Intra-vital microscopy of lung tissue: A simulation based analysis of the image formation

In the course of pulmonary research, understanding alveolar tissue dynamics plays a critical role in the treatment of patients suffering from acute lung diseases. As a gold standard technique for monitoring micro scale changes of lung tissue, real-time intra-vital microscopy (IVM) has been established to evaluate the behavior of the alveolar tissue. To allow profound qualitative and quantitative conclusions, characteristic features of the obtained images have to be thoroughly understood. These factors are strongly influenced by the imaging setup and physiological condition of the lung. To circumvent misinterpretations, a ray-tracing approach has been applied in this study using an idealized geometry of the mouse lung parenchyma deduced from optical coherence tomography (OCT) as a complementary imaging technique. Basic features of IVM images are double ring structures and disappearing of alveoli related to liquid infiltration. Ray propagation analysis reveals the formation of these features by two major reflection processes: partial reflection and total internal reflection. The results give rise to quantification errors of the alveolar area related to reflexes misinterpreted as alveolar borders and should further be used to yield a correction factor for future IVM lung tissue studies.