Patent Publication Number: US-11653895-B2

Title: Lined variable braided differential durometer multi-lumen shaft with a cross-shaped inner profile

Description:
This application is the U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2017/074151, filed on Sep. 25, 2017, which claims the benefit of Provisional Application Ser. No. 62/401,464, filed Sep. 29, 2016. These applications are hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to ultrasound catheters, in particular, to an intracardiac echocardiography (ICE) catheter shaft structured to improve flexibility, kink resistance, and steerability and to facilitate alignment during manufacturing. 
     BACKGROUND 
     Diagnostic and therapeutic ultrasound catheters have been designed for use inside many areas of the human body. In the cardiovascular system, two common diagnostic ultrasound methods are intravascular ultrasound (IVUS) and intra-cardiac echocardiography (ICE). Typically a single rotating transducer or an array of transducer elements is used to transmit ultrasound at the tips of the catheters. The same transducers (or separate transducers) are used to receive echoes from the tissue. A signal generated from the echoes is transferred to a console which allows for the processing, storing, display, or manipulation of the ultrasound-related data. 
     IVUS catheters are typically used in the large and small blood vessels (arteries or veins) of the body, and are almost always delivered over a guidewire having a flexible tip. ICE catheters are usually used to image chambers of the heart and surrounding structures, for example, to guide and facilitate medical procedures, such as transeptal lumen punctures, left atrial appendage closures, atrial fibrillation ablation, and valve repairs. Commercially-available ICE catheters are not designed to be delivered over a guidewire, but instead have distal ends which can be articulated by a steering mechanism located in a handle at the proximal end of the catheter. For example, an ICE catheter may be inserted through the femoral or jugular artery when accessing the anatomy, and steered in the heart to acquire images necessary to the safety of the medical procedures. 
     One type of ICE catheter (EP Medsystems ViewFlex™ Intracardiac Ultrasound Deflectable catheter) has a distal articulation in a single plane (both directions), operated by a single wheel that rotates about the lengthwise axis of the handle. The wheel is turned to a specific position for the desired catheter shape, staying in place due to the inherent friction on the wheel mechanism. The catheter is torquable, and can be rotated with the handle to facilitate steering in a second plane. The motions required to simultaneously torque and rotate the catheter often require two-handed operation. 
     Another type of ICE catheter (Siemens/ACUSON AcuNav™ Ultrasound Catheter) has an additional steering plane, and each steering plane is utilized by turning one of two corresponding wheels on the handle. These wheels rotate about the lengthwise axis of the handle. A third wheel, which also rotates about the lengthwise axis of the handle, is a locking mechanism for freezing each of the two steering wheels in its respective orientation. The entire catheter need not be torqued. The two steering planes allow a large combination of possible catheter configurations. 
     ICE catheters commonly provide steering through pullwires secured to the distal portions of the catheters near the tip assemblies. The pullwires are also referred to as steering lines. The pullwires extend through the bodies of the catheters and are coupled to control wheels at handles of the catheters located at the proximal end of catheters. For example, a pair of pullwires may provide steering in a left-right plane and another pair of pullwires may provide steering in an anterior-posterior plane. Thus, the maneuvering or turning of a control wheel in turn actuates a corresponding pullwire to deflect the distal portion of a catheter in a corresponding direction. 
     An ICE catheter typically includes an ultrasound imaging core that generates and receives acoustic energy. The imaging core may include a linear array of transducer elements or transducer elements arranged in any suitable configuration. The imaging core is encased in a tip member located at a furthest distal tip of the catheter. The tip member is covered with acoustic adhesive materials. An electrical cable is soldered to the imaging core and extends through the core of the body of the catheter. The electrical cable may carry control signals and echo signals to facilitate imaging of the heart anatomy. 
     Current commercial ICE catheters are manufactured as one time use disposable devices. However, customers commonly employ third party vendors to reprocess the used devices for additional procedures up to a certain limit (e.g., about 6). For examples, the catheter shaft can be adapted as the primary shaft and actuating body for any steerable disposable, including other types of diagnostic catheters, such as optical coherence tomography (OCT), electrophysiology (EP) mapping, and pressure sensing catheters, delivery catheters, guide sheathes, and therapeutic devices (e.g., ablation catheters). 
     SUMMARY 
     The invention provides devices, systems, and related methods that overcome the limitations associated with existing designs and provide durable and flexible catheter shafts. 
     Embodiments of the present disclosure provide a catheter with a lined variable braided catheter shaft. The body or the wall of the catheter shaft includes a high differential durometer between a distal segment and a proximal segment, creating a sharp transition. The body or the wall of the catheter shaft includes an embedded variable braided reinforcement layer. For example, the braided layer includes braids with a higher per inch count (PIC) at the distal segment than at the proximal segment. In addition, a portion of the braided layer around the sharp transition includes braids with varying PIC to provide a smooth transition from the high PIC at the distal segment to the low PIC at the proximal segment. The catheter shaft includes a central lumen with a cross-shaped cross-sectional profile that can facilitate alignment of pullwire lumens during manufacturing. 
     In one embodiment, an imaging catheter is provided. The imaging catheter includes a flexible elongate member that includes a proximal portion comprising a first material embedded with a first braid with a first braid pitch; a distal portion comprising a second material embedded with a second braid with a second braid pitch, wherein the second material is a lower durometer than the first material and wherein the second braid pitch includes a higher per inch count than the first braid pitch such that the distal portion is more flexible than the proximal portion; a primary lumen extending at least partially through the proximal portion and the distal portion; and a plurality of secondary lumens extending at least partially through the proximal portion and the distal portion; and an imaging component coupled to the distal portion of the flexible elongate member. 
     In some embodiments, the first material comprises a polyether block amide of durometer 72D. In some embodiments, the second material comprises a polyether block amide of durometer 35D or 45D. In some embodiments, the first braid and the second braid are constructed from flat wires. In some embodiments, the flat wires are composed of steel. In some embodiments, the first braid pitch includes a first per inch count, and wherein the second braid pitch includes a second per inch count that is about twice the first per inch count. In some embodiments, the flexible elongate member includes a third braid embedded within the first material and the second material across a transition between the proximal portion and the distal portion, and wherein the third braid includes variable braid pitches that transition between a first per inch count of the first braid pitch and a second per inch count of the second braid pitch. In some embodiments, the primary lumen includes a cross-shaped cross-section. In some embodiments, the plurality of secondary lumens are positioned relative to the primary lumen between arms of the cross-shaped cross-section. In some embodiments, the imaging catheter further includes a communication cable coupled to the imaging component and extending through the primary lumen. In some embodiments, the imaging catheter further includes a plurality of steering lines coupled to the distal portion of the flexible elongate member and extending through the plurality of secondary lumens. In some embodiments, the imaging component is an ultrasound transducer array. In some embodiments, the distal portion is deflectable up to a radius curvature of about 14 millimeters (mm). 
     In one embodiment, a method of manufacturing an imaging catheter is provided. The method includes forming a proximal portion of a flexible elongate member with a first material embedded with a first braid with a first braid pitch, wherein the proximal portion includes a first primary lumen and a first plurality of secondary lumens; forming a distal portion of the flexible elongate member with a second material embedded with a second braid with a second braid pitch, wherein the second material is a lower durometer than the first material and wherein the second braid pitch includes a higher per inch count than the first braid pitch such that the distal portion is more flexible than the proximal portion; and coupling an imaging component to the distal portion of the flexible elongate member. 
     In some embodiments, the first material comprises a polyether block amide of durometer 72D. In some embodiments, the second material comprises a polyether block amide of durometer 35D or 45D. In some embodiments, the first braid and the second braid are constructed from stainless steel flat wires. In some embodiments, the first braid pitch includes a first per inch count, and wherein the second braid pitch includes a second per inch count that is about twice the first per inch count. In some embodiments, the method further includes forming a third braid within the first material and the second material across a transition between the proximal portion and the distal portion, and wherein the third braid includes variable braid pitches that transition between a first per inch count of the first braid pitch and a second per inch count of the second braid pitch. In some embodiments, the forming the proximal portion includes forming the proximal portion to define a cross-shaped cross section for the first primary lumen and to position the first plurality of secondary lumens relative to arms of the cross-shaped cross section. In some embodiments, the forming the distal portion includes forming the distal portion to define a second primary lumen in communication with the first primary lumen and to define a second plurality of secondary lumens in communication with the first plurality of secondary lumens. In some embodiments, the method of claim further includes coupling a communication cable to the imaging component; and extending the communication cable through the second primary lumen of the distal portion and the first primary lumen of the proximal portion. In some embodiments, the method further includes coupling a plurality of steering lines to the distal portion; and extending the plurality of steering lines through the second plurality of secondary lumens of the distal portion and the first plurality of secondary lumens of the proximal portion. In some embodiments, the imaging component is an ultrasound transducer array. 
