Patent Publication Number: US-2013245371-A1

Title: Apparatus and methods for coronary sinus access

Description:
This application is a continuation of application Ser. No. 13/210,234, filed Aug. 15, 2011, issuing as U.S. Pat. No. 8,439,824, which is a continuation of application Ser. No. 11/269,976, filed Nov. 8, 2005, now U.S. Pat. No. 8,016,748, which is a divisional of application Ser. No. 10/447,526, filed May 29, 2003, now U.S. Pat. No. 6,979,290, which claims benefit of provisional application Ser. No. 60/384,262, filed May 30, 2002, the disclosures of which are expressly incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to apparatus and methods for visualizing and/or cannulating body lumens, and, more particularly, to visualizing and cannulating a coronary sinus ostium of a heart, e.g., for delivering one or more instruments and/or fluids into coronary veins. 
     BACKGROUND 
     Minimally invasive procedures have been implemented in a variety of medical settings, e.g., for vascular interventions, such as angioplasty, stenting, embolic protection, electrical heart stimulation, heart mapping and visualization, and the like. One such procedure involves delivering an electrical lead into a coronary vein of a patient&#39;s heart that may be used to electrically stimulate the heart. 
     During such procedures, instruments, fluids, and/or medicaments may be delivered within a patient&#39;s vasculature using visualization tools, such as x-ray, fluoroscopy, ultrasound imaging, endoscopy, and the like. In many procedures, it may be desired to deliver instruments through opaque fluids, such as blood, or other materials. Endoscopes have been suggested that include devices for displacing these materials from an optical path, e.g., by introducing a clear fluid from the endoscope in an attempt to clear its field of view. Yet there are still improvements that may be made to such devices. 
     Accordingly, apparatus and methods for imaging within body lumens and/or for delivering instruments and/or fluids into a patient&#39;s body would be useful. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to apparatus and methods for delivering instruments and/or fluids within a patient&#39;s body, and, more particularly, to apparatus and methods for visualizing, accessing, and/or cannulating body lumens, such as a coronary sinus ostium of a heart, e.g., for delivering electrical leads, devices, wire, or other instruments, medicaments, fluids, and/or other agents, e.g., into a coronary vein. 
     In accordance with one aspect of the present invention, an apparatus is provided for locating morphological features within a body cavity that may include a flexible tubular member including a proximal end, a distal end having a size for introduction into a body cavity, and defining a longitudinal axis extending between the proximal and distal ends. An optical imaging assembly may be carried by the distal end of the tubular member for imaging beyond the distal end. 
     A substantially transparent displacement member may also be carried by the distal end of the tubular member that at least partially surrounds the optical imaging assembly. In one embodiment, the displacement member may be an expandable member, e.g., a compliant or noncompliant balloon that extends from the distal end of the tubular member. Optionally, the expandable member may include a channel extending through an interior of the expandable member and/or communicating with a cannulation lumen extending through the tubular member. 
     In addition, the apparatus may include a localization member slidably received in a cannulation lumen of the tubular member. The localization member may be movable beyond the distal end of the tubular member for temporarily localizing the distal end of the tubular member at a morphologic feature within a body cavity. For example, where the expandable member includes a channel communicating with the cannulation lumen, the localization member may be movable from a retracted position proximal to the surface through the channel to a deployed position beyond the surface for localizing the distal end of the tubular member. Optionally, the localization member may terminate in a distal tip configured for engaging a morphological feature, e.g., a tapered distal tip, a forked distal tip, and a steerable distal tip. 
     Optionally, the apparatus may also include a capture device coupled to the proximal end of the tubular member and/or coupled to the optical imaging assembly for acquiring images obtained using the optical imaging assembly. For example, the capture device may include a display, a processor for processing the acquired images, and/or memory for storing the acquired images. 
     In accordance with another aspect of the present invention, an apparatus is provided for accessing a coronary sinus ostium extending from a right atrium of a heart. The apparatus may include a flexible tubular member including a proximal end, a distal end having a size for introduction into a right atrium, and a cannulation lumen extending between the proximal and distal ends, thereby defining a longitudinal axis. A localization member may be slidably received in the cannulation lumen, the localization member being movable beyond the distal end of the tubular member for temporarily localizing the distal end of the tubular member at a morphologic feature within a body cavity. 
     In addition, an array of oxygen sensors may be carried on the distal end of the tubular member for localizing a position of a coronary sinus ostium. In one embodiment, the oxygen sensors may be carried on ends of a plurality of filaments extending from the distal end of the tubular member. Alternatively, the oxygen sensors may be carried on an expandable member, e.g., a balloon, on the distal end of the tubular member. 
     In accordance with yet another aspect of the present invention, an apparatus for imaging within a body lumen that may include a flexible tubular member including proximal and distal ends defining a longitudinal axis therebetween, an expandable member on the distal end of the tubular member, and an optical imaging element disposed within the interior of the expandable member, the imaging element extending from the distal end of the tubular member in a direction at least partially transversely relative to the longitudinal axis. 
     In one embodiment, a channel may extend through the expandable member that communicates with a lumen extending between the proximal and distal ends of the tubular member. A source of fluid may be coupled to the proximal end of the tubular member, the source of fluid communicating with the lumen for delivering fluid through the channel to a location beyond the expandable member. In addition, or alternatively, an elongate member may be insertable through the lumen such that a distal end of the elongate member may be extended through the channel to a location beyond the expandable member. 
     Preferably, the lumen and channel extend substantially concentrically along a central longitudinal axis of the tubular member. Alternatively, the lumen may extend along a periphery of the tubular member, and the channel may extend along a wall of the expandable member. 
     In accordance with still another aspect of the present invention, an apparatus is provided for accessing a body lumen communicating with a body cavity that may include a flexible tubular member including a proximal end, a distal end having a size for introduction into a body cavity, and defining a longitudinal axis extending between the proximal and distal ends. An inner member may be slidably coupled to the tubular member, and a substantially transparent expandable member may be attached to the distal end of the tubular member and to a distal end of the inner member. 
     Te expandable member may be expandable from a contracted condition to an enlarged condition when fluid is introduced through the tubular member into an interior of the expandable member. The inner member may be slidable from a refracted position wherein a distal end of the expandable member at least partially everts into an interior of the expandable member, and an extended position wherein the expandable member defines a stabilizing element or nipple insertable into a body lumen extending from a body cavity for stabilizing the tubular member relative to the body lumen. Preferably, the apparatus also includes an optical imaging element carried by the distal end of the tubular member for imaging through the expandable member. 
     In accordance with yet another aspect of the present invention, a method is provided for cannulating a body lumen communicating with a body cavity of a patient. A distal end of a tubular member may be inserted into the body cavity, the tubular member including a substantially transparent expandable member thereon in a contracted condition. The expandable member may be expanded within the body cavity, and a surface of the expandable member may be placed in contact with a wall of the body cavity in order to image the wall through the expandable member. Preferably, sufficient force is applied to clear fluid, e.g., blood, from between the surface and the wall that may otherwise obscure imaging the wall. 
     The tubular member may be manipulated to move the expandable member along the wall, while imaging the wall through the expandable member, until the body lumen is identified. For example, the distal end of the tubular member may be steerable from the proximal end of the tubular member. Once the body lumen is identified, an instrument may be advanced from the tubular member into the body lumen. Alternatively, a localization member may be advanced at least partially into the body lumen to localize and/or stabilize the distal end of the tubular member. 
     In a preferred embodiment, the body cavity is a right atrium of a patient&#39;s heart, and the body lumen is a coronary sinus ostium. In this embodiment, the tubular member may be advanced from a peripheral vein through a vena cava to insert the distal end into the right atrium. Once the coronary sinus is cannulated, a procedure may be performed within the coronary veins via the coronary sinus. For example, the coronary sinus may be occluded and contrast injected to obtain a venogram of the coronary veins. In addition or alternatively, a guidewire may be advanced through the tubular member into the coronary sinus, e.g., to provide a rail for other instruments. In one embodiment, an electrical lead, e.g., for a pacemaker, may be delivered into a coronary vein via the coronary sinus using the tubular member and/or instruments introduced into the coronary sinus via the tubular member and/or guidewire. 
     Other objects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings constitute a part of this specification and include exemplary embodiments to the invention, which may be embodied in various forms. It is to be understood that in some instances various aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention. 
         FIG. 1A  is a perspective view of a first preferred embodiment of an apparatus for cannulating a body lumen, in accordance with the present invention. 
         FIG. 1B  is a cross-sectional detail of a distal end of the apparatus of  FIG. 1A , showing a guidewire inserted through the apparatus. 
         FIG. 1C  is a cross-section of the apparatus of  FIG. 1A , taken along line  1 C- 1 C. 
         FIG. 2A  is a perspective view of an alternative embodiment of the apparatus of  FIG. 1A , having two degrees of steering. 
         FIG. 2B  is a cross-section of the apparatus of  FIG. 2A , taken along line  2 B- 2 B. 
         FIG. 3A  is a cross-sectional detail, showing an alternative embodiment of an apparatus for cannulating a body lumen including a balloon, in accordance with the present invention. 
         FIGS. 3B and 3C  are cross-sections of the apparatus of  FIG. 3A , taken along lines  3 B- 3 B, and  3 C- 3 C, respectively. 
         FIG. 4  is a cross-sectional detail, showing another alternative embodiment of an apparatus for cannulating a body lumen including a balloon, in accordance with the present invention. 
         FIGS. 5A-5C  are cross-sectional side views of an embodiment of a mechanically expandable member that may be substituted for an inflatable balloon in an apparatus, in accordance with the present invention. 
         FIG. 6  is a cross-sectional side view of a distal end of another embodiment of an apparatus for cannulating a body lumen, in accordance with the present invention. 
