Abstract:
An apparatus for sterilizing a female patient in a transcervical procedure comprises an elongated catheter with a piezoelectric ultrasound transducer at its distal end. The catheter is inserted transcervically into the uterus and guided to the intramural region of a fallopian tube. The transducer is inserted into the intramural region in direct contact with the surrounding tissue. The transducer produces a radially dispersing acoustical wave front, heating the adjacent tissue and forming a thermal lesion therein. A fibrous tissue forms during the healing process, sealing the fallopian tube. An embodiment of the apparatus includes a movable thermal sensor for monitoring the tissue temperature at multiple locations along the lesion. Another embodiment of the apparatus includes a spring that centers the distal end of the catheter at the opening of the fallopian tube and provides a tactile means to determine that the catheter and transducer have been correctly positioned.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to apparatus and methods for transcervical sterilization of a female patient and, more particularly, to transcervical methods and apparatus utilizing a piezoelectric transducer to create thermal lesions in fallopian tubes.  
         BACKGROUND OF THE INVENTION  
         [0002]    Surgical procedures used to sterilize women for the prevention of pregnancy commonly involve coagulation of fallopian tubes by the electrosurgical generation of heat. The fallopian tubes typically are exposed by abdominal incisions so that the surgeon may observe the extent of coagulation as the operation progresses.  
           [0003]    Various methods utilize the application of radiofrequency (RF) electrical current to heat the tissue to the temperatures at which it coagulates. As discussed, for example, in U.S. Pat. No. 6,066,139, these techniques sometimes fail to provide the necessary certainty of a successful sterilization, whether because of difficulties in controlling the application of the electrical energy, uncertainty in placement of the electrical probe, or for other reasons.  
           [0004]    Various devices have been developed utilizing ultrasound generated by piezoelectric transducers to ablate tissues by heating. For instance, U.S. Pat. No. 5,620,479 discloses an ultrasound applicator comprising a plurality of piezoelectric transducers on a “semi-flexible” central tube for insertion in a body lumen or directly into tissue. A sealant coating is provided around the transducers, while an air cooling system is provided to control treatment temperature. Thermal sensors are embedded in the sealant.  
           [0005]    U.S. Pat. No. 5,733,315 relates to the thermal ablation of prostate tissue with the use of ultrasound. Piezoelectric transducers are utilized as the acoustical energy sources. The transducers are formed so as to direct the acoustical waves to the prostate tissue and away from the rectal wall by creation of an acoustical “dead zone”. The transducers are covered by a protective sheath and a water-coolant system is provided to control the catheter temperature.  
           [0006]    U.S. Pat. No. 6,066,139 describes the use of ultrasound to generate lesions in a fallopian tube without surgical exposure of the tube. The lesions are then allowed to heal naturally, forming fibrous growths which seal the tubes. Transducers of the device disclosed in this patent are covered by a sealant, and a coolant is supplied for temperature control. Temperature measurement is performed with thermal sensors affixed to a catheter.  
           [0007]    The devices disclosed in the references cited above present a number of undesirable features. For example, the sealants or sheaths around piezoelectric transducers absorb and attenuate the acoustical waves that would otherwise reach the tissues, as well as adding bulk and increasing the size of the devices. Absorption of the acoustical energy causes the sealants or sheaths to self-heat, causing the affected tissue to desiccate too rapidly or become charred, thereby increasing the risk of excessive tissue damage. The provision of a coolant system for the probe can reduce this risk, but it increases the overall diameter of the probe, making the probe less flexible, and it increases the complexity of the treatment device.  
           [0008]    There remains a need to develop a reliable method for sterilization to prevent pregnancy, preferably one that reduces the need for surgery or other invasive techniques to observe the extent of coagulation and allows the controlled application of energy to the tissue without attenuation or the need for coolants. It is also preferable that the method allow the thermal energy source to be placed accurately within the fallopian tube without relying on invasive visualization techniques.  
