U.S. patent application number 14/276945 was filed with the patent office on 2015-04-16 for efficient closed loop feedback navigation.
The applicant listed for this patent is STEREOTAXIS, INC.. Invention is credited to Walter M. Btume, Raju R. Viswanathan.
Application Number | 20150105653 14/276945 |
Document ID | / |
Family ID | 35783386 |
Filed Date | 2015-04-16 |
United States Patent
Application |
20150105653 |
Kind Code |
A1 |
Viswanathan; Raju R. ; et
al. |
April 16, 2015 |
EFFICIENT CLOSED LOOP FEEDBACK NAVIGATION
Abstract
The present invention provides a means for guiding a medical
device within the body to approach a target destination. The system
and method provide a means for determining a predicted length and
orientation, navigating the device to an intermediate point less
than the predicted length, determining an error between the
projected destination and actual target destination, and
successively updating a predicted value of a control variable to
yield an orientation within a predetermined distance error before
advancing the device the remaining distance to the destination.
This provides a physician with the capability of verifying the
device will be accurately guided to the target destination without
trial and error. A method is also provided for intuitive navigation
to targets with limited trial and error based on user-applied
device orientation adjustments, where the user chooses the
magnitude of the adjustments and the system determines the
adjustment direction.
Inventors: |
Viswanathan; Raju R.; (St.
Louis, MO) ; Btume; Walter M.; (St. Louis,
MO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
STEREOTAXIS, INC. |
St. Louis |
MO |
US |
|
|
Family ID: |
35783386 |
Appl. No.: |
14/276945 |
Filed: |
May 13, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10879694 |
Jun 29, 2004 |
8721655 |
|
|
14276945 |
|
|
|
|
10844056 |
May 12, 2004 |
|
|
|
10879694 |
|
|
|
|
PCT/US03/10893 |
Apr 9, 2003 |
|
|
|
10844056 |
|
|
|
|
60371555 |
Apr 10, 2002 |
|
|
|
Current U.S.
Class: |
600/424 |
Current CPC
Class: |
A61B 2017/003 20130101;
A61B 2090/376 20160201; A61B 34/20 20160201; A61B 2034/2051
20160201; A61M 25/0108 20130101; A61B 2034/733 20160201; A61B 34/70
20160201; A61B 6/5235 20130101; A61B 90/10 20160201; A61B 34/73
20160201; A61B 2018/00839 20130101; A61B 1/00147 20130101; A61B
17/22 20130101; A61B 6/466 20130101; A61B 6/12 20130101; A61B
2090/3954 20160201; A61B 90/00 20160201; A61B 6/4441 20130101; A61B
2034/107 20160201; A61B 34/25 20160201; A61B 6/463 20130101; A61B
90/36 20160201 |
Class at
Publication: |
600/424 |
International
Class: |
A61B 6/12 20060101
A61B006/12; A61B 6/00 20060101 A61B006/00; A61M 25/01 20060101
A61M025/01 |
Claims
1.-18. (canceled)
19. A navigation system for navigating the distal end of an
elongate medical device in an operating region in a subject, the
navigation system comprising: an orientation system for remotely
orienting the distal end of the medical device in a selected
direction in the operating region; a movement system for
controlling the length of the elongate medical device in the
operating region; location data input from a localization system
that determines the current position and orientation of the distal
end of medical device; and a method of registering localized
catheter positional data obtained from the localization system to
the navigation system coordinates.
20. The navigation system of claim 19, wherein the control receives
data input of an anatomical surface normal from the localization
system, and uses the surface normal information is used to compute
an optimal change of control variable in order to enhance device
contact with the anatomical surface.
21. The navigation system of claim 19, further comprising a three
dimensional window display, and wherein the controller displays the
current location and orientation of the device.
22. The navigation system of claim 19, wherein the current location
and orientation of the device is graphically displayed together
with a three dimensional preoperative image rendering.
23. The navigation system of claim 19, wherein the current location
and orientation of the device is graphically displayed together
with a surface rendering of a preoperative image.
24. The navigation system of claim 19, wherein the current location
and orientation of the device is graphically displayed together
with a three dimensional intra-operative image rendering.
25. The navigation system of claim 19, further comprising a
connection to an X-ray system, wherein images can be transferred
from the X-ray system to the navigation system, and the current
location and orientation of the device as determined by the
localization system is suitably projected and graphically overlaid
on a transferred X-ray image.
26. The navigation system of claim 25, wherein the current location
and orientation of the device as determined by the localization
system is suitably projected and corresponding graphics sent to the
X-ray system for display on the live X-ray image display.
