Abstract:
A method for ablating tissue with ultrasonic energy is provided. The method including: generating ultrasonic energy from one or more ultrasonic transducers; and focusing the ultrasonic energy in the radial direction by one of: shaping the one or more ultrasonic transducers to focus ultrasonic energy in the radial direction; and arranging one or more lenses proximate the one or more ultrasonic transducers for focusing the ultrasonic energy from the one or more ultrasonic transducers in a radial direction.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to ultrasonic medical instrumentation, and more particularly, to an ultrasonic radial focused transducer for pulmonary vein (PV) ablation. 
   2. Prior Art 
   Ultrasonic transducers are used in medical instrumentation for ablation of the pulmonary veins of the heart. A distal end of such an instrument is shown in  FIG. 5 , generally referred to by reference numeral  100 . The instrument  100  has an outer sheathing  102  having an ultrasonic transducer  104  housed therein. The ultrasonic transducer  104  is operatively connected to an ultrasonic generator (not shown) by wiring. The ultrasonic generator may be integrally formed with the instrument or remote therefrom. The acoustic energy (alternatively referred to as ultrasonic energy or an ultrasonic wave) emanating from the ultrasonic transducer  104  is shown throughout this disclosure by dashed lines A. To fit within the geometry of the pulmonary vein, the ultrasonic transducer  104  is cylindrical in shape and can be hollow to create an air backing, as is known in the art. The acoustic intensity of the ultrasonic wave generated by the cylindrical transducer decreases with the distance from its surface (e.g., in the radial direction R as shown in  FIG. 6 ). In the pulmonary vein ablation, the acceptable diameter of the ultrasonic transducer  104  is also limited by the application and the approach taken so that the initial power available is also limited. As a result, the acoustic energy generated by the small diameter cylindrical transducer  104  is too low at the surface of larger diameter pulmonary veins, which can be as large as 35 mm in diameter. Therefore, the acoustic energy available is not sufficient to properly ablate the surface of the larger pulmonary veins. 
   SUMMARY OF THE INVENTION 
   Therefore it is an object of the present invention to provide ultrasonic devices and methods for their use, which overcome the disadvantages of conventional ultrasonic instrumentation known in the art. 
   Accordingly, a first embodiment of an ultrasonic instrument for ablation of tissue is provided. The first embodiment of the ultrasonic instrument comprising one or more ultrasonic transducers, the one or more ultrasonic transducers being shaped to focus ultrasonic energy in a radial direction. 
   The one or more ultrasonic transducers can comprise two ultrasonic transducers, each of the two ultrasonic transducers having a shape of a truncated cone having a truncated end, the truncated end from each of the two ultrasonic transducers being arranged to face each other. The truncated ends can be separated by a predetermined distance to form a gap. Further, a cylindrical ultrasonic transducer can be disposed in the gap. The cylindrical ultrasonic transducer can have a length substantially equal to the predetermined distance. Alternatively, the truncated ends can be separated by a variable distance to form a gap. 
   The one or more ultrasonic transducers can comprise two ultrasonic transducers separated by a gap, where the ultrasonic instrument further comprises means for varying the length of the gap. 
   In a first variation of the ultrasonic instrument for ablation of tissue according to the first embodiment, the ultrasonic instrument can comprise: a body having a distal end; one or more ultrasonic transducers, the one or more ultrasonic transducers being shaped to focus ultrasonic energy in a radial direction; and an ultrasonic generator operatively connected to the one or more ultrasonic transducers. 
   In a second variation of the ultrasonic instrument according to the first embodiment, the ultrasonic instrument can comprise: a body having a distal end; and one or more ultrasonic transducers, the one or more ultrasonic transducers being shaped to focus ultrasonic energy in a radial direction. 
   Also provided is a second embodiment of an ultrasonic instrument for ablation of tissue. The second embodiment of the ultrasonic instrument comprising: an ultrasonic transducer; and one or more lenses for focusing ultrasonic energy from the ultrasonic transducer in a radial direction. 
   The ultrasonic transducer can be cylindrical. The one or more lenses can be a single concave lens that surrounds the cylindrical ultrasonic transducer. The second embodiment of the ultrasonic instrument can further comprise a body for housing the one or more ultrasonic transducers, the body having a sidewall proximate the one or more ultrasonic transducers, the one or more lenses being integral with at least a portion of the sidewall. 