         SUMMARY OF THE INVENTION  
         [0009]    One aspect of the invention includes an apparatus for sterilizing a female patient in a transcervical procedure, comprising an elongated catheter with a piezoelectric ultrasound transducer at its distal end. The apparatus is arranged for creating a thermal lesion in a fallopian tube through acoustical heating of the tissue. In a preferred embodiment of the apparatus, the transducer is cylindrical in shape and sized to be inserted into a fallopian tube with the outer surface of the cylinder in direct contact with the surrounding tissue. A source of radiofrequency (RF) current is provided for energizing the transducer, thereby generating a radially dispersing acoustical wave front that can be applied directly to the surrounding tissue. In another preferred embodiment, the apparatus includes a thermal sensor that can be moved independently of the catheter to measure the tissue temperature at multiple locations along the lesion. Another preferred embodiment provides a conical, helical spring attached to the catheter for centering the distal end of the catheter in the opening of a fallopian tube and guiding insertion of the transducer. The spring also provides a tactile means for determining that the spring and transducer have been correctly positioned in the uterus for the sterilization procedure.  
           [0010]    Another aspect of the invention includes transcervical procedures for performing sterilization of a female patient using acoustical heating by ultrasound transmission. In a preferred procedure, the distal end of a catheter with an attached cylindrically shaped ultrasound transducer is introduced into the uterus transcervically and guided to the opening of a fallopian tube. The transducer is inserted into the intramural region of the fallopian tube with the outer surface of the transducer in direct contact with the tissue of the fallopian tube. A radiofrequency (RF) current is applied to the transducer, causing it to generate a radially dispersing acoustical wave front that heats the adjacent tissue, thereby forming a thermal lesion around the circumference of the transducer. Another preferred procedure includes the step of positioning a thermal sensor at two or more different positions along the distal end of the catheter to monitor the changes in temperature as the lesion forms. The RF current may be intermittently interrupted or the power adjusted in response to a signal from the thermal sensors so as to control the tissue temperature.  
           [0011]    The apparatus and method provide a minimally invasive means for performing a sterilization through a controlled application of energy to the tissue of the fallopian tube. As the surface of the lesion heals, a fibrous tissue forms that reliably closes off the fallopian tube. The absence of a sheath or sealant around the piezoelectric transducer keeps the diameter of the transducer small enough for convenient insertion and reduces the potential for attenuation of the acoustic wave front or self-heating of the apparatus.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    For a more complete understanding of the present invention, reference is made to the following detailed description of the present invention considered in conjunction with the accompanying drawings, in which:  
         [0013]    [0013]FIG. 1 is a top plan view of a transcervical sterilization apparatus constructed in accordance with the present invention;  
         [0014]    [0014]FIG. 2 is an exploded perspective view of a piezoelectric transducer assembly of the apparatus shown in FIG. 1;  
         [0015]    [0015]FIG. 3 is an exploded perspective view of an arrangement for electrically connecting the transducer assembly shown in FIG. 2 to an end of a catheter;  
         [0016]    [0016]FIG. 4 is a perspective view of a modified version of the arrangement shown in FIG. 3;  
         [0017]    [0017]FIG. 5 is a partially cutaway view of the apparatus shown in FIG. 1 with its distal end inserted into a fallopian tube for sterilization showing a thermal sensor in its retracted position;  
         [0018]    [0018]FIG. 6 is a view similar to FIG. 5, except that the thermal sensor is shown in its extended position;  
         [0019]    [0019]FIG. 7 is a schematic view of the apparatus shown in FIG. 1 as deployed during a sterilization procedure;  
         [0020]    [0020]FIG. 8 is a schematic diagram of electronic power control unit for controlling a supply of RF current to the apparatus shown in FIG. 1;  
         [0021]    [0021]FIG. 9 is a perspective view of a centering device of the apparatus shown in FIG. 1;  
         [0022]    [0022]FIG. 10 is a top view of the centering device shown in FIG. 9;  
         [0023]    [0023]FIG. 11 is a partially cutaway view of a pre-deployment arrangement of the centering device shown in FIG. 9;  
         [0024]    [0024]FIG. 12 is a partially cutaway view of another pre-deployment arrangement of the centering device shown in FIG. 9;  
         [0025]    [0025]FIG. 13 is a perspective view of the centering device of FIG. 9 deployed in the body of a patient prior to the insertion of the transducer assembly into a fallopian tube;  
         [0026]    [0026]FIG. 14 is a view of the centering device of FIG. 9 in its partially compressed state during the insertion of the transducer assembly into the fallopian tube; and  
         [0027]    [0027]FIG. 15 is a side view of the centering device of FIG. 9 shown in its fully compressed state. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]    [0028]FIG. 1 illustrates a sterilization apparatus  10  constructed in accordance with the present invention. More particularly, the apparatus has a piezoelectric transducer  12  for performing transcervical sterilization. A flexible catheter  14 , which has distal and proximal ends  16 ,  18 , carries the piezoelectric transducer  12  on the distal end  16 . The catheter  14  is generally circular in cross-section and is sized and shaped for transcervical insertion into a fallopian tube. The catheter  14  is provided with a branch  20  that terminates in a connector  22  for electrically connecting the apparatus  10  to a power generator, a signal conditioner or other electronic circuitry used in a transcervical sterilization procedure (see FIG. 8). Alternatively, the connector  22  can be integrated into the proximal end  18  of the catheter  14 .  
