Patent Publication Number: US-2021169448-A1

Title: Intravascular device with capitively-held filling

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. application Ser. No. 15/148,421, filed May 6, 2016, now U.S. Pat. No. 10,925,581, which claims priority to and the benefit of the U.S. Provisional Patent Application No. 62/158,757, filed May 8, 2015, each of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to intravascular devices and, in particular, to catheters that have a pre-filled lumen that minimizes the difficulties associated with flushing the catheter prior to use. 
     BACKGROUND 
     Minimally invasive sensing systems are routinely utilized by medical professionals to evaluate, measure, and diagnose conditions within the human body. As one example, intravascular ultrasound (IVUS) imaging is widely used in interventional cardiology as a diagnostic tool for assessing 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. An IVUS device includes one or more ultrasound transducers arranged at a distal end of an elongate member. The elongate member is passed into the vessel thereby guiding the transducers to the area to be imaged. The transducers emit ultrasonic energy in order to create an image of the vessel of interest. Ultrasonic waves are partially reflected by discontinuities arising from tissue structures (such as the various layers of the vessel wall), red blood cells, and other features of interest. Echoes from the reflected waves are received by the transducer and passed along to an IVUS imaging system. The imaging system processes the received ultrasound echoes to produce a cross-sectional image of the vessel where the device is placed. 
     There are two general types of IVUS devices in use today: rotational and solid-state (also known as synthetic aperture phased array). For a typical rotational IVUS device, a single ultrasound transducer element is located at the tip of a flexible driveshaft 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 device. As the driveshaft rotates, 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. The IVUS imaging system assembles a two dimensional display of the vessel cross-section from a sequence of pulse/acquisition cycles occurring during a single revolution of the transducer. 
     The spinning transducer and driveshaft of a rotational IVUS device are positioned within the sheath to protect the vessel tissue from damage. (In contrast, solid-state IVUS devices have no rotating mechanical element and an array of ultrasound transducers distributed around the circumference of the device can be placed in direct contact with the blood and vessel tissue with minimal risk of vessel trauma.) Ultrasonic signals do not propagate well through air. If the sheath were only filled with air, the IVUS image of the vessel would be distorted and have limited diagnostic value. Thus, a user, such as a physician or other medical professional, always performs a preparation step of filling the space between the sheath and the transducer with saline prior to using the transducer to image the vessel. This step is generally referred to as flushing. Conventionally, intravascular devices have an entry port at the proximal end that is used to inject the saline. Flushing eliminates air bubbles in the space between the sheath and transducer, which can degrade or inhibit image quality. However, performing this preparation step prior to the imaging procedure requires the user&#39;s time and attention. Sometimes, the user needs to re-flush, which interrupts the imaging procedure. Flushing may also be difficult to perform because the gap between the drive cable and the sheath is small. Further, the design options for rotational IVUS devices, particularly at the proximal end, are limited by the need to include components for flushing. 
     Accordingly, there remains a need for intravascular devices, systems, and methods that preserve or improve IVUS image quality while eliminating difficulties associated with flushing. 
     SUMMARY 
     Some embodiments of the present disclosure are directed to an intravascular device having a sealed lumen with a filling (e.g., saline, ultrasound gel, etc.) that facilitates ultrasound data collection. A drive cable, with an intravascular ultrasound (IVUS) transducer attached at a distal end, is positioned within the lumen. The lumen is filled, e.g., during manufacture, with the filling so that the IVUS transducer is surrounded. The filling can improve collection of ultrasound data and generation of high quality images of a patient&#39;s blood vessel. An IVUS imaging procedure is more efficient because a user, such as a physician or other medical professional, does not have to flush the lumen with a fluid before starting the procedure. 
     In one exemplary implementation, an intravascular imaging device is provided. The intravascular imaging device includes a flexible elongate member including a lumen having a proximal portion and a distal portion; a drive cable disposed within the lumen such that an ultrasound transducer coupled to the drive cable is positioned within the distal portion of the lumen; and a filling captively held within at least the distal portion of the lumen and surrounding the ultrasound transducer, the filling facilitating transmission and receipt of ultrasound signals. 
     In one aspect of the present disclosure, the intravascular imaging device further includes a sealing element disposed within the lumen to captively hold the filling within the distal portion of the lumen. In one aspect, the drive cable extends through the sealing element. In one aspect, the drive cable is configured to rotate within the lumen. In one aspect, the sealing element comprises an o-ring or a bearing. In one aspect, the filling is captively held within the proximal and distal portions of the lumen. In one aspect, the filling comprises a solid, a liquid, a polymer, or a gel. In one aspect, the filling comprises saline or ultrasound gel. In one aspect, at least a portion of the flexible elongate member is formed of a material permeable to the filling such that the filling fills at least the distal portion of the lumen and surrounds the ultrasound transducer after the at least a portion of the flexible elongate member is positioned in the filling. 
     In one exemplary implementation, an intravascular imaging device is provided. The intravascular imaging device includes a flexible elongate member including a first lumen having a proximal portion and a distal portion; a sealing element disposed within the first lumen between the proximal and distal portions to isolate the proximal and distal portions; and a second lumen in fluid communication with the distal portion of the first lumen; and a drive cable disposed within the first lumen such that an ultrasound transducer coupled to the drive cable is positioned within the distal portion of the first lumen. 
