Patent Application
20120108980
The present invention relates to actuators employable for oscillating movement of a load, and more particularly, to actuators employing one or more shaped memory members. The invention is particularly apt to imaging catheters having an ultrasound transducer disposed for oscillating movement to scan a volume encompassing an internal anatomical region of interest.
Actuators are employed in a variety of applications for controlled movement of a mechanism, or load. Increasingly, actuator applications have been recognized which have small space, high-reliability and low power requirements that present unique design challenges.
Actuators may employ shape memory materials to produce movement. Shape memory materials are materials that experience dimensional changes under application of an external stimulus such as temperature or magnetic field. There are two types of shape memory materials that can achieve thermally-induced reversible shape changes: 1) Shape memory alloys (SMA) that are metallic alloys that undergo reversible phase changes between two different crystallographic phases upon a change in temperature and 2) Shape memory polymers (SMP) that typically consist of two polymer components and two phases, one with a higher melting temperature than the other. When shape memory polymers are heated above a specific glass transition temperature, one phase is generally in a rubbery phase and can deform easily. When subsequently cooled below this glass transition temperature, the SMP retains its given permanent shape. The distinguishing feature of SMP compared to all other polymers is that this dimensional change is marked by a sharp transition temperature and a rubbery plateau, along with a capacity to enable large strains without producing permanent local material damage.
Examples of significant shape memory alloys (SMA) are Nitinol, an alloy of nickel and titanium, copper-base alloys, and FeMnSiCrNi shape memory stainless steels. These metallic alloys are distinguished in that they may be heated to produce a corresponding martensite-to-austenite crystallographic phase transformation which results in a reduction in the length. Subsequent cooling of the shape memory alloy may result in an austenite-to-martensite phase transformation and the shape remains unchanged, whereby it may be returned to its original length under an applied stress. If the shape memory material is operatively associated with other members, the phase changes may be used to generate forces that may be used to create movement of the other members. Such heating may be created by passing a current through the shape memory material.
Catheters are medical devices that may be inserted into a body vessel, cavity or duct, and manipulated utilizing a portion that extends out of the body. Typically, catheters are relatively thin and flexible to facilitate advancement/retraction along non-linear paths. Catheters may be employed for a wide variety of purposes, including the internal bodily positioning of diagnostic and/or therapeutic devices. For example, catheters may be employed to position internal imaging devices (e.g., ultrasound transducers), to deploy implantable devices (e.g., stents, stent grafts, vena cava filters), and/or to deliver therapy (e.g., ablation catheters, drug delivery).
In this regard, use of ultrasonic imaging techniques to obtain visible images of structures is increasingly common. Broadly stated, an ultrasound transducer, typically comprising a number of individually actuated piezoelectric elements arranged in an array, is provided with suitable drive signals such that a pulse of ultrasonic energy travels into the body of the patient. The ultrasonic energy is reflected at interfaces between structures of varying acoustic impedance. The same or a different transducer detects the receipt of the return energy and provides a corresponding output signal. This signal can be processed in a known manner to yield an image, visible on a display screen, of the interfaces between the structures and hence of the structures themselves.
Intracardiac Echocardiography (ICE) catheters have become the preferred imaging modality for use in structural heart intervention because they provide high resolution 2D ultrasound images of the soft tissue structure of the heart. Additionally, ICE imaging does not contribute ionizing radiation to the procedure. ICE catheters can be used by the interventional cardiologist and staff within the context of their normal procedural flow and without the addition of other hospital staff. Current ICE catheter technology does have limitations though. The conventional ICE catheters are limited to generating only 2D images. Furthermore, the clinician must steer and reposition the catheter in order to capture multiple image planes within the anatomy. The catheter manipulation needed to obtain specific 2D image planes requires that a user spend a significant amount of time becoming facile with the catheter steering mechanisms.
The Philips iE33 echocardiography system running the new 3D transesophageal (TEE) probe (available from Philips Healthcare, Andover, Mass., USA) represents the first commercially-available real-time 3D (four dimensional (4D)) TEE ultrasound imaging device. This system provides the clinician with the 4D imaging capabilities needed for more complex interventions, but there are several significant disadvantages associated with this system. Due to the large size of the TEE probe (50 mm circumference and 16.6 mm width), patients need to be anesthetized or heavily sedated prior to probe introduction (G. Hamilton Baker, MD 4t al., Usefulness of Live Three-Dimensional Transesophageal Echocardiography in a Congenital Heart Disease Center, Am J Cardiol 2009; 103: 1025-1028). This requires that an anesthesiologist be present to induce and monitor the patient on anesthesia. In addition the hemodynamic status of the patient may require monitoring. Furthermore, minor and major complications from TEE probe use do occur including complications ranging from sore throat to esophageal perforation. The complexity of the Phillips TEE system and probe require the participation of additional staff such as an anesthesiologist, echocardiographer and ultrasound technician. This increases procedure time and cost.
Of particular interest are imaging catheter applications for small-scale actuators. The present inventors have realized the need for an imaging platform that is catheter-based and small enough for percutaneous access with three dimensional imaging in real-time (4D) capabilities. Using such a catheter-based imaging system for visualizing the three dimensional (3D) architecture of the heart, for example, on a real-time basis during intervention is highly desirable from a clinical perspective as it would facilitate more complex procedures such as left atrial appendage occlusion, mitral valve repair, and ablation for atrial fibrillation. 3D imaging would also allow the clinician to fully determine the relative position of structures. This capability would be of particular import in cases of structural abnormalities in the heart where typical anatomy is not present. Two dimensional transducer arrays provide a means to generate 3D images, but currently available 2D arrays require a high number of elements in order to provide sufficient aperture size and corresponding image resolution. This high element count results in a 2D transducer that is prohibitive with respect to clinically acceptable catheter profiles.