   Also provided is an ultrasonic instrument comprising: one or more ultrasonic transducers for transmitting ultrasonic energy in at least a radial direction; and focusing means for focusing the ultrasonic energy from the one or more ultrasonic transducers in the radial direction, wherein the focusing means is one of: shaping the one or more ultrasonic transducers to focus the ultrasonic energy in the radial direction; and one or more lenses for focusing the ultrasonic energy from the one or more ultrasonic transducers in a radial direction. 
   Still provided is a method for ablating tissue with ultrasonic energy where the method comprises: generating ultrasonic energy from one or more ultrasonic transducers; and focusing the ultrasonic energy in the radial direction by one of: shaping the one or more ultrasonic transducers to focus ultrasonic energy in the radial direction; and arranging one or more lenses proximate the one or more ultrasonic transducers for focusing the ultrasonic energy from the one or more ultrasonic transducers in a radial direction. 
   The one or more ultrasonic transducers can comprise two ultrasonic transducers and the shaping can comprise providing each of the two ultrasonic transducers in a shape of a truncated cone having a truncated end, the truncated end from each of the two ultrasonic transducers being arranged to face each other. 
   The method can further comprise separating the truncated ends by a predetermined distance to form a gap and disposing a cylindrical ultrasonic transducer in the gap. The method can further comprise varying the distance between the truncated ends. The one or more lenses can be a single concave lens, the one or more ultrasonic transducers can be a cylindrical ultrasonic transducer, and the arranging can comprise surrounding the cylindrical ultrasonic transducer with the single concave lens. The method can further comprise a body for housing the one or more ultrasonic transducers, the body having can have a side wall proximate the one or more ultrasonic transducers, and the surrounding can comprise integrally forming the one or more lenses with at least a portion of the side wall. The method can further comprise inserting at least a portion of the one or more ultrasonic transducers into a pulmonary vein of the heart prior to or simultaneous with the generating. The one or more ultrasonic transducers can be enclosed in an inflatable balloon, and the method can further comprise inflating the balloon to fix the one or more ultrasonic transducers in a predetermined position in the pulmonary vein. 
   The method can further comprise varying the distance to which the ultrasonic energy is focused in the radial direction. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects, and advantages of the apparatus and methods of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
       FIG. 1  illustrates a sectional view of a distal end of an ultrasonic instrument shown disposed in a pulmonary vein of the left atrium of the heart. 
       FIG. 2  illustrates a schematic view of the ultrasonic transducers of the instrument of  FIG. 1 . 
       FIG. 3  illustrates a schematic view of an alternative configuration of ultrasonic transducers for the instrument of  FIG. 1 . 
       FIG. 4  illustrates another embodiment of a distal end of an ultrasonic instrument. 
       FIG. 5  illustrates a sectional view of a distal end of an ultrasonic instrument of the prior art. 
       FIG. 6  illustrates a sectional view of the instrument of  FIG. 5  as taken along line  6 — 6  in  FIG. 5 . 
       FIG. 7  is a partial section view of an instrument having a means for varying a distance between ultrasonic transducers. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Although this invention is applicable to numerous and various types of surgical procedures, it has been found particularly useful in the environment of ablation of the pulmonary vein. Therefore, without limiting the applicability of the invention to ablation of the pulmonary veins, the invention will be described in such environment. 
   Referring now to  FIG. 1 , there is shown a first embodiment of an ultrasonic instrument for ablation of tissue, the ultrasonic instrument is generally referred to herein with reference numeral  200 . A distal end  202  of the instrument  200  is shown disposed in a pulmonary vein  204  by way of the left atrium  206  of the heart  208 . The ultrasonic instrument  200  can be configured in any number of ways known in the art, however, when accessing the pulmonary vein  204 , it is preferred to be configured as a rigid device having an articulating distal end  202  which accesses the pulmonary vein through a puncture/access port in the heart wall (which is closed after the procedure). Preferably, the rigid ultrasonic instrument  200  will have a 12–15″ long shaft operatively connected to the distal end  202  and a handle at a proximal end of the shaft. The ultrasonic instrument  200  can also be configured as a flexible catheter and introduced into the heart in any manner known in the art, such as by catherization of the heart. 
   The ultrasonic transducer generally has a body  210 . Since the diameter of the instrument  200  is preferably approximately 3 to 4 mm in diameter and the inside diameter of the pulmonary vein is approximately 25 to 35 mm, the body may have an inflatable balloon  213  which when inflated positions the instrument  200  in the mouth of the pulmonary vein  204  and fixes it in position. The balloon  213  is preferably expanded by filling it with a medium, such as water or saline from an appropriate source (not shown). 
