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TECHNICAL FIELD
The present invention relates generally to a stereotactic guide apparatus
for neurosurgery, and relates more specifically to a stereotactic guide
apparatus which removably mounts to a neurosurgical headframe and provides
three-dimensional control guidance of an instrument.
BACKGROUND OF THE INVENTION
Headframes for stereotactic neurosurgery are well known. These headframes
are ring-shaped structures which are mounted to the skull of a patient to
provide a fixed reference with respect to the patient's brain. An arcuate
rail has its opposite ends fastened to opposing sides of the headframe and
extends above and across the patient's skull. A guide is movably mounted
on the rail and can be positioned at any suitable location along the
length of the rail to serve as a guide for surgical instruments. Such
headframes are commonly used for brain biopsies, tumor removal, or any
other modality of deep brain surgery where the surgeon requires guidance
to properly position an instrument. In addition, such headframes are
useful for cryosurgical treatment of Parkinson's disease, epilepsy,
microelectrode guidance, brain nuclei and mapping, placement, positioning,
neuronal micro stimulation, recording, lesioning, resection, localization
of brain nuclei, micro-injection cannula system, micro injection of drugs,
donor human tissue, and the like.
Although a substantial advance over unguided neurosurgery, prior art
headframes have significant drawbacks. While the guide can be repositioned
to any other location along the plane of the rail, the guide cannot be
repositioned transverse to the plane of the rail without removing the
headframe from the patient, rotating the headframe so that the plane of
the rail passes through the new location, and then remounting the
headframe to the patient's skull. Moving the headframe in this manner is
too time consuming and too inaccurate.
Thus there is a need for a stereotactic guide apparatus for use with a
neurosurgical headframe which permits a tool to be repositioned along any
of three axes without having to remove the headframe from the patient.
Another difficulty associated with use of prior art tool guides used with
conventional headframes for neurosurgery do not provide adequate control
and precision over the positioning of a tool. Since such tool guides are
used to position surgical instruments within the brain of a patient,
precise control and accuracy are of paramount importance. Thus there is a
need for a stereotactic guide apparatus for use with a neurosurgical
headframe which provides guidance for a surgical instrument with greater
precision and control than heretofore possible.
SUMMARY OF THE INVENTION
Stated generally, the present invention comprises a stereotactic guide and
headstage apparatus that is adapted for localizing on any portion of the
brain, with maximum accuracy and a positive finite degree. This
stereotactic guide apparatus can be used for brain mapping such as for the
treatment of Parkinson's disease, deep seated brain tumors, hyperkinetic
disorders, various maladies of the human brain, and the like.
Stated somewhat more specifically, the present invention comprises an
stereotactic guide apparatus for use with neurosurgical headframe which
has an arc extending above and across the skull of a patient to whom the
headframe is mounted and a slide mounted for sliding movement along the
arc. The stereotactic guide apparatus includes a platform defining a plane
and X, Y, and Z axes. Means are provided for mounting the platform to the
slide on the arc of the headframe. An X-slide is movably supported on the
platform for movement along the X-axis, and a Y-slide is movably supported
on the X-slide for movement along the Y-axis. A tubular instrument guide
is mounted to the Y-slide and extends parallel to the Z-axis. A surgical
instrument can be advanced through the tubular instrument guide, and the
X-slide and the Y-slide can be moved to position the surgical instrument
with respect to the X and Y axes.
In a preferred embodiment the stereotactic guide apparatus further includes
a Z-stage. The Z-stage comprises a base which is mounted to the Y-slide. A
Z-axis support means is mounted to the Z-stage base and extends parallel
to the Z-axis. An instrument slide is movably mounted to the Z-axis
support means for movement parallel to the Z-axis. An instrument
attachment means is operatively associated with the instrument slide for
attaching a surgical instrument to the instrument slide. The instrument
attachment means and the instrument slide are arranged such that when a
surgical instrument is attached to the instrument slide and the instrument
slide is moved along the Z-axis support means, the surgical instrument is
advanced through the tubular instrument guide.
