Implantable Medical Device Orientation Detection Utilizing an External Magnet and a 3D Accelerometer Sensor

• US 20100010338A1
• Filed: 09/30/2008
• Published: 01/14/2010
• Est. Priority Date: 07/08/2008
• Status: Abandoned Application

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Scholten, Patrick, van Dam, Peter
• Application Number:
  US12/242,798
• Publication Number:
  US 20100010338A1
• Time in Patent Office: Days
• US Class Current: 600/424
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/061 Determining position of a probe within the body employing means separate from the probe, e.g. sensing internal probe position employing impedance electrodes on the surface of the body A61B1/00158 takes precedence
• CPC Class Codes: A61B 5/11 Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb for measuring pulse A61B5/02 ;A61B5/1038 takes precedence; motion detection to correct for motion artifacts in physiological signals A61B5/721
• CPC Class Codes: A61N 1/36542 controlled by body motion, e.g. acceleration

Abstract

A method and device for detecting the implanted orientation of an implantable medical device (IMD) in a patient. IMD includes an accelerometer for measuring acceleration signals in three orthogonal directional axes. A y-axis orientation of IMD is determined from the measured accelerometer signals using a gravitational force analysis. IMD includes a magnetic sensor that senses a varying magnetic field exerted on the magnetic sensor from an external magnet moved along a medial-lateral direction with respect to IMD. The z-axis orientation of IMD is determined from the location of the external magnet where the magnetic field exerted on the magnetic sensor is greatest. Based on a known relationship between the accelerometer and magnetic sensor, an orthogonal transformation calculation is performed on the y-axis and z-axis orientations to yield the x-axis orientation. The implanted orientation of IMD with respect to the patient is thus known and used to compensate accelerometer measurements.

Claims

1. A method of determining the orientation of an implantable medical device, comprising:

determining a y-axis orientation of the device using accelerometer signals from a 3D accelerometer positioned within the device using gravity as an external force;

determining an z-axis orientation of the device based on properties of a magnetic field between a magnetic sensor positioned within the device and an external magnet; and

determining an x-axis orientation of the device from an orthogonal transformation calculation using the previously determined y-axis and z-axis orientations.

2. The method of claim 1, further comprising determining the y-axis orientation when a patient in which the implantable medical device is implanted is in an upright posture.

3. The method of claim 1, further comprising:

monitoring the accelerometer signals from the 3D accelerometer to detect certain low frequency periodic signals signifying that a patient in which the implantable medical device is implanted is involved in an upright activity.

4. The method of claim 1, further comprising determining the z-axis orientation by:

moving the external magnet and magnetic sensor with respect to each other between so that the external magnet moves between lateral and medial positions of a patient in which the implantable medical device is implanted;

measuring a strength of a magnetic field imparted on the magnetic sensor by the moving external magnet;

identifying the location at which the magnetic field between the external magnet and magnetic sensor has a maximum value; and

determining the z-axis orientation of the device based on the location at which the magnetic field has a maximum value.

5. The method of claim 1, further comprising determining the z-axis orientation by:

positioning the external magnet such that the external magnet includes a stationary, known position with respect to the magnetic sensor;

measuring a strength of a magnetic field imparted on the magnetic sensor by the external magnet;

determining the z-axis orientation of the device based on the strength of the magnetic field imparted on the magnetic sensor and the known position of the external magnet.

6. The method of claim 1, further comprising calibrating the 3D accelerometer using the determined y-axis, z-axis and x-axis orientations.

7. The method of claim 1, further comprising positioning the external magnet in an in-home patient monitoring system so that a patient can compensate the orientation of the device by moving with respect to the in-home patient monitoring system to determine compensate the x-axis orientation.

