Abstract:
A method for advancing a device positioned coaxially with respect to a cannula comprises rigidizing a portion of the cannula and advancing the device until a first preestablished limit of relative displacement between the cannula and the device is reached. The method further comprises relaxing the portion of the cannula and advancing the cannula until a second preestablished limit of relative displacement between the cannula and the device is reached.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application and claims the benefit of U.S. patent application Ser. No. 10/899,561 (filed Jul. 27, 2004; now U.S. Pat. No. 8,075,476 B2) which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to devices, systems, and processes useful for exploration of hollow body structures, particularly those areas accessed through a tortuous, unsupported path. More particularly, the present invention relates to a system and method for navigation of an endoscope having a steerable tip. 
     2. Description of Related Art 
     Endoscopes are frequently used for medical exploratory procedures, either alone or in combination with an overtube for aiding the insertion of the endoscope. When an overtube is used it may be fully inserted in a single step prior to the insertion of the endoscope. The overtube and endoscope may also be incrementally inserted in an alternating fashion. 
     Overtubes may have a controllable rigidity in order to facilitate their introduction and to provide a firm guide for subsequent insertion of an endoscope. An overtube with controllable rigidity is typically in a relaxed state during its insertion or retraction in order to minimize the force transmitted to the body in which it resides. During the insertion or retraction of an endoscope through the overtube, the overtube is maintained in a rigidized state. 
     In addition to controllable rigidity, the prior art also teaches the use of a steerable tip for achieving a favorable contact angle between the inserted device and the body in which it is being introduced. Steering may be achieved by the use of control wires or by rotation of the inserted device. 
     Controllable rigidity and steering in prior art medical exploratory devices are used to minimize the forces applied to the body into which the exploratory device is inserted (e.g., a colon). Steering provides a low contact angle with a body surface and minimized rigidity reduces the force transmitted at sites of contact during movement of the inserted device. 
     Although the prior art has recognized the desirability of reducing the forces applied to a body being explored, present medical exploratory devices typically depend upon a finite reactive force from the body under investigation during use. Unfortunately, even a reduced contact force has the potential for patient discomfort and tissue trauma. 
     An example of a potential operator error associated with an incremental advance system is that involving excessive advancement of an endoscope with a steerable tip within a rigidizable overtube. Excessive advancement of the endoscope exposes a section of the endoscope that is not steerable and thus the tip may be inadvertently directed at a large contact angle against the wall of the body being explored. Although the prior art teaches various methods for reducing contact discomfort, a large contact angle resulting from a poorly directed tip may be difficult to overcome. The prior art frequently relies upon excessive advancement in combination with reaction forces from tissue walls to advance an instrument. 
     An example of a potential operator error associated with an incremental advance system is that involving excessive advancement of an endoscope with a steerable tip within a rigidizable overtube. Excessive advancement of the endoscope exposes a section of the endoscope that is not steerable and thus the tip may be inadvertently directed at a large contact angle against the wall of the body being explored. Although the prior art teaches various methods for reducing contact discomfort, a large contact angle resulting from a poorly directed tip may be difficult to overcome. 
     Thus, a need exists for system and method for medical exploration that does not depend upon reactive forces from the body being explored. There is also a need for a system prevents operator error through excessive advancement of an insertable device. It is also desirable that such a system be capable of providing free-space navigation interchangeably for endoscopes and other tools. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention combines a cannula with a displacement limiting coupling for attaching to an endoscope or other insertable device. The cannula includes a rigidizable portion and acts as a guide for the inserted device. The displacement limiting coupling establishes functional limits on the relative displacement between the cannula and the insertable device. 
     In one embodiment of the invention the cannula includes a tubular section coupled to a rigidizable segment. The rigidity of the tubular section is not controlled during operation, whereas the rigidity of the rigidizable segment is controllable. 
     In a further embodiment the cannula includes a rigidizable segment that is larger in cross-section than the remainder of the cannula. The larger cross-section may be circular or non-circular. The rigidizable segment may be coupled to another rigidizable segment or to a tubular section whose rigidity is not controlled during operation. 
     In another embodiment the control of the rigidizable segment is provided by a compound cable system that generates a compressive force for rigidization that is greater in magnitude than the tensile force in the cables of the system. 