     In one aspect of the present disclosure, the drive cable is configured to rotate within the first lumen, and wherein the sealing element is positioned relative the drive cable to permit rotation of the drive cable and to hold a filling captive within the distal portion of the first lumen. In one aspect, the second lumen extends from a proximal section of the flexible elongate member to the distal portion of the first lumen. In one aspect, the second lumen extends from a distal section of the flexible elongate member to the distal portion of the first lumen. In one aspect, the second lumen extends from an imaging window of the flexible elongate member to the distal portion of the first lumen. In one aspect, the intravascular imaging device further includes a third lumen in fluid communication with the distal portion of the first lumen. 
     In one exemplary implementation, a method of manufacturing an intravascular imaging device is provided. The method includes acquiring a flexible elongate member including a lumen; inserting a drive cable into the lumen, a rotational ultrasound transducer being coupled to the drive cable; inserting a filling that facilitates transmission and receipt of ultrasonic signals into the lumen such that the filling surrounds rotational ultrasound transducer; and sealing the filling within the lumen. 
     In one aspect of the present disclosure, the inserting a filling includes introducing a solid, a liquid, a polymer, or a gel into a distal portion of the lumen. In one aspect, the inserting a filling includes introducing a solid, a liquid, a polymer, or a gel into proximal and distal portions of the lumen. In one aspect, the sealing the filling includes positioning a sealing element around the drive cable. In one aspect, the sealing element includes an o-ring or a bearing. In one aspect, the inserting a filling includes introducing the filling into a distal portion of the lumen via a further lumen of the flexible elongate member, wherein a sealing element is positioned between the distal and a proximal portion of the lumen to isolate the distal and proximal portions. In one aspect, the sealing the filling includes introducing the filling into the distal portion of the lumen via a check valve disposed within the further lumen or positioning a plug within further lumen. In one aspect, the inserting a filling includes positioning at least a portion of the flexible elongate member in the filling, the at least a portion of the flexible elongate member being formed of a permeable material such that the filling surrounds the ultrasound transducer. 
     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 diagrammatic schematic view of an intravascular imaging system according to an embodiment of the present disclosure. 
         FIG. 2  is a partial cutaway, perspective view of an intravascular device according to an embodiment of the present disclosure. 
         FIG. 3  is a cross-sectional side view of an intravascular device, including a rapid exchange port, showing a filling captively held within proximal and distal portions of a lumen according to an embodiment of the present disclosure. 
         FIG. 4  is a cross-sectional side view of an intravascular device similar to that of  FIG. 3  but including a monorail guidewire lumen in lieu of a rapid exchange port according to an embodiment of the present disclosure. 
         FIG. 5  is a cross-sectional side view of an intravascular device showing a filling captively held within a distal portion of a lumen according to an embodiment of the present disclosure. 
         FIG. 6  is a cross-sectional side view of an intravascular device having first and second lumens according to an embodiment of the present disclosure. 
         FIG. 7  is a cross-sectional side view of an intravascular device similar to that of  FIG. 6  but including a filling captively held within a distal portion of a lumen according to an embodiment of the present disclosure. 
         FIG. 8  is a cross-sectional side view of an intravascular device having first and second lumens according to another embodiment of the present disclosure. 
         FIG. 9  is a cross-sectional side view of an intravascular device having first and second lumens according to another embodiment of the present disclosure. 
         FIG. 10  is a cross-sectional side view of an intravascular device having first, second, and third lumens according to an embodiment of the present disclosure. 
         FIG. 11  is a cross-sectional side view of an intravascular device formed of a permeable material according to an embodiment of the present disclosure. 
         FIG. 12  is a cross-sectional side view of an intravascular device of which a portion is formed of a permeable material according to an embodiment of the present disclosure. 
         FIG. 13  is a cross-sectional side view of an intravascular device of which a portion is formed of a permeable material according to another embodiment of the present disclosure. 
         FIG. 14  is a flow diagram of a method of manufacturing an intravascular device according to an embodiment 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 implementations illustrated in the drawings and specific language will be used to describe them. It will nevertheless be understood that no limitation of the scope of the disclosure is intended. Any alterations and further modifications to the described devices, instruments, methods, and any further application of the principles of the present disclosure are fully contemplated 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 or more implementations may be combined with the features, components, and/or steps described with respect to other implementations of the present disclosure. For simplicity, in some instances the same reference numbers are used throughout the drawings to refer to the same or like parts. 
     Some embodiments of the present disclosure relate generally to intravascular imaging devices, systems and methods having a lumen with a captive filling. The filling, such as saline, ultrasound gel, etc., facilitates transmission of ultrasound signals and reception of ultrasound echoes. A drive cable, with an intravascular ultrasound (IVUS) transducer coupled thereto, is positioned within the lumen such that the filling surrounds at least the transducer. The filling can be disposed within the distal portion of the lumen or within both proximal and distal portions of the lumen. The filling is captively maintained within the lumen by a sealing element (e.g., an o-ring, a bearing, etc.) positioned within the lumen. The sealing element both prevents the filling from leaking and allows the drive cable to rotate. Other embodiments of the present disclosure include a further lumen in fluid communication directly with a distal portion of the lumen in which the IVUS transducer is positioned. Thus, a user need only fill the distal portion of the lumen, rather than the entire lumen. 
     The devices, systems, and methods of the present disclosure provide numerous advantages. Utilizing an intravascular imaging device with a pre-filled imaging core lumen may reduce the set up time and/or total time for an imaging procedure. For example, a user does not need to flush the intravascular device prior to the imaging procedure and/or reflush the device during the procedure. Intravascular devices of the present disclosure can also provide high quality IVUS images because there are no bubbles within the imaging core lumen. The imaging core lumen can be pre-filled with a variety of substances, such as ultrasound gel, which are not conventionally used for flushing. The imaging core lumen can be sealed such that it is less likely for air bubbles to be deposited into the blood stream. A medical services provider, such as a hospital or catheterization lab, can also stock fewer supplies because flushing fluid is no longer needed. Similarly, an intravascular device manufacturer may need not ship accessories associated with flushing with each intravascular device. Manufacturers face fewer design constraints because components for flushing need not be included in the intravascular device. 
