U.S. patent application number 10/985340 was filed with the patent office on 2005-06-02 for catheter navigation within an mr imaging device.
Invention is credited to Broaddus, William C., Garibaldi, Jeffrey M., Gillies, George T., Hastings, Roger N..
Application Number | 20050119556 10/985340 |
Document ID | / |
Family ID | 25094240 |
Filed Date | 2005-06-02 |
United States Patent
Application |
20050119556 |
Kind Code |
A1 |
Gillies, George T. ; et
al. |
June 2, 2005 |
Catheter navigation within an MR imaging device
Abstract
A method of magnetically manipulating a medical device within a
body part of a human patient in conjunction with MR imaging
includes applying a navigating magnetic field with magnets from the
MR imaging device, and changing the magnetic moment of the medical
device to change the orientation of the medical device within the
body part
Inventors: |
Gillies, George T.;
(Charlottesville, VA) ; Hastings, Roger N.; (Maple
Grove, MN) ; Garibaldi, Jeffrey M.; (St. Louis,
MO) ; Broaddus, William C.; (Midlothian, VA) |
Correspondence
Address: |
HARNESS, DICKEY, & PIERCE, P.L.C
7700 BONHOMME, STE 400
ST. LOUIS
MO
63105
US
|
Family ID: |
25094240 |
Appl. No.: |
10/985340 |
Filed: |
November 10, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10985340 |
Nov 10, 2004 |
|
|
|
10429524 |
May 5, 2003 |
|
|
|
6834201 |
|
|
|
|
10429524 |
May 5, 2003 |
|
|
|
09772188 |
Jan 29, 2001 |
|
|
|
Current U.S.
Class: |
600/410 |
Current CPC
Class: |
G01R 33/285 20130101;
A61B 2034/732 20160201; A61M 25/01 20130101; A61B 34/73 20160201;
A61B 5/055 20130101; A61B 5/06 20130101 |
Class at
Publication: |
600/410 |
International
Class: |
A61B 005/05 |
Claims
We claim:
1. A method of navigating a medical device having a variable
magnetic moment within an operating region within a patient, using
an MR imaging device, the method comprising: applying a static
magnetic field to the operating region with an external magnet of
an MR imaging device; creating temporary magnetic moments in the
medical device to change the orientation of the medical device with
respect to the static magnetic field, and orient the medical device
in a selected direction within the operating region.
2. The method according to claim 1 further comprising the step of
varying the direction of the static magnetic field applied to the
operating region by the external magnet of an MR imaging device to
change the orientation of the medical device.
3. The method according to claim 1 wherein the medical device
comprises at least one electromagnetic coil, and wherein the step
of creating temporary magnetic moments in the medical device
comprises energizing the at least one electromagnetic coil.
4. The method according to claim 1 wherein the MR imaging device is
used to image the operating region in the patient's body between
navigations.
5. The method according to claim 1 in which the medical device
comprises at least one set of three current carrying coils, and the
step of creating temporary magnetic moments in the medical device
comprises apply current to one or more of the current carrying
coils
6. The method according to claim 5 wherein there are at least two
sets of three current carrying coils.
7. The method according to claim 1 in which the medical device
comprises at least one set of three current carrying coils, and
wherein the coils are used to receive signals during MR imaging to
determine at least one of the location and orientation of the
medical device.
8. The method according to claim 1 in which the medical device
comprises at least one set of three current carrying coils, and
wherein the coils are used to transmit and/or receive signals
during MR imaging to enhance imaging adjacent the medical
device.
9. The method according to claim 5 wherein the coils are mutually
orthogonal.
10. The method according to claim 5 further comprising actively
removing heat from the medical device generated by the current
carrying coils.
11. The method according to claim 10 wherein heat is removed by
circulating a cooling medium with the medical device.
12. The method according claim 10 wherein heat is removed using
thermoelectric devices.
13. The method according to claim 10 wherein heat is removed using
a heat pipe.
14. A method of navigating a medical device within an operating
region in the body of a patient, the medical device having at least
one coil therein, the method comprising: establishing a navigating
magnetic field in the operating region with an MR imaging device
outside of the patient's body; selectively energizing the at least
one coil in the medical device to create a magnetic moment in the
medical device and creating a torque tending to align the magnetic
moment of the magnetic medical device with the applied magnetic
field.
15. The method according to claim 14 further comprising varying the
direction and/or intensity of the applied magnetic field applied by
the MR imaging device to orient the medical device
16. The method according to claim 14 wherein the step of
selectively energizing the at least one coil comprises applying
electrical energy in pulses to the at least one coil in the medical
device.
17. The method according to claim 16 wherein the medical device is
flexible and has a characteristic recovery time in which the device
recovers from being flexed, and wherein the time between pulses in
less than the characteristic recovery time of the medical
device.
18. In a method of navigating a medical device by applying a static
magnetic field and selectively changing the magnetic moment of the
medical device to change the orientation of the medical device, a
method of turning the medical device on a plane perpendicular to
local applied field direction in two steps comprising applying a
magnet current to the medical device to bend the medical device out
of the plane of the desired turn and subsequently applying a magnet
moment to the medical device to cause the medical device to turn
back into the plane of the desired turn, in the desired
orientation.
