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BACKGROUND TO THE INVENTION
The field of so-called frameless stereotaxy, which includes use of
digitized stereotactic navigators of a variety of kinds, has been well
known for several years. Many types of stereotactic or so-called frameless
digitizers are available, and such stereotactic navigators include
mechanical operating arms, ultrasonic localizers, infrared light-tracking
digitizers, magnetic digitizers, and others. These digitizers are designed
to provide data relative to detection apparatus that can be used to track
their position or the position of an instrument in space relative to a
surgical field. For example, a surgical instrument mounted with
light-emitting diodes or attached to a mechanical operating arm can send
electronic signals to a computer graphic workstation which can assimilate
these signals and determine the position and movement of the stereotactic
navigator. Typically, to relate the position quantitatively of the
stereotactic navigator to the patient's anatomy, a calibration maneuver is
performed. For example, taking the case of neurosurgery, where the
selected target position would be inside the brain, the patient is scanned
in an imaging scanner. The image scan data is usually stacks of
two-dimensional data that has been referenced into a stereotactic scanner
coordinate frame by means of index markers placed on the patient's head or
use of natural landmarks that are identifiable both in the image scan data
and also physically on the patient's anatomy. The calibration process for
the stereotactic navigator might consist of touching the instrument which
holds the navigator devices to a series of three or more index marker
points located on the surface of the patient's head or even contour
tracings or natural anatomical landmarks on the patient's head, and by
registering the electronic data in these particular calibration point
positions, the stereotactic navigator can be "calibrated" relative to the
patient's physical anatomy and therefore relative to the image scanner
data representative of the tomographic or three-dimensional image (CT,
MRI, PET, SPECT, etc.) of the patient's head stored in a computer graphic
workstation. Once the calibration process is complete, then movement of
the stereotactic navigator relative to the patient's anatomy will enable
visualization on the computer graphic workstation of where the instrument
probe is pointing towards the anatomy and inside of the anatomy. In this
way, the navigator can be used to plan interventions in the brain or to
visualize the internal anatomy of the brain including pathology,
pre-operative planning, or intraoperative guidance to neurosurgery. This
technique is now known in the state of the art.
One of the problems associated with such stereotactic navigators can occur
in the sequence of the operation. For example, if markers are placed on
the patient's skin during the image scanning and the patient is then
brought to the operating room, he is anesthetized and put into a head
clamp. Such a head clamp is shown in FIG. 1. The stereotactic navigator is
then calibrated off of the positions of the index markers, and typically
there are three or more of these markers located around the patient's
head. By the way, these markers could be natural anatomical landmarks or
the surface contour of the patient's head, for that matter. Once the
calibration of the navigator is complete, the patient's head is sterile
draped and the operation can begin. The navigator can then be used to
point at the patient's head, and assessment can be made of the appropriate
approach, for example, to a target within the head. A problem can occur,
however, after sterile draping because the sterile draping will frequently
cover up or totally obscure the index markers which enable the calibration
in the first place, at a time when the field was not sterilely prepared.
After sterile draping and the procedure begins, if for any reason, such as
a power failure or movement of the navigator's interrogation system
relative to the head, the navigator may be out of calibration relative to
the patient's anatomy, and thus the navigator will be out of calibration
with the three-dimensional data set from the image scanner. The utility of
the navigator is then lost. One example of this might be power failure
during the operation which, for the case of the mechanical operating arm,
would shut down the readouts for the encoders which read out the position
of the articulating links of the arm. Another example might be the
movement of the patient's head relative to interrogation cameras in the
case of light-emitting diode (LED) tracking systems of an instrument or a
microscope. Yet another example of an intraoperative calibration loss
would be movement of the relative position of a mechanical operating arm
or camera or ultrasonic tracking system devices relative to the patient's
head, which, again, would throw off the pre-calibration information
relative to the navigator. All of these situations have the very
undesirable effect of shutting down the use of the navigator at a time in
the operation when it might be crucially needed. After sterile draping,
the calibration points, be they natural landmarks or markers on the
patient's skin or other localizers, cannot be accessed by the navigator
since they are covered by the sterile drape, and therefore a recalibration
based on these points is not feasible without breaking sterility. Breaking
sterility might be impossible if a surgical opening has already been made.
