representation of
the relationship of the constrained trajectory and the target point
includes displaying a representation of the target point,
displaying a representation of the range of possible orientations
of the guidance fixture, displaying a first line segment
corresponding to possible orientations of the guidance fixture that
could result from pivoting the upper portion at a current degree of
rotation of the upper portion, and displaying an indication of a
current degree of pivoting of the upper portion.
10. A guidance fixture for guiding a surgical instrument into a
body during stereotactic surgery, comprising: an upper portion
including an instrument guide for moving the surgical instrument
along a constrained trajectory relative to the upper portion; an
adjustable base supporting the upper portion, including a mounting
base for attaching the guidance fixture to a body, the mounting
base having central opening and a central axis passing through the
central opening, and an orientation adjustment mechanism coupled
between the mounting base and the upper portion, a configuration of
the adjustment mechanism determining the orientation of the upper
portion relative to the mounting base; and a plurality of tracking
markers for tracking with a remote sensing device.
11. The guidance fixture of claim 10 wherein the plurality of
tracking markers includes a plurality of light emitting diodes and
the remote sensing device includes a plurality of cameras.
12. A guidance fixture for guiding a surgical instrument into a
body during stereotactic surgery, comprising: an upper portion
including an instrument guide for moving the surgical instrument
along a constrained trajectory relative to the upper portion; an
adjustable base supporting the upper portion, including a mounting
base for attaching the guidance fixture to a body, the mounting
base having central opening and a central axis passing through the
central opening, and an orientation adjustment mechanism coupled
between the mounting base and the upper portion, a configuration of
the adjustment mechanism determining the orientation of the upper
portion relative to the mounting base; wherein the orientation
adjustment mechanism includes a rotation adjustment mechanism and a
pivoting adjustment mechanism, wherein adjustment of the rotation
adjustment mechanism rotates the upper portion about the central
axis, and adjustment of the pivoting adjustment mechanism adjusts
an angle between the upper portion and the central axis.
13. The guidance fixture of claim 12 wherein the rotation
adjustment mechanism includes a rotating collar attached to the
mounting base and the pivoting adjustment mechanism includes a
pivoting collar coupling the rotating collar to the upper
portion.
14. The guidance fixture of claim 13 wherein the adjustable base
further includes a rotation locking screw for preventing rotation
of the rotating collar and a pivoting locking screw for preventing
pivoting of the pivoting collar.
15. The guidance fixture of claim 14 wherein the upper portion
includes an x-y table adjustment of which displaces the constrained
trajectory.
16. A guidance fixture for guiding a surgical instrument into a
body during stereotactic surgery, comprising: an upper portion
including an instrument guide for moving the surgical instrument
along a constrained trajectory relative to the upper portion
wherein the instrument guide includes a driving mechanism for
positioning the instrument along the constrained trajectory; and an
adjustable base supporting the upper portion, including a mounting
base for attaching the guidance fixture to a body, the mounting
base having central opening and a central axis passing through the
central opening, and an orientation adjustment mechanism coupled
between the mounting base and the upper portion, a configuration of
the adjustment mechanism determining the orientation of the upper
portion relative to the mounting base.
17. The guidance fixture of claim 16 wherein the constrained
trajectory is a linear trajectory.
18. The guidance fixture of claim 16 wherein the upper portion
includes a plurality of tracking markers and the driving mechanism
includes an instrument tracking marker for tracking a location of
the instrument using a remote sensing device.
19. A system for stereotactic surgery on a body, comprising: a
remote sensing device; a tracking frame for attachment to the body,
including a plurality of tracking markers for tracking a location
and an orientation of the body by using the remote sensing device;
a guidance fixture including an upper portion including an
instrument guide for moving the a surgical instrument along a
constrained trajectory relative to the upper portion, an adjustable
base supporting the upper portion, including a mounting base for
attaching the guidance fixture to a body, the mounting base having
central opening and a central axis passing through the central
opening, and an orientation adjustment mechanism coupled between
the mounting base and the upper portion, configuration of the
adjustment mechanism determine the orientation of the upper portion
relative to the mounting base, and a plurality of tracking markers
for tracking a location of the upper portion of the guidance
fixture; a tracking system for accepting the locations of the
tracking markers on the tracking frame and the locations of the
tracking markers on the guidance fixture, and computing a geometric
relationship between the constrained trajectory and the body; and a
display system for presenting an image of the body and the
geometric relationship between the constrained trajectory and the
body.
