WO2013033490A1

WO2013033490A1 - Rotational imaging systems with stabilizers

Info

Publication number: WO2013033490A1
Application number: PCT/US2012/053271
Authority: WO
Inventors: Robert K. Jenner
Original assignee: Volcano Corporation
Priority date: 2011-08-31
Filing date: 2012-08-31
Publication date: 2013-03-07

Abstract

The invention generally relates to rotational imaging systems that include rotational stabilizers. In certain embodiments, the invention provides a rotational imaging system that includes a rotational drive motor, a rotational imaging apparatus operably coupled to the drive motor, and a mechanism that maintains stability of the imaging apparatus while the imaging apparatus is rotating.

Description

Title

ROTATIONAL IMAGING SYSTEMS WITH STABILIZERS Related Application

The present application claims the benefit of and priority to U.S. provisional application serial number 61/529,740, filed August 31, 2011, the content of which is incorporated by reference herein in its entirety.

Field of the Invention

The invention generally relates to rotational imaging systems that include rotational stabilizers. Background of the Invention

[0001] Rotational imaging systems, for example, optical coherence tomography (OCT), intravascular ultrasound (IVUS), and near infrared (NIR) spectroscopy, typically employ a rotating probe at a distal end of a flexible drive cable that is inserted into a lumen of any anatomical or mechanical conduit, vessel, tube, or the like. When used in vivo, the flexible drive cable may be snaked through a patient's vasculature to an imaging location. An increase in rotation speed of the probe allows for capture of an increased number of images per rotation. Capture is achieved by axial movement of the probe in the vessel while the probe is rotating. Imaging quality depends on maintaining a uniform rotational speed for the flexible drive cable.

[0002] A problem with these rotational imaging systems is that the drive cables of the imaging systems vibrate during operation and image capture, leading to a degradation in image quality. As the rotational speed of the imaging system increases, e.g., in excess of 20,000 rpm, so do vibrational effects on the drive cable, thus the greater the rotational speed, the greater the degradation in image quality. Further, vibrational effects make it difficult to maintain a uniform rotational speed of the drive cable, leading to further image degradation. Existing drive assemblies are inadequate for alleviating the problems of excessive vibration and/or buckling failure, especially at rotational speeds in excess of 20,000 rpm.

Summary of the Invention

[0003] The invention generally relates to rotational imaging systems that include stabilizers that maintain the stability of a rotational imaging system during operation. In this manner, systems of the invention reduce vibrational effects on the imaging system during operation while also facilitating maintenance of a uniform rotational speed during operation of the imaging system. Thus, systems of the invention overcome the problems of excessive vibration and/or buckling failure and are able to produce high quality images at high rotational speeds, e.g., rotational speeds in excess of 20,000 rpm.

[0004] In certain aspects, the invention provides a rotational imaging system that includes a rotational drive motor, a rotational imaging apparatus operably coupled to the drive motor, and a mechanism that maintains stability of the imaging apparatus while the imaging apparatus is rotating. The imaging apparatus generally includes a flexible drive cable and a probe at a distal end of the drive cable. Exemplary imaging apparatuses include an optical coherence tomography apparatus (OCT), an intravascular ultrasound apparatus (IVUS), and a near infrared spectroscopy apparatus. The imaging system may also be a combinations of these apparatuses, e.g., an OCT apparatus in combination with an IVUS apparatus.

[0005] Numerous different types of stabilizers may be used with systems of the invention and any stabilizer that reduces vibrational effects on the imaging system while facilitating maintenance of a uniform rotational speed during operation of the imaging system is envisioned for systems of the invention. An exemplary mechanism that maintains stability of the imaging apparatus while the imaging apparatus is rotating includes a stiffener adapted to be axially rotated by the drive motor attached to a proximal end of the stiffener, and a first tube including metal coaxially joined to a distal end of the stiffener, in which the flexible drive cable is coaxially joined to a distal end of the first tube. The mechanism may further include a support housing having a first axial lumen disposed therethrough and sufficiently large to accommodate the stiffener. The mechanism may further include a vibrational dampening mechanism disposed around the support housing, in which the vibrational dampening mechanism is adapted to be attached between the support housing and an external housing.

[0006] The mechanism may further include a second tube having polyimide and fixedly secured within the first tube. Exemplary materials for the second tube include braid reinforced polyimide, a blend of polyimide and polytetrafluoroethylenes, coil reinforced polyimide, and combinations thereof.

[0007] Systems of the invention may further include a catheter sheath coaxially joined to a distal end of the support housing and including a second axial lumen disposed therethrough sufficiently large to accommodate the first tube. Alternatively, systems of the invention may further include a catheter sheath coaxially joined to a distal end of the external housing and including a second axial lumen disposed therethrough sufficiently large to accommodate the first tube. In certain embodiments, the stiffener is disposed substantially within the support housing and the first tube is disposed substantially within the catheter sheath in a first configuration. In other embodiments, the stiffener is disposed substantially proximally external to the support housing, the flexible drive cable is disposed substantially within the catheter sheath, and the first tube is disposed substantially within the support housing in a second configuration.

[0008] Another aspect of the invention provides a rotational imaging system that includes a rotational drive motor, a rotational imaging apparatus operably coupled to the drive motor, and a vibration dampening mechanism that reduces vibrational effects while maintaining substantial uniform speed of the imaging apparatus while the imaging apparatus is rotating.

Brief Description of the Drawings

[0009] The foregoing description of the figures is provided for a more complete understanding of the drawings. It should be understood, however, that the embodiments are not limited to the precise arrangements and configurations shown.

[0010] FIG. 1 is a cross-sectional view of an exemplary catheter sheath including an exemplary imaging modality and disposed within human vasculature.

[0011] FIG. 2A is an illustration of an embodiment of a rotational drive shaft assembly in a first configuration.

[0012] FIG. 2B is an illustration of modes of vibration of the rotational drive shaft assembly of FIG. 2A.

[0013] FIG. 2C is an illustration of the rotational drive shaft assembly of FIG. 2A in a second configuration.

[0014] FIG. 2D is an illustration of the rotational drive shaft assembly of FIG. 2A in a third configuration.

[0015] FIGS. 3A-3C illustrate another embodiment of a rotational drive shaft assembly.

[0016] FIG. 3D illustrates a cross-sectional view of the drive shaft assembly of FIGS. 3A-3C.

