Catheter for in vivo imaging

[0001] The present application claims priority to U.S. Provisional Application Ser. No. 60/949,511, filed Jul. 12, 2007, incorporated by reference herein.

[0002] The present invention relates generally to an apparatus for in vivo imaging. More particularly, the present invention pertains to a catheter for imaging within a mammalian body, including luminal systems, such as imaging the vasculature system, including, without limitation, cardiac vasculature, peripheral vasculature and neural vasculature.

[0003] For intravascular imaging, it is difficult to achieve and maintain a uniform rotational velocity due to cables and shafts binding and/or whipping around as it is rotated in the blood vessel. Intravascular probes rotate at a nonuniform angular velocity even though the motor rotates at a uniform angular velocity. This is a problem because the angles assumed by the image processor in assembling the image vectors into the cross-sectional image of the body lumens are different from the actual angles at which the image vectors were taken. This causes the cross-sectional image of the blood vessel to be distorted in the azimuthal and radial direction. The resulting distortion is referred as Nonuniform Rotational Distortion (“NURD”). The embodiments disclosed herein attempt to solve these problems, as well as others.

[0004] The foregoing and other features and advantages are defined by the appended claims. The following detailed description of exemplary embodiments, read in conjunction with the accompanying drawings is merely illustrative rather than limiting, the scope being defined by the appended claims and equivalents thereof.

[0005] A catheter for in vivo imaging comprising a monolithic outer sheath terminating in a monolithic atraumatic tip having a guidewire lumen passing through the monolithic atraumatic tip. The catheter for in vivo imaging comprises a rotary drive shaft that passes through a central lumen of the catheter monolithic outer sheath to impart rotary motion.

[0027] The methods, apparatuses, and systems can be understood more readily by reference to the following detailed description of the methods, apparatuses, and systems, the non-limiting embodiments, and the accompanying figures.

[0028] With particular reference to FIG. 1, a catheter 10 is depicted comprising a monolithic outer sheath 20 including a central sheath lumen extending substantially the entire length of the monolithic outer sheath 20 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.

[0029] The catheter 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 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. 1, the catheter 10 comprises the monolithic outer sheath 20 that houses an acoustical or optical train 30. The optical train 20 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 20. 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.

[0030] As shown in FIG. 1, 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 20 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 20 by means of mechanical thread engagement and adhesive.

[0031] The rotary drive shaft 40 is concentrically or coaxially positioned within the central lumen of the monolithic outer sheath 20 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 20 may be accomplished with the OD of the rotary drive shaft 40 matching the ID of the monolithic outer sheath 20 or varying the OD of the rotary drive shaft to the ID of the monolithic outer sheath 20. 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.

[0032] 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. A protection bearing 70 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.

[0033] 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.

[0034] In one embodiment of the monolithic outer sheath 20, 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. 2b, 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.

[0035] As shown in FIG. 2a, a guidewire lumen 22 is formed in the distal portion of the monolithic outer sheath 20, while a central sheath lumen 32 extends proximally from the distal portion of the monolithic outer sheath 20. 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 70 within the central lumen of the catheter sheath 20.

[0036] In accordance with a another embodiment, the rotary drive shaft 40 includes the protection bearing 70, which houses the distal end optics or distal end acoustics at the distal end of the catheter 10, as shown in FIG. 2b. The protection bearing 70 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 70. The protection bearing 70 may include a diameter to coaxially engage the distal end optics to ensure a 1:1 rotation of the protection bearing 70 with the distal end optics. In one embodiment, the protection bearing 70 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. 2b. The Platinum/Iridium tube may comprise about 75-97% Pt and about 3-25% Ir, which provides radiopacity. Alternatively, the metal hypotube of the rotary drive shaft replaces the protection bearing 70, where the metal hypotube extends coaxially over the distal end optics and includes an opening for the distal end optics. Alternatively, the protection bearing 70 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 70 may include an epoxy rounded tip to ensure smooth rotational translation of the protection bearing 70. Alternatively, the protection bearing 70 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 70, 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.

