Abstract:
A catheter assembly for an intravascular ultrasound system includes a catheter and an imaging core. The catheter has a longitudinal length, a distal end, and a proximal end. The catheter includes a sealable lumen extending along the longitudinal length of the catheter from the proximal end to the distal end, and a movable plunger or a movable seal in fluid communication with the lumen. The movable plunger or the movable seal provides a gas-tight seal. The movable plunger or the movable seal is configured and arranged for adjusting to changes in volume of the lumen when the lumen is filled with an acoustically-favorable medium and sealed. The imaging core is configured and arranged for inserting into the sealable lumen and for coupling to a control module.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/045,904, filed Apr. 17, 2008, the entire contents of which is incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention is directed to the area of intravascular ultrasound imaging systems and methods of making and using the systems. The present invention is also directed to an intravascular ultrasound imaging system with a catheter having a sealed lumen filled with an acoustically-favorable medium, as well as methods of making and using the intravascular ultrasound systems. 
     BACKGROUND 
     Intravascular ultrasound (“IVUS”) imaging systems have proven diagnostic capabilities for a variety of diseases and disorders. For example, IVUS imaging systems have been used as an imaging modality for diagnosing blocked blood vessels and providing information to aid medical practitioners in selecting and placing stents and other devices to restore or increase blood flow. IVUS imaging systems have been used to diagnose atheromatous plaque build-up at particular locations within blood vessels. IVUS imaging systems can be used to determine the existence of an intravascular obstruction or stenosis, as well as the nature and degree of the obstruction or stenosis. IVUS imaging systems can be used to visualize segments of a vascular system that may be difficult to visualize using other intravascular imaging techniques, such as angiography, due to, for example, movement (e.g., a beating heart) or obstruction by one or more structures (e.g., one or more blood vessels not desired to be imaged). IVUS imaging systems can be used to monitor or assess ongoing intravascular treatments, such as angiography and stent placement in real (or almost real) time. Moreover, IVUS imaging systems can be used to monitor one or more heart chambers. 
     IVUS imaging systems have been developed to provide a diagnostic tool for visualizing a variety is diseases or disorders. An IVUS imaging system can include a control module (with a pulse generator, an image processor, and a monitor), a catheter, and one or more transducers disposed in the catheter. The transducer-containing catheter can be positioned in a lumen or cavity within, or in proximity to, a region to be imaged, such as a blood vessel wall or patient tissue in proximity to a blood vessel wall. The pulse generator in the control module generates electrical pulses that are delivered to the one or more transducers and transformed to acoustic pulses that are transmitted through patient tissue. Reflected pulses of the transmitted acoustic pulses are absorbed by the one or more transducers and transformed to electric pulses. The transformed electric pulses are delivered to the image processor and converted to an image displayable on the monitor. 
     BRIEF SUMMARY 
     In one embodiment, a catheter assembly for an intravascular ultrasound system includes a catheter and an imaging core. The catheter has a longitudinal length, a distal end, and a proximal end. The catheter includes a sealable lumen extending along the longitudinal length of the catheter from the proximal end to the distal end, and a movable plunger or a movable seal in fluid communication with the lumen. The movable plunger or the movable seal provides a gas-tight seal. The movable plunger or the movable seal is configured and arranged for adjusting to changes in volume of the lumen when the lumen is filled with an acoustically-favorable medium and sealed. The imaging core is configured and arranged for inserting into the sealable lumen and for coupling to a control module. 
     In another embodiment, an intravascular ultrasound imaging system includes a catheter, an imaging core, and a control module. The catheter has a longitudinal length, a distal end, and a proximal end. The catheter includes a sealable lumen extending along the longitudinal length of the catheter from the proximal end to the distal end, and a movable plunger or a movable seal in fluid communication with the lumen. The movable plunger or the movable seal provides an acoustically-favorable-medium-tight seal. The movable plunger or the movable seal is configured and arranged for adjusting to changes in volume of the lumen to maintain an acoustically-favorable-medium-filled environment within the lumen when the lumen is filled with an acoustically-favorable medium and sealed. The imaging core is disposed within the lumen. The control module is coupled to the imaging core. The control module includes a pulse generator and a processor. The pulse generator and the processor are both electrically coupled to the imaging core. The pulse generator is configured and arranged for providing electric pulses to the imaging core. The processor is configured and arranged for processing received electrical pulses from the imaging core to form at least one image. 