As internal diagnostic and therapeutic procedures continue to evolve, the desirability of enhanced procedure imaging via compact and maneuverable catheters has been recognized by the present inventors. More particularly, the present inventors have recognized the desirability of providing catheter features that facilitate selective positioning and actuator control of imaging componentry (e.g., to produce real time 3D images) located at a distal end of a catheter, while maintaining a relatively small profile, thereby yielding enhanced functionality for various clinical applications. As may be appreciated, the utilization of ultrasound transducers on catheters presents dimensional challenges, particularly for vascular applications. For example, for cardiovascular applications it may be desirable to maintain a maximum cross-dimension of less than about 12 French (Fr), and more preferably less than about 10 Fr, during advancement of an imaging catheter into the right atrium or other chambers of the heart. Due to the size constraints of some anatomical locations, e.g., that in the heart, it is desirable that the selective positioning necessary to achieve desired viewing angles be obtainable within a small anatomical volume such as, for example, a volume with a maximum cross dimension of less than about 3 cm.
The present invention relates to actuators employable for oscillating movement of a load. An improved actuator may include at least a first shape memory member (e.g., comprising a shape memory material) that is actuatable to affect at least a portion of the oscillating movement of the load. In contemplated embodiments, the actuator may further comprise a second shape memory member (e.g., comprising a shape memory material) actuatable to affect at least a second portion of the oscillating movement of the load. The utilization of one or more shape memory members facilitates the realization of controllable and reliable oscillating movement of a load in a compact and low-power manner. The first and second shape memory members may be actuatable in at least partially-offset timed relation to affect at least a portion of the oscillating movement of the load.
In one aspect, the actuator may include an enclosure defining an enclosed volume. The enclosed volume may contain a fluid. The fluid may be a liquid (e.g., to facilitate acoustic signal transmission). At least a portion of a first shape memory member of an actuator may be immersed within the fluid, and a first thermal insulation layer may be disposed about the immersed portion of the first shape memory member. Similarly, at least a portion of a second shape memory member of an actuator may be immersed within the fluid, and a second thermal insulation layer may be disposed about the immersed portion of the second thermal insulation layer. As may be appreciated, the provision of a thermal insulation layer on one or more shape memory member(s) may advantageously affect the rate of transfer of thermal energy between the contained fluid and the shape memory member(s). In such an aspect, for example, the load may comprise an ultrasound transducer.
In an implementation, the load is immersed within the fluid and disposed for oscillating movement through an angular range about a pivot axis within the enclosed volume, wherein the pivot axis is fixed relative to the enclosed volume. In this regard, the actuator may include first and second shape memory members operatively associated with the load, wherein the first and second shape memory members are actuatable in at least partially-offset timed relation to affect at least a portion of the pivotal movement of the load. Such an implementation, for example, may be in the form of a catheter having an elongate catheter body and a distal end portion supportably disposed at the distal end of the catheter body and defining the enclosed volume containing the load and the fluid. In such an implementation, the load may be an ultrasound transducer and the ultrasound transducer may be immersed in the fluid for ultrasound signal transmission and/or receipt.
In certain embodiments, the first and second shape memory members may be interconnected to the load within the enclosed volume and immersed within the contained fluid. In turn, first and second thermal insulation layers may be disposed about at least a portion of the first and second shape memory members, respectively, within the enclosed volume and immersed within the fluid. Further, the first and second shape memory members may be individually insulated for electrical isolation.
In arrangements, the first and/or second thermal insulation layers may have a thermal conductance of between about 0.03 watts per meter per Kelvin (W/mK) and 0.20 W/mK when measured at about 25° C. In arrangements, the first and/or second thermal insulation layers may have a thermal conductance of between about 0.05 W/mK and 0.08 W/mK when measured at about 25° C. In one approach, the first and/or second thermal insulation layers may comprise a fluoropolymer. In one implementation, the first and/or second thermal insulation layers may comprise at least one material selected from a group consisting of: a polytetrafluoroethylene (PTFE), an expanded polytetrafluoroethylene (ePTFE), an electrostatic spray-coated PTFE, a fluorinated ethylene propylene, an expanded fluorinated ethylene propylene, a perfluoroalkoxy copolymer, a polyvinylidene fluoride, a polyurethane, a silicone rubber, a plasma-coated polymer film (e.g., a low temperature plasma-enhance trimethylsilane), PARYLENE™, and blends and copolymers thereof. Other materials having a similar thermal conductance may also be employed. In one approach, the first and/or second thermal insulation layers may comprise a microporous material.
In addition to first and/or second thermal insulation layers as noted above, the actuator may include corresponding first and/or second outer layers, respectively, disposed (e.g., adherently disposed) about the first and/or second thermal insulation layers, respectively. In this regard, the first and/or second outer layers may be advantageously adapted for immersion within the contained fluid within the enclosure. In this regard, the first and/or second outer layers may each comprise a hydrophobic material. In one approach, the first and/or second outer layers may be selected to have a surface energy of less than about 50 dyn/cm2. Additionally, or alternatively, the first and/or second outer layers may be selected to have a dielectric withstand voltage of at least about 500 kV/m.
In an approach, in addition to the thermal properties of the first and/or second thermal insulation layers as noted above, the first and/or second thermal insulation layers may be advantageously adapted or configured for immersion within the contained fluid within the enclosure. In this regard, first and/or second thermal insulation layers may perform both the above-described function of the first and/or second thermal insulation layers and the above-described function of the first and/or second outer layers. Thus, the first and/or second thermal insulation layers may each comprise a hydrophobic material. In one approach, the first and/or second thermal insulation layers may be selected to have a surface energy of less than about 50 dyn/cm2. Additionally, or alternatively, the first and/or second thermal insulation layers may be selected to have a dielectric withstand voltage of at least about 500 kV/m. In this regard, the first and/or second thermal insulation layers may be capable of providing the above-noted insulative properties along with the above-noted hydrophobicity and dielectric withstand voltage.
Layers disposed about at least a portion of the first and second shape memory members, such as the above-described first and/or second thermal insulation layers and the above-described first and/or second outer layers, may have an elongation modulus that allows the layers to move with the shape memory members as the shape memory members change length. In this regard, the layers may be operable to elongate and shrink along with the shape memory members without peeling, cracking or delaminating. The layers may be adhesively joined to the shape memory members.
