Abstract:
A compact and efficient drive shaft for an in vivo imaging system and a method of making the same is provided by the present disclosure. In one aspect, the drive shaft includes a plurality of conductors secured to the exterior of a flexible elongate core. The conductors connect an imaging element at the distal end to a connection assembly near the proximal end of the drive shaft.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to and the benefit of the U.S. Provisional Patent Application No. 62/013,448, filed Jun. 17, 2014, which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates generally to elongate catheters for a rotational probe for insertion into a vessel, and in particular, to an intravascular ultrasound (IVUS) imaging catheter. 
       BACKGROUND 
       [0003]    Intravascular ultrasound (IVUS) imaging is widely used in interventional cardiology as a diagnostic tool for a diseased vessel, such as an artery, within the human body to determine the need for treatment, to guide the intervention, and/or to assess its effectiveness. IVUS imaging uses ultrasound echoes to create an image of the vessel of interest. The ultrasound waves pass easily through most tissues and blood, but they are partially reflected from discontinuities arising from tissue structures (such as the various layers of the vessel wall), red blood cells, and other features of interest. The IVUS imaging system, which is connected to an IVUS catheter by way of a patient interface module (PIM), processes the received ultrasound echoes to produce a cross-sectional image of the vessel where the catheter is placed. 
         [0004]    In a typical rotational IVUS catheter, a single ultrasound transducer element fabricated from a piezoelectric ceramic material is located at the tip of a flexible drive shaft that spins inside a plastic sheath inserted into the vessel of interest. The transducer element is oriented such that the ultrasound beam propagates generally perpendicular to the axis of the catheter. The fluid-filled sheath protects the vessel tissue from the spinning transducer and drive shaft while permitting ultrasound signals to freely propagate from the transducer into the tissue and back. As the drive shaft rotates (typically at 30 revolutions per second), the transducer is periodically excited with a high voltage pulse to emit a short burst of ultrasound. The same transducer then listens for the returning echoes reflected from various tissue structures, and the IVUS imaging system assembles a two dimensional display of the vessel cross-section from a sequence of several hundred of these ultrasound pulse/echo acquisition sequences occurring during a single revolution of the transducer. 
         [0005]    A typical drive shaft is made with stainless steel wires with a hollow core where electrical cables are placed inside the hollow core to electrically couple the transducer to the IVUS imaging system at the patience interface module (PIM). As the drive shaft can be made quite long for certain applications, e.g., in the range of 100 centimeter (cm) to 250 cm, threading the electrical cables through the hollow core can be a difficult task. Furthermore, due to size limitations, the drive shaft has to be unfinished at both ends, requiring that the termination or final connections of the electrical cables in the IVUS catheter be made by hand after threading the electrical cables through the drive shaft. Such tasks are difficult and time consuming. 
         [0006]    Accordingly, there remains a need for improved devices, systems, and methods for providing a compact and efficient drive shaft in an intravascular ultrasound system. 
       SUMMARY 
       [0007]    Embodiments of the present disclosure provide a compact and efficient drive shaft in an intravascular ultrasound system. 
         [0008]    In an embodiment, an elongate catheter for a rotational probe for insertion into a vessel is provided. The elongate catheter comprises a flexible body; a proximal connector adjacent a proximal portion of the flexible body; and an elongate shaft disposed within the flexible body, the shaft having a drive cable and a work element coupled to the drive cable adjacent a distal portion of the flexible body, the drive cable having a torque transmission core and at least one conductor disposed lengthwise outside of the torque transmission core, and the at least one conductor coupling the work element to a proximal portion of the elongate shaft. In some instances, the at least one conductor is an electrical conductor. In some instances, the at least one conductor is an optical fiber. The number of conductors depends on the application. For example, there may be two conductors or four conductors in the drive cable in some applications. 
         [0009]    In some instances, the drive cable further comprises an electrical insulating layer between the at least one conductor and the torque transmission core. In some instances, the drive cable further comprises a polymer jacket, the polymer jacket securing the at least one conductor to the torque transmission core. In some instances, the drive cable further comprises a plurality of polymer bands, the plurality of polymer bands securing the at least one conductor to the torque transmission core. In some embodiments, the at least one conductor is embedded in a polymer jacket that is secured to the torque transmission core. 
         [0010]    In some embodiments, the torque transmission core of the drive cable is made with stainless steel. In some embodiments, the torque transmission core of the drive cable is an optical fiber and the at least one conductor is an electrical conductor. In some embodiments, the work element of the elongate catheter is a piezoelectric micro-machined ultrasound transducer (PMUT) or a capacitive micro-machined ultrasound transducer (CMUT). 