   The ultrasonic instrument  200  comprises one or more ultrasonic transducers  216  housed in or on the body  210  (collectively referred to herein as housed in the body). The one or more ultrasonic transducers  216  are operatively connected to an ultrasonic generator  219  for generating acoustic energy to ablate tissue. The ultrasonic generator  219  may be integrally housed within the instrument or remotely connected through wiring  218 .  FIG. 1  shows two such ultrasonic transducers  220   a  and  220   b  by way of example only. The ultrasonic transducers  220   a ,  220   b  are shaped to focus ultrasonic energy A in a radial direction R. As will be discussed below, more than two may be provided or a single integrally formed ultrasonic transducer may also be provided having a shape which focuses the ultrasonic energy A in the radial direction R. However, those skilled in the art will appreciate that two or more such ultrasonic transducers are preferred for their ease of fabrication. 
   Referring now to  FIGS. 1 and 2  in combination, each of the ultrasonic transducers  220   a  and  220   b  can have a shape of a truncated cone having a truncated end  222   a ,  222   b  where the truncated ends  222   a ,  222   b  from each of the two ultrasonic transducers  220   a ,  220   b  are arranged to face each other. In  FIG. 2 , the ultrasonic transducers  220   a ,  220   b  are shown schematically outside the body  210  of the instrument  200  for illustration purposes only. The ultrasonic energy A from ultrasonic transducer  220   a  is shown as a dotted line, while the ultrasonic energy A from ultrasonic transducer  220   b  is shown as a solid line. Only one plane of ultrasonic energy A in the radial direction R is shown in the Figures, however, those skilled in the art will appreciate that the ultrasonic energy A irradiates in all radial directions around the circumference of the ultrasound transducers  220   a ,  220   b . Furthermore, although the ultrasound transducers  220   a ,  220   b  are shown as truncated cones, those skilled in the art will appreciate that other shapes which focus the ultrasound energy A in the radial direction R are possible. The ultrasound transducers  220   a ,  220   b  may be hollow to provide an air backing, as is known in the art, which may also be used for routing the wiring  218 . However, if transducers  220   a ,  220   b  are hollow, their wall thickness t should be constant along the length of the transducers  220   a ,  220   b . If the wall thickness varies, only a small part of the transducer would emit an appreciable amount of energy which may not be sufficient for creating a lesion. The ultrasound transducers  220   a ,  220   b  may be fixed in the distal portion  212  of the body  210  by any means known in the art, such as with caps  212   a ,  212   b  and/or adhesive. Furthermore, a spacer  214  may be provided between the transducers  220   a ,  220   b.    
   As shown in  FIG. 2 , the ultrasonic energy A from each of the ultrasound transducers  220   a ,  220   b , irradiate perpendicular to the conic surface  224   a ,  224   b . The conic surfaces  224   a ,  224   b  are shown to be linear, however, such surfaces may also be concavely and/or convexly shaped and may also include linear sections. If the conic surfaces  224   a ,  224   b  are curved, as discussed above, the wall thickness t should be maintained constant which may be very difficult to fabricate. 
   The energy A from each of the ultrasound transducers  220   a ,  220   b , intersect at line  226  which is rotated 360 degrees around the ultrasound transducers  220   a ,  220   b  to form a cylinder of focused energy. The line  226  of focused ultrasonic energy is at a distance D 1  from the center of the ultrasound transducers  220   a ,  220   b  and is greater than the ultrasound energy from a similarly sized cylindrical transducer of the prior art (see  FIG. 5 ). The distance D 1  is a function of the geometry of the one or more ultrasound transducers  216  including the angle α that the conic surfaces  224   a ,  224   b  make with the center of the ultrasound transducers  220   a ,  220   b  and the length of the gap G between the ultrasound transducers  220   a ,  220   b . Since the balloon  213  is filled with a medium for expanding the balloon  213 , such as water or saline, the flow of blood is blocked and the ultrasonic energy is not directed through blood that could potentially create blood clots at a hot surface of the pulmonary vein. Additionally, the water or saline provides an acoustic coupling to transmit the ultrasonic energy from the transducers  220   a ,  220   b . Furthermore, the water or saline provides cooling to the tissue and the transducers  220   a ,  220   b . Preferably, the transducers  220   a ,  220   b  are in direct contact with the water or saline (e.g., there is no sheath over the transducers  220   a ,  220   b ) to increase the efficiency by which the water or saline cools the transducers  220   a ,  220   b . The water or saline can be re-circulated through the balloon  213  to increase the cooling efficiency. 
