 |
Description  |
|
|
FIELD OF THE INVENTION
This invention relates to a method and apparatus for guiding a penetrating
tool into a three-dimensional object to reach a point of interest therein.
In particular, this invention relates to a method and apparatus for
assisting a brain surgeon in guiding a penetrating tool into a brain
during surgery to accurately reach a point of interest therein, such as a
tumor, and for monitoring the position of the tumor during surgery.
BACKGROUND OF THE INVENTION
One of the most delicate of all surgeries is that in which the skull is
opened and the brain is penetrated to reach a point of interest, such as
an embedded brain tumor which the surgeon must remove. The surgeon first
must determine the location of the tumor, and then determine the optimum
point of entry through the skull and into the brain to reach the tumor,
taking into consideration the anatomy and physiology of the portions of
the brain that will be penetrated, and possible movement of the brain and
tumor within the skull resulting from loss of fluid and pressure when the
skull is opened. Having selected the point of entry, the surgeon then must
select and maintain the proper angle of penetration so that the surgical
tools will reach the tumor and be able to remove it.
Recent advances in imaging technologies including magnetic resonance
imaging (MRI), computer tomography (CT), and positron emission tomography
(PET) have greatly improved the ability to determine non-invasively the
structure within almost any portion of the human body. This ability is
especially valuable in diagnostics. Such imaging technologies permit the
determination of the exact location of a point of interest such as a tumor
within a region of the anatomy such as the brain without any preliminary
exploratory surgery. Scans of the brain are taken along a series of
planes, the data is digitized, and the digitized data can be converted by
computer into three-dimensional images showing the size and location of
the tumor within the brain. The surgeon then uses this computerized
information with other medical knowledge to determine the optimum point of
entry into the brain. The computerized information is available to the
surgeon during surgery to help the surgeon determine the depth of
penetration required to reach the tumor and to estimate the amount of
material that must be removed. This diagnostic data cannot, however,
monitor changes in position of the brain and tumor within the skull during
surgery resulting from loss of fluid and pressure when the skull is
opened.
One of the most difficult aspects of brain surgery is estimating and
maintaining the slope of entry along which the surgeon should guide the
tools through the pre-determined point of entry to the point of interest
within the brain. Even when the surgeon has computerized scans showing
three dimensional images of the exact pre-surgery location of the point to
be reached, determining and maintaining the slope of entry necessary to
reach that point inside the brain from the predetermined point of entry
is, at best, sophisticated guesswork. Simple geometry dictates that, even
when the exact point of entry into the skull is preselected, there are an
infinite number of slopes of entry through that point into the brain. The
surgeon can only estimate the correct slope of entry and depth of
penetration, based on knowledge and years of experience. FIG. 1
illustrates what can happen when a surgeon errs even slightly in
estimating or maintaining the slope of entry. As may be seen, the surgeon,
even though starting precisely at the preselected point of entry "P" and
directing the surgical tools as best as can be determined in the direction
of the tumor "T", nevertheless has missed a substantial portion of the
tumor to be removed. The surgeon must reposition the penetrating tools
through the brain in order to remove the remaining part of the tumor. In
addition, except by comparing the amount of material removed with the mass
of material apparent from the computerized image, the surgeon cannot
determine if all the tumor has been removed.
Accordingly, there is a need for a method and apparatus that will assist in
the guidance of a penetrating tool into a solid three-dimensional object
to reach a point of interest therein. In particular, there is a need for a
method and apparatus that will assist a brain surgeon in guiding a
penetrating tool into a patient's brain to reach a point of interest, such
as a brain tumor that has previously been identified and located by MRI or
other diagnostic techniques.
The following description of the invention throughout this patent
specification will be given in terms of a method and apparatus for
assisting a surgeon in guiding a penetrating tool to a brain tumor, the
location of which has been previously determined by MRI diagnostic
techniques, and for monitoring movement of the tumor during the procedure.
It will be recognized, however, that the basic principles of the invention
are not so limited, and can be applied to any problem dealing with
determining and maintaining the slope of entry into a solid
three-dimensional object to reach a pre-determined point of interest
therein.
