US20110137124A1

US20110137124A1 - Optical imaging catheter for aberration balancing

Info

Publication number: US20110137124A1
Application number: US12/941,548
Authority: US
Inventors: Thomas E. Milner; Nathaniel J. Kemp
Original assignee: Volcano Corp
Current assignee: Philips Image Guided Therapy Corp
Priority date: 2007-07-12
Filing date: 2010-11-08
Publication date: 2011-06-09
Also published as: EP2178442B1; JP5524835B2; WO2009009799A1; US20090018393A1; US9622706B2; EP2178442A4; EP2178442A1; JP2010533049A

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.

Description

CROSS-RELATED REFERENCE TO RELATED APPLICATIONS

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

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.
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

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

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.

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

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.

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.

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.

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.

FIG. 7 is a perspective view of the monolithic catheter sheath depicting the sheath lumen and the guidewire lumen in phantom.

FIG. 8 is a photographic representation of an embodiment of the rotary shaft in accordance with one embodiment.

FIG. 9 is a side cross-sectional view of an embodiment of the rotary shaft.

FIG. 10 is a side cross-sectional view of an embodiment of the stranded hollow core shaft.

FIGS. 11A-B are graphs illustrating the torsion/bending ratio of the rotary shaft in accordance with the one embodiment.

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.

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.

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 μm; 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 μm.

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 μm; 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 μm.

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 μm; 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 μm.

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 μm; 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 μm.

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 μm; 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 μm.

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 μm; 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 μm.

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.

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

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).
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.
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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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®) 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.
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.
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):
$\begin{matrix} \frac{index of sheath - index of air}{radius of the inner surface} = opitcal power of the inner surface & (1) \end{matrix}$
index of sheath−index of air=optical power of the inner surface (1) radius of the inner surface
The optical power of the outer surface of the sheath may be related by Equation (2)
$\begin{matrix} \frac{index of flushing agent - index of outer surface}{radius of the outer surface} = opitcal power of the outer surface & (2) \end{matrix}$
index of flushing agent−index of outer surface=optical power of the outer surface (2) radius of the outer surface
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.
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.
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.
Alternatively, the optical power given by a flushing fluid, for example, saline or a blood-substitute, which may have an index of refraction of ˜1.3, then the sheath 120 is made with a similar index of refraction, i.e., ˜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.
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 w₀at 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.
FIG. 2B is the “top” view of lens 150-prism 110; and FIG. 2C is the “side” view of lens 150-prism 110.
Optical Imaging Catheter System
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.
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.
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.
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.
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.
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.
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®) 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.
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.
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.
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.
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.
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.
Catheter Sheath
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® 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® 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® 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® 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.
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).
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.
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.
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.
Rotary Drive Shaft
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
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_f) along the length by means of heat treatment, cold working, or some combination thereof. M_fis the temperature at which the transition to Martensite is finished during cooling. Accordingly, during heating A_sand A_fare 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.
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

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.
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.
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.
Resolution Mask
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 μm line width mask would consist of a 50 μm line with high reflection and a 50 μm line with low reflection or a 100 μm resolution mask.
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 μm; 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 μm.
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 μm; 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 μm.
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 μm; 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 μm.
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 μm; 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 μm.
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 μm; 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 μm.
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 μm; 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 μm.
Zemax Modeling
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.
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.
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.
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.
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× from 25 to 80 μm. 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˜1.3) and the outer sheath material (n˜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 μm.
In the orthogonal lateral dimension (along the x-axis of the catheter), the catheter axial dimension, the resolution is approximately 25 μm for both filled and unfilled cases.
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.

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.