         [0011]    In another embodiment, a rotational probe for insertion into a vessel is provided. The probe includes an elongate catheter having a flexible body, a proximal connector adjacent a proximal portion of the flexible body, and an elongate shaft disposed within the flexible body, the shaft having a drive cable and a work element coupled to the drive cable adjacent a distal portion of the flexible body, the drive cable having a torque transmission core and at least one conductor disposed lengthwise outside of the torque transmission core, and the at least one conductor coupling the work element to a proximal portion of the elongate shaft; and an interface module configured to interface with the proximal connector of the elongate catheter, the interface module including: a spinning element configured to be fixedly coupled to a proximal portion of the shaft; a stationary element positioned adjacent to and spaced from the spinning element, wherein the stationary element is configured to pass signals to and receive signals from the work element through the spinning element; and a motor coupled to the spinning element for rotating the spinning element and the shaft when the spinning element is fixedly coupled to the proximal portion of the shaft. 
         [0012]    In another embodiment, a method of manufacturing a catheter for a rotational probe for insertion into a vessel is provided. The method includes: providing an elongate torque transmission core; and securing at least one conductor to the elongate torque transmission core lengthwise. In some instances, the method further includes, before securing the at least one conductor to the elongate torque transmission core, forming an electrical insulating layer over the elongate torque transmission core, wherein the at least one conductor is placed adjacent to the electrical insulating layer. In some instances, the method further includes securing a polymer jacket over both the at least one conductor and the elongate torque transmission core. In some instances, the method further includes securing a plurality of polymer bands over both the at least one conductor and the elongate torque transmission core. 
         [0013]    In some embodiments, the at least one conductor is embedded in a polymer jacket and the securing the at least one conductor includes securing the polymer jacket over the elongate torque transmission core. In that regard, securing the polymer jacket includes heat shrinking the polymer jacket over the elongate torque transmission core, or extruding the polymer jacket over the elongate torque transmission core. In some embodiments, the securing the at least one conductor includes co-extruding a polymer jacket and the at least one conductor over the elongate torque transmission core. 
         [0014]    In some instances, the method further includes coupling a distal portion of the at least one conductor to a work element; and securing a distal portion of the torque transmission core to a housing that holds the work element. In that regard, the work element is a transducer in some embodiments. 
         [0015]    Some embodiments of the present disclosure provide a compact and efficient drive cable in an intravascular ultrasound (IVUS) system. The drive cable is flexible yet with requisite torque for insertion into a vessel of interest. With conductors disposed outside a torque transmission core, the drive cable is easier to manufacture than the existing drive cables where electrical wires need to be threaded therein. In some embodiments, the conductors of the provided drive cable can be terminated in a subassembly in an early step of the manufacturing process, simplifying the tasks of making and/or using the drive cable downstream. Furthermore, since there is no need to thread wires through the torque transmission core, the dimensions and tolerance of the drive cable can be reduced, allowing for more space for additional components for the IVUS system. In addition or alternatively, the drive cable can be made stronger, allowing for more reliable operation and longer usable life. 
         [0016]    In another embodiment, an elongate catheter for a rotational probe for insertion into a vessel is provided. The elongate catheter includes a flexible body; a proximal connector adjacent a proximal portion of the flexible body; and an elongate shaft disposed within the flexible body. The elongate shaft includes a drive cable and a work element coupled to the drive cable adjacent a distal portion of the flexible body. The drive cable includes a dielectric insulating layer, at least two conductors disposed lengthwise inside the dielectric insulating layer, a shield over the dielectric insulating layer, and an outer sheath over the shield. The at least two conductors couple the work element to a proximal portion of the elongate shaft. In some instances, the drive cable includes four conductors. In some instances, the drive cable further includes a strengthening layer embedded in the dielectric insulating layer and the strengthening layer can be made an electrical shield for the at least two conductors. In various instances, the drive cable of this embodiment provides a one-piece design for both data signal transmission and torque transmission, eliminating the need for a separate torque transmission core. Additional aspects, features, and advantages of the present disclosure will become apparent from the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Illustrative embodiments of the present disclosure will be described with reference to the accompanying drawings, of which: 
           [0018]      FIG. 1  is a simplified fragmentary diagrammatic view of a rotational IVUS probe, according to some embodiments. 
           [0019]      FIG. 2  is a simplified fragmentary diagrammatic view of an embodiment of an interface module and catheter for the rotational IVUS probe of  FIG. 1 , in accordance with an embodiment. 
           [0020]      FIG. 3A  is a diagrammatic, cross-sectional side view of a distal portion of the rotational IVUS probe of  FIG. 1 , in accordance with an embodiment. 
           [0021]      FIG. 3B  is a diagrammatic top view of a work element coupled to a distal portion of a drive cable, in accordance with an embodiment. 
           [0022]      FIG. 4A  is a diagrammatic perspective view of a drive cable, according to various aspects of the present disclosure. 