[0037] In accordance with one embodiment, the optical train 30 includes the monolithic outer sheath 20 the optical fiber 50 in association with the rotary drive shaft 40, the protection bearing 70 housing a ferrule/gradient index lens (“GRIN”) assembly 80 at a distal end of the optical fiber 50, as shown in FIG. 2a. 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 70 and rotate with the protection bearing 70, under the influence of the rotary drive shaft 40, within the central lumen 32 of the catheter sheath 20. 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 20.

[0038] As shown in FIG. 2b, 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 mirror 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 prism angles 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 20, and protection bearing 70. 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 20 to communicate with the body tissue being imaged throughout 360 degrees.

[0039] 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” Ser. No. 61/040,630, filed Mar. 28, 2008, herein incorporated by reference. Alternatively, the catheter may include an air-filled sheath, as described in commonly assigned provisional application Ser. No. 61/051,340, filed May 7, 2008, incorporated by reference herein.

[0040] Catheter Sheath

[0041] As shown in FIG. 3a, one embodiment of the monolithic outer sheath 20 may include an outer layer 110 and an inner layer 120 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. 3b shows the solid monolithically formed tip 28 and a base layer 130 and a top layer 140. The base layer 130 may be constructed of Pebax® substantially along the base of the catheter sheath and provides greater structural rigidity relative to the top layer 140. The greater structural rigidity allows the monolithic outer sheath greater pushability along the proximal portion of the monolithic outer sheath. Alternatively, the base layer 130 may include a plug 132. The plug 132 may include a space between the protection bearing 70 when the protection bearing 70 engages with the monolithic outer sheath 20. 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 20. 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 20 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.

[0042] FIG. 4 depicts the monolithic outer sheath 20 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 150, preferably placing a forming mandrel in the central sheath lumen 152 of the tubular catheter sheath precursor 150, then thermoforming the solid tip 154 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).

[0043] The guidewire lumen 156, as shown in phantom depicted in FIG. 5 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 156 during the thermoforming process by providing the appropriate mold. The resulting guidewire lumen 156 may or may not maintain a straight longitudinal axis, where the longitudinal axis runs along the x-axis of the sheath 20, as shown in phantom in FIG. 5. In one embodiment, the guidewire lumen 156 includes a straight longitudinal axis 160 and a non-longitudinal axis 162. The straight longitudinal axis 160 is included for some length along the distal portion of the catheter sheath body and associated with the guidewire entrance 162. The non-longitudinal axis 162 is included for some length along the proximal portion of the catheter body and is associated with the guidewire exit 164. The angled measurements for the non-longitudinal axis 162 near the guidewire exit can be any angle relative to the longitudinal axis 160 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.

[0044] The monolithic outer sheath 20 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 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.

[0045] 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.

