Abstract:
Actuators employable for oscillating movement of a load. An improved actuator may include at least a first shape memory member that is actuatable to affect at least a portion of the oscillating movement of the load. The actuator may further include a second shape memory member 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 manner. Such actuators may be used in imaging catheters having an ultrasound transducer disposed for oscillating movement to scan across an internal region of interest. Such imaging catheters may be used in generating three dimensional and/or real-time three dimensional (4D) images.

Description:
RELATED APPLICATIONS 
       [0001]    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. 
     
    
     FIELD OF THE INVENTION 
       [0002]    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. 
       BACKGROUND OF THE INVENTION 
       [0003]    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. 
         [0004]    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. 
         [0005]    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. 
         [0006]    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). 
         [0007]    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. 
         [0008]    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. 
         [0009]    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. 
         [0010]    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. 
         [0011]    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. 
       SUMMARY OF THE INVENTION 
       [0012]    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. 
         [0013]    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. 
         [0014]    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. 
         [0015]    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. 
         [0016]    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. 
         [0017]    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/cm 2 . 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. 
         [0018]    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/cm 2 . 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. 
         [0019]    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. 
         [0020]    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. 
         [0021]    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. 
         [0022]    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. 
         [0023]    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. 
         [0024]    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. 
         [0025]    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. 
         [0026]    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). 
         [0027]    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. 
         [0028]    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. 
         [0029]    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. 
         [0030]    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. 
         [0031]    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. 
         [0032]    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. 
         [0033]    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. 
         [0034]    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. 
         [0035]    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. 
         [0036]    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. 
         [0037]    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. 
         [0038]    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. 
         [0039]    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. 
         [0040]    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. 
         [0041]    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. 
         [0042]    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. 
         [0043]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]      FIG. 1  is a side view of one embodiment of an actuator comprising the present invention. 
           [0045]      FIG. 2A  is a perspective view of selected components of the actuator embodiment of  FIG. 1 . 
           [0046]      FIG. 2B  is a perspective view of selected components of the actuator embodiment of  FIG. 1  along with alternative actuator components. 
           [0047]      FIGS. 3A and 3B  are end views of selected componentry of the actuator embodiment of  FIG. 1  shown at different times of operation. 
           [0048]      FIG. 3C  is an end view of selected componentry of the actuator embodiment of  FIG. 1  with a first example of magnetic assist. 
           [0049]      FIG. 3D  is an end view of selected componentry of the actuator embodiment of  FIG. 1  with a second example of magnetic assist. 
           [0050]      FIG. 4A  is a side view of another embodiment of an actuator comprising the present invention. 
           [0051]      FIG. 4B  is a side view of an additional embodiment of an actuator comprising the present invention. 
           [0052]      FIG. 4C  is a side view of a further embodiment of an actuator comprising the present invention. 
           [0053]      FIGS. 5A ,  5 B and  5 C are end views of selected componentry of the actuator embodiment of  FIG. 4A  shown at different times of operation. 
           [0054]    FIGS.  5 AA,  5 BB and  5 CC are end views of selected componentry of a modified arrangement of the actuator embodiment off  FIG. 4A  shown at different times of operation. 
           [0055]      FIG. 6  is a side view of another embodiment of an actuator comprising the present invention. 
           [0056]      FIG. 7  is a side view of another embodiment of an actuator comprising the present invention. 
           [0057]      FIGS. 8 and 9  illustrate a distal end of a catheter body connected by a hinge to the actuator embodiment of  FIG. 7 . 
           [0058]      FIG. 10  illustrates an ultrasound imaging system with a handle, a catheter, and the actuator embodiment of  FIG. 7 . 
           [0059]      FIGS. 11 and 12  show placement of a steerable catheter embodiment that includes the actuator embodiment of  FIG. 7  for intracardiac echocardiography within the right atrium of the heart. 
           [0060]      FIG. 13  shows placement of the embodiment of  FIG. 11  in the right atrium of the heart with the actuator embodiment of  FIG. 7  in a second position. 
           [0061]      FIG. 14  shows placement of the embodiment of  FIG. 11  in the right atrium of the heart with the actuator embodiment of  FIG. 7  in a third position. 
           [0062]      FIG. 15A  is a graph of a drive signal used to drive shape memory members and of the corresponding position of a load being driven. 
           [0063]      FIG. 15B  is a graph of another drive signal used to drive shape memory members and of the corresponding position of a load being driven. 
       
    
    
     DETAILED DESCRIPTION 
       [0064]      FIG. 1  illustrates one embodiment of an actuator  10  comprising a first shape memory member  12  and a second shape memory member  14  that are actuatable to effect oscillating, pivotal movement of a load  20  about a pivot axis AA. In this regard, pivot axis AA may be defined by a shaft member  30  which is journaled at each end and rotatable relative to an enclosure  40 . The enclosure  40  includes a first end piece  42   a , a second end piece  42   b , and an outer shell  42   c  (shown as transparent in  FIG. 1 ). In turn, load  20  may be supportably mounted to the shaft member  30  for pivoting movement therewith. 
         [0065]    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). 
