Electrical Impedance Tomography of human brain function

This thesis shows for the first time that Electrical Impedance Tomography (EIT) is able to detect and image changes in impedance during brain activity in humans. The work described is both experimental and theoretical. In the first instance, the impedance change associated with epilepsy was imaged with EIT in the exposed cortex of anaesthetised rabbits. Although the impedance change was correctly localised, both increases and decreases in impedance were present. The characteristics of the impedance change were examined using probes placed directly on the cortex. Additional measurements were used to examine the physiological mechanisms for this change. Following this, a reconstruction technique was developed, designed for imaging the human head in 3D. The head was modelled as a homogeneous sphere and images reconstructed from this were tested using simulated data and data obtained in saline-filled tanks. This algorithm was then used to generate images from EIT data recorded during evoked responses in human volunteers. Although images reconstructed from saline-filled tanks were able to localise an impedance change accurately, images reconstructed from human data localised the impedance change correctly in around a half of the experiments. The possibility that the incorrect localisation was due to modelling errors was investigated by incorporating a finite element model of a real human head into the reconstruction process. The results from this method were similar to those obtained using the spherical model of the head