19. A system for navigating a medical device within an MRI
consisting of a medical device containing at least one set of three
orthogonal current carrying coils, power supplies for energizing
said coils, a computer for controlling said power supplies, and an
MRI images of the local environment of the coils, said images used
by an operator to guide the movements of said medical device
through a computer interface.
20. The system of claim 19 in which local visualization of tissues
is additionally provided to guide navigation.
21. The system of claim 20 in which visualization is optical.
22. The system of claim 20 in which visualization is through an
ultrasonic image.
23. The system of claim 19 in which said coils are energized with
pulses of currents, the root-mean-square values of which exceed
direct current levels that overheat the catheter.
24. The system of claim 19 in which currents are applied to the
coils to produce oscillatory or periodic movements of the catheter
tip.
25. A method for rotating a catheter tip containing a variable
magnetic moment about the direction of an external magnetic field
with which the moment interacts, the method consisting of directing
the magnetic moment vector in a series of directions which
successively rotate the catheter tip out of and into the plane
perpendicular to the field direction.
26. A method of navigating an elongate medical device within an
operating region in the body of a patient, the medical device
having a proximal end, a distal end, and at least one coil adjacent
the distal end, the method comprising: introducing the distal end
of the medical device into the operating region in the patient's
body; establishing a navigating magnetic field in the operating
region with a magnet of an MR imaging system; selectively
energizing the at least one coil adjacent the distal end of the
elongate medical device to create a magnetic moment at the distal
end of the elongate medical device to turn the distal end of the
elongate medical device in the desired direction.
27. The method according to claim 26 further comprising varying the
direction and or intensity of the navigating magnetic field applied
by the MR imaging device to orient the elongate medical device.
28. The method according to claim 26 wherein the step of
selectively energizing the at least one coil comprises applying
electrical energy in pulses to the at least one coil in the medical
device.
29. The method according to claim 26 wherein the elongate medical
device is flexible, and has a characteristic recovery time in which
the device returns to its normal configuration from a deflected
configuration, and wherein the at least one coil is energized at a
pulse rate faster than the characteristic recovery time of the
elongate medical device
30. The method according to claim 29 wherein the coil is pulsed to
retain the coils below a temperature that is harmful to tissue.
31. The method according to claim 29 wherein the at least one coil
is pulsed to retain a temperature below about 45.degree. C.
32. The method according to claim 29 wherein the at least one coil
is pulsed to retain a balance between the heat generated in the
coil and the heat conducted from the coil by the flow of body
fluids past the coils.
33. The method according to claim 26 wherein there are at least two
coils adjacent the distal end of the magnetic medical device.
34. The method according to claim 33 wherein there are at least
three coils adjacent the distal end of the magnetic medical
device.
35. The method according to claim 26 wherein there are three coils
spaced around the circumference of the magnetic medical device.
36. The method according to claim 26 wherein at least one coil
extends around the circumference of the magnetic medical
device.
37. The method according to claim 26 wherein the coils are used to
locate the magnetic medical device.
Description
FIELD OF THE INVENTION
[0001] This invention relates to an apparatus for navigating
medical devices within the body to sites of treatment delivery, and
methods of using this apparatus to achieve this navigation. More
specifically, this invention relates to the use of a magnetic field
from an MR imaging device to navigate a magnetic medical device
within the body.
BACKGROUND OF THE INVENTION
[0002] The need for improved surgical navigation techniques
stimulated the development of magnetic stereotaxis as a novel means
for guiding a surgical implant, such as a catheter, along nonlinear
paths within a body part. In particular, it is useful in
intraparenchymal applications within the brain, where linear
stereotactic techniques (either framed or frameless) do not permit
the probe to follow single-pass curvilinear paths to a target
location deep within the brain, as first taught by Howard et al. in
U.S. Pat. No. 4,869,247 incorporated herein by reference. Howard et
al. subsequently taught magnetic stereotactic techniques for
volume-contoured therapy delivery within the brain and elsewhere in
the human body in succeeding U.S. Pat. Nos. 5,125,88, 5,707,334,
and 5,779,694 incorporated herein by reference. Advanced versions
of magnetically guided surgical systems capable of performing
magnetic stereotactic procedures in the brain and in other body
parts have been disclosed in U.S. patents by Werp et al., U.S. Pat.
No. 5,9331,818; Blume et al., U.S. Pat. No. 6,014,580; Werp et al.,
U.S. Pat. No. 6,015,414; Ritter et al., U.S. Pat. No. 6,128,174;
and Blume et al., U.S. Pat. No. 6,157,853. In all of these
approaches, as well as in any of the other known techniques for
magnetic manipulation of a probe mass or implant located within the
body (see Gillies et al., "Magnetic manipulation instrumentation
for medical physics research," Review of Scientific Instruments,
pp. 533-562 (USA 1994)), incorporated herein by reference, the
controlled movement of the probe mass or implant is actuated by a
magnetic field created external to the body. In all such
arrangements the magnetic component of the implant (typically
located at the tip of a catheter) is a passive ferromagnetic or
permanent magnetic element of a geometry consistent with that of
the catheter's form and function, and within which there either
exists or can be made to exist, adequate magnetic moment to create
the forces and torques needed to steer and/or guide the implant
within the body part into which it has been inserted.
[0003] Magnetic stereotaxis is particularly useful for navigation
of medical devices throughout body tissues, cavities, and vessels.