     Referring to  FIG. 1 , shown therein is an IVUS imaging system  100  according to an embodiment of the present disclosure. In some embodiments of the present disclosure, the IVUS imaging system  100  is a rotational IVUS imaging system. In that regard, the main components of the rotational IVUS imaging system are the rotational IVUS catheter  102 , a patient interface module (PIM) and/or rotational pullback device  104 , an IVUS console or processing system  106 , and a monitor  108  to display the IVUS images generated by the IVUS console  106 . 
     Referring now to  FIG. 2 , shown therein is a diagrammatic, partial cutaway perspective view of the rotational IVUS catheter  102  according to an embodiment of the present disclosure. In that regard,  FIG. 2  shows additional detail regarding the construction of the rotational IVUS catheter  102 . In many respects, this catheter is similar to traditional rotational IVUS catheters, such as the Revolution® catheter available from Volcano Corporation and described in U.S. Pat. No. 8,104,479, or those disclosed in U.S. Pat. Nos. 5,243,988 and 5,546,948, each of which is hereby incorporated by reference in its entirety. The rotational IVUS catheter  102  includes an imaging core  110  and an outer catheter/sheath assembly  112 . The outer catheter/sheath assembly  112  can be described as a flexible elongate member. The imaging core  110  includes a flexible drive shaft or drive cable  150  that is terminated at the proximal end by a rotational interface  114  providing electrical and mechanical coupling to the PIM and/or rotational pullback device  104  of  FIG. 1 . The distal end of the flexible drive shaft  150  of the imaging core  110  is coupled to a housing  116  containing the ultrasound transducer  152  and, in some instances, associated circuitry. 
     The catheter/sheath assembly  112  includes a hub  118  that supports the rotational interface and provides a bearing surface and a fluid seal between the rotating and non-rotating elements of the catheter assembly. In some embodiments of the present disclosure (as shown in and described with respect to, e.g.,  FIGS. 6 and 7 ), the hub  118  includes a luer lock flush port  120  through which saline or other biocompatible and ultrasound-compatible fluid is injected to flush out the air and fill the inner lumen  154  of the sheath  112  at the time of use of the catheter  102 . The saline or other fluid also acts a lubricant for the rotating driveshaft  150 . The hub  118  is coupled to a telescope  122  that includes nested tubular elements and a sliding fluid seal that permit the catheter/sheath assembly  112  to be lengthened or shortened to facilitate axial movement of the transducer housing  116  within an acoustically transparent window  124  of the distal portion of the catheter  102 . In some embodiments, the window  124  is composed of thin-walled plastic tubing fabricated from material(s) that readily conduct ultrasound waves between the transducer and the vessel tissue with minimal attenuation, reflection, or refraction. A proximal shaft  126  of the catheter/sheath assembly  112  bridges the segment between the telescope  122  and the window  124 , and is composed of a material or composite that provides a lubricious internal lumen and optimum stiffness, but without the need to conduct ultrasound. A distal shaft  156  of the catheter/sheath assembly  112  includes the window  124 . In the embodiment of  FIG. 2 , a distal portion  130  of the flexible elongate member  112  includes a rapid-exchange port  132  configured to receive a guidewire utilized to guide advancement of the catheter  102  to a desired location within a patient. 
     Referring now to  FIG. 3 , shown therein is a cross-sectional side view of the rotational IVUS catheter  102 . Generally, the catheter  102  includes the sheath or flexible elongate member  112 , the drive cable  150  positioned with the lumen  154  of the flexible elongate member  112 , the proximal shaft  126 , the distal shaft  156 , the acoustically transparent window  124 , a sealing element  158 , and a filling  160 .  FIG. 3  includes various components that are similar to those described with reference to other Figures in this disclosure, and description of the components will not be repeated here. 
     The lumen  154  can be described as an imaging core lumen because the imaging core  110  is disposed therein. The lumen  154  can also be described as a central lumen because, as shown in the  FIG. 3 , the lumen  154  is aligned with a central or longitudinal axis LA of the catheter  102 . In other embodiments, the lumen  154  can be offset from the longitudinal axis LA. The lumen  154  extends along a majority of the working length (e.g., the length that is insertable into a patient&#39;s vasculature) of the flexible elongate member  112 . In that regard, the working length of the flexible elongate member  112  and/or the length of the lumen  154  can be between approximately 50 cm and approximately 200 cm, between approximately 75 cm and approximately 200 cm, and between approximately 100 cm and approximately 200 cm, including values such as 90 cm, 135 cm, 150 cm, and/or other suitable values both larger and smaller. The outer diameter  168  of the flexible elongate member  112  can be any suitable value between approximately 0.020 in and approximately 0.125 in, between approximately 0.025 in and approximately 0.110 in, and between approximately 0.030 in and approximately 0.075 in, and/or other values both larger and smaller. The diameter of the lumen  170  can be any suitable value between approximately 0.010 in and approximately 0.10, between approximately 0.010 in and approximately 0.075 in, between approximately 0.010 in and 0.050 in, and/or other values both larger and smaller. In that regard, the outer diameter  168  of the proximal shaft  126  can be larger or smaller than the outer diameter of the distal shaft  156  and vice versa. The lumen  154  of the flexible elongate member  112  has a proximal portion  162  and a distal portion  164 . In that regard, the diameter  170  of the proximal portion  162  of the lumen  154  can be larger or smaller than the diameter of the distal portion  164  and vice versa. 
