Free-breathing Pulmonary MR Imaging to Quantify Regional Ventilation

Purpose: To measure regional specific ventilation with free-breathing hydrogen 1 (H-1) magnetic resonance (MR) imaging without exogenous contrast material and to investigate correlations with hyperpolarized helium 3 (He-3) MR imaging and pulmonary function test measurements in healthy volunteers and patients with asthma. Materials and Methods: Subjects underwent free-breathing H-1 and static breath-hold hyperpolarized He-3 MR imaging as well as spirometry and plethysmography; participants were consecutively recruited between January and June 2017. Free-breathing H-1 MR imaging was performed with an optimized balanced steady-state free-precession sequence; images were retrospectively grouped into tidal inspiration or tidal expiration volumes with exponentially weighted phase interpolation. MR imaging volumes were coregistered by using optical flow deformable registration to generate H-1 MR imaging-derived specific ventilation maps. Hyperpolarized He-3 MR imaging- and H-1 MR imaging-derived specific ventilation maps were coregistered to quantify regional specific ventilation within hyperpolarized He-3 MR imaging ventilation masks. Differences between groups were determined with the Mann-Whitney test and relationships were determined with Spearman (rho) correlation coefficients. Statistical analyses were performed with software. Results: Thirty subjects (median age: 50 years; interquartile range [IQR]: 30 years), including 23 with asthma and seven healthy volunteers, were evaluated. Both H-1 MR imaging-derived specific ventilation and hyperpolarized He-3 MR imaging-derived ventilation percentage were significantly greater in healthy volunteers than in patients with asthma (specific ventilation: 0.14 [IQR: 0.05] vs 0.08 [IQR: 0.06], respectively, P < .0001; ventilation percentage: 99% [IQR: 1%] vs 94% [IQR: 5%], P < .0001). For all subjects, H-1 MR imaging-derived specific ventilation correlated with plethysmography-derived specific ventilation (rho = 0.54. P = .002) and hyperpolarized He-3 MR imaging-derived ventilation percentage (rho = 0.67, P < .0001) as well as with forced expiratory volume in 1 second (FEV1) (rho = 0.65, P = .0001), ratio of FEV1 to forced vital capacity (rho = 0.75, P < .0001), ratio of residual volume to total lung capacity (rho = -0.68, P < .0001), and airway resistance (rho = -0.51. P = .004). 1H MR imaging-derived specific ventilation was significantly greater in the gravitational-dependent versus nondependent lung in healthy subjects (P = .02) but not in patients with asthma (P = .1). In patients with asthma, coregistered H-1 MR imaging specific ventilation and hyperpolarized He-3 MR imaging maps showed that specific ventilation was diminished in corresponding He-3 MR imaging ventilation defects (0.05 +/- 0.04) compared with well-ventilated regions (0.09 +/- 0.05) (P < .0001). Conclusion: H-1 MR imaging-derived specific ventilation correlated with plethysmography-derived specific ventilation and ventilation defects seen by using hyperpolarized He-3 MR imaging. (C) RSNA, 2018