Abstract:
A device is for thermal treatment of tissue. The device includes (a) an elongated member extending from a proximal end to a distal end insertable to a target position within a body; (b) a housing coupled to the distal end of the elongated member sized and shaped for insertion to a target organ within a living body, the housing including an opening permitting fluid surrounding the housing to enter the housing, the housing further including first and second deflecting elements shaped to diffuse pulses of fluid directed thereagainst; and © a piezoelectric element mounted within the housing between the first and second deflecting elements. The piezoelectric element is oriented to generate pulses in liquid received within the housing toward the first and second deflecting elements.

Description:
PRIORITY CLAIM 
     This application is a which is Continuation application of U.S. patent application Ser. No. 12/748,964 filed on Mar. 29, 2010, now U.S. Pat. No. 8,287,472; which claims the priority to U.S. Provisional Application Ser. No. 61/174,225 on Apr. 30, 2009. All applications/patents are expressly incorporated herein, in their entirety, by reference. 
    
    
     BACKGROUND 
     sound energy has been applied to tissue for various thermal treatments and has been used in mechanical actuators based on motion/deformation of a piezoelectric element. Separately, heated fluids have been employed in the thermal treatment of tissue such as ablation. For example, in hydrothermal ablation, fluid heated to approximately to 90° C. is introduced into the uterus to ablate the lining thereof. To ensure even temperature distribution, this fluid must be agitated and circulated within the uterus via, for example, an external heater and pump. The fluid is heated as it passes through the heater while being pumped in a cycle into and out of the uterus. However, as this fluid circulates in and out of an organ such as the uterus, tissue particles in the fluid may become lodged in the external heater or the pump reducing the circulation of the fluid and the uniformity of the ablation of the endometrium. 
     SUMMARY OF THE INVENTION 
     The present invention is a method and a device to deliver heat and mechanical agitation to a liquid. More specifically, the present invention is directed to a method and device for thermal treatment of tissue within a living body, the device comprises a housing extending from a distal end to a proximal end, the housing including a first opening exposing an inner chamber of the device to the fluid, the housing being sized and shaped for insertion to a target location within the body and a piezoelectric element fixed within the housing and generating pulses of ultrasound energy directed substantially along a longitudinal axis of the housing in combination with first and second deflecting elements, the first deflecting element being mounted within the housing on a distal side of the piezoelectric element, the second deflecting element being mounted within the housing on a proximal side of the piezoelectric element, the first and second deflecting elements deflecting a portion of ultrasound energy from the piezoelectric element away from the axis of the housing so that the deflected ultrasound energy exits the housing via the first opening. In general, this invention reveals a method and device to deliver heat and agitation in a liquid using ultrasound. 
     The present invention is further directed to a method, comprising immersing a device in a fluid within a living body, the device including a housing extending from a distal end to a proximal end and including openings exposing an inner chamber of the device to the fluid, a piezoelectric element mounted within the housing aligned so that, when excited, the piezoelectric element generates pulses of ultrasound energy directed substantially along a longitudinal axis of the housing and first and second deflecting elements, the first deflecting element being mounted within the housing on a distal side of the piezoelectric element and the second deflecting element being mounted within the housing on a proximal side of the piezoelectric element. The piezoelectric element is excited to generate ultrasound energy of a desired frequency and amplitude directed toward the first and second deflecting elements so that a portion of the ultrasound energy impinging on the first and second deflecting elements is deflected therefrom to target tissue. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective view of a device according to an exemplary embodiment of the present invention; 
         FIG. 2  shows an enlarged perspective view of the device of  FIG. 1 ; 
         FIG. 3  shows an enlarged perspective view of the device of  FIG. 1  with a portion of a housing of the device removed; 
         FIG. 4  shows the device of  FIG. 1  in which a piezoelectric element generates ultrasound energy; and 
         FIG. 5  shows the device of  FIG. 1  heating and agitating a fluid. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention, which may be further understood with reference to the following description and the appended drawings, relates to devices for thermal treatment of tissue. Exemplary embodiments of the present invention heat and/or agitate fluids within a living body (e.g., within a hollow organ) to treat tissue. One exemplary procedure that will be described below is hydrothermal ablation of the lining of the uterus. It should be noted, however, that although the embodiments of the present invention are described in regard to the ablation of the endometrium, the invention is relevant to the use of an ultrasound device which heats fluids within the body for any thermal treatment of tissue and may be employed, for example, in organs such as the urinary bladder, the stomach, etc. 