     In yet another embodiment the cannula is enclosed by a sheath that is secured at the distal end of the inserted device and at the proximal end of the cannula. The sheath may be secured by an elastic band or by an “o”-ring fitted to a groove. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an assembled cannula system in accordance with an embodiment of the present invention. 
         FIG. 2  shows an exploded view of the cannula system shown in  FIG. 1 . 
         FIG. 3  shows an exploded view of a rigidizing actuator in accordance with an embodiment of the present -invention. 
         FIG. 4  shows a cannula system with low-friction rigidizing cable sleeves in accordance with an embodiment of the present invention. 
         FIG. 5  shows a cannula system having a non-rigidizable segment in accordance with an embodiment of the present invention. 
         FIG. 6  shows a cutaway view of a portion of the cannula system of  FIG. 5  in accordance with an embodiment of the present invention. 
         FIG. 7  shows a cannula system with a sheath in accordance with an embodiment of the present invention. 
         FIG. 8  shows a detailed view of the distal end of the cannula system shown in  FIG. 7 . 
         FIGS. 9A and 9B  show two views of a non-circular link component of a rigidizable segment in accordance with an embodiment of the present invention. 
         FIGS. 10A-10D  show cross-section views of cable sheaths in combination with a non-rigidizable segment in accordance with embodiments of the present invention. 
         FIG. 11  shows a portion of a cannula system with a compound rigidizing cable linkage in accordance with an embodiment of the present invention. 
         FIGS. 12A-12C  show the relative positions of the cannula system and an inserted device during an advancement cycle in accordance with an embodiment of the present invention. 
         FIG. 13  shows a cutaway view of the heart and a transseptal path for a valvuloplasty. 
         FIG. 14  shows a cutaway view of the heart and a transseptal path for an ablation procedure. 
         FIGS. 15A-15C  show a displacement limited coupling with accommodation for cannula compression in accordance with an embodiment of the present invention. 
         FIG. 16  shows a displacement limited coupling with enhanced clearance for a cannula in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an embodiment of a cannula system  100 . A cannula  101  includes a rigidizing actuator  120 . The actuator  120  is used to control the rigidity of the cannula  101 . A displacement limiting coupling  115  couples the cannula  101  to an insertable device (e.g., an endoscope)  125 . The displacement limiting coupling  115  aligns the axes of the endoscope  125  and the cannula  101 , and allows a limited relative axial displacement “D” between the endoscope  125  and the cannula  101 . The displacement limiting coupling slidably couples the cannula  101  to the insertable device  125 . The insertable device may include a steerable tip  128 . 
     A discussion of rigidizable structures for use in a cannula system may be found in the copending U.S. patent application Ser. No. 10/661,159, “Shape Transferring Cannula System and Method of Use”, by the inventor of the present invention, filed Sep. 12, 2003, and is incorporated herein by reference. The cannula  101  may include segments with independently controllable rigidity, or may include a first segment  105  with a cross-section that is different from a second segment  110 . In particular embodiments the second segment  110  is adapted to accommodate a steerable tip  128  of the insertable device  125 , wherein the displacement limited coupling maintains an overlap between the steerable tip  128  and the second segment  110 . The displacement limited coupling may also act to prevent overlap between steerable tip  128  and the first segment  105 . 
       FIG. 2  shows an exploded view of the cannula system shown in  FIG. 1 . The displacement limiting coupling  115  has a portion  205  that mates to a surface  210  of the endoscope  125 , thus capturing the endoscope  125  and maintaining it in a fixed position with respect to the displacement limiting coupling  115 . The displacement limiting coupling  115  also captures the cannula  101 . A first wall  215  and a second wall  220  define the limits for the axial travel of the cannula  101 . A guide  225  extending from the second wall  220  may be used to support the cannula  101 . The difference between the width of the actuator  120  and the distance between the first wall  215  and second wall  220  establishes the maximum allowable axial displacement between the cannula  101  and the endoscope  125 . In one embodiment, the range of allowable positions of the endoscope within the cannula  101  is preferably limited to those positions in which the steerable tip  128  is overlapped by the cannula  101 . 
