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-REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of U.S. patent application Ser. No. 11/747,862 (Attorney Docket No. 027680-000120US) now U.S. Pat. No. ______ filed May 11, 2007, which is a non-provisional of, and claims the benefit of U.S. Provisional Patent Application Nos. 60/747,137 (Attorney Docket No. 027680-000100US) filed May 12, 2006, and 60/919,831 (Attorney Docket No. 027680-000110US) filed Mar. 23, 2007; the entire contents of which are incorporated herein by reference. 
         [0002]    All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    In this invention we describe a device and a method for creating ablation zones in human tissue. More specifically, this invention pertains to the treatment of atrial fibrillation of the heart by using ultrasound energy. 
         [0005]    2. Background 
         [0006]    The condition of atrial fibrillation is characterized by the abnormal (usually very rapid) beating of 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 sin θ-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 in the pulmonary veins (“PV”) [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]. 
         [0007]    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 [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; and 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; 2110:485-95]. This procedure is shown to be 99% effective [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] but requires special surgical skills and is time consuming. 
         [0008]    There has been considerable effort to copy the Cox-Maze procedure for 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 conduction block within the heart tissue) 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. 
         [0009]    There has been considerable effort in developing the catheter based systems for the treatment of AF using radiofrequency (RF) energy. One such method is described in U.S. Pat. No. 6,064,902 to Haissaguerre et al. In this approach, a catheter is made of distal and proximal electrodes at the tip. The catheter can be bent in a J 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. Other RF based catheters are described in U.S. Pat. No. 6,814,733 to Schwartz et al., U.S. Pat. No. 6,996,908 to Maguire et al., U.S. Pat. No. 6,955,173 to Lesh; and U.S. Pat. No. 6,949,097 to Stewart et al. 
         [0010]    A source used in ablation is microwave energy. One such device is described by Dr. Mark Levinson [(Endocardial Microwave Ablation: A New Surgical Approach for Atrial Fibrillation; The Heart Surgery Forum, 2006] and Maessen et al. [Beating heart surgical treatment of atrial fibrillation with microwave ablation. Ann Thorac Surg 74: 1160-8, 2002]. This intraoperative device consists of a probe with a malleable antenna which has the ability to ablate the atrial tissue. Other microwave based catheters are described in U.S. Pat. No. 4,641,649 to Walinsky; U.S. Pat. No. 5,246,438 to Langberg; U.S. Pat. No. 5,405,346 to Grundy, et al.; and U.S. Pat. No. 5,314,466 to Stern, et al. 
         [0011]    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 [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]. Cryo-based techniques have been a part of the partial Maze procedures [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; and 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-[800]. More recently, Dr. Cox and his group [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, and 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] have used cryoprobes (cryo-Maze) to duplicate the essentials of the Cox-Maze III procedure. Other cryo-based devices are described in U.S. Pat. Nos. 6,929,639 and 6,666,858 to Lafontaine and U.S. Pat. No. 6,161,543 to Cox et al. 
         [0012]    More recent approaches for the AF treatment 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 is described by Lesh et al. in U.S. Pat. No. 6,502,576. Here the catheter distal tip portion is equipped with a balloon which contains 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. The inventors describe various configurations for the energy emitter and the anchoring mechanisms. 
         [0013]    Yet another catheter device using ultrasound energy is described by 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]. Here the catheter tip is made of 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. In a separate publication [Medical Device Link, Medical Device and Diagnostic Industry, February 2006], in the description of the device, the authors assert that the pulmonary veins can be imaged and “a doctor would be able to electrically isolate the pulmonary veins by putting a linear lesion around them” (emphasis by inventors). It is unclear from this statement whether the ablation ring is placed around one single target vein, or around a plurality of veins. In the described configuration of the catheter tip, it can be easily seen that the described ring ultrasound energy source can only emit the ultrasound beam of a size to ablate only one pulmonary vein at a time. 
         [0014]    Other devices based on ultrasound energy to create circumferential lesions are described in U.S. Pat. Nos. 6,997,925; 6,966,908; 6,964,660; 6,954,977; 6,953,460; 6,652,515; 6,547,788; and 6,514,249 to Maguire et al.; U.S. Pat. Nos. 6,955,173; 6,052,576; 6,305,378; 6,164,283; and 6,012,457 to Lesh; U.S. Pat. Nos. 6,872,205; 6,416,511; 6,254,599; 6,245,064; and 6,024,740; to Lesh et al.; U.S. Pat. Nos. 6,383,151; 6,117,101; and WO 99/02096 to Diederich et al.; U.S. Pat. No. 6,635,054 to Fjield et al.; U.S. Pat. No. 6,780,183 to Jimenez et al.; U.S. Pat. No. 6,605,084 to Acker et al.; U.S. Pat. No. 5,295,484 to Marcus et al.; and WO 2005/117734 to Wong et al. 
         [0015]    In all above approaches, the inventions involve the ablation of tissue inside a pulmonary vein or at the location of the ostium. The anchoring mechanisms engage the inside lumen of the target pulmonary vein. In all these approaches, the anchor is placed inside one vein, and the ablation is done one vein at a time. 
       BRIEF SUMMARY OF THE INVENTION 
       [0016]    One aspect of the invention provides a cardiac ablation system including an ablation catheter having an anchor adapted to support the ablation catheter within an atrium of a heart and an ultrasound emitter disposed radially outward from a rotation axis and from the anchor, and a control mechanism adapted to rotate the ultrasound emitter about the rotation axis and to provide ablation energy to the ultrasound emitter to ablate heart tissue. Some embodiments also include an ultrasound emitter support extending radially outward from the rotation axis and supporting the ultrasound emitter, which may be the a distal portion of the ablation catheter or may be a separate element. 
         [0017]    In some embodiments, the emitter is disposed to emit ultrasound energy through a distal end of the support, and in other embodiments the emitter is disposed to emit ultrasound energy radially outward from a side of the support. In some embodiments, the emitter is disposed at an angle greater than zero with respect to the outer surface of the support. 
         [0018]    In some embodiments, the emitter includes an ultrasound transducer and an ultrasound reflective surface disposed to reflect ultrasound energy from the transducer. The transducer may be disposed to direct ultrasound energy proximally toward the reflective surface. 
         [0019]    In some embodiments, the control mechanism is adapted to bend the emitter support at a desired angle from the rotation axis. This angle may be formed at a first location along the emitter support, with the control mechanism being further adapted to bend the emitter support at a second location along the emitter support. 
         [0020]    In some embodiments, the ultrasound emitter support includes or serves as an electrode in electrical communication with the control mechanism and the anchor includes or serves as an electrode in electrical communication with the control mechanism. 
         [0021]    The control mechanism may be adapted to move the anchor within a left atrium. The anchor may extend substantially along the rotation axis, with the ablation catheter being adapted to rotate with respect to the anchor. Alternatively, the anchor may extend along an axis other than the rotation axis. In embodiments in which the system further includes a delivery sheath adapted to contain the ablation catheter, either the delivery sheath or the ablation catheter may have a port through which the anchor extends. Some embodiments also include a second anchor supporting the ablation catheter. 
         [0022]    In some embodiments, the emitter is distally and proximally translatable with respect to the anchor. In some embodiments, the emitter is supported by a transducer support extending radially outward from the rotation axis and is distally and proximally translatable with respect to the anchor. 
         [0023]    The anchor may be adapted to contact a heart tissue surface, such as the interior wall of the atrium or an interior surface of a pulmonary vein. Some embodiments have a delivery sheath surrounding the ablation catheter, and the anchor is expandable to contact a support catheter surrounding the ablation catheter. 
         [0024]    In embodiments in which the ultrasound emitter includes an ultrasound transducer, the system may also include a fluid source and a fluid flow path adjacent to the transducer. The system may also have a fluid exit port adjacent to the transducer and extending from the fluid flow path to the exterior of the ablation catheter. In embodiments in which the ultrasound emitter is disposed proximal to a distal end of the ablation catheter, the ablation catheter may also have a fluid chamber in communication with the fluid source, disposed between the ultrasound emitter and the distal end of the catheter, and in fluid communication with the distal end of the catheter. The fluid chamber may have a plurality of fluid exit channels formed in the distal end of the catheter. 
         [0025]    Some embodiments also have a distance sensor adapted to sense distance between the ultrasound emitter and a tissue surface. The ultrasound emitter and the distance sensor may both be an ultrasound transducer. Some embodiments may also have an ablation depth sensor. The ultrasound emitter and ablation depth sensor may both be an ultrasound transducer. 
         [0026]    Another aspect of the invention provides a cardiac ablation system including an ablation catheter having an ultrasound emitter and an ultrasound emitter support extending radially outward from a rotation axis and supporting the ultrasound emitter, and a control mechanism adapted to rotate the ultrasound emitter about the rotation axis and to provide ablation energy to the ultrasound emitter to ablate heart tissue and adapted to bend the emitter support at a desired angle from rotation axis. In some embodiments, the desired angle is formed at a first location along the emitter support, the control mechanism being further adapted to bend the emitter support at a second location along the emitter support. 
         [0027]    In some embodiments, the ultrasound emitter includes an ultrasound transducer, with the system further comprising a fluid source and a fluid flow path adjacent to the transducer. The system may also include a fluid exit port adjacent to the transducer and extending from the fluid flow path to the exterior of the ablation catheter. 
         [0028]    Some embodiments also have a distance sensor adapted to sense distance between the ultrasound emitter and a tissue surface. The ultrasound emitter and the distance sensor may both be an ultrasound transducer. Some embodiments may also have an ablation depth sensor. The ultrasound emitter and ablation depth sensor may both be an ultrasound transducer. 
         [0029]    Yet another aspect of the invention provides a cardiac ablation method including the following steps: inserting a treatment catheter into an atrium of a heart, the treatment catheter including an ultrasound emitter; positioning the ultrasound emitter to face heart tissue within the left atrium outside of a pulmonary vein; emitting ultrasound energy from the ultrasound emitter while rotating the ultrasound emitter about a rotation axis; and ablating heart tissue with the ultrasound energy to form a lesion outside of a pulmonary vein. In some embodiments, the positioning step includes the step of bending an ultrasound emitter support. In some embodiments, the positioning step includes the step of moving the ultrasound emitter parallel to the rotation axis. In some embodiments, the positioning step includes the step of anchoring the treatment catheter, such as against the heart wall or by placing an anchor against an atrial wall outside of a pulmonary vein or within a pulmonary vein. The anchoring step may also involve placing a plurality of anchors within a plurality of pulmonary veins and/or expanding an anchor within a support catheter. 
         [0030]    In some embodiments, the rotating step includes the step of rotating the treatment catheter about the anchor. The rotation may include the step of rotating the ultrasound emitter less than 360° around the rotation axis or rotating the ultrasound emitter at least 360° around the rotation axis. 
         [0031]    In some embodiments, the ablating step includes the step of forming a lesion encircling at least two pulmonary vein ostia. The method may also include forming a second lesion around two other pulmonary vein ostia, possibly forming a third lesion extending from the first lesion to the second lesion, and possibly forming a fourth lesion extending from the first, second or third lesion substantially to a mitral valve annulus. 
         [0032]    In some embodiments, the emitting step includes the step of transmitting ultrasound energy distally from a distal end of the treatment catheter and/or radially from the treatment catheter. In some embodiments, the emitting step includes the step of transmitting ultrasound energy from an ultrasound transducer (possibly in a proximal direction) and reflecting the ultrasound energy from a reflector. These embodiments may also include the step of rotating the reflector. 
         [0033]    Some embodiments include the step of passing fluid through the ablation catheter and through an exit port adjacent the ultrasound emitter. The fluid may pass into a fluid chamber disposed between the ultrasound emitter and the heart tissue. 
         [0034]    Some embodiments include the step of sensing distance between the ultrasound emitter and a tissue surface, such as by using the ultrasound emitter to sense distance between the emitter and the tissue surface. The distance sensing step may include the step of sensing distance between the ultrasound emitter and the tissue surface over an intended ablation path prior to the ablating step and may include the step of repositioning the ultrasound emitter as a result of sensed distance determined in the sensing step. 
         [0035]    Some embodiments include the step of sensing depth of ablation in the heart tissue, such as by using the ultrasound emitter to sense depth of ablation in the heart tissue. The speed of rotation of the ultrasound emitter and/or the power delivered to the ultrasound emitter may be based on sensed depth of ablation. 
         [0036]    Some embodiments include the step of sensing thickness of the heart tissue. The speed of rotation of the ultrasound emitter and/or the power delivered to the ultrasound emitter may be based on sensed tissue thickness. In some embodiments, the ablating step includes the step of forming a substantially elliptical lesion segment in the heart tissue. 
         [0037]    Still another aspect of the invention provides a cardiac ablation method including the following steps: inserting a treatment apparatus into an atrium of a heart, the treatment apparatus having an ultrasound emitter and an ultrasound emitter support; positioning the ultrasound emitter to face heart tissue within the left atrium outside of a pulmonary vein; emitting ultrasound energy from the ultrasound emitter while changing a bend angle in the ultrasound emitter support; and ablating heart tissue with the ultrasound energy to form a lesion outside of a pulmonary vein. In some embodiments, the positioning step includes the step of bending an ultrasound emitter support. In some embodiments, the positioning step includes the step of anchoring the treatment catheter. 
         [0038]    Some embodiments add the step of rotating the ultrasound emitter about a rotation axis during the emitting step. In some embodiments, the ablating step includes the step of forming a substantially linear lesion and/or a substantially elliptical lesion segment in the heart tissue. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]    The novel features of the invention are set forth with particularity in the claims that follow. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which: 
           [0040]      FIG. 1  shows the device including a catheter in one embodiment of the invention. 
           [0041]      FIG. 2  shows the construction of the shaft of the catheter in one embodiment of the invention. 
           [0042]      FIGS. 3A-C  show bending of a distal portion of the catheter of  FIG. 1 . 
           [0043]      FIG. 3D  shows bending of the distal end of the catheter of  FIG. 1  and an anchor mechanism. 
