Source: http://www.google.com/patents/US20080015569?dq=5,838,906
Timestamp: 2015-01-25 19:08:37
Document Index: 259730776

Matched Legal Cases: ['art. 34', 'art. 55', 'art. 91', 'art 150', 'art 150', 'art 162']

Patent US20080015569 - Methods and apparatus for treatment of atrial fibrillation - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsApparatus and methods for the treatment of atrial fibrillation are described herein where tissue to be ablated may be monitored under direct visualization. Such a system may include a deployment catheter and an attached imaging hood deployable into an expanded configuration. In use, the imaging hood...http://www.google.com/patents/US20080015569?utm_source=gb-gplus-sharePatent US20080015569 - Methods and apparatus for treatment of atrial fibrillationAdvanced Patent SearchPublication numberUS20080015569 A1Publication typeApplicationApplication numberUS 11/775,819Publication dateJan 17, 2008Filing dateJul 10, 2007Priority dateFeb 2, 2005Publication number11775819, 775819, US 2008/0015569 A1, US 2008/015569 A1, US 20080015569 A1, US 20080015569A1, US 2008015569 A1, US 2008015569A1, US-A1-20080015569, US-A1-2008015569, US2008/0015569A1, US2008/015569A1, US20080015569 A1, US20080015569A1, US2008015569 A1, US2008015569A1InventorsVahid Saadat, Ruey-Feng Peh, Edmund Tam, Chris RotheOriginal AssigneeVoyage Medical, Inc.Export CitationBiBTeX, EndNote, RefManPatent Citations (2), Referenced by (18), Classifications (31), Legal Events (3) External Links: USPTO, USPTO Assignment, EspacenetMethods and apparatus for treatment of atrial fibrillationUS 20080015569 A1Abstract Apparatus and methods for the treatment of atrial fibrillation are described herein where tissue to be ablated may be monitored under direct visualization. Such a system may include a deployment catheter and an attached imaging hood deployable into an expanded configuration. In use, the imaging hood is placed against or adjacent to the tissue to be imaged in a body lumen that is normally filled with an opaque bodily fluid such as blood. A translucent or transparent fluid can be pumped into the imaging hood until the fluid displaces any blood leaving a clear region of tissue to be imaged via an imaging element in the deployment catheter. An ablation probe may be advanced into the contained region where the tissue may be ablated and monitored for changes in color as well as appropriate positioning. Images(84) Claims(97)
1. A tissue imaging and treatment system, comprising: a deployment catheter defining at least one lumen therethrough; a barrier or membrane projecting distally from the deployment catheter and defining an open area therein, wherein the open area is in fluid communication with the at least one lumen; a visualization element disposed within or along the barrier or membrane for visualizing tissue adjacent to the open area; and an ablation energy transmitting surface positionable to ablate tissue adjacent to or contained within the open area. 2. The system of claim 1 further comprising a delivery catheter through which the deployment catheter is deliverable. 3. The system of claim 1 wherein the deployment catheter is steerable. 4. The system of claim 3 wherein the deployment catheter is steered via pulling at least one wire. 5. The system of claim 3 wherein the deployment catheter is steered via computer control. 6. The system of claim 1 wherein the barrier or membrane is comprised of a compliant material. 7. The system of claim 1 wherein the barrier or membrane defines a peripheral contact edge for placement against a tissue surface so that the tissue surface spans along and within the contact edge, wherein the energy transmitting surface comprises an electrode electrically coupleable to the tissue surface span for ablating the visualized tissue. 8. The system of claim 1 wherein the barrier or membrane is adapted to be reconfigured from a low-profile delivery configuration to an expanded deployed configuration. 9. The system of claim 8 wherein the barrier or membrane is adapted to self-expand into the expanded deployed configuration. 10. The system of claim 8 wherein the barrier or membrane comprises one or more support struts along the barrier or membrane. 11. The system of claim 1 wherein the barrier or membrane is conically shaped. 12. The system of claim 1 wherein the visualization element comprises at least one optical fiber, CCD imager, or CMOS imager. 13. The system of claim 1 wherein the visualization element is disposed within a distal end of the deployment catheter. 14. The system of claim 1 wherein the visualization element is articulatable off-axis relative to a longitudinal axis of the deployment catheter. 15. The system of claim 1 further comprising a fluid reservoir fluidly coupled to the barrier or membrane. 16. The system of claim 15 wherein the fluid comprises saline, plasma, water, or perfluorinated liquid. 17. The system of claim 1 wherein the barrier or membrane further comprises a distal membrane extending over the open area such that the energy transmitting surface comprises an ablation electrode circumferentially disposed over the distal membrane. 18. The system of claim 1 wherein the barrier or membrane further comprises a distal membrane extending radially inwardly near a distal edge of the barrier or membrane partially over the open area such that the distal membrane defines an aperture through which the ablation electrode is extendable. 19. The system of claim 1 wherein the energy transmitting surface comprises an ablation electrode, and wherein the ablation electrode is articulatable. 20. The system of claim 1 wherein the energy transmitting surface comprises an ablation electrode, and wherein the ablation electrode comprises a monopolar or bipolar radio-frequency electrode. 21. The system of claim 1 wherein the energy transmitting surface is reconfigurable from a first linear profile to a second extended profile. 22. The system of claim 21 wherein the second extended profile defines a linear configuration transverse relative to a longitudinal axis of the deployment catheter. 23. The system of claim 21 wherein the energy transmitting surface is contained within a linear housing which is articulatable between a linear profile and an expanded Y-shaped profile. 24. The system of claim 21 wherein the second extended profile defines a circular configuration. 25. The system of claim 1 wherein the energy transmitting surface is circumferentially disposed over a contact lip or edge of the barrier or membrane. 26. The system of claim 1 wherein the ablation probe comprises a plurality of needles. 27. The system of claim 26 wherein the plurality of needles is extendable from a retracted configuration into an ablation configuration. 28. The system of claim 1 further comprising an occlusion balloon which is expandable into an inflated shape sufficiently sized to occlude a vessel lumen. 29. The system of claim 1 further comprising a first articulatable tissue grasper positioned upon a first support member extending distally from the barrier or membrane. 30. The system of claim 29 further comprising a second articulatable tissue grasper positioned upon a second support member extending distally from the barrier or membrane, wherein the second tissue grasper is articulatable independently of the first tissue grasper. 31. The system of claim 29 further comprising a length of wire or suture slidably passed through the tissue grasper, wherein a first end of the wire or suture is attached to the tissue imaging and treatment system and a second end of the wire or suture is pulled from outside a patient body. 32. The system of claim 1 further comprising an intra-atrial balloon disposed upon a distal end of the catheter, wherein the balloon is expandable from a low-profile deflated configuration to an inflated configuration. 33. The system of claim 32 wherein the inflated configuration occupies up to 75% or more of volume of an atrial chamber within a patient heart. 34. The system of claim 32 wherein the intra-atrial balloon comprises one or more radio-opaque markers. 35. A tissue imaging and treatment system for treating a tissue region within a heart, the heart having a chamber, the chamber including a tissue surface and containing blood, the system comprising: a catheter body having a lumen; a visualization element disposed adjacent the catheter body, the visualization element having a field of view; a translucent fluid source in fluid communication with the lumen; and a barrier or membrane extendable from the catheter body to localize, between the visualization element and the field of view, displacement of blood by translucent fluid that flows from the lumen; and an ablation energy transmitting surface positionable for ablating the tissue within the field of view. 36. The system of claim 35 wherein the membrane or barrier is disposed about an open area between the visualization element and the field of view, the fluid source configured to inject translucent fluid so as to displace the blood from the open area sufficiently to allow optical imaging of the tissue surface though the open area while the heart is beating. 37. The system of claim 36 wherein the membrane is expandable from a low-profile delivery configuration to an expanded configuration to encompass an imaged tissue surface larger than a cross-section of the catheter. 38. The system of claim 37 further comprises a frame supporting the membrane outside of the open area in the expanded configuration. 39. The system of claim 38 wherein the frame comprises a shape memory alloy, and wherein the visualization element is supported by the frame. 40. The system of claim 35 wherein the barrier or membrane comprises a hood, the barrier or membrane having a contact edge surrounding an aperture adjacent the field of view so that, during use, transparent fluid from the lumen is released into the chamber of the heart through the aperture, wherein the energy transmitting surface is translatable through the aperture. 41. The system of claim 35 wherein the barrier or membrane has an inner surface and an outer surface, a volume disposed within the inner surface being greater than a volume disposed between the inner surface and the outer surface. 42. The system of claim 35 wherein the catheter body is included in a steerable catheter, the steerable catheter having an elongate proximal portion and an articulable section adjacent the barrier, the steerable section comprising a plurality of links and steerable from a proximal end of the proximal portion so as to impose a smooth axial curvature on the catheter body. 43. The system of claim 35 wherein the catheter body has a working lumen slidably receiving the energy transmitting surface, a lumen for receiving a steering element to laterally deflect the catheter body, a translucent fluid flow lumen, and an image conduit for transmitting images of the tissue surface from the visualization element. 44. The system of claim 35 wherein the barrier or membrane further comprises a distal membrane extending partially over the open area such that the distal membrane defines an aperture through which the energy transmitting surface is extendable. 45. The system of claim 35 wherein the energy transmitting surface comprises an articulatable ablation electrode. 46. The system of claim 35 wherein the energy transmitting surface comprises a monopolar or bipolar radio-frequency electrode. 47. The system of claim 35 wherein the energy transmitting surface comprises a plurality of needles. 48. The system of claim. 47 wherein the plurality of needles is extendable from a retracted configuration into an ablation configuration. 49. The system of claim 35 further comprising an occlusion balloon which is expandable into an inflated shape sufficiently sized to occlude a vessel lumen. 50. The system of claim 35 further comprising a first articulatable tissue grasper positioned upon a first support member extending distally from the barrier or membrane. 51. The system of claim 50 further comprising a second articulatable tissue grasper positioned upon a second support member extending distally from the barrier or membrane, wherein the second tissue grasper is articulatable independently of the first tissue grasper. 52. The system of claim 50 further comprising a length of wire or suture slidably passed through the tissue grasper, wherein a first end of the wire or suture is attached to the tissue imaging and treatment system and a second end of the wire or suture is pulled from outside a patient body. 53. A method for intravascularly treating a tissue region within a body lumen, comprising: positioning an open area of a barrier or membrane against or adjacent to the tissue region to be treated; displacing an opaque bodily fluid with a translucent fluid from an open area defined by the barrier or membrane and the tissue region; visualizing the tissue region within the open area through the translucent fluid; and ablating at least a portion of the tissue region within the open area. 54. The method of claim 53 wherein positioning an open area of a barrier or membrane comprises advancing the barrier or membrane into a left atrial chamber of a heart. 55. The method of claim 53 wherein positioning an open area of a barrier or membrane comprises deploying the barrier or membrane from a low-profile delivery configuration into an expanded deployed configuration. 56. The method of claim 53 wherein positioning an open area of a barrier or membrane comprises stabilizing a position of the barrier or membrane relative to the tissue region. 57. The method of claim 53 wherein positioning an open area of a barrier or membrane comprises steering the deployment catheter to the tissue region. 58. The method of claim 53 wherein displacing an opaque bodily fluid with a translucent fluid comprises infusing the translucent fluid into the open area through a fluid delivery lumen defined through the deployment catheter. 59. The method of claim 58 wherein infusing the translucent fluid comprises pumping saline, plasma, water, or perfluorinated liquid into the open area such that blood is displaced from therefrom. 60. The method of claim 53 wherein displacing an opaque bodily fluid with a translucent fluid comprises partially retaining the fluid within the open area via at least one transparent distal membrane disposed at least partially over a distal end of the barrier or membrane. 61. The method of claim 60 wherein partially retaining the fluid comprises allowing the fluid to leak through at least one aperture defined through the distal membrane. 62. The method of claim 61 wherein ablating comprises ablating the tissue region through the at least one aperture. 63. The method of claim 53 wherein visualizing the region of tissue comprises viewing the tissue via an imaging element positioned off-axis relative to a longitudinal axis of the barrier or membrane. 64. The method of claim 53 wherein ablating comprises contacting the tissue region with an ablation probe advanced through the open area. 65. The method of claim 64 further comprising articulating the ablation probe within the open area. 66. The method of claim 53 wherein ablating comprises forming a linear or circular lesion upon the tissue region. 67. The method of claim 53 further comprising occluding a blood flow through a pulmonary vein via an occlusion balloon inflated within the pulmonary vein distal to the barrier or membrane prior to ablating. 68. The method of claim 53 further comprising temporarily engaging a first and second tissue region in an alternating manner such that the barrier or membrane is moved from a first location to a second location through the body lumen prior to displacing an opaque bodily fluid. 69. The method of claim 53 wherein ablating comprises advancing a plurality of ablation needles into the tissue region. 70. The method of claim 53 further comprising visually monitoring the tissue region for changes in color while ablating as an indication of sufficient tissue ablation. 71. The method of claim 53 further comprising visually monitoring the tissue region for indications of endocardiac disruptions. 72. The method of claim 71 wherein if an endocardiac disruption is detected, adjusting a power of an ablation probe or ceasing ablating the tissue region. 73. The method of claim 72 further comprising further visually inspecting the tissue region. 74. The method of claim 71 wherein if an endocardiac disruption occurs, containing any tissue debris released from the disruption within the barrier or membrane. 75. The method of claim 74 further comprising suctioning the tissue debris contained within the barrier or membrane proximally through the deployment catheter. 76. The method of claim 53 further comprising drawing the tissue region within the open area at least partially into the barrier or membrane to create a seal between therebetween. 77. The method of claim 76 wherein ablating comprises ablating the sealed tissue region within the open area. 78. The method of claim 53 further comprising visually inspecting a lesion formed upon the tissue region within the open area. 79. The method of claim 78 further comprising repositioning the barrier or membrane upon a second tissue region to treated. 80. A method for treating a target tissue of a heart of a patient, the target tissue underlying an intracardiac heart tissue surface region within a chamber of the heart, the method comprising: optically imaging the tissue surface region; ablating the target tissue; and monitoring tissue response to the ablation using the optical imaging while the heart is pumping blood. 81. The method of claim 80 the heart of the patient having an arrhythmia, wherein the optical imaging provides a system user sufficient feedback to verify coupling between an energy transmitting surface and the tissue surface region during formation of an ablation lesion such that the lesion inhibits the arrhythmia. 82. The method of claim 81 wherein the energy delivery surface comprises an electrode surface, and wherein the system user can induce movement of the electrode surface or interrupts lesion formation in response to loss of contact between the target tissue and the electrode surface during formation of the lesion. 83. The method of claim 81 wherein the optical imaging feedback provided to the system user during formation of the lesion comprises changes in color along the tissue surface region, lesion-formation induced deformation along the tissue surface region, vaporization adjacent the tissue surface region, formation of bubbles adjacent the tissue surface region, positioning of the energy transmitting surface, movement of the energy transmitting surface, and/or ablation debris. 84. The method of claim 80 the heart of the patient having an arrhythmia, wherein the target tissue comprises an elongate lesion pattern, and wherein the optical imaging provides a system user sufficient feedback to verify contiguity along a length of the lesion pattern such that the lesion pattern inhibits propagation of the arrhythmia. 85. The method of claim 84 wherein the lesion pattern comprises a plurality of discrete ablation lesions formed sequentially in the target tissue, and wherein a movement of an energy transmitting surface from alignment with a first portion of the target tissue to a second portion of the target tissue is performed using optical feedback from the tissue response along a first discrete lesion associated with the first region of the target tissue. 86. The method of claim 84 wherein the lesion pattern is formed by moving an energy transmitting surface relative to the tissue surface region while transmitting energy from the energy transmitting surface to the target tissue, and wherein the movement is performed using optical feedback on progress of the tissue response along the length of the lesion pattern. 