Discussion of applications to catheter navigation within the
chambers of the heart for electrophysiologic mapping and ablation
can be found in Hall et al., U.S. patent application Ser. No.
09/405,314, incorporated herein by reference. Disclosure of
navigation of catheters within the myocardial tissue of the heart
can be found in Sell et al., U.S. patent application Ser. No.
09/398,686, incorporated herein by reference. Removal of tissues
from body lumens and cavities via magnetic navigation of
atherectomy tools is disclosed in Hall et al., U.S. patent
application Ser. No. 09/352,161, incorporated herein by reference.
Catheters for magnetic navigation within the blood vessels of the
brain and other body parts are disclosed in Garibaldi, U.S. Patent
Application Ser. No. 60/153,307, incorporated herein by
reference.
[0004] Four inherent limitations to this general design of magnetic
stereotaxis system are the following. First, it is generally unsafe
to perform magnetic resonance (MR) imaging studies during or after
a magnetic stereotaxis procedures in which the magnetic element of
the implant is still resident within the patient, as might be
contemplated in situations where updated MR data might be needed
for ongoing magnetic stereotaxis navigation requirements. This is
because the large fields intrinsic to all types of MR scanners
(either standard bore-type systems or the lower-field
interventional-style systems) are large enough to cause otherwise
uncontrolled displacement of the implant within the patient. The
nature of this particular problem is discussed in the broader
context of MR-driven forces on implants, by Planert et al.,
"Measurements of magnetism-related forces and torque moments
affecting medical instruments, implants, and foreign objects during
magnetic resonance imaging at all degrees of freedom," Medical
Physics, pp. 851-856 (USA 1996) and by Manner et al., "MR Imaging
in the presence of small circular metallic implants," Acta
Radiological, pp. 551-554 (Denmark 1996), the disclosures of both
of which are incorporated herein by reference.
[0005] A second limitation of the existing art is that relatively
complex arrangements of magnetic field sources external to the
patient must be assembled and controlled in order to carry out
magnetic stereotactic movement of the implant. A single static
background field is virtually always inappropriate for effecting
controlled movement of the magnetic element in the implant used in
existing magnetic stereotaxis procedures. A third limitation,
related to the second, is that a magnetic element left in the brain
or another body part can create a significant imaging artifact when
that body part is imaged by an MR scanner, most typically rendering
that imaging data set useless or of greatly reduced diagnostic and
therapeutic value to the clinician and patient.
[0006] A fourth limitation is that appreciably and clinically
precious time could be lost when carrying out a sequential and
reciprocal process of conducting a magnetic stereotaxis procedure
that must be interleaved with intra-operative MR imaging studies
for diagnostic, therapeutic or navigational purposes. These
limitations are not traversed by Kucharczyk et al. in their U.S.
patent application Ser. No. 09/174,189 and in their International
application Ser. No. PCT/US99/24253, (the disclosure of both of
which are incorporated herein by reference), which teach means for
serial and reciprocal movement of the patient from a magnetic
stereotaxis system to an MR scanner for purposes of updating the
imaging information used for the reference portion of the magnetic
stereotaxis procedure.
[0007] A more nearly ideal situation would arise if it were
possible to integrate the form and function of a MR scanner and a
magnetic stereotaxis system in such a way that magnetic stereotaxis
procedures could be carried out within an MR scanner (or vice
versa), and all done in such a way that the form and function of
the MR scanning process would not interfere with those of the
magnetic stereotaxis process, but that the respective forms and
functions would instead complement and/or enhance each other. The
subject of the present invention is a means and technique that
accomplishes this goal and circumvents the existing limitations by
incorporating a triaxial arrangement of miniature electromagnets as
the magnetic element at the tip of the medical device or catheter.
By externally regulating the electrical currents that pass through
each of the independent coils, the torque and force on the tip of
the medical device or catheter can be made to react to a static
magnetic field of a MR scanner in such a way that the tip of the
medical device or catheter can be guided along a preferred path to
reach a target location within a brain or other body part. The
resulting means and technique will thus exhibit all of the
advantages of conventional magnetic stereotaxis (primarily the
ability to navigate the medical device or catheter along complex
curvilinear paths), while incorporating the further advantages of
rapid sequential MR imaging of the patient, without introducing
imaging artefacts on the MR images, since imaging is performed
during periods when no currents flow through the triaxial coil
components.
[0008] Medical devices with one or more miniaturized coils on them
have been disclosed for a variety of other purposes, but none have
been designed for use as the actuator in a combined magnetic
stereotaxis and MR imaging process such as the type that is the
subject of the present invention. Instead, such coil systems have
been limited in function to identifying the location of the probe
(in which they are housed) in relation to the body part into which
the probe is inserted. Examples of such disclosures include
Grayzel, U.S. Pat. No. 4,809,713; Dunoulin et al., U.S. Pat. No.
5,211,165; Twiss et al., U.S. Pat. No. 5,375,596; Acker et al.,
U.S. Pat. No. 5,558,091; Martinelli, U.S. Pat. No. 5,592,939;
Calhoun et al., U.S. Pat. No. 5,606,980; Golden et al. U.S. Pat.
No. 5,622,169; Shapiro et al., U.S. Pat. No. 5,645,065; Heruth et
al., U.S. Pat. No. 5,713,858; Watkins et al., U.S. Pat. No.