It has been practice in some use of the Radionics OAS Operating Arm, after
a skin incision has been made and the skull exposed, to make small drill
holes or divot holes in the patient's skull surrounding the surgical
opening or burr hole so that once the draping and sterile field have been
achieved, access of these secondary registration or calibration points
could be made, their position having been known or determined from the
initial calibration step. This type of natural bony landmark recalibration
process is possible to "restart" or "recalibrate" the digitizer, however,
if the digitizer fails before such divots or bony landmarks can be
established for reference, then there is still no way of recalibrating the
navigator to the anatomy, and the navigator is of no use further.
Thus, one of the objectives of the present invention is to provide a means
of recalibrating a stereotactic navigator in an intraoperative setting,
and especially after a sterile draping has been made.
Another object of the present invention is to enable recalibration of a
stereotactic digitizer in the event that the patient's anatomy, such as
the patient's head with a head clamp on it, has moved relative to the
means of tracking the digitizer, for example, moves with respect to the
base of an operating arm that has been damped relative to a patient's head
clamp or relative to cameras or ultrasonic detectors which are tracking
stereotactic digitizers.
Another object of the present invention is to provide a means of
recalibrating a stereotactic digitizer should there be a power failure or
interruption of the equipment for any reason, especially between the time
of initial calibration when the surgical field is unsterile and the time
when the surgical field has been sterile draped and a surgical opening
made.
Yet another object of the present invention is to provide a recalibration
system that can be used with any type of stereotactic navigator, whether
it be mechanical arm, LED optical tracking, ultrasonic tracking, magnetic
tracking, etc. Another object of the present invention is to provide a
recalibration device which can be moved with the patient's head in the
case of neurosurgery so that it is always well established in mechanical
relationship to the patient's anatomy.
Yet another object of the present invention is to have a recalibration
device which can be used unsterile in a given position relative to the
patient's anatomy during a calibration process and then, after sterile
draping, the device can be autoclaved or otherwise sterilized during the
operation and reset back onto the patient's head or head clamping means
during the operation in a repeated or repeatable fashion and/or in exactly
the same position as it was previously. In this context, an object of the
present invention is to have a recalibration device that can be repeatedly
relocated relative to a patient immobilization structure in exactly the
same position so that it can be removed if it is in the way of the
surgery, but can be put back on in the event that intraoperative
recalibration is necessary.
The description of the invention which follows shows how these and other
objectives can be achieved by it.
DESCRIPTION OF THE FIGURES
FIG. 1 shows a patient's head in a head clamp with an optical or ultrasonic
digitizing probe and index marks within the head clamp that the digitized
navigator can access before or after the sterilization has been made.
FIG. 2 shows a digitized operating arm relative to a patient's head clamped
in a head clamp and a recalibration structure which can be held with
respect to said head damp and having a docking or holster means in which
the digitized probe can be recalibrated.
FIG. 3 shows a recalibration plate or array of index points that can be
mounted repeatedly onto a head damp in an identical position, the
recalibration plate having index spots which can be touched off by said
stereotactic navigator so as to recalibrate itself relative to the head
clamp and therefore the patient's anatomy intraoperatively.
DESCRIPTION OF THE INVENTION
The embodiments shown below are intended as examples or illustrations of
the present invention. Those skilled in the art can make variations of
these examples and yet still remain within the scope of the present
invention. Therefore, the examples are not meant to limit the scope of the
invention described and claimed herein.