       FIGS. 1-5  show a device  100  according to an exemplary embodiment of the present invention. As shown in  FIG. 1 , the device  100  may be connected to an external power source  150  via a flexible elongate member  160 . The device  100  may be mounted on a distal end  162  of the elongate member  160  while the power source  150  may be connected to a proximal end  164  such that the power source  150  may remain external to the body when the device  100  is inserted into the body. Once inserted, the device  100  may be immersed in a fluid  170  within the body (e.g., within an organ such as the uterus). As shown in  FIG. 2 , the device  100  may further comprise a piezoelectric element  102 , a pair of deflecting elements  104 ,  106 , a housing  108  and a transmission line  110 . The piezoelectric element  102  and the deflecting elements  104 ,  106  between which the piezoelectric element  102  is positioned are held in the housing  108  while the transmission line  110  extends from the piezoelectric element  102  to the external power source  140  along or within the elongate member  160  to transmit power (e.g., RF energy) from the power source  150  to the device  100 . 
     As shown in  FIG. 3 , the piezoelectric element  102  may be formed as a thin, substantially flat disc fixed within the housing  108  with first and second surfaces  112 ,  114 , respectively, thereof substantially exposed while an outer perimeter  116  thereof remains encased by the housing  108 . The piezoelectric element  102  may be manufactured of any known material exhibiting a piezoelectric effect such as, for example, crystals and ceramics. One such suitable material is PZT (i.e., lead zirconate titanate). As understood by those skilled in the art, the piezoelectric effect generates mechanical stress in the material when an electric potential is applied thereto. Thus, the first and second surfaces  112 ,  114  are metal-plated (e.g., silver, nickel and gold) such that an electric potential may be applied across the piezoelectric element  102 . The transmission line  110  may be formed, for example, as an elongated electrically conducting member a distal end  116  of which is attached to the piezoelectric element  102  while a proximal end  118  thereof is accessible at a proximal end  122  of the device  100  for coupling to an external source of electric energy  150 . When pulsed electrical energy is transferred to the piezoelectric element  102  via the transmission line  110 , the changes in electric potential applied thereto cause the piezoelectric element  102  to vibrate, creating pressure pulses adjacent to the first and second surfaces  112 ,  114 . Ultrasound energy in the form of pulses in the fluid  170  moves away from the first and second surfaces  112 ,  114 , substantially perpendicular to those surfaces as shown in  FIG. 3 . As the piezoelectric element  102  is positioned between the two deflecting elements  104 ,  106 , the ultrasound energy is reflected out of the housing  108  from one of the deflecting elements  104 ,  106 . 
     The deflecting elements  104 ,  106  are fixed to the housing  108  on either side of the piezoelectric element  102  with the distal surface  112  of the piezoelectric element  102  facing a first one of the deflecting elements  104  while the proximal surface  114  faces the second deflecting element  106 . The first deflecting element  104  is fixed at a distal end  120  of the housing  108  while the second deflecting element  106  is fixed at the proximal end  122  of the housing  108 . The arrangement of the piezoelectric element  102  within the housing  108  generating pulses directed substantially along the longitudinal axis thereof and deflecting elements  104 ,  106  to diffuse and redirect this ultrasound energy out of the housing  108  prevents the bulk of the ultrasound energy from directly impacting and burning the tissues of the uterus. The deflecting elements  104 ,  106  are preferably shaped such that the ultrasound energy from the piezoelectric element  102  is not directly reflected therefrom but is scattered to distribute the energy over a wider tissue surface area. For example, a surface  124  of the deflecting element  104  and a surface  126  of the deflecting element  106  may be substantially spherically convex such that the pulses of ultrasound energy are dispersed upon reflection therefrom. Each of the surfaces  124 ,  126  may also include a plurality of protrusions  128 ,  130 , respectively, which roughen the surfaces  124 ,  126  to further scatter the ultrasound energy in various directions. To deflect the ultrasound energy in a directional stream for better heat transfer and distribution to a desired target area, the surfaces  124 ,  126  may be angled with respect to a plane of the piezoelectric element  102 . In a preferred embodiment, the surface  124  may be angled in a direction opposite that of the surface  126  such that pulses of ultrasound energy which contact these angled surfaces  124 ,  126  are scattered in opposite directions to form a generally circulatory pattern of fluid flow. Thus, the surface  124  agitates the fluid  170 , causing it to circulate through the organ without being overwhelmingly directed to a single spot which would otherwise be burned. 
