Abstract:
Intra-organ ultrasound images are obtained by integrating ultrasound array configurations at the distal region of a sheath or guiding catheter integral to any catheter based intervention. A dual mode ablation/imaging circular ultrasound array is used to create circular or partial circular lesions. The sites of the individual lesion segments are identified in an ultrasound 2D image. In the case of PV isolation the process of ablating individual segments identified in the ultrasound image is repeated until a circumferential, continuous lesion has been achieved and PV isolation has been confirmed with the coaxial loop sensing catheter which also serves as a guide wire.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/770,810 filed Feb. 28, 2013 and the benefit of U.S. Provisional Application No. 61/770,818 filed Feb. 28, 2013. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates in part to integrated ultrasound imaging with a catheter delivery sheath as used for electrophysiology (EP), interventional cardiology and interventional radiology procedures. 
         [0003]    The present invention also relates to percutaneous catheter based treatments of various diseases as, for example, Atrial Fibrillation (AF), GERD, urinary tract disease, valve disease and lung tumors in mammalian subjects. 
       BACKGROUND OF THE INVENTION 
       [0004]    Ultrasound imaging is well established to guide interventional procedures. Ultrasound imaging has the advantage that real time guidance with morphological information (unlike with fluro guidance which does not provide morphological information) is obtained without radiation burden. However, today&#39;s ultrasound imaging catheters do not provide simultaneous guidance relative to the intervention or therapy if the imaging catheter is exchanged for the treatment catheter. For many procedures either the therapy catheter is inserted or the ultrasound imaging catheter. Therefore, the image guidance cannot be obtained simultaneously to the therapeutic action. If the anatomy allows, both, imaging as well as treatment catheter can be inserted to obtain real time or simultaneous guidance. However, this requires an additional puncture for the imaging catheter. 
         [0005]    A typical example for the above situation is abdominal aortic aneurysm (AAA) repair. An imaging run is performed to confirm graft selection and planning of placement. Then the imaging catheter is withdrawn and the treatment catheter (in this case carrying the graft) is inserted and the graft is deployed. After the deployment an imaging run is performed to confirm correct placement (i.e. mechanical stability) and proper expansion (i.e. lack of leaks). It would be desirable to obtain the ultrasound imaging guidance simultaneously with the therapeutic procedure, i.e. without having to perform a diagnostic/therapeutic catheter exchange. This way the procedure would be optimized and much easier to perform. 
         [0006]    Many heart disease conditions are treated by guidance with Intra Cardiac Echocardiography (ICE) catheter imaging as, for example, catheter ablation to treat Atrial Fibrillation (AF) or appendage closure. Many more treatments are evolving like percutaneous valve repair procedures which greatly benefit from ultrasound imaging guidance. Currently, percutaneous valve repair procedures utilize Trans Esophageal Echocardiography (TEE) imaging for guidance due to the lack of high quality ICE imaging and 3D ICE imaging. 
         [0007]    The current ICE imaging is limited to 2 dimensional imaging with rather limited image quality. Two approaches utilized are phased array all electronic imaging and mechanically rotating imaging. The mechanical approach utilizes a rotating transducer at the distal catheter end which is limited in aperture (to the catheter diameter or less) and therefore needs to be advanced close to the ablation site (typically a pulmonary vein antrum in case of AF ablations) in the left atrium in order to obtain useful images. Consequently imaging and therapy are performed in an alternating fashion by advancing either the therapeutic or the imaging catheter unless a double trans-septal puncture and an additional percutaneous access are performed. 
         [0008]    For phased array imaging, with larger long axis apertures, the catheter is positioned in the right atrium to image and guide ablations in the left atrium. While this approach is advantageous over the mechanical approach because it allows for simultaneous therapeutic action under image guidance, there is a need for better image quality in particular in the far field where the catheter ablation takes place in the case of left pulmonary vein isolations. In addition the long axis imaging format makes orientation difficult which requires a significant learning curve for electronic ICE imaging. 
         [0009]    U.S. Pat. No. 5,135,001 proposes to obtain ultrasound image guidance through a removable circular transducer section attached to a medical instrument. This type of imaging device will not be isometric and increases the instrument diameter significantly. Also cable management from the imaging sensor(s) to the ultrasound instrument is challenging. Other proposals suggest the use of an additional lumen in the sheath to advance an imaging catheter which of course increases the overall sheath diameter significantly (see U.S. Pat. No. 5,201,315 describing a sheath with three lumens to accommodate guide wire, probe and imaging catheter). 
         [0010]    Perhaps for these reasons, none of these proposals have been widely adopted. 
         [0011]    With respect to the treatment of cardiac disease states such as atrial fibrillation (AF), it is noted that humans and other mammals have a four-chambered heart. Blood from the body flows into the right atrium, and from the right atrium through the tricuspid valve to the right ventricle. The right ventricle pumps the blood through the pulmonary arteries to the lungs. Blood from the lungs returns through the pulmonary veins to the left atrium, and flows from the left atrium through the mitral valve, into the left ventricle. The left ventricle, in turn, pumps the blood through the body. As the heart beats, the atria contract to pump the blood into the ventricles, and then the ventricles contract, during a phase of the heart rhythm referred to as “systole,” to pump the blood through the lungs and through the body. 
