U.S. patent application number 12/941548 was filed with the patent office on 2011-06-09 for optical imaging catheter for aberration balancing.
This patent application is currently assigned to Volcano Corporation. Invention is credited to Nathaniel J. Kemp, Thomas E. Milner.
Application Number | 20110137124 12/941548 |
Document ID | / |
Family ID | 40229117 |
Filed Date | 2011-06-09 |
United States Patent
Application |
20110137124 |
Kind Code |
A1 |
Milner; Thomas E. ; et
al. |
June 9, 2011 |
OPTICAL IMAGING CATHETER FOR ABERRATION BALANCING
Abstract
An Optical imaging catheter that balances optical aberrations
and allows recording of high quality optical images while relaxing
the requirement of a fluid occupying the space between the prism
and the inner sheath of the catheter.
Inventors: |
Milner; Thomas E.; (Austin,
TX) ; Kemp; Nathaniel J.; (Concord, MA) |
Assignee: |
Volcano Corporation
San Diego
CA
|
Family ID: |
40229117 |
Appl. No.: |
12/941548 |
Filed: |
November 8, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/US2009/043183 |
May 7, 2009 |
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12941548 |
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12172922 |
Jul 14, 2008 |
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PCT/US2009/043183 |
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61051340 |
May 7, 2008 |
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60949511 |
Jul 12, 2007 |
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Current U.S.
Class: |
600/160 |
Current CPC
Class: |
A61B 8/12 20130101; A61B
5/6852 20130101; A61B 5/0066 20130101; A61M 25/0052 20130101; A61B
5/0062 20130101; A61M 2025/0183 20130101; A61B 8/4461 20130101 |
Class at
Publication: |
600/160 |
International
Class: |
A61B 1/06 20060101
A61B001/06 |
Claims
1. An optical imaging catheter comprising: a prism to receive and
direct optical radiation through a catheter sheath; and a space is
between the prism and the catheter sheath to balance optical
aberrations in optical images obtained from a sample.
2. The catheter of claim 1, wherein the space is occupied by air or
gas.
3. The catheter of claim 1, wherein the catheter sheath includes an
inner surface and an outer surface, wherein the inner surface and
outer surface include an optical power and a refractive index.
4. The catheter of claim 3, wherein the absolute value of the
optical power of the inner surface is higher than the outer
surface.
5. The catheter of claim 3, wherein the catheter sheath includes a
refractive index matched to the refractive index of a medium
exterior the outer surface.
6. The catheter of claim 3, wherein the inner surface includes a
radius between about 0.3000 to 0.4000 mm and the outer surface
includes a radius between about between about 0.4100 to 0.5100
mm.
7. The catheter of claim 1, wherein the prism includes a
bi-cylindrical micromirror/microlens comprising a reflective
cylindrical surface to collect the optical radiation diverging
longitudinally out of an optical fiber and redirect the optical
radiation with a cylindrical surface into a radial component, and a
second cylindrical transmissive/lensing surface to focus the
optical radiation along an axis orthogonal to the longitudinal axis
of the catheter body.
8. The catheter of claim 1, wherein the prism is a toroidal minor
including a mirrored surface with a toroidal surface to collect,
refocus, and tilt the optical radiation into a radial component
non-perpendicular with the longitudinal axis of the catheter
body.
9. The catheter of claim 1, wherein the catheter is coupled to an
imaging modality.
10. A method for performing optical imaging through a catheter,
comprising: directing optical radiation through a prism and a
catheter sheath, wherein a space is between the prism and the
catheter sheath to balance optical aberrations in an optical image
obtained from a sample.
11. The catheter of claim 10, wherein the space is occupied by air
or gas.
12. The method of claim 10, wherein the catheter sheath includes an
index of refraction matched to the refractive index of a medium
exterior the outer surface of the catheter sheath.
13. The method of claim 10, wherein the catheter sheath includes an
inner surface and an outer surface, wherein the inner surface and
outer surface include an optical power and a refractive index.
14. The method of claim 13, wherein the absolute value of the
optical power of the inner surface is higher than the outer
surface.
15. The method of claim 13, wherein the catheter sheath includes a
refractive index matched to the refractive index of a medium
exterior the outer surface.
16. The method of claim 13, wherein the inner surface includes a
radius between about 0.3000 to 0.4000 mm and the outer surface
includes a radius between about between about 0.4100 to 0.5100
mm.
17. The method of claim 10, wherein the prism includes a
bi-cylindrical micromirror/microlens comprising a reflective
cylindrical surface to collect the optical radiation diverging
longitudinally out of an optical fiber and redirect the optical
radiation with a cylindrical surface into a radial component, and a
second cylindrical transmissive/lensing surface to focus the
optical radiation along an axis orthogonal to the longitudinal axis
of the catheter body.
18. The method of claim 10, wherein the prism is a toroidal minor
including a mirrored surface with a toroidal surface to collect,
refocus, and tilt the optical radiation into a radial component
non-perpendicular with the longitudinal axis of the catheter
body.
19. The method of claim 10, wherein the catheter is coupled to an
imaging modality.
20. A system for performing optical imaging through a catheter,
comprising: a prism to receive and direct optical radiation through
a catheter sheath; a space is between the prism and the catheter
sheath to balance aberrations in optical images obtained from a
sample; the space is occupied by air or gas with a refractive index
of about 1; the catheter sheath includes an inner surface and an
outer surface; the inner surface and outer surface include an
optical power and a refractive index, wherein the absolute value of
the optical power of the inner surface is higher than the outer
surface; and the catheter sheath includes a refractive index
matched to the refractive index of a medium exterior the outer
surface.
Description
CROSS-RELATED REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to PCT application No.
PCT/US2009/043183, which was filed May 7, 2009 and which claims
priority to U.S. Provisional application Ser. No. 61/051,340, which
was filed May 7, 2008, and claims priority to U.S. patent
application Ser. No. 12/172,922, which was filed Jul. 14, 2008 and
claims priority to U.S. provisional application Ser. No.
60/949,511, which was filed Jul. 12, 2007, all herein incorporated
by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to an apparatus for
in vivo imaging, and more particularly, pertains to a catheter for
optical imaging within luminal systems, such as imaging the
vasculature system, including, without limitation, cardiovascular,
neurovascular, gastrointestinal, genitor-urinary tract, or other
anatomical luminal structures.
[0003] Still more specifically, the present invention relates to an
imaging catheter that does not require an optical transmitter
placed between the prism and the outer sheath of the catheter.
Typically, a fluid with an index of refraction is matched to the
medium exterior the catheter to prevent image distortion due to
astigmatism, and the like. The present invention solves these
problems, as well as others.
SUMMARY OF THE INVENTION
[0004] The Optical imaging catheter substantially reduces the
composite optical aberrations in optical imaging, such as
astigmatism, by balancing the contributions of each optical
interface to any optical aberrations. By aberration balancing, the
Optical imaging catheter provides good imaging performance without
introducing a fluid in the space between the prism and inner
surface of the outer catheter sheath. The aberration balancing is
accomplished through the contributions of the various optical
interfaces including, but not limited to, the following elements: a
prism/gas (air), a gas/inner surface of the outer catheter sheath
interface, and an outer surface of catheter sheath/flush material
interface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1A is a cross-sectional side view of the Optical
imaging catheter; and FIG. 1B is a cross section view of the
Optical imaging catheter taken from view B in FIG. 1A; and FIG. 1C
is a cross-sectional view of the Optical imaging catheter.
[0006] FIG. 2A is a graph showing the encircled energy at focus for
the spot size; FIG. 2B is the "top" view of lens-prism; and FIG. 2C
is the "side" view of lens-prism
[0007] FIG. 3A is a cross-sectional side view of one embodiment of
the prism; and FIG. 3B is a cross-sectional top view of one
embodiment of the prism.
[0008] FIG. 4A is a cross-sectional view of the Optical imaging
catheter system in accordance with one embodiment; and FIG. 4B is
an enlarged portion of A of FIG. 4A, and is a partial fragmentary
view of the Optical imaging catheter in accordance with one
embodiment.
[0009] FIG. 5A is a side elevational, cross-sectional view of one
embodiment of the monolithic catheter sheath; and FIG. 5B is a side
elevational, cross-sectional view of an embodiment of a distal tip
and guidewire lumen of a monolithic imaging catheter in accordance
with one embodiment.
[0010] FIG. 6 is a side elevational, cross-sectional view of a
distal end of an embodiment of the monolithic imaging catheter
showing the guidewire lumen in accordance with one embodiment.
[0011] FIG. 7 is a perspective view of the monolithic catheter
sheath depicting the sheath lumen and the guidewire lumen in
phantom.
[0012] FIG. 8 is a photographic representation of an embodiment of
the rotary shaft in accordance with one embodiment.
[0013] FIG. 9 is a side cross-sectional view of an embodiment of
the rotary shaft.