5,715,822; Saad, U.S. Pat. No. 5,727,553; Weber et al., U.S. Pat.
No. 5,728,079; Acker, U.S. Pat. No. 5,729,129; Darrow et al., U.S.
Pat. No. 5,730,129; Young et al., U.S. Pat. No. 5,735,795; Glantz,
U.S. Pat. No. 5,749,835; Acker et al., U.S. Pat. No. 5,752,513;
Slettenmark, U.S. Pat. No. 5,758,6670; Polvani, U.S. Pat. No.
5,762,064; Kelly et al., U.S. Pat. No. 5,787,886; Vesely et al.,
U.S. Pat. No. 5,797,849; Ferre et al. U.S. Pat. No. 5,800,352;
Kuhn, U.S. Pat. No. 5,810,728; Young et al., U.S. Pat. No.
5,817,017; Young et al., U.S. Pat. No. 5,819,737; Kovacs, U.S. Pat.
No. 5,833,603; Crowley, U.S. Pat. No. 5,840,031; Webster, Jr. et
al., U.S. Pat. No. 5,843,076; Johnston et al., U.S. Pat. No.
5,843,153; Lemelson, U.S. Pat. No. 5,845,646, Lemelson, U.S. Pat.
No. 5,865,744, Glowinski et al., U.S. Pat. No. 5,868,674; Horzewski
et al., U.S. Pat. No. 5,873,865; Haynor et al., U.S. Pat. No.
5,879,297; Daum et al., U.S. Pat. No. 5,895,401; Ponzi, U.S. Pat.
No. 5,897,529; Golden et al., U.S. Pat. No. 5,902,238; Vander Salm
et al., U.S. Pat. No. 5,906,579; Weber et al., U.S. Pat. No.
5,908,410; Lee et al., U.S. Pat. No. 5,911,737; Bladen et al., U.S.
Pat. No. 5,913,820; Snelten et al., U.S. Pat. No. 5,916,162;
Lemelson, U.S. Pat. No. 5,919,135; Chen et al., U.S. Pat. No.
5,921,244; Navab, U.S. Pat. No. 5,930,329; Rasche et al., U.S. Pat.
No. 5,938,599; Lloyd, U.S. Pat. No. 5,938,602; Ponzi, U.S. Pat. No.
5,938,603; Johnson, U.S. Pat. No. 5,941,858; Cermak. U.S. Pat. No.
9,941,889; Johnson et al., U.S. Pat. No. 5,944,023; Derbyshire et
al., U.S. Pat. No. 5,947,900; Beisel, U.S. Pat. No. 5,947,940; Van
Vaals et al., U.S. Pat. No. 5,951,472; Lev, U.S. Pat. No.
5,951,566; Rogers et al., U.S. Pat. No. 5,951,881; Wan, U.S. Pat.
No. 5,952,825; Rosenberg et al., U.S. Pat. No. 5,959,613; Ponzi,
U.S. Pat. No. 5,964,757; Ferre et al., U.S. Pat. No. 5,967,980;
Wittkampf, U.S. Pat. No. 5,983,126; Taniguchi et al., U.S. Pat. No.
5,997,473; Mouchawar et al., U.S. Pat. No. 6,002,963; Van Der Brug
et al., U.S. Pat. No. 6,006,127; Pflueger, U.S. Pat. No. 6,013,038;
Vesely et al., U.S. Pat. No. 6,019,725; Webb, U.S. Pat. No.
6,019,726; Murata, U.S. Pat. No. 6,019,737; Wendt et al., U.S. Pat.
No. 6,023,636; and Holdaway et al., U.S. Pat. No. 6,083,166. The
disclosures of all of the foregoing are incorporated herein by
reference. Other uses for miniature coils or microcoils on
catheters include the controlled introduction of local
electromagnetic fields during the MR imaging process for the
purpose of improving imaging contrast in the tissues adjacent to
the catheter or probe, as taught for instance by Truwit et al.,
U.S. Pat. No. 5,964,705, incorporated herein by reference.
Miniature triaxial arrangements for field sensing in medical probes
have been disclosed by Acker, U.S. Pat. No. 5,833,608,
incorporating herein by reference. Additional publications that
document related uses for microcoils on catheters for either
tracking or imaging purposes include the papers of Wildermuth et
al., "MR Inaging-guided intravascular procedures: initial
demonstration in a pig model," Radiology, 578-583 (USA 1997),
Bakker et al., "MR-guided endovascular interventions:
susceptibility-based catheter and near-real-time imaging
technique," Radiology, pp. 273-276 (USA 1997), Rasche et al.,
"Catheter tracking using continuous radial MRI," MRM, pp. 963-968
(USA 1997), Worley, "Use of a real-time three-dimensional magnetic
navigation system for radiofrequency ablation of accessory
pathways," PACE, pp. 1636-1645 (USA 1998), Burl et al.,
"Twisted-pair RF coil suitable for locating the track of a
catheter," MRM, pp. 636-638 (USA 1999) and Coutts et al,
"Integrated and interactive position tracking and imaging of
interventional tools and internal devices using small fiducial
receiver coils," MRM, pp.908-913 (USA 1998). The disclosures of
which are incorporated by reference. Coils in the catheter tip can
be used to both locate the tip, and to measure the orientation of
the tip in three dimensional space, as discussed by Shapiro et al,
U.S. Pat. No. 5,645,065, and Haynor et al, U.S. Pat. No. 5,879,297,
the disclosures of which are incorporated by reference.