[0017] FIG. 3E is an enlarged cross-sectional view of another embodiment of the drive shaft assembly of FIG. 3D. [0018] FIG. 3F is a cross-sectional view of the drive shaft assembly of FIG. 3E taken generally along the line 3F-3F of FIG. 3E.

[0019] FIG. 3G is a cross-sectional view of the drive shaft assembly of FIG. 3E taken generally along the line 3G-3G of FIG. 3E.

[0020] FIG. 4 is a partial cross-sectional view of another embodiment of a rotary drive shaft assembly.

[0021] FIG. 5 is a partial cross- sectional view of a further embodiment of a rotary drive shaft assembly.

[0022] FIG. 6 is a partial cross-sectional view of yet another embodiment of a rotary drive shaft assembly.

[0023] FIG. 7 is a partial cross-sectional view of yet a further embodiment of a rotary drive shaft assembly.

[0024] FIG. 8A is a partial cross-sectional view of another embodiment of a rotary drive shaft assembly.

[0025] FIG. 8B is a partial cross-sectional view of yet another embodiment of a rotary drive shaft assembly.

[0026] FIG. 9 is a partial cross- sectional view of a further embodiment of a rotary drive shaft assembly.

[0027] FIG. 10 is a partial cross-sectional view of yet a further embodiment of a rotary drive shaft assembly.

[0028] FIG. 11 is a partial cross-sectional view of another embodiment of a rotary drive shaft assembly.

[0029] FIG. 12 is a partial cross-sectional view of yet another embodiment of a rotary drive shaft assembly.

[0030] FIG. 13 is a partial cross-sectional view of a further embodiment of a rotary drive shaft assembly.

[0031] FIG. 14 is a partial cross-sectional view of yet a further embodiment of a rotary drive shaft assembly.

Detailed Description of the Preferred Embodiments

[0032] 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.

[0033] Language indicative of a relative geometric relationship between components includes use of the terms "proximal" and "distal" herein. In this context, "proximal" refers to an end of a component nearest to the medical practitioner during use and "distal" refers to the end of the component furthest from the medical practitioner during use.

[0034] An improved drive shaft assembly for a rotational imaging system is disclosed herein. More particularly, the drive shaft assembly is self-supporting within a patient interface module (PEVI) during extended axial motion at rotational speeds between about 5,000 revolutions per minute (rpm) and 30,000 rpm. The rotational imaging system may be suitable for insertion into a lumen of any anatomical or mechanical conduit, vessel, tube, or the like, including insertion in vivo through a patient's vasculature. The rotational imaging system may comprise an Optical Coherence Tomography ("OCT") system, or may comprise another type of imaging system, including by way of example and not limitation, spectroscopic devices, (including fluorescence, absorption, scattering, and Raman spectroscopies), intravascular ultrasound (IVUS), Forward- Looking IVUS (FLIVUS), high intensity focused ultrasound (HIFU), radiofrequency, thermal imaging or thermography, optical light-based imaging, magnetic resonance, radiography, nuclear imaging, photoacoustic imaging, electrical impedance tomography, elastography, pressure sensing wires, intracardiac echocardiography (ICE), forward looking ICE and orthopedic, spinal imaging and neurological imaging, image guided therapeutic devices or therapeutic delivery devices, diagnostic delivery devices, and the like. In the case of an optical imaging system, light sources can be any laser source, broadband source, superluminescent diode, tunable source, and the like. Communication between any proximal and distal end of any of the rotational imaging systems noted hereinabove may be by any communication devices, such as wires, optics, including fiberoptics and/or lens systems, wireless, RF, etc.

[0035] FIG. 1 illustrates an exemplary catheter sheath 100 for rotational imaging inside a lumen of any anatomical or mechanical conduit, vessel, or tube. The exemplary catheter sheath 100 is suitable for in vivo imaging, particularly for imaging of an anatomical lumen or passageway, such as a cardiovascular, neurovascular, gastrointestinal, genitor-urinary tract, or other anatomical luminal structure. For example, FIG. 1 illustrates a vascular lumen 102 within a vessel 104 including a plaque buildup 106. The exemplary catheter sheath 100 may include a rapid access lumen 108 suitable for guiding the catheter sheath 100 over a guidewire 110. [0036] As shown in FIG. 1, the catheter sheath 100 houses an exemplary rotational imaging modality 112 that rotates about a longitudinal axis 114 thereof as indicated by arrow 116. The catheter sheath 100 is held stationary and coaxial relative to the rotational imaging modality 112, which includes a probe 118 at a distal end of a flexible drive cable 120. The flexible drive cable 120 includes a lumen 122 longitudinally disposed therethrough. In one embodiment, the flexible drive cable 120 includes a stranded hollow core shaft extending the substantial length of the flexible drive cable 120. In alternative embodiment, the flexible drive cable 120 includes a stranded hollow core shaft extending along at least a portion of the length of the drive cable 120. The stranded hollow core shaft may comprise a plurality of helically wound wire strands so that mechanical rotation of the flexible drive cable 120 is in the same direction as the helical wire strands. The stranded hollow core shaft may include an inner stranded portion and an outer stranded portion, where the outer stranded portion is wound in the opposite helical direction than the inner stranded portion.

[0037] The flexible drive cable 120 rotates under the influence of an external rotary drive motor 400 (See FIGS. 2C-3D). The rotary drive motor 400 may rotate at high rotational speeds in excess of 20,000 rpm. An exemplary rotary drive motor 400 capable of producing rotational speeds in excess of 20,000 rpm is available as part number 283833 from Maxon Precision Motors, Inc., Fall River, Massachusetts. In addition, the flexible drive cable 120 may be translated longitudinally, as indicated by arrow 126 to provide a catheter "pull back." An example of a catheter sheath 100 for rotational imaging including a flexible drive cable 120, for example, may be found in Dick et al. U.S. Patent Application Publication No. 2009/0018393, incorporated by reference in its entirety herein.