27. The system according to claim 19, wherein the control uses data
input from a localization system associated with the distal end of
the medical device to determine the current position and
orientation of the distal end of medical device, and wherein the
control determines the error by determining the minimum distance
between a projection from a distal end of the medical device in its
current orientation and the destination point.
28. The system according to claim 19 wherein the control operates
the movement system to make the length of the elongate device less
than the predicted length by operating the movement system to make
the length of the medical device a predetermined fraction of the
predicted length.
29. The system according to claim 19, wherein the control operates
the movement system to make the length of the elongate device less
than the predicted length by operating the movement system to make
the length of the medical device a predetermined fraction of the
predicted length.
30.-72. (canceled)
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 10/879,694, filed Jun. 29, 2004, which claims priority to U.S.
application Ser. No. 10/844,056, filed May 12, 2004, which is based
on PCT Patent Application Serial No. PCT/US03/10893, filed Apr. 9,
2003, which claims priority to U.S. Provisional Application Ser.
No. 60/371,555, filed Apr. 10, 2002, all of which has been
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to a system and methods for
interventional medicine, and more specifically to navigation of
catheter and medical devices through the body to an operating
region.
BACKGROUND OF THE INVENTION
[0003] Interventional medicine is the collection of medical
procedures in which access to the site of treatment is made through
one of the patient's blood vessels, body cavities or lumens. For
example, angioplasty of a coronary artery is most often performed
using a catheter which enters the patient's arterial system through
a puncture of the femoral artery in the groin area. The procedure
is referred to as PTCA, or Percutaneous (through the skin),
Transluminal (through the blood vessel), Coronary (in the vessel of
the heart), Angioplasty. Other interventional medical procedures
include assessment and treatment of tissues on the inner surfaces
of the heart (endocardial surfaces) accessed via peripheral veins
or arteries, treatment of vascular defects such as cerebral
aneurysms, removal of embolic clots and debris from vessels,
treatment of tumors via vascular access, endoscopy of the
intestinal tract, etc.
[0004] Interventional medicine technologies have been applied to
manipulation of instruments which contact tissues during surgical
procedures, making these procedures more precise, repeatable and
less dependent of the device manipulation skills of the physician.
Some presently available interventional medical systems for
directing and manipulating the distal tip of a medical device by
actuation of the distal portion of the device use computer assisted
navigation and an imaging system for providing imaging of the
device and blood vessels and tissues. Such systems can control the
navigation of a medical device, such as a catheter, to a target
destination in an operating region using a computer to orient and
guide the distal tip through blood vessels and tissue. In some
cases, when the computed direction for reaching the target
destination is determined and the medical device is extended, the
device tip may not reach the intended target exactly due to
inaccuracies in the device or deviations in physical or geometric
characteristics of the device from its ideal properties. A steering
correction may be required to properly reorient the device to reach
the intended target. To reach the target destination, a navigation
system must accurately orient the device tip as it approaches the
target before advancing the remaining distance to reach the given
target. A method is therefore desired for controlling movement of a
medical device approaching the target destination that will verify
the device tip is being accurately guided to the intended
destination before advancement, and will allow for accurate
navigation in real time.
SUMMARY OF THE INVENTION
[0005] According to the principles of the present invention, a
system and method are provided for control of a navigation system
for deploying a catheter or medical device within the body in a
manner such that a physician can input a target destination, and
the navigation system will guide the catheter device within a short
distance of the target and determine an orientation for the
catheter tip that is within a predetermined error before advancing
the catheter tip to the target destination. The present system and
method provide a means for determining a predicted length and
orientation, navigating the catheter device to an intermediate
point less than the predicted length, determining an error between
the projected destination and actual target destination, and
successively updating a predicted value of a control variable to
yield an orientation within a predetermined distance error before
advancing the catheter device the remaining distance to the
destination. A preferred embodiment of the present invention
utilizes a magnetic navigation system that orients the distal end
of a medical device in a selected direction through the interaction
of magnetic fields associated with the medical device and one or
more external source magnets outside the patient's body. The
magnetic navigation system utilizes a field angle control variable
for controlling the orientation direction of the medical device.
