MODEL REFERENCE IDENTIFICATION AND CANCELLATION OF MAGNETICALLY-INDUCED VOLTAGES IN A GRADIENT MAGNETIC FIELD

• US 20090210025A1
• Filed: 02/10/2009
• Published: 08/20/2009
• Est. Priority Date: 02/19/2008
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Ameri, Masoud
• Granted Patent: US 8,160,717 B2
• Time in Patent Office: Days
• US Class Current: 607/30
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61N 1/086 Magnetic resonance imaging [MRI] compatible leads
• CPC Class Codes: A61N 1/3718 Monitoring of or protection against external electromagnetic fields or currents
• CPC Class Codes: A61N 2/02 using magnetic fields produced by coils, including single turn loops or electromagnets A61N2/12 takes precedence
• 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

Systems and methods of dynamically controlling an implanted medical device located within a patient'"'"'s body in the presence of a gradient magnetic field or other external interference are disclosed. The system can include a reference model of the implanted medical device and of body tissue within the patient'"'"'s body in the absence of a gradient magnetic field, and a control unit configured to dynamically control voltages or currents applied to a lead of the implanted medical device based on predicted parameters determined by the reference model.

Claims

1. A method of dynamically controlling an implanted medical device located within a patient'"'"'s body in the presence of an external interference, the method comprising:

creating a model of an implantable lead and of body tissue within the body;

detecting the presence of an external interference within the body;

measuring the response of an excitation voltage or current applied to the lead in the presence of the external interference;

comparing the measured response obtained in the presence of the external interference with a predicted response outputted by the model; and

dynamically modifying a voltage or current applied to the lead based at least in part on the predicted response outputted by the model.

2. The method of claim 1, wherein creating a model of an implantable lead and of body tissue within the body includes:

measuring the response of an excitation voltage or current applied to the lead in the absence of an external interference;

comparing the measured response in the absence of the external interference to a predicted response generated by the model and outputting an error signal; and

adjusting one or more model parameters of the model to minimize the error signal.

3. The method of claim 1, wherein the implantable lead is a bipolar lead including a plurality of lead electrodes electrically coupled to a pulse generator, and wherein creating a model of an implantable lead and of body tissue within the body includes creating a model of the lead implanted within the heart and of the cardiac tissue disposed between the lead electrodes.

4. The method of claim 3, wherein the model includes one or more impedance parameters associated with the implanted lead and the cardiac tissue between the lead electrodes.

5. The method of claim 1, wherein the implantable lead is a unipolar lead including an electrode electrically coupled to a pulse generator, and wherein creating a model of an implanted lead and of body tissue within the body includes creating a model of the lead implanted within the heart and of the body tissue disposed between the electrode and the pulse generator.

6. The method of claim 5, wherein the model includes one or more impedance parameters associated with the implanted lead and the body tissue between the electrode and the pulse generator.

7. The method of claim 1, wherein creating a model of an implantable lead and of body tissue within the body is performed in the absence of the external interference.

8. The method of claim 1, wherein measuring the response of the excitation voltage or current includes measuring the current in the implanted lead.

9. The method of claim 1, wherein dynamically modifying the voltage or current applied to the lead based on the predicted response outputted by the model includes minimizing an error signal generated by comparing the measured response of the lead in the presence of the external interference to a predicted response from the model determined in the absence of the external interference.

10. The method of claim 9, wherein dynamically modifying the voltage or current applied to the lead based on the predicted response outputted by the model is performed by a control unit including a closed-loop feedback controller.

11. A method of dynamically controlling an implanted medical device located within a patient'"'"'s body in the presence of a gradient magnetic field, the method comprising:

measuring the response of an excitation voltage or current applied to a lead implanted in or near the heart in the absence of a gradient magnetic field;

creating a model of the implanted lead and of body tissue within the body, the model including one or more impedance parameters associated with the implanted lead and the body tissue;

comparing the measured response in the absence of the gradient magnetic field to an anticipated response generated by the model and outputting an error signal;

adjusting one or more of the model parameters to minimize the error signal;

detecting the presence of a gradient magnetic field within the body;

measuring the response of an excitation voltage or current applied to the lead in the presence of the gradient magnetic field;

comparing the measured response obtained in the presence of the gradient magnetic field with a predicted response outputted by the model; and

modifying a voltage or current applied to the lead based at least in part on the predicted response from the model.

12. The method of claim 11, wherein the lead is a bipolar lead including a plurality of lead electrodes electrically coupled to a pulse generator, and wherein creating a model of the implanted lead and of body tissue includes creating a model of the lead implanted within the heart and of the cardiac tissue disposed between the lead electrodes.

13. The method of claim 12, wherein the one or more impedance parameters includes an impedance parameter associated with the implanted lead and an impedance parameter associated with the cardiac tissue between the lead electrodes.

14. The method of claim 11, wherein the lead is a unipolar lead including an electrode electrically coupled to a pulse generator, and wherein creating a model of the implanted lead and of body tissue includes creating a model of the lead implanted within the heart and of the body tissue disposed between the electrode and the pulse generator.

15. The method of claim 14, wherein the one or more impedance parameters includes an impedance parameter associated with the implanted lead and an impedance parameter associated with the body tissue between the electrode and the pulse generator.

16. The method of claim 11, wherein creating a model of the lead is performed in the absence of the gradient magnetic field.

17. The method of claim 11, wherein measuring the response of the excitation voltage or current includes measuring the current in the implanted lead.

18. The method of claim 11, wherein dynamically modifying the voltage or current applied to the lead based on the predicted response outputted by the model includes minimizing an error signal generated by comparing the measured response of the lead in the presence of the magnetic field to a predicted response outputted from the model.

19. The method of claim 18, wherein dynamically modifying the voltage or current applied to the lead based on the predicted response outputted by the model is performed by a control unit including a closed-loop feedback controller.

20. A system for cancelling magnetically-induced voltages on an implanted medical device having a lead implanted in or near the heart, the system comprising:

a reference model of the lead including one or more model parameters associated with the lead and the heart; and

a control unit adapted to control a voltage or current applied to the lead in the presence of a gradient magnetic field;

wherein the control unit is configured to dynamically control the voltage or current based at least in part on the one or more model parameters of the model.

21. The system of claim 20, further comprising a sensor configured to sense the presence of a magnetic field within the body.

22. The system of claim 20, wherein the model parameters include an impedance parameter associated with the lead and an impedance parameter associated with the heart.