Abstract:
A tissue ablation system for treating fibrillation in a patient comprises a steerable interventional catheter having an energy source that emits a beam of energy to ablate tissue thereby creating a conduction block for aberrant electrical pathways. The system also includes a handle disposed near a proximal end of the interventional catheter and has an actuation mechanism for steering the interventional catheter. A console allows the system to be controlled and provides power to the system, and a display pod is electrically coupled with the console. The display pod has a display panel to display system information to a user and allows the user to control the system. A catheter pod is releasably coupled with the handle electrically and mechanically, and also electrically coupled with the display pod.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of U.S. patent application Ser. No. 12/909,642 (Attorney Docket No. 31760-720.201) filed Oct. 21, 2010, which is a non-provisional of, and claims the benefit of U.S. Provisional App. No. 61/254,997 (Attorney Docket No. 31760-720.101) filed Oct. 26, 2009, the entire contents of each are incorporated herein by reference. 
         [0002]    The present application is related to U.S. patent application Ser. Nos. 11/747,862; 11/747,867; 12/480,929; 12/480,256; 12/483,174; 12/482,640; 12/505,326; 12/505,335; 12/620,287; 12/695,857; 12/609,759; 12/609,274; and 12/609,705, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present application generally relates to systems and methods for creating ablation zones in human tissue. More specifically, the present application relates to the treatment of atrial fibrillation of the heart by using ultrasound energy. While the present application emphasizes treatment of atrial fibrillation, one of skill in the art will appreciate that this it not intended to be limiting, and that the systems and methods disclosed herein may also be used to treat other arrhythmias such as ventricular fibrillation. 
         [0005]    The condition of atrial fibrillation is characterized by the abnormal (usually very rapid) beating of the left atrium of the heart which is out of synch with the normal synchronous movement (normal sinus rhythm) of the heart muscle. In normal sinus rhythm, the electrical impulses originate in the sino-atrial node (‘SA node’) which resides in the right atrium. The abnormal beating of the atrial heart muscle is known as ‘fibrillation’ and is caused by electrical impulses originating instead at points other than the SA node, for example, in the pulmonary veins (PV). 
         [0006]    There are pharmacological treatments for this condition with varying degree of success. In addition, there are surgical interventions aimed at removing the aberrant electrical pathways from PV to the left atrium (‘LA’) such as the ‘Cox-Maze III Procedure’. This procedure has been shown to be 99% effective but requires special surgical skills and is time consuming. Thus, there has been considerable effort to copy the Cox-Maze procedure using a less invasive percutaneous catheter-based approach. Less invasive treatments have been developed which involve use of some form of energy to ablate (or kill) the tissue surrounding the aberrant focal point where the abnormal signals originate in PV. The most common methodology is the use of radio-frequency (‘RF’) electrical energy to heat the muscle tissue and thereby ablate it. The aberrant electrical impulses are then prevented from traveling from PV to the atrium (achieving the ‘conduction block’) and thus avoiding the fibrillation of the atrial muscle. Other energy sources, such as microwave, laser, and ultrasound have been utilized to achieve the conduction block. In addition, techniques such as cryoablation, administration of ethanol, and the like have also been used. Some of these methods and devices are described below. 
         [0007]    There has been considerable effort in developing catheter based systems for the treatment of AF using radiofrequency (RF) energy. One such method includes a catheter having distal and proximal electrodes at the catheter tip. The catheter can be bent in a coil shape, and positioned inside a pulmonary vein. The tissue of the inner wall of the PV is ablated in an attempt to kill the source of the aberrant heart activity. 
         [0008]    Another source used in ablation is microwave energy. One such intraoperative device consists of a probe with a malleable antenna which has the ability to ablate the atrial tissue. 
         [0009]    Still another catheter based method utilizes the cryogenic technique where the tissue of the atrium is frozen below a temperature of −60 degrees C. This results in killing of the tissue in the vicinity of the PV thereby eliminating the pathway for the aberrant signals causing the AF. Cryo-based techniques have also been a part of the partial Maze procedures described above. More recently, Dr. Cox and his group have used cryoprobes (cryo-Maze) to duplicate the essentials of the Cox-Maze III procedure. 
         [0010]    More recent approaches for the treatment of AF involve the use of ultrasound energy. The target tissue of the region surrounding the pulmonary vein is heated with ultrasound energy emitted by one or more ultrasound transducers. One such approach includes a catheter distal tip portion equipped with a balloon and containing an ultrasound element. The balloon serves as an anchoring means to secure the tip of the catheter in the pulmonary vein. The balloon portion of the catheter is positioned in the selected pulmonary vein and the balloon is inflated with a fluid which is transparent to ultrasound energy. The transducer emits the ultrasound energy which travels to the target tissue in or near the pulmonary vein and ablates it. The intended therapy is to destroy the electrical conduction path around a pulmonary vein and thereby restore the normal sinus rhythm. The therapy involves the creation of a multiplicity of lesions around individual pulmonary veins as required. 
         [0011]    Yet another catheter device using ultrasound energy includes a catheter having a tip with an array of ultrasound elements in a grid pattern for the purpose of creating a three dimensional image of the target tissue. An ablating ultrasound transducer is provided which is in the shape of a ring which encircles the imaging grid. The ablating transducer emits a ring of ultrasound energy at 10 MHz frequency. 
         [0012]    In all above approaches, the inventions involve the ablation of tissue inside a pulmonary vein or of the tissue at the location of the ostium. This may require complex positioning and guiding of the treatment devices to the target site. The ablation is achieved by means of contact between the device and the tissue. Therefore, it would be advantageous to provide an ablation system that does not require such precise positioning and tissue contact and that can create a conduction block in the atrium adjacent the pulmonary vein or around a plurality of pulmonary veins in a single treatment. Moreover, it would be desirable to provide a device and methods of ablation where three dimensional movement of the tip is controlled such that one can create a contiguous lesion in the tissue of desired shape in the wall of the chamber, e.g. the atrium of the heart. Furthermore, the movement of the ultrasound beam is controlled in a manner such that the beam is presented to the target tissue substantially at a right angle to maximize the efficiency of the ablation process. It would also be desirable to provide an ablation system that is easy to use, easy to manufacture and that is lower in cost than current commercial systems. 
         [0013]    2. Description of the Background Art 
         [0014]    Patents related to the treatment of atrial fibrillation include, but are not limited to the following: U.S. Pat. Nos. 6,997,925; 6,996,908; 6,966,908; 6,964,660; 6,955,173; 6,954,977; 6,953,460; 6,949,097; 6,929,639; 6,872,205; 6,814,733; 6,780,183; 6,666,858; 6,652,515; 6,635,054; 6,605,084; 6,547,788; 6,514,249; 6,502,576; 6,416,511; 6,383,151; 6,305,378; 6,254,599; 6,245,064; 6,164,283; 6,161,543; 6,117,101; 6,064,902; 6,052,576; 6,024,740; 6,012,457; 5,405,346; 5,314,466; 5,295,484; 5,246,438; and 4,641,649. 
         [0015]    Patent Publications related to the treatment of atrial fibrillation include, but are not limited to International PCT Publication No. WO 99/02096; and U.S. Patent Publication No. 2005/0267453. 
