Patent Publication Number: US-2021178140-A1

Title: Catheter with multiple ultrasound radiating members

Description:
PRIORITY APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/112,364, filed Aug. 24, 2018, now U.S. Pat. No. 10,926,074, which is a continuation of U.S. patent application Ser. No. 15/207,371, filed Jul. 11, 2016, now U.S. Pat. No. 10,080,878, which is a continuation of U.S. patent application Ser. No. 14/196,225, filed Mar. 4, 2014, now U.S. Pat. No. 9,415,242, which is a continuation of U.S. patent application Ser. No. 13/431,798, filed Mar. 27, 2012, now U.S. Pat. No. 8,696,612, which is a continuation of U.S. patent application Ser. No. 12/762,254, filed Apr. 16, 2010, now U.S. Pat. No. 8,167,831, which is a divisional of U.S. patent application Ser. No. 11/643,471, filed Dec. 21, 2006, now U.S. Pat. No. 7,727,178, which is a divisional of U.S. patent application Ser. No. 10/309,388, filed Dec. 3, 2002, now U.S. Pat. No. 7,220,239, which claims the benefit of U.S. Provisional Patent Application No. 60/336,744, filed Dec. 3, 2001, U.S. Provisional Patent Application No. 60/336,630, filed Dec. 3, 2001, and U.S. Provisional Patent Application No. 60/394,093, filed Jul. 3, 2002. The entire disclosure of all of these priority documents is hereby incorporated by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED R &amp; D 
     The invention was made with government support under Grant No. NIH R44 HL057739 awarded by the National Institutes of Health. The government has certain rights in the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates generally to an ultrasonic catheter and more specifically to an ultrasonic catheter configured to deliver ultrasonic energy and a therapeutic compound to a treatment site. 
     Description of the Related Art 
     Several medical applications use ultrasonic energy. For example, U.S. Pat. Nos. 4,821,740, 4,953,565 and 5,007,438 disclose the use of ultrasonic energy to enhance the effect of various therapeutic compounds. An ultrasonic catheter can be used to deliver ultrasonic energy and a therapeutic compound to a treatment site in a patient&#39;s body. Such an ultrasonic catheter typically includes an ultrasound assembly configured to generate ultrasonic energy and a fluid delivery lumen for delivering the therapeutic compound to the treatment site. 
     As taught in U.S. Pat. No. 6,001,069, such ultrasonic catheters can be used to treat human blood vessels that have become partially or completely occluded by plaque, thrombi, emboli or other substances that reduce the blood carrying capacity of the vessel. To remove or reduce the occlusion, the ultrasonic catheter is used to deliver solutions containing dissolution compounds directly to the occlusion site. Ultrasonic energy generated by the ultrasound assembly enhances the therapeutic effect of the dissolution compounds. For example, in one application of such an ultrasonic catheter, an ultrasound-enhanced thrombolytic therapy dissolves blood clots in arteries and veins in the treatment of diseases such as peripheral arterial occlusion or deep vein thrombosis. In such applications, ultrasonic energy enhances thrombolysis with agents such as urokinase, tissue plasminogen activator (“TPA”) and the like. 
     Ultrasonic catheters can also be used to enhance gene therapy at a treatment site within the patient&#39;s body. For example, U.S. Pat. No. 6,135,976 discloses an ultrasonic catheter having one or more expandable sections capable of occluding a section of a body lumen, such as a blood vessel. A gene therapy composition is then delivered to the occluded vessel through the catheter fluid delivery lumen. Ultrasonic energy generated by the ultrasound assembly is applied to the occluded vessel, thereby enhancing the delivery of a genetic composition into the cells of the occluded vessel. 
     Ultrasonic catheters can also be used to enhance delivery and activation of light activated drugs. For example, U.S. Pat. No. 6,176,842 discloses methods for using an ultrasonic catheter to treat biological tissues by delivering a light activated drug to the biological tissues and exposing the light activated drug to ultrasound energy. 
     SUMMARY OF THE INVENTION 
     In certain medical procedures, it is desirable to provide ultrasonic energy along a substantial length of a body lumen. For example, long segment peripheral arterial occlusions, such as those in the arteries of the leg, may have an axial length in the range of 10 to 50 cm. To date, it has been difficult to design an ultrasonic catheter capable of efficiently applying ultrasound energy over such lengths. 
     One method for emitting ultrasonic energy over such lengths is to provide the ultrasonic catheter with a plurality of ultrasonic transducers spaced along a distal region of the catheter. Such an arrangement faces several technical hurdles. For example, because the ultrasonic transducers are relatively rigid, the catheter may become too inflexible to be navigated through the lumens of the patient&#39;s body. One solution is to use smaller transducers. However, smaller transducers may not be capable of producing sufficient energy at the proper frequency to enhance the therapeutic effect of a therapeutic agent. 
     Another solution is disclosed in U.S. Pat. No. 6,296,610. This patent discloses a catheter with a plurality of transducers that are moved back and forth within the catheter through the treatment zone. However, this arrangement is generally undesirable because it requires a translation system for moving the ultrasonic elements within the catheter. 
     Additionally, for ease of manufacturing and reduced costs, it is generally desirable to use ultrasonic transducers that are in the form of rectangular bars as compared to, for example, cylindrical transducers. However, such arrangements should still generate a therapeutically effective ultrasonic energy field. 
     A need, therefore, exists for an improved ultrasonic catheter capable of providing ultrasonic energy over a substantial length of a body lumen with little or no movement of the ultrasonic elements within the patient during treatment. Such a catheter preferably uses flat rectangular ultrasonic transducers. 
     As such, according to one embodiment of the present invention, a catheter system for delivering ultrasonic energy and a therapeutic compound to a treatment site within a body lumen comprises a tubular body. The tubular body has a proximal end, a distal end and an energy delivery section positioned between the proximal end and the distal end. The catheter system further comprises a fluid delivery lumen extending at least partially through the tubular body. The fluid delivery lumen has at least one outlet in the energy delivery section. The catheter system further comprises an inner core configured for insertion into the tubular body. The inner core comprises an elongate electrical conductor having a plurality of flattened regions. Each flattened region has a first flat side and a second flat side opposite the first flat side. The inner core further comprises a plurality of ultrasound radiating members mounted in pairs to the flattened regions of the elongate electrical conductor. A first ultrasound radiating member is mounted to the first flat side of the elongate electrical conductor, and a second ultrasound radiating member is mounted to the second flat side of the elongate electrical conductor. The inner core further comprises wiring such that a voltage can be applied from the elongate electrical conductor across the first and second ultrasound radiating members. The first and second ultrasound radiating members can be driven simultaneously. 
     According to another embodiment of the present invention, a catheter system for delivering ultrasonic energy to a treatment site comprises a tubular body. The tubular body has a proximal end, a distal end and a treatment zone located between the distal end and the proximal end. The catheter system further comprises an ultrasonic assembly positioned within the treatment zone. The ultrasonic assembly comprises an electrical conductor and an ultrasonic transducer pair. The ultrasonic transducer pair includes a first ultrasound transducer having a first portion and a second ultrasound transducer having a second portion. The first portion of the first transducer and the second portion of the second transducer face each other and are electrically coupled to the electrical conductor. 
     According to another embodiment of the present invention a catheter system for delivering ultrasonic energy to a treatment site comprises a tubular body. The tubular body has a proximal end, a distal end and a treatment zone located between the distal and proximal ends. The catheter system further comprises an ultrasonic assembly positioned within the treatment zone. The ultrasonic assembly comprises an electrical conductor and an ultrasonic transducer pair. The ultrasonic transducer pair includes a rectangular solid first ultrasonic element and a rectangular solid second ultrasonic element. The first and second ultrasonic elements are mounted on opposite sides of the electrical conductor. 
     According to another embodiment of the present invention, an apparatus comprises an elongate tubular body having a fluid delivery lumen. The apparatus further comprises an inner core configured for insertion into the tubular body. The inner core comprises a common wire and a plurality of ultrasound radiating members. The plurality of ultrasound radiating members are positioned and electrically coupled to the common wire in pairs. The apparatus further comprises a control system configured to drive each pair of ultrasound radiating members. 
     According to another embodiment of the present invention, a method of delivering ultrasonic energy and a therapeutic compound to a treatment site comprises providing a catheter with a plurality of ultrasound radiating members. The plurality of ultrasound radiating members are allocated into electrical groups comprising more than one ultrasound radiating member. The method further comprises independently driving each group of ultrasonic radiating members. The method further comprises delivering the therapeutic compound through the catheter to the treatment site. 
