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Claims  |
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What is claimed is:
1. In a stereotactic instrument for neurosurgery of the brain for use with
a noninvasive scanner such as a CT scanner having a moveable table, said
instrument having a rigid frame, means for attaching the frame to the
patient's skull, means for determining scanner coordinates indicating a
precise brain location from scanner measurements, means attached to said
frame for defining a set of frame coordinates, and means attached to said
frame for precisely guiding a surgical implement to said brain location in
accordance with said scanner coordinates, the improvement comprising,
means for releasably fastening said frame to said CT scanner table, and
means for adjusting the plane of said frame to a predetermined position
relative to the plane of said CT scanner table.
2. In a stereotactic instrument, the improvement according to claim 1,
wherein the adjustment means comprises,
means for adjusting the plane of the frame to be perpendicular to the plane
of the table, and
means for rotating the frame so that the frame coordinates can be aligned
to a predetermined position relative to the scanner coordinates.
3. In a stereotactic instrument, the improvement according to claim 2,
wherein the CT scanner has a zero reference plane and the predetermined
position is the zero reference plane.
4. In a stereotactic instrument, the improvement according to claim 3
wherein the scanner coordinates are graduated in divisions and the means
for defining frame coordinates is graduated in the same divisions as the
scanner coordinates.
5. In a stereotactic neurosurgical instrument, the improvement according to
claim 1 the adjusting means including means for rotating said frame
relative to said table so that said frame coordinates can be aligned to a
predetermined position relative to said scanner coordinates.
6. In a stereotactic neurosurgical instrument, the improvement according to
claim 5, wherein said rotating means rotates said frame so that said frame
coordinates coincide with said scanner coordinates.
7. In a stereotactic neurosurgical instrument, the improvement according to
claim 1, wherein said adjusting means adjusts the plane of said frame to
be perpendicular to the plane of said table.
8. In a stereotactic instrument for neurosurgery of the brain for use with
a noninvasive scanner such as a CT scanner having a moveable table, said
instrument having a rigid frame, means for attaching the frame to the
patient's skull, means for determining scanner coordinates indicating a
precise brain location from scanner measurements, means attached to said
frame for defining a set of frame coordinates, and means attached to said
frame for precisely guiding a surgical implement to said brain location in
accordance with said scanner coordinates, the improvement comprising,
a first attachment plate,
means for rigidly attaching said first plate to said scanner table,
a second attachment plate,
means for rigidly attaching said second plate to said frame,
means for moveably connecting said first plate to said second plate,
means for adjusting the plane of said first plate relative to the plane of
said second plate so that the plane of said frame can be adjusted to a
predetermined position relative to the plane of said CT scanner table.
9. In a stereotactic neurosurgical instrument, the improvement according to
claim 8, wherein said connecting means comprises an adjustable fastening
means which fastening means can be loosened to allow relative movement
between said first and second plate and tightened to lock said plates
together.
10. In a stereotactic neurosurgical instrument, the improvement according
to claim 8, wherein said adjusting means comprises at least one adjustment
screw, said screw being threaded into said one of said plates and bearing
against said other plate.
11. A stereotactic instrument for neurosurgery of the brain for use with a
noninvasive scanner such as a CT scanner having a moveable table and means
for determining scanner coordinates indicating a precise brain location,
said instrument comprising,
a rigid frame,
means for attaching the frame to the patient's skull,
means attached to said frame for defining a set of frame coordinates,
means attached to said frame for precisely guiding a surgical implement to
said brain location in accordance with said frame coordinates,
a first attachment plate,
means for rigidly attaching said first plate to said scanner table,
a second attachment plate,
means for rigidly attaching said second plate to said frame,
means for moveably connecting said first plate to said second plate,
means for adjusting the plane of said first plate relative to the plane of
said second plate so that the plane of said frame can be adjusted to a
predetermined position relative to the plane of said CT scanner table.
12. A stereotactic neurosurgical instrument according to claim 11, wherein
said frame coordinate defining means further comprises,
means attached to the frame for defining the AC-PC line of the brain from
CT scanner coordinates while maintaining the frame in fixed position in
relation to the skull, and
means attached to the AC-PC defining means for adjusting the position of
the means for guiding the surgical implement.
