Charger Alignment in an Implantable Medical Device System Employing Reflected Impedance Modulation

• US 20130096651A1
• Filed: 09/10/2012
• Published: 04/18/2013
• Est. Priority Date: 10/13/2011
• Status: Active Grant

• Current Assignee: Boston Scientific Neuromodulation Corporation (Boston Scientific Corporation)
• Original Assignee: Boston Scientific Neuromodulation Corporation (Boston Scientific Corporation)
• Inventors: Ozawa, Robert, Aghassian, Daniel
• Granted Patent: US 9,446,254 B2
• Time in Patent Office: Days
• US Class Current: 607/61
• CPC Class Codes: A61F 2250/0001 Means for transferring electromagnetic energy to implants
• CPC Class Codes: A61N 1/3787 from an external energy source

Abstract

The disclosed means of determining alignment between an external charger and an implantable medical device (IMD) involves the use of reflected impedance modulation, i.e., by measuring at the external charger reflections arising from modulating the impedance of the charging coil in the IMD. During charging, the charging coil in the IMD is pulsed to modulate its impedance. The difference in the coil voltage (ΔV) produced at the external charger as a result of these pulses is assessed and is used by the external charger to indicate coupling. If the magnitude of ΔV is above a threshold, the external charger considers the coupling to the IMD to be adequate, and an alignment indicator in the external charger is controlled accordingly. The magnitude of Vcoil can be assessed in addition to ΔV to determine alignment with the IMD with improved precision, and/or to further define a high quality alignment condition.

Claims

1. An external charger for an implantable medical device, comprising:

a coil for producing a magnetic field for providing power to the implantable medical device;

an alignment detector for receiving an electrical parameter of the coil, wherein the alignment detector assesses at least a magnitude of a change in the electrical parameter, wherein the change is inducible by the implantable medical device, wherein the alignment detector determines an alignment between the external charger and the implantable medical device based upon the magnitude of the change; and

at least one alignment indicator for indicating the alignment between the external charger and the implantable medical device.

2. The external charger of claim 1, wherein the alignment detector determines the alignment by comparing the magnitude of the change to a threshold.

3. The external charger of claim 2, wherein the indicated alignment comprises either an alignment condition when the magnitude is greater than the threshold, or a no-alignment condition when the magnitude is less than the threshold.

4. The external charger of claim 1, wherein the alignment detector comprises an A/D converter.

5. The external charger of claim 1, wherein the alignment detector comprises control circuitry for the external charger.

6. The external charger of claim 1, wherein the indicated alignment comprises either an alignment condition or a no-alignment condition.

7. The external charger of claim 1, wherein the indicated alignment comprises a degree of alignment between the external charger and the implantable medical device.

8. The external charger of claim 1, wherein the indicated alignment is either visual, audible, or tactile.

9. The external charger of claim 1, further comprising a demodulator, wherein the demodulator determines data transmitted from the implantable medical device by demodulating the electrical parameter of the coil.

10. The external charger of claim 1, further comprising charging circuitry for passing a AC current through the coil to produce the magnetic field.

11. The external charger of claim 1, further comprising a memory for storing coupling information, wherein the alignment detector uses the information to determine the alignment.

12. The external charger of claim 11, wherein the coupling information comprises calculated, simulation, or experimental data indicative of a relationship between a coupling parameter and at least a magnitude of a change in the electrical parameter.

13. The external charger of claim 12, wherein the coupling information is further indicative of a relationship between the coupling parameter and a magnitude of the electrical parameter.

14. The external charger of claim 1, wherein the alignment detector further detects a magnitude of the electrical parameter, and wherein the alignment detector determines the alignment based upon the magnitude of the change and the magnitude of the electrical parameter.

15. The external charger of claim 14, wherein the indicated alignment comprises either a first alignment condition or a second alignment condition.

16. The external charger of claim 15, wherein the first alignment condition comprises a condition for which power provided to the implantable medical device is relatively low, and wherein the second alignment condition comprises a condition for which power provided to the implantable medical device is relatively high.

17. The external charger of claim 15, wherein the external charger comprises a first alignment indicator for indicating the first alignment condition, and a second alignment indicator for indicating the second alignment condition.