         FIG. 7A  is a side view of a catheter that may be included in the apparatus of  FIG. 6 . 
         FIG. 7B  is a side view detailing a set of light guides that may be included in the catheter of  FIG. 7A . 
         FIGS. 8A-8C  are cross-sections of the catheter of  FIG. 7 , taken along lines  8 A- 8 A,  8 B- 8 B, and  8 C- 8 C, respectively. 
         FIGS. 9A-9C  are cross-sections of the light guides of  FIG. 7B , taken along lines  9 A- 9 A,  9 B- 9 B, and  9 C- 9 C, respectively. 
         FIG. 10  is a perspective detail of the apparatus of  FIGS. 6 and 7A , with the balloon omitted for clarity. 
         FIGS. 11A and 11B  are exploded and perspective views of a optical fiber bundle having a lens attached thereto. 
         FIGS. 12A-12D  are partial cross-sectional views, showing a method for cannulating a body lumen communicating with a body cavity using the apparatus of  FIGS. 6-10 . 
         FIGS. 13A-13D  show representative images that may be seen during respective steps of the cannulation method shown in  FIGS. 12A-12D . 
         FIG. 14  is a cross-section detail showing a balloon attached to a tubular member. 
         FIG. 15  is a partial cross-sectional side view of a distal end of yet another embodiment of an apparatus including an off-axis imaging element, in accordance with the present invention. 
         FIGS. 16A and 16B  are end views of the apparatus of  FIGS. 6 and 15 , respectively, showing an improved field of view obtaining using an off-axis imaging element. 
         FIGS. 17A-17F  are perspective views of an alternative embodiment of an apparatus including a plurality of off-axis imaging elements. 
         FIGS. 18A and 18B  are cross-sectional side views of yet another embodiment of an apparatus for cannulating a body lumen, in accordance with the present invention. 
         FIGS. 19A and 19B  are cross-sectional side views, showing a method for cannulating a body lumen, in accordance with the present invention. 
         FIGS. 20A-20C  are cross-sectional side views of yet another embodiment of an apparatus for cannulating a body lumen, in accordance with the present invention. 
         FIGS. 21A-21C  are cross-sectional side views of still another embodiment of an apparatus for cannulating a body lumen, in accordance with the present invention. 
         FIGS. 22A-22C  are cross-sectional side views of yet another embodiment of an apparatus for cannulating a body lumen, in accordance with the present invention. 
         FIGS. 23A and 23B  are cross-sectional side views of alternative embodiments of an apparatus for cannulating a body lumen, in accordance with the present invention. 
         FIGS. 24A and 24B  are end views of the apparatus of  FIGS. 23A and 23B , respectively. 
         FIG. 25A  is a cross-sectional side view of another embodiment of an apparatus for cannulating a body lumen, in accordance with the present invention. 
         FIG. 25B  is an end view of the apparatus of  FIG. 25A . 
         FIG. 26  is a perspective view of a computer that may be coupled to an optical imaging assembly of an apparatus, such as that shown in  FIGS. 1A-1C . 
         FIG. 27A  is a perspective view of yet another embodiment of an apparatus for cannulating a body lumen, including a plurality of oxygen sensors, in accordance with the present invention. 
         FIG. 27B  is a perspective detail, showing a catheter of the apparatus of  FIG. 27A . 
         FIG. 27C  is a cross-sectional view of the apparatus of  FIGS. 27A and 27B , taken along line  27 C- 27 C. 
         FIG. 27D  is a detail of a tubular segment extending to an oxygen sensor of the apparatus of  FIGS. 27A-27C . 
         FIG. 28A  is a cross-sectional side view of still another embodiment of an apparatus for cannulating a body lumen, including an oxygen sensor and an occlusion balloon. 
         FIG. 28B  is a cross-section of the apparatus of  FIG. 28A , taken along line  28 A- 28 A. 
         FIGS. 29A-29C  are cross-sectional views, showing a method for cannulating a coronary sinus ostium extending from a right atrium of a heart, in accordance with the present invention. 
         FIGS. 30A-30C  are details, showing alternate tips of a stabilization member that may be included in the apparatus shown in  FIGS. 29A-29C . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning to the drawings,  FIGS. 1A-1C  show a first preferred embodiment of an apparatus  10  for imaging a body lumen, e.g., for visualizing, accessing, and/or cannulating a body lumen from a body cavity (not shown). In a preferred embodiment, as explained further below, the apparatus  10  may be used for imaging a wall of a right atrium of a heart, e.g., for visualizing, accessing, and/or cannulating a coronary sinus ostium, although the apparatus  10  may be used for visualizing, accessing, and/or cannulating other body lumens as well. Generally, as shown in  FIG. 1A , the apparatus  10  may include a catheter or other elongate member  12 , a balloon or other expandable member  50  on a distal end  16  of the catheter  12 , and an imaging assembly  62  carried by the distal end  16  of the catheter  12  for imaging through the balloon  50 . 
     The catheter  12  generally is an elongate tubular body including a proximal end  14 , a distal end  16  having a size and shape for insertion into a patient&#39;s body, and a central longitudinal axis  18  extending between the proximal and distal ends  14 ,  16 . The catheter  12  may include one or more lumens  20  also extending between the proximal and distal ends  14 ,  16 , e.g., a cannulation lumen  20   a , an inflation lumen  20   b , and one or more lumens  20   c ,  20   d  (best seen in  FIG. 1C ) for the imaging assembly  62 . 
     The catheter  12  may be substantially flexible, semi-rigid, and/or rigid along its length, and may be formed from a variety of materials, including plastic, metal, and/or composite materials, as is well known to those skilled in the art. For example, the catheter  12  may be substantially flexible at the distal end  16  to facilitate advancement through tortuous anatomy, and/or may be semi-rigid or rigid at the proximal end  14  to enhance pushability of the catheter  12  without substantial risk of buckling or kinking. 
     Preferably, the catheter  12  is steerable, i.e., the distal end  16  may be controllably deflected transversely relative to the longitudinal axis  18 . In the embodiment shown in  FIGS. 1A-1C , a single pullwire or other steering element  22  may be provided, e.g., within one of the lumens  20 , for steering the distal end  16  of the catheter  12  in one transverse plane (thereby providing one degree of freedom). Alternatively, in another embodiment, such as that shown in  FIGS. 2A and 2B , two pullwires  22 ′ may be provided for steering the distal end  16 ′ of the catheter  12 ′ in two orthogonal planes (thereby providing two degrees of freedom). 
     The pullwire(s)  22  may be a cable, wire, band, and the like that may be slidably disposed within a lumen, such as the inflation lumen  20   b  shown in  FIG. 1C . The pullwire(s)  22  may be attached or otherwise fixed relative to the catheter  12  at a location adjacent the distal end  16 , preferably offset radially outwardly from the central axis  18 . Thus, when the pullwire  22  is pulled proximally, e.g., from the proximal end  14  of the catheter  12 , a bending force may be applied to the distal end  16 , causing the distal end  16  to bend transversely relative to the central axis  18 . 
     The catheter  12  may also include a handle or other control mechanism  30  coupled to or otherwise provided on the proximal end  14  of the catheter  12 . The handle  30  may include one or more steering controls  32  that may be actuated to steer the distal end  16  of the catheter  12 . For example, as shown in  FIG. 1 , a dial  32  may be provided that may be coupled to the pullwire  22 . The dial  32  may be rotated to apply a proximal force on the pullwire  22 , thereby bending the distal end  16  of the catheter  12 . 
     Alternatively, as shown in  FIGS. 2A and 2B , a dial  32   a ′ and a trigger  32   b ′ may be provided on the handle  30 ′ that may be coupled to respective pullwires  22   a ,′  22   b .′ Thus, the dial  32 ′ may be rotated to bend the catheter  12 ′ in a first direction and the trigger  32   b ′ may be pulled to bend the catheter  12 ′ in a second direction, preferably substantially perpendicular to the first direction. The steering control(s) may be biased, e.g., to return the distal end  32  or  32 ′ of the catheter  12  or  12 ′ to a generally straight configuration when the control(s) is(are) released. Alternatively, each steering control may be coupled to a pair of opposing pullwires opposite one another relative to the central axis (not shown) such that actuating the control in one direction bends the distal end one direction, while actuating the control in an opposite direction bends the distal end in an opposite direction. It will be appreciated that other control mechanisms and/or steering arrangements may be provided, including one, two, or more degrees of freedom, as are well known to those skilled in the art. 
     The handle  30  may also include ports and/or other connections for connecting other components to the catheter  12 . It will be appreciated that any known connectors may be provided for permanently or temporarily connecting components to the catheter  12 . For example, a luer lock connector may be used to connect tubing or other fluid-conveying components to the handle  30 . 
     As shown in  FIG. 1A , a syringe or other source of fluid  34 , e.g., including saline, carbon dioxide, nitrogen, or air, may be connected via tubing  36  to the inflation lumen  20   b  (not shown, see  FIG. 1C ) for inflating the balloon  50 . The syringe  34  may also provide a source of vacuum for deflating the balloon  50 , as is known in the art. Another source of fluid  38 , e.g., saline, and/or a therapeutic or diagnostic agent, may be connected via tubing  40  to the cannulation lumen  20   a  for delivering fluid beyond the distal end  16  of the catheter  12 . 
     In addition, an access port  42  may also communicate with the cannulation lumen  20   a , e.g., including a hemostatic seal and the like (not shown), for delivering one or more instruments (such as guidewire  80 , shown in  FIG. 1B ) through the cannulation lumen  20   a , as explained further below. Optionally, the handle  30  may include a shape, size, and/or contour (not shown) for facilitating manipulating the catheter  12  during use. 