     The drive cable  150  is configured to spin or rotate about the longitudinal axis LA of the catheter  102 . The drive cable  150  is disposed within the lumen  154  such that the transducer  152  is positioned within the distal portion  164  of the lumen  154 . The transducer  152  is also positioned within the length  166  of the acoustically transparent window  124 . In that regard, the length  166  of the window  124  can be between approximately 1 cm and approximately 30 cm, between approximately 1 cm and approximately 20 cm, and between approximately 1 cm and approximately 15 cm, including values such as 10 cm, 12 cm, 15 cm, and/or other suitable values both larger and smaller. The length  166  of the window may be greater than or equal to the length of a pullback (e.g., during the IVUS imaging procedure). 
     The filling  160  is disposed within the lumen  154 . For example, the filling  160  fills the lumen  154  such that the transducer  152 , which is also disposed within the lumen  154 , is surrounded by the filling  160 . The filling  160  facilitates transmission of ultrasound signals from the transducer  152  and receipt of ultrasound echoes at the transducer. For example, the refractive index of the filling  160  can be approximately equal to the refractive index of blood. As described herein, the window  124  may be formed of a material that minimizes unintentional attenuation, reflection, or refraction. Accordingly, waves associated with ultrasound signals pass through the transition between the filling  160 , the window  124 , and blood within the patient&#39;s vasculature without being bent or curved in a manner that degrades the IVUS image. In some embodiments, the acoustical characteristics of the filling  160  may enhance the ultrasound signal, such as by focusing and/or otherwise modifying the waves associated with the ultrasound signals to improve the IVUS image. 
     The filling  160  can be biocompatible and/or ultrasound compatible. In various embodiments, the filling  160  can be a solid, a liquid, a polymer, a gel, other suitable material(s), and/or combinations thereof. For example, the filling  160  can be a saline, ultrasound gel, etc. In some embodiments, the filling is a solid, such as a powder, or a polymer that has a melting point similar to that of normal human body temperature. In such embodiments, the filling may transition from a solid to a liquid or from a crystalline/semi-crystalline phase to an amorphous solid phase when the catheter  102  is inserted into the patient&#39;s vasculature. The filling  160  may also provide lubrication for drive cable  150  as it rotates within the lumen  154 . 
     In the embodiment of  FIG. 3 , the filling  160  is disposed within both the proximal and distal portions  162 , 164  of the lumen  154 . In that regard, the filling  160  may occupy a length  172  similar to that of the total length of the lumen  154  and/or the working distance of the flexible elongate member  112 . Thus, the length  172  of the lumen  154  that is filled with the filling  160  can be between approximately 50 cm and approximately 200 cm, between approximately 75 cm and approximately 200 cm, and between approximately 100 cm and approximately 200 cm, including values such as 90 cm, 135 cm, 150 cm, and/or other suitable values both larger and smaller. In some embodiments, the filling  160  may occupy the lumen  154  from the telescope  122  (e.g., at a proximal end of the lumen  154 ) and extend distally to a distal end  176  of the lumen  154 . In other embodiments, the lumen  154  includes an unfilled section  174  that is proximate to the telescope  122 . In such embodiments, the filling  160  does not occupy a proximal-most portion of the lumen  154 . Thus, the filling  160  may be disposed within some parts (e.g., more distal parts) of the proximal portion  162  and not others (e.g., more proximal parts). In some embodiments, the unfilled section  174  may be the telescope  122  and/or the hub  118 . The entire length of the drive cable  150  or portions thereof extending through the unfilled section  174  may be coated with a lubricant to facilitate smooth and uniform rotation of drive cable  150 . 
     The filling  160  is captively held within the lumen  154 . For example, during manufacture of the catheter  102 , the filling  160  can be inserted into and sealed within the lumen  154 . Thus, the manufacturer or distributer can ship the catheter  102  to a medical services provider, such as a hospital or other catheterization lab, with the filling  160  disposed within the lumen  154 . In the illustrated embodiment, the sealing element  158  is disposed within the proximal portion  162  of the lumen  154 . The sealing element  158  can be positioned at any point along length of the proximal portion  162  of the lumen  154 . The sealing element  158  captively holds the filling  160  within the proximal and distal portions  162 ,  164  of the lumen  154 . The sealing element  158  is configured to seal the filling  160  within the lumen  154  while simultaneously allowing the drive cable  150  to rotate. In that regard, the sealing element  158  may be circumferentially disposed around the drive cable  150  such that the drive cable extends through the sealing element. Within the drive cable  150  extending through the sealing element  158 , the filling  160  is sealed within the lumen  154 . The sealing element  158  may be in contact with the drive cable  150  and a wall  178  of the lumen  154 . In some embodiments, the sealing element  158  may be annularly-shaped, ring-shaped, and/or donut-shaped. An inner surface of the sealing element  158  (e.g. the surface of the sealing element in contact with the drive cable  150 ) and/or an outer surface of the drive cable in contact with the sealing may be lubricated to facilitate smooth and uniform rotation of the drive cable. In various embodiments, the sealing element  158  may be an o-ring, a bearing, and/or other suitable components. Generally, the sealing element  158  may be formed of any suitable material including a metal, such as stainless steel, chrome steel, carbon alloy, etc., or a plastic, such as a polymer or elastomer, etc. As described herein, the hub  118  and/or the telescope  112  may include sealing and/or bearing component(s). In some embodiments, the sealing element  158  within the lumen  154  is provided in addition to any other sealing and/or bearing component(s) of the catheter  102 . In such embodiments, the sealing element  158  is positioned distally of the proximal end of the flexible elongate member  112  (e.g., between the unfilled section  174  and the filled section  175 ). In other embodiments, the sealing element  158  is the sealing and/or bearing component of the hub  118  and/or the telescope  112 . 