     Additional aspects, features, and advantages of the present disclosure will become apparent from the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Illustrative embodiments of the present disclosure will be described with reference to the accompanying drawings, of which: 
         FIG.  1    is a schematic diagram of an ICE imaging system according to embodiments of the present disclosure. 
         FIG.  2    is a schematic diagram of a portion of an ICE device according to embodiments of the present disclosure. 
         FIG.  3    is a schematic diagram of a portion of an ICE device under deflection according to embodiments of the present disclosure. 
         FIG.  4    is a schematic diagram illustrating deflections planes of an ICE device according to embodiments of the present disclosure. 
         FIG.  5    is a schematic diagram illustrating an interconnection within an ICE device between a tip assembly and a flexible elongate member according to embodiments of the present disclosure. 
         FIG.  6 A  is a perspective view of a crown element according to embodiments of the present disclosure. 
         FIG.  6 B  is a bottom view of a crown element according to embodiments of the present disclosure. 
         FIG.  6 C  is a side view of a crown element according to embodiments of the present disclosure. 
         FIG.  7    is a side view of a crown element with a pullwire in position according to embodiments of the present disclosure. 
         FIG.  8 A  is a perspective view of a sleeve element according to embodiments of the present disclosure. 
         FIG.  8 B  is a top view of a sleeve element according to embodiments of the present disclosure. 
         FIG.  9    is a top view of a sleeve element according to embodiments of the present disclosure. 
         FIG.  10    is a flow diagram of a method of assembling an ICE device according to aspects of the disclosure. 
         FIG.  11    is a schematic diagram illustrating a crown element fitted over an electrical cable, in a stage of assembly, according to embodiments of the disclosure. 
         FIG.  12    is a schematic diagram illustrating a pair of pullwires anchored to a crown element, in a stage of assembly, according to embodiments of the disclosure. 
         FIG.  13    is a schematic diagram illustrating a pair of pullwires anchored to a crown element and threaded through a flexible elongate member, in a stage of assembly, according to embodiments of the disclosure. 
         FIG.  14    is a schematic diagram illustrating a crown element positioned for coupling, in a stage of assembly, according to embodiments of the disclosure. 
         FIG.  15    is a schematic diagram illustrating a sleeve element positioned for coupling, in a stage of assembly, according to embodiments of the disclosure. 
         FIG.  16    is a schematic diagram illustrating a sleeve element bonded to a tip assembly and a flexible elongate member, in a stage of assembly, according to embodiments of the disclosure. 
         FIG.  17    is a side view of a tip member according to embodiments of the present disclosure. 
         FIG.  18    is a side perspective view of a tip member according to embodiments of the present disclosure. 
         FIG.  19    is a cross-sectional view of a tip member according to embodiments of the present disclosure. 
         FIG.  20    is a cross-sectional view of a tip member according to embodiments of the present disclosure. 
         FIG.  21    is a cross-sectional view of a tip member according to embodiments of the present disclosure. 
         FIG.  22    is a cross-sectional view of a tip member according to embodiments of the present disclosure. 
         FIG.  23    is a back perspective view of a tip member according to embodiments of the present disclosure. 
         FIG.  24    is a back perspective view of a tip member with an imaging core in position according to embodiments of the present disclosure. 
         FIG.  25    is a cross-sectional side view of an imaging core according to embodiments of the present disclosure. 
         FIG.  26    is a perspective view of a tip assembly and a sleeve element positioned for coupling according to embodiments of the present disclosure. 
         FIG.  27    is a side perspective view of a tip member according to embodiments of the present disclosure. 
         FIG.  28    is a back perspective view of a tip member with an imaging core in position according to embodiments of the present disclosure. 
         FIG.  29    is a side perspective view of a tip member according to embodiments of the present disclosure. 
         FIG.  30    is a back perspective view of a tip member with an imaging core in position according to embodiments of the present disclosure. 
         FIG.  31    is a cross-sectional view of a lined variable braided differential durometer multi-lumen catheter shaft according to embodiments of the present disclosure. 
         FIG.  32    is a cross-sectional longitudinal view of a lined variable braided differential durometer multi-lumen catheter shaft according to embodiments of the present disclosure. 
         FIG.  33    is a perspective view of a multi-lumen inner extrusion in a stage of manufacturing according to embodiments of the present disclosure. 
         FIG.  34    is a perspective view of a braid reinforced inner extrusion in a stage of manufacturing according to embodiments of the present disclosure. 
         FIG.  35    is a perspective view of a single-lumen outer extrusion inserted over a braided inner extrusion in a stage of manufacturing according to embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     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. For example, while the ICE system is described in terms of cardiovascular imaging, it is understood that it is not intended to be limited to this application. The system is equally well suited to any application requiring imaging within a confined cavity. 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. 
       FIG.  1    is a schematic diagram of an ICE imaging system  100  according to embodiments of the present disclosure. The system  100  may include an ICE device  110 , a connector  124 , a control and processing system  130 , such as a console and/or a computer, and a monitor  132 . The ICE device  110  includes a tip assembly  102 , a flexible elongate member  108 , and a handle  120 . The flexible elongate member  108  includes a distal portion  104  and a proximal portion  106 . The distal end of the distal portion  104  is attached to the tip assembly  102 . The proximal end of the proximal portion  106  is attached to the handle  120  for example, by a resilient strain reliever  112 , for manipulation of the ICE device  110  and manual control of the ICE device  110 . The tip assembly  102  can include an imaging core with ultrasound transducer elements and associated circuitry. The handle  120  can include actuators  116 , a clutch  114 , and other steering control components for steering the ICE device  110 , such as deflecting the tip assembly  102  and the distal portion  104 , as described in greater details herein. 
     The handle  120  is connected to the connector  124  via another strain reliever  118  and an electrical cable  122 . The connector  124  may be configured in any suitable configurations to interconnect with the processing system  130  and the monitor  132  for processing, storing, analyzing, manipulating, and displaying data obtained from signals generated by the imaging core at the tip assembly  102 . The processing system  130  can include one or more processors, memory, one or more input devices, such as keyboards and any suitable command control interface device. The processing system  130  can be operable to facilitate the features of the ICE imaging system  100  described herein. For example, the processor can execute computer readable instructions stored on the non-transitory tangible computer readable medium. The monitor  132  can be any suitable display device, such as liquid-crystal display (LCD) panel or the like. 
     In operation, a physician or a clinician advances the flexible elongate member  108  into a vessel within a heart anatomy. The physician or clinician can steer the flexible elongate member  108  to a position near the area of interest to be imaged by controlling the actuators  116  and the clutch  114  on the handle  120 . For example, one actuator  116  may deflect the tip assembly  102  and the distal portion  104  in a left-right plane and the other actuator  116  may deflect the tip assembly  102  and the distal portion  104  in an anterior-posterior plane, as discussed in greater details herein. The clutch  114  provides a locking mechanism to lock the positions of the actuators  116  and in turn the deflection of the flexible elongate member while imaging the area of interest. 
     The imaging process may include activating the ultrasound transducer elements on the tip assembly  102  to produce ultrasonic energy. A portion of the ultrasonic energy is reflected by the area of interest and the surrounding anatomy, and the ultrasound echo signals are received by the ultrasound transducer elements. The connector  124  transfers the received echo signals to the processing system  130  where the ultrasound image is reconstructed and displayed on the monitor  132 . In some embodiments, the processing system  130  can control the activation of the ultrasound transducer elements and the repletion of the echo signals. In some embodiments, the processing system  130  and the monitor  132  may be part of the same system. 
     The system  100  may be utilized in a variety of applications such as transeptal lumen punctures, left atrial appendage closures, atrial fibrillation ablation, and valve repairs and can be used to image vessels and structures within a living body. Although the system  100  is described in the context of ICE catheterization procedures, the system  100  is suitable for use with any catheterization procedure. In addition, the tip assembly  102  may include any suitable physiological sensor or component for diagnostic, treatment, and/or therapy. 
       FIG.  2    is a schematic diagram of a portion of the ICE device  110  according to embodiments of the present disclosure. The tip assembly  102  and the flexible elongate member  108  are shaped and sized for insertion into vessels of a patient body. The flexible elongate member  108  can be composed of any suitable material, such as polyether block amides. Polyether block amides are commonly manufactured under the tradename Pebax®. The distal portion  104  and the proximal portion  106  are tubular in shape and may include a primary lumen and one or more pullwire lumens extending longitudinally along the flexible elongate member  108 . The primary lumen is sized and shaped to accommodate an electrical cable interconnecting the tip assembly  102  and the connector  124  for transferring echo signals obtained from the transducer elements. In some embodiments, the primary lumen can be shaped and sized to accommodate other components for diagnostic and/or therapy procedures. The pullwire lumens are sized and shaped to accommodate pullwires, for example, extending from the distal portion  104  to the handle  120 . The pullwires may be coupled to the actuators  116  and the clutch  114  such that the flexible elongate member  108  and the tip assembly  102  are deflectable based on actuations of the actuators  116  and the clutch  114 . In an embodiment, the primary lumen is shaped to facilitate alignment of the pullwire lumens. In addition, the tubular body of the flexible elongate member  108  may include a lined variable braided reinforcement layer configured to provide flexibility and kink resistance. The arrangements and configurations of the pullwires, the primary lumen, the pullwire lumens, the tip assembly  102 , and the lined variable braided reinforcement layer are described in greater details herein. Dimensions of the flexible elongate member  108  can vary in different embodiments. In some embodiments, the flexible elongate member  108  can be a catheter having an outer diameter between about 8 and about 12 French (Fr) and can have a total length  206  between about 80 centimeters (cm) to about 120 cm, where the proximal portion  106  can have a length  204  between about 70 cm to about 118 cm and the distal portion  104  can have a length  202  between about 2 cm to about 10 cm. 
