Method and device for detecting a neural response in a neural measurement

1. A method for processing a neural measurement in order to determine a magnitude of a neural response in the neural measurement, the method comprising:

applying a first electrical stimulus to neural tissue of a patient, the first electrical stimulus defined by at least one stimulus parameter;

obtaining the neural measurement from one or more sense electrodes subsequent to the first electrical stimulus;

determining, based on the neural measurement, a time delay of a window to be applied to a subsequent neural measurement;

applying the window at the time delay to the subsequent neural measurement to produce a windowed neural measurement; and

determining from the windowed neural measurement the magnitude of the neural response evoked by an electrical stimulus in the subsequent neural measurement.

2. The method of claim 1 , wherein the determining the magnitude of the neural response comprises correlating the windowed neural measurement against a filter template.

3. The method of claim 2 , wherein the filter template comprises at least three half cycles of an alternating waveform, amplitude modulated by a template window.

4. The method of claim 3 wherein the template window comprises a triangular window.

5. The method of claim 4 wherein the triangular window is a standard triangular window of length L comprising coefficients w(n) as follows:

For L odd:

w ( n )=2 n /( L+ 1) for 1≤ n ≤( L+ 1)/2=2−2 n /( L+ 1) for ( L+ 1)/2+1≤ n≤L

For L even:

w ( n )=(2 n− 1)/ L for 1≤ n≤L/ 2=2−(2 n− 1)/ L for L/ 2+1≤ n≤L.

6. The method of claim 4 wherein the triangular window is a Bartlett window of length L in which samples 1 and L are zero.

7. The method of claim 3 wherein the template window comprises one of a Hanning window, a rectangular window, and a Kaiser-Bessel window.

8. The method of claim 3 wherein the window comprises one or more basis functions derived from a sinusoidal binomial transform.

9. The method of claim 3 wherein the filter template comprises four half-cycles of an alternating waveform.

10. The method of claim 3 wherein the filter template comprises half cycles of a sine wave, amplitude modulated by the template window.

11. The method of claim 3 wherein the filter template comprises half cycles of a cosine wave, amplitude modulated by the template window.

12. The method of claim 2 wherein determining the magnitude comprises calculating only a single point of correlation.

13. The method of claim 2 , wherein determining the time delay comprises:

applying the window at an approximate time delay to the neural measurement;

computing real and imaginary parts of the fundamental frequency of the discrete Fourier Transform (DFT) of the windowed neural measurement;

calculating a phase defined by the real and imaginary parts;

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

determining the time delay as the sum of the approximate time delay and the time adjustment.

14. The method of claim 1 , wherein the time delay is re-determined prior to every processing of the neural measurement.

15. The method of claim 1 , wherein the time delay is re-determined in response to a detected change in a posture of the patient.

16. The method of claim 1 , further comprising using the magnitude of the neural response in a closed loop feedback circuit to determine the at least one stimulus parameter for a subsequent electrical stimulus.

17. An implantable device for processing a neural measurement in order to determine a magnitude of a neural response in the neural measurement, the device comprising:

an electrical stimulus source configured to generate a first electrical stimulus to be applied to neural tissue, the first electrical stimulus defined by at least one stimulus parameter;

measurement circuitry for obtaining the neural measurement from one or more sense electrodes subsequent to the first electrical stimulus; and

a processor configured to:

determine, based on the neural measurement, a time delay of a window to be applied to a subsequent neural measurement;

apply the window at the time delay to the subsequent neural measurement to produce a windowed neural measurement; and

determine from the windowed neural measurement the magnitude of the neural response evoked by the an electrical stimulus in the subsequent neural measurement.