         [0066]    Reference is now made to  FIG. 1 , together with  FIGS. 2A ,  3 A and  3 B which illustrate the operative interface between the first shape memory member  12 , the second shape memory member  14  and shaft member  30 . For explanatory purposes, the load  20 , first and second end pieces  42   a ,  42   b , and the outer shell  42   c  are not shown in  FIGS. 2A through 3D . In the illustrated embodiment, first shape memory member  12  may be fixedly interconnected at a first end  12   a  to an anchor  52   a . The anchor  52   a  may be interconnected to an elastically deformable member (e.g., a spring-like member such as a resilient, compressible member)  53   a , which in turn is interconnected to first end piece  42   a . In this regard, via compression of the elastically deformable member  53   a , anchor  52   a  is able to move a limited amount relative to the first end piece  42   a . First shape memory member  12  may be fixedly interconnected at a second end  12   b  to an anchor  52   b  (partly visible in  FIG. 2A ). Likewise, the anchor  52   b  may be interconnected to an elastically deformable member  53   b , which in turn is interconnected to second end piece  42   b . Similarly, second shape memory member  14  may be fixedly interconnected at a first end  14   a  to an anchor  54   a . The anchor  54   a  may be interconnected to an elastically deformable member  55   a , which in turn is interconnected to first end piece  42   a . Second shape memory member  14  may be fixedly interconnected at a second end  14   b  to an anchor  54   b  (partly visible in  FIG. 2A ). The anchor  54   b  may be interconnected to an elastically deformable member  55   b , which in turn is interconnected to second end piece  42   b.    
         [0067]    The elastically deformable members  53   a ,  53   b ,  55   a ,  55   b  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  53   a ,  53   b ,  55   a ,  55   b  may help to prevent excessive elastic tension in the shape memory members  12 ,  14 . Additionally, the elastically deformable members  53   a ,  53   b ,  55   a ,  55   b  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. 
         [0068]    The first shape memory member  12  may be operatively interconnected to shaft member  30  via engagement member  32   a  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  32   b  fixedly interconnected to and laterally extending away from shaft member  30  on another side of pivot axis AA. The engagement members  32   a ,  32   b  may be grooved to help positively locate the shape memory members  12 ,  14  relative thereto. In embodiments where the distances between engagement member  32   a  and anchor  52   a , and between engagement member  32   a  and anchor  52   b  are unequal, and/or where the distances between engagement member  32   b  and anchor  54   a , and between engagement member  32   b  and anchor  54   b  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  32   a ,  32   b  (e.g., at a mid-point along the corresponding length thereof). 
         [0069]    As illustrated in  FIG. 3A , first shape memory member  12  may operatively interconnect via engagement member  32   a  to shaft member  30  at a location offset from pivot axis AA so as to define a first moment arm I 1 . Similarly, second shape memory member  14  may operatively interconnect via engagement member  32   b  to shaft member  30  at a location offset from pivot access AA so as to define a second moment arm I 2 . In the illustrated arrangement, moment arms I 1  and I 2  are substantially equal. Arrangements may be implemented in which moment arms I 1  and I 2  are not equal. 
         [0070]    In  FIGS. 2A and 3A , the first shape memory member  12  has been actuated, e.g., heated, so as to cause the first shape memory member  12  to shrink in length and thereby rotate shaft member  30  in a first direction (e.g., clockwise) by y 1  degrees. As noted, first shape memory member  12  may be actuated during a first time period that is at least partially non-overlapping with a second time period during which second shape memory member  14  is actuated. In this regard, actuation of first shape memory member  12  may function to apply a tensile force to second shape memory member  14  so as to facilitate a return of shape memory member  14  to an extended state (e.g., in conjunction with its austenitic-to-martensitic phase transformation after actuation). 
         [0071]    In  FIG. 3B , the second shape memory member  14  has been actuated (e.g., heated) so as to cause the second shape memory member  14  to shrink in length and thereby rotate shaft member  30  in a second direction (e.g., counterclockwise) by y 2  degrees. In arrangements in which second shape memory member  14  is actuated in at least partially offset timed relation to actuation of the first memory shape member  12 , the actuation of the second shape memory member  14  may function to apply a tensile force to the first shape memory member  12  so as to facilitate a return of first shape memory member  12  to an extended state (e.g., in conjunction with its austenitic-to-martensitic phase transformation after actuation). 
         [0072]    Referring again to  FIGS. 1 and 2A , portions of first shape memory member  12  extend away from engagement member  32   a  and load  20  to define an included angle of x 1  degrees therebetween. Similarly, portions of second shape memory member  14  extend away from engagement member  32   b  and load  20  to define an included angle of x 2  degrees therebetween. As may be appreciated, included angle x 1  increases and included angle x 2  decreases during actuation of first shape memory member  12 , and included angle x 2  increases and included angle x 1  decreases during actuation of second shape memory member  14 . The angular configurations of first shape memory member  12  and second shape memory member  14  illustrated in  FIG. 1  facilitate pivoting movement of load  20  across a relatively large angular range of y 1 +y 2  degrees (see  FIGS. 3A and 3B ). In this regard, where the shape memory members  12 ,  14  are varied in length of about 1% to 5% (e.g., 4%) and where the angles x 1  and x 2 , in a neutral or “home” position (e.g., with the load  20  in a horizontal position), are about 100 to 170 degrees, the total angular range of y 1 +y 2  degrees may be on the order of about 50-60 degrees. The same total angular range may be achieved in another embodiment by, for example, making the angles x 1  and x 2  in the home position larger and correspondingly decreasing the variation in length of the shape memory members  12 ,  14 . Such a variation may result in higher stress on the shape memory members  12 ,  14 . In another variation, making the angles x 1  and x 2  in the home position smaller and correspondingly increasing the variation in length of the shape memory members  12 ,  14 , may increase the linearity between the change in length of the shape memory members  12 ,  14  and the change in angle of the load  20 . The location of the fixed ends of the shape memory members  12 ,  14  on the first and second end pieces  42   a ,  42   b  relative to the where the shape memory members  12 ,  14  interface with the engagement members  32   a ,  32   b  may be adjusted to, for example, provide a maximum force imparted on the engagement member  32   a ,  32   b  by the shape memory members  12 ,  14  at a selected point in the motion cycle of the load  20 . The location of the fixed ends of the shape memory members  12 ,  14  may also be selected such that a particular overall volume of space taken up by the actuator  10  may be achieved. Thus, for a particular application, the actuator  10  may be configured to achieve a certain size, while in another configuration, the actuator may be configured to achieve a certain linearity, while in another configuration, a particular angular range of y 1 +y 2  degrees may be achieved. In one example, the actuator may be configured such that it occupies a volume of space defined by an imaginary cylinder created by rotating the load  20  through 360 degrees about the pivot axis AA. In such an example, the overall diameter of the actuator  10  may be determined by the load  20  size as opposed to the size of the mechanisms used to drive the load  20 . In this regard, load  20  size (e.g., length, width, thickness) may be a factor in the configuration of the shape memory members  12 ,  14 . 