The navigation system applies a magnetic field in a specific
direction based on the field angle to orient the distal end of the
medical device in the patent's body. An error of the predicted
orientation and the actual orientation is determined by estimating
the distance between a projected destination of the medical device
if advanced in its current orientation and the desired target
destination. The predicted orientation is iteratively updated and
evaluated using a cost function until the distance error is within
a predetermined minimum, to yield an optimum field angle that is
applied to the catheter tip before advancing the catheter the
remaining distance to the target destination. An estimation of the
model response of predicted orientation relative to the field angle
control variable may also be utilized to determine an updated field
angle that will provide correction for variation in field
direction, and will bring the actual orientation closer to the
target destination. An updated field angle is determined and then
applied, after which a new error and updated field angle are
determined. This iterative process may be used to further correct
the optimum angle to compensate for magnetic field variations,
prior to advancing the catheter device to the intended target
destination. The use of this method would provide the physician
with the capability of verifying the medical device will be
accurately guided to the target destination with only minimal or
without any trial and error, to thereby reduce damage of the
surrounding tissue.
[0006] In alternate embodiments, the actuation method could be
based on mechanical, hydraulic, electrostrictive or other
technologies known to those skilled in the art. The general scheme
described here for device control is applicable to such other
actuation methods as well. Thus while the methods taught herein
detail the case of magnetic actuation for non-limiting illustrative
purposes, the details can be adapted to other actuation techniques
by those skilled in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is an illustration of an X-ray imaging system capable
of providing images on at least two separate planes, together with
an actuation system such as a magnetic field generator, for use in
guiding a medical device through the lumens and cavities in the
operating regions in a subject in accordance with the principles of
this invention;
[0008] FIG. 2 is a diagram illustrating the approach of the tip of
a medical device to a target destination, in accordance with the
principles of this invention;
[0009] FIG. 3 is a graph illustrating the approach error of the tip
of the medical device as the orientation angle of the tip of the
device nears the optimum orientation for approaching the target
destination;
[0010] FIG. 4 is an illustration of a navigation system user
interface displaying X-ray images from two separate planes, a
series of points obtained from a localization system, a surface
normal obtained from a localization system's map of an anatomical
surface and a projection of the distal tip of a medical device
localized from a localization system for use in guiding the medical
device in a patient in accordance with the principles of this
invention;
[0011] FIG. 5 is an illustration of a "drag" method of continuously
acquiring a series of surface points by retracting a medical device
in contact with a tissue surface while maintaining device
deflection for good surface contact by suitable device
actuation;
[0012] FIG. 6 is an illustration of a series of target destinations
on the roof of a heart chamber to be ablated by the medical device
that is guided by the system in accordance with the principles of
this invention;
[0013] FIG. 7 is an image showing the real-time location and
orientation of a medical device displayed on a registered
pre-operative three dimensional image of a heart;
[0014] FIG. 8 is an image of a surface rendering of a heart, which
could alternatively be used to display the real-time location and
orientation of a medical device.
[0015] FIG. 9A is a an electrical activity surface rendering of an
endocardial chamber, with gaps 111 in the surface where there was
insufficient surface location data to permit closing the surface;
and
[0016] FIG. 9B is an an electrical activity surface rendering of an
endocardial chamber, showing closure of the gaps shown in FIG.
9A.
[0017] FIG. 7 is a view of a display of the real-time location and
orientation of the device together with a registered pre-operative
three dimensional image of the anatomy of interest;
[0018] FIG. 8 is view of a display of a surface rendering of the
anatomy of interest, an intraoperative reconstruction of the
anatomy of interest, or any other three dimensional reconstruction
of the anatomy;
[0019] FIG. 9A is a view of a display illustrating an electrical
activity surface rendering of an endocardial chamber, with gaps in
the surface where there was insufficient surface location data to
permit closing the surface; and
[0020] FIG. 9B is a view of a display illustrating an electrical
activity surface rendering of an endocardial chamber, with gaps in
the surface closed.
DETAILED DESCRIPTION OF THE INVENTION
[0021] An automated system for navigating a medical device through
the lumens and cavities in an operating region in a patient in
accordance with the principles of this invention is indicated
generally as 20 in FIG. 1. The system 20 comprises an elongate
medical device 22, having a proximal end and a distal end adapted
to be introduced into the operating region in a subject. The system
20 also comprises an imaging system 30 for displaying an image of
the operating region on a display 32, including a representation of
the distal end of the medical device 22 in the operating
region.
[0022] The system also includes a navigation system for
manipulating the distal end of the medical device 22. In this
preferred embodiment the navigating system is a magnetic navigation
system 50. Of course, the navigation system could alternatively be
a piezoelectric system or a mechanical guide wire system or other
suitable system for orienting the distal tip of the medical device.
The magnetic navigation system 50 orients the distal end of the
medical device 22 in a selected direction through the interaction
of magnetic fields associated with the medical device 22 inside the
operating region and at least one external source magnet outside
the subject's body. The catheter may then be advanced in the
selected direction, to reach the target destination through the
successive reorientation stepwise process and advancement.
