Patent Publication Number: US-2022233199-A1

Title: Dual ultrasonic catheter and methods of use

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit from U.S. Provisional Patent Application Ser. No. 63/140,372, filed Jan. 22, 2021, entitled “Dual Ultrasonic Probe and Methods of Use,” the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     The embodiments described herein relate generally to devices used in conjunction with an ultrasonic transducer assembly and, more specifically, to an ultrasonic probe assembly configured to transfer ultrasonic energy to a bodily tissue from an ultrasonic energy source. 
     Known ultrasonic energy transmission systems are used in many different medical applications, such as, for example, medical imaging, to disrupt obstructions and/or to ablate bodily tissue. In known ultrasonic energy transmission systems for tissue ablation, ultrasonic energy is transferred from an ultrasonic energy source through a transducer assembly (e.g., including an ultrasonic horn) and then to a transmission member, such as a wire or other elongate member, to a distal head. The transmission member can be, for example, an ultrasonic probe assembly. Ultrasonic energy propagates through the transmission member as a periodic wave thereby causing the distal head to vibrate. Such vibrational energy can be used to ablate or otherwise disrupt bodily tissue, for example, a vascular obstruction, a kidney stone or the like. To effectively reach various sites for treatment of intravascular occlusions or regions within the urinary tract, such ultrasonic transmission members often have lengths of about 65 cm or longer. 
     Known ultrasonic transmission members (e.g., prob assemblies) are constructed to be flexible enough to be passed through various bodily lumens, but also with sufficient strength to transmit ultrasonic energy to the distal tip (e.g., to ablate vascular or urinary obstructions). A stronger, more durable transmission member allows for greater transmission of energy but may not be flexible or thin enough to be advanced through the vasculature to a desired treatment area. A thinner transmission member can be more flexible but is less durable and more susceptible to breakage. 
     In an attempt to find a balance between strength and flexibility, some known ultrasonic transmission members have a reduced size or are less rigid, and therefore may not be well suited for treating occlusions (e.g., chronic total occlusion (CTO) within the vasculature). For example some known ultrasonic transmission members are too small to sufficiently expand against or deliver ultrasonic energy to the occlusion. Other known ultrasonic transmission members are not sufficiently rigid to penetrate the occlusion, thus limiting the effectiveness of delivering ultrasonic energy. Although some known systems include a lager guide catheter within which a transmission member can be placed, many known systems transmit energy via the inner transmission member to ablate the occlusion. Thus, in many instances, the energy transmitted from the inner transmission member is limited to a smaller portion of the occlusion. 
     Although some known systems include multiple transmission members through which energy (e.g., electrical energy) can be transmitted to ablate bodily tissue, such known systems do not provide for the ability to selectively transmit energy between the multiple transmission members. Further, such known systems may require the individual transmission members to each be separately coupled to an energy source. 
     Thus, a need exists for an improved apparatus and methods for transferring ultrasonic energy from an ultrasonic energy source to a bodily tissue. A need also exists for improved methods of ablating a chronic total occlusion (CTO) within the vasculature. 
     SUMMARY 
     Devices and methods of use of an ultrasonic probe assembly for use with an ultrasonic ablation system are described herein. In some embodiments, an apparatus includes a transducer assembly, a first probe, and a second probe. The transducer assembly includes a transducer housing and an ultrasonic transducer horn disposed within (or coupled to) the transducer housing. The transducer horn includes a probe coupling. The first probe includes a first coupler and a first elongate member coupled to the first coupler. The first coupler has a first coupling portion and a second coupling, portion, and the first coupling portion is configured to be releasably coupled to the probe coupling of the transducer horn such that the first probe is coupled to the ultrasonic transducer. The second probe includes a second coupler and a second elongate member coupled to the second coupler. The second coupler has a third coupling portion releasably couplable to the second coupling portion of the first coupler such that the second probe is coupled to the Ultrasonic transducer. 
     In some embodiments, a method includes introducing a distal portion of an ultrasonic probe assembly into a vessel of a patient. The ultrasonic probe assembly can be coupled to an ultrasonic transducer assembly and includes a first probe and a second probe. The first probe includes a first coupler and a first elongate member coupled to the first couple, and is coupled to the transducer assembly via the first coupler. The second probe includes a second coupler and a second elongate member coupled to the second coupler and is releasably coupled to the first coupler such that the second probe is coupled to the ultrasonic, transducer assembly via the first probe. The distal portion of the ultrasonic probe assembly is moved through an obstruction in the vessel such that a distal end portion of the first elongate member penetrates the obstruction and a distal end portion of the second elongate member penetrates the obstruction. Ultrasonic energy is transmitted from the ultrasonic transducer assembly to the first probe and to the second probe such that ultrasonic energy is delivered through the first elongate member and the second elongate member to the obstruction. 
     In some embodiments, a method includes introducing a distal portion of an ultrasonic probe assembly into a vessel of a patient. The ultrasonic probe assembly can be coupled to an ultrasonic transducer assembly and includes a first probe and a second probe. The first probe includes a first coupler and a first elongate member coupled to the first coupler and is coupled to the ultrasonic transducer assembly via the first coupler. The second probe includes a second coupler and a second elongate member coupled to the second coupler and the second elongate member defines a lumen. The first elongate member is within the lumen of the second elongate member such that a first distal tip of the first elongate member extends through a second distal tip of the second elongate member and outside the lumen of the second elongate member. The second coupler is releasably coupled to the first coupler. The distal portion of the ultrasonic probe assembly is moved through an obstruction in the vessel such that at least the distal tip of the first elongate member penetrates the obstruction. Ultrasonic energy is transmitted from the ultrasonic transducer assembly to at least the first probe such that ultrasonic energy is delivered through at least the first elongate member to the obstruction. The first probe is removed from within the second probe. A third probe is inserted into the lumen of the second probe. The third probe includes a third coupler and a third elongate member coupled to the third coupler. The third elongate member has a third distal tip that is sized to limit movement of the third distal tip through the second distal tip of the second elongate member. The second probe and the third probe are positioned through the obstruction in the vessel. After inserting the third probe, the second coupler of the second probe is coupled to the third coupler of the third probe, which includes moving the second elongate member proximally relative to the third elongate member causing the second distal tip to engage the third distal tip and deform a distal portion of the second elongate member to produce a contact location between the third elongate member and the second elongate member. Ultrasonic energy is transmitted from the ultrasonic transducer assembly to at least the third probe. At least a portion of the ultrasonic energy is delivered from the third elongate member through the contact location and the second elongate member to the obstruction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a system for delivering ultrasonic energy to a bodily tissue according to an embodiment. 
         FIG. 2  is a cross-sectional view of an ultrasonic transducer included in the system of  FIG. 1 . 
         FIG. 3A  is a perspective view of an ultrasonic probe assembly, according to an embodiment. 
         FIG. 3B  is an enlarged view of detail C in  FIG. 3A . 
         FIG. 4A  is a side view of the ultrasonic probe assembly of  FIG. 3A . 
         FIG. 4B  is a cross-sectional side view taken along line A-A in  FIG. 4A . 
         FIG. 5  is an enlarged view of detail B in  FIG. 4B . 
         FIG. 6A  is a perspective view of an inner probe of the ultrasonic probe assembly of  FIG. 3A . 
         FIG. 6B  is a perspective view of an outer probe of the ultrasonic probe assembly of  FIG. 3A . 
         FIG. 7A  is a schematic illustration of an inner probe and an outer probe of an ultrasonic probe assembly, according to an embodiment. 
         FIG. 7B  is a schematic illustration of an inner probe and an outer probe of an ultrasonic probe assembly according to another embodiment. 
         FIG. 7C  is a schematic illustration of an inner probe and an outer probe of an ultrasonic probe assembly according to yet another embodiment. 
         FIG. 8  is a schematic side view of a ultrasonic probe assembly, according to an embodiment, shown inserted within a vessel near an obstruction. 
         FIG. 9A  is a side view of a vessel of a patient with an obstruction, with a first and second ultrasonic probe assembly, according to an embodiment, shown inserted within the vessel near the obstruction and in a use configuration to apply ultrasonic energy to the obstruction. 
         FIG. 9B  is a side view of the vessel of  FIG. 9A  with a third ultrasonic probe assembly shown inserted within the first ultrasonic probe assembly in a first configuration near the obstruction. 
         FIG. 9C  is a side view of the vessel and third ultrasonic probe assembly of  FIG. 9C  in a second configuration near the obstruction to apply ultrasonic energy to the obstruction. 
         FIG. 10A  is a perspective view of an ultrasonic probe assembly, according to another embodiment. 
         FIG. 10B  is an enlarged view of detail C in  FIG. 10A . 
         FIG. 11A  is a side view of the ultrasonic probe assembly of  FIG. 10A . 
         FIG. 11B  is a cross-sectional side view taken along line A-A in  FIG. 11A . 
         FIG. 12  is an enlarged view of detail B in  FIG. 10B . 
         FIG. 13A  is a perspective view of an inner probe of the ultrasonic probe assembly of  FIG. 8A . 
         FIG. 13B  is a perspective view of an outer probe of the ultrasonic probe assembly of  FIG. 8A . 
         FIG. 14  is a side view of an ultrasonic probe assembly, according to another embodiment. 
         FIG. 15A  is side view of an inner probe of the ultrasonic probe assembly of FIG. 
         14 . 
         FIG. 15B  is side view of an outer probe of the ultrasonic probe assembly of FIG. 