         [0012]    For proper pumping action, the atria as well as ventricles need to contract in an organized synchronized fashion. Atrial fibrillation diminishes the pumping action of the heart. 
         [0013]    Atrial fibrillation is a common problem with high healthcare consumption and increased morbidity and mortality. 
         [0014]    As disclosed, for example, in U.S. Patent Application Publication No. 2009/0228003A1 or U.S. Pat. No. 7,326,201 B2, an electrode or ultrasonic transducer is advanced into the heart and actuated so as to heat the pulmonary vein annulus. It is difficult though to provide such accurate positioning of a transducer or RF electrode within a beating heart. 
         [0015]    Numerous patents and patent applications describe the advantages of ultrasound over other energy forms, mainly radio frequency (RF). The advantage lies in the non thrombogenic nature of ultrasound which makes non contact tissue ablation possible. See US Patent Application Publication No. 2011/0137298A1; U.S. Pat. No. 7,950,397B2; US Patent Application Publication No. 2006/0064081A1; U.S. Pat. No. 7,285,116E2. 
         [0016]    A trend can be observed to make the ablation process easier by applying a complete lesion shape instantaneously rather than forming the lesion shape through a point by point ablation procedure. See, for example, U.S. Pat. No. 7,326,201B2. Unfortunately a fixed, complete lesion shape does not completely fit all anatomic variations. Also, the risk of collateral damage is increased since these lesion shapes are rather fixed (i.e. balloon shapes) and therewith do not avoid energy deposition into collateral structures. One prominent example is phrenic nerve injury in case of RSPV ablation with balloon based systems. Anther example is esophageal injury in case of left pulmonary vein (PV) isolations. Perhaps for these reasons, none of these proposals has been widely adopted. 
         [0017]    Many techniques have been proposed to improve catheter orientation, i.e., electromagnetic mapping techniques as commercialized by BioSense Webster or mapping combined with imaging. US Patent Application Publication No. US2008/0255449A1 assigned to ProRhythm, Inc., proposes to combine ultrasound imaging into the ablation catheter. 
         [0018]    As far as valve repair is concerned, as disclosed, for example, in U.S. Pat. Nos. 6,306,133; 6,355,030; 6,485,489; 6,669,687; 7,229,469; and Int&#39;l Applications PCT/US2003/008192 and PCT/US2007/087501, it has been proposed to insert a catheter-like device bearing a transducer such as an electrode or ultrasonic transducer into the heart and actuate the transducer so as to heat the, mitral annulus, denature the collagen fibers which constitute the annulus, and thereby shrink the annulus. In theory, such a procedure could bring about shrinkage of the annulus and repair mitral insufficiency. However, all of these proposals involve positioning of one or more transducers in contact with the mitral annulus during the procedure. It is difficult to provide such accurate positioning of a transducer within a beating heart. Although it is possible to momentarily halt the heartbeat, perform the procedure and then restart the heart, this adds considerable risk to the procedure. Moreover, localized heating of the annulus by a transducer in contact with the annulus introduces the further risk of damage to the epithelial cells overlying the annulus with attendant risk of thrombus formation after the procedure. 
         [0019]    Perhaps for these reasons, none of these proposals has been widely adopted. An improvement to bringing the ultrasound transducer in indirect contact with the mitral annulus is described in U.S. Provisional Patent Application 61/204,744 by ProRhythm Inc. In this application direct contact is not required and the ultrasound transducer is positioned by means of a positioning balloon centrally in the posterior/lateral portion of the mitral annulus. However, also this approach involves potential collateral damage because of the difficulty of limiting catheter movement and therewith unwanted energy deposition superior and inferior to the mitral annulus. Besides this collateral energy deposition there is always the risk of damaging the mitral leaflets and chordae tendinae by unintentional energy deposition. Also, since the energy is directed from the inside of the heart outward there is always a potential for collateral damage in neighboring organs or structures, for example, AV node damage or atrio-esophageal fistulae. Therefore, it would be desirable to deposit heat in the mitral annulus under real time image guidance with energy selection based on target tissue distance and thickness. 
       SUMMARY OF THE INVENTION 
       [0020]    The present invention aims in part to generate high quality 2D images and 3D images in an all-electronic fashion by integrating an imaging transducer array into the distal end of a catheter delivery sheath. Pursuant to the invention, a separate imaging catheter does not need to be inserted and image guidance can be obtained simultaneously to the therapy through sheath manipulation. This aspect of the invention is cost wise advantageous and provides also from a procedure time and convenience point of view significant advantages, since a separate percutaneous access for the imaging catheter is not needed. 
