Lead electrode for use in an MRI-safe implantable medical device

• US 20050222642A1
• Filed: 03/02/2005
• Published: 10/06/2005
• Est. Priority Date: 03/30/2004
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Olsen, James M., Wahlstrand, Carl D., Hrdlicka, Gregory A., Przybyszewski, Piotr, Davis, Timothy J.
• Granted Patent: US 8,989,840 B2
• Time in Patent Office: Days
• US Class Current: 607/48
• CPC Class Codes: A61N 1/0534 Electrodes for deep brain stimulation
• CPC Class Codes: A61N 1/0551 Spinal or peripheral nerve electrodes
• CPC Class Codes: A61N 1/086 Magnetic resonance imaging [MRI] compatible leads
• CPC Class Codes: A61N 1/3605 Implantable neurostimulators for stimulating central or peripheral nerve system
• CPC Class Codes: A61N 1/36071 Pain
• CPC Class Codes: A61N 1/36125 Details of circuitry or electric components
• CPC Class Codes: A61N 1/36142 for improving safety
• CPC Class Codes: A61N 1/3718 Monitoring of or protection against external electromagnetic fields or currents

Abstract

An implantable stimulation system comprises a stimulator for generating electrical stimulation and a conductive stimulation lead having a proximal end electrically coupled to the stimulator, wherein at least a first component of the impedance looking into the stimulator is substantially matched to the impedance of the stimulation lead. At least one distal stimulation electrode is positioned proximate the distal end of the stimulation lead.

Claims

1. An implantable medical system, comprising:

an implantable medical device;

a conductive lead having a proximal end electrically coupled to said device and having a distal end, the impedance looking into said device being substantially matched to the characteristic impedance of said lead; and

at least one distal therapy electrode proximate the distal end of said therapy lead.

2. The medical system according to claim 1 wherein said device is a stimulator for generating electrical stimulation, said lead is a stimulation lead, and said electrode is a stimulation electrode.

3. The medical system according to claim 1 wherein said electrode is a sensing electrode for conveying sensed activity to said device via said lead.

4. The medical system according to claim 1 wherein said device is a neurostimulator.

5. The medical system according to claim 1 wherein the characteristic impedance is real.

6. The medical system according to claim 1 wherein the characteristic impedance is imaginary.

7. The medical system according to claim 1 wherein the characteristic impedance is a complex impedance having a real component and an imaginary component.

8. The medical system according to claim 7 wherein the characteristic impedance of said stimulation lead is substantially the complex conjugate of the impedance of said device.

9. The medical system according to claim 1 further comprising an impedance adjusting circuit coupled to said device and to said lead for monitoring the degree of mismatch between the characteristic impedance of said lead and the impedance of said device.

10. The medical system according to claim 2 further comprising an impedance matching element.

11. The medical system according to claim 10 wherein said impedance matching element is a resistor.

12. The medical system according to claim 11 wherein said medical system has a stimulation path from said stimulator to said stimulation electrode and wherein said matching resistor is in series with said stimulation path.

13. The medical system according to claim 11 wherein said medical system has a stimulation path from said stimulator to said stimulation electrode and wherein said matching resistor is in parallel with said stimulation path.

14. The medical system according to claim 10 wherein said stimulator comprises an encasement, a feedthrough pin through said encasement, a connector block coupled to said encasement, and a contact in said connector block and wherein said impedance matching element is electrically coupled in series between said feedthrough pin and said contact.

15. The medical system according to claim 14 wherein said impedance matching element is hermetically sealed.

16. The medical system according to claim 13 further comprising:

an inductive circuit in said stimulation path between said stimulator and a point on said stimulation path; and

a capacitive circuit coupled between said point and said matching resistor.

17. The medical system according to claim 13 further comprising:

a comparator having a first input, a second input, and an output, said first input coupled to said impedance matching element, and said output of said comparator for generating a signal related to the voltage across said impedance matching element;

a processor having a first input coupled to the output of said comparator, a first output coupled to the second input of said comparator, and having a second output; and

a variable impedance circuit coupled to said impedance matching element and to the second output of said processor, said processor for adjusting the impedance of said variable impedance circuit in response to the output of said comparator.

18. The medical system according to claim 17 wherein the second output of said processor corresponds to the previous maximum voltage across said impedance matching element.

19. An implantable stimulation system for generating and delivering therapy to a patient, said stimulation system comprising:

a stimulator for generating the therapy;

a conductive stimulation lead having a proximal end electrically coupled to said stimulator;

a stimulation electrode positioned proximate a distal end of said stimulation lead; and

impedance matching means electrically coupled to said lead for substantially matching the impedance of said stimulator to the characteristic impedance of said lead.

20. The stimulation system according to claim 19 wherein said stimulator comprises a hermetically sealed encasement and wherein said impedance matching means is housed within said encasement.

21. The stimulation system according to claim 20 wherein said stimulator comprises a first hybrid circuit hermetically sealed in said encasement for generating said therapy and wherein said impedance matching means is configured on said first hybrid circuit.

22. The stimulation system according to claim 20 wherein said stimulator comprises a first hybrid circuit hermetically sealed in said encasement for generating said therapy and wherein said impedance matching means is configured on a second hybrid circuit hermetically sealed within said encasement.

23. The stimulation system according to claim 19 wherein said stimulator comprises a first hermetically sealed encasement and wherein said impedance matching means is hermetically sealed in a second hermetically sealed encasement.

24. An implantable stimulation system for generating and delivering therapy to a patient, said stimulation system comprising:

a stimulator for generating the therapy;

a conductive stimulation lead having a proximal end electrically coupled to said stimulator;

a stimulation electrode positioned proximate a distal end of said stimulation lead; and

an impedance matching circuit electrically coupled to said lead for substantially matching the impedance of said stimulator to the characteristic impedance of said lead.

25. The stimulation system according to claim 24 wherein said impedance matching circuit comprises a resistive circuit for producing a frequency independent component.

26. The stimulation system according to claim 25 wherein said impedance matching circuit comprises a circuit for generating a frequency dependent component.

27. The stimulation system according to claim 26 wherein said impedance matching circuit comprises a monitoring circuit for measuring the impedance of the stimulation lead.

28. The stimulation system according to claim 27 wherein said impedance matching circuit includes a variable impedance circuit responsive to said monitoring circuit.

29. The stimulation system according to claim 25 wherein said stimulation system has a stimulation path from said stimulator and to said stimulation electrode through said stimulation lead and wherein said resistive circuit comprises a matching resistor in series with said stimulation path.

30. The stimulation system according to claim 25 wherein said stimulation system has a stimulation path from said stimulator and to said stimulation electrode through said stimulation lead and wherein said resistive circuit comprises a matching resistor in parallel with said stimulation path.

31. The stimulation system according to claim 29 wherein said stimulator comprises an encasement, a feedthrough pin through said encasement, a connector block coupled to said encasement, and a contact in said connector block and wherein said matching resistor is electrically coupled in series between said feedthrough pin and said contact.

32. The stimulation system according to claim 31 wherein said matching resistor is hermetically sealed.

33. The stimulation system according to claim 25 further comprising:

a comparator having a first input, a second input, and an output, said first input coupled to said resistor and said output of said comparator for generating a signal related to the voltage across said resistor;

a processor having a first input coupled to the output of said comparator, a first output coupled to the second input of said comparator, and having a second output; and

a variable impedance circuit coupled to said resistor and to the second output of said processor, said processor for adjusting the impedance of said variable impedance circuit in response to the output of said comparator.

34. The stimulation system according to claim 33 wherein the second output of said processor corresponds to the previous maximum voltage across said resistor.