           [0023]      FIG. 4B  is a diagrammatic cross-sectional view of a drive cable, according to various aspects of the present disclosure. 
           [0024]      FIG. 4C  is a diagrammatic cross-sectional view of a drive cable, according to various aspects of the present disclosure. 
           [0025]      FIG. 4D  is a diagrammatic schematic view of a drive cable, according to various aspects of the present disclosure. 
           [0026]      FIG. 5  is a method of manufacturing a catheter, according to various aspects of the present disclosure. 
           [0027]      FIG. 6  is a diagrammatic, cross-sectional side view of a distal portion of the rotational IVUS probe of  FIG. 1 , in accordance with an embodiment. 
           [0028]      FIG. 7  is a diagrammatic cross-sectional view of an embodiment of the drive cable in  FIG. 6 , according to various aspects of the present disclosure. 
           [0029]      FIG. 8  is a diagrammatic cross-sectional view of another embodiment of the drive cable in  FIG. 6 , according to various aspects of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It is nevertheless understood that no limitation to the scope of the disclosure is intended. Any alterations and further modifications to the described devices, systems, and methods, and any further application of the principles of the present disclosure are fully contemplated and included within the present disclosure as would normally occur to one skilled in the art to which the disclosure relates. In particular, it is fully contemplated that the features, components, and/or steps described with respect to one embodiment may be combined with the features, components, and/or steps described with respect to other embodiments of the present disclosure. For the sake of brevity, however, the numerous iterations of these combinations will not be described separately. 
         [0031]    As used herein, “flexible elongate member” or “elongate flexible member” includes at least any thin, long, flexible structure that can be inserted into the vasculature of a patient. While the illustrated embodiments of the “flexible elongate members” of the present disclosure have a cylindrical profile with a circular cross-sectional profile that defines an outer diameter of the flexible elongate member, in other instances all or a portion of the flexible elongate members may have other geometric cross-sectional profiles (e.g., oval, rectangular, square, elliptical, etc.) or non-geometric cross-sectional profiles. Flexible elongate members include, for example, guidewires and catheters. In that regard, catheters may or may not include a lumen extending along its length for receiving and/or guiding other instruments. If the catheter includes a lumen, the lumen may be centered or offset with respect to the cross-sectional profile of the device. 
         [0032]    In most embodiments, the flexible elongate members of the present disclosure include one or more electronic, optical, or electro-optical components. For example, without limitation, a flexible elongate member may include one or more of the following types of components: a pressure sensor, a temperature sensor, an imaging element, an optical fiber, an ultrasound transducer, a reflector, a minor, a prism, an ablation element, an RF electrode, a conductor, and/or combinations thereof. Generally, these components are configured to obtain data related to a vessel or other portion of the anatomy in which the flexible elongate member is disposed. Often the components are also configured to communicate the data to an external device for processing and/or display. In some aspects, embodiments of the present disclosure include imaging devices for imaging within the lumen of a vessel, including both medical and non-medical applications. However, some embodiments of the present disclosure are particularly suited for use in the context of human vasculature. Imaging of the intravascular space, particularly the interior walls of human vasculature can be accomplished by a number of different techniques, including ultrasound (often referred to as intravascular ultrasound (“IVUS”) and intracardiac echocardiography (“ICE”)) and optical coherence tomography (“OCT”). In other instances, infrared, thermal, or other imaging modalities are utilized. 
         [0033]    The electronic, optical, and/or electro-optical components of the present disclosure are often disposed within a distal portion of the flexible elongate member. As used herein, “distal portion” of the flexible elongate member includes any portion of the flexible elongate member from the mid-point to the distal tip. As flexible elongate members can be solid, some embodiments of the present disclosure will include a housing portion at the distal portion for receiving the electronic components. Such housing portions can be tubular structures attached to the distal portion of the elongate member. Some flexible elongate members are tubular and have one or more lumens in which the electronic components can be positioned within the distal portion. 
         [0034]    The electronic, optical, and/or electro-optical components and the associated communication lines are sized and shaped to allow for the diameter of the flexible elongate member to be very small. For example, the outside diameter of the elongate member, such as a guidewire or catheter, containing one or more electronic, optical, and/or electro-optical components as described herein are between about 0.0007″ (0.0178 mm) and about 0.118″ (3.0 mm), with some particular embodiments having outer diameters of approximately 0.014″ (0.3556 mm) and approximately 0.018″ (0.4572 mm)). As such, the flexible elongate members incorporating the electronic, optical, and/or electro-optical component(s) of the present application are suitable for use in a wide variety of lumens within a human patient besides those that are part or immediately surround the heart, including veins and arteries of the extremities, renal arteries, blood vessels in and around the brain, and other lumens. 
         [0035]    “Connected” and variations thereof as used herein includes direct connections, such as being glued or otherwise fastened directly to, on, within, etc. another element, as well as indirect connections where one or more elements are disposed between the connected elements. 