     The user can use the catheter  102  in an imaging procedure without flushing the lumen  154  (e.g., filing the lumen with a fluid) because the proximal and distal portions  162 ,  164  of the lumen  154  already contain the filling  160 . In that regard, the user can remove the catheter  102  from its sterile packaging, connect the hub  118  to the PIM and/or rotational pullback device  104  ( FIG. 1 ), insert the catheter  102  into the patient&#39;s vasculature, and collect ultrasound data, e.g., based on a workflow generated by the console  106  and/or displayed on the monitor  108 . High quality IVUS images of the vasculature, based on the collected ultrasound data, are generated by the console  106  and displayed on the monitor  108 . According to an aspect of the present disclosure, these and other steps may be performed without flushing the lumen  154  to remove air bubbles. 
     Referring now to  FIG. 4 , shown therein is a cross-sectional side view of a rotational IVUS catheter  402 .  FIG. 4  includes various components that are similar to those described with reference to other Figures in this disclosure, and description of the components will not be repeated here. In particular, the catheter  402  is similar to the catheter  102  ( FIGS. 2 and 3 ) except that the catheter  402  includes a monorail lumen  180  that receives a guide wire  182  (as opposed to the rapid exchange port  132  illustrated in  FIGS. 2 and 3 ). In that regard, the monorail lumen  180  is disposed parallel to the longitudinal axis LA of the catheter  102 . For example, the monorail lumen  180  may be coupled to the flexible elongate member  112 . As another example, the monorail lumen  180  may be integrally formed with the flexible elongate member  112 . As shown in  FIGS. 2-4 , the teachings of the present disclosure may be implemented in intravascular devices with rapid exchange or monorail configurations. 
     Referring now to  FIG. 5 , shown therein is a cross-sectional side view of a rotational IVUS catheter  502 .  FIG. 5  includes various components that are similar to those described with reference to other Figures in this disclosure, and description of the components will not be repeated here. In particular, the catheter  502  is similar to the catheter  102  ( FIG. 3 ) except that filling  160  in the catheter  502  is captively held within the distal portion  164  of the lumen  154 . That is, the filled section  175  of the lumen  154  includes the distal portion  164 . The unfilled section  174  of the lumen  154  includes portions of the lumen  154  that are proximal to the distal portion  164 . Because the transducer  152 , coupled to the drive cable  150 , is also positioned within the distal portion  164  of the lumen  154 , the filling  160  surrounds the transducer  152  and facilitates the transmission and reception of ultrasound signals. In the illustrated embodiment, the length  172  of the lumen  154  that is filled with the filling  160  is approximately equal to the length  166  of the acoustically transparent window  124 . In other embodiments, the length  172  may be larger or smaller than the length  166 . The sealing element  158  is positioned within the distal portion  164  of the lumen  154  to seal the filling  160  while allowing the drive cable  150  to rotate. The sealing element  158  can be positioned at any point along the length of the distal portion  164  of the lumen  154  while the transducer  152  is surrounded by the filling  160 . The length  172  of the portion of the lumen  154  filled with the filling  160  may be greater than or equal to the length of a pullback (e.g., during the IVUS imaging procedure). The sealing element  158  can positioned between the proximal portion  162  and the distal portion  164  of the lumen  154 . As described herein, the entire length of the drive cable  150  or portions thereof extending through the unfilled section  174  and/or the sealing element  158  may be coated with a lubricant to facilitate smooth and uniform rotation of drive cable  150 . The user can use the catheter  502  in an imaging procedure without flushing the lumen  154  (e.g., filing the lumen with a fluid) because the distal portion  164  of the lumen  154  already contains the filling  160 . 
     Referring now to  FIG. 6 , shown therein is a cross-sectional side view of a rotational IVUS catheter  602 .  FIG. 6  includes various components that are similar to those described with reference to other Figures in this disclosure, and description of the components will not be repeated here. The sealing element  158  is disposed within the lumen  154  between the proximal portion  162  and the distal portion  164 . With the drive cable  150  extending through the sealing element  158 , the proximal and distal portions  162 ,  164  are fluidly isolated or separated from one another. The drive cable  150  is configured to rotate within the lumen  154 . 
     The catheter  602  includes a lumen  184  in fluid communication with the distal portion  164  of the lumen  154 . The lumen  184  is disposed within a side wall of the flexible elongate member  102 . In the illustrated embodiment, the lumen  184  extends from the proximal portion of flexible elongate member  112  to the distal portion  164 . In use, a user may introduce a fluid or other filling that facilitates transmission and receipt of ultrasound signals into the lumen  184  to fill the distal portion  164  of the lumen  154 . For example, the lumen  184  can be in fluid communication with the flush port  120  ( FIG. 2 ). The user may inject fluid or other filling into the flush port  120 , and the fluid may travel through the lumen  184  into the distal portion  164  of the lumen  154 . The transducer  152  is surrounded by the fluid when the distal portion  164  of the lumen  154  is filled with the fluid. In the illustrated embodiment, the proximal portion  162  of the lumen  154  does not include a filling. As described herein, the entire length of the drive cable  150  or portions thereof extending through the portion  162  (e.g., the unfilled section) of the lumen  154  and/or the sealing element  158  may be coated with a lubricant to facilitate smooth and uniform rotation of drive cable  150 . In different embodiments, the size of the lumen  184  may vary such that a diameter of the lumen  184  is, for example, smaller than, the same size as, or larger than the diameter of the lumen  154 . 