8. An implantable medical device comprising:

a 3D accelerometer sensor configured for measuring acceleration signals in three orthogonal directional axes comprising an x-axis, z-axis and y-axis;

a magnetic sensor configured to sense a magnetic field exerted on the magnetic sensor from a moving magnetic field source; and

a controller coupled to the 3D accelerometer for receiving acceleration signals and to the magnetic sensor for receiving magnetic field value signals,

the controller configured for determining a y-axis orientation of the device from a y-axis acceleration signal received from the 3D accelerometer, the controller further configured for determining an z-axis orientation based on magnetic field value signals received from the magnetic sensor, the controller further configured for determining an x-axis orientation of the device from an orthogonal transformation calculation using the previously determined y-axis and z-axis orientations.

9. The implantable medical device of claim 8, wherein the controller is configured to determine the y-axis orientation of the device when a patient in which the device is implanted is positioned in an upright posture.

10. The implantable medical device of claim 8, wherein the controller is configured to monitor the accelerometer signals received from the 3D accelerometer sensor to detect certain low frequency periodic signals signifying that a patient in which the implantable medical device is implanted is involved in an upright activity, wherein the y-axis orientation of the device is determined when the patient is determined to be involved in the upright activity.

11. The implantable medical device of claim 8, wherein the controller is configured to determine the z-axis orientation by:

monitoring magnetic field value signals received from the magnetic sensor from a magnetic field imparted on the magnetic sensor from an external magnet that is moved with respect to the magnetic sensor between lateral and medial positions of a patient in which the device is implanted;

identifying a magnetic field value signal having a maximum value and identifying a corresponding position of the external magnet when generating the maximum magnetic field value signal; and

determining the z-axis orientation of the device based on the location at which the magnetic field value signal has a maximum value.

12. The implantable medical device of claim 8, wherein the controller is configured to calibrate the 3D accelerometer using the determined y-axis, z-axis and x-axis orientations.

13. The implantable medical device of claim 8, wherein the external magnet in positioned in an in-home patient monitoring system so that a patient can compensate the orientation of the device by moving with respect to the in-home patient monitoring system to determine compensate the x-axis orientation.

14. An implantable medical device, comprising:

means for determining a y-axis orientation of the device using accelerometer signals from a 3D accelerometer positioned within the device;

means for determining an z-axis orientation of the device based on properties of a magnetic field between a magnetic sensor positioned within the device and an external magnet; and

means for determining an x-axis orientation of the device from an orthogonal transformation calculation using the previously determined y-axis and z-axis orientations.

15. The implantable medical device of claim 14, wherein the means for determining the y-axis orientation is further configured for determining the y-axis orientation when a patient in which the implantable medical device is implanted is in an upright posture.

16. The implantable medical device of claim 14, wherein the means for determining the y-axis orientation is further configured for monitoring the accelerometer signals from the 3D accelerometer to detect certain low frequency periodic signals signifying that a patient in which the implantable medical device is implanted is involved in an upright activity.

17. The implantable medical device of claim 14, wherein the means for determining the z-axis orientation is further configured for:

monitoring magnetic field value signals received from the magnetic sensor from a magnetic field imparted on the magnetic sensor from an external magnet that is moved with respect to the magnetic sensor between lateral and medial positions of a patient in which the device is implanted;

identifying a magnetic field value signal having a maximum value and identifying a corresponding position of the external magnet when generating the maximum magnetic field value signal; and

determining the z-axis orientation of the device based on the location at which the magnetic field value signal has a maximum value.

18. The implantable medical device of claim 14, wherein the means for determining the z-axis orientation is further configured for:

monitoring magnetic field value signals received from the magnetic sensor from a magnetic field imparted on the magnetic sensor from an external magnet that is positioned in a stationary, known position with respect to the magnetic sensor;

measuring a strength of the magnetic field imparted on the magnetic sensor by the external magnet;

determining the z-axis orientation of the device based on the strength of the magnetic field imparted on the magnetic sensor and the known position of the external magnet.

19. The implantable medical device of claim 14, further comprising means for calibrating the 3D accelerometer using the determined y-axis, z-axis and x-axis orientations.

20. The implantable medical device of claim 14, further comprising positioning the external magnet in an in-home patient monitoring system so that a patient can compensate the orientation of the device by moving with respect to the in-home patient monitoring system to determine compensate the x-axis orientation.