Abstract:
Shape-controllable catheters are provided that are versatile in application and that, in human-imaging applications, minimize or reduce patient discomfort. One such catheter is provided with at least one control wire that extends inside the catheter and a control mechanism for tensioning the control wire to produce in the catheter a humped shape or a cantilevered configuration. Hardness of the catheter may be varied along the length thereof to facilitate desired bending. For example, hardness may be reduced in bend areas. Hardness may be maintained or increased in other areas for performance reasons, for example to maintain planarity of an imaging array.

Description:
BACKGROUND 
       [0001]    The present invention relates to catheters and catheter systems, including ultrasound catheter systems. 
         [0002]    Various catheter systems, including ultrasound catheter systems, are known. One such catheter system is the AcuNav™ catheter system of the present assignee. As shown in  FIG. 6 , that system uses an ultrasound array  601  mounted at the end of a small-diameter catheter  603  to, in one application, obtain access to the heart through the venous system in order to obtain ultrasound images. Manipulation of the end of the catheter  603  is performed using control wires (not shown) that run through lumens inside the catheter  603 . Using four control wires, both anterior/posterior (A/P) and right/left (R/L) control may be achieved. An operator handle  610  is provided with two rotating rings  611  and  613 , one for A/P control and one for R/L control. Additional details of the system of  FIG. 6  may be found in U.S. Pat. Nos. 5,938,616 and 5,846,205, incorporated herein by reference. 
         [0003]    Another known system includes a tubular probe designed for trans-esophageal (TE) use such as trans-esophageal echocardiology (TEE). Cardiac imaging is the most common application. Again, an ultrasound array is mounted at the end of the probe. The probe in this instance, however, is considerably thicker. For an adult version, the probe may be of the approximate thickness of an adult&#39;s thumb; for a pediatric version, the probe may be of the approximate thickness of an adult&#39;s little finger. Such thicknesses have been required to obtain sufficiently good contact with the esophageal wall to enable effective imaging. The thickness and bulk of these probes produces user discomfort. Furthermore, the versatility of such probe systems is limited. For example, nasal access is not possible with such systems. 
       SUMMARY 
       [0004]    Shape-controllable catheters are provided that are versatile in application and that, in human-imaging applications, minimize or reduce patient discomfort. One such catheter is provided with at least one control wire that extends inside the catheter and a control mechanism for tensioning the control wire to produce in the catheter a humped shape or a cantilevered configuration. Hardness of the catheter may be varied along the length thereof to facilitate desired bending. For example, hardness may be reduced in bend areas. Hardness may be maintained or increased in other areas for performance reasons, for example to maintain planarity of an imaging array. Such catheters may be used instead of and may provide a less expensive alternative to known TE probes. 
     
    
     
       DRAWING FIGURES 
         [0005]      FIG. 1A  is a diagram of a shape-controllable catheter in a relaxed state. 
           [0006]      FIG. 1B  is a diagram of the catheter of  FIG. 1A  in a non-relaxed state. 
           [0007]      FIG. 1C  is a cross-sectional view of a portion of the catheter of  FIG. 1A . 
           [0008]      FIG. 1D  is a partial cutaway view of a catheter like those of  FIGS. 1 and 3 . 
           [0009]      FIG. 1E  is partial cutaway view of a catheter like those of  FIGS. 2 and 4 . 
           [0010]      FIG. 2  is a diagram of another catheter in a non-relaxed state. 
           [0011]      FIG. 3A  is a diagram of another shape-controllable catheter in a relaxed state. 
           [0012]      FIG. 3B  is a diagram of the catheter of  FIG. 3A  in a non-relaxed state. 
           [0013]      FIG. 4  is a diagram of another catheter in a non-relaxed state. 
           [0014]      FIG. 5  is a diagram of another catheter in a non-relaxed state. 
           [0015]      FIG. 6  is a diagram of a known catheter. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    In the following detailed description, catheter systems are described and shape-controllable catheters are described that can be manipulated to form a curved shape, either a simple curved shape or a compound curved shape. In a relaxed state, insertion of the catheter into a body is readily accomplished. In a non-relaxed state, a contact condition conducive to quality operation may be obtained. In the case of an imaging operation, for example, close and even contact of an imaging array with a body wall may be achieved. 
