Abstract
Intraoperative Neurophysiological Monitoring is a set of monitoring techniques consisting of reading electrical activity generated by the nervous system structures during surgeries. In order to guarantee signal quality, contact impedance between the sensing electrodes and the patient’s skin needs to be as low as possible. Hence, monitoring this impedance while signals are measured is an important feature of current medical devices. The most commonly used technique involves injection of a known current and measurement of the voltage drop in the contact interface. This method poses several problems, such as power consumption (critical in battery-powered systems), frequency dependency and regulation issues, which are overcome by using a passive method. The fundamentals of the method proposed in this paper are based on the utilization of the variation suffered by the input random signal when a known resistance is connected in parallel to the input terminals of the low-noise amplifier (LNA) of the analog front-end of the acquisition system. Controlling the connection of the resistors and computing the root mean square of the LNA output voltage has been proved to be a useful tool to assess that the contact impedance is suitably low, allowing the user to know if the neural measurements obtained are valid.
Highlights
Due to the context of utilization, it is of paramount importance to guarantee the accuracy of the biological signals acquired
The first stage of a biopotential monitoring system consists of a low-noise amplifier (LNA) that receives the analog signal sensed by several electrodes connected to the patient
Kubendran et al.19 highlight the drawbacks of using sinusoidal sources or square waves when performing an analysis of this kind
Summary
The passive method (without the injection of a probe current) proposed here is based in the changes in the measured signal when a purely resistive load is connected in parallel to either the positive or the negative input terminals of the LNA. The voltage at the input of the positive terminal of the LNA can be calculated, ignoring the effect of the DC voltage source due to the filter and assuming that the input impedance of the amplifier is large enough: v′+ = v+ ⋅. One can define α and β as the attenuation coefficients caused by the relation between the contact impedance R+ and R− and the known resistance (R) when the corresponding switches are closed These coefficients become useful when defining a set of voltage measurements that can be obtained when combining the different positions of the switches shown in Fig. 2: va = G ⋅ (v+).
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