[0014] FIG. 10 is a side cross-sectional view of an embodiment of
the stranded hollow core shaft.
[0015] FIGS. 11A-B are graphs illustrating the torsion/bending
ratio of the rotary shaft in accordance with the one
embodiment.
[0016] FIG. 12A is an OCT image of the Optical imaging catheter
where the catheter sheath is filled with a fluid; and FIG. 12B is
an OCT image of the Optical imaging catheter where the catheter
sheath contains no fluid and the space is occupied by air.
[0017] FIG. 13A is an OCT image of the Optical imaging catheter
where the catheter sheath is filled with a fluid; and FIG. 13B is
an OCT image of the Optical imaging catheter where the catheter
sheath contains no fluid and the space is occupied by air.
[0018] FIG. 14A is an OCT image of the Optical imaging catheter
where the catheter sheath is filled with a fluid and a resolution
mask of 100 .mu.m; and FIG. 14B is an OCT image of the Optical
imaging catheter where the catheter sheath contains no fluid and
the space is occupied by air a resolution mask of 100 .mu.m.
[0019] FIG. 15A is an OCT image of the Optical imaging catheter
where the catheter sheath is filled with a fluid and a resolution
mask of 80 .mu.m; and FIG. 15B is an OCT image of the Optical
imaging catheter where the catheter sheath contains no fluid and
the space is occupied by air a resolution mask of 80 .mu.m.
[0020] FIG. 16A is an OCT image of the Optical imaging catheter
where the catheter sheath is filled with a fluid and a resolution
mask of 60 .mu.m; and FIG. 16B is an OCT image of the Optical
imaging catheter where the catheter sheath contains no fluid and
the space is occupied by air a resolution mask of 60 .mu.m.
[0021] FIG. 17A is an OCT image of the Optical imaging catheter
where the catheter sheath is filled with a fluid and a resolution
mask of 50 .mu.m; and FIG. 17B is an OCT image of the Optical
imaging catheter where the catheter sheath contains no fluid and
the space is occupied by air a resolution mask of 50 .mu.m.
[0022] FIG. 18A is an OCT image of the Optical imaging catheter
where the catheter sheath is filled with a fluid and a resolution
mask of 40 .mu.m; and FIG. 18B is an OCT image of the Optical
imaging catheter where the catheter sheath contains no fluid and
the space is occupied by air a resolution mask of 40 .mu.m.
[0023] FIG. 19A is an OCT image of the Optical imaging catheter
where the catheter sheath is filled with a fluid and a resolution
mask of 30 .mu.m; and FIG. 19B is an OCT image of the Optical
imaging catheter where the catheter sheath contains no fluid and
the space is occupied by air a resolution mask of 30 .mu.m.
[0024] FIG. 20A is a Zemax model of the Optical imaging catheter
where the catheter sheath is filled with a fluid; and FIG. 20B is a
Zemax model of the Optical imaging catheter where the catheter
sheath contains no fluid and the space is occupied by air.
[0025] FIGS. 21A-B are spot diagrams plots showing the arrangement
of individual light rays traced through the system and incident
upon the image plane of the system. The ray patterns are shown at
the best focus of the system as well as at two positions on either
side of the focus in increments of 400 um, showing a total imaging
range of 1.6 mm, where FIG. 21A is the spot diagram for the filled
catheter sheath, and FIG. 21B is the spot diagram for the air
filled catheter sheath.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] Generally speaking, the Optical imaging catheter 100 is
shown in FIG. 1A, comprising a prism 110 and a catheter sheath 120
including a generally tubular body, wherein a space 130 is between
the prism 110 and the catheter sheath 120. The prism 110 receives
an optical radiation 118 from an optical fiber 140 and radially
directs the optical radiation 118 through the catheter sheath 120
to a sample 168 or the luminal surface of a vessel in order to
obtain an optical image. The radial direction may be in the y-axis
or lateral axis of the optical imaging catheter. The optical
radiation 118 may be any electromagnetic radiation from infrared to
ultraviolet wavelengths, particularly radiation of perhaps 380-750
nm. The space 130 may be occupied by air, gas, or fluid. In luminal
imaging, a flushing fluid is typically introduced on the exterior
138 of the catheter sheath 120 to clear the lumen of a vessel for
optical imaging. In one embodiment, the space 130 is occupied by
air, or vacuum, or any other reasonable selection of gas having a
refractive index equal to 1 for practical calculation of the
optical power from corresponding surface; although some variation
exists in the refractive index of air (1.0008), vacuum (1.0000), or
other gases (1.000036-1.00045). The catheter sheath 120 includes an
inner surface 122 and an outer surface 124, which includes an
optical power and a refractive index. The optical power is a
property of the combined radius of curvature and the difference in
the refractive indexes on either side of the surface. The inner
surface 122 and the outer surface 124 have an optical power due to
their boundaries. Typically, a fluid is introduced into space 130
between the inner surface 122 and the prism 110 interface to reduce
the optical power of the inner surface 122 of the catheter sheath.
In one embodiment, the optical power of the catheter sheath 120 is
anisotropic with most of the optical power in one direction. The
prism 110 includes an anterior prism interface 112 and a posterior
prism interface 114. The Optical imaging catheter 100 comprises the
optical fiber 140 optically coupled to a lens 150, and a protection
bearing 170 housing the lens 150 and prism 110, whereby the
catheter sheath 120 is coupled to the posterior surface of the
protection bearing 170. The protection bearing 170 includes an
opening 172 optically coupled to the prism 110 to direct the
optical radiation through the catheter sheath 120. Alternatively,
the Optical imaging catheter 100 includes a ferrule 160 optically
coupled to the optical fiber 140 and the lens 150. In one
embodiment, the lens 150 is a gradient index lens (GRIN).
[0027] The optical catheter 100 is optically coupled to an imaging
modality for imaging of anatomical passageways, such as
cardiovascular, neurovascular, gastrointestinal, genitor-urinary
tract, or other anatomical luminal structures. In one embodiment,
the imaging modality is an Optical Coherence Tomography ("OCT")
system. OCT is an optical interferometric technique for imaging
subsurface tissue structure with micrometer-scale resolution.
Alternative optical imaging modalities include spectroscopy,
optical therapies, Raman spectroscopy, and the like. In another
embodiment, the imaging modality is an ultrasound imaging modality,
such as intravascular ultrasound ("IVUS), either alone or in
combination with OCT imaging. The OCT system may include tunable
light source, a tunable laser, a broadband light source, or a
tunable superluminescent diode, or multiple tunable light sources
with corresponding detectors, may be a spectrometer based OCT
system or a Fourier Domain OCT system, as disclosed in U.S.
application Ser. No. 12/172,980, herein incorporated by reference,
or may be a Doppler OCT system. The Optical imaging catheter may be
integrated with IVUS by an OCT-IVUS catheter for concurrent
imaging, as described in U.S. application Ser. No. 12/173,004,
herein incorporated by reference. Alternatively, the imaging
modality may be spectroscopic, ultrasound or IVUS, therapeutic
modalities, diagnostic modalities, or alternative imaging
modalities.
[0028] As shown in FIGS. 1A and 1B, the Optical imaging catheter
100 comprises a plurality of optical interfaces including a
posterior prism interface 114, an anterior prism interface 112, an
inner surface of the catheter sheath 122, and the outer surface of
the catheter sheath 124, a fiber-tip/lens interface 142, a
lens/prism interface 152, a prism/space interface, a space
130/inner surface of the outer catheter sheath 122 interface, an
outer surface of the catheter sheath 122/flush material interface.
The optical interfaces contribute to optical aberrations in the
Optical imaging catheter 100. Optical aberrations are departures of
the performance of an optical system from the predictions of
paraxial optics. Aberrations lead to a blurring of the image
produced by an image-forming optical system and occurs when light
from one point of an object after transmission through the system
does not converge into (or does not diverge from) a single point.
The Optical imaging catheter balances optical aberrations and
allows recording of high quality images, while relaxing the
requirement of a fluid occupying the space 130 between the prism
110 and the inner surface of the catheter sheath 120.
[0029] A number of factors can contribute to the optical
aberrations, such as spherical aberration, coma, astigmatism, field
curvature, chromatic aberration, distortion, and the like, in the
Optical imaging catheter system. Astigmatism occurs with different
focal lengths for rays of different orientations, resulting in a
distortion of the image. In particular, rays of light in horizontal
and vertical planes are not focused at the same plane. Chromatic
aberration occurs when bringing different colors or wavelengths of
light that are focused at different points. Distortion is caused
because the transverse magnification may be a function of the
off-axis image distance. Distortion is classified as positive
(so-called pincushion distortion), or negative (so-called barrel
distortion). Field curvature (a.k.a. Petzval field curvature)
results because the focal plane is actually not planar, but
spherical. Field curvature and distortion are not typically of
concern for catheter-based designs in which the entire optical
system is moved for each point; and these would be considered if,
for example, the lens was stationary and some other scanning
element moved in order to point the beam at the location of
interest. Spherical aberration commonly occurs in a spherical lens
or mirror because these do not focus parallel rays to a point, but
instead along a line. Therefore, off-axis rays are brought to a
focus closer to the lens or minor than are on-axis rays. Spherical
aberration can have a sign--positive or negative.