         [0036]    “Secured” and variations thereof as used herein includes methods by which an element is directly secured to another element, such as being glued or otherwise fastened directly to, on, within, etc. another element, as well as indirect techniques of securing two elements together where one or more elements are disposed between the secured elements. 
         [0037]    Reference will now be made to a particular embodiments of the concepts incorporated into an intravascular ultrasound system. However, the illustrated embodiments and uses thereof are provided as examples only. Without limitation on other systems and uses, such as but without limitation, imaging within any vessel, artery, vein, lumen, passage, tissue or organ within the body. While the following embodiments may refer to a blood vessel and a blood vessel wall for illustrative purposes, any other tissue structure may be envisioned to be imaged according to methods disclosed herein. More generally, any volume within a patient&#39;s body may be imaged according to embodiments disclosed herein, the volume including vessels, cavities, lumens, and any other tissue structures, as one of ordinary skill may recognize. 
         [0038]    Referring now to  FIG. 1 , a rotational probe  100  for insertion into a patient for diagnostic imaging is shown. In some embodiments, the rotational probe  100  is an intravascular ultrasound (IVUS) probe. The probe  100  comprises a catheter  101  having a catheter body  102  and an elongate drive shaft or shaft  104 . The catheter body  102  is flexible and has both a proximal portion  106  and a distal portion  108 . The catheter body  102  is a sheath surrounding the shaft  104 . For explanatory purposes, the catheter body  102  in  FIG. 1  is illustrated as visually transparent such that the shaft  104  disposed therein can be seen, although it will be appreciated that the catheter body  102  may or may not be visually transparent. The shaft  104  is flushed with a sterile fluid, such as saline, within the catheter body  102 . The fluid serves to eliminate the presence of air pockets around the shaft  104  that adversely affect image quality. The fluid can also act as a lubricant. The shaft  104  has a proximal portion  110  disposed within the proximal portion  106  of the catheter body  102  and a distal portion  112  disposed within the distal portion  108  of the catheter body  102 . 
         [0039]    The distal portion  108  of the catheter body  102  and the distal portion  112  of the shaft  104  are inserted into a patient during the operation of the probe  100 . The usable length of the probe  100  (the portion that can be inserted into a patient) can be any suitable length and can be varied depending upon the application. The distal portion  112  of the shaft  104  includes a work element  118 . 
         [0040]    The proximal portion  106  of the catheter body  102  and the proximal portion  110  of the shaft  104  are connected to an interface module  114  (sometimes referred to as a patient interface module or PIM). The proximal portions  106 ,  110  are fitted with a catheter hub  116  that is removably connected to the interface module  114 . In some embodiments, the interface module  114  couples the probe  100  to a control system and/or a monitor (not shown) for direct user control and image viewing. 
         [0041]    The rotation of the shaft  104  within the catheter body  102  is controlled by the interface module  114 , which provides a plurality of user interface controls that can be manipulated by a user. The interface module  114  also communicates with the work element  118  by sending to and receiving signals from the work element  118  via conductors within the shaft  104 . In some embodiments, the signals to and from the work element  118  are electrical signals and the conductors within the shaft  104  are electrical conductors such as metal wires. In some embodiments, the signals to and from the work element  118  are optical signals and the conductors within the shaft  104  are optical fibers. The interface module  114  can receive, analyze, and/or display information received through the shaft  104 . It will be appreciated that any suitable functionality, controls, information processing and analysis, and display can be incorporated into the interface module  114 . 
         [0042]    The shaft  104  includes a work element  118 , a housing  120 , and a drive cable  122 . The work element  118  is coupled to the housing  120 . The housing  120  is attached to the drive cable  122  at the distal portion  112  of the shaft  104 . The drive cable  122  is rotated within the catheter body  102  via the interface module  114  and it in turn rotates the housing  120  and the work element  118 . The work element  118  can be of any suitable type, including but not limited to one or more transducer technologies such as PMUT or CMUT. The work element  118  can include either a single transducer or an array. In some embodiments, the work element  118  includes sensor components or optical lens, such as those used in an OCT system. 
         [0043]      FIG. 2  shows a diagrammatic view of the proximal portion of the probe  100  and the interior of the interface module  114 , in accordance with an embodiment. As shown, the catheter hub  116  includes a stationary exterior housing  224 , a dog  226 , and a connector  228 . The connector  228  is represented with four conductive lines, such as  254 , shown in this embodiment. It will be appreciated, however, that any suitable number of conductive lines and any type of conductive media can be utilized. For example, an optical coupler, a coaxial cable, or six electrically conductive lines can be utilized in various embodiments. 