In an embodiment, within the enclosed volume, electrically active components may be insulated to limit undesired current flow (e.g., short circuiting). Such electrically active components may include, for example, electrical interconnections to the shape memory members and ultrasound transducer immersed in the fluid. Such insulation may be particularly beneficial where the fluid within the enclosed volume is a liquid.
In another aspect, a first shape memory member may be actuatable to rotate a load (e.g., an ultrasound transducer) in a first direction about the pivot axis. Conversely, a second shape memory member may be actuatable to rotate the load (e.g., an ultrasound transducer) in a second direction about the pivot axis, wherein the first direction is opposite to the second direction.
In an arrangement, the shape memory members may be operable to vary in length by at least about 1% due to actuation (e.g., by heating by passing current therethrough). In another arrangement, the shape memory members may be operable to vary in length by at least about 2% due to actuation. In a particular arrangement, the shape memory members may be varied in length by about 4% due to actuation.
In various embodiments, the first and second shape memory members may be defined by corresponding first and second shape memory wire lengths, respectively. In one approach, the first and second shape memory wire lengths may comprise physically-separate first and second wires. In another approach, the first and second shape memory wire lengths may be defined by different segments, e.g., first and second lengths, respectively, of a continuous shape memory wire.
A first end of the first shape memory wire length may be interconnected in fixed relation to one of an enclosure (e.g., at a distal end portion of a catheter) and a load (e.g., an ultrasound transducer) on a first side of the pivot axis. Similarly, a first end of the second shape memory wire length may be interconnected in fixed relation to one of the enclosure (e.g., at a distal end portion of a catheter) and a load (e.g., an ultrasound transducer) on a second side of the pivot axis, opposite to the first side.
In one approach, the first shape memory wire length may be interconnected to a corresponding other one of the load (e.g., an ultrasound transducer) and enclosure at a first interconnection location. Further, the second shape memory wire length may be interconnected to a corresponding other one of the load (e.g., an ultrasound transducer) and enclosure at a second interconnection location, wherein the first and second interconnection locations are located on opposite sides of the pivot axis.
In one embodiment, each of the first and second shape memory wire lengths may have corresponding second ends that are interconnected in fixed relation to the corresponding one of the enclosure and the load (e.g., an ultrasound transducer). Further, the first and second shape memory wire lengths may be interconnected between their opposing first and second ends to the corresponding other one of the enclosure and the load (e.g., an ultrasound transducer). In this regard, the noted first and second interconnection locations may be offset on opposite sides of the pivot axis. In one implementation, the first and second offset locations may be substantially equidistance from the pivot axis. In such arrangement, the first and second shape memory wire lengths may be symmetrically disposed relative to the load (e.g., an ultrasound transducer).
The first and second shape memory wire lengths may be disposed to each include corresponding first and second portions thereof that correspondingly define first and second included angles. In turn, the first and second shape memory wire lengths may be arranged so that the first and second included angles increase and decrease to displace the load in response to corresponding actuation and deactuation of the first and second shape memory members, respectively. By arranging the first and second shape memory wire lengths to include such included angles, an effective displacement of at least about 10% to 20% of the wire length may be achieved. Stated differently, an effective elongation of at least about 10% to 20% may be achieved, wherein an effective elongation is the elongation that would be needed to produce a similar movement of a load by a shape memory member disposed generally perpendicular to the load and disposed within a similar volume as the shape memory wire lengths with included angles.
In another embodiment, the first shape memory wire length may comprise a first end interconnected to an enclosure (e.g., at a distal end portion of actuator) on a first side of the pivot axis, and a second end interconnected to the load (e.g., an ultrasound transducer) on a second side of the pivot axis opposite to the first side. Similarly, the second shape memory wire length may have a first end interconnected to the enclosure on the first side of the pivot axis, and a second end interconnected to the load (e.g., an ultrasound transducer) on the second side of the pivot axis.
In yet another embodiment, the first shape memory wire length may comprise first and second ends interconnected in fixed relation to one of an enclosure (e.g., at a distal end portion of a catheter) and a load (e.g., an ultrasound transducer). Further, an engagement member (e.g., a stanchion, post, etc.) may be provided in fixed relation to the other one of the enclosure and the load, wherein the first shape memory wire length engages the engagement member to rotate the load in the first direction during actuation of the first shape memory wire length. Similarly, the second shape memory wire length may comprise a first end and a second end interconnected in fixed relation to said one of the enclosure and the load, wherein the second shape memory wire length engages the engagement member to rotate the load in a second direction during actuation of the second shape memory wire length.
In some embodiments, a central axis of a load (e.g., an ultrasound transducer) may be parallel to the pivot axis. In other embodiments, such central axis may be coincide with the pivot axis.
In various embodiments, a drive energy source may be included for repeatedly providing first and second energy signals during corresponding first and second time periods to the first and second shape memory members, respectively. The drive energy source may be operable to define a first time interval between an end of each first time period and a start of each second time period, wherein at least the second shape memory member is provided to be in elastic tension during at least a portion of each first time interval so that the second shape memory member is operable to affect at least a portion of the oscillating, pivotal movement of the load (e.g., an ultrasound transducer) during each first time interval. Further, the drive energy source may be operable to repeatedly provide the first and second energy signals with a second time interval defined between an end of each second time period and the start of each first time period. In turn, the first shape memory member may be provided to be in elastic tension during at least a portion of each second time interval so that the first shape memory member is operable to affect at least a portion of the oscillating, pivotal movement of the load (e.g., an ultrasound transducer) during each second time interval. As may be appreciated, the first and second shape memory members may be utilized to affect different portions of the oscillating, pivotal movement of the load corresponding with opposite end portions of an angular range of the pivotal movement.
In certain implementations, at least a first magnetic member may be supportably interconnected to one of an enclosure (e.g., at a distal end portion of a catheter) and a load (e.g., an ultrasound transducer), and located to affect at least a portion of the oscillating, pivotal movement of the load (e.g., an ultrasound transducer). In one approach, the first magnetic member may include a permanent magnet; for example, a permanent magnet comprising coated neodymium iron boron or samarium cobalt. In another approach, the first magnetic member may comprise an electromagnetic member.
