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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to the medical diagnostic and surgical arts.
It finds particular application in conjunction with neurosurgery and will
be described with particular reference thereto. However, it is to be
appreciated, that the invention will also find application in conjunction
with neurobiopsy, CT-table needle body biopsy, breast biopsy, endoscopic
procedures, orthopedic surgery, other invasive medical procedures,
industrial quality control procedures, and the like.
Three-dimensional diagnostic image data of the brain, spinal cord, and
other body portions is produced by CT scanners, magnetic resonance
imagers, and other medical diagnostic equipment. These imaging modalities
typically provide structural detail with a resolution of a millimeter or
better.
Various frameless stereotactic procedures have been developed which take
advantage of the three-dimensional image data of the patient. These
procedures include guided-needle biopsies, shunt placements, craniotomies
for lesion or tumor resection, and the like. Another area of frameless
stereotaxy procedure which requires extreme accuracy is spinal surgery,
including screw fixation, fracture decompression, and spinal tumor
removal.
In spinal screw fixation procedures, for example, surgeons or other medical
personnel drill and tap a hole in spinal vertebra into which the screw is
to be placed. The surgeon relies heavily on his own skill in placing and
orienting the bit of the surgical drill prior to forming the hole in the
vertebra. Success depends largely upon the surgeon's estimation of
anatomical location and orientation in the operative field. This approach
has led to suboptimal placement of screws that may injure nerves, blood
vessels, or the spinal cord.
The present invention provides a new and improved technique which overcomes
the above-referenced problems and others.
SUMMARY OF THE INVENTION
According to one aspect of the present application, a stereotaxic wand is
provided. The wand has a tip portion, a portion extending along a pointing
axis of the wand, an offset portion which is offset from the pointing axis
of the wand, and at least three wand emitters. The three wand emitters
selectively emit wand signals which are received by at least two receivers
positioned on a frame assembly. The frame assembly mounts the receivers in
a fixed relationship to a subject support closely adjacent a means for
securing a portion of the patient to the subject support. A wand position
determining means determines a position of the wand tip portion from the
intersection of the emitter signals between the wand emitters and the two
receivers mounted on the frame. A tool guide defines a bore extending
longitudinally therethrough along a guide axis. The bore is configured for
selectively receiving either a tool or the tip portion of the wand.
According to another aspect of the present application, the tool guide
includes teeth on one end to inhibit the guide from slipping on bone.
One advantage of the present application is that it facilitates more
accurate surgical procedures.
Another advantage of the present invention is that it promotes patient
safety.
Still further advantages of the present invention will become apparent to
those of ordinary skill in the art upon reading and understanding the
following detailed description of the preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may take form in various components and arrangements of
components, and in various steps and arrangements of steps. The drawings
are only for purposes of illustrating a preferred embodiment and are not
to be construed as limiting the invention.
FIG. 1A is a perspective view of an operating room in which the present
invention is deployed;
FIG. 1B is a block diagram of the image data manipulation of the system of
FIG. 1A;
FIGS. 2A, 2B, 2C, 2D, 2E, and 2F illustrate alternate embodiments of the
wand and guide;
FIGS. 3A and 3B are diagrammatic illustrations of the wand and locator
relationship;
FIGS. 3C is a flow diagram of the wand location procedure;
FIGS. 4A, 4B, 4C, and 4D are illustrative of a preferred coordinate
transform between the coordinate system of the data and the patient.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to FIG. 1A, a subject, such as a human patient, is received
on an operating table or other subject support 10 and appropriately
positioned within the operating room. A frame 12 is mounted in a fixed
relationship to the patient such that it is precisely positioned within
the subject or subject support coordinate system. In the illustrated
embodiment, the frame 12 is mounted to the patient support 10. Mounting
the frame 12 to the patient support permits the patient support to be
turned, raised, lowered, wheeled to another location, or the like, without
altering the patient coordinate system. Alternately, the support may be
mounted to a pole or other stationary support, the ceiling of the room, or
the like. The frame 12 supports a plurality of receivers 14 such as
charge-coupled device (CCD) arrays, infra-red cameras, light sensitive
diodes, other light sensitive receivers, and the like mounted at fixed,
known locations thereon. Alternately, the receivers can receive other
types of radiant energy such as ultrasound, X-rays, radiation, radio,
magnetics, or the like. A securing means such as a head clamp 16, securely
positions a portion of the subject under consideration. The frame is
mounted at a fixed or selectable angle from vertical such that the frame
is positionable more toward the patient, yet still focusing on the region
of interest of the patient.