87. The method of claim 84 wherein the optical imaging feedback provided to the system user during formation of the lesion comprises changes in color along the tissue surface region, lesion-formation induced deformation along the tissue surface region, vaporization adjacent the tissue surface region, formation of bubbles adjacent the tissue surface region, positioning of the energy transmitting surface, movement of the energy transmitting surface, and/or ablation debris. 88. The method of claim 80 further comprising interrupting the ablating of the target tissue during the ablation in response to optical indicia of a potential tissue surface disruption, wherein the ablation is interrupted prior to embolization of ablation debris or bursting along the tissue surface region. 89. The method of claim 81 further comprising cooling the imaged tissue surface region during the imaging and the ablation. 90. The method of claim 80 wherein the tissue surface region is imaged by locally displacing blood from an imaging volume within the chamber of the heart. 91. The method of claim 90 wherein the translucent fluid comprises a transparent fluid, wherein the chamber of the heart pumps blood disposed around the imaging volume, and wherein-the transparent fluid is in contact with the tissue surface region. 92. The method of claim 91 wherein the transparent fluid flows along the tissue surface region so as to purge blood from between the energy transmitting surface and the tissue surface region. 93. The method of claim 92 wherein the transparent fluid cools the tissue surface region. 94. The method of claim 91 further comprising introducing a barrier or membrane into the chamber, expanding the barrier or membrane within the chamber, and limiting intrusion of the blood from within the chamber into the imaging volume with the barrier or membrane during the imaging. 95. The method of claim 80 wherein the optical imaging is performed so as to image a plurality of anatomical landmarks, and further comprising aligning the energy delivery surface with the target tissue in response to an image of one or more of the imaged landmarks. 96. The method of claim 80 wherein the anatomical landmarks comprise a pulmonary vein, an ostium of the pulmonary vein, a left atrial septum, a left atrial appendage, a mitral valve, a tricuspid valve, a fossa ovalis and a right atrial appendage. 97. A system for treating a target tissue of the heart of a patient, the target tissue underlying an intracardiac heart tissue surface region within a chamber of the heart, the method comprising: an intracardiac catheter having a proximal end, a distal end, and at least one lumen; an optical imaging element advanceable distally using the catheter into the chamber of the heart; an energy transmitting surface advanceable distally using the catheter into alignment with the tissue surface region for ablation of the target tissue; and an imaging fluid flow path extendable distally from a translucent fluid source, through the catheter, and toward the tissue surface region, the extended flow path encompassing the optical imaging element and the aligned energy transmitting surface so as to inhibiting persistence of blood within a field of view of the imaging element when optically directing the ablation while the heart is pumping the blood. Description
FIELD OF THE INVENTION The present invention relates generally to medical devices used for accessing, visualizing, and/or treating regions of tissue within a body. More particularly, the present invention relates to methods and apparatus for accessing, visualizing, and/or treating conditions such as atrial fibrillation within a patient heart. BACKGROUND OF THE INVENTION Conventional devices for visualizing interior regions of a body lumen are known. For example, ultrasound devices have been used to produce images from within a body in vivo. Ultrasound has been used both with and without contrast agents, which typically enhance ultrasound-derived images. Other conventional methods have utilized catheters or probes having position sensors deployed within the body lumen, such as the interior of a cardiac chamber. These types of positional sensors are typically used to determine the movement of a cardiac tissue surface or the electrical activity within the cardiac tissue. When a sufficient number of points have been sampled by the sensors, a �map� of the cardiac tissue may be generated. Another conventional device utilizes an inflatable balloon which is typically introduced intravascularly in a deflated state and then inflated against the tissue region to be examined. Imaging is typically accomplished by an optical fiber or other apparatus such as electronic chips for viewing the tissue through the membrane(s) of the inflated balloon. Moreover, the balloon must generally be inflated for imaging. Other conventional balloons utilize a cavity or depression formed at a distal end of the inflated balloon. This cavity or depression is pressed against the tissue to be examined and is flushed with a clear fluid to provide a clear pathway through the blood. However, such imaging balloons have many inherent disadvantages. For instance, such balloons generally require that the balloon be inflated to a relatively large size which may undesirably displace surrounding tissue and interfere with fine positioning of the imaging system against the tissue. Moreover, the working area created by such inflatable balloons are generally cramped and limited in size. Furthermore, inflated balloons may be susceptible to pressure changes in the surrounding fluid. For example, if the environment surrounding the inflated balloon undergoes pressure changes, e.g., during systolic and diastolic pressure cycles in a beating heart, the constant pressure change may affect the inflated balloon volume and its positioning to produce unsteady or undesirable conditions for optimal tissue imaging. Accordingly, these types of imaging modalities are generally unable to provide desirable images useful for sufficient diagnosis and therapy of the endoluminal structure, due in part to factors such as dynamic forces generated by the natural movement of the heart. Moreover, anatomic structures within the body can occlude or obstruct the image acquisition process. Also, the presence and movement of opaque bodily fluids such as blood generally make in vivo imaging of tissue regions within the heart difficult. Other external imaging modalities are also conventionally utilized. For example, computed tomography (CT) and magnetic resonance imaging (MRI) are typical modalities which are widely used to obtain images of body lumens such as the interior chambers of the heart. However, such imaging modalities fail to provide real-time imaging for intra-operative therapeutic procedures. Fluoroscopic imaging, for instance, is widely used to identify anatomic landmarks within the heart and other regions of the body. However, fluoroscopy fails to provide an accurate image of the tissue quality or surface and also fails to provide for instrumentation for performing tissue manipulation or other therapeutic procedures upon the visualized tissue regions. In addition, fluoroscopy provides a shadow of the intervening tissue onto a plate or sensor when it may be desirable to view the intraluminal surface of the tissue to diagnose pathologies or to perform some form of therapy on it. Thus, a tissue imaging system which is able to provide real-time in vivo images of tissue regions within body lumens such as the heart through opaque media such as blood and which also provide instruments for therapeutic procedures upon the visualized tissue are desirable. BRIEF SUMMARY OF THE INVENTION A tissue imaging and manipulation apparatus that may be utilized for procedures within a body lumen, such as the heart, in which visualization of the surrounding tissue is made difficult, if not impossible, by medium contained within the lumen such as blood, is described below. Generally, such a tissue imaging and manipulation apparatus comprises an optional delivery catheter or sheath through which a deployment catheter and imaging hood may be advanced for placement against or adjacent to the tissue to be imaged. The deployment catheter may define a fluid delivery lumen therethrough as well as an imaging lumen within which an optical imaging fiber or assembly may be disposed for imaging tissue. When deployed, the imaging hood may be expanded into any number of shapes, e.g., cylindrical, conical as shown, semi-spherical, etc., provided that an open area or field is defined by the imaging hood. The open area is the area within which the tissue region of interest may be imaged. The imaging hood may also define an atraumatic contact lip or edge for placement or abutment against the tissue region of interest. Moreover, the distal end of the deployment catheter or separate manipulatable catheters may be articulated through various controlling mechanisms such as push-pull wires manually or via computer control The deployment catheter may also be stabilized relative to the tissue surface through various methods. For instance, inflatable stabilizing balloons positioned along a length of the catheter may be utilized, or tissue engagement anchors may be passed through or along the deployment catheter for temporary engagement of the underlying tissue. In operation, after the imaging hood has been deployed, fluid may be pumped at a positive pressure through the fluid delivery lumen until the fluid fills the open area completely and displaces any blood from within the open area. The fluid may comprise any biocompatible fluid, e.g., saline, water, plasma, Fluorinert�, etc., which is sufficiently transparent to allow for relatively undistorted visualization through the fluid. The fluid may be pumped continuously or intermittently to allow for image capture by an optional processor which may be in communication with the assembly. In an exemplary variation for imaging tissue surfaces within a heart chamber containing blood, the tissue imaging and treatment system may generally comprise a catheter body having a lumen defined therethrough, a visualization element disposed adjacent the catheter body, the visualization element having a field of view, a transparent fluid source in fluid communication with the lumen, and a barrier or membrane extendable from the catheter body to localize, between the visualization element and the field of view, displacement of blood by transparent fluid that flows from the lumen, and a piercing instrument translatable through the displaced blood for piercing into the tissue surface within the field of view. The imaging hood may be formed into any number of configurations and the imaging assembly may also be utilized with any number of therapeutic tools which may be deployed through the deployment catheter. More particularly in certain variations, the tissue visualization system may comprise components including the imaging hood, where the hood may further include a membrane having a main aperture and additional optional openings disposed over the distal end of the hood. An introducer sheath or the deployment catheter upon which the imaging hood is disposed may further comprise a steerable segment made of multiple adjacent links which are pivotably connected to one another and which may be articulated within a single plane or multiple planes. The deployment catheter itself may be comprised of a multiple lumen extrusion, such as a four-lumen catheter extrusion, which is reinforced with braided stainless steel fibers to provide structural support. The proximal end of the catheter may be coupled to a handle for manipulation and articulation of the system. In additional variations of the imaging hood and deployment catheter, the various assemblies may be configured in particular for treating conditions such as atrial fibrillation while under direct visualization. In particular, the devices and assemblies may be configured to facilitate the application of energy to the underlying tissue in a controlled manner while directly visualizing the tissue to monitor as well as confirm appropriate treatment. Generally, the imaging and manipulation assembly may be advanced intravascularly into the patient's heart, e.g., through the inferior vena cava and into the right atrium where the hood maybe deployed and positioned against the atrial septum and the hood may be infused with saline to clear the blood from within to view the underlying tissue surface. Once the hood has been desirably positioned over the fossa ovalis, a piercing instrument, e.g., a hollow needle, may be advanced from the catheter and through the hood to pierce through the atrial septum until the left atrium has been accessed. A guidewire may then be advanced through the piercing instrument and introduced into the left atrium, where it may be further advanced into one of the pulmonary veins. With the guidewire crossing the atrial septum into the left atrium, the piercing instrument may be withdrawn or the hood may be further retracted into its low profile configuration and the catheter and sheath may be optionally withdrawn as well while leaving the guidewire in place crossing the atrial septum. A dilator may be advanced along the guidewire to dilate the opening through the atrial septum to provide a larger transseptal opening for the introduction of the hood and other instruments into the left atrium. Further examples of methods and devices for transseptal access are shown and described in further detail in commonly owned U.S. patent application Ser. No. 11/763,399 filed Jun. 14, 2007, which is incorporated herein by reference in its entirety. Those transseptal access methods and devices may be fully utilized with the methods and devices described herein, as practicable. With the hood advanced into and expanded within the left atrium, the deployment catheter and/or hood may be articulated to be placed into contact with or over the ostia of the pulmonary veins. Once the hood has been desirably positioned along the tissue surrounding the pulmonary veins, the open area within the hood may be cleared of blood with the translucent or transparent fluid for directly visualizing the underlying tissue such that the tissue may be ablated. An ablation probe, which may be configured in a number of different shapes, may be advanced into and through the hood interior while under direct visualization and brought into contact against the tissue region of interest for ablation treatment. One or more of the ostia may be ablated either partially or entirely around the opening to create a conduction block. In performing the ablation, the hood may be pressed against the tissue utilizing the steering and/or articulation capabilities of the deployment catheter as well as the sheath. Alternatively and/or additionally, a negative pressure may be created within the hood by drawing in the transparent fluid back through the deployment catheter to create a seal with respect to the tissue surface. Moreover, the hood may be further approximated against the tissue by utilizing one or more tissue graspers which may be advanced through the hood, such as helical tissue graspers, to temporarily adhere onto the tissue and create a counter-traction force. Because the hood allows for direct visualization of the underlying tissue in vivo, the hood may be used to visually confirm that the appropriate regions of tissue have been ablated and/or that the tissue has been sufficiently ablated. Visual monitoring and confirmation may be accomplished in real-time during a procedure or after the procedure has been completed. Additionally, the hood may be utilized post-operatively to image tissue which has been ablated in a previous procedure to determine whether appropriate tissue ablation had been accomplished. Generally, in ablating the underlying visualized tissue with the ablation probe, one or more ostia of the pulmonary veins or other tissue regions within the left atrium may be ablated by moving the ablation probe within the area defined by the hood and/or moving the hood itself to tissue regions to be treated, such as around the pulmonary vein ostium. Visual monitoring of the ablation procedure not only provides real-time visual feedback to maintain the probe-to-tissue contact, but also provides real-time color feedback of the ablated tissue surface as an indicator when irreversible tissue damage may occur. This color change during lesion formation may be correlated to parameters such as impedance, time of ablation, power applied, etc. Moreover, real-time visual feedback also enables the user to precisely position and move the ablation probe to desired locations along the tissue surface fore creating precise lesion patterns. Additionally, the visual feedback also provides a safety mechanism by which the user can visually detect endocardial disruptions and/or complications, such as steam formation or bubble formation. In the event that an endocardial disruption or complication occurs, any resulting tissue debris can be contained within the hood and removed from the body by suctioning the contents of the hood proximally into the deployment catheter before the debris is released into the body. The hood also provides a relatively isolated environment with little or no blood so as to reduce any risk of coagulation. The displacement fluid may also provide a cooling mechanism for the tissue surface to prevent over-heating by introducing and purging the saline into and through the hood. Once the ablation procedure is finished, the hood may be utilized to visually evaluate the post-ablation lesion for contiguous lesion formation and/or for visual confirmation of any endocardial disruptions by identifying cratering or coagulated tissue or charred tissue. If determined desirable or necessary upon visual inspection, the tissue area around the pulmonary vein ostium or other tissue region may be ablated again without having to withdraw or re-introduce the ablation instrument. To ablate the tissue visualized within hood, a number of various ablation instruments may be utilized. For example, ablation probe having at least one ablation electrode utilizing, e.g., radio-frequency (RF), microwave, ultrasound, laser, cryo-ablation, etc., may be advanced through deployment catheter and into the open area of the hood. Alternatively, variously configured ablation probes may be utilized, such as linear or circularly-configured ablation probes depending upon the desired lesion pattern and the region of tissue to be ablated. Moreover, the ablation electrodes may be placed upon the various regions of the hood as well. Ablation treatment under direct visualization may also be accomplished utilizing alternative visualization catheters which may additionally provide for stability of the catheter with respect to the dynamically moving tissue and blood flow. For example, one or more grasping support members may be passed through the catheter and deployed from the hood to allow for the hood to be walked or moved along the tissue surfaces of the heart chambers. Other variations may also utilize intra-atrial balloons which occupy a relatively large volume of the left atrium and provide direct visualization of the tissue surfaces. A number of safety mechanisms may also be utilized. For instance, to prevent the inadvertent piercing or ablation of an ablation instrument from injuring adjacent tissue structures, such as the esophagus, a light source or ultrasound transducer may be attached to or through a catheter which can be inserted transorally into the esophagus and advanced until the catheter light source is positioned proximate to or adjacent to the heart. During an intravascular ablation procedure in the left atrium, the operator may utilize the imaging element to visually (or otherwise such as through ultrasound) detect the light source in the form of a background glow behind the tissue to be ablated as an indication of the location of the esophagus. Another safety measure which may be utilized during tissue ablation is the utilization of color changes in the tissue being ablated. One particular advantage of a direct visualization system described herein is the ability to view and monitor the tissue in real-time and in detailed color. The devices and methods described herein provide a number of advantages over previous devices. For instance, ablating the pulmonary vein ostia and/or endocardiac tissue under direct visualization provides real-time visual feedback on contact between the ablation probe and the tissue surface as well as visual feedback on the precise position and movement of the ablation probe to create desired lesion patterns. Real-time visual feedback is also provided for confirming a position of the hood within the atrial chamber itself by visualizing anatomical landmarks, such as a location of a pulmonary vein ostium or a left atrial appendage, a left atrial septum, etc. Real-time visual feedback is further provided for the early detection of endocardiac disruptions and/or complications, such as visual detection of steam or bubble formation. Real-time visual feedback is additionally provided for color feedback of the ablated endocardiac tissue as an indicator when irreversible tissue damage occurs by enabling the detection of changes in the tissue color. Moreover, the hood itself provides a relatively isolated environment with little or no blood so as to reduce any risk of coagulation. The displacement fluid may also provide a cooling mechanism for the tissue surface to prevent over-heating. Once the ablation is completed, direct visualization further provides the capability for visually inspecting for contiguous lesion formation as well as inspecting color differences of the tissue surface. Also, visual inspection of endocardiac disruptions and/or complications is possible, for example, inspecting the ablated tissue for visual confirmation for the presence of tissue craters or coagulated blood on the tissue. If endocardiac disruptions and/or complications are detected, the hood also provides a barrier or membrane for containing the disruption and rapidly evacuating any tissue debris. Moreover, the hood provides for the establishment of stable contact with the ostium of the pulmonary vein or other targeted tissue, for example, by the creation of negative pressure within the space defined within the hood for drawing in or suctioning the tissue to be ablated against the hood for secure contact.