In another aspect, the present invention pertains to a novel electrode
especially adapted for use in mapping brain activity. The electrode
includes an elongated hollow shaft comprised of an electrically conductive
material. An electrode wire comprised of an electrically conductive
material is mounted within a forward end of the elongated hollow shaft in
electrically conductive communication with the shaft and extending forward
from the forward end of the shaft. A glass tip encapsulates the forward
end of the elongated hollow shaft and the electrode wire projecting
therefrom. In a preferred embodiment, a tube of electrically insulating
material is disposed around the elongated hollow shaft, a forward end of
the tube being bonded to a rearward portion of the glass tip.
Accordingly, it is an object of the present invention to provide for a
stereotactic guide and headstage apparatus that can be utilized
successfully for any stereotactic neurosurgery, functional neurosurgery,
deep brain microstimulation, brain mapping, and treating Parkinson's
disease, epilepsy, sleep disorders, and movement disorders.
Still another object of the present invention is to provide a stereotactic
guide and headstage apparatus which will overcome the deficiencies,
drawbacks, and disadvantages of conventional stereotactic guide apparatus,
transplant devices, or method thereof.
Yet another object of the present invention is to provide an apparatus
which will accurately, precisely locate a target area in the brain of a
patient, penetrate the brain, utilizing the cannula and stylet assembly,
and enabling the precise activity on the target area (i.e. donor tissue
transplant, brain nuclei, micro-stimulations, localization, etc.) while
minimizing trauma or damage to the recipient brain tissue.
It is yet another object of the present invention to provide for a
stereotactic guide and headstage apparatus which includes a Z-stage for
permitting movement along the Z-axis of the Z-direction.
Still another object of the present invention is to provide a Z-stage that
is adapted to be removably secured to an XY-stage.
Another object of the present invention is to provide a Z-stage which
includes a means of accepting and maintaining a carrier tube assembly for
enabling successful insertion of a microelectrode into the brain of a
patient.
A further object of the present invention is to provide for a stereotactic
guide and headstage apparatus which includes an interlocking cannula and
stylet system for electrode guidance to permit utilization of transplant
cannulae, stimulation implants, and micro and macro electrodes.
It is still a further object of the present invention to provide for a
stereotactic guide and headstage apparatus which will provide for precise
localization of tumors, lesion, abnormalities and the like.
Yet another object of the present invention, to be specifically enumerated
herein, is to provide a stereotactic guide and headstage apparatus in
accordance with the preceding objects and which will be of easy and
efficient to be utilized so as to provide an apparatus that would be
economically feasible, long lasting and relatively trouble free in
operation.
Other objects, features, and advantages of the present invention will
become apparent upon reading the following specification, when taken in
conjunction with the drawings and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of an XY-stage of a stereotactic guide
apparatus according to the present invention.
FIG. 2 is a top view of the XY-stage of FIG. 1.
FIG. 3 is a side view of the XY-stage of FIG. 1.
FIG. 4 is a side view of an outer guide tube, an inner guide tube, and a
stylet.
FIG. 5 is a cross-sectional view of a guide tube assembly comprising the
outer and inner guide tubes and the stylet of FIG. 4.
FIG. 6 is a cutaway view of the XY-stage as seen along line 6--6 of FIG. 1
with the guide tube assembly of FIG. 5 mounted thereto.
FIG. 7 is a perspective view of a prior art neurosurgical headframe of a
general type with which the stereotactic guide apparatus of the present
invention is adapted to be used.
FIG. 8 is a front view of an arc slide for use on the neurosurgical
headflame of FIG. 7.
FIG. 9 is a side cross-sectional view of the arc slide of FIG. 8.
FIG. 10 is a perspective view of a Z-stage component of the stereotactic
guide apparatus of the present invention.
FIG. 11 is a front elevation view of the Z-stage component of FIG. 10.
FIG. 12 is a side elevation view of the Z-stage component of FIG. 10.
FIG. 13 is a rear elevation view of the Z-stage component of FIG. 10.
FIG. 14 is a schematic representation of a microdrive unit of the general
type used with the stereotactic guide apparatus of the present invention.
FIG. 15 is an enlarged view of a front portion of an electrode slide of the
Z-stage component of FIGS. 10-13.