[0038] The exemplary rotational imaging modality 112 may comprise, in one embodiment, an OCT system. OCT is an optical interferometric technique for imaging subsurface tissue structure with micrometer-scale resolution. In another embodiment, the exemplary rotational imaging modality 112 may comprise an ultrasound imaging modality, such as an F/US system, either alone or in combination with an OCT imaging system. The OCT system may include a 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 Kemp et al. U.S. Patent Application Publication No. 2009/0046295, incorporated by reference in its entirety herein. The exemplary catheter sheath 100 may be integrated with IVUS by an OCT- IVUS system for concurrent imaging, as described in, for example, Castella et al. U.S. Patent Application Publication No. 2009/0043191, incorporated by reference in its entirety herein.

[0039] Referring to FIGS. 2A-2D, a rotary drive shaft assembly 200 operationally connects the rotary drive motor 400 to the flexible drive cable 120. The rotary drive shaft assembly 200 may include a longitudinal translation mechanism or axially translatable drive stage 202 for longitudinal translation of the probe 118 during rotation thereof. The axially translatable drive stage 202 may include a stepping motor or other mechanism for precise control of translation velocity and position of the rotary drive motor 400 as may be known in the art.

[0040] In one embodiment, the rotary drive shaft assembly 200 includes a stiffener or section of rigid tubing 310 that is sized to be coaxially accommodated by a lumen 206 of a support housing 208. In one embodiment, the stiffener 310 is a hollow shaft that accommodates an optical fiber disposed therethrough. In another embodiment, the stiffener 310 may be a solid shaft or rod that is longitudinally transmissive to light similar to an optical fiber. The stiffener 310 may be manufactured from a material including by way of example and not limitation, stainless steel, titanium, beryllium, copper, alloys of titanium, beryllium and/or copper, ceramic material such as alumina, light transmissive material such as glass or plastic, etc. It has been found that the rigidity of a ceramic material may be beneficial in helping to control vibration; however, due to inherent brittleness a ceramic material may crack or break if dropped or jarred. A distal end of the stiffener 310 is connected to a proximal end of a metal hypotube shaft 210.

[0041] Referring to FIG. 2B, during pullback at high rotational speeds, the metal hypotube shaft 210 may vibrate, wobble, or flop around within the lumen 206 in one or a combination of vibrational harmonics or mode shapes, for example, the vibrational mode shapes indicated by dashed lines 211 and/or 213, and/or higher vibrational harmonics (not shown). The particular vibrational mode(s) and amplitudes thereof depend upon many factors including, for example, speed of rotation, diameter of the metal hypotube shaft 210, material properties of the metal hypotube shaft 210, and the level of compressive or tensile force applied longitudinally along the metal hypotube shaft 210. In the absence of the support housing 208, such vibrational modes may grow in radial amplitude until the hypotube shaft 210 catastrophically fails. Such failure may be particularly problematic if the pullback includes a compressive force applied along the metal hypotube shaft 210. [0042] It is contemplated that as long as the metal hypotube shaft 210 includes a diameter that is properly sized within a predetermined range of diametric sizes relative to the diameter of the lumen 206, the radial amplitude of the wobble of the metal hypotube shaft 210 may be sufficiently limited by the inner wall of the support housing 208 such that the metal hypotube shaft remains intact despite wobbling during rotation at speeds in excess of 20,000 rpm. For example, in one embodiment, the lumen 206 of the support housing 208 has an internal diameter having a size about four times an outer diameter of the metal hypotube shaft 210. Other embodiments include other relative sizes of the internal diameter of the lumen 206 and the outer diameter of the metal hypotube shaft 210. For example, the lumen 206 of the support housing 208 may include an internal diameter having a size of at least between about 1.5 times to about 6 times the outer diameter of the metal hypotube shaft 210. However, if the metal hypotube shaft 210 is sized outside of the predetermined range of diametric sizes relative to the diameter of the lumen 206, the metal hypotube shaft 210 may be at risk of wobbling or flopping at such a radial amplitude as to result in catastrophic failure at rotational speeds in excess of 20,000 rpm.

[0043] The metal hypotube shaft 210 may comprise nitinol, i.e. nickel titanium alloy, or another biocompatible alloy such as stainless steel, tantalum, gold, platinum, titanium, copper, nickel, vanadium, zinc metal alloys thereof, copper-zinc-aluminum alloy, and combinations thereof. A proximal end of the flexible drive cable 120 is operably coupled to a distal end of the metal hypotube shaft 210.

[0044] As described hereinabove with regard to FIGS. 2 A and 2B, one embodiment of the rotary drive shaft assembly 200 includes a combination of the support housing 208, the rigid tubing 310, the metal hypotube shaft 210, and the flexible drive cable 120, and facilitates maintenance of a uniform rotational speed of the flexible drive cable at high rotational speeds in excess of 20,000 rpm. Referring to FIGS. 2A-2D, in another embodiment, a vibration dampening mechanism 810, for example, an elastomeric vibrational dampener 810, may be disposed concentrically around the support housing 208 and between the support housing 208 and an external housing 800, for example, a catheter handle disposed at a proximal end of the catheter sheath 100. The vibration dampening mechanism 810 may include one or more layers 216 of an elastomer or other mechanically compressible material and may thereby provide a mechanism to dampen high speed rotational vibrations on the proximal end of the rotary drive shaft assembly 200. [0045] By dampening high speed rotational vibrations, the vibration dampening mechanism 810 inhibits catastrophic failure of the rotary drive shaft assembly 200 when axially translated or "pulled back" by the translatable drive stage 202 during rotation at speeds in excess of 20,000 rpm. Without the vibration dampening mechanism 810, the metal hypotube shaft 210 may be free to vibrate, limited in amplitude of vibration only by the support housing 208 as described hereinabove with regard to FIGS. 2A and 2B. However, in the presence of the vibration dampening mechanism 810, the metal hypotube shaft 210 is additionally inhibited from excessive vibration amplitude. Thus, it is contemplated that the vibration dampening mechanism 810 facilitates a longer range of translation or "pull back" for a given configuration of the stiffener 310, the support housing 208, and the metal hypotube shaft 210. The vibration dampening mechanism 810 may provide dampening further inhibiting the rotational vibrations from being translated to the distal end of the rotary drive shaft assembly 200 or near the sample probe 118. Such dampening may also be beneficial for maintaining alignment of optics and therefore maintaining signal strength integrity along an optical path through the support housing 208.