         [0016]    Scientific publications related to the treatment of atrial fibrillation include, but are not limited to: Haissaguerre, M. et al., Spontaneous Initiation of Atrial Fibrillation by Ectopic Beats Originating in the Pulmonary Veins, New England J. Med., Vol. 339:659-666; J. L. Cox et al., The Development of the Maze Procedure for the Treatment of Atrial Fibrillation, Seminars in Thoracic &amp; Cardiovascular Surgery, 2000; 12: 2-14; J. L. Cox et al., Electrophysiologic Basis, Surgical Development, and Clinical Results of the Maze Procedure for Atrial Flutter and Atrial Fibrillation, Advances in Cardiac Surgery, 1995; 6: 1-67; J. L. Cox et al., Modification of the Maze Procedure for Atrial Flutter and Atrial Fibrillation. II, Surgical Technique of the Maze III Procedure, Journal of Thoracic &amp; Cardiovascular Surgery, 1995; 110:485-95; J. L. Cox, N. Ad, T. Palazzo, et al. Current Status of the Maze Procedure for the Treatment of Atrial Fibrillation, Seminars in Thoracic &amp; Cardiovascular Surgery, 2000; 12: 15-19; M. Levinson, Endocardial Microwave Ablation: A New Surgical Approach for Atrial Fibrillation; The Heart Surgery Forum, 2006; Maessen et al., Beating Heart Surgical Treatment of Atrial Fibrillation with Microwave Ablation, Ann Thorac Surg 74: 1160-8, 2002; A. M. Gillinov, E. H. Blackstone and P. M. McCarthy, Atrial Fibrillation: Current Surgical Options and their Assessment, Annals of Thoracic Surgery 2002; 74:2210-7; Sueda T., Nagata H., Orihashi K., et al., Efficacy of a Simple Left Atrial Procedure for Chronic Atrial Fibrillation in Mitral Valve Operations, Ann Thorac Surg 1997; 63:1070-1075; Sueda T., Nagata H., Shikata H., et al.; Simple Left Atrial Procedure for Chronic Atrial Fibrillation Associated with Mitral Valve Disease, Ann Thorac Surg 1996; 62:1796-1800; Nathan H., Eliakim M., The Junction Between the Left Atrium and the Pulmonary Veins, An Anatomic Study of Human Hearts, Circulation 1966; 34:412-422; Cox J. L., Schuessler R. B., Boineau J. P., The Development of the Maze Procedure for the Treatment of Atrial Fibrillation, Semin Thorac Cardiovasc Surg 2000; 12:2-14; and Gentry et al., Integrated Catheter for 3-D Intracardiac Echocardiography and Ultrasound Ablation, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 51, No. 7, pp 799-807. 
       BRIEF SUMMARY OF THE INVENTION 
       [0017]    The present application generally relates to systems and methods for creating ablation zones in human tissue. More specifically, the present application relates to the treatment of atrial fibrillation of the heart by using ultrasound energy. 
         [0018]    In a first aspect of the present invention, a tissue ablation system for treating fibrillation in a patient comprises a steerable interventional catheter having an energy source that emits a beam of energy that ablates tissue and creates a conduction block therein. The conduction block blocks aberrant electrical pathways in the tissue so as to reduce or eliminate the fibrillation. A handle is disposed near a proximal end of the interventional catheter and has an actuation mechanism for steering the interventional catheter. A console is used to control the system and provides power thereto. A display pod is electrically coupled with the console and has a display panel to display system information to a physician or other operators and allows the operators to control the system. A catheter pod is releasably coupled with the handle both electrically and mechanically, and also electrically coupled with the display pod. 
         [0019]    The system may also include a bedside monitor or a connection thereto. The power contained in the beam of energy may be in the range of 2 to 10 watts. A distal portion of the interventional catheter may comprise a plurality of resilient shaping wires. The shaping wires may form a shepherd&#39;s hook along the interventional catheter when the distal portion is unconstrained. The distal portion may be substantially linear when constrained. The system may have a plurality of actuatable wires coupled with a distal portion of the catheter. Actuation of the wires may deflect the catheter from a substantially linear configuration to a configuration having a shepherd&#39;s hook along the catheter. The system may further comprise a single use, sterile adaptor disposed between a proximal end of the handle and the catheter pod. The adaptor may be electrically and mechanically coupled with the handle and the catheter pod. The adaptor may permit the handle to be connected to and unconnected from the catheter pod while maintaining sterility thereof. 
         [0020]    In another aspect of the present invention, a tissue ablation system for treating fibrillation in a patient comprises a steerable elongate flexible shaft having a proximal end and a distal end, and a housing coupled to the elongate flexible shaft near the distal end thereof. An energy source is disposed adjacent the housing and is adapted to emit a beam of energy to ablate tissue and create a conduction block therein. The conduction block blocks aberrant electrical pathways in the tissue so as to reduce or eliminate the fibrillation. The system may further comprise a fluid flowing through the housing and in fluid communication with the energy source. The housing may be closed at a distal end thereof, or the housing may comprise one or more apertures near a distal end thereof to allow the fluid to exit the housing. The apertures may allow flow of fluid out of the housing but fluid outside the housing may be inhibited from entering into the housing via the apertures. The housing may also comprise a castellated distal region, and the housing may be substantially cylindrical. At least a portion of the housing may be transparent to the beam of energy. The housing may be resilient and deflects when pressed against the tissue. One or more electrodes or whiskers may be disposed in the housing for contacting the tissue. The housing may also include a flow deflector for directing fluid flow past the energy source. The power contained in the beam of energy may be in the range from 2 to 10 watts. Also, a distal portion of the elongate flexible shaft may comprise a plurality of resilient shaping wires that form a shepherd&#39;s hook along the shaft when the distal portion is unconstrained. The distal portion may be substantially linear when constrained. The system may have a plurality of actuatable wires coupled with a distal portion of the shaft. Actuation of the wires may deflect the shaft from a substantially linear configuration to a configuration having a shepherd&#39;s hook along the shaft. 
         [0021]    In still another aspect of the present invention, a tissue ablation catheter for treating fibrillation in a patient comprises a steerable shaft having a central lumen extending between a proximal end and a distal end thereof, and an elongate flexible shaft slidably disposed in the lumen. The shaft has a proximal end and a distal end. A housing is coupled to the elongate flexible shaft near the distal end thereof and an energy source is disposed adjacent the housing. The energy source is adapted to emit a beam of energy to ablate tissue and create a conduction block therein. The conduction block blocks aberrant electrical pathways in the tissue so as to reduce or eliminate the fibrillation. Steering the shaft directs the energy beam to different regions of the tissue. 
         [0022]    The central lumen may be lined with a spring and a plurality of pullwires may be slidably disposed in pullwire lumens extending between the proximal and distal ends of the steerable shaft. The pullwire lumens may be lined with springs. Any of the springs may be encased in a soft matrix of flexible material. The pullwire lumens may be circumferentially disposed around the central lumen. The power contained in the beam of energy may be in the range of 2 to 10 watts. Additionally, a distal portion of the steerable shaft may comprise a plurality of resilient shaping wires that form a shepherd&#39;s hook along the shaft when the distal portion is unconstrained. The distal portion may be substantially linear when constrained. A plurality of actuatable wires may be coupled with a distal portion of the shaft. Actuation of the wires may deflect the shaft from a substantially linear configuration to a configuration having a shepherd&#39;s hook along the shaft. 
         [0023]    In yet another aspect of the present invention, a tissue ablation catheter for treating atrial fibrillation in a patient comprises a steerable elongate flexible shaft having a proximal end and a distal end, and a housing is coupled to the elongate flexible shaft near the distal end thereof. A non-expandable reflector element is disposed in the housing, and an energy source is disposed adjacent the housing. The reflector element may be a rigid, fixed size element having a planar surface or a curved surface. The energy source is adapted to emit energy, wherein the energy is reflected off the reflector forming a beam of energy directed to tissue. The energy beam ablates the tissue and creates a conduction block therein. The conduction block blocks aberrant electrical pathways in the tissue so as to reduce or eliminate the fibrillation. The power contained in the beam of energy may be in the range of 2 to 10 watts. Additionally, a distal portion of the steerable shaft may comprise a plurality of resilient shaping wires that form a shepherd&#39;s hook along the shaft when the distal portion is unconstrained. The distal portion may be substantially linear when constrained. A plurality of actuatable wires may be coupled with a distal portion of the shaft. Actuation of the wires may deflect the shaft from a substantially linear configuration to a configuration having a shepherd&#39;s hook along the shaft. 