FIG. 16 is a side view of a carrier tube which is used with the Z-stage of
FIGS. 10-13.
FIG. 17 is an elevation view of the stereotactic guide apparatus of the
present invention, comprising the Z-stage of FIG. 10 mounted to the
XY-stage of FIG. 1.
FIG. 18 is a side view of an electrode assembly for use with the
stereotactic guide apparatus of FIG. 17.
FIG. 19 is a side view showing the stereotactic guide apparatus of FIG. 17
used to perform a neurosurgical procedure; FIG. 19A is an enlarged view of
the portion of FIG. 19 indicated by the circle 19A.
FIG. 20 shows an alternate embodiment of an XY-stage.
DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENT
Referring now to the drawings, in which like numerals indicate like
elements throughout the several views, the drawing figures illustrate
various views of a stereotactic guide apparatus 10 of the present
invention. Referring first to FIGS. 1 and 2, an XY-stage 11 of the
stereotactic guide apparatus 10 is depicted. The XY-stage 11 includes a
base member 12. For ease of description, X and Y axes are designated by
the arrows 13. A round hole 14 is located in the center of the base member
12. A pair of support blocks 26a, 26b is located on the top surface 16 of
the base member 12 along opposite edges thereof.
Extending between the supports 26a, 26b adjacent the remaining two edges of
the base 12 is a pair of parallel, spaced-apart, horizontal medial slide
support rods 28. A pair of medial/lateral slides, or "X-slides" 30a, 30b
are slidably disposed one on each of the medial slide supports 28. A
medial movement mechanism 32 is operatively connected to the X-slide 30a
for effecting movement of the X-slide 30a in the medial/lateral direction,
or X-direction. The medial movement mechanism 32 comprises a threaded rod
33 which is inserted through a smooth bore in the support 26a and is
threadably received within a corresponding threaded bore in the adjacent
end of the X-slide 30a. Turning the threaded rod 33, advantageously by
means of a knurled thumbscrew 35 at the head of the rod, moves the X-slide
30a toward or away from the support 26a.
Extending perpendicularly between the X-slides 30a, 30b is an anterior
slide support means comprising a pair of parallel, spaced-apart anterior
slide support tracks 34. Suspended on the anterior slide support tracks 34
is an anterior/posterior slide, or "Y-slide" 36. The Y-slide 36 includes a
top panel 40 having a central threaded aperture 42. A pair of upstanding
pins 44 project upward from the top panel 40 adjacent a longitudinal edge
thereof and spaced equidistant from the central aperture 42. In addition,
a pair of threaded holes 46 are formed in the upper surface of the
platform 40.
The XY-stage 11 further includes an anterior movement mechanism 38
operatively connected to the Y-slide 36 for effecting movement of the
Y-slide in the anterior/posterior direction, or Y-direction. The anterior
movement mechanism 38 comprises a threaded rod 37 which is inserted
through a smooth bore in the X-slide 30a and is threadably received within
a corresponding threaded bore in the adjacent end of the Y-slide 36.
Turning the threaded rod 37, advantageously by means of a knurled
thumbscrew 39 at the head of the rod, moves the Y-slide 36 toward or away
from the X-slide 30a.
It will be appreciated that the pair of X-slides 30a, 30b is linked
together by the anterior slide support tracks 34. Accordingly, when the
threaded rod 33 is turned to move the first X-slide 30a along the X-axis,
the second X-slide 30b is also displaced toward or away from the support
26a.
Referring now to FIG. 3, a tubular mounting adapter 20 is positioned within
the round hole 14 in the base member 12 of the XY-stage. The mounting
adapter 20 includes a hollow cylindrical body 22 and has a flange 24
located at its upper end. The lower surface of the flange 24 bears against
the upper surface 16 of the base member 12 when the bushing is properly
seated within the round hole 14 in the base member. The mounting adapter
20 is then secured to the base member 12 by means of threaded fasteners 25
which pass through the flange 24 of the mounting adapter and engage the
base member.
