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TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to the field of surgery. More
specifically, the present invention relates to devices and techniques for
guiding a surgical instrument to a target within a body part.
BACKGROUND OF THE INVENTION
Less invasive surgery techniques are usually more desirable than more
invasive techniques because the patient suffers less trauma, suffers fewer
side effects, and heals quicker. For a given pathology, endoscopic surgery
is often less invasive than other surgical options. In endoscopic surgery,
a surgeon guides a relatively small endoscope configured as a probe to a
target region of a body part. The endoscope generates live video images of
anatomy encountered at the tip of the probe, and the surgeon uses these
video images as an aid in guiding the probe to the target region.
Similarly, a guided microscope can be employed to show where a variety of
instruments should be applied. Once the probe has been guided to the
target, a variety of surgical techniques may then be performed at the
target region.
However, endoscopic surgery has conventionally been considered too
dangerous where few distinctive visual features are available within a
subject body part. When few distinctive visual features are available, the
surgeon risks becoming disoriented while guiding the probe to the target
region. This disorientation may cause the surgeon to inflict extensive
trauma on the patient while failing to reach the target region. Since few
distinctive visual features are found in the interior of many internal
organs, such as the brain, many pathologies have not been successfully
operated upon endoscopically.
Endoscopic surgery within the brain has often been considered exceptionally
risky because a path followed by a probe in traversing from outside the
body to a target region, for example a tumor, should avoid critical or
eloquent areas of the brain to the maximum extent possible to prevent
permanent brain damage. Consequently, not only does a probe or needle need
to be guided to a target region, but the probe should be guided to the
target region over a specific route or trajectory. Disorientation and a
resulting deviation from a specific trajectory may lead to severe
consequences even when the target region is successfully reached.
Various systems and techniques have been devised to let a surgeon know the
location of a surgical instrument within a body even though few visual
clues may be available. For example, various framed and frameless
stereotactic surgical techniques incorporate systems for informing a
surgeon of an instrument position. When such position information is
accurate, it may help a surgeon find a target region. However, mere
position information fails to inform a surgeon about whether an instrument
is on a specific trajectory, and such information fails to inform a
surgeon of actions needed to cause an instrument to more closely approach
a specific trajectory. Consequently, a high risk of disorientation still
remains when limited visual clues are present.
In addition, various systems present tomogram images in combination with
surgical instrument position information. For example, during surgery a
surgical instrument's position may be superimposed or otherwise indicated
on a tomogram which is viewable by the surgeon. These tomogram-based
systems attempt to better inform a surgeon of whether an instrument is
positioned as desired because a surgeon can view instrument position
relative to an overall tomogram image.
However, tomograms represent anatomy at a past point in time and in a
situation where the anatomy is not being influenced by the surgery itself.
Tomograms fail to reveal actual anatomy at the instant of surgery and
under the influence of surgery. Consequently, tomograms often fail to
provide accurate anatomical renditions existing during surgery, and
relative position information indicated on tomograms may not be accurate.
Moreover, even if a tomogram-based system happens to accurately portray
relative instrument position, nothing informs a surgeon about whether an
instrument's position is consistent with a specific trajectory or about
actions needed to cause an instrument to more closely achieve a specific
trajectory.
Still other systems attempt to perform extensive 3-D computer enhancement
and reconstruction of tomogram images during surgery in response to
instrument position information in an attempt to better allow a surgeon to
visualize instrument orientation and anatomy traversed by the surgical
instrument. However, no amount of computer reconstruction can make
tomogram images taken at a past point in time under non-surgical
conditions to accurately portray anatomy under the influence of surgery.
Moreover, complex 3-D computer analysis of tomogram images requires
extensive computing power, causing a time lag between the actual
instrument positioning and the resulting enhanced or reconstructed images.
Such systems merely react to actions already taken by a surgeon and fail
to adequately inform a surgeon of what future actions are needed to guide
an instrument along a specific trajectory to a target region.
SUMMARY OF THE INVENTION
Accordingly, it is an advantage of the present invention that an improved
method and apparatus for guiding an instrument to a target are provided.