[0030] The Optical imaging catheter balances the optical
aberrations due to different surfaces at the optical interfaces so
that the composite aberration or total aberration is substantially
reduced or nearly zero. The Optical imaging catheter system reduces
optical aberrations such as astigmatism, by aberration balancing
all of the optical interfaces while maintaining the space 130
between the prism and inner surface of the catheter sheath filled
with air.
[0031] There is an assumption that air at the inner catheter 122
and prism 110 interface, the cylinder of the sheath 120 distorts
the optical image and introduces astigmatism and other optical
aberrations into the optics of the catheter making the system
unsuitable for imaging. Typically, a fluid is introduced into space
between the inner surface 122 and prism 110 interface to reduce the
optical power of the inner surface 122 of the catheter sheath.
Reduction of the optical power of the inner surface of the catheter
sheath 122 reduces optical aberrations (e.g., astigmatism) so as to
prevent the OCT image quality from being altered. By not including
the fluid in the space 130 between the prism 110 and inner surface
122 of the catheter sheath, a reduction of NURD, maintaining
sterility of the catheter environment, and relaxing requirement for
additional ports to allow air and some index-matched fluid to exit
the distal end of the catheter are implicated for the Optical
imaging catheter 100.
[0032] The magnitude of aberrations introduced at each surface is
dependent on the curvature of the surface, tilt or angular
orientation of the surface, difference in refractive index of
materials on each side of the interface. For a spherical surface,
the optical power is given by power=(n_1-n_2)/R where n_1 is
refractive index of the first material, n_2 is the refractive index
of the second material and R is the radius of curvature. The
curvature of a surface may be anisotropic where the principal
surface curvatures are unequal. The inner surface 122 of the
catheter sheath is a surface with anisotropic curvature, because
the curvature in a plane perpendicular to longitudinal axis of the
catheter is not equal to the curvature in a plane containing the
longitudinal axis of the catheter. Surfaces with anisotropic
curvature introduce astigmatism (one of the third order Seidel
aberrations).
[0033] Alternatively, the index mismatch between the air in the
space 130 and inner surface 122 of the catheter sheath may
contribute to clear images, when not including a fluid in the space
130 between the prism 110 and the inner surface 124 of the catheter
sheath. When a gas (such as air) occupies the space 130 between the
prism 110 and inner surface 122 of the catheter sheath, the
anisotropic curvature of the inner surface 122 of the catheter
sheath introduces astigmatism and other aberrations into the
optical radiation 118. The outer surface 124 of the catheter can
also introduce optical aberrations if the flushing fluid is not
index matched to the catheter outer sheath material.
[0034] In the Optical imaging catheter 100, the space 130 between
the prism 110 and inner surface 124 of the outer catheter sheath is
occupied by a gas and the aberrations introduced by the inner
surface 124 of the outer catheter sheath are balanced by
configuring other elements of the catheter. For example, by tilting
the prism by an angle of 1-10 degrees off the y-axis or x-axis so
that light exiting the prism is not directed perpendicular to the
longitudinal axis of the Optical imaging catheter, as shown in FIG.
1C, and has a directional component along the longitudinal axis of
the catheter, the astigmatism introduced by the catheter sheath may
be modified to better balance optical aberrations. As shown in FIG.
1A, the light exiting the prism, or the output beam, is shown in a
perpendicular direction. As shown in FIG. 1C, the prism may be
tilted to produce a non-perpendicular output beam, such as by
connecting the prism to the ferrule at an angle with optical glue,
and the like. Alternatively, the prism 110 may include a tilted
surface or angled surface, such that the output beam is
non-perpendicular relative the longitudinal axis of the Optical
imaging catheter. Such a design does not require aspheric surfaces
or aspheric lenses.
[0035] Alternatively, the prism 110 and lens 150 may be a
bi-cylindrical integrated micromirror/microlens 162 for collecting,
redirecting, and focusing light, as shown in FIG. 3A-3B. The
bi-cylindrical micromirror/microlens comprises an optical element
to collect light diverging longitudinally out of a fiber optic
cable 140, redirect the light with a cylindrical surface 164 radial
component, and then refocus the light with a second cylindrical
surface 166 along a y-axis. The bi-cylindrical
micromirror/microlens is one integrated element including a
reflective cylindrical surface 164 to collect, redirect, and focus
light in one dimension (x-axis), and a second cylindrical
transmissive/lensing surface 166 to focus light in the orthogonal
(y or z-axis) direction. The reflective cylindrical surface 164 may
include a mirrored coating or a totally-internally-reflecting
surface. The second cylindrical transmissive/lensing surface 166
may be a convex lens. Cylindrical surfaces can have cylindrical
radii of curvature optimized using simulation or optical design
software to provide a focused spot profile, which will likely be
less ideal than spherical or toroidal surfaces. The bi-cylindrical
micromirror/microlens is easier to shape than a single toroidal
surface because collecting/focusing of light in both spatial
dimensions is accomplished in separate cylindrical surfaces which
are individually more straightforward to grind or mold. The
bi-cylindrical micromirror/microlens can be made with glass or
transparent polymer material; can be rotated for cylindrical/radial
scanning apparatus, or translated longitudinally for linear
scanning apparatus; can be designed/constructed to compensate for
capsule astigmatism; and can be mounted directly to cleaved fiber
tip using index-matching epoxy or other optical adhesive.
[0036] Alternatively, the prism 110 comprises a toroidal minor to
collect light diverging longitudinally out of a fiber optic cable,
redirect the light with a radial component (in the y-axis), and
then refocus the light onto a sample. The toroidal minor includes a
mirrored surface with a toroidal surface to collect and refocus and
a tilt to introduce radial component. The toroidal surface is not
spherical or parabolic and compensates for astigmatism introduced
by tilting the reflecting element. The toroidal surface can also be
designed to compensate for astigmatism introduced into the beam by
an encapsulating cylindrical element. The toroidal mirror can be
rotated for cylindrical/radial scanning apparatus, or translated
longitudinally for linear scanning apparatus. The toroidal minor's
mirrored surface can be on concave (air) side or substrate (convex)
side of element and the mirrored surface could include a metallic
coating similar to any standard mirror.
[0037] Alternatively, the prism 100 comprises a curved output face
with a radius of curvature similar to that of the optical fiber or
inner surface 122 or radius of the catheter sheath. In this design,
the prism 110 curved output face and the inner surface 122 of the
catheter sheath act as a negative and positive lens, cancelling out
the majority of the focusing power in this lateral dimension and
eliminating much (not all) of the advantage of a fluid filled
catheter design.
[0038] In another embodiment, the refractive index of the catheter
sheath 120 material may be selected to control the aberrations
introduced at the inner surface 122 of the outer catheter sheath
and the outer surface 124 of the outer catheter sheath. In one
embodiment, a polymer with a refractive index equal to 1.34 may be
used. The polymer of the sheath is detailed below, such as
perfluoroalkoxy (PFA) polymer, polytetrafluoroethylene (PTFE)
partially covered with a polyether block amide (Pebax.RTM.) at the
distal end, or tetrafluoroethylene and hexafloropropylene
co-polymer (FEP), and the like. Alternatively, the catheter sheath
120 may include a refractive index similar to the medium outside
exterior surface 168 at which the catheter is imaging, such as
saline or blood. Alternatively, the catheter sheath 120 may have a
refractive index so that the aberrations (astigmatism) of the
flush-sheath material balance other aberrations in the imaging
system.
[0039] In one embodiment, the catheter sheath may include an index
of refraction between about 1.29 to 1.39; alternatively, between
about 1.30 to 1.38; alternatively, between about 1.31 to 1.37;
alternatively, between about 1.30-1.39. In one embodiment, the
catheter sheath 120 includes a reduced refractive index, which is
approximately 1.34. The inner surface 122 of the catheter sheath
includes a radius of curvature, where the radius of curvature is
larger than the outer surface 124 of the catheter sheath, and where
a smaller radius results in more optical power.