With continuing reference to FIG. 1A and further reference to FIG. 1B, an
operator console 18 houses a computer system 20. Alternately, the computer
system can be remotely located and connected with the control console 18
by cabling. The computer system includes a three-dimensional data memory
22. The stored three-dimensional image data preferably contains a video
pixel value for each pixel or point in a three-dimensional rectangular
grid of points, preferably a 256.times.256.times.256grid. When each image
value represents one millimeter cube, the image data represents about a
25.6 centimeter cube through the patient with one millimeter resolution.
Because the data is in a three-dimensional rectangular grid, selectable
orthogonal and other oblique planes of the data can readily be withdrawn
from the three-dimensional memory using conventional technology. A plane
or slice selector 24 selects various two-dimensional planes of pixel
values from the three-dimensional memory for display.
The plane or slice selector preferably selects at least: axial, sagittal,
coronal, and oblique planes through a selectable point of the patient. The
pixel values which lie on the selected axial, sagittal, coronal, and
oblique planes are copied into corresponding image memories 26a, 26b, 26c,
and 26d. A video processor 28 converts the two-dimensional digital image
representations from one or more of image memories 26 into appropriate
signals for display on video monitors 30 or other appropriate image
displays.
With continuing reference to FIG. 1A and further reference to FIG. 2A, a
wand 40, formed of suitable resilient material such as metal, has an
offset handle portion 42 and a tip portion or proximal end 44. The offset
handle 42 is connected to a portion extending along a pointing axis 46 of
the wand. In this preferred embodiment, a first emitter 4e is mounted on
the pointing axis 46 while two other emitters 50 and 52 are mounted off
the axis. Each emitter selectively emits an infra-red signal that is
received by the receivers 14. The first emitter 48 is located at x.sub.1,
Y.sub.1, z.sub.1 along the axis 46 a fixed known distance l.sub.1 from the
tip 44. The second emitter 50 may then be calculated to be at x.sub.1
+.DELTA.x.sub.2, y.sub.1 +.DELTA.y.sub.2, Z.sub.1 +.DELTA.Z.sub.2 (where
.DELTA.+x.sub.2, .DELTA.Y.sub.2 and .DELTA.z.sub.2 represent constant
values based on the geometry of the second emitter relative to the tip).
The third emitter 52 is at x.sub.1 +.DELTA.x.sub.33, y.sub.1l
+.DELTA.y.sub.3, z.sub.1 +.DELTA.z.sub.3 (where .DELTA.x.sub.3,
.DELTA.Y.sub.3 and .DELTA.z.sub.3 represent constant values based on the
geometry of the third emitter relative to the tip).
Emitters 48, 50, and 52 emit infra-red positioning signals used by a
locator system 54 to locate a coordinate and trajectory of the wand.
Infra-red signals are received from each of the emitters at the two
receivers. The three infra-red signals received by each receiver are used
to calculate the axis 46 and the location of the tip. The plane or slice
selector 24 (FIG. 1B) selects patient image planes based on the coordinate
and trajectory located. It is to be appreciated that more than three
emitters may be mounted on the wand to provide additional positioning
signals to be used by a locator system to locate the coordinate and
trajectory of the wand.