     According to another embodiment of the present invention, an ultrasonic catheter comprises a tubular body. The tubular body has a proximal end, a distal end and a treatment zone located between the distal end and the proximal end. The ultrasonic catheter further comprises a plurality of fluid delivery lumens defined within the tubular body. The ultrasonic catheter further comprises an inner core comprising at least one ultrasound radiating element. The ultrasonic catheter further comprises a plurality of cooling fluid channels defined between at least an inner surface of the tubular body and an outer surface of the inner core. Each cooling fluid channel is positioned generally radially between two fluid delivery lumens. 
     According to another embodiment of the present invention, an ultrasonic catheter system comprises a tubular body. The tubular body has a proximal end, a distal end and a treatment zone located between the distal end and the proximal end. The ultrasonic catheter system further comprises a fluid delivery lumen. The ultrasonic catheter system further comprises at least one ultrasound radiating element positioned in the treatment zone. The ultrasonic catheter system further comprises wiring electrically coupled to the at least one ultrasound radiating element. The wiring extends through the tubular body and terminates at a connector. The ultrasonic catheter system further comprises a control system. The control system comprises external circuitry and an isolation pod. The isolation pod is configured to be electrically connected to the connector. The isolation pod is also positioned between the tubular body and the external system. The isolation pod comprises an isolation barrier and circuitry for driving the ultrasound radiating element. 
     According to another embodiment of the present invention, an ultrasonic catheter comprises a tubular body. The tubular body has a proximal end, a distal end and a treatment zone located between the distal end and the proximal end. The ultrasonic catheter further comprises at least one fluid delivery lumen incorporated into the tubular body. The ultrasonic catheter further comprises a plurality of ultrasound radiating members mounted within an inner core. The inner core is positioned within the tubular body such that at least one of the ultrasound radiating members is located within the treatment zone. The ultrasonic catheter further comprises means for independently driving each of the ultrasound transducers. 
     For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described above. It is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. 
     All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an ultrasonic catheter configured for insertion into large vessels of the human body. 
         FIG. 2  is a cross-sectional view of the ultrasonic catheter of  FIG. 1  taken along line  2 - 2 . 
         FIG. 3  is a schematic illustration of an elongate inner core configured to be positioned within the central lumen of the catheter illustrated in  FIG. 2 . 
         FIG. 4  is a cross-sectional view of the elongate inner core of  FIG. 3  taken along line  4 - 4 . 
         FIG. 5  is a schematic wiring diagram illustrating a preferred technique for electrically connecting five groups of ultrasound radiating members to form an ultrasound assembly. 
         FIG. 6  is a schematic wiring diagram illustrating a preferred technique for electrically connecting one of the groups of  FIG. 5 . 
         FIG. 7A  is a schematic illustration of the ultrasound assembly of  FIG. 5  housed within the inner core of  FIG. 4 . 
         FIG. 7B  is a cross-sectional view of the ultrasound assembly of  FIG. 7A  taken along line  7 B- 7 B. 
         FIG. 7C  is a cross-sectional view of the ultrasound assembly of  FIG. 7A  taken along line  7 C- 7 C. 
         FIG. 7D  is a side view of an ultrasound assembly center wire twisted into a helical configuration. 
         FIG. 8  illustrates the energy delivery section of the inner core of  FIG. 4  positioned within the energy delivery section of the tubular body of  FIG. 2 . 
         FIG. 9  illustrates a wiring diagram for connecting a plurality of temperature sensors with a common wire. 
         FIG. 10  is a block diagram of a feedback control system for use with an ultrasonic catheter. 
         FIG. 11A  is a side view of a treatment site. 
         FIG. 11B  is a side view of the distal end of an ultrasonic catheter positioned at the treatment site of  FIG. 11A . 
         FIG. 11C  is a cross-sectional view of the distal end of the ultrasonic catheter of  FIG. 11B  positioned at the treatment site before a treatment. 
         FIG. 11D  is a cross-sectional view of the distal end of the ultrasonic catheter of  FIG. 11C , wherein an inner core has been inserted into the tubular body to perform a treatment. 
         FIG. 12  is a circuit diagram of an isolation pod. 
         FIG. 13  illustrates the connection of ultrasound radiating members within a catheter to an isolation pod. 
         FIG. 14  illustrates a selective activation of ultrasound radiating members within a catheter. 
         FIG. 15  illustrates a second selective activation of ultrasound radiating members within a catheter. 
         FIG. 16  illustrates a third selective activation of ultrasound radiating members within a catheter. 
         FIG. 17  illustrates one embodiment for connecting ultrasound radiating members within a catheter to an isolation pod. 
         FIG. 18  illustrates a second embodiment for connecting ultrasound radiating members within a catheter to an isolation pod. 
         FIG. 19  illustrates the connection of temperature sensors within a catheter to an isolation pod. 
         FIG. 20  is a cross-sectional view of a catheter connector. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     As described above, it is desired to provide an ultrasonic catheter having various features and advantages. Examples of such features and advantages include the ability to apply ultrasonic energy to a treatment site. In another embodiments, the catheter has the ability to deliver a therapeutic compound to the treatment site. Preferred embodiments of an ultrasonic catheter having certain of these features and advantages are described herein. Methods of using such an ultrasonic catheter are also described herein. 
     The ultrasonic catheters described herein can be used to enhance the therapeutic effects of therapeutic compounds at a treatment site within a patient&#39;s body. As used herein, the term “therapeutic compound” refers broadly, without limitation, to a drug, medicament, dissolution compound, genetic material or any other substance capable of effecting physiological functions. Additionally, any mixture comprising any such substances is encompassed within this definition of “therapeutic compound”, as well as any substance falling within the ordinary meaning of these terms. The enhancement of the effects of therapeutic compounds using ultrasonic energy is described in U.S. Pat. Nos. 5,318,014, 5,362,309, 5,474,531, 5,628,728, 6,001,069 and 6,210,356, the entire disclosure of which are hereby incorporated by herein by reference. Specifically, for applications that treat human blood vessels that have become partially or completely occluded by plaque, thrombi, emboli or other substances that reduce the blood carrying capacity of a vessel, suitable therapeutic compounds include, but are not limited to, an aqueous solution containing Heparin, Uronkinase, Streptokinase, TPA and BB-10153 (manufactured by British Biotech, Oxford, UK). 
     Certain features and aspects of the ultrasonic catheters disclosed herein may also find utility in applications where the ultrasonic energy itself provides a therapeutic effect. Examples of such therapeutic effects include preventing or reducing stenosis and/or restenosis; tissue ablation, abrasion or disruption; promoting temporary or permanent physiological changes in intracellular or intercellular structures; and rupturing micro-balloons or micro-bubbles for therapeutic compound delivery. Further information about such methods can be found in U.S. Pat. Nos. 5,261,291 and 5,431,663, the entire disclosure of which are hereby incorporated by herein by reference. 
     The ultrasonic catheters described herein are configured for applying ultrasonic energy over a substantial length of a body lumen, such as, for example, the larger vessels located in the leg. However, it should be appreciated that certain features and aspects of the present invention may be applied to catheters configured to be inserted into the small cerebral vessels, in solid tissues, in duct systems and in body cavities. Additional embodiments that may be combined with certain features and aspects of the embodiments described herein are described in U.S. patent application, Attorney Docket EKOS.026A, entitled “Ultrasound Assembly For Use With A Catheter” and filed Nov. 7, 2002, the entire disclosure of which is hereby incorporated herein by reference. 
     With initial reference to  FIG. 1  schematically illustrates an ultrasonic catheter  10  configured for use in the large vessels of a patient&#39;s anatomy. For example, the ultrasonic catheter  10  illustrated in  FIG. 1  can be used to treat long segment peripheral arterial occlusions, such as those in the vascular system of the leg. 
     As illustrated in  FIG. 1 , the ultrasonic catheter  10  generally comprises a multi-component, elongate flexible tubular body  12  having a proximal region  14  and a distal region  15 . The tubular body  12  includes a flexible energy delivery section  18  located in the distal region  15  of the catheter  10 . The tubular body  12  and other components of the catheter  10  can be manufactured in accordance with any of a variety of techniques well known in the catheter manufacturing field. Suitable materials and dimensions can be readily selected based on the natural and anatomical dimensions of the treatment site and on the desired percutaneous access site. 