FIG. 4 shows an outer guide tube 228, an inner guide tube 230, and a stylet
or occluder 232. The outer guide tube 228 includes a hollow shaft 234a
having a bore 238a. In the disclosed embodiment the shaft 234a of the
outer guide tube 228 is approximately 90 millimeters in length. The outer
guide tube 228 further comprises a cap 236a having an internally threaded
bore 240a. Located beneath the cap 236a of the outer guide tube 228 is an
externally threaded collar 242a.
The inner guide tube 230 includes a hollow shaft 234b having a bore 238b.
The diameter of the shaft 234b of the inner guide tube 230 is sized to fit
within the bore 238a of the shaft 234a of the outer guide tube. In the
disclosed embodiment the shaft 234b is approximately 150 millimeters in
length. The inner guide tube 230 further includes a cap 236b having an
internally threaded bore 240b. Located beneath the cap 236b of the inner
guide tube 230 is an externally threaded collar 242b.
The stylet 232 includes a solid shaft 234c and a cap 236c. The diameter of
the shaft 234c of the stylet 232 is sized to fit within the bore 238b of
the shaft 234b of the inner guide tube 230. In the disclosed embodiment
the shaft 234c is approximately 150 millimeters in length. An externally
threaded collar 242c is located beneath the cap 236c.
FIG. 5 shows a guide tube assembly 250 comprising the outer guide tube 228,
the inner guide tube 230, and the stylet 232. The shaft 234b of the inner
guide tube 230 is inserted into the upper end of the outer guide tube 228
and advanced until the externally threaded collar 242b of the inner guide
tube engages the internal threads 240a of the outer guide tube. Turning
the inner guide tube 230 relative to the outer guide tube 228 will engage
the threaded collar 242b of the inner guide tube with the threads 240a of
the outer guide tube to couple the inner and outer guide tubes together.
Similarly the shaft 234c of the stylet 232 is inserted into the upper end
of the inner guide tube 230, and the externally threaded collar 242c of
the stylet engage the internal threads 240b of the inner guide tube 230 to
couple the stylet 232 and the inner guide tube 230 together.
Because of the relative lengths of the shafts 234a, 234b, and 234c, when
the outer guide tube 228, inner guide tube 230, and stylet 232 of the
disclosed embodiment are assembled into the guide tube assembly 250, the
shaft 234b of the inner guide tube 230 projects approximately 60
millimeters beyond the end of the outer guide tube 228, and the forward
end of the solid shaft 234c of the stylet 232 extends just slightly beyond
the end of the shaft 234b of the inner guide tube 230.
FIG. 6 shows the guide tube assembly 250 assembled onto the XY-stage 11.
The externally threaded collar 242a of the outer guide tube 228 is
threaded into the threaded aperture 42 in the center of the top panel 40
of the Y-slide 36. The shafts 234a, 234b, and 234c of the outer guide tube
228, inner guide tube 230, and styler 232 respectively extend downward
through the hollow cylindrical body 22 of the mounting adapter 20.
Also shown in FIG. 6 is a scale 47 extending between corresponding ends of
the X-slides 30a, 30b. The scale 47 includes markings in one millimeter
increments. A reference mark 48 on the Y-slide 36 identifies a
corresponding one of the incremental markings to indicate the displacement
of the needle assembly 250 from center in the direction of the Y-axis. A
similar scale (not shown) is provided extending between corresponding ends
of the supports 26a, 26b, and a reference mark along an edge of the
X-slide 30b indicates the displacement of the needle assembly 250 in the
X-direction.
FIG. 7 depicts a conventional prior art neurosurgical headframe 49 of the
general type with which the stereotactic guide apparatus 10 of the present
invention is adapted to be used. The headframe 49 illustrated in FIG. 7 is
manufactured by CRW and Elekta, though it will be understood that the
headframe 49 is only illustrative of a headframe with which the
stereotactic guide apparatus 10 can be used and is by no means intended to
limit the invention. The headframe 49 is mounted to the skull of a patient
in a conventional manner and includes an arc 50 which extends above and
across the patient's skull in spaced-apart relation thereto. An arc slide
51 is slidably mounted to the arc 50 for movement thereon.
