In-water electrical impedance tomography: EIT and the sea

Objective.Electrical impedance tomography (EIT) has shown the ability to provide clinically useful functional information on ventilation in humans and other land mammals. We are motivated to use EIT with sea mammals and human divers, since EIT could provide unique information on lung ventilation that can help address diver performance and safety, and veterinary and behavioral questions. However, in-water use of EIT is challenging, primarily because sea water is more conductive than the body.Approach.We first address this issue by modeling the in-water component and evaluating image reconstruction algorithms.Main results.EIT is able to produce reasonable images if an outer insulating layer allows a water layer thickness <2% of the body radius. We next describe the design of custom EIT belts with an outer neoprene insulator to minimize current leakage. We show example underwater EIT recordings in human and dolphin subjects.Significance.We demonstrate in-water EIT is feasible with appropriate techniques.