           [0044]      FIG. 4  shows the distal tip assembly of the catheter of  FIG. 1 . 
           [0045]      FIG. 5  is a view of the device in a second embodiment. 
           [0046]      FIG. 6  shows the distal tip assembly of the catheter of  FIG. 5 . 
           [0047]      FIG. 7  is a view of the device in a third embodiment. 
           [0048]      FIG. 8  shows the distal tip assembly of the catheter of  FIG. 7 . 
           [0049]      FIG. 9  is a view of the device in a fourth embodiment. 
           [0050]      FIG. 10  shows the distal tip assembly of the catheter of  FIG. 9 . 
           [0051]      FIG. 11  shows an ablation zone encircling four pulmonary veins and the device in one embodiment of the invention. 
           [0052]      FIG. 12  shows two ablation zones each around two pulmonary veins. 
           [0053]      FIG. 13  shows an ablation zone around three pulmonary veins. 
           [0054]      FIGS. 14 to 17  show various mechanisms for the anchoring a portion of the catheter. 
           [0055]      FIG. 18  shows yet another embodiment of the invention as positioned in the left atrium of the heart. 
           [0056]      FIG. 19  shows the use of the device of  FIG. 18  in the atrium of the heart. 
           [0057]      FIG. 20  shows the distal end of the device of  FIG. 18  beyond the guiding sheath. 
           [0058]      FIG. 21A  shows the details of the transducer housing at the distal tip of the catheter. 
           [0059]      FIG. 21B  shows the transducer mounting header with fluid flow channels. 
           [0060]      FIG. 21C  shows an alternative design for the fluid pocket containment component. 
           [0061]      FIG. 22  is a view of the construction of the therapy catheter. 
           [0062]      FIG. 23  shows a view of the construction of the outer catheter. 
           [0063]      FIG. 24  is a view of the characteristics of the ultrasound beam as it exits from the transducer. 
           [0064]      FIG. 25  shows formation of the shape of an ablation lesion. 
           [0065]      FIGS. 26  A-D show the development of the ablation lesion as function of time. 
           [0066]      FIGS. 27  A-D show the interaction of the ultrasound beam with the tissue at various distances from the ultrasound transducer. 
           [0067]      FIGS. 28  A-B are views of the interaction of the ultrasound beam with the tissue when the tissue is presented to the beam at an angle. 
           [0068]      FIG. 29  shows the effect of the movement of heart muscle during ablation. 
           [0069]      FIG. 30  shows the transmission and reflections of ultrasound beam from the target tissue. 
           [0070]      FIG. 31  shows position of the catheter set in the left atrium in a condition when it may not be desirable to create an ablation zone. 
           [0071]      FIG. 32  shows a catheter set designed to address the right pulmonary veins. 
           [0072]      FIG. 33  shows a lesion set according to one embodiment of this invention. 
           [0073]      FIG. 34  shows the creation of an ablation zone near the left pulmonary veins. 
           [0074]      FIGS. 35A-C  show the formation of a line lesion from the left pulmonary veins to the right pulmonary veins. 
           [0075]      FIG. 36  shows a vertical line of ablation ending at the mitral valve annulus. 
           [0076]      FIG. 37  shows the use of the device of  FIG. 31  in creating the ablation zone in the right pulmonary veins. 
           [0077]      FIGS. 38A-J  show a variety of candidate lesion sets in the left atrium. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0078]    The invention described herein includes a device and methods for creating ablation zones in tissue. The device of the invention includes an elongated member (e.g., a catheter) and an anchor mechanism. The elongate member includes a distal tip assembly for directing energy to a tissue. Uses of the invention include but are not limited to providing a conduction block for treatment of atrial fibrillation in a subject, for example, in a patient. 
         [0079]    One aspect of a first embodiment of the invention is shown in  FIG. 1 . As shown, the device  100  includes an elongate member that can be a catheter  110 . In other implementations, the elongate member is a cannula, tube or other elongate structure having one or more lumens. The catheter  110  can be made of a flexible multi-lumen tube. As shown, the catheter  110  can include a distal tip assembly  112  positioned at a distal portion of the catheter  110 . The tip assembly  112  can house an energy delivery structure, for example, an ultrasound transducer subassembly  114  (described in more detail in reference to  FIG. 4 ). 
         [0080]    Although the ablation device described herein includes a distal tip assembly having an ultrasound transducer as a source of ablation energy, it is envisioned than any of a number of energy sources can be used with various implementations of the invention. Suitable sources of ablation energy include but are not limited to, radio frequency (RF) energy, microwaves, photonic energy, and thermal energy. It is envisioned that ablation could alternatively be achieved using cooled fluids (e.g., cryogenic fluid). Additionally, although use of a single ultrasound transducer is described herein as an exemplary energy delivery structure, it is envisioned that a plurality of energy delivery structures, including the alternative energy delivery structures described herein, can be included in the distal portion of the elongate member. In one implementation the elongate member is a catheter wherein the distal portion of the catheter includes multiple energy delivery structures, for example, multiple ultrasound transducers. Such a catheter distal portion can be deployable as a loop or other shape or arrangement to provide positioning of one or more of the energy delivery structures for a desired energy delivery. 
         [0081]    The elongate member of the device can include a bending mechanism for bending a distal portion of the elongate member (e.g., a catheter) at various locations (an example of such bending is shown in  FIGS. 3A-D ). The bending mechanism can include but is not limited to lengths of wires, ribbons, cables, lines, fibers, filament or any other tensional member. In one implementation the bending mechanism includes one or more pull wires, for example, a distal pull wire and a proximal pull wire. A variety of attachment elements for connecting the bending mechanism and the elongate member are envisioned. As shown in  FIG. 1 , in one implementation where the elongate member is a catheter  110 , the distal pull wire  116  and the transducer subassembly  114  are secured to the tip assembly  112  by means of a distal adhesive band  118 . Other means of attaching the distal pull wire  116  to a portion of the tip assembly  112  include but are not limited to attachment using: adhesive, welding, pins and/or screws or the likes. Pull wire  116  can be contained in a lumen (not shown) of the catheter  110  and can terminate at a slider  120  in a proximal housing  122 . The proximal housing  122  can include various actuating mechanisms to effect various features of the catheter, as described below. In one implementation, the slider  120  can move in a slot  124  which pulls or pushes the wire  116 . Since the distal end of the wire  116  is secured to the tip  112 , the result is that the catheter tip  112  can be bent and unbent as desired at a distal bend location  126  by moving the slider  120 . Distal bend location  126  can be positioned on the distal tip assembly  112  as needed to achieve the desired bending of the catheter  110 . 
         [0082]    A second analogous bending mechanism can be provided in the catheter which is more proximally positioned with respect to the distal tip assembly. As shown in  FIG. 1 , a proximal pull wire  128  can reside in a lumen (not shown) of the catheter  110  and the wire  128  distal end can be secured in the catheter  110  by a proximal adhesive band  130 . This proximal pull wire  128  can terminate in a second slider  132  at the proximal housing  122 . The slider  132  can move in a second slot  134  which allows the distal tip assembly  112  to be bent at a proximal bend location  136 . 
         [0083]    The elongate member can further include an anchor mechanism by which the distal portion of the elongate member can be held in a relatively predictable position relative to a tissue, for example, inside a chamber such as the left atrium of the heart. As shown in  FIG. 1 , in one implementation an anchor mechanism  140  includes a pre-shaped wire loop  138 . In a specific implementation, the wire loop  138  is made of a shapeable wire, for example, made from a shape-memory material such as Nitinol (nickel-titanium alloy). Alternatively, the anchor mechanism can include a loop made from any of a number of materials such as metal, plastic and/or fiber or combinations thereof. Although a loop is described, it is envisioned that any of a number of shapes, curved and/or angular, two-dimensional and/or three-dimensional can provide the anchoring required. The anchor  140  can reside in a lumen (not shown) of the catheter  110 , and can exit from the catheter  110  through a notch  142  near the distal end of the catheter  110  (see  FIG. 1 ). The proximal end of the anchor mechanism  140  can terminate in a third slider  148  at the proximal housing  122 . The third slider  148  can move in a third slot  150  at the proximal housing  122 , thereby producing a corresponding anchor mechanism movement  144  of the anchor mechanism  140 . 
         [0084]    In one implementation, when the slider  148  is in a proximal position, the wire loop  138  can be maintained in a substantially linear shape inside the lumen of the catheter  110  (not shown). In use, as third slider  148  is advanced distally in the slot  150 , a distal tip of the wire loop  138  exits the notch  142  (not shown). As the slider  148  is further advanced, the wire loop  138  can take on the shape of a pre-formed loop as it is unrestricted by the confines of a lumen (see  FIG. 3D ). As shown in  FIG. 1 , the wire loop  138  of the anchor  140  can be advanced further until it makes a firm contact with the tissue such as the ceiling wall  146  of the left atrium of the heart. One function of the wire loop  138  is to provide a firm contact and/or stabilization between the anchor mechanism  140  and the tissue, and thereby between a region of the catheter  110  and the tissue (see  FIG. 1 ). An additional function of the anchor mechanism is to provide an axis around which all or a portion of the catheter shaft can be rotated. Such rotation of the catheter is illustrated in  FIG. 1 , as arrow  152 . As shown in  FIG. 1 , in one implementation a rotation mechanism  154 , for example, a wheel, is provided at the proximal housing  122  by which all or a portion of the catheter  110  shaft can be rotated around the axis defined by the anchor mechanism  140 . As can be easily envisioned, through rotational movement about such an axis, the most distal portion of the tip assembly  112  can be swept in a desired path in relation to target tissue. In one implementation, the path of the tip assembly  212  can be a substantially circular path  262  inside a tissue chamber such as the left atrium of the heart (see  FIG. 11 ). 
         [0085]    A transducer subassembly can be secured in the distal tip assembly of the catheter. As shown in  FIG. 1 , in one implementation a transducer subassembly  114  is secured by the distal adhesive band  118 . The transducer subassembly is described in more detail herein for various embodiments of the invention. In one implementation, the transducer subassembly  114  includes a temperature measuring device such as a thermistor or a thermocouple (not shown). The transducer can be energized by the wires which, along with the temperature sensor wires, can be contained in a lumen of the catheter (not shown). As shown in  FIG. 1 , such wires can terminate in a connector, for example, a transducer connector  156  at the proximal housing  122 . The connector  156  can be attached to and detached from a power generator and/or controller (not shown). It is envisioned that such a power generator and/or controller can energize the transducer, display temperature readings and perform any of a number of functions relating to such transducers as well understood in the art. For example, monitoring A-mode signal and the like (e.g., B-mode). In use, as the transducer is energized, it can emit an ultrasound beam  158  towards the tissue  146 . As the energy is transferred from the ultrasound beam into the tissue, the targeted tissue portion can be heated sufficiently to achieve ablation. Thus, as shown in  FIG. 1 , an ablation zone  160  can be created in the tissue. 
         [0086]    During the energizing of the transducer, the transducer may become heated. It is envisioned that the transducer can be maintained within a safe operating temperature range by cooling the transducer. In one implementation cooling of the transducer can be accomplished by contacting the transducer subassembly with a fluid, for example, saline. In some implementations the transducer can be cooled using a fluid having a lower temperature relative to the temperature of the transducer. In one implementation a fluid for cooling the transducer is flushed past the transducer subassembly from a lumen in the catheter (see e.g.,  FIG. 2 ). Accordingly, as shown in  FIG. 1 , the proximal end of a lumen of the catheter  110  can be connected to a fluid port  162 , for example, a luer fitting, in the proximal housing  122 . As further shown in  FIG. 1 , in one implementation fluid used for cooling the transducer can exit the catheter tip  112  through a one or more apertures  164 . The apertures can be a grating, screen, holes, weeping structure or any of a number of suitable apertures. In one implementation apertures  164  are drip holes. 
         [0087]    Referring to  FIG. 2 , in one implementation where the elongate member of the device is a catheter, the shaft of the catheter  110  includes a multi-lumen tubing  170  having one or more lumens  176 , which is encased in a braid  166  of suitable metallic or non-metallic filaments and is encased in a smooth jacket  168  made of conventional biocompatible material. Lumens  176  can accommodate any of a number of features of the invention including but not limited to, pull wires, fluids, gases, and electrical connections. 
         [0088]    In  FIGS. 3A-C , an exemplary series of drawings illustrate bending of the catheter distal portion in more detail. In the implementation shown, the distal pull wire  116  is secured at a distal portion of the tip assembly  112  by means of the distal adhesive band  118 . In use, as the distal pull wire  116  is pulled by moving the first slider  120  (see  FIG. 1 ), the catheter distal portion is bent at location  126  in the direction  172 , thereby moving from position X to position Y, as shown in  FIG. 3B . Next, the proximal pull wire  128 , which is secured in the catheter lumen at a position by proximal adhesive band  130 , is pulled by moving the second slider  132  (see  FIG. 1 ). This results in the catheter  110  distal portion bending at location  136  and moving in the direction  174  to position Z, away from the longitudinal axis of the catheter, as shown  FIG. 3C . 
         [0089]    It is envisioned that the pull wire attachment points, and correspondingly the bend locations in the device can be configured, in any of a number of ways, not limited to the examples described herein. For example, it is envisioned that a single pull wire or other bend inducing mechanism can be used. Alternatively, the use of three or more such mechanism is envisioned. With respect to attachment points for bend inducing mechanism, it is envisioned that any location along the distal tip assembly as well as the catheter distal portion are suitable optional attachment points. With respect to the number and location of bend locations in the device, it is envisioned that a spectrum of suitable bend locations can be provided. For example, while one and two bends are illustrated herein, it is envisioned that three or more bends can be used to achieve a desired catheter configuration and/or application of energy using the device. 