Relatedly, a second magnetic member may be supportably interconnected to one of the enclosure and the load to affect at least a second portion of the oscillating, pivotal movement of the load. In this regard, the first and second portions of the oscillating, pivotal movement of the load may correspond with opposite end portions of a predetermined angular range of pivotal movement of the load. In certain implementations, the first magnetic member and/or second magnetic member may be operable to apply an attractive force. Similarly, in certain arrangements the first magnetic member and/or second magnetic member may be operable to apply a repulsive force. The application of force by the first and/or second magnetic members may be to a magnetizable member interconnected to the other one of the enclosure and the load. In another implementation, the application of force by the first and/or second magnetic members may be to at least one additional magnetic member interconnected to the other one of the enclosure and the load.
As noted, the above-described actuators are particularly apt for catheter implementations. In this regard, the first and second shape memory members may be disposed in an enclosure for affecting oscillating movement of an ultrasound transducer array at a distal end portion of the catheter. Further, the distal end portion may be provided to be selectively positionable by a user relative to a catheter body. In some embodiments, the distal end portion may be provided to be selectively angled across a range of angles relative to a catheter body. By way of example, the catheter may include a hinge for interconnecting the distal end portion to the catheter body. In other embodiments, the distal end portion may be provided to be selectively rotated about a range of angles relative to a catheter body.
In still another aspect, a method of affecting oscillating, pivoting motion of a load is provided. The method may include first actuating a first shape memory member operatively associated with the load to pivot the load in a first direction, and then second actuating a second shape memory member operatively associated with the load to pivot the load in a second direction opposite to the first direction. The method may further include repeating the first and second actuating steps in accordance with a predetermined cycle to affect oscillating, pivotal movement of the load through an angular range relative to a pivot axis. In an embodiment, the method may be a method for use in a catheter where the load is an ultrasound transducer immersed within a fluid and disposed for pivotal movement about the pivot axis within the enclosed volume where the enclosed volume is defined by a distal end portion supportably disposed at a distal end of an elongate catheter body. In such an embodiment, the method may further include operating the ultrasound transducer to transmit and/or receive acoustic signals through the fluid during at least a portion of each occurrence of the first and/or second actuating steps.
In an approach, the first actuating step may include first applying a first electrical signal to the first shape memory member to change the first shape memory member from a first configuration to a second configuration and thereby impart a first force to the load. The approach may also include the second actuating step comprising second applying a second electrical signal to the second shape memory member to change the second shape memory member from a first configuration to a second configuration and thereby impart a second force to the load. The method may include using the first force to return the second shape memory member from its second configuration to its first configuration, and using the second force to return the first shape memory member from its second configuration to its first configuration.
In an implementation, the oscillating, pivotal movement of the ultrasound transducer achieved by repeating the first and second actuating steps may occur at a rate between 1 and 50 Hz, or between 8 and 30 Hz. In another implementation, the oscillating, pivotal movement of the ultrasound transducer achieved by repeating the first and second actuating steps may occur at a rate of at least 10 Hz; in still another implementation, the rate may be at least 50 Hz.
In an arrangement, the first shape memory member may shorten during the first applying step, and the second shape memory member may shorten during the second applying step. The shape memory members may be in the form of shape memory wires.
In various embodiments, the first and second shape memory members may be defined by corresponding first and second shape memory wire lengths, respectively. In one approach, the first and second shape memory wire lengths may comprise physically-separate first and second wires. In another approach, the first and second shape memory wire lengths may be defined by different first and second lengths, respectively, of a continuous shape memory wire. The first and second portions may be defined by different first and second lengths, respectively, of a continuous shape memory wire, or by physically-separate first and second wires.
In certain implementations, the first and second shape memory members may each include corresponding first and second portions that define corresponding first and second included angles, respectively. In such implementations, the method may include increasing the first included angle and decreasing the second included angle during the first applying step, and increasing the second included angle and decreasing the first included angle during the second applying step.
In an approach, the predetermined cycle may include a first time interval between an end of the first applying step and a start of the second applying step. Such an approach may include employing an elastic response of the second shape memory member during each first interval to initiate pivotal movement of the load in the second direction. The predetermined cycle may include a second time interval between an end of the second applying step and a start of the first applying step, and the present approach may further include employing an elastic response of the first shape memory member during each occurrence of the second interval to initiate pivotal movement of the load in the first direction.
In an arrangement, the method may include employing a magnet to apply a magnetic force to the load to affect at least a portion of the oscillating pivotal movement. The method may also include employing a second magnet to apply a magnetic force to affect at least a different portion of the oscillating pivotal movement. In one approach, the first and second magnets may affect opposite end portions of the angular range.
Numerous additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the embodiment descriptions provided hereinbelow.
FIGS. 5AA, 5BB and 5CC are end views of selected componentry of a modified arrangement of the actuator embodiment off
The first and second shape memory members 12, 14 may each comprise a length of shape memory material (e.g., Nitinol, a metal alloy of nickel and titanium), wherein the first and second shape memory members 12, 14 may be heated in at least partially offset timed relation to yield corresponding martensitic-to-austenitic phase transformation and corresponding reductions (e.g., shrinkage) in the length of each member. As will be appreciated, such alternating length reductions causes shaft member 30 to rotate back and forth, thereby causing load 20 to pivot back and forth about pivot axis AA in an oscillating manner. Such heating may be achieved by applying electrical energy to the shape memory members 12, 14. The applied energy may be in the form of an applied voltage that induces a current flow in the shape memory members 12, 14, which produces the heating. The first and second shape memory members 12, 14 may each comprise a length of shape memory wire or any other appropriate shape memory form (e.g., a shape memory ribbon, a multiple element member such as a multiple filament wire, a coil, a helically wound strand).
Reference is now made to
The elastically deformable members 53a, 53b, 55a, 55b may be operable to elastically deform (e.g., resiliently compress and uncompress) in a manner that compensates for possible mismatches between the lengths of the shape memory members 12, 14 as they simultaneously change length (e.g., one of the shape memory members 12, 14 may be contracting in length as the other is lengthening). By compressing, the elastically deformable members 53a, 53b, 55a, 55b may help to prevent excessive elastic tension in the shape memory members 12, 14. Additionally, the elastically deformable members 53a, 53b, 55a, 55b may help compensate for elastic tension variations due to changes in geometry as the shape memory members 12, 14 pivot during load 20 oscillating movement.
