Imaging Conductivity Distribution of Ventilation with Single-frequency and Frequency-difference Electrical Impedance Tomography

Electrical Impedance Tomography (EIT) is a technique to image the conductivity distribution that has been used in many medical applications. For lung application, EIT can image lung ventilation with a good temporal resolution which is helpful for diagnosis and providing information for lung recovery. The image reconstruction of EIT is usually based on a single excitation frequency. The reconstruction also usually uses a common chest model instead of an exact chest model due to limited availability resulting in a modeling error in the reconstruction process. In this study, the change in conductivity of frequency difference was investigated whether it can be used for lung ventilation monitoring. A method to construct a frequency difference image was proposed. Some techniques to reduce the influence of modeling error were also investigated whether they could improve the reconstruction or not. An experiment result on a subject showed that the frequency difference method can be used for monitoring the respiration activity with higher discriminability i.e. the conductivity change in each lung region was clearly seen. However, the single-frequency method still provided a better shape of the change that was consistent with the lungs' shape. The implementation of the modeling error reduction could significantly increase the image amplitude for both methods, but it could reduce the artifacts for only the single-frequency method.