         [0017]    Referring to  FIG. 1A  and  FIG. 1B , perspective views are shown of a portion of one exemplary catheter  100  that can be manipulated to form the shape of a compound curve, for example a reentrant curve. The catheter  100  may be described as a “hump-shaped” catheter in that the catheter  100  may be manipulated ( FIG. 1B ) to form a hump before the end of the catheter  100 . In the case of an ultrasound catheter system, an ultrasound array  101  may be located at the peak point of the hump. Furthermore, in the case of trans-esophageal ultrasound imaging, manipulation of the catheter  100  to form the hump may be used to bring the ultrasound array  101  into intimate contact with the esophageal wall, enabling more effective imaging. Instead of the entire catheter  100  being of a size currently typical of esophageal use, the catheter  100 , in a relaxed state ( FIG. 1A ), may be of a size typical of venous applications. Only in a “hump-shaped”state ( FIG. 1B ) does the catheter  100  effectively become “esophagus-sized.” In this state, a device such as an imaging array  101  is pressed against one wall  111  of the esophagus while nearby portions of the catheter are pressed against an opposite wall of the esophagus  113 . A desirable operation condition (for example, imaging array planarity) may be obtained in this manner. 
         [0018]    The catheter  100 , and other catheters described herein, may be incorporated into a catheter system, for example one that uses the same or similar control mechanism as that illustrated in  FIG. 6 . They may be used to image any of a wide variety of structures, including living structures (e.g., human and other animal structures) and non-living structures. 
         [0019]    Referring to  FIG. 1C , a simplified partial longitudinal cross-section is shown of the catheter  100  of  FIG. 1A . In one exemplary embodiment, two control wires  121 ,  123  are used to control the catheter  100  to form a humped shape. Anchor points A 1 , A 2  of the control wires  121 ,  123  may be such that a first control wire  123  is anchored at a first distance prior to the end of the catheter  100  and a second control wire  121  is anchored at a second distance d prior to the anchor point of the first control wire. In one exemplary embodiment, the first distance may be about a few centimeters, and the second distance d may be about 6-9 centimeters (e.g., about three inches). The two control wires  121 ,  123  may be provided in addition to control wires providing A/P and L/R control. Alternatively, two of the existing control wires in an existing catheter system (for example, the L/R control wires) may be re-purposed to provide control of the hump-shaped feature. 
         [0020]    Note that the foregoing arrangement is exemplary only. The catheter system may use other controls or additional controls. For example, an angular control may be provided as described, for example, in U.S. Patent Application 2008/0146941, incorporated herein by reference. 
         [0021]    In other embodiments, stiffness of the catheter may be varied strategically in order to promote a desired configuration of the catheter in a flexed state. For example, the stiffness of the catheter may be reduced on one side or on both sides of the operative device, such as an ultrasound array. In the area of the ultrasound array itself, the catheter may be kept relatively stiff, or even made more stiff, in order to maintain planarity of the array. In one exemplary embodiment, such variation in stiffness may be achieved by using polymer materials of different hardnesses, one such family of suitable polymer materials being Pebax™ polymer materials. Using the Shore D hardness scale, hardness in the area of the ultrasound array may be around 40d, while hardness in areas on both sides of the ultrasound array may be reduced to around 25d. A resulting configuration of a catheter  200  in a flexed state is shown in  FIG. 2 , the catheter  200  having areas of reduced stiffness on either side of the ultrasound array  201 , such as those areas marked by “X” in  FIG. 2 . 
         [0022]    In still further embodiments, the catheter may be configured so as to produce a single bend using a single control wire, as illustrated for example in  FIGS. 3A and 3B . Such a catheter  300  may be referred to as “cantilevered,” since in a non-relaxed state a device  301  (such as an imaging array) is borne on a length of the catheter that is supported at one end and that, relative to the remainder of the catheter  300 , projects away and forward. 