SUMMARY OF THE INVENTION
[0009] The invention relates to the interaction between the static
magnetic field of an MR scanner and one or more independent
magnetic dipole moments created by a plurality of electromagnetic
elements that are located within a medical device or catheter
within a patient. The concept of utilizing a variable magnetic
moment in the tip of a catheter for navigation in a static magnetic
field was disclosed by Garibaldi et al., U.S. patent application
Ser. No. 09/504,835, which is incorporated herein in its entirety
by reference. Garibaldi et al. discusses a variety of permanent and
electromagnetic means for generating a variable moment at the
catheter tip for navigation in a static field, which may be
energized for the purpose of navigation. The present invention
employs the static field of an MRI imager, and the combined
sequential processes of navigation and MR imaging. Our discussion
focuses on the static field of an MR imager which is always on, and
for practical purposes cannot be turned off or otherwise changed or
interrupted. For this reason, the present invention cannot employ
permanent or inducible magnetic materials within the medical
device. Consequently, the variable moment must be generated by
coils, and preferably air-core coils.
[0010] If a static magnetic field H is acting along the z direction
of the bore of a MR imaging, and a magnetic dipole moment m is
present in the magnetic element of an implanted probe or catheter,
then the vectors representing H and m in a three-dimensional space
can be written H=Hk along the z-axis and
m=m.sub.xi+m.sub.yj+m.sub.zk and the torque experienced by the
dipole moment in the field of the MR scanner is .tau.=m.times.B.
The x, y, and z components of the moment m are controlled
independently, so that the vector m can point in any arbitrary
direction in three dimensional space.
[0011] Evaluation of the vector cross product produces the
components .tau..sub.x=m.sub.yH, .tau..sub.y=-m.sub.xH, and
.tau..sub.z=0. The torque acting on the dipole is perpendicular to
m and H and in this case has no component about the z-axis along
which the magnetic field lies. It is possible, however, to navigate
a catheter to points lying in the plane perpendicular to H via
successive small displacements of the moment out of this plane.
This process can be referred to as compound rotation about the H
axis. The first step in the process is to rotate the catheter tip
upward out of the x-y plane at an angle which advances the catheter
projection on the x-y plane, followed by a second rotation which
rotates the catheter back down to the x-y plane, while once again
advancing the catheter orientation angle. The net rotation of the
catheter tip about the z-axis thus follows a sawtooth or triangular
trajectory, each step in the advancement being made up of two
allowed out-of-plane rotations.
[0012] One can make numerical estimates of the sizes of the torques
that can act on the dipole in the presence of the MR scanner field
by noting that the magnitude of the torque is given by expanding
the cross product .tau.=m.times.H to obtain .tau.=mH cos .theta.
where .theta. is the angle between m and H. .tau. is a maximum when
.theta.=90.degree.. If the dipole moment is produced by a coil that
has N turns of wire windings carrying an electrical current I, and
has a cross-sectional area A, then the expression for the torque
acting on the coil can be written as .tau.=NIAB where B=.mu..sub.oH
defines the relationship between the magnetic induction B and the
magnetic field strength H, with .mu..sub.o being the permeability
of free space. As a practical example of the application of these
principles in a clinically realistic setting, the mechanical torque
required to rotate a dipole moment produced by 350 turns of wire
carrying 1.4 A of current and having a diameter of 2 mm with
associated cross-sectional area of 3.14.times.10.sup.-6 m.sup.2
would be 2.3.times.10.sup.-3 N-m or 230 gram-mm in a MR scanner
field of 1.5 T. If this coil is 5 mm long, the effective force
couple producing the torque is 230/5=46 grams, which is adequately
large for catheter navigation.
[0013] In the preferred embodiment of the present invention, three
miniaturized coils of appropriate length, radius and current
carrying capacity are assembled into a triaxial configuration in
which the cross-sectional planes of each are orthogonal to those of
the others. There are a number of different ways of doing this. In
one preferred embodiment, the coils are wound on a common hollow
coil form or mandrel in the shape of a rectangular parallelepiped
that is made from non-conducting, non-susceptible materials which
are MR compatible. In one embodiment, the coils are approximately 1
cm in length, have a diameter of 2 mm and a thickness of 0.25 mm.
One transverse coil is wound around a long axis of the
parallelepiped mandrel, a second transverse coil is wound along the
other long axis perpendicular to the first and the third (axial)
coil is wound around the other two. The latter coil has a similar
cross sectional area times number of turns as the transverse coils,
so that all three coils have approximately equal dipole moment
magnitude for equal energizing currents. This assembly is fixed
inside the tip of a supple catheter with the leads from the coils
brought down the internal length of the catheter tube to an exit
point at which they are connected to three independent power
supplies, one for each coil.
[0014] Cooling water or some other heat exchange medium can be made
to flow through an internal jacket inside the catheter, thus
bathing the triaxial coil assembly and carrying away a substantial
amount of the heat generated during operation of the independent
coils. The amount of cooling power available to the coils limits
the level of current flow and ohmic heating that they can sustain;
for example 16 W of cooling would establish a limit of 2.3 A
maximum per coil assuming that the total resistance of a given coil
is approximately 3 .OMEGA.. The pressure driving the flow would
ideally be 100 psi or less, with the flow entering the catheter at
body temperature and leaving it at some higher temperature governed
by considerations of patient safety and comfort.