Referring to FIG. 1, a patient's head 1 is clamped within a surgical head
damp 2 by means of securing screws 3 and 4 which stabilize onto the
patient's skull and keep the patient's head 1 in a relatively securely
fixed relationship to the head clamp 2. A surgical instrument 5 is shown,
which, in this case, has emitters 6 and 7, which could be light-enitting
diodes (LEDs), ultrasonic emitters, or other forms of energy which are
being detected by detectors 8 and 9 which may be placed in a known
position relative to the surgical field or have a known relationship to
one another and to be so calibrated or precalibrated that they can track
the position of sensors 6 and 7, and thus track the position of the
surgical probe 5. Extrapolation to the probe tip 10 can easily be done
geometrically so that the position of the tip and the orientation of the
instrument itself can be tracked by the receivers 8 and 9 by observing
only the positions of points 6 and 7. In the case of LEDs, 8 and 9 might
be optical cameras. More than two optical cameras can be used in such a
context. This is exemplified by, for example, the Radionics OTS Optical
Tracking System. The patient's head and its anatomy can be registered with
respect to a CT, MR, or other type of tomographic scan which may have been
done on the patient's head prior to the operation. For example, the
placement of index markers such as 15, 16, 17, and 18 on the patient's
head at various positions around the periphery can be used to do such
registration essentially of the physical patient's anatomy to the
coordinate space of the CT scanner. Observing the index marks in the
scanner in their particular slice and position within slices can
reasonably calibrate the CT scan data to the physical anatomy via these
point locations. By touching these points with the tip of the instrument
10 at the time of operation, one can essentially establish the calibration
of the instrument 5 with respect to the patient's anatomy via these index
marks and therefore establish the relationship of the instrument relative
to the image scan data or the coordinate system of the scanner which had
scanned the patient's anatomy. One of the objectives of this type of
stereotactic navigator is then, after such calibration, to be able to
point with the navigator at the patient's head and better assess where to
make an entry hole such as the burr hole 20 to access anatomy within the
depths of the brain, for example, a tumor which must be resected. Such a
tumor can be visualized in the image scan data, its position can then be
known relative to the index markers, and the index markers can be sources
of calibration relative to the anatomy for the digitizer, and therefore
the digitizer can be used to point at the direction of the tumor and
navigate through the brain to the tumor and tumor volume. Visualization of
the patient's anatomy via the image scan data can be shown on a computer
graphic workstation represented by the unit 22 in FIG. 1, and a graphic
rendering 23 of the patient's head showing the internal sections 24 and
the position of the navigator which is approaching those sections 25. All
is possible for real-time, interactive planning and surgery based on scan
data and graphic representations of such scan data.
A typical procedure of setting up such an operation and calibrating the
instrument relative to the anatomy would be as follows. The patient's
anatomy has been pre-scanned, for example, by a CT tomographic scanner,
and the image scan data from such a scan imager can be downloaded into the
computer workstation 22 and renderings of the external and internal
anatomy of the patient's head can be examined on the graphics display
means of the computer graphic workstation for preplanning. Later the
patient can be brought to the operating room and his head 1 can be clamped
into the head clamp 2 as described above. Index markers such as 16, 17,
and 18 may have been placed on his head prior to the scan, and those index
markers seen in the image scan data then represent benchmarks or
calibration points for the stereotactic navigator. With the head placed in
the head clamp, as shown in FIG. 1, the navigator tip 10 can be used to
touch off the physical points 15, 16, 17, and 18, and thereby the
navigator is calibrated relative to the patient's anatomy, the index
markers, and to the CT scan data previously done. At this phase, the
patient's head is typically not sterile draped, since the index markers or
position of the index markers are placed around the periphery of the
patient's head and may be outside the point of surgical opening. It might
be said that the index points 15, 16, 17, and 18 could be natural
landmarks such as the tip of the nose, the nasion, the ear openings, or
indeed the entire convexity and surface of the patient's head. These can
all be used as calibration points for their stereotactic digitizer 5.
When the surgery must be done and the position of the opening decided upon
by use of the navigator, typically the entire head and head damp are
draped out by a sterile drape so the entire surgical field can be
sterilely protected. A surgical opening such as 20 is made through the
surgical drape, and access to the interior of the brain is thus possible.
