Capacitively Coupled Electrical Impedance Tomography in Lung Imaging

Electrical impedance tomography (EIT) has been applied in bedside respiratory monitoring since it is a nonradioactive and noninvasive method. However, adverse effects of direct skin contact limit its usage. This article proposes the application of capacitively coupled EIT (CCEIT) for lung monitoring which avoids the limitation of galvanic contact measurement by using contactless measurements suitable for wearable devices, and it could provide a comfortable and hygienic user experience. This study primarily confirms the feasibility of CCEIT in monitoring respiration through a human body experiment, showing that both magnitude and phase angle of respiratory impedance effectively reflect breathing status. Numerical simulation is conducted to further explore the effects of frequency and insulation layer on CCEIT's impedance measurements and image reconstruction through constructing a digital twin lung model coupling biomechanical and electrical fields as a novel imaging modality. The time-difference imaging based on variations in magnitude and phase angle of impedance is proposed for imaging the respiratory phases of the lungs. CCEIT shows excellent performance in lung monitoring, particularly when operating at high frequencies and with small insulating layer thickness. Utilizing phase angle of impedance yields better imaging outcomes than magnitude, and at a high frequency of 20 MHz, even a 9 mm air gap can still provide satisfactory imaging results. CCEIT has broader applications than EIT, operating over a wide frequency range and utilizing both magnitude and phase angle information of impedance. This makes it promising for more accurate lung image reconstruction and impedance measurements in lung monitoring.