Three-Dimensional Free-Breathing Ultrashort Echo Time (UTE) 1H MRI Regional Ventilation: Comparison With Hyperpolarized 129Xe MRI and Pulmonary Function Testing in Healthy Volunteers and People With Cystic Fibrosis

Abstract

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.

Keywords: 1H ventilation; UTE; hyperpolarized 129Xe.