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 [27].

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 [28]. 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 [27].