         [0090]    The anchor mechanism  140  of the device can be deployed in a separate or simultaneous step from bending the device, as shown in  FIG. 3D . The anchor mechanism  140 , which can be configured to reside in a lumen (not shown) of the catheter  110 , is advanced out of the catheter  110  and through the anchor notch  142  by moving the third slider  148  (see  FIG. 1 ). In the implementation shown in  FIG. 3D , as the anchor mechanism  140  exits the notch  142  a distal portion of the mechanism  140  takes on the pre-formed shape of a loop  138 . This loop  138  is advanced further in axial direction  144  until it firmly engages tissue, for example in the inside wall of a tissue chamber such as the left atrium of the heart. The anchor mechanism provides a rotational axis for the distal tip assembly. The transducer subassembly  114  can be intentionally displaced away from this axis so that when the catheter shaft is rotated (see arrow  152 ) around the axis provided by the anchor mechanism  140 , the transducer can traverse a substantially circular loop inside the tissue chamber. The result of this motion is to create a substantially circular ablation zone inside the tissue chamber (described in more detail in  FIG. 11 ). It is envisioned that an arc-shaped or other curved ablation zone could alternatively be created with the device. 
         [0091]    The design of the distal tip subassembly can include a variety of configurations providing alternative means of delivering energy to tissue. A first embodiment of the distal tip subassembly  1112  is shown in  FIG. 4 . As illustrated, the tip assembly  1112  can include a closed end tube casing  1142  which is transparent to ultrasound waves. It can further contain a transducer subassembly  1114  including an ultrasound transducer  1120 . The transducer  1120  can be made of a piezoelectric material such as PZT (lead zirconate titanate) or PVDF (polyvinylidine difluoride) and the like. The transducer  1120  can be configured as a disc and the faces of the disc can be coated with a thin layer of a metal such as gold. In one implementation the disc is a circular flat disc. Other suitable transducer coating metals include but are not limited to stainless steel, nickel-cadmium, silver or a metal alloy. As shown in  FIG. 4 , in one implementation the transducer  1120  can be connected to electrical attachments  1130  and  1132  at two opposite faces. These connections can be made of insulated wires  1134  which can be, for example, a twisted pair or a coaxial cable so as to minimize electromagnetic interference. When a voltage is applied across the transducer, ultrasonic sound beam  1158  is emitted. The frequency of the ultrasound beam is in the range of about 1 to 50 megaHertz. 
         [0092]    As shown in  FIG. 4 , a temperature sensor  1136  can be coupled with the transducer  1120 , for example, attached to the back face of the transducer  1120 . The temperature sensor can be comprised of a thermocouple or a thermistor or any other suitable means. As shown in  FIG. 4 , the sensor  1136  can include wires  1138  which carry the temperature information to the catheter proximal end. The wires  1134  and  1138  together can form a wire bundle  1140  extending to the catheter proximal end. 
         [0093]    As further shown in  FIG. 4 , the transducer  1120  can be attached to a backing  1126  by means of an adhesive ring  1122  or other attachment, which creates a void or pocket  1124  between the transducer  1120  and the backing  1126 . The pocket  1124  can include a material which efficiently reflects sound waves generated by the transducer  1120 . The material of the pocket  1124  can be air or any other suitable material such as metal or plastic which reflects the sound waves. Advantageously, the sound waves thus can be directed to exit from the front face of the transducer, resulting in a minimum amount of sound energy lost out through the transducer back face into the backing. The backing can be made of a thermally conductive material such as metal or plastic for aiding in the dissipation of heat which is created when the transducer is energized. 
         [0094]    As illustrated in  FIG. 4 , the wire bundle  1140  can be fed through a passageway or hole  1128  in the backing  1126  and can be housed in a lumen of the catheter  1110 . The wire bundle can terminate in the connector  156  at the proximal housing  122  (see  FIG. 1 ). As shown in  FIG. 4 , the proximal end of the backing  1126  can be secured to the casing  1142  by means of the distal adhesive band  1118 . This creates a void or chamber  1146  between the distal end of the casing  1142  and the distal adhesive band  1118 . The chamber  1146  is configured to be filled with a thermally conductive fluid such as saline so that the transducer  1120  can be cooled while energized. The distal adhesive band  1118  can include a passageway  1148  which is used in connecting the chamber  1146  to a fluid carrying lumen. The passageway  1148  can be in fluid communication with the fluid port  162  at the proximal housing  122  through one of the lumens (not shown) of the catheter  1110  (see  FIGS. 1 and 4 ). As shown in  FIG. 4 , the chamber  1146  can include one or more apertures  1164 , for example, drip holes distributed circumferentially at the chamber  1146  distal portion. In use, prior to insertion of the device into the body, the chamber can be filled with a fluid such as saline. This can be accomplished using a suitable fluid supply device such as a syringe connected to the fluid port (not shown). The fluid from the syringe can flow through the passageway of the distal adhesive band, into the chamber while expelling the air out from the chamber through the apertures. During the use of the device in the body, a constant drip of saline can be maintained, if necessary, to cool the transducer. 
         [0095]    Still referring to  FIG. 4 , a distal pull wire  1116  can be secured to the distal tip subassembly  1112  by the distal adhesive band  1118 . The distal pull wire  1116  can reside in one of the lumens  1176  of the catheter  1110  and can be connected to the slider  120  in the proximal housing  122  (see  FIG. 1  and  FIG. 4 ). As described above in reference to  FIG. 3A , the distal pull wire  1116  can be utilized in bending the distal portion of the catheter  1110 . As shown in  FIG. 4 , the distal tip subassembly  1112  can be securely attached to the catheter tubing  1170  of the catheter  1110  by the proximal adhesive band  1144 . As further shown in  FIG. 4 , lumens  1176  of the catheter tubing  1170  can be utilized for passage of various elements of the tip subassembly  1112  and any of their related features, in addition to instruments, gases, fluids, or other substances. 
         [0096]    A second embodiment of the invention including an alternative distal tip assembly arrangement is shown in  FIG. 5 . Here the transducer subassembly  1214  is mounted in the distal tip assembly  1212  such that the ultrasound transducer  1220  face is substantially parallel to the longitudinal axis of the catheter  1210  (that is to say the longitudinal axis of the catheter  1210  before bending the distal tip assembly  1212  or catheter  1210 ). In this configuration, the sound beam  1258  exits from a lateral surface of the tip assembly  1212 . The construction of the catheter in this configuration can be essentially same as that described herein for the first embodiment (see  FIGS. 1-4 ). 
         [0097]    As shown in  FIG. 5 , the distal tip assembly  1212  and catheter  1210  bend points, distal bend location  1272  and proximal bend location  1274  respectively, can be arranged and configured such that the ultrasound beam  1258  is presented to the tissue  146  in a substantially right angle from the catheter  1210  longitudinal axis. In this manner an ablation zone  1260  is produced laterally through the tip assembly  1212 .  FIG. 6  shows details of the distal tip assembly  1212  for this embodiment. As illustrated, the tip assembly  1212  can be assembled in a tube  1242  which is substantially transparent to the ultrasound waves  1258 . The transducer subassembly  1214  can include a transducer  1220  which has electrical connections  1230  and  1232  on opposite flat faces. As discussed herein, the transducer  1220  can include a temperature sensor  1236  on, for example, a back side which has wire connections. The transducer wires and the temperature sensor wires together form a bundle  1240  which resides in a lumen  1276  of the catheter tubing  1270 . 
         [0098]    Still referring to  FIG. 6 , the distal end of the tube housing  1242  can be sealed. As shown in  FIG. 6 , in one implementation the distal end is sealed with a thermally conductive adhesive  1250 . The back side of the transducer subassembly  1214  can be secured to an adhesive ring  1222  that is connected to a backing  1226 . Thus, a void or pocket  1224  is created between the transducer  1220  and the backing  1226 . As shown in  FIG. 6 , the backing  1226  can be secured to the inner wall of the tube  1242 , for example, by the distal adhesive band  1218 . There can be a passageway  1248  in the adhesive band  1218  to allow the flow of a fluid such as saline to be introduced into the chamber  1246 . The passageway  1248  can be in fluid communication with the fluid port  162  at the proximal housing  122  of the catheter  1210  (see  FIGS. 1 and 6 ). As discussed herein the chamber  1246  can include a number of apertures  1264 , for example, drip holes distributed circumferentially at the chamber  1246  distal end. As further described herein, prior to insertion of the device into the body, the chamber  1246  can be filled with a fluid such as saline. In addition, during the use of the device in the body, a constant drip of saline can be maintained, as required to cool the transducer  1220 . 
         [0099]    Again referring to  FIG. 6 , a distal pull wire  1216  can be secured to the distal tip subassembly  1212  by the distal adhesive band  1218 . The distal pull wire  1216  can reside in one of the lumens  1276  of the catheter  1210  and can be connected to the slider  120  in the proximal housing  122  (see  FIG. 1  and  FIG. 6 ). As described above in reference to  FIG. 3A , the distal pull wire  1216  can be utilized in bending the distal portion of the catheter  1210 . As shown in  FIG. 6 , the distal tip subassembly  1212  can be securely attached to the catheter tubing  1270  of the catheter  1210  by the proximal adhesive band  1244 . As further shown in  FIG. 6 , lumens  1276  of the catheter tubing  1270  can be utilized for passage of various elements of the tip subassembly  1212  and any of their related features, in addition to instruments, gases, fluids, or other substances. 
         [0100]    A third embodiment of the invention including an alternative distal tip assembly arrangement is shown in  FIG. 7 . Various details, features and uses of this embodiment include those as described herein regarding other embodiments. In this embodiment an alternative transducer subassembly is provided as shown in detail in  FIG. 8 . As shown in  FIG. 8 , the ultrasound transducer  1320  can be mounted on an angled backing  1326 . The angle of the backing can range between substantially 0-90°. In one implementation the angle is substantially 10-80°. In another implementation the angle is substantially 30-60°. In another implementation the angle is substantially 40-50°. In a further embodiment the angle is substantially 45°. The transducer can include a shape. In one implementation the transducer is in the shape of an elliptical disc. In another implementation the transducer has a rectangular shape. As shown in  FIGS. 7 and 8 , in one implementation the transducer  1320  can emit energy in the form of an ultrasound beam  1358  at an angle to the longitudinal axis of the catheter  1310 . As shown in  FIG. 7 , the ultrasound beam  1358  can be directed to the tissue  146  by appropriately bending the distal tip assembly  1312  using, for example, pull wires as described herein. The ultrasound energy beam  1358  can create an ablation zone  1360  in the tissue  146 . Cooling of the transducer in this implementation can be achieved as described herein. 
         [0101]    As shown in  FIG. 8  the angled backing  1326  can be secured in the distal tip assembly  1312  by the distal adhesive band  1318 . It is envisioned that other means of securing the backing to the distal tip assembly can include but are not limited to attachment using: adhesive, welding, pins and/or screws or the likes. Still referring to  FIG. 8 , a distal pull wire  1316  can be secured to the distal tip subassembly  1312  by the distal adhesive band  1318 . The distal pull wire  1316  can reside in one of the lumens  1376  of the catheter  1310  and can be connected to the slider  120  in the proximal housing  122  (see  FIG. 1  and  FIG. 8 ). As described above in reference to  FIG. 3A , the distal pull wire  1316  can be utilized in bending the distal portion of the catheter  1310 . As shown in  FIG. 8 , the distal tip subassembly  1312  can be securely attached to the catheter tubing  1370  of the catheter  1310  by the proximal adhesive band  1344 . As further shown in  FIG. 8 , lumens  1376  of the catheter tubing  1370  can be utilized for passage of various elements of the tip subassembly  1312  and any of their related features, in addition to instruments, gases, fluids, or other substances. 
         [0102]    A fourth embodiment of the invention including an alternative distal tip assembly arrangement is shown in  FIG. 9 , and the details of the tip assembly are shown in  FIG. 10 . Various details, features and uses of this embodiment include those as described herein regarding other embodiments. In this embodiment an alternative transducer subassembly is provided as shown in detail  FIG. 10 . As shown in  FIG. 10 , in this implementation, the ultrasound transducer  1420  is mounted at a distal portion of the distal tip assembly  1412 . Further, the transducer  1420  is directed substantially toward the proximal direction. As illustrated, in this orientation the transducer  1420  can emit an ultrasound wave  1457  substantially parallel to the longitudinal axis of the distal tip assembly  1412 . 
         [0103]    As shown in  FIG. 10 , proximal to the transducer  1420  an angled reflector device can be mounted. For example, the reflector device can be a cylindrical reflector  1452  with having a face cut at an angle to the distal tip assembly  1412  longitudinal axis. The reflector  1452  can be arranged to reflect the ultrasound energy wave  1457  produced by the transducer  1420  as an outgoing ultrasound wave  1458  which exits the tubing  1442  and travels to the intended ablation site  1460  in the tissue  146 . It is envisioned that the reflector can alternatively include a non-planar face, for example, a curved, convex or concave surface. The angle of the reflector can range between substantially 0-90°. In one implementation the angle is substantially 10-80°. In another implementation the angle is substantially 30-60°. In another implementation the angle is substantially 40-50°. In a further embodiment the angle is substantially 45°. 
         [0104]    The reflector  1452  can be secured to the tubing  1442  by means of the distal adhesive band  1418  which can also secure the distal pull wire  1416 . The adhesive band  1418  can include a passageway  1448  for the flow of a cooling fluid as describe herein. The transducer subassembly  1414  can be secured at the distal portion of the tip assembly  1412  by means of thermally conductive adhesive  1450  which, together with the adhesive band  1418  forms a chamber  1446 . The chamber  1446  can include one or more apertures  1464 . As shown in  FIG. 10 , in one implementation the apertures  1464  are drip holes distributed circumferentially about the distal portion of the distal tip assembly  1412 . 