     For example, in a preferred embodiment the proximal region  14  of the tubular body  12  comprises a material that has sufficient flexibility, kink resistance, rigidity and structural support to push the energy delivery section  18  through the patient&#39;s vasculature to a treatment site. Examples of such materials include, but are not limited to, extruded polytetrafluoroethylene (“PTFE”), polyethylenes (“PE”), polyamides and other similar materials. In certain embodiments, the proximal region  14  of the tubular body  12  is reinforced by braiding, mesh or other constructions to provide increased kink resistance and pushability. For example, nickel titanium or stainless steel wires can be placed along or incorporated into the tubular body  12  to reduce kinking. 
     In an embodiment configured for treating thrombus in the arteries of the leg, the tubular body  12  has an outside diameter between about 0.060 inches and about 0.075 inches. In another embodiment, the tubular body  12  has an outside diameter of about 0.071 inches. In certain embodiments, the tubular body  12  has an axial length of approximately 105 centimeters, although other lengths may by appropriate for other applications. 
     The energy delivery section  18  of the tubular body  12  preferably comprises a material that is thinner than the material comprising the proximal region  14  of the tubular body  12  or a material that has a greater acoustic transparency. Thinner materials generally have greater acoustic transparency than thicker materials. Suitable materials for the energy delivery section  18  include, but are not limited to, high or low density polyethylenes, urethanes, nylons, and the like. In certain modified embodiments, the energy delivery section  18  may be formed from the same material or a material of the same thickness as the proximal region  18 . 
     In certain embodiments, the tubular body  12  is divided into at least three sections of varying stiffness. The first section, which preferably includes the proximal region  14 , has a relatively higher stiffness. The second section, which is located in an intermediate region between the proximal region  14  and the distal region  15  of the tubular body  12 , has a relatively lower stiffness. This configuration further facilitates movement and placement of the catheter  10 . The third section, which preferably includes the energy delivery section  18 , is generally lower stiffness than the second section in spite of the presence of the ultrasound radiating members  40 . 
       FIG. 2  illustrates a cross section of the tubular body  12  taken along line  2 - 2  in  FIG. 1 . In the embodiment illustrated in  FIG. 2 , three fluid delivery lumens  30  are incorporated into the tubular body  12 . In other embodiments, more or fewer fluid delivery lumens can be incorporated into the tubular body  12 . The arrangement of the fluid delivery lumens  30  preferably provides a hollow central lumen  51  passing through the tubular body  12 . The cross-section of the tubular body  12 , as illustrated in  FIG. 2 , is preferably substantially constant along the length of the catheter  10 . Thus, in such embodiments, substantially the same cross-section is present in both the proximal region  14  and the distal region  15  of the catheter  10 , including the energy delivery section  18 . 
     In certain embodiments, the central lumen  51  has a minimum diameter greater than about 0.030 inches. In another embodiment, the central lumen  51  has a minimum diameter greater than about 0.037 inches. In one preferred embodiment, the fluid delivery lumens  30  have dimensions of about 0.026 inches wide by about 0.0075 inches high, although other dimensions may be used in other applications. 
     As described above, the central lumen  51  preferably extends through the length of the tubular body  12 . As illustrated in  FIG. 1 , the central lumen  51  preferably has a distal exit port  29  and a proximal access port  31 . The proximal access port  31  forms part of the backend hub  33 , which is attached to the proximal region  14  of the catheter  10 . The backend hub preferably further comprises cooling fluid fitting  46 , which is hydraulically connected to the central lumen  51 . The backend hub  33  also preferably comprises a therapeutic compound inlet port  32 , which is in hydraulic connection with the fluid delivery lumens  30 , and which can be hydraulically coupled to a source of therapeutic compound via a hub such as a Luer fitting. 
     The central lumen  51  is configured to receive an elongate inner core  34  of which a preferred embodiment is illustrated in  FIG. 3 . The elongate inner core  34  preferably comprises a proximal region  36  and a distal region  38 . Proximal hub  37  is fitted on the inner core  34  at one end of the proximal region  36 . One or more ultrasound radiating members are positioned within an inner core energy delivery section  41  located within the distal region  38 . The ultrasound radiating members  40  form an ultrasound assembly  42 , which will be described in detail below. 
     As shown in the cross-section illustrated in  FIG. 4 , which is taken along lines  4 - 4  in  FIG. 3 , the inner core  34  preferably has a cylindrical shape, with an outer diameter that permits the inner core  34  to be inserted into the central lumen  51  of the tubular body  12  via the proximal access port  31 . Suitable outer diameters of the inner core  34  include, but are not limited to, about 0.010 inches to about 0.100 inches. In another embodiment, the outer diameter of the inner core  34  is between about 0.020 inches and about 0.080 inches. In yet another embodiment, the inner core  34  has an outer diameter of about 0.035 inches. 
     Still referring to  FIG. 4 , the inner core  34  preferably comprises a cylindrical outer body  35  that houses the ultrasound assembly  42 . The ultrasound assembly  42  comprises wiring and ultrasound radiating members, described in greater detail in  FIGS. 5 through 7D , such that the ultrasound assembly  42  is capable of radiating ultrasonic energy from the energy delivery section  41  of the inner core  34 . The ultrasound assembly  42  is electrically connected to the backend hub  33 , where the inner core  34  can be connected to a control system  100  via cable  45  (illustrated in  FIG. 1 ). Preferably, an electrically insulating potting material  43  fills the inner core  34 , surrounding the ultrasound assembly  42 , thus preventing movement of the ultrasound assembly  42  with respect to the outer body  35 . In one embodiment, the thickness of the outer body  35  is between about 0.0002 inches and 0.010 inches. In another embodiment, the thickness of the outer body  35  is between about 0.0002 inches and 0.005 inches. In yet another embodiment, the thickness of the outer body  35  is about 0.0005 inches. 
     In a preferred embodiment, the ultrasound assembly  42  comprises a plurality of ultrasound radiating members  40  that are divided into one or more groups. For example,  FIGS. 5 and 6  are schematic wiring diagrams illustrating one technique for connecting five groups of ultrasound radiating members  40  to form the ultrasound assembly  42 . As illustrated in  FIG. 5 , the ultrasound assembly  42  comprises five groups G 1 , G 2 , G 3 , G 4 , GS of ultrasound radiating members  40  that are electrically connected to each other. The five groups are also electrically connected to the control system  100 . 
     As used herein, the terms “ultrasonic energy”, “ultrasound and “ultrasonic” are broad terms, having their ordinary meanings, and further refer to, without limitation, mechanical energy transferred through longitudinal pressure or compression waves. Ultrasonic energy can be emitted as continuous or pulsed waves, depending on the requirements of a particular application. Additionally, ultrasonic energy can be emitted in waveforms having various shapes, such as sinusoidal waves, triangle waves, square waves, or other wave forms. Ultrasonic energy includes sound waves. In certain embodiments, the ultrasonic energy has a frequency between about 20 kHz and about 20 MHz. For example, in one embodiment, the waves have a frequency between about 500 kHz and about 20 MHz. In another embodiment, the waves have a frequency between about 1 MHz and about 3 MHz. In yet another embodiment, the waves have a frequency of about 2 MHz. The average acoustic power is between about 0.01 watts and 300 watts. In one embodiment, the average acoustic power is about 15 watts. 
     As used herein, the term “ultrasound radiating member” refers to any apparatus capable of producing ultrasonic energy. For example, in one embodiment, an ultrasound radiating member comprises an ultrasonic transducer, which converts electrical energy into ultrasonic energy. A suitable example of an ultrasonic transducer for generating ultrasonic energy from electrical energy includes, but is not limited to, piezoelectric ceramic oscillators. Piezoelectric ceramics typically comprise a crystalline material, such as quartz, that change shape when an electrical current is applied to the material. This change in shape, made oscillatory by an oscillating driving signal, creates ultrasonic sound waves. In other embodiments, ultrasonic energy can be generated by an ultrasonic transducer that is remote from the ultrasound radiating member, and the ultrasonic energy can be transmitted, via, for example, a wire that is coupled to the ultrasound radiating member. 
     Still referring to  FIG. 5 , the control circuitry  100  preferably comprises, among other things, a voltage source  102 . The voltage source  102  comprises a positive terminal  104  and a negative terminal  106 . The negative terminal  106  is connected to common wire  108 , which connects the five groups G 1 -G 5  of ultrasound radiating members  40  in series. The positive terminal  104  is connected to a plurality of lead wires  110 , which each connect to one of the five groups G 1 -G 5  of ultrasound radiating members  40 . Thus, under this configuration, each of the five groups G 1 -G 5 , one of which is illustrated in  FIG. 6 , is connected to the positive terminal  104  via one of the lead wires  110 , and to the negative terminal  106  via the common wire  108 . 