     Returning to  FIGS. 1A and 1B , a substantially transparent balloon  50  may be provided on the distal end  16  of the tubular member  12 . The balloon  50  may be expandable from a contracted condition (not shown) to an enlarged condition when fluid is introduced into an interior  60  of the balloon  50 . In the embodiment shown, a channel  52  may extend through the balloon  50  that communicates with a lumen  20  of the catheter  12 , e.g., the cannulation lumen  20   a . Preferably, the channel  52  extends through the balloon  50  concentrically with the central axis  18 , as best seen in  FIG. 1B . 
     In an exemplary embodiment, the balloon  50  may be formed from substantially noncompliant material, e.g., polytetrafluoroethylene (PTFE), expanded polytetrafluoroethylene (EPTFE), fluorinated ethylenepropylene (FEP), polyethylene teraphathalate (PET), urethane, olefins, and polyethylene (PE), such that the balloon  50  may expand to a predetermined shape when fully inflated to the enlarged configuration. Preferably, in the enlarged configuration, the balloon  50  may have a distal surface  54  that is substantially flat or otherwise configured for contacting a wall of a body cavity, such as the right atrium (not shown). Alternatively, as shown in  FIGS. 19A and 19B , an apparatus  710  may be provided that carries a balloon  750  having a frustoconical shape and/or a convex distal surface  754 . 
     The material may be sufficiently flexible and/or elastic such that the distal surface  54  may conform substantially to the wall of the body cavity. Preferably, the balloon  50  is also sufficiently noncompliant to displace blood or other fluid from between the distal surface  54  and the wall of the body cavity to facilitate imaging the wall through the balloon  50 , as explained further below. Alternatively, the balloon  50  may be formed from compliant and/or elastomeric materials, such as silicone, latex, isoprene, and chronoprene. 
     In the exemplary embodiment shown in  FIG. 1B , the balloon  50  may be formed from one or more panels that may be attached to one another, e.g., using an adhesive (such as an adhesive cured using ultraviolet (“UV”) light), sonic welding, and/or heating, after lapping or butting adjacent panels together. Alternatively, the balloon  50  may be molded around or within a mold (not shown) having a desired shape for the balloon  50  in the enlarged condition. 
     The resulting balloon  50  may include a proximal end  56  that may be attached to an outer surface of the catheter  12 , e.g., using an adhesive, heating, sonic welding, an interference fit, and/or an outer sleeve. The channel  52  may be formed from the same material as the rest of the balloon  50 , and a proximal end  58  of the channel may be attached to the distal end  16  of the catheter  12 , e.g., within or concentric with the cannulation lumen  20   a . Alternatively, the channel may be formed from a semi-rigid or rigid tubular member, as shown in  FIGS. 6-10 , and described further below. 
     As best seen in  FIG. 1B , the interior  60  of the balloon  50  may have a generally annular shape that preferably communicates with the inflation lumen  20   b  (not shown, see  FIG. 1C ) of the catheter  12 . Substantially transparent inflation media, e.g., saline, carbon dioxide, nitrogen, air, and the like, may be introduced into the interior  60  of the balloon  50  to expand the balloon  50  towards the enlarged condition shown in  FIGS. 1A and 1B . As used herein, “transparent” refers to any material and/or fluid that may permit sufficient light to pass therethrough in order to identify or otherwise visualize objects through the material and/or fluid. “Light” as used herein may refer to light radiation within the visible spectrum, but may also include other spectra, such as infrared (“IR”) or ultraviolet (“UV”) light. 
     Alternatively, the balloon and/or channel may have different configurations, such as that shown in  FIGS. 3A-3C  and  4 . For example, as shown in  FIGS. 3A-3C , an apparatus  110  is shown that includes a catheter  112  that may include one or more lumens, e.g., lumens  120   c ,  120   d  for receiving components of an imaging assembly  162  therethrough, similar to the previous embodiment. Unlike the previous embodiment, a cannulation lumen  120   a  extends along an outer surface of the catheter  112  that extends between a proximal end (not shown) to a distal end  116  of the catheter  112 . The lumen  120   a  may be a separate tubular member attached to the catheter  112  or may be an integral part of the catheter  112 , e.g., formed as a single extrusion. 
     A balloon  150  may be carried on the distal end  116  of the catheter  112  that defines an interior  160  communicating with an inflation lumen (not shown) that extends to the proximal end of the catheter  112 , similar to the previous embodiment. A channel  152  may extend along a wall of the balloon  150  that communicates with the cannulation lumen  120   a . The channel  152  may be defined by a panel of material attached to the balloon  150 , similar to the materials and methods for making balloon  50 , as described above. Alternatively, an inner balloon panel may be provided within an outer balloon panel and the panels may be attached to one another, e.g., along one or more seams defining the channel  152 . 
     A nipple or annular collar  157  may be provided on the distal surface  154  of the balloon  150 , e.g., to guide a guidewire  80  or other instrument out of the balloon  150 , and/or to stabilize the device relative to a body lumen or other tissue structure (not shown). Thus, a guidewire  80  may be inserted into the cannulation lumen  120   a  from the proximal end of the catheter  112 , the channel  152  guiding the guidewire  80  through the balloon  150  until it exits through the nipple  157  to a location beyond the distal surface  152  of the balloon  150 . 
     In another alternative, shown in  FIG. 4 , an inner balloon  251  may be provided within an interior  260  of an outer balloon  250 . The inner balloon  251  may be expandable to a size and/or shape that is smaller than the outer balloon  250 , thereby defining a channel  252  between the balloons  251 ,  252 . Thus, a guidewire  80  or other instrument (not shown) may be inserted into a cannulation lumen  220   a , e.g., extending along an outer surface of the catheter  212 . The guidewire  80  may enter the channel  252  between the balloons  251 ,  252  until it exits through a nipple  257 , similar to the embodiment shown in  FIGS. 3A-3C . 
     In a further alternative, a balloon may be provided without a channel extending therethrough, as shown, for example, in  FIGS. 20A-22C , and described further below. 
     In yet another alternative, shown in  FIGS. 5A-5C , an apparatus  310  may be provided that includes a mechanically expandable member  350  carried on a distal end  316  of a catheter  312 . A frame  352  may be coupled to the distal end  316  that may support a substantially transparent, flexible membrane  354 . The frame  352  may include a plurality of members that are movable away from and towards one another, thereby causing the membrane  354  to move between contracted and enlarged conditions. 
     The frame  352  may be actuated from a proximal end (not shown) of the catheter  312 , e.g., to cause the frame  352  to expand radially outwardly, as shown in  FIGS. 5B and 5C . As the frame  352  expands, the membrane  354  may provide a substantially transparent surface  356  through which an optical imaging assembly, e.g., including an optical fiber bundle  364  and/or a light guide  368 , similar to that described further below, may obtain optical images. Optionally, an interior  358  of the membrane  354  may be filled with a substantially transparent fluid, similar to the balloons described above, to facilitate imaging through the expandable member  350 . 
     Returning to  FIGS. 1A-1C , the imaging assembly  62  generally includes an optical imaging element  64  that is exposed within the interior  60  of the balloon  50  for capturing light images through the balloon  50 . In a preferred embodiment, the optical imaging element  64  includes a bundle of optical fibers, e.g. a coherent image bundle, that extends between the proximal and distal ends  14 ,  16  of the catheter  12 , e.g., through the lumen  20   d , as shown in  FIG. 1C . Preferably, the fiber bundle  64  includes about ten thousand (10,000) optical fibers, although it may include between about one and fifty thousand (1,000-50,000) fibers in order to provide a desired resolution in the images obtained by the fiber bundle  64 . 
     A lens  66 , e.g., a GRIN or self-oc lens, may be coupled to the fiber bundle  64  in order to focus light from beyond the distal surface  54  of the balloon  50  onto the fiber bundle  64  in order to generate a resolved image at the proximal end of the fiber bundle  64 , as is well known to those skilled in the art. Optionally, a directional prism or other optical element (not shown) may be provided for directing a field of view of the fiber bundle  64  as desired, as explained further below. 
     In addition, the imaging assembly  62  may include one or more light guides  68  carried by the distal end  16  of the catheter  12  for delivering light into the interior  60  and/or through the distal surface  54  of the balloon  50 . Although a single light guide  68  is shown in  FIGS. 1B and 1C , it will be appreciated that a plurality of light guides (not shown) may be provided in a common lumen or separate lumens (also not shown) within the catheter  12 . The light guide(s)  68  may include a plurality of optical fibers, e.g., formed from acrylic and the like, that may extend to the proximal end  14  of the catheter  12 . As shown in  FIG. 1A , a source of light  70  may be coupled to the light guide(s)  68 , e.g., via the handle  30 , for delivering light through the light guide(s)  68  and into the balloon  50 . 
     A device  72  may be coupled or otherwise provided at the proximal end  14  of the apparatus  10  for acquiring and/or capturing images obtained by the optical imaging assembly  62 . For example, one or more lenses (not shown) may be coupled to the fiber bundle  64  for focusing and/or resolving light passing through the fiber bundle  64 , e.g., to pass the image to the device  72 . The device  72  may include a CCD, CMOS, and/or other device, known to those skilled in the art, e.g., to digitize or otherwise convert the light images from the fiber bundle  64  into electrical signals that may be transferred to a processor and/or display (not shown). 
     For example, as shown in  FIG. 26 , a computer  82  may be coupled to the device  72  (not shown, see  FIG. 1A ), e.g., by a cable  84 . Alternatively, instead of the computer  82 , other display or capture devices may be coupled to the device  72 , such as a laptop computer, handheld or PDA device, a computer terminal, a LCD display, standard video monitor, and the like (not shown), to display and/or store the images acquired from the fiber bundle  64 . Optionally, the computer  82  (or other capture device) may provide electrical power to the device  72 , light source  70 , and/or other components of the apparatus  10 . 