SUMMARY OF THE INVENTION
In accordance with the invention, the apparatus for assisting in guiding a
penetrating tool into a brain at a particular slope of entry during
surgery comprises a plurality of markers capable of being fixedly
positioned in a non-coplanar configuration about the periphery of the
skull, each of said markers capable of propagating a distinct signal; a
receiver capable of receiving and distinguishing the respective signals
from the markers; a movable light source capable of emitting a precisely
directed ray of light; and a computer for determining whether the slope of
the light ray emanating from the source coincides with the desired slope
of entry. In accordance with the inventive method, an MRI scan is taken
with the markers fixed in position about the skull, the scan including the
point of interest within the brain and all the markers, and the data is
digitized. From these digitized images, the co-ordinates of the markers
relative to the point of interest in three dimensions is measured, and the
data is stored in the computer. The patient is brought into surgery, and
the light source is placed in the vicinity of the pre-selected desired
point of entry, generally along an imaginary line passing through the
point of interest within the brain and the point of entry on the skull.
The coordinates of the light source are inputted in the computer. The
receiver then receives the distinct signals from each of the markers and
transmits this information to the computer. Based on this information, the
computer calculates the position of the light source relative to each of
the markers. Since the position of each of the markers relative to the
point of interest in the brain is known and stored in the computer memory,
the computer can also calculate the exact position of the light source
relative to the point of interest. The position of the light source can be
adjusted, and its precise location relative to the markers and thus to the
point of interest can be recalculated, until the light source is exactly
in line with the point of interest within the brain and the predetermined
point of entry on the skull. The light ray emanating from the light source
then can be directed to the point of entry along the exact slope of entry
which will cause the penetrating tool to reach the point of interest. In
one embodiment, the receiver is movable and the light source is mounted
directly on the receiver, the receiver is moved in response to
instructions received from the computer until the light ray emanating from
the light source on the receiver exactly coincides with the desired slope
of entry.
The surgeon can then direct the penetrating tools along the exact slope of
entry indicated by the ray of light. Preferably, this procedure can be
facilitated by the use of a new and inventive apparatus that will be
referred to herein as an angular guide means. In one embodiment, the
angular guide means comprises a support frame which supports a lockable
swivel joint. A hollow guide tube extends through the swivel joint, the
guide tube having an inner diameter large enough to accommodate the
surgeon's penetration tools yet small enough to provide accurate guidance
thereof. The angular guide means is secured in place adjacent the
predetermined point of entry. The slope of the hollow guide tube is
adjusted by means of the swivel joint until the light ray from the
receiver passes exactly through the guide tube, i.e., until the guide tube
is directed along the exact slope of entry toward the point of interest,
and the swivel joint is locked. The surgeon can then direct the surgical
instruments through the fixed guide tube, and know with certainty that the
instruments will reach the precise point of interest within the brain.
DESCRIPTION OF THE FIGURES
The invention may be better understood by reference to the following
drawings, which are for purposes of illustration only and are not
necessarily to scale.
FIG. 1 is an illustration of the problem of the prior art which is
addressed by the instant invention, in which the surgeon has inaccurately
estimated the slope of entry into the brain, and therefore has missed a
substantial portion of the tumor to be excised.
FIG. 2 is a flow chart showing the sequence of steps of the method of the
instant invention.
FIG. 3 is a plan diagrammatic view of a patient having a brain tumor to be
excised, and showing the positions of the markers and the initial position
of the light source.
FIG. 4 is an elevation perspective view of the patient having a brain tumor
to be excised, showing the marker positions, and showing the light source
repositioned to be in line with the tumor and the predetermined point of
entry.
FIG. 5 is a perspective view showing the angular guide means in position to
guide the surgeon in introducing the surgical tools into the patient's
brain.
FIG. 6 is a top plan view of the angular guide means.
FIG. 7 is a cross-sectional side view of the angular guide means.
FIG. 8 is a partially exploded detailed view of an embodiment of the hollow
guide tube.
FIG. 9 illustrates an embodiment of the invention wherein additional
markers are also positioned within and at the periphery of the tumor to be
excised.
DETAILED DESCRIPTION OF THE INVENTION
The following description of the method of the instant invention is
illustrated schematically in the flow chart of FIG. 2.