         [0021]    The present invention recognizes that the prior art catheter based ultrasound imaging technique limits the size of the imaging catheter (diameter) to the inner sheath diameter and therewith the image quality which is greatly determined by the aperture which is limited by the catheter diameter. Accordingly, the present invention contemplates the mounting of a circular ultrasound imaging array on the outside of the sheath at the distal end. Such a structure provides the largest possible aperture (given a certain access diameter) and therewith the best possible image quality and penetration. 
         [0022]    The present invention contemplates 3D imaging which makes instrument orientation much easier and shortens the learning curve. 
         [0023]    For intra-cardiac procedures the sheath desirably is advanced into the right atrium, for example, to guide AF ablation procedures. In case of interventional radiological procedures the sheath is advanced into the organ to be treated as for example, the aorta, for AAA repair procedures. As long as blood filled organs are examined and (or) treated, blood will provide for acoustic coupling for the ultrasound waves emitted and received by the transducer. In the case where organs not filled with blood are treated (for example, Endo Bronchial Ultrasound Procedures, EBUS) a coupling fluid is injected through the sheath (special side holes next to the transducer array might be advantageous). 
         [0024]    The right atrial position in case of intra-cardiac procedures allows the user to obtain real time guidance of the trans-septal puncture as well as the catheter ablation itself. The image quality in particular in the far field will be advantageous compared to catheter based imaging due to the increased aperture size. 
         [0025]    Additionally, the sheath can be advanced into the left atrium so that the imaging array is positioned inside the left atrium which will allow for different cross sectional imaging planes as well as near field imaging with improved image quality vs. far field imaging. 
         [0026]    Yet, another aspect of the invention provides for shorter and less invasive procedures since there is no need for a separate imaging catheter which, for simultaneous imaging, does require a separate percutaneous puncture. 
         [0027]    The apparatus of this invention most desirably includes a therapy catheter delivery sheath having proximal and distal ends, and a sheath steering structure carried on the sheath and operative to selectively bend the distal region of the sheath. The distal end of the sheath is the end which is inserted into the patient first. The opposite end is the proximal sheath end. The imaging section is desirably mounted on the distal end of the sheath so that different imaging planes can be obtained by bending or steering the distal sheath section. 
         [0028]    Another aspect of the present invention provides methods of creating lesions inside the heart under simultaneous image guidance. The present invention recognizes the need, not for separate imaging tools or combinations of ablation tools with imaging, but a combination device, providing dual mode simultaneous ablation under image guidance with flexibility to adjust the ablation parameters depth, distance, shape, based on the image information. With such a device anatomical variations can be addressed by, for example, varying lesion shape and ablation depth. By optimizing ablation parameters based on anatomic variations a high degree of efficacy can be achieved; for example, varying wall thickness requires varying energy settings for the ablation to achieve trans-mural lesions, but to avoid collateral damage through over-ablation. Also, ultrasound imaging makes the procedure safer since collateral damage can be avoided by creating lesion shapes which spare collateral structures from being ablated. 
         [0029]    Pursuant to the present invention, the combination imaging/ablation catheter assembly is advanced preferably into the right atrium, and after septal puncture through the septum advanced into the left atrium. The step of advancing the catheter may include advancing a delivery sheath through the septum into the left atrium of the heart and steering a distal end portion of the treatment catheter into the selected pulmonary vein opening. 
         [0030]    The method might be performed with or without a guide wire. The guide wire might be a sensing loop shaped catheter with the loop portion at the distal end and with electrodes mounted on the loop portion. This loop catheter allows monitoring the PV isolation process real time during the ablation. Depending on the positioning of the sensing loop, the electrodes can pick up electrical cardiac voltages on the distal or proximal side of a preferentially circumferential lesion. A treatment method pursuant to the present invention mechanically stabilizes the treatment catheter so that fluoroscopy time and therewith ionizing radiation can be significantly reduced. Once the catheter is placed, the operator can actually perform the ablation procedure from the control room by placing ablation markers (via cursor and/or touch screen) on the 2D ultrasound image screen. 
         [0031]    Methods of treating AF according to a further aspect of the invention desirably include the step of preferentially applying energy to a selected cross section of the PV antrum, which section is remote from collateral structures like the esophagus. In particular, compensation for thickness variations of the PV antrum can be achieved through output power and application time adjustments. The ablation progress and the appropriate dosing of the energy are monitored preferably through ultrasound imaging from the same circular dual mode array (or a section thereof) which generates the therapeutic beam. 
         [0032]    Another aspect of the invention provides for a duplex emitter configuration to combine imaging with therapy. In the case of ultrasound energy the simplest configuration would be a single rotatable Tx structure allowing for A mode recording of the PV antrum thickness and distance from the transducer while using the same Tx for therapeutic ultrasound application in an interleaved timing mode. A more sophisticated combination consists of a dual mode circular array Tx to allow for true 2D ultrasound imaging and therapeutic ultrasound application quasi-simultaneously (interleaved) in the same plane. 