   Those skilled in the art will appreciate that these factors can be varied to provide a focusing distance D 1  appropriate for various diameter pulmonary veins  204 . Those skilled in the art will also appreciate that the length of the gap G may be made variable with simple mechanisms known in the art, thus eliminating the need for manufacturing instruments  200  corresponding to various focusing distances D 1  for various pulmonary vein geometries. 
   Referring now to  FIG. 7 , there is shown an instrument having means for varying the length of the gap G between the ultrasonic transducers  220   a ,  220   b , the instrument generally referred to by reference numeral  400 . In instrument  400 , one of the transducers  220   a  is fixed as described previously with regard to  FIG. 1 . However, the other transducer  220   b  is movable distally towards the fixed transducer  220   a  and/or proximally away from the fixed transducer  220   a  to vary the gap G between the transducers  220   a ,  220   b . The movable transducer  220   b  is preferably mounted on a tubular bearing  402  that is slidingly disposed over the body  210 . The tubular bearing includes a projection  404  that projects into an interior of the body  210  through a slot  406 . At a proximal end  408  of the instrument  400 , or merely at a location proximal to the distal end  202 , there is provided a means for controlling the movable transducer  220   b  to move distally and/or proximally. Preferably, such means comprises a handle  410  having a lever  412  rotatably disposed in the handle  410  through a slot  414  such that a portion of the lever  412  is exterior to the handle  410  and a portion of the lever  412  is interior to the handle  410 . The lever  412  is preferably rotatably disposed by way of a pin  416  fixed to the handle  410  and rotatably disposed on the lever  412 . A control rod  420  is rotatably disposed at an end of the lever  412  internal to the handle  410  by way of a pin  420 . The control rod  418  is preferably disposed in an interior of both the handle  410  and body  210  and rotatably connected to the projection  404  by a pin  422 . Operation of the lever  412  in the direction of B+ serves to move the movable transducer  220   b  proximally to increase the gap G and focus the ultrasound energy at a greater distance D 2  while operation of the lever  412  in the direction of B− serves to move the movable transducer  220   b  distally to decrease the gap G and focus the ultrasound energy at a smaller distance D 1 . The lever  412  may be biased, such as with a spring (not shown), in either the B− or B+ directions. Furthermore, the lever  412  may be provided with a locking means for locking the lever  412  (and movable transducer  220   b ) in a predetermined position, such as with a ratchet mechanism (not shown). Still further, the handle  410  and/or lever  412  may be provided with markings (not shown) that indicate the length of the gap G and/or focusing distance D at any given position of the lever  412 . 
   Although, the means for varying the length of the gap G is shown and described as moving one of the ultrasonic transducers  220   b  and fixing the other  220   a , those skilled in the art will appreciate that both ultrasonic transducers  220   a ,  220   b  can be moved. Furthermore, although the means for varying the length of the gap G is shown and described as actively moving one of the ultrasonic transducers  220   b  distally and/or proximally, those skilled in the art will appreciate that the movable ultrasonic transducer  220   b  may be actively moved in only one direction, such as proximally, and be biased, such as with a spring, in the other direction. Thus, in such a configuration, a cable may be used to actively pull the ultrasonic transducer proximally and locked into a predetermined position. Releasing the ultrasonic transducer from the predetermined position will automatically cause the transducer  220   b  to move distally under the biasing force of the spring. 
   Referring now to  FIG. 3 , there is shown an alternative ultrasound transducer geometry, generally referred to by reference numeral  216   a . As in  FIG. 2 , the ultrasound transducers in  FIG. 3  are shown schematically outside the body  210  for the sake of simplicity. Furthermore, as also discussed previously with regard to  FIG. 2 , the ultrasonic energy A is shown irradiating in only a single radial direction R for the sake of simplicity. In the alternative ultrasound transducer  216   a  of  FIG. 3 , a cylindrical ultrasonic transducer  228  is disposed in the gap G. Therefore, the amount of energy focused at line  226   a  can be greater than that focused at line  226  of  FIG. 2  (assuming all other geometry is the same). However, in order to accommodate the cylindrical ultrasound transducer  228  in the gap G, the length of the gap G may be increased which increases the distance D 1  to D 2  (assuming all other geometry is the same). Although not necessary, the cylindrical ultrasonic transducer  228  can have a length substantially equal to the length of the gap G. 