       FIG.  3    is a schematic diagram of a portion of the ICE device  110  under deflection according to embodiments of the present disclosure. For example, the flexible elongate member  108  shown in  FIG.  2    is referred to as a neutral position. In  FIG.  3   , the tip assembly  102  and the distal portion  104  of the flexible elongate member  108  are deflected from the neutral position. In an embodiment, the distal portion  104  may be deflected up to a bend radius  305  of about 27 millimeters (mm) to about 28 mm. 
       FIG.  4    is a schematic diagram illustrating deflections planes of the ICE device  110  according to embodiments of the present disclosure. As shown, the tip assembly  102  and the distal portion  104  can be deflected along a first plane as shown by the solid arrows and a second plane as shown by the dotted arrows. In  FIG.  3   , the first plane is represented by an x-y plane and the second plane is represented by an x-z plane. For example, the x-y plane may correspond to a left-right plane and the x-z plane may correspond to an anterior-posterior plane for imaging the heart anatomy. 
       FIG.  5    is a schematic diagram illustrating an interconnection within the ICE device  110  between the tip assembly  102  and the flexible elongate member  108  according to embodiments of the present disclosure. As shown, the interconnection between the tip assembly  102  and the distal portion  104  of the flexible elongate member  108  includes a crown element  520  and a sleeve element  540 . The crown element  520  is coupled to the distal end of the distal portion  104 . The sleeve element  540  is coupled to the crown element  520  and the proximal end of the tip assembly  102 . The tip assembly  102  includes an imaging core  562  encased in a tip member  560 . For example, the imaging core  562  is a planar element. The tip assembly  102  can include an alignment portion (not shown) shaped to facilitate alignment during manufacturing, as described in greater detail herein. The imaging core  562  is connected to an electrical cable  566  via an electrical interconnection  564 . The electrical cable  566  extends longitudinally along the flexible elongate member  108 . The crown element  520  and the sleeve element  540  are fitted around the electrical cable  566 . 
     The electrical cable  566  may include one or more cables and/or one or more wires formed into cables. In certain embodiments, the one or more cables or wires are encased or surrounded at least partially along their length with a heat shrink tubing. In some instances, the one or more cables may be split or arranged into separate heat shrink tubing. The heat shrink tubing is typically a polymeric material. An ideal polymeric material is polyethylene terephthalate (PET). The heat shrink tubing material may be manufactured using an extrusion process. Ideally the tubing is manufactured such that the expanded ID clears width of the cables to be threaded there through, and the shrunked ID is such that it forms a interference fit with the cables threaded there through. 
     A more detailed view of the crown element  520  is illustrated in  FIG.  6 A  and dimensions of the crown element  520  are illustrated in  FIGS.  6 B  and C. The crown element  520  functions as an anchor for pullwires  507  such that the tip assembly  102  and the distal portion  104  may be deflectable upon actuations of the pullwires  507  in the proximal direction as shown in  FIGS.  3  and  4    and described in greater detail herein. The anchoring of the pullwires  507  to the crown element  520  is illustrated in  FIG.  7   . The sleeve element  540  functions as an alignment agent to align the crown element  520  and the pullwires  507  such that the deflection may provide predictable or predetermined articulation views as described in greater detail herein. A more detailed view of the sleeve element  540  is illustrated in  FIG.  8 A . The alignment between the sleeve element  540  and the tip assembly  102  is illustrated in  FIG.  26   . 
     In an embodiment, the flexible elongate member  108  may include a lined variable braided enforcement layer to provide flexibility and kink resistance as described in greater detail herein. In such an embodiment, the interconnection further includes a braid containment  502  positioned between an anchoring segment  503  and the distal end of the flexible elongate member  108 . The braid containment  502  may be composed of material such as polyethylene terephthalate (PET) or any suitable material. The anchoring segment  503  can be composed of similar material as the flexible elongate member  108 . The braid containment  502  functions as a termination for the braided reinforcement layer. The braid containment  502  encases the termination of the materials (e.g., stainless steel wires) of the braided reinforcement layer to prevent exposure of the materials outside of the ICE device  110 . The structure of the flexible elongate member  108  and the braided reinforcement layer are described in greater detail herein. The anchoring segment  503  couples the braid containment  502  to the crown element  520  and the sleeve element  540  to allow for thermal reflow when bonding the components at the interconnection. 
     The interconnection may further include support members  508  and  509 , which are thin sleeves, to provide protection over connections of different components. The support members  508  and  509  may be composed of any suitable polymeric material. As shown, the support member  508  is positioned over the connections among the sleeve element  540 , the tip assembly  102 , the crown element  520 , and the anchoring segment  503 . The support member  509  is positioned over the connections among the braid containment  502 , the anchoring segment  503 , and the distal portion  104  of the flexible elongate member  108 . 
       FIG.  6 A  is a perspective view of the crown element  520  according to embodiments of the present disclosure.  FIG.  6 B  is a bottom view of the crown element  520  according to embodiments of the present disclosure.  FIG.  6 C  is a side view of the crown element  520  taken along the line  601  of  FIG.  6 B  according to embodiments of the present disclosure. The crown element  520  includes an annular ring  522  and support legs or posts  528  and  529 . The crown element  520  is composed of a material dissimilar or incompatible with the material of the flexible elongate member  108 . For example, the crown element  520  is composed of a thermoset material such as metal or plastic polymer. The annular ring  522  includes a top surface  524  and a bottom surface  526 . The posts  528  and  529  are positioned about radially opposite of each other on the annular ring  522  and extend about perpendicularly from the bottom surface  526 . Each of the posts  528  and  529  has a hole  530  positioned at an end of each of the posts  528  and  529 , respectively, away from the annular ring  522  and along a central axis of the posts  528  and  529 , respectively. A pair of pullwires such as the pullwires  507  can be secured to the crown element  520 , one at each of the posts  528  and  529 . The edges of the annular ring  522  are curved or rounded, for example, with small radii, to eliminate breakage of the pullwires during multiple actuations. 
     Dimensions of the crown element  520  can vary in different embodiments depending on the dimensions of the flexible elongate member  108 . In some embodiments, the annular ring  522  can have an outer radius  611  between about 5 FR and about 11 FR and an inner radius  612  between about 4 FR and about 10 FR. Each of the posts  528  and  529  can have a height  613  between about 1 mm and 3 mm and a width  614  between about 0.25 mm and 1.5 mm. Each hole  530  can have a radius  615  between about 0.05 mm and 0.7 mm. In some embodiments, the outer radius  611  can be less than the outer diameter of the flexible elongate member  108  while the inner radius  612  can be greater than the radius of the primary lumen of the flexible elongate member  108 . 
       FIG.  7    is a side view of the crown element  520  taken along the line  601  of  FIG.  6 B  with a pullwire  700  similar to the pullwires  507  in position according to embodiments of the present disclosure. The pullwire  700  can be composed of metal, hard plastic, or any suitable material. As shown, the pullwire  700  is anchored to the crown element  520  by forming a knot  710  at the post  528  creating segments  721  and  722  separated by the post  528 . The post  528  provides connection security and stability when the segments  721  and  722  are actuated. The separation of the segments  721  and  722  by the post  528  allows actuations of the segments  721  and  722  to be independent of each other, and thus provides consistent bending of the ICE device  110  over multiple actuations of the segments  721  and  722 . For example, an actuation of the segment  721  deflects the ICE device  110  in one direction and actuation of the segment  722  deflects the ICE device  110  in another direction. Another pullwire similar to the pullwires  700  and  507  can be anchored to the crown element  520  at the other post  529  using similar mechanisms to provide deflection of the ICE device  110  along a different plane. Thus, the crown element  520  enables independent and consistent actuations of the pullwire segments. In addition, the head  711  of the knot  710  is placed at the inner wall of the crown element  520  to minimize the amount of dissimilar material outside of the crown element  520  that can weaken the joint between the crown element  520  and the sleeve element  540  after bonding. 