The instant invention is to be used for the benefit of any patient who has
been diagnosed as having a tumor, aneurysm, or other disorder of the brain
which requires surgery directed to a precisely defined spot within the
brain. For purposes of illustration only, the disorder requiring surgery
will be described as a tumor, although it will be understood that surgery
for other disorders of the brain will be greatly aided by the inventive
apparatus and method as described herein. According to known techniques,
generally indicated as the first three process steps 100, 105, 110 at the
beginning of the flow chart of FIG. 2, such a diagnosis will have been
confirmed by MRI (or CT or PET) imaging in step 100; further, the MRI (or
CT or PET) image will be used in step 105 to exactly pinpoint the location
of the disorder within the brain. Based on the size and location of the
tumor and other medical, anatomical and physiological considerations, in
step 110 the surgeon will determine the desired point of entry through the
skull to reach the tumor.
FIG. 3 is a top plan diagrammatic view showing a patient's head 10 having a
brain tumor T which must be surgically excised. Prior to surgery, and now
proceeding in accordance with the invention (FIG. 2, step 120) the surgeon
has fixedly embedded within the patient's skull in a non-coplanar
configuration a plurality of markers, illustrated in FIG. 3 as M.sub.1,
M.sub.2, M.sub.3, and M.sub.4. It will be recognized, in accordance with
the most fundamental principles of geometry, that any three markers will
necessarily lie in a plane. The fourth marker, which is not in the same
plane as the other three, permits calculations to be made in three
dimensions. Additional markers may be used as desired.
A series of MRI images is taken (step 125) with the markers in position.
The MRI data is digitized (step 130) and stored in computer 90 (not
shown). From the digitized data the computer can calculate the
co-ordinates of each marker relative to the center point of tumor T (FIG.
2, step 135). Specifically, the center of the tumor T and each of the
markers define a plurality of non-coplanar line segments M.sub.1 T,
M.sub.2 T, M.sub.3 T, and M.sub.4 T illustrated in FIG. 3; further, the
markers define a plurality of non-coplanar line segments M.sub.1 M.sub.2,
M.sub.1 M.sub.3, M.sub.1 M.sub.4, M.sub.2 M.sub.3, M.sub.2 M.sub.4, and
M.sub.3 M.sub.4, omitted from FIG. 3 for the sake of clarity. From the
digitized MRI data, the computer 90 will be able to calculate the exact
length of each line segment; then, based on the length of each line
segment, the computer will be able to calculate the angles between the
line segments defined by the tumor T and the markers. For example, the
angles A, B, C, and D indicated by the dotted curves in FIG. 3 are defined
by the point sets M.sub.1 -T-M.sub.2, M.sub.2 -T-M.sub.3, M.sub.3
-T-M.sub.4, and M.sub.4 -T-M.sub.1 respectively. The computer will also
calculate the angles defined by the point sets M.sub.1 -T-M.sub.3, M.sub.1
-T-M.sub.4, M.sub.2 -T-M.sub.3, M.sub.2 -T-M.sub.4, and M.sub.3
-T-M.sub.4, although curves indicating these angles have been omitted from
FIG. 3 for the sake of clarity. It will be appreciated that while FIG. 3
is necessarily a two-dimensional projection of the marker and tumor
positions, segments, and angles so described, computer 90 will in fact
calculate the segments and angles in three dimensions based on the
digitized data from the series of scans and using known principles of
solid geometry.
After the MRI scan has been taken with the markers in place, and the
various distances and angles described above have been determined and
stored in computer 90, the patient is brought into surgery. At this time,
based on the previously available MRI data, and further considering
anatomical and physiological limitations, the surgeon will already have
determined (FIG. 2, step 110) the optimum point of entry, indicated in
FIG. 3 as point P, where the skull should be opened and the brain
penetrated. Using known methods and a surgical securing frame generally
indicated at 22 in FIG. 5, the patient's head is secured in a desired
fixed position for the duration of the surgical procedure to allow the
surgeon the best possible access to the preselected point of entry P. The
exact co-ordinates of point of entry P are entered into computer 90.
Referring to FIG. 3, the slope in three dimensions of the line segment PT
is the desired slope of entry from the point of entry P to the tumor T.
Computer 90 calculates both the length of the line segment PT and its
slope, relative to the configuration of fixed markers, FIG. 2, step 140.
These values, along with the locations of the markers relative to the
tumor T, are stored in computer 90 (FIG. 2, step 145).
