Event Abstract

Electrical Impedance Tomography on High-density Microelectrode Arrays

  • 1 ETH Zürich, D-BSSE, Switzerland

Electrical impedance tomography (EIT) is a non-invasive, label-free imaging technique that enables to reconstruct the conductivity distribution in a body from a series of impedance measurements. Impedance measurements can be used to determine the position, morphology, and growth of cells or tissues, as well as pathological signs, e.g., precancerous tissue conditions (Gersing 1999). The newest high-density microelectrode array (MEA) system developed in our group features 59,760 integrated electrodes (Dragas et al. 2017). The chip features a variety of electrophysiological functions: Action-potential recording (2048 channels), cyclic voltammetry (28 channels), local-field-potential recording (32 channels) and extracellular stimulation (16 channels) [Fig 1A]. The chip can also measure impedance through 32 channels, which enables EIT measurements. We were able to establish a proof of concept for EIT (Viswam et al. 2017). The current goal of this project is to develop an impedance measurement protocol and an appropriate reconstruction algorithm that allow for single-cell-resolution impedance imaging. Material and Methods An acute slice of mouse brain was placed on the array within a well containing carbogen-bubbled calcium-free artificial cerebrospinal fluid. A sinusoidal voltage, generated with the chip’s built-in wave generator was applied to the reference electrode, and the induced current was sensed with the MEA electrodes. Using 120 configurations of 3840 sparsely configured electrodes, an impedance map was measured. The raw data, containing the magnitude and phase of the measured signals was then processed in Matlab using a custom-made code. We are currently working on an alternate impedance measurement protocol, where selected electrodes in the array are used for the input signal, and the induced currents are then measured in adjacent electrodes [Fig. 1B]. By rapidly changing electrode configurations, a scan of the region of interest can be obtained. Results By creating an impedance magnitude heat map of the tissue, we established a proof of concept for EIT measurements with our chip. Discussion As a pixel of the array is 13.5 µm x 13.5 µm, it should be possible to improve the resolution down to single cell level, which enables exact localization of cells on the array. This is the focus of our ongoing work. After establishing a suitable electrode configuration sequence, we will develop a reconstruction code, drawing on the material available through the Electrical Impedance and Diffuse Optical Reconstruction Software project (Adler et al. 2017).

Figure 1
Figure 2

References

• E. Gersing, “Monitoring Temperature-Induced Changes in Tissue during Hyperthermia by Impedance Methods”. Annals of the New York Academy of Sciences, 873: 13–20, 1999.
doi:10.1111/j.1749-6632.1999.tb09444.x
• J. Dragas et al., "In Vitro Multi-Functional Microelectrode Array Featuring 59 760 Electrodes, 2048 Electrophysiology Channels, Stimulation, Impedance Measurement, and Neurotransmitter Detection Channels," in IEEE Journal of Solid-State Circuits, vol. 52, no. 6, pp. 1576-1590, June 2017.
doi: 10.1109/JSSC.2017.2686580
• V. Viswam et al., “High-Density Mapping of Brain Slices using a Large Multi-Functional High-Density CMOS Microelectrode Array System. International Solid-State Sensors, Actuators and Microsystems Conference : [proceedings] International Conference on Solid-State Sensors, Actuators, and Microsystems. 2017;2017:135-138. doi:10.1109/TRANSDUCERS.2017.7994006.
• Adler, Andy, Boyle, Alistair, Braun, Fabian, Crabb, Michael G., Grychtol, Bartłomiej, Lionheart, William R. B., … Yerworth, Rebecca. (2017, June 21). EIDORS v3.9. Zenodo. http://doi.org/10.5281/zenodo.583266

Keywords: high-density MEA, EIT, Bioimpedance, Electrophysiology, Inverse conductivity problem

Conference: MEA Meeting 2018 | 11th International Meeting on Substrate Integrated Microelectrode Arrays, Reutlingen, Germany, 4 Jul - 6 Jul, 2018.

Presentation Type: Poster Presentation

Topic: Microelectrode Array Technology

Citation: Urwyler CI, Bounik R, Viswam V and Hierlemann AR (2019). Electrical Impedance Tomography on High-density Microelectrode Arrays. Conference Abstract: MEA Meeting 2018 | 11th International Meeting on Substrate Integrated Microelectrode Arrays. doi: 10.3389/conf.fncel.2018.38.00084

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Received: 18 Mar 2018; Published Online: 17 Jan 2019.

* Correspondence:
Mr. Cedar I Urwyler, ETH Zürich, D-BSSE, Zurich, Switzerland, curwyler@student.ethz.ch
PhD. Vijay Viswam, ETH Zürich, D-BSSE, Zurich, Switzerland, vijay.viswam@bsse.ethz.ch

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