[0040] Air, catheter sheath material, and the fluid material each
has an optical power contributing or affecting the refractive
index. The optical power is equal to the index of refraction
divided by the radius of the surface. The optical power of the
inner surface may be related by Equation (1):
index of sheath - index of air radius of the inner surface =
opitcal power of the inner surface ( 1 ) ##EQU00001##
index of sheath-index of air=optical power of the inner surface (1)
radius of the inner surface
[0041] The optical power of the outer surface of the sheath may be
related by Equation (2)
index of flushing agent - index of outer surface radius of the
outer surface = opitcal power of the outer surface ( 2 )
##EQU00002##
index of flushing agent-index of outer surface=optical power of the
outer surface (2) radius of the outer surface
[0042] The two optical powers of the inner and outer surface may
cancel each other or provide for compensating optical power as to
reduce aberrations. In one embodiment, the absolute value of the
optical power of the inner surface 122 is higher than the outer
surface 124 because the radius of the inner surface is shorter than
the outer surface, as discussed below.
[0043] The cylindrical lens effects of the sheath are shown in FIG.
1B. The outer sheath includes a thickness T, which results in the
inner surface 122 and an outer surface 124. In one embodiment, the
thickness T is constant over the entire circumference of the
catheter sheath. The inner surface 122 includes a radius R1 and the
outer surface 124 includes a radius R2, which results in the
generally tubular body of the catheter sheath. The curvature of the
inner and outer surface of the catheter sheath is related to the
radii R1 and R2, respectively, where curvature equals the
reciprocal of the radius, i.e. curvature=1/R. In between the inner
surface 122 of the sheath is the air space 130, which continues
through the protection bearing 170 to the prism 110.
[0044] In one embodiment, the R1 is between about 0.3000 to 0.4000
mm; alternatively, between about 0.3100 to 0.3900 mm;
alternatively, between about 0.3200 to abut 0.3800 mm;
alternatively, about 0.3302 mm. In one embodiment, the R2 is
between about 0.4100 to 0.5100 mm; alternatively between about
0.4200 to 0.5000 mm; alternatively, between about 0.4400 to 0.4900
mm; alternatively, about 0.4826. In one embodiment, the capsule
thickness T is between about 0.1300 to 0.1700 mm; alternatively,
between about 0.1400 to 0.1600 mm; alternatively, between about
0.1500 to 0.1599 mm; alternatively about 0.1524 mm. In one
embodiment, the thickness T contributes to maintaining a ratio
between R1 and R2, such that the ratio of R1:R2 is between about
0.60 to 0.80; alternatively, between about 0.65 to 0.75;
alternatively between about 0.67 to 0.70; alternatively about 0.68.
In one embodiment, the cylindrical surface of the inner surface 122
of the outer sheath contributes to an optical power and the
cylindrical surface of the outer surface 124 of the outer sheath
contributes to an optical power. The optical power of the inner
surface 122 is cancelled by the optical power of the outer surface
124 to prevent any major detriments or aberrations to the imaging
quality of the Optical imaging catheter system. Therefore, the
index-matching of the sheath material to the sample medium is no
longer necessary. If the flush material has a small refractive
index compared to the catheter sheath material then some aberration
balancing is obtained.
[0045] Alternatively, the optical power given by a flushing fluid,
for example, saline or a blood-substitute, which may have an index
of refraction of .about.1.3, then the sheath 120 is made with a
similar index of refraction, i.e., .about.1.3 by varying the
optical power of the inner surface 122 and the outer surface 124 of
outer sheath. The differences between the refractive indices of the
sample medium, the air between the sheath and the prism is
accounted for by the optical power of the catheter sheath 120.
Lenses that have an aspheric surface are also within the scope of
the embodiments. Aspheric lenses are most easily made using the
reflow technology generally known in the art.
[0046] FIG. 2A shows the encircled energy at focus to verify spot
size. For a Gaussian beam propagating in free space, the spot size
w(z) will be at a minimum value w.sub.0 at one place along the beam
axis, known as the beam waist. In one embodiment, the spot size
estimate is between about 5 to 40 microns, alternatively, between
about 10 to 30 microns, alternatively, between about 15 to 25
microns, alternatively about 20 microns. The working distance is
the distance between the posterior prism interface and the sample
being imaged. In one embodiment, the working distance is from the
outer surface to focus (catheter sheath capsule OD to focus) is
between about 1.50000 to 1.79999 mm, alternatively, between about
1.55555 to about 1.71111, alternatively, between about 1.599999 to
about 1.65555, alternatively about 1.61452 mm.
[0047] FIG. 2B is the "top" view of lens 150-prism 110; and FIG. 2C
is the "side" view of lens 150-prism 110.
[0048] Optical Imaging Catheter System
[0049] With particular reference to FIG. 4A, a Optical imaging
catheter system 10 is depicted comprising a monolithic outer sheath
120 including a central sheath lumen extending substantially the
entire length of the monolithic outer sheath 120 and a
monolithically formed flexible tip 28. The term "monolithic" or
"monolithically formed" is without any joints or junctions formed
by thermal, chemical or mechanical bonding.
[0050] The catheter system 10 construct for in vivo imaging,
particularly, imaging of anatomical passageways, such as
cardiovascular, neurovascular, gastrointestinal, genitor-urinary
tract, or other anatomical luminal structures. The catheter 10 is
coupled to an imaging modality, and in one embodiment the imaging
modality is an Optical Coherence Tomography ("OCT") system. OCT is
an optical interferometric technique for imaging subsurface tissue
structure with micrometer-scale resolution. In another embodiment,
the imaging modality is an ultrasound imaging modality, such as
intravascular ultrasound ("IVUS), either alone or in combination
with OCT imaging. The OCT system may include tunable laser or
broadband light source or multiple tunable laser sources with
corresponding detectors, and may be a spectrometer based OCT system
or a Fourier Domain OCT system, as disclosed in U.S. Provisional
Application 60/949,467, herein incorporated by reference. The
catheter system 10 may be integrated with IVUS by an OCT-IVUS
catheter for concurrent imaging, as described in U.S. Provisional
Application 60/949,472, herein incorporated by reference. As shown
in FIG. 4B, the catheter system 10 comprises the monolithic outer
sheath 120 that houses an acoustical or optical train 30. The
optical train 30 includes a length of d, and the catheter 10
includes a length of D from the distal portion of the FORJ 60 to
the distal monolithic tip 28 of the catheter monolithic outer
sheath 120. In use, the optical train 30 rotates under the
influence of an external rotary drive motor (not shown) coupled to
a rotary drive shaft 40 and an optical fiber 50 through a Fiber
Optic Rotary Junction 60 ("FORJ"), thereby also rotating the
optical train 30. The rotary drive shaft 40 includes a drive shaft
lumen, through which the optical fiber 50 is concentrically or
coaxially disposed.
[0051] As shown in FIG. 4B, a plug-in connector 62 is coupled to
the proximal end of the rotary drive shaft 40, to couple the
catheter 10 to the rotary drive motor. The plug-in connector may
include a Subscription Channel (SC)-Angled Physical Contact (APC)
connectors to ensure lower insertion loss and back reflection. The
FORJ 60 may include fiber pigtail, ST, FC, SC, FC/UPC receptacles,
or any combination receptacles on the rotor or the stator side
(Princetel, Lawrenceville, N.J.). Alternatively, the connector 62
may include a centering boot to center the optical fiber with
respect to the rotary drive shaft 40. The centering boot includes a
first lumen to accept the optical fiber and a second lumen to
accept the rotary drive shaft 40. The FORJ is provided to permit
rotation of the optical fiber and rotary shaft while maintaining
optical communication with the radiant light source (e.g., tunable
laser or broadband emitter) with minimal insertion loss and return
loss performance. The rotary drive motor imparts rotational
movement to the rotary drive shaft 40 either by a DC brushless
motor and the like. The rotary drive motor may rotate at
revolutions per minute (RPM) for a 360 degree rotation of the
rotary drive shaft 40. A linear pull back mechanism may also be
coupled to the rotary drive shaft, which may include a stepping
motor. The monolithic outer sheath 120 is held stationary, relative
to the rotary drive shaft 40, by use of a permanently affixed
retaining bead 42 that is connected to the frame of the rotary
drive motor. The bead includes a first lumen and a second lumen
smaller than the first lumen, whereby the second lumen communicates
through the first lumen. In one embodiment, the bead is a single
machined aluminum part that is attached to the monolithic outer
sheath 120 by means of mechanical thread engagement and
adhesive.
[0052] The rotary drive shaft 40 is concentrically or coaxially
positioned within the central lumen of the monolithic outer sheath
120 and substantially extends along the longitudinal length D of
the central lumen. Coaxially engagement between the rotary drive
shaft 40 and the central lumen of the monolithic outer sheath 120
may be accomplished with the OD of the rotary drive shaft 40
matching the ID of the monolithic outer sheath 120 or varying the
OD of the rotary drive shaft to the ID of the monolithic outer
sheath 120. The rotary drive shaft 40 terminates at its distal end
in proximity to the distal end of the central lumen adjacent the
proximal end of the catheter 10. The optical train 30 is carried by
the rotary drive shaft 40, with the optical fiber 50 running the
length of the rotary drive shaft 40 through the drive shaft lumen.