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A shows a side view of one variation of a tissue imaging apparatus during deployment from a sheath or delivery catheter. FIG. 1B shows the deployed tissue imaging apparatus of FIG. 1A having an optionally expandable hood or sheath attached to an imaging and/or diagnostic catheter. FIG. 1C shows an end view of a deployed imaging apparatus. FIGS. 1D to 1F show the apparatus of FIGS. 1A to 1C with an additional lumen, e.g., for passage of a guidewire therethrough. FIGS. 2A and 2B show one example of a deployed tissue imager positioned against or adjacent to the tissue to be imaged and a flow of fluid, such as saline, displacing blood from within the expandable hood. FIG. 3A shows an articulatable imaging assembly which may be manipulated via push-pull wires or by computer control. FIGS. 3B and 3C show steerable instruments, respectively, where an articulatable delivery catheter may be steered within the imaging hood or a distal portion of the deployment catheter itself may be steered. FIGS. 4A to 4C show side and cross-sectional end views, respectively, of another variation having an off-axis imaging capability. FIG. 5 shows an illustrative view of an example of a tissue imager advanced intravascularly within a heart for imaging tissue regions within an atrial chamber. FIGS. 6A to 6C illustrate deployment catheters having one or more optional inflatable balloons or anchors for stabilizing the device during a procedure. FIGS. 7A and 7B illustrate a variation of an anchoring mechanism such as a helical tissue piercing device for temporarily stabilizing the imaging hood relative to a tissue surface. FIG. 7C shows another variation for anchoring the imaging hood having one or more tubular support members integrated with the imaging hood; each support members may define a lumen therethrough for advancing a helical tissue anchor within. FIG. 8A shows an illustrative example of one variation of how a tissue imager may be utilized with an imaging device. FIG. 8B shows a further illustration of a hand-held variation of the fluid delivery and tissue manipulation system. FIGS. 9A to 9C illustrate an example of capturing several images of the tissue at multiple regions. FIGS. 10A and 10B show charts illustrating how fluid pressure within the imaging hood may be coordinated with the surrounding blood pressure; the fluid pressure in the imaging hood may be coordinated with the blood pressure or it may be regulated based upon pressure feedback from the blood. FIG. 11A shows a side view of another variation of a tissue imager having an imaging balloon within an expandable hood. FIG. 11B shows another variation of a tissue imager utilizing a translucent or transparent imaging balloon. FIG. 12A shows another variation in which a flexible expandable or distensible membrane may be incorporated within the imaging hood to alter the volume of fluid dispensed. FIGS. 12B and 12C show another variation in which the imaging hood may be partially or selectively deployed from the catheter to alter the area of the tissue being visualized as well as the volume of the dispensed fluid. FIGS. 13A and 13B show exemplary side and cross-sectional views, respectively, of another variation in which the injected fluid may be drawn back into the device for minimizing fluid input into a body being treated. FIGS. 14A to 14D show various configurations and methods for configuring an imaging hood into a low-profile for delivery and/or deployment. FIGS. 15A and 15B show an imaging hood having an helically expanding frame or support. FIGS. 16A and 16B show another imaging hood having one or more hood support members, which are pivotably attached at their proximal ends to deployment catheter, integrated with a hood membrane. FIGS. 17A and 17B show yet another variation of the imaging hood having at least two or more longitudinally positioned support members supporting the imaging hood membrane where the support members are movable relative to one another via a torquing or pulling or pushing force. FIGS. 18A and 18B show another variation where a distal portion of the deployment catheter may have several pivoting members which form a tubular shape in its low profile configuration. FIGS. 19A and 19B show another variation where the distal portion of deployment catheter may be fabricated from a flexible metallic or polymeric material to form a radially expanding hood. FIGS. 20A and 20B show another variation where the imaging hood may be formed from a plurality of overlapping hood members which overlie one another in an overlapping pattern. FIGS. 21A and 21B show another example of an expandable hood which is highly conformable against tissue anatomy with varying geography. FIG. 22A shows yet another example of an expandable hood having a number of optional electrodes placed about the contact edge or lip of the hood for sensing tissue contact or detecting arrhythmias. FIG. 22B shows another variation for conforming the imaging hood against the underlying tissue where an inflatable contact edge may be disposed around the circumference of the imaging hood. FIG. 23 shows a variation of the system which may be instrumented with a transducer for detecting the presence of blood seeping back into the imaging hood. FIGS. 24A and 24B show variations of the imaging hood instrumented with sensors for detecting various physical parameters; the sensors may be instrumented around the outer surface of the imaging hood and also within the imaging hood. FIGS. 25A and 25B show a variation where the imaging hood may have one or more LEDs over the hood itself for providing illumination of the tissue to be visualized. FIGS. 26A and 26B show another variation in which a separate illumination tool having one or more LEDs mounted thereon may be utilized within the imaging hood. FIG. 27 shows one example of how a therapeutic tool may be advanced through the tissue imager for treating a tissue region of interest. FIG. 28 shows another example of a helical therapeutic tool for treating the tissue region of interest. FIG. 29 shows a variation of how a therapeutic tool may be utilized with an expandable imaging balloon. FIGS. 30A and 30B show alternative configurations for therapeutic instruments which may be utilized; one variation is shown having an angled instrument arm and another variation is shown with an off-axis instrument arm. FIGS. 31A to 31C show side and end views, respectively, of an imaging system which may be utilized with an ablation probe. FIGS. 32A and 32B show side and end views, respectively, of another variation of the imaging hood with an ablation probe, where the imaging hood may be enclosed for regulating a temperature of the underlying tissue. FIGS. 33A and 33B show an example in which the imaging fluid itself may be altered in temperature to facilitate various procedures upon the underlying tissue. FIGS. 34A and 34B show an example of a laser ring generator which may be utilized with the imaging system and an example for applying the laser ring generator within the left atrium of a heart for treating atrial fibrillation. FIGS. 35A to 35C show an example of an extendible cannula generally comprising an elongate tubular member which may be positioned within the deployment catheter during delivery and then projected distally through the imaging hood and optionally beyond. FIGS. 36A and 36B show side and end views, respectively, of an imaging hood having one or more tubular support members integrated with the hood for passing instruments or tools therethrough for treatment upon the underlying tissue. FIGS. 37A and 37B illustrate how an imaging device may be guided within a heart chamber to a region of interest utilizing a lighted probe positioned temporarily within, e.g., a lumen of the coronary sinus. FIGS. 38A and 38B show an imaging hood having a removable disk-shaped member for implantation upon the tissue surface. FIGS. 39A to 39C show one method for implanting the removable disk of FIGS. 38A and 38B. FIGS. 40A and 40B illustrate an imaging hood having a deployable anchor assembly attached to the tissue contact edge and an assembly view of the anchors and the suture or wire connected to the anchors, respectively FIGS. 41A to 41D show one method for deploying the anchor assembly of FIGS. 40A and 40B for closing an opening or wound. FIG. 42 shows another variation in which the imaging system may be fluidly coupled to a dialysis unit for filtering a patient's blood. FIGS. 43A and 43B show a variation of the deployment catheter having a first deployable hood and a second deployable hood positioned distal to the first hood; the deployment catheter may also have a side-viewing imaging element positioned between the first and second hoods for imaging tissue between the expanded hoods. FIGS. 44A and 44B show side and end views, respectively, of a deployment catheter having a side-imaging balloon in an un-inflated low-profile configuration. FIGS. 45A to 45C show side, top, and end views, respectively, of the inflated balloon of FIGS. 44A and 44B defining a visualization field in the inflated balloon. FIGS. 46A and 46B show side and cross-sectional end views, respectively, for one method of use in visualizing a lesion upon a vessel wall within the visualization field of the inflated balloon from FIGS. 45A to 45C. FIGS. 47A to 470 illustrate an example for intravascularly advancing the imaging and manipulation catheter into the heart and into the left atrium for ablating tissue around the ostia of the pulmonary veins for the treatment of atrial fibrillation. FIGS. 48A and 48B illustrate partial cross-sectional views of a hood which is advanced into the left atrium to examine discontiguous lesions. FIG. 49A shows a perspective view of a variation of the transmural lesion ablation device with, in this variation, a single RF ablation probe inserted through the working channel of the tissue visualization catheter. FIG. 49B shows a side view of the device performing tissue ablation within the hood under real time visualization. FIG. 49C shows the perspective view of the device performing tissue ablation within the hood under real time visualization. FIG. 50A shows a perspective view of a variation of the device when an angled ablation probe is used for linear transmural lesion formation. FIG. 50B shows a perspective view of another variation of the device when a circular ablation probe is used for circular transmural lesion formation. FIG. 51A shows a perspective view of another variation of the transmural lesion ablation device with a circularly-shaped RF electrode end effector placed on the outer circumference of an expandable membrane covering the hood of the tissue visualization catheter. FIG. 51B shows a perspective view of another variation of an expandable balloon also with a circularly-shaped RF electrode end effector and without the hood. FIG. 52 shows a perspective view of another variation of the transmural lesion ablation device with RF electrodes disposed circumferentially around the contact lip or edge of the hood. FIGS. 53A and 53B show perspective and side views, respectively, of another variation of the transmural lesion ablation device with an ablation probe positioned within the hood which also includes at least one layer of a transparent elastomeric membrane over the distal opening of the hood. FIG. 54A shows a perspective view of another variation of the transmural lesion ablation device having an expandable linear ablation electrode strip inserted through the working channel of the tissue visualization catheter. FIG. 54B shows the perspective view of the device with the linear ablation electrode strip in its expanded configuration. FIGS. 55A and 55B illustrate perspective views of another variation where a laser probe, e.g., an optical fiber bundle coupled to a laser generator, may be inserted through the work channel of the tissue visualization catheter and activated for ablation treatment. FIG. 55C shows the device of FIGS. 55A and 55B performing tissue ablation or transmural lesion formation under direct visualization while working within the hood of the visualization catheter apparatus. FIG. 56 shows a partial cross-sectional view of the tissue visualization catheter with an inflated occlusion balloon to temporarily occlude blood flow through the pulmonary vein while viewing the pulmonary vein's ostia. FIG. 57 shows a perspective view of first and second tissue graspers deployed through the hood for facilitating movement of the hood along the tissue surface. FIGS. 58A to 58C illustrate the tissue visualization catheter navigating around a body lumen, such as the left atrium of the heart, utilizing two tissue graspers to �walk� the catheter along the tissue surface. FIG. 59 shows a partial cross-sectional view of the tissue visualization catheter in a retroflexed position for accessing the right inferior pulmonary vein ostium. FIG. 60 show a partial cross-sectional view of the tissue visualization catheter intravascularly accessing the left atrium via a trans-femoral introduction through the aorta, the aortic valve, the left ventricle, and into the left atrium. FIG. 61A shows a side view of the tissue visualization catheter retroflexed at a tight angle accessing the right inferior pulmonary vein ostium with a first tissue grasper and length of wire or suture configured as a pulley mechanism. FIG. 61B illustrates the tissue visualization catheter pulling itself to access the right inferior PV ostium at a tight angle using a suture pulley mechanism. FIG. 61C illustrates the tissue visualization catheter prior to the suture being tensioned. FIG. 61D illustrates the tissue visualization catheter being moved and approximated towards the ostium as the suture is tensioned. FIG. 62A shows a partial cross-sectional view of a tissue visualization catheter having an intra-atrial balloon inflated within the left atrium. FIG. 62B shows the partial cross-sectional view with a fiberscope introduced into the balloon interior. FIG. 62C shows the partial cross-sectional view with the fiberscope advancing and articulating within the balloon. FIG. 62D shows the partial cross-sectional view of the intra-atrial balloon having radio-opaque fiducial markers and an ablation probe deployed within the balloon. FIG. 63 shows a detail side view of an ablation probe deployed within the balloon and penetrating through the balloon wall. FIGS. 64A and 64B show perspective views of ablation needles deployable from a retracted position to a deployed position. FIG. 64C shows the perspective view of an ablation needle having a bipolar electrode configuration. FIG. 65A to 65E illustrate a stabilizing catheter accessing the left atrium with a stabilizing balloon deployed in the right atrium and examples of the articulation and translation capabilities for directing the hood towards the tissue region to be treated. FIG. 66A to 66E illustrate another variation of a stabilizing catheter accessing the left atrium with proximal and distal stabilizing balloons deployed about the atrial septum and examples of the articulation and translation capabilities for directing the hood towards the tissue region to be treated. FIG. 67A to 67F illustrate another variation of a stabilizing catheter accessing the left atrium with a combination of proximal and distal stabilizing balloons deployed about the atrial septum and an intra-atrial balloon expanded within the left atrium with a hollow needle for piercing through the balloon and deploying the hood external to the balloon. FIG. 68A illustrates a side view of the tissue visualization catheter deploying an intra-atrial balloon with an articulatable imager capturing multiple images representing different segments of the heart chamber wall from different angles. FIG. 68B schematically illustrates the mapping of the multiple captured images processed to create a panoramic visual map of the heart chamber. FIG. 69A shows a partial cross-sectional view of the tissue visualization catheter in the left atrium performing RF ablation, with a light source or ultrasound crystal source inserted transorally into the esophagus to prevent esophageal perforation. FIGS. 69B and 69C illustrate the image viewed by the user prior to the ablation probe being activated. FIGS. 69D and 69E illustrate the image viewed by the user of the ablated tissue changing color as the ablation probe heats the underlying tissue. FIGS. 69F and 69G illustrate the image viewed by the user of an endocardiac disruption and the resulting tissue debris captured or contained within the hood. FIG. 69H illustrates the evacuation of the captured tissue debris into the catheter. FIGS. 69I to 69K illustrate one method for adhering the tissue to be ablated via a suction force applied to the underlying tissue to be ablated.