[0046] Referring to FIGS. 2A-2D, operation of the rotary drive shaft assembly 200 may begin, for example, in the configuration illustrated in FIG. 2D, wherein the stiffener or rigid tubing 310 is accommodated substantially coaxially within the lumen 206 of the support housing 208, which is fixedly attached to the external housing 800 via the vibration dampening mechanism 810. In all of the configurations to be described hereinbelow with regard to FIGS. 2A-2D, the flexible drive cable 120 is supported by the catheter sheath 100. In this configuration, the metal hypotube shaft 210 is supported within the catheter sheath 100.

[0047] In one embodiment, the catheter sheath 100 may include the external housing 800 disposed on a proximal end thereof, as illustrated by regions enclosed by dashed lines 218 in FIGS. 2A-2D. The flexible drive cable 120 and the metal hypotube shaft 210 are operably coupled with the distal end of the rigid tubing 310. The rigid tubing 310 is sufficiently rigid and/or has a sufficient diameter to be self-supporting in free space; however, in this configuration the rigid tubing is further supported against large amplitude wobbling or flopping at rotational speeds in excess of 20,000 rpm by an inner wall of the support housing 208. Such support of the flexible drive cable 120, the metal hypotube shaft 210, and the rigid tubing 310 facilitates maintenance of a uniform rotational speed thereof. [0048] FIG. 2C represents the rotary drive shaft assembly 200 configured such that the flexible drive cable 120 and the metal hypotube shaft 210 are translated proximally relative to the configuration illustrated in FIG. 2D (or distally relative to the configuration illustrated in FIG. 2A). In this configuration, the flexible drive cable 120 remains supported within the catheter sheath 100 and operably coupled with the metal hypotube shaft 210 on the proximal end of the catheter sheath 100. The metal hypotube shaft 210 is supported on a distal end by the catheter sheath 100 and on a proximal end by connection to the rigid tubing 310. As noted with regard to FIG. 2D, the rigid tubing 310 is sufficiently rigid and/or has a sufficient diameter to be self-supporting in free space. However, in this configuration the rigid tubing 310 is further supported by being partially within the proximal end of the support housing 208, and is therefore further supported against large amplitude wobbling or flopping at rotational speeds in excess of 20,000 rpm by the inner wall of the support housing 208. The proximal end of the rigid tubing 310 extends from the proximal end of the lumen 206 and is operably coupled with the rotary drive motor 400. Such support of the flexible drive cable 120, the metal hypotube shaft 210, and the rigid tubing 310 facilitates maintenance of a uniform rotational speed thereof.

[0049] Referring once again to FIG. 2A, in this configuration the rigid tubing 310 has been translated proximally relative to the configuration illustrated in FIG. 2C so as to be substantially external to the proximal end of the lumen 206 of the support housing 208. The metal hypotube shaft 210 is now disposed substantially within the support housing 208; however, the flexible drive cable 120 remains within the catheter sheath 100 and operably coupled to the metal hypotube shaft 120 at the distal end of the support housing 208. Thus, the flexible drive cable 120 remains supported within the catheter sheath 100.

[0050] As noted, the rigid tubing 310 is sufficiently rigid and/or has a sufficient diameter to be self-supporting in free space. In addition, assuming that the metal hypotube shaft 210 is correctly sized within a range of predetermined diametric sizes as noted hereinabove, the metal hypotube shaft 210 may wobble or flop around within the lumen 206 yet remain sufficiently supported by the inner wall of the supporting housing 208, which limits the amplitude of the flopping or wobbling that may otherwise lead to destructive vibrations and/or catastrophic buckling of the metal hypotube shaft 210. Such support of the flexible drive cable 120, the metal hypotube shaft 210, and the rigid tubing 310 facilitates maintenance of a uniform rotational speed thereof at high rotational speeds. [0051] Another consideration in designing the drive shaft assembly 200 involves the relative sizing of the rotational components thereof, in particular the metal hypotube shaft 210, the support housing 208, and the stiffener 310. As noted hereinabove, in all configurations the rigid tubing 310 is sufficiently rigid and/or has a sufficient diameter to be self-supporting in free space. Also, in all configurations the lumen 206 accommodates the rigid tubing 310. Thus, the rigid tubing 310 should be large enough in diameter to be self-supporting in free space, but not so large as to cause the lumen 206 to be too large for the support housing 208 to provide adequate amplitude limitation to wobbling or flopping of the metal hypotube shaft 210 at rotation speeds in excess of 20,000 rpm.

[0052] Although the metal hypotube shaft 210 is free to wobble within the lumen 206 at any of the configurations described in FIGS. 2A-2D or during longitudinal translation therebetween, the amplitude of the wobble is limited by the lumen 206 such that the rotary drive assembly 200 doesn't catastrophically fail. Thus, the rotary drive assembly 200 provides sufficient support to the flexible drive cable 120 and the metal hypotube shaft 210 at any of the configurations described in FIGS. 2A-2D or during longitudinal translation therebetween to facilitate maintenance of a uniform rotational speed with limited vibration thereof.

[0053] As illustrated in FIGS. 3A-3C, in another embodiment, the motor 400 is fixedly held within a lumen 410 longitudinally disposed through a motor housing 450 that may include or be attached to the carriage or longitudinally translatable drive stage 202 (See FIGS. 2A-2D) that provides longitudinal translation of the motor 400 (and the stiffener 310) relative to a receiver 700. A coupling 300 is disposed within a catheter handle 800. The stiffener 310 rotates freely within the vibration dampening mechanism 810 that is fixedly held to an internal surface 820 of the catheter handle 800. Connections of the motor 400 to the motor housing 450 and the vibration dampening mechanism 810 to the internal surface 820 may be by connection methods including by way of example and not limitation, a friction fit with or without shims, a weld, an adhesive, etc.

[0054] Referring to FIG. 3A, in one embodiment, the receiver 700 includes a lumen 720 disposed longitudinally therethrough. The motor housing 450 is disposed coaxially within the lumen 720 such that an annular space 730 is defined therebetween. As illustrated in FIG. 3B, upon initial engagement of the catheter handle 800 and the receiver 700, the catheter handle 800 is accommodated by the annular space 730. Such accommodation creates a preliminary alignment of the coupling 300 with the lumen 410.