     In one embodiment, the cannula  101  and displacement limiting coupling  115  may be separated from the insertable device  125  without disturbing the coupling between the cannula  101  and the displacement limiting coupling  115 . This arrangement facilitates the use of interchangeable or disposable insertable devices, or reusable insertable devices with a disposable cannula system. 
       FIG. 3  shows an exploded view of the rigidizing actuator  120  of  FIG. 2  in accordance with an embodiment of the present invention. A chamber  305  includes a hollow shaft  310 . A piston disk  315  having a bore  316  fits over the shaft  310 . The piston disk  315  has bore groove  318  and a perimeter groove  320  for accepting “o”-ring seals. In operation, the piston disk  315  is advanced and retracted along the shaft  310  by the application of pressure or vacuum to the chamber  305 . The cable  330  may extend from the rigidizing structure  325 , loop through the piston  315 , and be re-routed back to the rigidizing structure such that the assembly requires only two cable terminations and is self-adjusting with regard to the lengths of cable running through the two cable channels. Cable  330  may be multi-strand cable or a single wire, fiber, or equivalent tension-transmission medium. 
     The piston disk  316  is coupled to a rigidizing cable  330 . Retraction of the piston disk through the application of vacuum produces tension in the cable  330 , thus placing the rigidizable section  325  in compression and placing it in a rigidized state. An end plate  322  retains the piston disk  315 . The sliding piston disk  316  may be replaced with a flexible bellows to avoid the sliding seals required of piston designs. 
       FIG. 4  shows an alternative embodiment in which the cable  330  is sheathed in flexible sleeves  405  having a low coefficient of friction. The sleeves improve the rigidizing behavior of the cannula system by minimizing cable drag that can reduce the compressive force produced at the distal end of the cannula  101 . In a preferred embodiment the sleeves are fabricated from polytetrafluoroethylene (PTFE). The sleeves  405  may be continuous tubes and run the length of the sheath or may consist of individual PTFE liners for each link. 
       FIG. 5  shows an embodiment of a cannula system having a flexible non-rigidizable segment  505 . In this embodiment the displacement limiting coupling  530 , actuator  535  and endoscope  525  are similar to the displacement limiting coupling  115 , actuator  120  and endoscope  125  of  FIG. 1 . The use of the non-rigidizable segment  505  simplifies the cannula system and improves the control over the rigidity of the rigidizable segment  510  of the cannula. In this example the rigidizable segment  510  includes a rigidizable segment  515  with a first cross-section and a rigidizable segment  520  with a second cross-section. 
       FIG. 6  shows a cutaway view of a portion of the cannula system of  FIG. 5 . Cable guides  605  are used to sheath the rigidizing cable within the non-rigidizable segment  505 . In this embodiment the cable guides  605  are fabricated from spiral-wound wire and may have inner and outer liners to reduce friction. 
       FIG. 7  shows a cannula system  700  with an outer sheath  705  and an inner sheath  712  in accordance with an embodiment of the present invention. The cannula system  700  is similar to that shown in  FIG. 5 . The addition of the sheath  705  provides a smooth continuous surface that may be used to cover discontinuities. The sheath may also be used to prevent undesired lubrication of rigidizable structures. A flat elastic band is used to provide a seal at the distal end  710  and an “o”-ring is used to provide a seal at the proximal end  715 . Adhesives or heat-shrink materials may also be used to provide sealing at the proximal or distal ends. 
       FIG. 8  shows a detailed view of the distal end of the cannula system shown in  FIG. 7 . Wrinkles  805  may form in the surface of the steerable tip  528  in areas with a negative radius of curvature. The wrinkles  805  may interfere with the smooth advancement and retraction of the tip  720 . The inner sheath  712  masks the wrinkles  805  and may be a continuous material or a woven mesh. 
       FIGS. 9A and 9B  show two views of a non-circular link component for a rigidizable segment such as segment  520  of  FIG. 5 . An endoscope may have a section with low flexibility adjacent to the steerable tip. The use of a non-circular cross-section link may be used to facilitate the passage of a low-flexibility section while providing a smaller increase in the cross-section than would result from simply increasing the radius of a circular link. A rigidizing segment having non-circular cross-section links may include a terminal distal link with a circular cross-section in order provide more precise direction for an advancing insertable device. The circular cross-section of the terminal distal link may be smaller than that of segment  515  of  FIG. 5  in order to maximize the locational accuracy of steering tip  528 . 