     In yet another embodiment, a method for forming a catheter of an intravascular ultrasound imaging system includes degassing a sealable lumen of the catheter, filling the sealable lumen with an acoustically-favorable medium through at least one flush port, and sealing the lumen using a movable plunger or a movable seal in fluid communication with the sealable lumen. The catheter includes at least one transducer mounted to a driveshaft extending along at least a portion of a longitudinal length of the sealable lumen. The movable plunger or the movable seal is configured and arranged to adjust to changes in volume of the lumen to maintain the substantially degassed environment in the lumen. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following drawings. In the drawings, like reference numerals refer to like parts throughout the various figures unless otherwise specified. 
       For a better understanding of the present invention, reference will be made to the following Detailed Description, which is to be read in association with the accompanying drawings, wherein: 
         FIG. 1  is a schematic view of one embodiment of an intravascular ultrasound imaging system, according to the invention; 
         FIG. 2  is a schematic side view of one embodiment of a catheter of an intravascular ultrasound imaging system, according to the invention; 
         FIG. 3  is a schematic perspective view of one embodiment of a distal end of an elongated member of the catheter shown in  FIG. 2  with an imaging core disposed in a lumen in the distal end of the elongated member, according to the invention; 
         FIG. 4  is a schematic longitudinal cross-sectional view of one embodiment of a hub of a catheter, the hub including a movable plunger disposed in a main flush port, according to the invention; 
         FIG. 5A  is a schematic longitudinal cross-sectional view of one embodiment of a hub with a movable seal or a movable plunger disposed in a main flush port and an open auxiliary input port, according to the invention; and 
         FIG. 5B  is a schematic longitudinal cross-sectional view of another embodiment of a hub with a movable seal or a movable plunger disposed in a main flush port and a seal disposed in an auxiliary input port, according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is directed to the area of intravascular ultrasound imaging systems and methods of making and using the systems. The present invention is also directed to an intravascular ultrasound imaging system with a catheter having a sealed lumen filled with an acoustically-favorable medium, as well as methods of making and using the catheter and intravascular ultrasound system. 
     Suitable intravascular ultrasound (“IVUS”) imaging systems include, but are not limited to, one or more transducers disposed on a distal end of a catheter configured and arranged for percutaneous insertion into a patient. Examples of IVUS imaging systems with catheters are found in, for example, U.S. Pat. Nos. 7,306,561; and 6,945,938; as well as U.S. Patent Application Publication Nos. 20060253028; 20070016054; 20070038111; 20060173350; and 20060100522, all of which are incorporated by reference. 
       FIG. 1  illustrates schematically one embodiment of an IVUS imaging system  100 . The IVUS imaging system  100  includes a catheter  102  that is coupleable to a control module  104 . The control module  104  may include, for example, a processor  106 , a pulse generator  108 , a motor  110 , and one or more displays  112 . In at least some embodiments, the pulse generator  108  forms electric pulses that may be input to one or more transducers ( 312  in  FIG. 3 ) disposed in the catheter  102 . In at least some embodiments, mechanical energy from the motor  110  may be used to drive an imaging core ( 306  in  FIG. 3 ) disposed in the catheter  102 . In at least some embodiments, electric pulses transmitted from the one or more transducers ( 312  in  FIG. 3 ) may be input to the processor  106  for processing. In at least some embodiments, the processed electric pulses from the one or more transducers ( 312  in  FIG. 3 ) may be displayed as one or more images on the one or more displays  112 . In at least some embodiments, the processor  106  may also be used to control the functioning of one or more of the other components of the control module  104 . For example, the processor  106  may be used to control at least one of the frequency or duration of the electrical pulses transmitted from the pulse generator  108 , the rotation rate of the imaging core ( 306  in  FIG. 3 ) by the motor  110 , the velocity or length of the pullback of the imaging core ( 306  in  FIG. 3 ) by the motor  110 , or one or more properties of one or more images formed on the one or more displays  112 . 