         [0033]    Apparatus according to this aspect of the invention most desirably further includes a delivery sheath having proximal and distal ends, and a sheath steering structure carried on the sheath and operative to selectively bend a region of the sheath. The catheter and the emitter unit desirably are constructed and arranged so that the distal region of the catheter and the emitter unit can be advanced into the left atrium of the heart through the sheath. The catheter may also include a catheter steering mechanism carried on the catheter and operative to selectively bend a region of the catheter proximal to the emitter unit. The apparatus may also include a guide-wire, the catheter being constructed and arranged so that the catheter can be advanced over the guide-wire or the guide-wire can be advanced through the catheter. 
         [0034]    A preferred embodiment of the invention utilizes a sensing loop shaped guide-wire. Sensing electrodes are mounted on the guide-wire loop to allow for electrical measurements distal to the ablation plane to monitor the progress of the PV isolation (entrance block) or to pace with the loop electrodes (exit block). 
         [0035]    Further objects, features, and advantages of the present invention will be more readily apparent from the detailed described embodiments set forth below, taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]      FIG. 1  is a schematic view of a distal end portion of an elongate flexible isometric (constant outer diameter) sheath, showing the placement of a circular ultrasound imaging array at the distal section of the sheath. 
           [0037]      FIG. 2A  is a schematic view of the distal end portion of the isometric sheath of  FIG. 1  inside a heart, showing the sheath as used in a typical medical procedure monitoring a trans-septal puncture. 
           [0038]      FIG. 2B  is a schematic elevational view of a video monitor or display showing an image of a cardiac septum during the ultrasound-guided procedure of  FIG. 2A . 
           [0039]      FIG. 3A  is a schematic isometric view of a distal end portion of another sheath monitoring a trans-septal puncture in a heart, the sheath having a longitudinal ultrasound imaging array. 
           [0040]      FIG. 3B  is a schematic elevational view of a video monitor or display showing an image of a cardiac septum during the ultrasound-guided procedure of  FIG. 3A . 
           [0041]      FIG. 4  is a view of the imaging sheath of  FIG. 1  in a related operating procedure, placed inside the left atrium of a heart and monitoring catheter-mediated ablation at the left superior pulmonary vein (LSPV). 
           [0042]      FIG. 5  is a schematic view of a distal end portion of a modified elongate flexible medical sheath, depicting additional ultrasound imaging components mounted into a wall of the isometric sheath. 
           [0043]      FIG. 6  is a schematic longitudinal cross-sectional view of a distal end portion of another embodiment of an elongate flexible medical sheath, in accordance with the present invention, showing an annular ultrasound imaging array divided into imaging and therapeutic sections. 
           [0044]      FIG. 7  is a schematic perspective view of an imaging/treatment catheter in accordance with the present invention, which is introduced into a patient over a circular guide wire mapping catheter. 
           [0045]      FIG. 8  is a schematic perspective view of the imaging/treatment catheter of  FIG. 7  inserted through a sheath and positioned at the left superior pulmonary vein (LSPV) inside the left atrium with a sensing loop at the distal end advanced into the LSPV. 
           [0046]      FIG. 9  is a flow chart depicting major steps of a PV isolation process utilizing the instrument of  FIGS. 7 and 8 . 
           [0047]      FIG. 10  is partially a schematic perspective view of the imaging/treatment catheter of  FIGS. 7 and 8  and partially a block diagram of a control system connected to the imaging/treatment catheter. 
           [0048]      FIG. 11  is a block diagram of selected components of an electronic control unit and image generating components of a computer unit of an apparatus in accordance with the present invention for generating ablation zones of predetermined shape on inner surfaces of hollow internal organs of a mammalian subject. 
           [0049]      FIG. 12  is a cross-sectional view of a portion of a right bronchial branch, showing a treatment catheter advanced through a bronchoscope into the right bronchial branch. 
       
    
    
     DETAILED DESCRIPTION 
       [0050]    Apparatus according to one embodiment of the invention includes a sheath  1  ( FIG. 1 ) generally in the form of an elongated tube having a proximal end  20 , a distal end  30  and a proximal-to-distal axis. As used in this disclosure with reference to elongated elements for insertion into the body, the term “distal” refers to the end which is inserted into the body first, i.e., the leading end during advancement of the element into the body, whereas the term “proximal” refers to the opposite end. 
         [0051]    Sheath  1  has an interior bore or lumen (not separately designated) extending between its proximal end  20  and its distal end  30 . Desirably, sheath  1  has a relatively stiff proximal wall section  41  extending from its proximal end  20  to a juncture  40 , and a relatively limber distal wall section or sheath end portion  42  extending from the juncture  40  to the distal end or tip  30 . One or more pull wires  44  (only one shown) are slideably mounted in the proximal wall section  41  and connected to the distal wall section or end portion  42 . The pull wire  44  is linked to a pull wire control apparatus (not shown), which can be manipulated by a physician during use of the sheath  1 . By actuating the pull wire control, the physician exerts tension on the wire  44  and bends the distal end portion  42  of the sheath  1  in a predetermined or desired direction transverse to a proximal-to-distal direction or axis  46  of the sheath. The structure of sheath  1  and pull wire control may be generally as shown in U.S. Patent Application Publication No. 2006-0270976 (“the &#39;976 Publication”), the disclosure of which is incorporated by reference herein. As discussed in greater detail in the &#39;976 Publication, transition desirably is oblique to the proximal-to-distal axis  46  of the sheath. 
