Automatic Determination of the Threshold of an Evoked Neural Response

• US 20080319508A1
• Filed: 06/15/2005
• Published: 12/25/2008
• Est. Priority Date: 06/15/2004
• Status: Active Grant

• Current Assignee: Cochlear Americas Corporation (Cochlear Limited)
• Original Assignee: Cochlear Americas Corporation (Cochlear Limited)
• Inventors: Botros, Andrew, Killian, Matthijs, van Dijk, Bastiaan
• Granted Patent: US 8,965,520 B2
• Time in Patent Office: Days
• US Class Current: 607/57
• CPC Class Codes: A61B 5/24 Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
• CPC Class Codes: A61B 5/7264 Classification of physiological signals or data, e.g. using neural networks, statistical classifiers, expert systems or fuzzy systems neural networks per se G06N3/00; expert systems per se G06N5/00
• CPC Class Codes: A61B 5/7275 Determining trends in physiological measurement data; Predicting development of a medical condition based on physiological measurements, e.g. determining a risk factor
• CPC Class Codes: A61B 5/7282 Event detection, e.g. detecting unique waveforms indicative of a medical condition A61B5/4094, A61B5/4818, A61B5/349, A61B5/0823 take precedence
• CPC Class Codes: A61N 1/00 Electrotherapy; Circuits therefor A61N2/00 takes precedence; irradiation apparatus A61N5/00
• CPC Class Codes: A61N 1/0541 Cochlear electrodes
• CPC Class Codes: A61N 1/36039 fitting procedures
• CPC Class Codes: G16H 50/20 for computer-aided diagnosis, e.g. based on medical expert systems

Abstract

Automatically analysing an evoked neural response. The method comprises: applying electrical stimulation to a target neural region at incrementally greater current levels beginning with an initial current level that is as close as possible to a typical threshold-NRT level; recording an NRT measurement of an auditory signal which generated by the target neural region in response to the stimulation; and utilizing a machine-learned expert system to predict whether the NRT measurement contains a neural response based on a plurality of features extracted from the auditory signal.

Claims

1. A method for automatically analysing an evoked neural response comprising:

applying electrical stimulation to a target neural region at incrementally greater current levels beginning with an initial current level that is as close as possible to a typical threshold-NRT level;

recording an NRT measurement of an auditory signal which generated by the target neural region in response to the stimulation; and

utilizing a machine-learned expert system to predict whether the NRT measurement contains a neural response based on a plurality of features extracted from the auditory signal.

2. The method of claim 1, further comprising:

selecting the initial current level to insure safety while minimizing a quantity of measurements required to determine the threshold NRT.

3. The method of claim 2, wherein selecting the initial current level comprises:

in intraoperative applications, selecting as an initial current level a current level at which a neural response is not expected to be evoked.

4. The method of claim 3, wherein selecting the initial current level comprises:

selecting an initial current level substantially below the typical T-NRT.

5. The method of claim 3, wherein selecting the initial current level comprises:

in intra-operative applications, selecting an initial current level that is above or below the typical T-NRT.

6. The method of claim 1, wherein when the machine-learned expert system predicts that the NRT measurement does not contain a neural response, the method further comprises:

incrementing the current level of the electrical stimulus;

repeating the applying, recording and utilizing steps; and

repeating the incrementing and repeating steps until a neural response has been evoked.

7. The method of claim 1, further comprising:

locally establishing the T-NRT at a finer stimulus resolution.

8. A cochlear implant system comprising:

a cochlear implant configured to communicate with an external device; and

an automatic neural response measurement system, communicably coupled to the cochlear implant, configured to record Neural Response Telemetry (NRT) measurements of neural activity within a cochlea in response to electrical stimulation of the cochlear by electrodes of the cochlear implant, wherein an initial current level of a stimulus applied to evoke a neural response is set to a level which is as close as possible to a typical threshold current level which would cause a neural response to occur, the system comprising an expert system configured to determine whether the NRT measurement contains a neural response based on a plurality of the extracted features.

9. A method for determining a minimum stimulus threshold at which a neural response is evoked, comprising:

applying a neural stimulus;

obtaining a measurement of a neural response to the neural stimulus;

evaluating whether a neural response has been evoked by applying an expert system to the measurement, wherein the expert system considered a plurality of features extracted from the neural response.

10. An expert system comprising a machine learning algorithm such as the induction of at least one decision tree comprises one or more of:

a parameter relating to peak-to-peak amplitude of the measurement;

a parameter relating to the noise of the measurement;

a parameter relating to the ratio of the peak-to-peak amplitude of the measurement to the noise of the measurement;

a parameter relating to the correlation of the measurement to a predefined expected neural response;

a parameter relating to the correlation of the measurement to a predefined expected trace containing neural response plus stimulus artefact;

a parameter relating to the correlation of the measurement to a predefined expected trace containing stimulus artefact only;

a parameter relating to the correlation of the measurement to a previous measurement with neural stimulus of similar level; and

a parameter relating to a stimulus current level.

11. An evoked neural response automatically analysing system comprising:

means for applying electrical stimulation to a target neural region at incrementally greater current levels beginning with an initial current level that is as close as possible to a typical threshold-NRT level;

means for recording an NRT measurement of an auditory signal which generated by the target neural region in response to the stimulation; and

means for predicting whether the NRT measurement contains a neural response based on a plurality of features extracted from the auditory signal.

12. The system of claim 11, further comprising:

means for selecting the initial current level to insure safety while minimizing a quantity of measurements required to determine the threshold NRT.

13. The system of claim 12, wherein the means for selecting the initial current level, in intraoperative applications, selects as an initial current level a current level at which a neural response is not expected to be evoked.

14. The system of claim 13, wherein the means for selecting the initial current level selects an initial current level substantially below the typical T-NRT.

15. The system of claim 13, wherein the means for selecting the initial current level, in intra-operative applications, selects an initial current level that is above or below the typical T-NRT.