20. The system of claim 19 wherein the remote sensing device
includes a plurality of cameras, and the tracking markers are light
emitting diodes.
21. A method for positioning a surgical instrument during
stereotactic surgery, comprising: providing a guidance fixture that
includes an upper portion, including an instrument guide for moving
the surgical instrument along a constrained trajectory relative to
the upper portion, and includes an adjustable base supporting the
upper portion, including a mounting base and an adjustment
mechanism; attaching the guidance fixture to a body, including
attaching the mounting base to the body; sensing using a remote
sensing device locations of a plurality of tracking markers affixed
to the upper portion of the guidance fixture; determining a
location and an orientation of the upper portion using the
plurality of sensed locations of the tracking markers; sensing
using the remote sensing device a location of a tracking marker
affixed to the instrument guide; determining a location of the
instrument using the determined location and orientation of the
upper portion and the sensed location of the tracking marker
affixed to the instrument guide.
22. An adjustable guidance fixture for stereotactic surgery
comprising: an upper portion including an instrument guide for
moving a surgical instrument along a constrained trajectory
relative to the upper portion; an adjustable base, including a
mounting base for attaching the guidance fixture to a body, and an
orientation adjustment mechanism coupled between the mounting base
and the upper portion; a plurality of tracking markers affixed to
the upper portion for tracking a location and an orientation of the
upper portion using a remote sensing device; and a tracking marker
affixed to the instrument guide for tracking a motion of the
surgical instrument using the remote sensing device.
23. A method for adjusting a guidance fixture for stereotactic
surgery, comprising: attaching the guidance fixture to the body at
an entry point to the body, the guidance fixture having an
adjustable orientation; displaying a planar section of a
three-dimensional image of the body, including displaying a
representation of the orientation of the guidance fixture, the
planar section containing a target point within the body; adjusting
the orientation of the guidance fixture using a first constrained
motion of the guidance fixture until the orientation lies in a
plane corresponding to the displayed planar section; adjusting the
orientation of the guidance fixture using a second constrained
motion of the guidance fixture, such that the orientation continues
to lie in the plane corresponding to the displayed planar section,
until the orientation passes through the target point.
24. A guidance fixture for stereotactic surgery on a body,
comprising: an instrument guide for moving a surgical instrument
along a constrained trajectory relative to the instrument guide; an
adjustable base supporting the instrument guide, including a
mounting base having a central axis and an adjustment mechanism
coupled between the mounting 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 mounting base; and a signaling device for providing a signal
representation of the configuration of the adjustment mechanism;
wherein the adjustment mechanism includes a rotation adjustment
mechanism and a pivoting adjustment mechanism, adjustment of the
rotation adjustment mechanism rotates the instrument guide about
the central axis, and adjustment of the pivoting adjustment
mechanism adjusts an angle between the instrument guide and the
central axis.
25. The guidance fixture of claim 24 wherein the mounting base
includes a portion for mating directly with the body.
26. A guidance fixture for stereotactic surgery on a body,
comprising: an instrument guide for moving a surgical instrument
along a constrained trajectory relative to the instrument guide; an
adjustable base supporting the instrument guide, including a
mounting base having a central axis and an adjustment mechanism
coupled between the mounting 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 mounting base; and a signaling device for providing a signal
representation of the configuration of the adjustment mechanism
wherein the signaling device includes a plurality of tracking
markers and the signal representation of the configuration includes
a plurality of signals propagating from corresponding tracking
markers.