DETAILED DESCRIPTION OF THE INVENTION A tissue-imaging and manipulation apparatus described below is able to provide real-time images in vivo of tissue regions within a body lumen such as a heart, which is filled with blood flowing dynamically therethrough and is also able to provide intravascular tools and instruments for performing various procedures upon the imaged tissue regions. Such an apparatus may be utilized for many procedures, e.g., facilitating transseptal access to the left atrium, cannulating the coronary sinus, diagnosis of valve regurgitation/stenosis, valvuloplasty, atrial appendage closure, arrhythmogenic focus ablation, among other procedures. One variation of a tissue access and imaging apparatus is shown in the detail perspective views of FIGS. 1A to 1C. As shown in FIG. 1A, tissue imaging and manipulation assembly 10 may be delivered intravascularly through the patient's body in a low-profile configuration via a delivery catheter or sheath 14. In the case of treating tissue, such as the mitral valve located at the outflow tract of the left atrium of the heart, it is generally desirable to enter or access the left atrium while minimizing trauma to the patient. To non-operatively effect such access, one conventional approach involves puncturing the intra-atrial septum from the right atrial chamber to the left atrial chamber in a procedure commonly called a transseptal procedure or septostomy. For procedures such as percutaneous valve repair and replacement, transseptal access to the left atrial chamber of the heart may allow for larger devices to be introduced into the venous system than can generally be introduced percutaneously into the arterial system. When the imaging and manipulation assembly 10 is ready to be utilized for imaging tissue, imaging hood 12 may be advanced relative to catheter 14 and deployed from a distal opening of catheter 14, as shown by the arrow. Upon deployment, imaging hood 12 may be unconstrained to expand or open into a deployed imaging configuration, as shown in FIG. 1B. Imaging hood 12 may be fabricated from a variety of pliable or conformable biocompatible material including but not limited to, e.g., polymeric, plastic, or woven materials. One example of a woven material is Kevlar� (E.I. du Pont de Nemours, Wilmington, Del.), which is an aramid and which can be made into thin, e.g., less than 0.001 in., materials which maintain enough integrity for such applications described herein. Moreover, the imaging hood 12 may be fabricated from a translucent or opaque material and in a variety of different colors to optimize or attenuate any reflected lighting from surrounding fluids or structures, i.e., anatomical or mechanical structures or instruments. In either case, imaging hood 12 may be fabricated into a uniform structure or a scaffold-supported structure, in which case a scaffold made of a shape memory alloy, such as Nitinol, or a spring steel, or plastic, etc., may be fabricated and covered with the polymeric, plastic, or woven material. Hence, imaging hood 12 may comprise any of a wide variety of barriers or membrane structures, as may generally be used to localize displacement of blood or the like from a selected volume of a body lumen or heart chamber. In exemplary embodiments, a volume within an inner surface 13 of imaging hood 12 will be significantly less than a volume of the hood 12 between inner surface 13 and outer surface 11. Imaging hood 12 may be attached at interface 24 to a deployment catheter 16 which may be translated independently of deployment catheter or sheath 14. Attachment of interface 24 may be accomplished through any number of conventional methods. Deployment catheter 16 may define a fluid delivery lumen 18 as well as an imaging lumen 20 within which an optical imaging fiber or assembly may be disposed for imaging tissue. When deployed, imaging hood 12 may expand into any number of shapes, e.g., cylindrical, conical as shown, semi-spherical, etc., provided that an open area or field 26 is defined by imaging hood 12. The open area 26 is the area within which the tissue region of interest may be imaged. Imaging hood 12 may also define an atraumatic contact lip or edge 22 for placement or abutment against the tissue region of interest. Moreover, the diameter of imaging hood 12 at its maximum fully deployed diameter, e.g., at contact lip or edge 22, is typically greater relative to a diameter of the deployment catheter 16 (although a diameter of contact lip or edge 22 may be made to have a smaller or equal diameter of deployment catheter 16). For instance, the contact edge diameter may range anywhere from 1 to 5 times (or even greater, as practicable) a diameter of deployment catheter 16. FIG. 1C shows an end view of the imaging hood 12 in its deployed configuration. Also shown are the contact lip or edge 22 and fluid delivery lumen 18 and imaging lumen 20. The imaging and manipulation assembly 10 may additionally define a guidewire lumen therethrough, e.g., a concentric or eccentric lumen, as shown in the side and end views, respectively, of FIGS. 1D to 1F. The deployment catheter 16 may define guidewire lumen 19 for facilitating the passage of the system over or along a guidewire 17, which may be advanced intravascularly within a body lumen. The deployment catheter 16 may then be advanced over the guidewire 17, as generally known in the art. In operation, after imaging hood 12 has been deployed, as in FIG. 1B, and desirably positioned against the tissue region to be imaged along contact edge 22, the displacing fluid may be pumped at positive pressure through fluid delivery lumen 18 until the fluid fills open area 26 completely and displaces any fluid 28 from within open area 26. The displacing fluid flow may be laminarized to improve its clearing effect and to help prevent blood from re-entering the imaging hood 12. Alternatively, fluid flow may be started before the deployment takes place. The displacing fluid, also described herein as imaging fluid, may comprise any biocompatible fluid, e.g., saline, water, plasma, etc., which is sufficiently transparent to allow for relatively undistorted visualization through the fluid. Alternatively or additionally, any number of therapeutic drugs may be suspended within the fluid or may comprise the fluid itself which is pumped into open area 26 and which is subsequently passed into and through the heart and the patient body. As seen in the example of FIGS. 2A and 2B, deployment catheter 16 may be manipulated to position deployed imaging hood 12 against or near the underlying tissue region of interest to be imaged, in this example a portion of annulus A of mitral valve MV within the left atrial chamber. As the surrounding blood 30 flows around imaging hood 12 and within open area 26 defined within imaging hood 12, as seen in FIG. 2A, the underlying annulus A is obstructed by the opaque blood 30 and is difficult to view through the imaging lumen 20. The translucent fluid 28, such as saline, may then be pumped through fluid delivery lumen 18, intermittently or continuously, until the blood 30 is at least partially, and preferably completely, displaced from within open area 26 by fluid 28, as shown in FIG. 2B. Although contact edge 22 need not directly contact the underlying tissue, it is at least preferably brought into close proximity to the tissue such that the flow of clear fluid 28 from open area 26 may be maintained to inhibit significant backflow of blood 30 back into open area 26. Contact edge 22 may also be made of a soft elastomeric material such as certain soft grades of silicone or polyurethane, as typically known, to help contact edge 22 conform to an uneven or rough underlying anatomical tissue surface. Once the blood 30 has been displaced from imaging hood 12, an image may then be viewed of the underlying tissue through the clear fluid 30. This image may then be recorded or available for real-time viewing for performing a therapeutic procedure. The positive flow of fluid 28 may be maintained continuously to provide for clear viewing of the underlying tissue. Alternatively, the fluid 28 may be pumped temporarily or sporadically only until a clear view of the tissue is available to be imaged and recorded, at which point the fluid flow 28 may cease and blood 30 may be allowed to seep or flow back into imaging hood 12. This process may be repeated a number of times at the same tissue region or at multiple tissue regions. In desirably positioning the assembly at various regions within the patient body, a number of articulation and manipulation controls may be utilized. For example, as shown in the articulatable imaging assembly 40 in FIG. 3A, one or more push-pull wires 42 may be routed through deployment catheter 16 for steering the distal end portion of the device in various directions 46 to desirably position the imaging hood 12 adjacent to a region of tissue to be visualized. Depending upon the positioning and the number of push-pull wires 42 utilized, deployment catheter 16 and imaging hood 12 may be articulated into any number of configurations 44. The push-pull wire or wires 42 may be articulated via their proximal ends from outside the patient body manually utilizing one or more controls. Alternatively, deployment catheter 16 may be articulated by computer control, as further described below. Additionally or alternatively, an articulatable delivery catheter 48, which may be articulated via one or more push-pull wires and having an imaging lumen and one or more working lumens, may be delivered through the deployment catheter 16 and into imaging hood 12. With a distal portion of articulatable delivery catheter 48 within imaging hood 12, the clear displacing fluid may be pumped through delivery catheter 48 or deployment catheter 16 to clear the field within imaging hood 12. As shown in FIG. 3B, the articulatable delivery catheter 48 may be articulated within the imaging hood to obtain a better image of tissue adjacent to the imaging hood 12. Moreover, articulatable delivery catheter 48 may be articulated to direct an instrument or tool passed through the catheter 48, as described in detail below, to specific areas of tissue imaged through imaging hood 12 without having to reposition deployment catheter 16 and re-clear the imaging field within hood 12. Alternatively, rather than passing an articulatable delivery catheter 48 through the deployment catheter 16, a distal portion of the deployment catheter 16 itself may comprise a distal end 49 which is articulatable within imaging hood 12, as shown in FIG. 3C. Directed imaging, instrument delivery, etc., may be accomplished directly through one or more lumens within deployment catheter 16 to specific regions of the underlying tissue imaged within imaging hood 12. Visualization within the imaging hood 12 may be accomplished through an imaging lumen 20 defined through deployment catheter 16, as described above. In such a configuration, visualization is available in a straight-line manner, i.e., images are generated from the field distally along a longitudinal axis defined by the deployment catheter 16. Alternatively or additionally, an articulatable imaging assembly having a pivotable support member 50 may be connected to, mounted to, or otherwise passed through deployment catheter 16 to provide for visualization off-axis relative to the longitudinal axis defined by deployment catheter 16, as shown in FIG. 4A. Support member 50 may have an imaging element 52, e.g., a CCD or CMOS imager or optical fiber, attached at its distal end with its proximal end connected to deployment catheter 16 via a pivoting connection 54. If one or more optical fibers are utilized for imaging, the optical fibers 58 may be passed through deployment catheter 16, as shown in the cross-section of FIG. 4B, and routed through the support member 50. The use of optical fibers 58 may provide for increased diameter sizes of the one or several lumens 56 through deployment catheter 16 for the passage of diagnostic and/or therapeutic tools therethrough. Alternatively, electronic chips, such as a charge coupled device (CCD) or a CMOS imager, which are typically known, may be utilized in place of the optical fibers 58, in which case the electronic imager may be positioned in the distal portion of the deployment catheter 16 with electric wires being routed proximally through the deployment catheter 16. Alternatively, the electronic imagers may be wirelessly coupled to a receiver for the wireless transmission of images. Additional optical fibers or light emitting diodes (LEDs) can be used to provide lighting for the image or operative theater, as described below in further detail. Support member 50 may be pivoted via connection 54 such that the member 50 can be positioned in a low-profile configuration within channel or groove 60 defined in a distal portion of catheter 16, as shown in the cross-section of FIG. 4C. During intravascular delivery of deployment catheter 16 through the patient body, support member 50 can be positioned within channel or groove 60 with imaging hood 12 also in its low-profile configuration. During visualization, imaging hood 12 may be expanded into its deployed configuration and support member 50 may be deployed into its off-axis configuration for imaging the tissue adjacent to hood 12, as in FIG. 4A. Other configurations for support member 50 for off-axis visualization may be utilized, as desired. FIG. 5 shows an illustrative cross-sectional view of a heart H having tissue regions of interest being viewed via an imaging assembly 10. In this example, delivery catheter assembly 70 may be introduced percutaneously into the patient's vasculature and advanced through the superior vena cava SVC and into the right atrium RA. The delivery catheter or sheath 72 may be articulated through the atrial septum AS and into the left atrium LA for viewing or treating the tissue, e.g., the annulus A, surrounding the mitral valve MV. As shown, deployment catheter 16 and imaging hood 12 may be advanced out of delivery catheter 72 and brought into contact or in proximity to the tissue region of interest. In other examples, delivery catheter assembly 70 may be advanced through the inferior vena cava IVC, if so desired. Moreover, other regions of the heart H, e.g., the right ventricle RV or left ventricle LV, may also be accessed and imaged or treated by imaging assembly 10. In accessing regions of the heart H or other parts of the body, the delivery catheter or sheath 14 may comprise a conventional intra-vascular catheter or an endoluminal delivery device. Alternatively, robotically-controlled delivery catheters may also be optionally utilized with the imaging assembly described herein, in which case a computer-controller 74 may be used to control the articulation and positioning of the delivery catheter 14. An example of a robotically-controlled delivery catheter which may be utilized is described in further detail in US Pat. Pub. 2002/0087169 A1 to Brock et al. entitled �Flexible Instrument�, which is incorporated herein by reference in its entirety. Other robotically-controlled delivery catheters manufactured by Hansen Medical, Inc. (Mountain View, Calif.) may also be utilized with the delivery catheter 14. To facilitate stabilization of the deployment catheter 16 during a procedure, one or more inflatable balloons or anchors 76 may be positioned along the length of catheter 16, as shown in FIG. 6A. For example, when utilizing a transseptal approach across the atrial septum AS into the left atrium LA, the inflatable balloons 76 may be inflated from a low-profile into their expanded configuration to temporarily anchor or stabilize the catheter 16 position relative to the heart H. FIG. 6B shows a first balloon 78 inflated while FIG. 6C also shows a second balloon 80 inflated proximal to the first balloon 78. In such a configuration, the septal wall AS may be wedged or sandwiched between the balloons 78, 80 to temporarily stabilize the catheter 16 and imaging hood 12. A single balloon 78 or both balloons 78, 80 may be used. Other alternatives may utilize expandable mesh members, malecots, or any other temporary expandable structure. After a procedure has been accomplished, the balloon assembly 76 may be deflated or re-configured into a low-profile for removal of the deployment catheter 16. To further stabilize a position of the imaging hood 12 relative to a tissue surface to be imaged, various anchoring mechanisms may be optionally employed for temporarily holding the imaging hood 12 against the tissue. Such anchoring mechanisms may be particularly useful for imaging tissue which is subject to movement, e.g., when imaging tissue within the chambers of a beating heart. A tool delivery catheter 82 having at least one instrument lumen and an optional visualization lumen may be delivered through deployment catheter 16 and into an expanded imaging hood 12. As the imaging hood 12 is brought into contact against a tissue surface T to be examined, anchoring mechanisms such as a helical tissue piercing device 84 may be passed through the tool delivery catheter 82, as shown in FIG. 7A, and into imaging hood 12. The helical tissue engaging device 84 may be torqued from its proximal end outside the patient body to temporarily anchor itself into the underlying tissue surface T. Once embedded within the tissue T, the helical tissue engaging device 84 may be pulled proximally relative to deployment catheter 16 while the deployment catheter 16 and imaging hood 12 are pushed distally, as indicated by the arrows in FIG. 7B, to gently force the contact edge or lip 22 of imaging hood against the tissue T. The positioning of the tissue engaging device 84 may be locked temporarily relative to the deployment catheter 16 to ensure secure positioning of the imaging hood 12 during a diagnostic or therapeutic procedure within the imaging hood 12. After a procedure, tissue engaging device 84 may be disengaged from the tissue by torquing its proximal end in the opposite direction to remove the anchor form the tissue T and the deployment catheter 16 may be repositioned to another region of tissue where the anchoring process may be repeated or removed from the patient body. The tissue engaging device 84 may also be constructed from other known tissue engaging devices such as vacuum-assisted engagement or grasper-assisted engagement tools, among others. Although a helical anchor 84 is shown, this is intended to be illustrative and other types of temporary anchors may be utilized, e.g., hooked or barbed anchors, graspers, etc. Moreover, the tool delivery catheter 82 may be omitted entirely and the anchoring device may be delivered directly through a lumen defined through the deployment catheter 16. In another variation where the tool delivery catheter 82 may be omitted entirely to temporarily anchor imaging hood 12, FIG. 7C shows an imaging hood 12 having one or more tubular support members 86, e.g., four support members 86 as shown, integrated with the imaging hood 12. The tubular support members 86 may define lumens therethrough each having helical tissue engaging devices 88 positioned within. When an expanded imaging hood 12 is to be temporarily anchored to the tissue, the helical tissue engaging devices 88 may be urged distally to extend from imaging hood 12 and each may be torqued from its proximal end to engage the underlying tissue T. Each of the helical tissue engaging devices 88 may be advanced through the length of deployment catheter 16 or they may be positioned within tubular support members 86 during the delivery and deployment of imaging hood 12. Once the procedure within imaging hood 12 is finished, each of the tissue engaging devices 88 may be disengaged from the tissue and the imaging hood 12 may be repositioned to another region of tissue or removed from the patient body. An illustrative example is shown in FIG. 8A of a tissue imaging assembly connected to a fluid delivery system 90 and to an optional processor 98 and image recorder and/or viewer 100. The fluid delivery system 90 may generally comprise a pump 92 and an optional valve 94 for controlling the flow rate of the fluid into the system. A fluid reservoir 96, fluidly connected to pump 92, may hold the fluid to be pumped through imaging hood 12. An optional central processing unit or processor 98 may be in electrical communication with fluid delivery system 90 for controlling flow parameters such as the flow rate and/or velocity of the pumped fluid. The processor 98 may also be in electrical communication with an image recorder and/or viewer 100 for directly viewing the images of tissue received from within imaging hood 12. Imager recorder and/or viewer 100 may also be used not only to record the image but also the location of the viewed tissue region, if so desired. Optionally, processor 98 may also be utilized to coordinate the fluid flow and the image capture. For instance, processor 98 may be programmed to provide for fluid flow from reservoir 96 until the tissue area has been displaced of blood to obtain a clear image. Once the image has been determined to be sufficiently clear, either visually by a practitioner or by computer, an image of the tissue may be captured automatically by recorder 100 and pump 92 may be automatically stopped or slowed by processor 98 to cease the fluid flow into the patient. Other variations for fluid delivery and image capture are, of course, possible and the aforementioned configuration is intended only to be illustrative and not limiting. FIG. 8B shows a further illustration of a hand-held variation of the fluid