A method of estimating blood flow in a brain, comprising: a) causing currents to flow inside the head by producing electric fields inside the head b) measuring at least changes in the electric fields and the currents c) estimating changes in the blood volume of the head, using the measurements of the electric fields and the currents, where the current are produced in children or using electrodes at or near holes in the skull. Optionally, the configuration is selected to focus the flow of current to be inside the brain to a significant degree.