[0046] Another embodiment of the monolithic catheter sheath 200 is shown in FIG. 6a. The monolithic catheter sheath 200 includes a sheath lumen 210, a guidewire lumen 220, and a monolithic atraumatic tip 230. The sheath lumen 210 includes a rounded distal end 212 for the placement of the optical train 30. The sheath lumen 210 includes a longitudinal axis substantially along the x-axis direction of the monolithic catheter sheath 200. The guidewire lumen 220 includes a guidewire exit 222, a guidewire entrance 224, and a distal marker band 226. The distal marker band 226 is of a radiopaque material. The guidewire lumen 220 includes a diameter 236, which may remain constant along the longitudinal length of the guidewire lumen 220. The longitudinal axis of the guidewire lumen 210 is at a slight angle A and offset from the longitudinal axis of the sheath lumen 210. The offset angle A may be about 1 to 20 degrees, from about 1 to 5 degrees, and from about 2 to 4 degrees The offset angle A minimizes space between the guidewire and the catheter body, which helps to minimize chance of the guidewire getting entangled when crossing stents. The catheter sheath 200 also includes a buffer 240 of solid material between guide wire lumen 220 and the sheath lumen 210 to prevent the passage of fluid and offset the guidewire lumen 220 from the sheath lumen 210. The guide wire lumen 220 is approximately straight along its longitudinal axis, as to permit free passage of guide wire (not shown). The guidewire lumen 200 includes a guidewire lumen wall 228 that includes at least two thicknesses. In one embodiment, the guidewire lumen wall 228 includes a first thickness 232 near the guidewire exit 222 slightly larger than a second thickness 234 near the guidewire entrance 224. The guidewire lumen wall 228 first thickness near guidewire exit 222 evenly distributes strain on the monolithic catheter sheath 200 and prevents kinking of the guidewire at the guidewire exit 222. An outer transparent view of the monolithic catheter sheath 200 is shown in FIG. 6b, showing the sheath lumen 210 and guidewire lumen 220 in phantom.

[0047] As shown in phantom in FIG. 7a, in another embodiment of the monolithic catheter sheath 200, a flushing port 250 is coupled to the sheath lumen 210 and the exterior of the catheter sheath 200. The flushing port 250 between the sheath lumen 210 and the exterior of the catheter sheath 200 allows an operator to flush air or any fluid out of the sheath lumen 210. The monolithic catheter sheath 200 may use standard luer connections at the proximal end of the catheter sheath 200 to provide the flushing fluid. Luer connection systems are the standard way of attaching catheters, IV tubes, and so on to each other, and they consist of round male and female interlocking tubes, slightly tapered to hold together better with even just a simple pressure/twist fit. Luer connections can either be a luer slip, or can have an additional outer rim of threading. Alternatively, the embodiment of the monolithic catheter sheath 200 includes a flushing port 252 coupled to the guidewire lumen 220 and the sheath lumen 210 to allow the operator to flush air or fluid out of the sheath lumen 210, as shown in phantom in FIG. 7b.

[0048] Another embodiment of the monolithic catheter sheath 300 is shown in FIG. 8a. The monolithic catheter sheath 300 includes a sheath lumen 310, a guidewire lumen 320, and a plug 330. The sheath lumen 310 includes a longitudinal axis substantially along the x-axis of the monolithic catheter sheath 300. The sheath lumen 310 houses the protection bearing 312 coupled to the drive shaft 314 and the OCT imaging port 316. The guidewire lumen 320 includes a guidewire exit 322, a guidewire entrance 324, and a curvature 326 offset lumen. The distal portion of the guidewire lumen 320 includes a longitudinal axis along the x-axis of the catheter sheath 300. The catheter sheath 300 also includes a plug 330 of solid material between guidewire lumen 320 and the sheath lumen 310 to prevent the passage of fluid and offset the guidewire lumen 320 from the sheath lumen 310. The curvature lumen 326 is offset from the distal longitudinal axis of the guidewire lumen and the longitudinal axis of the sheath lumen 310. The curvature 326 offset minimizes space between the guidewire (not shown) and the monolithic catheter body, which helps to minimize the wire entangling when crossing stents and tortuous pathways. An outer transparent view of the monolithic catheter sheath 300 embodiment is shown in FIG. 8b, with the sheath lumen 310, the guidewire lumen 320, and the curvature lumen 326 in phantom.

[0049] Rotary Drive Shaft

[0050] Turning now to FIGS. 9-11, 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. 9a, 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.

[0051] As shown in FIG. 9b, 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.

[0052] 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.

[0053] 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.

[0054] 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. 10a. 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. 10b. 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 70, where the protection bearing may include an epoxy rounded tip 72 to ensure smooth rotational translation of the protection bearing 70.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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).

[0059] 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.

[0060] 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_f is the temperature at which the transition to Martensite is finished during cooling. Accordingly, during heating A_s and A_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.

