 |
Claims  |
|
|
I claim:
1. A method for performing stereotactic surgery with a medical instrument
upon a target within a skull comprising the steps of:
(a) establishing a first, predetermined geometric relationship between a
skull mount fixture, attached to both the skull and to a support surface
upon which the skull is disposed, and the support surface;
(b) scanning the skull to produce images of the skull mount fixture and the
target within the skull;
(c) determining the linear coordinates of the target along X, Y and Z axes
with respect to the skull mount fixture;
(d) disposing a displacement bar, having first and second ends upon the
skull mount fixture to establish a second, predetermined geometric
relationship therebetween, which is identical to the first, predetermined
geometric relationship;
(e) disposing the first end of the displacement bar directly over the
target in the skull;
(f) associating a means for guiding a medical instrument with the first end
of the displacement bar; and
(g) inserting the medical instrument through the means for guiding a
medical instrument, whereby the medical instrument will intersect the
target in the skull.
2. The method of claim 1, wherein the first, predetermined geometric
relationship is the skull mount fixture disposed in a plane which lies
perpendicular with respect to the longitudinal axis of the support
surface; and the second, predetermined geometric relationship is the
displacement bar disposed in a plane parallel with the plane in which lies
the skull mount fixture, whereby the scanned images all lie in planes
parallel with the planes in which lie the skull mount fixture and the
displacement bar.
3. The method of claim 2, including the steps of securing in a first
position the first end of an elongate post, having first and second ends,
to the skull mount fixture and releasably securing the displacement bar
with respect to the second end of the post along the post; the post, in
the first position, being disposed in a plane which is perpendicular to
the planes in which lie the skull mount fixture and the displacement bar.
4. The method of claim 3, including the step of utilizing two cooperating
guide bars to dispose the first end of the displacement bar directly over
the target in the skull, one of the guide bars being associated with the
linear coordinate of the target along the X-axis, and the other guide bar
being associated with the linear coordinate of the target along the
Y-axis.
5. The method of claim 4, wherein each guide bar has first and second ends,
and the first end of one guide bar is fixedly secured to the post and the
first end of the other guide bar is movably mounted on the first end of
the displacement bar.
6. The method of claim 5, including the step of interconnecting the guide
bars to one another intermediate the first and second ends of each guide
bar, the guide bars being movable with respect to one another, whereby
movement of one guide bar causes the first end of the displacement bar to
move.
7. The method of claim 1, including the steps of movably mounting an arc
bar, having a fixed radius of curvature, to the first end of the
displacement bar; and movably mounting the medical instrument guide means
upon the arc bar, whereby the target in the skull may be intersected by a
medical instrument that has the capability to pass through the skull from
a variety of different locations on the surface of the skull, dependent
upon the locations of the arc bar with respect to the displacement bar and
the medical instrument guide means with respect to the arc bar.
8. The method of claim 3, further including the steps of angularly
offsetting the post from its first position to a second position, the
displacement bar lying in a plane which is perpendicular to the angularly
offset post, whereby the location of a target may be determined, which
target lies in a plane which is not parallel to the planes in which lie
the scanned images.
9. A system for performing stereotactic surgery with a medical instrument
upon a target within a skull, comprising:
(a) a skull mount fixture, having associated therewith a means for
attaching the skull mount fixture to both the skull and to a support
surface upon which the skull is disposed;
(b) a straight, elongate displacement bar, having first and second ends,
movably mounted upon the skull mount fixture for both longitudinal and
rotational movement with respect to the skull mount fixture, the
longitudinal axis of the displacement bar being disposed in a plane which
lies parallel to the plane in which lies the longitudinal axis of the
skull mount fixture; and
(c) a means for guiding a medical instrument, the means for guiding a
medical instrument being associated with the first end of the displacement
bar.
10. The system of claim 9, wherein the skull mount fixture further includes
an elongate post having first and second ends, the first end being secured
to the skull mount fixture, the post lying in a plane which is
perpendicular to the planes in which lie the longitudinal axes of the
skull mount fixture and the displacement bar, the displacement bar being
releasably secured with respect to the second end of the post.
11. The system of claim 10, including first means for adjustably securing
the displacement bar along the length of the post in order to vary the
distance of the displacement bar from the skull mount fixture.
