Three-Dimensional Free-Breathing Ultrashort Echo Time (UTE) ¹H MRI Regional Ventilation: Comparison With...

MRI can provide localized assessment of lung function for monitoring people with lung disease. Hyperpolarized ¹²⁹Xe MRI directly images pulmonary gas distribution but requires specialized hardware. Conventional ¹H MRI acquisitions can also provide functional maps using free-breathing approaches. The purpose of this study is to evaluate regional ventilation derived from 3D ultrashort echo-time (UTE) ¹H MRI using Motion-Compensated Low-Rank constrained reconstruction (MoCoLoR), by comparing against ¹²⁹Xe MRI and pulmonary function testing as reference-standard. The study is retrospective in design. The study included 57 participants (25.4 ± 15.8 years, 35 males and 22 females): 12 healthy volunteers, 20 pediatric, and 25 adult people with cystic fibrosis (CF) scanned between January 2022 and February 2023. Field strength/sequence: 3T; ¹²⁹Xe: 2D multislice spoiled gradient-recalled sequence; UTE ¹H: variable-density 3D radial sequence. K-means-based ¹²⁹Xe ventilation defect percent (VDP), forced expiratory volume in 1 s (FEV₁), and lung clearance index (LCI) were evaluated against UTE ¹H VDP from a modified k-means method. The correspondence of ventilation defect maps from ¹²⁹Xe and UTE ¹H was also evaluated. Statistical tests included the Pearson correlation coefficient (r) and t tests, with p < 0.05 considered significant. ¹²⁹Xe and UTE ¹H VDP were significantly correlated (r = 0.64, p =  $9.1\times {10}^{-8}$ ). Bland-Altman analysis showed a bias of -0.05 (p =  $7.2\times {10}^{-5}$ ) and limits of agreement of (0.07, -0.17). The Dice spatial accuracy of the UTE-based ventilation defect regions using ¹²⁹Xe as reference was 0.64 ± 0.05. UTE ¹H VDP was significantly correlated with FEV₁ (r = -0.54, p =  $2.9\times {10}^{-4}$ ) and LCI (r = 0.48, p =  $5.9\times {10}^{-3}$ ) and was significantly different between healthy and CF participants (p = 0.017), although the correlations and differences were stronger for ¹²⁹Xe VDP. UTE ¹H VDP correlated with ¹²⁹Xe VDP, FEV₁, and LCI, and demonstrated high, consistent Dice spatial accuracy against ¹²⁹Xe VDP. UTE ¹H VDP captured variations in lung ventilation and has the advantage that it can be widely implemented on any MR system for evaluation and monitoring of patients with lung disease.