     The sealing element  158  is positioned relative the drive cable  150  to permit rotation of the drive cable and to hold the fluid or other filling captive within the distal portion  164  of the lumen  154 . The fluid may also be held captive within the distal portion  164  by a sealing element  186  disposed within the lumen  184 . In some embodiments, the sealing element  186  is a check valve that allows fluid to flow into the distal portion  164  but does not permit fluid to flow out of the distal portion. In other embodiments, the sealing element  186  is a plug that is inserted into the lumen  184  to prevent the fluid within the distal portion  164  and/or the lumen  184  from leaking. While the sealing element  186  is positioned adjacent to the proximal portion  164  in the illustrated embodiment, it is understood that the sealing element  186  may be positioned at any point along the length of the lumen  184  (e.g., at a proximal portion of the flexible elongate member  112 , at or near the flush port  120 , etc.). In use, air bubbles that may surround the transducer  152  can be eliminated by filling the distal portion  164  (as opposed to the entire length of the lumen  164 ) with fluid. Filling only the distal portion  164  (and not the entire length of the lumen  154 ) may allow for faster and more efficient setup for the IVUS imaging procedure. 
     Referring now to  FIG. 7 , shown therein is a cross-sectional side view of a rotational IVUS catheter  702 .  FIG. 7  includes various components that are similar to those described with reference to other Figures in this disclosure, and description of the components will not be repeated here. In particular, the catheter  702  is similar to the catheter  602  ( FIG. 6 ) except that the filling  160  is captively held within the proximal portion  162  of the lumen  154  (as opposed to the proximal portion  162  not including the filling). In that regard, the sealing element  158  seals the filling  160  within the proximal portion  162 . The length  172  of the lumen  154  that is filled with the filling  160  may be approximately equal to a total length of the flexible elongate member  112  less the length  166  of the window  124  and the length of any portions of the catheter  702  distal to the window  124 . The filling  160  provides lubrication to facilitate smooth and uniform rotation of the drive cable  150  within the lumen  154 . In the illustrated embodiment, the filling  160  can extends proximally to and occupies a proximal-most portion of the lumen  154 . At the proximal portion of the catheter  102 , the hub  118  and/or the telescope  122  can fluidly seal the filling within the lumen  154 . In other embodiments, a further sealing element is provided near the proximal-most portion of the lumen  154  (e.g., as shown in  FIGS. 3 and 4 ) such at the filling  160  is sealed between the two sealing elements. In such embodiments, the filling  150  does not occupy the proximal-most portion of the lumen  154 . 
     Referring now to  FIG. 8 , shown therein is a cross-sectional side view of a rotational IVUS catheter  802 .  FIG. 8  includes various components that are similar to those described with reference to other Figures in this disclosure, and description of the components will not be repeated here. In particular, the catheter  802  is similar to the catheter  602  ( FIG. 6 ) except that a lumen  188  extends from the distal portion  130  of the flexible elongate member  112  to the distal portion  164  of the lumen  154 . In use, a user may introduce a fluid or other filling that facilitates transmission and receipt of ultrasound signals into the lumen  188  to fill the distal portion  164  of the lumen  154 . For example, the user may inject a fluid into the lumen  188  and the distal portion  164 . As another example, the user may immerse or soak at least the distal portion  130  of the flexible elongate member  112  in the fluid. The fluid may flow into the lumen  188  and the distal portion  164  by force of gravity or via capillary action, for example. The transducer  152  is surrounded by the fluid when the distal portion  164  of the lumen  154  is filled with the fluid. The sealing element  186  can be disposed at any point along the length of the lumen  188 , including proximate to an outer surface of the catheter  102 , as shown in the illustrated embodiment. The sealing element  186 , such as a plug or check valve, along with the sealing element  158  captively holds fluid within the distal portion  164  and/or the lumen  188 . 
     Referring now to  FIG. 9 , shown therein is a cross-sectional side view of a rotational IVUS catheter  902 .  FIG. 9  includes various components that are similar to those described with reference to other Figures in this disclosure, and description of the components will not be repeated here. In particular, the catheter  902  is similar to the catheter  602  ( FIG. 6 ) except that a lumen  190  extends from the acoustically transparent window  124  to the distal portion  164  of the lumen  154 . In use, a user may introduce a fluid or other filling that facilitates transmission and receipt of ultrasound signals into the lumen  190  to fill the distal portion  164  of the lumen  154 . For example, the user may inject a fluid into the lumen  190  and the distal portion  164 . As another example, the user may immerse or soak at least the distal portion  130  of the flexible elongate member  112  in the fluid. The fluid may flow into the lumen  190  and the distal portion  164  by force of gravity or via capillary action, for example. The transducer  152  is surrounded by the fluid when the distal portion  164  of the lumen  154  is filled with the fluid. The sealing element  186  can be disposed at any point along the length of the lumen  190 , including proximate to an outer surface of the catheter  102 , as shown in the illustrated embodiment. The sealing element  186 , such as a plug or check valve, along with the sealing element  158  captively holds fluid within the distal portion  164  and/or the lumen  190 . 