       FIG.  8 A  is a perspective view of the sleeve element  540  according to embodiments of the present disclosure.  FIG.  8 B  is a top view of the sleeve element  540  according to embodiments of the present disclosure. The sleeve element  540  has a tubular body and includes flat outer surface portions  542  and  544  and curved outer surface portions  546  and  548 . The sleeve element  540  is composed of a material compatible to the flexible elongate member  108  and the tip assembly  102 . For example, the sleeve element  540  can be composed of a plastic polymer. The flat outer surface portions  542  and  544  have about the same surface area. The curved outer surface portions  546  and  548  have about the same surface area. The flat outer surface portion  542  is adjacent to the curved outer surface portions  546  and  548 . The flat outer surface portion  544  is adjacent to the curved outer surface portions  546  and  548 . The flat outer surface portions  542  and  544  are about radially opposite of each other. The sleeve element  540  further includes slots  551  and  552  extending longitudinally along the tubular body. The slot  551  is positioned proximal to the flat outer surface portion  542  and curved outer surface portion  546 . The slot  552  is positioned proximal to the flat outer surface portion  544  and curved outer surface portion  548 . 
     During assembly or manufacturing, the posts  528  and  529  of the crown element  520  are fitted into the slots  551  and  552 , respectively, and thermally bonded. After the bonding, the holes  530  are filled with the material of the sleeve element  540 . Thus, the holes  530  allow for a stronger bond and improve tensile strength at the joint between the crown element  520  and the sleeve element  540 . Since the pullwires are anchored at the posts  528  and  529  and the posts  528  and  529  are fitted into the slots  551  and  552 , respectively, the positioning of the slots  551  and  552  relative to the flat outer surface portions  542  and  544  can facilitate alignment of the pullwires to the imaging core  562  such that actuations of the pullwires can provide consistent articulation views, as described in greater detail herein. 
     Dimensions of the sleeve element  540  can vary in different embodiments depending on the dimensions of the flexible elongate member  108 . For example, the outer diameter  814  may be smaller than the inner diameter of the proximal opening  568  of the tip member  560  such that the sleeve element  540  may be fitted into the proximal opening  568  of the tip member  560 . The widths  813  of the slots  551  and  552  may be greater than the widths  614  of the posts  528  and  529  such that the posts  528  and  529  may be inserted into the slots  551  and  552 , respectively. For example, the material of the sleeve element  540  may be pliable and may conform to the inserted posts  528  and  529 . 
       FIG.  9    is a top view of a sleeve element  900  according to embodiments of the present disclosure. The sleeve element  900  can be employed by the ICE device  110  in place of the sleeve element  540 . The sleeve element  900  is similar to the sleeve element  540 , but has a curved outer surface  910  without any flat portion as in the sleeve element  540 . The sleeve element  900  can include slots  921  and  922  similar to the slots  551  and  552 , which can be used for fitting the posts  528  and  529 , respectively, when bonded with the crown element. The sleeve element  900  can be used when the tip assembly  102  does not include an alignment portion for alignment. In some embodiments, a sleeve element can be shaped to have an outer surface portion different from remaining outer surface to allow for alignment, where the outer surface portion can be in any shape suitable for alignment. 
     A method  1000  of assembling the ICE device  110  is described with reference made to  FIGS.  10 - 16   .  FIG.  10    is a flow diagram of a method  1000  of assembling the ICE device  110  according to aspects of the disclosure. It is understood that additional steps can be provided before, during, and after the steps of method  1000 , and some of the steps described can be replaced or eliminated for other embodiments of the method. The steps of the method  1000  can be carried out by a manufacturer of an ICE device.  FIG.  11    is a schematic diagram illustrating the crown element  520  fitted over the electrical cable  566 , in a stage of assembly, according to embodiments of the disclosure.  FIG.  12    is a schematic diagram illustrating a pair of pullwires  700  and  740  anchored to the crown element  520 , in a stage of assembly, according to embodiments of the disclosure.  FIG.  13    is a schematic diagram illustrating the pair of pullwires  700  and  740  anchored to the crown element  520  and threaded through the flexible elongate member  108 , in a stage of assembly, according to embodiments of the disclosure.  FIG.  14    is a schematic diagram illustrating the crown element  520  positioned for coupling, in a stage of assembly, according to embodiments of the disclosure.  FIG.  15    is a schematic diagram illustrating the sleeve element  540  positioned for coupling, in a stage of assembly, according to embodiments of the disclosure.  FIG.  16    is a schematic diagram illustrating the sleeve element  540  bonded to the tip assembly  102  and the flexible elongate member  108 , in a stage of assembly, according to embodiments of the disclosure. 
     Referring to the step  1005  of the method  1000 , in an embodiment, the tip assembly  102  coupled to the electrical cable  566  is obtained. Referring to the step  1010  of the method  1000  and  FIG.  11   , in an embodiment, the crown element  520  is positioned around the electrical cable  566 .  FIG.  11    illustrates the electrical cable  566  pre-loaded with the crown element  520 . As shown, the crown element  520  is positioned such that the posts  528  and  529  extend towards the tip assembly. 
     Referring to the step  1015  of the method  1000  and  FIG.  12   , in an embodiment, the pullwire  700  is secured to the crown element  520  by looping the pullwire  700  around the annular ring  522  at the post  528  to form the two segments  721  and  722 .  FIG.  12    illustrates a pair of pullwires  700  and  740  anchored to the crown element  520 . The pullwire  700  is anchored to the annular ring  522  at the post  528  using similar knotting mechanisms shown in  FIG.  7   . Similarly, the pullwire  740  is anchored to the annular ring  522  at the post  529  by forming a Larks knot  743 , which creates segments  741  and  742 . It should be noted that the heads of the knots  710  and  743  are placed adjacent to the inner wall of the crown element  520 . In an embodiment, the segments  721  and  722  are for steering the distal portion  104  and the tip assembly  102  in a left direction and an anterior direction, respectively. The segments  741  and  742  are for steering the distal portion  104  and the tip assembly  102  in a right direction and a posterior direction, respectively. 
     Referring to the step  1020  of the method  1000  and  FIG.  13   , in an embodiment, each segment  721  or  722  is positioned within one of a plurality of pullwire lumens  582  of the flexible elongate member  108 .  FIG.  13    illustrates the pair of pullwires  700  and  740  anchored to the crown element  520  and threaded through the flexible elongate member  108 . As shown, the segment  721  is threaded through one of the pullwire lumens  582  of the flexible elongate member  108 . Although not shown, each of the segments  722 ,  741 , and  742  can be thread through one of the pullwire lumens  582 . 
     Referring to the step  1025  of the method  1000  and  FIGS.  14  and  15   , in an embodiment, the sleeve element  540  is positioned between the crown element  520  and the tip assembly  102 .  FIG.  14    illustrates the crown element  520  positioned for coupling. As shown, the crown element  520  is positioned abutting the distal end of the flexible elongate member  108 .  FIG.  15    illustrates the sleeve element  540  positioned for coupling. As shown, the sleeve element  540  is positioned between the crown element  520  and the tip assembly  102 . 
     Referring to the step  1030  of the method  1000 , in an embodiment, the posts  528  and  529  are fitted into the slots  551  and  552 , respectively, of the sleeve element  540 . 
     Referring to the step  1035  of the method  1000 , in an embodiment, the sleeve element  540  is cut lengthwise. 
     Referring to the step  1040  of the method  1000 , in an embodiment, the sleeve element  540  is wrapped around the electrical cable  566 . 
     Referring to the step  1045  of the method  1000 , in an embodiment, the flat outer surface portions  542  and  544  are aligned to the flat portions of the tip assembly  102 . The alignment is described in greater detail herein. 
     Referring to the step  1050  of the method  1000  and  FIG.  16   , in an embodiment, thermal reflow is applied to the sleeve element  540  to bond the sleeve element  540  to the tip assembly  102 , the crown element  520 , and the flexible elongate member  108 . In  FIG.  16   , the bonding forms a joint  1610  between the tip assembly  102  and the flexible elongate member  108 . As described above, the sleeve element  540  is composed of a material similar to the materials of the flexible elongate member  108  and the tip assembly  102  while the crown element  520  is composed of a dissimilar material that is thermoset. Thus, the thermal reflow can fuse the sleeve element  540  the flexible elongate member  108  and the tip assembly  102  together while the crown element  520  is embedded within the fused material. As such, the sleeve element  540  can fill the gap and/or space at the joint  1610 . The sleeve element  540  can prevent collapse at the joint  1610  after the reflowing of different parts. In addition, the sleeve element  540  functions as a stopper in adding adhesive to the joint  1610  to maintain adhesive level at the surface of the joint. Further, the sleeve element  540  can increase the tensile strength of the joint  1610 . In some embodiments, the crown element  520  and the sleeve element  540  are concentrically aligned to a primary lumen of the flexible elongate member  108 . 
