Methods

Thoracic Electrical Impedance Tomography (EIT) involves the attachment of an electrode array around the thorax and the successive injections of low frequency and low magnitude current, each via a different electrode pair, and the simultaneous voltage measurement via the remaining electrodes. By employing sophisticated reconstruction algorithms, EIT is capable of retrieving information regarding the inner-thoracic resistivity spatial distribution (see figure 1 for basic EIT block diagram).

The system incorporates a Finite Volume numerical solver and a parameterized Newton-Raphson optimization scheme for assessing the left-lung and right-lung resistivity values. These values are used for diagnosing and monitoring Pulmonary Edema (PE). This is done by solving the governing volume conductor equation, which relates the spatial resistivity (ρ), potential (ψ) and the current sources (Ι):



In addition, the cardiac cycle alters the inner resistivity spatial distribution due to blood perfusion. Based on this principle, the system is also capable of estimating the heart volumes in end-systole and end-diastole, thus supplying the important cardiac functionality information of Stroke Volume (SV).


Figure 1 – EIT block diagram