[0061] Characterizing Torsion, Bending, and NURD

[0062] Generally speaking, the angular deflection (θ) for NURD in a homogenous hollow tube including a cross section is given by Equation (1):
θ=TL/JG,  (1)
where θ=Angular deflection, T=Torque, L=length of shaft, J=Polar Second Moment of Area, and G=modulus of rigidity (shear modulus). Since the Polar Second Moment of Area J=π/32 (d_o⁴−d_i⁴), then Equation (1) becomes:

[0063] $\begin{array}{cc}\theta =\frac{\mathrm{TL}}{\frac{\pi }{32}\left(d_o^4-d_i^4\right)G}.& \left(2\right)\end{array}$

[0064] The change in the angular velocity (i.e. the second derivative and angular deflection) is given by the following:

[0065] $\begin{array}{cc}\frac{d^2\theta }{d{t}^2}=\frac{L}{\mathrm{JG}}·\frac{d^{2}T}{d{t}^2}\Rightarrow \frac{d^2\theta }{d{t}^2}=\frac{32L}{\pi G\left(d_o^4-d_i^4\right)}·\frac{d^{2}T}{d{t}^2},& \left(3\right)\end{array}$
where minimizing NURD is minimizing

[0066] $\frac{d^2\theta }{d{t}^2},$
which can be achieved by minimizing L or T, and/or maximizing G or Δd=d_o−d_i. The load can be reduced by reducing the friction or by reducing the section modulus.

[0067] The bending load, as shown in FIG. 11a, is generally M=Fl, where M=the bending morphology, F is the Force (load on the tube), and l is the length. The Section modulus (S) is given by the equation S=I/C, and I is given by Equation (4):

[0068] $\begin{array}{cc}I=\frac{\pi d^{3}t}{8},& \left(4\right)\end{array}$
where t is the thickness of the tube and d=2r, r is the radius of the tube. The load can be reduced by reducing the friction or by reducing section modulus S, which can rewritten as

[0069] $S=\frac{\pi d^{3}t}{8C}.$

[0070] The bending state σ=M/S can be rewritten as:

[0071] $\begin{array}{cc}\sigma =\frac{F·l}{S}\Rightarrow \frac{S\sigma }{l}=F& \left(5\right)\end{array}$

[0072] The reduction of Sσ/l or the reduction of F will reduce the load. Alternatively, the load can be reduced by reducing the friction, which is dependent upon the material coefficient and force by equation (6):
F_k=μ_kN,  (6)
where F_k is the kinetic friction and μ_k is the coefficient of kinetic friction of material, and N is the normal force. The values of the coefficient of friction depend on many things, including, but not limited to the surface finish, coating, temperature, and the like. There are several contact points that are continuously changing during pullback which may consist of: (1) the surface of the stranded hollow core shaft strands (2) the ID of the FEP monolithic outer sheath if no water, fill solution, or coatings are present; and (3) the surface of the OD of the protection bearing to the ID of the FEP monolithic outer sheath if no water, fill solution, or coatings are present. Thus the normal force is between: (1) the shaft OD and sheath ID; and/or (2) the protection bearing OD and sheath ID.

[0073] As shown in FIG. 11b, the catheter, at any bending point in a vessel 600, there will be several friction points 610. Friction is a function of the normal force (N) between the drive shaft and the inner wall of the outer sheath, so then the bending moment is related to friction by the section modulus as follows: Friction force F_k=μ_kN, Normal force

[0074] $N=\frac{S\sigma }{l},\mathrm{and}S=\frac{\pi d^{3}t}{8C}\mathrm{so}$
then:

[0075] $\begin{array}{cc}{F}_k=\frac{{\mu }_{k}S\sigma }{l},& \left(7\right)\end{array}$
where μ_k, σ, and l are constants. By reducing the diameter (d) of the tube, a reduction of friction F_k is achieved by the following equation:

