Abstract:
Wires are used for conducting ultrasound energy. These wires achieve optimum properties by creating a multiple material coaxial construction. For example, in a particular embodiment it is desirable to have an elastic core (nitinol) for conducting axial vibrations (sonic or ultrasonic) and a thin stiff cladding (stainless steel) in order to minimize traverse vibrations which result in loss of energy.

Description:
RELATED APPLICATION 
     This is a continuation of U.S. Ser. No. 08/756,187 filed Nov. 25, 1996 now abandoned, which is a continuation of U.S. Ser. No. 08/527,749 filed Sep. 13, 1995 now abandoned, which is a continuation of U.S. Ser .No. 07/861,253, filed Mar. 31, 1992, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to an ultrasound medical device. Noninvasive medical procedures reduce the risk of surgery by introducing medical devices to a body cavity through small incisions or body orifices. The devices are carefully designed so that they may be controlled from the proximal end remaining outside the body to carry out the requirement treatment at the desired location inside the body. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention features a medical device having at least a portion (e.g., an elongated wire-form or draw-form wire) for use within the body. The portion includes an extended metal outer member having an exposed outer surface and a core within the outer member formed of a metal different than the metal of the outer member. The core is secured within and substantially enclosed by the outer member. The portion is in the form of an ultrasonic probe. In embodiments, for example, the probe is an elastic probe having a titanium core and nitinol outer member. The outer member and the core are constructed of materials of substantially different acoustic impedance. The acoustic energy is provided by axial excitation. 
     The invention features wires (e.g., elongated wire-forms or draw-form wires) that can be used for conducting ultrasound energy. These wires achieve optimum properties by creating a multiple material coaxial construction. For example, in a particular embodiment it is desirable to have an elastic core (nitinol) for conducting axial vibrations (sonic or ultrasonic) and a thin stiff cladding (stainless steel) in order to minimize traverse vibrations which result in loss of energy. 
     The term “metal” as used herein includes electropositive chemical elements characterized by ductility, malleability, luster, and conductivity of heat and electricity, which can replace the hydrogen of an acid and forms bases with the hydroxyl radical and including mixtures including these elements and alloys. Many examples are given below. 
     Further aspects feature and advantages follow. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS(S) 
     We first briefly describe the drawings. 
    
    
     DRAWINGS 
     FIG. 1 is a schematic illustration of an ultrasound wire device of the invention and FIG. 1 a  is longitudinal cross-sectional view of a portion of another embodiment of an ultrasound device, having air-filled microspheres (shown greatly enlarged) at the interface of the core and outer member. 
    
    
     DESCRIPTION 
     Referring to FIGS. 1 and 1 a,  an ultrasound device  70  is shown to include a wire  72  including an inner core  74  and an outer member  76 . The wire  72  extends from a proximal end  78 , attached to an ultrasound source mechanism  80 , to a distal end  82  which is positioned at a location where ultrasound energy is to be delivered. Briefly, the source  80  includes a clamping mechanism  86  to couple the core near the distal end  78  of the wire to a diaphragm  88  which is vibrated ultrasonically by a piston transducer  90 . The transducer  90  includes a phosphorous-bronze bell  92  whose tension may be adjusted by screw member  94 . The magnetic field from coils  96  cause the transducer to vibrate when electrical energy is supplied through leads  98 . Cooling vents  100  surround the coils  98 . Ultrasound energy supplied by the mechanism  80  to the core at the proximal portion  78  of the wire is transmitted through the core to the distal end  82  where it can be utilized to treat tissue. 
     Referring to FIG. 1 a,  in some embodiments, the core  74  is bonded to the outer member  76  at intermittent points, leaving therebetween air-filled microspheres  102  which impede the transmission of ultrasound energy laterally. The microspheres could be produced by machining grooves into the core or outer member before assembly. 
     By proper selection of the outer and core metals enhanced transmission of ultrasound energy through the core may be achieved while minimizing lateral mode losses through the outer material. Preferably, the metals are selected based on their acoustic impedance (Z 1 , Z 2 ) to induce internal reflection of acoustic waves propagating off axis. An advantage of the system is that lower power may be applied so that the transmission system operates at lower temperature. The outer member can further be selected to reduce vibration. A preferred embodiment of an elastic probe employs high acoustic transmitting titanium at the core and nitinol as the outer member. In another embodiment, the core member may be for example, nitinol and the outer member stainless steel. In another embodiment, the core is tantalum. The outer member could also be formed of a non-metal, e.g., carbon or glass. The ultrasound energy could be used to ablate tissue, enhance delivery of drugs and induce relaxation of tissue, e.g., tumors and in eye surgery e.g., to dissolve cataracts. The acoustic energy can be provided to the probe by axial excitation as illustrated above or by torsional excitation or a combination thereof. Preferably, the outer member is formed of a continuous solid mass of a highly elastic biocompatible metal. 
     Superelastic or pseudo-elastic metal alloys include, for example, a nitinol (e.g., 55% nickel, 45% titanium). Other examples of superelastic materials include, e.g., Silver-Cadmium (Ag—Cd), Gold-Cadmium (Au—Cd), Gold-Copper-Zinc (Au—Cu—Zn), Copper-Aluminum-Nickel (Cu—Al—Ni), Copper-Gold-Zinc (Cu—Au—Zn), Copper-Zinc (Cu—Zn), Copper-Zinc-aluminum (Cu—Zn—Al), Copper-Zinc-Tin (Cu—Zn—Sn), Copper-Zinc-Xenon (Cu—Zn—Xe), Iron Beryllium (Fe 3 Be), Iron Platinum (Fe 3 Pt), Indium-Thallium (In—Tl), iron-manganese (Fe—Mn) Nickel-Titanium-Vanadium (Ni—Ti—V), Iron-Nickel-Titanium-Cobalt (Fe—Ni—Ti—Co) and Copper-Tin (Cu—Sn). See Schetsky, L. McDonald, “Shape Memory Alloys”,  Encyclopedia of Chemical Technology  (3rd ed.), John Wiley &amp; Sons, 1982, vol. 20. pp. 726-736 for a full discussion of superelastic alloys. Other examples of metals suitable for the outer member include stainless steel, titanium and various alloys of these metals and the precursor of superelastic alloys. Precursors of superelastic alloys are those alloys which have the same chemical constituents as superelastic alloys, but have not been processed to impart the superelastic property. Such alloys are further described in co-owned and co-pending U.S. Ser. No. 07/507,375, filed Apr. 10, 1990, the entire contents of which is hereby incorporated by reference. 
     The outer member and core may be in many cross-sectional geometric configurations, such as circular, square, triangular, hexagonal, octagonal, trapezoidal and the geometrical configuration of the core may differ from that of the longitudinal member. For example, the wire may be rectangular in cross-section with a rectangular core or triangular or hexagonal in cross-section with a circular core. The wire may also take on the form of tubing with a lumen within the core extending along the axis of the wire. The wire may also include successive layers of different metals to form a composite system. The core may extend intermittently along the axis in a desired pattern. 
     The medical device may be formed, for example, by drilling a relatively large rod of the outer member material to form a lumen, positioning a rod of core material in the lumen, sealing the ends of the lumen, e.g., by crimping and drawing as known in the art, through a series of dies of decreasing diameter until the desired outer diameter is achieved. The device may be heat treated to anneal, harden or impart superelastic properties. Other methods of formation may be, e.g., by coating the core with the desired outer material such as by electro- or electroless plating. The materials used in the outer member and core are also selected based on their workability for forming the wire, including factors such as machinability, for forming the longitudinal member into a tubular piece and the core member into a rod shaped piece, stability in gaseous environments at annealing temperatures, properties related to welding, drawing, forging, swaging, the ability to accept coatings such as adhesives, polymers, lubricants and practical aspects such as cost and availability. 
     An example is given below in which the wire has a tantalum core and a nitinol outer member. 
     EXAMPLE 1 
     A 500 foot length of wire (0.0052 inch in diameter) having an outer member formed of a precursor of a nitinol (55% Ni/45% Ti) superelastic alloy and a core material of tantalum (0.00175 inch in diameter) is formed by drilling a 0.25 inch diameter bore in a 0.75 inch rod of the outer member material and providing in the drilled lumen a tantalum member of substantially matched outer diameter. The rod is mechanically forged in a standard hot forging and rolling apparatus, then hammered such that no substantial voids between the core and outer longitudinal member are present. One end of the rod is sealed and the opposite end is cold drawn longitudinally through a dye to the final diameter of about 0.038 inch, with a core diameter of 0.0052 inch. Initially, the outer member of the wire is the precursor of a superelastic alloy, i.e., it has not been heat treated to impart the superelastic property. The wire may be annealed at 460° C. for 3 to 15 minutes, to induce the superelastic nature of the wire. 
     Other embodiments are in the following claims.