Ultrasonic transducer

• US 5,002,058 A
• Filed: 04/18/1989
• Issued: 03/26/1991
• Est. Priority Date: 04/25/1986
• Status: Expired due to Term

• Current Assignee: Surgical Navigation Technologies, Inc. (Medtronic Plc)
• Original Assignee: Intra-Sonix, Inc.
• Inventors: Martinelli, Michael A.
• Primary Examiner(s): JAWORSKI, FRANCIS J
• Application Number:
  US07/340,050
• Time in Patent Office: 707 Days
• Field of Search: 128/660.03, 128/24 A, 128/662.06
• US Class Current: 600/463
• CPC Class Codes: A61B 2034/2051 Electromagnetic tracking systems
• CPC Class Codes: A61B 2034/2063 Acoustic tracking systems, e.g. using ultrasound
• CPC Class Codes: A61B 5/062 using magnetic field
• CPC Class Codes: A61B 8/0833 involving detecting or locating foreign bodies or organic structures
• 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 8/4254 using sensors mounted on the probe

Abstract

A miniature transducer designed for use in a medical imaging system catheter probe is disclosed. The transducer has an electric cavity and coaxial construction for preventing electric fields from being emitted or received by the transducers. The construction of the transducer enables two to be mounted very close to one another on a thin catheter probe, one for transmitting acoustic pulses and the other for sensing echoes in response to the acoustic pulses, for imaging extremely close targets. The transducers can be secured to the catheter probe in such a way as to substantially acoustically isolate one from the other.

A method of making the transducer by applying several electrically-conductive and insulating coatings and layers to a core in selected sequence so as to create a transducer having an electrical cavity, coaxial construction.

Claims

1. A probe device for use in a medical imaging system, said probe device comprising:

an elongated catheter having a distal portion for insertion into a portion of a living body;

transducer means secured to said distal portion of said catheter and comprising a first electro-acoustic transducer for transmitting an acoustic signal into at least a part of said portion of said living body and a second electro-acoustic transducer, positioned adjacent said first electro-acoustic transducer, for receiving acoustic echoes from said part of said portion of said living body in response to said acoustic signal; and

isolation means for substantially electrically and magnetically isolating said first and second transducers relative to one another.

2. A probe device according to claim 1, wherein said first and second transducers includes a piezoelectric device comprising a material having an acoustic impedance relatively close to the acoustic impedance of body fluids.

3. A probe device according to claim 2, wherein said material includes a polymer piezoelectric material.

4. A probe device according to claim 2, wherein said polymer piezoelectric material is a polyvinylidene fluoride.

5. A probe device according to claim 2, further including means for securing said first and second transducers to said catheter.

6. A probe device according to claim 5, wherein said means for securing said first and second transducers to said catheter includes a sheet of material wrapped around said catheter and transducers so as to secure said transducers in place.

7. A probe device according to claim 6, wherein said sheet of material has an acoustic impedance approximately equal to the geometric mean of the acoustic impedances of said polymer piezoelectric material and said body fluids.

8. A probe device according to claim 7, wherein said sheet of material is made of polyethylene.

9. A probe device according to claim 1 wherein said transducers are secured to said distal end adjacent one another at a distance of the order of approximately 0.15 mm separation.

10. A probe device according to claim 1, further including means for substantially acoustically isolating said first and second transducers from one another.

11. A probe device according to claim 10, wherein said distal portion of said catheter includes a surface for supporting said first and second transducers, and said means for substantially acoustically isolating each of said transducers from one another includes means for creating an impedance mismatch between each of said transducers and said surface of said catheter.

12. A probe device according to claim 11, wherein said means for creating said impedance mismatch includes means formed on said surface of said catheter for forming dead air space between each of said transducers and said surface of said catheter.

13. A device according to claim 12, wherein said means formed on said surface includes a roughened surface.

14. A device according to claim 13, wherein said roughened surface includes burrs in said surface for supporting each of said transducers.

15. A device according to claim 1, wherein said isolation means for substantially electrically and magnetically isolating said transducers with respect to one another comprises an electrically-conductive casing.

16. A device according to claim 1, wherein each of said transducers comprises:

a substrate having a first surface;

a piezoelectric device mounted on said first surface;

a coaxial line, having inner and outer conductors respectively electrically coupled to the opposite sides of said sheet of piezoelectric material, for providing a potential to said opposite sides,

wherein said isolation means comprises;

(a) a first layer of an electrically insulative material encasing the entire substrate, except for said first surface; and

(b) a second layer of electrically conductive material covering said first layer of said electrically insulative material and formed so as to provide an electrical path between the outer conductor of said coaxial line and the other side of said sheet of piezoelectric material.

17. A probe device for use in a medical imaging system, said device comprising:

an elongated catheter having a distal portion for insertion into a portion of the body and a flat surface formed on said distal portion;

transmit transducer means secured to said flat surface for converting an electrical excitation signal into an acoustic signal, and for transmitting said acoustic pulse away from said catheter transversely to said flat surface into at least a part of said portion of said body, wherein said transmit transducer means comprises an electric casing for substantially preventing said transmit transducer means from emitting or receiving electric fields through said casing; and

receive transducer means secured to said flat surface adjacent said transmit transducer means for receiving an acoustic echoes from said part of said body in response to said acoustic pulse, and for converting the echoes into an electrical response signal, wherein said receive transducer means comprises an electric casing for substantially preventing said receive transducer means from emitting or receiving electric fields through said casing.

18. The probe device according to claim 17, further wherein said electric casing on said transmit transducer means and said electric casing on said receive transducer means together substantially eliminate any electrical cross talk between said transmit transducer means and said receive transducer means.

19. The probe device according to claim 17, wherein said shaft comprises acoustic damping means for acoustically isolating said receive transducer means from said transmit transducer means so as to substantially eliminate acoustic cross talk between said transmit transducer means and said receive transducer means.

20. The probe device according to claim 19, wherein said acoustic damping means comprises a plurality of burrs formed in said flat surface, wherein said transmit transducer means and said receive transducer means rest on said burrs in spaced relation to said flat surface so as to provide dead air space between said transducers and said surface.

21. The probe device according to claim 17, further comprising a wrapping sheet for securing said transmit and receive transducer means to said surface.

22. The probe device according to claim 21, wherein said wrapping sheet is made of polyethylene.