         [0024]    In another aspect of the present invention, a system for ablating tissue in a patient comprises a steerable elongate flexible shaft having a proximal end, a distal end, and a diameter. A housing is coupled to the elongate flexible shaft near the distal end thereof. The housing has a length, and a diameter greater than the diameter of the elongate flexible shaft. An energy source is disposed adjacent the housing and is adapted to emit a beam of energy. The energy beam ablates the tissue and creates a conduction block therein. The conduction block blocks aberrant electrical pathways in the tissue so as to reduce or eliminate fibrillation. The system also includes a sheath having a proximal end and a distal end. The steerable elongate flexible shaft is slidably disposed in the sheath. A curved distal region of the sheath is configured to accommodate passage of the housing therethrough when the distal region of the sheath is deflected into a curve. The distal region may comprise an enlarged region or an aperture cut out of the sheath that accommodates the housing length and diameter. 
         [0025]    In another aspect of the present invention, a method for ablating tissue in a patient as a treatment for fibrillation comprises positioning a transseptal sheath across an atrial septum. The transseptal sheath has a lumen extending therethrough. Advancing an interventional catheter through the transseptal sheath lumen disposes at least a portion of the interventional catheter in a left atrium of the patient. The interventional catheter comprises an energy source near a distal end thereof. A target treatment region to be ablated is located and the interventional catheter is steered within the left atrium so that the energy source is moved adjacent the target treatment region and also so that energy emitted from the energy source is directed toward the target treatment region. Tissue in the target region is ablated with the emitted energy thereby creating a conduction block in the tissue that blocks aberrant electrical pathways in the tissue so as to reduce or eliminate the fibrillation. Isolation of the target region from the remainder of the atrium is then confirmed. 
         [0026]    The ablating step may comprise ablating the tissue with an ultrasound beam of energy from the energy source having power in the range of 2 to 10 watts. The ablating step may comprise ablating a spot in the tissue, a line, a closed loop path in the tissue, or a path encircling one or more pulmonary veins in the left atrium. The ablating step may also comprise ablating a path encircling at least one left pulmonary vein and at least one right pulmonary vein. 
         [0027]    The steering step may comprise actuating a plurality of pullwires disposed in the interventional catheter so as to bend a distal portion of the interventional catheter along at least two axes. Steering may also comprise unconstraining a distal portion of the interventional catheter so that shaping wires in the interventional catheter cause the catheter to resiliently take on a shepherd&#39;s hook shape. The steering step may comprises actuating a plurality of actuatable wires coupled with a distal portion of the interventional catheter, thereby deflecting the catheter from a substantially linear configuration to a configuration having a shepherd&#39;s hook along the catheter. The locating step may comprise actuating the interventional catheter in a raster pattern, and the locating step may also comprise locating a pulmonary vein. 
         [0028]    In yet another aspect of the present invention, a method for ablating tissue in a patient as a treatment for fibrillation comprises positioning a transseptal sheath having a lumen therethrough, across an atrial septum, and advancing an interventional catheter through the transseptal sheath such that at least a portion of the interventional catheter is disposed in a left atrium. Ostia of the left pulmonary veins are then located and a first contiguous lesion path encircling at least one ostium of the left pulmonary veins is defined. Tissue along the first defined lesion path is ablated and then the interventional catheter may be positioned adjacent the right pulmonary veins so that the ostia of the right pulmonary veins may be located. A second contiguous lesion path encircling at least one ostium of the right pulmonary veins is defined and tissue along the second path is ablated. Tissue between the first and the second lesion paths is ablated such that a first substantially linear path contiguous with both the first and second lesion paths is created. Also, a second substantially linear path contiguous with the first substantially linear path and extending toward the mitral valve is ablated. Isolation of the left and right pulmonary veins is confirmed. The ablation paths create a conduction block in the tissue that blocks aberrant electrical pathways in the tissue so as to reduce or eliminate the fibrillation. 
         [0029]    The step of locating the ostia of the right or left pulmonary veins may comprise actuating the interventional catheter in a raster pattern. Ablating tissue along the first or the second defined lesion paths may comprise ablating the tissue with a beam of ultrasound energy in the range of 2 to 10 watts. The interventional catheter may be actuated to move the catheter distal end in a closed loop. The first or the second defined lesion paths may be modified. Positioning of the interventional catheter adjacent the right pulmonary veins may comprise unconstraining a distal portion of the interventional catheter so that shaping wires in the interventional catheter cause the catheter to resiliently take on a shepherd&#39;s hook shape. Positioning of the interventional catheter adjacent the right pulmonary veins may comprise actuating a plurality of actuatable wires coupled with a distal portion of the interventional catheter thereby deflecting the catheter from a substantially linear configuration to a configuration having a shepherd&#39;s hook along the catheter. 
         [0030]    These and other embodiments are described in further detail in the following description related to the appended drawing figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1  shows the components of the ablation system. 
           [0032]      FIG. 2  shows an exemplary embodiment of an ablation catheter. 
           [0033]      FIG. 3  shows the details of the distal end of the catheter. 
           [0034]      FIG. 4  shows the detailed view of the distal end of the catheter. 
           [0035]      FIGS. 5   a - 5   h  show various configurations of the distal housing. 
           [0036]      FIG. 6  shows the details of the XY tube. 
           [0037]      FIG. 7  shows the axial transducer with a reflector. 
           [0038]      FIG. 8  shows the transseptal sheath with a cut-out opening. 
           [0039]      FIG. 9  shows the position of the catheter in the transseptal sheath. 
           [0040]      FIG. 10  shows the transseptal sheath with a larger diameter distal end. 
           [0041]      FIG. 11  shows the position of the catheter in the transseptal sheath. 
           [0042]      FIG. 12  shows the formation of a lesion around the left pulmonary veins. 
           [0043]      FIG. 13  shows the formation of a lesion around right pulmonary veins. 
           [0044]      FIG. 14  shows the schematic of the console, display pod, and the catheter pod. 
           [0045]      FIG. 15  is a schematic showing the details of the console. 
           [0046]      FIG. 16  is a schematic showing the details of the display pod. 
           [0047]      FIG. 17  shows the schematic of the catheter pod. 
           [0048]      FIG. 18  shows the components of the handle. 
           [0049]      FIG. 19  shows a desired lesion set in the left atrium. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0050]    An exemplary embodiment of an ablation system is shown in  FIG. 1 . The system consists of five main components: a) catheter; b) console; c) display pod; d) catheter pod; and e) handle. Catheter  10  has a distal end  12  and a proximal end  14 . The distal-most end has a housing  16  which contains the energy generating element (described in detail below) attached to a tube  18 . Tube  18  moves axially in a bendable member  20  which in turn is attached to the main body  22  of the catheter  10 . Bendable tube  20  is made of multilumen tubing and is actuatable normal to the axis in an x-y manner to form bend angles .phi. and .theta. described below. The details of the member  20  are described later in this description. The main body  22  of the catheter is made of a braided multilumen tube. Braiding aids in torquing and rotating of the catheter  10 . The proximal end  14  of the tube  22  terminates in a handle  24  which contains the mechanism to actuate the movement of the tube  18  as well as the bending of the tube  20 . The handle  24  has a fluid port  26  used to irrigate the housing  16  through the tube  18 . Handle  24  also has an electrical connector  28  which provides auxiliary connections to various points at the distal end  12 . Handle  24  connects detachably to a catheter pod  30  making mechanical and electrical connections. Optionally, a single use, sterile adaptor  29  is disposed between and operably coupled with the proximal end of handle  24  and the catheter pod  30 . This adaptor  29  is preferably provided sterile, or it may be sterilized just prior to use, and provides a convenient interface between the sterile catheter handle  24  and the non-sterile catheter pod  30 . The adaptor  29  allows the handle  24  to be operably coupled with the catheter pod  30  by a physician without compromising the handle&#39;s sterility. The adaptor  29  allows electrical and mechanical connections to be easily made between the two components. An exemplary embodiment of a single use, sterile adaptor  29  includes a sterile tubular shaft having mechanical and electrical connections on both proximal and distal ends that mate with the corresponding mechanical and electrical connections on the handle  24  and catheter pod  30 . In preferred embodiments, the adaptor  29  is keyed so that it may only be connected to the handle  24  and catheter pod  30  in one direction. Optionally, the adapter  29  may also be resterilized and reused. This catheter pod  30  contains the electronics, motors, and actuators which, among other functions, aid in the movement and control of members  18  and  20  at the distal end of the catheter  10 . Catheter pod  30  is connected to a display pod  32  by means of an electrical cable  34 . Display pod  32  provides power and logic signals to the catheter pod  30  for various functions of the catheter  10 . Display pod  32  has a display panel  36  to display a variety of information to assist the physician to perform the intended function of the ablation system. In addition, the control pod  32  may have other hand controls  38  or a stylus interface with a touch screen on the display panel  36 . The display pod  32  is electrically connected to the console  40  by means of a cable  42 . The console  40  controls the functions of the ablation system by providing the required power to the energy element in the housing  16 , managing the movements of the tubes  18  and  20  through the motors and actuators in catheter pod  30 , and providing the interface and controls to the physician through the display pod  32 . The console  40  optionally includes power cord  41  to allow the system to be powered from a wall socket or in alternative embodiments, batteries may be used to power the system. 