27. The guidance fixture of claim 26 wherein at least some of the
plurality of tracking markers are in fixed locations relative to
the instrument guide.
28. The guidance fixture of claim 26 wherein the signals
propagating from the tracking markers are electromagnetic
signals.
29. The guidance fixture of claim 26 wherein the tracking markers
are light emitting diodes and the signals propagating from the
tracking markers are optical signals.
30. The guidance fixture of claim 26 wherein the signals
propagating from the tracking markers are acoustic signals.
31. The guidance fixture of claim 10 wherein the tracking markers
emit signals to the remote sensing device.
32. The guidance fixture of claim 10 wherein the tracking markers
reflect signals to the remote sensing device.
Description
RELATED APPLICATION
[0001] This application is a continuation and claims the benefit of
priority under 35 USC 120 of U.S. application Ser. No. 09/063,658,
filed Apr. 21, 1998. The disclosure of the prior application is
considered part of (and is incorporated by reference in) the
disclosure of this application.
BACKGROUND
[0002] This invention relates to guidance of surgical instruments
using stereotactic localization.
[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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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
[0015] In one aspect, in general, the invention is a method for
positioning a surgical instrument during stereotactic surgery by
providing a guidance fixture that includes an upper portion,
including an instrument guide for moving the surgical instrument
along a constrained trajectory relative to the upper portion, and
also includes an adjustable base supporting the upper portion,
including a mounting base and an adjustment mechanism. The method
includes attaching the guidance fixture to a body, including
attaching the mounting base to the body. The method also includes
determining, using a remote sensing device, the orientation of the
upper portion of the guidance assembly in relation to the body, and
displaying a representation of a relationship of the constrained
trajectory and a target point in the body. The method also includes
aligning the guidance fixture, including aligning the orientation
of the upper portion to achieve a desired relation between the
constrained trajectory and the target point.
[0016] The invention can include one or more of the following
features.
[0017] Aligning the orientation of the upper portion includes
rotating the upper portion about a central axis of the mounting
base and pivoting the upper portion to adjust an angle between the
upper portion and the central axis.
[0018] Determining the orientation of the upper portion includes
determining the locations of a first set of tracking markers
affixed to the upper portion, determining the locations of a second
set of tracking markers affixed to the body, and computing the
orientation using the locations of the first and the second sets of
tracking markers.
[0019] The method can include locking the adjustment mechanism to
fix the orientation of the upper portion in relation to the body,
and then determining a displacement of the surgical instrument
along the constrained trajectory. For example, a remote sensing
device can be used to locate a tracking marker affixed in a fixed
relationship to the surgical instrument, and used to locate a set
of tracking markers affixed to the guidance assembly. The
displacement can then be computed using the location of the marker
affixed in a fixed relationship to the surgical instrument and the
locations of the set of tracking markers affixed to the guidance
assembly. The method can also include displaying a representation
of a location of the surgical instrument in relation to the body,
and guiding the surgical instrument into the body along the
constrained trajectory.
[0020] The method can also include attaching to the body a scanning
frame that includes a set of scanning markers and then scanning a
three-dimensional image of the body, including locating images of
the scanning markers in the three-dimensional image. The method
then includes attaching to the body a tracking frame that includes
a set of tracking markers, and registering the body and the
three-dimensional image, including tracking the tracking markers in
the tracking frame and locating points on the body corresponding to
the scanning markers. The tracking frame can be attached in a
predetermined location in relation to the attachment location of
the scanning frame. Locating points on the body can be done by
tracking the location of a point on a probe using the remote
sensing device, and positioning the point on the probe at each of
the points on the body corresponding to the scanning markers.
[0021] Aligning the orientation of the upper portion can include
rotating the upper portion about a central axis of the mounting
base, and pivoting the upper portion to adjust an angle between the
upper portion and the central axis. Displaying the representation
of the relationship of the constrained trajectory and the target
point then includes displaying a representation of the target
point, displaying a representation of the range of possible
orientations of the guidance fixture, displaying a first line
segment corresponding to possible orientations of the guidance
fixture that could result from pivoting the upper portion at a
current degree of rotation of the upper portion, and displaying an
indication of a current degree of pivoting of the upper
portion.
