for this approach is lung tissue during breathing due to linear conductivity changes between inspiration and expiration which are caused by varying contents of insulating air during each breath cycle. This permits digital subtraction of recorded measurements obtained during the breath cycle and results in functional images of lung ventilation. One major advantage is that relative changes of conductivity remain comparable between measurements even if one of the recording electrodes is less conductive than the others, thereby reducing most artifacts and image distortions. However, incorporating a priori data sets or meshes in difference EIT is still useful in order to project images onto the most likely organ morphology, which depends on weight, height, gender, and other individual factors. The open source project EIDORS provides a suite of programs (written in Matlab / GNU Octave) for data reconstruction and display under the GNU GPL license. The direct nonlinear D-bar method for nonlinear EIT reconstruction is available in Matlab code at . The Open Innovation EIT Research Initiative is aimed at advancing the development of electrical impedance tomography (EIT) in general and to ultimately accelerate its clinical adoption. A plug-and-play EIT hardware and software package is available through Swisstom and can be acquired at net cost price. Image reconstruction and processing of raw data obtained with this set can be carried out without any limitations by the software tools provided through EIDORS. Properties In contrast to most other tomographic imaging techniques, EIT does not apply any kind of ionizing radiation. Currents typically applied in EIT are relatively small and certainly below the threshold at which they would cause significant nerve stimulation. The frequency of the alternating current is sufficiently high not to give rise to electrolytic effects in the body and the Ohmic power dissipated is sufficiently small and diffused over the body to be easily handled by the body's thermoregulatory system. These properties qualify EIT to be continuously applied in humans, e.g. during mechanical ventilation in an intensive care unit (ICU). Because the equipment needed in order to perform EIT is much smaller and less costly than in conventional tomography, EIT qualifies for continuous real time visualization of lung ventilation right at the bedside. EIT's major disadvantage versus conventional tomography is its lower maximum spatial resolution (approximately 15% of electrode array diameter in EIT compared to 1 mm in CT and MRI). However, resolution can be improved using 32 instead of