SU-E-T-511: Distribution of Hysteresis Magnitude during Free Breathing

Abstract

Purpose: To characterize and quantify the hysteresis motion component distribution during free breathing. Methods: We have hypothesized that lung tissue motion can be represented as a linear combination of two components: due to volume filling and due to hysteresis. Lung tissue trajectories were calculated using an existing 5D lung tissue trajectory model that uses two vector fields, alpha and beta, which were previously determined. Physically, the alpha motion vector was the tissue‐specific volume filling component and beta was the tissue‐specific hysteresis component. Due to natural variations in breathing patterns, we developed the concept of a characteristic breath. Each breath was corrected with a linear drift model from exhalation to exhalation. In order to characterize the hysteresis motion, the ratio of the volume filling to hysteresis components was examined throughout the subject's lungs by generating a bounding box with one side parallel to the alpha vector and the box lying in the plane defined by the alpha and beta vectors. The lungs were subdivided into geographic quadrants to observe the variation of the bounding box elongation. Because the displacement varied, the 15th and 85th percentile tidal volume displacements were selected to define the range of analyzed displacements. This study utilized 50 subject data sets from a 16 slice CT scanner. Results: The 15th and 85th percentile bounding box elongations were 0.090±0.005 and 0.187±0.037, and 0.083±0.013 and 0.203±0.053, in the upper and lower left lung and 0.092±0.006 and 0.184±0.038, and 0.085±0.013 and 0.196±0.043, in the upper and lower right lung, respectively, for volume displacements between 5–15mm. Conclusion: Hysteresis motion was relatively small compared to the volume‐filling motion, contributing between 8% and 20% of the overall motion. Little difference in this range was observed for upper and lower lung regions. This work supported in part by NIHR01CA116712 and NIHR01CA96679.