       FIGS. 10A-10D  show embodiments of a non-rigidizable segment in combination with cable sheaths.  FIG. 10A  shows unattached cable sheaths  1005  disposed outside of a non-rigidizable segment  1010 .  FIG. 10B  shows attached cable sheaths  1006  disposed inside of a non-rigidizable segment  1011 .  FIG. 10C  shows unattached cable sheaths  1007  disposed inside of a non-rigidizable segment  1012 .  FIG. 10D  shows attached cable sheaths  1006  disposed outside of a non-rigidizable segment  1013 . Attached cable sheaths  1006  or  1008  may be formed as a channel within non-rigidizable segments  1011  or  1013 . 
       FIG. 11  shows a portion of a cannula system with a compound rigidizing cable linkage in accordance with an embodiment of the present invention. A cable section  1105  is shown disposed in a rigidizable segment  1110 . The cable section is wrapped around a pulley  1105  associated with a distal link  1116  and routed to an anchor point  1120  associated with an interior link  1125  of the rigidizable segment  1110 . The effect of the anchor point  1120  and pulley  1115  is similar to that of a block-and-tackle and results in an increased compressive force on the links between the distal link  1116  and the intermediate link  1125 . The compound linkage is thus able to provide a compressive force that is greater in magnitude than the tensile force in the cable. A fixed ferrule or loop back may be used in place of a pulley at the expense of an increase in friction relative to the pulley. The compound rigidizing cable linkage may be used to compensate for frictional losses and may also be used to reduce the size of the cable used to rigidize the cannula. 
       FIGS. 12A-12C  show the relative positions of the cannula system and an inserted device during an advancement cycle in accordance with a method embodiment of the present invention.  FIGS. 12A-12C  are intended to show a cycle of steps that may be repeated as part of a medical exploratory process using a cannula system such as that shown in  FIG. 1 . 
       FIG. 12A  shows the cannula  101  in a retracted position relative to the steerable tip  128 . The actuator  120  is at the left hand limit of the displacement limiting coupler  115  and the cannula  101  maintains a degree of overlap with the steerable tip  128 . The cannula is placed in a relaxed state prior to the advancement shown in  FIG. 12B , and the steerable tip provides the reactive force that guides the advancing cannula and determines its shape at its distal end. 
       FIG. 12B  shows the cannula  101  advanced over the steerable tip. In this position, the actuator  120  is at the right hand limit of the displacement limiting coupler  115  and steerable tip is largely covered by the cannula  101 . The cannula  101  may then be placed into a rigid state prior to the advancement of the endoscope shown in  FIG. 12C . 
       FIG. 12C  shows the steerable tip advanced and steered in a new direction. In this position, the actuator  120  is at the left hand limit of the displacement limiting coupler  115  and overlap is maintained between the cannula  101  and steerable tip  128 . In advancing the steerable tip, the rigid cannula  101  provides the reactive force that guides the endoscope except for the exposed portion of the steerable tip  128 . 
     A steerable tip may be a specific structure connected to the distal end of an insertable device, or it may be a distal portion of an insertable device having a homogeneous structure. A steerable tip may also be considered to include a coupling that is used to connect it to the remainder of the insertable device. An example of a specific structure is a segment whose bend radius is remotely controllable, or a guidewire having a straight section and a curved section. Alternatively, a guidewire may lack a straight section and have a continuous curve with a variable radius of curvature. For such a guidewire or other insertable device having a homogeneous structure, the preferred length of the steerable tip (section to be overlapped) may defined in relation to the body that is being explored. 
     For maximum inspection coverage it may be desirable that an endoscope be capable of being retroflexed, that is, being formed into an arc of 180 degrees within the body being inspected. Thus, a steerable tip may be defined as the portion of a homogeneous insertable device that has a bend radius that is less than or equal to one half of the width of the body being explored. 