     The crown element  520  and the sleeve element  540  provide several benefits. The crown element  520  provides connection security and stability for individual pullwire segments  721 ,  722 ,  741 , and  742  when the pullwire segments  721 ,  722 ,  741 , or  742  is actuated in a proximal direction to deflect the tip assembly  102  and the distal portion  104  in a corresponding direction. In addition, the anchoring of the pullwires  700  and  740  at the posts  528  and  529 , respectively, allow actuations of the pullwire segments  721 ,  722 ,  741 , and  742  to provide consistent deflection angles. The holes  530  allow for bonding of the sleeve element  540  to the crown element  520  during the thermal reflow, and thus increasing the tensile strength. Further, the crown element  520  is shaped with rounded edges to prevent breakage of the pullwires  700  and  740  over actuations or increase the lifetime of the ICE device  110 . The sleeve element  540  is shaped with the flat outer surface portions  542  and  544  to allow for easy, precise, and consistent alignment of the pullwires  700  and  740  to the imaging core  562 . Thus, the employment of the sleeve element  540  allow for consistent angle of articulations. In addition, the sleeve element  540  can improve tensile strength at the joint between the tip assembly  102  and the flexible elongate member  108 . 
       FIG.  17    is a side view of a tip member  1700  according to embodiments of the present disclosure. The tip member  1700  can be employed by the tip assembly  102  in place of the tip member  560 . The tip member  1700  has a tubular body  1728  with a closed round distal tip  1720  and an opened proximal end  1732 . The tip member  1700  includes a distal portion  1702 , a tapered portion  1704 , and a proximal portion  1706  coupled in order from the closed round distal tip  1720  to the opened proximal end  1732 . The tip member  1700  includes a curved bottom outer wall  1734  coupled to a proximal curved top outer wall  1730  at the proximal portion  1706  that smoothly transitions into a distal flat top outer wall  1722  at the distal portion  1702 . The smooth radius transition at the tapered portion  1704  eliminates the need of a perpendicular surface to join the distal flat top outer wall  1722  and the proximal curved top outer wall  1730 . As such, the outer geometry of the tip member  1700  reduces friction and provides smooth surfaces to avoid catching on tissue structures when the tip member  1700  traverses through a patient body and reduces trauma to the patient. In some embodiments, the tip member  1700  can additionally be treated with a hydrophilic material to further reduce friction. 
     The tubular body  1728  can be composed of a thermoplastic elastomer material or any suitable biocompatible material that has acoustic impedance matching to blood within a vessel of a patient body when in use. In an embodiment, the tip member  1700  is constructed from a Pebax® polyether block amides  3533  SA  01  MED material. Dimensions of the tip member  1700  can vary in different embodiments. In an embodiment, the tip member  1700  is constructed from a Pebax® polyether block amides  3533  SA  01  MED material. Dimensions of the tip member  1700  can vary in different embodiments. In some embodiments, the tip member  1700  can include a length  1714  between about 15 mm to about 30 mm. The distal flat top outer wall  1722  can extend a length  1712  between about 5 mm to about 15 mm. The tip member  1700  can include a height  1710  proportional to the outer diameter  1711  of the tip member  1700 . In some embodiment, the height  1710  is at least about 50% of the outer diameter  1711 , with some particular embodiments between about 50% to about 75% of the outer diameter  1711 . The tapered portion  1704  can extend a length  1716  between about 0.5 mm to about 2 mm and tapers at an angle  1718  between about 15 degrees to about 75 degrees relative to a central longitudinal axis of the tip member  1700 . 
       FIG.  18    is a side perspective view of the tip member  1700  according to embodiments of the present disclosure. The tip member  1700  includes an inner cavity  1800  having an interface portion  1846 , an alignment portion  1844 , and a receiving portion  1842  coupled in order from the opened proximal end  1732  towards the closed round distal tip  1720 . In addition, the inner cavity  1800  includes a chamber  1834  adjacent and distal to the receiving portion  1842  used for accommodating kerf seal as described in greater detail herein. 
     The interface portion  1846  is sized and shaped to couple to the flexible elongate member  108 , for example, via the sleeve element  540 . The alignment portion  1844  is sized and shaped to align to the sleeve element  540  or any suitable connecting member. In an embodiment, the alignment portion  1844  is molded to form alignment members  1830  and  1832  along an inner wall portion of the inner cavity  1800 . In an embodiment, the alignment members  1830  and  1832  are configured to have first keyed surfaces inter-engaging with second keyed surfaces (e.g., flat outer surface portions  542  and  544 ) of the sleeve element  540 . 
     The receiving portion  1842  is sized and shaped to receive the imaging core  562 . The geometry of the receiving portion  1842  is configured to facilitate the alignment and positioning of the imaging core  562 . The receiving portion  1842  includes a proximal curved top inner wall  1828  that smoothly transitions into a distal flat top inner wall  1826 . The proximal curved top inner wall  1828  is opposite the proximal curved top outer wall  1730  and the distal flat top inner wall  1826  is opposite the distal flat top outer wall  1722 . In an embodiment, the receiving portion  1842  is molded to form a guide member  1820  having a stepped ledge with a first step  1822  and a second step  1824  extending longitudinally along a sidewall portion of the receiving portion  1842 . The receiving portion  1842  can include another guide member  1850  (shown in  FIG.  19   ) similar to the guide member  1820  extending longitudinally along a radially opposite sidewall portion of the receiving portion  1842 . The distal flat top inner wall  1826  and the guide members  1820  and  1850  restrict the positioning of the imaging core  562  within the receiving portion  1842 . In an embodiment, the imaging core  562  includes an array of ultrasound transducer elements and is positioned such that ultrasonic waves propagates towards and through the distal flat top inner wall  1826  and the distal flat top outer wall  1722  as shown by the dashed arrows and described in greater details herein. The alignment members  1830  and  1832  are positioned in a pre-defined relation to an orientation of the imaging core  562 . 
     Dimensions of the tip member  1700  can vary in different embodiments. In some embodiments, the tip member  1700  includes a uniform thickness  1810  between the distal flat top inner wall  1826  and the distal flat top outer wall  1722  of less than 200 microns such that distortion such as reflection and attenuation of the ultrasonic waves may be minimized. The receiving portion  1842  can extend a length  1812  between about 10 mm to about 28 mm. The alignment portion  1844  can extend a length  1814  between about 1 mm to about 5 mm. The interface portion  1846  can extend a length  1816  between about 1 mm to about 5 mm. 
       FIG.  19    is a cross-sectional view of the tip member  1700  taken along the line  1801  of  FIG.  18    according to embodiments of the present disclosure.  FIG.  19    illustrates the opened proximal end  1732  with interface portion  1846  of the inner cavity  1800 . Dimensions of the opened proximal end  1732  can vary in different embodiments. In some embodiments, the proximal opened end  1732  has a substantially circular shape. The outer diameter  1711  and the inner diameter  1713  may be sized to match the body of a catheter shaft (e.g., the flexible elongate member  108 ) such that the tip member  1700  can be coupled to the catheter shaft. For example, a catheter shaft body between about 8 FR and about 12 FR may have a wall thickness between about 100 microns and about 400 microns. To couple to such a catheter shaft, the outer diameter  1711  may be between about 8 FR and about 12 FR and a difference between outer diameter  1711  and the inner diameter  1713  may be between about 100 microns and about 400 microns. 
       FIG.  20    is a cross-sectional view of the tip member  1700  taken along the line  1802  of  FIG.  18    according to embodiments of the present disclosure.  FIG.  20    illustrates the alignment portion  1844  of the inner cavity  1800 . The tip member  1700  is molded to form the alignment members  1830  and  1832  along portions of the inner wall of the alignment portion  1844 . For example, the alignment members  1830  and  1832  are ledges extending transversely across the portions of the inner wall and positioned radially opposite of each other. Each ledge has a flat surface  2020  about perpendicular to the ultrasonic beam propagate direction of the imaging core  562 . Dimensions of the alignment members  1830  and  1832  can vary in different embodiments. For example, the alignment members  1830  and  1832  may be shaped and sized to adapt to the sleeve element  540  (e.g., the flat outer surface portions  542  and  544 ) such that the sleeve element  540  and the tip member  1700  may be aligned by inter-engaging the alignment members  1830  and  1832  with the flat outer surface portions  542  and  544 . 
       FIG.  21    is a cross-sectional view of the tip member  1700  taken along the line  1803  according to embodiments of the present disclosure.  FIG.  21    illustrates the receiving portion  1842  of the inner cavity  1800 , where the tip member  1700  has the proximal curved top outer wall  1730  and the proximal curved top inner wall  1828 . The tip member  1700  is molded to form the guide members  1820  and  1850  along portions of the inner wall of the receiving portion  1842 . The guide members  1820  and  1850  are positioned radially opposite of each other within the receiving portion  1842 . The guide member  1820  includes the step ledge with the first step  1822  and the second step  1824 . Similarly, the guide member  1850  includes a step ledge with a first step  1852  and a second step  1854 . In addition, the tip member  1700  is molded to form a raised U-shaped bottom inner wall  1856  extending longitudinally along the receiving portion  1842  and coupled to the guide members  1820  and  1850 . As described in greater detail herein, the guide members  1820  and  1850  restrict the positioning of the imaging core  562  (not shown). Dimensions of the guide members  1820  and  1850  and the raised U-shaped bottom inner wall  1856  can vary in different embodiments. For example, the dimensions of the guide members  1820  and  1850  and the separation distance  2112  between the guide members  1820  and  1850  are shaped and sized to accommodate the imaging core  562 . The wall thickness of the raised U-shaped bottom inner wall  1856  is configured to minimize acoustic attenuation. 