         14 . 
         FIG. 16  is a side view of a proximal end portion of the probe assembly of  FIG. 14  with the outer probe disconnected from the inner probe. 
         FIG. 17A  is a side view of a proximal end portion of the probe assembly of  FIG. 14  with the outer probe connected to the inner probe. 
         FIG. 17B  is a side view of a distal end portion of the probe assembly of  FIG. 14 . 
         FIG. 18A  is a side view of a proximal end portion of the outer probe of the probe assembly of  FIG. 14 . 
         FIG. 18B  is a side view of a distal end portion of the outer probe of the probe assembly of  FIG. 14 . 
         FIG. 18C  is a proximal end perspective view of the outer probe of the probe assembly of  FIG. 14 . 
         FIG. 19  is a side view of a proximal end portion of the inner probe of the probe assembly of  FIG. 14 . 
         FIG. 20  is a flowchart illustrating a method for transferring ultrasonic energy to a bodily tissue. 
     
    
    
     DETAILED DESCRIPTION 
     Devices and methods of use of an ultrasonic ablation system having a transducer assembly and an ultrasonic probe assembly that can be coupled thereto are described herein. The ultrasonic ablation system can be used to transfer ultrasonic energy to a bodily tissue from an ultrasonic energy source. For example, the ultrasonic ablation system can be used to transfer ultrasonic energy to an obstruction within a vessel of a patient. The vessel can be for example, a vein, artery, ureter, bile duct, etc. 
     In some embodiments, a transducer assembly includes a transducer horn and a transducer. The ultrasonic probe assembly can include a first probe and a second probe that can each be coupled to the transducer assembly to selectively couple the first probe and the second probe to the transducer and/or the transducer horn. Thus, the first probe and the second probe can each receive ultrasonic energy from the same transducer. The transducer can, for example, include one or more piezoelectric transducer members. In some embodiments, the transducer can include a stack of transducers (and can be referred to as an ultrasonic stack). The first and second probes can be coupled together in a coaxial or non-coaxial relationship to each other as described in more detail herein. 
     As used in this specification, the terms “proximal” and “distal” refer to the direction closer to and away from, respectively, a user who would place the device into contact with a patient. Thus, for example, the end of a device first touching the body of the patient would be the distal end, while the opposite end of the device (e.g., the end of the device being manipulated by the user) would be the proximal end of the device. 
     As used herein, the terms “about” and “approximately” generally mean plus or minus 10% of the value stated. For example, about 0.5 would include 0.45 and 0.55, about 10 would include 9 to 11, about 1000 would include 900 to 1100. 
     As used herein, the term “set” can refer to multiple features or a singular feature with multiple parts. For example, when referring to set of walls, the set of walls can be considered as one wall with multiple portions, or the set of walls can be considered as multiple, distinct walls. Thus, a monolithically-constructed item can include a set of walls. Such a set of walls can include, for example, multiple portions that are either continuous or discontinuous from each other. A set of walls can also be fabricated from multiple items that are produced separately and are later joined together (e.g., via a weld, an adhesive, or any suitable method). 
     As used herein, the term “target tissue” refers to an internal or external tissue of or within a patient to which ultrasonic energy ablation techniques are applied. For example, a target tissue can be cancer cells, tumor cells, lesions, vascular occlusions, thrombosis, calculi, uterine fibroids, bone metastases, adenomyosis, or any other bodily tissue. Furthermore, the presented examples, of target tissues are not an exhaustive list of suitable target tissues. Thus, the ultrasonic energy systems described herein are not limited to the treatment of the aforementioned tissues and can be used on any suitable bodily tissue. Moreover, a “target tissue” can also include an artificial substance within or associated with a body, such as for example, a stent, a portion of an artificial tube, a fastener within the body or the like. Thus, for example, the ultrasonic energy systems described herein can be used on or within a stent or artificial bypass graft. 
     As used herein, the term “stiffness” relates to an object&#39;s resistance to deflection, deformation, and/or displacement produced by an applied force, and is generally understood to be the opposite of the object&#39;s “flexibility.” For example, a wall of a tube with greater stiffness is more resistant to deflection, deformation and/or displacement when exposed to a force than a wall of a tube having a lower stiffness. Similarly stated, a tube having a higher stiffness can be characterized as being more rigid than a tube having a lower stiffness. Stiffness can be characterized in terms of the amount of force applied to the object and the resulting distance through which a first portion of the object deflects, deforms, and/or displaces with respect to a second portion of the object. When characterizing the stiffness of an object, the deflected distance may be measured as the deflection of a portion of the object different than the portion of the object to which the force is directly applied. Said another way, in some objects, the point of deflection is distinct from the point where force is applied. 
     Stiffness (and therefore, flexibility) is an extensive property of the object being described, and thus is dependent upon the material from which the object is formed as well as certain physical characteristics of the object (e.g., cross-sectional shape, length, boundary conditions, etc.). For example, the stiffness of an object can be increased or decreased by selectively including in the object a material having a desired modulus of elasticity, flexural modulus and/or hardness. The modulus of elasticity is an intensive property of (i.e., is intrinsic to) the constituent material and describes an object&#39;s tendency to elastically (i.e., non-permanently) deform in response to an applied force. A material having a high modulus of elasticity will not deflect as much as a material having a low modulus of elasticity in the presence of an equally applied stress. Thus, the stiffness of the object can be decreased, for example, by introducing into the object and/or constructing the object of a material having a relatively low modulus of elasticity. 
     The stiffness of an object can also be increased or decreased by changing a physical characteristic of the object, such as the shape or cross-sectional area of the object. For example, an object having a length and a cross-sectional area may have a greater stiffness than an object having an identical length but a smaller cross-sectional area. As another example, the stiffness of an object can be reduced by including one or more stress concentration risers (or discontinuous boundaries) that cause deformation to occur under a lower stress and/or at a particular location of the object. Thus, the stiffness of the object can be decreased by decreasing and/or changing the shape of the object. 
     Embodiments described herein relate to ultrasonic energy ablation systems. In such systems an ultrasonic probe assembly can be operably coupled to an ultrasonic energy source to deliver ultrasonic energy to a target tissue. For example,  FIG. 1  is an illustration of an ultrasonic energy ablation system  100 , according to an embodiment. The ultrasonic energy ablation system  100  (also referred to herein as “ultrasonic system” or “ultrasonic ablation system” or simply “system”) includes an ultrasonic generator  180  (also referred to herein as “generator”), a foot switch  170 , an ultrasonic transducer assembly  150 , and an ultrasonic probe assembly  110  (also referred to herein as “probe assembly”). The ultrasonic generator  180  can be any suitable generator configured to generate, control, amplify, and/or transfer an electric signal (e.g., a voltage) to the transducer assembly  150 . 
     The ultrasonic generator  180  includes at least a processor, a memory and the circuitry (not shown in  FIG. 1 ) to produce an electronic signal (i.e., a current and a voltage) having the desired characteristics that can be received by the ultrasonic transducer assembly  150  and converted into ultrasonic energy. In some embodiments, the ultrasonic generator  180  can be electrically coupled to (e.g., “plugged into”) an electric receptacle such that the ultrasonic generator  180  receives a flow of electric current. For example, in some embodiments, the ultrasonic generator  180  can be plugged into a wall outlet that delivers alternating current (AC) electrical power at a given voltage (e.g., 120V, 230V, or other suitable voltage) and a given frequency (e.g., 60 Hz, 50 Hz, or other suitable frequency). 
     Although not shown in  FIG. 1 , the ultrasonic generator  180  includes the electronic circuitry, hardware, firmware and or instructions to cause the ultrasonic generator  180  to act as a frequency inverter and/or voltage booster. In this manner, the ultrasonic generator  180  can produce and/or output a voltage to the transducer assembly  150  having the desired characteristics to produce the desired ultrasonic energy output. For example, in some embodiments, the ultrasonic generator  180  can receive AC electrical power at a frequency of approximately 60 Hz and a voltage of approximately 120 V and convert the voltage to a frequency up to approximately 20,000 Hz to 35,000 Hz with a voltage of approximately 500-1500 VAC (RMS). Thus, the ultrasonic generator  180  can supply the transducer assembly  150  with a flow of AC electrical power having an ultrasonic frequency. 
     As shown in  FIG. 1 , the system  100  can optionally include the foot switch  170  that is in electric communication with the ultrasonic generator  180  via a foot switch cable  171 . The foot switch  170  includes a set of pedals  172  (e.g., two pedals as shown) that are operative in controlling the delivery of the ultrasonic electrical energy supplied to the ultrasonic transducer assembly  150 . For example, in some embodiments, a user (e.g., a physician, technician, etc.) can engage and/or depress one or more of the pedals  172  to control the current supplied to the ultrasonic transducer assembly  150  such that, in turn, the probe assembly  110  delivers the desired ultrasonic energy to the bodily tissue, as further described in detail herein. 
     The transducer assembly  150  is in electric communication with the ultrasonic generator  180  via a transducer cable  167 . In this manner, the transducer assembly  150  can receive an electrical signal (i.e., voltage and current) from the ultrasonic generator  180 . The transducer assembly  150  is configured to produce and amplify the desired ultrasonic energy via a set of piezoelectric members  162  (i.e., piezoelectric rings) and a transducer horn  163  (see e.g.,  FIG. 2 ), and transfer the ultrasonic energy to the probe assembly  110  and/or the transmission member  120 . The transducer assembly  150  can be any suitable assembly of the types shown and described herein. 