         [0051]    Catheter  10  is introduced into the right atrium  44  through a sheath  46  having a bend  140  near the distal end. The housing  16  of the catheter  10  can be manipulated inside the right atrial chamber  44  to position the catheter adjacent various regions of the chamber such as the right pulmonary veins RPV, left pulmonary veins LPV, or the mitral valve MV. As discussed later, the housing  16  emits an energy beam  52  towards the atrial tissue  48 . The beam can be directed in any desired path inside the atrium  44  by the combination of various movements of the tubes  18  and  20 . 
         [0052]    A. Catheter.  FIG. 2  shows the catheter of the present invention. Catheter  10  has a distal end  12  having a housing  16  which contains an energy emitting element  50 . This element emits an energy beam  52  which exits the housing  16  in generally an axial direction. The housing  16  is attached to a tube  18  (Z tube). Tube  18  is contained in a multilumen tube  20 . Tube  18  slides axially in tube  20  (XY tube) in a manner  54 . The movement  54  is controlled by the mechanism in catheter pod  30  at the bedside of the patient. The degree of movement  54  is determined by the necessity to maintain the distance of the housing  16  from the tissue  48  in a certain range. Tube  20  is a short section of tubing that is attached at its proximal end to tube  22  and tube  20  may be manipulated in the X-Y directions as indicated by arrows  56 . Details of tube  22  are described later. 
         [0053]      FIG. 3  shows the distal end  12  of the catheter  10  in more detail. Housing  16  is generally of a cylindrical tubular shape with a distal opening  59 . Housing  16  is configured in an optional ‘castle-head’ type ending  58  at its distal end and contains a transducer  68 . The purpose of the openings in the castle-head  58  is to allow unimpeded outflow of irrigant fluid  60  from the castle-head  58  in the event of the entire castle-head distal end being in contact with the tissue. The proximal end of the housing  16  is attached to the base  62  by means of an appropriate adhesive. The base  62  itself is attached to the tube  18  by means of an adhesive. 
         [0054]    Housing  16  contains an energy emitting element  50  in the form of a transducer subassembly  64  at its proximal side such that there is a pocket  66  between the transducer subassembly  64  and the castle-head  58 .  FIG. 3  also illustrates how housing  16  is coupled to tube  18  which is slidably movable through tube  20  which has a coupler  118  on its distal end. Tube  20  in turn is coupled to tube  22  via coupler  122  and has a smooth tapered transition  21  therebetween, and one or more pullwires  120  travel through lumens in tubes  20 ,  22  to bend tube  20  in the X and Y directions indicted by arrows  56  thereby forming desired bend angles Φ and θ. 
         [0055]    As shown in detail in  FIG. 4 , the transducer subassembly  64  consists of a transducer  68 , electrical connections  70  and  72 , a backing  74  which provides for an air pocket  76 , and a front matching layer  78 . The transducer  68  is generally the shape of a flat disc, but can be any other desirable shape such as convex or concave. Transducer  68  can also have configurations such as donut, multi-element and the like as disclosed in copending U.S. patent application Ser. Nos. 12/620,287; 12/609,759; 12/609,274; 12/480,256; 12/482,640; and 12/505,335; the entire contents previously incorporated herein by reference. Electrical attachments  70  and  72  are connected to a pair of wires  80  which resides in the tube  18  and runs the length of the catheter  10  terminating at the handle  24  for connection to catheter pod  30 . Wires  80  can be in the form of a twisted pair or a coaxial cable or similar configuration. Transducer  68  is attached by means of adhesive or solder  84  to the backing  74  which provides for the air pocket  76 . The purpose of the air pocket is to reflect the acoustic energy towards the distal face of the transducer  68 . The proximal side of the transducer  68  has attached thereto a temperature measuring device  86 , such as a thermocouple, for monitoring the temperature of the transducer during its use. This information can be used to shut down the system if the temperature of the transducer  68  rises above a preset level indicating some malfunction. The electrical connections to the two faces of the transducer  68  are provided by contacts  70  and  72 . These contacts can be in the form of rings with tabs. The rings have an open area in the center which provides an opening for the emitting of the acoustic energy beam  52  from the transducer  68 . The tabs on the rings are bent at substantially 90 degrees and serve as a standoff for the transducer. Said rings have sufficient rigidity and when imbedded in the base  62 , support the transducer subassembly  64  in the housing  16 . Wires  80  are electrically attached to the two respective tabs and thereby provide for the electrical connection to the two faces of the transducer  68 . The distal side of the transducer  68  has an acoustic matching layer  78  attached thereto. Additional details regarding the acoustic matching layer  78  may be found in copending U.S. patent application Ser. Nos. 12/620,287; 12/609,759; 12/609,274; 12/480,256; 12/483,174; 12/482,640; and 12/505,326; the entire contents previously incorporated herein by reference. The purpose of the matching layer is to provide a wide acoustic bandwidth and to maximize the output of acoustic energy from the transducer  68 . 
         [0056]    Still referring to  FIG. 4 , tube  18  is attached to the base  62 , and traverses the length of the catheter  10  terminating in a sliding mechanism (not shown) in the handle  24 . The tube  18  has a number of functions. First, it provides a conduit for the fluid flow  60  to the housing  16 . Wire pair  80  resides in the tube  18 . Also, tube  18  serves as a shaft for the axial movement of the housing  16 . Tube  18  is constructed of a braided composite such as polyimide and multiplicity of wires  88 . Wires  88  imbedded in the wall of tube  18  can be in the form of a braid, and are attached to the thermocouple  86  of the transducer  68  via wire  87 , another thermocouple or other suitable sensor  90  attached to the housing  16  for monitoring the temperature of fluid  60 , and contact(s)  92  on the housing  16  for forming additional electrical contacts with optional electrodes on the housing or for forming other electrical contacts as required. Additional wires imbedded in tube  18  can be used to serve other additional attachments and functions as needed. The braid can also be used as an electrical shield to minimize the electrical interference in the transducer signals. 
         [0057]    Tubing  18  also provides for a fluid flow path from the port  26  to the housing  16 . The fluid is sterilized, and can be water, saline, or any other such physiologically compatible fluid. The fluid flows through the housing  16  as shown by fluid flow lines  60 . The purpose of the flowing fluid is two-fold. First, it provides cooling for the transducer  68  while it is emitting the energy beam  52 . Said fluid can be at any appropriate temperature so as to provide efficient cooling of the transducer  68 . Secondly, the flowing fluid maintains a fluid pocket  66  which provides for a separation barrier between the transducer and the surrounding blood. This is important as the transducer may be at a higher temperature while emitting the beam  52 , and any blood in contact with the transducer may form a thrombus which is not a desirable occurrence. In addition, any clot formation on the transducer would diminish the power output of the transducer. Thus a fluid column in front of the transducer avoids a clot formation, and keeps the transducer at a lower temperature to help it function efficiently. 
