U.S. patent application number 10/945845 was filed with the patent office on 2005-07-07 for ceramic reinforcement member for mri devices.
This patent application is currently assigned to Scimed Life Systems, Inc.. Invention is credited to Weber, Jan.
Application Number | 20050148865 10/945845 |
Document ID | / |
Family ID | 21725266 |
Filed Date | 2005-07-07 |
United States Patent
Application |
20050148865 |
Kind Code |
A1 |
Weber, Jan |
July 7, 2005 |
Ceramic reinforcement member for MRI devices
Abstract
The present invention relates to a reinforced magnetic resonance
imaging catheter. The catheter comprises a medical device having at
least one lumen extending therethrough. The elongated body also
includes a proximal end, a distal end, and circumference, a
longitudinal axis running between the proximal and distal ends, and
a coaxial layer that incorporates at least one elongated ceramic
member that is substantially covered with a coating. An antenna is
operably disposed proximate the distal end the medical device.
Inventors: |
Weber, Jan; (Maple Grove,
MN) |
Correspondence
Address: |
FISH & RICHARDSON P.C.
PO BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
Scimed Life Systems, Inc.
Maple Grove
MN
55311
|
Family ID: |
21725266 |
Appl. No.: |
10/945845 |
Filed: |
September 21, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10945845 |
Sep 21, 2004 |
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10007284 |
Nov 9, 2001 |
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6807440 |
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Current U.S.
Class: |
600/423 |
Current CPC
Class: |
A61L 29/18 20130101;
G01R 33/285 20130101; A61B 5/055 20130101; A61L 29/02 20130101;
A61M 25/0045 20130101 |
Class at
Publication: |
600/423 |
International
Class: |
A61B 005/05 |
Claims
1-27. (canceled)
28. An intravascular guidewire for use in magnetic resonance
imaging, comprising: a portion comprised of ceramic fibers; and a
coating on an exterior surface of the portion comprised of ceramic
fibers, the coating comprised of a polymeric materials.
29. The intravascular guidewire of claim 28, where the ceramic
fibers are woven together.
30. The intravascular guidewire of claim 28, where the ceramic
fibers are braided together.
31. The intravascular guidewire of claim 28, further comprising: a
central wire portion axially engaged with the portion comprised of
ceramic fibers.
32. The intravascular guidewire of claim 28, further comprising: an
antenna.
33. The intravascular guidewire of claim 32, where the guidewire
includes a proximate and a distal end, and the antenna is operably
disposed proximate the distal end of the guidewire.
34. The intravascular guidewire of claim 28, where the guidewire is
of an overall flexibility that the guidewire can be bent without
breaking.
35. The intravascular guidewire of claim 28, where the portion
comprised of ceramic fibers is further comprised of non-ceramic
fibers woven together with the ceramic fibers.
36. The intravascular guidewire of claim 28, where the portion
comprised of ceramic fibers is further comprised of non-ceramic
fibers braided together with the ceramic fibers.
37. The intravascular guidewire of claim 28, where the portion
comprised of ceramic fibers includes a plurality of surface
scratches and where the coating fills the scratches and allows the
ceramic fibers to be bent without breaking.
38. The intravascular guidewire of claim 28, where the ceramic
fibers are comprised of at least one of carbon, silicon carbide or
aluminum oxide.
39. An intravascular guidewire for use in magnetic resonance
imaging, comprising: a portion comprised of ceramic fibers; and a
coating on an exterior surface of the portion comprised of ceramic
fibers, the coating comprised of a material including pyrolytic
carbon.
40. The intravascular guidewire of claim 39, where the ceramic
fibers are woven or braided together.
41. The intravascular guidewire of claim 39, further comprising: a
central wire portion axially engaged with the portion comprised of
ceramic fibers.
42. The intravascular guidewire of claim 39, further comprising: an
antenna.
43. The intravascular guidewire of claim 42, where the guidewire
includes a proximate and a distal end, and the antenna is operably
disposed proximate the distal end of the guidewire.
44. The intravascular guidewire of claim 39, where the guidewire is
of an overall flexibility that the guidewire can be bent without
breaking.
45. The intravascular guidewire of claim 39, where the portion
comprised of ceramic fibers is further comprised of non-ceramic
fibers woven or braided together with the ceramic fibers.
46. The intravascular guidewire of claim 39, where the portion
comprised of ceramic fibers includes a plurality of surface
scratches and where the coating fills the scratches and allows the
ceramic fibers to be bent without breaking.
47. The intravascular guidewire of claim 39, where the ceramic
fibers are comprised of at least one of carbon, silicon carbide or
aluminum oxide.