         [0105]    In use, a cooling fluid can be flowed from the passageway  1448  in the distal adhesive band, past the reflector  1452  and exit by way of the apertures  1464 . This fluid flow can serve to cool the transducer  1420  and keep it within nominal operating temperatures. It is envisioned that cooling of the transducer can be controlled to provide nominal transducer operation. As shown in  FIG. 10 , the transducer  1420  can include a temperature sensor  1436 , for example, attached to the back side of the transducer. The temperature sensor  1436  can include associated lead wires, which along with the wires for the transducer can form a bundle  1440  which is subsequently contained in a lumen  1476  of the catheter tube  1470 . Similarly, the fluid passageway  1448  can be in fluid communication with a lumen  1476  of the catheter tubing  1470 . As further shown in  FIG. 10 , the distal pull wire  1416  can also be contained in a lumen  1476  of the catheter tubing  1470 . As shown in  FIG. 10 , in one implementation tubing  1442  is bonded to the catheter tubing  1470  by means of proximal adhesive band  1444 . 
         [0106]    Still referring to  FIG. 10 , a distal pull wire  1416  can be secured to the distal tip subassembly  1412  by the distal adhesive band  1418 . The distal pull wire  1416  can reside in one of the lumens  1476  of the catheter  1410  and can be connected to the slider  120  in the proximal housing  122  (see  FIG. 1  and  FIG. 10 ). As described above in reference to  FIG. 3A , the distal pull wire  1416  can be utilized in bending the distal portion of the catheter  1410 . As shown in  FIG. 10 , the distal tip subassembly  1412  can be securely attached to the catheter tubing  1470  of the catheter  1410  by the proximal adhesive band  1444 . As further shown in  FIG. 10 , lumens  1476  of the catheter tubing  1470  can be utilized for passage of various elements of the tip subassembly  1412  and any of their related features, in addition to instruments, gases, fluids, or other substances. 
         [0107]    The anchoring mechanism of the device can be configured in any of a number ways in addition to the mechanism as illustrated, for example in  FIGS. 3 and 14  wherein a wire loop is included. One function of the anchor mechanism is to provide a firm axis of rotation to the catheter as it is rotated so that the ultrasound beam can be directed to provide a partial or complete zone of ablation. Another function of the anchor mechanism in some implementations is to provide stabilization of the catheter when manipulating the catheter distal portion. As shown in  FIG. 14  the anchor mechanism  140  can include a wire loop  138  that can be firmly pressed against the ceiling wall of a heart chamber. 
         [0108]    As shown in  FIG. 15 , in another implementation anchor mechanism  370  including an expandable member, for example, an inflatable balloon is provided. The anchoring member can be in the shape of a disc  372  that is inflatable, for example, an inflatable balloon. The shaft of the anchor mechanism  370  in this case can be made of a suitable tubing  374  for inflating and deflating the disc  372 . The disc can be constructed such that when in a deflated profile, the disc can move through an assigned lumen in the catheter (not shown). In use, the device is placed in a heart chamber as described herein. The implementation of the anchor member  374  illustrated in  FIG. 15  can be advanced beyond the notch  342 , and after deployment the disc  372  can be inflated. The inflated disc can be firmly pressed against the ceiling wall of the heart chamber (not shown). The shaft  374  of the anchor mechanism  370  in this implementation provides an axis of catheter rotation  352  around which the distal tip assembly can be rotated to sweep the ultrasound energy beam to create a zone of ablation. Anchor mechanism  370  shown in  FIG. 15  can be withdrawn into the catheter by deflating the disc and pulling the anchor mechanism  370  proximally into the lumen through the notch  342 , for example, by actuating a slider mechanism provided at the proximal housing of the catheter. 
         [0109]    Although the disc  372  of this anchor mechanism  370  implementation is described as a balloon (see  FIG. 15 ), it is envisioned that any type of expandable member could be used. Suitable expandable members can include but are not limited to a cage, stent, or other self-expanding device that can be deployed and collapsed as required. Such structures are well known in the art. 
         [0110]    Another implementation of an anchor mechanism is illustrated in  FIG. 16 . In this implementation, the distal portion of the anchor mechanism  470  includes one or more barb members  472  or similar tissue engaging hooks. As the anchor mechanism  470  is deployed by advancing the mechanism  470  distally beyond the catheter notch  442 , the barb members  472  deploy to an open configuration. Upon further advancement of the anchor mechanism, the barb members can engage firmly in the tissue, for example the ceiling wall of the heart chamber (not shown). Again, as shown in  FIG. 16 , the shaft  474  of the anchor mechanism  470  provides an axis of rotation  452  for the catheter  410  when the catheter  410  is used for creating a zone of ablation. The barb members  472  can collapse as the anchor mechanism  470  is withdrawn into a lumen of the catheter by way of the notch  442 , for example, by actuating a slider mechanism at the proximal housing of the catheter. 
         [0111]    In general, in another aspect, an ablation device including a catheter having a distal tip assembly as described herein, but without a need for physical anchoring to the ceiling wall of the heart chamber is provided. As shown in  FIG. 17 , in one implementation, the anchor mechanism  570  of the ablation device includes a double wall tubing  580  having an annulus  582  between an inner wall  584  and an outer wall  586 . Anchor mechanism  570  is an elongate structure spanning from a distal portion of the ablation catheter (see  FIG. 17 ) to substantially the proximal portion of the device (not shown). The distal portion of the anchor mechanism  570  includes an expandable member, for example, an inflatable balloon  588  (see  FIG. 17 ) which can communicate with a connector, for example, a luer fitting at the proximal end of the anchor mechanism  570  (not shown). Although a balloon is described as an exemplary expandable member, it is envisioned that other expandable members including but not limited to a cage or stent can be used. The inner lumen  590  of the anchor mechanism  570  provides a passageway for the ablation catheter  510  such that the catheter is free to move axially  554  and radially  552  within. As shown in  FIG. 17 , during use, the anchor mechanism  570  can be positioned inside the guide catheter  522  and advanced distally until a distal portion of the anchor mechanism  570  extends beyond the guide catheter  522  while the balloon  588  remains inside the guide catheter  522  substantially proximal to the guide catheter  522  end. In another implementation at least a part of the expandable member of the anchor mechanism remains inside the guide catheter, while another part of the expandable member extends distally beyond the guide catheter end (not shown). In yet another implementation the distal portion of the anchor mechanism remains substantially proximal to the distal end of the guide catheter (not shown). 
         [0112]    To effect anchoring, the balloon can be inflated with a suitable fluid (e.g., saline or CO.sub.2) sufficiently such that a distal portion of the anchor mechanism is held firmly in the guide catheter. The ablation catheter  510  can then be advanced distally (see arrow  554  in  FIG. 17 ) through the inner lumen  590  of the anchor  570 . As shown in  FIG. 17 , when the balloon  588  is inflated, the distal portion of the catheter  510  exiting from the anchor mechanism  570  is free to rotate in a manner  552  about a longitudinal axis, yet is held firmly in the guide catheter  522 . As required, the catheter distal portion can be shaped by bending as described herein to a desired position (e.g., see  FIGS. 3A-C ). When anchored at the end of the guide catheter, the distal portion of the ablation catheter can be caused to follow a fixed rotational path without being susceptible to wavering or wandering as the catheter is rotated or otherwise guided in the heart chamber to create a zone of ablation. 
         [0113]    The creation of a zone of ablation is facilitated by moving the distal portion of the catheter sufficiently away from the longitudinal axis of the catheter followed by rotation around an axis of rotation provided by an anchor mechanism. The location and orientation of the distal tip assembly, and the resulting direction of the ultrasound energy beam, is determined by the bending of the catheter distal portion at one, two or more locations along the catheter. In one implementation an ultrasound beam is presented to the tissue at a substantially orthogonal angle to achieve efficient ablation of the tissue. The direction of the sound beam can be adjusted by manipulating the bending of the catheter distal portion. This can be achieved by presenting the beam to the tissue in a duty cycle manner where the beam is energized for a pre-determined period followed by a quiet period. During this quiet period, a portion of the sound beam is reflected by the tissue, and the intensity of the reflection is measured by the same transducer being used in a receive mode. An operator or a control system can manipulate the angle of the ultrasound energy beam to maximize the intensity of the reflected sound beam. This ensures that the beam is substantially orthogonal to the tissue. As the beam is swept along the tissue, the distal tip assembly angle can be continuously manipulated such that the beam is presented to the tissue in a substantially orthogonal manner at all times. This can be achieved by a microprocessor controlled system (not shown) which utilizes the information provided by the reflected signal and then manipulates the tip bending through the pull wires connected to appropriate stepping motors. The motor mechanism can be contained in a separate module connected to the generator by means of an electrical cable (not shown). The proximal housing of the ablation catheter can be arranged to engage with the motor module making appropriate connections between the slider mechanisms and the corresponding motors (not shown). The resulting zone of ablation would then achieve maximum ablation, and the irregular anatomy, if any, of the heart chamber would be effectively addressed. 
         [0114]    It is envisioned that a zone of ablation produced using the device described herein can be lesion in tissue having a shape including but not limited to a ring, elliptical, linear, and curvilinear as created by a combination of bending and/or rotating motions of the device. 
         [0115]    In general, in another aspect, methods of using the embodiments described herein, for example, in treating atrial fibrillation, are provided. By way of example, a use of the device of the first embodiment is illustrated in  FIG. 11 . One method of using the device can include the following steps: 
         [0116]    1. A guide catheter sheath  222  is positioned across the atrial septum  224  of a heart in a conventional way. One such technique is described by Gill (J. S. Gill, How to perform pulmonary vein isolation, Europace 2004 6(2):83-91). The opening of the guide catheter  222  is directed towards the ceiling  226  of the heart chamber. 
         [0117]    2. Ablation catheter  210  is advanced through the guide catheter  222  and beyond the guide catheter  222  open end towards the tissue area in the middle of the pulmonary veins (PV) such that the distal tip assembly  212  points generally towards a part of the tissue surrounded by the PV. 
         [0118]    3. Anchor mechanism  240  is deployed from within the catheter  210  and wire loop  238  is securely positioned against the tissue of the ceiling  226  of the heart chamber thereby providing an axis of rotation for the catheter  210 . 
         [0119]    4. Tip assembly  212  of the catheter  210  is moved away from the wire loop  238  by using the bending mechanism described herein and as shown  FIGS. 3A-C . In general, the distal pull wire  116  is pulled by moving the first slider  120  (see  FIG. 1 ), the catheter distal portion is bent at location  126  in the direction  172 , thereby moving from position X to position Y, as shown in  FIG. 3B . Next, the proximal pull wire  128 , which is secured in the catheter lumen at a position by proximal adhesive band  130 , is pulled by moving the second slider  132  (see  FIG. 1 ). This results in the catheter  110  distal portion bending at location  136  and moving in the direction  174  to position Z, away from the longitudinal axis of the catheter, as shown  FIG. 3C . In this way a portion or all of the tip assembly  212  can be positioned outside an area circumscribing the PV. More specifically, it is envisioned that the tip assembly  212  can be positioned suitably, in terms of distance and incident angle (e.g., orthogonal), to ablate tissue outside of an area defined by the PV. 
         [0120]    5. The tip assembly  212  is oriented towards the tissue  226 , and the device is energized by a generator (not shown) to provide a beam  258  of emitted ultrasound energy which impinges on the tissue  226 . This energy beam  258  creates an ablation zone  260  in the tissue  226 . 
         [0121]    6. The treatment of the tissue is continued until a complete ablation of transmural thickness is achieved. 
         [0122]    7. Catheter  210  is progressively rotated in a manner  252  about an axis as indicated in  FIG. 11 , such that the tip assembly  212  and the sound beam  258  traverses in a substantially circular path in the heart chamber (indicated as dashed lines  262  in  FIG. 11 ). The treatment of tissue along a tissue path is continued until a complete ablation of transmural thickness is achieved along the entire path to create a partial or a complete zone of ablation  262  around all the targeted pulmonary veins, thereby achieving a conduction block. 
         [0123]    8. The anchor mechanism  240  is retracted into a lumen through the notch  242  by actuating the appropriate slider mechanism at the proximal housing (not shown). 
         [0124]    9. Distal tip assembly  212  is returned to a relaxed position by releasing the pull tension on the respective pull wires (not shown) thereby readying the catheter  210  for retraction into the guide catheter  222 . 
         [0125]    10. The ablation catheter  212  and the guide catheter  222  are removed from the body. 
         [0126]    The method outlined above provides for a zone of ablation, having a shape as described herein, around four pulmonary veins. However, as shown in  FIG. 12 , in another method of using the device a conduction block can be achieved by providing two zones of ablation, for example, ablation rings  264  and  266 , each around two PV. Alternatively, an ablation ring  268  can be placed around three PV as shown in  FIG. 13 . It is envisioned that any combination of ablation zones including but not limited to rings could be placed around one, two, three, or four pulmonary veins to achieve a complete conduction block. 
         [0127]    In another implementation a method of using the device described herein can include the following steps: 
         [0128]    1. A guide catheter sheath  222  is positioned across the atrial septum  224  of a heart in a conventional way. The opening of the guide catheter  222  is directed towards the ceiling  226  of the heart chamber. 
         [0129]    2. Ablation catheter  210  is advanced through the guide catheter  222  and beyond the guide catheter  222  open end towards the tissue area in the middle of the pulmonary veins (PV) such that the distal tip assembly  212  points generally towards a part of the tissue surrounded by the PV. 
         [0130]    3. Tip assembly  212  of the catheter  210  is moved away from the wire loop  238  by using the bending mechanism described herein and as shown  FIGS. 3A-C . In general, the distal pull wire  116  is pulled by moving the first slider  120  (see  FIG. 1 ), the catheter distal portion is bent at location  126  in the direction  172 , thereby moving from position X to position Y, as shown in  FIG. 3B . Next, the proximal pull wire  128 , which is secured in the catheter lumen at a position by proximal adhesive band  130 , is pulled by moving the second slider  132  (see  FIG. 1 ). This results in the catheter  110  distal portion bending at location  136  and moving in the direction  174  to position Z, away from the longitudinal axis of the catheter, as shown  FIG. 3C . In this way a portion or all of the tip assembly  212  can be positioned outside an area circumscribing the PV. More specifically, it is envisioned that the tip assembly  212  can be positioned suitably, in terms of distance and incident angle (e.g., orthogonal), to ablate tissue outside of an area defined by the PV. 