         [0073]    Returning to the embodiment of  FIGS. 1 ,  2 A,  3 A and  3 B, actuation of the first shape memory member  12  may be realized via the provision of energy signals to anchors  52   a  and  52   b , which may be electrically interconnected to shape memory member  12 . In this regard, anchors  52   a  and  52   b  may serve as connector blocks facilitating electrical interconnection to shape memory member  12 . Similarly, actuation of the second shape memory member  14  may be realized via the provision of energy signals to anchors  54   a  and  54   b , which may be electrically interconnected to shape memory member  14 . For example, anchors  52   a ,  52   b , and  54   a ,  54   b  may be interconnected via electrical signal lines to an electrical energy source comprising logic to provide electrical signals to anchors  52   a ,  52   b  and  54   a ,  54   b  (and therefore to shape memory members  12 ,  14 ) in offset, timed-relation, wherein such electrical signals may vary in magnitude according to a predetermined algorithm. Such predetermined algorithm may be established to realize a relatively constant angular velocity of load  20  as it pivots, or rotates, about pivot axis AA in a oscillating manner. Alternatively, a predetermined algorithm may be established to realize other desired motion profiles for the load  20 . Indeed, by altering the algorithms used to drive shape memory members, the motion profile of any of the embodiments discussed herein may be adjusted as desired. 
         [0074]    Magnets may be used under various circumstances to control the motion of the load  20 . For example, as shown in  FIG. 3C , a magnet  62  may be positioned at or near the end of travel of the engagement member  32   a . In such a configuration, the engagement members  32   a ,  32   b  may be made from a magnetizable (e.g., ferrous) material. Alternatively, the engagement members  32   a ,  32   b  may be made from a non-magnetizable material and one or more magnetizable members may be fixedly interconnected to the engagement members  32   a ,  32   b  to enable the magnet  62  and a second magnet  60  to impart a magnetic force on the engagement members  32   a ,  32   b . The magnet  62  may impart an attractive force on the engagement member  32   a , thus reducing the elastic tension necessary in the first shape memory member  12  to achieve the end of travel position shown in  FIG. 3C . Such an arrangement may also reduce the level of heating of the shape memory member  12  necessary to achieve the end of travel position. The second magnet  60  may be correspondingly positioned to have a similar effect on the load  20  at the other end of travel position. In a variation of the embodiment illustrated in  FIG. 3C , the magnet  62  may be positioned such that it comes in direct contact with the engagement member  32   a  at the end of travel position. Such a configuration may serve to positively determine the position of the load  20  (i.e., by driving the engagement member  32   a  into contact with the magnet  62 , the position of the load  20  will be known). Moreover, such a configuration may be used to provide a force capable of holding or assisting in holding the position of the load  20  at the end of travel for a predetermined length of time. In another variation, a non-ferrous spacer (not shown) may be fitted to the magnet  62  (or alternatively to the engagement member  32   a ) such that the spacer serves as a hard stop to the motion of the engagement member  32   a  (thus providing a positive determination of the position of the load  20 ), but does not allow magnet  62  to come into direct contact with the engagement member  32   a.    
         [0075]    In another example of magnetic assist shown in  FIG. 3D , a pair of like-pole magnets  66 ,  70  may be positioned such that they impart a repulsive force on each other as the load  20  approaches the end of travel position shown in  FIG. 3D . Such a configuration may assist in decelerating the load  20  and may be particularly applicable to relatively high speed and/or high load mass applications that may benefit from assisted deceleration. A similarly configured pair of like-pole magnets  64 ,  68  positioned to have a similar effect on the load  20  at the other end of travel position may be used. 
         [0076]    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  32   a ,  32   b  of  FIG. 3C  may have a square cross section (as opposed to the circular cross section shown in  FIG. 1 ) such that a flat surface is presented to the magnets  60 ,  62 . 
