Closed-Loop DBS Signal Sampling Synchronization
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Solution Overview
Problem
Current closed-loop deep brain stimulation (DBS) systems face challenges due to electrical artefacts from stimulation signals, leading to distorted and suboptimal electrophysiological signal measurement, which affects the accuracy of closed-loop control.
Innovation Solution
Synchronizing the generation of stimulation signals with the sampling of electrophysiological signals to occur outside the stimulation pulses, ensuring that sampling happens when artefacts are not present, and selecting a sampling frequency that complies with the Shannon-Whittaker-Kotelnikov sampling theorem to maintain signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrophysiological signals are sampled at high frequency to capture signal details, then measurement precision is improved, but voltage artefacts from stimulation become extremely large (a million times the signal level)
Solution Approach 1:
The patent applies periodic action by synchronizing the sampling operation to occur at specific phases of the stimulation pulse cycle. The sampling is timed to happen during the inter-pulse interval when stimulation artefacts are minimal, creating a periodic sampling pattern that avoids the harmful voltage artefacts while maintaining high measurement precision
Solution Approach 2:
The patent implements preliminary action by predicting the timing of stimulation pulses and pre-scheduling sampling operations to occur just before or during the inter-pulse intervals. This allows the system to proactively avoid artefact contamination rather than reacting to it after the fact
2Device complexity
If electrophysiological signals are sampled at low frequency to reduce processing load, then device complexity is reduced, but aliasing occurs leading to elevated noise floor and low signal-to-noise ratio
Solution Approach 1:
The patent changes the sampling frequency parameter to be synchronized with the stimulation pulse frequency. By setting the sampling frequency as an integer multiple of the stimulation frequency and adjusting the phase relationship, the system achieves optimal signal-to-noise ratio without requiring excessively high sampling rates or complex processing
3Speed
If stimulation and recording occur simultaneously to enable closed-loop control, then response time is improved, but electrical artefacts from stimulation corrupt the electrophysiological signal
Solution Approach 1:
The patent uses periodic action by implementing synchronized sampling that occurs at regular intervals during the inter-pulse periods. This allows simultaneous stimulation and recording while periodically capturing artefact-free signals that can be used for closed-loop control
Solution Approach 2:
The patent maintains continuity of useful action by ensuring that sampling occurs continuously during the inter-pulse intervals, capturing electrophysiological signals without interruption while stimulation continues. This enables real-time closed-loop control without requiring separate stimulation and recording phases
Data Source
AI summary
When generating a stimulation signal comprising stimulation pulses delivered to a target area of a human or animal body, an electrophysiological signal measured from the body for closed-loop control of the stimulation signal, is sampled, at a sampling frequency in an analogue-to-digital converter for deriving a feedback signal for closed-loop control of the stimulation signal. The generation of the stimulation signal and the sampling of the electrophysiological signal are synchronised and have a relative phase selected to cause the sampling to occur outside the stimulation pulses, which prevents the effect of the stimulation pulses from interfering with the digital electrophysiological signal, whiles allowing maintenance of Nyquist-Shannon rules and the integrity of the discrete Laplace transform (z-transform) required in discrete control theory.