[0015] With the coils being open circuit at the beginning of a
procedure, the patient is imaged, and the location of the catheter
noted. The coils themselves, rather than being passive open circuit
coils, could actually serve as pick up coils for the MRI rf signal,
providing an enhanced image at the site of the catheter, as
discussed in the cited literature. Following this essentially real
time imaging, the coils are energized, following the predictions of
a coil-current vs. torque algorithm that would determine the
catheter's directional advancement within the MR scanner's field,
thus permitting the tip of the catheter to be steered along a
desired direction. Subsequent imaging sequences are then carried
out to verify the new location of the catheter's tip, and the next
movement sequence is then planned and executed.
[0016] In some modern MRI machines, the patient can actually be
rotated during a procedure relative to a transverse MRI magnetic
field residing in a gap between magnets. Such patient rotations may
be employed to further enhance navigation. In particular, the
patient may be rotated in these machines to ensure that maximum
torque can always be applied about directions that would otherwise
be parallel with the MRI field.
[0017] Using this means and technique, catheters can be manipulated
through a body part, for example the brain, and positioned such
that the lumen of the catheter is left along a curvilinear path
that might be optimized for contoured drug delivery for the
treatment of a neurodegenerative disorder intrinsic to the brain.
Many other possible scenarios can also be achieved in the same way,
for instance the nonlinear stereotactic guidance of an electrode
for recording of potentials, ablation of a zone of tissue or deep
brain stimulation for pain or tremor control. Likewise,
electrophysiological mapping and ablation procedures can be carried
out within the chambers of the heart. We note that the cooling
required to adequately energize the coils can also cool the
electrode tip of an ablation catheter. Such cooling results in
larger ablative lesions, with fewer complications associated with
clot formation on the electrode tip. Steering of catheters and
devices can also be carried out within the endovascular system, for
diagnostic and therapeutic purposes.
[0018] A host computer can coordinate and control the power
supplies used to drive the individual coils, interpreting
instruction from a clinician operating an intuitive interface such
as a joy stick. The control algorithm requires as input the present
orientation of the triaxial coil assembly within the patient, the
direction and magnitude of the MR scanner field at the location of
the triaxial coil assembly, the desired new angular orientation or
curvilinear displacement that is to be taken in the next step in
the movement sequence, and any related anatomical or physiological
information about the patient as might be required to safely and
efficaciously carry out the procedure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a schematic diagram of a system for implementing
the method of this invention;
[0020] FIG. 2a is a schematic diagram of a catheter adapted for use
with the method of this invention;
[0021] FIG. 2b is a schematic diagram of a triaxial coil system
wound on a rectangular parallelepiped coil form or mandrel;
[0022] FIG. 2c is a schematic diagram of the structure of a
triaxial coil system formed from the nesting together of three
orthogonally oriented planar coils each having a circular cross
section;
[0023] FIG. 3a is an enlarged partial longitudinal cross-sectional
view of the distal tip of a catheter adapted for use in the method
of this invention;
[0024] FIG. 3b is an enlarged transverse cross-sectional view of
the distal tip of a catheter, adapted for use in the method of this
invention; adapted for fluid cooling;
[0025] FIG. 4 is a schematic diagram of the electrical connections
and components for a system for implementing the method of this
invention;
[0026] FIG. 5 is a schematic diagram of a cooling system adapted
for use in the system for implementing the method of this
invention;
[0027] FIG. 6 is a schematic diagram showing the navigation of a
catheter in the cerebrovasculature of a human patient in accordance
with the method of this invention;
[0028] FIG. 7a is a schematic diagram of the head of a human
patient, illustrating the navigation of a catheter through the
intraparenchymal tissues of the brain of the patient;
[0029] FIG. 7b is a schematic diagram of the head of a human
patient, illustrating the navigation of a catheter through the
intraparenchymal tissues of the brain of the patient;
[0030] FIG. 8 is a flow chart of the method of navigating a medical
device in accordance with the method of this invention;
[0031] FIG. 9 is a flow chart of the computational algorithm that
could be used to execute the method of navigating a medical device
in accordance with the method of this invention;
[0032] FIGS. 10a, 10b, 10c and 10d are schematic view of successive
steps in a method for accomplishing rotation about the H field
direction using compound rotations in accordance with the
principles of this invention;
[0033] FIGS. 11a, 11b, 11c and 11d are schematic views of
successive steps in a method for accomplishing rotation about the H
field direction using compound rotations in accordance with the
principles of this invention; and
[0034] FIGS. 12a and 12b are schematic diagrams illustrating
unidirectional torque applied to a catheter, for example to relieve
strain built up in the catheter due to multiple torques applied in
one direction.