         [0077]    In an alternative arrangement of the components of the embodiment of  FIG. 1 , the ends of the shape memory members  12 ,  14  may be fixedly interconnected to the load  20  in a manner similar to how the ends of the shape memory members  12 ,  14  are fixedly attached to the first and second end pieces  42   a ,  42   b  in  FIG. 1 . In such an embodiment, the engagement members or equivalent structure may be fixedly (relative to the outer shell  42   c ) disposed below (i.e., below when in the orientation shown in  FIG. 1 ) the load  20  such that the shape memory members  12 ,  14  may each have a first end fixedly interconnected to the load  20  at one end of the load  20 , a second end fixedly interconnected to the load  20  at the other end of the load  20 , and a central portion positioned partially about the fixedly disposed engagement members or equivalent structure. 
         [0078]    In an additional alternative arrangement of the components of the embodiment of  FIG. 1 , the actuator  10  may include additional shape memory members to provide redundancy in the case of a failure of one or both of the shape memory members  12 ,  14 . For example, an additional shape memory member, similarly configured to shape memory member  12 , may be disposed such that it is operable to produce the same motion of the load  20  as shape memory member  12 . In this regard, the additional shape memory member may be disposed generally parallel to shape memory member  12 . In one embodiment, the additional shape memory member may be actuated in tandem with the shape memory member  12 . Another shape memory member may be disposed and/or actuated relative to shape memory member  14  in a similar manner. Consequently, in such an arrangement, if one or both of the shape memory members  12 ,  14  were to fail, the redundant shape memory members could be employed to produce the reciprocating motion of the load  20 . 
         [0079]      FIG. 2B  illustrates the shaft member  30  and engagement members  32   a ,  32   b  in the same orientation as  FIG. 2A . In the embodiment of  FIG. 2B , the shape memory members  12 ,  14  and corresponding elastically deformable members  53   a ,  53   b ,  55   a ,  55   b  and anchors  52   a ,  52   b ,  54   a ,  54   b  of  FIG. 2A  have been replaced with helically wound shape memory members  16 ,  18  and anchor members  22 ,  24 . The helically wound shape memory members  16 ,  18  may be operable to achieve a higher percentage of reduction in length (e.g., along a longitudinal axis of helically wound coils) as compared to the non-helically wound shape memory members  12 ,  14 . Thus, as illustrated in  FIG. 2B , the helically wound shape memory members  16 ,  18  may be disposed generally perpendicular to the ends of the engagement members  32   a ,  32   b  to affect oscillating, pivotal movement of the shaft member  30  similar to that created by shape memory members  12 ,  14 . Moreover, the helically wound shape memory members  16 ,  18  may be operable to produce such motion within a similar volume of space (e.g., within the enclosure  40  of  FIG. 1 ). The anchor members  22 ,  24  may include elastically deformable members. Moreover, additional helically wound shape memory members may be used to provide redundancy similar to as described above with reference to additional shape memory members  12 ,  14 . 
         [0080]      FIG. 4A  illustrates another embodiment of an actuator  100  comprising a first shape memory member  112  and a second shape memory member  114  that are actuatable to affect oscillating, pivotal movement of a load  120  about a pivot axis AA. Pivot axis AA may be defined by a shaft member  130  that is journaled at each end and rotatable relative to an enclosure  140 . The enclosure  140  includes a first end piece  142   a , a second end piece  142   b , and an outer shell  142   c  (shown as transparent in  FIG. 4A ). As illustrated, load  120  may be supportably mounted to the shaft member  130  for pivoting movement therewith. 
         [0081]    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. 
         [0082]    As shown in  FIG. 4A , first shape memory member  112  may be fixedly interconnected at a first end  112   a  to an anchor  152   a  interconnected to enclosure  140  via an elastically deformable member  156   a , and first shape memory member  112  may be fixedly interconnected at a second end  112   b  to an anchor  152   b  interconnected to enclosure  140  via an elastically deformable member  156   b . Each of anchors  152   a  and  152   b  may be disposed on a common side of a vertical plane that contains both pivot axis AA and an axis BB, which, when the load  120  is in a “home” position (as shown in  FIG. 4A ), lies along a engagement member  132  that extends downwardly away from shaft member  130  in fixed relation thereto (see  FIG. 5A ). The second shape memory member  114  may be interconnected at a first end  114   a  to an anchor  154   a  interconnected to the enclosure  140  via an elastically deformable member  158   a , and second shape memory member  114  may be fixedly interconnected at a second end  114   b  to an anchor  154   b  interconnected to the enclosure  140  via an elastically deformable member  158   b . Each of the anchors  154   a  and  154   b  may be disposed on a common side of the vertical plane, defined by axes A-A and B-B, opposite to the side on which anchors  152   a ,  152   b  are disposed. Alternatively, only a single elastically deformable member (e.g., elastically deformable members  156   a ,  158   a ) may be interconnected to each shape memory member  112 ,  114 , or no elastically deformable member may be employed. 
         [0083]    As further illustrated in  FIG. 4A , first shape memory member  112  and second shape memory member  114  are disposed to operatively interconnect with shaft member  130  via engagement with opposing sides of the engagement member  132 . More particularly, first shape memory member  112  engages a side of engagement member  132  that faces away from the side of the engagement member  132  on which anchors  152   a ,  152   b  are disposed. Conversely, second shape memory member  114  engages a side of engagement member  132  that opposes the side of the engagement member  132  engaged by first shape memory member  112  and that faces away from the side of the engagement member  132  on which anchors  154   a ,  154   b  are disposed. 