         [0029]    An inserter  24  (see FIG. 1) is provided so as to facilitate insertion of the catheter  14  through a cervix and into a fallopian tube. More particularly, the catheter  14  is movably mounted in the inserter  24  such that it is extendable and retractable through the inserter  24 . The inserter  24  is flexible and is, preferably, provided with a preformed bend  26  to guide the catheter  14  in a proper direction within a uterus. The apparatus  10  is also provided with conventional mechanisms to manipulate the catheter  14 , such as handles  28 ,  30  illustrated in FIG. 1.  
         [0030]    The apparatus  10  is also provided with a flexible guide wire  32  that extends through the length of the catheter  14 . The guide wire  32  has a distal end  34  adapted for insertion into a fallopian tube and hence made so as to be softer and more flexible than the main body of the guide wire  32 . The guide wire  32  also has a proximal end  36  that is straight and substantially stiff such that it is suitable for use in manipulating the guide wire  32 . As is conventional in the catheter field, the proximal end  36  can be provided with calibrated markings (not shown) indicating a distance traveled by the guide wire  32 .  
         [0031]    With reference to FIGS. 1 and 2, the piezoelectric transducer  12  is adapted to function as an energy source for creating a thermal lesion within a fallopian tube. When energized by a radiofrequency (RF) current, the transducer  12  generates an acoustical wave that is absorbed by a surrounding tissue and converted into heat. Because the acoustical energy radiates as a collimated wave front in a direction perpendicular to the surface of a transducer, the transducer  12  is provided with a cylindrical shape for causing the wave front to be directed radially outwardly from the central axis  37  of the transducer  12  toward tissue around the entire surface of the transducer  12 . The transducer  12  and its surrounding tissue are acoustically coupled by direct contact between the transducer  12  and the tissue. Energy emitted from the transducer  12  is easier to control than energy emitted from bipolar or monopolar RF devices known in the prior art, as the extent of the affected tissue does not depend on the placement of an antipolar electrode or ground plate or on tissue electrical properties that vary with tissue desiccation.  
         [0032]    Referring to FIG. 2, the transducer  12  is constructed as a thin cylinder made of a ceramic material (e.g., ceramic materials sold under part nos. PZT4, PZT8 or C5800 by ValpeyFischer Corp., Hopkinton, Mass.). An outer surface  38  and an inner surface  40  of the transducer  12  are coated with thin layers of conductive metal, e.g., nickel, gold or platinum, so as to form conductive coatings  39 ,  41  (see FIG. 3) along the entire outer and inner surfaces  38 ,  40  respectively. The conductive coatings  39 ,  41  may be formed by vapor deposition or other methods known in the art and are deposited so that the conductive coating  39  of the outer surface  38  does not come in contact with, and is hence electrically insulated from, the conductive coating  41  of the inner surface  40 .  
         [0033]    Still referring to FIG. 2, the transducer  12  is sized to fit within a fallopian tube and to directly come in contact with a sufficient length of tissue so that the fallopian tube can be sealed when the lesioned tissue heals. For instance, transducer  12  can be provided with an outer diameter D of 1-2 mm, preferably the same outer diameter as catheter  14 , and a length L of 5-10 mm.  