     For a cable connection between the device  72  and the computer  82 , various protocols may be used, such as USB, Firewire, standard video signal protocols, and the like. Alternatively, the computer  82  may be coupled to the device  72  via a wireless connection, for example, including one or more transmitters and/or receiving using radio frequency signals, Bluetooth, infrared links, and the like. 
     In addition, the computer  82  may run software modules to enable capture, viewing, and/or manipulation of images obtained by the optical imaging assembly  62 . The cable  84 , the handle  30  (not shown, see  FIG. 1A ), or other component of the apparatus  10  may include interface features  86 , such as buttons, toggles, scroll bars, dials, and the like, to facilitate interfacing with software running on the computer  82 . Functions that may be performed using the interface  86  may include launching image acquisition software on the computer  82 , initiating or terminating image capture, initiating still frame capture, reviewing or displaying captured images, etc. The handle  30  or other component of the apparatus  10  may also contain feedback features, e.g., one or more LEDs or LCDs, to provide feedback from software on the computer  82 , e.g., related to the status of connection(s) between the computer  82  and the apparatus  10 , the power status of the apparatus  10 , the function of the apparatus  10 , and the like. 
     Optionally, the apparatus  10  may include additional data acquisition features, such as a microphone (not shown), e.g., allowing procedure notes to be dictated during an imaging procedure or allowing the apparatus  10  and/or computer  10  to be controlled by voice commands. In addition or alternatively, drivers and/or software may be stored on a memory chip (not shown) in the apparatus  10  that may be uploaded to the computer  82  when connected to the apparatus  10 . When a complex interface is used to connect the apparatus  10  to the computer  82  or other display device, the apparatus  10  and/or the computer  82  may be capable of disabling the complex interface and enable simple video output. 
     Turning to  FIGS. 6-10 , another preferred embodiment of an apparatus  410  is shown for visualizing and/or cannulating a body lumen. Similar to the previous embodiments, the apparatus  410  generally includes a catheter  412 , a balloon  450  carried by the catheter  412 , and an imaging assembly  462  for imaging through the balloon  450 . 
     Also, similar to the previous embodiments, the catheter  412  may be an elongate tubular body including a proximal end  414 , a distal end  416 , and a central longitudinal axis  418  extending therebetween. The catheter  412  may be substantially flexible, semi-rigid, and/or rigid along its length, and may be formed from a variety of materials, including plastic, metal, and/or composite materials. The catheter  412  may have a diameter between about five and ten French (1.67-3.33 mm), and preferably between about six and eight French (2.00-2.67 mm). 
     The catheter  412  may include one or more lumens  420  also extending between the proximal and distal ends  414 ,  416 , e.g., a cannulation lumen  420   a , an inflation lumen  420   b , and one or more lumens  420   c - f  for the imaging assembly  462  and/or one or more pullwires or other steering elements  422 . In addition, the catheter  412  may include a handle (not shown) and/or other components, e.g., sources of fluid, a light source, an image capture device, and the like (also not shown) on the proximal end  414 , similar to the other embodiments described herein. 
     Preferably, the catheter  412  includes multiple extrusions that are attached to one another to provide a desired length. For example, the catheter  412  may include a proximal portion  412   a  having a first cross-section, shown in  FIGS. 8A and 8B , and a distal portion  412   b  having a second cross-section, shown in  FIG. 8C . The proximal portion  412   a  may have a length between about nine and thirty six inches (22-90 cm), and preferably between about eighteen and twenty eight inches (45-70 cm). 
     The proximal portion  412   a  preferably includes three lumens, a cannulation lumen  420   a , an inflation lumen  420   b , and an accessories lumen  420   c . The cannulation lumen  420   a  may provide a path for a guidewire or other instrument, fluid, and the like to pass between the proximal and distal ends  414 ,  416  of the catheter  412 . Optionally, a tube  424 , e.g., made from polyamide and the like, may be provided within the cannulation lumen  420   a , e.g., to reinforce the cannulation lumen  420   a  and/or catheter  412 . The inflation lumen  420   b  may communicate with an interior  460  of the balloon  450 , similar to the previous embodiments, for delivering substantially transparent inflation media into the balloon  450 . The accessories lumen  420   c  may carry a plurality of components, e.g., an optical imaging (fiber optic) bundle  464 , pull-wire  422 , and/or a set of light guides  468 , similar to the previous embodiments described above. 
     With reference to  FIGS. 7A and 8C , the distal portion  412   b  may have a length between about 25.4-101.6 millimeters (mm), and preferably between about 50.8-76.2 millimeters (mm). The distal portion  412   b  may be substantially permanently attached to the proximal portion  412   a , e.g., using a lap or butt joint, and/or an adhesive, interference fit, heating, and/or sonic welding. The distal portion  412   b  may include continuations of the cannulation lumen  420   a  and inflation lumen  420   b  from the proximal portion  412   a . In addition, the distal portion  412   b  may include a light guide lumen  420   d , a fiber optic lumen  420   e , and a pullwire lumen  420   f  that may communicate with the accessories lumen  420   c  when the proximal and distal portions  412   a ,  412   b  are attached to one another. 
     Preferably, the fiber optic lumen  420   e  is located as far away from the cannulation lumen  420   a  as possible in order to maximize a field of view of the fiber bundle  464  received therein. For example, as shown in  FIG. 8C , the distal portion  412   b  may include a ridge  421  extending axially along an outer surface of the distal portion  412   b , thereby maximizing a distance that the fiber optic lumen  420   e  may be disposed away from the cannulation lumen  420   a . When the fiber bundle  464  is inserted into the catheter  412 , the fiber bundle  464  may be received in the fiber optic lumen  420   e  in the distal portion  412   b , and in the accessories lumen  420   c  in the proximal portion  412   a . The fiber bundle  464  may be secured at one or more locations within the lumens  420   e ,  420   c , e.g., using an adhesive and the like. Thus, the location of the fiber bundle  464  may be fixed in the distal portion  412   b  to stabilize its field of view relative to the catheter  412 . 
     The pullwire lumen  420   f  may also be located as far away from the central axis  418 , e.g., due to another ridge extending the outer surface. This arrangement may maximize a bending force applied to the catheter  412  when the pullwire  422  is pulled proximally. 
     Turning to FIGS.  7 B and  9 A- 9 C, the set of light guides  468  may be received in the accessories lumen  420   c  in the proximal portion  412   a  and in the light guide lumen  420   d  in the distal portion  412   b . The set of light guides  468  may include between about one and twenty five, and preferably between about four and ten, elongate light guides. Each of the light guides  468  may be formed from a substantially transparent acrylic fiber or other light transmitting material, e.g., having a diameter between about twenty five micrometers and one millimeter (25 μm-1 mm), and preferable between about two hundred fifty and five hundred micrometers (250-500 μm). 
     At the proximal end  414  of the catheter  412 , the light guides  468  may be substantially cylindrical, while towards the distal end  416  of the catheter  412 , the light guides  468  may be tapered and/or flattened. For example, the light guides  468  may taper within a few inches of the proximal end  414  of the catheter  412 , preferably reducing an overall cross-section of the light guides  468  by as much as fifty percent (50%). The light guides  468  may be disposed loosely within the accessories lumen  420   c  of the proximal portion  412   a.    
     The enlarged size of the light guides  468  at the proximal end  414  of the catheter  412  may facilitate connecting the light guides  468  to a light source (not shown), as will be appreciated by those skilled in the art. Optionally, exposed lengths (not shown) of the light guides  468  beyond the proximal end  414  of the catheter  412  may be further enlarged to facilitate such connections. For example, if the light guides  468  are acrylic fibers, heat may be applied, e.g., up to one hundred seventy degrees Fahrenheit (170° F.), to cause the light guides  468  to shorten. The acrylic material may increase in diameter as it shortens, thereby increasing the diameter of the light guides  468  by as much as three times as they shorten. This may allow the light guides  468  to be columnated and connected to a light source without requiring a lens (not shown). 
     As the light guides  468  transition from the proximal portion  412   a  to the distal portion  412   b , they may be linearly aligned and/or secured to each other, e.g., using an epoxy or other adhesive, and/or by reflowing the fiber material, such that surfaces of adjacent fibers are bonded at adjacent contact points. To align the light guides  468  in a desired orientation within the distal portion  412   b , the light guides  468  may be received in an axial ridge or slot  423  within the distal portion  412   b , as shown in  FIG. 8C . 
     The bonded array of light guides  468  may provide a hinge, i.e., biasing the distal portion  412   b  of the catheter  412  to bend in a predetermined direction. Specifically, the light guides  468  may provide a higher bending moment along a bond axis “x” (shown in  FIG. 9C ), while exhibiting a much lower bending moment along an axis orthogonal to the bond axis “x.” As the pullwire  422  is pulled proximally, the force may be transferred to the distal portion  412   b  of the catheter  412 . Because of the asymmetric bending moments created by the light guides  468 , the distal portion  412   b  of the catheter  412  may bend in one plane orthogonal to the bond axis “x,” i.e., towards the pullwire  422 , while resisting bending along the bond axis “x.” This may cause the catheter  412  to curve from a location where the pullwire  422  transitions from being located at the center of the catheter  412  (e.g., as shown in  FIG. 8A ) to a location on the distal end  416  where the pull wire  422  is fixed (e.g., as shown in  FIG. 8C ). 
     Turning to  FIGS. 10-11B , a bundle  464  of optical fibers may be provided, similar to the embodiments described above. Preferably, a lens  466  is coupled to the fiber bundle  464 , e.g., a GRIN or self-oc lens, as described above. For example, as shown in  FIGS. 11A and 11B , a sleeve  467 , e.g., shrink wrap and the like, may be provided that may be secured around the lens  466  and the optical imaging bundle  464 . Optionally, a fluid or other material (not shown) may be provided between the lens  466  and the optical imaging bundle  464  to minimize losses and/or reflection at the transition, as is known to those skilled in the art. 