         [0084]    It will be appreciated that, as shown in  FIG. 4A , the first and second shape memory members  112 ,  114  are not configured such that they interface with the engagement member  132  at the same distance away from the load  120 . Thus, the first and second shape memory members  112 ,  114  may not symmetrically act upon the engagement member  132 . In a variation of the actuator  100  of  FIG. 4 , the first and second shape memory members  112 ,  114  may be configured such that they each interface with the engagement member  132  at a common distance from the load  120 . In such a configuration, symmetry may, for example, be achieved by symmetrically adjusting the positions of the anchors  152   a ,  152   b ,  154   a ,  154   b  such that the first and second shape memory members  112 ,  114  do not interfere with each other during pivoting of the load  120 . 
         [0085]      FIG. 4B  illustrates a modified embodiment of the actuator  100  shown in the  FIG. 4A  embodiment. In relation to the  FIG. 4A  embodiment it was noted that the first and second shape memory members  112 ,  114  may comprise lengths of shape memory wire.  FIG. 4A  illustrates physically-separate first and second shape memory members  112 ,  114 . In the  FIG. 4B  embodiment, the first and second shape memory members  112 ′,  114 ′ may be defined by separate segments, or lengths, of a continuous shape memory wire  113 . By way of example, the shape memory alloy wire  113  may be crimped at a first end  113   a  to a crimp anchor  153   a  and crimped at a second end  113   b  to a crimp anchor  153   b . Further, the shape memory alloy wire  113  may be crimped at crimp anchor  153   c  to define a wire segment corresponding with first shape memory member  112 ′ (i.e., between crimp anchor  153   a  and  153   c ), and crimped at crimp anchor  153   d  to define the second shape memory member  114 ′ (i.e., between crimp anchor  153   b  and  153   d ). In this arrangement, the shape memory alloy wire  113  may be electrically interconnected to a common electrical ground  155  (e.g., between crimp anchors  153   c  and  153   d ). As illustrated, the first end  113   a  of the shape memory alloy wire  113  may be electrically interconnected to a first electrical drive signal source V A , and the second end  113   b  may be electrically interconnected to a second electrical drive signal source V B . The first and second electrical drive signal sources V A , V B  may be alternately operated for actuation of first and second shape memory members  112 ′,  114 ′, respectively. 
         [0086]      FIG. 4C  illustrates a modified version of the embodiment of  FIG. 4B . As illustrated, a shape memory alloy wire  113  may be crimped at a single crimp anchor  153   c . In such arrangement, a first shape memory member  112 ″ and second shape memory member  114 ″ may define a V-shaped configuration between the first end piece  142   a  and engagement member  132 . The crimp anchor  153   c  may electrically interconnect to the common electrical ground  155 . 
         [0087]    The first and second shape memory members  112 ,  114  of  FIG. 4A , the first and second shape memory members  112 ′,  114 ′ of  FIG. 4B , and the first and second shape memory members  112 ″,  114 ″ of  FIG. 4C , may each be in the form of shape memory wire lengths. In one approach, such shape memory wire lengths may comprise physically-separate first and second wires (e.g., first and second shape memory members  112 ,  114 ). In another approach, such shape memory wire lengths may be defined by different segments of a continuous shape memory wire (e.g., first and second shape memory members  112 ′,  114 ′ and first and second shape memory members  112 ″,  114 ″). 
         [0088]    Reference is now made to  FIGS. 5A ,  5 B and  5 C which illustrate the operative interface between the first shape memory member  112  and shaft member  130  via engagement member  132 , and between the second shape memory member  114  and shaft member  130  via engagement member  132 . In  FIG. 5A , actuator  100  is shown in a “home” position, e.g., prior to actuation with shape memory members  112 ,  114  each in a martensitic state and with the load  120  disposed in a position that is substantially centered between the two extremes of the load&#39;s  120  range of oscillating movement. In  FIG. 5B , the first shape memory member  112  has been actuated, e.g., heated, so as to cause the first shape memory member  112  to shrink in length and thereby rotate engagement member  132 , shaft member  130  and load  120  in a first direction (e.g., clockwise) by z 1  degrees. As noted, first shape memory member  112  may be actuated during a first time period that is at least partially non-overlapping with a second time period during which second shape memory member  114  is actuated. In this regard, actuation of first shape memory member  112  may function to apply a tensile force to second shape memory member  114  so as to lengthen second shape memory member  114  (e.g., in conjunction with an austenitic-to-martensitic phase transformation after actuation). 
         [0089]    In  FIG. 5C , the second shape memory member  114  has been actuated (e.g., heated) so as to cause the second shape memory member  114  to shrink in length and thereby rotate engagement member  132 , shaft member  130  and load  120  in a second direction (e.g., counterclockwise) by z 2  degrees. In arrangements in which second shape memory member  114  is actuated in at least partially offset timed-relation to actuation of the first shape memory member  112 , the actuation of the second shape memory member  114  may function to apply a tensile force to the first shape memory member  112  so as to lengthen first shape memory member  112  (e.g., in conjunction with an austenitic-to-martensitic phase transformation after actuation). 
         [0090]    FIGS.  5 AA,  5 BB and  5 CC illustrate a modified arrangement of the embodiment shown in  FIG. 4A , in corresponding relation to the views of  FIGS. 5A ,  5 B and  5 C. As illustrated, engagement member  132  is provided with apertures  132   a ,  132   b  for receiving first and second shape memory members  112 ,  114  therethrough, respectively. 
