Medical Device Sensing and Detection During MRI

• US 20070238975A1
• Filed: 03/30/2006
• Published: 10/11/2007
• Est. Priority Date: 03/30/2006
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Zeijlemaker, Volkert
• Granted Patent: US 7,693,568 B2
• Time in Patent Office: Days
• US Class Current: 600/411
• CPC Class Codes: A61N 1/3718 Monitoring of or protection against external electromagnetic fields or currents

Abstract

Sensing and detection means of a medical device includes sensing for an MRI gradient magnetic field and responding to the detected gradient magnetic field by switching from a first electrical signal processing mode to a second electrical signal processing mode, such that electrical signals induced by the gradient magnetic field and an associated RF burst are not counted as cardiac events.

Claims

1. A medical device, comprising:

a coiled transducer for detecting gradient magnetic fields associated with MRI, via inductive coupling; and

a signal processing mode activated by the coiled transducer when the transducer detects the gradient magnetic field.

2. The device of claim 1, further comprising an MRI static magnetic field sensor adapted to activate the coiled transducer when the static magnetic field is detected by the sensor.

3. An implantable medical system, comprising:

a device housing containing electronics for generating cardiac therapies;

a lead extending from the device housing for detecting cardiac signals and delivering cardiac therapies generated by the housing electronics;

a gradient sensor for sensing the presence of an MRI gradient magnetic field, the sensor coupled to the housing electronics; and

the housing electronics switching between first and second modes of operation, the housing electronics generating appropriate cardiac therapies based on signals received through the lead in the first mode of operation, the housing electronics switching to the second mode of operation based on sensing of MRI gradient magnetic fields, the housing electronics discounting signals induced by the gradient fields and associated MRI RF pulses received through the lead in the second mode of operation.

4. The system of claim 3, wherein the gradient sensor includes a coiled transducer.

5. The system of claim 3, wherein the gradient sensor includes three coiled transducers oriented orthogonally to each other.

6. The system of claim 3, further comprising a static sensor for sensing an MRI static magnetic field, the static sensor coupled to the gradient sensor and adapted to activate the gradient sensor when the static magnetic field is detected by the static sensor.

7. A medical device, having a computer readable medium programmed with instructions for a sensing and detection method, the sensing and detection method comprising:

sensing for an MRI gradient magnetic field; and

responding to the gradient magnetic field, detected by the sensing, by switching from a first mode for processing electrical signals received through a lead wire of the device to a second mode for processing electrical signals, such that electrical signals induced by the gradient magnetic field and an associated MRI RF pulse are not counted as cardiac events.

8. The device of claim 7, wherein sensing the gradient magnetic field is accomplished via inductive coupling between the gradient field and a coiled transducer of the device.

9. The device of claim 7, wherein sensing the gradient field is accomplished via inductive coupling with a one of three orthogonal coiled transducers of the device.

10. The device of claim 7, wherein the second mode includes an introduction of a blanking period.

11. The device of claim 10, wherein a duration of the blanking period is pre-programmed into the device.

12. The device of claim 7, wherein the second mode includes comparing a timing of electrical signals received through the lead wire with an extrapolated series of cardiac events.

13. The device of claim 12, wherein the second mode further includes comparing the timing of the electrical signals with incidences of gradient magnetic field detection.

14. The device of claim 13, wherein the second mode further counts the electrical signals as cardiac events if the signals do not coincide with the incidences of gradient magnetic field detection.

15. The device of claim 13, wherein the second mode further counts the electrical signals as ‘

virtual’

cardiac events if the signals coincide with the extrapolated series of cardiac events and with the incidences of gradient magnetic field detection.

16. The device of claim 13, wherein the second mode further counts the electrical signals as noise events if the signals coincide with the incidences of gradient magnetic field detection and do not coincide with the extrapolated series of cardiac events.

17. The device of claim 13, wherein:

the second mode further counts the electrical signals as ‘

virtual’

cardiac events, if the signals coincide with the extrapolated series of cardiac events and with the incidences of gradient magnetic field detection; and

the second mode counts the electrical signals as noise events, if the signals coincide with the incidences of gradient magnetic field detection and do not coincide with the extrapolated series of cardiac events; and

further comprising ignoring the electrical signals after a consecutive count of the ‘

virtual’

cardiac events and noise events exceeds a predetermined number.

18. The device of claim 7, wherein the sensing and detection method further comprises:

adjusting from the second mode back to the first mode when the gradient magnetic field is no longer detected; and

remaining in the first mode until another gradient magnetic field is detected.

19. The device of claim 7, wherein the sensing and detection method further comprises adjusting from the second mode back to the first mode after a pre-programmed period of time.

20. The device of claim 7, wherein the sensing and detection method further comprises:

detecting an MRI static magnetic field; and

enabling a transducer to sense for the MRI gradient magnetic field when the static magnetic field is detected.