         [0023]    Another example of a cantilevered catheter  400  is shown in  FIG. 4 , the cantilevered catheter  400  being provided with an operative device such as an ultrasound array  401 . In the area of the ultrasound array  401  itself, the catheter  400  may be kept relatively stiff, or even made more stiff, in order to maintain planarity of the array  401 . In one exemplary embodiment, stiffness in the area of the ultrasound array  401  may be around 40d, while stiffness in other areas such as the marked by “X” on the near side of the ultrasound array  401  may be reduced to around 25d. 
         [0024]    Referring to  FIG. 1D  and  FIG. 1E , partial cutaway views are shown of catheters like those of  FIGS. 1 and 3  and those of  FIGS. 2 and 4 , respectively, showing in greater detail possible arrangements of control wires. As seen in  FIG. 1D , in the case of a catheter configured to assume a cantilevered configuration, a first control wire may be used to control shape. Second and third control wires may be used for articulation in one plane, for example A/P articulation. Optionally, fourth and fifth control wires may be used for articulation in another plane, for example L/R articulation. As seen in  FIG. 1E , in the case of a catheter configured to assume a humped shape, first and control wires may be used to control shape. Third and fourth control wires may be used for articulation in one plane, for example A/P articulation. Optionally, fifth and sixth control wires may be used for articulation in another plane, for example L/R articulation. 
         [0025]    In the case of trans-esophageal use of a hump-shaped ultrasound catheter, typically a series of images will be acquired. For each image acquisition, the catheter may be manipulated to cause it to go from a relaxed state to a hump-shaped state. Between image acquisitions, the catheter may be allowed to resume a relaxed state during which the position of the catheter may be adjusted, for example. Similarly, in the case of trans-esophageal use of a cantilevered ultrasound catheter, for each image acquisition, the catheter may be manipulated to cause it to go from a relaxed state to a hump-shaped state. Between image acquisitions, the catheter may be allowed to resume a relaxed state during which the position of the catheter may be adjusted, for example. 
         [0026]    Referring to  FIG. 5 , in another embodiment, a catheter  500  like that of any of the preceding figures, such as that of  FIG. 1A , may be provided with a device or combination of devices  501 ′ that includes a pressure sensor or otherwise incorporates pressure sensing capabilities. One of the advantages of the present catheters and catheter systems is the ability to achieve greater pressure (and greater uniformity of pressure) of an imaging device or other device against a vessel wall. Using the catheter  500  and the device(s)  501 ′, a pressure reading may be obtained during control of the catheter  500 . This pressure information may be displayed and/or recorded, either periodically, continuously in real time, or upon the occurrence of certain events. 
         [0027]    The foregoing pressure information may be used in various ways. For example, if the pressure information is displayed continuously to an operator, the operator may initiate an imaging operation or other operation only when pressure conditions are such as to ensure satisfactory results. In other embodiments, pressure information may be used for elastography or the like. Elastography uses pressure applied to tissue to obtain information about the tissue. For example, if tissue is abnormally stiff, such stiffness may be indicative of a tissue abnormality. In other instances, if tissue is abnormally soft, such softness may be indicative of a tissue abnormality. Using the catheter  500  and the device(s)  501 ′, various techniques may be used to sense tissue stiffness. To take one example, from the onset of measurable pressure against the vessel wall, the rate at which pressure increases may be taken as an indication of tissue stiffness. If the pressure increases abnormally quickly, such rapid increase may be attributed to abnormally stiff tissue. If the pressure increases abnormally slowly, such slow increase may be attributed to abnormally soft tissue. 
         [0028]    Although the shape-controllable catheters described herein are especially suitable for imaging applications using imaging devices, any of various kinds of devices may be mounted in or on the catheter, including both imaging and non-imaging devices, electronic devices, mechanical devices, pharmacological devices, etc. 
         [0029]    The described shape-controllable catheters are versatile in application. Because of their relatively small diameter, the catheters are suitable for nasal insertion, for example. In the case of an imaging operation, close and even contact of an imaging array with a body wall may be achieved. Moreover, in human-imaging applications, because of the relatively small diameter of the catheters, patient discomfort is minimized or reduced. 
         [0030]    It will be appreciated by those of ordinary skill in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential character thereof. The foregoing description is therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims, not the foregoing description, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.