       FIG. 2  is a schematic side view of one embodiment of the catheter  102  of the IVUS imaging system ( 100  in  FIG. 1 ). The catheter  102  includes an elongated member  202  and a hub  204 . The elongated member  202  includes a proximal end  206  and a distal end  208 . In  FIG. 2 , the proximal end  206  of the elongated member  202  is coupled to the catheter hub  204  and the distal end  208  of the elongated member is configured and arranged for percutaneous insertion into a patient. In at least some embodiments, the catheter  102  defines at least one flush port, such as flush port  210 . In at least some embodiments, the flush port  210  is defined in the hub  204 . In at least some embodiments, the hub  204  is configured and arranged to couple to the control module ( 104  in  FIG. 1 ). In some embodiments, the elongated member  202  and the hub  204  are formed as a unitary body. In other embodiments, the elongated member  202  and the catheter hub  204  are formed separately and subsequently assembled together. 
       FIG. 3  is a schematic perspective view of one embodiment of the distal end  208  of the elongated member  202  of the catheter  102 . The elongated member  202  includes a sheath  302  and a lumen  304 . An imaging core  306  is disposed in the lumen  304 . The imaging core  306  includes an imaging device  308  coupled to a distal end of a rotatable driveshaft  310 . 
     The sheath  302  may be formed from any flexible, biocompatible material suitable for insertion into a patient. Examples of suitable materials include, for example, polyethylene, polyurethane, plastic, spiral-cut stainless steel, nitinol hypotube, and the like or combinations thereof. 
     One or more transducers  312  may be mounted to the imaging device  308  and employed to transmit and receive acoustic pulses. In a preferred embodiment (as shown in  FIG. 3 ), an array of transducers  312  are mounted to the imaging device  308 . In other embodiments, a single transducer may be employed. In yet other embodiments, multiple transducers in an irregular-array may be employed. Any number of transducers  312  can be used. For example, there can be two, three, four, five, six, seven, eight, nine, ten, twelve, fifteen, sixteen, twenty, twenty-five, fifty, one hundred, five hundred, one thousand, or more transducers. As will be recognized, other numbers of transducers may also be used. 
     The one or more transducers  312  may be formed from one or more known materials capable of transforming applied electrical pulses to pressure distortions on the surface of the one or more transducers  312 , and vice versa. Examples of suitable materials include piezoelectric ceramic materials, piezocomposite materials, piezoelectric plastics, barium titanates, lead zirconate titanates, lead metaniobates, polyvinylidenefluorides, and the like. 
     The pressure distortions on the surface of the one or more transducers  312  form acoustic pulses of a frequency based on the resonant frequencies of the one or more transducers  312 . The resonant frequencies of the one or more transducers  312  may be affected by the size, shape, and material used to form the one or more transducers  312 . The one or more transducers  312  may be formed in any shape suitable for positioning within the catheter  102  and for propagating acoustic pulses of a desired frequency in one or more selected directions. For example, transducers may be disc-shaped, block-shaped, rectangular-shaped, oval-shaped, and the like. The one or more transducers may be formed in the desired shape by any process including, for example, dicing, dice and fill, machining, microfabrication, and the like. 
     As an example, each of the one or more transducers  312  may include a layer of piezoelectric material sandwiched between a conductive acoustic lens and a conductive backing material formed from an acoustically absorbent material (e.g., an epoxy substrate with tungsten particles). During operation, the piezoelectric layer may be electrically excited by both the backing material and the acoustic lens to cause the emission of acoustic pulses. 
     In at least some embodiments, the one or more transducers  312  can be used to form a radial cross-sectional image of a surrounding space. Thus, for example, when the one or more transducers  312  are disposed in the catheter  102  and inserted into a blood vessel of a patient, the one more transducers  312  may be used to form an image of the walls of the blood vessel and tissue surrounding the blood vessel. 