Description
[0001] The present application is a continuation of and claims
priority of U.S. patent application Ser. No. 10/007,284, filed Nov.
9, 2001, the content of which is hereby incorporated by reference
in its entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to intravascular
devices used in magnetic resonance imaging. More particularly, the
present invention relates to a ceramic reinforcement member for
reinforcing elongated intravascular magnetic resonance imaging
devices.
[0003] Tracking of catheters and other devices positioned within a
body may be achieved by means of a magnetic resonance imaging (MRI)
system. Typically, such a magnetic resonance imaging system may be
comprised of a magnet, a pulsed magnetic field gradient generator,
a transmitter for electromagnetic waves in radio frequency (RF), a
radio frequency receiver, and a controller. In a common
implementation, an antenna is disposed either on the device to be
tracked or on a guidewire or a catheter (commonly referred to as a
magnetic resonance catheter or an MR catheter) used to assist in
the delivery of the device to its destination. In one known
implementation, the antenna comprises an electrically conductive
coil that is coupled to a pair of elongated electrical conductors
that are electrically insulated from each other, and that together
comprise a transmission line adapted to transmit the detected
signal to the RF receiver.
[0004] In one embodiment, the coil is arranged in a solenoid
configuration. A patient is placed into or proximate the magnet and
the device is inserted into the patient. The magnetic resonance
imaging system generates electromagnetic waves in radio frequency
and magnetic field gradient pulses that are transmitted into the
patient and that induce a resonant response signal from selected
nuclear spins within the patient. This response signal induces
current in the coil of electrically conductive wire attached to the
device. The coil thus detects the nuclear spins in the vicinity of
the coil. The transmission line transmits the detected response
signal to the radio frequency receiver, which processes it and then
stores it with the controller. This is repeated in three orthogonal
directions. The gradients cause the frequency of the detected
signal to be directly proportional to the position of the
radio-frequency coil along each applied gradient.
[0005] The position of the radio frequency coil inside the patient
may therefore be calculated by processing the data using Fourier
transformations so that a positional picture of the coil is
achieved. In one implementation, this positional picture is
superposed with a magnetic resonance image of the region of
interest. This picture of the region may be taken and stored at the
same time as the positional picture or at any earlier time.
[0006] Elongated intravascular devices utilized in association with
MRI applications must generally be made from low magnetic
susceptible materials, otherwise they will disturb the magnetic
resonance (MR) image of the surrounding body tissue. It is not
uncommon for elongated intravascular devices, such as catheters and
guidewires, to utilize a reinforcement mechanism so as to enable
particular desired mechanical characteristics, such as a desired
tensile strength or desired features related to flexibility. It is
therefore necessary, within the context of MRI-related
applications, that reinforcement mechanisms within elongated
intravascular devices be made from low magnetic susceptible
materials.
[0007] Presently, it is not uncommon for an elongated intravascular
member, such as a catheters or a guidewire, to incorporate a strand
of reinforcement material, or a layer of braided or woven
reinforcement material, into a coaxial layer of the elongated
member. In non-MRI applications, strands, wires and/or fibers
incorporated into these types of reinforcement mechanisms can be
constructed of highly magnetic materials such as stainless steel.
In many instances, highly magnetic materials demonstrate desirable
mechanical characteristics (i.e., a desirable tensile strength,
flexibility, etc.) In MRI applications, however, to avoid
interference with magnetically generated images, such highly
magnetic materials are typically replaced with lower magnetic
metals or special alloys (like Tantalum, Elgiloy, MP35N). In the
context of MRI applications, however, all metal materials and metal
alloy materials will still have some negative influence on the
magnetic image.
[0008] In some instances, polymer fibers which have, of course, no
negative influence on the magnetic image have been incorporated
into elongated intravascular MRI devices for reinforcement. Polymer
fibers, however, as compared to the metal and metal alloy
materials, have generally inferior mechanical qualities.
[0009] The present invention addresses at least one of these and
other problems and offers advantages over the prior art.
SUMMARY OF THE INVENTION
[0010] The present invention generally pertains to elongated
intravascular MRI-related devices adapted to be advanced through a
vessel of a subject. In particular, the present invention provides
one or more constructions of such intravascular devices that
incorporate reinforcement mechanisms that enable both desirable
mechanical qualities and minimal negative magnetic interference
with MR imaging.
[0011] One embodiment of the present invention pertains to a
reinforced magnetic resonance imaging catheter. The catheter
comprises a medical device having at least one lumen extending
therethrough. The medical device also includes a proximal end, a
distal end, a circumference, a longitudinal axis running between
the proximal and distal ends, and a coaxial layer that incorporates
at least one elongated ceramic member that is substantially covered
with a coating. An antenna is operably disposed proximate the
distal end the medical device.