     For example, in some embodiments, as shown in  FIG. 2 , the transducer assembly  150  includes a housing  151  having a proximal end portion  152  and a distal end portion  153 . The housing  151  is configured to house or otherwise enclose at least a portion of a flow tube  157 , a bolt  158 , a back plate  160 , a set of insulators  161 , a set of piezoelectric rings  162  (the set of insulators and piezoelectric rings can be referred to as the ultrasonic stack), and a transducer horn  163 . 
     The proximal end portion  152  of the housing  151  is coupled to a proximal cover  154  (e.g., via an adhesive, a press or friction fit, a threaded coupling, a mechanical fastener, or the like). The proximal cover  154  defines an opening  155  such that the proximal cover  154  can receive a portion of a connector  156  (e.g., a luer connector) on a proximal side thereof (e.g., substantially outside the housing  151 ) and a portion of the flow tube  157  on a distal side thereof (e.g., substantially inside the housing  151 ). Expanding further, the proximal cover  154  can receive the connector  156  and the flow tube  157  such that the proximal cover  154  forms a substantially fluid tight seal with the connector  156  and the flow tube  157 . In this manner, a vacuum can be applied via the connector  156  to irrigate and/or aspirate the region of the body within which the probe assembly  110  is disposed. Similarly stated, this arrangement results in the connector  156  being placed in fluid communication with a lumen defined by the transmission member  120 . Although the transducer assembly  150  is shown as including a flow path (and the connector  156 ) to facilitate irrigation and/or aspiration through the transducer assembly  150 , in other embodiments, the flow path(s) for irrigation and/or aspiration need not be within the transducer assembly, but can instead be solely within other portions of the system (e.g., within the probe assembly). 
     The distal end portion  153  of the housing  151  is configured to receive the transducer horn  163  such that the transducer horn  163  is coupled to an inner surface of the housing  151 . More specifically, the transducer horn  163  can be disposed at least partially within the housing  151  such that the transducer horn  163  can be moved relative to the housing  151  (e.g., when amplifying the ultrasonic energy), but not moved out of the housing  151  during normal use. The transducer horn  163  includes a proximal end portion  164  and a distal end portion  165  and defines a lumen  166  therethrough. The lumen  166  is configured to receive a portion of the bolt  158  at the proximal end portion  164  of the transducer horn  163  and a portion of the probe assembly  120  at the distal end portion  165  of the transducer horn  163 , both of which are described in further detail herein. 
     As shown in  FIG. 2 , the back plate  160 , the insulators  161 , and the piezoelectric members  162  are disposed within the housing  151  and about the bolt  158 . Thus, the piezoelectric members  162  and insulators  161  can be in the form of rings. More specifically, the arrangement of the back plate  160 , the insulators  161 , and the piezoelectric members  162  is such that the back plate  160  is disposed proximal to the insulators  161  and the piezoelectric members  162 . The piezoelectric members  162  are each disposed between the insulators  161 . Similarly stated, a first insulator  161  is disposed proximal to the piezoelectric members  162  and a second insulator  161  is disposed distal to the piezoelectric rings  162 . The piezoelectric members  162  are in electric communication (e.g., via wires not shown in  FIGS. 1 and 2 ) with the ultrasonic generator  180 , as described in further detail herein. 
     As shown in  FIG. 2 , a portion of the bolt  158  is configured to be disposed within the lumen  166  defined by the transducer horn  163 . More specifically, the portion of the bolt  158  forms a threaded fit with an inner surface of the transducer horn  163  that defines the lumen  166 . In this manner, the bolt  158  can be advanced within the lumen  166  such that the bolt  158  exerts a compressive force on the backing plate  160 , the insulators  161 , and the piezoelectric members  162 . Thus, the backing plate  160 , the insulators  161 , and the piezoelectric members  162  are retained between a head of the bolt  158  (e.g., at the proximal end) and a proximal surface of the transducer horn  163 . The torque applied to the bolt and/or the clamping force exerted between the head of the bolt  158  and the proximal surface of the transducer horn  163  is such that that the deviation of the transducer natural frequency deviation is within ten percent from nominal. Therefore, in use, the piezoelectric members  162  can vibrate and/or move the transducer horn  163 , as further described herein. 
     The bolt  158  further defines a lumen  159  such that a proximal end portion of the bolt  158  can receive a distal end portion of the flow tube  157 . In this manner, the lumen  159  defined by the bolt  158  and the flow tube  157  collectively place the lumen  166  defined by the transducer horn  163  in fluid communication with the connector  156 . Thus, the lumen  166  of the transducer horn  163  can be placed in fluid communication with a volume substantially outside of the proximal end of the housing  151 . 
     As shown in  FIGS. 1 and 2 , the probe assembly  110  includes at least an elongate transmission member  120  (also referred to herein as “transmission member” or “elongate member”) and a coupler  130 . In some embodiments the probe assembly  110  can include multiple probes, each having an elongate member and a coupler. Such embodiments are described below. For example, in some embodiments, the transducer assembly  150  can be used with (or coupled to) the probe assembly  210 . The coupler  130  includes a proximal end portion  131  and a distal end portion  132  and defines a lumen  133  that extends therethrough. The proximal end portion  131  of the coupler  130  is disposed within the lumen  166  at the distal end portion  165  of the transducer horn  163  and forms a threaded fit with a probe coupling  168  at the inner surface of the transducer horn  163  that defines the lumen  166 . In this embodiment, the probe coupling  168  is a threaded coupling. The distal end portion  131  of the coupler  130  is configured to receive a portion of the transmission member  120  to fixedly couple the transmission member  120  to the coupler  130 . In this manner, the probe assembly  110  can be removably coupled to the transducer assembly  150  via the coupler  130 . 
     The transmission member  120  is an elongate tube having a proximal end portion  121  and a distal end portion  122 . The transmission member  120  can be any suitable shape, size, or configuration and is described in further detail herein with respect to specific embodiments. In some embodiments, the transmission member  120  can optionally include any suitable feature configured to increase the flexibility (e.g., decrease the stiffness) of at least a portion of the transmission member  120 , thereby facilitating the passage of the transmission member  120  through a tortuous lumen within a patient (e.g., a urinary tract, a vein, artery, etc.). For example, in some embodiments, a portion of the transmission member  120  can be formed from a material of lower stiffness than a different portion of the transmission member  120  formed from a material of greater stiffness. In some embodiments, the stiffness of at least a portion of the transmission member  120  can be reduced by defining an opening (e.g., notch, a groove, a channel, a cutout, or the like), thereby reducing the area moment of inertia of the portion of the transmission member  120 . 
     In use, a user (e.g., a surgeon, a technician, physician, etc.) can operate the ultrasonic system  100  to deliver ultrasonic energy to a target bodily tissue within a patient. For example, the ultrasonic system  100  can be used to treat a chronic total occlusion (CTO) in a patient. The user can, for example, engage the pedals  172  of the foot switch  170  such that the ultrasonic generator  180  generates an alternating current (AC) and voltage with a desired ultrasonic frequency (e.g.,  20 , 000 Hz). In this manner, the ultrasonic generator  180  can supply AC electric power to the piezoelectric rings  162 . The AC electric power can urge the piezoelectric rings  162  to oscillate (e.g., expand, contract, or otherwise deform) at the desired frequency, which, in turn, causes the transducer horn  163  to move relative to the housing  151 . Thus, with the probe assembly  110  coupled to the transducer horn  163 , the movement of the transducer horn  163  vibrates and/or moves the probe assembly  110 . In this manner, the distal end portion  122  of the transmission member  120  can be disposed with a portion of the patient adjacent to a target tissue such that the transmission member  120  transfers at least a portion of the ultrasonic energy to the target tissue (not shown in  FIGS. 1 and 2 ). For example, in some embodiments, a distal tip of the transmission member  120  can impact a target tissue such as, for example, to break apart an occlusion. In some embodiments, the movement of the distal end portion  122  of the transmission member  120  is such that cavitations occur within the portion of the patient. In this manner, the cavitations can further break apart a target tissue. In some embodiments, the ultrasonic system  100  can optionally be used to aspirate and/or to supply irrigation to a target tissue site. For example, a portion of the probe assembly  110  can include a port coupled to a fluid line that can be used to supply irrigation or aspirate particles from an obstruction at the treatment site. 