12. The system of claim 10, including second means for securing the
displacement bar to the post, whereby the distance from the first end of
the displacement bar to the post may be varied.
13. The system of claim 10, including two cooperating guide bars, each
guide bar having first and second ends; the first end of one guide bar
being fixedly secured to the post and the first end of the other guide bar
being movably mounted to the first end of the displacement bar; the guide
bars are interconnected to one another intermediate the first and second
ends of each guide bar; and the guide bars being movable with respect to
each other, whereby movement of the guide bar mounted to the first end of
the displacement bar causes the displacement bar to move longitudinally
and rotationally with respect to the post.
14. The system of claim 13, further comprising an arc bar, having a fixed
radius of curvature, the arc bar is movably mounted to the first end of
the displacement bar; and the medical instrument guide means is movably
mounted upon the arc bar.
15. The system of claim 10, including a protractor plate secured to the
post to determine the angular orientation of the longitudinal axis of the
displacement bar with respect to the longitudinal axis of the post.
16. The system of claim 15, wherein an arc bar, having a fixed radius of
curvature is movably mounted to the first end of the displacement bar; and
the medical instrument guide means is movably mounted upon the arc bar.
17. The system of claim 10, wherein the post is rotatably mounted and
secured to the post, whereby the post may be rotated and the longitudinal
axis of the displacement bar can be caused to lie in planes which are not
parallel to the plane in which lies the longitudinal axis of the skull
mount fixture. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
FIELD OF THE INVENTION
The invention relates to a method and apparatus for performing stereotactic
surgery with a medical instrument upon a target within a skull.
DESCRIPTION OF THE PRIOR ART
One of the ongoing interests of neurosurgeons is the practice of
stereotactic surgery; gaining precise access to a specific point in the
cranium through the application of an external three-dimensional
coordinate system. Much time and effort has gone into the development of
instrumentation for implementing such an approach to the human brain. With
the development of computerized tomographic ("CT") scanning, and its
precise imaging, stereotactic surgery is becoming the diagnostic and
therapeutic procedure of choice for many disorders involving the
intracranial cavity.
CT scanning produces an image representing a "slice" of brain tissue
displayed with anatomical accuracy. The series of "slices", which
constitute the complete CT study, represent a three-dimensional picture of
the brain, defining the relationship of neurological structures or
accurately localizing lesions. CT scanning has allowed physicians to
visualize the brain directly, thus making identification of anatomical and
pathological areas of interest much more precise, and thus much more
accessible to the precise mechanics of stereotactic surgery. Mating CT
scanning and stereotactic surgery involves a coordinate transformation
from the two-dimensional space of CT scanning to the three-dimensional
space of stereotactic surgery.
Although there has been a wide range of methods and devices designed to
implement such a coordinate conversion, most of the devices have had a
similar conceptual approach, wherein the resulting devices have left
stereotactic surgery as being perceived as an esoteric, cumbersome,
expensive, and time consuming procedure.
These prior art devices and methods typically utilize a bulky frame mounted
to the patient's skull by four pins or screws. Such devices have been
found to be quite accurate and reliable and have allowed targets within a
skull to be accessed with an accuracy of 1 mm. or less. They have allowed
small, relative inaccessible tumors to be biopsied with minor morbidity
and practically absent mortality. These devices have also given surgeons a
means of biopsying accessible tumors that are radiosensitive without the
need for a formal craniotomy, a procedure that carries a much higher
mortality and morbidity than stereotactic surgical procedures. In
addition, such devices have provided a means for implementing new
modalities for treating hematomas and abscesses, as well as the placement
of radioisotopes and chemotherapeutic agents in the treatment of malignant
brain tumors.
Despite these advances, there are characteristics of current stereotactic
instruments which have severely limited their potential widespread
application. The performance of careful stereotactic procedures on a
regular basis with the prior art systems available requires much operating
room time to be wasted during the procedure. Processing of X-ray pictures,
target point calculations, and cumbersome mechanical adjustments on
stereotactic frames add time to the operation. The inability of these
systems to be reused on the same patient without recalculating target
points also adds to their inefficiency. Although the prior art
stereotactic instruments are adequate for reaching a single intracranial
target point, rapid access to multiple targets during a procedure is
inconvenient. Furthermore, the prior art devices are extremely expensive
and are quite complicated to employ, thereby making their appeal to the
surgeon in private practice quite limited. Some of the prior art systems
require modifications of existing CT scanning software, or alternatively,
require software generated coordinates determined from a hand-held
calculator as part of the system. The frame required by these prior art
devices require fixation to the skull of the patient, typically via four
screws, whereby the frame is quite cumbersome and uncomfortable.