         [0052]    Sheath  1  desirably also is arranged so that at least the proximal section  41  is “torquable.” That is, at least the proximal section  41  of the sheath  1  is arranged to transmit torsional motion about axis  46  from the proximal end  20  ( FIG. 1 ) along the axial extent of the sheath. Thus, by turning the proximal end  20  of the sheath  1 , one can rotate the distal wall section or end portion  42  of the sheath about the proximal-to-distal axis  46 . When the sheath is in a curved or bent configuration owing to tension on the pull wire  44 , rotational motion of the distal wall section or end portion  42  will swing the bent section around the proximal-to-distal axis  46 . Thus, by combined pulling on the pull wire  44  and rotational motion, the distal end  30  of sheath  1  and therewith an ultrasound imaging plane  47  ( FIGS. 2A ,  3 A) can be aimed in essentially any desired direction. As disclosed in the aforementioned &#39;976 Publication, the pull wire control can be incorporated into a handle which is physically attached to the proximal end  20  of the sheath  1 . Thus, the physician can maneuver the sheath  1  by actuating the pull wire control and turning the handle, desirably with one hand, during the procedure. 
         [0053]    The apparatus further includes, in the distal wall section or sheath end portion  42 , a circular array  2  of electromechanical (e.g., PZT or piezoelectric) transducer elements for ultrasound imaging. As described above, the sheath steering allows the physician to aim the sheath distal opening (at  30 ) in any direction and through the same steering operation to aim the ultrasound imaging plane  47  in any direction. 
         [0054]    In order to keep the sheath wall reasonably thin printed flexible circuits  11  (see  FIG. 5 ) are employed to electrically connect the ultrasound transducer array  2  with one or more multiplexer integrated circuits (ICs)  12 . In one embodiment this flex circuit  11  can be an outermost sheath layer dimensioned to act as a lambda/4 impedance matching layer. The acoustic impedance of this matching layer is selected to optimize the acoustic transition from the semiconductor material of the ultrasound transducers of array to body tissue or blood: Z match =SQRT(Z PZT ×Z Blood ). Preferably, several matching layers are provided. In this embodiment the ultrasound array  2 , which can consist of PZT, is mounted with a die attach film  48  onto the flex circuit  11 . The material of die attach film  48  (e.g., Henkel CF3350) and the thickness thereof are chosen so that the film acts as a second matching layer: Z MatchFilm =SQRT(Z pzt ×Z flex ) and Z MatchFlex =SQRT (Z film ×Z blood ). In an alternative embodiment the electronic circuitry is printed onto the innermost, extruded, sheath layer and then covered isometrically with an outer sheath layer which acts as one or one of several matching layers. 
         [0055]    Another desirable feature of the present imaging sheaths is to keep the overall diameter isometric (no bulge). 
         [0056]    In order to keep the sheath wall reasonably thin the number of connections with the ultrasound imaging console has to be minimized. Therefore a multiplexer approach is employed: with two 64:16 multiplexers  12  as shown in  FIG. 5 , 128 transducer elements of array  2  can be controlled with 2×16 signal lines plus supply voltage and control lines  13  running within the sheath wall from proximal end  20  to the distal end portion  42 . For 3D imaging 2-dimensional arrays are required and several (n) multiplexers are employed to reduce the high array element numbers by n×64 (in case of 64:16 multiplexers). 
         [0057]    At the proximal end the lines are terminated in a connector  52  ( FIG. 5 ) which is mated with a connector cable  54  from a control unit  56  which feeds a video signal to an imaging console or display  58 . This connector cable  52  is supplied sterile and one end placed by the sterile operator in the sterile field (to be connected to the imaging sheath) while the other end is connected to the system in the non-sterile field. 
         [0058]    Particular attention has to be paid to the backing of array  2 . For imaging purposes highly absorptive backing is desirable. This contradicts with the size requirements to keep the sheath wall acceptably thin. Accordingly, minimal backing is applied to array  2  of sheath  1 . Rather than absorbing the backwards emitted ultrasound portion a diffraction layer  60  is employed to cause the backward-propagating ultrasound waves to bounce back and forth in chaotic fashion within the blood filled sheath  1 . This way the backwardly emitted ultrasound is prevented from generating reverberations within the ultrasound image. Diffraction layer  60  may be made of polyimide with a conductive layer, for example, Pyralux from DuPont. 