         [0034]    The transducer  12  is also provided with a tapered tip  44  (see FIG. 2) to minimize tissue damage and to facilitate the entry of the transducer  12  into a fallopian tube. The tip  44  is constructed as a separate piece of electrically insulating material for attachment to a distal end  50  of the transducer  12 . The separately-formed tip  44  is provided with a protruding plug  46  that fits into a hollow interior  52  of the transducer  12  and functions to align the tip  44  with respect to the transducer  12 . An axial passage  48  extends through the tip  44  to accommodate passage of the guide wire  32  therethrough. Alternatively, the tip  44  may be formed integrally with the distal end  50  of the transducer  12 . In such circumstances, the tip  44  can be electrically insulated from the surfaces  38 ,  40  of the transducer  12  to prevent the tip  44  from being energized. In the absence of a tapered tip  44 , the transducer  12  may simply be plugged at its distal end  50 .  
         [0035]    Now-referring to FIG. 3, the transducer  12  is adapted to be energized by an RF current supplied through a bipolar pair of conductive leads  54 ,  56  which extend through the catheter  14  and terminate at the connector  22 . Other arrangements for carrying and terminating the conductive leads  54 ,  56  will be obvious to ordinarily-skilled practitioners in the field of medical instrumentation. An RF current is supplied to the transducer  12  at the resonant frequency of the transducer  12  which is proportional to the thickness t (see FIG. 2) of a wall  42  of the transducer  12 . Typically, the resonant frequency of the transducer  12  is between 6-12 MHz and, preferably, is about 10 MHz.  
         [0036]    Still referring to FIG. 3, the leads  54 ,  56  are electrically connected to the conductive coatings  39 ,  41 , respectively, of the surfaces  38 ,  40 , respectively, of the transducer  12 . The electrical connection between the outer conductive coating  39  and the conductive lead  54  is preferably formed so that it does not increase the outer diameter D of the transducer  12 . In this regard, the transducer  12  is coupled to the catheter  14  in an end-to-end manner such that the catheter  14  can be provided with the same outer diameter as the transducer  12 . The thicknesses of the wall  42  of the transducer  12  and a wall  64  of the catheter  14  are exaggerated in FIG. 3 for the sake of clarity. The transducer wall  42  terminates in an end face  62  which, preferably, is substantially flat and perpendicular to the axis  37  of the transducer  12 . The conductive coating  39  of the outer surface  38  extends onto the end face  62 , forming a conductive area  58 . The conductive coating  41  of the inner surface  40  also extends onto the end face  62 , forming a conductive area  60  which is separated and hence electrically isolated from the conductive area  58  and the outer surface  38 . The distal end  16  of the catheter  14  terminates in an end face  66  which, preferably, is sized and shaped to fit against the end face  62  of the transducer  12 . The conductive leads  54 ,  56  are exposed at the end face  66 . The end face  62  of the transducer  12  is attached to the end face  66  of the catheter  14  so that the lead  54  makes contact with the conductive area  58  and the lead  56  makes contact with the conductive area  60 . The end faces  62 ,  66  are secured to each other, preferably, by an adhesive layer provided between the end faces  62 ,  66 . The conductive leads  54 ,  56  are preferably embedded within the catheter wall  64  so as to minimize the risk of damage to the leads  54 ,  56  during fabrication and use of the assembly  10 . Alternatively, the conductive leads  54 ,  56  can be routed through a lumen  68  of the catheter  14 . Conductive leads  54 ,  56  may also be arranged in a co-axial fashion with conductive lead  54  being the inner conductor and conductive lead  56  being the outer conductor. The conductive areas  58 ,  60  would be arranged to make electrical contact with the conductive leads  54 ,  56 , respectively.  
         [0037]    The transducer  12  is not provided with a sealant or other covering. Rather, the transducer  12  remains exposed so that it may come in direct contact with tissue of a fallopian tube along the entire outer coating  39  of the transducer  12 . Such contact allows an acoustical wave generated by the energized transducer  12  to be transmitted to the tissue without absorption or attenuation by an intervening material. The absence of a sealant or other covering also keeps the diameter of the transducer  12  small, so that the transducer  12  fits more readily into the entrance of the fallopian tube.  