Additionally, the frame cannot be left on the patient's head if the same
procedure is to be repeated at a later date. If subsequent stereotactic
procedures are to be performed, the frame must be reapplied at the time of
the second procedure, including the step of again using a CT scanner to
calculate the coordinates of the target point within the skull.
Many, if not all, of the foregoing disadvantages and problems associated
with prior art devices and methods were solved by the method and apparatus
for performing stereotactic surgery taught in U.S. Pat. No. 4,805,615,
wherein a compact, easy to use positioning fixture is used in conjunction
with a phantom fixture. The positioning fixture of that patent utilized a
ball and socket approach. Although the method and apparatus taught in that
patent constituted a significant advance in the art, there are still
certain disadvantages associated with the use of the method and apparatus
taught in that patent.
Because of the use of the ball and socket approach in the method and
apparatus of that patent, it is an angular system, whereby the target
within the skull is reached by passing a probe through the ball along a
path which represents a compound angle with respect to the frame of
reference of the system, which is the plane of the imaging process. In
order to move the probe, or medical instrument, in any given direction a
prescribed amount, a new compound angular trajectory must be calculated.
Linear offset applications are presently a part of many stereotactic
procedures, and they require the ability to move the target point around
inside the skull in a linear fashion in any plane. One of these linear
offset applications is in the field of functional procedures. The targets
for many of these procedures are referenced on the AC PC line, as are
standard physiologic and anatomic atlases. Although with current
stereotactic systems, the approximate location of the target within the
skull can be generated from CT scanning or magnetic resonance ("MR")
imaging, physiologic verification based upon anatomic parameters are
needed prior to lesioning the target. This requires offsetting the target
in a linear fashion, in any plane, such as the linear coordinates of the
target along the X, Y, and Z axes, until the precise lesion location is
identified.
Another example of linear offset applications is if the surgeon is
performing a thalamotomy, wherein a lesion is made in the thalamus for
functional or motor disorders, and the surgeon may find through electrical
stimulation that the initial target point within the skull was off by 2 mm
AP direction. It is desirable to have a system which, without the need for
recalculating the location of the target within the skull, could be
adjusted so that the new target point would vary by 2 mm in only the AP
direction.
Another disadvantage associated with the method and apparatus of U.S. Pat.
No. 4,805,615, as well as many, if not all, of the other prior art methods
and apparatus, is that it is necessary to use a phantom fixture in order
to determine the trajectory of a medical instrument to the desired target
within the patient's skull. It is typically necessary to perform several,
rapid, but somewhat cumbersome manipulations and transfers of the
component pieces of the equipment between the patient and the phantom
fixture in order to generate the trajectory to the desired target. Each of
these transfers of equipment represents a potential source of error in
usage of the system. Additionally, the required use of a phantom fixture
increases the cost, size, and weight of the stereotactic system.
Accordingly, prior to the development of the present method and apparatus
for performance stereotactic surgery, there has been no method and
apparatus for performing stereotactic surgery which: is compact,
inexpensive, easy to use, precise, and comfortable; does not require a
bulky skull mounted frame; does not require the use of a phantom fixture
or a ball and socket positioning fixture; and permits linear offset
applications to be conducted. Therefore, the art has sought a method and
apparatus for performing stereotactic surgery which: does not require a
skull mounted frame; is compact, inexpensive, easy to use, precise and
comfortable; does not require the use of a phantom fixture or a ball and
socket positioning fixture; and permits linear offset applications to be
performed.
SUMMARY OF THE INVENTION
In accordance with the invention, the foregoing advantages have been
achieved through the present method and apparatus for performing
stereotactic surgery. The method for performing stereotactic surgery, in
accordance with the present invention, includes the steps of: establishing
a first, predetermined geometric relationship between a skull mount
fixture, attached to both the skull and to a support surface upon which
the skull is dispersed, and the support surface; scanning the skull to
produce images of the skull mount fixture and the target within the skull;
determining the linear coordinates of the target along X, Y, and Z axes
with respect to the skull mount fixture; disposing a displacement bar,
having first and second ends, upon the skull mount fixture to establish a
second, predetermined geometric relationship therebetween, which is
identical to the first, predetermined geometric relationship; disposing
the first end of the displacement bar directly over the target in the
skull; associating a means for guiding a medical instrument with the first
end of the displacement bar; and inserting the medical instrument through
the medical instrument guide means, whereby the medical instrument will
intersect the target in the skull.