     Turning to  FIG. 10  with continued reference to  FIG. 6 , a tubular extension  430  may extend from the distal end  416  of the catheter  412 . The tubular extension  430  may include a lumen  432  extending between proximal and distal ends  434 ,  436  of the tubular extension  430 . Preferably, the tubular extension  430  has a substantially smaller diameter or other cross-section than the distal end  416  of the catheter  412 . 
     The proximal end  434  of the tubular extension  430  may be attached to the distal end  416  of the catheter  412  such that it is coextensive with the cannulation lumen  420   a . Thus, an instrument or fluid introduced through the cannulation lumen  420   a  may pass freely through the lumen  432  of the tubular extension  430 . In addition, attaching the tubular extension  430  eccentrically to the catheter  412  opposite the optical imaging bundle  464  may minimize the extent that the tubular extension  430  obstructs the field of view of the optical imaging bundle  464 . 
     In one embodiment, the proximal end  434  of the tubular extension  430  may be at least partially received in the cannulation lumen  420   a  or in a recess (not shown) concentric with the cannulation lumen  420   a . Alternatively, the proximal end  434  of the tubular extension  430  may be butted against the distal end  416  of the catheter  412 . In addition or alternatively, the tubular extension  4430  may be bonded to the catheter  412 , e.g., using an adhesive, heating, sonic welding, and the like. 
     The balloon  450  may include a proximal end  452  attached to the distal end  416  of the catheter  412  and a distal end  456  attached to the distal end of the tubular extension  430 . The proximal end  452  of the balloon  450  may be secured to the outer surface of the catheter  412 , e.g., using an adhesive, heating, an interference fit, an outer collar (not shown), and the like, similar to the other embodiments described herein. 
     Turning to  FIG. 14 , the distal end  456  of the balloon  450  may be attached to the distal end  436  of the tubular extension  430  such that the balloon  450  at least partially inverts on itself. This may facilitate close contact between the balloon  450  and a tissue surface being viewed (not shown), which may reduce optical distortion and/or facilitate clearing fluid from between the balloon  450  and the contacted tissue surface. In addition, this arrangement may prevent the distal end  436  of the tubular extension  430  from extending substantially beyond the distal surface  454  of the balloon  450 . 
     Similar to the previous embodiments, the balloon  450  may be expandable from a contracted condition, as shown in  FIG. 12A , to an enlarged condition, as shown in FIGS.  6  and  12 B- 12 D. In the enlarged condition, the balloon  450  may define a substantially flat distal surface  454  that may facilitate imaging tissue structures beyond the balloon  450  with the optical imaging bundle  464 . Optionally, the balloon  450  may include a reflective coating (not shown) on an inside surface thereof, e.g., the proximal surface(s) opposite the distal surface  454 , e.g., to concentrate light towards the distal surface  454  that may otherwise reflect or pass proximally through the balloon  450 . 
     Turning to  FIGS. 12A-13D , a method is shown for cannulating a body lumen communicating with a body cavity, e.g., a coronary sinus ostium  90  extending from a right atrium  92 . Although the apparatus  410  shown is similar to that shown in  FIGS. 6-10 , other embodiments described herein may be used to complete similar methods. Initially, as shown in  FIG. 12A , the apparatus  410  may be provided with the balloon  450  in the contracted condition. If the balloon  450  is formed from noncompliant and/or inflexible material, the balloon  450  may be folded, twisted, or otherwise compressed into the contracted condition. With the balloon collapsed, the fiber optic imaging bundle  464  may provide an unfocused image, as shown in  FIG. 13A . 
     The distal end  416  of the apparatus  410  may be introduced into a patient&#39;s body using conventional methods used for delivering catheters or other instruments. For example, the apparatus  410  may be introduced percutaneously into the patient&#39;s vasculature from a peripheral vein, such as the femoral vein. The apparatus  410  may be advanced endoluminally, e.g., into the vena cava (not shown) and into the right atrium  92  of the heart. Optionally, the apparatus  410  may be carried within a sheath, catheter, or other delivery device (not shown) that may protect the balloon  450  or otherwise facilitate advancing the apparatus  410  through the patient&#39;s vasculature. 
     Once located within the right atrium  92 , the balloon  450  may be expanded, as shown in  FIGS. 6 and 12B  (e.g., after deploying at least the distal end  416  from any delivery device). The apparatus  410  may then be manipulated to place the distal surface  454  of the balloon  450  into contact with the wall  94  of the heart within the right atrium  92 , as shown in  FIG. 12B . Optionally, this manipulation may involve steering the distal end  416  of the apparatus  450 , e.g., using one or more pullwires or other steering mechanisms actuated from the proximal end (not shown) of the apparatus  410 . 
     In addition or alternatively, other imaging systems may be used to monitor the apparatus  410  to facilitate accessing the coronary sinus  90 . For example, external imaging systems, such as fluoroscopy, ultrasound, magnetic resonance imaging (MRI), and the like, may provide feedback as to the location and/or relative position of the distal end  416  of the apparatus  412 . The distal end  416  may include markers, e.g., radiopaque bands and the like (not shown), that may facilitate such imaging. External imaging may ensure that the apparatus  410  is generally oriented towards the coronary sinus ostium  90  before optical images are acquired and the apparatus  410  is manipulated more precisely. 
     With the distal surface  454  of balloon  450  placed against the wall  94  of the heart, the fiber bundle  464  may be activated to image the wall  94 . Sufficient distal force may be applied to the apparatus  410  to squeeze blood or other fluid from between the distal surface  454  and the wall  94 , thereby clearing the field and facilitating imaging the wall  94 . Optionally, a substantially transparent fluid, e.g., saline, may be delivered through the catheter  412  and the tubular extension  430  to further direct blood or other fluid away from the distal surface  454  of the balloon  450  or otherwise clear the field of view of the fiber bundle  464 . 
     Using the fiber bundle  464  to image the wall  94 , the apparatus  410  may be moved along the wall  94  until a target structure is within the field of view. For example, as shown in  13 B, the coronary sinus ostium  90  may be seen entering the field of view, as the balloon  450  approaches the coronary sinus ostium  90 , as shown in  FIG. 12B . The apparatus  410  may be moved further, as shown in  FIG. 12C , until the coronary sinus ostium  90  is centered in the field of view, as shown in  FIG. 13C . Preferably, the center of the field of view corresponds to the central axis  418  of the apparatus  410 , e.g., aligning the tubular extension  430  with the coronary sinus ostium  90 . 
     Once the coronary sinus ostium  90  is aligned with the tubular extension, the balloon  450  may be partially deflated, as shown in  FIG. 12D , and the tubular extension  430  may be advanced at least partially into the coronary sinus  90 . Thus, the tubular extension  430  may stabilize the apparatus  410  relative to the coronary sinus  90 . One or more instruments, e.g., a guidewire (not shown), may be advanced into the coronary sinus  90  to access one or more coronary veins (also not shown) via the coronary sinus  90 . Alternatively, the balloon  450  may be fully deflated, and the tubular extension  430  may be advanced into the coronary sinus  90  to guide the distal end  416  of the apparatus  410  into the coronary sinus  90  and/or into the coronary veins. 
     In one embodiment, a guidewire may provide a rail over which other instruments may be advanced into the coronary veins. For example, before or after the guidewire has been placed within a target coronary vein, the apparatus  410  may be removed from the right atrium  92  and/or completely from the patient&#39;s body. A catheter or sheath (not shown) may be advanced over the guidewire to access the coronary vein and/or to perform a procedure there. For example, with the catheter or sheath placed within the target coronary vein, the guidewire may be removed, and an electrical lead, e.g., a pacing lead for a pacemaker (also not shown), may be advanced into the coronary vein for implantation. 
     In one embodiment, an expandable sheath (not shown) may be delivered via the tubular extension  430  into the coronary veins, e.g., to deliver a pacing lead. Exemplary sheath apparatus and methods are disclosed in co-pending application Ser. No. 10/423,321, filed Apr. 24, 2003, the disclosure of which is expressly incorporated by reference herein. In another embodiment, the apparatus  410  may be used to deliver fluids or other materials into the coronary sinus  90 . For example, a radiopaque fluid may be retro-perfused into the coronary sinus  90 , e.g., for obtaining a venogram of one or more coronary veins within the heart. 
     Turning to  FIG. 15 , yet another embodiment of an apparatus  510  is shown for visualizing and/or cannulating a body lumen, e.g., a coronary sinus ostium  90 , similar to the previous embodiment. Similar to the embodiment shown in  FIGS. 6-10 , the apparatus  510  generally includes a catheter  512 , a balloon  550  carried by the catheter  512 , and an imaging assembly  562  for imaging through the balloon  550 . The catheter  512  may be an elongate tubular body including a proximal end (not shown), a distal end  516 , and a central longitudinal axis  518  extending therebetween. 
     The catheter  512  may include one or more lumens  520  also extending between the proximal and distal ends  514 ,  516 , e.g., a cannulation lumen  520   a , an inflation lumen (not shown), and one or more lumens (also not shown) for the imaging assembly  562  and/or one or more pullwires or other steering elements (also not shown). A tubular extension  530  may extend from the distal end  516  of the catheter  512 , including a lumen  532  extending between proximal and distal ends  534 ,  536  of the tubular extension  430  that preferably communicates with the cannulation lumen  520   a.    
     Similar to the previous embodiments, the balloon  550  may be expandable from a contracted condition (not shown) to an enlarged condition, shown in  FIG. 15 . In the enlarged condition, the balloon  550  may define a substantially flat distal surface  554  that may facilitate imaging tissue structures beyond the balloon  550  with the imaging assembly  562 . 