13. A stereotactic neurosurgical instrument according to claim 12 wherein
the CT scanner defines X, Y and Z coordinates and the AC-PC defining means
is characterized by
means attached to the frame for defining a Y set of frame coordinates
corresponding to the Y coordinates of the CT scanner,
means attached to the Y coordinate means for defining a Z set of frame
coordinates corresponding to the Z coordinates of the CT scanner
means attached to the Z coordinate means for defining an X set of frame
coordinates corresponding to the X coordinates of the CT scanner, and
means corresponding to the AC-PC line and positionable by adjusting the X,
Y and Z frame coordinate means.
14. A stereotactic neurosurgical instrument according to claim 13 wherein
the Y coordinate means is characterized by a detachable graduate scalebar
attached to the frame,
the Z coordinate means is characterized by a first pair of graduated bars,
each of the bars being connected perpendicularly to the scalebar and
capable of independent movement laterally along the scalebar,
the X coordinate means is characterized by a second pair of graduated bars
attached perpendicularly to the first pair of graduated bars and capable
of independent movement along the X axis, and
the means corresponding to the AC-PC line is characterized by a bridge
piece pivotably connecting the second pair of graduated bars.
15. In a stereotactic instrument, the improvement according to claim 11
wherein the CT scanner has a zero reference plane and the predetermine
position is the zero reference plane.
16. In a stereotactic instrument, the improvement as claimed in claim 15
wherein the scanner coordinates are graduated in divisions and the means
for defining frame coordinates is graduated in the same divisions as the
scanner coordinates.
17. A stereotactic neurosurgical instrument according to claim 11, wherein
said connecting means comprises a plurality of connecting screws, said
screws being threaded into one of said plates, and said screws passing
through oversized holes in said other plate so that said screws can be
loosened to allow relative movement between said first and second plates
and tightened to lock said plates together.
18. A stereotactic neurosurgical instrument according to claim 17, wherein
said adjusting means comprises a plurality of adjustment screws, each of
said plurality of screws being threaded into said one of said plates and
bearing against said other plate.
19. A stereotactic neurosurgical instrument according to claim 18, wherein
said adjustment screws are threaded into said one plate in a geometrical
pattern.
20. A stereotactic neurosurgical instrument according to claim 19, wherein
said pattern comprises a rectangle with said screws being threaded into
said one plate at the corners of said rectangle.
21. A stereotactic neurosurgical instrument according to claim 20, wherein
said means for rigidly attaching said first plate to said scanner table
comprises a thumbwheel and a screw attached to said thumbwheel, said
thumbwheel screw engaging a tapped hole in said table.
22. A stereotactic neurosurgical instrument according to claim 21, wherein
said means for rigidly attaching said second plate to said frame comprises
a plurality of brackets.
23. A stereotactic neurosurgical instrument according to claim 22, wherein
said frame is square.
24. A stereotactic neurosurgical instrument according to claim 23, wherein
said defining means comprises a plurality of marker posts, each of said
posts containing a radio-opaque marker which generates a dot image on said
scanner.
25. In a stereotactic instrument, the improvement as claimed in claim 24
wherein the CT scanner has a zero reference plane, the predetermined
position is the zero reference plane and the plane of the frame is located
in the zero reference plane by locating the dots in the zero reference
plane.
26. In a stereotactic instrument, the improvement as claimed in claim 25
further comprising means for securing the frame to a headrest for
immobilizing the patient's skull during surgical procedures.
27. In a stereotactic instrument, the improvement as claimed in claim 26
wherein the scanner coordinates are graduated in divisions and the means
for defining frame coordinates is graduated in the same divisions as the
scanner coordinates.
