Programming of neuromodulation therapy
Disclosed is an implantable device for lead offset determination, comprising first and second electrode leads. A stimulus is delivered from one lead to tissue, and a signal is sensed from the tissue by the other lead. The sensed signal is processed to produce a measure of a stimulus artefact present in the signal. The stimulus artefact measure is used to produce a measure of an offset between the first electrode lead and the second electrode lead, such as by applying a distance-squared analytical model to measures of stimulus artefact obtained from at least two sense electrodes. And/or, a compound action potential evoked by the stimulus is sensed from neural tissue, a latency of the evoked compound action potential is measured, and a measure of an offset between the first electrode lead and the second electrode lead is produced from the latency.
1. An implantable device for lead offset determination, the device comprising:
a first electrode lead comprising a first plurality of electrodes;
a second electrode lead comprising a second plurality of electrodes;
a stimulus source for providing a stimulus to be delivered from one or more stimulus electrodes to tissue proximal to one or more stimulus electrodes, the one or more stimulus electrodes being selected from the first plurality of electrodes and the second plurality of electrodes;
measurement circuitry for recording from one or more sense electrodes a signal sensed from the tissue and resulting from the stimulus, the one or more sense electrodes being selected from the first plurality of electrodes and the second plurality of electrodes;
wherein at least one electrode of the first plurality of electrodes serves as either a stimulus electrode or as a sense electrode, and wherein at least one electrode of the second plurality of electrodes serves as either a stimulus electrode or as a sense electrode; and
a processor configured to process the signal from the measurement circuitry in order to produce a measure of a stimulus artefact present in the signal; and
the processor further configured to process the measure of the stimulus artefact to produce a measure of an offset between the first electrode lead and the second electrode lead.
2. The implantable device of claim 1 , wherein a stimulus phase configuration is selected to maximise a stimulus artefact resulting from application of the stimulus.
3. The implantable device of claim 2 , wherein the stimulus phase configuration comprises a biphasic pulse.
4. The implantable device of claim 2 wherein the stimulus phase configuration comprises a triphasic stimulus in which a ratio of charge of a first phase relative to a third phase is selected to effect increased stimulus artefact.
5. The implantable device of claim 1 , wherein a stimulus electrode configuration is selected to spatially constrain a maximal region of a stimulus artefact resulting from application of the stimulus.
6. The implantable device of claim 5 wherein a shielded anode tripolar stimulus electrode configuration is selected.
7. The implantable device of claim 1 wherein the device is configured to provide stimuli repeatedly to be delivered from unchanged stimulus electrodes and with iteratively altered selection of sense electrode.
8. The implantable device claim 1 wherein the processor is configured to produce the measure of the offset by applying a distance-squared analytical model to measures of stimulus artefact obtained from at least two sense electrodes.
9. The implantable device of claim 8 wherein the model comprises a relationship:
A
(
d
)
=
a
(
d
-
b
)
2
+
c
2
where A (d) is a function of measured stimulus artefact A relative to a distance d of the sense electrode from the stimulus electrode, and a, b and c are fitting parameters, with b constituting the measure of the offset.
10. The implantable device of claim 9 , further configured to apply an iterative fitting process to seek values for a, b and c which best fit the model to the measures of stimulus artefact.
11. The implantable device of claim 1 wherein the processor is configured to produce the measure of the offset by applying a fractional pole components model of artefact, in which each edge of each voltage step in the tissue resulting from the delivered stimulus is treated as a singularity at which is defined an independent set of step and impulse components based on a constant phase element (CPE) characterisation of an interface between the tissue and the one or more sense electrodes.
12. The implantable device of claim 1 , wherein the measure of the offset comprises a measure of a rostro-caudal offset between the first electrode lead and the second electrode lead.
13. A method for lead offset determination, the method comprising:
delivering a stimulus from one or more stimulus electrodes to tissue proximal to the one or more stimulus electrodes, the one or more stimulus electrodes being selected from a first plurality of electrodes of a first electrode lead and a second plurality of electrodes of a second electrode lead;
recording from one or more sense electrodes a signal sensed from the tissue and resulting from the stimulus, the one or more sense electrodes being selected from the first plurality of electrodes and the second plurality of electrodes;
wherein at least one electrode of the first plurality of electrodes serves as either a stimulus electrode or as a sense electrode, and wherein at least one electrode of the second plurality of electrodes serves as either a stimulus electrode or as a sense electrode; and
processing the signal in order to produce a measure of a stimulus artefact present in the signal; and
processing the measure of the stimulus artefact to produce a measure of an offset between the first electrode lead and the second electrode lead.
14. The method of claim 13 , wherein a stimulus phase configuration is selected to maximise a stimulus artefact resulting from application of the stimulus.
15. The method of claim 14 , wherein the stimulus phase configuration comprises a biphasic pulse.
16. The method of claim 14 wherein the stimulus phase configuration comprises a triphasic stimulus in which a ratio of charge of a first phase relative to a third phase is selected to effect increased stimulus artefact.
17. The method of claim 13 , wherein a stimulus electrode configuration is selected to spatially constrain a maximal region of a stimulus artefact resulting from application of the stimulus.
18. The method of claim 17 wherein a shielded anode tripolar stimulus electrode configuration is selected.
19. The method of claim 13 further comprising delivering stimuli repeatedly from unchanged stimulus electrodes and with iteratively altered selection of sense electrode.
20. The method of claim 13 further comprising producing the measure of the offset by applying a distance-squared analytical model to measures of stimulus artefact obtained from at least two sense electrodes.
21. The method of claim 20 wherein the model comprises a relationship:
A
(
d
)
=
a
(
d
-
b
)
2
+
c
2
where A(d) is a function of measured stimulus artefact A relative to a distance d of the sense electrode from the stimulus electrode, and a, b and c are fitting parameters, with b constituting the measure of the offset.
22. The method of claim 21 , further comprising applying an iterative fitting process to seek values for a, b and c which best fit the model to the measures of stimulus artefact.
23. The method of claim 13 further comprising producing the measure of the offset by applying a fractional pole components model of artefact, in which each edge of each voltage step in the tissue resulting from the delivered stimulus is treated as a singularity at which is defined an independent set of step and impulse components based on a constant phase element (CPE) characterisation of an interface between the tissue and the one or more sense electrodes.
24. The method of claim 13 , wherein the measure of the offset comprises a measure of a rostro-caudal offset between the first electrode lead and the second electrode lead.
25. A non-transitory computer readable medium for lead offset determination, comprising instructions which, when executed by one or more processors, causes performance of the following:
delivering a stimulus from one or more stimulus electrodes to tissue proximal to the one or more stimulus electrodes, the one or more stimulus electrodes being selected from a first plurality of electrodes of a first electrode lead and a second plurality of electrodes of a second electrode lead;
recording from one or more sense electrodes a signal sensed from the tissue and resulting from the stimulus, the one or more sense electrodes being selected from the first plurality of electrodes and the second plurality of electrodes;
wherein at least one electrode of the first plurality of electrodes serves as either a stimulus electrode or as a sense electrode, and wherein at least one electrode of the second plurality of electrodes serves as either a stimulus electrode or as a sense electrode; and
processing the signal in order to produce a measure of a stimulus artefact present in the signal; and
processing the measure of the stimulus artefact to produce a measure of an offset between the first electrode lead and the second electrode lead.
26. The non-transitory computer readable medium claim 25 , wherein the instructions contained upon the non-transitory computer readable medium comprise a clinical programming application, the clinical programming application further configured to provide clinical programming functions for an implantable device comprising the first and second electrode leads, so as to program the implantable device based on the measure of the offset.