         [0038]    With reference to FIG. 5, a thermal sensor  80  is provided to monitor the temperature of the transducer  12  and the adjacent tissue of a fallopian tube. The thermal sensor  80  is preferably placed on an exterior surface of the guide wire  32  or embedded within the guide wire  32  adjacent the distal end  34  thereof so that the thermal sensor  80  can be positioned to monitor the temperature at various locations relative to the transducer  12  during a sterilization procedure. For example, the thermal sensor  80  may be initially positioned in its retracted position (see FIG. 5), in which it is placed within the catheter  14  near the transducer  12 , and then moved through the transducer  12  to its extended position (see FIG. 6), in which it is located outwardly beyond the taper tip  44  (i.e., it is located outside of the apparatus  10 ). The temperature profile obtained by measuring temperatures at various locations between the retracted and extended positions of the thermal sensor  80  may be used to determine the length of the tissue subjected to heating. Because of their small diameters and direct contact with the surrounding tissue, both transducer  12  and the adjacent regions of the catheter  14  rapidly reach thermal equilibrium with the tissue, allowing accurate measurement of the temperature of the tissue from within the transducer  12  or the catheter  14 . The thermal sensor  80  is also adapted to provide a rapid response to temperature differences as it is moved between locations. The thermal sensor  80  may be a thermistor or thermocouple, or a sensor or probe used in other measurement techniques such as fiber optic measurement of phosphorescent decay times. In other embodiments, the thermal sensor  80  may be fixedly mounted to another element of the apparatus  10 , such as within the lumen  68  or wall  64  of the catheter  14 , on the inner surface  40  of the transducer  12  or within the tapered tip  44 . The thermal sensor  80  is provided with a signal lead (not shown) for transmitting an analog signal from the thermal sensor  80  to terminals at the connector  22  or the apparatus  10 .  
         [0039]    Referring to FIG. 8, a power control unit  91  is provided to supply RF power to the transducer  12  through connector  22  and conductive leads  54 , 56 . The power control unit  91  includes an RF generator  92  operating at fixed gain, a temperature signal processor  94  for converting the analog signal received from the thermal sensor  80  to a digital data signal, a power meter  96  for monitoring the power supplied to and returned from the transducer  12  and converting the measured power values to a digital data signal, and a microprocessor  98  for controlling the operation of the RF generator  92  in response to digital data signals received from the temperature signal processor  94  and the power meter  96 .  
         [0040]    In order to perform transcervical sterilization using the apparatus  10 , conventional preparation procedures (e.g., local or general anesthesia) are performed to prepare the patient. The catheter  14  is then inserted through a cervix  82  (see FIG. 7) and advanced toward a fundus  84  in a conventional manner. More particularly, the catheter  14  is advanced by a sequence of predetermined distances until it extends through an entrance  86  of a fallopian tube  88  by a distance sufficient such that the transducer  12  is placed approximately 1-2 cm into the fallopian tube  88 , but within the uterus. Placement of the catheter  14  is facilitated by the preformed bend  26  of the inserter  24 , which functions to direct the catheter  14  toward the entrance  86 . The guide wire  32  may also be used to position the catheter  14  by advancing the guide wire  32  into the entrance  86  and then moving the catheter  14  over the guide wire  32 . During the insertion process, the position of the catheter  14  relative to the entrance  86  may be viewed with the use of an invasive method (e.g., using a fiber optic probe carried by the catheter  14 ) or an echogenic ultrasound technique, such as sonography, or by using the transducer  12  as an ultrasound source detectable by external sensors.  
         [0041]    After the transducer  12  is properly positioned in the fallopian tube  88 , a fixed level of RF current is supplied to the transducer  12  by the RF generator  92  (see FIG. 8) through the leads  54 ,  56 . The rate of power delivery and the rate of return, or reflected, power are monitored continuously by power meter  96  in a conventional manner. Power is delivered to the transducer  12  at the resonant frequency of the transducer  12  which may be determined in a conventional manner (e.g., by tuning the frequency of the delivered current to obtain the maximum transmission of acoustical energy).  