         [0131]    4. Anchor mechanism  240  is deployed from within the catheter  210  and wire loop  238  is securely positioned against the tissue of the ceiling  226  of the heart chamber thereby providing an axis of rotation for the catheter  210 . 
         [0132]    5. The device is energized by a generator (not shown) to provide a beam  258  of emitted ultrasound energy which impinges on the tissue  226 . This energy beam  258  creates an ablation zone  260  in the tissue  226 . 
         [0133]    6. The treatment of the tissue is continued until a complete ablation of transmural thickness is achieved. 
         [0134]    7. Catheter  210  is progressively rotated in a manner  252  about an axis as indicated in  FIG. 11 , such that the tip assembly  212  and the sound beam  258  traverses in a substantially circular path in the heart chamber (indicated as dashed lines  262  in  FIG. 11 ). The treatment of tissue along a tissue path is continued until a partial or a complete zone of ablation of transmural thickness is achieved along the entire path to create complete ablation, for example, shaped as a ring  262  around all the targeted pulmonary veins, thereby achieving a conduction block. 
         [0135]    8. The anchor mechanism  240  is retracted into a lumen through the notch  242  by actuating the appropriate slider mechanism at the proximal housing (not shown). 
         [0136]    9. Distal tip assembly  212  is returned to a relaxed position by releasing the pull tension on the respective pull wires (not shown) thereby readying the catheter  210  for retraction into the guide catheter  222 . 
         [0137]    10. The ablation catheter  212  and the guide catheter  222  are removed from the body. 
         [0138]    In a further implementation, wherein the anchor mechanism of the device is the mechanism as shown in  FIG. 17  and as described herein, a method of using the device can include the following steps: 
         [0139]    1. Referring to generally to  FIG. 11  (disregarding the anchor mechanism  240  depicted therein), a guide catheter sheath  222  is positioned across the atrial septum  224  of a heart in a conventional way. The opening of the guide catheter  222  is directed towards the ceiling  226  of the heart chamber. 
         [0140]    2. Referring now to  FIG. 17 , anchor mechanism  570  is advanced through the guide catheter  522  and beyond the guide catheter  522  open end towards the tissue area in the middle of the pulmonary veins (PV) (not shown) such that the anchor mechanism  522  points generally towards a part of the tissue surrounded by the PV. 
         [0141]    3. Referring still to  FIG. 17 , the balloon  588  of the anchor mechanism  570  is inflated with a fluid such that a distal portion of the anchor mechanism  570  is held firmly in the guide catheter  522 . 
         [0142]    4. The ablation catheter  510  is advanced through the inner lumen  590  of the anchor mechanism  570  and into the heart chamber. 
         [0143]    5. Referring generally again to  FIG. 11  (disregarding the anchor mechanism  240  depicted therein), the tip assembly  212  of the catheter  210  is bent into a shape using the bending mechanism described herein and as shown  FIGS. 3A-C . Thus, a portion or all of the tip assembly  212  is positioned outside of an area circumscribing the PV. 
         [0144]    6. The device is energized by a generator (not shown) to provide a beam  258  of emitted ultrasound energy which impinges on the tissue  226 . This energy beam  258  creates an ablation zone  260  in the tissue  226 . 
         [0145]    7. The treatment of the tissue is continued until a complete ablation of transmural thickness is achieved. 
         [0146]    8. Referring again to  FIG. 17 , catheter  510  is progressively rotated about an axis in a manner  552  such that the tip assembly and the sound beam traverses in a substantially circular path in the heart chamber (indicated as dashed lines  262  in  FIG. 11 ). The treatment of tissue along a tissue path is continued until a partial or a complete ablation of transmural thickness is achieved along the entire path. Thus, a complete ablation ring  262  is made around all the targeted pulmonary veins, thereby achieving a conduction block. 
         [0147]    9. The catheter  512  is returned to a relaxed position by releasing the pull tension on the respective pull wires (not shown) and the catheter  510  is retracted through the anchor mechanism. 
         [0148]    10. The balloon  588  of the anchor mechanism  570  is deflated and the anchor mechanism  570  is retracted through the guide catheter  522  and the guide catheter  522  is removed from the body. 
         [0149]    In another implementation, the methods described herein can be used to treat the left atrial appendage of the heart. In this case, the method can include use of the ablation device as described herein to produce a conduction block circumscribing the atrial appendage. It is envisioned that the atrial appendage can be treated alone or in conjunction with treatment of the PV using the ablation device of the invention. 
         [0150]    Referring to the embodiment of  FIG. 18 , the system consists of a catheter set  100 , two positioning wires  2128  and  2130 , and a guide sheath  2118 . The catheter set  100  is composed of two catheters, a therapy catheter  2110  which is slideably contained in an outer catheter  2112 . Catheter  2110  consists of a housing  2114  which contains the ultrasound transducer  2116 . A more detailed description of the housing  2114  is presented later in this specification. Catheter  2110  is contained in the outer catheter  2112 . The catheter  2112  is further contained in the transseptal guiding tube  2118 . Catheter  2112  has three independent movements available. First, the catheter  2112  can move axially in the guide tube  2118  as depicted by  2120 . The distal tip of the catheter  2112  is equipped to be bent in a manner  2122 . Finally, the catheter  2112  can be rotated in the guide sheath  2118  in a manner  2124 . Catheter  2112  contains a lumen  2126  which houses the locating wire springs  2128  and  2130 . Wires  2128  and  2130  are independently movable in the lumen  2126  of catheter  2112 . 
         [0151]    The elements of the catheter systems are positioned in the left atrium (LA) of the heart. The wires  2128  and  2130  are positioned in the left pulmonary veins (LPV). The therapy catheter  2110 , outer catheter  2112 , and the distal portion of the guide sheath  2118  are positioned in the chamber of the left atrium. Other structures of the heart shown in  FIG. 18  are the mitral valve opening (MV), left atrial appendage (LAA), and right pulmonary veins (RPV). 
         [0152]    At the proximal end, the various catheter elements are connected to a variety of controls in a connector console  2132 . After placement in the septum of the heart, the guide sheath  2118  is locked in position by means of the lever  2134 . The locating wires  2128  and  2130  have markers  129  and  131  respectively at their proximal ends. The locating wires  2128  and  2130  are designed to be guided by hand by the surgeon, and after the intended positioning, are locked in by means of the lever mechanisms  2136  and  2138  at the position of the markers  129  and  131 . The linear movement  2120  of the outer catheter  2112  is achieved by moving the slider  2140  which moves linearly in slot  2142 . Once the desired position of the catheter  2112  is achieved, the slider  2140  can be locked in position. The rotational movement  2124  of the outer catheter  2112  is achieved by the gear mechanism  2144  and  2146 . Gear  2144  is attached to the proximal end of the outer catheter  2112 . Gear  2144  is driven by the pinion  2146  which is attached to a motor (not shown). The bending mechanism  2122  of the distal tip of the catheter  2112  is achieved by means of the pull wire  2148  which terminates in a slider mechanism  2150  which is lockable once the desired position of the bending of the catheter  2112  is achieved. All the motions described here can be achieved by hand or by using appropriate motors, linkages, and actuators in the console  2132 . 
         [0153]    Similar to the outer catheter  2112 , the catheter  2110  also is provided with three independent movements. First, the catheter  2110  can be moved axially in the catheter  2112  as shown by movement  2152 . This movement  2152  is controlled at the proximal end by means of the slider  2158  which is lockable once the desired position of the therapy catheter  2110  is achieved in the outer catheter  2112 . Second, the distal portion of the catheter  2110  can be bent in the manner  2124  by means of a pull wire (not shown) connected to the slider mechanism  2160  at the proximal end console  2132 . Again, the slider  2160  is lockable in position once the desired position of the bend of the tip of the catheter  2110  is achieved. Finally, the catheter  2110  can be rotated in the outer catheter  2112  in a manner shown as  2156 . This motion is effected by the gear mechanism  2162  and  2164  in the console  2132 . Gear  2162  is attached to the proximal end of the catheter  2110 , and it is driven by the pinion  2164  which is connected to a motor (not shown). The catheters  2110  and  2112  contain the corresponding orientation marks  2166  and  2168  provided on the shafts thereof. The console also consists of a connector  2170  which electrically connects to a power generator and controller (not shown). The connector  2170  also provides electrical connections to the positioning wires  2128  and  2130  by means of being connected to the locking levers  2136  and  2138  in the console  2132 . As described later, the connector  2170  provides electrical connections to the ultrasound transducer  2116 , a temperature sensor at the housing  2114 , and the positioning wires  2128  and  2130 . 
         [0154]      FIG. 36  shows the positions of the catheter elements in the left atrium. The locating wires  2128  and  2130  are positioned in the two pulmonary veins (LPV 1  and LPV 2 ). As shown in the figure, the housing  2114  at the tip of the catheter  2110  points towards the wall tissue  2174  of the atrium. As described in detail later, the ultrasound element  2116  in the housing  2114  emits an ultrasound beam to establish an ablation window  2172 . Now, as the outer catheter  2112  is rotated inside the guide sheath  2118  in the manner  2124  and around the locating wires  2128  and  2130 , the ultrasound beam  2172  sweeps a generally circular path  2176  creating a section of a conical shell. The purpose of the two positioning wires  2128  and  2130  is to assure that the rotation of the housing  2114  will occur in a path outside the pulmonary vein LPV 1  and LPV 2 . The objective of the invention is to find at least one such curve where the sweep path  2176  of the ultrasound beam  2172  intersects with the atrial wall tissue  2172  in a contiguous locus. 
         [0155]      FIG. 20  shows the catheter apparatus. The therapy catheter  2110  and the outer catheter  2112  form a conjoined set  100  which can be freely moved axially in the guide sheath  2118 . The very tip section  186  of the sheath  2118  has a snug fit over the outer catheter  2112  so as to provide a firm grip on the catheter  2112  while it is performing its rotation  2124 . Catheter  2112  can also be moved axially inside the guide sheath  2118  in a manner  2120 . In addition, the tip of the catheter  2112  can be bent about a pivot point  182  in a manner  2122 . Catheter  2112  has a separate lumen  2126  which houses the locating wires  2128  and  2130 . These wires exit at the notch  127  and can be advanced or retracted in a manner  178  and  180 . The wires  2128  and  2130  are constructed from a material such as nitinol so as to take the shape of conical springs  194  and  196  respectively when in free space. The ends of the positioning wires can also be shaped in a suitable configuration other than the conical shapes described herein. The tips  190  and  192  of the wires  2128  and  2130  are made of a soft spring coil so as not to cause any injury to the tissue of the heart where the tips might be in contact and move against. The wires  2128  and  2130  can be advanced in the atrial chamber with the intention of being positioned in the two pulmonary veins. The wires  2128  and  2130 , when residing completely inside the lumen  2126  of the catheter  2112 , are held in a generally straight shape conforming to confines of the lumen  2126  (ref.  FIG. 23 ). As they are advanced outwards, and as they exit the notch  127 , they take on the predetermined shape of conical springs  194  and  196 . The rotation  2124  of the catheter  2112  is essentially around the wires  2128  and  2130  with lumen  2126  serving as the axis of said rotation. 
         [0156]    As described earlier, the therapy catheter  2110  similarly has three degrees of motion. It can move axially in the outer catheter  2112  in a manner  2152 . Catheter  2110  can be bent in a manner  2154  around a pivot point  184 . Finally, the catheter  2110  can be rotated in the manner  2156 . The tip end  188  of the outer catheter  2112  has a snug fit over the catheter  2110  to provide a firm support during the rotation  2156  of the catheter  2110 . Otherwise, the catheter  2110  is freely movable inside the outer catheter  2112  in a manner  2152 . 
         [0157]    The tip of the catheter  2110  has a housing  2114  which contains an ultrasound transducer  2116 .  FIG. 21A  shows the details of the housing  2114 . The transducer  2116 , which is of a generally circular shaped disc fabricated from a suitable piezoelectric material, is bonded to the end of a cylindrical backing  198  by means of an adhesive ring  200 . The attachment of the transducer  2116  to the backing  198  is such that there is an air pocket  202  between the back surface of the transducer  2116  and the backing  198 . This air pocket  202  is useful in the sense that when the transducer  2116  is energized by the application of electrical energy, the emitted ultrasound beam is reflected by the air pocket  202  and directed outwards from the transducer  2116 . The air pocket  202  can be replaced by any other suitable material such that a substantial portion of the ultrasound beam is directed outwards from the transducer  2116 . Backing  198  can be made of a metal or a plastic, as shown in more detail in  FIG. 21B , such that it provides a heat sink for the transducer  2116 . The cylindrical backing  198  has a series of grooves  204  disposed longitudinally along the outside cylindrical wall. The purpose of the grooved backing is to provide for the flow of a cooling fluid  2224  substantially along the outer surface of backing  198  and past the face of the transducer  2116 . The resulting fluid flow lines are depicted as  206  in  FIG. 21A . In an actual clinical situation, saline or any other physiologically compatible fluid can be used as the cooling fluid  2224  at any safe temperature preferably below the body temperature of 37° Celsius. 