A feature of the present invention is that the first, predetermined
geometric relationship is the skull mount fixture disposed in a plane
which lies perpendicular with respect to the longitudinal axis of the
support surf ace; and the second, predetermined geometric relationship is
the displacement bar disposed in a plane parallel with the plane in which
lies the skull mount fixture, whereby the scanned images all lie in planes
parallel with the planes in which lie the skull mount fixture and
displacement bar.
Another feature of the present invention is the step of securing in a first
position the first end of an elongate post, having first and second ends,
to the skull mount fixture and releasably securing the displacement bar
with respect to the second end of the post along the post; the post, in
the first position, being disposed in a plane which is perpendicular to
the planes in which lie the skull mount fixture and the displacement bar.
Another feature of the present invention is the step of utilizing two
cooperating guide bars to dispose the first end of the displacement bar
directly over the target in the skull, one of the guide bars being
associated with the linear coordinate of the target along the X axis, and
the other guide bar being associated with the linear coordinate along the
Y-axis. A further feature of the present invention is the step of movably
mounting an arc bar, having a fixed radius of curvature, to the first end
of the displacement rod; and movably mounting the medical instrument guide
means upon the arc bar, whereby the target in the skull may be intersected
by a medical instrument that has the capability to pass through the skull
from a variety of different locations on the surface of the skull,
depending upon the locations of the arc bar with respect to the
displacement bar and the medical instrument guide means with respect to
the arc bar. Another feature of the present invention includes the step of
angularly offsetting the post from its first position to a second
position, the displacement bar lying in a plane which is perpendicular to
the angularly offset post, whereby the location of a target may be
determined, which target lies in a plane which is not parallel to the
planes in which lie the scanned images.
In accordance with the invention, the foregoing advantages have also been
achieved through the present system for performing stereotactic surgery.
The system for performing stereotactic surgery, in accordance with the
present invention, may include: a skull mount fixture, having associated
therewith a means for attaching the skull mount fixture to both the skull
and to a support surface upon which the skull is disposed; a straight,
elongate displacement bar, having first and second ends, movably mounted
upon the skull mount fixture for both longitudinal and rotational movement
with respect to the skull mount fixture, the longitudinal axis of the
displacement bar being disposed in a plane which lies parallel to the
plane in which lies the longitudinal axis of the skull mount fixture: and
a means for guiding a medical instrument associated with the first end of
the displacement bar.
Another feature of the system in accordance with the present invention is
that the skull mount fixture may further include an elongate post having
first and second ends, the first end being secured to the skull mount
fixture, the post lying in a plane which is perpendicular to the planes in
which lie the longitudinal axis of the skull mount fixture and the
displacement bar, the displacement bar being releasably secured with
respect to the second end of the post. An additional feature of the
present invention is that the system may include two cooperating guide
bars, each guide bar having first and second ends, the first end of one
guide bar being fixedly secured to the post and the first end of the other
guide bar being movably mounted to the first end of the displacement bar;
the guide bars being interconnected to one another intermediate the first
and second ends of each guide bar; the guide bars being movable with
respect to each other, whereby movement of the guide bar mounted to the
first end of the displacement bar causes the displacement bar to move
longitudinally and rotationally with respect to the post.
An additional feature of the system of the present invention is that an arc
bar, having a fixed radius of curvature may be movably mounted to the
first end of the displacement bar; and the medical instrument guide means
may be movably mounted upon the arc bar. A further feature of the present
invention is that a protractor plate may be secured to the post to
determine the angular orientation of the longitudinal axis of the
displacement bar with respect to the longitudinal axis of the post.