[0055] A tapered feature 415 may be disposed at a distal end of the lumen 410. As illustrated in FIG. 3C, upon further engagement of the catheter handle 800 and the receiver 700, the coupling 300 is guided by the tapered feature 415 into accommodation by the lumen 410. In an alternative embodiment, a tapered guide feature may be implemented on the proximal end of coupling 300 instead of, or in addition to, the tapered feature 415. Such accommodation creates in turn a preliminary alignment of a hollow drive shaft 500 with a lumen 360 of a lens holder 350 (See FIGS. 3D and 3E).

[0056] Referring to FIG. 3A, in one embodiment, a distal end of the hollow drive shaft 500 includes an externally beveled feature 515. In this embodiment, upon further engagement of the catheter handle 800 and the receiver 700, the lens holder 350 is guided by the beveled feature 515 to engage the lumen 360 and the hollow drive shaft 500. In an alternative embodiment, a guide feature, for example, tapered feature 365 (See FIG. 3A) may be disposed at a proximal end of the lumen 360 instead of, or in addition to, beveled feature 515. The shape of the beveled features 415, 515, or the alternate embodiments may be straight or rounded to suit the intended used.

[0057] So aligned, the hollow drive shaft 500 may be removably attached within the lumen 360. In an alternate embodiment, the engagement of lumen 360 and hollow shaft 500 may be effected by motion of the motor 400 and associated components instead of, or in addition to, further engagement of catheter handle 800 and receiver 700.

[0058] Coincident with the removable attachment of the hollow drive shaft 500 within the lumen 360, the catheter handle 800 removably attaches to the receiver 700, by any method of removable attachment as known in the art. For example, in one embodiment, slots 710 on the receiver 700 accommodate ribs 830 on the catheter handle 800. In this embodiment, as illustrated in FIGS. 3A-3C, the receiver 700 and the catheter handle 800 are oriented such that each rib 830 is disposed at an open end of each slot 710. So oriented, the receiver 700 is rotated relative to the catheter handle 800 so that each rib 830 enters each slot 710. Each rib 830 may further include a radial protrusion (not shown) at an end thereof that serves to snap onto a radial depression (not shown) at a closed end of each of the slots 710. Such a snap fit may facilitate a locking attachment of the catheter handle 800 to the receiver 700. [0059] Referring to FIGS. 3D and 3E, in one embodiment, the coupling 300 is fixedly connected to the stiffener 310 that extends from a distal end 315 of the coupling 300, such that the stiffener 310 rotates with the coupling 300. Connection of the stiffener 310 to the coupling 300 may be via a connection method including by way of example and not limitation, a frictional fit, a snap fit, crimping, swaging, overmolding, an adhesive, a weld, etc. The materials for the coupling 300 may be any plastic, metal, or Polyether-ether-ketone (PEEK).

[0060] In one embodiment, a first optical fiber 320 is disposed longitudinally through the stiffener 310 such that a first fiber ferrule 330 fixedly connects over a proximal end 325 of the first optical fiber 320. The first optical fiber 320 may be a single mode or multi-mode optical fiber as known in the art. The first fiber ferrule 330 is made from a material that has properties similar to that of the first optical fiber 320. For example, the first fiber ferrule 330 may be made from glass to match coefficient of thermal expansion with the first optical fiber 320. The first optical fiber 320 may be connected to the first fiber ferrule 330 by a connection method including by way of example and not limitation, an adhesive, a weld, splicing, fusion, etc. Alternatively, the first optical fiber 320 may be manufactured integrally with the first fiber ferrule 330.

[0061] In one embodiment, the first optical fiber 320 is disposed approximately concentrically within the stiffener 310 and rotates with the stiffener 310. The stiffener 310 connects on a distal end thereof to the metal hypotube shaft 210 and ultimately to an optical probe (not shown) at a distal end of the flexible drive cable 120. Examples of a flexible drive cable 120, an imaging system including an optical probe rotating at a distal end of a flexible drive cable 120, may be found, for example, in Dick et al. U.S. Patent Application Publication No. 2009/0018393, Kemp et al. U.S. Patent Application Publication No. 2009/0046295, and/or Castella et al. U.S. Patent Application Publication No. 2009/0043191, all of which are hereby incorporated by reference in their entirety herein.

[0062] In one embodiment, a first collimating lens 340 is disposed in optical communication with a proximal end of the first optical fiber 320. The first collimating lens 340 may be made from an optical material having an internally variable index of refraction. For example, in one embodiment, the first collimating lens 340 is a lens having a radial index gradient. Such a lens, known in the art as a gradient index ("GRIN") or self focusing ("SELFOC") lens facilitates the ability to precisely focus light using a simple, compact lens geometry, and is available, for example, from NSG Europe, Advanced Materials and Applications Division, Belgium. In other embodiments, other types of collimating lenses as known in the art may be used.

[0063] In one embodiment, the first collimating lens 340 is fixedly attached to the proximal end of the first fiber ferrule 330. The first collimating lens 340 may attached to the first fiber ferrule 330 via a connection method including by way of example and not limitation, a frictional fit, a snap fit, a weld, an adhesive, etc. It is contemplated that the first fiber ferrule 330 facilitates stronger attachment of the first optical fiber 320 to the first collimating lens 340.

[0064] In another embodiment, referring to FIG. 3E, the first fiber ferrule 330 may be disposed within a ferrule sleeve or ring 335 to reinforce attachment of the first fiber ferrule 330 and the first collimating lens 340. The ferrule sleeve 335 may be manufactured from a material including by way of example and not limitation, stainless steel, polymethylmethacrylate (PMMA), other plastic, or other material as known in the art. The ferrule sleeve 335 may attach over the first fiber ferrule 330 and/or the first collimating lens 340 via a press fit, an adhesive, a snap fit, or other methods of attachment as known in the art.

[0065] In one embodiment, the first collimating lens 340 is fixedly held by a lens holder 350. In this embodiment, for example referring to FIGS. 3D and 3E, the first collimating lens 340 is disposed within a distal end of the lumen 360 disposed longitudinally through the lens holder 350 by a connection method including by way of example and not limitation, a frictional fit, a snap fit, an adhesive, a split sleeve with a clamping ring, etc. The lens holder 350 may be manufactured from any material having good dimensional stability, low dynamic coefficient of friction, and good stiffness. Suitable materials for the lens holder 350 include by way of example and not limitation, stainless steel, aluminum, or thermoplastics such as polyetheretherketone (PEEK) or polyoxymethylene (POM), which is sold under the trademark Delrin^® by E. I. du Pont de Nemours and Company, USA.