     Referring now to  FIG. 6 , each group G 1 -G 5  comprises a plurality of ultrasound radiating members  40 . Each of the ultrasound radiating members  40  is electrically connected to the common wire  108  and to the lead wire  310  via one of two positive contact wires  112 . Thus, when wired as illustrated, a constant voltage difference will be applied to each ultrasound radiating member  40  in the group. Although the group illustrated in  FIG. 6  comprises twelve ultrasound radiating members  40 , one of ordinary skill in the art will recognize that more or fewer ultrasound radiating members  40  can be included in the group. Likewise, more or fewer than five groups can be included within the ultrasound assembly  42  illustrated in  FIG. 5 . 
       FIG. 7A  illustrates one preferred technique for arranging the components of the ultrasound assembly  42  (as schematically illustrated in  FIG. 5 ) into the inner core  34  (as schematically illustrated in  FIG. 4 ).  FIG. 7A  is a cross-sectional view of the ultrasound assembly  42  taken within group G 1  in  FIG. 5 , as indicated by the presence of four lead wires  110 . For example, if a cross-sectional view of the ultrasound assembly  42  was taken within group G 4  in  FIG. 5 , only one lead wire  310  would be present (that is, the one lead wire connecting group GS). 
     Referring still to  FIG. 7A , the common wire  108  comprises an elongate, flat piece of electrically conductive material in electrical contact with a pair of ultrasound radiating members  40 . Each of the ultrasound radiating members  40  is also in electrical contact with a positive contact wire  312 . Because the common wire  108  is connected to the negative terminal  106 , and the positive contact wire  312  is connected to the positive terminal  104 , a voltage difference can be created across each ultrasound radiating member  40 . Lead wires  110  are preferably separated from the other components of the ultrasound assembly  42 , thus preventing interference with the operation of the ultrasound radiating members  40  as described above. For example, in one preferred embodiment, the inner core  34  is filled with an insulating potting material  43 , thus deterring unwanted electrical contact between the various components of the ultrasound assembly  42 . 
       FIGS. 7B and 7C  illustrate cross sectional views of the inner core  34  of  FIG. 7A  taken along lines  7 B- 7 B and  7 C- 7 C, respectively. As illustrated in  FIG. 7B , the ultrasound radiating members  40  are mounted in pairs along the common wire  108 . The ultrasound radiating members  40  are connected by positive contact wires  112 , such that substantially the same voltage is applied to each ultrasound radiating member  40 . As illustrated in  FIG. 7C , the common wire  108  preferably comprises wide regions  108 W upon which the ultrasound radiating members  40  can be mounted, thus reducing the likelihood that the paired ultrasound radiating members  40  will short together. In certain embodiments, outside the wide regions  108 W, the common wire  108  may have a more conventional, rounded wire shape. 
     In a modified embodiment, such as illustrated in  FIG. 7D , the common wire  108  is twisted to form a helical shape before being fixed within the inner core  34 . In such embodiments, the ultrasound radiating members  40  are oriented in a plurality of radial directions, thus enhancing the radial uniformity of the resulting ultrasonic energy field. 
     One of ordinary skill in the art will recognize that the wiring arrangement described above can be modified to allow each group G 1 , G 2 , G 3 , G 4 , G 5  to be independently powered. Specifically, by providing a separate power source within the control system  100  for each group, each group can be individually turned on or off, or can be driven with an individualized power. This provides the advantage of allowing the delivery of ultrasonic energy to be “turned off” in regions of the treatment site where treatment is complete, thus preventing deleterious or unnecessary ultrasonic energy to be applied to the patient. 
     The embodiments described above, and illustrated in  FIGS. 5 through 7 , illustrate a plurality of ultrasound radiating members grouped spatially. That is, in such embodiments, all of the ultrasound radiating members within a certain group are positioned adjacent to each other, such that when a single group is activated, ultrasonic energy is delivered at a specific length of the ultrasound assembly. However, in modified embodiments, the ultrasound radiating members of a certain group may be spaced apart from each other, such that the ultrasound radiating members within a certain group are not positioned adjacent to each other. In such embodiments, when a single group is activated, ultrasonic energy can be delivered from a larger, spaced apart portion of the energy delivery section. Such modified embodiments may be advantageous in applications wherein it is desired to deliver a less focused, more diffuse ultrasonic energy field to the treatment site. 
     In a preferred embodiment, the ultrasound radiating members  40  comprise rectangular lead zirconate titanate (“PZT”) ultrasound transducers that have dimensions of about 0.017 inches by about 0.010 inches by about 0.080 inches. In other embodiments, other configuration may be used. For example, disc-shaped ultrasound radiating members  40  can be used in other embodiments. In a preferred embodiment, the common wire  108  comprises copper, and is about 0.005 inches thick, although other electrically conductive materials and other dimensions can be used in other embodiments. Lead wires  110  are preferably  36  gauge electrical conductors, while positive contact wires  112  are preferably  42  gauge electrical conductors. However, one of ordinary skill in the art will recognize that other wire gauges can be used in other embodiments. 
     As described above, suitable frequencies for the ultrasound radiating member  40  include, but are not limited to, from about 20 kHz to about 20 MHz. In one embodiment, the frequency is between about 500 kHz and 20 MHz, and in another embodiment 1 MHz and 3 MHz. In yet another embodiment, the ultrasound radiating members  40  are operated with a frequency of about 2 MHz. 
       FIG. 8  illustrates the inner core  34  positioned within the tubular body  12 . Details of the ultrasound assembly  42 , provided in  FIG. 7A , are omitted for clarity. As described above, the inner core  34  can be slid within the central lumen  51  of the tubular body  12 , thereby allowing the inner core energy delivery section  41  to be positioned within the tubular body energy delivery section  18 . For example, in a preferred embodiment, the materials comprising the inner core energy delivery section  41 , the tubular body energy delivery section  18 , and the potting material  43  all comprise materials having a similar acoustic impedance, thereby minimizing ultrasonic energy losses across material interfaces. 
       FIG. 8  further illustrates placement of fluid delivery ports  58  within the tubular body energy delivery section  18 . As illustrated, holes or slits are formed from the fluid delivery lumen  30  through the tubular body  12 , thereby permitting fluid flow from the fluid delivery lumen  30  to the treatment site. Thus, a source of therapeutic compound coupled to the inlet port  32  provides a hydraulic pressure which drives the therapeutic compound through the fluid delivery lumens  30  and out the fluid delivery ports  58 . 
     By evenly spacing the fluid delivery lumens  30  around the circumference of the tubular body  12 , as illustrated in  FIG. 8 , a substantially even flow of therapeutic compound around the circumference of the tubular body  12  can be achieved. In addition, the size, location and geometry of the fluid delivery ports  58  can be selected to provide uniform fluid flow from the fluid delivery ports  30  to the treatment site. For example, in one embodiment, fluid delivery ports closer to the proximal region of the energy delivery section  18  have smaller diameters then fluid delivery closer to the distal region of the energy delivery section  18 , thereby allowing uniform delivery of fluid across the entire energy delivery section. 
     For example, in one embodiment in which the fluid delivery ports  58  have similar sizes along the length of the tubular body  12 , the fluid delivery ports  58  have a diameter between about 0.0005 inches to about 0.0050 inches. In another embodiment in which the size of the fluid delivery ports  58  changes along the length of the tubular body  12 , the fluid delivery ports  58  have a diameter between about 0.001 inches to about 0.005 inches in the proximal region of the energy delivery section  18 , and between about 0.005 inches to 0.0020 inches in the distal region of the energy delivery section  18 . The increase in size between adjacent fluid delivery ports  58  depends on the material comprising the tubular body  12 , and on the size of the fluid delivery lumen  30 . The fluid delivery ports  58  can be created in the tubular body  12  by punching, drilling, burning or ablating (such as with a laser), or by any other suitable method. Therapeutic compound flow along the length of the tubular body  12  can also be increased by increasing the density of the fluid delivery ports  58  toward the distal region  15  of the tubular body  12 . 
     It should be appreciated that it may be desirable to provide non-uniform fluid flow from the fluid delivery ports  58  to the treatment site. In such embodiment, the size, location and geometry of the fluid delivery ports  58  can be selected to provide such non-uniform fluid flow. 