         [0044]    As shown, the interior of the interface module  114  includes a motor  236 , a motor shaft  238 , a main printed circuit board (PCB)  240 , a spinning element  232 , and any other suitable components for the operation of the probe  100 . The motor  236  is connected to the motor shaft  238  to rotate the spinning element  232 . The main printed circuit board  240  can have any suitable number and type of electronic components  242  including but not limited to the transmitter and the receiver for the work element  118  ( FIG. 1 ). 
         [0045]    The spinning element  232  has a complimentary connector  244  for mating with the connector  228  on the catheter hub  116 . The connector  244  can have conductive lines, such as  255 , that contact the conductive lines, such as  254 , on the connector  228 . As shown, the spinning element  232  is coupled to a rotary portion  248  of a rotary transformer  246 . The rotary portion  248  of the transformer  246  passes signals to and from the stationary portion  250  of the transformer  246  using a set of windings  251  and  252 . The stationary portion  250  of the transformer  246  is electrically connected to the printed circuit board  240 . It will be appreciated that any suitable number of windings may be used to transmit any suitable number of signals across the transformer  246 . Also as shown, the spinning element  232  includes printed circuit boards  256 ,  257  comprising a plurality of circuit components. It will be appreciated that  FIG. 2  is merely an example and is not intended to limit the present disclosure. For example, a pullback mechanism may be employed to pull the shaft  122  proximally within the catheter  102  to generate a longitudinal image of a vessel. More examples of the proximal portion of the probe  100  and the interior of the interface module  114  can be found in U.S. Pat. No. 8,403,856 entitled “Rotational Intravascular Ultrasound Probe with an Active Spinning Element,” the contents of which are hereby incorporated by reference in their entirety. 
         [0046]      FIG. 3A  shows a cross-sectional side view of a distal portion of the catheter  101  according to an embodiment of the present disclosure. In particular,  FIG. 3A  shows an expanded view of aspects of the distal portion of the shaft  104 . In this exemplary embodiment, the shaft  104  is terminated at its distal tip by a housing  120  fabricated from stainless steel and provided with a rounded nose  326  and a cutout  328  for the ultrasound beam  330  to emerge from the housing  120 . The drive cable  122  of the shaft  104  includes a torque transmission core  332  and one or more electrical cables  334  secured thereon by a polymer jacket  336 . In some embodiments, the electrical cables  334  are secured to the torque transmission core  332  by a plurality of polymer bands instead of a polymer jacket. In some embodiments, the torque transmission core  332  is composed of two or more layers of counter wound stainless steel wires, welded, or otherwise secured to the housing  120  such that rotation of the drive cable  122  also imparts rotation on the housing  120 . In the illustrated embodiment, the work element  118  includes a PMUT microelectromechanical system (MEMS)  338  and an application specific integrated circuit (ASIC)  344  mounted thereon. The PMUT MEMS  338  includes a spherically focused transducer  342 . The work element  118  is mounted within the housing  120 . As shown in  FIG. 3A , one of the electrical cables  334  with an optional shield  333  is attached to the work element  118  with a solder  340 . The electrical cables  334  extends through an outer portion of the drive cable  122  to the proximal portion of the shaft  104  where it is terminated to the electrical connector  228  ( FIG. 2 ). In the illustrated embodiment, the work element  118  is secured in place relative to the housing  120  by an epoxy  348  or other bonding agent. The epoxy  348  also serves as an acoustic backing material to absorb acoustic reverberations propagating within the housing  120  and as a strain relief for the electrical cable  334  where it is soldered to the work element  118 . It will be appreciated that  FIG. 3A  is merely an example and is not intended to limit the present disclosure. More examples of the distal portion of the shaft  104  and the work element  118  can be found in U.S. Patent Application Publication No. 2013/0303919 on Nov. 14, 2013, now U.S. Pat. No. 8,864,674, entitled “Circuit Architectures and Electrical Interfaces for Rotational Intravascular Ultrasound (IVUS) Devices,” the contents of which are hereby incorporated by reference in their entirety. 
         [0047]      FIG. 3B  shows additional aspects of the PMUT MEMS component  338  of the work element  118 . The MEMS component  338  in the embodiment of  FIG. 3B  is a paddle-shaped silicon component with the piezoelectric polymer transducer  342  located in the widened portion  349  of the substrate located at the distal portion of the MEMS component  338 . The narrow portion of the substrate positioned proximal of the widened portion  349  is where the ASIC  344  is mounted to the MEMS component  338 . In that regard, the MEMS component  338  includes ten bond pads, with bond pads  350 ,  351 ,  352 ,  354 ,  356 , and  358  configured to match up respectively with bond pads on the ASIC  344  for mounting the ASIC  344  thereon, and bond pads  362 ,  364 ,  366 , and  368  serving as terminations for the four electrical cables  334  of the drive cable  122 . In that regard, the four electrical cables  334  of the drive cable  122  are exposed at a distal portion of the drive cable  122 , and are soldered or otherwise fixedly attached to bond pads  362 ,  364 ,  366 , and  368 , which are electrically coupled with the bond pads  352 ,  354 ,  356 , and  358  by conductive traces included on the MEMS substrate. Other embodiments of connecting the electrical cables  334  to the work element  118  are possible, such as those disclosed in U.S. Patent Application Publication No. 2013/0303919 on Nov. 14, 2013, now U.S. Pat. No. 8,864,674, entitled “Circuit Architectures and Electrical Interfaces for Rotational Intravascular Ultrasound (IVUS) Devices.” 
