EIT is a non-invasive, radiation free technique that images an object by injecting tiny currents through electrodes on its boundary, and measures the resulting potentials developed on the same or other electrodes. This process permits the estimation of the distribution of the inner conductance (impedance) of the object. When applied to the thorax this allows both global and regional changes in aeration and ventilation, and ventilation/perfusion mismatch, to be ascertained in real time. The images do not provide static structural equivalence to MRI or CT of the lung but represent the air volume change in the lung with high temporal resolution (up to 100  images per second).