Room: Karl Dean Ballroom C
Purpose: Lung ventilation has been investigated as a metric for functional avoidance treatment planning and treatment response assessment. This study aims to also investigate lung strain as an additional metric to assess respiratory mechanics, and compare both metricsâ€™ sensitivity to changes in displacement vector fields using Hyperpolarized He-3 tagging Magnetic Resonance Imaging (MRI) data.
Methods: Lung images for three healthy subjects were acquired using a tagging Hyperpolarized Helium-3 MRI technique at both end-of-inhalation (EOI) and end-of-exhalation (EOE) phases. The center of mass of the tagged grids were tracked to obtain a sparse physiologically-based displacement vector field (DVF) between EOI and EOE phases. The DVF for the whole lung area was estimated through a cubic interpolation method of the sparse tagging DVF. Ventilation maps for all three subjects were generated through the Jacobian of the interpolated DVF. The principal strain maps were also computed at each voxel. Uniform and randomly distributed modifications were made to each subjectâ€™s DVFs and the modified strain and ventilation maps were compared to those generated from the original DVFs to assess their response and sensitivity to these changes.
Results: For uniform changes in DVF magnitude, the mean of the absolute percent differences within the lungs between original vs. modified ventilation maps ranged from 49.5-257.1% on average for all 3 subjects compared to 30.6-125.8% for the principal strain maps; average standard deviations were in the ranges of 21.3-135.0%, 3.6-9.7% respectively. For randomly distributed modifications to the DVF, the mean of absolute percent differences between ventilation maps were in the range of 712.0-2743.7% and 115.2-299.0% for principal strain, with standard deviations ranging from 235.9-1517.8% and 35.6-368.6% respectively.
Conclusion: Preliminary results suggest that ventilation might be a more sensitive metric to deformation changes compared to strain, showing larger mean absolute percent differences and standard deviations among all three subjects.
Funding Support, Disclosures, and Conflict of Interest: NIH grant: R21CA195317
Ventilation/perfusion, MRI, Deformation
IM/TH- MRI in Radiation Therapy: Development (new technology and techniques)