In accordance with the invention, the foregoing advantages have also been
achieved through another method for performing stereotactic surgery. This
other method for performing stereotactic surgery, in accordance with the
present invention, includes the steps of: establishing a first,
predetermined geometric relationship between a skull mount fixture,
attached to both the skull and to a support surface upon which the skull
is disposed, and the support surface; scanning the skull to produce images
of the skull mount fixture and the target within the skull; determining
the linear coordinates of the target along X, Y, and Z axes with respect
to the skull mount fixture; disposing a rectangular shaped frame structure
upon the skull mount fixture to establish a second predetermined geometric
relationship therebetween, which is identical to the first-predetermined
geometric relationship; movably mounting two straight, elongate first and
second coordinate bars to the frame structure, the coordinate bars being
disposed perpendicular to each other and the first coordinate bar being
disposed in the plane parallel with the plane in which lies the skull
mount fixture; movably mounting a means for guiding a medical instrument
on an arc bar having a fixed radius of curvature, the arc bar being
movably mounted on the first coordinate bar and inserting the medical
instrument through the medical instrument guide means where, whereby the
medical instrument will intersect the target in the skull.
A further feature of the present method, in accordance with the present
invention, includes the step of rotating the frame structure with respect
to the skull mount fixture, whereby the location of a target may be
determined, which target lies in the plane which is not parallel to the
plane which lie the scanned images.
In accordance with the invention, the foregoing advantages have also been
achieved through another system for performing stereotactic surgery. The
system for performing stereotactic surgery, in accordance with the present
invention, may include: a skull mount fixture having associated therewith
a means for attaching the skull mount fixture to both the skull and to a
support structure upon which a skull is disposed: a rectangular shaped
frame structure including means for attaching the frame structure to the
skull mount fixture, the frame structure lying in a plane which is
parallel with the plane in which lies the skull mount fixture; two
straight, elongate, first and second, coordinate bars movably mounted to
the frame structure, the coordinate bars being disposed perpendicular to
each other, and the first coordinate bar is disposed in a plane which is
parallel with the plane in which lies the skull mount fixture: and means
for guiding a medical instrument movably mounted on an arc bar, having a
fixed radius of curvature, the arc bar being movably mounted on the first
coordinate bar. An additional feature of the system present invention is
that the skull mount fixture may include means for rotably mounting the
frame structure with respect to the skull mount fixture.
The method and apparatus for performing stereotactic surgery of the present
invention, when compared with previously proposed prior art methods and
apparatus, have the advantages of being: compact, inexpensive, easy to
use, precise, and comfortable for the patient; does not require a skull
mounted frame, a ball and socket positioning fixture, or a phantom
fixture; and permits linear offset applications to be conducted.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a side view of a patient disposed upon a support surface with a
skull mount fixture of the present invention disposed on the patient's
skull;
FIG. 2 is a side view of a patient disposed upon a support surface with
another embodiment of a skull mount fixture of the present invention
disposed upon this patient's skull;
FIG. 3 is a perspective view of a skull mount fixture in accordance with
the present invention;
FIG. 4 is a perspective view of a skull mount fixture, cooperating and
mating with a support surface;
FIG. 5 is a perspective view of another embodiment of a skull mount fixture
in accordance with the present invention;
FIG. 6 is a top view of a skull mount fixture disposed upon a support
surface, with the skull mount fixture being disposed on the patient's
skull (shown in dotted lines), with the scanned images, or "slices", being
illustrated;
FIG. 7 is a perspective view illustrating the geometric relationships
involved in the present invention:
FIG. 8 is a side view of a patient having the modified skull mount fixture
of FIG. 5 disposed on the patient's skull, and illustrating the planes in
which lie the scanned images, or "slices";
FIG. 9 is a perspective view of the system for performing stereotactic
surgery in accordance with the present invention;
FIG. 10 is a cross-sectional view taken along line 10--10 of FIG. 9;
FIG. 11 is an exploded, perspective view of a system for performing
stereotactic surgery in accordance with the present invention;
FIG. 12 is a perspective view of another system for performing stereotactic
surgery in accordance with the present invention;
FIGS. 13-15 illustrate a patient having a stereotactic procedure conducted,
utilizing the system illustrated in FIG. 12;
While the invention will be described in connection with the preferred
embodiment, it will be understood that it is not intended to limit the
invention to that embodiment. On the contrary, it is intended to cover all
alternatives, modifications, and equivalents as may be included within the
spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
With reference to FIGS. 1, 6, 7, and 11, the method for performing
stereotactic surgery with a medical instrument upon a target within a
skull will be generally described. A patient's skull 160 is shown to have
a target 161 therein which is desired to be treated. For example, target
161 could be a hematoma, abscess, or tumor. With reference to FIGS. 1 and
6, a skull mount fixture 162 is attached to skull 160 in a manner to be
hereinafter described in greater detail. Preferably, skull mount 162 is
constructed in accordance with the present invention, as will be
hereinafter described in greater detail. Preferably, the location upon
skull 160 at which skull mount fixture 162 is attached to skull 160 is
determined by the location of target 161 within skull 160 and skull mount
fixture preferably straddles the centerline of the patient's skull, as
seen in FIG. 6, and is disposed upon the top of patient's skull 160 as
seen in FIG. 1. Preferably, skull mount fixture 162 is disposed on the
parietal boss portion of the patient's skull 160. Thus, skull mount 162
may be disposed in the approximate position shown in FIG. 1, or
alternatively, disposed in a lower position from that shown in FIG. 1.