The first shape memory member 12 may be operatively interconnected to shaft member 30 via engagement member 32a fixedly interconnected to and laterally extending away from shaft member 30 on one side of pivot axis AA. Similarly, second shape memory member 14 may be operatively interconnected to shaft member 30 via engagement member 32b fixedly interconnected to and laterally extending away from shaft member 30 on another side of pivot axis AA. The engagement members 32a, 32b may be grooved to help positively locate the shape memory members 12, 14 relative thereto. In embodiments where the distances between engagement member 32a and anchor 52a, and between engagement member 32a and anchor 52b are unequal, and/or where the distances between engagement member 32b and anchor 54a, and between engagement member 32b and anchor 54b are unequal, the corresponding groove(s) may be configured to allow the corresponding shape memory member(s) 12, 14 to slide therein as its length changes and the load 20 undergoes oscillating movement. In embodiments where such distances are substantially equal, the corresponding shape memory member 12, 14 may be fixed to the corresponding engagement member 32a, 32b (e.g., at a mid-point along the corresponding length thereof).
As illustrated in
In
In
Referring again to
Returning to the embodiment of
Magnets may be used under various circumstances to control the motion of the load 20. For example, as shown in
In another example of magnetic assist shown in
The above-described magnets may be permanent magnets and/or electromagnets. Where the magnets are electromagnets, they may be actively controlled to assist in providing a desired motion profile. Any other embodiment described herein may use magnets as described above to assist in the control of the motion of the loads. In embodiments utilizing magnets, the various parts that interface with the magnets may be shaped to provide particular performance characteristics. For example, the engagement members 32a, 32b of
In an alternative arrangement of the components of the embodiment of
In an additional alternative arrangement of the components of the embodiment of
The first and second shape memory members 112, 114 may each comprise a length of shape memory wire or any other appropriate shape memory form (e.g., a shape memory ribbon, a multiple element member such as a multiple filament wire, a coil, a helically wound strand) and may be heated in at least partially offset, timed-relation to yield corresponding martensitic-to-austenitic phase transformations and corresponding reductions (e.g., shrinkage) in the length of each wire. In turn, such alternating length reductions causes shaft member 130 to pivot, or rotate back and forth, thereby causing load 120 to pivot back and forth about pivot axis AA in an oscillating manner.
As shown in
As further illustrated in
It will be appreciated that, as shown in
The first and second shape memory members 112, 114 of
Reference is now made to
In
FIGS. 5AA, 5BB and 5CC illustrate a modified arrangement of the embodiment shown in
As illustrated, load 220 may be supportably mounted to the shaft member 230 for pivoting movement therewith. The first and second shape memory members 212, 214 may each comprise a length of shape memory wire and may be heated in at least partially offset timed-relation to yield corresponding martensitic-to-austenitic phase transformations and corresponding reductions (e.g., shrinkage) in the length of each wire. In turn, such alternating length reductions cause shaft member 230 to rotate back and forth, thereby causing load 220 to pivot back and forth about pivot axis AA in an oscillating manner. As shown, first shape memory member 212 may be fixedly interconnected at a first end to an anchor 252a interconnected to enclosure 240 via an elastically deformable member 253a, and first shape memory member 212 may be fixedly interconnected at a second end to an anchor 252b fixedly interconnected to a bottom surface of load 220. Similarly, second shape memory member 214 may be fixedly interconnected at a first end to an anchor 254a interconnected to the enclosure 240 via an elastically deformable member 255a and second shape memory member 214 may be fixedly interconnected at a second end to an anchor 254b fixedly interconnected to the bottom surface of load 240. Alternatively, anchor 252b may be fixedly interconnected to an elastically deformable member (not shown) that in turn is interconnected to the load 220, and anchor 254b may be fixedly interconnected to another elastically deformable member (not shown) that in turn is interconnected to the load 220. In such an alternate embodiment, the elastically deformable members 253a, 253b are optional.
Anchors 252a and 254a may be located at opposing ends of the enclosure 240 and on opposite sides of a plane that includes the pivot axis AA and is perpendicular to the plane of the load 220 when the load is in a “home” position, e.g., prior to actuation with shape memory members 212, 214. Further, anchors 252b and 254b may be disposed at offset locations relative to the plane when the load is in a “home” position. In an embodiment, anchor 252a and anchor 252b may be disposed on opposite side of the plane when the load is in a “home” position, and anchor 254a and anchor 254b may be disposed on opposite sides of the plane when the load is in a “home” position. In this regard, when the load is in the “home” position each of the shape memory members 212, 214 may cross the plane as they extend from their respective anchors 252a, 254a on the enclosure 240 to their respective anchors 252b, 254b on the load 220.
In
Where the active block 320c is an ultrasound transducer array, the ultrasound transducer array may be operable to transmit acoustic signals that may be used to generate an image of a two-dimensional plane extending from a length dimension of the ultrasound transducer array. By affecting oscillating motion of the ultrasound transducer array using the shape memory members 312, 314, the two-dimensional imaging plane of the ultrasound transducer array may be swept through a three-dimensional volume thus enabling creation of three dimensional images. Such three dimensional images may be real-time (4D).