[0023] A preferred embodiment of the present invention describes a
method for efficiently using real-time location information
associated with an elongate flexible catheter or medical device
provided by a localization system and controlling navigation in an
automated or semi-automated manner to a desired target with the aid
of a computer-controlled navigation system. The control or
actuation means used to steer or navigate the medical device with
computer controlled navigation system may be any of a variety of
method known to those skilled in the art, such as mechanical,
magnetic, electrostrictive, hydraulic, or others. One preferred
embodiment is one where an externally applied magnetic field is
used to steer the device, while device advancement and retraction
is mechanically driven. Such a navigation system is typically used
in conjunction with an X-ray system with a mutually known
registration between the systems. Registration of coordinates
between the localization system and the navigation system may be
performed by placing suitable radio-opaque markers (at known
locations in localization system coordinates) within the apparatus
associated with the localization system, bringing these into the
X-ray field of view, and fluoro-localizing these markers on the
navigation system. Following this marker identification, a best-fit
algorithm that attempts to match corresponding points employing a
standard registration method such as the Procrustes method can be
used to register the localization coordinate system with the
navigation coordinate system. Alternatively, the catheter tip can
be fluoro-localized and the localization system coordinates of the
catheter tip can be suitably translated to match the fluoroscopy
system coordinates of the catheter. If desired, orientation
adjustment can also be included in the latter scheme.
[0024] Given a three dimensional target location that is input from
a user interface together with a pivot point and pivot orientation
that defines a base support for the catheter device beyond which
the device is extended and steered, a computational model of device
response may be used to compute the magnetic field orientation and
length of device ideally required to reach the target destination.
The medical device is preferably deployed from the distal end of a
relatively stiff sheath. The distal end of such a sheath functions
as a base for the distal end of a medical device deployed
therefrom. One efficient method to mark the pivot or base of the
medical device is to position the catheter distal tip at the
intended base, for example at the distal tip of a sheath, and then
record the current real-time location and orientation (using a
button as shown in FIG. 4 at 68) of the catheter tip as the pivot
location and orientation. In some cases, however, when the computed
field required to reach the target is applied and the device
suitably extended beyond the base, the catheter tip may not reach
the intended target exactly due to inaccuracies in device base
information, deviations in physical or geometrical characteristics
of the device away from its ideal properties, cardiac or anatomical
motion, and such other factors. In such instances, one or more
steering corrections can be applied to the device in order to
account for changes in orientation due to length extension needed
reach the intended target. Examples of the corrections that can be
applied to the device are described below in one preferred
embodiment.
[0025] Following a suitable registration of the localization system
(used to generate the real-time location information) to the
navigation system, real-time catheter location and orientation
information can be used to render the catheter in a graphical
display which is either three dimensional or two dimensional such
as in X-ray projections. The three dimensional window, labeled 103
in FIG. 6, is a display on the user interface of the navigation
system wherein objects such as point locations, curves, surfaces,
device shapes, device tip locations and various other objects of
interest are graphically displayed in three dimensions, so that the
entire set of objects in the display may be rotated and viewed from
any orientation by suitable computer mouse movements. Likewise the
entire three dimensional display can be scaled up or down to choose
a desired level of zoom, most conveniently from a suitable use of
the mouse. Such a display significantly aids the understanding of
the spatial relationships between the objects of interest in the
anatomy. In the case of X-ray images the device tip, suitably
rendered graphically, can be overlaid or projected on at least one
static X-ray image to visualize real-time device position,
orientation and movement in an anatomical context, as shown in FIG.
4 at 74, while in the case of a three dimensional window in the
user interface the localized device can be displayed within this
window of the navigation system as shown by 72 in FIG. 4. By
overlaying an updated display of the catheter over the X-ray images
of the operating region, the graphical display provides a powerful
means of visualizing the catheter in real time without the need for
constantly updated fluoroscopic imaging, reducing the exposure to
radiation of both physician and patient.
[0026] Likewise the real-time location and orientation of the
device may be displayed (shown as 109 in FIG. 7) together with a
registered pre-operative three dimensional image of the anatomy of
interest (a heart is shown in FIG. 7 as an example), a surface
rendering (FIG. 8) of the anatomy of interest, an intraoperative
reconstruction of the anatomy of interest, or any other three
dimensional reconstruction of the anatomy.