Another advantage is that the present invention displays information to a
user which indicates whether or not a surgical instrument is positioned
along a specific trajectory.
Another advantage is that the present invention displays information to a
user which indicates in which direction to move a probe tip to cause a
probe tip to intersect a specific trajectory.
Another advantage is that the present invention automatically displays
trajectory guidance information in real time.
Another advantage is that the present invention may combine trajectory
guidance information with one or more of tomogram and endoscopic images.
The above and other advantages of the present invention are carried out in
one form by a method for presenting guidance information to a user engaged
in guiding a probe to a target within a body. The method calls for
identifying a location for the target. A location for an initial point
relative to the body is identified. A current location for a tip of a
probe is determined. A graphic object is then displayed. The graphic
object indicates a direction in which to move the probe tip to cause the
probe tip to intersect a predetermined trajectory which includes the
target and the initial point locations.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the present invention may be derived by
referring to the detailed description and claims when considered in
connection with the Figures, wherein like reference numbers refer to
similar items throughout the Figures, and:
FIG. 1 shows a block diagram of a guidance system;
FIG. 2 shows a schematic view of a display presented to a user who is
engaged in guiding a probe to a target within a body;
FIG. 3 shows a flow chart of a setup procedure performed by the guidance
system;
FIG. 4 shows a schematic view of a probe tip indicator feature of a graphic
guidance object;
FIG. 5 shows a schematic view of a trajectory indicator included in the
graphic object;
FIG. 6 shows a flow chart of a track procedure performed by the guidance
system;
FIG. 7 shows exemplary geometrical relationships between a probe, an
initial point, and a target;
FIG. 8 shows a schematic view of the graphic object in a situation where a
probe tip is below and to the left of a desired trajectory; and
FIG. 9 shows a schematic view of a roll feature of the graphic object.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a block diagram of a guidance system 10. Guidance system 10
provides information which aids the guidance of a probe 12 to a target
located inside a body 14. Probe 12 represents any instrument which may be
inserted into body 14. While any type of instrument constitutes probe 12
for purposes of the present invention, an endoscope represents one
particularly desirable form of probe 12. FIG. 1 illustrates body 14 in the
form of a human head because system 10 is particularly suited to
endoscopic surgery within the brain. However, system 10 is not limited to
brain or endoscopic surgeries. System 10 may be used to advantage in any
surgery where a tool is desired which aids guiding probe 12 along a
selected trajectory to a target.
System 10 includes a guidance system controller 16. Conventional medical,
personal, or industrial computer components, such as a processor board,
may serve as controller 16. Controller 16 couples to a memory 18, a data
link port 20, a user input device 22, and a display unit 24. Memory 18,
data link port 20, user input device 22, and display 24 all represent
conventional computer components commonly used in connection with medical,
personal, industrial, and other computers.
Memory 18 stores databases used by system 10 and computer programs which
define the operation of system 10 along with other data items. Such
databases may include digitized tomograms. The tomograms may be formed in
accordance with conventional CT, MRI, PET, or other tomographic
techniques. Portions of the computer programs which are relevant to the
present invention are discussed below in connection with FIGS. 2-10.
Data link port 20 allows controller 16 to import external data. For
example, port 20 may represent a LAN port, modem, removable disk drive, or
tape drive. Among other data items, tomogram databases, which may be
supplied by external radiology or other computers, are received through
port 20.
User input device 22 allows a surgeon or other user of system 10 to enter
selections and otherwise provide data to system 10. Such selections
control the operation of system 10 before, during, and after surgery.
Conventional touch screens, remote control devices, keyboards, pointing
devices, and the like all represent suitable examples of user input device
22. However, user input device 22 is desirably located for easy
manipulation by a surgeon during surgery and sterilized at least to the
extent that it is manipulated by the surgeon.
Display 24 is desirably a CRT, LCD, plasma, or other video terminal or
projection device which visually presents information to a surgeon or
other user of system 10. Regardless of where other components of system 10
may be located, display 24 is desirably located so that its visually
presented information may be conveniently viewed by a surgeon during
surgery.