     Referring still to  FIG. 8 , placement of the inner core  34  within the tubular body  12  further defines cooling fluid lumens  44 . Cooling fluid lumens  44  are formed between an outer surface  39  of the inner core  34  and an inner surface  16  of the tubular body  12 . In certain embodiments, a cooling fluid can is introduced through the proximal access port  31  such that cooling fluid flow is produced through cooling fluid lumens  44  and out distal exit port  29  (see  FIG. 1 ). The cooling fluid lumens  44  are preferably evenly spaced around the circumference of the tubular body  12  (that is, at approximately 120° increments for a three-lumen configuration), thereby providing uniform cooling fluid flow over the inner core  34 . Such a configuration is desirably to remove unwanted thermal energy at the treatment site. As will be explained below, the flow rate of the cooling fluid and the power to the ultrasound assembly  42  can be adjusted to maintain the temp of the inner core energy delivery section  41  within a desired range. 
     In a preferred embodiment, the inner core  34  can be rotated or moved within the tubular body  12 . Specifically, movement of the inner core  34  can be accomplished by maneuvering the proximal hub  37  while holding the backend hub  33  stationary. The inner core outer body  35  is at least partially constructed from a material that provides enough structural support to permit movement of the inner core  34  within the tubular body  12  without kinking of the tubular body  12 . Additionally, the inner core outer body  35  preferably comprises a material having the ability to transmit torque. Suitable materials for the inner core outer body  35  include, but are not limited to, polyimides, polyesters, polyurethanes, thermoplastic elastomers and braided polyimides. 
     In a preferred embodiment, the fluid delivery lumens  30  and the cooling fluid lumens  44  are open at the distal end of the tubular body  12 , thereby allowing the therapeutic compound and the cooling fluid to pass into the patient&#39;s vasculature at the distal exit port. Or, if desired, the fluid delivery lumens  30  can be selectively occluded at the distal end of the tubular body  12 , thereby providing additional hydraulic pressure to drive the therapeutic compound out of the fluid delivery ports  58 . In either configuration, the inner core  34  can prevented from passing through the distal exit port by making providing the inner core  34  with a length that is less than the length of the tubular body. In other embodiments, a protrusion is formed on the internal side of the tubular body in the distal region  15 , thereby preventing the inner core  34  from passing through the distal exit port. 
     In still other embodiments, the catheter  10  further comprises an occlusion device (not shown) positioned at the distal exit port  29 . The occlusion device preferably has a reduced inner diameter that can accommodate a guidewire, but that is less than the inner diameter of the central lumen  51 . Thus, the inner core  34  is prevented from extending through the occlusion device and out the distal exit port  29 . For example, suitable inner diameters for the occlusion device include, but are not limited to, about 0.005 inches to about 0.050 inches. In other embodiments, the occlusion device has a closed end, thus preventing cooling fluid from leaving the catheter  10 , and instead recirculating to the proximal region  14  of the tubular body  12 . These and other cooling fluid flow configurations permit the power provided to the ultrasound assembly  42  to be increased in proportion to the cooling fluid flow rate. Additionally, certain cooling fluid flow configurations can reduce exposure of the patient&#39;s body to cooling fluids. 
     In certain embodiments, as illustrated in  FIG. 8 , the tubular body  12  further comprises one or more temperature sensors  20 , which are preferably located within the energy delivery section  18 . In such embodiments, the proximal region  14  of the tubular body  12  includes a temperature sensor lead which can be incorporated into cable  45  (illustrated in  FIG. 1 ). Suitable temperature sensors include, but are not limited to, temperature sensing diodes, thermistors, thermocouples, resistance temperature detectors (“RTDs”) and fiber optic temperature sensors which use thermalchromic liquid crystals. Suitable temperature sensor  20  geometries include, but are not limited to, a point, a patch or a stripe. The temperature sensors  20  can be positioned within one or more of the fluid delivery lumens  30  (as illustrated), and/or within one or more of the cooling fluid lumens  44 . 
       FIG. 9  illustrates one embodiment for electrically connecting the temperature sensors  20 . In such embodiments, each temperature sensor  20  is coupled to a common wire  61  and is associated with an individual return wire  62 . Accordingly, n+1 wires can be used to independently sense the temperature at n distinct temperature sensors  20 . The temperature at a particular temperature sensor  20  can be determined by closing a switch  64  to complete a circuit between that thermocouple&#39;s individual return wire  62  and the common wire  61 . In embodiments wherein the temperature sensors  20  comprise thermocouples, the temperature can be calculated from the voltage in the circuit using, for example, a sensing circuit  63 , which can be located within the external control circuitry  100 . 
     In other embodiments, each temperature sensor  20  is independently wired. In such embodiments, 2n wires through the tubular body  12  to independently sense the temperature at n independent temperature sensors  20 . In still other embodiments, the flexibility of the tubular body  12  can be improved by using fiber optic based temperature sensors  20 . In such embodiments, flexibility can be improved because only n fiber optic members are used to sense the temperature at n independent temperature sensors  20 . 
       FIG. 10  illustrates one embodiment of a feedback control system  68  that can be used with the catheter  10 . The feedback control system  68  can be integrated into the control system that is connected to the inner core  34  via cable  45  (as illustrated in  FIG. 1 ). The feedback control system  68  allows the temperature at each temperature sensor  20  to be monitored and allows the output power of the energy source  70  to be adjusted accordingly. A physician can, if desired, override the closed or open loop system. 
     The feedback control system  68  preferably comprises an energy source  70 , power circuits  72  and a power calculation device  74  that is coupled to the ultrasound radiating members  40 . A temperature measurement device  76  is coupled to the temperature sensors  20  in the tubular body  12 . A processing unit  78  is coupled to the power calculation device  74 , the power circuits  72  and a user interface and display  80 . 
     In operation, the temperature at each temperature sensor  20  is determined by the temperature measurement device  76 . The processing unit  78  receives each determined temperature from the temperature measurement device  76 . The determined temperature can then be displayed to the user at the user interface and display  80 . 
     The processing unit  78  comprises logic for generating a temperature control signal. The temperature control signal is proportional to the difference between the measured temperature and a desired temperature. The desired temperature can be determined by the user (at set at the user interface and display  80 ) or can be preset within the processing unit  78 . 
     The temperature control signal is received by the power circuits  72 . The power circuits  72  are preferably configured to adjust the power level, voltage, phase and/or current of the electrical energy supplied to the ultrasound radiating members  40  from the energy source  70 . For example, when the temperature control signal is above a particular level, the power supplied to a particular group of ultrasound radiating members  40  is preferably reduced in response to that temperature control signal. Similarly, when the temperature control signal is below a particular level, the power supplied to a particular group of ultrasound radiating members  40  is preferably increased in response to that temperature control signal. After each power adjustment, the processing unit  78  preferably monitors the temperature sensors  20  and produces another temperature control signal which is received by the power circuits  72 . 
     The processing unit  78  preferably further comprises safety control logic. The safety control logic detects when the temperature at a temperature sensor  20  has exceeded a safety threshold. The processing unit  78  can then provide a temperature control signal which causes the power circuits  72  to stop the delivery of energy from the energy source  70  to that particular group of ultrasound radiating members  40 . 
     Because, in certain embodiments, the ultrasound radiating members  40  are mobile relative to the temperature sensors  20 , it can be unclear which group of ultrasound radiating members  40  should have a power, voltage, phase and/or current level adjustment. Consequently, each group of ultrasound radiating member  40  can be identically adjusted in certain embodiments. In a modified embodiment, the power, voltage, phase, and/or current supplied to each group of ultrasound radiating members  40  is adjusted in response to the temperature sensor  20  which indicates the highest temperature. Making voltage, phase and/or current adjustments in response to the temperature sensed by the temperature sensor  20  indicating the highest temperature can reduce overheating of the treatment site. 
     The processing unit  78  also receives a power signal from a power calculation device  74 . The power signal can be used to determine the power being received by each group of ultrasound radiating members  40 . The determined power can then be displayed to the user on the user interface and display  80 . 
     As described above, the feedback control system  68  can be configured to maintain tissue adjacent to the energy delivery section  18  below a desired temperature. For example, it is generally desirable to prevent tissue at a treatment site from increasing more than 6° C. As described above, the ultrasound radiating members  40  can be electrically connected such that each group of ultrasound radiating members  40  generates an independent output. In certain embodiments, the output from the power circuit maintains a selected energy for each group of ultrasound radiating members  40  for a selected length of time. 
     The processing unit  78  can comprise a digital or analog controller, such as for example a computer with software. When the processing unit  78  is a computer it can include a central processing unit (“CPU”) coupled through a system bus. As is well known in the art, the user interface and display  80  can comprise a mouse, a keyboard, a disk drive, a display monitor, a nonvolatile memory system, or any another. Also preferably coupled to the bus is a program memory and a data memory. 