         [0042]    When energized by the RF current supplied from the RF generator  92 , the transducer  12  generates an acoustical wave that radiates as a radially dispersing, collimated wave front from the outer surface  38  of the transducer  12  to the surrounding tissue of the fallopian tube  88 . The acoustical energy is absorbed by the tissue and transformed into heat, thereby raising the temperature of the tissue. By this process, known as acoustical heating, the temperature of the tissue is increased until a lesion  90  is formed in the tissue surrounding the transducer  12 . The level and rate of energy application is monitored and controlled to prevent excessive damage to the tissue of the fallopian tube  88 . Tissue that is heated too rapidly or maintained at temperatures above a preferred range of 95° C.-105° C. may desiccate too quickly or char excessively. Either of these conditions may inhibit the natural collapse of the fallopian tube  88  when the catheter  14  is removed and interfere with the subsequent closure of the fallopian tube  88  as the lesion  90  is healed. Rapid or excessive heating may also cause steam and pressure waves in the narrow confines of the fallopian tube, which can result in perforation of tube wall or other damage.  
         [0043]    The progression of the thermal lesion  90  is controlled by limiting the rate of temperature rise in the surrounding tissue and maintaining the temperature of the tissue near the midpoint of the preferred temperature range of 95° C.-105° C. Tissue temperature is continuously monitored with the use of the thermal sensor  80 , which may be moved along the axis of catheter  14  by moving the guide wire  32  to create a temperature profile of the affected tissues. The temperature signal processor  92  processes an analog temperature signal received from the thermal sensor  80  to eliminate RF interference and then converts the same to digital temperature data for interpretation by the microprocessor  98 . The microprocessor  98  regulates the temperature rise and tissue temperature by sending analog control signals to the RF generator  92  to intermittently interrupt power transmission to the transducer  12 , effectively turning the transducer  12  on and off for short intervals. Alternatively, the level of power delivered to the transducer  12  may be controlled by adjusting the current or voltage. To achieve such control, the microprocessor  98  provides the digital-to-analog converter  99  digital data describing the power level and frequency. The convertor  99  forms an analog signal (i.e., a sine wave of the required amplitude) and transmits the analog signal to the RF generator  92  which, in turn, adjusts the rate or frequency of the supplied power. The power meter  96  monitors the forward and reflected power levels and transmits the corresponding data to microprocessor  98  sends signals to microprocessor  98  to adjust the supplied power until the targeted levels are achieved. This process is mediated by the microprocessor  98  according to known methods.  
         [0044]    The formation of the lesion  90  may also be monitored by changes in reflected power from the transducer  12 . As the tissue of the fallopian tube  88  surrounding the transducer  12  becomes desiccated, its acoustical properties change, and absorption of the acoustical energy by the desiccated tissue becomes less efficient, typically being reduced by 10-40%. As the tissue desiccates, a mismatch may occur between the transducer  12  and the tissue, resulting in a higher reflected power measured at the power meter  96 . The forward and reflected power levels are monitored by the power meter  96  which transmits digital data relating to the changes in power to the microprocessor  98 . Changes in the acoustical properties of the lesioned tissue also affect the transmission of acoustical energy through the lesion  90 , allowing the formation of the lesion  90  to be monitored by ultrasound detectors positioned outside of the patient&#39;s body. Invasive monitoring methods, such as transmission of visual images through fiber optic probes carried on the catheter  14  that function may also be used to observe blanching of the tissue as it becomes desiccated. Such fiber optic probes, used, e.g., in visualizing scopes, transmit light to illuminate the area of the affected tissue and return video images for viewing. Other phenomena related to lesion formation, such as charring of tissue or formation of steam or smoke, may also be observed by invasive monitoring methods.  
         [0045]    After the lesion  90  has been properly formed, the catheter  14  is withdrawn from the fallopian tube  88  and then removed from the uterus through the cervix  82 . The fallopian tube  88 , which normally is a closed structure, collapses upon itself in the area of the lesion  90  and undergoes an immediate inflammatory response. Over a period of 3-10 days, fibrous growth of the damaged tissue causes the surfaces of the lesion  90  to adhere to each other, thereby closing the fallopian tube  88  and hence completing the sterilization of a female patent.  
