MEDICAL LEADS WITH FREQUENCY INDEPENDENT MAGNETIC RESONANCE IMAGING PROTECTION

• US 20080147154A1
• Filed: 12/10/2007
• Published: 06/19/2008
• Est. Priority Date: 12/11/2006
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Smith, Lon E., Gray, Robert W., MacDonald, Stuart G.
• Granted Patent: US 8,768,486 B2
• Time in Patent Office: Days
• US Class Current: 607/115
• CPC Class Codes: A61N 1/086 Magnetic resonance imaging [MRI] compatible leads
• CPC Class Codes: A61N 1/37 Monitoring; Protecting
• CPC Class Codes: A61N 1/3718 Monitoring of or protection against external electromagnetic fields or currents
• CPC Class Codes: G01R 33/288 Provisions within MR facilities for enhancing safety during MR, e.g. reduction of the specific absorption rate [SAR], detection of ferromagnetic objects in the scanner room

Abstract

A medical device having a frequency independent circuit that substantially reduces induced currents in a lead assembly and at a tissue interface. The frequency independent circuit configures an electrical path such that a stimulation pulse travels from the medical device to a selected tissue, and a current induced by an external changing electromagnetic signal is prevented from travelling the electrical path from the selected tissue to the medical device.

Claims

1. A medical device for delivering a therapy pulse to a patient in a changing magnetic field environment, the device comprising:

a lead assembly having a proximal end and a distal end;

a first conductor having a proximal end and a distal end contained within the lead assembly for conducting the therapy pulse;

a first electrode coupled to the distal end of the first conductor; and

a first diode coupled in series with the first conductor and the first electrode, the first diode having a proximal anode and a distal cathode, the first diode substantially reducing current that is flowing from the first electrode through the first diode induced in the first conductor by the changing electromagnetic field.

2. A medical device according to claim 1 further comprising a second diode coupled in series with the first diode, the second diode having a distal anode and a proximal cathode, the second diode allowing the therapy pulse to reach the first electrode and substantially reducing current induced in the first conductor by the changing magnetic field from flowing through the first conductor to the electrode.

3. A medical device according to claim 2 wherein the second diode is a Zener diode.

4. A medical device according to claim 3 wherein the Zener diode has a breakdown voltage substantially less than the voltage of the therapy pulse.

5. A medical device according to claim 3 wherein the Zener diode is chosen to have a breakdown voltage that allows the therapy pulse to pass through while substantially blocking current induced in the first conductor by the changing magnetic field from flowing through the conductor to the first electrode.

6. A medical device according to claim 2 further comprising a third diode coupled proximate the proximal end of the first conductor and in series with the first conductor and the first electrode, the third diode having a proximal anode and a distal cathode.

7. A medical device according to claim 1 wherein the medical device receives a sensing signal and further comprises:

a second conductor contained within the lead assembly and having a proximal end and a distal end for conducting the sensing signal;

a second electrode coupled to the distal end of the second conductor; and

a fourth diode coupled in series with the second conductor and the second electrode, the fourth diode having a distal anode and a proximal cathode.

8. A medical device according to claim 1 further comprising a resonant circuit coupled in series with the first diode.

9. A medical device according to claim 8 wherein the resonant circuit is a parallel LC circuit.

10. A medical device according to claim 8 further comprising the resonant circuit and the first diode coupled proximate the distal end of the first conductor and a third diode coupled proximate the proximal end of the first conductor.

11. A medical device according to claim 10 wherein the resonant circuit is a parallel LC circuit.

12. A medical device for delivering a therapy pulse to a patient in a changing magnetic field environment, the device comprising:

a lead assembly having a proximal end and a distal end;

a first conductor having a proximal end and a distal end contained within the lead assembly;

a first electrode coupled to the distal end of the first conductor; and

a first frequency independent component coupled in series with the first conductor and the first electrode, the first frequency independent component for propagating the therapy pulse from the proximal end to the distal end of the first conductor and substantially reducing current flowing from the first electrode through the first frequency independent component induced in the first conductor by the changing magnetic field.

13. A medical device according to claim 12 further comprising a second frequency independent component coupled in series with the first conductor and the first electrode, the second frequency independent component substantially reducing current flowing from the first conductor to the first electrode induced in the first conductor by the changing magnetic field.

14. A medical device according to claim 13 further comprising a third frequency independent component coupled at the proximal end of the first conductor and in series with the first and second frequency independent components, the third frequency independent component for substantially reducing current flowing from the first electrode through the third frequency independent component induced in the first conductor by the changing magnetic field.

15. A medical device according to claim 12 further comprising a resonant circuit coupled in series with the first conductor and the first frequency independent component

16. A medical device according to claim 15 further comprising a third frequency independent component coupled in series with the first conductor at the proximal end of the conductor.

17. A medical device according to claim 15 wherein the resonant circuit is a parallel LC circuit.

18. A medical device according to claim 16 wherein the resonant circuit is a parallel LC circuit.

19. A medical device according to claim 12 wherein the medical device receives a sensing signal and further comprises:

a second conductor contained within the lead assembly and having a proximal end and a distal end for conducting the sensing signal;

a second electrode coupled to the distal end of the second conductor; and

a fourth frequency independent component coupled in series with the second conductor and the second electrode, the fourth frequency independent component for propagating the sensing pulse from the distal end to the proximal end of the second conductor.