Imaging resistivity changes of the adult brain during the cardiac cycle

Images of electrical resistivity changes during the cardiac cycle have been produced from adult heads using applied potential tomography in 12 normal subjects. The images are consistent in the same individual but there are differences when two different subjects are compared. Using a simple, three-sphere model, the way in which resistivity changes inside and outside of the skull are imaged by the system is investigated. It is concluded that the observations are not just the backprojection of scalp blood flow into the center of the image and that resistivity changes originating within the skull can be demonstrated. The direction and amplitude of the changes are consistent with that expected from cerebral blood flow, although this origin has not yet been proved