The rotary drive shaft 40 permits transmission of torque from the
rotary motor to the optical train 30 along the entire length of the
catheter shaft. As such, the rotary dive shaft 40 includes having
sufficient torsional rigidity or torqueability and lateral
flexibility or flexion to navigate potentially tortuous anatomical
pathways while minimizing NURD to ensure accurate imaging.
Torqueability is the ability of the rotary drive shaft to be turned
or rotated while traversing bends or turns in the patient's
vasculature.
[0053] In one embodiment, the rotary drive shaft 40 includes a
hypotube metal over a proximal portion or the entire proximal
section of the rotary drive shaft 40. Alternatively, the rotary
drive shaft 40 includes a stranded hollow core shaft extending the
substantial length of the rotary drive shaft 40. The stranded
hollow core shaft may comprise a plurality of helically wound wire
strands so that mechanical rotation of the rotary drive shaft is in
the same direction as the helical wire strands. The stranded hollow
core shaft may include an inner stranded drive shaft and outer
stranded drive shaft, where in outer stranded drive shaft is wound
in the opposite helical direction than the inner stranded drive
shaft. The protection bearing 170 may be coupled to either the
stranded hollow core shaft or the hypotube metal. The stranded
hollow core shaft, the hypotube metal, or a combination thereof
provides sufficient lateral flexibility to ensure access through
highly tortuous passageways, such as the aortic arch and coronary
arteries. In another embodiment, the hypotube metal is
concentrically or coaxially fitted over a proximal portion or the
entire proximal section of the stranded hollow core shaft. The
coaxial fitting of the hypotube metal over the stranded hollow core
shaft may be accomplished by allowing the OD of the stranded hollow
core shaft to vary from the ID of the hypotube metal tube by about
0.001 to 0.009 inches. In this manner the highly flexible stranded
hollow core shaft lessens NURD by the relatively less flexible
hypotube metal at the more distal end of the catheter to permit
greater distal end flexion or lateral flexibility. While
maintaining flexibility, the rotary drive shaft also maintains the
pushability, the ability of the catheter to be efficiently and
easily pushed through the vasculature of the patient without damage
to the catheter or patient, getting blocked, kinked, whipped,
etc.
[0054] In accordance with another embodiment, the rotary drive
shaft 40 includes a shortened hypotube metal shaft attached in a
generally overlapping attachment with a section of stranded hollow
core shaft, with there being a very slight mismatch in the outer
diameters between the hypotube metal and the stranded hollow core
shaft to permit concentric or coaxial engagement and attachment
between the respective end sections. Alternatively, the hypotube
metal and the stranded hollow core shaft may have generally the
same outer diameter to permit end-to-end connection, such as a butt
weld there between. The stranded hollow core shaft includes single
layer uni-directional and multi-layer directional winding
configurations when coupled to the hypotube metal shaft.
[0055] In one embodiment of the monolithic outer sheath 120, at
least a portion of the monolithic outer sheath is fabricated of an
optically transparent polymer, such as, for example,
perfluoroalkoxy (PFA) polymer, polytetrafluoroethylene (PTFE)
partially covered with a polyether block amide (Pebax.RTM.) at the
distal end, or tetrafluoroethylene and hexafloropropylene
co-polymer (FEP). The optically transparent polymer is transparent
in the spectral region of light being used for imaging. Similar
biocompatible optically transparent polymers having similar
properties of lubricity, flexibility, optical clarity,
biocompatible and sterilizability may alternatively be employed to
form the catheter shaft. In accordance with one embodiment, FEP is
used to fabricate the catheter sheath. The catheter sheath is
fabricated in a monolithic manner such that the central lumen
terminates at the atraumatic monolithic tip without any intervening
joints. Atraumatic is not producing injury or damage. As shown in
FIG. 4B, a rapid exchange guidewire lumen 22 is formed entirely
within the atraumatic monolithic tip with both the proximal
guidewire port and the distal guidewire port accessing the
guidewire lumen distal the termination of the central lumen of the
catheter sheath. The guidewire is the thin wire over which the
catheter rides.
[0056] As shown in FIG. 4B, a guidewire lumen 22 is formed in the
distal portion of the monolithic outer sheath 120, while a central
sheath lumen 32 extends proximally from the distal portion of the
monolithic outer sheath 120. The guidewire lumen 22 includes a
guidewire exit 24 and a guidewire entrance 26. The guidewire lumen
22 is positioned entirely in the distal terminus of the central
sheath lumen 32 such that the guidewire (not shown) may be rapidly
exchanged and does not interfere with the rotational movement of
the optical train 30, rotary drive shaft 40 or the protection
bearing 170 within the central lumen of the catheter sheath
120.
[0057] In accordance with a another embodiment, the rotary drive
shaft 40 includes the protection bearing 170, which houses the
distal end optics or distal end acoustics at the distal end of the
catheter 10, as shown in FIG. 4B. The protection bearing 170 may be
coaxially mounted over the distal end optics, or alternatively,
molded over the distal end optics or the distal end optics molded
into the protection bearing 170. The protection bearing 170 may
include a diameter to coaxially engage the distal end optics to
ensure a 1:1 rotation of the protection bearing 170 with the distal
end optics. In one embodiment, the protection bearing 170 may
include a Platinum/Iridium tube and is formed with an opening 92.
The opening may be positioned in optical alignment with the prism
90 in order to permit light to pass through the opening 92 and
optically communicate with the sample being imaged, as shown in
FIG. 4B. The Platinum/Iridium tube may comprise about 75-97% Pt and
about 3-25% Jr, which provides radiopacity. Alternatively, the
metal hypotube of the rotary drive shaft replaces the protection
bearing 170, where the metal hypotube extends coaxially over the
distal end optics and includes an opening for the distal end
optics. Alternatively, the protection bearing 170 may include other
metals nitinol, i.e. nickel titanium alloy, or another
pseudometallic biocompatible alloy such as stainless steel,
tantalum, gold, platinum, titanium, copper, nickel, vanadium, zinc
metal alloys thereof, copper-zinc-aluminum alloy, and combinations
thereof, with radiopaque markers in order to provide visible
reference points. Alternatively, the protection bearing 170 may
include an epoxy rounded tip to ensure smooth rotational
translation of the protection bearing 170. Alternatively, the
protection bearing 170 includes a bearing plug 74 within the distal
portion of the protection bearing's distal lumen. The bearing plug
74 may coaxially fit into the distal portion of the protection
bearing 170, or may be secured by adhesive, welding, and the like.
The bearing plug 74 may include a metal material, alternatively a
metal/polymer material, alternatively stainless steel.
[0058] In accordance with one embodiment, the optical train 30
includes the monolithic outer sheath 120 the optical fiber 50 in
association with the rotary drive shaft 40, the protection bearing
170 housing a ferrule/gradient index lens ("GRIN") assembly 80 at a
distal end of the optical fiber 50, as shown in FIG. 1A. The
ferrule/GRIN assembly 80 optically coupled to a prism 90 or mirror
to conduct light between the optical fiber 50, ferrule/GRIN
assembly and the sample being imaged. The distal end of the optical
train 30, i.e., the distal end optical fiber 50, the ferrule/GRIN
lens assembly and the prism 90, are all secured within the
protection bearing 170 and rotate with the protection bearing 170,
under the influence of the rotary drive shaft 40, within the
central lumen 32 of the catheter sheath 120. In use, the optical
train 30 rotates under the influence of an external rotary drive
motor coupled to the rotary drive shaft and optical fiber through
the FORJ 60, thereby also rotating the ferrule/GRIN lens 80
assembly and the prism 90 to emit optical energy 94 at an angle and
through 360 degrees around the monolithic outer sheath 120.
[0059] As shown in FIG. 1A, the ferrule/GRIN assembly 80 includes a
GRIN lens 82 and a ferrule 84. The optical fiber 50 may include a
core, cladding and buffer and is optically coupled to the ferrule
84. The ferrule 84 is optically coupled to the GRIN lens 82 and
prism 90 to transmit light between the optical fiber 50, GRIN lens
82 and the sample being imaged. The ferrule 84 at a distal end of
the optical fiber 50 supports and terminates the distal end of the
optical fiber 50, where the optical fiber 50 may be coaxially
fitted within the ferrule 84. The ferrule may include a lumen and a
tapered cladding to coaxially couple the core of the optical fiber
50. When the optical fiber 50 core is coupled with the ferrule 84,
the fiber 50 may not include the buffer. The optical fiber 50 may
be potted or adhesively secured to the ferrule 84 at point 86 with
optical glue, curing adhesive, and the like, as to provide a
coaxial alignment of the optical fiber and the ferrule. The GRIN
lens 82 is optically coupled to a distal surface of the ferrule 84
at point 88, such as by optically transparent adhesive. The GRIN
lens 82 and the ferrule 84 may include an angled engagement, where
the angle offset of the distal end of the ferrule 84 matches the
angle offset of the proximal end of the GRIN lens 82. The prism or
minor 90 is optically coupled to the distal surface of the GRIN
lens 82 at point 98, such as by optically transparent adhesive. The
distal surface of the GRIN lens 82 may include an angled offset.
