METHOD AND DEVICE FOR DETECTING A NEURAL RESPONSE IN A NEURAL MEASUREMENT

1 . A method for processing a neural measurement obtained in a presence of artifact, in order to measure an intensity of a neural response in the neural measurement, the method comprising:

obtaining a neural measurement from one or more sense electrodes positioned in the epidural space;

estimating the artifact by fitting a model of artifact to the neural measurement, wherein the model of artefact comprises an exponential function;

subtracting the estimated artifact from the neural measurement; and

measuring the intensity of the neural response in the neural measurement as a peak-to-peak amplitude of the neural measurement.

2 . The method of claim 1 , wherein the fitting the model of artefact to the neural measurement comprises:

at a first time offset, correlating the neural measurement against a first filter template to produce a first measure m 1 , the first filter template comprising an alternating waveform of a first phase;

at the first time offset, correlating the neural measurement against a second filter template to produce a second measure m 2 , the second filter template comprising an alternating waveform of a second phase 90 degrees offset to the first phase;

at a second time offset, being at a non-integer multiple of 180 degrees offset from the first time offset, correlating the neural measurement against the first filter template to produce a third measure m 3 ;

at the second time offset, correlating the neural measurement against the second filter template to produce a fourth measure m 4 ; and

processing m 1 to m 4 to estimate a time constant and an amplitude of the exponential function of the model of artefact.

3 . The method of claim 2 wherein the first filter template is anti-symmetric so as to create an imaginary DFT output, while the second filter template is symmetric so as to create a real DFT output.

4 . The method of claim 2 wherein the second time offset is offset by 90 degrees or 270 degrees out of phase from the first time offset.

5 . The method of claim 2 wherein the first filter template comprises four half cycles of a first alternating waveform and the second filter template comprises four half cycles of a second alternating waveform 90 degrees out of phase with the first alternating waveform.

6 . The method of claim 2 wherein the first filter template and second filter template are amplitude modulated by a triangular window.

7 . The method of claim 2 wherein only a single point of a correlation is calculated.

8 . The method of claim 7 wherein the single point of the correlation is calculated at a predefined optimal time delay.

9 . The method of claim 8 , further comprising determining the predefined optimal time delay when a signal to artifact ratio is greater than one, at which a first point or a single point of a cross-correlation between the neural measurement and a filter template should be produced, by:

at an approximate time delay between the neural response and the filter template, computing real and imaginary parts of a fundamental frequency of a DFT of the neural measurement;

calculating a phase defined by the real and imaginary parts;

relative to a fundamental frequency of the filter template, calculating a time adjustment needed to change a calculated phase to π/2; and

defining the predefined optimal time delay as being the sum of an approximate time delay and the time adjustment.

10 . The method of claim 8 further comprising determining the predefined optimal time delay by:

at the first time offset, correlating the neural measurement against a third filter template to produce a fifth measure m 5 , the third filter template comprising an alternating waveform at double the frequency of the first filter template and of a third phase;

at the second time offset, correlating the neural measurement against the third filter template to produce a sixth measure m 6 ; and

determining from m 5 and m 6 a decay in artifact between the first time offset and the second time offset.

11 . The method of claim 8 wherein the predefined optimal time delay is recalculated prior to every attempted detection of a neural response.

12 . The method of claim 8 wherein the predefined optimal time delay is recalculated in response to a detected change in a user's posture.

13 . The method of claim 1 wherein measuring the intensity of the neural response in the neural measurement comprises correlating the neural measurement against a filter template, the filter template comprising at least three half cycles of an alternating waveform, amplitude modulated by a window.

14 . A device for processing a neural measurement obtained in a presence of artifact, in order to measure an intensity of a neural response in the neural measurement, the device comprising:

measurement circuitry for obtaining a neural measurement from one or more sense electrodes positioned in the epidural space; and

a processor configured to:

estimate the artifact by fitting a model of artifact to the neural measurement, wherein the model comprises an exponential function;

subtract the estimated artifact from the neural measurement; and

measure the intensity of the neural response in the neural measurement as a peak-to-peak amplitude of the neural measurement.

15 . The device of claim 14 wherein the processor is configured to fit the model of artefact to the neural measurement by:

at a first time offset, correlating the neural measurement against a first filter template to produce a first measure m1, the first filter template comprising an alternating waveform of a first phase;

at the first time offset, correlating the neural measurement against a second filter template to produce a second measure m2, the second filter template comprising an alternating waveform of a second phase 90 degrees offset to the first phase;

at a second time offset, being at a non-integer multiple of 180 degrees offset from the first time offset, correlating the neural measurement against the first filter template to produce a third measure m3;

at the second time offset, correlating the neural measurement against the second filter template to produce a fourth measure m4; and

process m1 to m4 to estimate a time constant of the exponential function of the model.

16 . The device of claim 14 wherein the first filter template is anti-symmetric so as to create an imaginary DFT output, while the second filter template is symmetric so as to create a real DFT output.

17 . The device of claim 14 wherein the second time offset is offset by 90 degrees or 270 degrees out of phase from the first time offset.

18 . The device of claim 14 wherein the first filter template comprises four half cycles of a first alternating waveform and the second filter template comprises four half cycles of a second alternating waveform 90 degrees out of phase with the first alternating waveform.

19 . The device of claim 14 wherein the first template and second filter template are amplitude modulated by a triangular window.

20 . The device of claim 14 wherein the processor is further configured to calculate only a single point of a correlation.

21 . The device of claim 20 wherein the processor is further configured to calculate the single point of the correlation at a predefined optimal time delay.

22 . The device of claim 21 , wherein the processor is further configured to determine the predefined optimal time delay when a signal to artifact ratio is greater than one, at which a first point or single point of a cross-correlation between the neural measurement and a filter template should be produced, by:

at an approximate time delay between the neural response and the filter template, computing real and imaginary parts of a fundamental frequency of a DFT of the neural measurement;

calculating a phase defined by the real and imaginary parts;

relative to a fundamental frequency of the filter template, calculating a time adjustment needed to change a calculated phase to π/2; and

defining the predefined predefined optimal time delay as being the sum of an approximate time delay and the time adjustment.

23 . The device of claim 21 wherein the processor is further configured to determine the predefined optimal time delay by:

at the first time offset, correlating the neural measurement against a third filter template to produce a fifth measure m 5 , the third filter template comprising an alternating waveform at double the frequency of the first filter template and of a third phase;

at the second time offset, correlating the neural measurement against the third filter template to produce a sixth measure m 6 , and

determining from m 5 and m 6 a decay in artifact between the first time offset and the second time offset.

24 . The device of claim 21 wherein the processor is further configured to recalculate the predefined optimal time delay prior to every attempted detection of a neural response.

25 . The device of claim 21 wherein the processor is further configured to recalculate the predefined optimal time delay in response to a detected change in a user's posture.

26 . The device of claim 14 wherein the processor is configured to measure the intensity of the neural response in the neural measurement by:

correlating the neural measurement against a filter template, the filter template comprising at least three half cycles of an alternating waveform, amplitude modulated by a window.