     In at least some embodiments, the imaging core  306  may be rotated about a longitudinal axis of the catheter  102 . As the imaging core  306  rotates, the one or more transducers  312  emit acoustic pulses in different radial directions. When an emitted acoustic pulse with sufficient energy encounters one or more medium boundaries, such as one or more tissue boundaries, a portion of the emitted acoustic pulse is reflected back to the emitting transducer as an echo pulse. Each echo pulse that reaches a transducer with sufficient energy to be detected is transformed to an electrical signal in the receiving transducer. The one or more transformed electrical signals are transmitted to the control module ( 104  in  FIG. 1 ) where the processor  106  processes the electrical-signal characteristics to form a displayable image of the imaged region based, at least in part, on a collection of information from each of the acoustic pulses transmitted and the echo pulses received. In at least some embodiments, the rotation of the imaging core  306  is driven by the motor  110  disposed in the control module ( 104  in  FIG. 1 ). 
     As the one or more transducers  312  rotate about the longitudinal axis of the catheter  102  emitting acoustic pulses, a plurality of images are formed that collectively form a radial cross-sectional image of a portion of the region surrounding the one or more transducers  312 , such as the walls of a blood vessel of interest and the tissue surrounding the blood vessel. In at least some embodiments, the radial cross-sectional image can be displayed on one or more displays  112 . 
     In at least some embodiments, the imaging core  306  may also move longitudinally along the blood vessel within which the catheter  102  is inserted so that a plurality of cross-sectional images may be formed along a longitudinal length of the blood vessel. In at least some embodiments, during an imaging procedure the one or more transducers  312  may be retracted (i.e., pulled back) along the longitudinal length of the catheter  102 . In at least some embodiments, the catheter  102  includes at least one telescoping section that can be retracted during pullback of the one or more transducers  312 . In at least some embodiments, the motor  110  drives the pullback of the imaging core  306  within the catheter  102 . In at least some embodiments, the motor  110  pullback distance of the imaging core is at least 5 cm. In at least some embodiments, the motor  110  pullback distance of the imaging core is at least 10 cm. In at least some embodiments, the motor  110  pullback distance of the imaging core is at least 15 cm. In at least some embodiments, the motor  110  pullback distance of the imaging core is at least 20 cm. In at least some embodiments, the motor  110  pullback distance of the imaging core is at least 25 cm. 
     The quality of an image produced at different depths from the one or more transducers  312  may be affected by one or more factors including, for example, bandwidth, transducer focus, beam pattern, as well as the frequency of the acoustic pulse. The frequency of the acoustic pulse output from the one or more transducers  312  may also affect the penetration depth of the acoustic pulse output from the one or more transducers  312 . In general, as the frequency of an acoustic pulse is lowered, the depth of the penetration of the acoustic pulse within patient tissue increases. In at least some embodiments, the IVUS imaging system  100  operates within a frequency range of 5 MHz to 60 MHz. 
     In at least some embodiments, one or more conductors  314  electrically couple the transducers  312  to the control module  104  (See  FIG. 1 ). In at least some embodiments, the one or more conductors  314  extend along a longitudinal length of the rotatable driveshaft  310 . 
     In at least some embodiments, the catheter  102  with one or more transducers  312  mounted to the distal end  208  of the imaging core  308  may be inserted percutaneously into a patient via an accessible blood vessel, such as the femoral artery, at a site remote from the selected portion of the selected region, such as a blood vessel, to be imaged. The catheter  102  may then be advanced through the blood vessels of the patient to the selected imaging site, such as a portion of a selected blood vessel. 