The prism 90 may include a right angled prism and the angles
between prism facets may be constructed to provide balancing of
astigmatism introduced by the sheath. An optical pathway is formed
along the longitudinal axis of the rotary drive shaft 40, the
catheter sheath 120, and protection bearing 170. The prism or
mirror 90 serves to redirect at least some portion of the light
away from the central longitudinal axis and generally radially
outward, through the optically transparent portion of the
monolithic outer sheath 120 to communicate with the body tissue
being imaged throughout 360 degrees.
[0060] Some of the incident light may not be redirected radially
outward. The prism angles may be constructed to provide a balancing
of astigmatism introduced by the catheter sheath. The incident
light may not necessarily all be used for imaging, where additional
optical energy beams are for therapeutic purposes or possibly some
other energy source, as disclosed in commonly assigned application
entitled "Method and Apparatus for Simultaneous Hemoglobin
Reflectivity Measurement and OCT Scan of Coronary Arteries,
Thrombus Detection and Treatment, and OCT Flushing", PCT
application No. PCT/US2009/038832, filed Mar. 30, 2009, herein
incorporated by reference.
[0061] Catheter Sheath
[0062] As shown in FIG. 5A, one embodiment of the monolithic outer
sheath 120 may include an outer layer 210 and an inner layer 220 to
form a laminate structure 100. The outer layer 110 may be
constructed of Pebax.RTM. extending the substantial length along
the proximal portion of the catheter sheath and the outer layer 110
provides greater structural rigidity relative to the inner layer
120. The inner layer 120 may be constructed of PTFE, with the PTFE
inner layer 120 extending distally from the Pebax.RTM. outer layer
110 and forming the most distal section, which is optically
transparent and flexible to permit optical communication to the
sample and greater traversability for the catheter during insertion
or retraction within the anatomical passageway. Alternatively,
various other materials, such as FEP, could be used in place of
PTFE in the given example. FIG. 5B shows the solid monolithically
formed tip 28 and a base layer 230 and a top layer 240. The base
layer 230 may be constructed of Pebax.RTM. substantially along the
base of the catheter sheath and provides greater structural
rigidity relative to the top layer 240. The greater structural
rigidity allows the monolithic outer sheath greater pushability
along the proximal portion of the monolithic outer sheath.
Alternatively, the base layer 230 may include a plug 232. The plug
232 may include a space between the protection bearing 170 when the
protection bearing 170 engages with the monolithic outer sheath
120. The plug 132 may include an angled engagement with distal
portion of the sheath lumen to impart increased flexibility to the
distal end of the monolithic outer sheath 120. The plug 132 may
include polymeric material, including, but not limited to PTFE,
FEP, and the like. The top layer 140 may be constructed of PTFE,
with the PTFE top layer 140 extending distally from the Pebax.RTM.
base layer 130, which provides greater flexibility along the distal
end of the monolithic outer sheath for navigating tortuous
pathways. Alternatively, the layers of the monolithic sheath 120
include a coating either on the outer layers or inner layers for
smooth transitioning and less friction during navigation. Such
coatings may be biocompatible, polymeric, saline, and the like.
[0063] FIG. 6 depicts the monolithic outer sheath 120 prior to the
guidewire lumen 22 being formed. In one embodiment, the solid
monolithically formed tip 28 is formed by first providing a tubular
catheter sheath precursor 250, preferably placing a forming mandrel
in the central sheath lumen 252 of the tubular catheter sheath
precursor 250, then thermoforming the solid tip 254 into a desired
shape. Thermoforming is any process of forming thermoplastic sheet,
which consists of heating the sheet and forcing it onto a mold
surface. The sheet or film is heated between infrared, natural gas,
or other heaters to its forming temperature, then it is stretched
over or into a temperature-controlled, single-surface mold. The
sheet is held against the mold surface unit until cooled, and the
formed part is then trimmed from the sheet. There are several
categories of thermoforming, including vacuum forming, pressure
forming, twin-sheet forming, drape forming, free blowing, simple
sheet bending, and the like. The shape of the monolithic tip 28 may
be rounded, radiused, tapered, or generally frustroconical with an
atraumatic distal end formed. A radiused tip includes an angle of
curvature that is derived from the radius of the outer sheath OD,
where the angle or degree of curvature equals the reciprocal of the
radius (1/R).
[0064] The guidewire lumen 256, as shown in phantom depicted in
FIG. 7 may then be formed by bending the solid distal tip 28 and
drilling a straight hole angularly through the distal end and to a
lateral side of the distal tip, then releasing the bend in the tip
to provide distal end and proximal side guidewire ports and a
curved lumen. Alternatively, the tip may be formed with the
guidewire lumen 256 during the thermoforming process by providing
the appropriate mold. The resulting guidewire lumen 256 may or may
not maintain a straight longitudinal axis, where the longitudinal
axis runs along the x-axis of the sheath 120, as shown in phantom
in FIG. 7. In one embodiment, the guidewire lumen 256 includes a
straight longitudinal axis 260 and a non-longitudinal axis 262. The
straight longitudinal axis 260 is included for some length along
the distal portion of the catheter sheath body and associated with
the guidewire entrance 262. The non-longitudinal axis 262 is
included for some length along the proximal portion of the catheter
body and is associated with the guidewire exit 264. The angled
measurements for the non-longitudinal axis 262 near the guidewire
exit can be any angle relative to the longitudinal axis 260 as to
provide for the rapid exchange of the guidewire and no kinking or
whipping of the guidewire. In one embodiment, the angle or degree
of curvature for the non-longitudinal axis relative the
longitudinal axis is about 0.1 to 10 degrees, about 1 to 8 degrees,
or about 1.5 to 6 degrees.
[0065] The monolithic outer sheath 120 includes the absence of or
potential for uneven surfaces that may irritate or damage tissues
in anatomical passageways or interfere with the guiding catheter
during retraction or advancement of the catheter, the absence of
joints which could separate and dangerously embolize, and the
absence of joints which could leak fluid into or out of the sheath.
Because of its monolithic construction, the central lumen of the
outer catheter sheath may be filled with air or a fluid that could
serve to (a) provide lubrication between the monolithic outer
sheath and the rotary shaft, (b) reduce optical astigmatism
originating from the cylindrical curvature of the inner sheath
surface due to the lower index of refraction mismatch of liquid
when compared with air, (c) provide additional column strength and
kink resistance to the catheter, (d) viscously dampen NURD, or (e)
provide negative torsional feedback to stabilize or dampen
non-uniformities in rotation.
[0066] The monolithic design of the catheter outer sheath and the
monolithic atraumatic tip further permit different engineering of
material properties along the length of the monolithic outer
sheath. For example, the durometer of the catheter sheath may be
varied along the length of the catheter sheath during manufacture
of the sheath precursor material; the inner and/or outer diameter
of the catheter sheath may be made to vary, such as by tapering,
along the length of the continuous monolithic tube; the wall
thicknesses of the catheter sheath and the concomitant flexibility
profiles may be varied along the longitudinal length of the
catheter sheath, or the catheter sheath may be variably reinforced
to alter the flexibility profiles along the longitudinal axis of
the catheter sheath, such as by applying a braiding material, a
concentric reinforcement, such as another overlaid tube, or
combinations of the foregoing. The braiding material may be a
polymer formed from conventional braiding machines. The durometer
is the hardness of the material, as defined as the material's
resistance to permanent indentation. The two most common scales,
using slightly different measurement systems, are the ASTM D2240
type A and type D scales. The A scale is for softer plastics, while
the D scale is for harder ones. However, the ASTM D2240-00 testing
standard calls for a total of 12 scales, depending on the intended
use; types A, B, C, D, DO, E, M, O, OO, OOO, OOO-S, and R. Each
scale results in a value between 0 and 100, with higher values
indicating a harder material.
[0067] Rotary Drive Shaft
[0068] Turning now to FIGS. 8-10, alternative embodiments of the
rotary drive shaft 40 are illustrated. As discussed above, the
rotary drive shaft 40 connects the distal end optical train and
optics to the rotary motor and the transmission of rotary torque to
the distal end optics while minimizing NURD. As shown in FIG. 8,
the rotary drive shaft 40 may comprise entirely of a hypotube metal
drive shaft 400, a stranded hollow core shaft 500 or a combination
of the hypotube metal drive shaft 400 joined with the stranded
hollow core shaft 500, or alternating combinations of the hypotube
metal drive shaft 400 and stranded hollow core shaft 500. The
hypotube metal drive shaft may comprise nitinol, i.e. nickel
titanium alloy, or another pseudometallic biocompatible alloy such
as stainless steel, tantalum, gold, platinum, titanium, copper,
nickel, vanadium, zinc metal alloys thereof, copper-zinc-aluminum
alloy, and combinations thereof. Alternatively, the metal hypotube
shaft 400 may include a reinforced telescoping inner assembly
coaxially coupled over the proximal end of the metal hypotube shaft
400. The reinforced telescoping inner assembly is stronger than the
metal hypotube shaft 400 to prevent buckling, bending, or shearing.
