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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.
A 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 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 two wand emitters mounted in a spaced
relationship to the offset section in alignment with the pointing axis of
the wand. In this manner, the tip portion and the wand emitters are
colinear. The two wand emitters selectively emit wand signals which are
received by at least three 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. Reference emitters are mounted in a fixed known
distance from the receivers. The reference emitters emit a reference
signal which travels from the reference emitter the fixed distance to the
receivers. A calibration means measures a reference travel time of the
reference signal over the preselected distance. The calibration means
generates a corresponding calibration factor. A wand position determining
means determines a position of the wand tip portion by measuring wand
signal travel times of the wand signals between the wand emitters and the
three receivers mounted on the frame. The wand position determining means
is connected with the calibration means to calibrate the wand signal
travel times with the reference travel time. 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 a grooved portion defined along the guide axis. The groove is
configured to receive the tool.
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, 2F, and 2G illustrate alternate embodiments of
the wand and guide;
FIG. 3 is a detailed illustration of the locator assembly of FIG. 1;
FIG. 4 is a diagrammatic illustration of one embodiment of calibration
procedure in accordance with the present invention;
FIGS. 5A and 5B are diagrammatic illustrations of the wand and locator
relationship;
FIG. 5C is a flow diagram of the wand location procedure;
FIGS. 6A, 6B, 6C, and 6D 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
microphones, radio frequency receivers, light sensitive diodes, other
light sensitive receivers, and the like mounted at fixed, known locations
thereon. 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 voxel or point in a three-dimensional rectangular
grid of points, preferably a 256.times.256.times.256 grid. 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 selects at least three planes: 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 42 and a tip portion or proximal end 44. The offset 42 is connected
to a portion extending along a pointing axis 46 of the wand. In this
preferred embodiment, a pair of emitters 48 and 50 are mounted on the
offset and disposed along the pointing axis 46 of the wand. The emitters,
such as a spark emitter, radio frequency transmitter, infrared LED, or the
like emit a signal that is received by the receivers 14. The first emitter
48 is a fixed known distance .lambda..sub.1 from the tip 44 and the second
emitter 50 is a fixed known distance .lambda..sub.2 from the first emitter
48. The wand is readily sterilized by conventional techniques. Emitters 48
and 50 emit positioning signals used by a locator system to locate a
coordinate and trajectory of the wand. 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 two emitters
may be mounted on the offset 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 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 handle 62 and a tube member 64
which defines an internal bore 66 to receive and accurately position the
wand. 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. In intraoperative use, the wand 40 is
inserted in the tool guide bore until the tip 44 aligns with a tool guide
distal end 72. A wand stop 70 is positioned on the wand and abuts a
proximal end surface 68 of the tool guide when the wand tip aligns with
the proximal end 68. With the wand tip aligned with the tool guide end,
the surgeon may commence 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 in calculating 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 planes. The
details of the process for correlating the coordinate system of the
patient and the wand with the coordinate system of the image data is
described below.
By viewing the display 30, the surgeon can identify the location of the
wand tip with respect to anatomic structure, and the trajectory of the
bore. If the trajectory is satisfactory, the wand is removed, the surgical
tool is inserted, and the procedure is performed. 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 the appropriate
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 required to perform the surgical procedure.
The wand and tool guide are particularly useful in accurately identifying
the optimal entry point, trajectory, and depth of insertion of screws to
be placed into the patient's spinal column, as will be more fully
described below.
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 two or more emitters for emitting
positioning signals. As in the preferred embodiment, emitters 48 and 50
are disposed along a pointing axis 46 of the wand. However, in the
alternative embodiments, the central axis or pointing direction 46 aligns
with a longitudinal axis of the guide means formed integrally with the
wand. In each of the alternative embodiments, the guide means is connected
to the wand offset portion via an extension.
With reference to FIG. 2B, a tubular portion 74 is integrated with the
wand. The tubular portion defines a bore 76 extending along its
longitudinal axis. In intraoperative use, the surgeon probes the patient
with the proximal 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 78 is mounted to the offset
portion. Light emitting from the laser travels along the longitudinal
pointing axis 46 of the bore 76 of the tubular member. 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. Once a proper coordinate and
trajectory are identified, the integrated wand is held in place while the
surgeon activates the laser. Light emitting from the laser intersects the
bore center point at the proximal end.
With reference to FIG. 2D, a third embodiment is shown in which a grooved
member 80 is incorporated into the wand. The grooved guide member portion
is connected to the offset portion. The grooved member contains a groove
82 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
84 is positioned within the groove so that a tip 86 of the biopsy needle
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 88 attached to the sides of the grooved member.
In the embodiment of FIG. 2E, the wand has emitters 50, 50', 50" mounted
off the axis 46. Because the relationship between the emitter location and
the axis 46 is fixed, once the emitters are located, the axis 46 is
determined.
In the embodiment of FIG. 2F, there are more than two emitters 50.sub.1,
50.sub.2, 50.sub.3, . . . . 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. 2G, the wand has interchangeable tips. The wand
includes a first connector portion 90 which selectively connects with a
second connector portion 92 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 94 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 96 is provided for accurate
registration. A longer tip 98 facilitates reaching deeper into interior
regions of the subject. Tubular drill guides 100 can be provided in
various diameters to accommodate different size drills. An adapter 102
enables endoscopes and other tools to be attached to the wand. Tools and
equipment, such as an array of ultrasonic transducers 104, can be
connected to the adaptor 102 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.
With reference to FIG. 3, when the receivers 14 are microphones, a
plurality of reference emitters 106 are mounted on the frame 12. The
reference emitters are each spaced along side edges of the frame by known
distances from adjacent receivers or microphones 14, e.g. by distances
S.sub.1 and S.sub.2. Preferably S.sub.1 =S.sub.2 =S. Each reference
emitter is also spaced by a distance D across the frame from an oppositely
disposed reference emitter.
The distance from the wand emitters to the frame, hence the position of the
wand relative to the patient, is determined by the travel time of the
sound. The velocity of the sound pulse through air is dependent upon both
the temperature, the humidity, and the chemical composition of the air.
These factors can and do vary significantly during an operation and from
procedure to procedure. As shown in FIG. 4, a calculation is performed to
determine the speed of sound in the operating room. A calibration
procedure 110 selectively pulses the reference emitters 106, receives the
signals at microphone receivers 14, and processes the elapsed time
information in accordance with the procedure of FIG. 4. More specifically,
the calibration procedure 110 includes a step 112 for causing a first of
the reference emitters 106 to emit a signal pulse. A step 114 acquires the
range values D', i.e. the time required for the ultrasonic pulses to
traverse the distance D. A step 116 causes this procedure to be repeated a
preselected number of times, such as once for each of the four emitters
illustrated in FIG. 3.
Once the travel time between each emitter and receiver pair has been
obtained a preselected number of times, a step 120 corrects the times for
fixed machine delays. That is, there is a fixed, small delay between the
time when the command is given to fire the reference emitters 106 and the
time that they actually produce a detectable ultrasonic signal.
Analogously, there is a small delay between the time that the ultrasonic
pulses reach the receiver or microphone 14 and the time that it becomes a
measurable electrical signal received by the computer processor. These
delays are subtracted from the times measured by step or step 114. An
averaging means 122 averages the actual times after correction for the
machine delays for transmission of the ultrasonic pulse between the
transmitter and receiver. The time over the range values D' provide the
most accurate results. A step 124 computes a calibration factor F
indicative of the current speed of the ultrasound signal adjacent the
patient in the operating room. In the preferred embodiment, the
calibration factor F is a ratio of the sonicly measured distance D' versus
a precise mechanical measurement of the distance D.
With reference to FIGS. 5A, 5B, and 5C, a wand coordinate and trajectory
determining procedure 130 determines the position of the two emitters 48
and 50, respectively. More specifically, a step 132 causes the emitter 48
to emit an ultrasonic signal. The receivers 14 on the frame 12 receive the
ultrasonic signal at corresponding times L.sub.1 -L.sub.4. A step 134
acquires and retains these times. A step 136 causes the second emitter 50
to transmit. A step 138 acquires the four times L.sub.1 -L.sub.4 which are
required for the ultrasonic signals to pass from the second emitter to the
microphones 14. The speed of ultrasonic transmission and accuracy of
transmission times are such that these distances can be measured to within
a millimeter or better. A step 140 causes the emitters to emit and
corresponding data values L.sub.1 -L.sub.4 to be acquired each of a
plurality of times to improve digitation accuracy, e.g. two times.
When sonic emitters are used, a step 142 causes the calibration means 110
to perform the steps described in conjunction with FIG. 4 in order to
provide a current indication of the velocity of sound adjacent to the
patient. Of course, the calibration procedure of FIG. 4 may be performed
immediately before steps 132-138 or intermittently during the collection
of several data values for averaging. A step 144 corrects the values
L.sub.1 -L.sub.4 for the fixed machine delay discussed above in
conjunction with step 120. A step 146 corrects each of the times L.sub.1
-L.sub.4 that were required for the ultrasonic signals to travel from the
first and second emitters 48, 50 to the receivers 14 in accordance with
the correction factor F determined by step 124. An averaging means 148
averages the delay and calibration corrected times L.sub.1 -L.sub.4, hence
distances between each of the wand emitters 48, 50 and each of the
receivers 14. From these distances, provided at least three receivers 14
are provided, a step 150 calculates the Cartesian coordinates
(x.sub.1,y.sub.1,z.sub.1) and (x.sub.2,y.sub.2 ,z.sub.2) in the patient
space for the two emitters 48 and 50. The first emitter coordinates
x.sub.1,y.sub.1,z.sub.1 are calculated from three of the four range values
L.sub.1 -L.sub.4. With L.sub.4 disregarded, the coordinates are calculated
as follows:
x.sub.1 =[(L.sub.1.sup.2 -L.sub.2.sup.2)+S.sup.2 ]/2S (1a),
y.sub.1 =[(L.sub.1.sup.2 -L.sub.3.sup.2)+S.sup.2 ]/2S (1b),
z.sub.1 =[(L.sub.1.sup.2 -x.sub.1.sup.2 -y.sub.1.sup.2 ].sup.1/2 (1c),
where S=S.sub.1 =S.sub.2 as defined in FIG. 3. Preferably, the three
selected range values are the three shortest of L.sub.1 -L.sub.4. Similar
computations are calculated for x.sub.2, y.sub.2, and z.sub.2 coordinates
of the second emitter. A step or means 152 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 and x.sub.2,y.sub.2,z.sub.2 of the wand emitters,
i.e.:
.vertline.Sep.sub.known -[(x.sub.1 -x.sub.2).sup.2 +(y.sub.1
-y.sub.2).sup.2 +(z.sub.1 -z.sub.2).sup.2 ].sup.1/2
.vertline..ltoreq.error. (2)
If the measured and known separation 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 two emitters 48, 50, and from the geometry of
the wand discussed in FIG. 2, calculates a step 154 the Cartesian
coordinates (x.sub.0,y.sub.0,z.sub.0) for the wand tip 44.
The tip coordinates x.sub.0, y.sub.0, z.sub.0 are defined by:
r=.lambda..sub.1 /.lambda..sub.2 (3a),
x.sub.0 =(1+r)x.sub.1 -rx.sub.2 (3b),
y.sub.0 =(1+r)y.sub.1 -ry.sub.2 (3c),
z.sub.0 =(1+r)z.sub.1 -rz.sub.2 (3d).
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
(x,y,z) is aligned with the image space (x',y',z') stored in memory.
Aligning the spaces begins with referencing known positions or points 164
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 164
on the vertebra are compared with the relative position of pixels 162 in
the image space. Thereafter, with reference to FIG. 6, a transform 160, as
shown in FIG. 6, transforms the coordinates of the patient space into the
coordinate system of the image space. Fiducials can also be used by the
transform 160 to transform or match the coordinates of other patient space
points 164 into the coordinate system of the 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 164 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. To
align the images of the fiducials with the fiducial positions in patient
space, the tip of the wand is placed on each fiducial or tattooed marker
point 164. The coordinates in patient space of each vertebra process tip
or fiducial are determined with the procedure described in conjunction
with FIGS. 5A-5C.
The position of the three fiducials or process tips are compared with the
relative position of the pixels 162 in the image space. The patient space
coordinates of marks 164 or the process tips of the patient in the
coordinate system of the patient support are measured. A like coordinate
system through the pixels 162 is defined and compared to the patient space
coordinate system. The translation and rotational relationship between
image space and patient space coordinate systems is determined. With
reference to FIG. 6A, 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, two coordinate systems are defined. The translation
means first determines the offset 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. 6B, 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. 6B, 6C, and 6D, 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 means 130 is connected
through the transform 160 with one of the plane selecting means 24 and the
video processor 28 to cause a marker, e.g. cross hairs, to be displayed on
the monitors 30 at the coordinates of the wand tip. This enables the
surgeon to coordinate specific points on the patient or in the incision
with the images.
Having aligned the image and patient spaces the wand and tool guide can be
used to identify the entry coordinate and trajectory at which the surgical
tool will be applied to the patient. For example, the surgeon may use the
wand and tool guide in combination to identify the trajectory and
coordinate on the spinal column at which the surgeon will utilize a
surgical drill in order to drill a hole for the placement of a spinal
screw. Holding the wand and drill guide in one hand, the surgeon moves the
combination around the exposed vertebra while viewing images displayed on
a monitor selected in accordance with the wand tip. The image provide a
cross-sectional view of the vertebra and allow the surgeon to plan with
greater accuracy the angle and depth at which the drill will be operated.
Once the coordinate and trajectory of the drill application is identified,
the surgeon may remove the wand while holding the tool guide in place.
Since the tool guide comes with a handle, the surgeon can hold the tool
guide in place even when the spinal column moves in response to patient
breathing. In other words, the surgeon can easily hold the bore of the
tool guide at the trajectory identified even while the spinal column
experiences movement. With the guide properly oriented, the surgeon
inserts into t | | |
