Minimization of electrical stimulus artifact during measurement of evoked neural response

• US 20070225767A1
• Filed: 05/24/2007
• Published: 09/27/2007
• Est. Priority Date: 04/18/2001
• Status: Active Grant

• Current Assignee: Cochlear Limited
• Original Assignee: Cochlear Limited
• Inventors: Daly, Christopher, Nygard, Tony, Eder, Helmut
• Granted Patent: US 8,454,529 B2
• Time in Patent Office: Days
• US Class Current: 607/2
• CPC Class Codes: A61B 5/24 Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
• CPC Class Codes: A61B 5/4041 Evaluating nerves condition
• CPC Class Codes: A61B 5/7217 of noise originating from a therapeutic or surgical apparatus, e.g. from a pacemaker
• CPC Class Codes: A61N 1/36038 Cochlear stimulation

Abstract

The invention provides a method of electrical artefact compensation in measurement of a neural response. The neural response is evoked by a first stimulus, after which a compensatory stimulus is applied in order to counteract a stimulus artefact caused by the first stimulus. The invention also provides for short circuiting the stimulating electrode subsequent to the first stimulus. A system for implementing such steps is also provided. The invention may be of application in measurement of physiological responses, including neural responses and in particular a neural response of the auditory nerve.

Claims

1. A method of electrical artifact compensation in measurement of a neural response evoked by a first stimulus, the method comprising:

subsequent to the first stimulus, applying a compensatory stimulus configured to substantially counteract a stimulus artifact caused by the first stimulus.

2. The method of claim 1, wherein the first stimulus comprises:

a first phase during which an electrical stimulus of first polarity is applied; and

a second phase, subsequent to the first phase, during which an electrical stimulus of second polarity opposite to the first polarity is applied.

3. The method of claim 2, wherein the first phase and second phase are charge balanced.

4. The method of claim 2, wherein the compensatory stimulus is of the first polarity.

5. The method of claim 1, wherein the compensatory stimulus has a profile and duration configured to substantially counteract the stimulus artifact caused by the first stimulus.

6. The method of claim 1, wherein the compensatory stimulus is adaptive.

7. The method of claim 1 further comprising:

determining characteristics of the compensatory stimulus from a measured effectiveness of a previously applied compensatory stimulus.

8. The method of claim 7, wherein determining characteristics of the compensatory stimulus comprises:

iteratively determining characteristics of the compensatory stimulus from a measured effectiveness of a previously applied compensatory stimulus, thereby providing an ongoing optimization of the compensatory stimulus.

9. The method of claim 7, further comprising:

determining the measured effectiveness of the previously applied compensatory stimulus, comprising;

obtaining at least one neural response measurement of an actual performance of the previously applied compensatory stimulus; and

comparing the actual performance against a target performance, in order to determine an error between the actual performance and the target performance.

10. The method of claim 9, wherein measuring the actual performance of the previously applied compensatory stimulus comprises:

applying the first stimulus and the previously applied compensatory stimulus; and

subsequent to the application of the first and previously applied compensatory stimuli, obtaining a first measurement comprising a first plurality of temporally spaced neural samples from a sensor.

11. The method of claim 10, wherein measuring the actual performance of the previously applied compensatory stimulus further comprises:

secondly applying the first and previously applied compensatory stimuli; and

subsequent to the second application of the first and previously applied compensatory stimuli, obtaining a second plurality of measurements each comprising one or more temporally spaced neural samples.

12. The method of claim 11, wherein measuring the actual performance of the previously applied compensatory stimulus further comprises:

discarding an initial number of the second plurality of measurements to allow the sensor and other measurement components to settle.

13. The method of claim 12, wherein measuring the actual performance of the previously applied compensatory stimulus further comprises:

taking an average of the remaining non-discarded measurements of the second plurality of measurements, to obtain an averaged measurement.

14. The method of claim 13, wherein measuring the actual performance of the previously applied compensatory stimulus further comprises:

determining a stimulus artifact from the averaged measurement; and

assessing the performance of the previously applied compensatory stimulus with reference to the determined stimulus artifact.

15. The method of claim 10, wherein obtaining a first measurement comprising a first plurality of temporally spaced neural samples from a sensor comprises:

obtaining a first measurement comprising approximately 64 neural samples taken at approximately 48 microsecond intervals.

16. The method of claim 11, wherein obtaining the second plurality of measurements comprises:

obtaining substantially 20 measurements.

17. The method of claim 12, wherein discarding an initial number of the second plurality of measurements comprises:

discarding approximately the first 10 of the second plurality of measurements.

18. The method of claim 14, wherein determining the stimulus artifact from the averaged measurement comprises:

determining a deviation of the averaged measurement from a desired response.

19. The method of claim 7, wherein determining characteristics of the compensatory stimulus from the measured effectiveness of the previously applied compensatory stimulus comprises:

determining an incremental change to be made to characteristics of the previously applied compensatory stimulus in order to reduce an error between an actual performance and a target performance; and

deriving the characteristics of the compensatory stimulus by altering the characteristics of the previously applied compensatory stimulus in accordance with the incremental change.

20. The method of claim 19, wherein the incremental change is determined so as to maximize a rate of convergence of the actual performance to the target performance.

21-79. -79. (canceled)