Referring now to FIGS. 8 and 9, the arc slide 51 comprises a bracket member
52 which is L-shaped in cross-section. The bracket member 52 comprises a
base 54, an upstanding leg 56, and a head portion 58. A circular bore 59
is formed through the base 54 of the bracket member 52. A horizontal,
rectangular channel 60 is formed in the forward face 62 of the head
portion 58. A block 64 is positioned within the channel 60 and has an
arcuate track 66 formed on its interior surface. The track 66 on the
interior surface of the block 64 is dovetail-shaped in cross-section and
has edges 66a, 66b, 66c, and 66d. The track 66 receives the arc 50 of the
headframe 49 therewithin. The block 64 is secured within the channel 60 of
the bracket member 52, such as by an interference fit or by threaded
fasteners (not shown), thereby coupling the arc slide 51 to the arc 50 of
the headframe assembly 49.
Referring now to FIGS. 10-13, the stereotactic guide apparatus 10 further
comprises a Z-stage 70, which is adapted to be removably secured to the
XY-stage 11. The Z-stage 70 comprises a base 72 having a pair of alignment
holes 74 formed therein. The alignment holes 74 are located and sized to
receive the upstanding pins 44 projecting upward from the top panel 40 of
the Y-slide 36. The base 72 of the Z-stage 70 further comprises a circular
opening 76 which is located and sized to correspond to the central
aperture 42 of the top panel 40 of the Y-slide 36 when the base 72 is
mounted to the Y-slide. The base 72 of the Z-stage 70 further comprises a
pair of securing screws 78 received within threaded bores of the base 72,
which are located and configured to engage the threaded holes 46 in the
upper surface of the platform 40 of the Y-slide 36 to secure the base 72
of the Z-stage 70 to the Y-slide. Because the arrangement of the
upstanding pins 44 and the threaded holes 46 of the XY-stage 11 is
asymmetrical, the Z-stage 70 cannot be accidentally installed onto the
XY-stage improperly.
The Z-stage 70 further comprises a pair of upstanding main support rods 80
and a pair of electrode slide rods 82 projecting upward from the base 72.
A substantially U-shaped top plate 84 is mounted to the upper ends of the
rods 80, 82. A carrier tube holder 86 is fixedly mounted to the main
support rods 80 at a location spaced upward from the base 72 by a distance
of approximately one-third the height of the main support rods 80. The
carrier tube holder 86 is essentially T-shaped and includes a forward
projecting leg 88. A circular opening 90 is formed in the forward
projecting leg 88 of the carrier tube holder 86 adjacent its forward end.
The circular opening 90 is dimensioned to receive the shaft and collar of
the carrier tube therethrough. A thumb screw 92 threadably mounted in the
forward edge 94 of the carrier tube holder 86 has its tip extending
radially into the circular opening 90.
The carrier tube holder 86 is adapted to support a carrier tube 95, which
is illustrated in FIG. 16. The carrier tube 95 comprises a hollow tubular
shaft 96, a head 97 located at the upper end of the shaft, and an annular
collar 98 located immediately below the head 97. The shaft 96 of the
carrier tube 95 of the disclosed embodiment has a diameter sized such that
the shaft of the carrier tube can be received within the bore 234b of the
inner guide tube 230. The shaft 96 of the carrier tube 95 is approximately
180 millimeters in length. The head 97 of the carrier tube 95 is larger
than the circular opening 90 in the carrier tube holder 86, and the collar
98 is dimensioned to be received snugly within the circular opening 90.
FIGS. 11-13 show the assembled Z-stage 70 with the carrier tube 95
installed onto the carrier tube holder 86. The carrier tube 95 is
positioned onto the carrier tube holder 86 with the annular collar 98 of
the carrier tube disposed within the circular opening 90 of the carrier
tube holder 86, the lower end of the cap 97 resting on the upper surface
of the carrier tube holder 86, and the shaft 96 of the carrier tube 95
extending downward from the carrier tube holder. When the carrier tube 95
is thus positioned, the thumb screw 92 on the carrier tube holder 86 is
tightened to secure the carrier tube to the carrier tube holder.
