Abstract:
An imaging probe for use in a catheter for ultrasonic imaging is provided. The catheter may be of the type including a sheath having an opening at a distal end for conducting a fluid there through. The imaging probe includes a distal housing coupled to a drive shaft for rotation, a transducer within the distal housing for generating and sensing ultrasonic waves, and a fluid flow promoter that promotes flow of the fluid within the sheath across the transducer.

Description:
PRIORITY CLAIM 
       [0001]    The present application claims the benefit of copending U.S. Provisional Patent Application Ser. No. 61/008,725, filed Dec. 20, 2007, which application is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present invention generally relates to an imaging probe of an imaging catheter. The present. invention more specifically relates to mechanically scanned imaging probes for use in, for example, an intravascular ultrasound (IVUS) or intra-cardiac echo-cardiography (ICE) catheter. The present invention still further relates to such an imaging probe wherein the imaging probe is configured to assure efficient and complete fluid flushing from the catheter sheath to preclude formation of air bubbles in the vicinity of the ultrasonic transducer of the imaging probe. In addition this invention relates to imaging probe configuration to ensure the prevention of air bubbles during rotational operation by continuously directing fluid across the imaging probes transmission surface. 
         [0003]    IVUS catheters enable the imaging of internal structures in the body. ICE catheters enable the imaging of larger internal structures in the body. Coronary IVUS catheters are used in the small arteries of the heart to visualize coronary artery disease, for example. Coronary ICE catheters are used in the cavity of the heart to visualize structural heart. disease, including atrial septal defects (ASD), patent foramen ovale (PFO) and to guide various procedures including septal puctures, percutaneous valvular replacement, and various ablations treatment strategies. To that end, an IVUS or an ICE catheter will employ at least one ultrasonic transducer that creates pressure waves to enable visualization. At least one transducer is usually housed within a surrounding sheath or catheter member and rotated to enable 360 degree visualization. Because air is not an efficient medium for the transmission of the ultrasonic waves produced by at least one transducer, a fluid interface between the transducer and the sheath in which it is disposed is usually provided. Unfortunately, current imaging probe configurations do not always prevent the formation of air bubbles in the fluid in the vicinity of the transducer resulting in compromised performance of the imaging catheter. The present invention addresses this and other issues. 
       SUMMARY 
       [0004]    The invention provides an imaging probe for use in a catheter for ultrasonic imaging. The catheter may include a sheath having an opening at a distal end for conducting a fluid there through. The imaging probe comprises a distal housing coupled to a drive shaft for rotation, a transducer within the distal housing for generating and sensing ultrasonic waves, and 
         [0005]    a fluid flow promoter that promotes flow of the fluid within the sheath across the transducer. 
         [0006]    The imaging probe may further include a wall distal to the transducer and the fluid flow promoter may include an opening within the wall and adjacent. to the transducer. The distal housing preferably has a first profile at a proximal end of the distal housing, a second profile at the wall distal to the transducer, and the fluid flow promoter includes the second profile being greater than the first profile to promote fluid flow over the transducer and through the opening within the wall. 
         [0007]    The catheter has a center axis and the fluid flow promoter may further include a mounting for the transducer that disposes the transducer at an angle sloping toward the catheter center axis in a proximal direction. 
         [0008]    The distal housing has a proximal extent and the fluid flow promoter may include at least one aqua duct within the proximal extent of the distal housing. The at least one aqua duct is preferably formed within the proximal extent of the distal housing at an angle to the center axis, The at least one aqua duct may comprise at least two aqua ducts. The transducer includes a face surface. The at least two aqua ducts may include a first aqua duct that directs fluid directly onto the face surface of the transducer and a second aqua duct that directs fluid onto the face surface of the transducer from a side of the transducer. The at least one aqua duct has a proximal side and a distal side and may be formed so that the proximal side leads the distal side in the direction of rotation of the distal housing. The at least one aqua duct may include a radius of curvature. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The features of the present invention which are believed to be novel are set. forth with particularity in the appended claims. The invention, together with further features and advantages thereof, may best be understood by making reference to the following description taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify identical elements, and wherein: 
           [0010]      FIG. 1  is a side view, partly in section, of an ultrasonic imaging catheter in accordance with a first embodiment of the invention; 
           [0011]      FIG. 2  is a partial perspective view of the imaging probe of the catheter of  FIG. 1 ; and 
           [0012]      FIG. 3  is a perspective view showing another imaging probe embodying the invention connected to a drive cable of an intravascular ultrasound (IVUS) catheter. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 1  shows an imaging catheter  10  with the first embodiment of the present invention. The imaging catheter  10  is particularly adapted for use as an IVUS catheter, but those skilled in the art will appreciate that the invention may be used in many other forms of ultrasound catheters as well without departing from the present invention. The catheter  10  generally includes a sheath or catheter member  12  and an imaging probe  14 . As shown, the imaging probe  14  is disposed within the sheath  14 . 
         [0014]    The imaging probe  14  is moveable axially within the sheath  12  to enable the sheath to remain stationary as the imaging probe is moved to scan the internal body structures to be visualized. Also, as well known, the imaging probe  14  is also rotatable to enable 360 degree scanning. 