If the sterile drape is cloth, then the index points 15, 16, 17, and 18
will be covered up, and thus not accessible for a recalibration maneuver.
When an incision is made in the scalp and the skull is exposed, a bone
opening such as 20 may be made or small divot points can be made around
the bone opening such as small drill holes which can be touched off by the
tip 10 of the instrument 5. By touching off these points in a secondary
calibration setup, they then can become reference points for
recalibration. However, as stated above, if a problem arises such as a
power failure between the time of covering up the patient's head with a
sterile drape and the time possible to make a skin incision, all
calibration might be lost, and the entire procedure restarted or the use
of the navigator abandoned altogether. This is a highly undesirable state
of affairs, and a solution is much needed to provide the surgeon with a
way of recalibrating, even after sterile draping and even without using
the drill holes in the bony opening. The drill holes in the bony opening,
for example, will only give you a calibration base line which is local to
the incision, and this is typically not very large. It would be better to
have a base line of relocation points which is more stable and precise and
yet still not compromise sterility. This is one of the objectives of the
present invention. One means of doing such intraoperative calibrations is
by means of indent positions such as 30, 31, 32, and 33, which are
mechanical spots on the head clamp 2 itself. If the sterile drape is a
thin sterile drape such as a polyethylene sheet, such indents can be seen
and accessed by the tip 10 of the surgical instrument, and thus they can
serve as recalibration points. For example, to repeat the setup steps in
this context, the surgical instrument may have been touched off
calibration landmarks 15, 16, 17, and 18, and thus calibrated to the
patient's anatomy. Immediately upon doing this, and prior to sterile
draping, the navigator in a recalibration setup maneuver can be touched
off divot points 30, 31, 32, and 33 so as to establish a secondary set of
reference points which are solidly fixed to the mechanical head clamp. As
the head clamp is solidly affixed to the patient's head clamp 2, and as
the head clamp 2 is solidly affixed to the patient's head 1, these
represent good secondary reference points for recalibration of the probe
if they are accessible after draping. As just mentioned, a thin,
relatively transparent sterile drape can be used in this context, and if
the points such as 30 are, for example, conical indentations in the metal
of the head clamp, the thin sterile drape can contour into these conical
indentations, and the point 10 of the instrument can be set down,
therefore, into the conical indent with a thin drape in between and a good
registration of the tip to the probe 10 can be made to the registration
mark represented by 30. Thus, after such sterile draping with a thin,
transparent drape, the divot points 30, 31, 32, and 33 represent touch-off
points for the navigator after sterile draping and prior, during, or after
making of the surgical skin incision. Should the divot points on the head
clamp be too low in profile beneath the drape, an alternative means such
as illustrated by the vertical post 35, which may have a divot point 36 on
its top, may be set down and affixed into the head clamp through the
sterile drape or be draped out around by sterile cloth and still the tip
may remain sterile. For example, these may be sterilizable posts which can
be put onto or attached to the head clamp after draping around to the side
of the drape or underneath. This might be illustrated by the post 37,
which can be clamped around the head clamp even with the sterile drape on
it, illustrated by the clamp means 38. Thus, even after sterile draping,
such a post can be attached to the head clamp in several positions and
relocated by pin indents in the clamp so it can be positioned precisely
and can be used, therefore, as relocatable elements or touch points for
the stereotactic digitizer. Thus there are a variety of ways of making
index spots or markings or posts or divots on or attached to the head
clamp in relocatable and reproducible positions and orientations which can
be touched off as secondary reference points to be used intraoperatively
so as to re-establish, check, or confirm calibration of the navigator. For
example, there may be one post which can be attached to the head clamp to
which one can mount a sterilizable apparatus which may contain three or
more conical indentations.
