Electrical Impedance Tomography of acute stroke

Electrical Impedance Tomography (EIT) could provide a novel method for imaging in acute stroke as it could be used as an inexpensive portable imaging system, which could distinguish haemorrhage from ischaemia in acute stroke and so allow rapid deployment of thrombolysis. First, an extensive literature of the dielectrical properties of normal and pathological head tissues was undertaken to inform further studies. The recently developed UCLH Mk2 EIT system was then shown to produce reliable images in a head shaped tank and in human subjects where changing of the concentrations of a fixed volume of saline in the stomach allowed validation in-vivo with skin electrodes. This was then tested in human patients with chronic stroke, brain tumours and arteriovenous malformations as simulations of acute stroke or haemorrhage. An optimal current waveform was then found which enabled high quality imaging over the optimal band of 20Hz-500kHz with some lower frequency currents reduced to avoid painful skin stimulation. A study in a headshaped tank with improved hardware then indicated that reconstruction algorithms available were the main constraint on EIT stroke imaging. Finally, the efficacy of newly developed frequency difference algorithms was assessed in a first pilot study of patients with acute ischaemic or haemorrhagic stroke. Overall, there was no definite or statistically significant correlation between the CTs and EIT image analysis, although there were encouraging correlations in some examples. The imaging algorithm with the least errors was Weighted Frequency Difference applied to neighbouring frequency pairs. Although it was not possible to achieve the ideal goal of robust clinical imaging with EIT in human stroke subjects with scalp electrodes, this work has provided a sound foundation and specification for further studies. These are continuing in my research group in collaboration with an international medical device manufacturer.