Regional lung strains via a volumetric mass conserving optical flow model

The main function of the respiratory system is gas exchange. Since many disease or injury conditions can cause biomechanical or material property changes that can alter lung function, there is great interest in measuring regional lung function and regional mechanical changes. The mechanical properties of lung parenchymal tissue are both elastic and dissipative, as well as being highly nonlinear. A novel lung-specific optical flow energy function for computing motion field from planar CT images was previously proposed. The main advantage of the proposed optical flow framework is the possibility to enforce physical constraints on the numerical solutions. In this paper, a 3-D extension of the aforementioned technique is proposed and the principal tissue strains from the 3-D displacement field are derived. Both the 3-D calculated deformation fields and strains are evaluated on a contracting/expanding simulated sponge volume simulating lung motion and POPI-model data from a human subject.