         [0048]      FIG. 4A  shows a diagrammatic schematic view of the drive cable  122 , according to various aspects of the present disclosure. Referring to  FIG. 4A , the drive cable  122  includes a torque transmission core  402 , an optional electrical insulating layer  404 , one or more conductors  406 , and a polymer jacket  408 . The torque transmission core  402  possesses a certain torsional stiffness in order to adequately deliver rotational force along the relatively long path traversed by the drive cable  122 . At the same time, the torque transmission core  402  is sufficiently flexible to bend around the tight turns presented by the vascular system while maintaining the ability to rotate and to axially translate through the catheter  101  ( FIG. 1 ). The torque transmission core  402  can be made of any suitable material. In an embodiment, the torque transmission core  402  is made of stainless steel, such as two or more layers of counter wound stainless steel wires or braided wires. In an embodiment, the torque transmission core  402  is an optical fiber. The conductors  406  are electrical conductors in some embodiments. In that regard, the conductors  406  may be optionally shielded. In various embodiments, the conductors  406  may be wire (Cu, etc.), carbon nanotube fiber conductors, conductive ink, conductive polymer, conductive film, and/or combinations thereof. In some embodiments, the conductors  406  are optical pathways, such as optical fibers used in OCT systems. In some embodiments, the drive cable  122  includes both electrical conductors  406  and optical conductors  406  in one cable. In some embodiments, the insulating layer  404  serves to electrically isolate the conductors  406  from the torque transmission core  402 . The insulating layer  404  may be formed of any suitable material. In some implementations, the insulating layer  404  is a parylene layer. The polymer jacket  408  secures the conductors  406  and the optional electrical insulating layer  404  over the torque transmission core  402 . In some embodiments, such as those will be described with reference to  FIG. 4C , the polymer jacket  408  can serve as insulating layer for the conductors  406 . Furthermore, the polymer jacket  408  also serves to protect the various components of the drive cable  122  from the fluid filled inside the catheter  101 . The polymer jacket  408  may be of any polymeric, insulating, and/or dielectric material, such as polyvinyl chloride (PVC), Kapton™ polyimide film from DuPont, ethylene tetrafluoroethylene (ETFE), nylon, or similar polyimide films. In some embodiments, the polymer jacket  408  is an elongate piece, such as a continuous layer in the drive cable  122 . In some embodiments, the polymer jacket  408  comprises a plurality of polymer bands that may be separate or be alternatively joined or fused. In yet another embodiment, the polymer jacket  408  is a spiral wrap. In various embodiments, the polymer jacket  408  can be coated, extruded, or shrunk over the torque transmission core  402 . 
         [0049]    An advantage of the drive cable  122  of  FIG. 4A  over conventional drive cables is that it is easier to manufacture because the conductors  406  are placed outside the torque transmission core  402 , rather than having to be threaded therein as is the case in the conventional drive cables. Furthermore, since there is no need to thread conductors through the torque transmission core  402 , the dimensions and tolerance of the drive cable  122  can be reduced, allowing for more space for additional components for the IVUS system. A smaller drive cable  122  also allows for a bigger space between the drive cable and the inside surface of the catheter lumen for easier flushing or injection operations. In addition or alternatively, the drive cable  122  can be made stronger, allowing for more reliable operation and longer usable life. 
         [0050]      FIG. 4B  shows a cross-sectional view of the drive cable  122  of  FIG. 4A , in accordance with an embodiment. Referring to  FIG. 4B , in this embodiment, the torque transmission core  402  is shown as a solid core. In alternative embodiments, the torque transmission core  402  is a helical winding having an inner lumen, potentially much smaller than that of existing drive cables. Also shown in  FIG. 4B , there are four conductors  406  spaced evenly around the electrical insulating layer  404 . In other embodiments, any number of conductors  406  is possible and different arrangement of the conductors  406  is also possible. The polymer jacket  408  wraps around and secures the conductors  406  to the insulating layer  404 . In an embodiment, the polymer jacket  408  is a heat shrinkable elongate jacket with a large lumen through which a subassembly of the conductors  406 , the insulating layer  404  and the torque transmission core  402  is threaded. The polymer jacket  408  is subsequently heated so as to securely wrap around the subassembly. Also shown in  FIG. 4B  with dashed lines  412 , portions of the polymer jacket  408  are removed at the proximal and/or distal portion of the drive cable  122  to expose the conductors  406 . This makes it easier for downstream manufacturing of the rotational probe  100  ( FIG. 1 ), e.g., when the drive cable  122  is to be coupled with the work element  118  ( FIG. 3B ) or to be terminated with the connector  228  of the catheter hub  116  ( FIG. 2 ). 