       FIG.  22    is a cross-sectional view of the tip member  1700  taken along the line  1804  according to embodiments of the present disclosure.  FIG.  22    illustrates the receiving portion  1842  of the inner cavity  1800 , where the tip member  1700  has the distal flat top outer wall  1722  and the distal flat top inner wall  1826 . The guide members  1820  and  1850  and the distal flat top inner wall  1826  restrict the positioning of the imaging core  562 . For example, the imaging core  562  can be positioned in the tip member  1700  guided by the guide members  1820  and  1850  and the distal flat top inner wall  1826  as shown by the dashed box. The guide members  1820  and  1850  restrict the positioning of the imaging core  562  along a first axis and in a first direction along a second axis about perpendicular to the first axis. In  FIG.  22   , the first axis is shown as the x-axis and the second axis is shown as the y-axis. The distal flat top inner wall  1826  restricts the positioning of the imaging core  562  in an opposite direction along the second axis. As described above, the tip member  1700  is sized such that the thickness  1810  between the distal flat top outer wall  1722  and the distal flat top inner wall  1826  is less than 200 micron to minimize distortions such as reflections and/or deflections of ultrasonic waves (dashed arrows) produced by the imaging core  562  during operation. 
       FIG.  23    is a back perspective view of the tip member  1700  according to embodiments of the present disclosure.  FIG.  23    illustrates the structure of the inner cavity  1800  viewing from the opened proximal end  1732  as shown by the line  1801 . As shown, the inner cavity  1800  includes the alignment member  1830  and  1832 , the raised U-shaped bottom inner wall  1856 , the guide members  1820  and  1850 , and the distal flat top inner wall  1826 . The raised U-shaped bottom inner wall  1856  is adjacent and distal to the alignment member  1832  and coupled to the guide members  1820  and  1850 . 
       FIG.  24    is a back perspective view of the tip member  1700  with the imaging core  562  in position according to embodiments of the present disclosure.  FIG.  24    illustrates the positioning of the imaging core  562  in the inner cavity  1800  viewing from the opened proximal end  1732  as shown by the line  1801 . The imaging core  562  is encased within the inner cavity  1800  guided by the guide members  1820  and  1850  and the distal flat top inner wall  1826 . The imaging core  562  can include a transducer circuit layer  2414  embedded between an acoustic stack  2412  and a backing material layer  2416 . The transducer circuit layer  2414  includes ultrasound transducer elements and associated circuitry. The acoustic stack  2412  is composed of materials acoustically matched to the ultrasound transducer elements, the transmission medium, and the target tissue for imaging. The backing material layer  2416  is composed of an acoustically absorptive material so that the backing material layer  2416  can absorb or deaden the ultrasonic waves coming from the back of the transducer circuit layer  2414 . For example, the acoustic stack  2412  can include materials such as PZT, single crystal, CMUT, PMUT, etc. and the backing material layer  2416  can include an epoxy material. The acoustic stack  2412  is positioned almost against the distal flat top inner wall  1826 , creating a thin bond line to further minimize acoustic distortion of the ultrasonic waves. The spaces of the inner cavity  1800  are filled with an encapsulating material to enclose the imaging core  562 . For example, the encapsulating material may include polydimethylsiloxane (PDMS), polyurethane, ultraviolet (UV) adhesives, or any suitable material that have desirable characteristics such as acoustic properties, bonding strength, and ease to work with during manufacturing. In some embodiments, the acoustic stack  2412  includes non-filled air kerfs, for example, along a perimeter of the acoustic stack  2412 . In such embodiments, the perimeter of the acoustic stack  2412  is sealed with a sealing material such as an UV adhesive to seal the non-filled air kerfs prior to filling the inner cavity  1800  with the encapsulating material. The chamber  1834  shown in  FIG.  18    can be used to accommodate the sealing material. 
       FIG.  25    is a cross-sectional side view of the imaging core  562  taken along the line  2402  of  FIG.  24    according to embodiments of the present disclosure. The transducer circuit layer  2414  includes an array of ultrasound transducer elements  2510  coupled to one or more multiplexer chips  2512 , for example, via conductive traces and/or associated circuitry. In some embodiments, the number of ultrasound transducer elements  2510  may be 8, 16, 32, 64, or any suitable number. The ultrasound transducer elements  2510  are composed of piezoelectric material. Exemplary transducers for ICE have a typical thickness of approximately 0.28 mm in the piezoelectric material to enable an 8 megahertz (MHz) ultrasound signal to be generated and transmitted at a typical velocity of 1500 meter per second (m/sec) through blood. The transducer thickness can be of various thicknesses ranging approximately from 0.56 mm to 0.19 mm to generate sufficient penetration depth in tissue imaging. In general, the thickness of the transducers can be adjusted for the frequency of sound in the transmission medium for the desired penetration depth in any tissue imaging. Image intensity can be adjusted by driving voltage on the transducers. 
     The multiplexer chips  2512  multiplex control signals, for example, generated by the processing system  130 , and transfer the control signals to corresponding ultrasound transducer elements  2510 . The controls signals can control the emission of ultrasound pulses and/or the reception of echo signals. In the reverse direction, the multiplexer chips  2512  multiplexes echo signals reflected by target tissue and received by the ultrasound transducer elements  2510  multiplexer chips  2512  and transfer the received echo signals, for example, to the processing system  130  for processing and/or display. 
       FIG.  26    is a perspective view of the tip assembly  102  and the sleeve element  540  positioned for coupling according to embodiments of the present disclosure. The tip assembly  102  is illustrated with the imaging core  562  in position within the tip member  1700 . The imaging core  562  is coupled to the electrical cable  566  via the electrical interconnection  564 . The electrical cable  566  extends through the alignment portion  1844  and the interface portion  1846  of the inner cavity  1800  and sleeve element  540 . The electrical cable  566  can further extend through the flexible elongate member  108  as shown in  FIG.  5   . During manufacturing, the interface portion  1846  can extend over and cover a portion of the sleeve element  540 , the crown element  520 , and the flexible elongate member  108 , thus improving the bonding strength. 
     As shown, the tip member  1700  is oriented such that the alignment members  1830  and  1832  are aligned to the flat outer surface portions  542  and  544  of the sleeve element  540 . As described above, the sleeve element  540  includes the flat outer surface portions  542  and  544  and the slots  551  and  552 , which are configured to couple to the crown element  520  in a particular orientation associated with the positioning of the pullwires  700  and  740 . Thus, the sleeve element  540 , the alignment members  1830  and  1832 , and the crown element  520  can be conjunctively designed to allow coupling of the sleeve element  540 , the alignment members  1830  and  1832 , and the crown element  520  in a particular orientation. As such, the sleeve element  540 , the alignment members  1830  and  1832 , and the crown element  520  can be consistently aligned during manufacturing without additional alignment measurement or adjustment. Since the alignment members  1830  and  1832  are oriented in a pre-defined relation with the ultrasound beam propagation direction of the imaging core  562  and the pullwires  700  and  740  are configured to provide steering of the tip assembly  102 , the actuations of the pullwires  700  and  740  can provide consistent articulation view for imaging. It should be noted that the alignment keying of the sleeve element  540  and the alignment members  1830  and  1832  can be alternatively configured as determined by a person of ordinary skill in the art to achieve similar functionalities. 
     The configuration and structure of the tip member  1700  described above provide several benefits such as safe and easy delivery for catheterization, improved tensile strength for steering or navigation, consistent or automatic alignment, and improved image quality. For example, the outer geometry of the tip member  1700  is configured to provide smooth surfaces and smooth edges with small radii. The smooth edges reduce friction when the tip member  1700  traverses a vessel during insertion. The smooth surfaces prevent tears and/or damages to tissue structures during the insertion. The smooth, radius transition from the proximal curved top outer wall  1730  to the distal flat top outer wall  1722  ensure that there are no ledges that can catch on outer features during the insertion. In addition, the smooth edges and smooth surfaces can facilitate crossing of a septum or other anatomical feature during a catheterization procedure. The material type and the wall thickness (e.g., the uniform thickness  1810 ) of the tip member  1700  are selected to minimize acoustic distortion, attenuation, and/or reflection. The internal geometry of the tip member  1700  is configured to facilitate alignment during manufacturing. As described, the alignment members  1830  and  1832  provide consistent and predictable alignment between the imaging core  562  and the pullwires  700  and  740 . The tip member  1700  can also include other features, for example, a guidewire lumen, holes, or other geometry to accommodate additional devices or features such as pressure sensors, drug delivery mechanisms, and/or any suitable interventional features. 