DETAILED DESCRIPTION OF THE INVENTION
[0035] Referring to the drawings, FIG. 1 is a schematic of a system
for carrying out a stereotactic procedure in accordance with the
method of this invention. A patient 1 rests on the gurney or
transport table 2 of an interventional MR imager 3, as supplied,
for example, by Fonar Corp., Melville, N.Y. The procedure might
alternatively be carried out inside the bore of a standard high
field MR scanner, as supplied, for example, by Philips Medical
Systems, Best, The Netherlands. A catheter 4 is disposed within the
body of the patient 1. Leads 5 from the catheter 4 are connected to
the power supplies or amplifiers 10, 11, 12 each of which drives
one of three coils located inside the tip of the catheter 4. The
power supplies 10, 11, 12 are controlled by an algorithm resident
in the host computer 9. The physician (not shown) views the
location of the catheter tip inside the body and the structure of
the body part on the monitors 7 of the MR scanner 3. The monitors 7
show the sagittal, axial and coronal views and a composite
three-dimensional view of the body part and the location of the
catheter's tip. The physician adjusts the controls 6 that determine
the parameters operating in the host computer's algorithm, in such
a way that the next desired location or orientation of the
catheter's tip is projected on the monitors 7. The physician then
implements the motion sequence by activating the algorithm, and
then observes the new location of the catheter's tip on the
monitors 7. The surgeon or physician's instructions are conveyed
from the control panel 6 to the host computer 9 over the system's
control/data bus. Alternatively, the physician can pre-plan the
path of the catheter tip on a suitable interface, and the catheter
can then be directed along the desired path entirely under computer
control.
[0036] FIG. 2a is a schematic view of a catheter (4 in FIG. 1). An
outer lumen 13 houses an inner lumen 14. A triaxial coil 23 is
located inside the tip of the inner lumen 14 near the distal end of
the outer lumen 13. The distal end of the outer lumen 13 is coupled
to the main body of the outer lumen via a soft and pliable coupling
24 that permits easy and rapid articulation of the distal end. The
proximal end of the outer lumen 13 connects to cooling water inlet
tube 19 which is connected to a source of cooling water 21. The
inner lumen 14 of the catheter 4 is connected to the water inlet
tube 19 by a tubular means 15 internal to the outer lumen 13. The
proximal end of the outer lumen 13 also connects to cooling water
outlet tube 20 through which the flux of cooling water 22 flows.
The leads 5 from the triaxial coil 23 extend from the proximal end
of the catheter's outer lumen 13 and are separated into three pairs
16, 17, 18 one for each of the microcoils in the triaxial coil.
FIG. 2b shows one preferred embodiment of the triaxial coil 23
based on a rectangular parallelepiped coil frame 25 on which are
wound orthogonally oriented microcoils 26, 27, 28 each of which has
one pair of the jumper wires 29, 30, 31 that make contact with one
of the corresponding pair of the set of lead wires 5 that then run
the length of the inner lumen 14. The lead wires 5 can
alternatively pass through lumen 14, or be embedded in the material
making up the various walls of the catheter. FIG. 2c shows another
preferred embodiment of a triaxial coil 23 in which three sets of
windings 32, 33, 34 having circular cross sections are nested
together with their planes orthogonal to each other, and with the
assembly held together by glue means 38. Each of the coil means 32,
33, 34 has one pair of jumper wires 35, 36, 37 that make contact
with one of the corresponding pair of the set of lead wires 5 that
then run the length of the inner lumen 14.
[0037] FIG. 3a shows one embodiment of the distal tip of the
catheter. The outer lumen 13 and the soft pliable coupling section
24 of the wall of the outer lumen form the containment for the
return flow path of the cooling water that arrives at the distal
tip by flowing through the inner lumen 14. The distal end of the
inner lumen 14 also has a section of soft pliable coupling material
40 that (like the segment 24) facilitates the articulation of the
catheter's tip for steering purposes. The outlet port 41 for the
cooling water at the distal end of the inner lumen 14 is located in
close proximity to the inside surface of the distal end of the
outer lumen 13. The distal tip of the catheter 39 may be
constructed from a radio-opaque material or be coated on its inside
surface with a layer of material 39 that is radio-opaque and
MR-visible for imaging purposes. The tip 39 may also serve as an
ablation electrode, which is cooled during ablation by cooling
water circulating through lumens 13 and 14. One embodiment of the
triaxial coil assembly 23 with its leads 5 is shown in place at the
distal end of the inner lumen 14. A mounting mechanism 38 holds the
triaxial coil assembly in place within the inner lumen 14.
[0038] FIG. 4 shows a block diagram of some details of the power
handling part of the system. The host computer 9 for the system is
connected by the usual data bus to the power supplies 10, 11, 12
that drive currents through the triaxial coil assembly. Each power
supply has digital input and analog output hence must have an
integral digital to analog converter and a means for monitoring the
current as indicated. The leads from the power supply might be
brought forward in twisted pairs 42 to minimize the effects of
magnetic field couplings that might drive extraneous currents
through them. The twisted pairs connect with the leads 5 of the
triaxial coil assembly. During the MRI imaging step, the host
computer 9 may receive and/or transmit rf signals from the coils 23
via leads 42 to enhance the local MRI image and/or to measure the
location and orientation of the coils.
[0039] FIG. 5 shows some additional details of the cooling water
connections. The inner lumen 14 of the catheter 4 conveys the
cooling water to the triaxial coil means. The inlet connection is
made via the coupling tube 20. The input port 44 on the coupling
tube is hooked to a source of the cooling water. Inside the
coupling tube 20 is a temperature sensor 45 the leads of which
traverse the wall of the coupling tube and are connected to the
temperature monitor 46 to read the inlet water temperature. A
reciprocal arrangement is placed on the outlet side, where the
outlet water temperature is measured at its highest point, at the
coil set 23. An outlet coupling tube 21 is connected to the
catheter's outer lumen 13. The outlet port 43 of the outlet
coupling tube 21 allows the water to exit the coupling tube and
flow into a drain, or be continuously recirculated. A temperature
sensor 47 monitors the outlet water temperature at the coils 23,
and its leads pass through the wall of the tube and are corrected
to the temperature monitor 48 that is used to read the outlet water
temperature.