Each marker is capable of propagating a distinct signal which can be
detected by receiver R, indicated schematically in FIG. 3. Each marker's
signal has a unique identifying characteristic, such as phase or
frequency, by which the receiver R can distinguish each marker's signal
from the others. The receiver-marker system can be either a passive
localization system, in which case each marker can be a transmitter which
generates a distinct electromagnetic signal which is received by receiver
R, or the receiver-marker system can be an active localization system, in
which case the receiver actively transmits a radar signal or an array of
radar signals toward the markers, and each marker reflects a distinct
soundwave signal back to the receiver R. The received signals are then
inputted to computer 90, which uses this information to calculate the
distance between the receiver R and each marker. The system of receivers
and markers can be operated in a manner analogous to the Global
Positioning System (GPS), in that the markers around the skull serve the
same function as the satellites around the earth. The mathematical and
physical principles and techniques useful in passive localization systems
are described in D. H. Johnson and D. E. Dudgeon, Array Signal Processing
Concepts and Techniques, PTR Prentice Hall, 1993, at pages 349-402; Radar
Handbook, 2nd edition, edited by M. Skolnik, McGraw-Hill Publishing
Company, 1990, at pages 3.32-3.38; and Electronics Engineering Handbook,
by D. Christiansen, 4th edition, McGraw-Hill Publishing Company, 1996, pp.
29.83-29.86. The mathematical and physical principles and techniques
useful in active localization systems are described in these same standard
reference works, in Johnson et. al. at pp. 266-318; Skolnik at pp.
3.1-3.25 and 5.4-5.32; and Christiansen at pp. 29.58-29.83. All of the
foregoing reference works are incorporated herein by reference in their
entirety. Those skilled in the art will be able to apply these standard
and well-known localization systems to various applications of the method
and apparatus of the instant invention.
The receiver R is in the operating room and is operatively linked to
computer 90 so as to provide computer 90 with data from the signals
received from the markers. Also in the operating room is a movable light
source 95, capable of emitting a specifically directed beam of visible
light, such as a laser beam. Preferably, the position of light source 95
and the slope of the light ray emanating from light source 95 are
adjustable in response to instructions from computer 90. For example,
light source 95 may include a swivel ball mechanism to redirect the slope
of the ray as instructed by computer 90. The coordinates of movable light
source 95 are known to computer 90. This may be accomplished by using an
additional marker at light source 95. Alternatively, light source 95 may
be built integrally with receiver R as indicated schematically in FIG. 3,
and receiver R can be movable in response to instructions from computer
90. The following description of the invention will be with reference to
the embodiment in which the light source 95 is integral with movable
receiver R. It will be understood that the description of this embodiment
is for illustrative purposes only, and is not intended to limit the scope
of the invention described and claimed.
In this embodiment, the receiver R with integral light source 95 may be
mounted on a robotic arm (not shown), the position of which can also be
controlled by computer 90 according to known robotic principles. Initially
the receiver R is in an arbitrary position relative to the markers and to
the desired point of entry P, as shown generally in FIG. 3. The distinct
electromagnetic or sound wave signals are received by receiver R from each
of the markers (FIG. 2, step 150) and the values are converted in real
time to values corresponding to the distance from a fixed point of origin
of light source 95 on receiver R to each of the markers (FIG. 2, step
155), which data is stored in computer 90 (FIG. 2, step 160). These
distances correspond to initial line segments M.sub.1 L, M.sub.2 L,
M.sub.3 L, and M.sub.4 L, in three dimensions, which are omitted from FIG.
3 for clarity. (It will be understood in the discussion which follows that
"L" refers to the position of the light source, whether or not integral
with the receiver, and the distances between L and either the tumor T or
markers M are all based on the specific position of light source 95).
Based on these distances, and the known position of each of the markers
relative to the tumor T, computer 90 then calculates the position of light
source 95 relative to the tumor T (FIG. 2, step 165), i.e., it calculates
the length and slope of the line segment LT between the light source 95
and tumor T, indicated as a dashed line in FIG. 3. Light source 95 then
emits a ray directed generally toward point of entry P (FIG. 2, step 170).
