Electrical Impedance Tomography
Electrical impedance tomography (EIT) is a noninvasive, radiation-free, bedside lung imaging technique, which tracks changes in regional electrical resistivity of the lung tissue, corresponding to changes in regional gas content in relation to a reference state. Only functionally active lung structures are displayed, whereas structures - either normal or pathological (e.g., stable pneumothoraces or pleural effusions) - that do not change over time are functionally mute and cannot be represented as an image .
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is a functional technique that can provide information about ventilation-perfusion heterogeneity, pulmonary end-capillary diffusion of oxygen, and lung microstructure. According to the physical properties of the noble gas used as contrast agent, it can provide different information; in fact 3helium remains into the airways and alveolar spaces, and 129xenon follows the diffusion pathway of oxygen. An experimental study showed the redistribution of alveolar gas due to the application of recruitment maneuvers and PEEP using 3 helium in mechanically ventilated rats with atelectasis . At now, MRI data on ICU patients are limited; however, this technique could offer the possibility to match information about regional lung microstructure, function, and ventilation .