         [0051]      FIG. 4C  shows a cross-sectional view of the drive cable  122  of  FIG. 4A , in accordance with another embodiment. Many respects of this embodiment are similar to those of the drive cable  122  of  FIG. 4B . However, in this embodiment, the polymer jacket  408  has the conductors  406  embedded therein. The polymer jacket  408  is secured around the insulating layer  404  and the torque transmission core  402  by, e.g., a heat shrink process or any other processes. Having the polymer jacket  408  with the conductors  406  embedded therein further simplifies the manufacturing of the drive cable  122  and the rotational probe  100  ( FIG. 1 ). In this embodiment, the polymer jacket  408  itself may offer sufficient insulation between the torque transmission core  402  and the conductors  406 , and therefore, the insulating layer  404  may be unnecessary in some instances. 
         [0052]      FIG. 4D  shows a diagrammatic schematic view of the drive cable  122 , in accordance with an embodiment. Referring to  FIG. 4D , in this embodiment, the torque transmission core  402 , the conductors  406 , and the polymer jacket  408  are formed as one piece. For example, the conductors  406  and the polymer jacket  408  can be co-extruded over the torque transmission core  402  during a manufacturing process. 
         [0053]      FIG. 5  shows a method  500  of manufacturing a catheter for a rotational probe for insertion into a vessel, such as the catheter  101  ( FIG. 1 ), according to various aspects of the present disclosure. The method  500  is merely an example, and is not intended to limit the present disclosure beyond what is explicitly recited in the claims. Additional operations can be provided before, during, and after the method  500 , and some operations described can be replaced, eliminated, or moved around for additional embodiments of the method  500 . Various operations of  FIG. 5  will be described below in conjunction with  FIGS. 1-4D  discussed above. 
         [0054]    Operation  510  includes providing an elongate torque transmission core, such as the torque transmission core  402  of  FIG. 4A . The torque transmission core has desired length and dimension for the catheter to be manufactured. In some embodiments, the torque transmission core is electrically conductive, such as counter wound stainless steel wires. In some embodiments, the torque transmission core is not electrically conductive, such as an optical fiber. 
         [0055]    Operation  512  includes optionally forming an electrical insulating layer over the torque transmission core. This is usually the case when the torque transmission core is electrically conductive and the conductors to be assembled onto the torque transmission core are also electrically conductive and are not shielded. 
         [0056]    Operation  514  includes securing at least one conductor to the elongate torque transmission core. The number of conductors depends on the intended function of the catheter. For example, an advanced PMUT transducer catheter may need to have four or six conductors. Some catheters may require only one or two conductors. In addition, the conductors are suitable for conducting energy for the intended catheter. In that regard, the conductors may be electrical conductors, waveguides such as optical fibers, or a combination thereof. The at least one conductor may be secured to the torque transmission core by gluing, electrically printing (micro-dispense, aero-jet, ink-jet, transfer, gravure, etc.), or plating a conductive material over the insulating layer, or by helically wrapping the conductor around the torque transmission core. 
         [0057]    Operation  516  includes securing a polymer jacket over both the at least one conductor and the elongate torque transmission core. In an embodiment, securing the polymer jacket includes wrapping the polymer jacket over the at least one conductor and the elongate torque transmission core. In an embodiment, securing the polymer jacket includes sliding the polymer jacket over the at least one conductor and the elongate torque transmission core. In an embodiment, securing the polymer jacket further includes heating the polymer jacket so as to axially shrink its dimension. In some embodiments, the polymer jacket has the requisite conductors embedded therein. In such cases, operations  514  and  516  are combined into one operation. In some embodiments, operation  516  secures a plurality of polymer jacket bands over both the at least one conductor and the elongate torque transmission core. 
         [0058]    Operation  518  includes coupling a distal portion of the at least one conductor to a work element, such as shown in  FIG. 3B . In that regard, a distal portion of the polymer jacket are removed so as to expose the at least one conductor. Subsequently, the conductors are coupled to the work element through appropriate methods, such as soldering. 
         [0059]    Operation  520  includes coupling a distal portion of the torque transmission core to a housing that holds the work element, such as shown in  FIG. 3A . In some instances, some steps may be performed before operation  520 , such as applying epoxy so as to secure the work element and the conductors in the housing. The torque transmission core can be secured to the housing by a suitable method, such as welding. 