The first and second shape memory members 312, 314 may be configured similarly to the first and second shape memory members 12, 14 of
The first shape memory member 312 may be fixedly interconnected at a first end to an anchor 352a. The anchor 352a may be interconnected to an elastically deformable member 353a, which in turn is interconnected to first end piece 342a. First shape memory member 312 may be fixedly interconnected at a second end to an anchor 352b. Likewise, the anchor 352b may be interconnected to an elastically deformable member 353b, which in turn is interconnected to second end piece 342b. Thus, first shape memory member 312 may be configured similarly to first shape memory member 12 of
The first shape memory member 312 may be operatively interconnected to load 320 via a cross shaft 332. The cross shaft 332 may in turn be fixedly interconnected to a cross shaft bracket 333 that may be fixedly interconnected to the load 320. The cross shaft 332 may be disposed in an orientation and position similar to that of the engagement members 32a, 32b of
The first and second shape memory members 312, 314 may be disposed along the cross shaft 330 in a manner similar to how first and second shape memory members 12, 14 of
An electrical interconnection member 360 may be electrically interconnected to the active block 320c. For example, the electrical interconnection member 360 may be a multiple conductor member that provides electrical interconnections to the active block 320c. The electrical interconnection member 360 may be routed through second end piece 342b, between the cross shaft 332 and the active block 320c, to the end of the active block 320c proximate to the first end piece 342a. In this regard, the portion of the electrical interconnection member 360 disposed between the second end piece 342b and the cross shaft 332 may be operable to flex while maintaining an electrical connection to the active block 320c. By way of example, the electrical interconnection member 360 may comprise flexboard (a flexible/bendable electrical member or plurality of members). In an embodiment, the flexboard may be disposed in a service loop or clockspring arrangement. Such a clockspring arrangement may be disposed within the actuator 300. For example, the end member 362 may house the clockspring arrangement.
An end member 362 may be interconnected to the actuator 300 at an end opposite from the end cap 340d. The end member 362 may provide a structure that is capable of interfacing with external components, such as components of a catheter body, to enable the actuator 300 to be interconnected to other structures, such as a catheter body. The end member 362 may also serve to seal the actuator 300 such that an enclosed volume is defined by the end member 362, the end cap 340d and the outer shell 342c.
The actuator 300 may be interconnected to a distal end of a catheter body such that the actuator 300 is fixed relative to the distal end of the catheter body. In another arrangement, actuator 300 may be interconnected to a distal end of a catheter body such that the actuator is rotatably positionable relative to the distal end of the catheter body. For example, the actuator 300 may be interconnected to a drive member that extends along the length of the catheter body from a distal end to a proximal end thereof, wherein rotation of a proximal end of the drive member causes actuator 300 to rotate (e.g., rotate about an axis corresponding with a longitudinal or central axis of the catheter body at the distal end thereof).
Alternatively, and as illustrated in
Where the active block 320c is in the form of an ultrasonic transducer array, the ultrasonic transducer array may include an acoustic coupling medium attached to an active face of the ultrasonic transducer array. The acoustic coupling medium may comprise a hydrogel capable of absorbing liquid. By way of example, such acoustic coupling medium may be provided for acoustic coupling to the active face of the ultrasonic transducer array.
The enclosures 40 (
Alternatively, the actuators may not include an enclosed volume as described above, and the interior of the actuators may be open to the surrounding environment. For example, the enclosure 340 of the actuator 300 may include holes or open portions (not shown) that would allow fluid to pass between the interior of the actuator 300 and the surrounding environment. In this regard, fluid from the body of the patient in the region where the actuator 300 is to be disposed during imaging (e.g., blood where imaging the heart) may be allowed to flow into the interior of the actuator 300.
In another alternative, a portion of the actuators may be disposed within an enclosed volume, while at least portion of the load is open to the surrounding environment. For example, the load 320 of the actuator 300 may be sealably interconnected about a periphery of the load 320 to the enclosure 340 (e.g., by a flexible bellows), wherein a sealed lower portion and an upper portion may be defined. The lower portion may include a fluid and shape memory members 212, 214. The upper portion of the enclosure 340 may include holes, wherein a face of the active block 320c (e.g., an ultrasound transducer array) may be exposed to the surrounding environment (e.g., blood in heart imaging applications).
The shape memory members described herein may include one or more layers of material wrapped about a core that includes a shape memory wire. Such layers may act as thermal insulation layers, electrical insulation layers, or a combination of thermal and electrical insulation layers. For example, shape memory members 312, 314 may include an inner core comprising a shape memory wire and thermal insulation layer of PTFE. Other exemplary materials that may be used to insulate include ePTFE, and high strength toughened fluoropolymer (HSTF). Some thermal insulation layers may be microporous. Microporous thermal insulation layers entrap air that desirably contributes to an increase in thermal resistance. However, some microporous thermal insulation materials may wet out with blood and other body fluids, which may generally reduce their thermal resistance. Hydrophobic materials may be used in the microporous thermal insulation layers to reduce and/or prevent such wetting. Hydrophobic materials such as fluoropolymers may serve this purpose. Alternatively, non-hydrophobic materials may be treated with a hydrophobic and/or oleophobic treatment to render them suitable for this purpose. Preferred thermal insulation materials may have a surface energy less than 50 dyn/cm2. Others may have a surface energy less than 40 dyn/cm2. Still others may have a surface energy less than about 30 dyn/cm2.
The thermal insulation layer may serve to insulate the shape memory wire such that the rate of dissipation of heat from the shape memory wire may be advantageously selected. For example, by selecting a predetermined thickness of thermal insulation layer to achieve a predetermined level of insulation, the heat flow from the shape memory wire to the surrounding environment (e.g., fluid) while the shape memory wire is being heated may be advantageously controlled to achieve a desired response time and/or level of heat transfer. That is, by adding insulation to the shape memory wire, the amount of heat lost to the surrounding environment during the heating of the shape memory wire may be reduced (relative to a configuration without insulation) thus reducing the time and/or power needed to heat the shape memory wire to produce a desired length change. Moreover, by reducing the power needed to produce the desired length change, the overall heat transfer to the surrounding environment may be reduced (again, relative to a configuration without insulation). In applications such as catheters, such reduction of power and associated reduction of heat transferred to the surrounding environment (e.g., the body of a patient) may enable the catheter to remain within an acceptable temperature range (e.g., below a certain regulated threshold that may be mandated by, for example, the U.S. Food and Drug Administration and/or International Electrotechnical Commission international standard IEC60601) during operation of the actuator 300. In an exemplary embodiment, the thermal insulation layer may have a thermal conductance of between about 0.03 W/mK and 0.20 W/mK when measured at about 25° C. In another exemplary embodiment, the thermal insulation layer may have a thermal conductance of between about 0.05 W/mK and 0.08 W/mK when measured at about 25° C.