The wand 40 is readily sterilized by conventional techniques. It is used in
conjunction with a guide 60 to designate a coordinate and trajectory at
which a surgical tool will be applied to the patient. The guide can be any
guide or appliance which positions the wand 40 to establish a surgical
trajectory. In the preferred embodiment, the guide 60 is a portable tool
which has a hand-shaped handle 62 which extends from the drill guide, a
tube member 64 which defines an internal bore 66 to receive and accurately
position the wand, and teeth 68 at the distal end 70 of the bore to reduce
the possibility of the guide slipping on bone. The bore 66 of the tool
guide has a diameter which allows for the non-simultaneous insertion of
either the wand 40 or a surgical tool such as a drill, biopsy needle, and
the like. Rather than being hand-held, the guide 60 can be mounted to
other structures in the operating room, e.g. framed stereotaxic equipment
or a mechanical brace. In intraoperative use, the wand 40 is inserted in
the tool guide bore until the tip 44 aligns with the tool guide distal end
70. A wand stop 72 is positioned on the wand and abuts a proximal end
surface 74 of the tool guide when the wand tip aligns with the distal end
70.
With the wand tip aligned with the tool guide end, the surgeon commences
probing the patient to seek an optimal coordinate and trajectory in which
to insert the appropriate surgical tool. To this end, the surgeon
maneuvers the wand and tool guide in combination to a proposed trajectory
and actuates the emitters. Signals from the emitters are used to calculate
the trajectory 46 and the end point 44 of the wand. The trajectory and end
point are displayed on the monitor 30 superimposed on the
three-dimensional image or selected image plane(s).
By viewing the display 30, the surgeon identifies the location of the wand
tip with respect to anatomic structure, and the trajectory of the bore. If
the trajectory is unsatisfactory, the wand is repositioned and its new
trajectory determined and evaluated. This approach improves surgical
planning when compared with prior approaches in which surgeons relied
solely on their own estimation of the patient's anatomy. Following the
identification of a satisfactory trajectory and coordinate, the wand 40 is
removed from the bore 66 of the guide 60 while the guide is held in
position. Holding the guide 60 steady preserves the appropriate trajectory
and position coordinates in the axial and sagittal planes determined by
the wand. Thereafter, the appropriate surgical tool or appliance is
inserted within the guide 60. With this approach, the surgical tool is
properly positioned in the appropriate trajectory for performing the
surgical procedure.
The wand and tool guide are particularly useful in accurately identifying
the optimal entry point, trajectory, the depth of insertion of screws to
be placed into the patient's spinal column, the depth of insertion of a
biopsy needle, and the like.
With reference to FIGS. 2B, 2C, and 2D alternative embodiments of the
present invention are shown in which the guide is integrated into the
wand. In general, each of the alternative embodiments contain a wand
offset portion on which are mounted at least three emitters for emitting
positioning signals. In the illustrated embodiments, the central axis or
pointing direction 46 aligns with a longitudinal axis of the guide means
formed integrally with the wand for simplicity of use.
With reference to FIG. 2B, a tubular portion 76 is integrated with the
wand. The tubular portion defines a bore 78 extending along its
longitudinal axis. In intraoperative use, the surgeon probes the patient
with the distal end seeking to locate the proper coordinate and trajectory
for the surgical tool. Once the coordinate and trajectory are located, the
surgeon holds the offset portion while the surgical tool is inserted
within the tube. Thereafter, the surgical tool is operated to perform the
surgical procedure.
With reference to FIG. 2C, a second alterative embodiment is shown similar
to the previously described alternative embodiment. However, in addition
to the structure previously described, a laser 80 is mounted to the offset
portion. Light emitting from the laser travels along the longitudinal
pointing axis 46 of the bore 78 of the tubular member to provide a visual
indication of trajectory in the patient coordinate system. In
intraoperative use, the surgeon maneuvers the integrated wand and laser
while viewing images displayed on the monitor 30. The images selected for
display are based upon the coordinate and trajectory of the bore center
point at the proximal end of the integrated wand.