         [0060]      FIG. 6  shows a cross-sectional side view of a distal portion of the catheter  101  according to another embodiment of the present disclosure. Many respects of this embodiment are the same as or similar to those of the embodiment shown in  FIG. 3A . Therefore, they are labeled with the same reference numerals for the sake of brevity. However, this embodiment has some distinct features. For example, the drive cable, labeled as  122 A and also called data cable in this embodiment, has a different construction than the drive cable  122  in  FIG. 3A . Referring to  FIG. 6 , the drive cable  122 A includes one or more conductors  632 , a dielectric insulating layer  634 , a shield  636 , and an outer sheath  638 . The conductors  632  are attached to the work element  118  with solders  640  in the distal portion. They also extend through an inner cavity of the drive cable  122 A to the proximal portion of the shaft  104  where they are terminated to the electrical connector  228  ( FIG. 2 ). In various embodiments, the drive cable  122 A is made strong enough to carry torque needed for the operations of the catheter  101  without a need for a separate torque transmission core thereby achieving a one-piece design with both data transmission and torque transmission capabilities. 
         [0061]      FIG. 7  shows a diagrammatic cross-sectional view of an embodiment of the drive cable  122 A. Referring to  FIG. 7 , shown therein are four conductors  632  in a cavity  631  inside the dielectric insulating layer  634 . Each of the conductors  632  may be individually shielded. In an embodiment, the conductors  632  are similar to the inner conductors found in coaxial cables. In an embodiment, the conductors  632  are made of copper, solid or stranded. Although  FIG. 7  shows four conductors  632  in the drive cable  122 A, this is not intended to be limiting. In various embodiments, a different number of conductors are possible depending on the application. For example, there may be two conductors or six conductors. In an embodiment, there are at least two conductors  632 . The conductors  632  may be threaded through the cavity  631 . Alternatively, the dielectric insulating layer  634  may be extruded over the conductors  632 . The dielectric insulating layer  634  may be made of various materials, such as fluorinated ethylene propylene (FEP), poly tetrafluoroethylene (PTFE), or materials similar to those found in coaxial cables&#39; dielectric layer. In the present embodiment, the dielectric insulating layer  634  is made strong enough to transmit torque, for example, by having a relatively large dimension. In the illustrated embodiment, the insulating layer  634  is also a torque transmission layer that substantially files the volume within shield  636  and has a cross-sectional area greater than the cross-sectional area of the conductors  632 . The dielectric insulating layer  634  is reinforced by the shield  636  and the outer sheath  638 . The shield  636  may be braided or woven, and may be made of copper, aluminum, or other materials. In an embodiment, the shield  636  is grounded in the proximal portion and serves as an electrical shield for the conductors  632 . The outer sheath  638  may be made of PVC, tetrafluoroethylene (TFE), FEP, or a material similar to that of the polymer jacket  408  discussed above. In various embodiments, one or more of the dielectric insulating layer  634 , the shield  636 , and the outer sheath  638  are made strong enough for transmitting torque. Accordingly, various embodiments of the drive cable  122 A provide a one-piece design for both data signal transmission and torque transmission, eliminating the need for a separate torque transmission core. 
         [0062]      FIG. 8  shows a diagrammatic cross-sectional view of another embodiment of the drive cable  122 A. Referring to  FIG. 8 , this embodiment includes a strengthening layer  633  embedded in the dielectric insulating layer  634  (or  634 A/ 634 B). In an embodiment, the dielectric insulating layer  634  includes two insulating layers  634 A and  634 B, and the strengthening layer  633  is woven or braided over the insulating layer  634 A and is then covered by the insulating layer  634 B. In an embodiment, the strengthening layer  633  is made of a conductive material, such as copper, aluminum, or the like. To further this embodiment, the strengthening layer  633  can be made an electrical shield by grounding it in the proximal portion. Non-conductive materials can also be used for the strengthening layer  633 , for example, when the shield  636  provides sufficient electrical shield for the conductors  632 . Similar to the embodiment shown in  FIG. 7 , the drive cable  122 A in  FIG. 8  also provides a one-piece design for both data signal transmission and torque transmission, eliminating the need for a separate torque transmission core. 
         [0063]    The foregoing outlines features of several embodiments so that those of ordinary skill in the art may better understand the aspects of the present disclosure. Persons having ordinary skill in the art will also recognize that the apparatus, systems, and methods described above can be modified in various ways. Accordingly, persons having ordinary skill in the art will appreciate that the embodiments encompassed by the present disclosure are not limited to the particular exemplary embodiments described above. In that regard, although illustrative embodiments have been shown and described, a wide range of modification, change, and substitution is contemplated in the foregoing disclosure. It is understood that such variations may be made to the foregoing without departing from the scope of the present disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the present disclosure.