The thermal and/or electrical insulation layers discussed above may provide acceptable withstand voltage and/or hydrophobicity, or the shape memory members described herein may include an additional layer of material disposed outside of the thermal insulation layer to provide the desired characteristics. The additional layer may, for example, add to the withstand voltage of the shape memory members such that they have an overall dielectric withstand voltage of at least about 500 kV/m. The additional layers may, for example, comprise a hydrophobic material. Such additional layers of hydrophobic material may have a surface energy of less than about 50 dyn/cm2. Others may have a surface energy less than 40 dyn/cm2. Still others may have a surface energy less than about 30 dyn/cm2. The hydrophobic material may, for example, include ePTFE.
Hydrophobic materials may be beneficial as the additional layer in that they may act as a barrier layer to allow underlying layers to remain relatively free of liquid and thus maintain their insulative properties. Where the hydrophobic materials are used as the only layer, their use may be beneficial in that they do not absorb liquid to a degree that their thermal conductivity is significantly altered. Other materials that provide the same benefits (e.g., capable as acting as a barrier and/or capable of retaining insulative properties while immersed in liquid) as such hydrophobic materials may be utilized. The thermal and/or electrical insulation layers may also provide a lubricious and/or low friction interface to facilitate smooth motion over and/or around other components in the actuator during motion.
With respect to the above-described layers disposed about the shape memory members, a first step in determining the configuration of the layers may be to select a desired time constant for the system and then select the specific materials to achieve that time constant. For example, a time constant may be selected such that the cooling of the shape memory members is as slow as possible while still meeting desired load pivoting rates. Thus power dissipation could be minimized. Similarly, a particular power dissipation may be selected to allow for a particular application, then a corresponding time constant may be selected to provide for a maximum load pivoting rate for a particular application based on allowed power dissipation.
The use of shape memory members to produce oscillating motion of a load as illustrated in
The actuators described herein may further include an encoder and/or position detector (e.g., to detect a load at an end of travel and/or at the “home” position) capable of providing feedback as to the position of the load being actuated. Such encoders and/or position detectors may allow servo control systems to control the position of the load being actuated.
The actuators described herein may be capable of producing oscillating movement of the loads up to and exceeding 50 Hz. For example, the actuators may be employed to produce oscillating movement of the loads in the 1-50 Hz or 8-30 Hz ranges. Such movement may be steady state to, for example, move the load, in the form of an ultrasound transducer, to facilitate 4D images. The actuators described herein may also be employed to move the loads relatively quickly (e.g., at the 50 Hz rate) to facilitate the capture of a 3D image during a single pivoting of the ultrasound transducer in a single direction. An image captured during such a single pivoting may provide a sharper “snapshot” of a volume of interest than would an image captured during relatively slower load movement. Such “snapshots” may be beneficial in imaging moving subjects, such as portions of a heart.
To reposition the actuator 300 from the position of
The tether 408 may be a discrete device whose primary function is to control the angular repositioning of the actuator 300. In another embodiment, the tether 408 may be a flexboard or other multiple conductor component that, in addition to providing the tethering function, electrically interconnects components within the actuator 300 with components within the catheter body 402 or elsewhere. In another embodiment, the tether 408 may be a wire or wires used to electrically interconnect one or more components (e.g., shape memory members 312, 314) within the actuator 300 to componentry external to the actuator 300.
An application of the actuator 300 of
The ultrasound imaging system 500 may further include a controller 505 and an ultrasound console 506. The controller 505 may be operable to control the actuation of the shape memory members 312, 314 and thus the angular position of the ultrasound transducer array (i.e., active block 320c). The ultrasound console 506 may include an image processor, operable to process signals from the ultrasound transducer array, and a display device, such as a monitor. The various functions described with reference to the controller 505 and ultrasound console 506 may be performed by a single component or by any appropriate number of discrete components.
The handle 501 may be disposed at a proximal end 511 of the catheter 400. The user (e.g., clinician, technician, interventionalist) of the catheter 400 may control the steering of the catheter body 402, the angular repositioning of the actuator 300, and various other functions of the catheter 400. In this regard, the handle 501 includes two sliders 507a, 507b for steering the catheter body 402. These sliders 507a, 507b may be interconnected to control wires such that when the sliders 507a, 507b are moved relative to each other, a portion of the catheter body 402 may be curved in a controlled manner. Any other appropriate method of controlling control wires within the catheter body 402 may be utilized. For example, the sliders could be replaced with alternative means of control such as turnable knobs or buttons. Any appropriate number of control wires within the catheter body 402 may be utilized.
The handle 501 may further include an angular position controller 508. The angular position controller 508 may be used to control the angular position of the actuator 300 relative to a distal end 512 of the catheter body 402. The illustrated angular position controller 508 is in the form of a rotatable wheel, where a rotation of the angular position controller 508 will produce a corresponding angular position of the actuator 300. Other configurations of the angular position controller 508 are contemplated, including, for example, a slider similar to slider 507a.
The handle 501 may further include an actuator activation button 509. The actuator activation button 509 may be used to activate and/or deactivate the oscillating motion of the ultrasound transducer array within the actuator 300. The handle 501 may further include a port 510 in embodiments of the ultrasound imaging system 500 that include a lumen within the catheter body 402. The port 510 is in communication with the lumen such that the lumen may be used for conveyance of a device and/or material.
In use, the user may hold the handle 501 and manipulate one or both sliders 507a, 507b to steer the catheter body 402 as the catheter 400 is moved to a desired anatomical position. The handle 501 and sliders 507a, 507b may be configured such that the position of the sliders 507a, 507b relative to the handle 501 may be maintained, thereby maintaining or “locking” the selected position of the catheter body 402. The angular position controller 508 may then be used to angularly reposition the actuator 300 to a desired position. The handle 501 and angular position controller 508 may be configured such that the position of the angular position controller 508 relative to the handle 501 may be maintained, thereby maintaining or “locking” the selected angular position of the actuator 300. In this regard, the actuator 300 may be selectively angularly repositionable, and the catheter body 402 may be selectively steered, independently. Also, the angular position of the actuator 300 may be selectively locked, and the shape of the catheter body 402 may be selectively locked, independently. Such maintenance of position may at least partially be achieved by, for example, friction, detents, and/or any other appropriate means. The controls for the steering, angular repositioning, and motor may all be independently operated and controlled by the user.