       FIGS.  27 - 30    illustrate alternative tip member configurations that can provide substantially similar benefits as the tip member  1700 .  FIG.  27    is a side perspective view of a tip member  2700  according to embodiments of the present disclosure. The tip member  2700  can be employed by the tip assembly  102 . The tip member  2700  has a tubular body  2742  with a closed round distal end  2720  and an opened proximal end  2728 . The tip member  2700  includes a distal portion  2702  and a proximal portion  2704 . The tip member  2700  includes a curved outer wall  2724 . For example, the tip member  2700  has a uniform external circular profile. In some embodiments, the curved outer wall  2724  can be designed to provide a lens effect to focus ultrasonic waves. The tubular body  2742  can be constructed from similar materials as the tubular body  1728  of the tip member  1700  member. 
     The tip member  2700  includes an inner cavity  2730  extending from the closed proximal end  2728  towards the closed round distal end  2720 . The inner cavity  2730  is configured to receive the imaging core  562 . The inner cavity  2730  includes a proximal curved top inner wall  2726  at the proximal portion  2704  and a distal flat top inner wall  2722  at the distal portion  2702 . The inner cavity  2730  includes a curved bottom inner wall  2738  coupled to the proximal curved top inner wall  2726  and the distal flat top inner wall  2722 . The inner cavity  2730  is molded to form a pair of rails  2732  and  2734  extending along a sidewall portion of the inner cavity  2730  from the proximal opened end  2728  towards the closed round distal end  2720 . The rails  2732  and  2734  are circumferentially spaced apart from each other forming a space for positioning the imaging core  562 . The inner cavity  2730  further includes another pair of rails  2752  and  2754  (shown in  FIG.  28   ) similar to the rails  2732  and  2734  extending longitudinally along a radially opposite sidewall portion of the inner cavity  2730 . Thus, the rails  2732 ,  2734 ,  2752 , and  2754  operate as guide members to restrict the positioning of the imaging core  562 . For example, the imaging core  562  is positioned such that the ultrasound transducer elements  2510  emit ultrasonic waves towards and through the distal flat top inner wall  2722  and curved outer wall  2724  at the distal portion  2702  as shown by the dashed arrows. Dimensions of the tip member  2700  can be substantially similar to the tip member  1700 , but the wall thickness  2710  at the distal portion  2702  is greater than 200 microns. For example, the wall thickness  2710  can be between about 25% and about 50% of the outer diameter  2712  of the tip member  2700 . 
       FIG.  28    is a back perspective view of the tip member  2700  with the imaging core  562  in position according to embodiments of the present disclosure.  FIG.  28    illustrates the positioning of the imaging core  562  in the inner cavity  2730  viewing from the opened proximal end  2728  as shown by the line  2701 . The imaging core  562  is encased within the inner cavity  2730  guided by the rails  2732 ,  2734 ,  2752 , and  2754  along a first axis and a second axis about perpendicular to the first axis. In  FIG.  28   , the first axis is shown as the x-axis and the second axis is shown as the y-axis. The positioning of the imaging core  562  along the z-axis is restricted by the farthest distal end of the inner cavity  2730 . The spaces between the inner cavity  2730  and the imaging core  562  are filled with similar encapsulating material as used for the inner cavity  1800  of the tip member  1700 . The tip member  2700  can further include alignment members similar to the alignment members  1830  and  1832  to facilitate alignment with the sleeve element  540 , the crown element  520 , and the flexible elongate member  108 . 
       FIG.  29    is a side perspective view of a tip member  2900  according to embodiments of the present disclosure. The tip member  2900  can be employed by the tip assembly  102 . The tip member  2900  is similar to the tip member  2700 , but has a different internal geometry. The tip member  2900  has a tubular body  2942  with a closed round distal end  2920  and an opened proximal end  2928 . The tip member  2900  includes a distal portion  2902  and a proximal portion  2904 . The tip member  2900  includes a curved outer wall  2924 . The tubular body  2942  can be constructed from similar materials as the tubular body  1728  of the tip member  1700  member and the tubular body  2742  of the tip member  2700  member. 
     The tip member  2900  includes an inner cavity  2930  extending from the closed proximal end  2928  towards the closed round distal end  2920 . The inner cavity  2930  is configured to receive the imaging core  562 . The inner cavity  2930  includes a curved inner wall  2926 . The inner cavity  2930  is molded to form a pair of rails  2932  and  2934  extending along a sidewall portion of the inner cavity  2930  from the proximal opened end  2928  towards the closed round distal end  2920 . The rails  2932  and  2934  are circumferentially spaced apart from each other forming a space for positioning the imaging core  562 . The inner cavity  2930  further includes another pair of rails  2952  and  2954  (shown in  FIG.  30   ) similar to the rails  2932  and  2934  extending longitudinally along a radially opposite sidewall portion of the inner cavity  2930 . Thus, the rails  2932 ,  2934 ,  2952 , and  2954  operate as guide members to restrict the positioning of the imaging core  562 . For example, the imaging core  562  is positioned such that the ultrasound transducer elements  2510  emit ultrasonic waves towards and through a portion of the curved inner wall  2926  and a portion of curved outer wall  2924  at the distal portion  2902  as shown by the dashed arrows. 
       FIG.  30    is a back perspective view of the tip member  2900  with the imaging core  562  in position according to embodiments of the present disclosure.  FIG.  30    illustrates the positioning of the imaging core  562  in the inner cavity  2930  viewing from the opened proximal end  2928  as shown by the line  2901 . The imaging core  562  is encased within the inner cavity  2930  guided by the rails  2932 ,  2934 ,  2952 , and  2954  along a first axis and a second axis about perpendicular to the first axis. In  FIG.  28   , the first axis is shown as the x-axis and the second axis is shown as the y-axis. The positioning of the imaging core  562  along the z-axis is restricted by the farthest distal end of the inner cavity  2930 . The spaces between the inner cavity  2930  and the imaging core  562  are filled with similar encapsulating material as used for the inner cavity  1800  of the tip member  1700  and the inner cavity  2730  of the tip member  2700 . The tip member  2900  can further include alignment members similar to the alignment members  1830  and  1832  to provide consistent alignment with the sleeve element  540 , the crown element  520 , and the flexible elongate member  108 . 
       FIGS.  31  and  32    illustrate a lined variable braided differential durometer multi-lumen catheter shaft  3100 . The catheter shaft  3100  can be employed by the ICE device  110  in place of the flexible elongate member  108 .  FIG.  31    is a cross-sectional view of the lined variable braided differential durometer multi-lumen catheter shaft  3100  taken along a transverse axis of the catheter shaft  3100  according to embodiments of the present disclosure.  FIG.  32    is a cross-sectional longitudinal view of the lined variable braided differential durometer multi-lumen catheter shaft  3100  taken along the line  3101  of  FIG.  31    according to embodiments of the present disclosure. The catheter shaft  3100  has a distal end  3202  and a proximal end  3204 . The catheter shaft  3100  is tubular in shape with a tubular wall  3102  and a primary lumen  3108 . The primary lumen  3108  extends between the distal end  3202  and the proximal end  3204 , for example, along a central longitudinal axis of the catheter shaft  3100 . 
     The tubular wall  3102  is composed of a high durometer polymeric material at a distal segment  3206  and a low durometer polymeric material at a proximal segment  3208 . For example, the high durometer polymeric material may have a durometer between 63D-80D and include materials such as Pebax® 72D or a suitable nylon. The low durometer polymeric material may have a durometer between 30D to 55D and include materials such as Pebax® 35D, Pebax® 45D, or a suitable nylon. The highly differing durometer of the tubular wall  3102  between the distal segment  3206  and the proximal segment  3208  creates a sharp transition or a high stiff-to-flex ratio in the catheter shaft  3100 . Thus, the catheter shaft  3100  can be relatively rigid at the proximal segment  3208 , but substantially pliable or flexible at the distal segment  3206 . The steerability of the catheter shaft  3100 , the amount of force to bend the catheter shaft  3100 , and the locality of the bend force and/or actuations may depend on the durometer of the catheter shaft  3100 . The sharp transition may improve the steerability, the amount of force, and/or the locality of the force when the catheter shaft  3100  is in use. 
