The mechanics of lung deformation is traditionally assessed at a whole-lung or lobar level. We submit that key aspects of lung mechanics maybe better understood by studying regional patterns of lung deformation by leveraging recent developments in tomographic imaging and image processing techniques. Our group has developed an inverse consistent registration technique for estimating local displacement distributions from paired lung CT volumes [1,2]. This facilitates the estimation of strain distributions and consequently, the regional patterns in volume change and its preferential directionalities (anisotropy in deformation). In this study, we use this novel method to compare regional deformation in the lungs between static and dynamic inflations in an adult sheep. Much of our research has focused on registration of static lung images at different positive end-expiratory pressures (PEEP). More recently, respiratory-gated CT scans of supine, positive-pressure inflated sheep lungs have been gathered in order to compare the displacement fields of a dynamically inflating lung to the static lung scans. The theory is that scanning a dynamically inflating lung will more accurately reflect natural deformation during breathing by realizing time-dependent mechanical properties (viscoelasticity). The downside to human dynamic lung imaging is the increased radiation dose necessary to acquire the image data across the respiratory cycle, though low-dose CT scans are an option [3]. This experiment observed the difference in strain distribution between dynamically inflated lungs versus static apneic lungs using the inverse consistent image registration developed in our lab.

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