         [0046]    [0046]FIGS. 9 and 10 illustrate a centering spring  100  adapted for use in aligning the distal end  16  of the catheter  14  with an intramural region  87  of the fallopian tube  88  during the deployment of the transducer  12  into the fallopian tube  88 . For illustrative purposes, the diameters of the spring  100 , the catheter  14  and the transducer  12  are exaggerated in FIGS. 9 and 10 in relation to their respective lengths. The spring  100  is made preferably from a resilient (“elastic”) material, i.e., a material that returns to its original unstressed shape after being stretched, bent or compressed. While many different types of plastics or metal alloys can be used, a shape-memory alloy having optimal resilient (“superelastic”) properties at about 37° C., i.e, near human body temperature (e.g., the nickel-titanium alloy known as nitinol) is particularly suitable for use in connection with the spring  100 . In its relaxed or unstressed state (see FIG. 9), the spring  100  assumes the shape of a conical helix. The spring  100  is supported at its large-diameter end  102  by a support arm  104 , which has an end  106  affixed to the distal end  16  of the catheter  14  such that it is located axially inwardly from the transducer  12 . The connection between the affixed end  106  and the catheter  14  is sufficiently strong to withstand shear stresses resulting from the axial or radial compression of the spring  100 . In this regard, the end  106  can be affixed to the catheter  14  by adhesive, solder, mechanical means (e.g., a retaining ring), or other suitable mechanisms. Preferably, the support arm  104  is formed integrally with the spring  100 . The spring  100  is constructed from a ribbon of material and is hence provided with a rectangular cross-section. Alternatively, other shapes may be employed. For example, the spring  100  may be made from a wire-having a circular or square cross-section.  
         [0047]    With reference to FIG. 9, in its relaxed or unstressed state, the spring  100  assumes a conical, helical shape such that it encompasses (i.e., spirals around) the catheter  14  and the transducer  12  and such that a small-diameter end  108  of the spring  100  is located at or axially outward from the tapered tip  44  of the transducer  12 . Preferably, the small-diameter end  108  is centered relative to the tapered tip  44 . The affixed end  106  is located at a distance d (e.g., about 2 cm) from the transducer  12  in an axially inward direction such that when the support arm  104  is placed within the funnel-shaped entrance  86  of the fallopian tube  88 , transducer  12  is positioned in the intramural region  87  of the fallopian tube  88 . In its relaxed state, the spring  100  has sufficient resilience to prevent coils  110  of the spring  100  from overlapping each other (see FIG. 10). Moreover, the conical spring  100  preferably has a large-end diameter D L  of 4-6 mm and a small-end diameter D S  of at least 2 mm, large enough to encompass the catheter  14 . The shape of the spring  12  is not limited to the circular shape in the end view of FIG. 10. For example, the spring  12  may have an oval shape, conforming to the flattened shape of the uterus.  
         [0048]    The deployment and use of the spring  100  are illustrated in FIGS.  11 - 15 . Initially, the spring  100  is compressed or oriented into its compressed state so as to fit within the inserter  24 . For example, the spring  100  may be wrapped into a tight helical spiral in partially overlapping fashion around the distal end  16  of the catheter  14  (see FIG. 11). The spring  100  can also be wound into a flat spiral with the end  106  on the inside of the spiral and the end  108  on the outside of the spiral  100  (see FIG. 12). The spring  100  is maintained in its compressed state by the inserter  24  until it is deployed for use-during the performance of a sterilization operation.  