[0012] Another embodiment of the present invention pertains to a
medical device for intravascular manipulation during magnetic
resonance imaging of body tissue. The device includes a medical
device and a reinforcement mechanism disposed about a portion of
the medical device. The reinforcement mechanism comprises at least
one elongated ceramic member that is substantially covered with a
coating.
[0013] Another embodiment of the present invention pertains to a
reinforcement member for reinforcing an elongated intravascular
magnetic resonance imaging device. The reinforcement member
comprises an elongated ceramic fiber and a coating disposed about
the ceramic fiber.
[0014] These and various other features, as well as advantages
which characterize the present invention, will be apparent upon a
reading of the following detailed description and review of the
associated drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a partial block diagram of an illustrative
magnetic resonance imaging and intravascular guidance system in
which embodiments of the present invention can be employed.
[0016] FIG. 2 is a side view of a magnetic resonance catheter in
accordance with an illustrative embodiment of the present
invention.
[0017] FIG. 3 is a cross-sectional view of the catheter shown in
FIG. 2.
[0018] FIG. 4 is a side view of a portion of a braided or woven
coaxial layer according to an illustrative embodiment of the
present invention.
[0019] FIG. 5 is a side view of a ceramic reinforcement member in
accordance with an illustrative embodiment of the present
invention.
[0020] FIG. 6 is a cross-sectional view of the ceramic
reinforcement member of FIG. 5.
[0021] FIG. 7 is a partially exposed side view of a guidewire in
accordance with an illustrative embodiment of the present
invention.
[0022] FIG. 8 is a side view of a catheter in accordance with an
illustrative embodiment of the present invention.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS
[0023] FIG. 1 is a partial block diagram of an illustrative
magnetic resonance imaging and intravascular guidance system in
which embodiments of the present invention could be employed. In
FIG. 1, subject 100 on support table 110 is placed in a homogeneous
magnetic field generated by magnetic field generator 120. Magnetic
field generator 120 typically comprises a cylindrical magnet
adapted to receive subject 100. Magnetic field gradient generator
130 creates magnetic field gradients of predetermined strength in
three mutually orthogonal directions at predetermined times.
Magnetic field gradient generator 130 is illustratively comprised
of a set of cylindrical coils concentrically positioned within
magnetic field generator 120. A region of subject 100 into which a
device 150, shown as a catheter, is inserted, is located in the
approximate center of the bore of magnetic 120. Illustratively,
device 150 could be a guidewire or some other intravascular
device.
[0024] RF source 140 radiates pulsed radio frequency energy into
subject 100 and the MR active sample within device 150 at
predetermined times and with sufficient power at a predetermined
frequency to nutate nuclear magnetic spins in a fashion well know
to those skilled in the art. The nutation of the spins causes them
to resonate at the Larmor frequency. The Larmor frequency for each
spin is directly proportional to the strength of the magnetic field
experienced by the spin. This field strength is the sum of the
static magnetic field generated by magnetic field generator 120 and
the local field generated by magnetic field gradient generator 130.
In an illustrative embodiment, RF source 140 is a cylindrical
external coil that surrounds the region of interest of subject 100.
Such an external coil can have a diameter sufficient to encompass
the entire subject 100. Other geometries, such as smaller cylinders
specifically designed for imaging the head or an extremity can be
used instead. Non-cylindrical external coils such as surface coils
may alternatively be used.
[0025] Device 150 is inserted into subject 100 by an operator.
Illustratively, device 150 may alternatively be a guidewire, a
catheter, an abation device or a similar recanalization device.
Device 150 includes an RF antenna which detects MR signals
generated in both the subject and the device 150 itself in response
to the radio frequency field created by RF source 140. Since the
internal device antenna is small, the region of sensitivity is also
small. Consequently, the detected signals have Larmor frequencies
which arise only from the strength of the magnetic field in the
proximate vicinity of the antenna. The signals detected by the
device antenna are sent to imaging and tracking controller unit 170
via conductor 180.
[0026] External RF receiver 160 also detects RF signals emitted by
the subject in response to the radio frequency field created by RF
source 140. In an illustrative embodiment, external RF receiver 160
is a cylindrical external coil that surrounds the region of
interest of subject 100. Such an external coil can have a diameter
sufficient to have a compass the entire subject 100. Other
geometries, such as smaller cylinders specifically designed for
imaging the head or an extremity can be used instead.