     In lieu of the series of power adjustments described above, a profile of the power to be delivered to each group of ultrasound radiating members  40  can be incorporated into the processing unit  78 , such that a preset amount of ultrasonic energy to be delivered is pre-profiled. In such embodiments, the power delivered to each group of ultrasound radiating members  40  can then be adjusted according to the preset profiles. 
     The ultrasound radiating members are preferably operated in a pulsed mode. For example, in one embodiment, the time average power supplied to the ultrasound radiating members is preferably between about 0.1 watts and 2 watts and more preferably between about 0.5 watts and 1.5 watts. In certain preferred embodiments, the time average power is approximately 0.6 watts or 1.2 watts. The duty cycle is preferably between about 1% and 50% and more preferably between about 5% and 25%. In certain preferred embodiments, the duty ratio is approximately 7.5% or 15%. The pulse averaged power is preferably between about 0.1 watts and 20 watts and more preferably between approximately 5 watts and 20 watts. In certain preferred embodiments, the pulse averaged power is approximately 8 watts and 16 watts. The amplitude during each pulse can be constant or varied. 
     In one embodiment, the pulse repetition rate is preferably between about 5 Hz and 150 Hz and more preferably between about 10 Hz and 50 Hz. In certain preferred embodiments, the pulse repetition rate is approximately 30 Hz. The pulse duration is preferably between about 1 millisecond and 50 milliseconds and more preferably between about 1 millisecond and 25 milliseconds. In certain preferred embodiments, the pulse duration is approximately 2.5 milliseconds or 5 milliseconds. 
     In one particular embodiment, the transducers are operated at an average power of approximately 0.6 watts, a duty cycle of approximately 7.5%, a pulse repetition rate of 30 Hz, a pulse average electrical power of approximately 8 watts and a pulse duration of approximately 2.5 milliseconds. 
     The ultrasound radiating member used with the electrical parameters described herein preferably has an acoustic efficiency greater than 50% and more preferably greater than 75%. The ultrasound radiating member can be formed a variety of shapes, such as, cylindrical (solid or hollow), flat, bar, triangular, and the like. The length of the ultrasound radiating member is preferably between about 0.1 cm and about 0.5 cm. The thickness or diameter of the ultrasound radiating members is preferably between about 0.02 cm and about 0.2 cm. 
       FIGS. 11A through 11D  illustrate a method for using the ultrasonic catheter  10 . As illustrated in  FIG. 11A , a guidewire  84  similar to a guidewire used in typical angioplasty procedures is directed through a patient&#39;s vessels  86  to a treatment site  88  which includes a clot  90 . The guidewire  84  is directed through the clot  90 . Suitable vessels  86  include, but are not limited to, the large periphery blood vessels of the body. Additionally, as mentioned above, the ultrasonic catheter  10  also has utility in various imaging applications or in applications for treating and/or diagnosing other diseases in other body parts. 
     As illustrated in  FIG. 10B , the tubular body  12  is slid over and is advanced along the guidewire  84  using conventional over-the-guidewire techniques. The tubular body  12  is advanced until the energy delivery section  18  of the tubular body  12  is positioned at the clot  90 . In certain embodiments, radiopaque markers (not shown) are positioned along the energy delivery section  18  of the tubular body  12  to aid in the positioning of the tubular body  12  within the treatment site  88 . 
     As illustrated in  FIG. 10C , the guidewire  84  is then withdrawn from the tubular body  12  by pulling the guidewire  84  from the proximal region  14  of the catheter  10  while holding the tubular body  12  stationary. This leaves the tubular body  12  positioned at the treatment site  88 . 
     As illustrated in  FIG. 10D , the inner core  34  is then inserted into the tubular body  12  until the ultrasound assembly  42  abuts against the occlusion device and is positioned at least partially within the energy delivery section  18  of the tubular body  12 . Once the inner core  34  is properly positioned, the ultrasound assembly  42  is activated to deliver ultrasonic energy through the energy delivery section  18  to the clot  90 . As described above, suitable ultrasonic energy is delivered with a frequency between about 20 kHz and about 20 MHz. 
     In a certain embodiment, the ultrasound assembly  42  comprises sixty ultrasound radiating members  40  spaced over a length of approximately 30 to 50 cm. In such embodiments, the catheter  10  can be used to treat an elongate clot  90  without requiring movement of or repositioning of the catheter  10  during the treatment. However, it will be appreciated that in modified embodiments the inner core  34  can be moved or rotated within the tubular body  12  during the treatment. Such movement can be accomplished by maneuvering the proximal hub  37  of the inner core  34  while holding the backend hub  33  stationary. 
     Referring again to  FIG. 11D , arrows  48  indicate that a cooling fluid flows through the cooling fluid lumen  44  and out the distal exit port  29 . Likewise, arrows  49  indicated that a therapeutic compound flows through the fluid delivery lumen  30  and out the fluid delivery ports  58  to the treatment site  88 . 
     The cooling fluid can be delivered before, after, during or intermittently with the delivery of ultrasonic energy. Similarly, the therapeutic compound can be delivered before, after, during or intermittently with the delivery of ultrasonic energy. Consequently, the steps illustrated in  FIGS. 11A through 11D  can be performed in a variety of different orders than that described above. The therapeutic compound and ultrasonic energy are preferably applied until the clot  90  is partially or entirely dissolved. Once the clot  90  has been dissolved to the desired degree, the tubular body  12  and the inner core  34  are withdrawn from the treatment site  88 . 
     To reduce electric current leakage through the patient&#39;s body to ground, in certain embodiments the control system  100  may comprise an isolation pod  200 .  FIG. 12  illustrates one embodiment of an isolation pod  200  that is contains certain portions of the control system  100 , as described in more detail below. Preferably, the external control circuitry  100 , including the isolation pod  200  (if any), is positioned proximal to the backend hub  33  (see  FIG. 1 ), thereby preventing crosstalk between the wiring to the plurality of groups of ultrasound radiating members. 
     The isolation pod  200  comprises an isolation barrier  228  configured to reduce or eliminate unwanted electrical current flow through the patient&#39;s body. For example, in the illustrated embodiment, two transformers  256 ,  276  form an isolation barrier between the external control circuitry  100  and the certain components of the isolation pod  200 . 
     Referring still to  FIG. 12 , a transformer loop  278  is used to measure the leakage current of the catheter  10 . This leakage current represents the current that does not return to the isolation pod  200  through the return lines, but instead passes through the patient&#39;s body to ground. A center tap from the transformer loop  278  connects to two diodes that rectify the leakage current. In this example, zener diodes with a low threshold voltage are used to rectify the small signal provided from the transformer loop. 
     The external control circuitry  100  provides a radio frequency signal  224  for driving the ultrasound assembly  42 . The radio frequency signal  224  operates in the ultrasonic frequency range, and is tuned to a frequency that activates the ultrasound radiating members  40  in the inner core  34 . The radio frequency signal  224  is electromagnetically coupled to the isolation pod  200  using a transformer  256 . The dielectric layers of the transformer  256  form an isolation barrier. This isolation barrier substantially prevents electrical current from flowing from the isolation pod  200 , through the patient&#39;s body, and back into the isolation pod  200 . By electromagnetically coupling the driving radio frequency signal to the isolation pod  200 , the current loop is broken and electric current is thereby prevented from flowing through the patient&#39;s body. 
     In the embodiment illustrated in  FIG. 12 , the isolation pod  200  is compatible with multiple types of catheters. The different catheters can use different types or quantities of ultrasound radiating members, which in tum may cause variations in the input impedance seen by the radio frequency amplifier. Even if the ultrasound radiating members are configured to be identical, fabrication defects will often cause the impedance of ultrasound radiating members to vary. Additionally, the activation pattern or configuration of ultrasound radiating members within a catheter can also alter the input impedance. 
     The exemplary isolation pod  200  includes circuitry to enable matching the output impedance of the radio frequency amplifier to the input impedance of the ultrasound radiating members. For example, many radio frequency amplifiers have an output impedance of about 50 n. To maximize power efficiency, the isolation pod  200  attempts to match the impedance by providing a substantially equivalent 50 Q at the input. 
     Still referring to  FIG. 12 , the isolation pod  200  provides circuitry for tuning the input impedance of the isolation pod  200  to match the output impedance of the radio frequency amplifier. For example,  FIG. 12  illustrates the coupling transformer  256  with taps  258  on the secondary side. Selecting different taps modifies the turns ratio of the transformer and thereby changes the input impedance of the isolation pod  200 . 
     Changing the turns ratio of the coupling transformer  256  also affects the amplitude of the current passing through the ultrasonic assembly  42 . As needed, the external control circuitry  100  compensates for these changes in amplitude for example by driving the radio frequency signal at different levels. 