         [0015]    The imaging probe  14  generally includes a distal housing  16 , a flexible drive shaft  18 , and a coaxial cable  20 . The distal housing  16  is carried on the distal end of the flexible drive shaft  18  in a known manner. The drive shaft  18  may be formed, for example, by winding multiple strands of metal wire on a mandrel to create a long spring containing a repeating series of concentric rings, or windings, of the wire. Two or more springs may be wound, one over the other, with adjacent springs being wound in opposite directions to each other. This provides a drive shaft that is both flexible and with high torsional stiffness. 
         [0016]    The distal housing  16  generally includes the ultrasound transducer  22 , a distal tip wall  24 , and a proximal cutout surface  26 . The transducer  22  is mounted on a transducer backing  28  The backing  28  and the distal tip wall  24  are adhered together by a conductive adhesive  27 . The backing  28  is dimensioned and of such a material as to absorb ultrasonic waves from the backside of the transducer  22  so that only energy from the front side of the transducer is emitted from the imaging probe  14  in the general direction indicated by reference character  30  transverse to the exposed surface of the transducer The coaxial cable  20  extends down the drive shaft  18  and includes a center conductor  32  and a shield lead  34 . The center conductor  32  and shield lead  34  are coupled across the transducer  20  as shown. The coaxial cable  20  couples energy to the transducer to cause the transducer  22  to generate a pressure wave into the lumen  36  of the sheath  12 . The interior of the lumen  36  is preferably filled with a fluid, such as saline. The saline flows from the proximal end of the catheter  10  to the distal end of the catheter  10  and serves to efficiently couple the ultrasonic energy into the sheath and then to the body. To support the fluid flow, the sheath includes a point of egress (not shown) for the fluid at its distal end. As previously mentioned, it is important to prevent air bubbles from being formed or residing in the vicinity of the transducer  22 . 
         [0017]    To assure that air bubble formation in the vicinity of the transducer  22  is prevented, and with additional reference to  FIG. 2 , the distal extent of the distal housing  16  includes a distal tip wall  24  distal and adjacent to the transducer  22 . The distal tip wall  24  has an opening  38  therein adjacent to the transducer  22 . Proximal to the transducer  22 , the distal housing  16  has a proximal cutout forming a tapered surface  26  leading toward the transducer  22 . Fluid flow within the sheath from proximal to the transducer  22  to distal of the transducer  22  is conducted down the tapered cutout surface  26 , over the transducer  22 , and out the distal tip wall opening  38  in a continuous manner, without turbulence, to prevent air bubble formation in the vicinity of the transducer. 
         [0018]    The distal housing  16  at the proximal extent of the tapered cutout surface  26  has or defines a first profile substantially transverse to the catheter center axis  40  and the fluid flow. The distal tip wall  24  defines a second profile also substantially transverse to the catheter center axis  40  and the fluid flow. The second profile is greater in dimension than the first profile. Hence, this serves to promote fluid flow through the distal tip opening  38  and hence over the transducer  22 . 
         [0019]    To further promote fluid flow over the transducer  22 , the transducer has a surface  22   a  over which the fluid flows that is disposed at an angle sloping toward the catheter center axis in the proximal direction, This presents a greater surface resistance against. the fluid flow to assure fluid contact therewith. 
         [0020]      FIG. 3  shows another imaging catheter  110  according to a further embodiment of the present. invention. The catheter  110  is similar to the catheter  10  of  FIGS. 1 and 2  and hence, reference characters for like elements are repeated in  FIG. 3 . To further assure that air bubble formation in the vicinity of the transducer  22  is prevented during rotational operation, and with additional reference to  FIG. 3 , the proximal extent of the distal housing  26  is constructed with aqua ducts  41  and  42 . As shown in  FIG. 3 , one aqua duct directs fluid onto the transducer face  22  from the top of the proximal portion of the distal housing  26 , while the other aqua duct  41  directs fluid onto the transducer face  22  from the side. Further, the aqua ducts are built into the proximal portion  26  of the distal housing  16  at an angle with respect to a line extending along the catheter drive shaft  43 . This is shown in  FIG. 3  with the angle theta being formed with the intersection of a line  43  extending parallel to the catheter drive shaft  13  and a line  44  extending through the center of one of the aqua ducts  41 . Both aqua ducts  41  and  42  are constructed at such an angle such that the proximal side of each duct leads the distal side in the direction of rotation. This is shown in  FIG. 3  with the clockwise direction of rotation (from the view looking distally along the catheter drive shaft  13 ) indicated by  45 . Further, each side of each aqua duct is constructed with a small radius of curvature shown by  46  in  FIG. 3 , One way to achieve the duct side curvatures is to construct the ducts in a helical spiral with a small pitch, as, for example, on the order of 0.1 inch. The duct angle and curvature, coupled with rotation of the distal housing  16  and the fluid flow promoting structure shown in  FIG. 1 , act to continuously draw fluid residing within the catheter sheath  12 , proximal to the distal housing  16 , onto the face of the transducer  22  Fluid flow within the sheath from proximal to the transducer  22  to distal of the transducer  22  is conducted down the tapered cutout surface  26 , over the transducer  22 , and out the distal tip wall opening  38  in a continuous manner, without turbulence, to prevent air bubble formation in the vicinity of the transducer. 
         [0021]    While particular embodiments of the present invention have been shown and described, modifications may be made, and it is therefore intended in the appended claims to cover all such changes and modifications which fall within the true spirit and scope of the invention as defined by those claims.