[0022] In another aspect, in general, the invention is a guidance
fixture for guiding a surgical instrument into a body during
stereotactic surgery. The fixture includes an upper portion
including an instrument guide for moving the surgical instrument
along a constrained trajectory relative to the upper portion, and
an adjustable base supporting the upper portion, including a
mounting base for attaching the guidance fixture to a body, the
mounting base having central opening and a central axis passing
through the central opening, and an orientation adjustment
mechanism coupled between the mounting base and the upper portion,
configuration of the adjustment mechanism determine the orientation
of the upper portion relative to the mounting base. The guidance
fixture can include a set of tracking markers, such as light
emitting diodes, that can be located by a remote sensing device,
such as an array of camera.
[0023] The orientation adjustment mechanism of the guidance fixture
can include a rotation adjustment mechanism and a pivoting
adjustment mechanism, wherein adjustment of the rotation adjustment
mechanism rotates the upper portion about the central axis, and
adjustment of the pivoting adjustment mechanism adjusts an angle
between the upper portion and the central axis. The rotation
adjustment mechanism can include a rotating collar attached to the
mounting base and the pivoting adjustment mechanism includes a
pivoting collar coupling the rotating collar to the upper portion.
The adjustable base can further include a rotation locking screw
for preventing rotation of the rotating collar and a pivoting
locking screw for preventing pivoting of the pivoting collar.
[0024] The upper portion of the guidance fixture can include an x-y
table adjustment of which displaces the constrained trajectory.
[0025] The instrument guide of the guidance fixture can include a
driving mechanism for positioning the instrument along the
constrained trajectory, such as a linear trajectory.
[0026] In another aspect, in general, the invention is a system for
stereotactic surgery on a body, which includes a remote sensing
device, a tracking frame, including a plurality of tracking markers
for tracking a location and an orientation of the body by the
remote sensing device, and a guidance fixture. The system also
includes a tracking system for accepting the locations of the
tracking markers on the tracking frame and the locations of the
tracking markers on the guidance fixture, and computing a
relationship between the constrained trajectory and the body, and a
display system for presenting an image of the body and the
relationship between the constrained trajectory and the body.
[0027] The invention provides several advantages. A highly accurate
and reproducible way of guiding a surgical instrument deep into a
body is provided without requiring a frame to be fixed to the body
for the entire interval from scanning through subsequent surgery.
Not requiring the frame to be fixed for this time avoids the
inconvenience, discomfort, and inefficiency of placement of a
fiducial frame on a patient. Inaccuracy imparted to an MRI scan by
electromagnetic interaction with a reference frame or to a CT scan
by x-ray interaction with the frame is also improved. Furthermore,
by providing a compact and relatively lightweight guidance fixture,
the patient is not required to the be immobilized during surgery
and therefore may not require general anesthesia or heavy sedation.
This can allow immediate determination of the response to a
surgical intervention in behavioral or physiological terms without
interference of general anesthesia or heavy sedation. In addition,
both the patient and the sensors used to locate a patient and a
surgical instrument can be mobile providing further flexibility in
operating procedures.
[0028] An additional advantage is that the invention does not
require immobilizing (i.e., clamping in a fixed position) the
patient. This contributes to patient comfort which can extend the
time a surgical procedure can be carried out. Furthermore, since a
guidance fixture is not attached until a scan has been made,
surgical time is further extended as discomfort generally relates
to having a guidance fixture attached. Also, alignment of the
guidance fixture is made easier with this invention, and therefore,
less time can be spent on alignment, thereby leaving more time for
the actual surgical procedure.
[0029] Another advantage of the invention is that alignment of the
guidance fixture is performed using motions, each of which is
constrained to one degree of freedom (e.g., rotation or pivoting).