         [0059]    A further variation of an combined imaging/therapy sheath, depicted in  FIG. 6 , includes a tubular member  61  provided with a split transducer array  64 , where one circular or annular section  62  is optimized for imaging with the above described diffraction mechanism (layer  60 ) and another circular or annular section  68  optimized for therapy. The therapy section  68  employs a metallic backing  70  to reflect a backward-propagating ultrasound wave front forward. Preferably the reflector backing  70  is spaced by a water-filled gap or distance  71  of lambda/2 behind an inner or rear surface of the transducer section  68 .  FIG. 6  also depicts electrodes  72 ,  74  sandwiching a piezoelectric or PZT layer  76 , a die attach film  78 , and flex circuit layer  80  in the imaging transducer section  62 , with an analogous structure being present in the therapy transducer section  68 . The split array configuration is described in further detail hereinafter. 
         [0060]    Numerous other variations and combinations of the features discussed above can be utilized without departing from the present invention as defined by the claims. For example, the emitter structure can be slideably mounted within the sheath so that the sheath stays in place during the procedure. In still other arrangements, several emitters might be mounted on the sheath in a chain like fashion in order to apply energy over the length of the sheath portion inserted into the organ to be treated. Again this configuration does not require a movement of the sheath during treatment. In still other embodiments, focusing apparatus, such as lenses and diffractive elements can be employed in particular for short axis focusing of the ultrasonic energy. The right atrial position in case of intra cardiac procedures allows the user to obtain real time guidance of the trans-septal puncture as well as the catheter ablation itself. 
         [0061]    The right atrial sheath position in case of intra cardiac procedures allows the user to obtain real time guidance of the trans-septal puncture as well as the catheter ablation itself. As depicted in  FIG. 2A , sheath  1  in percutaneously inserted into the venous vascular system of a patient so that the distal wall section or sheath end portion  42  is disposed in the patient&#39;s right atrium RA. Sheath  1  carries circumferential imaging array  2 . A Brockenbrough needle  4  is advanced through sheath  1  under ultrasound imaging guidance to puncture the septum SP. The user will observe the tenting effect of the needle  4  on the septum SP in the ultrasound image  10  on display  58  ( FIG. 2B ). This will allow the user to choose an optimal puncture site and reduce the chances for collateral damage. 
         [0062]      FIG. 3A  shows a variation of the procedure of  FIG. 2A , with a sheath  72  having a longitudinal ultrasound imaging array  74 .  FIG. 3B  shows an associated ultrasound-obtained image  10  on display  58 . 
         [0063]    All left sided cardiac interventions require a trans-septal puncture to be performed. As described above ultrasound guidance has great value since tenting of the septum clearly indicates the puncture site. Once the septum has been crossed the imaging sheath  1  can be advanced into the left atrium LA to guide the therapeutic procedure. The case of an AF treatment procedure, a distal end portion (not separately enumerated) of an ablation catheter  5  is ejected from sheath  1  and maneuvered into a pulmonary vein, e.g., left superior pulmonary vein LSPV, as shown in  FIG. 4 . 
         [0064]      FIG. 7  illustrates related catheter-based composite imaging and therapy apparatus adapted for performing a pulmonary vein isolation procedure in treatment of atrial fibrillation. The same or similar apparatus can be used for forming annular ablations along inner surfaces of other tubular or hollow organs such as the urinary tract, the esophagus and bronchial tubes. 
         [0065]    An expansible structure in the form of a balloon  109  ( FIG. 7 ) is mounted to a distal end of a catheter  105 . In the inflated, operative condition the balloon  109  provides a water/contrast filled volume to cool an energy emitter in case of ultrasound energy and to make it easily visible in fluoroscopy. 
         [0066]    A tubular, cylindrical ultrasonic transducer array  112  is mounted to catheter  105  inside balloon  109 . Transducer array  112  includes a plurality of electrically isolated and independently energizable piezoelectric or PZT transducer elements organized into a therapy transducer section  202  and an imaging transducer section  204  ( FIG. 7 ). Therapy transducer section  202  is backed either with air or at a lamda/2 distance with a metal reflector ( 70 ,  FIG. 6 ) in water to reflect most ultrasound energy forward or outwardly into an active beam segment  114  which will overlap with the antrum of a PV annulus section being treated. In case of a reflector the space between the piezoelectric or PZT transducer elements and the reflector communicates with an interior cooling fluid filled space  206  within balloon  109  which provides additional cooling for the transducer  112 . Metallic coatings (see  72 ,  74 ,  FIG. 6 ) on the interior and exterior surfaces of the array elements (or front and back in case of a planar design) serve as excitation or poling electrodes and are connected to a ground wire  208  and a signal wire  210  which extend through a wiring support tube to the distal end of the catheter. The wires  208  and  210  are connected to an ultrasonic excitation source  115  ( FIG. 10 ) and a console or monitor  213  of an ultrasound imaging system. The process of forming such cylindrical arrays is well known and described in the prior art, see Eberle U.S. Pat. No. 6,049,958. 
         [0067]    Electrical connection of the piezoelectric elements of array  112  with generator  115  and an imaging display or monitor  213  of a control system  156  ( FIG. 10 ) is best achieved through flex circuit strip lines. In order to reduce the line count, multiplexer IC&#39;s can be deployed at the distal end of catheter  105 , preferably close to ultrasound array  112 . (See  12 ,  FIGS. 5 and 6 .) Of advantage are multiplexer circuits directly deposited at the distal end of the strip lines in a staggered fashion to keep the catheter diameter small. 