delivery and tissue manipulation system 110. In this variation, system 110 may have a housing or handle assembly 112 which can be held or manipulated by the physician from outside the patient body. The fluid reservoir 114, shown in this variation as a syringe, can be fluidly coupled to the handle assembly 112 and actuated via a pumping mechanism 116, e.g., lead screw. Fluid reservoir 114 may be a simple reservoir separated from the handle assembly 112 and fluidly coupled to handle assembly 112 via one or more tubes. The fluid flow rate and other mechanisms may be metered by the electronic controller 118. Deployment of imaging hood 12 maybe actuated by a hood deployment switch 120 located on the handle assembly 112 while dispensation of the fluid from reservoir 114 may be actuated by a fluid deployment switch 122, which can be electrically coupled to the controller 118. Controller 118 may also be electrically coupled to a wired or wireless antenna 124 optionally integrated with the handle assembly 112, as shown in the figure. The wireless antenna 124 can be used to wirelessly transmit images captured from the imaging hood 12 to a receiver, e.g., via Bluetooth� wireless technology (Bluetooth SIG, Inc., Bellevue, Wash.), RF, etc., for viewing on a monitor 128 or for recording for later viewing. Articulation control of the deployment catheter 16, or a delivery catheter or sheath 14 through which the deployment catheter 16 may be delivered, may be accomplished by computer control, as described above, in which case an additional controller may be utilized with handle assembly 112. In the case of manual articulation, handle assembly 112 may incorporate one or more articulation controls 126 for manual manipulation of the position of deployment catheter 16. Handle assembly 112 may also define one or more instrument ports 130 through which a number of intravascular tools may be passed for tissue manipulation and treatment within imaging hood 12, as described further below. Furthermore, in certain procedures, fluid or debris may be sucked into imaging hood 12 for evacuation from the patient body by optionally fluidly coupling a suction pump 132 to handle assembly 112 or directly to deployment catheter 16. As described above, fluid may be pumped continuously into imaging hood 12 to provide for clear viewing of the underlying tissue. Alternatively, fluid may be pumped temporarily or sporadically only until a clear view of the tissue is available to be imaged and recorded, at which point the fluid flow may cease and the blood may be allowed to seep or flow back into imaging hood 12. FIGS. 9A to 9C illustrate an example of capturing several images of the tissue at multiple regions. Deployment catheter 16 may be desirably positioned and imaging hood 12 deployed and brought into position against a region of tissue to be imaged, in this example the tissue surrounding a mitral valve MV within the left atrium of a patient's heart. The imaging hood 12 may be optionally anchored to the tissue, as described above, and then cleared by pumping the imaging fluid into the hood 12. Once sufficiently clear, the tissue may be visualized and the image captured by control electronics 118. The first captured image 140 may be stored and/or transmitted wirelessly 124 to a monitor 128 for viewing by the physician, as shown in FIG. 9A. The deployment catheter 16 may be then repositioned to an adjacent portion of mitral valve MV, as shown in FIG. 9B, where the process may be repeated to capture a second image 142 for viewing and/or recording. The deployment catheter 16 may again be repositioned to another region of tissue, as shown in FIG. 9C, where a third image 144 may be captured for viewing and/or recording. This procedure may be repeated as many times as necessary for capturing a comprehensive image of the tissue surrounding mitral valve MV, or any other tissue region. When the deployment catheter 16 and imaging hood 12 is repositioned from tissue region to tissue region, the pump may be stopped during positioning and blood or surrounding fluid may be allowed to enter within imaging hood 12 until the tissue is to be imaged, where the imaging hood 12 may be cleared, as above. As mentioned above, when the imaging hood 12 is cleared by pumping the imaging fluid within for clearing the blood or other bodily fluid, the fluid may be pumped continuously to maintain the imaging fluid within the hood 12 at a positive pressure or it may be pumped under computer control for slowing or stopping the fluid flow into the hood 12 upon detection of various parameters or until a clear image of the underlying tissue is obtained. The control electronics 118 may also be programmed to coordinate the fluid flow into the imaging hood 12 with various physical parameters to maintain a clear image within imaging hood 12. One example is shown in FIG. 10A which shows a chart 150 illustrating how fluid pressure within the imaging hood 12 may be coordinated with the surrounding blood pressure. Chart 150 shows the cyclical blood pressure 156 alternating between diastolic pressure 152 and systolic pressure 154 over time T due to the beating motion of the patient heart. The fluid pressure of the imaging fluid, indicated by plot 160, within imaging hood 12 may be automatically timed to correspond to the blood pressure changes 160 such that an increased pressure is maintained within imaging hood 12 which is consistently above the blood pressure 156 by a slight increase ΔP, as illustrated by the pressure difference at the peak systolic pressure 158. This pressure difference, ΔP, may be maintained within imaging hood 12 over the pressure variance of the surrounding blood pressure to maintain a positive imaging fluid pressure within imaging hood 12 to maintain a clear view of the underlying tissue. One benefit of maintaining a constant ΔP is a constant flow and maintenance of a clear field. FIG. 10B shows a chart 162 illustrating another variation for maintaining a clear view of the underlying tissue where one or more sensors within the imaging hood 12, as described in further detail below, may be configured to sense pressure changes within the imaging hood 12 and to correspondingly increase the imaging fluid pressure within imaging hood 12. This may result in a time delay, ΔT, as illustrated by the shifted fluid pressure 160 relative to the cycling blood pressure 156, although the time delays ΔT may be negligible in maintaining the clear image of the underlying tissue. Predictive software algorithms can also be used to substantially eliminate this time delay by predicting when the next pressure wave peak will arrive and by increasing the pressure ahead of the pressure wave's arrival by an amount of time equal to the aforementioned time delay to essentially cancel the time delay out. The variations in fluid pressure within imaging hood 12 may be accomplished in part due to the nature of imaging hood 12. An inflatable balloon, which is conventionally utilized for imaging tissue, may be affected by the surrounding blood pressure changes. On the other hand, an imaging hood 12 retains a constant volume therewithin and is structurally unaffected by the surrounding blood pressure changes, thus allowing for pressure increases therewithin. The material that hood 12 is made from may also contribute to the manner in which the pressure is modulated within this hood 12. A stiffer hood material, such as high durometer polyurethane or Nylon, may facilitate the maintaining of an open hood when deployed. On the other hand, a relatively lower durometer or softer material, such as a low durometer PVC or polyurethane, may collapse from the surrounding fluid pressure and may not adequately maintain a deployed or expanded hood. Turning now to the imaging hood, other variations of the tissue imaging assembly may be utilized, as shown in FIG. 11A, which shows another variation comprising an additional imaging balloon 172 within an imaging hood 174. In this variation, an expandable balloon 172 having a translucent skin may be positioned within imaging hood 174. Balloon 172 may be made from any distensible biocompatible material having sufficient translucent properties which allow for visualization therethrough. Once the imaging hood 174 has been deployed against the tissue region of interest, balloon 172 may be filled with a fluid, such as saline, or less preferably a gas, until balloon 172 has been expanded until the blood has been sufficiently displaced. The balloon 172 may thus be expanded proximal to or into contact against the tissue region to be viewed. The balloon 172 can also be filled with contrast media to allow it to be viewed on fluoroscopy to aid in its positioning. The imager, e.g., fiber optic, positioned within deployment catheter 170 may then be utilized to view the tissue region through the balloon 172 and any additional fluid which may be pumped into imaging hood 174 via one or more optional fluid ports 176, which may be positioned proximally of balloon 172 along a portion of deployment catheter 170. Alternatively, balloon 172 may define one or more holes over its surface which allow for seepage or passage of the fluid contained therein to escape and displace the blood from within imaging hood 174. FIG. 11B shows another alternative in which balloon 180 may be utilized alone. Balloon 180, attached to deployment catheter 178, may be filled with fluid, such as saline or contrast media, and is preferably allowed to come into direct contact with the tissue region to be imaged. FIG. 12A shows another alternative in which deployment catheter 16 incorporates imaging hood 12, as above, and includes an additional flexible membrane 182 within imaging hood 12. Flexible membrane 182 may be attached at a distal end of catheter 16 and optionally at contact edge 22. Imaging hood 12 may be utilized, as above, and membrane 182 may be deployed from catheter 16 in vivo or prior to placing catheter 16 within a patient to reduce the volume within imaging hood 12. The volume may be reduced or minimized to reduce the amount of fluid dispensed for visualization or simply reduced depending upon the area of tissue to be visualized. FIGS. 12B and 12C show yet another alternative in which imaging hood 186 may be withdrawn proximally within deployment catheter 184 or deployed distally from catheter 186, as shown, to vary the volume of imaging hood 186 and thus the volume of dispensed fluid. Imaging hood 186 may be seen in FIG. 12B as being partially deployed from, e.g., a circumferentially defined lumen within catheter 184, such as annular lumen 188. The underlying tissue may be visualized with imaging hood 186 only partially deployed. Alternatively, imaging hood 186′ may be fully deployed, as shown in FIG. 12C, by urging hood 186′ distally out from annular lumen 188. In this expanded configuration, the area of tissue to be visualized may be increased as hood 186′ is expanded circumferentially. FIGS. 13A and 13B show perspective and cross-sectional side views, respectively, of yet another variation of imaging assembly which may utilize a fluid suction system for minimizing the amount of fluid injected into the patient's heart or other body lumen during tissue visualization. Deployment catheter 190 in this variation may define an inner tubular member 196 which may be integrated with deployment catheter 190 or independently translatable. Fluid delivery lumen 198 defined through member 196 may be fluidly connected to imaging hood 192, which may also define one or more open channels 194 over its contact lip region. Fluid pumped through fluid delivery lumen 198 may thus fill open area 202 to displace any blood or other fluids or objects therewithin. As the clear fluid is forced out of open area 202, it may be sucked or drawn immediately through one or more channels 194 and back into deployment catheter 190. Tubular member 196 may also define one or more additional working channels 200 for the passage of any tools or visualization devices. In deploying the imaging hood in the examples described herein, the imaging hood may take on any number of configurations when positioned or configured for a low-profile delivery within the delivery catheter, as shown in the examples of FIGS. 14A to 14D. These examples are intended to be illustrative and are not intended to be limiting in scope. FIG. 14A shows one example in which imaging hood 212 maybe compressed within catheter 210 by folding hood 212 along a plurality of pleats. Hood 212 may also comprise scaffolding or frame 214 made of a super-elastic or shape memory material or alloy, e.g., Nitinol, Elgiloy, shape memory polymers, electroactive polymers, or a spring stainless steel. The shape memory material may act to expand or deploy imaging hood 212 into its expanded configuration when urged in the direction of the arrow from the constraints of catheter 210. FIG. 14B shows another example in which imaging hood, 216 may be expanded or deployed from catheter 210 from a folded and overlapping configuration. Frame or scaffolding 214 may also be utilized in this example. FIG. 14C shows yet another example in which imaging hood 218 may be rolled, inverted, or everted upon itself for deployment. In yet another example, FIG. 14D shows a configuration in which imaging hood 220 may be fabricated from an extremely compliant material which allows for hood 220 to be simply compressed into a low-profile shape. From this low-profile compressed shape, simply releasing hood 220 may allow for it to expand into its deployed configuration, especially if a scaffold or frame of a shape memory or superelastic material, e.g., Nitinol, is utilized in its construction. Another variation for expanding the imaging hood is shown in FIGS. 15A and 15B which illustrates an helically expanding frame or support 230. In its constrained low-profile configuration, shown in FIG. 15A, helical frame 230 may be integrated with the imaging hood 12 membrane. When free to expand, as shown in FIG. 15B, helical frame 230 may expand into a conical or tapered shape. Helical frame 230 may alternatively be made out of heat-activated Nitinol to allow it to expand upon application of a current. FIGS. 16A and 16B show yet another variation in which imaging hood 12 may comprise one or more hood support members 232 integrated with the hood membrane. These longitudinally attached support members 232 may be pivotably attached at their proximal ends to deployment catheter 16. One or more pullwires 234 may be routed through the length of deployment catheter 16 and extend through one or more openings 238 defined in deployment catheter 16 proximally to imaging hood 12 into attachment with a corresponding support member 232 at a pullwire attachment point 236. The support members 232 may be fabricated from a plastic or metal, such as stainless steel. Alternatively, the support members 232 may be made from a superelastic or shape memory alloy, such as Nitinol, which may self-expand into its deployed configuration without the use or need of pullwires. A heat-activated Nitinol may also be used which expands upon the application of thermal energy or electrical energy. In another alternative, support members 232 may also be constructed as inflatable lumens utilizing, e.g., PET balloons. From its low-profile delivery configuration shown in FIG. 16A, the one or more pullwires 234 may be tensioned from their proximal ends outside the patient body to pull a corresponding support member 232 into a deployed configuration, as shown in FIG. 16B, to expand imaging hood 12. To reconfigure imaging hood 12 back into its low profile, deployment catheter 16 may be pulled proximally into a constraining catheter or the pullwires 234 may be simply pushed distally to collapse imaging hood 12. FIGS. 17A and 17B show yet another variation of imaging hood 240 having at least two or more longitudinally positioned support members 242 supporting the imaging hood membrane. The support members 242 each have cross-support members 244 which extend diagonally between and are pivotably attached to the support members 242. Each of the cross-support members 244 may be pivotably attached to one another where they intersect between the support members 242. A jack or screw member 246 maybe coupled to each cross-support member 244 at this intersection point and a torquing member, such as a torqueable wire 248, may be coupled to each jack or screw member 246 and extend proximally through deployment catheter 16 to outside the patient body. From outside the patient body, the torqueable wires 248 may be torqued to turn the jack or screw member 246 which in turn urges the cross-support members 244 to angle relative to one another and thereby urge the support members 242 away from one another. Thus, the imaging hood 240 may be transitioned from its low-profile, shown in FIG. 17A, to its expanded profile, shown in FIG. 17B, and back into its low-profile by torquing wires 248. FIGS. 18A and 18B show yet another variation on the imaging hood and its deployment. As shown, a distal portion of deployment catheter 16 may have several pivoting members 250, e.g., two to four sections, which form a tubular shape in its low profile configuration, as shown in FIG. 18A. When pivoted radially about deployment catheter 16, pivoting members 250 may open into a deployed configuration having distensible or expanding membranes 252 extending over the gaps in-between the pivoting members 250, as shown in FIG. 18B. The distensible membrane 252 may be attached to the pivoting members 250 through various methods, e.g., adhesives, such that when the pivoting members 250 are fully extended into a conical shape, the pivoting members 250 and membrane 252 form a conical shape for use as an imaging hood. The distensible membrane 252 may be made out of a porous material such as a mesh or PTFE or out of a translucent or transparent polymer such as polyurethane, PVC, Nylon, etc. FIGS. 19A and 19B show yet another variation where the distal portion of deployment catheter 16 may be fabricated from a flexible metallic or polymeric material to form a radially expanding hood 254. A plurality of slots 256 may be formed in a uniform pattern over the distal portion of deployment catheter 16, as shown in FIG. 19A. The slots 256 may be formed in a pattern such that when the distal portion is urged radially open, utilizing any of the methods described above, a radially expanded and conically-shaped hood 254 may be formed by each of the slots 256 expanding into an opening, as shown in FIG. 19B. A distensible membrane 258 may overlie the exterior surface or the interior surface of the hood 254 to form a fluid-impermeable hood 254 such that the hood 254 may be utilized as an imaging hood. Alternatively, the distensible membrane 258 may alternatively be formed in each opening 258 to form the fluid-impermeable hood 254. Once the imaging procedure has been completed, hood 254 may be retracted into its low-profile configuration. Yet another configuration for the imaging hood may be seen in FIGS. 20A and 20B where the imaging hood may be formed from a plurality of overlapping hood members 260 which overlie one another in an overlapping pattern. When expanded, each of the hood members 260 may extend radially outward relative to deployment catheter 16 to form a conically-shaped imaging hood, as shown in FIG. 20B. Adjacent hood members 260 may overlap one another along an overlapping interface 262 to form a fluid-retaining surface within the imaging hood. Moreover, the hood members 260 may be made from any number of biocompatible materials, e.g., Nitinol, stainless steel, polymers, etc., which are sufficiently strong to optionally retract surrounding tissue from the tissue region of interest. Although it is generally desirable to have an imaging hood contact against a tissue surface in a normal orientation, the imaging hood may be alternatively configured to contact the tissue surface at an acute angle. An imaging hood configured for such contact against tissue may also be especially suitable for contact against tissue surfaces having an unpredictable or uneven anatomical geography. For instance, as shown in the variation of FIG. 21A, deployment catheter 270 may have an imaging hood 272 that is configured to be especially compliant. In this variation, imaging hood 272 may be comprised of one or more sections 274 that are configured to fold or collapse, e.g., by utilizing a pleated surface. Thus, as shown in FIG. 21B, when imaging hood 272 is contacted against uneven tissue surface T, sections 274 are able to conform closely against the tissue. These sections 274 may be individually collapsible by utilizing an accordion style construction to allow conformation, e.g., to the trabeculae in the heart or the uneven anatomy that may be found inside the various body lumens. In yet another alternative, FIG. 22A shows another variation in which an imaging hood 282 is attached to deployment catheter 280. The contact lip or edge 284 may comprise one or more electrical contacts 286 positioned circumferentially around contact edge 284. The electrical contacts 286 may be configured to contact the tissue and indicate affirmatively whether tissue contact was achieved, e.g., by measuring the differential impedance between blood and tissue. Alternatively, a processor, e.g., processor 98, in electrical communication with contacts 286 may be configured to determine what type of tissue is in contact with electrical contacts 286. In yet another alternative, the processor 98 may be configured to measure any electrical activity that may be occurring in the underlying tissue, e.g., accessory