[0040] FIG. 6 shows a catheter 4 as it would be navigated inside of
a vessel 49, located within a body part The catheter 4, is advanced
to a bifircation 50 in the vessel 49 having a lower branch 52 and
an upper branch 51. The catheter 4 is guided into the upper branch
51 of the vessel where it is to be used to treat a blockage 53 by
infusing a thrombolytic agent 55 through the distal array of port
holes 54 on this particular catheter. Many variations of this
embodiment are possible for treating a variety of diseases,
syndromes and conditions using different arrangements of the
catheter 13 either inside of body ducts or lumens, or inside of the
parenchymal tissues of a body part.
[0041] FIG. 7a shows a catheter 4 as it would be used inside of a
brain 57 of a patient 56. The catheter 13 has been inserted through
a surgically placed burr hole 58 and navigated via magnetic
stereotactic command of the triaxail coil means to reach a
specified point on a lesion 59 within the brain 57. In the context
of this drawing, the patient is lying flat on the gurney of a
standard high-field MR machine and rests within the axial bore. The
static magnetic field of the MRI is parallel to the long axis of
the patient's body, hence the burr hole 58 is placed on the top of
the patient's head in accordance with the access to the head
permitted by the construction of the MRI. FIG. 7b contains the same
elements as FIG. 7a. However, in the context of FIG. 7b the patient
is located within the open bore of an interventional MR scanner and
may not be lying flat but oriented at some angle with respect to
the horizontal, possibly even vertically. This may permit or even
require that the burr hole be placed occipitally or elsewhere on
the skull.
[0042] FIG. 8 is a flow chart showing several of the steps needed
to carry out a magnetic stereotaxis procedure using the triaxial
coil means inside of a catheter within a body part of a patient who
is located in a MR scanner. At 61 the MR scanner magnetic field is
measured. At 62 the position of the catheter tip is localized. At
63 the target location for the next catheter step is identified by
the physician. This can be done on a user-friendly computer
interface. At 64 a mathematical algorithm is executed to identify
the currents in the triaxial coil currents. At 65 the new target
location is displayed on the interface. At 66 the physician decides
whether to energize the coils. If the physician decides not to
energize the coils, the process turns to step 64 where a new set of
coil currents are calculated. If the physician decides to energize
the coils, at 67 the coils are energized and at 68 the physician
observes the location of the tip following the movement sequence.
At 69, the physician decides whether the catheter is at its desired
location, if it is, at 70 the procedure is over, if the catheter is
not at its desired position the process resumes at 62.
[0043] FIG. 9 shows a flow chart 71 that identifies several of the
steps needed to regulate the coil currents in the triaxial coil 23
that is being used to steer a catheter in the form of magnetic
stereotaxis that is the subject of the present invention. At 72 the
present location of the catheter tip is determined. At 73a the
orientation of the catheter tip with respect to the MR scanner
field is determined, and at 73b the target point for the next
movement sequence is established. At 74 the math model is applied,
and at 75 digital values of coil current are computed, and the
digital values are converted to analog signal. At 76a, 76b and 76c
the analog signals are applied to the x-axis, y-axis, and z-axis
coils. Also the output signals are fed back to the coil current
computation step.
[0044] FIGS. 10a-10d illustrate a method for rotation of a catheter
4 about the MR magnetic field axis, employing two successive
rotations about the orthogonal x and y axes. As shown in FIG. 10a,
a magnetic moment is created at the distal end of the catheter so
that the catheter bends out of the x-y plane to be parallel with
the z-axis (corresponding to the local magnetic field direction),
shown in FIG. 10b. As shown in FIG. 10c, a magnetic moment is
created at the distal end of the catheter so that the catheter
bends out of the x-z plane to be parallel to the y-axis. Thus
rotation about the magnetic field direction (z direction) is
possible by successive rotations about the y-axis and then the
x-axis. FIGS. 11a-11d show how rotation about the field axis is
accomplished by a series of incremental rotations out of the x-y
plane. As shown in FIG. 11a, a magnet moment is created at the
distal end of the catheter so that the catheter bends out of the
x-y plane to an angle in the x-z plan (z corresponding to the local
magnetic field direction), shown if FIG. 11b. As shown in FIG. 11c,
a magnetic moment is created at the distal end of the catheter so
that the catheter bends out of the x-z plane back into the x-y
plane to an angle with respect to the x-axis. Thus, rotation about
the magnetic field direction (z direction) is possible by
successive rotations about the y-axis and then the x-axis. FIGS.
12a-12b show a method to apply torque about the axis of the
catheter, which can be used, for example, to relieve strain built
up in the multiple rotations used in FIGS. 10a-d and 11a-d. As
shown in FIG. 12a a magnetic moment is created in the distal tip of
the catheter that in the applied magnetic field causes the catheter
to rotate about its longitudinal axis to "unwind" from twisting
caused by the compound navigations shown and described in
conjunction with FIGS. 10 and 11.
* * * * *