[0076] $\begin{array}{cc}{F}_k=\frac{{\mu }_k\mathrm{\sigma \pi }{d}^{3}t}{8\mathrm{cl}}.& \left(8\right)\end{array}$

[0077] Reducing the diameter (d) reduces

[0078] $\frac{d^2\theta }{d{t}^2},$
where

[0079] $\frac{d^2\theta }{d{t}^2}=\frac{L}{\mathrm{JG}}·\frac{d^{2}T}{d{t}^2}$
and the reduction of Torque (T). Since G is material dependent (or structure dependent), a different material or structure may be used. J is dependent on Δd by J=π/32 (d_o⁴−d_i⁴). Torque (T) T=F·l, and the change in Force is represented by:
ΣF=F_input−F_k  (9)

[0080] By using Equation (8) and substituting F_k for F results in:

[0081] $\begin{array}{cc}T=\frac{{\mu }_k\mathrm{\sigma \pi }{d}^{3}t}{8c},& \left(10\right)\end{array}$
where c is the distance to neutral axis, which is the case when d/2. By substituting d/2 for c gives the following:

[0082] $\begin{array}{cc}T=\frac{{\mu }_k\mathrm{\sigma \pi }{d}^{2}t}{4}.& \left(11\right)\end{array}$

[0083] By substituting T and J into

[0084] $\frac{d^2\theta }{d{t}^2}=\frac{L}{\mathrm{JG}}\frac{d^{2}T}{d{t}^2}$
results in:

[0085] $\frac{d^2\theta }{d{t}^2}=\frac{L}{\frac{\pi }{32}\left(d_o^4-d_i^4\right)G}\frac{d^2\left({\mu }_k\mathrm{\sigma \pi }{d}^{2}t\right)}{d{t}^2\left(4\right)}.$

[0086] The two competing mass moment of inertia terms are J and I. The two opposing factors are friction due to bending and torsional rigidity. Moment of inertial (I) from the section modulus in the bending portion is compared to the polar second moment of area (J).

[0087] For a hollow circular cross section, J=π/32 (d_o⁴−d_i⁴),

[0088] $I=\frac{\pi d^{3}t}{8},$
where c=d/2, d=(d_o+d_i)/2 and t=(d_o−d_i)/2. As shown in FIG. 11c, d_o is the outer diameter of the tube, d_i is the inner diameter of the tube, and d is the diameter from the midsection of the tube. Substituting in terms of (d_o+d_i)/2 gives:

[0089] $\begin{array}{cc}\begin{array}{c}I=\frac{{\pi \left(d_o+d_i/2\right)}^3\left(d_o+d_i/2\right)}{8}\\ =\frac{\pi }{128}\left(d_o^4-d_i^4+2d_o^3{d}_i-2d_o{d}_i^3\right),\end{array}\mathrm{and}& \left(12\right)\\ J=\frac{\pi }{32}\left(d_o^4+d_i^4\right).& \left(13\right)\end{array}$

[0090] Comparing equation (12) and (13) by varying inner diameter (ID) from about 0.11-0.024 inches and the outer diameter (OD) from about 0.015-0.025 inches, and holding OD constant at 0.200 inches and 0.025 inches, produces the graphs as illustrated in FIGS. 12a and 12b.

[0091] FIG. 12a is a chart illustrating the Torsion Term 620 and the Bending Term 622. FIG. 12b 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.

[0092] Active and Passive Characterizations of NURD

[0093] The measurement of rotary position of the catheter 10 may be used as input for a NURD-reduction software approach. As shown in FIG. 18, the catheter 10 is coupled to the proximal motor system 700, including a torque sensor 710, a rotary motor 720, a linear motor 730, and a computer/software program 740 operably coupled to the motor system 700. The method for estimating NURD in the rotational imaging catheter 10 is by measuring the torque on proximal end of the catheter 10 with the torque sensor 710. If NURD is characterized (e.g, in the form of an equation or data points representing angular position of imaging transducer vs. time) then removal of or correcting for NURD via post-processing of the image is straightforward. To truly characterize NURD, the angular position of the rotating imaging transducer must be known.