         [0058]    The housing  16  can have a variety of configurations. One configuration is shown in  FIG. 3  where the housing  16  has openings  58  at its distal end. The housing  16  takes a shape of a ‘castle-head’. The openings allow unimpeded flow of the fluid  60  through the housing  16 . As shown in  FIG. 5   a , the housing  16  is essentially of cylindrical shape. It has a rounded smooth distal end  94  so as to minimize the possibility of injury to the tissue should the housing edge rub against the surface of tissue  48  during the use of the device. The housing  16  also has optional holes  96  disposed in the cylindrical surface of the housing at its distal end. These holes provide for the outflow of the fluid  60  through the housing  16 . 
         [0059]    In another configuration, shown in  FIG. 5   b , the housing  16  has a closed end  98 . The passage of fluid is facilitated by the holes  96  at the distal end. The end  98  is made of a material, such as poly-methyl pentene (PMP), which is substantially transparent to the ultrasound beam  52 . Alternately, the entire housing  16  can be made of a material like PMP. In another configuration, the cylindrical portion  100  of the housing  16  can be made of an elastomeric material, such as latex, or polyurethane, with a PMP cap  98  attached thereto. In this case the weep holes  96  are configured to open up when there is a positive pressure of the fluid  60  inside the housing  16 . This allows only the outflow of the fluid  60 , and does not allow inflow of the surrounding blood into the housing  16 . 
         [0060]    In another configuration (not illustrated), the fluid  60  in the housing  16  can be administered in a ‘closed-loop’ manner, where the flow of the fluid through the housing is for the purpose of providing cooling to the transducer contained therein. In this configuration, the housing  16  has the acoustically transparent window  98 , but does not have the weep holes  96 . Tube  18  will then have at least two lumens for the closed loop pathway of the cooling fluid. Alternatively, housing  16  can be filled by a gel-like material which is acoustically transparent, and in this case, the flowing fluid will not be needed. 
         [0061]    In yet another configuration, shown in  FIGS. 5   c  and  5   d , the housing  16  is made of a spring-like structure. The spring material can be a round wire or a ribbon  102 . Additionally, the spring housing  16  can be encased in a thin flexible casing  104 . The purpose of the spring-like structure is to provide flexibility so that the housing can bend, as shown in  FIG. 5   d , in case it comes in contact with the tissue  48  during use. Alternatively, the housing  16  can be made of a softer wall material such as latex, polyurethane, or silicone to achieve the bending function. 
         [0062]    Another configuration of the housing  16  is shown in  FIG. 5   e . Here the housing  16  is made in a composite structure where the wall of the housing  16  is of an electrically insulating material, and a multiplicity of electrical conduction elements  106  (electrodes’) disposed longitudinally therein. The distal end of the electrode  106  is configured in a ball end  109  slightly protruding beyond the distal edge of the housing  16 . The proximal end of the electrode  106  is attached to a wire  108  at point  92 . Wire  108  is then connected to the conductors  88  in the tubing  18  of  FIG. 4 . Finally, the conductors  88  terminate in the auxiliary connector  28  ( FIG. 2 ) of the catheter  10 . The purpose of the electrodes  106  is to provide electrical connection to the tissue through the atraumatic ball end  109 . This electrical connection to the tissue can be used for pacing the heart tissue, or to obtain electrophysiologic information from the tissue in contact. The wires  108  can be in the form of a braid imbedded in the wall of the housing  16 . In this composite housing  16  can be configured in previously described embodiments of  FIGS. 5   a  to  5   d.    
         [0063]      FIG. 5   f  shows yet another embodiment of the housing  16 . The housing  16  is equipped with a deflector  110 . This deflector redirects the flow of the fluid  60  past the transducer  68  such that a more efficient cooling is provided to the surface of the transducer  68 . In this  FIG. 5   f , the details of the mounting of the transducer  68  are omitted for clarity. 
         [0064]      FIG. 5   g  shows yet another embodiment of the housing  16 . A plurality of whisker-like electrical sensors  111  are disposed at the distal end of the housing  16 . The whiskers  111  are made of radio-opaque wire material, such as platinum or its various alloys, in the form of springs for flexibility. The inner core of the whiskers  111  has a preferably tapered core wire of suitable material. The whiskers  111  are imbedded in the wall of the housing  16 , and electrically connected to wires  108  by means of contact  92 . The wires  108  connect to the wires contained in tube  18  ( FIG. 4 ), and terminate in the connector  28  at the proximal end of the catheter  10 . The purpose of the whiskers  111  is to provide electrical connection to the tissue surface, in an atraumatic manner by virtue of the soft spring-like structure. The electrical contacts allow for electrophysiological mapping of the tissues of the atrium of the heart of the patient. Another purpose of the whiskers  111  is to gage the distance of the housing edge from the target tissue by monitoring the degree of bending of the whiskers  111 . 
         [0065]    Yet another embodiment of the housing  16  is shown in  FIG. 5   h . The housing  16  is made of an elastomeric material such as latex, urethane, nitrile and the like. The elastomeric material is also substantially transparent to ultrasound. The housing  16  has a closed end  98 , and has optional weep holes  96  with characteristics and function described earlier. Housing  16  encases the transducer subassembly  64 . One important aspect of this embodiment is that the housing  16  can be secured around the base  62  and tube  18  by means of adhesive  113  as shown in  FIG. 5   h . The housing  16  is thus attached in a more secure manner by virtue of the elastomeric nature of the material of the housing  16 . 
         [0066]    The XY tube  20  of  FIG. 2  is described in more detail next. Tube  20  contains tube  18  such that tube  18  can move axially therethrough. Referring to  FIG. 3 , tube  20  is bendable in the X-Y manner as indicated by arrows  56 . When the XY tube  20  is bent in the XY plane  56 , the tube  18  is moved in a corresponding direction. The energy beam  52  is thus directed in various directions based on the bending and movement of the XY tube  20 . 
         [0067]    The details of the construction of tube  20  are shown in  FIG. 6 . In one embodiment, tube  20  consists of a multiplicity of flexible springs encased in a soft matrix  116  such as silicone or polyurethane. It contains a spring  112  surrounded by additional springs  114  in an annular configuration (some of the springs  114  are omitted in the drawing for clarity). These springs are preferably open pitch and are made of appropriate metals or plastics. The purpose of the spring  112  in the center is to provide a kink-free lumen for the z-axis tube  18 . Similarly, the purpose of the outside springs  114  to provide a kink-free passageway for the pull wires  120  which are used in the bending of the tube  20 . The distal end of the tube  20  is terminated with an adhesive in a coupler  118 . The pull wires  120  are adhesively secured on the distal side of the coupler  118 . The proximal side of the tube  20  is terminated with an adhesive in another coupler  122  which is provided with appropriate holes  123  for the pull wires  120  and tube  18  and facilitates the attachment of tube  20  to the catheter tube  22 . 
         [0068]    Tube  20  can be manipulated in a controlled manner using a multiplicity of pull wires  120 . The pull wires  120  can be metal such as steel or nitinol, or composite fibers such as Kevlar. These pull wires terminate at handle  24  in appropriate attachments which are then detachably engaged with the actuators and motors in the catheter pod  30 . Motors (not shown) in the catheter pod  30  control the pull wires under the direction of the computer in the console  40  in a prescribed precise manner so as to move the tube  20  precisely in a desired locus. The result is that the energy beam  52  is traversed in the atrial chamber is a specific controlled path such as a line, circle, or any other more complex pattern. 