       FIGS. 3A-6B  illustrate an ultrasonic probe assembly  210  that can be used within an ultrasonic energy ablation system, such as system  100  described above. For example, the ultrasonic probe assembly  210  can be releasably coupled to the transducer assembly  150 . In this embodiment, the probe assembly  210  includes a first probe  235  (see, e.g.,  FIGS. 5 and 6A ), and a second probe  245  (see, e.g.,  FIGS. 5 and 6B ) that can be releasably coupled to the first probe  235  as described in further details below. The first probe  235  includes a first elongate transmission member  220  (also referred to herein as “first transmission member” or “first elongate member” or “transmission member” or “elongate member”) and a coupler  230 . The coupler  230  includes a proximal end portion  231  and a distal end portion  232  and defines a central lumen  223  (see, e.g.,  FIG. 5 ) that extends at least partially through the coupler  230 . The coupler  230  also defines a side lumen  224  in fluid communication with the central lumen  223 . In some embodiments, a side port (e.g., similar to the side port  425  described below) can be coupled to and/or within the side lumen  224  to provide aspiration and/or irrigation through the first probe  235 . For example, the side lumen can be coupled to and in fluid communication with a transfer line that can be used to supply irrigation or aspirate particles from an obstruction at the treatment site. An embodiment illustrating a fluid line is discussed below for probe assembly  410 . In other embodiments, the coupler  230  need not include a side lumen, and can instead include only a central lumen therethrough that facilitates aspiration and/or irrigation. The proximal end portion  231  of the coupler  230  includes a first coupling portion  234  configured to be releasably coupled to a probe coupling (see e.g., the probe coupling  168  in  FIG. 2 ) at the distal end portion of the transducer assembly (e.g., distal end portion  165  of transducer assembly  150 ). For example, the first coupling portion  234  can be a threaded coupling that is threadably coupled within the transducer assembly  150  to a mating threaded probe coupling  168  within a lumen  166  at the distal end portion  165  of the transducer horn  163 . In this manner, the probe  235  can be removably coupled to the transducer assembly  150  via the coupler  230 . The coupler  230  also includes two flat indented surfaces  237  that can be used to receive a tool to assist in securing the coupler  230  to the probe coupling. For example, a tool such as a medical wrench can clamp onto the surfaces  237  and used to tighten the coupler  230  to the probe coupling. 
     The distal end portion  232  of the coupler  230  is configured to receive a portion of the transmission member  220  (i.e., within the central lumen  223 ) to fixedly couple the transmission member  220  to the coupler  230 . The transmission member  220  includes a proximal end portion  221  and a distal end portion  222 . The proximal end portion  221  is fixedly coupled to the distal end portion  232  of the coupler  230 . The distal end portion  222  is configured to be inserted into a body of a patient as described in more detail below. As described above, the first probe  235  also includes a second coupling portion  236  to releasably couple to the first probe  235  to the second probe  245 . 
     The second probe  245  includes an elongate transmission member  244  (also referred to herein as “second transmission member” or “second elongate member” or “transmission member” or “elongate member”) and a coupler  240 . The coupler  240  includes a proximal end portion  243  and a distal end portion  247  and defines a lumen  239  (see, e.g.,  FIG. 5 ) that extends at least partially therethrough. The transmission member  244  includes a proximal end portion  241  and a distal end portion  242 . The proximal end portion  241  is fixedly coupled to the distal end portion  247  of the coupler  240 . The proximal end portion  243  of the coupler  240  includes a coupling portion  246  (also referred to herein as “third coupling portion”) configured to be releasably coupled to the second coupling portion  236  of the first probe  235 . Thus, the second probe  245  can be removably or releasably coupled to the transducer assembly  150  via the first probe  235  (e.g., via the coupler  230 ). In this manner, both the first probe  235  and the second probe  245  can be coupled to the same transducer assembly and be driven by the same ultrasonic transducer. More specifically, the lumen  248  of the second probe  245  can receive at least a portion of the first elongate member  220  of the first probe  235  and the coupler  230  can be releasably coupled to the coupler  240 . The elongate member  220  of the first probe  235  can, for example, be inserted through the lumen  248  of the second elongate member  244  such that a distal end of the first elongate member  220  extends outside of the lumen  248 . In this manner, the second elongate member  244  can function as a guide catheter, as described below. By extending distally outside of the lumen  248 , the distal end portion  222  of the elongate member  220  can be advanced into the target tissue. 
     In this embodiment, the second coupling portion  236  is a quick release connector (e.g., a luer lock type connector) and the third coupling portion  246  of the second probe  245  is a mating quick release connector to provide a quick release connection between the first probe  235  and the second probe  245 . In alternative embodiments, the second coupling portion  236  can be a threaded coupling and the third coupling portion  246  can be a threaded coupling to threadably couple the first probe  235  to the second probe  246 . Such embodiments are described below with reference to probe assemblies  310  and  410 . In some embodiments, the second probe  245  can also include a tapered distal end portion that can be incorporated into the second elongate member  244  or provided as a separate component. Such an embodiment is discussed below with reference to probe assembly  410 , which includes a tapered distal end portion  449 , or for the alternative second probe  245 ′ (shown in  FIGS. 9A-9C ), which includes a tapered distal end portion  249 ′. In some embodiments, the tapered distal end portion of the second probe  245  can be angled between 30 and 40 degrees relative to a centerline of the second elongate member  244 . The tapered distal end portion  249 ′ of the second probe  245  can assist with insertion of the probe assembly  210  into a tissue to be treated. Moreover, as discussed with reference to  FIGS. 9A-9C , the tapered distal end portion  249 ′ can also facilitate desired deformation of the probe assembly to produce enhanced contact between the first probe and the second probe. This enhanced contact can lead to improved transmission of ultrasonic energy from the first (inner) probe to the target tissue. 
     The first elongate member  220  and the second elongate member  244  can each be any suitable shape, size, or configuration as described herein. In some embodiments, the elongate members  220  and  244  can optionally include any suitable feature configured to increase the flexibility (e.g., decrease the stiffness) of at least a portion of the transmission member  220 ,  244  thereby facilitating the passage of the elongate members  220 ,  244  through a tortuous lumen within a patient (e.g., a urinary tract, a vein, artery, etc.). For example, in some embodiments, a portion of the elongate members  220  and/or  244  can be formed from a material of lower stiffness than a different portion of the elongate member  220 ,  244  formed from a material of greater stiffness. In some embodiments, the stiffness of at least a portion of the elongate members  220  and/or  244  can be reduced by defining an opening(s) (e.g., notch, a groove, a channel, a cutout, or the like) in the elongate members  220  and/or  244  or providing openings within a braided material in which the elongate members  220  and/or  244  may be formed as described below, thereby reducing the area moment of inertia of the portion of the transmission members  220 ,  244 . 
     Further, the first elongate member  220  can be formed with the same or different material than the second elongate member  244 . In some embodiments, the second elongate member  244  is formed with a more flexible material than the first elongate member  220 . In other words, first elongate member  220  has a stiffness greater than the second elongate member  244 . In some embodiments, the second elongate member  244  is formed with a braided metal material. In some embodiments, the braided material is stainless steel (e.g.,  304  stainless steel), Nitinol® (i.e., a nickel-titanium alloy), or other metal alloys having a density of, for example,  60 - 75  PPI (picks per inch of length) and a diamond and/or spiral pattern. 
     As described above for the previous embodiment, in use, a user (e.g., a surgeon, a technician, physician, etc.) can operate the ultrasonic system  100  (described above) to deliver ultrasonic energy to a target bodily tissue within a patient. For example, the ultrasonic system  100  and probe assembly  210  can be used to treat a chronic total occlusion (CTO) in a patient. 
     The probe assembly  210 , having two ultrasonic probes (first probe  235  and second probe  245 ), allows the user to use both the first probe  235  and the second probe  245  to treat the target object, or the user can selectively decouple the second probe  245  from the first probe  235  such that ultrasonic energy is transferred only to the first elongate member  220 . In such a use, the second probe  245  can function, for example, as a guide catheter. The user can also selectively couple and decouple the second probe  245  from the first probe  235  while the probe assembly  210  is inserted within the patient&#39;s body. For example, in some instances, a user can connect the first probe  235  to the transducer assembly and use the second probe  245  as a guide catheter for inserting the first probe  235  into the patient&#39;s body. Ultrasonic energy can be provided via the transducer of the transducer assembly to the first probe and to a target tissue to be treated. The user can then connect the second probe  245  to the first probe  235  (via the coupler  230  and the second coupler  240 ) thereby connecting the second probe  245  to the transducer assembly and transducer, and apply ultrasonic energy through both probes to the target tissue. In some instances, the second probe  245  may not be used. In some instances, both the first probe  235  and the second probe  245  are coupled to the transducer and ultrasonic energy is applied through both probes to the target tissue. 
     When at least the first probe  235  of the probe assembly  210  is coupled to the transducer assembly  150  (instead of the probe assembly  110 ), the first elongate member  220  can receive ultrasonic energy from the ultrasonic transducer (e.g., piezoelectric members  162 ) of the transducer assembly  150  and convey the ultrasonic energy to a target object within a patient&#39;s body. Similarly, when the second probe  245  is coupled to the first probe  235 , the second elongate member  244  can receive ultrasonic energy from the ultrasonic transducer and convey the ultrasonic energy to the target object within the patient&#39;s body. Because the second (outer) probe  245  has a larger diameter, conveying the ultrasonic energy through the second probe  245  can produce a larger opening through the target tissue (e.g., CTO). 
     As described above, the user can, for example, engage the pedals  172  of the foot switch  170  such that the ultrasonic generator  180  generates an alternating current (AC) and voltage with a desired ultrasonic frequency (e.g., 20,000 Hz). In this manner, the ultrasonic generator  180  can supply AC electric power to the piezoelectric members  162 . The AC electric power can urge the piezoelectric members  162  to oscillate (e.g., expand, contract, or otherwise deform) at the desired frequency, which, in turn, causes the transducer horn  163  to move relative to the housing  151 . Thus, with the probe assembly  210  coupled to the transducer horn  163 , the movement of the transducer horn  163  vibrates and/or moves the probe assembly  210 , and more specifically, the first elongate member  220  and/or the second elongate member  244  when they are coupled to the transducer assembly  150 . 