     Referring now to  FIG. 10 , shown therein is a cross-sectional side view of a rotational IVUS catheter  1002 .  FIG. 10  includes various components that are similar to those described with reference to other Figures in this disclosure, and description of the components will not be repeated here. In particular, the catheter  1002  is similar to the catheter  602  ( FIG. 6 ) except that the lumen  184  and the lumen  188  are in fluid communication with the distal portion  164  of the lumen  154 . In use, a user may introduce a fluid or other filling that facilitates transmission and receipt of ultrasound signals into the lumen  184  to fill the distal portion  164  of the lumen  154  by providing suction at the lumen  188  (or vice versa). In that regard, the proximal portion and/or the distal portion  130  of the flexible elongate member  112  may be immersed or soaked in the fluid. By providing suction at either one of the lumens  184 ,  188 , the fluid can travel through the other one of the lumens  184 ,  188  and into the distal portion  164  of the lumen  154 . The transducer  152  is surrounded by the fluid when the distal portion  164  of the lumen  154  is filled with the fluid. The sealing elements  186  can be disposed at any point along the length of the lumens  184 ,  188 , including proximate to an outer surface of the catheter  102 , as shown in the illustrated embodiment. The sealing elements  186 , such as plugs or check valves, along with the sealing element  158 , captively hold fluid within the distal portion  164 , the lumen  184 , and/or the lumen  186 . 
     Referring now to  FIG. 11 , shown therein is a cross-sectional side view of a rotational IVUS catheter  1102 .  FIG. 11  includes various components that are similar to those described with reference to other Figures in this disclosure, and description of the components will not be repeated here. In particular, the catheter  1102  is similar to the catheter  102  ( FIGS. 3 and 4 ) except that the flexible elongate member  112  is formed of a material that is permeable to a fluid or other filling that facilitates transmission and receipt of ultrasound signals. In use, a user may introduce a fluid or other filling into the distal portion  164  of the lumen  154  by immersing or soaking all or a portion of the flexible elongate member  112  in the fluid. In some embodiments, the material forming the flexible elongate member  112  may be configured to allow fluid to flow into the material (and into the lumen  154 ) and restrict the fluid flow out of the material. The transducer  152  is surrounded by the fluid when the distal portion  164  of the lumen  154  is filled with the fluid. At the proximal portion of the catheter  102 , the hub  118  and/or the telescope  122  can fluidly seal the filling within the lumen  154 . In other embodiments, a further sealing element is provided near the proximal-most portion of the lumen  154  (e.g., as shown in  FIGS. 3 and 4 ). In some embodiments, the material forming the flexible elongate member  112  may be acoustically transparent such that it readily conducts ultrasound waves between the transducer  152  and the vessel tissue with minimal attenuation, reflection, or refraction. By filling the lumen  154  with the fluid by soaking or immersing the flexible elongate member  112 , the catheter  1102  need not include components related to conventional flushing (e.g., the flush port  120  of  FIG. 2 ). This can allow the manufacturer greater flexibility in designing the catheter  1102 . 
     Referring now to  FIG. 1202 , shown therein is a cross-sectional side view of a rotational IVUS catheter  1202 .  FIG. 12  includes various components that are similar to those described with reference to other Figures in this disclosure, and description of the components will not be repeated here. In particular, the catheter  1202  is similar to the catheter  1102  ( FIG. 11 ) except that only a portion of the flexible elongate member  112  is formed the material that is permeable to a fluid or other filling that facilitates transmission and receipt of ultrasound signals. In the illustrated embodiment, the portion of the flexible elongate member  112  that is aligned with the distal portion  164  of the lumen  154  is formed of the permeable material. In use, a user may introduce a fluid or other filling into the distal portion  164  of the lumen  154  by immersing or soaking at least the portion of the flexible elongate member  112  formed of the permeable material in the fluid. The transducer  152  is surrounded by the fluid when the distal portion  164  of the lumen  154  is filled with the fluid. The sealing element  158 , along with the one-way permeable material, captively holds the fluid within distal portion  164  while allowing the drive cable  150  to rotate within the lumen  154 . In the illustrated embodiment, the permeable material forms the acoustically transparent window  124 . 
     Referring now to  FIG. 13 , shown therein is a cross-sectional side view of a rotational IVUS catheter  1302 .  FIG. 13  includes various components that are similar to those described with reference to other Figures in this disclosure, and description of the components will not be repeated here. In particular, the catheter  1302  is similar to the catheter  1202  ( FIG. 12 ) except that a section  192  of the flexible elongate member  112  is formed the material that is permeable to a fluid or other filling that facilitates transmission and receipt of ultrasound signals. In the illustrated embodiment, the section  192  is at least partially aligned the proximal portion  162  of the lumen  154 . In different embodiments, the section  192  may have varying lengths such that it is partially or fully aligned with the proximal portion  162  of the lumen  154 . In use, a user may introduce a fluid or other filling into the distal portion  164  of the lumen  154  by immersing or soaking at least the section  192  of the flexible elongate member  112  in the fluid. The transducer  152  is surrounded by the fluid when the distal portion  164  of the lumen  154  is filled with the fluid. The sealing element  158 , along with the one-way permeable material, captively holds the fluid within distal portion  164  while allowing the drive cable  150  to rotate within the lumen  154 . As described herein, the window  124  can be composed of thin-walled plastic tubing fabricated from material(s) that readily conduct ultrasound waves between the transducer and the vessel tissue with minimal attenuation, reflection, or refraction. 
       FIG. 14  illustrates a flowchart of a method  1400  of a manufacturing an intravascular device. As illustrated, the method  1400  includes a number of enumerated steps, but implementations of the method  1400  may include additional steps before, after, and in between the enumerated steps. In some implementations, one or more of the enumerated steps may be omitted or performed in a different order. The steps of the method  1400  may be performed by an intravascular device manufacturer, for example. 