Controller 16 additionally couples to a localizer 26 through which
controller 16 obtains location data. While the preferred embodiment of
system 10 uses a magnetic location determination system, the present
invention may be practiced using acoustic, infrared, mechanical, or other
location determination systems known to those skilled in the art.
Non-mechanical embodiments of such systems typically include a transducer
28 which provides an acoustic, optic, or magnetic reference. Using
transducer 28, the location of various sensors 30 may be determined.
Transducer 28 and sensors 30 couple to localizer 26 via flexible cabling.
A sensor 30' is located on a handle 32 of probe 12 and generates location
data regarding the position of sensor 30'. Sensor 30' provides continuous
roll, pitch, and yaw signals that track any movement in sensor 30'. Probe
12 includes a shaft 34 at the end of which resides a probe tip 36. For a
given probe 12, tip 36 has a fixed spatial relationship to sensor 30'.
Controller 16 tracks the location of a tip 36 based upon location data
provided by sensor 30' and this fixed spatial relationship.
Controller 16 also couples to an endoscope controller 38. Controller 38 is
a conventional device for controlling endoscope parameters. While not
required, probe 12 is desirably fitted with an endoscope which couples to
controller 38 so that forward-looking, live video images taken from tip 36
of probe 12 are available to system 10. Guidance system controller 16
couples to endoscope controller 38 to control endoscope parameters and to
receive the resulting live video images.
System 10 may include other components which are not relevant to the
present invention. Such other components may include a video recorder
configured to record images appearing on display 24 during a surgery.
Moreover, additional displays may be driven by controller 16.
FIG. 2 shows a schematic view of an example display screen 40 presented to
a surgeon engaged in guiding probe 12 to a target within body 14 (see FIG.
1). Screen 40 includes a tomogram slice 42, including associated
alphanumeric data 42', a live video image 44, a graphic guidance object
46, a plurality of selection buttons 48, and alphanumeric position data
50.
Screen 40 is a tool to be used by a surgeon during surgery in any manner
deemed appropriate by the surgeon. In a typical scenario, the surgeon's
primary focus rests on graphic guidance object 46. Graphic object 46
changes in real time to track movement of probe 12 within body 14. Graphic
object 46 includes several features which aid the surgeon in guiding tip
36 (see FIG. 1) of probe 12 to a target 52 along a desired trajectory 54.
Generally, the relative orientation and positioning of these features
indicate whether probe tip 36 currently resides on trajectory 54. If probe
tip 36 does not reside on trajectory 54, then the relative orientation and
positioning of these features indicate a direction in which to move probe
tip 36 to cause probe tip 36 to intersect trajectory 54. These features
are discussed in detail below.
In the typical scenario, the surgeon's secondary focus rests on live video
image 44. When image 44 is generated by an endoscope, it informs a surgeon
of structures actually and immediately in front of probe tip 36. In an
alternate embodiment of the present invention, image 44 may be generated
by a microscope (not shown). When a surgeon notices an artery or other
critical structure, probe 12 may be maneuvered to avoid the structure. For
surgeries within the interior of the brain and other organs, few visually
distinctive structures may be seen in live video image 44 until probe 12
nears target 52. Consequently, image 44 typically receives a reduced level
of attention by the surgeon relative to object 46.
In the typical scenario, the surgeon's tertiary focus rests on tomogram
slice 42. Tomogram slice 42 provides a reference which may help the
surgeon maintain a correct sense of orientation. Those skilled in the art
will appreciate that various critical structures, such as arteries, may
not be readily visible in the particular tomogram slice 42 showing on
screen 40 at any given instant. Moreover, even if such structures are
visible, they may not actually be located at the precise position during
surgery where they were located during pre-surgery tomographic imaging.
Consequently, tomogram slice 42 typically receives a reduced level of
attention by the surgeon relative to object 46 and live video image 44.
FIG. 2 illustrates target 52 and trajectory 54 in connection with tomogram
slice 42. However, those skilled in the art will appreciate that tomogram
slice 42 is a 2-D image, that a typical target 52, such a tumor or the
like, may very well be visible on only a few tomogram slice images out of
an entire set of tomogram slice images, and that trajectory 54 may very
well traverse a 3-D space relative to displayed tomogram slice 42.
Accordingly, FIG. 2 illustrates only a projection of trajectory 54 on one
particular tomogram slice 42 from a set of tomogram slice images.
Selection buttons 48 form a menu structure which may be logically traversed
by the surgeon or other user of system 10 through manipulation of user
input device 22 (see FIG. 1). User data provided through buttons 48 prior
to surgery initialize system 10 for an upcoming surgery. During surgery
these user-supplied data may alter program settings to accommodate events
which may be encountered during the surgery. Alphanumeric position data 50
inform the user of the precise position of probe tip 36 in relation to an
X,Y,Z coordinate system used by system 10 and of the distance between
probe tip 36 and target 52 at any given instant.
FIG. 3 shows a flow chart of a setup procedure 56 performed by guidance
system 10. Procedure 56 is performed interactively between a user of
system 10 and controller 16 (see FIG. 1). Controller 16 performs its
portion of procedure 56 under the control of a computer program stored in
memory 18 (see FIG. 1). For convenience, FIG. 3 illustrates procedure 56
through a flow chart. However, many tasks performed during procedure 56
are independent of other tasks and need not be sequenced as indicated by
this flow chart.
Procedure 56 includes a task 58 which gets a tomogram image database. Task
58 involves obtaining external tomogram data through data link port 20
(see FIG. 1) and having a user select the appropriate tomogram database.
In the preferred embodiment, a tomogram database is selected by indicating
a patient name which is associated with a particular tomogram database. In
addition, nothing prevents multiple tomogram images from being obtained in
task 58. Thus, a selected patient may have any number of CT, MRI, or PET
image sets available for use during an upcoming surgery.
A task 60 identifies characteristics of a probe 12 to be used during an
upcoming surgery. Task 60 may be performed when a user selects a
particular make and model of surgical instrument from a menu selection of
such instruments. Task 60 defines a specific spatial relationship between
probe tip 36 and sensor 30' (see FIG. 1) which applies to the selected
instrument. Thus, system 10 may compensate for variations in the length of
the probe 12 and offsets between the axis of probe 12 and sensor 30' to
accommodate a variety of different types of probes 12.
A task 62 aligns localizer data with tomogram imaging so that patient
features match corresponding tomogram features. Referring back to FIGS. 1
and 2, task 62 may be performed by touching probe tip 36 to an alignment
feature 64 fixed to the patient. Desirably, alignment feature 64 is
configured to serve as a fiducial marker during tomographic imaging. Thus,
one or more tomogram slices 42 depict an object 64' corresponding to
feature 64. Alignment feature 64 desirably resides in a fixed position on
the patient during pre-surgery imaging and during surgery. Feature 64 may
be fixed by being attached to bone or by being attached to a mask worn by
the patient during both imaging and surgery.
At any given instant, system 10 knows the location of probe tip 36 through
the operation of localizer 26. By touching probe tip 36 to alignment
feature 64 (see FIG. 1) while simultaneously identifying a pixel where
object 64' (see FIG. 2) is depicted, system 10 may learn the position of
alignment feature 64. Thereafter system 10 may translate between a
coordinate system used by tomographic imaging and a coordinate system
imposed by localizer 26 through the use of well known trigonometric
relationships. Referring back to FIG. 3, at the conclusion of task 62
system 10 can obtain coordinates relative to localizer 26 for various
points depicted on the aligned tomograms.
Procedure 56 includes a query task 66 that determines whether an endoscope
is activated. As discussed above, probe 12 need not be an endoscope or
contain an endoscope. However, if an endoscope is available, a task 68
causes live video image 44 (see FIG. 2) to be displayed. Live video image
44 will thereafter continue to be displayed. Likewise, procedure 56
includes a query task 70 that determines whether tomographic images 42
(see FIG. 2) have been activated for display on screen 40 (see FIG. 2). If
activated, a task 72 causes a selected tomogram slice to be displayed.
Tasks 66 and 68 indicate that live video image 44 need not be displayed in
all situations, and tasks 70 and 72 indicate that tomograph images 42 need
not be displayed in all situations. Live video image 44 may be omitted,
for example, when image 44 is unlikely to be useful due to endoscope
clogging or when some other probe is being guided to target 52 (see FIG.
2). Tomograph images 42 may be omitted, for example, to allow larger
viewing areas for the remaining items on display screen 40.
Procedure 56 includes a task 74 in which probe roll is adjusted to a
desired angle when a roll sensitive probe 12 is used. Task 74 is primarily
a manual step. Roll represents a clockwise or counterclockwise rotation
around the axis of probe 12. An endoscope is one example of a
roll-sensitive probe 12. Live video image 44 is oriented on display screen
40 in response to roll angle. Desirably, the top, bottom, right, and left
sides of image 44 correspond to the top, bottom, right, and left sides,
respectively, of probe tip 36 when probe 12 is held in its normal,
operational orientation. Accordingly, during task 74 probe 12 is held
normally and roll angle is adjusted to a desired orientation. Task 74 may
be performed by observing a distinctive pattern, such as printed text, via
both live video image 44 and the naked eye. The endoscope may be rotated
so that the distinctive pattern shown in image 44 exhibits the same
orientation observed by the naked eye.
A task 76 identifies this roll orientation as an initial roll orientation
for system 10. In general, task 76 represents a counterpart of manual task
74 that is performed by system 10. At some time following completion of
task 74, task 76 causes system 10 to record the roll orientation of probe
12.
Setup procedure 56 includes a task 78 in which a location for target 52 is
identified. Target 52 may be identified when the user causes a tomogram
slice 42 in which target 52 is visible to be displayed at display 24. When
a tomographic image of target 52 is displayed, a user may cause a video
display pointer, cursor, or the like to reside over the tomographic image
of target 52. Using well known computer graphics techniques, the position
of the tomographic target image relative to the tomogram coordinate system
may be obtained from the location of pointer pixels. Due to alignment task
62 discussed above, this position may be translated into coordinates
consistent with a coordinate system used by location system 26.
A task 80 identifies an initial point 82, illustrated in FIG. 2, for
defining a desired trajectory 54 for probe 12 to follow in traversing body
14 to target 52. In accordance with conventional endoscopic surgery
techniques, initial point 82 typically corresponds to an entry incision or
burr hole into body 14 through which probe 12 will be guided to target 52.
Task 80 may be performed when a user touches probe tip 36 to initial point
82 while simultaneously instructing system 10 to "grab" the coordinates of
probe tip 36 for use as initial point 82. Initial point 82 is selected by
the surgeon based upon the surgeon's experience, the particular pathology
necessitating the surgery, and patient-specific anatomy considerations. In
an alternate embodiment of the present invention, trajectory 54 may be
coincident with an axis of a microscope. In this embodiment, initial point
82 may be outside the body somewhere along the axis of the microscope.
After the locations of target 52 and initial point 82 have been identified,
a task 84 determines trajectory 54 so that trajectory 54 includes the
coordinates of target 52 and initial point 82. In the preferred
embodiment, trajectory 54 is a straight line segment extending between
target 52 and initial point 82. A straight line trajectory accommodates
typical probes 12, which have straight shafts 34 (see FIG. 1). However,
straight line trajectories are not a requirement, and task 84 could
alternatively define various configurations of curves to include
coordinates for target 52 and initial point 82. Trajectory 54 desirably
represents a curve defined through three-dimensional space in accordance
with the coordinate system imposed by localizer 26.
Setup procedure 56 includes a task 86 to formulate a probe tip indicator 88
of graphic object 46, schematically shown in FIGS. 2 and 4. Referring to
FIGS. 2 and 4, probe tip indicator 88 desirably includes vertical and
horizontal cross hairs residing within a circle. A probe tip point 36'
resides at the intersection of the cross hairs. Probe tip point 36'
represents the axis of probe 12 as it would be viewed looking down the
axis of probe 12. The perimeter of probe tip indicator 88 is formed as a
circle to resemble the perimeter shape of live video image 44 (see FIG. 2)
from an endoscope.
In addition, probe tip indicator 88 includes a feature 90 for indicating
distances to trajectory 54. In the preferred embodiment, feature 90
represents a set of hash marks on both the vertical and horizontal cross
hairs of probe tip indicator 88. The hash marks are spaced apart to
indicate a predetermined distance, preferably in the range of 0.25 to 1.0
cm. Nothing requires the hash marks to be spaced apart this predetermined
distance in display screen 40. Once formulated, probe tip indicator 88
need not change. Accordingly, task 86 may be performed through software
programming which need not be configured or altered in preparation for an
upcoming surgery.
Likewise, a task 92 formulates a trajectory indicator 94, schematically
shown in FIGS. 2 and 5. Trajectory indicator 94 is a logical construction
and may be formulated through the structure of computer programming. Once
formulated, the nature of trajectory indicator 94 need not change. Thus,
task 92 may be performed through software programming which is not
configured or altered in preparation for an upcoming surgery.
Referring to FIG. 5, in the preferred embodiment trajectory indicator 94
includes a horizontal pitch line 96 and a vertical yaw line 98, which
together partition two-dimensional space into four quadrants. A trajectory
point 54' resides at the intersection between pitch and yaw lines 96 and
98. Trajectory point 54' represents trajectory 54 as viewed looking from
initial point 82 toward target 52 (see FIG. 2).
So that trajectory indicator 94 appears distinctively different from probe
tip indicator 88 (see FIG. 4), pitch and yaw lines 96 and 98 need not
actually be drawn. Rather, the four quadrants are defined to have
contrasting colors. A light color is defined for an upper-right quadrant,
medium colors are defined for lower-right and upper-left quadrants, and a
dark color is defined for a lower-left quadrant. Consequently, pitch and
yaw lines 96 and 98 and trajectory point 54' may be easily implied by the
intersections between quadrants of contrasting colors. Moreover, lines 96
and 98 and trajectory point 54' may be easily distinguished from probe tip
indicator 88 when overlaid thereon. FIG. 2 illustrates a situation where
probe tip indicator 88 has been overlaid on trajectory indicator 94, and
trajectory indicator 94 is aligned with probe tip indicator 88. Due to
this alignment, the cross hairs of probe tip indicator 88 overlie pitch
and yaw lines 96 and 98, and probe tip point 36' overlies trajectory point
54'. As shown in FIG. 2, any portion of trajectory indicator 94 which
might have otherwise been viewable outside probe tip indicator 88 has been
omitted from graphic object 46.
After completion of the above-discussed tasks included in procedure 56,
system 10 may proceed to a track procedure 100, which is performed to
assist the surgeon in the act of guiding probe tip 36 to target 52.
However, system 10 proceeds to track procedure 100 only in response to
user input, and such user input need not be provided until system 10 is
completely setup. In other words, any of the above-discussed tasks
included in procedure 56 may be repeated as desired until the surgeon is
satisfied that system 10 and the surgeon are ready for surgery.
FIG. 6 shows a flow chart of track procedure 100. The operation of
procedure 100 is described below in connection with FIG. 7, which shows
geometric relationships between probe 12, initial point 82, and target 52
for a hypothetical situation. Those skilled in the art will appreciate
that for clarity FIG. 7 shows only a two-dimensional projection of a
three-dimensional geometry.
Referring to FIGS. 6 and 7, procedure 100 includes a task 102 which
determines the coordinates for a current location of probe tip 36. Task
102 is performed in response to location data provided from localizer 26
and sensor 30' (see FIG. 1). In the preferred embodiment, current
coordinates for probe tip 36 are expressed in accordance with an X,Y,Z
coordinate system established through the operation of localizer 26. After
task 102, a task 104 determines a current probe roll angle. Roll angle is
also determined in response to location data provided from localizer 26
and sensor | | |