         [0069]    Referring to  FIG. 3 , tube  20  is attached to the catheter tube  22  by means of the coupler  122 . Tube  22  is generally of a higher durometer material (i.e. more stiff, but not rod-like) which may have a composite configuration. It can be made of a plastic material with an imbedded braid in the wall. Tube  22  constitutes the main body of the catheter  10 , and is connected to the handle  24  at the proximal end. The purpose of the tube  22  is to provide axial pushability and some torque control to the catheter  10 . Tube  22  also houses a multiplicity of shaping wires which force the tube to take on a predetermined shape in free space. The details of this configuration are described later in this application. 
         [0070]    The energy emitting element  68  ( FIG. 3 ) is preferably an acoustic transducer which emits ultrasound energy. The frequency of the ultrasound is preferably in the range of 5 to 25 megaHerz (MHz), more preferably in the range of 8 to 20 MHz, and even more preferably in the range of 10 to 18 MHz. The emitted energy is generally in the shape of a cylindrical beam  52  for a cylindrical transducer  68 . The acoustic power contained in the beam  52  is preferably in the range of 0.5 watts to 25 watts, more preferably in the range of 2 to 10 watts, and even more preferably in the range of 2 to 7 watts. The characteristics of the ultrasound energy beam  52  and its interaction with the tissue are described in a co-pending U.S. patent application Ser. Nos. 11/747,862; 11/747,867; 12/480,256; 12/482,640; 12/505,335; 12/620,287; 12/609,759; and 12/609,274; the entire contents of which have previously been incorporated herein by reference. The beam  52  interacts with the target tissue  48 , and at sufficient energy levels, ablates the said tissue. 
         [0071]    The transducer subassembly  64  ( FIG. 4 ) can have a number of embodiments, one of which is described above where the energy beam  52  is emitted axially outward from the housing  16 . Some of the other embodiments are described in the co-pending U.S. patent application Ser. Nos. 11/747,862; 11/747,867; 12/480,929; 12/505,326; and 12/505,335; the entire contents of which have previously been incorporated herein by reference. 
         [0072]    One alternate embodiment of the transducer subassembly is shown in  FIG. 7 . The transducer  124  is contained in a housing  16 . Transducer  124  is of a generally cylindrical shape and it emits ultrasound energy  126  radially outward. The transducer  124  can be of a square, hexagonal or any other suitable cross-section. The energy is redirected by a generally parabolic reflector  128  which redirects the ultrasound energy in an axial direction in a manner  130 . The reflector  128  can be any other suitable configuration. The reflected energy exits the housing  16  in the form of a beam  52 . The resulting exit beam  52  is similar to the one described in the prior embodiments above. The transducer  124  is secured in the base  132  by means of a support  134  and appropriate adhesives. Similar to earlier embodiments, the base  132  is attached to the tubing  18  which serves the functions described earlier. Wires  136  connect to the transducer  124  and terminate at the handle  24 . Fluid flow  60  allows the transducer to be cooled to prevent overheating. The fluid column  125  between the transducer  124  and the distal edge of the housing  16  provides the separation between the transducer  124  and the surrounding blood while the device is in the left atrium. 
         [0073]    Referring to  FIG. 1 , catheter  10  is introduced into the left atrium  44  through a trans-septal sheath  46 . Sheath  46  has a bend  140  at its distal portion so that it can be positioned towards and into the left atrium  44 . Also, the distal portion of the catheter, namely the housing  16 , is generally the shape of a rigid cylinder. As the catheter  10  is passed through the bend of the sheath  46 , the rigid portion requires that the sheath be of larger diameter for it to pass through the bend. It is generally desirable to keep the sheath diameter to a minimum size. The sheath is placed in the femoral vein of the patient through a surgical opening in the vein generally at the site of the patient&#39;s thigh. It is desirable to keep the surgical opening to a minimum size. In this invention, the passage of the catheter distal end is achieved by forming the sheath distal end in a manner which makes the passage easier without increasing the size of the sheath diameter in at least one of the exemplary embodiments disclosed below. 
         [0074]    One embodiment of the sheath is shown in  FIG. 8 . Sheath  138  is a tube and has a diameter D which is uniform over its entire length. Generally, the diameter D is slightly larger than the largest diameter of the catheter which is to be advanced through the sheath. In order to facilitate the advancement of the catheter through the bend  140  of the sheath  138 , the sheath is provided with an appropriately sized cutout opening  142  at the site of the inner radius of the bend.  FIG. 9  shows the advancement of the catheter  10  through the sheath  138 . Sheath  138  is positioned across the septum  144  providing a passageway into the left atrium  146 . As the distal housing  16  is advanced through the bend  140  in a manner  148 , the opening  142  provides for the required relief to accommodate the rigid portion of the housing to pass through. This way, the sheath  138  remains of a minimum needed diameter D. 
         [0075]    Another embodiment of the sheath of this invention is shown in  FIG. 10 . The sheath  150  has a diameter D 1  through its entire length, except at the bulged distal portion  154 , the diameter is expanded to a larger size D 2  in the vicinity of the bend  152 . The passing of the catheter through the sheath is shown in  FIG. 11 . The sheath  150  is positioned across the septum  144  providing a passageway into the left atrium  146 . The catheter  10  is advanced in a manner  148  through the sheath  150 . As it reaches the vicinity of the bend  152 , the larger diameter D 2  provides the relief for the rigid length of the housing  16  to negotiate the bend. The bulged portion  154  is of minimum required diameter for an easy passage of the catheter  10  into the atrium  146 . 
         [0076]    The position of the catheter  10  during use in the atrial chamber is shown in  FIGS. 12 and 13 . The catheter  10  is introduced into the left atrium (LA) through the sheath  150 . Referring to FIG.  12 , the distal end of the catheter generally points towards the left pulmonary veins (LPV). The tip of the catheter can be moved in an X-Y plane  56  by manipulating the tube  20  in the X-Y manner. The axial movement of the distal end  12  of the catheter is achieved with the aid of tube  18  in a manner  54 . As described earlier, the catheter emits a beam  52  of ultrasound energy towards the target tissue  48 . The impinging beam of energy heats the tissue at target site and creates a lesion  156 . The beam  52  is traversed around the LPV under computer control in a manner  158  to create a contiguous lesion to electrophysiologically isolate the LPV. The catheter tip  12  may thereafter be positioned to treat tissue adjacent the right pulmonary vein RPV and other locations in the left atrium. 
         [0077]      FIG. 13  shows the position of the catheter distal tip  12  pointing towards the right pulmonary veins (RPV). The distal end of the tube  22  takes the shape of a ‘shepherd&#39;s hook’ to point the catheter distal end  12  towards the RPV. The shepherd&#39;s hook is formed by one or more shaping wires  160  placed in the lumens of the tube  22 . The shaping wires  160  are made of a shape-memory metal, such as nitinol, and are heat-treated to hold the desired shape of a shepherd&#39;s hook. These wires are placed in the lumens of tube  22  and the tube  22  takes the shape of the shepherd&#39;s hook in free space when unconstrained from sheath  150 . When the catheter is being used for the treatment of the LPV, as shown in  FIG. 12 , the shepherd&#39;s hook portion of the tube  22  resides in the sheath  150 . When the treatment of the RPV is desired, the catheter is further advanced into the LA. As the catheter is advanced, the shape memory nitinol wires are deployed to take the predetermined shape, thus forcing the tube  22  to take on the shape of a shepherd&#39;s hook, facilitating the treatment of the region near RPV. In alternative embodiments, the shaping wires  160  may be substituted with actuator wires which are pushed or pulled by an actuator mechanism preferably near the proximal end of the catheter to bend the tube  22  into the desired shepherd&#39;s hook configuration. In other embodiments, a combination of shaping wires and actuator wires maybe used to bend the tube into a desired configuration such as the shepherd&#39;s hook. The ultrasound beam  52  is targeted towards tissue  48 . The impinging beam of energy heats the tissue at target site and creates a lesion  162 . The beam  52  may be moved by actuating tube  20  in the X-Y directions indicted by arrows  56  as well as by moving tube  18  axially as indicated by arrow  54 . Thus, the beam  52  is traversed around the RPV under computer control in a manner  164  to create a contiguous lesion to electrophysiologically isolate the RPV. 