Referring again to FIGS. 10-13, a coarse drive slide 100 is slidably
mounted on the main support rods 80 between the top plate 84 and the
carrier tube holder 86. The coarse drive slide 100 is a planar, generally
T-shaped member and includes a forward projecting leg 112. A threaded bore
114 is formed in the forward projecting leg 112. A threaded coarse drive
screw 102 extends downward through a clear bore in the top plate 84 and
engages a threaded bore in the coarse drive slide 100, such that rotating
the coarse drive screw 102 will cause the coarse drive slide 100 to raise
or lower. The purpose of the coarse drive screw 102 is twofold: first, to
permit movement of the coarse drive slide 100 to a location such that the
target tissue is within the range of movement of a microdrive system
(described below); and second, to permit manual adjustment of the coarse
drive slide if the physician so chooses or to permit the surgical
instrument to be withdrawn from the patient's brain in the event of a
power failure or the like.
FIG. 14 illustrates a conventional microdrive unit 104 of a general type
used with the stereotactic guide apparatus 10 of the present invention.
The microdrive unit 104 comprises a cylindrical housing 106 having an
externally threaded collar 108 located at its forward end. A push rod 110
extends through the collar 108 and projects from the forward end of the
housing 106. As shown in FIGS. 11-13, the microdrive unit 104 is mounted
to the coarse drive slide 100 of the Z-stage 70 by threading the
externally threaded collar 108 into the threaded bore 114. When the
microdrive unit 104 is energized, a screw drive mechanism located within
the housing 106 extends or retracts the push rod 110.
Referring again to FIGS. 10-13, an electrode slide 118 is slidably mounted
on the electrode slide rods 82. The electrode slide 118 has an upper
surface 119 and has an electrode holder assembly 120 located at its
forward edge 122. As can be seen in the enlarged view of FIG. 15, a pair
of support rods 124 project forward from the forward edge 122 of the
electrode slide 118. A thumb screw support plate 126 is fixedly mounted to
the forward ends of the support rods 124. An electrode holder pressure
plate 128 is slidably mounted on the support rods 124 between the thumb
screw support plate 126 and the forward edge of the electrode slide 118. A
thumb screw 130 is threaded through the thumb screw support plate 126 so
that its tip bears against the electrode holder pressure plate 128. A
vertical notch 132 is formed in the center of the forward edge 122 of the
electrode slide 118. To mount an electrode to the electrode slide 118, the
electrode is fed downward between the electrode holder pressure plate 128
and the forward edge of the electrode slide 118. The shaft of the
electrode is positioned within the notch 132 to align the electrode
vertically with respect to the electrode slide 118. The thumb screw 130 is
then tightened, causing the electrode holder pressure plate 128 to clamp
the electrode against the forward edge 122 of the electrode slide 118.
Still referring to FIGS. 10-13, a pair of slide return springs 136 have
their upper ends attached to the top plate 84 and their lower ends
attached to the electrode slide 118 to bias the electrode slide 118
upward. When the push rod 110 of the microdrive unit 104 is actuated to
extend downward, the push rod 110 bears against the upper surface 119 of
the electrode slide 118 to bias the electrode slide downward. When the
microdrive unit 104 is activated to retract the push rod 110, the slide
return springs 136 bias the electrode slide 118 upward. In this manner,
the electrode slide 118 moves in response to the microdrive unit 104.
Referring now to FIG. 13, two different means are illustrated for tracking
the position of the electrode slide 118. For visually tracking the
position of the electrode slide 118, a scale 138 is provided on the rear
of the Z-stage 70 extending between the base 72 and the top plate 84. A
pointer 139 is inscribed on the adjacent side of the electrode slide 118
to indicate the displacement of the electrode slide in the Z-direction.
For electronically tracking the position of the electrode slide 118, a
linear potentiometer 140 is provided. The linear potentiometer 140 is
mounted to the top plate 84 and has a potentiometer push rod 142 extending
from its lower end. The lower end of the push rod 142 is coupled to the
electrode slide 118. In the case of both visual and electronic tracking,
the position of the electrode slide 118 is directly measured, whether the
electrode slide is moved by way of the coarse drive 102 or the microdrive
104.