Non-cylindrical external coils, such as surface coils, may
alternatively be used. External RF receiver 160 can share some or
all of its structure with RF source 140 or can have a structure
entirely independent of RF source 140. The region of sensitivity of
RF receiver 160 is larger than that of the device antenna and can
encompass the entire subject 100 or a specific region of subject
100. However, the resolution which can be obtained from external RF
receiver 160 is less than that which can be achieved with the
device antenna. The RF signals detected by external RF receiver 160
are sent to imaging and tracking controller unit 170 where they are
analyzed together with the RF signals detected by the device
antenna.
[0027] The position of device 150 is determined in imaging and
tracking controller unit 170 and is displayed on display means 180.
In an illustrative embodiment of the invention, the position of
device 150 is displayed on display means 180 by superposition of a
graphic symbol on a conventional MR image obtained by external RF
receiver 160. Alternatively, images may be acquired by external RF
receiver 160 prior to initiating tracking and a symbol representing
the location of the tracked device be superimposed on the
previously acquired image. Alternative embodiments of the invention
display the position of the device numerically or as a graphic
symbol without reference to a diagnostic image.
[0028] FIG. 2 is side view of one illustrative embodiment of a
device that could be utilized similar to device 150 described above
in relation to FIG. 1. More particularly, FIG. 2 is a side view of
a magnetic resonance catheter 200 (MR catheter 200), in accordance
with an illustrative embodiment of the present invention. MR
catheter 200 includes an elongated body 210 having a proximal end
220 and a distal end 230. An antenna 240 is operably disposed
proximate distal end 230 and operates as described above in
relation to FIG. 1.
[0029] FIG. 3 is a cross-sectional view of MR catheter 200 taken
along line 3--3 in FIG. 2. As is illustrated in FIG. 3, MR catheter
200 includes a circumference 310 and an axis 320, that each
illustratively extend from proximal end 220 to distal end 230. The
MR catheter 200 also includes a lumen 330 that also illustratively
extends between ends 220 and 230. It should be noted that catheters
having additional lumens should be considered within the scope of
the present invention.
[0030] With further reference to FIG. 3, lumen 330 is
illustratively formed and defined by an undercoat layer of a
material such as urethane, PVC, polyamide, silicon or some other
similar material. Alternatively, lumen 330 may be directly defined
by a first coaxial layer 340. A second coaxial layer 350 is
illustratively a protective layer that provides catheter 200 with a
substantially smooth outer surface. In accordance with one
embodiment, second coaxial layer 350 is constructed of a polymeric
material. In accordance with another embodiment, the undercoat
layer defining lumen 330 and the second coaxial layer 350 are
formed of a product commercially designated as Desmopan sold by the
Polymers Division of Miles, Inc., which is located in Pittsburgh,
Pa. It should be noted that, without departing from the scope of
the present invention, any of the undercoat layer, the first
coaxial layer and the second coaxial layers could illustratively be
formed of multiple individual layers and/or constructed of any of
the above-described or other similar materials.
[0031] FIG. 4 is a side view of an exposed portion of first coaxial
layer 340, in accordance with an illustrative embodiment of the
present invention. First coaxial layer 340, as illustrated, is a
braided or woven layer of material that provides reinforcement to
catheter 200 (FIG. 2) and enables mechanical characteristics (i.e.,
desirable tensile strength, flexibility, etc.) that are
particularly useful in the context of intravascular manipulation of
catheter 200 (FIG. 2) during magnetic resonance imaging.
[0032] With further reference to FIG. 4, layer 340 includes
sectional bundles 410 of individual reinforcement members 420.
Illustratively, reinforcement members may be wires, fibers or some
other elongated element that can be bent and woven as illustrated.
It is to be emphasized that the particular weave pattern
illustrated in FIG. 4 is illustrative only. Reinforcement members
420 could be alternatively woven in an almost limitless range of
other patterns without departing from the scope of the present
invention. Such patterns may or may not include sectional bundles
410.
[0033] FIG. 5 is a side view of one illustrative embodiment of a
reinforcement member that could be utilized similarly to any of
reinforcement members 420 described above in relation to FIG. 4.
More particularly, FIG. 5 is a side view of a ceramic reinforcement
member 500, in accordance with an illustrative embodiment of the
present invention. Illustratively, ceramic reinforcement member 500
is constructed of low or non-magnetic materials and therefore will
not disturb an MR image of body tissue that surrounds an associated
catheter.
[0034] Ceramic reinforcement member 500 is a coated ceramic member,
illustratively a coated ceramic fiber. FIG. 6 is a cross-sectional
view of member 500 taken along line 6--6 in FIG. 5 and shows that
member 500 includes a ceramic core 610 and a coating 620. In
accordance with an embodiment of the present invention, the
mechanical characteristics and quality of ceramic reinforcement
member 500 are comparable to a highly magnetic metal member, such
as a stainless steel member.
