U.S. patent number 6,834,201 [Application Number 10/429,524] was granted by the patent office on 2004-12-21 for catheter navigation within an mr imaging device.
This patent grant is currently assigned to Stereotaxis, Inc.. Invention is credited to William C. Broaddus, Jeffrey M. Garibaldi, George T. Gillies, Roger N. Hastings.
United States Patent |
6,834,201 |
Gillies , et al. |
December 21, 2004 |
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) |
Assignee: |
Stereotaxis, Inc. (St. Louis,
MO)
|
Family
ID: |
25094240 |
Appl.
No.: |
10/429,524 |
Filed: |
May 5, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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772188 |
Jan 29, 2001 |
|
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Current U.S.
Class: |
600/411;
600/407 |
Current CPC
Class: |
A61B
5/055 (20130101); A61B 5/06 (20130101); G01R
33/285 (20130101); A61B 34/73 (20160201); A61B
2034/732 (20160201); A61M 25/01 (20130101) |
Current International
Class: |
A61B
5/055 (20060101); A61B 5/06 (20060101); G01R
33/28 (20060101); A61M 25/01 (20060101); A61B
005/05 () |
Field of
Search: |
;600/411,410,407,436
;324/307,308,309,310,207,207.11,207.23,207.24,207.25,207.26
;436/173 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
TP.L. Roberts et al., "Integrating X-ray Angiography and MRI for
Enovascular Interventions", Nov. 2000, Medica Mundi, p. 2-9. .
Seeber, "Triaxial magnetic field gradient system for microcoil
magnetic resonance imaging", Nov., 2000, Reviwe of Scientific
Instruments, vol. 71, No. 11, p. 4263-4272. .
Coutts et al., "Integrated and Interactive Position Tracking and
Imaging of Interventional Tools and Internal Devices Imaging Small
Fiducial Receiver Coils", Mar., 1999, ROMAC, pp. 908-913. .
Burl et al., "Twisted-Pair RF Coil Suitable for Locating the Track
of a Catheter", 1999, Magnetic Resonance in Medicine, 41, pp.
636-638. .
Worley, "Use of a Real-Time Three-dimensional Magnetic Navigation
System for Radiofrequency Ablation of Accessory Pathways", Aug.
1999, PACE, vol. 21, pp. 1636-1645 .
Nakamura et al., "A Prototype Mechanism for Three-Dimensional
Levitated Movement of a Small Magnet", Mar., 1997 Transactions of
Mechatronics, vol. 2, No. 1, pp. 41-50. .
Bakker et al., "MR-guided Endovascular Interventions:
Susceptibility-based Catheter and Near-Real-Time Imaging
Technique", Radiology, Nov., 1997, pp. 273-276. .
Rasche et al., "Catheter Tracking Using Continuous Radial MRI",
Nov., 1997, MRM, vol. 37, pp. 963-968. .
Wildermuth et al., "MR Imaging-guided Intravascular Procedures:
Initial Demonstration in a Pig Model", Radiology, Feb., 1997, pp.
578-583. .
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", Jun., 1996, Med. Phys, vol. 23, pp. 851-856. .
Manner et al., "MR Imaging in the Presence of Small Circular
Metallic Implants", ACTA Radiological, 1995, pp. 551-554. .
Gillies et al., "Magnetic manipulation instrumentation for medical
physics research", Mar., 1994, Rev. Sci. Instrum., vol. 65, pp.
533-562. .
T.P.L. Roberts et al., "Remote control of Catheter Tip Defelction:
An Opportunity for Interventional MRI", Magnetic Resonance in
Medicine, 48: 1091-1095 (2002)..
|
Primary Examiner: Robinson; Daniel
Attorney, Agent or Firm: Harness, Dickey & Pierce,
P.L.C.
Parent Case Text
CROSS-REFERENCE TO A PRIOR APPLICATION
This application is a divisional of U.S. patent application Ser.
No. 09/772,188, filed Jan. 29, 2001, now abandoned the disclosure
of which is incorporated by reference.
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; energizing at least one electromagnetic coil
overlapping another electromagnetic coil of the medical device to
create 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
moving a patient to vary 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 energizing at least one
electromagnetic coil comprises reducing an effect of magnetic field
coupling on the energizing using a twisted pair.
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; and actively removing heat from the at least one coil
through the medical device.
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. 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; wherein the
medical device comprises at least two sets of three current
carrying coils, and creating temporary magnetic moments in the
medical device comprises applying current to one or more of the
current carrying coils.
19. 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; and applying electrical energy to create
temporary magnetic moments in one or more coils 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; and actively
controlling heat resulting from applying the electrical energy in
the medical device.
20. The method of claim 19, wherein actively controlling heat
comprises applying the electrical energy in pulses to at least one
coil.
21. The method of claim 19, wherein actively controlling heat
comprises: carrying a heat exchange medium into the medical device;
and cooling the heat exchange medium leaving the medical device.
Description
FIELD OF THE INVENTION
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
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.
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.
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.
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.
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 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.
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.
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; Dumoulin 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 Imaging-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
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 MRI 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.
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.x i+m.sub.y j+m.sub.z k
and the torque experienced by the dipole moment in the field of the
MR scanner is .tau.=m.times.H. 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.
Evaluation of the vector cross product produces the components
.tau..sub.x =m.sub.y H, .tau..sub.y =-m.sub.x H, 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.
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.o
H 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.
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.
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.
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.
In some modem 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.
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.
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
FIG. 1 is a schematic diagram of a system for implementing the
method of this invention;
FIG. 2a is a schematic diagram of a catheter adapted for use with
the method of this invention;
FIG. 2b is a schematic diagram of a triaxial coil system wound on a
rectangular parallelepiped coil form or mandrel;
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;
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;
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;
FIG. 4 is a schematic diagram of the electrical connections and
components for a system for implementing the method of this
invention;
FIG. 5 is a schematic diagram of a cooling system adapted for use
in the system for implementing the method of this invention;
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;
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;
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;
FIG. 8 is a flow chart of the method of navigating a medical device
in accordance with the method of this invention;
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;
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;
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
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
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.
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.
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.
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.
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 connected
to the temperature monitor 48 that is used to read the outlet water
temperature.
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 bifurcation 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.
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.
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.
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.
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.
* * * * *