Computer 90 then calculates (FIG. 2, step 175) the light ray's actual
point of entry and actual slope of entry in three dimensions. The computer
then determines (FIG. 2, step 180) if the actual point of entry and actual
slope of entry of the light ray correspond to the line defined by the
surgeon's preselected point of entry P and desired slope of entry, i.e.,
computer 90 determines if the line segment LT intersects the point P and
has the same slope as the line segment PT. If it does, then the light
source 95 is in the correct position, and it is locked in place (FIG. 2,
step 185). If the light source is not in the correct position, then
computer 90 calculates where the light source 95 should be repositioned
(FIG. 2, step 190) so that LT will be closer to the desired point and
slope of entry. Light source 95 is then repositioned (FIG. 2, step 195),
such as by means of the robotic arm. Once again, based on the signals
received by the receiver R from each of the markers M.sub.1, M.sub.2,
M.sub.3, and M.sub.4, the new position of the light source 95 relative to
the tumor can be calculated (i.e., the computer software loops back to
step 165 in FIG. 2), and the new actual point and slope of entry can be
calculated and compared with the desired point and slope of entry values
preselected by the surgeon. As shown by the loop in the flow chart of FIG.
2, this process is repeated as often as necessary until the correct
position of the light source 95 is attained, as shown in FIG. 4.
When the light source 95 is in the correct position, a light ray such as a
laser is directed from the rotatable light source 95 to the exact point of
entry P and along the exact desired slope of entry. The proper orientation
of the light source 95 can be directed by computer 90. This light ray
guides the surgeon. First, the surgeon must cut away a portion of the
skull to allow access to the brain. The surgeon will be able to remove a
substantially smaller portion of skull than would have had to have been
removed without the use of the instant invention, because the desired
point of entry will be known very accurately, and will be indicated
clearly by the light ray. Whereas typically 2-3 square inches or more of
skull would have had to have been removed, when the apparatus and method
of the instant invention are used the area of skull to be removed can be
one square inch or even less.
After the skull has been opened, the light ray is then used to guide the
surgeon in actual penetration of the brain. Thus, even though any marker
that may have been placed on the skull directly at the point of entry P
will have been removed, the light ray will still be directed to the point
of entry on the soft brain tissue. In one embodiment of the invention, the
penetrating tool is simply equipped on one end with an indicating means
such as a reflector; as long as the light ray is reflected back to the
light source 95, then the surgeon knows that the tool is being held at the
correct slope of entry to reach the tumor. If the tool is not held at the
correct angle, then light will not be reflected back and an audible alarm
can be activated. This will guide the surgeon in reorienting the tools
along the desired slope of entry.
In a preferred embodiment of the invention, an apparatus known as an
angular guide means is used in conjunction with the light ray to guide the
surgeon. As shown in FIGS. 5-7, the angular guide means 20 comprises a
support frame 23 which is removably fixed to a portion of the surgical
securing frame 22 used to secure the patient in the desired operating
position. Support frame 23 supports a lockable swivel joint 25 through
which extends a hollow guide tube 28. In one embodiment, swivel joint 25
can be eccentrically mounted in rotatable gear 26, which in turn is
eccentrically mounted in rotatable gear 27. Gear 26 is rotated by means of
gear 29 which is operated by shaft 30 and powered by motor 31; gear 27 is
rotated by means of gear 32 which is operated by shaft 33 and powered by
motor 34. By cooperative rotation of gears 26 and 27, swivel joint 25 can
be positioned accurately substantially anywhere within the area of gear 27
indicated by dotted circle C.
Support frame 23 is fixed in position such that swivel joint 25 intersects
the light ray from source 95. If the coordinates of a fixed point on
angular guide means 20 is known to computer 90, either by inputting or by
measuring with a marker, then computer 90 can signal motors 31 and 34 to
rotate gears 26 and 27 so as to position swivel joint 25 to exactly
intersect line segment RT. Guide tube 28 is rotated through swivel joint
25 until the light ray passes uninterrupted through guide tube 28. The
proper orientation of guide tube 28 can be determined visually, by simply
observing the light reaching the point of entry P, or proper orientation
could be aided by use of an audible alarm such as described above with
respect to the use of the surgeon's hand tools. Once the guide tube 28 is
in proper position and slope, swivel joint 25 is locked in place.
Optionally, the | | |