[0066] In another embodiment, the lens holder 350 may further be fixedly held to the proximal end of the first fiber ferrule 330. In another embodiment, the lens holder 350 may be further fixedly held to a proximal end of the ferrule sleeve 335. In yet a further embodiment, the lens holder 350 may further be fixedly held to the proximal ends of both the first fiber ferrule 330 and the ferrule sleeve 335. Connection of the lens holder 350 to either or both of the fiber ferrule 330 and the ferrule sleeve 335 may be by a connection method including by way of example and not limitation, a frictional fit, a snap fit, a weld, an adhesive, etc. [0067] Referring to FIG. 3D, a distal portion of the hollow drive shaft 500 longitudinally extends from a distal end 405 of the motor 400. The distal portion of the hollow drive shaft 500 attaches within the lumen 360 that includes an opening on a proximal side of the lens holder 350 such that the hollow drive shaft 500 is longitudinally aligned with the first collimating lens 340. Attachment of the hollow drive shaft 500 within the lumen 360 of the lens holder 350 may be by a connection method including by way of example and not limitation, a frictional fit, a snap fit, an adhesive, a weld, etc. In one embodiment, the hollow drive shaft 500 removably attaches within the lumen 360 to facilitate removal and replacement of the motor 400 when in use in the field. Referring to FIG. 3E, the lumen 360 is illustrated as having a luminal surface including one or more internal shoulders 370 that may facilitate precise alignment between hollow drive shaft 500 and lens holder 350 and/or removable attachment of the hollow drive shaft 500 within the lumen 360.

[0068] The coupling 300 accommodates the stiffener 310, the first fiber ferrule 330, the first collimating lens 340, and the lens holder 350 in a way that transfers torque from the hollow drive shaft 500 to the stiffener 310, but also inhibits vibration of the stiffener 310 from affecting longitudinal alignment of the first collimating lens 340. It is contemplated that such accommodation may be achieved by a configuration that provides for co-rotation of the first optical fiber 320, the first fiber ferrule 330, and the first collimating lens 340 with the stiffener 310 without rigid or fixed attachment therebetween.

[0069] For example, referring to FIGS. 3E-3G, in one embodiment, the lens holder 350 engages the coupling 300 by having at least a proximal end 355 including a cross-sectional shape that is not free to rotate within a bore 365 of the coupling 300. Such a shape is illustrated in FIG. 3F as square; however, the cross-sectional shape of at least the proximal end 355 of the lens holder 350 and the bore 365 may be any complementary shape that does not allow rotation of at least the proximal end 355 of the lens holder 350 within the bore 365. Thus, the lens holder 350 is not fixedly held to the coupling 300; however, rotation of the lens holder 350 is coupled to rotation of the coupling 300, which, in turn is coupled to rotation of the stiffener 310.

[0070] It is further contemplated that effects of vibration of the stiffener 310 may be reduced by decoupling transfer of forces between the lens holder 350 and the coupling 300 in a direction transverse to the longitudinal axis. Such decoupling may be achieved, for example, by a configuration including a plurality of pins 375 that are accommodated within one or more circumferential grooves 380 disposed in an outer surface of the lens holder 350, as illustrated in FIGS. 3E and 3G. The plurality of pins 375 may be spring loaded and biased inward, or may be press fit through corresponding holes (not shown) disposed radially through the coupling 300. Such a configuration including the plurality of pins 375 disposed in the one or more circumferential grooves 380 facilitates longitudinal application of force between the lens holder 350 and the coupling 300 without a fixed or rigid connection therebetween.

[0071] The hollow drive shaft 500 is rotationally driven by the motor 400, as indicated by arrow 510 in FIG. 3D. In one embodiment, the motor 400 is disposed concentrically around the hollow drive shaft 500. Such an arrangement may facilitate a reduction in the number of moving parts and a reduction in size of the drive shaft assembly 200. In other embodiments, the motor 400 may include a separate housing (not shown) and be disposed apart from the hollow drive shaft 500 such that the hollow drive shaft 500 is driven by the motor 400 via, for example, an external gear train, belt, chain, or other mechanism for transfer of torque from the motor 400 to the hollow drive shaft 500 as may be known in the art. Such a configuration of the motor 400 and the hollow drive shaft 500 may, for example, be found in Bouma et al. U.S. Patent No. 7,382,949.

[0072] Attachment of any of the stiffener 310, the metal hypotube shaft 210, and the flexible drive cable 120 may be via a generally axially overlapping attachment between end sections thereof. The generally axially overlapping attachment may be via, for example, welding, adhesives, or other method as known in the art. The outer diameters of any of the stiffener 310, the metal hypotube shaft 210 and/or the flexible drive cable 120 may be slightly mismatched to permit concentric or coaxial engagement and attachment between respective end sections thereof. Alternatively, any of the stiffener 310, the metal hypotube shaft 210, and the flexible drive cable may be attached via an end-to-end or butt-joined connection such as, for example, by welding, adhesives, or other method as known in the art.

[0073] In one embodiment, as illustrated in FIG. 4, a rotary drive shaft assembly 900 includes the metal hypotube shaft 210, or a first tube comprising metal 902 coaxially butt-joined onto the proximal end of the flexible drive cable 120. Similarly, the metal hypotube shaft 210 is coaxially butt-joined onto the distal end of the stiffener 310. The first tube 902 may comprise nitinol, stainless steel, tantalum, gold, platinum, titanium, copper, nickel, vanadium, zinc metal alloys thereof, copper-zinc-aluminum alloy, and combinations thereof. A second tube 904 is fixedly secured within the first tube 902 by, for example, a friction fit or an adhesive. Any suitable adhesive as known in the art may be used, including by way of example and not limitation, cyanoacrylate. The second tube 904 comprises polyimide or a structural blend of polyimide and other components, including by way of example and not limitation, a blend of polyimide and polytetrafluorethylene, a polyimide tube reinforced by fibers braided around the tube, or a polyimide tube reinforced by a length of material coiled around the tube.

[0074] It has been found that the securement of the second tube 904 into the first tube 902 provides enhanced rigidity to minimize vibration and whip at high-rotation speeds in excess of 20,000 rpm relative to the first tube 902 alone. In this embodiment of the rotary drive shaft assembly 900, the second tube 904 may be as long as the first tube 902, as illustrated in FIG. 4.