     Acoustic pulses propagating from the one or more transducers  312  propagate through the lumen of the catheter  102  before passing through the sheath  302  to the region exterior of the catheter  102 , such as a blood vessel or a chamber of a heart. Likewise, echo pulses reflected back to the one or more transducers  312  from medium boundaries also propagate through the lumen of the catheter  102 . Typically, air is not a desirable transmission medium and image quality may, consequently, be reduced when acoustic pulses or echo pulses are required by catheter design to propagate through air. In the MHz range, acoustic pulses may not propagate at all through air. Accordingly, it is typically advantageous, and in some cases necessary, to purge air from the lumen  304  surrounding the one or more transducers  312  prior to the performance of an imaging procedure. One technique for purging air surrounding the one or more transducers  312  is to flush the lumen  304  with an acoustically-favorable medium through which acoustic pulses more easily propagate than through air Acoustically-favorable media may include one or more solvents such as, for example, water. An acoustically-favorable medium may include one or more solutes mixed with the one or more solvents such as, for example, one or more salts. In at least some embodiments, one or more agents may also be added, for example, to decrease the potential advancement of corrosion or microbial growth. In at least some embodiments, an acoustically-favorable medium may include a gel, and the like. In at least some embodiments, the acoustically-favorable medium may be input through the main flush port  210 . In at least some embodiments, the elongated member  202  also defines an output port  316  for outputting one or more gases. 
     When using a conventional IVUS imaging system, a lumen of a catheter may be flushed to remove air at the beginning of an IVUS imaging procedure. Additionally, the lumen of the catheter may also need to be flushed of air one or more additional times during the course of the IVUS imaging procedure. Unfortunately, each flushing of air from the catheter lumen can add to the amount of time it takes for a healthcare professional to perform an IVUS imaging procedure on a patient. Moreover, the use of IVUS imaging systems often results in changes in volume of the lumen. For example, the volume of the lumen may change as the lumen twists and turns around tortuous blood vessels during placement of a catheter. Additionally, during an IVUS imaging procedure the volume of a lumen may change during pullback, as the imaging core  306  moves longitudinally along a longitudinal length of the catheter  102 . As discussed above, in at least some embodiments the catheter  102  may include one or more telescoping sections that retract during pullback. In at least some embodiments, the retraction of the one or more telescoping sections may change the volume of the lumen. When the volume of a lumen changes, it may be the case that an air pocket develops across a portion of the path along which an acoustic pulse or an echo pulse propagates, thereby potentially reducing the quality of the IVUS image, or even prohibiting the IVUS imaging system  100  from forming an IVUS image. 
     To address these issues, in at least some embodiments the catheter  102  is filled with an acoustically-favorable medium and sealed so that the acoustically-favorable medium remains in the lumen  304 . By sealing the catheter  102  with an acoustically-favorable medium, it is not necessary to flush the lumen  304  of air either before or during an IVUS imaging procedure. In at least some embodiments, the catheter  102  utilizes one or more movable seals or movable plungers in fluid communication with the lumen  304 . The one or more movable seals or the movable plungers adjust to changes in the internal volume of the lumen  304  to maintain the lumen  304  of the catheter  102  filled with the acoustically-favorable medium.  FIG. 4  is a schematic longitudinal cross-sectional view of one embodiment of the hub  204 . The hub  204  includes a movable seal or a movable plunger  402  disposed in the main flush port  210 . In at least some embodiments, the movable seal or the movable plunger  402  act like a piston moving up and down as the volume of the lumen  304  changes. 
     In at least some embodiments, the lumen  304  is degassed, filled with an acoustically-favorable medium, and sealed with the movable seal or the movable plunger  402 . In at least some embodiments, degassing involves generating a vacuum in the lumen  304  and then filling the lumen  304  with an acoustically-favorable medium without introducing gas into the lumen  304 . For example, in at least some embodiments, air in the lumen  304  is flushed out of the main flush port  210 , an acoustically-favorable medium is input to the main flush port  210 , and the main flush port  210  is sealed with the movable seal or the movable plunger  402 . In at least some embodiments, the lumen  304  is degassed, filled with the acoustically-favorable medium, and the main flush port  210  is sealed all in one integrated step. In at least some embodiments, the operability of the imaging core  306  may be tested prior to sealing the main flush port  210 . 