[0035] Coating 620 is disposed on ceramic core 610 and
illustratively makes it possible for member 500 to be bent without
breaking, thereby enabling member 500 to be woven similar to
reinforcement members 420 in FIG. 4 (but not necessarily in the
same FIG. 4 pattern). Ceramic materials often have normally low
bending resistance due, at least in part, to surface scratches that
are inherent to the material. In some instances, surface scratches
are intentionally applied to create or enhance certain mechanical
characteristics. Regardless of the source of the scratches, coating
620 fills these scratches and allows the fibers to be bent and to
be incorporated into a braiding or weaving process. Notably, a
ceramic reinforcement member, such as member 500, can be processed
up to a very high temperature, which allows it to go through an
extrusion process. Ceramic reinforcement member 500 is additionally
advantageous in that it can be incorporated into a woven layer
using operations identical to known operations used to braid wires
or fibers constructed of high magnetic material, such as metal
wires, strands, fibers, etc. Ceramic reinforcement member 500
includes mechanical properties similar to metal or metal alloy
fibers but does not include an associated disadvantageous potential
for magnetic disturbance of magnetic resonance imaging.
[0036] In accordance with illustrative embodiments of the present
invention, ceramic core 610 is constructed of a material that
includes carbon (C), silicon carbide (SiC) and/or aluminum oxide
(Al.sub.2O.sub.3). Illustratively, coating 620 may comprise a
polymeric material or a material that includes pyrolytic carbon
(PyC). All of these materials should be considered illustrative
examples only. Other similar materials could be utilized without
departing from the scope of the present invention.
[0037] It should be pointed out that FIG. 4 is only one
illustrative example of how ceramic reinforcement member 500 (FIG.
5) might be utilized as at least one of the reinforcement members
420. It should be noted that not all members 400 need be
constructed similar to ceramic reinforcement member 500. For
example, in accordance with one embodiment, some of the individual
reinforcement members could be constructed similar to FIG. 5 while
others are otherwise constructed. For example, some of the members
420 could be constructed of polymeric or other low or non-metallic
materials. It is conceivable that an elongated intravascular
member, such as catheter 200 (FIG. 2) could achieve desirable
mechanical qualities utilizing a braided or woven reinforcement
layer that combines multiple members similar to ceramic
reinforcement member 500 with other low or non-metallic
reinforcement members.
[0038] It should be noted that the ceramic reinforcement members of
the present invention could be incorporated into MRI-related
elongated intravascular devices other than MR catheters. For
example, FIG. 7 is a partially exposed side view of a guidewire 700
in accordance with an illustrative embodiment of the present
invention. Guidewire 700 may (or may not) illustratively include an
MRI-related antennae similar to antennae 240 described in relation
to FIG. 2. Guidewire 700 includes a coating 705 that has been
partially exposed at sections 710 for the purpose of illustration.
Exposed portions 710 reveal that coating 705 covers a braided or
woven portion 720. Illustratively, braided or woven portion 720 may
or may not cover the entire length of guidewire 700. In accordance
with an embodiment of the present invention, braided or woven
portion 720 includes one or more reinforcement members similar to
that described in relation to FIGS. 5 and 6. Braided or woven
portion 720 illustratively axially engages a central wire portion
730. FIG. 7 is only intended to illustrate that the present
invention could be applied in contexts other than that of an MR
catheter. Precise configurations and braid or weave patterns may
vary without departing from the scope of the present invention. The
present invention could apply still to MRI-related elongated
intravascular devices other than catheters and guidewires.
[0039] FIG. 8 is a side view of a catheter 800 in accordance with
an illustrative embodiment of the present invention. Catheter 800
includes a lumen 830 that is similar to lumen 330 described above
in relation to FIG. 3 and a layer 840 that is similar to layer 350
also described in relation to FIG. 3. A ceramic reinforcement
member 820 is sandwiched between lumen 830 and layer 840. Member
820 is a single non-braided or woven member and is constructed of a
covered ceramic member similar to member 500 described in relation
to FIG. 5. Points 805 and 815 have been labeled to visibly clarify
the circumferentially-wrapped nature of the reinforcement member.
Illustratively, additional members 820 could be incorporated
between lumen 830 and layer 840 of catheter 800. Catheter 800 is
intended to illustrate the point that, in accordance with the
present invention, ceramic reinforcement members need not always be
applied in a braided or woven configuration.
[0040] Although the present invention has been described with
reference to illustrative embodiments, workers skilled in the art
will recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
* * * * *