A Versatile and Reproducible Multi-Frequency Electrical Impedance Tomography System.
A highly versatile Electrical Impedance Tomography (EIT) system, nicknamed the ScouseTom, has been developed. The system allows control over current amplitude, frequency, number of electrodes, injection protocol and data processing. Current is injected using a Keithley 6221 current source, and voltages are recorded with a 24-bit EEG system with minimum bandwidth of 3.2 kHz. Custom PCBs interface with a PC to control the measurement process, electrode addressing and triggering of external stimuli. The performance of the system was characterised using resistor phantoms to represent human scalp recordings, with an SNR of 77.5 dB, stable across a four hour recording and 20 Hz to 20 kHz. In studies of both haeomorrhage using scalp electrodes, and evoked activity using epicortical electrode mats in rats, it was possible to reconstruct images matching established literature at known areas of onset. Data collected using scalp electrode in humans matched known tissue impedance spectra and was stable over frequency. The experimental procedure is software controlled and is readily adaptable to new paradigms. Where possible, commercial or open-source components were used, to minimise the complexity in reproduction. The hardware designs and software for the system have been released under an open source licence, encouraging contributions and allowing for rapid replication.
Department Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, UK. j.avery@ucl.ac.uk.
James
J
Avery
Department Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, UK. t.dowrick@ucl.ac.uk.
Thomas
T
Dowrick
Department Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, UK. mayo.faulkner@ucl.ac.uk.
Mayo
M
Faulkner
Department Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, UK. n.goren@ucl.ac.uk.
Nir
N
Goren
Department Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, UK. d.holder@ucl.ac.uk.
David
D
Holder
D000818:Animals; D017097:Electric Impedance; D004566:Electrodes; D006801:Humans; D019047:Phantoms, Imaging; D014054:Tomography; D014057:Tomography, X-Ray Computed
Arduino; Electrical Impedance Tomography; brain imaging; evoked activity; long term monitoring; open source hardware