pathways, for the purposes of electrically mapping the cardiac tissue and subsequently treating, as described below, any arrhythmias which may be detected. Another variation for ensuring contact between imaging hood 282 and the underlying tissue may be seen in FIG. 22B. This variation may have an inflatable contact edge 288 around the circumference of imaging hood 282. The inflatable contact edge 288 may be inflated with a fluid or gas through inflation lumen 289 when the imaging hood 282 is to be placed against a tissue surface having an uneven or varied anatomy. The inflated circumferential surface 288 may provide for continuous contact over the hood edge by conforming against the tissue surface and facilitating imaging fluid retention within hood 282. Aside from the imaging hood, various instrumentation may be utilized with the imaging and manipulation system. For instance, after the field within imaging hood 12 has been cleared of the opaque blood and the underlying tissue is visualized through the clear fluid, blood may seep back into the imaging hood 12 and obstruct the view. One method for automatically maintaining a clear imaging field may utilize a transducer, e.g., an ultrasonic transducer 290, positioned at the distal end of deployment catheter within the imaging hood 12, as shown in FIG. 23. The transducer 290 may send an energy pulse 292 into the imaging hood 12 and wait to detect back-scattered energy 294 reflected from debris or blood within the imaging hood 12. If back-scattered energy is detected, the pump may be actuated automatically to dispense more fluid into the imaging hood until the debris or blood is no longer detected. Alternatively, one or more sensors 300 may be positioned on the imaging hood 12 itself, as shown in FIG. 24A, to detect a number of different parameters. For example, sensors 300 may be configured to detect for the presence of oxygen in the surrounding blood, blood and/or imaging fluid pressure, color of the fluid within the imaging hood, etc. Fluid color may be particularly useful in detecting the presence of blood within the imaging hood 12 by utilizing a reflective type sensor to detect back reflection from blood. Any reflected light from blood which may be present within imaging hood 12 may be optically or electrically transmitted through deployment catheter 16 and to a red colored filter within control electronics 118. Any red color which may be detected may indicate the presence of blood and trigger a signal to the physician or automatically actuate the pump to dispense more fluid into the imaging hood 12 to clear the blood. Alternative methods for detecting the presence of blood within the hood 12 may include detecting transmitted light through the imaging fluid within imaging hood 12. If a source of white light, e.g., utilizing LEDs or optical fibers, is illuminated inside imaging hood 12, the presence of blood may cause the color red to be filtered through this fluid. The degree or intensity of the red color detected may correspond to the amount of blood present within imaging hood 12. A red color sensor can simply comprise, in one variation, a phototransistor with a red transmitting filter over it which can establish how much red light is detected, which in turn can indicate the presence of blood within imaging hood 12. Once blood is detected, the system may pump more clearing fluid through and enable closed loop feedback control of the clearing fluid pressure and flow level. Any number of sensors may be positioned along the exterior 302 of imaging hood 12 or within the interior 304 of imaging hood 12 to detect parameters not only exteriorly to imaging hood 12 but also within imaging hood 12. Such a configuration, as shown in FIG. 24B, may be particularly useful for automatically maintaining a clear imaging field based upon physical parameters such as blood pressure, as described above for FIGS. 10A and 10B. Aside from sensors, one or more light emitting diodes (LEDs) may be utilized to provide lighting within the imaging hood 12. Although illumination may be provided by optical fibers routed through deployment catheter 16, the use of LEDs over the imaging hood 12 may eliminate the need for additional optical fibers for providing illumination. The electrical wires connected to the one or more LEDs may be routed through or over the hood 12 and along an exterior surface or extruded within deployment catheter 16. One or more LEDs may be positioned in a circumferential pattern 306 around imaging hood 12, as shown in FIG. 25A, or in a linear longitudinal pattern 308 along imaging hood 12, as shown in FIG. 25B. Other patterns, such as a helical or spiral pattern, may also be utilized. Alternatively, LEDs may be positioned along a support member forming part of imaging hood 12. In another alternative for illumination within imaging hood 12, a separate illumination tool 310 may be utilized, as shown in FIG. 26A. An example of such a tool may comprise a flexible intravascular delivery member 312 having a carrier member 314 pivotably connected 316 to a distal end of delivery member 312. One or more LEDs 318 may be mounted along carrier member 314. In use, delivery member 312 may be advanced through deployment catheter 16 until carrier member 314 is positioned within imaging hood 12. Once within imaging hood 12, carrier member 314 may be pivoted in any number of directions to facilitate or optimize the illumination within the imaging hood 12, as shown in FIG. 26B. In utilizing LEDs for illumination, whether positioned along imaging hood 12 or along a separate instrument, the LEDs may comprise a single LED color, e.g., white light. Alternatively, LEDs of other colors, e.g., red, blue, yellow, etc., may be utilized exclusively or in combination with white LEDs to provide for varied illumination of the tissue or fluids being imaged. Alternatively, sources of infrared or ultraviolet light may be employed to enable imaging beneath the tissue surface or cause fluorescence of tissue for use in system guidance, diagnosis, or therapy. Aside from providing a visualization platform, the imaging assembly may also be utilized to provide a therapeutic platform for treating tissue being visualized. As shown in FIG. 27, deployment catheter 320 may have imaging hood 322, as described above, and fluid delivery lumen 324 and imaging lumen 326. In this variation, a therapeutic tool such as needle 328 may be delivered through fluid delivery lumen 324 or in another working lumen and advanced through open area 332 for treating the tissue which is visualized. In this instance, needle 328 may define one or several ports 330 for delivering drugs therethrough. Thus, once the appropriate region of tissue has been imaged and located, needle 328 may be advanced and pierced into the underlying tissue where a therapeutic agent may be delivered through ports 330. Alternatively, needle 328 may be in electrical communication with a power source 334, e.g., radio-frequency, microwave, etc., for ablating the underlying tissue area of interest. FIG. 28 shows another alternative in which deployment catheter 340 may have imaging hood 342 attached thereto, as above, but with a therapeutic tool 344 in the configuration of a helical tissue piercing device 344. Also shown and described above in FIGS. 7A and 7B for use in stabilizing the imaging hood relative to the underlying tissue, the helical tissue piercing device 344 may also be utilized to manipulate the tissue for a variety of therapeutic procedures. The helical portion 346 may also define one or several ports for delivery of therapeutic agents therethrough. In yet another alternative, FIG. 29 shows a deployment catheter 350 having an expandable imaging balloon 352 filled with, e.g., saline 356. A therapeutic tool 344, as above, may be translatable relative to balloon 352. To prevent the piercing portion 346 of the tool from tearing balloon 352, a stop 354 may be formed on balloon 352 to prevent the proximal passage of portion 346 past stop 354. Alternative configurations for tools which may be delivered through deployment catheter 16 for use in tissue manipulation within imaging hood 12 are shown in FIGS. 30A and 30B. FIG. 30A shows one variation of an angled instrument 360, such as a tissue grasper, which may be configured to have an elongate shaft for intravascular delivery through deployment catheter 16 with a distal end which may be angled relative to its elongate shaft upon deployment into imaging hood 12. The elongate shaft may be configured to angle itself automatically, e.g., by the elongate shaft being made at least partially from a shape memory alloy, or upon actuation, e.g., by tensioning a pullwire. FIG. 30B shows another configuration for an instrument 362 being configured to reconfigure its distal portion into an off-axis configuration within imaging hood 12. In either case, the instruments 360, 362 may be reconfigured into a low-profile shape upon withdrawing them proximally back into deployment catheter 16. Other instruments or tools which may be utilized with the imaging system is shown in the side and end views of FIGS. 31A to 31C. FIG. 31A shows a probe 370 having a distal end effector 372, which may be reconfigured from a low-profile shape to a curved profile. The end effector 372 may be configured as an ablation probe utilizing radio-frequency energy, microwave energy, ultrasound energy, laser energy or even cryo-ablation. Alternatively, the end effector 372 may have several electrodes upon it for detecting or mapping electrical signals transmitted through the underlying tissue. In the case of an end effector 372 utilized for ablation of the underlying tissue, an additional temperature sensor such as a thermocouple or thermistor 374 positioned upon an elongate member 376 may be advanced into the imaging hood 12 adjacent to the distal end effector 372 for contacting and monitoring a temperature of the ablated tissue. FIG. 31B shows an example in the end view of one configuration for the distal end effector 372 which may be simply angled into a perpendicular configuration for contacting the tissue. FIG. 31C shows another example where the end effector may be reconfigured into a curved end effector 378 for increased tissue contact. FIGS. 32A and 32B show another variation of an ablation tool utilized with an imaging hood 12 having an enclosed bottom portion. In this variation, an ablation probe, such as a cryo-ablation probe 380 having a distal end effector 382, may be positioned through the imaging hood 12 such that the end effector 382 is placed distally of a transparent membrane or enclosure 384, as shown in the end view of FIG. 32B. The shaft of probe 380 may pass through an opening 386 defined through the membrane 384. In use, the clear fluid may be pumped into imaging hood 12, as described above, and the distal end effector 382 may be placed against a tissue region to be ablated with the imaging hood 12 and the membrane 384 positioned atop or adjacent to the ablated tissue. In the case of cryo-ablation, the imaging fluid may be warmed prior to dispensing into the imaging hood 12 such that the tissue contacted by the membrane 384 may be warmed during the cryo-ablation procedure. In the case of thermal ablation, e.g., utilizing radio-frequency energy, the fluid dispensed into the imaging hood 12 may be cooled such that the tissue contacted by the membrane 384 and adjacent to the ablation probe during the ablation procedure is likewise cooled. In either example described above, the imaging fluid may be varied in its temperature to facilitate various procedures to be performed upon the tissue. In other cases, the imaging fluid itself may be altered to facilitate various procedures. For instance as shown in FIG. 33A, a deployment catheter 16 and imaging hood 12 may be advanced within a hollow body organ, such as a bladder filled with urine 394, towards a lesion or tumor 392 on the bladder wall. The imaging hood 12 may be placed entirely over the lesion 392, or over a portion of the lesion. Once secured against the tissue wall 390, a cryo-fluid, i.e., a fluid which has been cooled to below freezing temperatures of, e.g., water or blood, may be pumped into the imaging hood 12 to cryo-ablate the lesion 390, as shown in FIG. 33B while avoiding the creation of ice on the instrument or surface of tissue. As the cryo-fluid leaks out of the imaging hood 12 and into the organ, the fluid may be warmed naturally by the patient body and ultimately removed. The cryo-fluid may be a colorless and translucent fluid which enables visualization therethrough of the underlying tissue. An example of such a fluid is Fluorinert� (3M, St. Paul, Minn.), which is a colorless and odorless perfluorinated liquid. The use of a liquid such as Fluorinert� enables the cryo-ablation procedure without the formation of ice within or outside of the imaging hood 12. Alternatively, rather than utilizing cryo-ablation, hyperthermic treatments may also be effected by heating the Fluorinert� liquid to elevated temperatures for ablating the lesion 392 within the imaging hood 12. Moreover, Fluorinert� may be utilized in various other parts of the body, such as within the heart. FIG. 34A shows another variation of an instrument which may be utilized with the imaging system. In this variation, a laser ring generator 400 may be passed through the deployment catheter 16 and partially into imaging hood 12. A laser ring generator 400 is typically used to create a circular ring of laser energy 402 for generating a conduction block around the pulmonary veins typically in the treatment of atrial fibrillation. The circular ring of laser energy 402 may be generated such that a diameter of the ring 402 is contained within a diameter of the imaging hood 12 to allow for tissue ablation directly upon tissue being imaged. Signals which cause atrial fibrillation typically come from the entry area of the pulmonary veins into the left atrium and treatments may sometimes include delivering ablation energy to the ostia of the pulmonary veins within the atrium. The ablated areas of the tissue may produce a circular scar which blocks the impulses for atrial fibrillation. When using the laser energy to ablate the tissue of the heart, it may be generally desirable to maintain the integrity and health of the tissue overlying the surface while ablating the underlying tissue. This may be accomplished, for example, by cooling the imaging fluid to a temperature below the body temperature of the patient but which is above the freezing point of blood (e.g., 2� C. to 35� C.). The cooled imaging fluid may thus maintain the surface tissue at the cooled fluid temperature while the deeper underlying tissue remains at the patient body temperature. When the laser energy (or other types of energy such as radio frequency energy, microwave energy, ultrasound energy, etc.) irradiates the tissue, both the cooled tissue surface as well as the deeper underlying tissue will rise in temperature uniformly. The deeper underlying tissue, which was maintained at the body temperature, will increase to temperatures which are sufficiently high to destroy the underlying tissue. Meanwhile, the temperature of the cooled surface tissue will also rise but only to temperatures that are near body temperature or slightly above. Accordingly, as shown in FIG. 34B, one example for treatment may include passing deployment catheter 16 across the atrial septum AS and into the left atrium LA of the patient's heart H. Other methods of accessing the left atrium LA may also be utilized. The imaging hood 12 and laser ring generator 400 may be positioned adjacent to or over one or more of the ostium OT of the pulmonary veins PV and the laser generator 400 may ablate the tissue around the ostium OT with the circular ring of laser energy 402 to create a conduction block. Once one or more of the tissue around the ostium OT have been ablated, the imaging hood 12 may be reconfigured into a low profile for removal from the patient heart H. One of the difficulties in treating tissue in or around the ostium OT is the dynamic fluid flow of blood through the ostium OT. The dynamic forces make cannulation or entry of the ostium OT difficult. Thus, another variation on instruments or tools utilizable with the imaging system is an extendible cannula 410 having a cannula lumen 412 defined therethrough, as shown in FIG. 35A. The extendible cannula 410 may generally comprise an elongate tubular member which may be positioned within the deployment catheter 16 during delivery and then projected distally through the imaging hood 12 and optionally beyond, as shown in FIG. 35B. In use, once the imaging hood 12 has been desirably positioned relative to the tissue, e.g., as shown in FIG. 35C outside the ostium OT of a pulmonary vein PV, the extendible cannula 410 may be projected distally from the deployment catheter 16 while optionally imaging the tissue through the imaging hood 12, as described above. The extendible cannula 410 may be projected distally until its distal end is extended at least partially into the ostium OT. Once in the ostium OT, an instrument or energy ablation device may be extended through and out of the cannula lumen 412 for treatment within the ostium OT. Upon completion of the procedure, the cannula 410 may be withdrawn proximally and removed from the patient body. The extendible cannula 410 may also include an inflatable occlusion balloon at or near its distal end to block the blood flow out of the PV to maintain a clear view of the tissue region. Alternatively, the extendible cannula 410 may define a lumen therethrough beyond the occlusion balloon to bypass at least a portion of the blood that normally exits the pulmonary vein PV by directing the blood through the cannula 410 to exit proximal of the imaging hood. Yet another variation for tool or instrument use may be seen in the side and end views of FIG. 36A and 36B. In this variation, imaging hood 12 may have one or more tubular support members 420 integrated with the hood 12. Each of the tubular support members 420 may define an access lumen 422 through which one or more instruments or tools may be delivered for treatment upon the underlying tissue. One particular example is shown and described above for FIG. 7C. Various methods and instruments may be utilized for using or facilitating the use of the system. For instance, one method may include facilitating the initial delivery and placement of a device into the patient's heart. In initially guiding the imaging assembly within the heart chamber to, e.g., the mitral valve MV, a separate guiding probe 430 may be utilized, as shown in FIGS. 37A and 37B. Guiding probe 430 may, for example, comprise an optical fiber through which a light source 434 may be used to illuminate a distal tip portion 432. The tip portion 432 may be advanced into the heart through, e.g., the coronary sinus CS, until the tip is positioned adjacent to the mitral valve MV. The tip 432 may be illuminated, as shown in FIG. 37A, and imaging assembly 10 may then be guided towards the illuminated tip 432, which is visible from within the atrial chamber, towards mitral valve MV. Aside from the devices and methods described above, the imaging system may be utilized to facilitate various other procedures. Turning now to FIGS. 38A and 38B, the imaging hood of the device in particular may be utilized. In this example, a collapsible membrane or disk-shaped member 440 may be temporarily secured around the contact edge or lip of imaging hood 12. During intravascular delivery, the imaging hood 12 and the attached member 440 may both be in a collapsed configuration to maintain a low profile for delivery. Upon deployment, both the imaging hood 12 and the member 440 may extend into their expanded configurations. The disk-shaped member 440 may be comprised of a variety of materials depending upon the application. For instance, member 440 may be fabricated from a porous polymeric material infused with a drug eluting medicament 442 for implantation against a tissue surface for slow infusion of the medicament into the underlying tissue. Alternatively, the member 440 may be fabricated from a non-porous material, e.g., metal or polymer, for implantation and closure of a wound or over a cavity to prevent fluid leakage. In yet another alternative, the member 440 may be made from a distensible material which is secured to imaging hood 12 in an expanded condition. Once implanted or secured on a tissue surface or wound, the expanded member 440 may be released from imaging hood 12. Upon release, the expanded member 440 may shrink to a smaller size while approximating the attached underlying tissue, e.g., to close a wound or opening. One method for securing the disk-shaped member 440 to a tissue surface may include a plurality of tissue anchors 444, e.g., barbs, hooks, projections, etc., which are attached to a surface of the member 440. Other methods of attachments may include adhesives, suturing, etc. In use, as shown in FIGS. 39A to 39C, the imaging hood 12 may be deployed in its expanded configuration with member 440 attached thereto with the plurality of tissue anchors 444 projecting distally. The tissue anchors 444 may be urged into a tissue region to be treated 446, as seen in FIG. 39A, until the anchors 444 are secured in the tissue and member 440 is positioned directly against the tissue, as shown in FIG. 39B. A pullwire may be actuated to release the member 440 from the imaging hood 12 and deployment catheter 16 may be withdrawn proximally to leave member 440 secured against the tissue 446. Another variation