         [0068]    The interior space  206  within balloon  109  is connected to a circulation device  116  ( FIG. 10 ) for circulating a liquid, preferably an aqueous liquid, from a liquid source or supply  211  through the balloon to cool the ultrasound transducer  112  in order to avoid blood coagulation. Circulation device  116  includes at least one pump. As further discussed below, during operation, the circulation device  116  continually circulates the aqueous fluid through the balloon  109  and maintains the balloon under a desired pressure and temperature. 
         [0069]    Catheter  105  is deployed via a sheath  100  ( FIG. 8 ) generally in the form of an elongated tube having a proximal end, a distal end and a proximal-to-distal axis. Sheath  100  is advanced over a guide-wire through femoral access into the right atrium. After a septal puncture has been performed the catheter  105  is advanced through the sheath  100  into the left atrium LA ( FIG. 8 ). 
         [0070]    Treatment catheter  105  is advanced under ultrasound image guidance until the antrum of the selected pulmonary vein (PV) is clearly visualized. Treatment catheter is advanced further so that ultrasound transducer array  112  is positioned within the antrum of a selected pulmonary vein (PV) (step  160 ,  FIG. 9 ). Ultrasound imaging guidance will reduce the need for fluoroscopic imaging and cut down on ionizing radiation. Once the treatment catheter has been positioned and mechanically stabilized by means of a sensing loop catheter  212  the ablation process can be controlled through the imaging system from the control room (steps  162 ,  FIG. 9 ). Interactively ablation targets are identified in the image with markers (step  164 ,  166 ). The markers are instructions input to the control unit  156  ( FIG. 11 , or  56 ,  FIG. 5 ), exemplarily via a touch screen ( 58 ,  213 ) or a keyboard and/or mouse input device ( 215 ), that indicate the location of a desired ablation on the organic structures represented in the displayed image. As discussed hereinafter in detail with reference to  FIG. 11 , the control system  156  translates these ablation markers into focusing, power and time parameters to control the ablation beam in the desired location and to ablate a lesion of the appropriate depth. During the ablation process the ablation site is monitored via ultrasound in an interlaced mode to allow the user to control the ablation process under essentially real time visualization. Since ablated tissue increases ultrasound reflectivity an intensity change can be observed during ablation. Ablated tissue clearly shows higher reflectivity than non ablated tissue so that the ablation can be terminated when a transmural lesion has been obtained. 
         [0071]    With the catheter in the operative position, the energy field  114  ( FIG. 7 ) is aligned with one point of the PV antrum image. In other words the therapy transducer section  202  is set under programming to focus ultrasonic vibration energy on the antrum wall at a particular location. The imaging transducer section  204  communicates, to the computer system control unit  156 , ultrasonic waveform data from which the computer calculates distance of the therapy transducer section  202  from the atrial wall and the thickness of the atrial wall at the particular location of the antrum. More specifically, ultrasonic waveform generator  115  transmits an electrical signal of one or more pre-established ultrasonic frequencies to a selected transmitting transducer element of transducer array  112 . Reflected ultrasonic waveform energy from internal organic structures of the patient is detected by sensor transducer elements of imaging transducer section  204  and processed by a preprocessor  214 . Preprocessor  214  is connected to a signal analyzer  216  that computes dimensions and shapes of the internal organic structures. Output of analyzer  216  is organized and compared by a distance detector  218  to determine the distance of therapy transducer section  202  from the target location on the antrum or atrial wall, while an organ thickness detector  220  operates to compare echo signals to thereby determine the thickness of the pulmonary vein at the target location. Distance detector  218  and thickness detector  220  are connected to a therapy signal control module  222  that controls signal generator  115  to so energize the piezoelectric or PZT elements of therapy transducer section  202  in a phased array operation mode as to focus ultrasonic mechanical waves on the target location for a limited ablation time and power. Control module  222  may include a calculation submodule for determining the power and duration parameters of each ablation burst of ultrasonic mechanical waveform energy. The user can monitor the lesion formation in the ultrasound image on display console  213  and override the therapy system if so desired. 
         [0072]    Control unit  156  includes an interface  224  for monitoring instructions input by the user via touch screen ( 60 ,  213 ) or keyboard and mouse ( 215 ). Signal analyzer  216  is connected to an image signal generator  226  that produces a video signal for display console  213  (or  60 ) and interface  224  is connected to control module  222  which interprets user directions in conjunction with the organic structures of the patient as detected, encoded and at least temporarily stored in memory  228  by analyzer  216 . 
         [0073]    As indicated above, ablation preferably in stepwise fashion around a circumferential locus defined by the user or surgeon via the input ablation markers. A neighboring ablation position is chosen as indicated in  FIG. 9  and so on until a circumferential, continuous lesion has been created. 