     The embodiment illustrated in  FIG. 12  also shows the use of inductors  260  for tuning the input impedance. As illustrated, the isolation pod  200  further comprises three individually controlled switches  262  that connect the three inductors with the radio frequency input circuit. In this example, a total of eight tuning settings are achievable by opening and closing the inductor switches in various combinations. The tuning circuitry is not limited to the use of inductors or transformer taps. Other components, such as capacitors and resistors, may also be used to tune the input impedance. 
     In one embodiment, tuning information is determined for a catheter at the time of manufacture. The tuning information is then embedded into the catheter, such as by saving the tuning information in an identification programmable read-only memory (“PROM”)  254 . Alternatively, the serial number or other identifying indicia of the catheter together with the tuning information is entered into a database. The isolation pod  200  then retrieves the tuning information from the database and appropriately adjusts the tuning circuitry to the catheter that is attached to the isolation pod  200 . 
     In another embodiment, the isolation pod  200  includes internal circuitry to detect the impedance of the ultrasound assembly  42  in the catheter and adjusts the tuning circuitry appropriately. 
       FIG. 12  further illustrates a configuration that is particularly adapted for the use of multiple ultrasound radiating members such as in the arrangements described above. In the illustrated embodiment, ten ultrasound radiating members are connected to the isolation pod  200  using five connections. The ultrasound radiating members are controlled by multiplexing the driving signal through five pairs of switches  268 . The ultrasound radiating member driving lines in the inner core  34  connect to the pairs of switches  268  within the isolation pod  200 . Each pair of switches  268  has four settings: (open, open), (open, closed), (closed, open) and (closed, closed). In operation, only three settings are used because the (closed, closed) setting short-circuits the driving signal. In the illustrated example, wherein there are five ultrasound radiating member driving lines, 3 5 =243 modes of operation are available. Examples of these modes are described in the embodiments that follow. 
       FIG. 13  illustrates an arrangement where the ultrasound radiating members are linearly spaced within the catheter. In the illustrated example, the catheter has five ultrasound radiating member driving lines  302 ,  304 ,  306 ,  308 , and  310 . 
     In one embodiment, one pair of switches is in the (closed, open) setting and the remaining four pairs of switches are in the (open, closed) setting. In this such embodiments, four ultrasound radiating members are active at a time. The remaining six ultrasound radiating members have both terminals short circuited, so they are not active. 
       FIG. 14  illustrates an embodiment wherein the pair of switches for the first ultrasound radiating member driving line  302  is in the (closed, open) setting and the pairs of switches for the remaining ultrasound radiating member driving lines  304 ,  306 ,  308 ,  310  are in the (open, closed) setting. In this configuration, four ultrasound radiating members  312 ,  314 ,  316 ,  318  are active, and six remaining ultrasound radiating members  320 ,  322 ,  324 ,  326 ,  328 ,  330  are inactive. The active ultrasound radiating members  312 ,  314 ,  316 ,  318  have substantially the same voltage differential appearing across the ultrasound radiating members terminals. 
       FIG. 15  illustrates an embodiment wherein one pair of switches is in the (closed, open) setting and another pair of switches is in the (open, closed) setting. As illustrated, the pair of switches for the first ultrasound radiating member driving line  302  is in the (closed, open) setting, the pair of switches for the second ultrasound radiating member driving line  304  is in the (open, closed) setting, and the pairs of switches for the remaining ultrasound radiating member driving lines  306 ,  308 ,  310  are in the (open, open) setting. The resulting network of connections between the ultrasound radiating member form several voltage dividers. This results in different voltage differences across the terminals of the various ultrasound radiating members. Assuming the ultrasound radiating members are equivalent, the first ultrasound radiating member  312  will have the full driving signal appearing across its terminals, six ultrasound radiating members  314 ,  316 ,  318 ,  320 ,  322 ,  324  will have a half-strength driving signal appearing across their terminals, and the remaining three ultrasound radiating members  326 ,  328 ,  330  will have no voltage differential appearing across their terminals. 
       FIG. 16  illustrates an embodiment wherein the pairs of switches for the first and third ultrasound radiating member driving lines  302 ,  306  are in the (closed, open) setting and the pairs of switches for the remaining ultrasound radiating member driving lines  304 ,  308 ,  310  are in the (open, closed) setting. In this configuration, six ultrasound radiating members  312 ,  316 ,  318 ,  320 ,  326 ,  328  are active, and the remaining four ultrasound radiating members  314 ,  322 ,  324 ,  330  are inactive. 
       FIG. 17  shows a modified catheter configuration with seven connections to the isolation pod  200 . In such a configuration, the isolation pod  200  uses four switches to connect the first terminal  278  of the driving signal to the first four ultrasound radiating member driving lines  352 ,  354 ,  356 ,  358 , and three switches to connect the second terminal  280  of the driving signal to the remaining three ultrasound radiating member driving lines  360 ,  362 ,  364 . When all of the switches connected to the first terminal  278  are in the (closed) setting, each switch connected to the second terminal  280  activates a bank of four ultrasound radiating members. For example, if all the switches to the first terminal  278  are closed, closing the switch for the ultrasound radiating member driving line  360  activates four ultrasound radiating members  372 ,  378 ,  384 ,  390 . Closing the switch for the ultrasound radiating member driving line  362  activates four ultrasound radiating members  374 ,  380 ,  386 ,  392 , and closing the switch for the ultrasound radiating member driving line  364  activates four ultrasound radiating members  376 ,  382 ,  388 ,  394 . The banks are independently operable, so zero, one or two banks can be active at any given time. 
     Alternatively, when all of the switches connected to the second terminal  280  are in the (closed) setting, each switch connected to the first terminal  278  activates a bank of three ultrasound radiating members. For example, if all the switches to the second terminal  280  are closed, closing the switch for the ultrasound radiating member driving line  352  activates three ultrasound radiating members  372 ,  374 ,  376 ,  378 . Other banks of three ultrasound radiating members are activated by the closing switches for the remaining three ultrasound radiating member driving lines  354 ,  356 ,  358 . Again, the banks are independently operable, so zero, one, two, or three banks can be active at any given time. 
     It is not necessary to activate the ultrasound radiating members in banks, because the switches can be individually controlled. A total of  2   7 =128 driving combinations are possible. The non-bank configurations include voltage divider circuits, so all of the ultrasound radiating members are not driven at full strength in these configurations. 
       FIG. 18  illustrates another catheter embodiment where the ultrasound radiating members are arranged in three banks with four ultrasound radiating members in each bank. Closing the switch for ultrasound radiating member driving line  430  activates four ultrasound radiating members  402 ,  408 ,  414 ,  420 . Closing the switch for ultrasound radiating member driving line  432  activates four ultrasound radiating members  404 ,  410 ,  416 ,  422 . Closing the switch for ultrasound radiating member driving line  434  activates four ultrasound radiating members  406 ,  412 ,  418 ,  424 . 
     One of ordinary skill in the art will understand that the illustrated embodiments are exemplary and that the catheter design is not limited to the illustrated configurations. For example, the catheter may include different numbers of ultrasound radiating members, ultrasound radiating member driving lines, or switches. Some or all of the switches may alternately be included as part of the catheter. 
     A catheter may include ultrasound radiating members tuned to resonate at multiple frequencies. Ultrasound radiating members having the same resonant frequency can be selected individually or in groups. Alternatively, ultrasound radiating members having different resonant frequencies can be driven by the same driving signal. In such embodiments, the amount of ultrasonic energy delivered by an ultrasound radiating member depends in part on the frequency at which the ultrasound radiating member is driven. 
     Controlling the amplitude and frequency of the driving signal and arranging the placement of the ultrasound radiating members allows the catheter to deliver appropriate ultrasonic energy levels to the treatment site. In certain applications, it is desired that the catheter delivers a uniform dose of ultrasonic energy to the treatment site. In other applications, it is desired to deliver greater amounts of ultrasonic energy or ultrasonic energy of a different frequency to different portions of the treatment site. The individual control of the ultrasound radiating members described above allows the ultrasound assembly to deliver the appropriate amount and quality of ultrasonic energy to the treatment site. 
     For example, piezoelectric transducers can be used to generate ultrasonic energy. Piezoelectric transducers produce ultrasonic energy when an electric voltage is applied to certain crystalline structures. The characteristics of the ultrasonic energy generated by a piezoelectric transducer is determined by the crystalline structure of the transducer, as well as by the frequency and voltage at which the transducer is driven. 