         [0158]    The transducer  2116  has an electrical contact  208  on the front surface of the transducer using a suitably insulated wire  214 . The electrical contact  208  can be made by standard bonding techniques such as soldering or wire bonding. The contact  208  is preferably placed closer to the edge of the transducer  2116  so as not to disturb the ultrasound beam  2226  emitted by the transducer  2116  upon being electrically energized. The front face of the transducer  2116  is covered with another material known as the matching layer  228 . The purpose of the matching layer  228  is to increase the efficiency of coupling of the ultrasound wave  2226  into the surrounding fluid  2224 . Generally, as the ultrasound energy moves from the transducer  2116  into the fluid  2224 , the acoustic impedances are different in the two media, resulting in a reflection of some of the ultrasound energy back into the transducer  2116 . A matching layer  228  provides a path of intermediate impedance so that the sound reflection is minimized, and the output sound from the transducer  2116  into the fluid  2224  is maximized. The thickness of the matching layer  228  is maintained at one quarter of the wavelength of the sound wave in the matching layer material. There are a number of material candidates, generally from a family of plastics, which can serve as the matching layer. One such material is parylene which can be easily placed on the transducer face by a vapor deposition technique. In addition one can deposit a multitude of matching layers, generally two or three, on the face of the transducer to achieve maximum energy transmission from the transducer  2116  into the fluid  2224 . Conversely, same reflection principle is used on the backside of the transducer  2116 . Here the air pocket  202  is provided. Ultrasound energy sees a large impedance mismatch, so a majority of energy is reflected back into the transducer  2116  and emitted from its front face. Thus by using a combination of the air pocket  202  on the back and matching layer(s)  228  on the front, the efficiency of the transducer  2116  is greatly enhanced. Alternatively, the air pocket  202  could be replaced with a backing block material that minimizes reflections from the behind the transducer  2116 . While this backing block can reduce the amount of energy transmitted from the front of transducer  2116 , it removes reverberations and other artifacts when transducer  2116  is operating as an ultrasound receiver. The backing block material is designed to maximize the efficiency of transducer  2116  while providing adequate suppression of imaging artifacts. 
         [0159]    The back side of the transducer  2116  also has an electrical connection  2210  to a suitably insulated wire  216 . Again, the bonding can be done in any of the conventional manner such as a solder joint or wire bonding. Wires  214  and  216  together form a pair  218  which can be a twisted pair or miniature coaxial cable. On the backside of the transducer  2116 , there is temperature sensor  2212 . Its purpose is to monitor the temperature of the transducer  2116  during its use. The sensor can be a thermocouple or a thermistor of appropriate size so as to cover a small portion of the transducer surface. Two wires  220  provide the electrical connection to the temperature sensor  2212 . The wire pairs  218  and  220  form a bundle  2222 . The flow of the cooling fluid is achieved through a lumen  2242  which is terminated in a fluid port  254  at the proximal end (ref.  FIG. 18 ). 
         [0160]    The transducer-backing subassembly is encased in a tubular jacket  230 . The material of the jacket can be metal or plastic. The tubular jacket protrudes distally beyond the transducer  2116  to form a fluid chamber or pocket  236 . This pocket  236  provides for a column of fluid  2224  which is in a physical and thermal contact with the transducer  2116 . This invention provides for the fluid column  2224  for two distinct objectives. First, the column  2224  provides for the thermal cooling of the ultrasound transducer  2116 . This column  2224  is at a lower temperature than the transducer face and therefore aids in cooling the transducer  2116 . The temperature of the fluid  2224  can be easily controlled by providing the cooling fluid at a suitable temperature. The temperature of the transducer is constantly monitored by the temperature sensor  2212  disposed on the back of the transducer  2116 . Secondly, the fluid column provides for a separation medium between the ultrasound transducer  2116  and the blood surrounding the housing  2114  during the use of the device in a clinical setting. 
         [0161]    Still referring to  FIG. 21A , the tubular jacket  230  is shown at its distal end in a “castle head” configuration with slots  239 . The purpose of the slots  239  is to provide for exit ports for the flowing fluid  2224 . The slots  239  are desirable for the situation when the front tip of the catheter is in contact with the tissue or other structures during the use of the device, to maintain the important flow of the cooling fluid. The fluid flow lines  206  flow along the grooves  204 , bathe the transducer  2116 , form the fluid column  236  and exit through the slots  239  at the castle head  2238 . The maintenance of the fluid flow through the tubular jacket  230  can be achieved in a number of different ways. One additional such way is shown in  FIG. 21C  where the tubular jacket  230  consists of an enclosed chamber with small holes  2240  on the cylindrical surface closer to the distal end. These holes  2240  provide for the exit path for the flowing fluid. 
         [0162]    It is important to maintain the transducer functioning at a lower temperature so as to operate at a safe temperature for the patient, and to preserve consistent performance of the piezoelectric material, which can be damaged by exposure to excessive heat. 
         [0163]    Another important function of the housing design of this invention is to provide a barrier between the face of the transducer  2116  and the blood residing in the atrium of the heart. If the fluid flow is not incorporated, and the transducer face is directly in contact with blood, the blood will coagulate on the surface of the transducer  2116 . The coagulation will be further aggravated if the transducer gets hotter during its operation. The coagulated blood will provide a barrier to transmission of the ultrasound energy in an unpredictable way depending on the coverage of the transducer face by the coagulated blood. Additionally, there is serious risk of forming a blood clot at the interface of the transducer  2116  and the surrounding blood. The incidence of any blood clot is undesirable in any situation in the heart chamber. The flow of the cooling fluid, as described in this invention, keeps the blood from getting in contact with the transducer face, thus avoiding the formation of blood clots. We have determined that a flow rate of approximately 1 ml per minute is sufficient to maintain the fluid column  236  and keep the separation between the blood and the face of the transducer. 
         [0164]      FIG. 21A  shows the mounting of the transducer  2116  at an angle of 90 degrees to the axis of the catheter housing  2114 . However, the transducer  2116  can also be mounted at any other angle. The exit path of the beam will be at 90 degrees to the face of the transducer. The remaining details of the catheter and the presentation of the ultrasound beam to the tissue will vary accordingly in order to achieve the intended effect of tissue ablation. 
         [0165]    The transducer disc  2116 , as shown in  FIG. 21A , has a flat front surface. This front surface of the transducer can be either concave or convex to achieve an effect of a lens. 
         [0166]    The tubular jacket  230  of the above description is attached to a catheter tubing  234  by means of adhesive  232 . A pull wire  248  also is secured in the adhesive  232 . The pull wire  248  is contained in a lumen  244 . This pull wire  248  is utilized in bending the tip of the catheter  2110  in a manner  2154  (ref.  FIG. 18 ). Another lumen  2242  provides the path for the fluid flow. The wire bundle  2222  is contained in a yet separate lumen  246  in the catheter tube  234 . 
         [0167]    Referring to  FIG. 22  showing the cut-away section, the catheter tubing  234  constitutes of a multilumen inner tubing  235  covered with a braid  250  and a jacket  2252 . The multilumen tubing  235  has three lumens. The lumen  2242  is terminated in a fluid port  254  (ref.  FIG. 18 ) at the proximal end of the catheter  2110 . This allows the cooling fluid to be passed through the length the catheter and exit at the ‘castle head’  2238  of housing  2114 . The lumen  246  contains the wire bundle  2222 , and the lumen  244  contains the pull wire  248 . The tubing  2240  is encased in a braid  250  in a conventional way. The material of the braid can be round or flat metal wires, plastic filaments, or Kevlar. It is understood that the braid can be replaced with a spring like wrapping or a wrapping of foil. Finally, the braid  250  is covered in a smooth jacket  2252 . The material of the jacket is generally plastic, and can be placed using conventional extrusion techniques. The braid  250  and the jacket  2252  together provide the tortional control of the catheter tubing  234 . The tortional control is required to achieve the rotation  2156  (ref.  FIG. 18 ) of the therapy catheter  2110 . 
         [0168]    Next, the construction of the outer catheter  2112  is shown in a cut-away section in  FIG. 23 . The catheter tubing  256  consists of a multilumen tubing  257  which is encased in a braid  2268  and a jacket  270 . The multilumen tubing  256  has three lumens, one lumen  2258  contains a pull wire  2260  which is terminated at the tip in an adhesive band  2262 . This pull wire is utilized in bending the outer catheter tubing in the manner  2122  (ref.  FIG. 18 ). Another lumen  2126  is provided for the positioning wires  2128  and  2130 . The multilumen tubing  256  is encased in a braid  2268  in a conventional way. The material of the braid can be round or flat metal wires, plastic filaments, or Kevlar. It is understood that the braid can be replaced with a spring like wrapping or a wrapping of foil. Finally, the braid  2268  is covered in a smooth jacket  270 . The material of the jacket is generally plastic, and can be placed using conventional extrusion techniques. The braid  2268  and the jacket  270  together provide the tortional control of the outer catheter tubing  2112 . The tortional control is required to achieve the rotation  2124  (ref.  FIG. 18 ) of the outer catheter  2112 . 
         [0169]    When energized with an electrical pulse or pulse train, the transducer emits a sound wave with properties determined by the characteristics of the transducer  2116 , the matching layer  228 , the backing  202 , the electrical pulse, and the tissue in front of the transducer. These elements determine the frequency, bandwidth and amplitude of the sound wave propagated into the tissue. Typically, the frequencies of the emitted sound are in the low megahertz range. For the intended use in this invention, for tissue imaging and ablation near the transducer, the useful frequencies range from 5 to 25 megahertz. 
         [0170]    During one of the actual uses of the device of this invention, it will be placed in the atrium of the heart. Referring to  FIG. 24 , the transducer  2116  is maintained separated from the surrounding blood  284  by a fluid column  236 . When the transducer  2116  is energized with an appropriate electrical pulse, it emits a beam  272  of ultrasound energy. A typical beam pattern is shown for the ultrasound wave as it is emitted by the transducer  2116 . This beam pattern illustrates the outline of the ultrasound beam by mapping where the sound pressure falls by 6 dB relative to the midline of the beam. The sound beam  272  travels in the direction  274  away from the transducer  2116  in a generally collimated manner up to a distance of L and then diverges thereafter. The diameter at the origin of the ultrasound beam  272  corresponds to the diameter D of the transducer disc  2116 . If the device relies on the natural focusing of a flat disc transducer, the ultrasound beam  272  converges slightly up to a depth of L, beyond which the beam diverges. The minimum beamwidth D′ occurs at the distance L. It is well known that the distance L is determined by the diameter of the transducer disc D and the operating frequency. These relationships are well summarized by Bushberg et al [The Essential Physics of Medical Imaging, 2nd edition, Bushberg, Seibert, Leidholdt and Boone, Lippincott Williams &amp; Wilkins, 2002; p. 491]. In this invention, a relatively large L is desired, since it establishes the size of the ablation window  2172 . A variety of disc diameters and operating frequencies can be used. In general, D is selected as large as possible for a given device diameter, so that L is maximized. A higher operating frequency will also increase the distance L. However since ultrasound is attenuated in tissue as a function of increasing frequency, the required depth of the lesions determines the useable maximum frequency. Given the constraints of device size and ultrasound attenuation, this invention uses, for example, an operating frequency of 12 MHz and a disc diameter of 2.5 mm, resulting in a depth L of 12 mm and a minimum beamwidth D′ of 1.6 mm. 
         [0171]    The natural focusing of a flat disc transducer provides adequate beam forming for typical uses of this invention. Adding an acoustic lens in front of transducer  2116  provides additional flexibility in adjusting the beam pattern. For example, an acoustic lens could create a beam that is more uniformly collimated, such that the minimum beamwidth D′ approaches the diameter of the disc D. This will provide a more uniform energy density in the ablation window  2172 , and therefore more uniform lesions as the tissue depth varies within the window. A lens could also be used to move the position of the minimum beamwidth D′, for those applications that may need either shallower or deeper lesion. This lens could be fabricated from plastic or other material with the appropriate acoustic properties, and bonded to the face of transducer  2166 . Alternatively, the circular piezoelectric disc could be fabricated with a front face that is curved instead of flat. A slight concave shape, for example, would move the focal point (i.e. smallest D′) in towards the transducer, while a slight convex shape would move the focus outwards. 
         [0172]    The interaction of the ultrasound beam with the tissue is shown in  FIG. 25 . The tissue  276  is presented to the ultrasound beam  272  within the collimated length L. The front surface  280  of the tissue  276  is at a distance d ( 282 ) away from the face of the castle head  2238 . As the ultrasound beam  272  travels through the tissue  276 , its energy is absorbed by the tissue  276  and converted to thermal energy. This thermal energy heats the tissue to temperatures higher than the surrounding tissue. The result is a heated zone  278  which has a typical shape of an elongated tear drop. The diameter D 1  of the zone  278  is smaller than the beam diameter D at the tissue surface  280 . This is due to the thermal cooling provided by the surrounding fluid (cooling fluid  286  or blood  284 ) which is flowing past the tissue surface  280 . As the ultrasound beam travels deeper into the tissue, the thermal cooling is provided by the surrounding tissue, which is not as efficient as that on the surface. The result is that the ablation zone  278  has a larger diameter D 2  than D 1  as determined by the heat transfer characteristics of the surrounding tissue as well as the continued input of the ultrasound energy from the beam  272 . During this ultrasound-tissue interaction, the ultrasound energy is being absorbed by the tissue, and less of it is available to travel further into the tissue. Thus a correspondingly smaller diameter heated zone is developed in the tissue, and the overall result is the formation of the heated ablation zone  278  which is in the shape of an elongated tear duct limited to a depth  288  into the tissue. 
         [0173]    The interaction of ultrasound energy with the live tissue is well studied and understood. One such description is presented in the article by Gail ter Haar “Acoustic Surgery, Physics Today, December 2001”. In the zone  278  where the tissue is heated, the tissue cells are rendered dead due to heat. The temperatures of the tissue typically are above 55° Celsius in the heated zone  278  and the tissue is said to be ablated. Hence, the zone  278  can be depicted as the ablation zone. 
         [0174]    Referring to  FIG. 25 , it is important to present the tissue  276  to the ultrasound beam  272  such that the tissue is within the collimated length L to achieve effective ablation. As the beam  272  is presented to the tissue for an extended period of time, the ablation zone  278  extends into the tissue, but not indefinitely. There is a natural limit of the depth of the ablation zone  278  as determined by the factors such as the attenuation of the ultrasound energy, heat transfer provided by the healthy surrounding tissue, and the divergence of the beam beyond the collimated length L. This effect is beneficial in the sense that there is a natural safety limit to the penetration of the ultrasound energy such that the ablation zone  278  stops growing as a steady state is reached between the input of ultrasound energy and its conversion in to thermal energy which is dissipated by the surrounding tissue. 