         [0074]    With the treatment catheter  105  and transducer array  112  in the operative position, the ultrasonic excitation source or waveform generator  115  actuates the therapy transducer section  202  of transducer array  112  to emit ultrasonic waves. Merely by way of example, the ultrasonic ablation waves (which are longitudinal compression waves) may have a frequency of about 1 MHz to a few tens of MHz, most typically about 8 MHz. The transducer typically is driven to emit, for example, about 10 watts to about 100 watts of acoustic power, most typically about 40 to 50 watts. The actuation is continued for about 10 seconds to about a minute or more, most typically about 20 seconds to about 40 seconds per lesion. Optionally, based on the ultrasound image the actuation may be repeated several times. The frequencies, power levels, and actuation times may be varied from those given above. 
         [0075]    The various components of control unit  156  may be hard wired circuits designed to perform the specific computations discussed herein. Alternatively, control unit  156  may take the form of a generic microprocessor or computer with the components realized as generic digital circuits modified by programming to carry out the delineated functions. 
         [0076]    The ultrasonic waves generated by the transducer array  112  propagate generally radially outwardly from the transducer elements, outwardly through the liquid within the balloon  109  to the wall of the balloon and then to the surrounding blood and tissue. The ultrasonic waves impinge on the tissues of the heart particularly on the PV antrum. Because all of the liquid within the balloon and the blood surrounding the balloon have approximately the same acoustic impedance, there is little or no reflection of ultrasonic waves at interfaces between the liquid within the balloon  109  and the blood outside the balloon. 
         [0077]    Essentially all of the annulus within the PV antrum lies within the “near field” region of the transducer and particularly the therapy transducer section  202 . Within this region, the outwardly spreading segmental beam  114  of ultrasonic waves tends to remain focused not only in the cross-sectional plane but also in elevation axis and has an axial length (the dimension of the beam along the catheter axis; see drawings in  FIGS. 1 and 2 ) approximately equal to the axial length of the transducer section  202 . 
         [0078]    The ultrasonic energy applied by the therapy transducer section  202  is effective to heat and thus necrose a section of the annulus in the PV antrum. A circular lesion formed by a continuous series of sectional ablations creates a conduction block which may be confirmed through lack of PV potentials detected with the loop sensing catheter  212 . (Catheter  212  carries a series of mutually spaced sensing electrodes  224  that detect voltage potentials in the cardiac tissue.) The circumferential lesion may take on a variety of shapes (oval or more complicated shapes) and depends on the surrounding anatomy of the PV antrum. The advantage of this approach is that all anatomical variations can be safely treated by moving the ablation plane axially to avoid ablating collateral structures and or by tilting the ablation plane by bending the distal portion of ablation catheter  105 . 
         [0079]    Numerous other variations and combinations of the features discussed above can be utilized without departing from the present invention as defined by the claims. For example, the emitter structure or transducer array  112  can be slideably mounted within the catheter so that the catheter stays in place during the treatment. In still other arrangements, several emitters might be mounted on the catheter in a chain like fashion in order to apply energy over the length of the catheter inserted into the left atrium. Again this configuration does not require a movement of the catheter during treatment. In still other embodiments, focusing devices, such as lenses and diffractive elements can be employed in case of ultrasonic energy. 
         [0080]    The state of the lesion annulus within the PV antrum can be monitored by ultrasound imaging during the treatment. During treatment, the tissue changes its physical properties, and thus its ultrasound reflectivity when heated. These changes in tissue ultrasound reflectivity can be observed using ultrasonic imaging to monitor the formation of the desired lesion in the annulus within the PV antrum. Other imaging modalities which can detect heating can alternatively or additionally be used to monitor the treatment. For example, magnetic resonance imaging can detect changes in temperature. In the case of reliance on non-ultrasound imaging modalities, it is optional to include the imaging transducer section  204  as part of the ultrasound transducer array  112 . 
         [0081]      FIG. 12  depicts use, in the bronchial system, of a combined imaging and treatment catheter  310  as exemplarily described hereinabove with respect to catheter  5 . Catheter  310  includes a composite or dual-mode transducer array  311  surrounded by a fluid-containing balloon  312 . Catheter  311  is advanced through a bronchoscope  305  (or a sheath) and over a guide wire  314  into the right bronchial branch  301  and a portion of the transducer array  311  is activated to treat bronchial or lung tissues. The ultrasound treatment volume is indicated at  313 . In its inflated condition, bladder  312  engages the bronchial wall and therewith allow for ultrasound to be conducted from transducer into the bronchial wall and surrounding tissues. Transducer array  311  is of a tubular shape and has an exterior composite emitting surface (an array of emitting surfaces) in the form of a cylindrical surface of revolution about the proximal-to-distal axis of the transducer array  311 . The transducer array  311  typically has an axial length of approximately 2-10 mm, and preferably 6 mm. The outer diameter of the transducer array  311  is approximately 1.5-3 mm in diameter, and preferably 2 mm. 
         [0082]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.