[0094] Methods for determining this position include active approaches such as distal accelerometers or passive approaches such as encoding a circumferential line pattern in the catheter outer sheath which can be detected within the image itself (OCT, IVUS, etc.) or encoding the catheter sheath thickness into the angular position and detecting within the OCT or IVUS image. An active method for estimating the angular position of the rotating imaging transducer as a function of time (i.e. rotational period) by measuring the slight variation in torque required to drive the catheter through one period of rotation (2π).

[0095] The proximal torque measurement is indirect because measurements are made on the proximal end of the driveshaft, however the torsional properties of the driveshaft are known and constant, and thus the mechanical response of the distal tip can be estimated by the mechanical response of the proximal shaft. Knowledge of the angular position vs. time is shown in FIG. 19, and is an important input to correct for NURD. The y-axis of the graph in FIG. 19 is the rotational time, where 1 rotation has occurred.

[0096] A passive method for indirectly determining the angular position of the rotating imaging transducer 750 as a function of time (i.e. rotational period) is by forcing the rotating transducer to be in an eccentric location with respect to the outer wall of the stationary sheath.

[0097] As shown in FIG. 20a, the outer wall of the stationary sheath 752 can be visualized in the image and because it is eccentric with respect to the transducer rotation. The outer sheath 752 includes a thickness S. The outer wall of the stationary sheath will experience a geometrical image distortion (i.e. the apple-like cross-sectional shape) when NURD is present and the catheter is not centered on the vessel axis, as shown in FIG. 20b. The eccentricity of the rotating portion with respect to the outer sheath 752 must only be large enough to visualize in the image (i.e. the difference in wall thickness as a function of angle due to the eccentricity must be larger than the depth resolution of the imaging modality).

[0098] To create a representation of angular position vs. rotational period, the image of the outer sheath 752 outer diameter OD 754 and the wall thickness S is compared to the a priori known eccentricity of the sheath. This comparison can be based on curve fitting to analytical models, statistical decision tree, or other numerical methods. The method for determining the thickness data from the angular position of a sensor within a catheter having a sheath wall of varying thickness can be found in U.S. Pat. No. 6,450,964, incorporated by reference herein.

[0099] The beam distortion (e.g. astigmatism) from the eccentrically oriented sheath will be minimal because the wall thickness vs. angle can be small relative to the beam diameter as it passes through the sheath. This can be further minimized by matching the wave speed in the sheath material with the fluid media bordering the ID and OD of the sheath (i.e. refractive index if OCT, acoustic impedance if ultrasound).

[0100] 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.

[0101] OCT images of a NURD mask for the catheter with a vessel in phantom are shown in FIGS. 14, 15, and 16. The examples span the range from mild to moderate NURD with for each case the angular position vs. time and the resulting B-scan profile. The catheter OCT system records 1000 A-lines per rotation. A tube called a resolution mask or NURD mask 650 is placed over the catheter system, as shown in FIG. 13. The NURD mask 650 may include several different sizes to measure the effects of NURD at different diameters. The NURD mask includes a plurality of slots 652, where the widths of the slots may range from about 0.157 to about 0.314 mm. The slots 652 intervene with struts 654. The slot width and strut width may be equal in diameter to give 20 slots 652 around the circumference of the NURD mask 650. No slag or burrs shall be present on finished NURD mask 650. The NURD mask 650 may include an aperture 656 to secure the NURD mask 650 to the catheter. The diameter of the aperture 656 may range from 0.3-0.6 mm. The NURD mask 650 may be constructed from metal, stainless steel, nitinol, and the like.