         [0091]      FIG. 6  illustrates another embodiment of an actuator  200  comprising a first shape memory member  212  and a second shape memory member  214  that are actuatable to affect oscillating, pivotal movement of a load  220  about a pivot axis AA. Pivot axis AA may be defined by a shaft member  230  that is journaled at each end and rotatable relative to an enclosure  240 . The enclosure  240  includes a first end piece  240   a , a second end piece  240   b , and an outer shell  240   c  (all shown as transparent in  FIG. 6 ). 
         [0092]    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  252   a  interconnected to enclosure  240  via an elastically deformable member  253   a , and first shape memory member  212  may be fixedly interconnected at a second end to an anchor  252   b  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  254   a  interconnected to the enclosure  240  via an elastically deformable member  255   a  and second shape memory member  214  may be fixedly interconnected at a second end to an anchor  254   b  fixedly interconnected to the bottom surface of load  240 . Alternatively, anchor  252   b  may be fixedly interconnected to an elastically deformable member (not shown) that in turn is interconnected to the load  220 , and anchor  254   b  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  253   a ,  253   b  are optional. 
         [0093]    Anchors  252   a  and  254   a  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  252   b  and  254   b  may be disposed at offset locations relative to the plane when the load is in a “home” position. In an embodiment, anchor  252   a  and anchor  252   b  may be disposed on opposite side of the plane when the load is in a “home” position, and anchor  254   a  and anchor  254   b  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  252   a ,  254   a  on the enclosure  240  to their respective anchors  252   b ,  254   b  on the load  220 . 
         [0094]    In  FIG. 6 , first shape memory member  212  has been actuated so as to cause shaft member  230  to rotate and load  220  to pivot in a clockwise direction (as viewed from the right side of the actuator  200  as shown in  FIG. 6 ). As may be appreciated, upon actuation of the second shape memory member  214  and deactuation of first shape memory member  212  the shaft member  230  may be rotated and load  220  may be pivoted by the second shape memory member  214  in a counterclockwise direction. 
         [0095]      FIG. 7  illustrates an actuator  300 , similar to that shown in the embodiment of  FIG. 1 , configured for use in an imaging catheter application. More particularly,  FIG. 7  illustrates actuator  300  comprising a first shape memory member  312  and a second shape memory member  314  that are actuatable to effect oscillating, pivotal movement of a load  320  about a pivot axis AA. The pivot axis AA is shown in  FIG. 7  to coincide with a central longitudinal axis of the actuator  300 . Alternatively, in an embodiment, the pivot axis AA may be offset from the central longitudinal axis of the actuator  300 . The load  320  comprises three portions, a first end block  320   a , a second end block  320   b , and an active block  320   c  fixedly interconnected to and disposed between the end blocks  320   a ,  320   b . The active block  320   c  may be in the form of an ultrasound transducer array. Pivot axis AA may be defined by collinear shaft members  330   a ,  330   b  which are journaled and rotatable relative to an enclosure  340 . In turn, load  320  may be supportably mounted to the shaft members  330   a ,  330   b  for pivoting movement therewith. The enclosure  340  includes a first end piece  342   a , a second end piece  342   b , and an outer shell  342   c  (shown as transparent in  FIG. 7 ). The enclosure  340  further includes an end cap  340   d , which may be rounded to facilitate movement through a body. The first end piece  342   a  and the second end piece  342   b , and therefore the pivot axis AA may be fixed relative to the enclosure  340 . 
         [0096]    Where the active block  320   c  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). 
         [0097]    The first and second shape memory members  312 ,  314  may be configured similarly to the first and second shape memory members  12 ,  14  of  FIG. 1 . As will be appreciated, alternating length reductions of the first and second shape memory members  312 ,  314  causes the load  320  to pivot back and forth about pivot axis AA in an oscillating manner. 
         [0098]    The first shape memory member  312  may be fixedly interconnected at a first end to an anchor  352   a . The anchor  352   a  may be interconnected to an elastically deformable member  353   a , which in turn is interconnected to first end piece  342   a . First shape memory member  312  may be fixedly interconnected at a second end to an anchor  352   b . Likewise, the anchor  352   b  may be interconnected to an elastically deformable member  353   b , which in turn is interconnected to second end piece  342   b . Thus, first shape memory member  312  may be configured similarly to first shape memory member  12  of  FIG. 1 . In a similar fashion, second shape memory member  314  may be configured similarly to second shape memory member  14  of  FIG. 1 . 
         [0099]    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  32   a ,  32   b  of  FIG. 1 . 
         [0100]    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  FIG. 1  interface with engagement members  32   a ,  32   b . In this regard, oscillating movement of load  320  via actuation of the first and second shape memory members  312 ,  314  may be achieved in a manner similar to that as described with respect to  FIG. 1 . 
         [0101]    An electrical interconnection member  360  may be electrically interconnected to the active block  320   c . For example, the electrical interconnection member  360  may be a multiple conductor member that provides electrical interconnections to the active block  320   c . The electrical interconnection member  360  may be routed through second end piece  342   b , between the cross shaft  332  and the active block  320   c , to the end of the active block  320   c  proximate to the first end piece  342   a . In this regard, the portion of the electrical interconnection member  360  disposed between the second end piece  342   b  and the cross shaft  332  may be operable to flex while maintaining an electrical connection to the active block  320   c . 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. 
         [0102]    An end member  362  may be interconnected to the actuator  300  at an end opposite from the end cap  340   d . 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  340   d  and the outer shell  342   c.    