28. In a stereotactic instrument for neurosurgery of the brain, said
instrument having a rigid frame, means for attaching the frame to the
patient's skull, means for determining coordinates of a lesion areas of
the brain, an arc attached to said frame for precisely guiding a surgical
implement to said brain location in accordance with said frame
coordinates, the improvement comprising,
a surgical implement holder connected to said arc,
said implement holder comprising,
a graduated slider,
means for removably attaching said slider to said arc,
an implement carrier,
means for slidably attaching said implement carrier to said slider, and
a calibrated micrometer drive means for advancing said surgical implement a
precise distance relative to said slider, whereby said carrier can be
preset to a precise location relative to said slider and said slider
together with said carrier can be removed from said arc during setup of
said instrument prior to surgery and replaced for surgery while
maintaining said preset location. |
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Claims |
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Description |
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FIELD OF THE INVENTION
This invention relates to stereotactic instruments for use in treatment and
biopsy of brain lesions and, in particular, to stereotactic instruments
which are adapted for use with computed tomographic scanners.
DESCRIPTION OF THE PRIOR ART
A typical problem in neurosurgery of the brain is to precisely position a
biopsy needle or an electrode to a point deep within the brain. It is
often necessary to place the end of the needle or electrode within a small
(often 1-2 mm) radius of a specific point within the brain to sample
tissue or to perform functional neurosurgery. If such accuracy is not
achieved, then improper diagnosis may result because a biopsy is taken of
tissue surrounding a lesion. Alternatively, serious damage may be caused
to the brain tissue. The positioning problem is complicated because
measurements must be made in three dimensions. Often, the desired point is
not accessible by open cranial surgery and thus it must be located
indirectly by using X-rays or other scanning equipment to locate certain
characteristic areas of the brain and then by determining the location of
the desired point relative to these characteristic areas.
After the desired point is located, apparatus known as a stereotactic
surgical instrument is used to assist the surgeon in mechanically guiding
the needle or electrode to the proper position. Stereotactic instruments
have been used on experimental animals as long ago as 1908 and until
recently, such instruments relied mainly on the use of X-rays to detect
the position of known areas of the brain, such as the anterior and
posterior commissures of the third ventricle. The instruments were
designed so that portions of the instruments known as "markers" appeared
on the X-ray image used to locate the known structures of the brain. Once
the location of the brain structures was established relative to the
marker locations, other points in the brain could be related to the marker
positions by means of brain anatomy charts. A needle holder was then
precisely positioned with respect to the marker locations by calculating
its position using the brain anatomy charts and the known brain area
positions and used to guide the needle or electrode to the desired brain
location.
Unfortunately, the anterior and posterior commissures in the third
ventricle of the brain are not opaque to X-rays and thus in order to use
such stereotactic instruments it was necessary to introduce radio-opaque
material into these portions of the brain so that sufficient contrast
could be obtained on the X-ray film to identify their location. This
procedure required two burr holes to be drilled in the skull. In addition,
the X-rays used to form the images of the brain structures were subject to
diffraction effects which either limited the accuracy of the procedure or
required complicated calculations to compensate for such effects.
Recently, computed tomographic (CT) scanners have been extensively used.
These devices rely on a moving X-ray source which generates low-level
X-rays that penetrate the subject from different angles. The intensity of
the radiation passing through and scattered by the subject is detected and
the intensity pattern produced by the moving source is analyzed by a
computer. The computer constructs a composite image of a thin
cross-section or "slice" of the subject on which is superimposed a "grid"
of coordinates. The computer can provide and display a direct computation
of the "coordinate" values of any location on the grid for each slice and
can indicate location of the slice relative to an initial reference slice
or plane.
The use of such scanners is advantageous over prior art devices using
X-rays because the scanners can directly identify portions of the brain
such as the anterior and posterior commissures. Accordingly, many existing
stereotactic instruments have been modified to allow their direct use with
a CT scanner. However, these instruments typically require modifications
in the software of the CT scanner or complicated calculations to convert
the coordinate values produced by the scanner to mechanical settings which
can be used to adjust the devices to place a needle or electrode at a
desired brain location. Still other instruments require that all surgical
operations be performed in the CT scanner room and some arrangements are
so elaborate that they require sophisticated computer knowledge to
operate.
More recently a stereotactic instrument known as the "Gouda Frame" was
modified for use with a CT scanner. Such modification is described in an
article entitled "Modification of the Gouda Frame to Allow Stereotactic
Biopsy of the Brain Using the GE 8800 Computed Tomographic Scanner", K.