for tissue manipulation and treatment may be seen in the variation of FIG. 40A, which illustrates an imaging hood 12 having a deployable anchor assembly 450 attached to the tissue contact edge 22. FIG. 40B illustrates the anchor assembly 450 detached from the imaging hood 12 for clarity. The anchor assembly 450 may be seen as having a plurality of discrete tissue anchors 456, e.g., barbs, hooks, projections, etc., each having a suture retaining end, e.g., an eyelet or opening 458 in a proximal end of the anchors 456. A suture member or wire 452 may be slidingly connected to each anchor 456 through the openings 458 and through a cinching element 454, which may be configured to slide uni-directionally over the suture or wire 452 to approximate each of the anchors 456 towards one another. Each of the anchors 456 may be temporarily attached to the imaging hood 12 through a variety of methods. For instance, a pullwire or retaining wire may hold each of the anchors within a receiving ring around the circumference of the imaging hood 12. When the anchors 456 are released, the pullwire or retaining wire may be tensioned from its proximal end outside the patient body to thereby free the anchors 456 from the imaging hood 12. One example for use of the anchor assembly 450 is shown in FIGS. 41A to 41D for closure of an opening or wound 460, e.g., patent foramen ovale (PFO). The deployment catheter 16 and imaging hood 12 may be delivered intravascularly into, e.g., a patient heart. As the imaging hood 12 is deployed into its expanded configuration, the imaging hood 12 may be positioned adjacent to the opening or wound 460, as shown in FIG. 41A. With the anchor assembly 450 positioned upon the expanded imaging hood 12, deployment catheter 16 may be directed to urge the contact edge of imaging hood 12 and anchor assembly 450 into the region surrounding the tissue opening 460, as shown in FIG. 41B. Once the anchor assembly 450 has been secured within the surrounding tissue, the anchors may be released from imaging hood 12 leaving the anchor assembly 450 and suture member 452 trailing from the anchors, as shown in FIG. 41C. The suture or wire member 452 may be tightened by pulling it proximally from outside the patient body to approximate the anchors of anchor assembly 450 towards one another in a purse-string manner to close the tissue opening 462, as shown in FIG. 41D. The cinching element 454 may also be pushed distally over the suture or wire member 452 to prevent the approximated anchor assembly 450 from loosening or widening. Another example for an alternative use is shown in FIG. 42, where the deployment catheter 16 and deployed imaging hood 12 may be positioned within a patient body for drawing blood 472 into deployment catheter 16. The drawn blood 472 may be pumped through a dialysis unit 470 located externally of the patient body for filtering the drawn blood 472 and the filtered blood may be reintroduced back into the patient. Yet another variation is shown in FIGS. 43A and 43B, which show a variation of the deployment catheter 480 having a first deployable hood 482 and a second deployable hood 484 positioned distal to the first hood 482. The deployment catheter 480 may also have a side-viewing imaging element 486 positioned between the first and second hoods 482, 484 along the length of the deployment catheter 480. In use, such a device may be introduced through a lumen 488 of a vessel VS, where one or both hoods 482, 484 may be expanded to gently contact the surrounding walls of vessel VS. Once hoods 482, 484 have been expanded, the clear imaging fluid may be pumped in the space defined between the hoods 482, 484 to displace any blood and to create an imaging space 490, as shown in FIG. 43B. With the clear fluid in-between hoods 482, 484, the imaging element 486 may be used to view the surrounding tissue surface contained between hoods 482, 484. Other instruments or tools may be passed through deployment catheter 480 and through one or more openings defined along the catheter 480 for additionally performing therapeutic procedures upon the vessel wall. Another variation of a deployment catheter 500 which may be used for imaging tissue to the side of the instrument may be seen in FIGS. 44A to 45B. FIGS. 44A and 44B show side and end views of deployment catheter 500 having a side-imaging balloon 502 in an un-inflated low-profile configuration. A side-imaging element 504 may be positioned within a distal portion of the catheter 500 where the balloon 502 is disposed. When balloon 502 is inflated, it may expand radially to contact the surrounding tissue, but where the imaging element 504 is located, a visualization field 506 may be created by the balloon 502, as shown in the side, top, and end views of FIGS. 45A to 45B, respectively. The visualization field 506 may simply be a cavity or channel which is defined within the inflated balloon 502 such that the visualization element 504 is provided an image of the area within field 506 which is clear and unobstructed by balloon 502. In use, deployment catheter 500 may be advanced intravascularly through vessel lumen 488 towards a lesion or tumor 508 to be visualized and/or treated. Upon reaching the lesion 508, deployment catheter 500 may be positioned adjacently to the lesion 508 and balloon 502 may be inflated such that the lesion 508 is contained within the visualization field 506. Once balloon 502 is fully inflated and in contact against the vessel wall, clear fluid may be pumped into visualization field 506 through deployment catheter 500 to displace any blood or opaque fluids from the field 506, as shown in the side and end views of FIGS. 46A and 46B, respectively. The lesion 508 may then be visually inspected and treated by passing any number of instruments through deployment catheter 500 and into field 506. In additional variations of the imaging hood and deployment catheter, the various assemblies may be configured in particular for treating conditions such as atrial fibrillation while under direct visualization. In particular, the devices and assemblies may be configured to facilitate the application of energy to the underlying tissue in a controlled manner while directly visualizing the tissue to monitor as well as confirm appropriate treatment. Generally, as illustrated in FIGS. 47A to 470, the imaging and manipulation assembly may be advanced intravascularly into the patient's heart H, e.g., through the inferior vena cava IVC and into the right atrium RA, as shown in FIGS. 47A and 47B. Within the right atrium RA (or prior to entering), hood 12 may be deployed and positioned against the atrial septum AS and the hood 12 may be infused with saline to clear the blood from within to view the underlying tissue surface, as described above. Hood 12 may be further manipulated or articulated into a desirable location along the tissue wall, e.g., over the fossa ovalis FO, for puncturing through to the left atrium LA, as shown in FIG. 47C. Once the hood 12 has been desirably positioned over the fossa ovalis FO, a piercing instrument 510, e.g., a hollow needle, may be advanced from catheter 16 and through hood 12 to pierce through the atrial septum AS until the left atrium LA has been accessed, as shown in FIG. 47D. A guidewire 17 may then be advanced through the piercing instrument 510 and introduced into the left atrium LA, where it may be further advanced into one of the pulmonary veins PV, as shown in FIG. 47E. With the guidewire 17 crossing the atrial septum AS into the left atrium LA, the piercing instrument 510 may be withdrawn, as shown in FIG. 47F, or the hood 12 may be further retracted into its low profile configuration and catheter 16 and sheath 14 may be optionally withdrawn as well while leaving the guidewire 17 in place crossing the atrial septum AS, as shown in FIG. 47G. Although one example is illustrated for crossing through the septal wall while under direct visualization, alternative methods and devices for transseptal access are shown and described in further detail in commonly owned U.S. patent application Ser. No. 11/763,399 filed Jun. 14, 2007, which is incorporated herein by reference in its entirety. Those transseptal access methods and devices may be fully utilized with the methods and devices described herein, as practicable. If sheath 14 is left in place within the inferior vena cava IVC, an optional dilator 512 may be advanced through sheath 14 and along guidewire 17, as shown in FIG. 47H, where it may be used to dilate the transseptal puncture through the atrial septum AS to allow for other instruments to be advanced transseptally into the left atrium LA, as shown in FIG. 47I. With the transseptal opening dilated, hood 12 in its low profile configuration and catheter 16 may be re-introduced through sheath 16 over guidewire 17 and advanced transseptally into the left atrium LA, as shown in FIG. 47J. Optionally, guidewire 17 may be withdrawn prior to or after introduction of hood 12 into the left atrium LA. With hood 12 advanced into and expanded within the left atrium LA, as shown in FIG. 47K, deployment catheter 16 and/or hood 12 may be articulated to be placed into contact with or over the ostia of the pulmonary veins PV, as shown in FIG. 47L. Once hood 12 has been desirably positioned along the tissue surrounding the pulmonary veins, the open area within hood 12 may be cleared of blood with the translucent or transparent fluid for directly visualizing the underlying tissue such that the tissue may be ablated, as indicated by the circumferentially ablated tissue 514 about the ostium of the pulmonary veins shown in FIG. 47M. One or more of the ostia may be ablated either partially or entirely around the opening to create a conduction block, as shown respectively in FIGS. 47N and 47O. Because the hood 12 allows for direct visualization of the underlying tissue in vivo, hood 12 may be used to visually confirm that the appropriate regions of tissue have been ablated and/or that the tissue has been sufficiently ablated. Visual monitoring and confirmation may be accomplished in real-time during a procedure or after the procedure has been completed. Additionally, hood 12 may be utilized post-operatively to image tissue which has been ablated in a previous procedure to determine whether appropriate tissue ablation had been accomplished. In the partial cross-sectional views of FIGS. 48A and 48B, hood 12 is shown advanced into the left atrium LA to examine discontiguous lesions 520 which have been made around an ostium of a pulmonary vein PV. If desired or determined to be necessary, the untreated tissue may be further ablated under direct visualization utilizing hood 12. To ablate the tissue visualized within hood 12, a number of various ablation instruments may be utilized. In particular, an ablation probe 534 having at least one ablation electrode 536 utilizing, e.g., radio-frequency (RF), microwave, ultrasound, laser, cryo-ablation, etc., may be advanced through deployment catheter 16 and into the open area 26 of hood 12, as shown in the perspective view of FIG. 49A. Hood 12 is also shown with several support struts 530 extending longitudinally along hood 12 to provide structural support as well as to provide a platform upon which imaging element 532 may be positioned. As described above, imaging element 532 may comprise a number of imaging devices, such as optical fibers or electronic imagers such as CCD or CMOS imagining elements. In either case, imaging element 532 may be positioned along a support strut 530 off-axis relative to a longitudinal axis of catheter 16 such that element 532 is angled to provide a visual field of the underlying tissue and ablation probe 536. Moreover, the distal portion of ablation probe 536 may be configured to be angled or articulatable such that probe 536 may be positioned off-axis relative to the longitudinal axis of catheter 16 to allow for probe 536 to reach over the area of tissue visualized within open field 26 and to also allow for a variety of lesion patterns depending upon the desired treatment. FIGS. 49B and 49C show side and perspective views, respectively, of hood 12 placed against a tissue region T to be treated where the translucent or transparent displacing fluid 538 is injected into the open area 26 of hood 12 to displace the blood therewithin. While under direct visualization from imaging element 532, the blood may be displaced with the clear fluid to allow for inspection of the tissue T, whereupon ablation probe 536 may be activated and/or optionally angled to contact the underlying tissue for treatment. FIG. 50A shows a perspective view of a variation of the ablation probe where a distal end effector 542 of the probe 540 may be angled along pivoting hinge 544 from a longitudinal low-profile configuration to a right-angled straight electrode to provide for linear transmural lesions. Probe 540 is similarly configured to the variation shown in FIGS. 31A and 31B above. Utilizing this configuration, an entire line of tissue can be ablated simultaneously rather than a spot of tissue being ablated. FIG. 50B shows another variation where an ablation probe 546 may be configured to have a circularly-shaped ablation end effector 548 which circumscribes the opening of hood 12. This particular variation is also similarly configured to the variation shown above in FIG. 31C. The diameter of the probe 548 may be varied and other circular or elliptical configurations, as well as partially circular configurations, may be utilized to provide for the ablation of an entire ring of tissue. While ablating the tissue, the saline flow from the hood 12 can be controlled such that the saline is injected over the heated electrodes after every ablation process to cool the electrodes. This is a safety measure which may be optionally implemented to prevent a heated electrode from undesirably ablating other regions of the tissue inadvertently. In yet another variation for ablating underlying tissue while under direct visualization, FIG. 51A shows an embodiment of hood 12 having an expandable distal membrane 550 covering the open area of hood 12. A circularly-shaped RF electrode end effector 552 having electrodes 554 spaced between insulating sections 556 may be coated or otherwise disposed, e.g., by chemical vapor deposition or any other suitable process, circumferentially around the expandable distal membrane 550. The electrode end effector 552 may be energized by an external power source which is in electrical communication by wires 558. Moreover, electrode end effector 552 may be retractable into the work channels of deployment catheter 16. Imaging element 532 may be attached to a support strut of the hood 12 to provide the visualization during the ablation process, as described above, for viewing through the clear fluid infused within hood 12. FIG. 51B shows a similar variation where an inflatable balloon 560 is utilized and hood 12 has been omitted entirely. In this case, electrode end effector 552 may be disposed circumferentially over the balloon distal end in a similar manner. In either variation, circular transmural lesions may be created by inflating infusing saline into hood 12 to extend membrane 550 or directly into balloon 560 such that pressure may be exerted upon the contacted target tissue, such as the pulmonary ostia area, by the end effector 552 which may then be energized to channel energy to the ablated tissue for lesion formation. The amount of power delivered to each electrode end effector 552 can be varied and controlled to enable the operator to ablate areas where different segments of the tissue may have different thicknesses, hence requiring different amounts of power to create a lesion. FIG. 52 illustrates a perspective view of another variation having a circularly-shaped electrode end effector 570 with electrodes 572 spaced between insulating sections 574 and disposed circumferentially around the contact lip or edge of hood 12. This variation is similar to the configuration shown above in FIG. 22A. Although described above for electrode mapping of the underlying tissue, electrode end effector 570 in this variation may be utilized to contact the tissue and to create circularly-shaped lesions around the target tissue. In utilizing the imaging hood 12 in any one of the procedures described herein, the hood 12 may have an open field which is uncovered and clear to provide direct tissue contact between the hood interior and the underlying tissue to effect any number of treatments upon the tissue, as described above. Yet in additional variations, imaging hood 12 may utilize other configurations, as also described above. An additional variation of the imaging hood 12 is shown in the perspective and side views, respectively, of FIGS. 53A and 53B, where imaging hood 12 includes at least one layer of a transparent elastomeric membrane 580 over the distal opening of hood 12. An aperture 582 having a diameter which is less than a diameter of the outer lip of imaging hood 12 may be defined over the center of membrane 580 where a longitudinal axis of the hood intersects the membrane such that the interior of hood 12 remains open and in fluid communication with the environment external to hood 12. Furthermore, aperture 582 may be sized, e.g., between 1 to 2 mm or more in diameter and membrane 580 be made from any number of transparent elastomers such as silicone, polyurethane, latex, etc. such that contacted tissue may also be visualized through membrane 580 as well as through aperture 582. Aperture 582 may function generally as a restricting passageway to reduce the rate of fluid out-flow from the hood 12 when the interior of the hood 12 is infused with the clear fluid through which underlying tissue regions may be visualized. Aside from restricting out-flow of clear fluid from within hood 12, aperture 582 may also restrict external surrounding fluids from entering hood 12 too rapidly. The reduction in the rate of fluid out-flow from the hood and blood in-flow into the hood may improve visualization conditions as hood 12 may be more readily filled with transparent fluid rather than being filled by opaque blood which may obstruct direct visualization by the visualization instruments. Moreover, aperture 582 may be aligned with catheter 16 such that any instruments (e.g., piercing instruments, guidewires, tissue engagers, etc.) that are advanced into the hood interior may directly access the underlying tissue uninhibited or unrestricted for treatment through aperture 582. In other variations wherein aperture 582 may not be aligned with catheter 16, instruments passed through catheter 16 may still access the underlying tissue by simply piercing through membrane 580. FIG. 54A shows yet another variation where a single RF ablation probe 590 may be inserted through the work channel of the tissue visualization catheter in its closed configuration where a first half 592 and a second half 594 are closed with respect to one another. Upon actuation, such as by pull wires, first half 592 and second half 594 may open up laterally via a hinged pivot 602 into a �Y� configuration to expose an ablation electrode strip 596 connected at attachment points 598, 600 to halves 592, 594, respectively and as shown in the perspective view of FIG. 54B. Tension is created along the axis of the electrode strip 596 to maintain its linear configuration. Linear transmural lesion ablation may be then accomplished by channeling energy from the RF electrode to the target tissue surface in contact while visualized within hood 12. FIGS. 55A and 55B illustrate perspective views of another variation where a laser probe 610, e.g., an optical fiber bundle coupled to a laser generator, may be inserted through the work channel of the tissue visualization catheter. When actuated, laser energy 612 may be channeled through probe 610 and applied to the underlying tissue T at different angles 612′ to form a variety of lesion patterns, as shown in FIG. 55C. When treating the tissue in vivo around the ostium OT of a pulmonary vein for atrial fibrillation, occluding the blood flow through the pulmonary veins PV may facilitate the visualization and stabilization of hood 12 with respect to the tissue, particularly when applying ablation energy. In one variation, with hood 12 expanded within the left atrium LA, guidewire 17 may be advanced into the pulmonary vein PV to be treated. An expandable occlusion balloon 620, either advanced over guidewire 17 or carried directly upon guidewire 17, may be advanced into the pulmonary vein PV distal to the region of tissue to be treated where it may then be expanded into contact with the walls of the pulmonary vein PV, as shown in FIG. 56. With occlusion balloon 620 expanded, the vessel may be occluded and blood flow temporarily halted from entering the left atrium LA. Hood 12 may then be positioned along or around the ostium OT and the contained space encompassed between the hood 12 and occlusion balloon 620 may be infused with the clear fluid 528 to create a cleared visualization area 622 within which the ostium OT and surrounding tissue may be visualized via imaging element 532 and accordingly treated using any of the ablation instruments described herein, as practicable. Aside from use of an occlusion balloon, articulation and manipulation of hood 12 within a beating heart with dynamic fluid currents may be further facilitated utilizing support members. In one variation, one or more grasping support members may be passed through catheter 16 and deployed from hood 12 to allow for the hood 12 to be walked or moved along the tissue surfaces of the