Determination of Lung Area in EIT Images

Electrical impedance tomography (EIT), as a noninvasive, radiation-free imaging technique, has the potential for bedside monitoring of regional lung function. Evaluation of EIT imaging requires the identification of the lung area in the images. By Hahn and Frerichs et al. a functional EIT based method (fEIT) was proposed to identify the lung area in EIT images for patients with healthy lungs. However, a method for patients with serious lung disease is missing. The aim of this study was to develop an improved method for lung area estimation in EIT images (LAE), which is also suitable for patients with serious pulmonary diseases. In LAE the lung area as determined by fEIT is mirrored and the cardiac related area is subtracted. 49 mechanically ventilated patients were investigated, including 39 patients waiting for thoracic surgery (test group) and 10 patients for orthopedic surgery without pulmonary disease (control group). The sizes of the lung area determined with fEIT are in control group S_C,fEIT=361plusmn35.1 (meanplusmnSD) and in test group S_T,fEIT=299plusmn60.8 (p<0.01). The sizes estimated with the LAE method in control group S_C,LAE= 353plusmn27.2 and in test group S_T,LAE=353plusmn61.1 (p=0.41). It is assumed that the fraction of the lung in the thorax for different people should be more or less in the same range, in spite of the state of the lung. The result demonstrates that the novel LAE method can better access the lung region in EIT images, from which the analysis of regional lung ventilation will benefit.