Transcranial acoustoelectric imaging (tABI) of seizure activity in human head model with neuronavigation.

Abstract

The human brain consists of multiple interacting neuronal networks that interleave at fine spatial and temporal scales. This complexity presents a challenge for scalp EEG and other noninvasive mapping techniques to accurately identify seizures and abnormal current patterns from background activity. To address this unmet need, this study investigates Transcranial Acoustoelectric Brain Imaging (tABI) with neuronavigation as a new method for mapping EEG-derived currents through the skull. In tABI, ultrasound (US) is focused and steered in the brain as surface electrodes record an acoustoelectric (AE) interaction signal. Space and time varying current maps are then generated at a resolution determined by the US focus. To test the efficacy of this method, a human skull was filled with conductive agarose gel, and a clinical depth electrode array was implanted 43 mm below the skull surface to generate artificial current waveform segments taken from normal and seizure activity. A 0.6 MHz 2D array was used to electronically focus and steer US through the skull while gold cup electrodes recorded high frequency AE signals and low frequency surface potentials. A 2D Wiener filter (WF) was introduced during preprocessing to enhance SNR followed by Singular Value Decomposition (SVD) to selectively identify pixels correlated with different temporal patterns. Whereas the WF enhanced SNR up to 16.9 dB at 6.4 mA of current, SVD enabled color-coding of tABI to highlight activation patterns correlated with different current waveforms with a spatial resolution of 5 mm. Finally, the current detection limit depended on the duration and bandwidth of the selected currents with the ictal waveform yielding the lowest detection (28 µA and 78 µA/cm2*MPa, p<0.05). These results support the development of tABI for noninvasive mapping of neuronal currents in epilepsy patients for surgical planning and other applications.