     Unlike the previous embodiment, at least part of the imaging assembly  562  may be provided on an arm  568  that is extendable from the distal end  516  of the catheter  512 . For example, a fiber optic imaging bundle  564  may be carried by the arm  568 , while one or more light guides (not shown) may be provided on the distal end  516  of the catheter  512 , similar to the apparatus  410  shown in  FIGS. 6-10 . Alternatively, one or more light guides (not shown) may be carried by the arm  568 , in addition or instead of the fiber bundle  564 . 
     A lens and/or prism  566  may also be carried by the arm  568  for focusing and/or redirecting the field of view of the fiber bundle  564 . Preferably, a lens and prism  566  may be provided for centering the field of view towards a location where the central axis  518  intersects the distal surface  554  of the balloon  550 . In addition or alternatively, the arm  568  may be bent to orient the fiber bundle  564  in a desired direction. 
     The arm  568  may be movable from a retracted profile (not shown), wherein the arm  568  lies close to or against the distal end  516  of the catheter  512 , and an extended profile, shown in  FIG. 15 , wherein the arm  568  extends laterally away from the distal end  516  of the catheter  512 . In one embodiment, the arm  568  may be biased to the extended profile, and may be restrained in the retracted profile, e.g., by the balloon  550  when the balloon  550  is deflated to the contracted condition. Alternatively, the arm  568  may be movable freely relative to the catheter  512 , and a tether (not shown) may be connected to the arm  568  that is also connected to the balloon  550 . Thus, as the balloon  550  expands, the tether may pull the arm  568  radially outwardly to the extended profile. In yet another alternative, the arm  568  may be extended and/or retracted using an actuator (not shown) operable from the proximal end of the apparatus  510 . 
     The apparatus  510  may be used in methods similar to the apparatus  410  shown in  FIGS. 6-10 . One advantage of the apparatus  510  is that it may maximize the field of view of the fiber bundle  564 , as compared to the apparatus  410 . For example, as shown in  FIG. 16A , the apparatus  410  (shown in  FIGS. 6-10 ) may include an fiber optic imaging bundle  464  that is carried by the catheter  412  opposite a tubular extension  430 . Because the tubular extension  430  extends distally into the field of view “F” of the fiber bundle  464 , a blind spot BS 1  is created. Because the fiber bundle  464  is disposed as far away as possible from the tubular segment  430  on the catheter  410 , the blind spot BS 1  is minimized compared to moving the fiber bundle and tubular extension closer to one another (not shown), as will be appreciated by those skilled in the art. 
     Turning to  FIG. 16B , a field of view “F” of the apparatus  510  of  FIG. 15  is shown, which has a similar diameter compared to the apparatus  410 , assuming comparably sized fiber bundles  464 ,  564 . Because the fiber bundle  564  is carried by the arm  568  (see  FIG. 15 ), it is offset radially away from the tubular extension  530 , thereby reducing a blind spot BS 2  as compared to the blind spot BS 1  shown in  FIG. 16A . Thus, the arrangement of the fiber bundle  564  of the apparatus  510  of  FIG. 15  may maximize the field of view, thereby reducing the risk of tissue structures passing through the blind spot undetected. 
     Turning to  FIGS. 17A-17F , another embodiment of an apparatus  610  is shown that includes a catheter  612 , a balloon  650  carried by the catheter  612 , and an imaging assembly  662  for imaging through the balloon  650 . The apparatus  610  differs from the previous apparatus  510  shown in  FIG. 15 , including a pair of fiber optic imaging bundles  664  carried by arms  668 . The arms  668  may be extendable from a retracted profile, e.g., as shown in  FIG. 17A  to an extended profile, as shown in  FIGS. 17C-17F . 
     In addition, the balloon  650  may be formed from an elastomeric material, such as silicone, latex, isoprene, and chronoprene, such that the balloon  650  may expand outwardly in proportion to the amount of fluid delivered into an interior  660  of the balloon  650 . Preferably, the balloon  650  is attached to a tubular extension  630  extending from the distal end  616  of the catheter  612  such that, as the balloon  650  expands, a distal surface  654  of the balloon  650  may become substantially flat and/or at least partially evert, as shown in  FIGS. 17E and 17F . This expanded configuration may facilitate increased contact between the distal surface  654  and a tissue structure (not shown) to be imaged. 
     As the balloon  650  expands, it may allow the arms  668  to expand radially outwardly to the extended profile. In addition, the arms  668  may be bent such that the fiber bundle  664  is oriented substantially distally, as shown in  FIGS. 17B-17F . One or more light guides  666  may be provided on the distal end  616  of the catheter  612 , similar to the previous embodiments for providing light to illuminate the distal surface  654  of the balloon  650  and beyond. Optionally, one or more electrodes  617  may be provided on the distal end  616  of the catheter, e.g., for measuring electrical potential and/or to serve as radiopaque markers to facilitate imaging the apparatus  610 . 
     The apparatus  610  may be delivered into a body cavity, e.g., a right atrium, similar to the previous embodiments for imaging a body lumen, e.g., a coronary sinus ostium not shown). The pair of fiber bundles  664  may increase a field of view of the apparatus  610 , possibly eliminating any blind spots created by the tubular extension  630 , as compared to the apparatus  510  described above and including a single offset fiber bundle  564 . 
     Turning to  FIGS. 18A and 18B , an alternative embodiment of an apparatus  810  is shown that includes a catheter  812 , a balloon  850  carried on a distal end  516  of the catheter  812 , and an imaging assembly  862  for imaging through the balloon  850 . The balloon  850  may be expandable between contracted and enlarged conditions, similar to other embodiments described elsewhere herein. The apparatus  810  may include one or more additional or different components or features (not shown) described elsewhere herein, similar to the other embodiments. 
     In addition, the apparatus  810  may include an elongate tubular member  830  extending from a proximal end (not shown) of the catheter  812  to the distal end  816 , and through an interior  860  of the balloon  850 . The tubular member  830  may include a lumen  832  extending therethrough through which an instrument, e.g., a guidewire  80 , and/or a fluid (not shown) may be delivered to a location distally beyond the balloon  850 . The tubular member  830  may be substantially flexible, but is preferably semi-rigid or substantially rigid. 
     The apparatus  810  may be used to deliver one or more instruments or fluids into a body lumen, similar to the other embodiments described herein. In one embodiment, the tubular member  830  is fixed relative to the catheter  512 . In another embodiment, similar to that described below, the tubular member  830  may be slidable axially, i.e., distally and/or proximally, relative to the catheter  512  for changing a shape of the balloon  850  during a procedure. 
     Turning to  FIGS. 19A and 19B , another embodiment of an apparatus  710  for cannulating a body lumen, such as a coronary sinus ostium  90 , is shown. Similar to the previous embodiments, the apparatus  710  may include a catheter  712 , a balloon  750  carried by the catheter  712 , and an imaging assembly (not shown for simplicity) for imaging through the balloon  750 . 
     In addition, the apparatus  710  may include an elongate cannulation member  730  that is slidably received in a lumen  720   a  of the catheter  712 . The cannulation member  730  may be an elongate tubular body, including a lumen  832  extending between a proximal end (not shown) and a distal end  836  of the cannulation member  730 . The cannulation member  730  may be substantially flexible, semi-rigid, and/or rigid, similar to the catheters described above. 
     The balloon  750  may be expandable between a contracted condition (not shown), and an enlarged condition, shown in  FIGS. 19A and 19B . In the enlarged condition, the balloon  750  may assume a frustoconical shape. In addition, the balloon  750  may include a convex distal surface  754  or a substantially flat distal surface (not shown) in the enlarged condition. The balloon  750  may include a channel section  756  that may be attached to the cannulation member  730 , e.g., adjacent its distal end  736 . The channel section  756  may at least partially evert into an interior  760  of the balloon  750 , as shown in  FIG. 19A , and/or may extend beyond the distal surface  754  of the balloon  750 , depending upon the axial position of the cannulation member  730 . 
     During use, the cannulation member  730  may be provided initially retracted such that the channel section  756  of the balloon  750  everts into the interior  760  of the balloon  750 , as shown in  FIG. 19A . With the balloon  750  collapsed in the contracted condition, the apparatus  710  may be introduced into a patient&#39;s body, e.g., until the distal end  716  is located within a right atrium  92  of the patient&#39;s heart, similar to the previous embodiments. The balloon  750  may be expanded, e.g., by delivering a substantially transparent fluid into the interior  760  until the balloon  750  assumes the enlarged condition, as shown in  FIG. 19A . 
     The distal surface  754  of the balloon  750  may be placed against the wall  94  of the heart, and manipulated while imaging through the distal surface  754  with the imaging assembly. Preferably, the distal end  836  of the cannulation member  730  may remain flush or proximal to the distal surface  754 , thereby allowing the wall  94  to be imaged through the balloon  750 . A more proximal position may prevent the cannulation member  730  from interfering substantially with a field of view of the imaging assembly, which may facilitate aligning the apparatus  710  with the coronary sinus ostium  90 . 
     When the apparatus  710  is aligned with the coronary sinus ostium  90 , as shown in  FIG. 19B , the cannulation member  730  may be advanced distally into the coronary sinus  90 . Optionally, the balloon  750  may be at least partially deflated as or after the cannulation member  730  is advanced, thereby allowing the distal end  716  of the catheter  712  to be inserted into the coronary sinus  90  as well. 
     An instrument, e.g., a guidewire, catheter, and the like (not shown), may be delivered through the lumen  732  of the cannulation member  730 , e.g., to perform a diagnostic and/or therapeutic procedure within a region accessed, e.g., within a coronary vein (not shown). Once the procedure(s) is(are) completed, the apparatus  710  may be removed from the patient&#39;s body. 