         [0175]    The ablation zone in the tissue is formed by the conversion of the ultrasound energy to thermal energy in the tissue. The formation of the ablation zone is dependent on time as shown in  FIGS. 26  A-D, which show the formation of the lesion at times t 1 , t 2 , t 3  and t 4 , respectively. As the sound beam  272  initially impinges on the front surface  280  of the tissue  276  at time t 1 , heat is created which begins to form the lesion  278  ( FIG. 26A ). As time passes on to t 2 , and t 3  ( FIGS. 26B and 26C , the ablation zone  278  continues to grow in diameter and depth. This time sequence from t 1  to t 3  takes as little as 3 to 5 seconds, depending on the ultrasound energy density. As the incidence of the ultrasound beam is continued beyond time t 3 , the ablation lesion  278  grows slightly in diameter and length, and then stops growing due to the steady state achieved in the energy transfer from its ultrasound form to the thermal form. The example shown in of  FIG. 26D  shows the lesion after an exposure t 4  of approximately 30 seconds to the ultrasound beam  272 . Thus the lesion reaches a natural limit in size and does not grow indefinitely. 
         [0176]    The ultrasound energy density determines the speed at which the ablation occurs. The acoustic power delivered by the transducer divided by the cross sectional area of the beamwidth determines the energy density per unit time. In this invention, effective acoustic power ranges from 0.3 watt to &gt;10 watts, and the corresponding energy densities range from 3 watts/cm.sup.2 to &gt;100 watts/cm.sup.2. These energy densities are developed in the ablation zone. As the beam diverges beyond the ablation zone, the energy density falls such that ablation will not occur, regardless of the time exposure. 
         [0177]    One aspect of this invention is to provide a device which will produce an ablation zone across the entire thickness of the wall of the atrial tissue in order to completely block the conduction of abnormal electrical impulses. This is termed as a transmural lesion. The transmural lesion  279 , as shown in  FIG. 26C , is formed when the entire thickness of the tissue  276  is in the ablation window  2172 , and sufficient time is allowed for the lesion to develop. 
         [0178]    The dependence of the formation of the ablation zone  278  on the gap distance  282  between the catheter tip and the tissue surface is shown in  FIGS. 27A-D . For a uniformly collimated beam, as the gap distance  282  increases, the depth  288  of the ablation zone  278  remains constant. Even for cases where the beam is not uniformly collimated, as in the case of this invention where the beam convergences slightly over distance L, the depth  288  of the ablation zone  278  varies little as long as the tissue resides in an approximately collimated zone L. This distance L where the ultrasound beam  272  is approximately collimated, and where an ablation zone is effectively created, is termed as the ablation window  2172 . Thereafter the depth  288  decreases dramatically mainly due to the divergence of the ultrasound beam  272 . 
         [0179]    In practice, the amount of beam convergence can be varied to partially compensate for tissue attenuation, thereby creating more uniform energy densities within the ablation window. This compensation helps reduce the variations in depth  288  of the ablation zone  278  for tissues falling in the ablation window  2172 . 
         [0180]    There is another important factor contributing to uniform ablation depths  288  within the ablation window  2172  independent of the gap distance  282 . The sound beam travels through the cooling fluid and blood in the gap  282  with very little attenuation. Therefore almost the entire acoustic energy is available and presented to the tissue  276  beginning at the front surface of the tissue  280 . 
         [0181]    For the practical use of the device of this invention, the discussion of some of the important parameters is presented. Above, we discussed the gap distance  282 . The gap distance  282  is the distance between the distal end of the castle head  2238  and the front surface  280  of the tissue  276 . Now we discuss the angle of incidence as shown in  FIGS. 28A and 28B . The tissue  276  is presented to the ultrasound beam  272  such that its front face  280  is at an angles .theta.1 and .theta.2 to the beam  272  at a gap distance  282 . The resulting ablation  278  is formed in the tissue in the line of the direction  274  of the beam travel. The formation of the zone  278  is somewhat independent of the angle of incidence .theta. Again, as long as the tissue  278  is presented to the ultrasound beam  272  within the ablation window  2172 , the resulting ablation zone  278  profiles will be generally similar in shape, size, and depth and somewhat independent of the incidence angle .theta. 
         [0182]    In the actual clinical setting, the wall of the atrial tissue is moving within some physical distances. In order to achieve a contiguous transmural lesion in the moving wall of the atrium, the entire movement must be within the ablation window  2172 . As shown in  FIG. 29 , the atrial wall tissue  276  is moving over a distance of R within the ablation window  2172 . So long as the movement R is within the ablation window  2172 , an effective transmural lesion  278  will be created. Therefore it is important to position the castle head  2238  close enough to the endocardial surface of the atrial wall to ensure a transmural lesion in a moving wall. 
         [0183]    One aspect of this invention is to present the ultrasound beam to the atrial tissue and move it across the tissue such that a contiguous ablation zone (lesion) is created in the tissue wall. Referring to  FIG. 19 , the zone  2172  depicts the cylindrical region in front of the transducer  2116  where the atrial wall tissue  2174  is effectively ablated. As the catheter  2112  is rotated in the manner  2124 , the zone  2172  sweeps in a circle creating a section  2176  of a cone. The catheter housing  2114  can also be moved inside the atrium in geometry other than a circle by utilizing the various other movements available for the catheters  2110  and  2112 . Thus the sweeping ultrasound beam will form a complex pattern  2176  inside the atrium. The atrial wall tissue  2174  intersects this pattern  2176  forming a somewhat complex shaped lesion of ablated tissue. The important requirement for effective therapy is to create a contiguous transmural lesion which will serve as a conduction block in stopping the aberrant electrical pathways in the atrium which cause the fibrillation of atrial tissue. 
         [0184]    Referring to  FIG. 18 , the ultrasound transducer  2116  is connected to an electrical generator (not shown) by means of the connector  2170  which contains the wires  214  and  216  connected to the two faces of the transducer  2116 . When energized by the generator (not shown), the transducer  2116  emits ultrasound energy at a frequency in the range of 1 to 20 megaHertz (MHz). A practical range of frequency is 5 to 15 MHz. It is well understood in physics of ultrasound, as the frequency increases, the depth of penetration of ultrasound energy in to the tissue is reduced resulting in an ablation zone  276  (ref.  FIG. 25 ) of shallower depth  288 . The energy of the ultrasound beam  272  is determined by the excitation voltage applied to the transducer. The generator provides the appropriate frequency and voltage to the transducer to create the desired sound beam  272 . For the purpose of the description of this invention, we are using a frequency in the range of 5 to 15 MHz, and a voltage in the range of 10 to 100 volts peak-to-peak. In addition, a variable duty cycle can be used to control the average power delivered to the transducer. The duty cycle ranges from 0% to 100%, with a repetition frequency of approximately 40 kHz, faster than the time constant of thermal conduction in the tissue. This results in an ablation zone  278  which is created within 2 to 5 seconds, and is of depth  288  of approximately 5 millimeters (mm), and of a maximum diameter of approximately 2.5 mm in correspondence to the diameter of the transducer  2116 . It is understood that the ultrasound transducer of different diameters and frequencies can be used and different voltages and duty cycles can be applied to get various outputs of ultrasound power resulting in different sized ablation zones  278 . 
         [0185]    A contiguous transmural lesion is intended as the ultrasound beam  272  is swept across the atrial wall. Therefore, it would be desirable to know if a contiguous transmural lesion is indeed being created as the ultrasound beam is moved across the moving atrial wall. This is achieved by using the same ultrasound transducer  2116  in a diagnostic mode as described below. 
         [0186]    The effectiveness of the creation of a transmural lesion  279  is in knowing and ensuring that the atrial wall tissue  2174  is being presented to the ultrasound beam with the pattern  2176  for effective ablation (ref.  FIG. 19 ). This is achieved by using the same ultrasound transducer  2116  for the purpose of tissue detection. On the one hand, in order to achieve ablation (i.e. killing of the live tissue cells), the ultrasound beam of sufficient energy is delivered to the tissue in a substantially continuous manner such that the energy input exceeds the thermal relaxation provided by the cooling due to the surrounding tissue. This mode of energizing the ultrasound transducer  2116  is termed as the ablation mode. On the other hand, the tissue detection is done by utilizing a pulse of ultrasound of short duration which is generally not sufficient for heating of the tissue. Ultrasound has been traditionally used for diagnostic purposes for a number of years. Typical uses are fetal ultrasound imaging, intravascular ultrasound imaging, and the like. For the purpose of this invention, we use the ultrasound to detect the gap (namely, the distance of the tissue surface from the castle head), the thickness of the tissue targeted for ablation, and the characteristics of the ablated tissue. This mode of energizing the transducer  2116  is termed as the diagnostic mode. One objective of this invention is to utilize the diagnostic mode in guiding the therapy provided by the ablation of the tissue. 
         [0187]    This invention uses a simple ultrasound imaging technique, referred to in the art as A Mode, or Amplitude Mode imaging. A short electrical pulse or train of pulses excites the ultrasound transducer creating a short duration ultrasound pulse wave that propagates into the blood and tissue. As the ultrasound pulse travels through the tissue, some of the acoustic energy is backscattered to the transducer, which converts the returning acoustic signal into an electrical voltage. The amplitude of the voltage is sensed in a receiver (not shown), as a function of the time elapsed from the initial transmitted pulse. Since ultrasound travels through blood and soft tissue at a known and approximately constant speed, the receiver can determine the distance from which the returning signals originate. The amplitude of the returning signals depends on the acoustic properties of the tissue. Homogeneous tissue backscatters the sound as the pulse wave propagates through it. Different tissues create differing amounts of backscatter, so the returning ultrasound signal has different amplitudes depending on the type of tissue. As the pulse travels passes from one tissue to another, a reflection occurs, the amplitude of which is determined by the acoustic impedance difference of the two tissues. 
         [0188]    Referring to  FIG. 30 , the transducer  2116  sends a pulse  290  of ultrasound towards the tissue  276 . A portion of the beam is reflected and backscattered as  292  from the front surface  280  of the tissue  276 . This reflected beam  292  is detected by the transducer  2116  a short time later and converted to an electrical signal which is sent to the electrical receiver (not shown). The reflected beam  292  is delayed by the amount of time it takes for the sound to travel from the transducer  2116  to the front boundary  280  of the tissue  276  and back to the transducer  2116  now serving as an ultrasound detector. This travel time represents a delay in receiving the electrical signal from the transducer  2116 . Based on the speed of sound in the intervening media (saline fluid  286  and blood  284 ), the gap distance d ( 282 ) can be determined. As the sound beam travels further into the tissue  276 , a portion  294  of it is reflected from the back surface and travels towards the transducer. Again, the transducer converts this sound energy into electrical signals and the generator converts this information into the thickness t ( 300 ) of the tissue  276  at the point of the incidence of the ultrasound pulse  290 . As the catheter housing  2114  is traversed in a manner  301  across the tissue  276 , the ultrasound transducer continuously detects the gap distance d ( 282 ) and the tissue thickness t ( 300 ). This information is used in delivering continuous ablation of the tissue  276  during therapy as discussed below. 
         [0189]    The returning echo from tissue boundaries has the same time duration as the transmitted pulse. The returning backscattered signal from the bulk of the tissue has a time duration equal to the path length of the pulse through the tissue. The returning signal from tissue  276  then is a composite of two short relatively high amplitude pulses returning from the front wall  280  and back wall  298 , along with the backscatter from within the tissue. The amplitude of the backscatter from the tissue will change as the pulse traverses the ablated tissue and the normal tissue. Therefore, by measuring the relative amplitudes of the returning signal, the receiver can determine the depth of the front wall, the depth of the lesion, residual tissue depth that is not yet ablated, and the depth of the back wall. 
         [0190]    The receiver compares the time delay of the first echo from the face of tissue  280  to a time threshold corresponding to the ablation window length  2172 . If the time delay is less than the threshold, this indicates that the front face of the tissue  280  lies within the window length  2172 . The receiver can indicate this by a display means, for example lighting a ‘green’ display. If the receiver detects the echo arriving later than the time threshold, then a ‘red’ display can be lit indicating that the gap  282  is too large, and a lesion may not be created in the tissue. 
         [0191]    The use of the above information in an actual clinical setting is depicted in  FIG. 31 . The catheter  100  of catheters  2110  and  2112  is introduced into the atrial chamber through the guide sheath  2118 . The positioning wires  2128  and  2130  are advanced in to the two left pulmonary veins LPV 1  and LPV 2 . In the diagnostic mode, as the outer catheter  2112  is rotated in a manner  2124 , the housing  2114  at the tip of the therapy catheter  2110  rotates in the atrial chamber. When the catheter is in position A near the LPV 1 , the ablation window  2172  intersects with the tissue wall  302 . This indicates a condition that the ablation of the tissue in its entire thickness can be achieved and is indicated by a ‘green’ light. As the housing  2114  continues to sweep the atrial chamber, it reaches position B near the LPV 2 . Here the ablation window  2172  does not intersect the tissue wall  304 . This indicates a condition that the tissue is either too far, or the ultrasound beam is pointed towards a structure such as a PV, or the atrial appendage, or the mitral valve opening. In this case, transmural ablation will not be achieved and a ‘red’ light will be indicated. 
         [0192]    It is the objective of the user physician to establish a contiguous beam path  2176  (ref.  FIG. 19 ) indicated by the ‘green’ light continuously lit during the movement along the entire intended lesion path. A check for this continuous green light, before energizing the ultrasound transducer, will insure that the proposed path will result in a contiguous ablation zone in the atrial wall. The situation shown in  FIG. 31  does not yield a contiguous beam path, therefore the physician would move the catheters  2110  and/or  2112  and sweep another circle of the housing  2114  in diagnostic mode to arrive at a situation such as that shown in  FIG. 19 . Once such contiguous path  2176  is established in the diagnostic mode, the physician can proceed with the ablation of the said path using the ablation mode. 