Gouda, S. Freidberg, C. Larsen, R. Baker, and M. Silverman, Neurosurgery,
V. 13, no. 2, August 1983. With this modified instrument it was possible
to directly use the scanner-generated coordinate values of a particular
area in the brain to mechanically adjust the frame.
There remained problems with this latter modified instrument, in that it
was difficult to align the modified frame properly with the initial
reference plane of the CT scanner. Any misalignment between the frame and
the reference plane of the scanner resulted in inaccuracy of the final
adjustments. In addition, the Gouda Frame contained a complicated
mechanical adjustment arrangement which, due to mechanical tolerances,
made adjustment of the frame to the required accuracy difficult.
Accordingly, it is an object of the present invention to provide a
stereotactic neurosurgical instrument which is directly compatible with a
CT scanner.
It is another object of the present invention, to provide a stereotactic
instrument which is simple to operate and is not subject to mechanical
tolerances which upset the accuracy of the instrument.
It is yet another object of the present invention to provide a stereotactic
instrument which can be easily and quickly aligned to the reference plane
of the CT scanner.
It is still a further object of the present invention to provide a
stereotactic instrument which does not require a surgical operation to be
performed in the CT scanner room.
SUMMARY OF THE INVENTION
The foregoing objects are achieved and the foregoing problems are solved in
one illustrative embodiment of the invention in which a modified Gouda
Frame is provided with adjustable adapter plates for attachment to the CT
scanner table and with a simplified coordinate adjustment mechanism. The
adjustable adapter plates can be precisely positioned with respect to each
other in two planes by means of adjustment screws and can be rotated with
respect to one another. One plate is fastened to the CT scanner table and
the other to the modified frame so that the relative alignment of the two
members can be adjusted prior to performing a surgical operation so that
the frame is exactly perpendicular to the scanner table.
In particular, the modified Gouda Frame consists of a rectangular metal
frame which is affixed to the skull by means of four pins in a known
manner. At the center of each side of the frame is located a plastic
alignment post on which is etched a cross-hair marking. A 1-mm lead shot
marker is embedded in the post at the center of the cross-hair marking.
Prior to performing an operation, the frame is attached to the CT scanner
table by the adapter plates. The CT scanner laser beams are visually
aligned with the cross-hairs on the alignment posts and an initial lateral
scout scan is taken with the CT scanner showing the scanner reference
plane. The screw adjustments on the adaptor plates can then be manipulated
until the zero reference line of the scanner reference plane passes
through the images of the four marker shots. An axial scan is then taken
and the frame is rotated until the images of the shots align with the "X"
and "Y" coordinate lines of the scanner image. At this point the adapter
plate settings are locked, thus insuring that the mechanical coordinates
determined by the frame will be correspond directly to the coordinates
generated by the scanner.
To perform a surgical operation, the frame is affixed to the head of the
patient in the usual manner. The alignment posts are placed on the frame
and lateral and axial scans are taken in the scanner reference plane to
insure that the frame alignment is correct. The alignment posts are then
removed from the frame and additional CT scans or "slices" are taken. The
patient and the frame are then detached from the CT table and moved to the
operating room. A set of manually-adjustable, graduated coordinate arms
are then mechanically attached to the frame. The graduated markings on the
arms are such that the target coordinates obtained from any slice of the
CT scan can be simply, manually set directly on the arms. Because the
frame has been pre-aligned to the CT table there need be no corrections
for misalignments.
Once the coordinates obtained from the scan have been set, an arc is fitted
to the measurement arms which guides the biopsy needle or electrode. The
needle is contained in a precision holder and can be preset a
predetermined distance to the target area location by means of a simple
calibration rod. The position of the needle on the arc can be moved and
the arc can be rotated in a circular path so that the needle can be
introduced into the skull through an existing burr hole. When the needle
has been extended the predetermined distance, the tip of the needle is
fixed on the target area.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a perspective view of the stereotactic frame with an array of
components used during the scanning and during subsequent operations.
FIG. 2 is an enlarged top view of the modified frame showing the adaptor
plates which attach the frame to the CT scanner table.
FIG. 3 is a side view of the frame as attached to the CT scanner table by
means of the adapter plates.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The modified Gouda frame consists of a rectangular metal frame 1 which may
be comprised of any suitable metal (such as aluminum) that is light and
rigid. Attached to the four corners of the frame are blocks 2-5,
respectively. Blocks 2-5 are comprised of a radio-translucent material,
such as a plastic material. A material suitable for use with the
illustrative embodiment is a plastic material known as Lexan manufactured
by the E. I. Dupont De Nemours, Inc.
Blocks 2-5 are used to support the screw mechanisms which fasten the frame
to the patient's skull. In particular, each block, such as block 2, is
provided with a thumbscrew 6 which is also comprised of a
radio-translucent material, for example, Lexan. Adjustment screw 6 is
fitted with a stainless-steel pin 7 which affixes the frame to the
patient's skull. The other blocks 3-5 are similarly fitted with adjustable
screws and pins.
Frame 1 is also provided with four alignment posts 8-14. Each of the
alignment posts, such as post 14, is provided on its outer surface with a
cross-hair marking 20. Embedded in the center of the block, directly
opposite the cross-hair marking is a 1-mm lead shot. Each of the other
blocks 8-12 is also provided with a similar cross-hair marking on its
outer surface and a lead shot in the corresponding center location.
Alignment posts 8-14 are initially positioned at the center of each side
of the frame and are used, as will hereinafter be described, to position
the frame in the zero reference plane of the CT scanner.
Frame 1 is also provided with a plurality of studs (of which studs 24 and
26 are shown) for attaching the graduated measurement arm mechanisms 30
and 31, as will hereinafter be described.
Frame 1 is also provided with tapped holes at locations 35 and 37 to which
adaptors 40 and 42 can be connected for attachment of the frame to the CT
scanner table and to an appropriate headrest, respectively.
In particular, adaptor 40 is comprised of a backplate 50 which is fastened
to the CT scanner table by means of a threaded screw that is rotated by
knob 53. A typical CT scanner has a moveable table on which the patient
lies and which rests on a fixed base. A gantry containing the scanning
mechanism is positioned in a fixed location relative to the base and the
table can be moved precisely with respect to the base to position the
patient relative to the scanning mechanism. As will be hereinafter
described, the screw from the frame 1 fits into a threaded hole located in
the CT scanner table and thus the patient and frame move as a unit. A
conventional example of a CT scanner which can be used with the
illustrative embodiment is a Model 8800 CT scanner manufactured by the
General Electric Company, Medical Systems Division, Milwaukee, Wis. 53201.
Frontplate 52 is attached to backplate 50 by means of screw adjustments 58
and 60. Frontplate 52 is, in turn, attached to frame 1 by means of
brackets, 55 and 57, and attaching screws, 54 and 56. Attaching screws 54
and 56 fit into holes 35 and 37, respectively.
In accordance with the invention, prior to performing a series of scans on
a patient, the relative alignment of the frame 1 and the CT scanner table
can be adjusted by manipulating the connection between front plate 52 and
back plate 50 so that the marker shots in the alignment markers 8-14 fall
precisely in the zero reference plane of the scanner and align with the
scanners internal coordinate system. Later, when the frame is affixed to
the patient, it provides a fixed set of mechanical reference coordinates
which directly correspond to the internal scanner coordinates because of
the initial alignment. More specifically, as will hereinafter be described
in detail, after backplate 50 has been attached to the CT scanner table
and frame 1 has been attached to frontplate 52, the relative alignment of
the two plates can be changed by manipulating adjustment screws 58 and 60
with Allen wrenches, 59 or 61. Since the adjustments 58 and 60 are
independent, the relative alignment can be adjusted in two axes.
After the CT scans have been performed, adaptor 40 is removed from frame 1
and adaptor 42 is attached to frame 1 by means of screws 66 and 68 which
fit into holes 35 and 37, respectively. Screws 66 and 68 pass through
plate 64 which is, in turn, attached to member 42. Member 42 is attached
in conventional manner to a known supporting arrangement, such as a
"Mayfield" headrest, to immobilize the patient's head for a subsequent
surgical operation.