     The catheter shaft  3100  further includes a plurality of secondary lumens  3106  extending longitudinally through a length of the tubular wall  3102 . The primary lumen has a cross-shaped cross-sectional profile. This profile may be rounded (as shown in  FIG.  31   ) or rectangular, for example. The secondary lumens  3106  are shaped and sized to accommodate pullwires such as the pullwires  507 ,  700 , and  740 . Thus, the secondary lumens  3106  are also referred to as pullwire lumens. The secondary lumens  3106  are positioned within the tubular wall  3102  radially spaced apart by an angle  3180  of about 90 degrees. The arms  3110  of the cross-shaped cross section form recesses that can anchor the angular positions of the secondary lumens  3106 . For example, the secondary lumens  3106  are positioned between adjacent arms  3110  during manufacturing as described in greater detail herein. The primary lumen  3108  and the secondary lumens  3106  can be lined with a lubricious lining material (not shown) such as a polytetrafluoroethylene (PTFE) material. The lining material creates frictionless surfaces for threading, delivery, and actuations of pullwires or any other suitable diagnostic sensor assembly. In addition, the lining material can function as a support structure to prevent the primary lumen  3108  and the secondary lumens  3106  from collapsing. Further, the lining material can function as a barrier to protect abrasion caused by the frequent shifting or actuations of the pullwires and/or threading of the other diagnostic sensor assembly. 
     The catheter shaft  3100  further includes a braided layer  3104  embedded within the tubular wall  3102 . The braided layer  3104  includes a distal portion  3212 , a proximal portion  3216 , and a transition portion  3214  between the distal portion  3212  and the proximal portion  3216 . The braided layer  3104  can be composed of any suitable material and geometry. For example, the braided layer  3104  may include stainless steel flat wires, which may provide optimal usage of radial space and additional strength. The braided layer  3104  has braids with pitches that vary along a length of the tubular wall  3102 . The braids can include any suitable braid pattern. The braid pattern may be selected to improve torque transmission (e.g., a 1:1 ratio from the proximal end  3204  to the distal end  3202 ), pushability, and/or kink resistance. 
     The braids at the distal portion  3212  are configured to have a higher per inch count (PIC) than the braids at the proximal portion  3216 , for example, by about two times. The higher PIC at the distal portion  3212  provides a great flexibility to the distal segment  3206 . The lower PIC at the proximal portion  3216  creates a stiffer support for the proximal segment  3208 . For example, the distal portion  3212  has a first PIC, the proximal portion  3216  has a second PIC, and the transition portion  3214  has a varying PIC that varies smoothly from the first PIC to the second PIC. As shown, the distal portion  3212  of the braided layer  3104  is aligned to the distal segment  3206  of the catheter shaft  3100 , the proximal portion  3216  of the braided layer  3104  is aligned to the proximal segment  3208  of the catheter shaft  3100 , and the transition portion  3214  extends across a coupling point at which the low durometer distal segment  3206  meets the high durometer proximal segment  3208  as shown by the line  3201 . The transition portion  3214  can extend a length  3280 , for example, between about 5 mm to about 20 mm. The smooth varying braid pitches in the short transition portion  3214  can alleviate the weak kink point resulting from the abrupt transition between the low durometer distal segment  3206  and the high durometer proximal segment  3208 . 
     Dimensions of the catheter shaft  3100  can vary in different embodiments. In some embodiments, the catheter shaft  3100  may be a 9 Fr catheter. Thus, the catheter shaft  3100  can have an outer diameter  3182  of about 3 mm. The distal segment  3206  can have a length  3282  between about 70 mm to about 81 mm. The length  3282  may vary based on a required bend radius for the catheter shaft  3100 . The proximal segment  3208  can have a length  3282  between about 872 mm to 877 mm. The dimensions of the cross-shaped primary lumen  1308  can be sized to allow components (e.g., a printed circuit board (PCB) and/or a coaxial cable) to be thread through the lumen  1308  during assembly instead of using the coaxial cable as an anchor as in some configurations, and thus may improve handling responsiveness during operation. The low durometer material used in in the distal segment  3206  and the braided layer  3104  allows the catheter shaft  3100  to deflect up to a bend radius (e.g., the bend radius  305 ) of between about 13 mm to about 14 mm instead of about 27 mm to about 28 mm. 
     A method of manufacturing the catheter shaft  3100  is described with reference made to  FIGS.  33 - 35   .  FIG.  33    is a perspective view of a multi-lumen inner extrusion  3300  in a stage of manufacturing according to embodiments of the present disclosure. The inner extrusion  3300  includes a high durometer proximal portion  3320  of a first material (e.g., Pebax® 72D) and a low durometer distal portion  3310  of a second material (e.g., Pebax® 35D or Pebax® 45D). The inner extrusion  3300  includes a primary lumen  3331  (e.g., primary lumen  3108 ) and a plurality of secondary lumens  3332  (e.g., secondary lumens  3106 ) extending between the high durometer proximal portion  3320  and the low durometer distal portion  3310 . 
       FIG.  34    is a perspective view of a braid reinforced inner extrusion  3400  in a stage of manufacturing according to embodiments of the present disclosure. As shown, a braided layer  3410  (e.g., the braided layer  3104 ) is formed over an outer surface of the inner extrusion  3300 . The braided layer  3410  has a first braid portion  3416  (e.g., the proximal portion  3216 ) with a first braid pitch (e.g., with a first PIC) over the high durometer proximal portion  3320 . The braided layer  3410  has a second braid portion  3412  (e.g., the distal portion  3212 ) with a second braid pitch (e.g., with a second PIC) over the low durometer distal portion  3310 . The braided layer  3410  has a third braid portion  3414  (e.g., the transition portion  3214 ) with variable braid pitches (e.g., varying between the first PIC and the second PIC) across a transition between the high durometer proximal portion  3320  and the low durometer distal portion  3310 . 
       FIG.  35    is a perspective view of a single-lumen outer extrusion  3500  inserted over the braided inner extrusion  3400  in a stage of manufacturing according to embodiments of the present disclosure. The outer extrusion  3500  includes a high durometer proximal portion  3520  of a first material (e.g., Pebax® 72D) and a low durometer distal portion  3510  of a second material (e.g., Pebax® 35D or Pebax® 45D). The inner extrusion  3300  and the outer extrusion  3500  form the tubular wall  3102  of the catheter shaft  3100 . The braided layer  3410  corresponds to the braided layer  3104  embedded within the tubular wall  3102 . 
     After forming the catheter shaft  3100 , pullwires such as the pullwires  700  and  740  may be thread through the secondary lumens  3106  according to predetermined orientations for providing the left, right, anterior, and posterior views. The distal end  3202  of the catheter shaft  3100  may be coupled to a tip assembly such as the tip assembly  102 . For example, the coupling may include terminating or enclosing the braided element  3104  in a braid containment such as the braid containment  502 . In addition, the coupling can include forming an interconnection as shown in  FIG.  5   . An electrical cable such as the electrical cable  566  connecting to the tip assembly may be threaded through the primary lumen  3108 . The proximal end  3204  of the catheter shaft  3100  may be coupled to a steering control handle such as the handle  120 . 
     The configuration of the lined variable braided differential durometer multi-lumen catheter shaft  3100  provides several benefits such as kink resistance, flexibility, high torquability, durability, and consistent alignment and articulations. The sharp transition between the low durometer distal segment  3206  and the high durometer proximal segment  3208  and the short transition portion  3214  of the braided element  3104  with varying PIC braids provide the kink resistance. The low durometer distal segment  3206 , the high durometer proximal segment  3208 , the high PIC braids at the distal portion  3212 , and the low PIC braids at the proximal portion  3216  provide flexibility at the distal segment  3206  and rigid support at the proximal segment  3208 . The cross-shaped cross-sectional profile of the primary lumen  3108  functions as an alignment agent to align the pullwire lumens or the secondary lumens  3106  such that pullwires such as the pullwires  507 ,  700 , and  740  threaded through the secondary lumens  3106  can provide consistent articulation views under actuations. The primary lumen  3108  and the secondary lumens  3106  are lined with a lining material to provide frictionless surfaces, which may improve durability over multiple usages. Materials of the tubular wall  3102  and the braided element  3104  are selected to improve mechanical characteristics (e.g., the steerability of the catheter shaft  3100 ). 
     Any suitable material may be used for pullwires of the claimed invention. In certain instances, one or more pullwires are formed from a para aramid strands or filaments. The para aramid strands or filaments may be braided and then partially fused together (e.g. via thermal fusion) to form a wire. A particular para aramid wire can be formed at least partially from Kelvar®. The most common and reliable braided patterns of a construct of this size are the ones specified by the following military specs, A-A-55195/MIL-T-44100. The secondary finishing thermal fuse process helps increase its tensile strength but also its usability, preventing the individual strands from coming unwound during handling and threading. 
     The properties of para aramid enables several anchoring options on the distal end of the device at the point which the actuation force distribution (shaft compression point) ends (E.g.  FIGS.  6 A- 6 C ). One option is a thermal fuse with an adjacent compatible polymeric material to allow the reflow of materials to encase its position. Another option is to use an additional component such as a washer or a ring to secure the wire&#39;s position and then reflow as you would the first option (e.g.  FIG.  7   ). These options are available because of the heat resistant and high tensile properties of the para armid wire. 
     Persons skilled in the art will recognize that the apparatus, systems, and methods described above can be modified in various ways. Accordingly, persons of 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.