Induced current measurement systems and methods

• US 7,873,412 B2
• Filed: 02/28/2007
• Issued: 01/18/2011
• Est. Priority Date: 02/28/2007
• Status: Expired due to Fees

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Wedan, Steve R.
• Primary Examiner(s): Manuel; George
• Assistant Examiner(s): Wieland; Robert N
• Application Number:
  US11/680,267
• Publication Number:
  US 20080208276A1
• Time in Patent Office: 1,420 Days
• Field of Search: 600/423, 600/500, 607/9, 607/63, 607/2, 607/27, 623/1.13
• US Class Current: 607/2
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61N 1/3718 Monitoring of or protection against external electromagnetic fields or currents
• CPC Class Codes: G01R 19/0092 measuring current only all subgroups of G01R19/00 take precedence
• CPC Class Codes: G01R 33/285 Invasive instruments, e.g. catheters or biopsy needles, specially adapted for tracking, guiding or visualization by NMR
• 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

In an embodiment, the invention includes a measurement system for measuring induced currents within an implantable medical device undergoing magnetic resonance imaging. The measurement system can include a resistor connected in series with a conductive loop and electronic circuitry configured to generate a signal representative of a voltage differential across the resistor. In some embodiments, the measurement system includes a fiber optic cable configured to transmit the signal away from the area subject to magnetic resonance imaging. In some embodiments, the measurement system includes a transmitter to wirelessly transmit the signal away from the area subject to magnetic resonance imaging. In an embodiment, the invention can include an implantable medical device including a measurement system for measuring induced currents. In an embodiment, the invention can include a method of measuring an induced current in an implantable medical device undergoing magnetic resonance imaging. Other embodiments are described herein.

Claims

1. A measurement system for measuring induced current in an implantable medical device undergoing magnetic resonance imaging, the measurement system comprising:

(i) a resistor connected in series with a conductive loop of the implantable medical device, wherein the conductive loop comprises a pulse generator and a lead;

(ii) electronic circuitry configured to generate an electronic signal representative of a voltage differential across the resistor and to generate an optical signal corresponding to the electronic signal;

(iii) an area shielded from magnetic fields generated by magnetic resonance imaging defined by a magnetic shielding wall; and

(iv) a fiber optic cable configured to transmit the optical signal away from an area subject to magnetic resonance imaging, the fiber optic cable configured to transmit the optical signal to the area shielded from magnetic fields generated by magnetic resonance imaging.

2. The measurement system of claim 1, further comprising a computing device configured to receive the optical signal.

3. The measurement system of claim 1, wherein the resistor has a resistance of between about 1 ohms and about 50 ohms.

4. The measurement system of claim 1, the implantable medical device comprising a cardiac rhythm management device comprising a lead in communication with a pulse generator.

5. The measurement system of claim 3, the resistor connected in series between the pulse generator and the lead.

6. The measurement system of claim 1, the electronic signal representing a voltage differential between two locations less than 5 mm apart.

7. The measurement system of claim 1, the electronic circuitry comprising an analog to digital converter.

8. The measurement system of claim 1, the electronic circuitry comprising a light emitting diode for generating the optical signal.

9. The measurement system of claim 2, wherein the computing device is further configured to determine an induced current level from the voltage differential signal.

10. The measurement system of claim 1, the induced current having a frequency of less than about 20 kHz.

11. A method of measuring an induced current in an implantable medical device undergoing magnetic resonance imaging, the method comprising:

(i) generating an electronic signal representative of the voltage differential across a resistor connected in series with a conductive loop of the implantable medical device, wherein the conductive loop comprises a pulse generator and a lead;

(ii) converting the electronic signal to a corresponding optical signal;

(iii) transmitting the optical signal through a fiber optic cable to an area not subject to magnetic resonance imaging, the fiber optic cable configured to transmit the optical signal to an area shielded from magnetic fields generated by magnetic resonance imaging, wherein the area shielded from magnetic fields generated by magnetic resonance imaging defined by a magnetic shielding wall; and

(iv) receiving the optical signal in a computing device that is configured to record the signal.

12. The method of claim 11, the resistor connected in series between a pulse generator and the lead.

13. The method of claim 11, the electronic voltage differential signal representing the voltage differential between two locations less than 5 mm apart.

14. The method of claim 11, further comprising the step of converting the electronic signal from analog to digital prior to the step of converting the electrical signal to an optical signal.

15. The method of claim 11, wherein the area not subject to magnetic resonance imaging is in a separate room shielded from magnetism generated by magnetic resonance imaging.

16. The method of claim 11, the computing device further configured to determine an induced current level from the voltage differential signal.

17. The method of claim 11, the computing device further configured to convert the optical signal to an electronic signal.