The reinforced telescoping inner assembly includes a metal tube
stainless steel design coupled to the centering boot to permit
longer push-forward capability and provide improved liquid seal
during flush.
[0069] As shown in FIG. 9, the stranded hollow core shaft 500
comprises a stranded hollow core or lumen 510 including a plurality
of helically wound metal wires 520. The helically wound metal wires
520 include an outer surface and a diameter, which may exist at
about 0.002 to about 0.005 inches. The helical wound metal wires
520 are fixedly engaged with neighboring metal wires on their
respective outer surfaces. The fixed engagement of the helical
wound metal wires 520 completely encases the stranded hollow lumen
510. The stranded hollow core shaft 500 with the helical wound
metal wires 520 are different from a spring coil wire, in that a
spring coil wire consists of a single metal wire wound about itself
in a helical fashion. The helically wound metal wires 520 may exist
in any number to form the stranded hollow core shaft 500, in one
embodiment from about 2 to 15 wires, from about 3 to 12 wires, or
from about 4 to 10 wires in the helical configuration. An
individual helical wound wire 520 may consist of only one metal
filament; however, the individual helical wound wire 520 may
include more than one metal filament. The helically wound metal
wires 520 may comprise nitinol, i.e. nickel titanium alloy, or
another pseudometallic biocompatible alloy such as stainless steel,
tantalum, gold, platinum, titanium, copper, nickel, vanadium, zinc
metal alloys thereof, copper-zinc-aluminum alloy, and combinations
thereof. The stranded hollow core shaft 500 may be helically wound
and that portion may consist of an inner helical stranded portion
and an outer helical stranded portion. The inner helical stranded
portion may wind in the opposite direction as the outer helical
stranded portion. In one embodiment, the stranded hollow core shaft
500 may include a helical wound configuration including a Picks Per
Inch (PPI), where there may be about 5 to 15, about 7 to 12 PPI,
and about 8 to 10 PPP for the helical configuration. The helical
wound configuration may have alternating symmetries along the
longitudinal axis of the rotary drive shaft, such as an infinite
helical symmetry, n-fold helical symmetry, and non-repeating
helical symmetry. The stranded hollow core shaft 500 may be coated
with some biocompatible material, such as PTFE or similar polymers
to provide lubricity within the monolithic catheter sheath.
[0070] The distal part of the rotary drive shaft 40 may be the
stranded hollow core 500 design, where flexibility is required at
the entry point to the body. From the proximal portion to the
distal portion of the rotary drive shaft 40, a single layer or
double layer wound stranded hollow core may be included at the
proximal portion, a hypotube metal drive shaft 400, and a single
layer or double layer wound at the distal portion as to have a
flexible distal tip.
[0071] The hypotube metal drive shaft 400 may include a solid wall
extending substantially the entire longitudinal length of the
central lumen of the rotary drive shaft 40 in combination with the
stranded hollow core shaft 500, which (a) increases torsional
rigidity of the rotating shaft and reduces NURD; (b) increases
column strength or axial rigidity to improve the pushability of the
catheter assembly; (c) reduces or eliminates the possibility of the
stranded or coiled hollow core shaft unraveling or disassociating
under the torsional forces applied; (d) improves the frictional
interface by replacing an interrupted or more concentrated load
transference between individual strands and the monolithic outer
sheath with a continuous and more distributed load across the
solid-walled hypotube metal shaft; and (e) the hypotube metal shaft
offers a good fluid seal against the monolithic outer sheath over
the proximal section of a fluid-filled catheter due to the
solid-walled design.
[0072] The solid-walled hypotube metal drive shaft 400 may,
alternatively be used in conjunction with the stranded hollow core
shaft by either butt-joining a distal end of the hypotube metal
shaft 400 onto a proximal end of the stranded hollow core shaft
500, as illustrated in FIG. 9. The butt-joining of the two ends may
be accomplished by welding or adhesives to ensure little to no
vibration during rotation. Alternatively, a portion of the hypotube
metal shaft 400 may be concentrically or coaxially engaged or
fitted with a portion of the stranded hollow core shaft 500, as is
illustrated in FIG. 10. The coaxial fitting ensures a 1:1 rotation
of the hypotube metal shaft 400 and the stranded hollow core shaft
500 to ensure little to no vibration during rotation. The stranded
hollow core shaft 500 is coaxially engaged with the protection
bearing 170, where the protection bearing may include an epoxy
rounded tip 72 to ensure smooth rotational translation of the
protection bearing 170.
[0073] Longer sections of the hypotube metal shaft 400 may be
employed proximal of the rotary drive shaft 40 to achieve a greater
reduction of NURD. Due to its relative rigidity, the length of the
hypotube metal shaft 400 should not extend too far distally so as
to interfere with the distal flexibility of the catheter and
prevent it from navigating tortuous anatomical passageways. The
wall-thickness of the hypotube metal shaft 400 may be varied along
its length to impart variable stiffness along the longitudinal axis
of the hypotube metal shaft 400. In this manner, relatively thinner
wall-thicknesses may be formed distally than those formed more
proximally, to impart greater flexibility at the distal end of the
hypotube metal shaft 400. The wall thickness may be varied by
extrusion processing, mechanical means, such as grinding, abrasive
blasting, turning, by chemical or electrochemical means, such as
electro-polishing or etching, or by combinations of the foregoing.
Alternatively, slots, holes or other aperture shape formations may
be formed by means of cutting, etching, ablating or other means to
generate designs in the tubular structure which permit additional
flexibility of the distal region of the hypotube metal shaft 400
while retaining substantial torsional rigidity.
[0074] The rotary drive shaft 40 design can include the following
considerations: (1) the material type and geometry of the material
that comprise a given segment; and (2) a number of distinct
material segments when progressing from the proximal to distal
portions of the catheter.
[0075] In one embodiment, the design of the rotary drive shaft 40
includes setting the lateral flexibility of the material at the
proximal end to a specific point and increasing the lateral
flexibility from the proximal end to the distal segments of the
rotary drive shaft. Generally speaking, a higher lateral
flexibility is desired in portions of the catheter that experience
the greatest geometric curvature when used for imaging. In
addition, the diameter of the rotary drive shaft may become
gradually or stepwise smaller from the proximal end to the distal
portions of the rotary drive shaft. By reducing the wall thickness
or by reducing the ID and OD or both the ID and OD, the diameter of
the rotary drive shaft becomes smaller. The geometry of catheter at
the surgical entry point and the geometry of the human coronary
tract generally put these regions at the surgical entry point to
the body and the aortic arch and the coronary blood vessel being
interrogated.
[0076] The material type and the geometry of the materials in a
given segment may vary in the rotary drive shaft. Different
geometries are recognized for a given segment of the rotary drive
shaft. Examples include, but are not limited to: (1) homogeneous
solid (e.g., nitinol, PEEK, or some polymer); (2) stranded hollow
core shaft (single wound, double counter-wound, or triple
coil-wound or generally multiple wound); (3) braided multi-stranded
hollow core shaft; (4) fibrous composite (fibers in a matrix); (5)
patterned solid (#1 with patterned holes or apertures); and (6)
patterned composite (#4 with patterned holes or apertures).
[0077] In one embodiment, the number of distinct segments may vary.
A two segment rotary drive shaft includes the metal hypotube shaft
in the proximal portion and a stranded hollow core at the distal
portion. Other possibilities and combinations include, but are not
limited to: (1) metal hypotube shaft proximal, and patterned metal
hypotube shaft distal with a selected hole pattern, where the
lateral flexibility of the solid metal hypotube shaft and patterned
metal hypotube shaft may be graded when going from proximal to
distal portions for increased flexibility; (2) a filament wound or
fiber reinforced composite material at the proximal end with
increased fiber density and a composite material at the distal end
with a decreased fiber density (i.e., with increased lateral
flexibility) or a fiber density that is graded downward going from
the proximal end to the distal end; (3) a composite material at the
proximal end with increased fiber density, nitinol in the
mid-portion and stranded hollow core at the distal end. The joints
between any segments may be joined end-to-end with for example a
butt-couple, weld, epoxy or other jointing technique. Alternately,
an overlapping style of joint may be used, i.e. male-female joints,
or by coaxial engagement, concentric alignment, and the like.
Connection of the segments of an overlapping style of joint may be
accomplished by means of welding, adhesive, or over-molding given
that at least one element is polymer.