As another aspect of such a situation, the head clamp 2 may be attached by
a shaft 39 to further head holding structures attached to the operating
table. Typically, shaft 39 is on a rotatable, dampable joint such as 40
attaching itself to the head clamp. If for any reason 39 moves during the
operation, or other movements of 1, 2, or other element occurs, then the
calibration position established by, for example, cameras 8 and 9 during
the first touch-off maneuver on index points 15, 16, 17, and 18 has been
corrupted. In this situation, access to index points which are both
available to be seen after sterilization and to be touched off or accessed
by the probe after sterilization is required, or the probe must be
recalibrated to the initial fiducials to continue. This, again, is a
context where such secondary mechanical reference points are important.
FIG. 2 shows another mechanical means for intraoperative sterile
recalibration of a surgical digitizer. Again, head 201 is clamped in head
clamp 202 by means of head screws 204 and 203. The index points
illustrated by the point 217 can be placed on the patient's head during
scanning and surgery for initial calibration. In this situation, an
operating arm, which is another form of digitizer, is represented by the
device on the right in FIG. 2, which has arm links 250 and 251 with double
bearings 252 and 253 and intermediate rotation joint 254 and, for example,
articulation joints 255 and 256, which lead to a probe such as 257. The
probe is shown in this situation inside of a probe holster 258 which is
attached by means of an articulating joint 259 and rod means 260 to a
clamp means 261 which can be attached to the periphery of the head clamp
202. The operating arm is further attached to the head clamp by linkages
represented by 262, which is attached to the base 263 of the operating
arm. Typically these linkages are fixed in place in a convenient location
and then the initial calibration prior to sterile draping is carried out
of the operating arm system. The links and joints of the operating arm
system are known in length, and the joints contain encoder structures to
provide electronic readouts of the position and angle of the articulating
joints and thus of the position and orientation of the tip 210 and the
probe 257, which is the instrument end of the entire operating arm system.
In this sense, the operating arm illustrated in FIG. 2 is analogous to the
stereotactic navigator in FIG. 1, except that instead of optical or
ultrasonic or magnetic coupling to detectors, the probe 257 is coupled by
mechanical arms and links to the base 263 which is in turn coupled to the
head clamp 202. The operating arm with its electronic readout can be
coupled and inputted to a computer graphic workstation such as 21 in FIG.
1 (not shown in FIG. 2), and digitized data can be used in an entirely
analogous fashion to that in FIG. 1. Intraoperatively, if there is a power
shutdown or electronic interface failure between the operating arm
encoders and computer graphic workstation, then the orientation and
digital information from the encoders can be lost and a recalibration
procedures must be instituted.
A way of recalibrating intraoperatively, as illustrated by FIG. 2, would
proceed as follows. The patient, having been scanned, is set into the head
clamp as described in the case of FIG. 1, and the operating arm probe 257
is touched off the reference points such as 217, and thus the arm is
calibrated relative to the head and to the three-dimensional image data.
At this point, and before the sterile draping is done, the clamp 261 is
put onto the head clamp 202 and the rod structure 260 is put at a
convenient angle, adjusted accordingly by the locking joint 271.
Similarly, the orientation and angle of the holster or calibration tube or
docking device 251 is oriented at a convenient angle. The probe from the
operating arm 257 is inserted to a particular docking position with a
depth or similar means down into or attached to the docking device 258,
and the computer graphic workstation or other means is used to record or
establish the encoder readings for that secondary calibration position and
orientation of the probe 257. The holster may have an angular index means
which enables docking of the probe or arm into it in the same position and
angular orientation with respect to the probe's shaft to insure that all
the encoders have the same repeated position. The storage of this
calibration data in the computer then serves as a benchmark for restarting
the system should there be an interruption or movement of the operating
arm's base position relative to the head. The storage of this data might
be done on a backup hard copy system such as a disk or magnetic tape so
that even if there is a power failure, the data can be re-accessed after
the power failure has resolved itself, and then the computer restarted.
