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Purpose To test the feasibility of 3D phase‐resolved functional lung (PREFUL) MRI in healthy volunteers and patients with chronic pulmonary disease, to compare 3D to 2D PREFUL, and to investigate the required temporal resolution to obtain stable 3D PREFUL measurement. Methods Sixteen participants underwent MRI using 2D and 3D PREFUL. Retrospectively, the spatial resolution of 3D PREFUL (4 × 4 × 4 mm3) was decreased to match the spatial resolution of 2D PREFUL (4 × 4 × 15 mm3), abbreviated as 3Dlowres. In addition to regional ventilation (RVent), flow‐volume loops were computed and rated by a cross‐correlation (CC). Ventilation defect percentage (VDP) maps were obtained. RVent, CC, VDPRVent, and VDPCC were compared for systematic differences between 2D, 3Dlowres, and 3D PREFUL. Dividing the 3D PREFUL data into 4‐ (≈ 20 phases), 8‐ (≈ 40 phases), and 12‐min (≈ 60 phases) acquisition pieces, the ventilation parameter maps, including the heterogeneity of ventilation time to peak, were tested regarding the required temporal resolution. Results RVent, CC, VDPRVent, and VDPCC presented significant correlations between 2D and 3D PREFUL (r = 0.64‐0.94). CC and VDPCC of 2D and 3Dlowres PREFUL were significantly different (P < .0113). Comparing 3Dlowres and 3D PREFUL, all parameters were found to be statistically different (P < .0045). Conclusion 3D PREFUL MRI depicts the whole lung volume and breathing cycle with superior image resolution and with likely more precision compared to 2D PREFUL. Furthermore, 3D PREFUL is more sensitive to detect regions of hypoventilation and ventilation heterogeneity compared to 3Dlowres PREFUL, which is important for early detection and improved monitoring of patients with chronic lung disease.

Background Regional flow volume loop ventilation‐weighted noncontrast‐enhanced proton lung MRI in free breathing has emerged as a novel technique for assessment of regional lung ventilation, but has yet not been validated with 129Xenon MRI (129Xe‐MRI), a direct visualization of ventilation in healthy volunteers, cystic fibrosis (CF), and chronic obstructive pulmonary disease (COPD) patients. Purpose To compare regional ventilation and regional flow volume loops measured by noncontrast‐enhanced ventilation‐weighted phase‐resolved functional lung MRI (PREFUL‐MRI) with 129Xe‐MRI ventilation imaging and with lung function test parameters. Study Type Retrospective study. Population Twenty patients with COPD, eight patients with CF, and six healthy volunteers. Field Strength/Sequence PREFUL and 129Xe‐MRI gradient echo sequences were acquired at 1.5T. Assessment Coronal slices of PREFUL‐MRI (free breathing) and 129Xe‐MRI (single breath‐hold) were acquired on the same day, matched by their ventrodorsal position and coregistered for evaluation. Ventilation defect percentage (VDP) was calculated based on regional ventilation (RV), regional flow volume loops (RFVL), or 129Xe‐MRI with two different threshold methods. A combined VDP was calculated for RV and RFVL. Additionally, lung function testing was performed (such as the forced expiratory volume in 1 second [FEV1]) was used. Statistical Tests The obtained parameters were compared using Wilcoxon tests, correlated using Spearman's correlation coefficient (r), and agreement between PREFUL and 129Xe‐MRI parameters was assessed using Bland–Altman analysis and Dice coefficients. Results VDP measured by PREFUL and 129Xe were significantly correlated with both thresholding techniques (r = 0.62–0.69, P < 0.05 for all) and with lung function test parameters. Combined RV and RFVL PREFUL defect maps correlated with lung function testing (eg, with FEV1 r = –0.87 P < 0.05), and showed better regional agreement to 129Xe‐MRI ventilation defects (Dice coefficient defect 0.413) with significantly higher VDP values (10.2 ± 27.3, P = 0.04) than either PREFUL defect map alone. Data Conclusion Combined RV and RFVL PREFUL defect maps likely increase sensitivity to mild airway obstruction with increased VDP values compared to 129Xe‐MRI, and correlate strongly with lung function test parameters. Level of Evidence 3 Technical Efficacy Stage 2

Lung diseases have a high prevalence amongst the world population and their early diagnosis has been pointed out to be key for successful treatment. However, there is still a lack of non-invasive examination methods with sensitivity to early, local deterioration of lung function. Proton-based lung MRI is particularly challenging due to short T times and low proton density within the lung tissue. Hyperpolarized gas MRI is aan emerging technology providing a richness of methodologies which overcome the aforementioned problems. Unlike proton-based MRI, lung MRI of hyperpolarized gases may rely on imaging of spins in the lung's gas spaces or inside the lung tissue and thereby add substantial value and diagnostic potential to lung MRI. This review article gives an introduction to the MR physics of hyperpolarized media and presents the current state of hyperpolarized gas MRI of Headvasd andXe in pulmonology. Key applications, ranging from static and dynamic ventilation imaging as well as oxygen-pressure mapping to Xe dissolved-phase imaging and spectroscopy are presented. Hyperpolarized gas MRI is compared to alternative examination methods based on MRI and future directions of hyperpolarized gas MRI are discussed.