Pulmonary Ventilation Analysis Using¹H Ultra-Short Echo Time (UTE) Lung MRI: A Reproducibility Study

Purpose: To evaluate methods for quantification of pulmonary ventilation with ultrashort echo time (UTE) MRI. Methods: We performed a reproducibility study, acquiring two free-breathing 1H UTE lung MRIs on the same day for six healthy volunteers. The 1) 3D + t cyclic b-spline and 2) symmetric image normalization (SyN) methods for image registration were applied after respiratory phase-resolved image reconstruction. Ventilation maps were calculated using 1) Jacobian determinant of the deformation fields minus one, termed regional ventilation, and 2) intensity percentage difference between the registered and fixed image, termed specific ventilation. We compared the reproducibility of all four method combinations via statistical analysis. Results: Split violin plots and Bland-Altman plots are shown for whole lungs and lung sections. The cyclic b-spline registration and Jacobian determinant regional ventilation quantification provide total ventilation volumes that match the segmentation tidal volume, smooth and uniform ventilation maps. The cyclic b-spline registration and specific ventilation combination yields the smallest standard deviation in the Bland-Altman plot. Conclusion: Cyclic registration performs better than SyN for respiratory phase-resolved 1H UTE MRI ventilation quantification. Regional ventilation correlates better with segmentation lung volume, while specific ventilation is more reproducible.