18. The external charger of claim 1, wherein the electrical parameter comprises voltage.

19. The external charger of claim 1, wherein the electrical parameter comprises current.

20. A system, comprising:

an implantable medical device, comprising;

a first coil for receiving a magnetic field for providing power to the implantable medical device; and

at least one switch for modulating an impedance of the first coil during receipt of the magnetic field; and

an external charger, comprising;

a second coil for producing the magnetic field;

an alignment detector for receiving an electrical parameter of the second coil, wherein the alignment detector assesses at least a magnitude of a change in the electrical parameter caused by modulation of the impedance of first coil; and

at least one alignment indicator for indicating the alignment between the external charger and the implantable medical device based upon the magnitude of the change.

21. The system of claim 20, wherein the implantable medical device comprises two switches, wherein each of the switches grounds an end of the first coil.

22. The system of claim 20, wherein the at least one switch is coupled in series with the first coil.

23. The system of claim 20, wherein the at least one switch is periodically pulsed during receipt of the magnetic field.

24. The system of claim 20, wherein the implantable medical device further comprises a rechargeable battery, and wherein the magnetic field provides power to recharge the battery.

25. The system of claim 20, wherein the external charger further comprises a demodulator, wherein the at least one switch is responsive to data to be sent to the external charger, and wherein the demodulator demodulates the data during production of the magnetic field.

26. The system of claim 20, wherein the alignment detector determines the alignment by comparing the magnitude of the change to a threshold.

27. The system of claim 20, wherein the indicated alignment comprises either an alignment condition or a no-alignment condition.

28. The system of claim 20, wherein the indicated alignment comprises a degree of alignment between the external charger and the implantable medical device.

29. The system of claim 20, wherein the indicated alignment is either visual, audible, or tactile.

30. The system of claim 20, further comprising a memory for storing coupling information, wherein the alignment detector uses the information to determine the alignment.

31. The system of claim 30, wherein the information comprises calculated, simulation, or experimental data indicative of a relationship between a coupling parameter and at least a magnitude of a change in the electrical parameter.

32. The system of claim 20, wherein the alignment detector further detects a magnitude of the electrical parameter, and wherein the alignment detector determines the alignment based upon the magnitude of the change and the magnitude of the electrical parameter.

33. The system of claim 32, wherein the indicated alignment comprises either a first alignment condition or a second alignment condition.

34. The system of claim 33, wherein the first alignment condition comprises a condition for which power provided to the implantable medical device is relatively low, and wherein the second alignment condition comprises a condition for which power provided to the implantable medical device is relatively high.

35. The system of claim 20, wherein the electrical parameter comprises voltage.

36. The system of claim 20, wherein the electrical parameter comprises current.

37. A method for determining alignment between an external charger and an implantable medical device, comprising:

modulating an impedance of a first coil in the implantable medical device while receiving a magnetic field from the external charger;

assessing at least a magnitude of a change in an electrical parameter of a second coil in the external charger caused by modulating the impedance of the first coil; and

determining at the external charger an alignment between the between an external charger and an implantable medical device based on the magnitude of the change.

38. The method of claim 37, wherein the impedance of the first coil is modulated by shorting the first coil.

39. The method of claim 37, wherein the impedance of the first coil is modulated by opening the first coil.

40. The method of claim 37, wherein the impedance of the first coil is periodically modulated.

41. The method of claim 37, wherein modulating the impedance of the first coil transmits data to the external charger.

42. The method of claim 37, further comprising indicating the alignment to a user of the external charger.

43. The method of claim 37, wherein the alignment is indicated to the user as either an alignment condition or a no-alignment condition.

44. The method of claim 37, wherein the alignment is indicated to the user as a degree of alignment.

45. The method of claim 37, wherein the alignment is determined by comparing the magnitude of the change to at least one threshold.

46. The method of claim 37, wherein the second coil produces the magnetic field.

47. The method of claim 37, further comprising

assessing at least a magnitude of the electrical parameter of the second coil in the external charger;

and

determining at the external charger the alignment between the between an external charger and an implantable medical device based on the magnitude of the change and the magnitude of the electrical parameter.

48. The method of claim 47, wherein the alignment is determined by comparing the magnitude of the change to at least one first threshold, and by comparing the magnitude of the electrical parameter to at least one second threshold.

49. The method of claim 47, wherein the alignment is indicated to the user as either a no-alignment condition, a first alignment condition, or a second alignment condition.

50. The method of claim 49, wherein the second alignment condition indicated stronger coupling between the external charger and the implantable medical device than does the first alignment condition.

51. The method of claim 37, wherein the implantable medical device comprises a battery, and further comprising using the received magnetic field to recharge the battery.