[0102] As shown in FIG. 14a, a rectangular OCT image of the NURD mask 650 with moderate NURD, where the NURD mask 650 includes 20 evenly spaced slots and where the tube slot width equals the tube strut width. The x-axis is sample number on the graph of FIG. 14a and the vessel is in phantom. As shown in FIG. 14b, a chart showing where the actual imaging beam is at any given point in time for one rotation, X-axis (sample #)=degrees in a single rotation of catheter inner member, Y-axis (intensity)=period of rotation divided into 1000 discrete points. The theoretical line for no NURD 640 is the non-white curve, the actual measured NURD 642 is the white curve, and the vertical distance between the white actual measured NURD 642 and non-white theoretical line 640 for no NURD determines the amount of NURD. For example, the more distance between the non-white theoretical line 640 for no NURD and the white actual measured NURD 642 indicates more NURD. For FIG. 14b, moderate NURD is shown between samples #160 and #200.

[0103] As shown in FIG. 15a, a rectangular OCT image of the NURD mask with minimal NURD with the image of the NURD mask including 20 evenly spaced slots, and where the tube slot width equals the tube strut width. The x-axis is sample number on the graph of FIG. 15a and the vessel is in phantom. As shown in FIG. 15b, the chart shows where the actual imaging beam is at any given point in time for one rotation X-axis (sample #)=degrees in a single rotation of catheter inner member. Y-axis=A-scan number with 1000 A-scans per rotation. The theoretical line for no NURD 640 is the non-white curve, the actual measured NURD 644 is the white curve, and the vertical distance between the white actual measured NURD 644 and the non-white theoretical line 640 determines the amount of NURD. For example, the more distance between the non-white theoretical line 640 for no NURD and the white actual measured NURD 644 indicates more NURD. For FIG. 15b, minimal NURD is shown between samples #1 and #360, with little to no vertical distance between the non-white theoretical line 640 and the white actual measured NURD 644.

[0104] FIGS. 16a-16c show polar images of the OCT catheter 10 system with the NURD mask. FIG. 16a shows the catheter 10 in a straight vessel where the NURD is small. FIG. 16b shows the catheter with the NURD mask in a sharp 90 bend in the distal end where the NURD is small. FIG. 16c shows the catheter in a tortuous model LAD Co-Pilot within a tight valve and small NURD values. The polar images in FIGS. 16a-16c show the OCT catheter 10 in the center of the vessel. The lack of radial distortion may be due to the centering of the OCT catheter. The catheter is centered in the images of the NURD mask in the vessel phantoms and the apple shape of the radial distortion only appears when the catheter is offset from the center.

[0105] FIGS. 17a-17c are polar OCT images demonstrating the simulated NURD effects in the same image where the catheter is not centered can show an apple-like shape of the vessel. The image was recorded with the catheter 10 in vivo in a pig coronary placed with a stent. In order to see the apple-like cross sections of the radial distortion, the catheter can be positioned in an off-center position. FIG. 17a is an image showing original/less NURD. In the original/least NURD case, the catheter is off center in the vessel lumen and the slots are fairly evenly spaced radially around the perimeter. A simulation NURD program was created to simulate NURD with the catheter, vessel, etc. in the FIG. 17a image in post-processing steps. FIG. 17b is a simulated image showing medium NURD. As the NURD increases compared to the original image (FIG. 17a), the lumen cross section is increasingly warped with the characteristic apple shape and the stent strut spacing becomes more irregular. FIG. 17c is a simulated image showing extreme NURD, with the lumen warped into an apple-like shape. FIGS. 17a-17c suggest that a non-centrally located catheter in combination non-uniform rotational velocity can result in azimuthal and radial distortion in the polar OCT image.

[0106] Additional objects, advantages and novel features of the embodiments as set forth in the description, will be apparent to one skilled in the art after reading the foregoing detailed description or may be learned by practice of the embodiments. The objects and advantages of the embodiments may be realized and attained by means of the instruments and combinations particularly pointed out here.