[0075] Alternatively, in another embodiment of a rotary drive shaft assembly 920, the second tube 904 may be somewhat shorter than the first tube 902 and is secured approximately centrally within the first tube 902, as illustrated in FIG. 5. FIG. 6 illustrates another embodiment of a rotary drive shaft assembly 940 where the second tube 904 is significantly shorter than the first tube 904 and is secured within the first tube 902 such that more than half of the second tube 904 is secured in a proximal half of the first 904 tube.

[0076] In yet another embodiment of a rotary drive shaft assembly 960, more than half of the second tube 904 may be fixedly secured in a distal half of the first 904 tube, as illustrated in FIG. 7. Further embodiments of the rotary drive shaft assemblies 900, 920, 940, 960 are possible, including by way of example and not limitation, a plurality of second tubes 904.

[0077] FIGS. 4-6 further illustrate embodiments for relative sizes of the first tube 902 and the flexible drive cable 120. FIG. 4 illustrates the first tube 902 having about the same diameter as the flexible drive cable 120. FIG. 5 illustrates the first tube 902 having a diameter smaller than the flexible drive cable 120. FIG. 6 illustrates the first tube 902 having a diameter larger than the flexible drive cable 120.

[0078] In other embodiments, a portion of the metal hypotube shaft 210 or the first tube comprising metal 902 may be concentrically or coaxially engaged or fitted with a portion of the flexible drive cable 120. Similarly, portion of the metal hypotube shaft 210 or the first tube comprising metal 902 may be concentrically or coaxially engaged or fitted with a portion of the stiffener 310. For example, in another embodiment of a rotary drive shaft assembly 980 the metal hypotube shaft 210 or the first tube 902 may be coaxially joined over the flexible drive cable 120 such that a distal end 906 of the first tube 902 overlaps a proximal end 908 of the flexible drive cable 120, as is illustrated in FIG. 8A. In a further embodiment of a rotary drive shaft assembly 990, the stiffener 310 may be coaxially joined over the first tube 902 such that a distal end 910 of the stiffener 310 overlaps a proximal end 912 of the first tube 902, as illustrated in FIG. 8B. In yet another embodiment of a rotary drive shaft assembly 1000, the flexible drive cable 120 may be coaxially joined over the first tube 902 such that the proximal end 908 of the flexible drive cable 120 overlaps the distal end 906 of the first tube 902, as illustrated in FIG. 9.

[0079] In other embodiments, the first tube 902 may be coaxially joined to the flexible drive cable 120 such that an inner helical stranded portion 796 of the flexible drive cable 120 is longitudinally displaced from an outer helical stranded portion 798 of the flexible drive cable 120. For example, FIG. 10 illustrates a rotary drive shaft assembly 1020, wherein the first tube 902 coaxially is joined over the inner helical stranded portion 796.

[0080] FIG. 11 illustrates a rotary drive shaft assembly 1040, wherein the outer helical stranded portion 798 is joined over the first tube 902. FIG. 12 illustrates a rotary drive shaft assembly 1060, wherein the outer helical stranded portion 798 is joined over the second tube 904 and the distal end 906 of the metal hypotube shaft 210 is joined to a proximal end 908 of the flexible drive cable 120. In this embodiment, the second tube 904 is partially contained within both the metal hypotube shaft 210 and the flexible drive cable 120. In any of the coaxially overlapping joining geometries described hereinabove with regard to FIGS. 8A-12, or for any other overlapping joining geometry involving a stranded hollow core flexible drive cable 120 having three or more helical stranded portions, the joining may be accomplished by any method known in the art, including by way of example and not limitation, welding, an adhesive, or a combination of welding and an adhesive. The coaxial fitting ensures a 1: 1 rotation of the metal hypotube shaft 210 and the flexible drive cable 120 to ensure little to no vibration during rotation.

[0081] The cross-sectional size and/or wall-thickness of the metal hypotube shaft 210 or the first and/or the second tubes 902, 904 may be varied along their length. For example, a rotary drive shaft assembly 1080 including a tapered first tube 916 having a tapered wall thickness is illustrated in FIG. 13. In this embodiment, the second tube 904 is longitudinally uniform in cross-section and wall thickness. [0082] Another embodiment of a rotary drive shaft assembly 1100 includes a tapered first tube 918 having a uniform wall thickness, as illustrated in FIG. 14. In this embodiment, a tapered second tube 920 having a tapered wall thickness is secured within the first tube 918. Such variation in cross-section and/or wall thickness may serve to impart variable stiffness along the longitudinal axis of the metal hypotube shaft 210 or the rotary drive shaft assemblies 1080, 1100. 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 metal hypotube shaft 210. 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 metal hypotube shaft 210 while retaining substantial torsional rigidity.

[0083] A rotary drive shaft assembly for an imaging system is presented. The assembly includes three staged portions that are designed facilitate long longitudinal translation of a small diameter imaging core and to minimize vibration at rotation speeds in excess of 20,000 rpm. A support housing provides additional support to the small diameter imaging core by limiting the radial amplitude of wobble or flopping at rotation speeds in excess of 20,000 rpm of the small diameter imaging core during longitudinal translation thereof.

[0084] It will be appreciated by those skilled in the art that changes could be made to the embodiments described hereinabove without departing from the broad concepts disclosed therein. It is understood, therefore, that this disclosure is not limited to the particular embodiments disclosed, but it is intended to cover modifications that may include a combination of features illustrated in one or more embodiments with features illustrated in any other embodiments. Various modifications, equivalent processes, as well as numerous structures to which the present disclosure may be applicable will be readily apparent to those of skill in the art to which the present disclosure is directed upon review of the present specification. Accordingly, this description is to be construed as illustrative only and is presented for the purpose of enabling those skilled in the art to make and use the rotary drive shaft assembly described herein and to teach the best mode of carrying out the same.

Claims

Claims We claim:

1. A rotational imaging system, the system comprising:

a rotational drive motor;

a rotational imaging apparatus operably coupled to the drive motor; and

a stabilizer that maintains stability of the imaging apparatus while the imaging apparatus is rotating.

2. The system according to claim 1, wherein the imaging apparatus further comprises:

a flexible drive cable; and

a probe at a distal end of the drive cable.

