Electrical Impedance Tomography of brain function

Electrical impedance tomography is recently developed imaging technique, with which images of the internal impedance of the subject can be rapidly collected with rings of external ECG - type electrodes. It is fast, inexpensive, portable and is very sensitive to physiological changes which affect the electrical impedance properties. Set against this is a relatively poor spatial resolution and ill posed nature of the procedure for reconstructing images, such that a small errors due to instrumentation translate into large errors in images. For about two decades, satisfactory images have been obtained of changes over time related to gastric emptying and ventilation and cardiac output in the thorax. The main work of the speakerpsilas group has been to adapt existing EIT designs for the demanding application of imaging changes in the brain due to conditions like stroke, epilepsy or normal physiological brain activity; the difficulty is that the skull is resistive and diverts current so that the signal to noise ratio is low. In addition, imaging of acute stroke requires one-off images where the use of time difference to correct for instrumentation errors is not possible. Approaches used to overcome these problems include the use of signal processing, improved numerical models for image reconstruction, and the use of frequency difference imaging.