         [0103]    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). 
         [0104]    Alternatively, and as illustrated in  FIG. 7 , the actuator  300  may be interconnected to a hinge  370 . The hinge  370 , in turn, may be interconnected to a distal end of a catheter body such that a portion of the hinge  370  is fixed relative to the distal end of the catheter body. The hinge  370  may include a catheter interface portion  372  operable to interconnect to a catheter body, an actuator interface portion operable to interconnect to the actuator  300 , and a bendable portion  376  operable to allow relative angular movement between the actuator interface portion  374  and the bendable portion  376 , thus allowing relative angular movement between the actuator  300  and a distal end of a catheter body. In this regard, the actuator  300  may be selectively positionable across a range of angles relative to a catheter body (e.g., relative to a longitudinal or central axis of a catheter body at a distal end thereof). As noted, the end member  362  may also serve to seal the actuator  300  or alternatively and as shown in  FIG. 7 , the end member  362  and the actuator interface portion may serve together to seal the actuator  300 . The catheter interface portion  372  may include a central lumen  378  that may align with a lumen in a catheter. 
         [0105]    Where the active block  320   c  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. 
         [0106]    The enclosures  40  ( FIG. 1 ),  140  ( FIG. 4 ),  240  ( FIG. 6) and 340  ( FIG. 7 ) may define enclosed volumes. The enclosed volumes may contain a fluid therein. The fluid may be a liquid. In this regard, the loads and the first and second shape memory members may be immersed within the fluid within the enclosed volume. With respect to actuator  300  of  FIG. 7 , where the active block  320   c  is in the form of an ultrasonic transducer array, the fluid may serve to acoustically couple the ultrasound transducer array to the outer shell  342   c . In this regard, the material of the outer shell  342   c  may be selected to correspond to (e.g., closely match) the acoustic impedance and/or the acoustic velocity of the fluid of the body of the patient in the region where the actuator  300  is to be disposed during imaging. One or more ports and/or valves may be provided to facilitate the placement of fluid within the actuators. Where the fluid is a liquid, multiple ports and or valves may be used to further facilitate the removal of bubbles from the enclosed volumes. 
         [0107]    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 . 
         [0108]    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  320   c  (e.g., an ultrasound transducer array) may be exposed to the surrounding environment (e.g., blood in heart imaging applications). 
         [0109]    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/cm 2 . Others may have a surface energy less than 40 dyn/cm 2 . Still others may have a surface energy less than about 30 dyn/cm 2 . 
         [0110]    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. 
         [0111]    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/cm 2 . Others may have a surface energy less than 40 dyn/cm 2 . Still others may have a surface energy less than about 30 dyn/cm 2 . The hydrophobic material may, for example, include ePTFE. 
         [0112]    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. 
         [0113]    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. 
         [0114]    The use of shape memory members to produce oscillating motion of a load as illustrated in  FIGS. 1 through 7  may be beneficial in that such systems may be relatively small. For example, the actuator  300  may include an ultrasound transducer array (e.g., active block  320   c ) that may be pivoted in an oscillating manner to generate real-time 3D images (4D images) while having an outer diameter of 12 Fr or less (e.g., 10 Fr). The shape memory wire used in the shape memory members may be about 1 mil in diameter. In the embodiment of  FIG. 7 , the moment arms I 1  and I 2  may be about 1.0 mm. 
         [0115]    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. 
         [0116]    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. 
         [0117]      FIGS. 8 and 9  illustrate a distal end of a catheter assembly  400  that includes an elongate catheter body  402  that is connected by the hinge  370  to the actuator  300 .  FIG. 8  illustrates the actuator  300  that is a distal end portion of the catheter assembly  400  in a position where it is aligned with the distal end of the catheter body  402 .  FIG. 9  illustrates the actuator  300  in a position where it is deployed at about a +90 degree, forward-facing angle with respect to the end of the catheter body  402 . For explanatory purposes only, an angular value (e.g., the +90 degree angle of displacement shown in  FIG. 9 ) may be used herein to describe the amount of angulation of the actuator  300  with respect to a central axis of the catheter body  402  away from a position where the actuator  300  and catheter body  402  are aligned. A positive value will be used to describe an angulation where the actuator  300  is moved such that it is at least partially forward-facing (e.g., the active block  320   c  in the “home” position is facing forward), and a negative value will generally be used to describe an angulation where the actuator  300  is moved such that it is at least partially rearward-facing. 
         [0118]    To reposition the actuator  300  from the position of  FIG. 8  to the position of  FIG. 9 , an inner tube  404  of the catheter body  402  may be advanced relative to an outer tube  406  of the catheter body  402 . By virtue of the actuator  300  being tethered to the outer tube  406  by a tether  408 , the advancement may cause the actuator  300  to be angled in a positive direction. The tether  408  may be anchored to the actuator  300  on one end and to the outer tube  406  on the other end. The tether  408  may be operable to prevent the tether anchor points from moving a distance away from each other greater than the length of the tether  408 . In this regard, through the tether  408 , the actuator  300  may be restrainably interconnected to the outer tube  406 . Similarly, where the tether  408  has adequate stiffness, retraction of the inner tube  404  relative to the outer tube  406  from the position shown in  FIG. 8  may cause the actuator  300  to be angled in a negative direction. The inner tube  404  may include a lumen therethrough. 
         [0119]    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 . 