[0078] In addition, a gradation, either gradual or stepwise, may be
accomplished by a change in material properties along the length of
the rotary drive shaft. For example, the material properties may be
adjusted such as the modulus of elasticity of the material via
methods including, but not limited to annealing, carburization, or
heat treat and subsequent quenching techniques. In the case of
nitinol, one may adjust the transition temperature (A.sub.f) along
the length by means of heat treatment, cold working, or some
combination thereof. M.sub.f is the temperature at which the
transition to Martensite is finished during cooling. Accordingly,
during heating A.sub.s and A.sub.f are the temperatures at which
the transformation from Martensite to Austenite starts and
finishes. Nitinol is typically composed of approximately 50 to
55.6% nickel by weight. Making small changes in the composition can
change the transition temperature of the alloy significantly. For
this reason, nitinol may or may not be superelastic at certain
temperatures, thus allowing the modulus of elasticity to be
adjusted according to the temperature of use.
[0079] FIG. 11A is a chart illustrating the Torsion Term 620 and
the Bending Term 622. FIG. 11B is a chart illustrating the change
in the Torsion/Bending Ratio 630 while measuring for NURD during
angular deflection testing of the rotary drive shaft within an
outer monolithic sheath. The characteristics of the rotary drive
shaft and/or the outer monolithic sheath may be tested from various
mechanical testing methods, such as tensile tests, torsion test,
bending test or compression test. The torsion and bending tests
provide useful information about the type of deformation of the
rotary drive shaft and catheter monolithic sheath to account for
NURD.
EXAMPLES
[0080] The following examples are put forth so as to provide those
of ordinary skill in the art with a complete disclosure and
description of how the articles, devices, systems, and/or methods
claimed herein are made and evaluated, and are intended to be
purely exemplary and are not intended to limit the scope of
articles, systems, and/or methods. Efforts have been made to ensure
accuracy with respect to numbers (e.g., amounts, temperature,
etc.), but some errors and deviations should be accounted for.
[0081] FIGS. 12-19 were created using the OCT imaging catheter
system 10 with the rotary drive shaft 40 and the catheter sheath
from FEP material with an index of 1.34. FIG. 12A is an OCT image
of the Optical imaging catheter where the catheter sheath is filled
with a fluid and the exterior of the catheter sheath is flushed
with a fluid, such as saline in a coronal artery; and FIG. 12B is
an OCT image of the Optical imaging catheter where the space
between the catheter sheath and the prism is occupied by air and
the exterior of the catheter sheath is flushed with a fluid, such
as saline in a coronal artery. Aberration balancing is achieved in
FIG. 12B, where astigmatism is reduced, as compared to FIG.
12A.
[0082] FIG. 13A is an OCT image of the Optical imaging catheter
where the catheter sheath is filled with a fluid and the exterior
of the catheter sheath is flushed with a fluid, such as saline in a
coronal artery; and FIG. 13B is an OCT image of the Optical imaging
catheter where the space between the catheter sheath and the prism
is occupied by air and the exterior of the catheter sheath is
flushed with a fluid, such as saline in a coronal artery.
Aberration balancing is achieved in FIG. 13B, where astigmatism is
reduced, as compared to FIG. 13A.
[0083] Resolution Mask
[0084] A resolution mask may be used to determine the resolution of
the OCT image. The resolution mask is formed from a material with a
sheet or planar geometry immersed in a scattering medial with
alternating spatial regions of high/low reflectivity. The
alternating regions of high/low reflectivity have a fixed spatial
period and allow testing the lateral spatial resolving power of the
OCT catheter imaging system. On an OCT image the resolution mask
appear as the lined images on the lower side of the OCT image and
are measured such that the length indicated is the resolution from
leading edge of one line to the leading edge of the next line. In
other words, the length indicated is 2 times the line width, such
that a 50 .mu.m line width mask would consist of a 50 .mu.m line
with high reflection and a 50 .mu.m line with low reflection or a
100 .mu.m resolution mask.
[0085] FIG. 14A is an OCT image of the Optical imaging catheter
where the catheter sheath is filled with a fluid and a resolution
mask of 100 .mu.m; and FIG. 14B is an OCT image of the Optical
imaging catheter where the catheter sheath contains no fluid and
the space is occupied by air a resolution mask of 100 .mu.m.
[0086] FIG. 15A is an OCT image of the Optical imaging catheter
where the catheter sheath is filled with a fluid and a resolution
mask of 80 .mu.m; and FIG. 15B is an OCT image of the Optical
imaging catheter where the catheter sheath contains no fluid and
the space is occupied by air a resolution mask of 80 .mu.m.
[0087] FIG. 16A is an OCT image of the Optical imaging catheter
where the catheter sheath is filled with a fluid and a resolution
mask of 60 .mu.m; and FIG. 16B is an OCT image of the Optical
imaging catheter where the catheter sheath contains no fluid and
the space is occupied by air a resolution mask of 60 .mu.m.
[0088] FIG. 17A is an OCT image of the Optical imaging catheter
where the catheter sheath is filled with a fluid and a resolution
mask of 50 .mu.m; and FIG. 17B is an OCT image of the Optical
imaging catheter where the catheter sheath contains no fluid and
the space is occupied by air a resolution mask of 50 .mu.m.
[0089] FIG. 18A is an OCT image of the Optical imaging catheter
where the catheter sheath is filled with a fluid and a resolution
mask of 40 .mu.m; and FIG. 18B is an OCT image of the Optical
imaging catheter where the catheter sheath contains no fluid and
the space is occupied by air a resolution mask of 40 .mu.m.
[0090] FIG. 19A is an OCT image of the Optical imaging catheter
where the catheter sheath is filled with a fluid and a resolution
mask of 30 .mu.m; and FIG. 19B is an OCT image of the Optical
imaging catheter where the catheter sheath contains no fluid and
the space is occupied by air a resolution mask of 30 .mu.m.
[0091] Zemax Modeling
[0092] The optical imaging catheter design was modeled in Zemax
Modeling software (Zemax Development Corporation, Bellevue, Wash.)
using a GRIN lens design for the lens 150 (GrinTech, Jena,
Germany), a BK7 glass for the prism 110, and a refractive index of
n=1.34 for the catheter sheath 120 constructed from FEP, as shown
in FIGS. 20A-20B. As shown in FIG. 20A, the fluid filled catheter
sheath included a fluid in space 130, which was modeled using the
optical properties of seawater as provided by Zemax while air was
assumed in the space 130 for unfilled catheter sheath, as shown in
FIG. 20B. The flush material along the exterior 138 of the catheter
sheath 120 was also modeled as seawater.
[0093] The catheter system is modeled using ray-tracing with all
rays in a sequential format. Modeling of multiple
scattering/reflection events within an element is not included. As
a result of the prism 110, which by design has a second reflection
or scattering event at the angled face, is modeled as two standard
surfaces with a zero-width fold-mirror between them. The Zemax
simulation represents a realistic model of the system in terms of
optical path, diffraction, and dispersion.
[0094] The surfaces following the prism are modeled as toroidal
geometries with a defined radius of curvature and an infinite
radius of rotation, making them essentially cylindrical lenses
consistent with the sheath geometry. The image plane is also
considered a cylindrical surface in this system, with a radius of
curvature given by distance from the central axis.
[0095] FIGS. 21A-B are spot diagrams plots showing the arrangement
of individual light rays traced through the system and incident
upon the image plane of the system. The ray patterns are shown at
the best focus of the system as well as at two positions on either
side of the focus in increments of 400 um, showing a total imaging
range of 1.6 mm. In FIGS. 21A-B, the airy disk or diffraction limit
is shown as the black ring, and these rings represent the best
possible resolution, regardless of the ray plots. The scales on
each of these plots are the same.
[0096] As shown FIGS. 21A-B, the changing of the index of
refraction of material within the catheter sheath introduces
astigmatism and distorts the spot maximally along the catheter
rotation dimension. In this dimension, the simulation results
suggest that the decrease in resolution is about 3.times. from 25
to 80 .mu.m. In the filled catheter case, the de-focusing power of
the catheter is almost completely removed due to the index of
refraction match between the filling fluid (n.about.1.3) and the
outer sheath material (n.about.1.34). In the filled case, it should
be noted that the optics are not diffraction limited at the outer
ranges of the imaging depth shown here, so at the limit of this
modeled range the lateral resolution of the filled catheter is
about 45 .mu.m.
[0097] In the orthogonal lateral dimension (along the x-axis of the
catheter), the catheter axial dimension, the resolution is
approximately 25 .mu.m for both filled and unfilled cases.
[0098] While the embodiments have been described, it will be
understood that the invention is capable of further modifications.
This application is intended to cover any variations, uses or
adaptations of the invention following, in general, the principles
of the invention, and including such departures from the present
disclosure as, within the known and customary practice within the
art to which the invention pertains.
* * * * *