heart chambers. FIG. 57 shows a perspective view of hood 12 with a first tissue grasping support member 630 having a first tissue grasper 634 positioned at a distal end of member 630. A distal portion of member 630 may be angled via first angled or curved portion 632 to allow for tissue grasper 634 to more directly approach and adhere onto the tissue surface. Similarly, second tissue grasping support member 636 may extend through hood 12 with second angled or curved portion 638 and second tissue grasper 640 positioned at a distal end of member 638. Although illustrated in this variation as a helical tissue engager, other tissue grasping mechanisms may be alternatively utilized. As illustrated in FIGS. 58A to 58C, with hood 12 expanded within the left atrium LA, first and second tissue graspers 634, 640 may be deployed and advanced distally of hood 12. First tissue grasper 634 may be advanced into contact with a first tissue region adjacent to the ostium OT and torqued until grasper 634 is engaged to the tissue, as shown in FIG. 58A. With grasper 634 temporarily adhered to the tissue, second tissue grasper 640 may be moved and positioned against a tissue region adjacent to first tissue grasper 636 where it may then be torqued and temporarily adhered to the tissue, as shown in FIG. 58B. With second grasper 640 now adhered to the tissue, first grasper 636 may be released from the tissue and hood 12 and first tissue grasper 636 may be angled to another region of tissue utilizing first second grasper 640 as a pivoting point to facilitate movement of hood 12 along the tissue wall, as shown in FIG. 58C. This process may be repeated as many times as desired until hood 12 has been positioned along a tissue region to be treated or inspected. FIG. 59 shows another view illustrating first tissue grasper 634 extended from hood 12 and temporarily engaged onto the tissue adjacent to the pulmonary vein, specifically the right inferior pulmonary vein PVRI which is generally difficult to access in particular because of its close proximity and tight angle relative to the transseptal point of entry through the atrial septum AS into the left atrium LA. With catheter 16 retroflexed to point hood 12 generally in the direction of the right inferior pulmonary vein PVRI and with first tissue grasper 634 engaged onto the tissue, hood 12 and deployment catheter 16 may be approximated towards the right inferior pulmonary vein ostium with the help of the grasper 634 to inspect and/or treat the tissue. FIG. 60 illustrates an alternative method for the tissue visualization catheter to access the left atrium LA of the heart H to inspect and/or treat the areas around the pulmonary veins PV. Using an intravascular trans-femoral approach, deployment catheter 16 may be advanced through the aorta AO, through the aortic valve AV and into the left ventricle LV, through the mitral valve MV and into the left atrium LA. Once within the left ventricle LV, a helical tissue grasper 84 may be extended through hood 12 and into contact against the desired tissue region to facilitate inspection and/or treatment. When utilizing the tissue grasper to pull hood 12 and catheter 16 towards the tissue region for inspection or treatment, adequate force transmission to articulate and further advance the catheter 16 may be inhibited by the tortuous configuration of the catheter 16. Accordingly, the first tissue grasper 634 can be used optionally to loop a length of wire or suture 650 affixed to one end of hood 12 and through the secured end of the first grasper 634, as shown in FIG. 61A. The suture 650, routed through catheter 16, can be subsequently pulled from its proximal end from outside the patient body (as indicated by the direction of tension 652) to provide additional pulling strength for the catheter 16 to move distally along the length of member 630 like a pulley system (as indicated by the direction of hood movement 654, as illustrated in FIG. 61B. FIGS. 61C and 61D further illustrate the tightly-angled configuration which catheter 16 and hood 12 must conform to and the relative movement of tensioned suture 650 with the resulting direction of movement 654 of hood 12 into position against the ostium OT. Under such a pulley mechanism, the hood 12 may also provide additional pressure on the target tissue to provide a better seal between the hood 12 and the tissue surface. In yet another variation for the ablation treatment of intra-atrial tissue, FIG. 62A shows sheath 14 positioned transseptally with a transparent intra-atrial balloon 660 inflated to such a size as to occupy a relatively large portion of the atrial chamber, e.g., 75% or more of the volume of the left atrium LA. Balloon 660 may be inflated by a clear fluid such as saline or a gas. Visualization of tissue surfaces in contact against the intra-atrial balloon 660 becomes possible as bodily opaque fluids, such as blood, is displaced by the balloon 660. It may also be possible to visualize and identify a number of ostia of the pulmonary veins PV through balloon 660. With the position of the pulmonary veins PV identified, the user may orient instruments inside the cardiac chamber by using the pulmonary veins PV as anatomical landmarks. FIGS. 62B and 62C illustrate an imaging instrument, such as a fiberscope 662, advanced at least partially within the intra-atrial balloon 660 to survey the cardiac chamber as well as articulating the fiberscope 662 to obtain closer images of tissue regions of interest as well as to navigate a wide range of motion. FIG. 62D illustrates a variation of balloon 660 where one or more radio-opaque fiducial markers 664 may be positioned over the balloon such that a position and inflation size of the balloon 660 may be tracked or monitored by extracorporeal imaging modalities, such as fluoroscopy, magnetic resonance imaging, computed tomography, etc. With balloon 660 inflated and pressed against the atrial tissue wall, in order to access and treat a tissue region of interest within the chamber, a needle catheter 666 having a piercing ablation tip 668 may be advanced through a lumen of the deployment catheter and into the interior of the balloon 660. The needle catheter 666 may be articulated to direct the ablation tip 668 to the tissue to be treated and the ablation tip 668 may be simply advanced to pierce through the balloon 660 and into the underlying tissue, where ablation treatment may be effected, as shown in FIG. 63. Provided that the needles projecting from ablation tip 668 are sized sufficiently small in diameter and are gently inserted through the balloon 660, leakage or bursting of the balloon 660 may be avoided. Alternatively, balloon 660 may be fabricated from a porous material such that the injected clear fluid, such as saline, may diffuse out of the balloon 660 to provide a medium for RF tissue ablation by enabling a circuit between the positive and negative electrode to be closed through the balloon wall by allowing the diffused saline to be an intermediate conductor. Other ablation instruments such as laser probes can also be utilized and inserted from within the balloon 660 to access the tissue region to be treated. FIGS. 64A and 64B illustrate detail views of a safety feature where one or more ablation probes 672 are deployable from a retracted configuration, as shown in FIG. 64A, where each probe is hidden its respective opening 670 when unused. This prevents an unintended penetration of the balloon 660 or inadvertent ablation to surrounding tissue around the treatment area. When the tissue is to be treated, the one or more probes 672 may be projected from their respective openings 670, as shown in FIG. 64B. The ablation probes 672 may be configured as a monopolar electrode assembly. FIG. 64C illustrates a perspective view of an ablation catheter 666 configured as a bipolar probe including a return electrode 674. Return electrode 674 may be positioned proximally of probes 672, e.g., about 10 mm, along shaft 666. In yet another variation, FIG. 65A shows a stabilizing sheath 14 which may be advanced through the inferior vena cava IVC, as above, in a flexible state. Once sheath 14 has been desirably positioned within the right atrium RA, its configuration may be optionally locked or secured such that its shape is retained independently of instruments which may be advanced therethrough or independently of the motion of the heart. Such a locking configuration may be utilized via any number of mechanisms as known in the art. In either case, sheath 14 may have a stabilizing balloon 680, similar to that described above, which may be expanded within the right atrium RA to inflate until the balloon 680 touches the walls of the chamber to provide stability to the sheath 14, as shown in FIG. 65B. The tip of the sheath 14 may be farther advanced to perform a transseptal procedure to the left atrium LA utilizing any of the methods and/or devices as described in further detail in U.S. patent application Ser. No. 11/763,399 filed Jun. 14, 2007, which has been incorporated above. Once the sheath 14 has been introduced transseptally into the left atrium LA, an articulatable section 682 may be steered as indicated by the direction of articulation 684 into any number of directions, such as by pullwires, to direct the sheath 14 towards a region of tissue to be treated, such as the pulmonary vein ostium, as shown in FIG. 65C. With the steerable section 682 desirably pointed towards the tissue to be treated, the amount of force transmission and steering of the tissue visualization catheter towards the tissue region is reduced and simplified. FIG. 65D shows illustrates an example of the telescoping capability of the deployment catheter 16 and hood 12 from the steerable sheath 14 into the left atrium LA, as indicated by the direction of translation 686. Furthermore, FIG. 65E also illustrates an example of the articulating ability of the sheath 14 with deployment catheter 16 and hood 12 extended from sheath 14, as indicated by the direction of articulation 690. Deployment catheter 16 may also comprise a steerable section 688 as well. With each degree of articulation and translation capability, hood 12 may be directed to any number of locations within the right atrium RA to effect treatment. FIGS. 66A and 66B illustrate yet another variation where sheath 14 may be advanced transseptally at least partially along its length, as shown in FIG. 66A, as above. In this variation, rather than use of a single intra-atrial stabilizing balloon, a proximal stabilization balloon 700 inflatable along the atrial septum within the right atrium RA and a distal stabilization balloon 702 inflatable along the atrial septum within the left atrium LA may be inflated along the sheath 14 to sandwich the atrial septum AS between the balloons 700, 702 to provide stabilization to the sheath 14, as shown in FIG. 66B. With sheath 14 stabilized, a separate inner sheath 704 may be introduced from sheath 14 into the left atrium LA. Inner sheath 704 may comprise an articulatable section 706 as indicated by the direction of articulation 708 and as shown in FIG. 66C. Also, inner sheath 704 may also be translated distally further into the left atrium LA as indicated by the direction of translation 710 to establish as short a trajectory for hood 12 to access any part of the left atrium LA tissue wall. With the trajectory determined by the articulation and translation capabilities, deployment catheter 16 may be advanced with hood 12 to expand within the left atrium LA with a relatively direct approach to the tissue region to be treated, such as the ostium OT of the pulmonary veins, as shown in FIG. 66E. FIGS. 67A and 67B illustrate yet another variation where sheath 14 may be advanced at least partially through the atrial septum AS and proximal and distal stabilization balloons 700, 702 may be expanded against the septal wall. Similar to the variation above in FIGS. 62A to 62C, an intra-atrial balloon 660 may be expanded from the distal opening of sheath 14 to expand and occupy a volume within the right atrium RA. Fiberscope 662 may be advanced at least partially within the intra-atrial balloon 660 to survey the cardiac chamber, as illustrated in FIG. 67C. Once a pulmonary vein ostium has been visually identified for treatment, inner sheath 704 may be introduced from sheath 14 into the left atrium LA and articulated and/or translated to direct its opening towards the targeted tissue region to be treated. With a trajectory determined, a penetrating needle 720 having a piercing tip 722 and a hollow lumen sufficiently sized to accommodate hood 12 and deployment catheter 16, may be advanced from inner sheath 704 and into contact against the balloon 660 to pierce through and access the targeted tissue for treatment, as shown in FIGS. 67D and 67E. With the piercing tip 722 extended into the pulmonary vein PV, penetrating needle 720 may be withdrawn to allow for the advancement of hood 12 in its low profile shape to be advanced through the pierced balloon 660 or hood 12 and deployment catheter 16 may be advanced distally through the lumen of needle 720 where hood 12 may be expanded externally of balloon 660. With the hood 12 deployed, catheter 16 may be retracted partially into inner sheath 704 such that hood 12 occupies and seals the pierced opening through balloon 660. Hood 12 may also placed into direct contact with the targeted tissue for treatment externally of balloon 660, as illustrated in FIG. 67F. In utilizing the intra-atrial balloon 660, a direct visual image of the atrial chamber may be provided through the balloon interior. Because an imager such as fiberscope 662 has a limited field of view, multiple separate images captured by the fiberscope 662 may be processed to provide a combined panoramic image or visual map of the entire atrial chamber. An example is illustrated in FIG. 68A where a first recorded image 730 (represented by �A�) may be taken by the fiberscope 662 at a first location within the atrial chamber. A second recorded image 732 (represented by �B�) may likewise be taken at a second location adjacent to the first location. Similarly, a third recorded image 734 (represented by �C�) may be taken at a third location adjacent to the second location. The individual captured images 730, 732, 734 can be sent to an external CPU via wireless technology such as Bluetooth� (BLUETOOTH SIG, INC, Bellevue, Wash.) or other wireless protocols while the tissue visualization catheter is within the cardiac chamber. The CPU can process the pictures taken by monitoring the trajectory of articulation of the fiberscope or CCD camera, and process a two-dimensional or three-dimensional visual map of the patient's heart chamber simultaneously while the pictures are being taken by the catheter utilizing any number of known imaging software to combine the images into a single panoramic image 736 as illustrated schematically in FIG. 68B. The operator can subsequently use this visual map to perform a therapeutic treatment within the heart chamber with the visualization catheter still within the cardiac chamber of the patient. The panoramic image 736 of the heart chamber generated can also be used in conjunction with conventional catheters that are able to track the position of the catheter within the cardiac chamber by imaging techniques such as fluoroscopy but which are unable to provide direct real time visualization. A potential complication in ablating the atrial tissue is potentially piercing or ablating outside of the heart H and injuring the esophagus ES (or other adjacent structures), which is located in close proximity to the left atrium LA. Such a complication may arise when the operator is unable to estimate the location of the esophagus ES relative to the tissue being ablated. In one example of a safety mechanism shown in FIG. 69A, a light source or ultrasound transducer 742 may be attached to or through a catheter 740 which can be inserted transorally into the esophagus ES and advanced until the catheter light source 742 is positioned proximate to or adjacent to the heart H. During an intravascular ablation procedure in the left atrium LA, the operator may utilize the imaging element to visually (or otherwise such as through ultrasound) detect the light source 742 in the form of a background glow behind the tissue to be ablated as an indication of the location of the esophagus ES. Different light intensities providing different brightness or glow in the tissue can be varied to represent different safety tolerances, e.g., the stronger the light source 742, the easier detection of the glow in the left atrium LA by the imaging element and potentially greater safety margin in preventing an esophageal perforation. An alternative method is to insert an ultrasound crystal source at the end of the transoral catheter instead of a light source. An ultrasound crystal receiver can be attached to the distal end of the hood 12 in the left atrium LA. Through the communication between the ultrasound crystal source and receiver, the distance between the ablation tool and the esophagus ES can be calculated by a processor. A warning, e.g., in the form of a beep or vibration on the handle of the ablation tools, can activate when the source in the heart H approaches the receiver located in the esophagus ES indicating that the ablation probe is approaching the esophagus ES at the ablation site. The RF source can also cut off its supply to the electrodes when this occurs as part of the safety measure. Another safety measure which may be utilized during tissue ablation is the utilization of color changes in the tissue being ablated. One particular advantage of a direct visualization system described herein is the ability to view and monitor the tissue in real-time and in detailed color. Thus, as illustrated in the side view of FIG. 69C, hood 12 is placed against the tissue T to be ablated and any blood within hood 12 is displaced with transparent saline fluid. Imaging element 532 may provide the off-axis visualization of the ablation probe 536 placed against the tissue surface for treatment, as illustrated in FIG. 69B by the displayed image of a representative real-time view that the user would see on monitor 128. As the tissue is heated by ablation probe 536, represented by heated tissue 745 in FIG. 69E, the resulting color change of the ablated tissue 744 may be detected and monitored on monitor 128 as the ablated tissue 744 turns from a pink color to a pale white color indicative of ablation or irreversible tissue damage, as shown in FIG. 69D. The user may monitor the real-time image to ensure that an appropriate amount and location of tissue is ablated and is not over-heated by tracking the color changes on the tissue surface. Furthermore, the real-time image may be monitored for the presence of any steam or micro-bubbles, which are typically indications of endocardial disruptions, emanating from the ablated tissue. If detected, the user may cease ablation of the tissue to prevent any further damage from occurring. In another indication of tissue damage, FIGS. 69F and 69G show the release of tissue debris 747, e.g., charred tissue fragments, coagulated blood, etc., resulting from an endocardial disruption or tissue �popping� effect. The resulting tissue crater 746 may be visualized, as shown in FIG. 69F, as well as the resulting tissue debris 747. When the disruption occurs, ablation may be ceased by the user and the debris 747 may be contained within hood 12 and prevented from release into the surrounding environment, as shown in FIG. 69G. The contained or captured debris 747 within hood 12 maybe evacuated and removed from the patient body by drawing the debris 747 via suction proximally from within hood 12 into the deployment catheter, as indicated by the direction of suction 748 in FIG. 69H. Once the captured debris 747 has been removed, ablation may be completed upon the tissue and/or the hood 12 may be repositioned to treat another region of tissue. Yet another method for improving the ablation treatment upon the tissue and improving safety to the patient is shown in FIGS. 69I to 69K. The hood 12 may be placed against the tissue to be treated T and the blood within the hood 12 displaced by saline, as above and as shown in FIG. 69I. Once the appropriate tissue region to be treated has been visually identified and confirmed, negative pressure may be formed within the hood 12 by withdrawing the saline within the hood 12 to create a suction force until the underlying tissue is drawn at least partially into the hood interior, as shown in FIG. 69J. The temporarily adhered tissue 749 may be in stable contact with hood 12 and ablation probe 536 may be placed into contact with the adhered tissue 749 such that the tissue 749 is heated in a consistent manner, as illustrated in FIG. 69K. Once the ablation has been completed, the adhered tissue 749 may be released and hood 12 may be re-positioned to effect further treatment on another tissue region. The applications of the disclosed invention discussed above are not limited to certain treatments or regions of the body, but may include any number of other treatments and areas of the body. Modification of the above-described methods and devices for carrying out the invention, and variations of aspects of the invention that are obvious to those of skill in the arts are intended to be within the scope of this disclosure. Moreover, various combinations of aspects between examples are also contemplated and are considered to be within the scope of this disclosure as well. 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