     At step  1410 , the method  1400  includes acquiring a flexible elongate member having a lumen. In some embodiments, the flexible elongate member can be polymer tube (which may be coil-embedded or not). In that regard, the flexible elongate member can have different sections formed of different materials. For example, a distal section of the flexible elongate member may be acoustically transparent while a proximal section is not. Acquiring the flexible elongate member can include forming or manufacturing the flexible elongate member or procuring a flexible elongate member having the desired characteristics (e.g., length, flexibility, etc.). 
     At step  1420 , the method  1400  includes inserting a drive cable into the lumen of the flexible elongate member. A rotational ultrasound transducer can be coupled to the distal end of the drive cable. Accordingly, in some embodiments, the method  1400  can include coupling the transducer to the drive cable. The flexible elongate member can include proximal opening through which the lumen is accessed. In the illustrated example of  FIG. 3 , for example, the distal end of the lumen of the flexible elongate member is sealed. Inserting the drive cable into the lumen can include threading the drive cable into the flexible elongate member, starting at the proximal opening and continuing along the length of the lumen. Inserting the drive cable into the lumen can include pulling the flexible elongate member onto the drive cable, starting at the proximal opening and continuing along the length of the lumen. 
     At step  1430 , the method  1400  includes inserting a filling that facilitates transmission and receipt of ultrasonic signals into the lumen such that the filling surrounds rotational ultrasound transducer. In that regard, the filling, such as a solid, a liquid, a polymer, a gel, other suitable materials, and/or combinations thereof may be introduced into a proximal portion and/or a distal portion of the lumen. Inserting the filling can include injecting, pouring, and/or otherwise placing the filling within the lumen. The lumen can be accessed by the proximal opening of the flexible elongate member. In some embodiments, the order of steps  1420  and  1430  may be reversed. For example, the lumen of the flexible elongate member may be filled with the filling before the drive cable is inserted. The lumen may be filled to capacity and as the drive cable is inserted, the excess filling may be removed from the lumen. In some embodiments, the steps  1420  and  1430  may be combined. For example, all or a portion of the drive cable maybe coated, e.g., with a gel or a polymer and then inserted into the lumen of the flexible elongate member. In various embodiments, additional filling may be inserted into lumen to ensure that no air bubbles are within the distal portion of the lumen where the transducer is located. 
     In embodiments in which the flexible elongate member is wholly or partially formed of a material permeable to the filling, the inserting a filling includes positioning at least a portion (e.g., the permeable portion) of the flexible elongate member in the filling. The filling can permeate into the lumen such the filling surrounds the ultrasound transducer. In embodiments in which the flexible elongate member includes a further lumen in fluid communication with a distal portion of the lumen (e.g., where the ultrasound transducer is located), inserting the filling can include introducing the filling into the distal portion of the lumen via the further lumen. Introducing the filling into the distal portion via the further lumen can include injecting, pouring, and/or otherwise placing the filling within the distal portion via the further lumen. In some embodiments, at least a portion (e.g. the portion containing an opening of the further lumen) of the flexible elongate member may be soaked or immersed in the filling such that filling enters the further lumen by force of gravity or via capillary action. In some embodiments, another lumen in fluid communication with the distal portion of the lumen may be provided such that suction can be applied to one of the further lumen or the other lumen to draw the fluid into the distal portion via the one of the further lumen or the other lumen. A sealing element can be positioned between the distal and proximal portions of the lumen to isolate the distal and proximal portions. In that regard, the method  1400  can further include inserting the sealing element between the proximal and distal portions of the lumen. 
     At step  1440 , the method  1400  includes sealing the filling within the lumen. For example, a mechanical component may be positioned within the lumen to prevent the filling from inadvertently being evacuated or leaking from the lumen (e.g., the distal portion of the lumen). If the filling were to leak, the ultrasound transducer may not be completely surrounded by the filling (e.g., circumferentially around the transducer and the entire axial distance between the transducer and the wall of the lumen), which may degrade IVUS image quality. In some embodiments, the sealing the filling can include positioning a sealing element around the drive cable. In that regard, the steps  1420  and  1440  can be combined in some embodiments. For example, the drive cable can be threaded through the sealing element prior to the drive cable being inserted into the flexible elongate member. Thus, as the drive cable is inserted into the lumen, the sealing element is also inserted into the lumen, surrounding the drive cable. In other embodiments, such as those with a further lumen in fluid communication with the distal portion of the lumen, sealing the filling can include introducing the filling into the distal portion via a check valve. The check valve can be disposed within the further lumen. The check valve seals the filling by permitting flow only into to the distal portion of the lumen. In still other embodiments, sealing the filling can include positioning a plug within further lumen to prevent backflow of the filing. 
     The method  1400  can include other suitable steps in different embodiments. For example, the method  1400  can include inserting the drive cable through a telescoping section at a proximal end of the flexible elongate member, inserting the drive cable through a hub at a proximal end of the flexible elongate member, coupling the flexible elongate member to the telescoping section and the hub, electrically coupling the transducer via wire(s), and/or other suitable steps to assemble the intravascular device. 
     While the present disclosure specifically refers to a catheter, it is understood that the features described herein may be implemented in guide wire, guide catheters, and/or other intravascular devices. Similarly, while the features of the present disclosure may be implemented with imaging modalities other than IVUS, include optical coherence tomography (OCT). As such, the housing  116  ( FIG. 2 ) of an OCT catheter can include optical fiber(s) and optical imaging element(s) (e.g., mirrors, prisms, scanners, etc.). Aspects of the present disclosure may be implemented in intravascular devices adapted for use in the coronary or peripheral vasculature. 
     Persons skilled in the art will also 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.