     In use, the distal end portion of the probe assembly  210  can be inserted within a vessel of a patient adjacent to or penetrating a target tissue (e.g., an obstruction, such as a CTO) such that the first elongate member  220  or the first elongate member  220  and the second elongate member  244  can transfer at least a portion of the ultrasonic energy to the target tissue. The distal end portion of the probe assembly  220  can be inserted into the vessel either before or after coupling the first probe  235  and/or second probe  245  to the transducer assembly. In some embodiments, a distal tip or end of the first elongate member  220  can extend outside of the lumen  248  of the second elongate member  244  and impact a target tissue such as, for example, to break apart an occlusion. In some embodiments, movement of the distal end portion  222  of the first elongate member  220  is such that cavitations occur within the portion of the patient. In this manner, the cavitations can further break apart a target tissue. As described herein, in some embodiments, the probe assembly  210  can optionally be used to aspirate and/or to supply irrigation to a target tissue site. For example, the port of the first probe can be coupled to a transfer line that can be used to supply irrigation or aspirate particles from an obstruction at the treatment site. 
     In some embodiments, the first elongate member  220  is coaxial with the second elongate member  244  when the first elongate member  220  is disposed at least partially within the lumen  248  of the second elongate member  244 , as shown schematically, for example in  FIG. 7A . As shown in  FIG. 7A , the first elongate member  220  of the first probe  235  and the second elongate member  244  of the second probe  245  share a common center axis A 1  (e.g., they are disposed coaxially). Further, the first elongate member  220  has a diameter D 1  and the second elongate member  244  has a diameter D 2  that is greater than the diameter D 1 , allowing the first elongate member  220  to be inserted through the second elongate member  244 . 
     In some embodiments, a first elongate member can be non-coaxial within the second elongate member when the first elongate member is disposed at least partially within the lumen of the second elongate member. This arrangement is shown schematically, for example in  FIG. 7B . As shown in  FIG. 7B , a first probe  635  includes a first coupler  630  coupled to a first elongate member  620  that has a first center axis Al and a second probe  645  includes a second coupler  640  coupled to second elongate member  644  that has a second axis A 2  that is offset from the first center axis A 1 . In other words, the first elongate member  620  is non-coaxial with the second elongate member  644 . In such a non-coaxial configuration, the close proximity, or in some cases contact, between the first elongate member  620  and the second elongate member  644 , allows for ultrasonic energy to be transferred from the first elongate member  620 , to the second elongate member  644  and then to the target tissue, providing a greater amount of ultrasonic energy at the treatment site. 
     Although the probe assembly  210  is described as including two probes (the first probe  235  and the second probe  245 ), in other embodiments, a probe assembly  210  can include any number of probes. For example, in some embodiments, a probe assembly can include more than one “inner” probe. The different inner probes can have different sizes and/or characteristics to facilitate the desired procedure. For example, in some embodiments a probe assembly can have a third probe (i.e., a second “inner probe”) that has a larger size (e.g., diameter of the elongate member) than the first probe. The increased size can facilitate better contact with the outer probe, thereby enhancing the transmission of ultrasonic energy from the inner probe to the outer probe (and therefore into the target tissue).  FIG. 7C  illustrates a third probe  275  that can be used with the probe assembly  210  or any other probe assemblies described herein. The third probe  275  includes a third elongate member  274  and a third coupler  270 . The third elongate member  274  of the third probe  275  has a diameter D 3  that is greater than the diameter D 1 . In some cases, the third elongate member  274  may have too large of a diameter to exit a distal end of the second elongate member  244 . An example use of the third probe  275  is described below with reference to  FIGS. 9A-9C . 
       FIG. 8  is a schematic illustration of the first probe  635  and the second probe  645  (shown in  FIG. 7B ) disposed within a vessel V of a patient near an obstruction  0 . As described above, in this example illustration, the first probe  635  is disposed in a non-coaxial relationship with the second probe  645 . With the distal portion of the probe assembly  610  inserted into the vessel V near the obstruction  0 , the transducer assembly can be actuated to deliver ultrasonic energy via the first elongate member  620  of the first probe  635  and the second elongate member  644  of the second probe  645  and into the obstruction. 
       FIGS. 9A-9C  illustrate an example use of a probe assembly as described herein.  FIG. 9A  illustrates a schematic illustration of a probe assembly  210 ′ including the first probe  235  and an alternative second (or outer) probe  245 ′ disposed within a vessel V of a patient near or within an obstruction  0 . In this example illustration, the first probe  235  is disposed in a coaxial relationship with the second probe  245 ′. The second probe  245 ′ can be configured the same as the second probe  245  or any of the second probes described herein. For example, the second probe  245  includes a second elongate member  244 ′. In this embodiment, the second elongate member  244 ′ includes a tapered distal end portion  249 ′. In some embodiments, the tapered distal end portion  249 ′ can be angled between  30  and  40  degrees relative to a centerline of the second elongate member  244 ′. As described above, the second probe  245 ′ can be coupled to the first probe  235  in the same manner as described herein for other embodiments. As shown in  FIG. 9A , a distal tip portion of the first probe  235  is extended outside of the second probe  245 ′. Although not shown, the distal portion of the probe assembly  210 ′ can in some cases penetrate into the obstruction. With the distal portion of the probe assembly  210 ′ inserted into the vessel V near or within the obstruction  0  (or penetrating the obstruction), the transducer assembly can be actuated to deliver ultrasonic energy along the first elongate member  220  of the first probe  235  and optionally the second elongate member  244 ′ of the second probe  245 ′ and into the obstruction. After delivering ultrasonic energy to at least partially disrupt the obstruction, in this example use, the first probe  235  is disconnected from the transducer assembly and from the second probe  245 ′ and removed from the patient&#39;s body. The removal of the first probe  235  from within the second probe  245 ′ can be performed while maintaining the second probe  245 ′ within the vessel V. In some embodiments, the second probe  245 ′ can be repositioned within the vessel V to at least partially penetrate into the obstruction (via the opening produced by the initial delivery of ultrasonic energy). 
     As shown in  FIG. 9B , a third probe  275  includes a third elongate member  274  that is inserted through the lumen of the second probe  245 ′. The third probe  275  includes a third coupler (not shown) to couple the third probe  275  to the coupler (not shown) of the second probe  245 ′. As shown in  FIG. 9B , the third elongate member  274  has a diameter greater than a diameter of the first elongate member  220  such that the third elongate member  274  cannot exit through the tapered distal end  249 ′ of the second elongate member  244 ′. In other words, the third elongate member  274  has a distal tip that is sized to limit movement of the distal tip through the distal tip of the second elongate member  245 ′. With the third probe  275  disposed within the second probe  245 ′, the distal portions of the second probe  245 ′ and the third probe  275  can be positioned within the obstruction. 
     After inserting the third probe  275 , the coupler of the second probe  245 ′ can be coupled to the coupler of the third probe  275  by moving the second elongate member  244 ′ proximally relative to the third elongate member  274 , as shown by the arrow AA in  FIG. 9B . The proximal movement of the second (outer) probe  245 ′ causes the tapered distal tip portion  249 ′ of the second elongate member  244 ′ to engage a distal tip portion of the third elongate member  274 . Continued proximal movement of the second (outer) probe  245 ′ (to couple the second probe  245 ′ to the coupler of the third probe  275 ), as shown by the arrow BB in  FIG. 9C  deforms a distal portion of the second elongate member  244 ′ and/or a distal portion of the third elongate member  274  to produce a contact location C between the third elongate member  274  and the second elongate member  244 ′. Specifically, this deformation causes contact (or enhances the existing contact) between the outer surface of the third elongate member  274  and the inner surface of the second elongate member  244 ′. Ultrasonic energy can then be transmitted from the ultrasonic transducer assembly to at least the third probe  275 , and at least a portion of the ultrasonic energy is delivered from the third elongate member  274  through the contact location C and the second elongate member  244 ′ to the obstruction (as shown by ultrasonic energy US in  FIG. 9C ). 
       FIGS. 10A-13B  illustrate another embodiment of an ultrasonic probe assembly that includes two ultrasonic probes and that can be coupled to and used within an ultrasonic energy ablation system, such as system  100  described above. In this embodiment, a probe assembly  310  includes a first probe  335  (see, e.g.,  FIGS. 12 and 13A ), and a second probe  345  (see, e.g.,  FIGS. 12 and 13B ) that can be releasably coupled to the first probe  335  as described in further details below. The first probe  335  includes a first elongate transmission member  320  (also referred to herein as “first transmission member” or “first elongate member” or “transmission member” or “elongate member”) and a coupler  330 . The coupler  330  includes a proximal end portion  331  and a distal end portion  332  and defines a central lumen  323  (see, e.g.,  FIG. 12 ) that extends at least partially the coupler  330 . The coupler  330  also defines a side lumen  324  in fluid communication with the central lumen  323 . In some embodiments, a side port (e.g., similar to the side port  425  described below) can be coupled to and/or within the side lumen  324  to provide aspiration and/or irrigation through the first probe  335 . For example, the side lumen  324  can be coupled to and in fluid communication with a transfer line that can be used to supply irrigation or aspirate particles from an obstruction at the treatment site. An embodiment illustrating a fluid line is discussed below for probe assembly  410 . In other embodiments, the coupler  330  need not include a side lumen, and can instead include only a central lumen therethrough that facilitates aspiration and/or irrigation. The proximal end portion  331  of the coupler  330  includes a first coupling portion  334  configured to be releasably coupled to a probe coupling (see e.g., the threaded probe coupling  168  in  FIG. 2 ) at the distal end portion of the transducer assembly (e.g., distal end portion  165  of transducer assembly  150 ). For example, in this embodiment, the first coupling portion  334  is a threaded coupling that is threadably coupled within the transducer assembly  150  to a mating threaded probe coupling  168  within a lumen  166  at the distal end portion  165  of the transducer horn  163 . In this manner, the first probe  335  can be removably coupled to the transducer assembly  150  via the coupler  330 . The coupler  330  also includes two flat indented surfaces  337  that can be used to receive a tool to assist in securing the coupler  330  to the probe coupling. For example, a tool such as a medical wrench can clamp onto the surfaces  337  and used to tighten the coupler  230  to the probe coupling. 