This means that absent any other access to reference markers such as 217,
if the operating arm pointer is reinserted into the holster 258 and that
has not moved relative to head clamp 202, then knowledge of the secondary
calibration data referred to above can mean that the operating arm can be
started up based on the initial calibration to the head through the
intermediary of the secondary recalibration encoder information when the
probe is in holder 258. The operating arm can be totally recalibrated in
the event of a power failure if the secondary recalibration has been
performed. The secondary recalibration relates coordinates of the
operating arm into patient image space. The arm can restart using its
manufactured zero position or the new position from the holster 258 in
FIG. 2. The arm can be calibrated from set angles from 258 and thus, by
referencing the points on the patient 264 and 265, can be recalibrated
using the transformation maneuver. The arm can also be recalibrated from a
mechanical fixture that is in the operating field as long as those points
were stored in patient data spaces. Another notable point is that drill
hole positions, such as the crosses represented by 264, may be placed in
the skull within a region exposed within the skin incision exposure
represented by the line 265. After making the incision 265, the operating
arm tip 210 can be touched off these skull-based reference points which
then can represent yet another recalibration data set local to the
surgical opening represented by the hole 220. If a power failure occurs,
the probe 257 can be put into the sterile holster 258 or the probe can
then be touched off the skull reference points 264, multiplicity of them
being placed around the bone opening 220, and the procedure restarted.
Another eventuality which can lead to need for recalibration is that the
links 261 or 263 may shift in their position relative to head clamp 202,
thus throwing the operating arm system out of calibration relative to the
patient's anatomy 201. This would require intraoperative recalibration,
and the recalibration holster 256 could be crucial to do so if the skull
surgical recalibration points such as 264 have not been made yet.
FIG. 3 shows yet another embodiment of a recalibration means according to
the present invention. Again, head clamp 302 clamps the patient's head 301
by means of clamp screws. The recalibration structure in this case is
represented by a clamp 380 which can be repeatedly attached to the head
clamp by indexing pins or screws 381 in known screw locations in the head
clamp. The lockable joint 382 holds the arm 383 which has a yoke 384 on
its top. The yoke has divot or marker points 388, 385, 386, and 387, into
which the tip 310 of the surgical instrument 305 may be touched. Sterile
draping can be done to the head clamp after calibration on such markers as
317 is done in the way described above. Shortly after this initial
calibration and still in the non-sterile situation, the recalibration
device 384 is clamped onto the ring by means of damp 380, and the
stereotactic navigator 305 is used to touch its tip 310 off the various
divot points such as 387, 386, 385, and 388, so as to establish a
secondary coordinate system data set that is rigidly affixed to the head
clamp 302, and therefore the patient's head 301. The clamp 380 may now be
removed and the patient's head be sterile draped. The unsterile damp 384
may now be autoclaved, and it may be repositioned with or without the
drape in place by means of pin holes, conical holes, or location docking
devices which could, for example, access underneath the drape to the
underside of the head clamp 302 without compromising the sterility of the
overall procedure or which may be prominent enough to allow docking of the
clamp even over the drape. The draping would then drape out the base of
the device 380, and all that would be remaining in the sterile field above
the sterile drape would be the index marker holder 384 with the divot
holes in them. These could then be touched off directly with the navigator
305 for a repeatable, relocatable recalibration maneuver after sterile
draping. This recalibration maneuver using the recalibration device can be
interleaved or iterated with the surgical opening recalibration bone
markers represented by 364 which are visible after the incision 365 has
been made and can also be used for intraoperative calibration if
necessary.