     If desired, the deflecting elements  104 ,  106  may be formed to absorb a portion of the ultrasound energy and convert it to heat to heat the surrounding fluid  170 . The deflecting elements  104 ,  106  may be formed of a thermally conductive ceramic, such as Aluminum Silicone Carbride, which is manufactured by CPS Technologies Corporation (Norton, Mass.). A thermally conductive material allows for quick heat dissipation. For optimal coupling of the ultrasound energy, an acoustic impedance of the ceramic should match the acoustic impedance of the fluid  170 . It will be understood by those of skill in the art that the closer the two values are to one another, the more acoustic energy the deflecting elements  104  will absorb. For example, the acoustic impedance of ceramic, Z ceramics =˜36 Mrayls, while the acoustic impedance of a fluid  170  such as water is Z water =1.5 Mrayls. Because of the substantial difference in acoustic impedance values, the deflecting element  104  will have difficulty coupling the ultrasound energy. However, any ultrasound energy that is coupled from the fluid into the deflectors, would be quickly converted into heat which would then be conducted into the fluid. A significant portion of the ultrasound energy impinging on the deflecting elements  104 ,  106  will be reflected from the deflecting elements  104 ,  106  because of the difference in acoustic impedance between the water and the material of the deflecting elements  104 ,  106 . Thus, a desired ratio of ultrasound energy reflected from the deflecting elements  104 ,  106  to energy coupled and absorbed thereby, may be achieved by selecting a composition of the deflecting elements  104 ,  106  to have an acoustic impedance which differs from that of the fluid  170  by an amount corresponding to the desired ratio. 
     So that the deflecting elements  104 ,  106  may better couple the ultrasound energy, the surfaces  124 ,  126  thereof may be coated with a thin layer of thermally conductive UV cured epoxy, filled with ceramic powder. One example of such an epoxy is manufactured by Dymax Corporation (Torrington, Conn.). The acoustic impedance of this UV cured epoxy layer is Z layer =˜5-7 Mrayls, which would make the acoustic impedance of the deflecting elements  104 ,  106  very close in value to the acoustic impedance of water since the acoustic impedance of the perfect matching layer would be calculated as Z layer =√(Z water XZ ceramics )=√(1.5×36)=7.3 Mrayls. For this particular Dymax manufactured UV cured epoxy layer, the thickness of the layer may be a multiple of an odd number of quarter wavelengths (i.e., (2n+1)×¼λ). The wavelength, λ is a function of a sound velocity in the material V and frequency F of the piezoelectric element vibration with λ=V/F. For example, if the velocity of sound in the ceramic filled epoxy is V=2×10 6  mm/sec and the frequency of excitation of the piezoelectric element is F=16 MHz=16×10 6  cycles/sec, then λ=(2×10 6  mm/sec)/(16×10 6  cycles/sec)=0.125 mm. This wavelength may be used to determine a desired thickness of the matching layer. It will be understood by those of skill in the art that various matching layers and frequencies may be used depending on the fluid  170  within which the piezoelectric element  102  will be immersed and on the material of the piezoelectric element  102 . It will also be understood by those of skill in the art that higher the frequencies allows for faster absorption of the ultrasound energy by the fluid  170  and the deflecting elements  104 ,  106 . In a preferred embodiment, the frequency may range from 5-100 MHz. 
     In another embodiment, the deflecting elements  104 ,  106  may be formed of a highly porous hydrophilic ceramic. An example of such a material is manufactured by Soilmoisture Equipment Corporation (Santa Barbara, Calif.). The open pore structure of the material provides a convoluted path of interconnecting networking channels, allowing a complete flow throughout the material for migrating fluid  170 . This allows efficient coupling of the mechanical energy from the fluid  170  into the deflecting elements  104 ,  106  and conversion of the energy into heat within the deflecting elements  104 ,  106 . It will be understood by those of skill in the art that a variety of porous materials may be selected for the deflecting elements  104 ,  106  depending on an appropriate pore size and void volume, which would be selected for optimal performance. 