When the two motions are clamped in position, this arrangement
provides a relatively stable alignment compared to alternative
arrangements in which a two degree of freedom motion (such as
alignment of a ball and socket arrangement) is clamped.
[0030] Yet another advantage of the invention is that the
constrained motions of the guidance fixture, that is, the rotation
and pivoting motions, are directly reflected in the computer
displayed navigational view, thereby greatly simplifying
targeting.
[0031] Other features and advantages of the invention will be
apparent from the following description, and from the claims.
DESCRIPTION OF THE DRAWING
[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-sectional 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] FIG. 17 is a retractor in a guidance fixture;
[0049] FIG. 18 is a calibration jig;
[0050] FIG. 19 is a phantom jig and a guidance fixture and a
tracking MIRRF attached to the jig;
[0051] FIG. 20 is an arc shaped MIRRF attached to a head including
a view of a threaded insert and mounting bolt;
[0052] FIG. 21 is a scanning marker and a tracking marker attached
to a threaded insert;
[0053] FIG. 22 is a guidance fixture and a tracking MIRRF attached
to a conventional stereotactic frame; and
[0054] FIG. 23 is a tracking MIRRF attached directly to a guidance
fixture.
DESCRIPTION
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] 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.
[0060] 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.
[0061] Other than an optional fixture validation (FIG. 1, step
130), all the preoperative steps are complete at this point.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] Composite image 599 typically includes a three-dimensional
surface view and three orthogonal planar views.
[0072] 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.
[0073] 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.
[0074] 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.
[0075] 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.
[0076] 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.
[0077] 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).
[0078] 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 can maintain a continuously updated
display.
[0079] 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.
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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.
[0086] 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.
[0087] 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.
[0088] 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.
[0089] 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.
[0090] 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.
[0091] 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).
[0092] 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 navigational view, is
orthogonal to planes 1020 and 1024 and passes through target point
1012.
[0093] 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.
[0094] 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 o.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 .sub.1 with the
desired orientation in plane 1020, while the angle .sub.2 between
the orthogonal projection line 1042 in plane 1022 and the desired
orientation in plane 1022 increases, ultimately to o.sub.2 when
line 1040 is coincident with plane 1022.
[0095] Referring to FIG. 14c, the second alignment motion reduces
the angle o.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 o.sub.2 is zero, that is, the
orientation line 1040 is coincident with the intersection of planes
1020 and 1022.
[0096] 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.
[0097] 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.
[0098] 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.
[0099] 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.
[0100] 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.
[0101] 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.
[0102] 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.
[0103] 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.
[0104] 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.
[0105] 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. 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 via a
compression fitting described above.
[0106] 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.
[0107] 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.
[0108] In certain surgical procedures, it is desirable to drive a
surgical instrument along several parallel tracks. This is
facilitated using x-y table 1150. 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.
[0109] 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.
[0110] Referring to FIG. 17, 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.
[0111] 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, ruler 1335 can be used to measure the
penetration of surgical instrument 1342.
[0112] 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.
[0113] Other embodiments of the invention use alternative scanning,
registration, and tracking markers, and methods of scanning and
registration.
[0114] 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.
[0115] In embodiments described above, threaded inserts are
inserted into the skull to provide the fixed points of attachment
for MIRRFs. Alternative embodiments use other types of anchors or
forms of mechanical attachment. Protruding posts can be attached to
the skull. A MIRRF is then attached to the posts. Also, inserts can
be implanted in the skull which provide precisely positioned
"divots." These divots are used to mate clamping posts on a MIRRF,
which hold the MIRRF in place. Such implanted divots can be covered
by the skin and remain in place for an extended period of time.
[0116] 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.
[0117] 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.
[0118] 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.
[0119] 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.
[0120] 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.
[0121] 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.
[0122] 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.
[0123] 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.
[0124] 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.
[0125] 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.
[0126] Alternative related embodiments can make use of known
geometric relationships of points on various devices.
[0127] 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 can 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.
[0128] 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.
[0129] 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.
[0130] 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.
[0131] 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.
* * * * *