     Turning to  FIGS. 20A-20C , still another embodiment of an apparatus  910  is shown for visualizing and/or cannulating a body lumen (not shown). Similarly to the previous embodiments, the apparatus  910  may include a catheter  912 , a balloon  950  carried by a distal end  916  of the catheter  912 , and an imaging assembly  962 , similar to the previous embodiments. 
     Unlike the previous embodiments, the balloon  950  may not include a channel extending therethrough, and instead includes an interior  960  that is substantially enclosed. A lumen, e.g., an inflation lumen  920   b , may extend from a proximal end (not shown) of the catheter  912  to the distal end  916  that communicates with the interior  960  of the balloon  950 . In addition, the catheter  912  may include a cannulation lumen  920   a  that may extend along an outer surface of the catheter  912  through which an instrument, e.g., guidewire  80 , and/or a fluid may be delivered to the distal end  916  of the catheter  912  outside the balloon  950 . 
     The apparatus  910  may also include an elongate member  930  that is slidable within the inflation lumen  920   b  or optionally through another lumen (not shown) that communicates with the interior  960  of the balloon  950 . Preferably, the elongate member  930  includes a substantially blunt distal end  936  that may be advanced into the interior  960  of the balloon  950 . For example, the elongate member  930  may be inserted into the inflation lumen  920   b  from the proximal end of the catheter  912 , or the elongate member  930  may not be removable from the catheter  912 , and, instead, may be slidable in a limited range within the inflation lumen  920   b.    
     During use, the apparatus  910  may be advanced into a patient&#39;s body, e.g., into a right atrium of a heart or other body cavity (not shown) with the balloon  950  collapsed, similar to the previous embodiments. Within the body cavity, the balloon  950  may be expanded, as shown in  FIG. 20A , such that the balloon  950  defines a substantially flat distal surface  954 . The distal surface  954  may be placed against a wall of the body cavity, and manipulated, e.g., steered and/or otherwise moved, until a target body lumen, e.g., a coronary sinus ostium (not shown) enters the field of view of a fiber optic imaging bundle  964  of the imaging assembly  962 , similar to the previous embodiments. 
     Once the target body lumen is located and the apparatus  910  is aligned with the body lumen, the elongate member  930  may be advanced through the inflation lumen  920   b  and into the interior  960  of the balloon  950 . The distal end  936  of the elongate member  930  may contact the distal surface  954  of the balloon  950 , whereupon, further distal movement of the elongate member  930  may cause the balloon  950  to change shape, as shown in  FIGS. 20B and 20C . Because of the substantially blunt shape of the distal end  936  of the elongate member, the balloon  950  may be changed without substantial risk of puncturing or otherwise damaging the balloon  950 . 
     For example, the elongate member  930  may be advanced to elongate the balloon  950  and/or reduce a diameter or other cross-section of the balloon  950 . This may at least partially introduce the balloon  950  into the body lumen, e.g., the coronary sinus, thereby stabilizing the apparatus  910  relative to the body lumen. Alternatively, the elongate member  930  may reduce a cross-section of the balloon  950 , thereby allowing an instrument, e.g., a guidewire  80 , to be advanced through the cannulation lumen  920   a  and past the balloon  950  without substantial risk of puncturing or otherwise damaging the balloon  950 . The guidewire  80  may be advanced into the body lumen, whereby additional instruments (not shown) may be advanced over the guidewire  80  into the body lumen, as described above. 
     Alternatively, as shown in  FIGS. 21A-21C , an apparatus  1010  may be provided that includes a balloon  1050  carried by a catheter  1012 , and an imaging assembly  1062  for imaging through the balloon  1050 . Similar to the previous embodiments, substantially transparent fluid, e.g., saline, may be introduced into the balloon  1050  to expand the balloon  1050  and allow a distal surface  1054  to be placed into contact with tissue structures, e.g., a wall of a heart, similar to the previous embodiments. 
     An elongate member, e.g., a guidewire  1030 , may be inserted through an inflation lumen  1020   b  of the catheter  912  into the interior of the balloon  1050 , e.g., after the balloon  950  has been inflated and/or used to identify and/or locate a body lumen (not shown), similar to the previous embodiment. As shown in  FIG. 21B , the guidewire  1030  may be advanced until a distal end  1036  of the guidewire  1030  punctures the balloon  1050  and passes therethrough into the target body lumen. Optionally, the distal end  1032  of the guidewire  1030  may be sharpened or otherwise adapted to facilitate puncturing the balloon  1050 . 
     As the inflation fluid escapes through the puncture created in the balloon  1050 , the balloon  1050  may collapse, as shown in  FIG. 21C . The guidewire  1030  may be advanced into the body lumen, and one or more instruments (not shown) may be advanced over the guidewire, e.g., after removing the apparatus  1010 , as described above. 
     In a further alternative, shown in  FIGS. 22A-22C , an apparatus  1110  may be provided that includes a catheter  1112 , a balloon  1150  carried on a distal end  1116  of the catheter  1112 , and an imaging assembly  1162  for imaging through the balloon  1150 . Similar to the previous embodiment, an inflation lumen  120   b  extends through the catheter  1112  to communicate with an interior  1160  of the balloon  1150 . Unlike the previous embodiment, a cannulation lumen  1120   a  extends along an outer surface of the catheter  1112 . 
     During use, as shown in  FIG. 22A , the apparatus  1110  may be introduced into a body cavity (not shown), whereupon the balloon  1150  may be expanded and contacted with a wall of the body cavity for imaging tissue structures therethrough. When the apparatus  1110  is aligned with a body lumen extending from the body cavity, the balloon  1150  may be at least partially deflated, as shown in  FIGS. 22B and 22C . Once the cannulation lumen  1120   a  is not obstructed by the balloon  1150 , a guidewire  80  or other instrument may be advanced through the cannulation lumen  1120   a  past the balloon  1150 , and preferably into the body lumen, similar to the procedures described above. 
     Turning to  FIGS. 23A-25B , yet another embodiment of an apparatus  1210  is shown for visualizing and/or cannulating a body lumen, e.g., a coronary sinus ostium extending from a right atrium of a heart (not shown). Similar to the previous embodiments, the apparatus  1210  includes a catheter  1212  carrying an imaging assembly  1262  on its distal end  1216 , which may include a fiber optic imaging bundle  1264  and one or more light guides  1268 , as described above. 
     In addition, the apparatus  1210  may include a solid bulb  1250  carried on the distal end  1216  of the catheter  1212 . The bulb  1250  may be formed from a substantially rigid or semi-rigid material that is substantially transparent, e.g., acrylic, polycarbonate, polymethlymethacrylate (PMMA), and nylon. The bulb  1250  may define an interior  1260  that may be filled with substantially transparent fluid, e.g., saline, to facilitate imaging through the bulb  1250  using the imaging assembly  1262 . 
     In the embodiment shown in  FIGS. 23A and 24A , the fiber optic imaging bundle  1264  and the light guide  1268  may be disposed side-by-side when viewed from the end of the catheter  1212 , as best seen in  FIG. 24A . In addition, similar to any of the embodiments described herein, the apparatus  1210  may include one or more pullwires, e.g., the two pullwires  1222  shown, for steering the catheter  1212 , as described above. 
     Alternatively, as shown in  FIGS. 23B and 24B , the apparatus  1210 ′ may include a centrally disposed fiber optic imaging bundle  1264 ,′ a plurality of light guides  1268 ′ may be disposed around the imaging bundle  1264 ,′ and one or more pullwires  1222 .′ 
     With reference to  FIGS. 23A and 24A , during use, the apparatus  1210  may be introduced into a body cavity (not shown), and the bulb  1250  may be placed against a wall of the body cavity to image the wall through the bulb  1250  using the imaging assembly  1262 . Preferably, sufficient distal force is applied to clear blood or other fluid from between the bulb  1250  and the wall of the body cavity. Optionally, an external cannulation lumen (not shown) may be provided on the catheter  1250  for delivering a guidewire or other instrument (not shown) into a body lumen (also not shown) communicating with the body cavity, as described above. The alternative embodiment shown in  FIGS. 23B and 24B  may be used in a substantially similar manner. 
     In another alternative, shown in  FIGS. 25A and 25B , an apparatus  1210 ″ may be provided that includes a substantially transparent bulb  1250 ″ and an imaging assembly  1262 ,″ similar to the previous embodiment. In addition, an occlusion member, e.g., a compliant balloon  1230 ″ may be provided on the catheter  1212 ″ proximal to the bulb  1250 .″ 
     The catheter  1212 ″ may include multiple lumens, e.g., an inflation lumen  1220   b ″ and a perfusion lumen  1220   c ″ that extend from a proximal end to the distal end  1216 ″ of the catheter  1212 .″ The inflation lumen  1220   b ″ may communicate with an interior  1232 ″ of the occlusion balloon  1230 ″ for inflating and/or deflating the balloon  1230 .″ The perfusion lumen  1220   c ″ may communicate with an outlet port  1225 ″ for delivering fluids from a proximal end of the catheter  1212 ″ to a location distal to the occlusion balloon  1230 .″ 
     During use, the apparatus  1210 ″ may be introduced into a body cavity, e.g., a right atrium of a heart (not shown), similar to the embodiments described above, with the occlusion balloon  1230 ″ collapsed. The bulb  1250 ″ may be pressed against a wall of the heart in order to image and locate the coronary sinus ostium (not shown), also similar to the previous embodiments. Once the coronary sinus ostium is located, the apparatus  1210 ″ may be inserted into the coronary sinus until the occlusion balloon  1230 ″ is at least partially received in the coronary sinus. 