     As shown in  FIG. 12 , the isolation pod  200  includes circuitry for controlling the generation of ultrasonic energy. In one embodiment, an alternating current (“AC”) signal is provided to the isolation pod  200  from an external source. In another embodiment, the AC signal is generated within the isolation pod  200  using circuitry such as a crystal oscillator. In one embodiment, the AC signal drives the ultrasound radiating members directly. In a modified embodiment, the isolation pod  200  includes additional circuitry to modify the AC signal before driving the ultrasound radiating members. 
     As discussed above, and as shown in  FIG. 12 , in certain embodiments the catheter further comprises temperature sensors. As illustrated, the current source applies a constant current bias across a silicon P—N diode junction. At a constant current bias, the voltage drop across a silicon P—N diode junction shows roughly a −2 mV ° C −1  temperature coefficient. The arrangement of temperature sensor diodes in the catheter together with the diode path selection switches and the reversible current source allows the isolation pod  200  to select a single diode from the set of twelve diodes for measuring the temperature. The remaining diodes are either switched out of the circuit or reverse biased. A pre-amplifier circuit amplifies the voltage drop across the diode and provides a signal to an analog to digital (AID) converter. 
       FIG. 19  illustrates a diode arrangement within a catheter. In this embodiment, configuring a first set of switches in the (open, closed) setting, a second set of switches in the (closed, open) setting, and the remaining to sets of switches in the (open, open) setting results in one diode being forward biased and a second diode being reverse biased. The remaining diodes are left floating at one or both terminals. 
     The direction of the current is controlled by a single-pull double-throw (SPDT) switch as illustrated in  FIG. 12 . The direction of the current determines which of the two non-floating diodes is forward biased. 
     Because there may be some variance in the diodes when used as temperatures sensors, one embodiment utilizes a calibration process. For example, calibration data may be included in the ID PROM  254 . In modified embodiments, the diodes can be calibrated against an ambient temperature reading. 
     In other embodiments, the temperature sensors  20  monitor the temperature of the treatment site at which the catheter is operating. For example, in one embodiment a temperature sensor is placed near an ultrasound radiating member to measure the temperature of the tissue near the catheter. In other embodiments, a temperature sensor is positioned between two ultrasound radiating members to measure the average energy delivered by the ultrasound assembly. 
     Referring again to the isolation pod  200  illustrated in  FIG. 12 , power is provided through the power isolation transformer  276 . Communications data can be modulated with the power signal. For example, the embodiment illustrated in  FIG. 12  further comprises a modulator/demodulator (“modem”) configured to transmit and receive signals modulated on the power signal. This allows a microcontroller  272  to communicate with the external control circuitry  100 . In such embodiments, the external control circuitry  100  can effectively control the activation of ultrasound radiating members and diodes by sending commands to the microcontroller. Or, in modified embodiments, the microcontroller can execute control sequences from memory. The microcontroller preferably includes outputs to control the switches and other drivers within the isolation pod  200 . 
     Still referring to  FIG. 12 , a PROM  254  contains information relating to a number of factors, including but not limited to the catheter length, the number of ultrasound radiating members, the center frequency at which each ultrasound radiating member should be run, the tuning parameters for the ultrasound radiating members, and the calibration factors for the temperature sensors. A catheter connector  230 , illustrated in  FIG. 20 , and which will be described in detail below, provides connection between the wires in the isolation pod  200  and the wires in the cable  45 . These wires carry electrical signals between the isolation pod  200  and the inner core  34  located within the catheter  10 . 
     As illustrated in  FIG. 20 , the connection between the isolation pod  200  and the catheter  10  generally comprises a catheter connector  230 . The catheter connector  230  is preferably integral with the isolation pod  200 , and generally comprises a customized slot  240  into which the cable  45  fits. One advantage of having the catheter connector  230  integral with the isolation pod  200  is the reduction in physical space and costs that are associated with using an additional cable and connection device outside the isolation pod  200 . In the illustrated embodiment, a toe-catch arrangement assures a proper fit and assists in keeping the connecting end of the cable  45  within the customized slot. The catheter connector  230  preferably includes a latch  244  to secure the connecting end of the cable  45  within the customized slot  240 . 
     Still referring to  FIG. 20 , the catheter connector  230  preferably comprises an array of gold spring contacts  246  which provide an electrical connection between the isolation pod  200  and the cable  45 . The wire contacts at the connecting end of the cable are configured to be aligned with the gold spring contacts  246  of the connector  230 . The catheter connector  230 , the cable  45 , and their respective components can be manufactured in accordance with any of the variety of techniques well known in the electrical interfacing and wiring fields. 
     In the embodiment illustrated in  FIG. 12 , a catheter houses the ultrasound radiating members and the temperature sensors. In such embodiments, the catheter is connected to the isolation pod  200  which houses the electronics capable of driving the ultrasound radiating members, as well as additional electronics capable of processing temperature signals received from the catheter. In one embodiment, the isolation pod  200  receives control signals from external circuitry  300 , and transmits data back to the external circuitry using a data interface  252 . 
     In another embodiment, all or part of the electronics for driving the ultrasound radiating members is housed within the backend hub  33 . Similarly, all or part of the electronics for processing the temperature signals is can be housed within the backend hub  33  as well. However, because certain catheters described herein are intended to be disposable, the cost of the catheter can be reduced by minimizing the amount of electronics contained within the catheter. Additionally, reducing the amount of electronics contained within the catheter also reduces the catheter size. Thus, catheters configured to operate in narrow passages such as small vessels will also benefit from the reduction of electronics contained within the catheter. Therefore, in other embodiments, minimal electronics is incorporated within the catheter. 
     A user may connect multiple types of catheter to a single isolation pod  200 . To identify the type of catheter connected to the isolation pod  200 , the catheter preferably includes electronics containing an identifying code. The identifying code conveys information such as the type of catheter, the serial number of the catheter, the manufacturing location of the catheter, the date of manufacture, or other identifying information. In one embodiment, the circuitry for storing the identifying code is a PROM  254 . Other types of memory such as flash memory or non-volatile random access memory (“RAM”) can also serve to identify the catheter. Electronics such as switches, jumpers, diodes, or hard wired connections can also serve to identify the catheter. One of ordinary skill in the art will recognize that other circuits not disclosed herein will also provide identification of the catheter. 
     Information contained on the identification PROM  254  can include, for example, the length of the catheter, the length of the treatment zone, the number of ultrasound radiating members in the catheter, the ultrasound radiating member layout, the resonant frequency of the ultrasound radiating members, tuning information for the ultrasound radiating members, compensation and/or calibration data for the diodes, or patterns for driving the ultrasound radiating members. 
     As illustrated in  FIG. 12 , in one embodiment, temperature sensitive diodes  238  are used as sensors to measure a temperature near the catheter. In such embodiments, a pair of temperature sensitive diodes  238  is selectively enabled, and an output signal is provided to an analog to digital (“AID”) converter. Or, in modified embodiments, multiple pairs of diodes are activated with the output signals being provided to the AID converter simultaneously. Other embodiments include a sensor to measure the ambient temperature, which is used, for example, to calibrate the temperature sensors. Additionally, the ambient temperature provides information as to whether the catheter and isolation pod are functioning properly. 
     Still referring to  FIG. 12 , the output of the AID converter  270  is provided to a microcontroller  272  for analysis. The microcontroller  272  monitors the heat produced by the various ultrasound radiating members and/or the temperature of the tissue near the catheter, and uses such information to provide control signals to adjust characteristics such as signal strength or frequency of the driving signal provided to the individual ultrasound radiating members. 
     One of ordinary skill m the art will recognize that the various embodiments of the isolation pod described above, and illustrated in  FIGS. 14 through 20 , can be used with the catheter and various ultrasound radiating member and temperature sensor configurations illustrated in  FIGS. 2 through 8 . In addition, the various embodiments of the isolation pod described above, and illustrated in  FIGS. 14 through 20 , can also be used with other ultrasound radiating member and temperature sensor configurations not specifically described herein. For example, the isolation pod may also be used with an ultrasonic catheter that has only one ultrasound radiating member and/or is configured to fit within the small vessels of the body such as the small vessel catheters described in co-pending U.S. patent application, entitled “Small Vessel Ultrasound Catheter”, filed on the same date as the present application. 
     While the foregoing detailed description has described several embodiments of the apparatus and methods of the present invention, it is to be understood that the above description is illustrative only and not limited of the disclosed invention. It will be appreciated that the specific dimensions of the various catheters and inner cores can differ from those described above, and that the methods described can be used within any biological conduit in a patient&#39;s body, while remaining within the scope of the present invention. Thus, the present invention is to be limited only by the claims that follow.