         [0078]    The details of the remaining components of the ablation system, namely, the handle, catheter pod, display pod, and the console, are described below. 
         [0079]      FIG. 14  shows the Console, Display Pod, and the Catheter Pod. The Handle is described later in  FIG. 18 . Referring to  FIG. 14 , the catheter handle  24  detachably connects to the catheter pod  202 . An optional single use, sterile adaptor  29  allows the handle  24  to be connected to and unconnected from the catheter pod  202  without compromising handle  24  sterility, as previously discussed above. The catheter pod  202  is connected to the display pod  204  by means of a cable  206 . The display pod  204  connects with the console  208  by means of a cable  210 . The system may also be configured with an optional bedside monitor  212 . Console  208 , which includes instrument  214  comprised of electronic hardware, firmware and software, controls and coordinates all parts of the ablation system. It is intended to be located away from the patient, outside of the sterile field, for use by an assistant during the ablation procedure. The other system components are intended to be located near the patient for use by the clinician conducting the ablation procedure. Display pod  204 , catheter pod  202 , and catheter  10  would typically be located in the sterile field. 
         [0080]    B. Console. Referring to  FIG. 14 , the console  208  includes a display monitor  216 , keyboard  218  and computer mouse  220 , all for users to interact with the ablation system. Two long (approximately 20 feet) cables,  222  and  210 , connect the console  208  to the bedside monitor  212  and display pod  204  respectively. Cable  222  is a video cable which provides communication between the console  208  and the bedside monitor  212 . Cable  210  is a multi-conductor cable (approximately 20 feet long) that directs electrical signals between the console  208  and the display pod  204 . Some of those electrical signals are used in the display pod  204 , others are routed through the display pod  204  and cable  206  to the catheter pod  202 . Some of those electrical signals are used in the catheter pod  202 , and some are routed through to the catheter  10  through handle  24 . Typically, cable  206  is shorter than cable  210 , has a smaller outside diameter, and is more flexible. 
         [0081]      FIG. 15  shows the principle components in instrument  214  of console  208 . The system is designed to use an embedded PC (computer)  224  which plugs into connectors in the instrument  214 . Embedded PC  224 , also commonly referred to as “a computer on a board”, is typically an industry standard configuration of size, interface and chip sets. In this way the embedded PC  224  can be upgraded as future generations of PC&#39;s become available, requiring minimal or no other changes in the instrument  214 . One such embedded PC uses the COM Express standard, and is available from a variety of vendors. 
         [0082]    Instrument  214  relies on FPGA  226  (Field Programmable Gate Array) for all time-critical system operations including coordinating all time-critical data transfer activities. In this way the instrument  214  can offer reliable real-time performance, while the operating system of the embedded PC  224  looks after all other routine, non-time-critical activities. The FPGA  226  is programmed with custom firmware to execute functions in response to instructions from the embedded PC  224 . For example, the embedded PC will request that the FPGA generate transmit pulse sequences, which are directed through the D/A (digital to analog) converter  228 , amplified and buffered by the ultrasound transceiver  230  and directed to the catheter  10 , via cables  210  and  206 . 
         [0083]    Ultrasound transceiver  230  acts as transmitter and receiver of ultrasound signals. It operates on a time-multiplexed basis as either a power transmitter creating an ultrasound beam at the distal end of catheter  10 , or as an ultrasound receiver sensing any ultrasound signals returning from the tissue. The ultrasound transceiver  230  can drive up to 25 watts electrical power, and more typically will provide between 2 to 10 watts, and even more preferably 2 to 7 watts, sufficient for typical catheter based applications. As a receiver, the transceiver  230  has sufficient dynamic range to detect returning ultrasound signals, typically over an 80 dB (decibel) dynamic range. 
         [0084]    The ultrasound signal returning (backscattered) from the tissue is directed to two parallel receiver paths: linear I/Q  232  and log detector  234 . Linear I/Q signals are derived by phase demodulating the received ultrasound signal to extract both the real and imaginary components (representing the amplitude and phase) of the signal, which are useful in a variety of processing algorithms used to extract signal information while maximizing signal-to-noise ratio. Alternatively, the signal from the log detector  234  provides a simple peak detection of the log-compressed returning ultrasound signal, which is commonly referred to as an “A-mode” signal in ultrasound imaging applications. The appropriate analog signal, I/Q or log detected, is selected via multiplexor mux  236  for conversion by A/D (analog to digital) converter  238 , and subsequent storage in digital form in memory  240 . The ultrasound data stored in memory  240  may include additional information such as a time stamps, motor positions, transmit waveforms, etc. which can be used during the subsequent signal processing accomplished by algorithms running in the embedded PC  224 . One such processing example is to determine the gap between the tip of catheter  10  and the atrial wall as the catheter is being moved around, and to present this information on display  216 . Another process may be to determine the progress of the lesion depth during ablation. A third may be to determine tissue wall thickness and use this information to control the amount of energy delivered to the tissue. Additionally, the topographical map of the inside surface of the atrium can be presented in a three dimensional rendering at any point during the cardiac cycle. 
         [0085]    In addition to controlling and coordinating the performance and processes in instrument  214 , the embedded PC  224  controls a variety of input/output ports, I/O  242 , to communicate to the keyboard  218 , mouse  220 , monitors  212  and  216  and for controlling and transferring data between itself, the display pod  204 , the catheter pod  202  and the catheter  10 . 
         [0086]    C. Display Pod. The display pod  204 , with internal components shown in  FIG. 16 , is used primarily as a means to present information to the clinician while the ablation system is in use, and to enable the clinician to control the ablation system. System status and control signals between the console  208  and display pod  204  are mediated via a serial link in micro-controller  244 . Data intended for the video display  246  are interpreted by the display controller  248 . Touch screen  250 , integrated over video display  246  provides a means for the clinician to interact with the console  208 , thereby controlling aspects of the ablation system. The clinician can use any appropriate pointing device, such as a stylus, finger, or non-sharp surgical instrument, to interact with the graphical user interface presented on the video display  246 . 
         [0087]    Also located in the display pod  204  is power regulator  252 , which is used to compensate and correct for any potential voltage drops occurring through the lengthy cable  210 , and to provide well regulated power to the servo motor components  254 ,  256 , and  258  in the catheter pod  202  as shown in  FIG. 17 . This power regulator  252  is located in display pod  204  rather than catheter pod  202  for two reasons: to minimize the size of the catheter pod and to minimize heat generated by the electronic components in the catheter pod  202 . 
         [0088]    D. Catheter Pod.  FIG. 17  shows the schematic of the catheter pod. FPGA  254  acts as interface between the console  208  and catheter pod  202 . Parameters for controlling the servo motors  260  are buffered in FPGA  254 , and available for use by motor controller  256 . Motor controller  256  controls the motion of servo motors  260  through a variety of feedback loops monitoring their operation. For example, the positions of the motors are determined by position sensing  266  and the loads on the motors are determined by torque sensing  268 . These signals are used by the motor controller  256  to modulate the servo amplifiers  258  that drive the servo motors  260 . 