         [0120]      FIGS. 8 and 9  illustrate a configuration where the hinge  370  is a living hinge. A live or living hinge is a compliant hinge (flexure bearing) made from a flexible or compliant material, such as polymer. Generally, a living hinge joins two parts together, allowing them to pivot relative to each other along a bend line of the hinge. Living hinges are typically manufactured by injection molding. Polyethylenes, polypropylenes, polyurethanes, or polyether block amides such as PEBAX® are possible polymers for living hinges, due to their fatigue resistance. 
         [0121]    An application of the actuator  300  of  FIGS. 7 through 9 , where the active block  320   c  is in the form of an ultrasound transducer array, will now be described with reference to  FIGS. 10 through 14 . 
         [0122]      FIG. 10  illustrates an ultrasound imaging system  500  suitable for real-time three dimensional (4D) imaging with a handle  501  and catheter  400 . The catheter  400  includes the catheter body  402  interconnected to the actuator  300  via the hinge  370 . The catheter body  402  may be flexible and capable of bending to follow the contours of a body vessel into which it is being inserted or track over a guidewire or through a sheath. The catheter body  402  may be steerable. 
         [0123]    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  320   c ). 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. 
         [0124]    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  507   a ,  507   b  for steering the catheter body  402 . These sliders  507   a ,  507   b  may be interconnected to control wires such that when the sliders  507   a ,  507   b  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. 
         [0125]    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  507   a.    
         [0126]    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. 
         [0127]    In use, the user may hold the handle  501  and manipulate one or both sliders  507   a ,  507   b  to steer the catheter body  402  as the catheter  400  is moved to a desired anatomical position. The handle  501  and sliders  507   a ,  507   b  may be configured such that the position of the sliders  507   a ,  507   b  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. 
         [0128]    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. 
         [0129]    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 ). 
         [0130]    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 . 
         [0131]    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  320   c  therein, alleviates such difficulties associated with the use of conventional ICE catheters. 
         [0132]      FIG. 11  shows placement of the catheter  400  for intracardiac echocardiography within the right atrium  602  of the heart  604 .  FIG. 12  shows placement of the catheter  400  within the right atrium  602  of the heart  604  after the catheter  400  has been repositioned (through steering of the catheter  400 ) to place the actuator  300  disposed at a distal end of the catheter  400  at a desired position. The clinician may establish and then set the catheter  400  position within the heart  604  by locking the catheter  400  position (locking mechanism on handle not shown). In this regard, once set, the catheter  400  position may remain substantially unchanged while the actuator  300  is angularly repositioned. 
         [0133]    With the actuator  300  positioned as illustrated in  FIG. 12 , a volumetric image may be generated from a three dimensional volume  606  of a first portion of the heart  604 . The clinician may then manipulate the actuator  300  orientation in order to capture the range of imaging volumes required. For example,  FIG. 13  shows the actuator  300  angularly repositioned to a second position to capture a volumetric image of a three dimensional volume  608  of a second portion of the heart  604 .  FIG. 14  shows the actuator  300  angularly repositioned to a third position to capture a volumetric image of a three dimensional volume  610  of a third portion of the heart  604 . Embodiments of actuator  300  described herein may be operable to achieve such positions and more within the right atrium  602  of the heart  604  that may have an intracardiac volume with cross dimension of about 3 cm. Volumetric images of such three dimensional volumes  606 ,  608 , and  610  are obtainable by angularly repositioning the actuator  300  and operation of the actuator  300  to effectuate oscillating pivoting of the ultrasound transducer array while the distal end of the catheter  400  remains in the position as shown in  FIG. 12 . 
         [0134]    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. 
         [0135]      FIG. 15A  is a graph  700  of a drive signal  702  used to drive shape memory members, such as shape memory members  312 ,  314  of actuator  300 , to produce oscillating movement of a load such as load  320 . The horizontal axis represents time and, for the drive signal  702 , the vertical axis represents applied voltage. For example, a first drive signal portion  706  may drive shape memory member  312  and a second drive signal portion  708  may drive shape memory member  314 . The corresponding position  704  of the load  320  is shown in the top half of the graph  700 . For the position  704 , the vertical axis represents angular position of the load  320 . In the drive scheme illustrated by  FIG. 15A , each shape memory member  312 ,  314  is sequentially driven in a non-overlapping fashion, i.e., substantially only one of the shape memory members  312 ,  314  is driven at a particular point in time and one of the shape memory members  312 ,  314  is substantially always being driven. This produces the motion pattern shown in the graph of the position  704  of the load  320  where the load  320  is substantially always being actively driven to one or the other of the ends points of its oscillating motion. 
         [0136]    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  FIG. 15B . In  FIG. 15B , as in  FIG. 15A , the horizontal axis represents time and, for the drive signal  722 , the vertical axis represents applied voltage and for the position  724 , the vertical axis represents angular position of the load  320 . As shown, a time interval  730  between pulses  726 ,  728  may be incorporated. During the time interval, motion of the load  320  may be generated by the stored elastic energy to produce a motion profile  724  that is very similar to the profile  704  of  FIG. 15A . Such a use of “rebound” (e.g., the expenditure of the stored elastic energy) may reduce overall power consumption of the actuator  300  as compared to the drive signal  702  of  FIG. 15A . The elastically deformable members may also contribute to the rebound. 
         [0137]    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. 
         [0138]    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. 
         [0139]    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). 
       Examples 
       [0140]    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. 
         [0141]    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.