     The distal end portion  332  of the coupler  330  is configured to receive a portion of the transmission member  320  to fixedly couple the transmission member  320  to the coupler  330  (i.e., within the central lumen  323 ). The transmission member  320  includes a proximal end portion  321  and a distal end portion  322 . The proximal end portion  321  is fixedly coupled to the distal end portion  332  of the coupler  330 . The distal end portion  322  is configured to be inserted into a body of a patient as described in more detail below. As described above, the first probe  335  also includes a second coupling portion  336  to releasably couple to the first probe  335  to the second probe  345 . 
     The second probe  345  includes an elongate transmission member  344  (also referred to herein as “second transmission member” or “second elongate member” or “transmission member” or “elongate member”) and a coupler  340 . The coupler  340  includes a proximal end portion  343  and a distal end portion  347  and defines a lumen  339  (see, e.g.,  FIG. 12 ) that extends at least partially therethrough. The transmission member  344  includes a proximal end portion  341  and a distal end portion  342 . The proximal end portion  341  is fixedly coupled to the distal end portion  347  of the coupler  340 . The proximal end portion  343  of the coupler  340  includes a coupling portion  346  (also referred to herein as “third coupling portion”) configured to be releasably coupled to the second coupling portion  336  of the first probe  335 . Thus, the second probe  345  can be removably or releasably coupled to the transducer assembly  150  via the first probe  335  (e.g., via the coupler  330 ). In this manner, both the first probe  335  and the second probe  345  can be coupled to the same transducer assembly and be driven by the same ultrasonic transducer. More specifically, the lumen  348  of the second probe  345  can receive at least a portion of the first elongate member  320  of the first probe  335  and the coupler  340  can be releasably coupled to the coupler  330 . The elongate member  320  of the first probe  335  can, for example, be inserted through the lumen  348  of the second elongate member  344  such that a distal end of the first elongate member  320  extends outside of the lumen  348 . In this embodiment, the second coupling portion  336  is a threaded coupling and the third coupling portion  346  is a threaded coupling to threadably couple the first probe  335  to the second probe  346 . The second probe  345  can also include a tapered distal end portion that can be incorporated into the second elongate member  344  or provided as a separate component. Such an embodiment is discussed below with reference to probe assembly  410 , which includes a tapered distal end portion  449 , or for the alternative second probe  245 ′ (shown in  FIGS. 9A-9C ), which includes a tapered distal end portion  249 ′. The tapered distal end portion of the second probe  345  can assist with insertion of the probe assembly  310  into a tissue to be treated. In this manner, the second elongate member  344  can function as a guide catheter, as described below. By extending distally outside of the lumen  348 , the distal end portion  322  of the elongate member  320  can be advanced into the target tissue. 
     The first elongate member  320  and the second elongate member  344  can each be any suitable shape, size, or configuration as described herein. In some embodiments, the elongate members  320  and  344  can optionally include any suitable feature configured to increase the flexibility (e.g., decrease the stiffness) of at least a portion of the transmission member  320 ,  344  thereby facilitating the passage of the elongate members  320 ,  344  through a tortuous lumen within a patient (e.g., a urinary tract, a vein, artery, etc.). For example, in some embodiments, a portion of the elongate members  320  and/or  344  can be formed from a material of lower stiffness than a different portion of the elongate member  320 ,  344  formed from a material of greater stiffness. In some embodiments, the stiffness of at least a portion of the elongate members  320  and/or  344  can be reduced by defining an opening (e.g., notch, a groove, a channel, a cutout, or the like), in the elongate members  320  and/or  344  or providing openings within a braided material in which the elongate members  320  and/or  344  may be formed, thereby reducing the area moment of inertia of the portion of the transmission members  320 ,  344 . 
     Further, the first elongate member  320  can be formed with the same or different material than the second elongate member  344 . In some embodiments, the second elongate member  344  is formed with a more flexible material than the first elongate member  320 . In other words, first elongate member  320  has a stiffness greater than the second elongate member  344 . In some embodiments, the second elongate member  344  is formed with a braided metal. The braided material can be the same as the braided material described above for elongate member  244 . 
     As described above for previous embodiments, the first elongate member  320  can be disposed coaxial with the second elongate member  344  when the first elongate member  320  is disposed at least partially within the lumen  348  of the second elongate member  344 . In other embodiments, the first elongate member  320  is non-coaxial with the second elongate member  344  when the first elongate member  320  is disposed at least partially within the lumen  348  of the second elongate member  344 . In such a non-coaxial configuration, the close proximity or in some cases contact, between the first elongate member  320  and the second elongate member  344 , allows for ultrasonic energy to be transferred from the first elongate member  320 , to the second elongate member  344  and then to the target tissue, providing a greater amount of ultrasonic energy at the treatment site. 
     As described above for the previous embodiment, in use, a user (e.g., a surgeon, a technician, physician, etc.) can operate the ultrasonic system  100  (described above) to deliver ultrasonic energy to a target bodily tissue within a patient. For example, the ultrasonic system  100  and probe assembly  310  can be used to treat a chronic total occlusion (CTO) in a patient. 
     The probe assembly  310 , having two ultrasonic probes (first probe  335  and second probe  345 ), allows the user to use both the first probe  335  and the second probe  345  to treat the target object, or the user can selectively decouple the second probe  345  from the first probe  335  such that ultrasonic energy is transferred only to the first elongate member  320 . In such a use, the second probe  345  can function, for example, as a guide catheter. The user can also selectively couple and decouple the second probe  345  from the first probe  335  while the probe assembly  310  is inserted within the patient&#39;s body. For example, in some instances, a user can connect the first probe  335  to the transducer assembly and use the second probe  345  as a guide catheter for inserting the first probe  335  into the patient&#39;s body. Ultrasonic energy can be provided via the transducer of the transducer assembly to the first probe and to a target tissue to be treated. The user can then connect the second probe  345  to the first probe  335  (via the coupler  330  and the second coupler  340 ) thereby connecting the second probe  345  to the transducer assembly and transducer, and apply ultrasonic energy through both probes to the target tissue. In some instances, the second probe  345  may not be used. In some instances, both the first probe  335  and the second probe  345  are coupled to the transducer and ultrasonic energy is applied through both probes to the target tissue. 
     When at least the first probe  335  of the probe assembly  310  is coupled to the transducer assembly  150  (instead of the probe assembly  110 ), the first elongate member  320  can receive ultrasonic energy from the ultrasonic transducer (e.g., piezoelectric members  162 ) of the transducer assembly  150  and convey the ultrasonic energy to a target object within a patient&#39;s body. Similarly, when the second probe  345  is coupled to the first probe  335 , the second elongate member  344  can receive ultrasonic energy from the ultrasonic transducer and convey the ultrasonic energy to the target object within the patient&#39;s body. Because the second (outer) probe  345  has a larger diameter, conveying the ultrasonic energy through the second probe  345  can produce a larger opening through the target tissue (e.g., CTO). 
     As described above, the user can, for example, engage the pedals  172  of the foot switch  170  such that the ultrasonic generator  180  generates an alternating current (AC) and voltage with a desired ultrasonic frequency (e.g., 20,000 Hz). In this manner, the ultrasonic generator  180  can supply AC electric power to the piezoelectric members  162 . The AC electric power can urge the piezoelectric members  162  to oscillate (e.g., expand, contract, or otherwise deform) at the desired frequency, which, in turn, causes the transducer horn  163  to move relative to the housing  151 . Thus, with the probe assembly  310  coupled to the transducer horn  163 , the movement of the transducer horn  163  vibrates and/or moves the probe assembly  310 , and more specifically, the first elongate member  320  and/or the second elongate member  344  when they are coupled to the transducer assembly  150 . 
     In use, the distal end portion of the probe assembly  310  can be inserted within a vessel of a patient adjacent to or penetrating a target tissue (e.g., an obstruction, such as a CTO) such that the first elongate member  320  or the first elongate member  320  and the second elongate member  344  can transfer at least a portion of the ultrasonic energy to the target tissue. The distal end portion of the probe assembly  320  can be inserted into the vessel either before or after coupling the first probe  335  and/or second probe  345  to the transducer assembly. In some embodiments, a distal tip or end of the first elongate member  320  can extend outside of the lumen  348  of the second elongate member  344  and impact a target tissue such as, for example, to break apart an occlusion. In some embodiments, movement of the distal end portion  322  of the first elongate member  320  is such that cavitations occur within the portion of the patient. In this manner, the cavitation can further break apart a target tissue. As described herein, in some embodiments, the probe assembly  310  can optionally be used to aspirate and/or to supply irrigation to a target tissue site. For example, the port of the first probe can be coupled to a transfer line that can be used to supply irrigation or aspirate particles from an obstruction at the treatment site. 