         [0049]    In use, with the spring housed within the inserter  24  (i.e., with the spring in its compressed state), the inserter  24  is passed through the cervix  82  and advanced toward the fundus  84  (see FIG. 11). The distal end  16  of the catheter  14  is then advanced out of the inserter  24 , thereby releasing the spring  100  and hence allowing the same to assume its conical, helical shape (see FIG. 13). The catheter  14  is then manipulated until the spring  100  is properly positioned in the funnel-shaped entrance  86  of the intramural region  87 . Because of the size and density of the spring  100 , the position of the spring  100  can be readily confirmed by using an echoic ultrasound (sonograph) method. Because the spring  100  creates some mechanical resistance as it is compressed, an operator manipulating the catheter  14  can also manually feel that the spring  100  is seated at the entrance  86 . As the catheter  14  is advanced further, the coils of the spring  100  press against the walls of the entrance  86 , causing the spring  100  to collapse axially (see FIG. 14) and allowing the transducer  12  to extend beyond the small-diameter end  108 . The spring  100  is constructed such that it resists radial compression, thereby causing the catheter  14  to remain centered relative to the spring  100 . The catheter  14  is advanced until the transducer  12  is inserted into the fallopian tube  88 . As shown in FIG. 15, the spring  100  may be compressed axially until its shape approaches that of a flat coil, at which point the support arm  104  blocks the further axial movement of coils  110 . Attempts to advance the transducer  12  past this point create a much greater mechanical resistance as the support arm  104  engages the coils  110 . When this resistance is detected, the operator may verify that the transducer  12  is in its desired position by a visualization method as discussed above. If necessary, the transducer  12  may be advanced further by applying sufficient axial force to deform the spring  100  so that the coils  110  are pushed over the support arm  104 .  
         [0050]    It should be appreciated that the present invention provides numerous advantages over the prior art discussed above. For example, the use of the piezoelectric transducer  12  as the energy source to create the thermal lesion allows better control of the extent of the lesion than use of the bipolar or monopolar RF devices known in the art. The transducer  12  transmits energy to the tissue independently of a return path, so electric current does not flow through the patient&#39;s body as in RF devices. The absence of a sealant or sheath around the transducer  12  allows transmission of acoustical energy to surrounding tissue without attenuation of the acoustical energy or self-heating of the apparatus  10 . Moreover, the movable thermal sensor  80  is adapted for use in providing a temperature profile that may be used to delineate the extent of the lesioned tissue and assess the effectiveness of the thermal treatment. The centering spring  100  attached to the catheter  14  also provides advantages over the prior art, such as automatically centering the distal end  16  of the catheter  14  and hence the transducer  12  within the entrance to the fallopian tube and providing a tactile, non-visual means for the operator to estimate the position of the transducer within the fallopian tube itself.  
         [0051]    It should be understood that variations and modifications can be made to the disclosed invention. For example, FIG. 4 illustrates a modified version of the electrical connection shown in FIG. 3 between the transducer  12  and the catheter  14 . Conductive leads  54 ′,  56 ′ are mounted on an outer surface  72 ′ of the catheter  14 ′. Preferably, the leads  54 ′,  56 ′ are formed from electrically conductive tapes attached to the outer surface  72 ′. The catheter  14 ′ has a distal end  16 ′ sized and shaped to fit into the hollow interior  52 ′ of the transducer  12 ′ such that the outer surface  72 ′ of the catheter  14 ′ is in contact with the inner surface  40 ′ of the transducer  12 ′. The conductive lead  54 ′ terminates at a conductive area  58 ′ located on the transducer  12 ′ such that the conductive area  58 ′ is in contact with the electrically conductive coating of the outer surface  38 ′ of the transducer  12 ′. The conductive lead  56 ′ is provided with a terminal  74 ′ located on the outer surface  72 ′ at the distal end  16 ′ such that the terminal  74 ′ is located at the interface between the distal end  16 ′ of the catheter  14 ′ and the inner surface  40 ′ of the transducer  12 ′ so as to make electrical contact with the conductive coating of the inner surface  40 ′. An insulating layer (not shown) surrounding the leads  54 ′,  56 ′ and the outer surface  72 ′ may be provided for protecting the leads  54 ′,  56 ′ during the handling and use of the apparatus  10 . Another possible variation would be to use more than one piezoelectric transducer, spaced along the axis of the catheter  14 . Each of the additional transducers can be mounted to the catheter  14  coaxially therewith and can preferably be provided with a separate pair of conductive leads, allowing the individual transducers to be controlled independently of each other. The additional transducers can have an axial length L that is substantially smaller than that of the transducer  12  and can be spaced sufficiently far apart from each other to avoid stiffening of the otherwise flexible catheter  14 . In another variation, a movable thermal sensor and guide wire may be provided outside of the piezoelectric transducer, rather than through it.  
         [0052]    Although the invention disclosed 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 invention as defined in the appended claims.