FIGS. 2 and 3 of the drawing show a top view and a side view, respectively,
of frame 1 as it is mounted on the end of the CT scanner table. FIGS. 2
and 3 also show a more detailed view of the adjustable mounting plates
which allow frame 1 to be adjusted relative to CT scanner table 200. In
particular, the adjustable plates consists of back plate 50 which is
fastened firmly to the movable CT table 200 by means of a thumbwheel 53.
As shown in FIG. 3, this thumbwheel drives screw 55 which engages a
threaded hole in the end of scanner table 200. Table 200, in turn, rests
on base 190.
As previously mentioned, frame 1 is attached by brackets 55 and 57 to front
plate 52. Plate 52 has a clearance hole 180 cut through it so that it does
not interfere with the operation of the thumb wheel 53. Plate 52 is
mechanically fastened to plate 50 by means of two screws, 58 and 60. These
screws pass through oversize holes 150 and 152 in plate 52 and thread into
the back plate 50. The heads of screws 58 and 60 bear against flat washers
160 and 162 which, in turn, bear against plate 52. Thus, when screws 58
and 60 are loosened, plate 52 may be moved relative to plate 50 within the
limits of the oversized holes 150 and 152. When screws 58 and 60 are
tightened, plates 50 and 52 are held in a fixed relationship.
The relative alignment of plates 52 and 50 is controlled by alignment set
screws 170-176. These screws are threaded through plate 52 and bear
against plate 50. By loosening attachment screws 58 and 60 and then by
adjusting one or more adjustment screws 170-176, the plane of plate 52
(and thus of the stereotactic frame 1) can be adjusted relative to the
plane of plate 50 (and thus of table 200). Once the proper alignment has
been made, screws 58 and 60 are tightened to lock the plates into
position.
In use, frame 1 must first be adjusted to the table of the particular CT
scanner with which the frame will be subsequently used to insure that the
plane of the frame lies in the zero reference plane of the scanner. In
order to perform this alignment, marker blocks 8-14 are placed on the
frame with the cross hair markings facing towards the outside. Frame 1 is
attached to plates 50 and 52 and then plate 50 is then affixed to CT
scanner table 200 by means of the thumbwheel 53 and screw 55.
The scanner table and the attached frame are then moved into the scanner
gantry area in the conventional manner so that the lead shot markers 20 in
each of alignment arms 8-14 lie within the scanner's reference plane as
indicated by impingement of the scanner's laser beam on the cross hairs of
markers 8-14. The scanner is then operated to generate a lateral view with
the gantry tilt equal to zero to check that frame is properly aligned. In
this view, the marker lead shots show as darkened point images and proper
alignment is indicated when a straight line can be passed through the four
images and the line is perpendicular to the graduated baseline of the
scanner. If a straight line cannot be passed through all images or the
line is not perpendicular to the scanner baseline, an Allen wrench 61 is
used to loosen the attachment screws 58 and 60 slightly so that frontplate
52 can be moved relative to backplate 50. Allen wrench 59 is then used to
adjust adjustment set screws 170-176 to change the plane of frame 1
relative to the plane of scanner table 200.
After appropriate adjustments have been made, screws 58 and 60 are
tightened to fix the position of the frame relative to the table and an
additional lateral view is generated to verify that the plane of frame 1
is properly aligned to the table. After a lateral view indicates that a
straight line passing through the marker shot images is perpendicular to
the scanner baseline, the CT operator can adjust the position of the table
so that the marker images lie in the scanner reference or "zero" plane.
After this latter adjustment has been made, an axial scan is taken in the
scanner reference plane with a 1.5 mm thickness. The image of the
resulting slice is examined to check that the images of the four marker
shots lie on the axes of the CT grid which are superimposed on the scan
image by the scanner electronics. If the marker images do not lie on the
scanner grid axes, frame 1 must be rotated in its plane with respect to
the scanner table. This rotation is performed by again loosening
attachment screws 58 and 60. Set screws 170-176 are not moved in this
adjustment. Instead, frame 1 is rotated slightly until the four marker
images are superimposed on the grid.
Once the above alignment procedure has been completed there is no need to
repeat the alignment when the frame is used with the same CT table
provided that the relative positions of the table or the gantry are not
disturbed. The frame may then be used to perform either brain biopsies or
surgical operations.
In order to use frame 1 for a biopsy, the frame must first be affixed to
the head of the patient. This may be done in the operating room, an
anteroom or the CT scanner room. To allow the scanning of the entire head
without interference between the images of the metal affixation pins and
the CT brain image, the frame is affixed to the head as low as possible.
To fix the frame it is initially centered on the head and the attachment
screws are turned in until they just touch the scalp. At this point, the
positions of the attachment pins are marked on the scalp with a marker.
The frame is then removed and local anesthetic is injected into the scalp
at the marked sites. The frame is then put back into position and the
affixation screws are advanced to firmly attach the frame to the head.
Adapter 40 is attached to the table by means of thumbwheel 53, the patient
is then placed on the CT table and frame is attached to adapter 40 by
means of screws 54 and 56. Marker blocks 8-14 are then placed on the frame
and the height of the table and the travel of the table are adjusted with
the help of the CT laser beam and the cross hair markings on the marker
blocks so that the laser beam strikes the alignment cross-hairs. When this
position has been reached, due to the previous alignment procedure, the
frame will be precisely aligned with the internal scanner coordinates.
The scanner table is then moved to the gantry and a lateral scout view of
the head is taken to check the alignment of the frame with the zero
reference plane of the scanner. Similarly, after ascertaining that the
lateral alignment is correct, an axial scan at the reference plane is
taken with a slice thickness of 1.5 mm to check the position of the marker
images to be sure that they are precisely superimposed on the X and Y axes
of the scanner.
After proper alignment is verified, the frame marker blocks are removed and
the scanner is operated to take the number of scans necessary to identify
the biopsy area.
At the CT scanner console, after the slice with the biopsy area is
identified, a cursor can be moved to the biopsy location and the X and Y
coordinates (computed by the scanner in a well-known manner) appear on the
scanner screen (on the model 8800 CT scanner mentioned previously, the X
and Y coordinate appear on the right lower corner of the screen. The Z
coordinate appears on the left upper corner of the screen and is the
distance that the slice is displaced from the zero plane). In accordance
with the invention, due to the initial alignment procedure, these
coordinates can be directly used to mechanically set the frame to guide
the biopsy needle to the precise biopsy location.
After the X,Y and Z scanner coordinates have been ascertained, the patient
and frame are disconnected from the CT table and transferred to an
operating room where the frame is attached to a suitable headrest on the
operating table which headrest holds the head immobile during the biopsy
procedure.
To perform the biopsy, the patient is then prepped for a surgical operation
in the conventional manner, and two graduated scale bars 70 and 71 (FIG.
1) are attached to frame 1 by means of four threaded fittings (only
fittings 24 and 26 are shown in FIG. 1) and corresponding screws (such as
screw 77). Each of these bars bears a scale (such as scale 73) which is
graduated in the same divisions as the Y-axis scale of the CT scanner
display. Due to the initial alignment, the Y coordinate number obtained
from the scanner display can be directly correlated to this scale markings
on bars 70 and 71.
A sliding attachment block 78 slides along a dovetail way 72 on bar 70 and
can be fixed at any position by means of screws 76 or 80. Attachment block
78 contains an index line 79 which can be set opposite the desired
Y-coordinate number on scale 73.
An additional graduated bar 75 is mounted on each side of the frame by
sliding a dovetail way into the dovetail socket 74 of block 78. Bar 75
also bears a graduated scale (not shown in FIG. 1) on which the
Z-coordinate number can be set. The Z-coordinate is determined by the
location of the CT slice in which the image of the biopsy area occurs and
may be set directly on the bar. After the Z-coordinate has been set, bar
75 is locked in place by means of set screw 76 which also locks the Y
movement A bar similar to bar 75 is attached on the opposite side of frame
1.
A third set of bars (such as bar 84) are then mounted perpendicularly on
the top of bar 75. Each of these bars also bear a graduated scale which
corresponds to the scanner X-coordinate. A similar graduated bar is
mounted on the opposite side of the frame.
With the graduated bars in place, the coordinates obtained from the scanner
are transferred and set as mechanical adjustments on the respective bar
scales. In order to set the depth of the biopsy needle, a centering rod
106 is mounted on arc 100 (centering rod 106 has a spring attachment which
allows it to be easily removed and inserted). Mounted on arc 100 is a
needle carrier 108 which consists of a slider 123 and a calibrated
micrometer drive unit 112. In order to set the needle depth, the
micrometer needle drive is first set to its "zero" point by turning knob
118 (which operates a rack-and-pinion gear arrangement) and then locked in
position by tightening screw 116. A biopsy needle is placed in the drive
unit 119 and positioned at a reasonable location where it is fixed by
tightening screw 121. Allen wrench 110 is then used to loosen set screw
109 on needle or electrode carrier 108 to move micrometer drive unit 112
until the needle tip touches the center point on rod 106. Allen wrench 110
is then used to tighten set screw 109 to fasten carrier 108 in position.
Slider 123 is then removed from arc 100 by loosening set screw 116.
Centering rod 106 is also removed.
Arc 100 is subsequently mounted on frame 1 by placing pins 102 into holes
90 on bar 84 which, as previously described, has been attached to frame 1.
The arc may be rotated about its axis using protractor 104 as a guide
until the needle position is aligned with an existing burr hole, if any.
At this point, the needle carrier 119 is remounted on the arc. Needle
carrier 119 is then advanced to its zero point with the micrometer drive
to position the needle point at the biopsy area. A biopsy sample is taken
in the usual manner.
In order to use frame 1 for functional neurosurgery (for example, a
thalamotomy), in accordance with the invention, each of the bars, such as
bar 75, that are used for biopsy purposes are replaced with a dual post
arrangement, 31. This arrangement comprises two bars, 130 and 132, which
are graduated in the same manner as bar 75 to allow for Z-axis adjustment.
At the top of each of bars 130 and 132 is mounted perpendicularly another
small bar (one of bars 134 and 136, respectively) to allow for X-axis
adjustment. Each of bars 134 and 136 bears a post and the top of each post
is joined to the other post by a bridge piece 138.
Post 136 is joined by a pivot to bridge piece 138 and post 134 is joined to
bridge piece 138 by a pin and slot arrangement. In use, rod 132 is aligned
to the anterior commissure position and rod 130 is aligned to the
posterior commissure location and thus the bridge portion 138 represents
the anterior commissure-posterior commissure line (AC-PC line). The
coordinates of the AC-PC line can be determined from the scanner using a
midline sagittal reconstruction of the region of the third ventricle in
the normal manner. Since the position of each of rods 130 and 132 and
bridge piece 138 can be adjusted independently, the mechanism allows for
compensation for the differing heights of the anterior commissure and the
posterior commissures and a lateral misalignment of the anterior and
posterior commissures.
Mounted on bridge 138, is an additional bar 140 which is used to set the
transverse coordinate of the target relative to the mid-line of the
patient's third ventricle. Bar 140 can slide over AC-PC bridge 138 (front
and back) with attachment block 137 to set the anterior-posterior
coordinate of the target. The level of the target above or below the AC-PC
line can be set with block 142.
In order to use the apparatus for functional neurosurgery, the patient is
taken to the CT room and the various scans are taken, as previously
described, for a biopsy procedure so that the AC-PC line can be
determined. In the operating room, dual-post bridge arrangements are
attached to the lateral bars 70 on each side of the frame. The coordinates
of the AC-PC line as determined from the CT scanner are set directly on
the bars 130 and 132.
A convenient burr hole is then drilled in the skull and an appropriate
lesion is made using a radio-frequency generator.
Although only one illustrative embodiment of the invention has been
described, other embodiments within the spirit and scope of the invention
will be immediately apparent to those skilled in the art.
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