     The occlusion balloon  1230 ″ may then be inflated to engage the wall of the coronary sinus, preferably substantially sealing the coronary sinus from fluid flow therethrough. Fluid may be delivered through the perfusion lumen  1220   c ″ until it exits the port  1225 ″ and enters the coronary sinus, thereby perfusing the coronary sinus in a retrograde direction. The fluid may include a diagnostic agent, e.g., contrast for performing a venogram or other procedure, and/or a therapeutic agent. Upon completing the procedure, the occlusion balloon  1230 ″ may be deflated, and the apparatus  1210 ″ may be removed from the patient&#39;s heart and/or body. 
     Turning to  FIGS. 27A-27D , another embodiment of an apparatus  1310  is shown for cannulating a coronary sinus ostium or other body lumen of a patient (not shown). Generally, the apparatus  1310  includes a catheter  1312 , including a proximal end  1314 , a distal end  1316 , and a longitudinal axis  1318  extending therebetween. In addition, the catheter  1312  may include one or more lumens, e.g., a cannulation lumen  1320 , which may extend along an outer surface of the catheter  1312 , as shown, or may be located within the catheter  1312  (not shown). In addition, the catheter  1312  may include one or more pullwires or other steering elements (no shown) that may be controlled from a handle  1330 , similar to the previous embodiments. 
     A plurality of oxygen sensors  1350  may be carried on the distal end  1316  of the catheter  1312 . Preferably, the oxygen sensors  1350  are disposed on the ends of wires or other elongate filaments  1352  that are biased away from one another, e.g., to provide an annular array of oxygen sensors. The filaments  1352  may extend through the catheter  1312  from the distal end  1316  to the proximal end  1314 . Alternatively, the oxygen sensors  1350  may be provided on an exterior of a balloon or other expandable member (not shown) carried on the distal end  1316  of the catheter  1312 . 
     Preferably, as shown in  FIG. 27D , each filament  1352  includes one or more electrical leads  1354 ,  1356 , and one or more stiffening members  1358 . The stiffening members  1358  may bias the oxygen sensors  1350  to the radial configuration shown. The electrical leads  1354 ,  1356  may be coupled to a capture device  1360 , shown in  FIG. 27A , which may include a power source, a controller, memory, or other components (not shown) for operating and/or receiving data from the oxygen sensors  1350 . The capture device  1360  may analyze and/or otherwise capture oxygen measurements from the oxygen sensors  1350 . 
     During use, the apparatus  1310  may be introduced into a right atrium or other body cavity (not shown), similar to the previous embodiments. Preferably, the oxygen sensors  1350  are constrained close to one another during advancement, e.g., to protect the oxygen sensors  1350  and/or to minimize a profile of the apparatus  1310 . For example, the apparatus  1310  may be provided within a sheath, catheter, or other delivery device (not shown) that may facilitate advancing the apparatus  1310  through the patient&#39;s vasculature. 
     Once the distal end  1316  is located within the right atrium, the oxygen sensors  1350  may be deployed from the delivery device. Because blood flowing from the coronary sinus ostium has less oxygen than blood flowing through the right atrium, the oxygen sensors  1350  may be used to locate the coronary sinus ostium. Once the coronary sinus ostium is located, the apparatus  1310  may be advanced into the coronary sinus, or a guidewire or other instrument (not shown) may be advanced from the apparatus  1310 , e.g., from the cannulation lumen  1320  into the coronary sinus, similar to the previous embodiments. Thus, the guidewire may provide a rail for advancing other instruments into the coronary sinus and/or into coronary veins accessed therethrough. 
     In an alternative embodiment, shown in  FIGS. 28A and 28B , an apparatus  1410  may be provided that includes a catheter  1412  carrying one or more oxygen sensors  1450  and a balloon or other occlusion member  1430 . In the preferred embodiment shown, a single oxygen sensor  1450  may be provided on the distal end  1416  of the catheter  1412 , and one or more electrical leads  1454 ,  1456  may extend from the oxygen sensor  1450  through the catheter  1412 , e.g., to a capture device (not shown), similar to the previous embodiment. The balloon  1430  may facilitate retrograde perfusion of the coronary sinus, similar to the embodiment shown in  FIG. 25A  and described above. Instead of using a fiber optic imaging bundle, the oxygen sensor, preferably a solid-state device, may facilitate monitoring perfusion of the coronary sinus or other body lumen. 
     Turning to  FIGS. 29A-29C , another embodiment of an apparatus  1510  is shown that may include a catheter  1512 , a balloon  1550 , and an imaging assembly (not shown for simplicity) carried by the catheter  1510 , similar to the embodiments described above. In addition, the apparatus  1510  may include an elongate member  1530  that may be deployed from a channel  1552  extending through the balloon  1550 . The elongate member  1530  may be slidable relative to the catheter  1512 , e.g., such that a distal end  1536  of the elongate member  1530  may be advanced through the channel  1552  and beyond a distal surface  1554  of the balloon  1550 , as shown in  FIG. 29B . 
     The apparatus  1510  may include a handle and/or one or more controls (not shown), e.g., at a proximal end (also not shown) of the catheter  1512 , e.g., for sliding the elongate member  1530  relative to the catheter  1512 . For example, a tab, bar, or other element (not shown) coupled to the elongate member  1530  may be slidable in a slot in a handle for limiting movement of the elongate member  1530 . 
     The elongate member  1530  may facilitate cannulating a coronary sinus ostium  90  or other body lumen, and/or may facilitate localizing other morphological features of tissue being imaged, e.g., to maintain a position of the distal end  1516  of the catheter  1512  relatively constant. Thus, the elongate member  1530  may act as a stabilization member or a localization member, e.g., allowing the balloon  1550  to be deflated, as shown in  FIG. 29C , without moving the distal end  1516  of the catheter  1512  laterally away from the ostium  90  or other morphological feature. In addition or alternatively, the elongate member  1530  may facilitate advancing the apparatus  1510  into the ostium  90  or other lumen, e.g., after the balloon  1550  has been deflated, also as shown in  FIG. 29C . 
     The distal end  1536  of the elongate member  1530  may be constructed for a particular purpose, e.g., having a size for cannulating an ostium of a particular size and/or having a substantially atruamatic tip. Optionally, the distal end  1536  may be shapeable and/or steerable, using an internal pullwire or other element, similar to the catheter embodiments described above. Alternatively, the elongate member  1530  may be adapted for stabilizing the distal end  1516  of the catheter  1512  using other morphologic features of tissue being imaged. 
     For example, as shown in  FIG. 30A , the distal end  1536 ′ may have a cone or wedge shape that may allow the distal end  1536 ′ to be wedged or otherwise inserted temporarily into a crevasse or depression (not shown), e.g., in a chamber of a heart, such as the trebaculae came on a wall of a heart. Alternatively, as shown in  FIG. 30B , an elongate member  1530 ″ may be provided that includes a bent distal end  1536 ,″ e.g., having an “S” or other curved shape. In a further alternative, shown in  FIG. 30C , an elongate member  1530 ′″ is shown that includes a forked distal end  1536 ′″ that may be used to straddle a ridge, such as the eustation ridge in the right atrium (not shown). 
     Returning to  FIGS. 29A-29C , preferably, the elongate member  1530  is movable between a retracted position, such as that shown in  FIG. 29A , and a deployed position, as shown in  FIG. 29B . The retracted position may allow substantial apposition of the distal surface  1554  of the balloon  1550  against a structure being imaged, e.g., a wall  94  of a heart, e.g., to facilitate imaging the structure, similar to the embodiments described previously. When the elongate member  1530  is moved towards the deployed position, as shown in  FIG. 29B , the distal end  1536  may interact with the structure of interest. 
     For example, as shown in  FIG. 29B , the distal end  1536  may at least partially enter the coronary sinus ostium  90  to temporarily localize the distal end  1516  of the catheter  1512  at the coronary sinus ostium  90 . During use, the apparatus  1510  may be introduced into the right atrium  92  of a heart, similar to the previous embodiments, and then the balloon  1550  may expanded and pressed against the wall  94  of the heart. The wall  94  may be imaged through the distal surface  1554 , and the distal end  1512  manipulated until the coronary sinus ostium  90  is aligned with the channel  1552 . 
     As shown in  FIG. 29B , the distal end  1536  of the elongate member  1503  may be deployed until at least partially received in the coronary sinus ostium  90 , thereby localizing and/or stabilizing the catheter  1512 . As shown in  FIG. 29C , the balloon  1550  may be at least partially deflated, whereupon the distal end  1516  of the catheter  1512  may be inserted into the coronary sinus ostium  90 , thereby cannulating the ostium  90 . 
     Although different embodiments have been described herein with particularity as including specific components and/or features, it will be appreciated that each of the embodiments described above may include components and/or features specifically described with respect to individual embodiments. For example, any of the embodiments described above may include one or more of the following: a handle on a proximal end of a catheter, one or more pullwires or other steering elements for steering a catheter and/or a localization/stabilization member, steering controls or actuator, a source of light, a capture device, e.g., including a display, processor for analyzing image data, and/or memory for storing imaging data, sources of fluid, e.g., for delivering inflation media, diagnostic, and/or therapeutic agents, and the like. Thus, different components may be provided on each of the embodiments, depending upon a specific application. 
     In addition, each of the apparatus described may be used to perform any of the procedures described herein and should not limited to the specific examples described. For example, any of the apparatus described may be used for imaging, accessing, and/or cannulating a collapsible lumen, such as the colon. Embodiments with channels through balloons or other expandable and/or displacement members may be used to deliver insufflation media, e.g., carbon dioxide, nitrogen, and/or air, into a collapsible lumen to facilitate performing a procedure therein. 
     While the invention is susceptible to various modifications, and alternative forms, specific examples thereof have been shown in the drawings and described herein in detail. It should be understood, however, that the invention is not to be limited to the particular forms or methods disclosed, but, to the contrary, the invention is to cover all modifications, equivalents and alternatives falling within the scope of the appended claims.