Systems and methods for sensing external magnetic fields in implantable medical devices

• US 9,766,307 B2
• Filed: 03/11/2014
• Issued: 09/19/2017
• Est. Priority Date: 07/26/2006
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Gauglitz, Karl, Bocek, Thomas M., Rutzer, Mark, Matthews, Lorin W., Reagor, William E., Erbstoeszer, Blair
• Primary Examiner(s): DOUGHERTY, SEAN PATRICK
• Application Number:
  US14/204,559
• Publication Number:
  US 20140194729A1
• Time in Patent Office: 1,288 Days
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61N 1/08 Arrangements or circuits for monitoring, protecting, controlling or indicating for external stimulators A61N1/3603; for implantable neurostimulators A61N1/36128; for heart stimulators A61N1/37; for defibrillators A61N1/3925
• CPC Class Codes: A61N 1/3605 Implantable neurostimulators for stimulating central or peripheral nerve system
• CPC Class Codes: A61N 1/3718 Monitoring of or protection against external electromagnetic fields or currents
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion
• CPC Class Codes: G01R 33/287 involving active visualization of interventional instruments, e.g. using active tracking RF coils or coils for intentionally creating magnetic field inhomogeneities
• CPC Class Codes: G01V 3/101 by measuring the impedance of the search coil; by measuring features of a resonant circuit comprising the search coil measuring impedance or characteristics derived therefrom G01R27/00, e.g. quality factor G01R27/26

Abstract

Systems and methods for sensing external magnetic fields in implantable medical devices are provided. One aspect of this disclosure relates to an apparatus for sensing magnetic fields. An apparatus embodiment includes a sensing circuit with at least one inductor having a magnetic core that saturates in the presence of a magnetic field having a prescribed flux density. The apparatus embodiment also includes an impedance measuring circuit connected to the sensing circuit. The impedance measuring circuit is adapted to measure impedance of the sensing circuit and to provide a signal when the impedance changes by a prescribed amount. According to an embodiment, the sensing circuit includes a resistor-inductor-capacitor (RLC) circuit. The impedance measuring circuit includes a transthoracic impedance measurement module (TIMM), according to an embodiment. Other aspects and embodiments are provided herein.

Claims

1. An omnidirectional magnetic resonance imaging (MRI) detection apparatus to communicate a presence of an MRI device to an implantable medical device (IMD), the apparatus comprising:

a sensing circuit including multiple inductors, each of the multiple inductors oriented in a different direction and having a magnetic core that saturates in the presence of a magnetic field having a flux density of the MRI device independent of direction, wherein sensing circuit is sized to fit within a housing of the IMD; and

a control module connected to the sensing circuit, the control module adapted to monitor the inductors and to send a signal to the IMD when at least one of the inductors saturates.

2. The apparatus of claim 1, wherein the control module is configured to measure impedance of a circuit including the inductor.

3. The apparatus of claim 2, wherein the control module is adapted to measure impedance of a circuit including the inductor at a frequency from 1 kHz to 1 MHz.

4. The apparatus of claim 2, wherein the control module is adapted to measure impedance of a circuit including the inductor at a frequency of 20 Hz.

5. The apparatus of claim 2, wherein the control module is adapted to measure impedance of a circuit including the inductor once every 30 seconds.

6. The apparatus of claim 1, wherein one or more of the inductors includes a ferrite drum core inductor.

7. The apparatus of claim 1, wherein one or more of the inductors includes a gapped toroidal inductor.

8. The apparatus of claim 1, wherein one or more of the inductors includes a tape wound core inductor.

9. The apparatus of claim 1, wherein one or more of the inductors includes an isotropic material.

10. The apparatus of claim 1, wherein one or more of the inductors has maximum dimensions of 0.4 inches in width, 0.4 inches in length and 0.3 inches in height.

11. The apparatus of claim 1, wherein the control module includes a transthoracic impedance measurement module (TIMM) electrically connected to one or more of the inductors, the TIMM configured to measure impedance of a circuit including the inductor.

12. The apparatus of claim 11, wherein the apparatus is implantable.

13. The apparatus of claim 11, wherein the 1 MB is configured to change a lead configuration in response to the signal.

14. The apparatus of claim 11, wherein the control module is configured to change the IMD to a pacing mode in response to the signal.

15. The apparatus of claim 11, wherein the control module is configured to change the IMD to a tachy mode in response to the signal.

16. The apparatus of claim 11, wherein the control module is configured to change the IMD to a protect mode in response to the signal.

17. The apparatus of claim 11, wherein the IMD includes a cardiac resynchronization therapy (CRT) device.

18. The apparatus of claim 11, wherein the IMD includes a defibrillator.

19. The apparatus of claim 11, wherein the IMD includes a neural stimulator.