Skull mount fixture 162 may have a post or alignment rod, 163, associated
therewith, which is disposed parallel with the centerline, longitudinal
axis of a support surface 165, as will be hereinafter described in greater
detail.
With reference to FIGS. 1 and 2, the patient is laid upon a support surface
165, and skull 160 is thus disposed upon support surface 165. Typically,
support surface 165 is a conventional, planar imaging table 166 which is
used in connection with a conventional scanning device, such as a CT
scanner. Alignment rod, or post, 163 is moved with respect to skull mount
fixture 162, so that alignment rod, or post, 163 may mate with an upright
bracket 167 which is secured to imaging table 166 in any suitable fashion,
such as by a clamp or screws 168. With the skull mount fixture 162 and
alignment rod 163 in the positions illustrated in FIGS. 1 and 6, a first,
predetermined geometric relationship has been established between the
skull mount fixture 162 and the support surface 165 upon which skull 160
is disposed. Preferably, this first, predetermined geometric relationship
is with the skull mount 162 being disposed in a plane 300 which lies
perpendicular with respect to the longitudinal axis 301 of the support
surface 165.
With patient's skull 160 disposed upon support surface 165, as shown in
FIGS. 1 and 6 and the skull mount fixture 162 being disposed in the first,
predetermined geometric relationship with respect to support surface 165
and attached therebetween as by alignment rod 163 and bracket 167, the
skull is then scanned by any suitable scanning device, such as a CT
scanner, in a conventional manner. A radiopaque marker, or reference
point, 303 (FIG. 7) is disposed in the center of the skull mount fixture
162, whereby the scanning procedure produces a series of images, or
slices, of the skull 160, including the target 161 with respect to the
skull mount fixture 162. As seen with reference to FIGS. 6 and 7, a
plurality of scanned images, or slices, 302A-302H. . . are obtained
because of the first, predetermined geometric relationship previously
described. Skull mount fixture 162, including the marker, or reference
point, 303 lies in plane 300 which plane also coincides with slice 302A.
The target 161 lies in the plane of slice, or scanned image, 302E which
plane, or slice 302E, is parallel to slice 302A, as is well known in the
art. The distance between the different slices, or images, 302 is a
predetermined distance depending upon the amount of movement of the
imaging table 166 of the CT scanner.
Because the axis of imaging 304 of the CT scanner coincides with the
longitudinal axis of the alignment rod, or post, 163 (FIGS. 6 and 7). the
linear coordinates of the target 161 with respect to the skull mount
fixture 162 along the X, Y, and Z axes, as illustrated in FIG. 7, can be
readily determined by direct measurements from the various slices 302, and
in particular slices 302A and 302E. The measurements along the X and Y
axes can be directly measured from the various slices, or images, 302, and
the linear coordinate along the Z axis is readily determined by the
predetermined distance between the slices 302, as previously discussed.