         [0193]    As an added safety feature, the system can regularly, on a time-shared basis, convert from ablation mode briefly to diagnostic mode. In this way, the correct gap can be checked even during the ablation. If the red light goes on, the system will automatically exit the ablation mode, until a correct gap (i.e. green light) is again detected. Then the ablation mode will be automatically resumed. This diagnostic sampling can occur at a relatively fast sampling frequency. In the current invention, it occurs at about 40 kHz, corresponding to the duty cycle repetition rate for the diagnostic power generator. Conversely, if the ‘green’ light remains lit throughout the movement along entire ablation path, then a contiguous lesion has been created. This measure off goodness can result in an additional display (flashing ‘green’ light, for example) to inform the physician that he has created a complete contiguous lesion. 
         [0194]    Furthermore, since the wall thickness and the lesion depth can also be checked in the diagnostic mode on a time-shared basis during the ablation, the system can dynamically control the lesion depth by varying the sweep rate along the intended ablation path, and/or changing the power provided from the generator. In this way the lesion is even more likely to be transmural contiguously all along the lesion path. In addition, the system can minimize the possibility of creating a lesion beyond the atrial wall. If the system detects the lesion extending beyond the outer wall, the generator will be turned off. Alternatively, the system can be configured such that the generator is turned off when the depth of the lesion reaches or exceeds a preset depth. 
         [0195]    The above description of the design and construction of the catheter set  100  is aimed at creating the ablation zone for the left pulmonary veins. A different catheter set is used for the right pulmonary veins, essentially of the same functioning principles but of a different geometry appropriate for the anatomical location of the right pulmonary veins in the left atrium of the heart. This catheter set  400  is shown in  FIG. 32 . The outer catheter  412  has a preset shape of a ‘shepherd&#39;s hook’ so as to point towards the right pulmonary veins when placed in the atrial chamber. The catheter  412  can move in the axial direction in the guide sheath  418  in a manner  420 . The therapy catheter  2410  moves inside the outer catheter  412  in the axial direction in a manner  2452 . In addition, catheter  412  can rotate in a manner  424 . A lumen  426  (not shown) in the catheter  2410  is used to house the positioning wires  428  and  430  which exit from the said lumen at the notch  427 . The catheter  2410  can also be rotated in the catheter  412  in a manner  456 . The distal tip portion of the catheter  2410  can be bent by means of a pull wire (not shown) in the manner  454 . The distal tip of the catheter  2410  is composed of a ‘castle head’ housing  414  which contains the ultrasound transducer  416 . The transducer has an ablation window  2472  similar to the ablation window  2172  (ref.  FIG. 19 ) of catheter  2110 . The additional construction of the elements of the catheter  2410  are identical to those of the catheter  2110  as described earlier in this specification. In addition, the catheter set  400  engages with the console  2132  in a similar manner as the catheter set  100 . 
         [0196]    Under the current state of knowledge, certain ablation lines are drawn in the atrium around the pulmonary veins in an attempt to block the conduction of aberrant electrical signals. This set of ablation lines is called a lesion set. In this invention, it is proposed to have a lesion set as shown in  FIG. 33 . One ablation ring  306  encircles the two left PV&#39;s and another ablation ring  308  encircles the right PV&#39;s. An ablation line  3310  is drawn joining the ablation rings  306  and  308 . Finally, another ablation line  312  is drawn intersecting the ablation line  3310  and down to the annulus of the mitral valve (MV). 
         [0197]    Next, a method for the use of the device of this invention in a clinical setting is presented as follows: 
         [0198]    1. Referring to  FIG. 18 , position the guide sheath  2118  across the atrial septum S using the conventional femoral vein approach. One technique for this procedure is described by Gill (J. S. Gill, How to perform pulmonary vein isolation, Europace 2004 6(2):83-91). 
         [0199]    2. Pre-load the positioning wires  2128  and  2130  in the lumen  2126  of the outer catheter  2112  such that the distal tips of the wires are entirely inside the lumen  2126 . 
         [0200]    3. Advance the catheter set  100  through the guide sheath  2118  into the atrial chamber. 
         [0201]    4. Advance one of the positioning wire  2128  through the opening notch  127  of the outer catheter  2112 . The conical spring like shape  194  of the wire will now deploy. Under conventional fluoroscopic guidance, position the wire in the pulmonary vein LPV 1 . The wire can be rotated gently to help it find and navigate the ostium and the opening of the pulmonary vein. Advance the wire slightly beyond the marker  129  at the proximal end to ensure its position inside the LPV 1  then lock it in position using the lever  2136 . 
         [0202]    5. Advance the second positioning wire  2130 , and guide its conical spring  196  into to second vein LPV 2  in a similar manner., positioning it beyond the marker  131  at its proximal end and lock in position using the lever  2138 . 
         [0203]    6. Referring to  FIG. 34 , move the outer catheter  2112  and the inner catheter  2110  to the most proximal position in the atrial chamber. Using the transducer  2116  in a diagnostic mode, rotate the outer catheter  2112  (either manually or using the motor drive of console  2132 ) in the chamber. The generator/receiver will sense for the position of the atrial wall tissue and indicate appropriately with a green or a red light. 
         [0204]    7. If the red light indication exists in a portion of the rotation, use the linear or bending motions of the catheters  2112  and/or  2110  to achieve a complete green circle. At this point, a contiguous beam path  2176  has been established. In the diagnostic mode, the navigation through a circle is quite rapid and can be completed in several seconds. Since the circular movement can not continue in one direction only, reverse the direction of rotation after a rotation of 360 degrees plus an overlap of about 10 to 15 degrees. If the physician chooses for the motor drive to achieve this function, the drive unit is programmed to automatically reverse the direction after a complete circle plus an overlap. 
         [0205]    8. Energize the transducer in the ablation mode and start the rotary motion of the catheter tip housing  2114  using the motor drive in the console  2132 . This movement is much slower, and will typically take several minutes to complete. Confirm that the green light stays green through the entire movement. 
         [0206]    9. If the red light persists over a portion of the circle, proceed with the ablation in the green zone, and later cover the red zone ablation in the following manner: [0205] a. The physician can use the other linear and bending movements of the catheters to establish a path in a set of other planes which would yield a green path covering the region where the original red arc appeared. [0206] b. The computer in the generator/receiver can memorize this complex green path, and upon activation, can establish an ablation zone in the tissue which is contiguous with the original green zone. 
         [0207]    10. The ablation around the two left pulmonary veins LPV 1  and LPV 2  is now complete as shown as curve  306  in  FIG. 34 . 
         [0208]    11. Next, the ablation lines  3310  and  312  of  FIG. 33  are created using a method as shown in  FIGS. 35A ,  35 B,  35 C, and  FIG. 36 . 
         [0209]    12. Starting at the position of the tip housing  2114  of the catheter  2110  at the end point of the just completed ablation ring  306  ( FIG. 34 ), orient the tip  2114  posteriorly in the atrium using the orientation markers  2166  and  2168  (ref.  FIG. 18 ) on the proximal ends of the catheters  2110  and  2112 . 
         [0210]    13. Advance the catheter  2112  distally towards the LPV 1  a few millimeters to establish the starting point  324  of the ablation line  3310 . 
         [0211]    14. Using the diagnostic mode, move the catheter  2112  towards the right pulmonary veins in a manner  314  by pulling it into the guide sheath  2118 . At the same time, bend the tip of the catheter  2112  in a manner  316 . If necessary, move the therapy catheter  2110  inside the outer catheter  2112  in a manner  318 , and bend the tip of the therapy catheter  2110  in a manner  320 . All these movements are carried out to establish the locus of the ablation window  2172  in the green&#39; region. Generally, this locus will be achieved by a combination of various movements of the catheters  2110  and  2112  and can be carried out by the computer in the generator/receiver. The finishing point  326  of this ‘green’ line is intended to be past the ostium of one of the right pulmonary veins. Once this horizontal green line  3310  is established, the computer can memorize the actual motions required therefor. 
         [0212]    15. Follow through with the formation ablation line  3310  ( FIG. 33 ) by moving the tip  2114  in the ablation mode all the while maintaining the ‘green’ light. The successive positions of the ablation window  2172  and the resulting ablation line is shown in the top view of the atrium in  FIGS. 35B and 35C . 
         [0213]    16. When the catheter tip is at its most proximal position, an ablation zone around the right pulmonary veins can be created as follows: [0214] a. In diagnostic mode, rotate the catheter  2112  in a manner  2124  to establish a ‘green’ curve around the right pulmonary veins. Other available motions of the catheter set  100  can be utilized to establish a ‘green’ curve. [0215] b. Once the ‘green’ curve is established, using the ablation mode, create the ablation zone  308 . 
         [0214]    17. Now referring to  FIG. 36 , move the tip  2114  of the catheter  2110  to an approximately middle position of the ablation line  3310 , and a few millimeters clockwise (i.e. above the line  3310 ) to establish the starting position  328  for the vertical ablation line  312 , as shown in  FIG. 33 . 
         [0215]    18. Using the catheter in the diagnostic mode, rotate the catheter  2112  counterclockwise in the manner  2124 , and ensure a ‘green’ path is established. The end point  330  of this line  312  is at the mitral valve annulus which can be detected by the transducer by virtue of the movements of the leaflet of the valve itself. If required, additional movements of the catheters can be used as appropriate to determine the locus of the ‘green’ line. Once this ‘green’ line is established, enable the computer to memorize the required movements. 
         [0216]    19. Using the transducer in the ablation mode, form an ablation line  312  from the horizontal line  2110  down to the annulus of the mitral valve (MV). 
         [0217]    20. Withdraw the positioning wires into the lumen of the catheter  2112  and withdraw the catheter set  100  from the body of the patient through the guide sheath  2118  while leaving the said guide sheath  2118  in position across the septum. 
         [0218]    21. The ablation zone encircling the right pulmonary veins is made using a different catheter set specifically designed for that anatomy of the region of the atrium. 
         [0219]    22. Referring to  FIG. 37 , advance the outer catheter  412  distally until its curved surface  498  is in contact with the inside left wall of the atrium. 
         [0220]    23. Place the positioning wires  428  and  430  in the lumen  426  (not shown) of the catheter using the technique described earlier. 
         [0221]    24. Position the wires  428  and  430  into the right pulmonary veins using the technique described earlier. 
         [0222]    25. Advance the therapy catheter  2410  to its most distal position. Using the diagnostic mode, rotate the tip housing  414  of the catheter  2410  in the manner  456 . Look for the presence of the ‘green’ circle. 
         [0223]    26. If the ‘green’ circle is not established, move the catheter  2410  a few millimeters proximal in the manner  2452  and repeat step 25. Repeat this step 26 until a ‘green’ circle is established. 
         [0224]    27. Now energize the transducer in ablation mode, and create the lesion  308  ( FIG. 33 ). 
         [0225]    28. If the ‘red’ light appears, follow the procedure in step 9 above. 
         [0226]    29. The formation of the right PV ablation zone  308  is now complete. 
         [0227]    30. Retract the positioning wires  428  and  430  from the atrium by withdrawing them through the lumen of the catheter  412 . 
         [0228]    31. Remove the catheter set  400  from the atrium through the guide sheath  2118 . 
         [0229]    32. Remove the guide sheath  2118  from the heart and follow the conventional closure technique for the femoral vein. 
         [0230]    The procedure above describes the formation of one lesion set. As the catheter sets  100  and  400  are provided with multiple degrees of motions, the physician can create a variety of other lesion sets to achieve a conduction block.  FIG. 38  shows some of the lesion sets which can be created with the device of the present invention. The possible lesion sets are not limited to those presented here, and it is important to recognize that the device of this invention allows the physician to create any other lesion set in the atrium of the heart. 
         [0231]    In a conventional catheter-based ablation procedures, the physician check the presence or absence of the conduction block by mapping of the atrial tissue. The technique involves checking the electrical conduction between the pulmonary veins and the other parts of the atrial wall on the endocardial side. The wires  428  and  430  are already positioned inside the pulmonary veins and can be easily used as electrodes for the sensing and mapping purposes. The electrical connections to the positioning wires  428  and  430  are provided at the console  2132 . 
         [0232]    This specification for the present invention discusses an ultrasound transducer as a single element in the shape of a disc mounted at the end of a cylindrical catheter. This invention is not intended to be limited to the use of a single element circular disc. A rectangular or oval shaped transducer can be mounted on the cylindrical side of the catheter tip. Appropriate fluid flow mechanism can be provided to cool the said transducer and to provide for the separation of the surrounding blood from the surface of the transducer. In addition, the transducer configuration is not intended to be limited to that of a disc. The transducer can be in the form of an array of multiple transducers. The transducer can also be fabricated as a set of concentric circles (known in the art as an annular array), for example, instead of the single element disc described in this invention. One skilled in the art will appreciate the wide possibility of possible shapes, sizes, and configurations which can be used for the transducer in this invention. 
         [0233]    This specification of the present invention discusses the use of a console  2132  that allows simple control of the catheter sets  100  and  400 . This invention is not intended to be limited to the use of this console. The catheter sets, with appropriate modifications, can also be controlled and manipulated by other means, for example mechanical robotic or magnetic controllers with remote user interfaces that manage all motions, with or without haptic feedback. 
         [0234]    In some embodiments, the tip of the treatment catheter and the anchor can both be made of metal and can communicate electrically with the control system so that they can serve as mapping electrodes for determining the electrical characteristics of the heart tissue. 
         [0235]    The description above of the device of this invention has been limited to the treatment of atrial fibrillation in the left atrium of the heart. However, the device, with appropriate modifications, can be used in other parts of the body. For example, if it is determined that the right atrium is also involved in the condition of atrial fibrillation, appropriate lesion set can be created in the wall of the right atrium as well. Another example is the use of another version of the device in the ventricular space for the treatment of ventricular arrhythmia. The transducer creates an ultrasound beam which is capable of creating transmural lesions in the myocardial tissue, and this beam can be moved around in the chambers of the heart to create intended lesions in the wall of the heart. 
         [0236]    While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention.