Ultra-thin acoustic transducer and balloon catheter using same in imaging array subassembly

• US 4,841,977 A
• Filed: 05/26/1987
• Issued: 06/27/1989
• Est. Priority Date: 05/26/1987
• Status: Expired due to Term

• Current Assignee: Boston Scientific Scimed (Boston Scientific Corporation)
• Original Assignee: InterTherapy, Inc. (Boston Scientific Corporation)
• Inventors: Griffith, James M., Henry, Walter L., Zalesky, Paul J., Maciel, Mario
• Primary Examiner(s): JAWORSKI, FRANCIS J
• Application Number:
  US07/053,692
• Time in Patent Office: 763 Days
• Field of Search: 128/344, 128/348.1, 128/772, 128/660, 128/661, 128/663, 128/642, 128/692, 128/660.03, 128/660.06, 29/25.35
• US Class Current: 600/439
• CPC Class Codes: A61B 8/12 in body cavities or body tracts, e.g. by using catheters catheters per se A61M25/00
• CPC Class Codes: A61B 8/445 Details of catheter construction
• CPC Class Codes: B06B 1/0685 on the back only of piezoelectric elements
• CPC Class Codes: G01N 2291/044 Internal reflections (echoes), e.g. on walls or defects
• CPC Class Codes: Y10T 29/42 Piezoelectric device making

Abstract

An array of miniature ultrasound crystals mounted on preassembled subassembly which is, in turn, mounted on a small lumen catheter provides dimensional and other quantitative information relating to arterial wall geometry and character at disease or obstruction sites. Balloons also mounted to the catheter make it possible to use the catheter for the angioplasty (PCTA) procedure while actually imaging, in real time, the artery being dilatated and unblocked by the procedure. Efficient, highly miniature transducers are presented along with several different configurations for catheter structure containing fluid lumen, through-lumen, and electrical microcable assemblies for conducting electrical signals to and from the transducers.

Claims

1. An ultra-thin electroacoustic transducer having an overall thickness less than 0.0075 inch and comprising:

an active piezoelectric layer having a thickness of approximately one-fourth wavelength at its acoustic operating frequency and having an acoustic impedance Z₁ ;

a backing layer affixed to a first face of said piezoelectric layer, said backing layer having an acoustic impedance Z₂ which is greater than Z₁ ;

a faceplate layer affixed to a second, opposite, face of said piezoelectric layer, said faceplate layer having a thickness of approximately one-fourth wavelength at said operating frequency and having an acoustic impedance Z₃ which is approximately the geometric mean of Z₁ and an ambient acoustic impedance during use; and

electrical lead means for making electrical connections to said first and second faces of the piezoelectric layer.

2. An ultra-thin electroacoustic transducer as in claim 1 wherein Z₁ is about 27×

10⁶ Kg/(M² sec) and Z₂ is about 30×

10⁶ to 40×

10⁶ Kg/(M² sec).

3. An ultra-thin electroacoustic transducer as in claim 1 wherein said electrical lead means includes metallic surfaces applied to said first and second faces of the piezoelectric layer and wherein said backing and faceplate layers each comprise an in situ cured layer of powders mixed with epoxy on respectively associated faces of the piezoelectric layer.

4. An ultra-thin electroacoustic transducer as in claim 1 wherein said backing and faceplate layers each comprise an in situ cured layer of an epoxy material respectively associated faces of the piezoelectric layer.

5. An ultra-thin electroacoustic transducer as in claim 1 wherein said backing layer comprises Tungsten powder mixed with epoxy.

6. An ultra-thin electroacoustic transducer as in claim 1 wherein said faceplate layer comprises Al₂ O₃ powder mixed with epoxy.

7. An array subassembly of ultra-thin electroacoustic transducers comprising:

a cylindrical carriage which includes means for defining (i) a plurality of circumferentially arranged wall apertures, and (ii) a through aperture along its axis; and

a corresponding plurality of transducers adhesively mounted in respective said wall apertures and thereby disposed in a circumferentially extending array so as to provide an array subassembly of plural said transducers disposed within the wall apertures of said cylindrical carriage; and

wherein

at least one of said transducers has an overall thickness of less than 0.0075 inch and includes,

(a) an active piezoelectric layer having a thickness of approximately one-fourth wavelength at its acoustic operating frequency and having an acoustic impedance Z1;

(b) a backing layer affixed to a first face of said piezoelectric layer, said backing layer having an acoustic impedance Z2 which is greater than Z1;

(c) a faceplate layer affixed to a second, opposite, face of said piezoelectric layer, said faceplate layer having a thickness of approximately one-fourth wavelength at said operating frequency and having an acoustic impedance Z3 which is approximately the geometric mean of Z1 and an ambient acoustic impedance during use; and

(d) electrical lead means for making electrical connections to said first and second faces of the piezoelectric layer.

8. An array subassembly of ultra-thin electroacoustic transducers as in claim 7 further comprising a catheter tube adhesively affixed within said through aperture of the cylindrical carriage.

9. An array subassembly of ultra-thin electroacoustic transducers as in claim 8 wherein said catheter tube includes a through-lumen for slidably passing a guidewire therethrough.

10. An electroacoustic transducer array subassembly for mounting about a catheter sized to pass through human blood vessels, said subassembly comprising:

a carriage structure having a generally cylindrical configuration and including means defining (i) a plurality of circumferentially spaced-apart wall apertures and (ii) an axially extending through aperture which is sized and configured to fit over at least a portion of said catheter; and

plural electroacoustic transducers each of which includes a backing layer having a portion which extends into a respective said defined wall aperture and is affixed therewithin by means of a cured adhesive material, wherein

said cylindrical carriage structure includes means which facilitate folding of an initially flat form of said carriage structure into said generally cylindrical configuration thereof, said fold-facilitating means including a number of axially extending regions of reduced material thickness which establish a corresponding number of axially extending fold lines, whereby said generally cylindrical configuration of said carriage structure is polygonal in cross-section.

11. An electroacoustic transducer array subassembly as in claim 10 wherein said cylindrical carriage is a solid body of material.

12. An electroacoustic transducer array subassembly as in claim 10 wherein said cylindrical carriage is made of a conductive metallic material.

13. An electroacoustic transducer array subassembly as in claim 10 wherein said cylindrical carriage includes wall apertures without transducers therein to facilitate subsequent adhesive affixation of the carriage to said catheter.

14. An electroacoustic transducer array subassembly as in claim 10 wherein said transducers include insulated lead wires connected therewith and said cylindrical carriage includes lead wire clamp means for relieving mechanical loads from connections to said transducers.

21. An electroacoustic transducer array subassembly as in claim 10 where said through aperture of said carriage is adhesively affixed to a catheter tube.

15. An electroacoustic transducer array subassembly for mounting about a catheter sized to pass through human blood vessels, said subassembly comprising:

a carriage structure having a generally cylindrical configuration and including means defining (i) a plurality of circumferentially spaced-apart wall apertures and (ii) an axially extending through aperture which is sized and configured to fit over at least a portion of said catheter; and

plural electroacoustic transducers each of which includes a backing layer having a portion which extends into a respective said defined wall aperture and is affixed therewithin by means of a cured adhesive material, wherein

each said electroacoustic transducer is an ultra-thin transducer having an overall thickness less than 0.0075 inch and comprises;

(a) an active piezoelectric layer having a thickness of approximately one-forth wavelength at an intended acoustic operating frequency and having an acoustic impedance Z₁ ;

(b) a backing layer affixed to a first face of said piezoelectric layer, said backing layer having an acoustic impedance Z₂ which is greater than Z₁ ;

(c) a faceplate layer affixed to a second, opposite, face of said piezoelectric layer, said faceplate layer having a thickness of approximately one-fourth wavelength at said operating frequency and having an acoustic impedance Z₃ which is approximately the geometric mean of Z₁ and an ambient acoustic impedance during use; and

(d) electrical lead means for making electrical connections to said first and second faces of the piezoelectric layer.

16. An electroacoustic transducer array subassembly as in claim 16 wherein Z₁ is about 27×

10⁶ Kg/(M² sec) and Z₂ is about 30×

10⁶ to 40×

10⁶ Kg/(M² sec).

17. An electroacoustic transducer array subassembly as in claim 16 wherein said electrical lead means includes metallic surfaces applied to said first and second faces of the piezoelectric layer and wherein said backing and faceplate layers each comprise are in situ cured layer of powders mixed with epoxy on respectively associated faces of the piezoelectric layer.

18. An electroacoustic transducer array subassembly as in claim 16 wherein said backing and faceplate layers each comprise an in situ cured epoxy material on respectively associated faces of the piezoelectric layer.

19. An electroacoustic transducer array subassembly as in claim 16 wherein said backing layer comprises Tungsten powder mixed with epoxy.

20. An electroacoustic transducer array subassembly as in claim 16 wherein said faceplate layer comprises Al₂ O₃ powder mixed with epoxy.

22. An electroacoustic transducer array subassembly as in claim 22 wherein said catheter tube has a through-lumen for slidably passing over a guidewire.

23. A dilatation angioplasty catheter of the type which is insertable into a blood vessel, said catheter comprising:

a hollow, elongated tubular body of sufficiently small size so as to be insertable into a blood vessel and defining a central lumen therethrough and a fluid passageway;

inflatable balloon means, fixedly disposed on an exterior portion of said body and fluid-connected to said fluid passageway, said balloon means varying in outside dimensions in response to fluid pressure with said fluid passageway; and

ultrasonic transducer means dispoed within said central lumen of said body and surrounded by said balloon means, for producing acoustical signals and for sensing echoes of said produced signals, said transducer means including means (i) providing a substantially cylindrical array of individual ultrasonic transducers and (ii) defining a through aperture substantially coaxially disposed with respect to said central lumen.

24. An angioplasty imaging system including:

a hollow, elongated tubular body defining a central lumen and a fluid passage therethrough, said body being of sufficiently small size and thereby adapted for insertion into a blood vessel;

inflatable balloon means, fixedly disposed on an exterior portion of said body and fluid-connected to said fluid passage, said balloon means varying in outside dimensions in response to fluid pressure within said fluid passage;

ultrasonic transducer means disposed within said central lumen of said body and surrounded by said balloon means, said transducer means including a number of individual ultrasonic transducers arranged in a substantially cylindrical configuration so as to establish a through aperture in axial communication with said central lumen, each said ultrasonic transducers for producing acoustical signals in response to electrical excitation signals and for generating electrical signals responsive to echoes of said produced acoustical signals;

driver/imaging means for alternately (a) producing said excitation signals, and (b) generating an image of said blood vessel in response to said transducer means-generated electrical signals; and

means disposed within said body for establishing a signal path between said drive/imaging means and said transducer means.

25. A system as in claim 25 wherein said driver/imaging means includes means for producing acoustic signals from said transducer means at a frequency of approximately 20 megahertz.

26. A miniature ultrasonic transducer small enough to be disposed within a vascular catheter body, said transducer comprising:

piezoelectric chip means for resonating at an operating frequency of approximately 20 MHz, said chip means having first and second opposing surfaces which establish therebetween a thickness of said chip means of approximately one-fourth wavelength at said operating frequency and having an acoustic impedance Z1;

backing means, disposed on said chip means first surface, and having an acoustic impedance Z2 which is greater than the acoustic impedance Z1 of said chip means for attenuating acoustical energy passing therethrough;

a layer of conductive material disposed on said chip means second surface and having a thickness of approximately one-fourth wavelength at said operating frequency and having an acoustic impedance Z3 which is approximately the geometric mean of Z1 and an ambient acoustic impedance during use;

a flattened electrical terminal electrically connected to said conductive material layer; and

matching layer means, disposed on said conductive material layer and over said electrical terminal, said matching layer means defining a dimension which is an odd multiple of a quarter wavelength of said operating frequency, said matching layer means for increasing the efficiency of acoustical energy transfer to and from said chip means.

27. A miniature transducer array subassembly comprising:

cylindrical sleeve defining plural substantially planar outer surfaces;

a miniature ultrasonic transducer disposed on one of said plural outer surfaces, said transducer having at least one electrical connection;

lead wire means including a flattened electrically conductive distal end attached to said electrical connection of said transducer for electrically connecting said transducer; and

means carried by said sleeve for affixation to said lead wire means for relieving stress from said connection, wherein said stree relieving means includes a longitudinal depression defined by means of said sleeve proximally of said one outer surface for receiving at least that portion of said lead wire means which is proximal to said flattened distal end thereof, and wire clamp means operatively associated with said defined depression for positionally retaining said proximal portion of said lead wire means within said defined depression.

28. A dilatation angioplasty cathether of the type which is insertable into a blood vessel, said catheter comprising:

a hollow, elongated tubular body defining a fluid passage therethrough;

inflatable balloon means, fixedly disposed on the exterior of said body and coupled to said fluid passage, said balloon means varying in outside dimensions in response to fluid pressure within said fluid passage;

piezoelectric chip means for resonating at an operating frequency of approximately 20 MHz, said chip means having first and second opposing surfaces which establish therebetween a thickness of said chip means of approximately one-fourth wavelength at said operating frequency and having an acoustic impedance Z1;

backing means, disposed on said chip means first surface, and having an acoustic impedance Z2 which is greater than the acoustic impedance Z1 of said chip means for attenuating acoustic energy passing therethrough;

a layer of conductive material disposed on said chip means second surface and having a thickness of approximately one-fourth wavelength at said operating frequency and having an acoustic impedance 23 which is approximately the geometric mean of Z1 and an ambient acoustic impedance during use;

a flattened electrical terminal electrically connected to said conductive material layer; and

matching layer means, disposed on said conductive material layer and over said electrical terminal, said matching layer means defining a dimension which is an odd multiple of a quarter wavelength of said operating frequency, said matching layer means for increasing the efficiency of acoustical energy transfer to and from said chip means; and

electrical cable means, disposed within said tubular body and electrically connected to said flattened electrical terminal, for conducting electrical signals to and from said terminal.

29. A dilatation angioplasty catheter of the type which is insertable into a blood vessel, said cathether comprising:

a hollow, elongated tubular body defining a fluid passage therethrough;

inflatable balloon means, fixedly disposed on the exterior of said body and coupled to said fluid passage, said balloon means varying in outside dimensions in response to fluid pressure within said fluid passage;

an electrically conductive cylindrical sleeve defining plural substantially planar outer surfaces, said sleeve enclosing at least a segment of said guide wire retaining passage;

a miniature ultrasonic transducer disposed on one of said sleeve plural outer surfaces, said transducer having first and second electrical connections;

lead wire means for electrically connecting to said transducer connections; and

stress relieving means, carried by said sleeve for affixation to said lead wire means for relieving stress from said connections, said stress relieving means including a longitudinal depression for receifing at least a portion of said lead wire means, and clamp means operatively associated with said depression for positionally retaining said lead wire means within said depression.

30. A carriage structure for supporting a plurality of electroacoustic transducers, said carriage structure being foldable into a generally cylindrical configuration and thereby being adapted to surround an exterior portion of a catheter for electroacoustic imaging of human blood vessels and the like, said carriage structure comprising:

a substantially planar sheet member having upper and lower surfaces which define therebetween a thickness dimension;

means for defining a number of individual apertures in said sheet member which are sized and configured to accept a discrete electroacoustic transducer therein; and

means for establishing a number of axially extending regions of said sheet member having a reduced thickness dimension as compared to the thickness dimension of said sheet member defined between said upper and lower surfaces thereof, to thereby define a number of fold lines which subdivide said planar sheet member into several planar regions having at least one of said apertures defined therein, wherein

said established axially extending regions and said defined fold lines collectively provide means which facilitate folding of said carriage structure into said generally cylindrical configuration by allowing adjacent ones of said several planar regions to be angularly disposed relative to one another along a respective said fold line.

31. A carriage structure as in claim 31, wherein said means for establishing includes a number of axially extending grooves which are each defined in said lower surface.

32. A carriage structure as in claim 31, further comprising means for defining a number of second apertures for facilitating adhesive connection of said carriage structure to said catheter portion.

33. A carriage structure as in claim 33, wherein said second apertures are located at a distal end of said carriage structure as compared to said first-mentioned apertures.