Optimizing Xenon 129 Ventilation MRI in Cystic Fibrosis with Spiral Imaging and Flip-Angle Correction.

Purpose To implement and evaluate two-dimensional spiral hyperpolarized xenon 129 (¹²⁹Xe) ventilation MRI with flip-angle (FA) correction, as compared with conventional N4ITK (N4) correction, in healthy individuals and those with cystic fibrosis (CF). Materials and Methods In this prospective study, participants with mild CF and age-matched healthy control participants underwent ¹²⁹Xe ventilation MRI using both rapid spiral (approximately 3 seconds) and conventional Cartesian (approximately 10 seconds) acquisitions. Images were corrected using N4 bias correction, and ventilation defect percentage (VDP) was calculated using median-anchored generalized linear binning (mGLB). Separately, B₁ inhomogeneities in spiral images were FA-corrected and analyzed using mGLB. Gravitational gradients in ventilation were quantified from uncorrected and N4- and FA-corrected images in healthy participants. VDP from N4-corrected (VDP_N4) and FA-corrected (VDP_FA) images were compared between participant groups and against reader-segmented VDP (VDP_RS). Statistical analyses included Wilcoxon signed rank test, Pearson correlation, and Bland-Altman analysis. Results The final analysis included 38 participants with CF (mean age, 16 years ± 6 [SD]; 20 female) and 25 healthy controls (mean age, 18 years ± 7; 13 male). Qualitatively, Cartesian and spiral acquisitions produced similar regional ventilation images. There was no evidence of a difference in VDP_N4 between acquisition types (Cartesian = 9.1% ± 8.1; spiral = 9.3% ± 8.7; P = .97) with strong correlation (r² = 0.95; P < .001) and no systemic bias (mean difference, -0.2%; 95% CI: 3.6, -3.9). FA correction removed coil-related inhomogeneities while preserving physiologic heterogeneity, including gravitational gradients that were removed by N4 correction (mean slope in healthy participants: FA-corrected = 0.026 S_Norm/cm ± 0.013; N4-corrected = 0.002 S_Norm/cm ± 0.001; P < .001). VDP_N4 and VDP_FA were strongly correlated with VDP_RS (r² = 0.94 and 0.95, respectively; P < .001 for both). Defect masks from FA-corrected images showed better agreement with reader segmentations compared with N4-corrected image-based defect masks (17% higher Dice score from FA-corrected images; mean Dice score: N4-corrected, 0.41 ± 0.31; FA-corrected, 0.48 ± 0.29; P =.001) and better depicted regional hypo- and hyperventilation. Conclusion Two-dimensional spiral acquisition combined with FA correction and mGLB analysis enabled rapid ¹²⁹Xe ventilation MRI, effectively mitigating inhomogeneities while preserving physiologic heterogeneity. This approach provided accurate and efficient quantification of ventilation abnormalities in both healthy individuals and individuals with CF. Keywords: MRI, Pulmonary, Lung, Xenon, Ventilation Supplemental material is available for this article. © RSNA, 2025.