       FIGS. 14-19  illustrate another embodiment of an ultrasonic probe assembly that includes two ultrasonic probes and that can be coupled to and used within an ultrasonic energy ablation system, such as system  100  described above. In this embodiment, a probe assembly  410  includes a first probe  435  (see, e.g.,  15 A), and a second probe  445  (see, e.g.,  FIGS. 15B ) that can be releasably coupled to the first probe  435  as described in further detail below. The first probe  435  includes a first elongate transmission member  420  (also referred to herein as “first transmission member” or “first elongate member” or “transmission member” or “elongate member”) and a coupler  430 . The coupler  430  includes a proximal end portion  431  and a distal end portion  432  and defines a central lumen (not shown) that extends at least partially therethrough. The proximal end portion  431  of the coupler  430  includes a first coupling portion  434  configured to be releasably coupled to a probe coupling (see e.g., the threaded probe coupling  168  in  FIG. 2 ) at the distal end portion of the transducer assembly (e.g., distal end portion  165  of transducer assembly  150 ). For example, in this embodiment, the first coupling portion  434  is a threaded coupling that is threadably coupled within the transducer assembly  150  to a mating threaded probe coupling  168  within a lumen  166  at the distal end portion  165  of the transducer horn  163 . In this manner, the first probe  435  can be removably coupled to the transducer assembly  150  via the coupler  430 . The coupler  430  also includes two flat indented surfaces  437  that can be used to receive a tool to assist in securing the coupler  430  to the probe coupling. For example, a tool such as a medical wrench can clamp onto the surfaces  437  and used to tighten the coupler  430  to the probe coupling. 
     The distal end portion  432  of the coupler  430  is configured to receive a portion of the transmission member  420  to fixedly couple the transmission member  420  to the coupler  430  (i.e., within the central lumen of the coupler  430 ). The transmission member  420  includes a proximal end portion  421  and a distal end portion  422 . The proximal end portion  421  is fixedly coupled to the distal end portion  332  of the coupler  430 . The distal end portion  422  is configured to be inserted into a body of a patient as described in more detail herein. As described above, the first probe  435  also includes a second coupling portion  436  to releasably couple to the first probe  435  to the second probe  445 . 
     The second probe  445  includes an elongate transmission member  444  (also referred to herein as “second transmission member” or “second elongate member” or “transmission member” or “elongate member”) and a coupler  440 . The coupler  440  includes a proximal end portion  443  and a distal end portion  447  and defines a lumen  439  that extends at least partially therethrough. The transmission member  444  includes a proximal end portion  441  and a distal end portion  442 . The proximal end portion  441  is fixedly coupled to the distal end portion  447  of the coupler  440 . The proximal end portion  443  of the coupler  430  includes a coupling portion  446  (see, e.g.,  FIG. 18C ) (also referred to herein as “third coupling portion”) configured to be releasably coupled to the second coupling portion  436  of the first probe  435 . Thus, the second probe  445  can be removably or releasably coupled to the transducer assembly  150  via the first probe  435  (e.g., via the coupler  430 ). In this manner, both the first probe  435  and the second probe  445  can be coupled to the same transducer assembly and be driven by the same ultrasonic transducer. More specifically, the lumen of the second probe  445  can receive at least a portion of the first elongate member  420  of the first probe  435  and the coupler  440  can be releasably coupled to the coupler  430 . The elongate member  420  of the first probe  435  can, for example, be inserted through the lumen of the second elongate member  444  such that a distal end of the first elongate member  420  extends outside of the lumen  448  as shown, for example, in  FIGS. 14 and 17B . In this embodiment, the second coupling portion  436  is a threaded coupling and the third coupling portion  446  is a threaded coupling (see, e.g.,  FIG. 18C ) to threadably couple the first probe  435  to the second probe  446 . The second probe  445  can also include a tapered distal end portion  449  that is in this embodiment a separate component coupled to the distal end portion  442  of the second elongate member  444 . The tapered distal end portion  449  of the second probe  445  can assist with insertion of the probe assembly  410  into a tissue to be treated. In this manner, the second elongate member  444  can function as a guide catheter, as described below. By extending distally outside of the lumen  448 , the distal end portion  422  of the elongate member  420  can be advanced into the target tissue. In some embodiments, the tapered distal end portion  449  can provide an angled distal end that is angled between  30  and  40  degrees relative to a centerline of the second elongate member  444 . 
     The first coupler  430  also includes a port  425  in fluid communication with the central lumen of the first elongate member  420 . The port  425  can be used to aspirate and/or to supply irrigation to a target tissue site. The port  425  is coupled to a transfer line  426  that can be coupled to a fluid source or disposal container via a connector  427  (see, e.g.,  FIGS. 14 and 15A ). The port  425  and fluid line  426  can be used to supply irrigation or aspirate particles from an obstruction at the treatment site. 
     The first elongate member  420  and the second elongate member  444  can each be any suitable shape, size, or configuration as described herein. In this embodiment, the first elongate member  420  is formed with a metal such as stainless steel, and the second elongate member  444  is formed with a braided metal material. The braided metal of the second elongate member  444  is more flexible than the stainless steel of the first elongate member  420 . Thus, the first elongate member  420  has a stiffness greater than the second elongate member  444 . In alternative embodiments, the first elongate member  420  can be formed with the same material than the second elongate member  444 . The combination of a flexible braided second elongate member  444  and a more rigid inner elongate member  420  provides both strength in the probe assembly  410  and flexibility to maneuver the probe assembly  410  through a vessel of a patient. 
     In some embodiments, the elongate members  420  and  444  can optionally include any suitable feature configured to increase the flexibility (e.g., decrease the stiffness) of at least a portion of the transmission member  420 ,  444  thereby facilitating the passage of the elongate members  420 ,  444  through a tortuous lumen within a patient (e.g., a urinary tract, a vein, artery, etc.). For example, in some embodiments, a portion of the elongate members  420  and/or  444  can be formed from a material of lower stiffness than a different portion of the elongate member  420 ,  444  formed from a material of greater stiffness. In some embodiments, the stiffness of at least a portion of the elongate members  420  and/or  444  can be reduced by defining an opening (e.g., notch, a groove, a channel, a cutout, or the like), in the elongate members  420  and/or  444  or providing openings within a braided material in which the elongate members  420  and/or  444  may be formed, thereby reducing the area moment of inertia of the portion of the transmission members  420 ,  444 . 
     As described above for previous embodiments, the first elongate member  420  can be disposed coaxial with the second elongate member  444  when the first elongate member  420  is disposed at least partially within the lumen of the second elongate member  344 . In other embodiments, the first elongate member  420  is non-coaxial with the second elongate member  444  when the first elongate member  420  is disposed at least partially within the lumen  448  of the second elongate member  444 . In such a non-coaxial configuration, the close proximity or in some cases contact, between the first elongate member  420  and the second elongate member  444 , allows for ultrasonic energy to be transferred from the first elongate member  420 , to the second elongate member  444  and then to the target tissue, providing a greater amount of ultrasonic energy at the treatment site. 
     As also described above for the previous embodiment, in use, a user (e.g., a surgeon, a technician, physician, etc.) can operate the ultrasonic system  100  (described above) to deliver ultrasonic energy to a target bodily tissue within a patient. For example, the ultrasonic system  100  and probe assembly  410  can be used to treat a chronic total occlusion (CTO) in a patient. 
     The probe assembly  410 , having two ultrasonic probes (first probe  435  and second probe  445 ), allows the user to use both the first probe  435  and the second probe  445  to treat the target object, or the user can selectively decouple the second probe  445  from the first probe  435  such that ultrasonic energy is transferred only to the first elongate member  420 . In such a use, the second probe  445  can function, for example, as a guide catheter. The user can also selectively couple and decouple the second probe  445  from the first probe  435  while the probe assembly  410  is inserted within the patient&#39;s body. For example, in some instances, a user can connect the first probe  435  to the transducer assembly and use the second probe  445  as a guide catheter for inserting the first probe  435  into the patient&#39;s body. Ultrasonic energy can be provided via the transducer of the transducer assembly to the first probe and to a target tissue to be treated. The user can then connect the second probe  445  to the first probe  435  (via the coupler  430  and the second coupler  440 ) thereby connecting the second probe  245  to the transducer assembly and transducer, and apply ultrasonic energy through both probes to the target tissue. In some instances, the second probe  445  may not be used. In some instances, both the first probe  435  and the second probe  445  are coupled to the transducer and ultrasonic energy is applied through both probes to the target tissue. 
     When at least the first probe  435  of the probe assembly  410  is coupled to the transducer assembly  150  (instead of the probe assembly  110 ), the first elongate member  420  can receive ultrasonic energy from the ultrasonic transducer (e.g., piezoelectric members  162 ) of the transducer assembly  150  and convey the ultrasonic energy to a target object within a patient&#39;s body. Similarly, when the second probe  445  is coupled to the first probe  435 , the second elongate member  444  can receive ultrasonic energy from the ultrasonic transducer and convey the ultrasonic energy to the target object within the patient&#39;s body. Because the second (outer) probe  445  has a larger diameter, conveying the ultrasonic energy through the second probe  445  can produce a larger opening through the target tissue (e.g., CTO). 