   Referring now to  FIG. 4 , there is shown a second embodiment of an ultrasonic instrument for ablation of tissue, the ultrasonic instrument being generally referred to by reference numeral  300 . Like the ultrasonic instrument  200 , the ultrasonic instrument  300  focuses ultrasonic energy A in the radial direction R. The ultrasonic instrument  300  comprises a body  302  which may be formed of a rigid distal portion  304  and a flexible insertion portion  306 . The body  302  houses an ultrasonic transducer  308  therein, which may be cylindrically shaped. The cylindrical ultrasonic transducer  308  may be retained in the body  302  by way of stepped portions  302   a  and/or adhesive. Furthermore, the distal portion  304  of the body  302  may be fastened to the insertion portion  306  by any means known in the art such as by a mechanical crimp or adhesive. The cylindrical ultrasound transducer  308  is operatively connected to an ultrasonic generator (not shown) by way of wiring  310 . As discussed above, the ultrasonic generator may be integrally housed in the instrument  300  or remote therefrom. 
   The ultrasonic instrument  300  further has one or more lenses  312  for focusing ultrasonic energy A from the ultrasonic transducer  308  in the radial direction R. The one or more lenses  312  can be fabricated from any material known in the art for focusing ultrasonic energy, such as aluminum, titanium and some types of plastics. The one or more lenses  312  can be a single concave lens that surrounds the cylindrical ultrasonic transducer  308 . Alternatively, the one or more lenses  312  can be a series of concave lenses that surround the cylindrical ultrasonic transducer  308 . The one or more lenses  312  may also be convexly shaped depending upon the speed of sound through the material of the lenses  312  relative to the speed of sound through water/tissue. Furthermore, the one or more lenses  312  can be integrally formed with at least a portion of a sidewall of the body  302 . However, the one or more lenses  312  can also be separately provided from the body  302 . 
     FIG. 4  illustrates the one or more lenses  312  as having a simple concavity  314  for focusing the ultrasonic energy A in the radial direction R at point  316 . Thus, the ultrasonic energy A from the ultrasonic transducer  308  is focused at point  316  in all radial directions (e.g., to form a ring of focused energy). Those skilled in the art will appreciate that other shapes for the one or more lenses  312  are possible, such as multiple concavities, which may be connected with straight sections or concavities having less or more of a curvature. Thus, the focusing of the energy, and the lesions resulted therefrom, can be customized for a particular procedure. Furthermore, the ultrasonic transducers  220 ,  220   b  of  FIG. 2  may be used in combination with the one or more lenses  312  and/or cylindrical shaped transducers  308  of  FIG. 4  to further customize the type of lesions that can be created. Still further, the ultrasonic transducers  220 ,  220   b  of  FIG. 2  may be used in combination with the one or more lenses  312  and/or cylindrical shaped transducers  308  of  FIG. 4  and each can be selectively activated to provide a single instrument capable of forming various types of lesions. 
   Although the embodiment of  FIG. 4  is shown and described as having a rigid distal end, it may also be configured similarly to that shown in  FIG. 1  where the conical transducers are replaced with a cylindrical transducer and one or more lenses. 
   The use of the ultrasonic transducers described above will now be briefly explained with regard to  FIG. 1  and by way of example for use in creating lesions in the pulmonary veins of the heart. The distal portion  212 ,  304  of the ultrasonic instrument  200 ,  300 , preferably in the form of a catheter, is advanced to the left atrium  206  of the heart  208  by any means known in the art, such as by catherization of the heart. The distal portion  212 ,  304  is inserted into a pulmonary vein  204  of the heart  208  and advanced until proximate an area in which the lesion is desired. The balloon  213  is then expanded by supplying water or saline (or other inflation medium) to the interior of the balloon  213  to fix the distal end of the catheter in the located position. The ultrasonic generator is then operatively connected to the ultrasonic transducers  220   a ,  220   b ,  228 ,  308 . The ultrasonic energy A produced by the transducers  220   a ,  220   b ,  228 ,  308  is focused according to the geometry of the transducers, lenses, and/or arrangement of the transducers relative to each other to create one or more lesions on the inner surface of the pulmonary vein  304 . The balloon  213  is then deflated and the procedure is repeated as necessary in other pulmonary veins. Such lesion patterns have been found to be beneficial in controlling cardiac arrhythmias, particularly atrial fibrillation. 
   While there has been shown and described what is considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.