Structural-functional lung imaging using a combined CT-EIT and a Discrete Cosine Transformation reconstruction method

Benjamin Schullcke, Bo Gong, Sabine Krueger-Ziolek, Manuchehr Soleimani, Ullrich Mueller-Lisse, Knut Moeller
2016 Scientific Reports  
Lung EIT is a functional imaging method that utilizes electrical currents to reconstruct images of conductivity changes inside the thorax. This technique is radiation free and applicable at the bedside, but lacks of spatial resolution compared to morphological imaging methods such as X-ray computed tomography (CT). In this article we describe an approach for EIT image reconstruction using morphologic information obtained from other structural imaging modalities. This leads to reconstructed
more » ... s of lung ventilation that can easily be superimposed with structural CT or MRI images, which facilitates image interpretation. The approach is based on a Discrete Cosine Transformation (DCT) of an image of the considered transversal thorax slice. The use of DCT enables reduction of the dimensionality of the reconstruction and ensures that only conductivity changes of the lungs are reconstructed and displayed. The DCT based approach is well suited to fuse morphological image information with functional lung imaging at low computational costs. Results on simulated data indicate that this approach preserves the morphological structures of the lungs and avoids blurring of the solution. Images from patient measurements reveal the capabilities of the method and demonstrate benefits in possible applications. Electrical Impedance Tomography (EIT) is used to visualize the internal conductivity distribution of a domain from voltage measurements on the surface of the domain. In clinical context EIT is most often used to visualize regional ventilation of the lungs which has proven useful to reduce ventilator induced lung injury (VILI) 1,2 and guide clinicians to set adequate PEEP levels for mechanically ventilated patients in the intensive care unit (ICU) 3 . In lung EIT an array of electrodes is attached around the patient's chest. The electrodes are used to inject small alternating currents into the body and simultaneously measure the resulting voltages between pairs of electrodes. Usually the electrodes are attached equidistantly in a plane around the 5th intercostal space (ICS5), which seems to be less influenced by lung tissue shifts than more cranial or caudal positions for the electrodes 4 . Compared to morphological imaging methods, such as X-ray computed tomography (CT) or magnetic resonance imaging (MRI), the spatial resolution of EIT is much lower (about 2-3 cm) 5 , whereas the temporal resolution is very high (up to 50 frames/s in commercially available devices). In comparison to established methods for functional imaging of the lungs, such as single photon emission computed tomography (SPECT) or positron emission tomography (PET), EIT is very cheap. Additionally it is non-invasive, radiation free, and currently the only technique capable for real-time and long-term bedside monitoring of regional lung ventilation 6,7 . Besides the application in the ICU, EIT has recently been used in spontaneously breathing patients, suffering from asthma bronchiole 8 , cystic fibrosis (CF) 9 or chronic obstructive pulmonary disease (COPD) 10 . It has been shown in these studies, that EIT is capable to identify functional abnormalities in obstructive lung diseases. However, in order to obtain a comprehensive insight into the pulmonary pathophysiology it is necessary to com-
doi:10.1038/srep25951 pmid:27181695 pmcid:PMC4867600 fatcat:vmycuvoxhjgjzmgujed3m7ycbe