The ultrasound imaging system 500 may be used to capture images of a three dimensional imaging volume 514 and/or capture 3D images in real-time (4D). The actuator 300 may be positioned by steering the catheter body 402, angularly repositioning the actuator 300, or by a combination of steering the catheter body 402 and angularly repositioning the actuator 300. Moreover, in embodiments with a lumen, the ultrasound imaging system 500 may further be used, for example, to deliver devices and/or materials to a selected region or selected regions within a patient.
The catheter body 402 may have at least one electrically conductive wire that exits the catheter proximal end 511 through a port or other opening in the catheter body 402 and is electrically connected to a transducer driver and image processor (e.g., within the ultrasound console 506).
Furthermore, in embodiments with a lumen, the user may insert an interventional device (e.g., a diagnostic device and/or therapeutic device) or material, or retrieve a device and/or material through the port 510. The user may then feed the interventional device through the catheter body 402 to move the interventional device to the distal end 512 of the catheter body 402. Electrical interconnections between the ultrasound console 506 and the actuator 300 may be routed through an electronics port 513 and through the catheter body 402.
One difficulty associated with the use of conventional ICE catheters is the need to steer the catheter to multiple points within the heart in order to capture the various imaging planes needed during the procedure. Catheter 400, incorporating the angularly repositionable actuator 300 with its oscillatingly pivotable ultrasound transducer array 320c therein, alleviates such difficulties associated with the use of conventional ICE catheters.
With the actuator 300 positioned as illustrated in
Clinical procedures that may be performed with embodiments disclosed herein include without limitation septal puncture, septal occluder deployment, ablation, mitral valve intervention and left atrial appendage occlusion. A method for right atrial imaging utilizing embodiments may include advancing the catheter body 400 to the right atrium, steering the distal end 512 of the catheter body 400 to a desired position, operating the actuator 300 to effectuate movement of the ultrasound transducer array disposed therein, and while maintaining the fixed catheter body 400 position, angularly reposition the actuator 300 comprising the ultrasound transducer array about the hinge 370 to capture at least one image over at least one viewing plane.
In actuator 300, when one of the shape memory members 312, 314 (the hot member) has been actuated such that it is at its substantially minimum operational length, the other shape memory member 312, 314 (the cool member) will be relatively cool and may contain a certain amount of elastic tension (e.g., spring load) due to elastic stretching. This does not unduly stress the hot member since it is a relatively small elastic tension. When the electrical current used to heat the hot member is removed, the cool member may reverse the direction of the load 320 due to the stored elastic energy within the cool member. Thus, it may not be necessary to always be driving one of the shape memory members 312, 314. Such a driving scheme 722 is illustrated in the graph 720 of
In an embodiment, the cool member may be heated such that it reaches its austenitic start temperature at the same time that the hot member cools to its martensitic start temperature. This procedure helps to prevent or limit the members from working directly against each other, which could cause excessive elastic tension and increase the risk of failure or reduced life of, in particular, the shape memory members. In this regard, the insulation level may be selected to produce the desired cooling rate that enables such balancing. Where the balancing is precisely controlled, the elastically deformable members may not be necessary.
The shape memory members 312, 314 may be configured such that prior to the application of energy to either shape memory members 312, 314, when they are both in a cooled (e.g., room temperature) state, the shape memory members 312, 314 may each be in elastic tension. This may enable the shape memory members 312, 314 to remain in contact with the cross shaft 332 prior to the application of energy to one of the shape memory members 312, 314. Furthermore, during operation, the shape memory members 312, 314 may be controlled such that each shape memory members 312, 314 is substantially always in some degree of elastic tension.
The drive signals used to drive the shape memory members 312, 314 may be capable of operating at relatively low voltages, such as, for example, voltages less than 35 V dc. Such low operating voltages may be beneficial in that they are within acceptable limits for devices to be inserted in patients. The actuator 300 may be operable to be driven at a frequency of 1 cycle per second or greater while meeting regulatory and/or other requirements for voltage levels and temperature (e.g., remaining below a maximum temperature while disposed within a patient).
An actuator with first and second shape memory members capable of pivoting a load was constructed. The overall dimensions of the actuator were approximately 14 mm long with a diameter of 3 mm. The outer shell was made of stainless steel tubing and the end pieces were each made from alumina ceramic. The load was a piezoceramic 64 element ultrasound transducer array with a composite acoustic backing. The end pieces were center bored and defined the pivot axis for the load. The actuator was operated with a total angular range for the load of 44° (±22° from the home position) and had a maximum total angular range of 60°. The first and second shape memory members were in the form of 0.0015″ diameter Nitinol wire. The drive signal comprised a 10 Hz square wave of approximately 4.8 V dc. The actuator produced 10 Hz oscillating load movement producing a bidirectional scan rate for the ultrasound transducer array of 20 Hz. The 10 Hz oscillating load movement was limited by the hardware producing the 10 Hz square wave. In another exemplary dual shape memory member actuator, first and second shape memory members were in the form of 0.0015″ diameter Nitinol wire with parylene coating; immersed in water. The drive signal comprised a 6 Hz wave of approximately 4.5 V dc. The actuator produced 6 Hz oscillating load movement through an angular range of 50° (±25° from the home position) through 50,000 continuous, full sweeps. In another exemplary dual shape memory member actuator, a linearity of motion of a load of 10% was achieved using a triangular waveform and insulation on the first and second shape memory members. The insulation was 7 micron thick HSTF ePTFE polymer, and the actuator was run at 2.5 Hz at 1000× actual volume.
The foregoing description of the present invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described hereinabove are further intended to explain known modes of practicing the invention and to enable others skilled in the art to utilize the invention in such or other embodiments and with various modifications required by the particular application(s) or use(s) of the present invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.
This application claims priority under 35 U.S.C. §119 to U.S. Provisional Patent Application No. 61/405,784, filed Oct. 22, 2010, entitled “CATHETER WITH SHAPE MEMORY ALLOY ACTUATOR”, which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61405784 | Oct 2010 | US |