[0027] The navigation system and method of the present invention
provide a means for accurately approaching a target destination in
the operating region of a patent. First, after input of the target
and the device base location and orientation, the present
navigation system initially determines a predicted insertion length
and orientation for deploying the catheter to the target
destination, and advances the catheter a fraction of the predicted
insertion length. In the preferred embodiment, this fraction is in
the range of 0.75 to 0.95, but may alternatively be any fraction
suitable for establishing an approach of the catheter tip 20 to the
destination target 28 as shown in FIG. 2. The fraction can be fixed
or it can be determined based on one or more variables. Next, the
real-time location and orientation are used to determine whether
the device tip is aimed directly at the target. If {right arrow
over (x)}.sub.0 is the current tip location, {right arrow over
(x)}.sub.t is the target location, and {right arrow over (t)} is
the current tip orientation (unit) vector, the normal {right arrow
over (n)}' to the plane defined by the catheter tip orientation and
the tip-to-target vector is {right arrow over (n)}=.left
brkt-bot.{right arrow over (t)}({right arrow over (x)}.sub.t-{right
arrow over (x)}.sub.0).right brkt-bot., which can be normalized by
defining {right arrow over (n)}={right arrow over (n)}'/|{right
arrow over (n)}'|. If the magnitude of {right arrow over (n)}' is
small, then the tip orientation is closely aligned with the target
and we are done. If not, a rotation about the unit normal {right
arrow over (n)} in a counterclockwise (m=.+-.1) or clockwise (m=-1,
with m defined as m=sign[(t.times.(x.sub.T-x.sub.0))n]) sense can
be used to point the catheter tip directly at the target. While the
extent of rotation is as yet undefined, in a semi-automated mode
the user can make such rotational adjustments by trial and error in
step-wise fashion until the real-time catheter tip can be seen to
be aimed directly at the target in graphical displays on the user
interface. The user does not need to specify the rotation axis,
since this is computed by the navigation system; only a step size
needs to be specified. In the case of a magnetic navigation system,
a magnetic field rotation of an angle .theta. about n can be
applied from suitable input buttons, in order to adjust the
orientation of the device tip. Buttons can be provided with
predetermined angle increments, which increments can dynamically
change depending on the error or other factors.
[0028] In one preferred implementation of a semi-automated mode,
small, medium and relatively large angular steps for .theta., such
as 2, 5 and 10 degrees respectively, are defined on the user
interface by means of suitable graphical buttons as shown in FIG. 4
at 78. Such steps can be iteratively applied by the user until the
catheter tip is seen to be aimed directly at the target in
graphical displays on the user interface directly, whereupon the
catheter can be advanced by a small amount in order to reach the
target. During the course of this iterative user application of
stepped moves, the above-described computation is repeatedly
performed and applied.
[0029] In another preferred embodiment, the above manually applied
process can be automated by means of a suitable graphical button as
shown in FIG. 4 at 76. For example, the system can apply a sequence
of small rotations, such as 2 degree steps, with the rotation axis
repeatedly updated as described above, until the tip alignment with
the desired target is satisfactory. A measure of tip alignment is
provided by the perpendicular distance, or its squared value D,
from the target to the line defined by the tip orientation vector
t. This measure or cost function D is given mathematically by
D=|({right arrow over (x)}.sub.t-{right arrow over
(x)}.sub.0)-{right arrow over (t)}[{right arrow over (t)}({right
arrow over (x)}.sub.t-{right arrow over (x)}.sub.0)]|.sup.2(1)
where the "" indicates a vector dot product. Once the tip alignment
is satisfactory, the catheter or other device may be advanced a
small amount in order to reach the target.
[0030] In another alternate embodiment, the automated method of
aligning the catheter tip with the target can be considerably
speeded up by the use of a rapidly converging algorithm based on
cost function minimization. In this case convergence is
mathematically guaranteed when adjustments are made in a single
plane. The process can start with this plane defined by the initial
catheter tip orientation and the tip-to-target vector. Where {right
arrow over (n)}.sub.0 is the corresponding unit normal as defined
earlier, this embodiment defines:
{right arrow over (y)}.sub.0={right arrow over (x)}.sub.0-{right
arrow over (n)}.sub.0[{right arrow over (n)}.sub.0({right arrow
over (x)}.sub.0-{right arrow over (x)}.sub.t)] (2)
{right arrow over (t)}.sub.p=[{right arrow over (t)}-{right arrow
over (n)}.sub.0({right arrow over (n)}.sub.0{right arrow over
(t)})]/|[{right arrow over (n)}-{right arrow over (n)}.sub.0{right
arrow over (t)})]| (3)
and the cost function
E=|({right arrow over (x)}.sub.t-{right arrow over
(y)}.sub.0)-{right arrow over (t)}.sub.p[{right arrow over
(t)}.sub.p({right arrow over (x)}.sub.t-{right arrow over
(y)}.sub.0)]|.sup.2 (4)
The function E as a function of the control variable (in the case
of magnetic navigation, the control variable is the magnetic field
orientation) has a minimum of zero when the tip-to-target vector
projected on the plane defined by {right arrow over (n)}.sub.0 is
aligned with (passes through) the target. Referring to FIG. 3, the
squared distance E illustrated by the general curve 52 as a
function of the field angle approaches zero at the optimum
orientation. To obtain this orientation, the initial functional
value E.sub.1 shown as 54 is determined using equation (4) for the
initial orientation angle, shown as 56 in FIG. 3, followed by an
adjustment process. The adjustment process is based on a quadratic
approximation of the behavior of the cost function and works as
follows in the case of a magnetic navigation system, it being
understood that a similar process may be constructed as well when
any other means of actuation is used by the navigation system.
[0031] Starting from the initial position with a cost function of
value E.sub.1, an initial rotation of the magnetic field about
{right arrow over (n)}.sub.0 is made in a sense defined by
m.sub.1=sign {.left brkt-bot.{right arrow over (t)}.sub.p({right
arrow over (x)}.sub.t-{right arrow over (p)}.sub.1).right
brkt-bot.{right arrow over (n)}.sub.0} where {right arrow over
(p)}.sub.1={right arrow over (y)}.sub.0+{right arrow over
(t)}.sub.p.left brkt-bot.{right arrow over (t)}.sub.p({right arrow
over (x)}.sub.t-{right arrow over (y)}.sub.0).right brkt-bot.. This
initial rotation is by an angular amount .theta..sub.2.about.10-30
degrees. Define initially .theta..sub.1=0. The catheter tip now
moves to a new position and orientation, the tip location and
orientation {right arrow over (x)}.sub.0 and {right arrow over (t)}
are updated from the new real-time location data, and new
quantities m.sub.2 and p.sub.2 are defined. The cost function
correspondingly has a new value E.sub.2., shown as 58 in FIG.
3.
[0032] The variable s can be defined as:
s = sign ( m 1 m 2 ) , and q = s ( E 2 E 1 ) 1 / 2 ##EQU00001##
[0033] Also define
.theta.*=(.theta..sub.2-q.theta..sub.1)/(1-q) (5)
and then apply a field rotation of (.theta.*-.theta..sub.2). The
values of .theta..sub.1 and .theta..sub.2 may be updated as:
.theta..sub.1.rarw..theta..sub.2, and .theta..sub.2.theta.*. The
real-time catheter tip position and orientation, and the other
quantities defined above including the cost function are also
updated as E.sub.1.rarw.E.sub.2, followed by a freshly evaluated
value of E.sub.2. The process is repeated until the value of E as
shown in FIG. 3 at points 60, 62 and 64 becomes sufficiently small,
or alignment with the target is achieved in the plane defined by
{right arrow over (n)}.sub.0; in practice convergence can be
achieved in a few iterations. In the preferred embodiment, the
predetermined minimum error is preferably less than 4 mm.sup.2 and
is achieved in only a few iterations, but may alternatively be any
value and any number of iterations that satisfies the level of
accuracy desired.
[0034] In the general case, at the end of this process, the
catheter may need a further adjustment in a second plane defined by
the present unit normal {right arrow over (n)}.sub.f (defined by
the catheter tip orientation and the tip-to-target vector); if so
the entire process above can be repeated one or more times.
[0035] It can be shown mathematically that alignment with the
target is certain at the completion of this step, at which point
the catheter can be advanced the remainder of the distance until
the target is reached.
[0036] In some cases the catheter device may deflect further by a
small amount as it is advanced the remainder of the distance to the
target. This can be corrected for by the use of a computational
model of device behavior that quantifies this further variation in
deflection. In the case of magnetic navigation, a linear dependence
of catheter tip orientation changes on field direction changes for
given lengths may be either pre-computed or calculated in real
time, and this information can be used to apply a further
correction of field orientation that will ensure the target is
accurately reached. These corrections to be applied to the device
are described below in one alternate embodiment.
[0037] Thus in an alternate embodiment of the present invention, a
supplemental correction method may also be utilized to correct for
variations in the magnetic field direction that may cause marginal
orientation error during advancement of the final distance to the
target destination. To correct for this error, the system uses a
virtual model of the catheter, to determine the orientation
.theta..sub.m,1 of the tip of the model catheter, which may differ
slightly from the actual orientation .theta..sub.a,1. A model-based
response coefficient is estimated as the ratio of the model
orientation .theta..sub.m,1 and the field angle .theta..sub.f,1
with respect to the base of the catheter. Using this coefficient, a
change in field angle to be applied to the tip of the catheter may
be determined as shown below:
.DELTA..theta. f , 1 = ( .theta. m , 1 - .theta. a , 1 ) k 1 ,
where k 1 = .theta. m , 1 .theta. f , 1 ( 6 ) ##EQU00002##
The navigation system may then apply the change in field angle and
further advance the catheter a second fraction of the predicted
length towards the target destination. The navigation system can
compute the updated orientation .theta..sub.m,2 of the tip of the
model catheter, the updated actual orientation .theta..sub.a,2 and
a new model-based response coefficient k.sub.2 from the ratio of
the updated model orientation and the changed field angle resulting
from the above equation (6). From the new response coefficient
k.sub.2, a new change in the field angle may be determined to apply
a field correction. This method may be repeated as necessary to
provide any level of correction accuracy desired.
[0038] Target locations and corresponding surface normals, or sets
of target locations may be sent to the navigation system from a
localization system for steering the catheter to these locations.
In particular, when it is desired to explore or visit portions of
the anatomy that have not been previously visited by the catheter,
interpolated locations may be sent from a surface rendering on the
localization system to the navigation system. The navigation system
can steer the catheter to these interpolated locations and beyond
if needed, thereby visiting more surface points to permit filling
in data gaps and construction of a more refined anatomical surface
rendering. The navigation system can steer the catheter in
semi-automated or automated manner in order to make the creation of
an anatomical map such as an electro-cardiogram or electrical
activity map of heart tissue considerably more efficient than a
manual trial and error method. FIG. 9A illustrates an electrical
activity surface rendering of an endocardial chamber, with gaps 111
in the surface where there was insufficient surface location data
to permit closing the surface. The navigation system can drive the
device to approximately reach an interpolated set of locations 113
shown in FIG. 9A and locations recorded when a suitable Electro
CardioGram signal is detected at the endocardial surface, thereby
permitting closure of the surface gaps as illustrated in FIG. 9B.
Likewise an idealized set of target locations, derived from an
idealized three dimensional anatomical model, can also be used to
make the mapping process more efficient. A drag method could also
be used to defined a set of points used to make the mapping process
more efficient, as shown in FIG. 5 at 82. While the field angle
remains applied to over-torque the tip of the medical device into
the tissue to establish contact, the device advancer may be
retracted to drag the tip along the surface for enabling continuous
acquisition of target points, which point locations may be suitably
entered using a graphical button as shown in FIG. 4 at 80.
[0039] The real time device location data can also be used in cases
where anatomical surface normal information is available to enhance
contact of a medical device with tissue for purposes of maintaining
a desired level of contact pressure, which is useful in the case of
catheter ablation in electrophysiological applications. In cardiac
applications when the device tip is within a use-specified distance
from the target and good intracardiac electrical signals are
maintained, a surface normal and device tip orientation vector may
be defined. The surface normal information could be provided from
three dimensional image data such as CT or MR data, or from an
electrical activity surface rendering such as those provided by
some localization systems such as the Carto system manufactured by
Biosense-Webster Inc. An axis could then be defined by the cross
product of the normal and orientation vector, and could be used to
change the control variables driving device configuration in a such
a manner as to increase tissue contact pressure. The amount of
rotation can be controlled by an over-torque slider shown as 70 in
FIG. 4, in an increased contact or decreased contact direction to
provide an intuitive control of catheter contact, where all of the
spatial computation of contact geometry is performed by the
navigation system. The surface normal 97 at the target location, as
obtained from the localization system and used in the computation
of contact geometry, is also shown in FIG. 4. The use of a refined
anatomical surface rendering could be used to determine a series of
target points for ablation, such as on the inner surface of a heart
chamber as shown in FIG. 6, along the line 84 comprising a series
of target points.
[0040] The steering control of the medical device can be further
augmented by the use of gated location data, for example where the
gating is performed with respect to ECG (Electro CardioGraph) data,
so that the device location is always measured at the same phase of
a periodic cycle of anatomical motion such as the cardiac cycle. In
a preferred embodiment, this data is input into the navigation
system together with the real-time location data.
[0041] It should be noted that the advancement of the medical
device could be manually controlled by a user input from an input
device such as a joystick, or it could automatically be controlled
by a computer. Alternatively, a joystick could also be used to
control the advancement of the catheter device within a fractional
amount of the length needed to approach the target destination,
after which the system could orient the tip of the catheter to
align with the target destination. Furthermore, a larger number of
intermediate course corrections can also be applied if desired
along the lines of the description given herein, in either
semi-automated (with user-driven advancement) or automated fashion.
Additional design considerations such as the above modifications
may be made without departing from the spirit and scope of the
invention. More particularly, the system and method may be adapted
to medical device guidance systems other than magnetic navigation
systems. Likewise, a variety of medical devices such as catheters,
cannulas, guidewires, microcatheters, endoscopes and others known
to those skilled in the art can be remotely guided according to the
principles taught herein. Accordingly, it is not intended that the
invention be limited by the particular form described above, but by
the appended claims.
Case 483
Efficient Closed Loop Feedback Navigation
Additional Multi-Modality Orientation Claims
[0042] 1.b The system according to claim 1 wherein the orientation
system for remotely orienting the distal end of the medical device
in a selected direction comprises at least one actuation means
selected from the group consisting of mechanical pull-wire
orientation means, mechanical advance, retraction, and orientation
means, piezo-electric orientation means, electrostrictive
orientation means, magnetostrictive orientation means, hydraulic
orientation means, and magnetic orientation means. 2.b The
navigation system according to claim 2 wherein the orientation
system for remotely orienting the distal end of the medical device
in a selected direction comprises at least one actuation means
selected from the group consisting of mechanical pull-wire
orientation means, mechanical advance, retraction, and orientation
means, piezo-electric orientation means, electrostrictive
orientation means, magnetostrictive orientation means, hydraulic
orientation means, and magnetic orientation means. 19.b The
navigation system according to claim 19 wherein the orientation
system for remotely orienting the distal end of the medical device
in a selected direction comprises at least one actuation means
selected from the group consisting of mechanical pull-wire
orientation means, mechanical advance, retraction, and orientation
means, piezo-electric orientation means, electrostrictive
orientation means, magnetostrictive orientation means, hydraulic
orientation means, and magnetic orientation means. 30.b The
navigation system according to claim 30 wherein the orientation
system for remotely orienting the distal end of the medical device
in a selected direction comprises at least one actuation means
selected from the group consisting of mechanical pull-wire
orientation means, mechanical advance, retraction, and orientation
means, piezo-electric orientation means, electrostrictive
orientation means, magnetostrictive orientation means, hydraulic
orientation means, and magnetic orientation means. 42.b The method
of controlling a navigation system according to claim 42 wherein
the orientation system for remotely orienting the distal end of the
medical device in a selected direction comprises at least one
actuation means selected from the group consisting of mechanical
pull-wire orientation means, mechanical advance, retraction, and
orientation means, piezo-electric orientation means,
electrostrictive orientation means, magnetostrictive orientation
means, hydraulic orientation means, and magnetic orientation means,
the method further comprising controlling the actuation means to
align the medical device distal end with the predicted orientation.
44.b The method of controlling a navigation system according to
claim 44 wherein the orientation system for remotely orienting the
distal end of the medical device in a selected direction comprises
at least one actuation means selected from the group consisting of
mechanical pull-wire orientation means, mechanical advance,
retraction, and orientation means, piezo-electric orientation
means, electrostrictive orientation means, magnetostrictive
orientation means, hydraulic orientation means, and magnetic
orientation means, and wherein the step of operating the
orientation system comprises controlling at least one orientation
system variable associated with the at least one actuation means.
56.b The method of controlling a navigation system according to
claim 56 wherein the orientation system for remotely orienting the
distal end of the medical device in a selected direction comprises
at least one actuation means selected from the group consisting of
mechanical pull-wire orientation means, mechanical advance,
retraction, and orientation means, piezo-electric orientation
means, electrostrictive orientation means, magnetostrictive
orientation means, hydraulic orientation means, and magnetic
orientation means, and wherein the step of applying a magnitude of
orientational adjustment in the determined adjustment direction
comprises controlling at least one orientation system variable
associated with the at least one actuation means. 61.b The method
of controlling a navigation system according to claim 61 wherein
the orientation system for remotely orienting the distal end of the
medical device in a selected direction comprises at least one
actuation means selected from the group consisting of mechanical
pull-wire orientation means, mechanical advance, retraction, and
orientation means, piezo-electric orientation means,
electrostrictive orientation means, magnetostrictive orientation
means, hydraulic orientation means, and magnetic orientation means,
and wherein least one of the predicted orientation system variable
is associated with the at least one actuation means.
* * * * *