     As described above, the user can, for example, engage the pedals  172  of the foot switch  170  such that the ultrasonic generator  180  generates an alternating current (AC) and voltage with a desired ultrasonic frequency (e.g., 20,000 Hz). In this manner, the ultrasonic generator  180  can supply AC electric power to the piezoelectric members  162 . The AC electric power can urge the piezoelectric members  162  to oscillate (e.g., expand, contract, or otherwise deform) at the desired frequency, which, in turn, causes the transducer horn  163  to move relative to the housing  151 . Thus, with the probe assembly  410  coupled to the transducer horn  163 , the movement of the transducer horn  163  vibrates and/or moves the probe assembly  410 , and more specifically, the first elongate member  420  and/or the second elongate member  444  when they are coupled to the transducer assembly  150 . 
     In use, the distal end portion of the probe assembly  410  can be inserted within a vessel of a patient adjacent to or penetrating a target tissue (e.g., an obstruction, such as a CTO) such that the first elongate member  420  or the first elongate member  420  and the second elongate member  444  can transfer at least a portion of the ultrasonic energy to the target tissue. The distal end portion of the probe assembly  420  can be inserted into the vessel either before or after coupling the first probe  435  and/or second probe  445  to the transducer assembly. In some embodiments, a distal tip or end of the first elongate member  420  can extend outside of the lumen of the second elongate member  444  and impact a target tissue such as, for example, to break apart an occlusion. In some embodiments, movement of the distal end portion  422  of the first elongate member  420  is such that cavitations occur within the portion of the patient. In this manner, the cavitation can further break apart a target tissue. 
       FIG. 20  is a flowchart illustrating a method  580  for transferring ultrasonic energy to a target tissue within a body of a patient using an ultrasonic probe assembly as described herein, according to an embodiment. In some embodiments, the method  580  includes inserting or introducing at least a distal end portion of a probe assembly (e.g., probe assembly  210 ,  310 ,  410 ) into a vessel of a patient, at  581 . The probe assembly can include a first probe and a second probe each couplable to an ultrasonic transducer assembly (e.g.,  150 ) of an ultrasonic ablation system (e.g.,  100 ). The first probe includes a first coupler and a first elongate member coupled to the first coupler, and is couplable o the transducer assembly via the first coupler. The second probe includes a second coupler and a second elongate member coupled to the second coupler, and the second coupler is releasably coupled to the first coupler such that the second probe is coupled to the ultrasonic transducer assembly via the first probe. In some embodiments, prior to introducing the distal portion of the probe assembly into the vessel, the second probe is coupled to the first probe by inserting the first elongate member of the first probe through a lumen of the second probe such that a distal tip portion of the first elongate member extends outside the lumen of the second elongate member. 
     At  582 , the distal portion of the ultrasonic probe assembly is moved through an obstruction in the vessel such that a distal end portion of the first elongate member penetrates the obstruction and a distal end portion of the second elongate member penetrates the obstruction. At  583 , ultrasonic energy is transmitted from the ultrasonic transducer assembly to the first probe and to the second probe such that ultrasonic energy is delivered through the first elongate member and the second elongate member to the obstruction. 
     In some embodiments, after transmitting ultrasonic energy to the first probe and the second probe, the distal end portion of the ultrasonic probe assembly is moved within the obstruction from a first location to a second location within the obstruction and ultrasonic energy is transmitted to the first probe and to the second probe such that ultrasonic energy is delivered through the first elongate member and the second elongate member to the second location within the obstruction and disrupts at least a portion of the obstruction. 
     In some embodiments, at  584 , after transmitting the ultrasonic energy, the second probe is optionally disconnected from the first probe and from the ultrasonic transducer assembly, and the first probe is removed from the vessel leaving the second probe disposed within the vessel. At  585 , a third ultrasonic probe is inserted into the lumen of the second probe. In some embodiments, the third probe has a third coupler and a third elongate member coupled to the third coupler. In some embodiments, the third elongate member has a distal end portion having a diameter greater than a diameter of a distal end portion of the first elongate member such that at least a portion of the distal end portion of the third elongate member contacts an inside wall of the second elongate member at a contact location on the second elongate member. 
     At  586 , the third probe is coupled to the ultrasonic transducer assembly and ultrasonic energy is transmitted to the third probe and to the second probe such that ultrasonic energy is delivered through the third elongate member and the second elongate member to the obstruction. In some embodiments, during the transmitting ultrasonic energy to the third probe, ultrasonic energy is delivered from the portion of the distal end portion of the third elongate member to the second elongate member where the portion of the distal end portion of the third elongate member contacts the inside wall of the second elongate member at the contact location such that ultrasonic energy is delivered to the obstruction proximate to the contact location. 
     The embodiments and/or components described herein can be packaged independently or any portion of the embodiments can be packaged together as a kit. For example, in some embodiments, a kit can include an ultrasonic transducer assembly (e.g., such as the ultrasonic transducer assembly  150  described above with reference to  FIG. 2 ) and a probe assembly (e.g.,  210 ,  310 ,  410 ), as described herein. 
     The processor included in any of the ultrasonic generators can be a general-purpose processor (e.g., a central processing unit (CPU)) or other processor configured to execute one or more instructions stored in the memory. In some embodiments, the processor can alternatively be an application-specific integrated circuit (ASIC) or a field programmable gate array (FPGA). The processor can be configured to execute specific modules and/or sub-modules that can be, for example, hardware modules, software modules stored in the memory and executed in the processor, and/or any combination thereof. The memory included in the ultrasonic generator  180  can be, for example, flash memory, one time programmable memory, a random access memory (RAM), a memory buffer, a hard drive, a read-only memory (ROM), an erasable programmable read-only memory (EPROM), and/or so forth. In some embodiments, the memory includes a set of instructions to cause the processor to execute modules, processes and/or functions used to generate, control, amplify, and/or transfer electric current to another portion of the system, for example, the transducer assembly  150 . 
     Some embodiments described herein, such as, for example, embodiments related to the ultrasonic generators described above, relate to a computer storage product with a non-transitory computer-readable medium (also can be referred to as a non-transitory processor-readable medium) having instructions or computer code thereon for performing various computer-implemented operations. The computer-readable medium (or processor-readable medium) is non-transitory in the sense that it does not include transitory propagating signals per se (e.g., a propagating electromagnetic wave carrying information on a transmission medium such as space or a cable). The media and computer code (also can be referred to as code) may be those designed and constructed for the specific purpose or purposes. Examples of non-transitory computer-readable media include, but are not limited to: magnetic storage media such as hard disks, floppy disks, and magnetic tape; optical storage media such as Compact Disc/Digital Video Discs (CD/DVDs), Compact Disc-Read Only Memories (CD-ROMs), and holographic devices; magneto-optical storage media such as optical disks; carrier wave signal processing modules; and hardware devices that are specially configured to store and execute program code, such as Application-Specific Integrated Circuits (ASICs), Programmable Logic Devices (PLDs), Read-Only Memory (ROM) and Random-Access Memory (RAM) devices. Other embodiments described herein relate to a computer program product, which can include, for example, the instructions and/or computer code discussed herein. 
     Examples of computer code include, but are not limited to, micro-code or micro-instructions, machine instructions, such as produced by a compiler, code used to produce a web service, and files containing higher-level instructions that are executed by a computer using an interpreter. For example, embodiments may be implemented using Java, C++, or other programming languages (e.g., object-oriented programming languages) and development tools. Additional examples of computer code include, but are not limited to, control signals, encrypted code, and compressed code. 
     While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Where methods and/or schematics described above indicate certain events and/or flow patterns occurring in certain order, the ordering of certain events and/or flow patterns may be modified. Additionally certain events may be performed concurrently in parallel processes when possible, as well as performed sequentially. While the embodiments have been particularly shown and described, it will be understood that various changes in form and details may be made. Although various embodiments have been described as having particular features and/or combinations of components, other embodiments are possible having a combination of any features and/or components from any of embodiments where appropriate. 
     For example, the probe assemblies described above ( 110 ,  210 ,  310 ,  410 ) can be used in any suitable ultrasonic energy system, such as the ultrasonic energy system  100  described with reference to  FIGS. 1 and 2 . As described above, the first and second probes of the probe assemblies can be coupled and decoupled from each other to allow a user to selectively use only the first probe or both the first probe and the second probe of the probe assembly to treat a target object. The elongate transmission members of the probe assemblies described herein can have various shapes and sizes (e.g., diameters, lengths, etc.). For example, in some embodiments, an outer elongate transmission member can have an outer diameter that is between 0.95 mm and 2.5 mm, and an inner diameter that is between 0.5 mm and 2.3 mm, and an inner elongate transmission member can have an outer diameter that is between 0.4 mm and 2.2 mm and an inner diameter that is between 0.1 mm and 2.0 mm. In some embodiments, an outer elongate transmission member can have a length that is between 450 mm and 1790 mm, and an inner elongate transmission member can have a length that is between 460 mm and 1800 mm. 
     Although the transducer assembly  150  is shown in  FIG. 2  as including two insulators  161  and two piezoelectric rings  162 , in other embodiments, a transducer assembly can include any suitable number of insulators  161  and/or piezoelectric rings  162  in any suitable arrangement. Moreover, the insulators  161  can be formed from any suitable insulating material, ceramic materials (e.g., polyamide, expanded polytetraflouroethylene (EPTFE), or the like). Similarly, the piezoelectric rings  162  can be any suitable piezoelectric material (e.g., lead zirkonate titanate (PZT-5), PZT-8, lead titanate (PT), lead metaniobate (PbNbO 6 ), polyvinylidenefluoride (PVDF), or the like).