With reference to FIG. 2D, another embodiment is shown in which a grooved
guide member position 82 is incorporated into the wand. The grooved member
is connected to the offset portion. The grooved member contains a groove
84 having a longitudinal axis which is in line with pointing axis 46 of
the wand. This alternative embodiment finds particular usefulness in
conjunction with needle biopsies. In intraoperative use, a biopsy needle
86 is positioned within the groove so that a tip 88 of the biopsy needle
86 aligns with the groove center point at the proximal end of the
integrated wand. The biopsy needle is held in place by a restraining means
such as Velcro.RTM.straps 90 attached to the sides of the grooved member.
In the embodiment of FIG. 2E, the wand has emitters 50.sub.1, 50.sub.2,
50.sub.3, 50.sub.4, mounted along the axis 46. Although any two emitters
would determine the axis 46, greater accuracy is obtained by redundantly
determining the axis 46 and averaging the results. Preferably, a least
squares fit is used to compensate for any deviation in the axis 46
determined by the various emitter pairs. In the embodiment of FIG. 2F, the
wand has interchangeable tips. The wand includes a first connector portion
92 which selectively connects with a second connector portion 94 of the
tips. Various connector systems are contemplated such as a threaded bore
and threaded shaft, a snap lock connector means, bayonet connector, spring
lock, or other connector systems. A key and keyway system 96 or other
means for fixing the alignment of the tips and the wand is particularly
advantageous when the connector is off the axis 46.
Various tips are contemplated. A short tip 98 is provided for accurate
registration. A longer tip 100 facilitates reaching deeper into interior
regions of the subject. Tubular drill guides 102 can be provided in
various diameters to accommodate different size drills. An adapter 104
enables endoscopes and other tools to be attached to the wand. Tools and
equipment, such as an array of ultrasonic transducers 106, can be
connected to the adaptor 104 or configured for direct connection to the
wand. A wide variety of other tips for various applications are also
contemplated.
The preferred embodiment uses the stereotaxic wand 40 to align the
coordinate system of the operating room including the patient, the tool
guide, and wand with the coordinate system of a previously prepared
three-dimensional image stored in memory. Prior to identifying the proper
coordinate and trajectory of the tool guide, the patient space is aligned
with or referenced to the stored three-dimensional image data preferably
using the following technique.
FIG. 3A illustrates infra-red CCD array cameras as receivers 14 which are
mounted on the frame 12. The location of the wand emitters in the
coordinate system of the frame and patient, hence the position of the wand
axes and tip relative to the patient, is determined by the intersection of
the light rays traveling between the emitter 48, 50 and 52 and the two
infra-red CCD array camera receivers 14. For example, emitter 48 emits an
infra-red signal which is received by both infra-red CCD array cameras 14.
From the cameras' perspective, the two infra-red signals intersect at a
single point. Preferably, a least squares fit is used to determine the
point of intersection. This point of intersection is the location of the
emitter 48.
With reference to FIGS. 3A, 3B, and 3C, a wand coordinate and trajectory
determining procedure 130 determines the coordinate positions of the three
emitters 48, 50 and 52, the central axis and the wand tip. More
specifically, a step 13 causes the emitters to emit an infra-red signal.
The CCD array receivers 14 on the frame 12 receive the infra-red signals.
A step 134 acquires the (i, j,) coordinate locations on the CCD array at
which each ray is received. From prior calibration, a step 136 converts
each (i,j) CCD coordinate into a trajectory. A step 138 causes the
emitters to emit an infra-red signal again. A step 140 acquires another
set of CCD coordinates and a step 142 determines another pair of
trajectories. A step 144 compares the trajectories from steps 136 and 144.
If the trajectories fail to match within a preselected tolerance, steps
132-144 are repeated.
If the trajectories are within the preselected tolerance of being the same
in the two acquisitions, an averaging step 146 averages the trajectories
between each of the wand emitters 48, 50 and 52 and each of the CCD array
receivers 14. From these trajectories, a step 148 calculates the Cartesian
coordinates (x.sub.1,y.sub.1,z.sub.1) in the frame or patient coordinate
system for the three emitters 48, 50 and 52.