3. The system according to claim 2, wherein the stabilizer comprises:

a stiffener adapted to be axially rotated by the drive motor attached to a proximal end of the stiffener; and

a first tube comprising metal coaxially joined to a distal end of the stiffener, wherein the flexible drive cable is coaxially joined to a distal end of the first tube.

4. The system according to claim 3, wherein the stabilizer further comprises a support housing having a first axial lumen disposed therethrough and sufficiently large to accommodate the stiffener.

5. The system according to claim 4, further comprising a vibrational dampening mechanism disposed around the support housing, wherein the vibrational dampening mechanism is adapted to be attached between the support housing and an external housing.

6. The system according to claim 5, further comprising a catheter sheath coaxially joined to a distal end of the support housing and including a second axial lumen disposed therethrough sufficiently large to accommodate the first tube.

7. The system according to claim 5, further comprising a catheter sheath coaxially joined to a distal end of the external housing and including a second axial lumen disposed therethrough sufficiently large to accommodate the first tube.

8. The system according to claim 4, further comprising a second tube comprising polyimide and fixedly secured within the first tube.

9. The system according to claim 8, wherein the second tube comprises material selected from a group of materials consisting of: braid reinforced polyimide tube, a blend of polyimide and polytetrafluoroethylenes, coil reinforced polyimide tube, and combinations thereof.

10. The system according to claim 4, wherein the stiffener is disposed substantially within the support housing and the first tube is disposed substantially within the catheter sheath in a first configuration.

11. The system according to claim 4, wherein the stiffener is disposed substantially proximally external to the support housing, the flexible drive cable is disposed substantially within the catheter sheath, and the first tube is disposed substantially within the support housing in a second configuration.

12. The system according to claim 1, wherein the imaging apparatus is selected from the group consisting of: an optical coherence tomography apparatus, an intravascular ultrasound apparatus, and a near infrared spectroscopy apparatus.

13. A rotational imaging system, the system comprising:

a rotational drive motor;

a rotational imaging apparatus operably coupled to the drive motor; and

a vibration dampening mechanism that reduces vibrational effects while maintaining substantial uniform speed of the imaging apparatus while the imaging apparatus is rotating.

14. The system according to claim 13, wherein the imaging apparatus comprises: a flexible drive cable; and

a probe at a distal end of the drive cable.

15. The system according to claim 14, wherein the vibration dampening mechanism comprises: a stiffener adapted to be axially rotated by the drive motor attached to a proximal end of the stiffener; and

16. The system according to claim 15, wherein the mechanism further comprises a support housing having a first axial lumen disposed therethrough and sufficiently large to accommodate the stiffener.

17. The system according to claim 16, further comprising a secondary vibrational dampening mechanism disposed around the support housing, wherein the secondary vibrational dampening mechanism is adapted to be attached between the support housing and an external housing.

18. The system according to claim 17, further comprising a catheter sheath coaxially joined to a distal end of the support housing and including a second axial lumen disposed therethrough sufficiently large to accommodate the first tube.

19. The system according to claim 17, further comprising a catheter sheath coaxially joined to a distal end of the external housing and including a second axial lumen disposed therethrough sufficiently large to accommodate the first tube.

20. The system according to claim 16, further comprising a second tube comprising polyimide and fixedly secured within the first tube.

21. The system according to claim 20, wherein the second tube comprises material selected from a group of materials consisting of: braid reinforced polyimide tube, a blend of polyimide and polytetrafluoroethylenes, coil reinforced polyimide tube, and combinations thereof.

22. The system according to claim 16, wherein the stiffener is disposed substantially within the support housing and the first tube is disposed substantially within the catheter sheath in a first configuration.

23. The system according to claim 16, wherein the stiffener is disposed substantially proximally external to the support housing, the flexible drive cable is disposed substantially within the catheter sheath, and the first tube is disposed substantially within the support housing in a second configuration.

24. The system according to claim 13, wherein the imaging system is selected from the group consisting of: an optical coherence tomography apparatus, an intravascular ultrasound apparatus, a near infrared spectroscopy apparatus, and a combination therof.

25. A method for imaging a patient, the method comprising:

providing a rotational imaging system comprising a rotational drive motor; a rotational imaging apparatus operably coupled to the drive motor; and a stabilizer that maintains stability of the imaging apparatus while the imaging apparatus is rotating;

inserting at least a portion of the system into a lumen of a vessel; and

using the system to image an inside of the vessel.

26. The method according to claim 25, wherein the imaging system is selected from the group consisting of: an optical coherence tomography apparatus, an intravascular ultrasound apparatus, a near infrared spectroscopy apparatus, and a combination thereof.

27. The method according to claim 24, wherein the vessel is a human vessel.

28. The method according to claim 25, wherein the imaging system further comprises:

a flexible drive cable; and

a probe at a distal end of the drive cable.

29. The method according to claim 28, wherein the stabilizer comprises: a stiffener adapted to be axially rotated by the drive motor attached to a proximal end of the stiffener; and

30. The method according to claim 29, wherein the stabilizer further comprises a support housing having a first axial lumen disposed therethrough and sufficiently large to accommodate the stiffener.

31. The method according to claim 30, further comprising a vibrational dampening mechanism disposed around the support housing, wherein the vibrational dampening mechanism is adapted to be attached between the support housing and an external housing.

32. The method according to claim 31, further comprising a catheter sheath coaxially joined to a distal end of the support housing and including a second axial lumen disposed therethrough sufficiently large to accommodate the first tube.

33. The method according to claim 31, further comprising a catheter sheath coaxially joined to a distal end of the external housing and including a second axial lumen disposed therethrough sufficiently large to accommodate the first tube.

34. The method according to claim 30, further comprising a second tube comprising polyimide and fixedly secured within the first tube.

35. The method according to claim 34, wherein the second tube comprises material selected from a group of materials consisting of: braid reinforced polyimide tube, a blend of polyimide and polytetrafluoroethylenes, coil reinforced polyimide tube, and combinations thereof.

36. The method according to claim 30, wherein the stiffener is disposed substantially within the support housing and the first tube is disposed substantially within the catheter sheath in a first configuration.

37. The method according to claim 30, wherein the stiffener is disposed substantially proximally external to the support housing, the flexible drive cable is disposed substantially within the catheter sheath, and the first tube is disposed substantially within the support housing in a second configuration.