     As would be understood by those skilled in the art, the device  100  may include a flexible insertion section similar to those of endoscopes and other minimally invasive surgical instruments with the housing  108  mounted at a distal end thereof. For such a device  100 , the housing  108  which encases the piezoelectric element  102  and the deflecting elements  104 ,  106  will be sized and shaped such that the device  100  may be inserted into the body via a naturally occurring bodily orifice and advanced through a body lumen to a target site therein or to an extralumenal target site. The housing  108  may be a substantially longitudinal and hollow member extending from the distal end  120  to the proximal end  122 . The distal and proximal ends  120 ,  122  may be open such that the deflecting elements  104 ,  106 , fixed within the housing  108  at these ends  120 ,  122  are exposed. The housing  108  may also include cut-outs  132 ,  134 ,  136 ,  138  through a surface  140  of the housing  108  to facilitate the transfer of energy from the piezoelectric element  102  to the surrounding area. The cut-outs  132 ,  134 ,  136 ,  138  may cover a substantial surface area of the housing  108  such that the first and second surfaces  112 ,  114  and the surfaces  124 ,  126  of the deflecting elements  104 ,  106  are substantially exposed to the outside of the device  100 . The cut-outs  132 ,  134 ,  136 ,  138  allow ultrasound energy in the form of pulses of fluid to easily pass through the device  100  such that the surrounding fluid  170  may be heated and agitated thereby. It will be understood by those of skill in the art that although the device  100  is shown in  FIGS. 1-5  as including four cut-outs, the housing  108  may include any number of cut-outs so long as an interior of the housing  108  is exposed to the exterior of the device  100  such that ultrasound energy may easily pass therethrough. 
     The fluid  170  may be water, as described above, saline, or another other fluid appropriate for hydrothermal ablation or any other thermal treatment utilizing heated fluid  170 . The fluid  170  may be supplied to the uterus, or any other treatment site via a catheter or other fluid supply tool as would be understood by those skilled in the art. After the fluid  170  has been supplied to the treatment site, the device  100  may be inserted into the organ via a naturally occurring orifice in the body or via any other opening (e.g., a surgical incision). Once at the treatment site, the device  100  is immersed in the fluid  170  and RF energy is delivered to the piezoelectric element  102 . As described above, the RF energy excites and vibrates the piezoelectric element  102  generating ultrasound energy in the form of pulses of fluid pressure moving away from the first and second surfaces  112 ,  114  toward the deflecting elements  104 ,  106  as shown in  FIG. 4 . This ultrasound energy is depicted by the directional arrows in  FIG. 4 . The pulses of energy move substantially perpendicularly to the piezoelectric element  102 , to impinge on the surfaces  124 ,  126  of the deflecting elements  104 ,  106  which face the piezoelectric element  102 . 
     Some of the beams of energy that hit the piezoelectric element  102  will be absorbed by the deflecting elements  104 ,  106  while some of the energy will be deflected by the angled surfaces  124 ,  126  of the deflecting elements  104  setting up a substantially circular fluid motion, as depicted in  FIG. 5 . The angles of the surfaces  124 ,  126  ensure that fluid pulses leaving the surfaces  124 ,  126  exit the housing  108  via the cutout  132 ,  134 ,  136 ,  138  shown in  FIG. 2 . In a preferred embodiment, the surfaces  124 ,  126  are positioned at opposite angles relative to one another such energy is deflected from these surfaces in opposite directions—i.e., diametrically opposed relative to a longitudinal axis of the housing  108 . For example, energy leaving the first surface  112  of the piezoelectric element  102  deflected from the surface  124  of the deflecting element  104  exits the housing  108  via the cut-out  132 . A portion of the energy deflecting off tissue (e.g., a wall of a body cavity within which the device  100  is located) may re-enter the housing  108  via cut-out  134 . Likewise, energy leaving the second surface  114  of the piezoelectric element  102  deflected from the surface  126  of the deflecting element  106  exits the housing  108  via the cut-out  136 . A portion of the energy deflecting off of the tissue may re-enter the housing  108  via cut-out  138 . Thus, the beams of energy are able to create a substantially circular pattern of motion. 
     Additionally, the spherically convex shape of the surfaces  124 ,  126 , along with the protrusions  128 ,  130 , scatter the ultrasound beams. The scattering also aids to de-focus the ultrasound beams such that the beams lacks the intensity necessary to produce a burn when it enters the tissue. An amount of energy that is absorbed by the deflecting elements  104 ,  106  will be dependent upon the acoustic impedance of both the fluid and the deflecting elements  104 ,  106 . The energy and fluid  170  that is absorbed by the deflecting elements  104 ,  106  are converted to heat such that the surrounding fluid  170 , or the fluid  170  within the deflecting elements  104 ,  106  if the material is highly porous, may be heated. As the deflecting elements  104 ,  106  also keeps the fluid  170  moving circularly through the organ, the heated fluid  170  is agitated and distributed evenly through the organ. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the structure and the methodology of the present invention, without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations of the invention provided that they come within the scope of the appended claims and their equivalents.