FIG. 17 illustrates the Z-stage 70 mounted to the XY-stage 11. The base 72
of the Z-stage 70 is mounted onto the top panel 40 of the Y-slide 36. The
upstanding pins 44 on the top panel 40 of the Y-slide 36 are received
within the alignment holes 74 in the base 72 of the Z-stage 70. The
securing screws 78 in the base 72 of the Z-stage engage the threaded holes
46 in the top panel 40 of the Y-slide 36. Actuation of the medial and
anterior movement mechanisms 32, 38 thus not only move the X-slides 30a,
30b and the Y-slide 36 but also move the Z-stage 70 with respect to the
X-and Y-axes.
Referring now to FIG. 18, a novel electrode 150 is disclosed. The electrode
150 comprises a hollow conductive shaft 156, an electrode wire 160, a
glass tip 162, and insulation 164. The shaft 156 will typically range from
210 to 300 millimeters in length. The electrode wire 160 tapers to a sharp
tip 166 at its forward end. In the disclosed embodiment, the sharp tip 166
is formed by chemically etching the electrode wire 160 in an acid bath. A
bend 168 is formed in the rearward end of the electrode wire 160 such that
when the rearward end of the electrode wire 160 is inserted into the
forward end of the hollow shaft 156, the bend will form an interference
fit which retains the electrode wire within the hollow shaft during
subsequent manufacturing steps. The glass tip 162 is then formed directly
onto the forward end of the shaft 156, encapsulating the portion of the
electrode wire 160 which extends forward of the hollow shaft 156. The
glass tip 162 tapers to a sharp forward tip 170 substantially coincident
with the forward end of the electrode wire 160. A tube of insulating
material 164 is then advanced forward over the shaft 156 and over the
rearward end of the glass tip 162. Glue is applied at the junction 172
between the insulation and the glass bulb to seal the joint. An electrical
lead 173 is attached in conductive communication with the rearward end of
the shaft 156 for connecting the electrode 150 to an associated electronic
device, such as for mapping electrical activity within a patient's brain.
Use of the apparatus for positioning a surgical instrument along three axes
during neurosurgery is accomplished as follows. For purposes of
illustration, a procedure will be described in which the stereotactic
guide apparatus 10 is used in conjunction with a mapping electrode to map
electrical activity within the brain.
The Z-stage of the stereotactic guide apparatus 10 is prepared for use as
follows. The microdrive unit 104 is installed onto the coarse drive slide
100 by engaging the externally threaded collar 108 of the microdrive unit
with the threaded bore 114 of the coarse drive slide. The carrier tube 95
is then installed onto the carrier tube holder 86 by inserting the hollow
shaft 96 of the carrier tube downward through the circular opening 90 of
the carrier tube holder 86. The annular collar 98 of the carrier tube 95
fits snugly within the circular opening 90 in the carrier tube holder 86,
with the head 97 of the carrier tube resting on the upper surface of the
carrier tube holder. The thumbscrew 92 on the carrier tube holder 86 is
then tightened to retain the carrier tube 95 in place.
An electrode 150 is now installed onto the electrode slide 118 of the
Z-stage 70. The electrical lead 173 and rearward end of the shaft 156 of
the electrode 150 are passed upward through the lower end of the carrier
tube 95. When the rearward end of the shaft 156 of the electrode 150 exits
the upper end of the carrier tube 95, the shaft of the electrode is passed
between the electrode holder pressure plate 128 and the forward edge 122
of the electrode slide 118. The shaft 156 of the electrode 150 is
positioned within the vertical notch 132 in the face 122 of the electrode
slide 118. When the electrode 150 has been advanced to a location in which
the glass tip 162 of the forward end of the electrode 150 resides just
within the lower end of the carrier tube 95, the thumb screw 130 of the
electrode holder assembly 120 is tightened, causing the electrode holder
pressure plate 128 to advance toward the forward edge 122 of the electrode
slide 118, thereby clamping the shaft 156 of the electrode 150 within the
notch 132. The electrical lead 173 is then attached to the positive
terminal of a conventional electrode mapping apparatus, and a wire is run
between the carrier tube 95 and the negative terminal of the electrode
mapping apparatus to complete the connection of the electrode 150.
The XY-stage 11 of the device 10 is prepared for use as follows. The outer
guide tube 228 is mounted to the Y-slide 36 by inserting the shaft 234a of
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