Effect on signal-to-noise ratio of splitting the continuous contacts of cuff electrodes into smaller recording areas.

BackgroundCuff electrodes have been widely used chronically in different clinical applications. This neural interface has been dominantly used for nerve stimulation while interfering noise is the major issue when employed for recording purposes. Advancements have been made in rejecting extra-neural interference by using continuous ring contacts in tripolar topologies. Ring contacts provide an average of the neural activity, and thus reduce the information retrieved. Splitting these contacts into smaller recording areas could potentially increase the information content. In this study, we investigate the impact of such discretization on the Signal-to-Noise Ratio (SNR). The effect of contacts positioning and an additional short circuited pair of electrodes were also addressed.MethodsDifferent recording configurations using ring, dot, and a mixed of both contacts were studied in vitro in a frog model. An interfering signal was induced in the medium to simulate myoelectric noise. The experimental setup was design in such a way that the only difference between recordings was the configuration used. The inter-session experimental differences were taken care of by a common configuration that allowed normalization between electrode designs.ResultsIt was found that splitting all contacts into small recording areas had negative effects on noise rejection. However, if this is only applied to the central contact creating a mixed tripole configuration, a considerable and statistically significant improvement was observed. Moreover, the signal to noise ratio was equal or larger than what can be achieved with the best known configuration, namely the short circuited tripole. This suggests that for recording purposes, any tripole topology would benefit from splitting the central contact into one or more discrete contacts.ConclusionsOur results showed that a mixed tripole configuration performs better than the configuration including only ring contacts. Therefore, splitting the central ring contact of a cuff electrode into a number of dot contacts not only provides additional information but also an improved SNR. In addition, the effect of an additional pair of short circuited electrodes and the "end effect" observed with the presented method are in line with previous findings by other authors

Electromyogram Interference Reduction In Neural Signal Recording Using Simple RC Compensation Circuits

Neuroprosthesis can partially restore lost motor functionalities of individuals such as bladder voiding using functional electrical stimulation (FES) techniques. FES involves applying pattern of electrical current pulses using implanted electrodes to trigger affected nerves that are damaged due to paralysis. A neural signal recorded using tripolar cuff electrodes is significantly contaminated due to the presence of EMG interference from the surrounding muscles. Conventional neural amplifiers are unable to remove such interferences and modifications to the design are required. The modification to the design of the Quasi-tripole (QT) amplifier is considered in this work to minimise the EMG interferences from neural signal recording. The analogy between this modified version of QT known as mQT and Wheatstone bridge claims to neutralise the EMG interference by adding compensation circuit to either end of the outer electrodes of the tripolar cuff and therefore balancing the bridge. In this work, we present simple 3 and 2 stage RC compensation circuits to minimise EMG interference in trying to balance the bridge in the neural frequency band of interest (500-10kHz). It is shown that simple RC compensation circuit in series reduces EMG interference only at the spot frequency rather than linearly in the entire frequency band of interest. However, two and three stages RC ladder compensation circuits mimicking electrode-electrolyte interface, can minimize the EMG interference linearly in the entire frequency band of interest, without requiring any readjustment to their components. The aim is to minimise EMG interference as close to null as possible. Invitro testing of about 20% imbalanced cuff electrode with proposed 3 and 2 stage RC ladder compensation circuits resulted in linear EMG interference reduction atleast by a factor of 6. On an average, this yielded an improvement of above 80% EMG minimisation, in contrast to above 90% observed in the optimisation results, when 1Ω transimpedance (EMG) was introduced into the setup. Further improvements to the setup and design can give more promising results in reliable neural signal recording for FES applications

On the viability of implantable electrodes for the natural control of artificial limbs: Review and discussion

The control of robotic prostheses based on pattern recognition algorithms is a widely studied subject that has shown promising results in acute experiments. The long-term implementation of this technology, however, has not yet been achieved due to practical issues that can be mainly attributed to the use of surface electrodes and their highly environmental dependency. This paper describes several implantable electrodes and discusses them as a solution for the natural control of artificial limbs. In this context "natural" is defined as producing control over limb movement analogous to that of an intact physiological system. This includes coordinated and simultaneous movements of different degrees of freedom. It also implies that the input signals must come from nerves or muscles that were originally meant to produce the intended movement and that feedback is perceived as originating in the missing limb without requiring burdensome levels of concentration. After scrutinizing different electrode designs and their clinical implementation, we concluded that the epimysial and cuff electrodes are currently promising candidates to achieving a long-term stable and natural control of robotic prosthetics, provided that communication from the electrodes to the outside of the body is guaranteed

Conception pour la testabilité des systèmes biomédicaux implantables

Architecture générale des systèmes implantables -- Principes de stimulation électrique -- Champs d'application des systèmes implantables -- Les particularités des circuits implantables -- Tendance future -- Conception pour la testabilité de la partie numérique des circuits implantables -- "Desigh and realization of an accurate built-in current sensor for Iddq testing and power dissipation measurement -- Conception pour la testabilité de la partie analogique des circuits implantables -- BIST for digital-to-analog and Analogo-to-digital converters -- Efficient and accurate testing of analog-to-digital converters using oscillation test method -- Design for testability of Embedded integrated operational amplifiers -- Vérification des interfaces bioélectroniques des systèmes implantables -- Monitorin the electrode and lead failures in implanted microstimulators and sensors -- Capteurs de température intégrés pour la vérification de l'état thermique des puces dédiées -- Built-in temperature sensors for on-line thermal monitoring of microelectronic structures -- Un protocole de communication fiable pour la programmation et la télémétrie des système implantables -- A reliable communication protoco for externally controlled biomedical implanted devices