After the linear coordinates of the target 161 with respect to the skull
mount fixture 162 have been determined, a displacement bar 170, having
first and second ends 171, 172 (FIG. 11) is disposed upon skull mount
fixture 162 to establish a second, predetermined geometric relationship
therebetween, which geometric relationship is identical to the first,
predetermined geometric relationship. Preferably, the second,
predetermined geometric relationship is with the displacement bar 170
disposed in a plane which is parallel with the plane 300 in which lies the
skull mount fixture 162. As will be hereinafter described in greater
detail, displacement bar 170 is preferably disposed upon skull mount
fixture 162 as by movably mounting it to alignment rod, or post 163; the
displacement bar 170 being mounted to post 163 perpendicular thereto,
whereby since post 163 is disposed perpendicular to skull mount fixture
162, displacement bar 170 and skull mount fixture 162 are disposed to lie
in parallel planes. Thus, both displacement bar 170 and skull mount
fixture 162 each lie in planes which are perpendicular to longitudinal
axis 301 of support surface 165 as seen in FIG. 7. Displacement bar 170
lies in plane 305, plane 305 being also parallel with the parallel planes
in which lie the images, or slices 302A and 302E. The distance between
plane 305 of displacement bar 170 and the plane, or slice. 302A in which
lies skull mount fixture 162 would be dependent upon where along post 163
displacement bar 170 is disposed, as will be hereinafter described in
greater detail. Accordingly, as seen in FIGS. 6 and 7, the scanned images,
or slices 302A-H . . . will all lie in planes parallel with the planes in
which lie the skull mount fixture 162 (plane 300, or slice, 302A) and the
displacement bar 170 (plane 305).
The first end 171 of the displacement bar 170 is then disposed directly
over the target 161 in the skull 160 as shown in dotted lines in FIG. 7.
The displacement bar 170 can be disposed in the position shown in FIG. 7
in two different manners as will be hereinafter described in greater
detail. After the first end 171 of displacement bar 170 has been disposed
directly over the target 161 in the skull 160, a means for guiding 180 a
medical instrument 181 (FIG. 9) is associated with the first end 171 of
displacement bar 170. As will be hereinafter described in greater detail,
two types of medical instrument guide means 180 may be utilized for
guiding medical instrument 181. In both types, however, the medical
instrument 181 will be inserted through the medical instrument guide means
180, until the medical instrument 181 intersects the target 161 in skull
160. With reference to FIG. 7, it is seen that the vertical distance from
the first end 171 of displacement bar 170 to the target 161 is readily
determined from knowing the spacing, or distance between, image, or slice,
302A and image, or slice, 302E, added to the distance between the
reference point 303 on the skull mount fixture 162 and the vertical
location of the displacement bar 170, along post 163. Knowing the distance
D' between the first end 171 of displacement bar 170 and target 161,
medical instrument 181 can be readily caused, in a conventional manner, to
only travel that distance D' so that it will intersect target 161 in the
desired manner.
Although it may be possible for the treatment of some targets 161, to
directly mount displacement bar 170 upon skull mount fixture 162, it is
preferred to utilize post 163, having first and second ends 175, 176, to
support displacement bar 170 in its desired relationship with respect to
skull mount fixture 162, so that the vertical spacing between skull mount
fixture 162 and displacement bar 170 may be varied, as will be hereinafter
described in greater detail. Preferably, first end 175 of post 163 is
secured to skull mount fixture 162, and displacement bar 170 is releasably
secured with respect to the second end 176 of the post 163, along the
length of post 163. In this position, or first position, illustrated in
FIGS. 9 and 10, as previously described, the post 163 is disposed in a
plane which is perpendicular to the planes in which lie the skull mount
fixture 162 and the displacement bar 170, as seen in FIG. 7, wherein post
163 is shown in phantom lines.
As previously discussed, the first end 171 of displacement bar 170 can be
caused to be disposed directly above target 161 in two different manners.
As seen in FIG. 7, the angular disposition or angle d, of target 161 with
respect to reference point 303, along the X and Y axes can be directly
determined from measuring linear X and Y coordinates and computing the
angle d in accordance with the standard geometric formula angle d=arc
tanX/Y. Alternatively, angle d can be directly measured using a protractor
and measuring the angle from the scanned images 302A-E. Likewise, the
distance D from the reference point 303 on skull mount fixture 162 to the
target 161 can be directly measured from the scanned images, or
alternatively, it is seen that the distance D is the hypotenuse of a right
triangle as seen in FIG. 7. Thus, knowing the X coordinate and the Y
coordinate of target 161, distance D can be determined from the geometric
formula X.sup.2 +Y.sup.2 =D.sup.2. Once the angle d and distance D h | | |