         [0089]    Multiplicity of servo motors  262  (motor  1 , motor  2 , motor  3  etc.) control the movement of the distal end of catheter  10  in the X-Y directions previously discussed, thereby bending the distal end of the catheter into a desired angle. In this implementation, the motors  262  tug on multiplicity of pull wires, which are located symmetrically in individual lumens of the catheter. In this way the distal end  12  of catheter  10  can be bent to the desired Φ and θ angles (illustrated in  FIG. 3 ) by the previously described X-Y motions. The fidelity of bending motion is a function of a number of parameters, including the relative tensions on the pull wires. One feature of this configuration allows for the automatic tensioning of the pull wires by the system. This can be accomplished by sensing the load on each motor and instructing the motor controller  256  to provide a consistent, predetermined low load on each motor  262 , which results in an appropriate tension on each pull wire in catheter  10 . This function is represented by auto-tension control  270 . 
         [0090]    Since the positions of motor  262  and the bending angle Φ and θ of the distal end  12  of catheter  10  are not proportional to each other, a “warping” algorithm is used to compensate and reduce the distortion introduced by the non-linear bending. The details of this algorithm are stored in the console  208 , and transferred via FPGA  254  to motor controller  256 . 
         [0091]    The additional motor  264  is coupled to tube  18  that moves the distal end of catheter  10  in and out, sometimes referred to as “the z axis.” In the 3-D space of the bending tip, this motor  264  controls to the radius r of the locus of the tip, while the other motors  262  and their corresponding pull wires control the Φ and θ positions. 
         [0092]    Another feature incorporated in catheter pod  202  is quick release clutch  272 . This electromechanical component responds to instructions from the console  208  or the emergency stop button  221 , and immediately removes any tension from motors  260 . This feature allows for easy and safe removal of the catheter  10  from the patient. 
         [0093]    Another feature incorporated in the catheter pod is a thermocouple amplifier  274  that provides a cold-junction compensated thermocouple-to-digital converter reference that sends readings from thermocouples in the catheter  10  to the console  208 . The temperature of critical components of the catheter  10  can be monitored and the system will react appropriately to out-of-range temperatures. For example, the system can post a warning if the transducer is rising beyond the range of optimal performance, and limit the power delivered to the transducer. Alternatively, a thermocouple located in the path of the saline drip adjacent to the transducer can monitor the adequacy of the drip rate. 
         [0094]    Another feature included in the catheter pod  202  is the primary patient isolation  276 , used to insure that the patient is protected from dangerous leakage currents under a variety of operating conditions, including fault conditions, consistent with regulatory requirements. 
         [0095]    E. Handle.  FIG. 18  shows a block diagram of internal system components in the catheter handle  24 . Both mechanical and electrical connections are made between the catheter handle  24  and the catheter pod  202 . The electrical signals used for control of the instrument are routed via a serial interface and router block  278 . This block allows for a standard network protocol, and minimizes the number of electrical interconnects to typically less than 5, and as few as 2. A typical protocol useful for this case is the “1-wire” network protocol. Serial data from the console  208 , via the display pod  204  and catheter pod  202  is interpreted in the serial interface and router  278 , where it is directed to the specified electrical component in catheter  10 , for example to the encryption engine  284 , the thermocouple amplifiers  288 , the load sensors  290  or the position sensors  292 . 
         [0096]    Another electrical connection from the catheter pod  202  is for the ultrasound transmit/receive signal. This signal passes through signal conditioner  282 , which can include noise suppression filters, impedance matching networks and balun (balanced-unbalanced) transformers, all used to maximize the transmit signal delivered to the transducer  64 , and to maximize the signal-to-noise ratio of the returning receive signal from the transducer  64 . 
         [0097]    Encryption engine  284  provides a method of securing the data stored in memory  286 . Memory  286  stores data specific to each catheter, and is read by the embedded PC  224  in the console  208 . The data could include calibration information regarding transducer performance, mechanical characteristics needed for calibrating steering, manufacturing process and date, and use history unique to each catheter  10 . 
         [0098]    Thermocouple  86  senses the temperature of the transducer  68 , while thermocouple  90  senses the temperature of the cooling fluid that flows past the transducer. Both connect via connections  294  and  296  to a thermocouple amplifier  288  that typically can convert the signal derived from the thermocouples to a digital value of temperature, in a format that can be sent via the router  278  back to the console  208 . It is understood that any of a variety of sensors can be used in place of thermocouples, for example thermistors are a useful alternative for this application. 
         [0099]    The mechanical connectors  280  couple the motors  260  in the catheter pod  202 . If typical rotary motors are used, then rotary to linear converters  298  are used to derive the push-pull motion needed for the pull wires as well as the z axis movement. Alternatively, these rotary to linear converters  298  could be located in the catheter pod  202 . 
         [0100]    Finally, the tension and motion of the pull wires  300 , which are connected to the coupler  118 , can be sensed by load sensors  290  and position sensors  292 . This information is fed back through the serial interface and router  278  to the motor controller  256  in the catheter pod  202 . This feedback will improve the precision of the bending of the distal end, and can sense if the bending at distal end of the catheter is compromised by contact with the atrial wall. 
         [0101]    Lesion Formation: The catheter disclosed herein is intended to create lesions of scarred tissue in the wall of the target tissue, often, the atrial wall, by impingement of energy on the wall tissue. The lesion is created when the ultrasound energy is directed towards the target point in the tissue and delivered there for sufficient time to heat the tissue to a temperature where the cells are killed. The energy emitted by the transducer is in the form of a beam, and this beam can be directed and moved around inside the atrial chamber is any desired path. The resulting lesion can thus be a spot, a line, a circle, or any other combination thereof. 
         [0102]    Method of use: The desired method of treatment for the atrial fibrillation in the left atrium is to create lines of scar tissue in the atrial wall which would block the conduction of the unwanted signals. The present systems and methods describe the means of creating the scar tissue lines (lesions) in a controlled manner by manipulating an ultrasound beam. By way of example, one such desired lesion set, known as the Maze lesion set, is shown in  FIG. 19 . The following method would be used in creating this lesion set: 
         [0103]    1. Place the transseptal sheath across the atrial septum. Advance the catheter through the sheath into the left atrium (LA) as previously shown in  FIG. 12 . 
         [0104]    2. Locate the ostia of the LPV by using the ‘raster’ technique. Additional details on this technique are disclosed in copending U.S. patent application Ser. Nos. 12/505,326; 12/695,857; 12/609,759; and 12/609,705; the entire contents of which have previously been incorporated herein by reference. 
         [0105]    3. Define a desired contiguous and preferably substantially transmural lesion path  168  encircling the LPV. Optionally, the system may suggest a continuous and transmural lesion path to the user and the user may select the suggested pattern, modify the suggested pattern, or define an alternative continuous pattern. 
         [0106]    4. Ablate the tissue along the defined lesion path  168  by moving the catheter as described previously. 
         [0107]    5. Advance the catheter further into the LA to deploy the shepherd&#39;s hook thereby targeting the RPV as previously shown in  FIG. 13 . 
         [0108]    6. Locate the ostia of the RPV using the ‘raster’ technique as described in the previous location step. 
         [0109]    7. Define the lesion path  170  encircling the RPV. Optionally, the system may also suggest a contiguous and preferably substantially transmural lesion path to the user and the user may select the suggested pattern, modify the suggested pattern, or define an alternative continuous pattern. 
         [0110]    8. Ablate the tissue along the defined lesion path  170  by moving the catheter as described previously. 
         [0111]    9. By using the various movements of the tip of the catheter, manipulate the direction of the energy beam to create the connecting lesions  172  and  174 . 
         [0112]    10. Using conventional mapping techniques, confirm the isolation of the pulmonary veins. 
         [0113]    In optional embodiments, the system may automatically perform steps 1-10 above in a continuous fashion. 
         [0114]    The above exemplary method describes ablation of tissue in the left atrium. One of skill in the art will of course appreciate that the ablation system described herein may also be used to ablate other tissues such as other regions of the heart (e.g. right atrium, ventricles, adjacent vessels) as well as non-cardiac tissue. 
         [0115]    While the above is a complete description of the preferred embodiments of the invention, various alternatives, modifications, and equivalents may be used. Therefore, the above description should not be taken as limiting in scope of the invention which is defined by the appended claims.