A step 150 checks the validity of the measurement. More specifically, the
known separation between the wand emitters is compared with the separation
between the measured coordinates x.sub.1,y.sub.1,z.sub.1,
x.sub.2,y.sub.2,z.sub.2 and X.sub.3,y.sub.3,Z.sub.3 Of the wand emitters.
If the difference between measured and known separation of any two
emitters is greater than the acceptable error, e.g. 0.75 mm when measuring
with a resolution of 1 mm, an erroneous measurement signal is given. The
measurement is discarded and the surgeon or other user is flagged to
perform the measurement process 130 again. From the coordinates of the
three emitters 48, 50 and 52, and from the geometry of the wand discussed
in conjunction with FIG. 2, a step 152 calculates the wand axis in the
frame and patient coordinate system. A step 154 calculates the Cartesian
coordinates (x.sub.0,y.sub.0,z.sub.0) for the wand tip 44.
With reference to FIG. 4A, before the wand and tool guide can be used to
locate a proper coordinate and trajectory for a surgical tool such as a
drill, the patient space or coordinate system (x,y,z) is aligned with the
image space or coordinate system (x', y', z') stored in memory. Aligning
the spaces begins with referencing known positions or points 160 in the
patient space with the wand tip. For example, the tip 44 of the wand may
be referenced to three independent positions of the vertebra, i.e. the
tips of the spinous and traverse processes. These positions 160 on the
vertebra are compared with the corresponding position of pixels 162 in the
image space. Fiducials can also be used to make the corresponding
coordinates in patient space and image space. To this end, three or more
fiducials or markers are affixed at three or more spaced points on the
patient's body. The fiducials are visible in the imaging medium selected
such that they show up as readily identifiable dots 162 in the resultant
image data. The fiducials are markers or small beads that are injected
with radiation opaque and magnetic resonance excitable materials. A small
dot or tattoo is made on the patient's skin and a fiducial is glued to
each dot. This enables the position 160 of the fiducials to be denoted
even if the fiducials are removed in the interval between the collection
of the image data and the surgical procedure. Thereafter, a transform 164,
as shown in FIG. 1B, transforms the coordinates of the patient space into
the coordinate system of the image space. To align the patient and image
spaces, the tip of the wand is placed on each fiducial, tattooed marker
point, or characteristic vertebra point 160.
With reference to FIGS. 4A-4D, the position of the three fiducials or
process tips 160 are compared with the relative position of the pixels 162
in the image space. Actuating the emitters while the tip of the wand is
touching each of its characteristic patient space points x, y, z defines
these points electronically. Like coordinates x',y',z' of the pixels 162
are defined electronically from the electronic image and compared to the
patient space coordinates x,y,z. The translation and rotational
relationship between image space and patient space coordinate systems is
determined. With reference to FIG. 4A, the position of the patient in
operating room space (x,y,z) and the relative position in image space
(x',y',z') are determined. That is, the transform between the two
coordinate systems are defined. The translation means first determines the
offsets X.sub.offset, Y.sub.offset, Z.sub.offset between the barycenters
166, 168 of the triangles defined by the coordinates of three fiducials or
process tips in data and patient space, respectively. This provides a
translation or an offset in the x, y, and z-directions between the two
coordinate systems. The values of X.sub.offset, Y.sub.offset, and
Z.sub.offset are added or subtracted to the coordinates of the patient
space and the coordinates of image space, respectively, to translate
between the two.
With reference to FIG. 4B, translating the origins of the two coordinate
systems into alignment, however, is not the complete correction. Rather,
the coordinate systems are normally also rotated relative to each other
about all three axes whose origin is at the barycenter. As illustrated in
FIGS. 4B, 4C, and 4D, the angle of rotation in the (y,z), (x,z), and (x,y)
planes are determined. Having made these determinations, it is a simple
matter to transform the patient support space coordinates into the image
space coordinates and, conversely, to rotate the image space coordinates
into patient space coordinates. The wand coordinate m | | |