     Whether an insertable device employs a distinct structure as a steerable tip, or a section with a bend radius having a particular characteristic, the displacement limiting coupling of the present invention may be used to maintain an overlap between a distal rigidizable segment of a cannula and the steerable tip. 
     In addition to endoscopic procedures, the cannula system of the present invention may also be used for surgical procedures. Examples of per-oral transgastric peritoneal surgery to which the invention may be applied are organ removal and repair (e.g., transgastric cholycistectomy), gastrO-jejunostomy (e.g., jejunum anastomosis to the stomach), and gynecological procedures such as transgastric fallopian tube ligation. 
     Per-oral transgastric surgery combines flexible endoscopic and surgical skills to do abdominal (peritoneal) surgery through a small stomach incision with per-oral access, and can reduce infection, peritonitis, and surgical adhesions. In contrast, conventional surgery performed through trans-abdominal ports or open incisions can result in significant morbidity and abdominal surgical adhesions. The lack of an external incision can reduce pain and the likelihood of infection, and outpatient abdominal surgeries under only moderate sedation become possible. 
     The cannula system of the present invention allows navigation in arbitrary directions in and around organs, and with sufficient mechanical support to apply force from the tip of an insertable device when necessary. 
     In cardiology, transseptal approaches such as percutaneous mitral valve repair and other therapies are currently limited by the positioning and angle-of-attack limitations of current catheter technology. The cannula system of the present invention may be used to provide control over position and angle of attack as well as a stiffer, more stable platform from which to apply force. Navigation to the coronary sinus and atrial fibrillation sites may be performed, as well as unsupported navigation in the atria and ventricles. 
       FIG. 13  shows a cutaway view of a heart  1305  and a transseptal path for a valvuloplasty. The path  1310  passes through the vena cava  1315  and into the right atrium  1320 . An insertable device and cannula system may thus be introduced into the right atrium. The cannula system may then be used to control the angle of approach to the septum  1325  and provide support for an insertable device that is used to penetrate the septum  1325  and enter the left atrium  1330 . The mitral valve  1335  may then be accessed from within the left atrium. Alternatively, perforation of the septum  1325  may be avoided by unsupported navigation through the aorta  1340  into the left ventricle  1345 , and through the mitral valve  1335 . 
       FIG. 14  shows a cutaway view of the heart and a transseptal path for an ablation procedure. The path  1410  passes through the vena cava  1415  and into the right atrium  1420 . An insertable device and cannula system may thus be introduced into the right atrium. The cannula system may then be used to control the angle of approach to the septum  1425  and provide support for an insertable device that is used to penetrate the septum  1425  and enter the left atrium  1430 . Ablation may then be performed at sites (e.g., pulmonary vein ostia) associated with cardiac electrical pathways  1435 . 
       FIG. 15A  shows a cannula system  1500  with a displacement limited coupling with an allowable displacement that is the sum of length A 1  and B. Length A 1  corresponds to an overlapped active length of a steerable tip  1505 . Length B is a length associated with a change in the length of cannula  1510  that may occur during rigidizing of the cannula through axial compression. The cannula  1510  is shown in a relaxed state. 
       FIG. 15B  shows the cannula system  1500  of  FIG. 15A  with the cannula  1510  in a rigidized state. In the rigidized state, an additional length B of the steerable tip  1505  is exposed. 
       FIG. 15C  shows the rigidized cannula  1510  of  FIG. 15B  in an advanced position, overlapping length A 1  and length B. A non-steerable portion  1515  of the steerable tip  1505  is exposed. Tip portion  1515  may be an optical assembly of an endoscope. 
       FIG. 16  shows a cannula system  1600  with a displacement limited coupling  1605  having enhanced clearance port  1610  for a cannula  1615 . In this embodiment, support for actuator  1608  and cannula  1615  are provided by the body of the displacement limited coupling  1605 . The enhanced clearance port  1610  may be used to allow the cannula  1615  to be advanced and retracted when it is in a curved state. 
     While the invention has been described in detail with reference to preferred embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. Specific examples of an actuator for rigidizing a cannula segment and housing walls have been described for limiting relative axial displacement. These specific examples are not exclusive of other applicable structures and methods.