     Once the lumen  304  is filled with the acoustically-favorable medium and the main flush port  210  is sealed, the movable seal or the movable plunger  402  moves along a longitudinal length of the main flush port  210  in a direction shown by directional arrow  404  when the volume of the lumen  304  decreases. Conversely, when the volume of the lumen  304  increases, the movable seal or the movable plunger  402  moves in a direction shown by directional arrow  406 . In at least some embodiments, each seal in fluid contact with the lumen  304  is provided with a vacuum seal. 
     In at least some embodiments, the volume of the main flush port  210  should be sufficient to allow the movable seal or the movable plunger  402  full movement for volume changes. In at least some embodiments, the movement of the movable seal or the movable plunger  402  may be restricted to a given longitudinal movement, thereby corresponding to a given volume. For example, in at least some embodiments, one or more stops may be used to limit the longitudinal movement of the movable seal or the movable plunger  402  within the main flush port  210 . In  FIG. 4 , stops  408  and  410  are shown for limiting the movement of the movable seal or the movable plunger  402  in the direction shown by the directional arrow  404 . In other embodiments, additional stops may be employed instead of, or in addition to, the stops  408  and  410  to limit the movement of the movable seal or the movable plunger  402  in the direction shown by the directional arrow  406 . 
     In at least some embodiments, air in the lumen  304  is flushed out of the output port  316  and an acoustically-favorable medium is input to the main flush port  210 . Once the air is removed from the lumen  304  and the acoustically-favorable medium is input to the main flush port  210 , the output port  316  may be sealed with a fixed seal. In some embodiments, the fixed seal is made permanent, for example, by fusing the output port  316  or plugging the output port  316  with a cap and applying epoxy around the edges of the cap. In other embodiments, the fixed seal is designed to be removable. In at least some embodiments, the output port  316  is sealed with a vacuum seal. In at least some embodiments, the lumen  304  is degassed, filled with the acoustically-favorable medium, and the main flush port  210  and the output port  316  are sealed all in one integrated step. In at least some embodiments, the imaging core  306  may be tested for operability prior to sealing the main flush port  210  and the output port  316 . 
     In at least some embodiments, the catheter  102  may also define one or more auxiliary ports. For example, in at least some embodiments, the catheter  102  may define one or more auxiliary flush ports.  FIG. 5A  is a schematic longitudinal cross-sectional view of one embodiment of the hub  204 . The hub  204  defines the main flush port  210  and an auxiliary flush port  502 . In  FIG. 5A , the movable seal or the movable plunger  402  is shown disposed in the main flush port  210  and the auxiliary flush port  502  is shown open. 
     In at least some embodiments, the movable seal or the movable plunger  402  may be disposed in the main flush port  210  and the auxiliary flush port  502  may be used to degas or flush the air out of the lumen  304 , as described above. Once the lumen  304  is degassed and filled with an acoustically-favorable medium, the auxiliary flush port  502  may be sealed with a fixed seal (either permanent or removable), as described above. In at least some embodiments, the auxiliary flush port  502  is sealed with a vacuum seal. 
       FIG. 5B  is a schematic longitudinal cross-sectional view of one embodiment of the hub  204  with the movable seal or the movable plunger  402  disposed in the main flush port  210  and a fixed seal  504  disposed in the auxiliary flush port  502 . In at least some embodiments, the movable seal or the movable plunger  402  is disposed in the auxiliary flush port  502  and the fixed seal  504  is disposed in the main flush port  210 . In at least some embodiments, a plurality of auxiliary flush ports are defined by the catheter  102 . In at least some embodiments, the fixed seal  504  or the movable seal or the movable plunger  402  is disposed in each of the auxiliary flush ports. 
     In at least some embodiments, one or more auxiliary output ports are defined in the catheter  102 . In at least some embodiments, the movable seal or the movable plunger  402  is disposed in the output port  316 . In at least some embodiments, the movable seal or the movable plunger  402  is disposed in one or more auxiliary output ports. In at least some embodiments, the movable seal or the movable plunger  402  is disposed in a reservoir in fluid communication with one or more of the main flush port  210 , the one or more of the auxiliary flush ports  502 , the output port  316 , or the one or more auxiliary output ports. 
     The above specification, examples and data provide a description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention also resides in the claims hereinafter appended.