It is noted that, although the embodiments herein indicate surgical
instruments or pointers, a wide range of such stereotactic navigators is
included within the scope of this patent. For example, the probes
illustrated in FIGS. 1, 2, and 3 could be surgical instruments, suction
tubes, bipolar forceps, etc. for use in surgical interventions. The
generic surgical probe could also refer to a microscope which is set up
and adapted to be a stereotactic navigating microscope. This can be done
by encoder joints of the microscope movements or by attachment of
localization devices such as LEDs, ultrasonic detectors, etc., so as to
make the microscope stereotactic. The microscope could be focused on
various of the recalibration points established by the device of the
present invention, and the microscope can be recalibrated at any time
during the surgical procedure. The holster of FIG. 1, for example, could
be a reticule-type tube which could be viewed through by the microscope so
as to establish a direction and depth calibration in such a way that the
microscope, with a single positioning maneuver, could be recalibrated back
to the space of the patient's anatomy and head clamp, and therefore the
imaging data, very much as the mechanical probe can be put into the
holster in FIG. 2 for such a purpose. The recalibration device described
here could be used in other applications in surgery as, for example, in
radiation therapy where a mechanically-attached reference system can be
securely fixed and secured to the patient's body for the purpose of
recalibration relative to a LINAC radiation machine, for example. The
recalibration device herein could also be unitized with a dynamic tracking
device which contains LEDs on the same plate or structure as is contained
the divots or recalibration markers. All of these concepts are included as
claims as part of the present invention.
Also as part of the present invention the mechanical relocation structures
such as 30, 31, 32, and 33 in FIG. 1, or 384, 385, 386, and 387 can have a
known physical relationship with each other which can further be used to
confirm the accuracy of the stereotactic navigator. For example, if these
divots or mechanical touch points are at a known millimeter relationship
or angular relationship one to the other, this could serve as an internal
test of the accuracy and internal calibration of the digitizer itself. The
predetermined knowledge of the relationship of these recalibration points
could be inputted into the computer graphic workstation such that when a
recalibration maneuver is done with the m, the work station will have a
software module that tests the physical relationship of these points
internally against the predetermined or known relationship of these points
in a mechanical structure. Thus, the recalibration process could be
consistency check or quality assurance check for the stereotactic
navigator at the same time.
We note that in FIG. 2, the operating arm structure with its base 263 can
be moveable with relation to the head clamp 202 so as to adjust its
orientation to a more convenient position for the surgeon. If such a
readjustment is made intraoperatively or accidentally during the surgery,
the existence of the recalibration holster 258 or recalibration marker
points such as in FIG. 1 or 3 would be very convenient for instantaneous
and sterile recalibration of the operating arm. The operating arm, though
attached mechanically by means of arm 262, is independently coupled to the
head clamp 202 from the damping of the holster 258 to the head clamp 202.
This can be significant in the sense that the operating arm, though
mechanically coupled in a mechanical relationship to the head clamp 202,
is not primarily coupled to the recalibration means 258. Thus the
relocation or recalibration integrity of the relocation device 258 is
independent of the position of the operating arm relative to the head
clamp. The same could be said, for example, in FIG. 1, where the cameras 8
and 9 can be in a fixed position initially relative to the anatomy 1 and
the head camp 2, however, the index points such as 30, 31, 32, and 33 are
in a primarily mechanically fixed relationship relative to the head clamp,
independent of the position of the cameras 8 and 9 relative to the head
clamp. Thereby they serve as reliable and stable mechanical recalibration
points relative to the patient's anatomy. Thus, the system of the
stereotactic navigator, including not only the probe or instrument with
its source means 6 and 7, but also the system of detection or digitization
such as the cameras 8 and 9 are the independently coupled to the patient's
anatomy from the coupling of the recalibration means so that inadvertent
or deliberate movement of the stereotactic navigator referencing system
will not affect the ability to recalibrate based on the recalibration
mechanical structures.
In the surgical setting, as has been cited above, the mechanical contact
structures, such as the divot points 30, 31, 32, 33 or the post 36 in the
head clamp 2 of FIG. 1, the clamp and holster mechanism 261, 258, as
attached to the head clamp 202 in FIG. 2 and the clamp and base structure
380 and 383, attached to head clamp 302 in FIG. 3, should be removable and
replaceable onto the head clamp. In some situations, this
remove-and-replace operation should put the structure in exactly the same
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