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Purpose\ud Imaging of the different resonances of dissolved hyperpolarized xenon‐129 (129Xe) in the lung is performed using a four‐echo flyback 3D radial spectroscopic imaging technique and is evaluated in healthy volunteers (HV) and subjects with idiopathic pulmonary fibrosis (IPF).\ud \ud Theory and Methods\ud 10 HV and 25 subjects with IPF underwent dissolved 129Xe MRI at 1.5T. IPF subjects underwent same day pulmonary function tests to measure forced vital capacity and the diffusion capacity of the lung for carbon monoxide (DLCO). A four‐point echo time technique with k‐space chemical‐shift modeling of gas, dissolved 129Xe in lung tissue/plasma (TP) and red blood cells (RBC) combined with a 3D radial trajectory was implemented within a 14‐s breath‐hold.\ud \ud Results\ud Results show an excellent chemical shift separation of the dissolved 129Xe compartments and gas contamination removal, confirmed by a strong agreement between average imaging and global spectroscopy RBC/TP ratio measurements. Subjects with IPF exhibited reduced imaging gas transfer when compared to HV. A significant increase of the amplitude of RBC signal cardiogenic oscillation was also observed. In IPF subjects, DLCO% predicted was significantly correlated with RBC/TP and RBC/GAS ratios and the correlations were stronger in the inferior and periphery sections of the lungs.\ud \ud Conclusion\ud Lung MRI of dissolved 129Xe was performed with a four‐echo spectroscopic imaging method. Subjects with IPF demonstrated reduced xenon imaging gas transfer and increased cardiogenic modulation of dissolved xenon signal in the RBCs when compared to HV.

Background\ud MRI with inhaled hyperpolarized helium 3 (3He) allows for functional and structural imaging of the lungs. Hyperpolarized gas diffusion-weighted (DW) MRI provides noninvasive and quantitative assessment of microstructural acinar changes in the lungs.\ud \ud Purpose\ud To investigate whether microstructural imaging metrics from in-vivo hyperpolarized 3He DW MRI are sensitive to longitudinal changes in a cohort of participants with idiopathic pulmonary fibrosis (IPF) and to evaluate the reproducibility of these metrics and their correlation with existing clinical measures of IPF disease severity.\ud \ud Materials and Methods\ud In this prospective study, 18 participants with IPF underwent 3He DW MRI at 1.5 T and 11 participants underwent an identical same-day examination for reproducibility assessment. Thirteen participants returned for 6- and 12-month follow-up examinations. Pulmonary function tests, including diffusing capacity of the lungs for carbon monoxide and forced vital capacity, were performed at each examination. The apparent diffusion coefficient (ADC) and stretched exponential model–derived mean diffusive length scale (LmD) from DW MRI was compared with baseline CT fibrosis scores and pulmonary function tests by using Spearman rank correlation coefficient. Longitudinal changes in DW MRI and pulmonary function test measurements were assessed with Friedman tests and post hoc Dunn test.\ud \ud Results\ud 3He ADC and LmD were reproducible (mean Bland-Altman analysis bias, 0.002 cm2 · sec-1 and −1.5 μm, respectively). Elevated ADC and LmD regions qualitatively corresponded to fibrotic regions at CT. ADC and LmD correlated with diffusing capacity of the lungs for carbon monoxide (respectively: r = −0.56, P = .017; and r = −0.54, P = .02) and CT fibrosis score (respectively: r = 0.71, P = .001; and r = 0.65, P = .003). LmD increased by 12 μm after 12 months (P = .001) whereas mean ADC (P = .17), forced vital capacity (P = .12), and diffusing capacity of the lungs for carbon monoxide (P > .99) were not statistically different between examinations.\ud \ud Conclusion\ud Helium 3 diffusion-weighted MRI-derived mean diffusive length scale demonstrates longitudinal changes in lungs affected by idiopathic pulmonary fibrosis.

Purpose\ud To compare in vivo lung morphometry parameters derived from theoretical gas diffusion models, the cylinder model and stretched exponential model, in a range of acinar microstructural length scales encountered in healthy and diseased lungs with 3He and 129Xe diffusion‐weighted MRI.\ud \ud Methods\ud Three‐dimensional multiple b‐value 3He and 129Xe diffusion‐weighted MRI was acquired with compressed sensing at 1.5 T from 51 and 31 subjects, respectively, including healthy volunteers, ex‐smokers, idiopathic pulmonary fibrosis, and chronic obstructive pulmonary disease patients. For each subject, the stretched exponential model–derived mean diffusive length scale (LmD) was calculated from the diffusion signal decay, and was compared with the cylinder model–derived mean chord length (Lm) and mean alveolar diameter (LAlv) in order to determine the relationships among the different lung morphometry parameters.\ud \ud Results\ud For both 3He and 129Xe diffusion‐weighted MRI, the mean global LmD value was significantly related (P < .001) to Lm in a nonlinear power relationship, whereas the LAlv demonstrated excellent linear correlation (P < .001) with LmD. A mean bias of +1.0% and urn:x-wiley:07403194:media:mrm27608:mrm27608-math-00012.6% toward LmD was obtained for Bland‐Altman analyses of 3He and 129Xe LmD and LAlv values, suggesting that the two morphometric parameters are equivalent measures of mean acinar dimensions.\ud \ud Conclusion\ud Within the experimental range of parameters considered here for both 3He and 129Xe, the stretched exponential model–derived LmD is related nonlinearly to cylinder model–derived Lm, and demonstrates excellent agreement with the cylinder model–derived LAlv.

Purpose: It is postulated that ILD causes PA dilatation independent of the presence of pulmonary hypertension (PH), so the use of PA size to screen for PH is not recommended. The aims of this study were to investigate the association of PA size with the presence and severity of ILD and to assess the diagnostic accuracy of PA size for detecting PH.\ud Methods: Incident patients referred to a tertiary PH centre underwent baseline thoracic CT, MRI and right heart catheterisation (RHC). Pulmonary artery diameter was measured on CT pulmonary angiography and pulmonary arterial areas on MRI. A thoracic radiologist scored the severity of ILD on CT from 0 to 4, 0 = absent, 1 = 1–25%, 2 = 26–50%, 3 = 51–75%, and 4 = 76–100% extent of involvement. Receiver operating characteristic analysis and linear regression were employed to assess diagnostic accuracy and independent associations of PA size.\ud Results: 110 had suspected PH due to ILD (age 65 years (SD 13), M:F 37:73) and 379 had suspected PH without ILD (age 64 years (SD 13), M:F 161:218). CT derived main PA diameter was accurate for detection of PH in patients both with and without ILD - AUC 0.873, p =< 0.001, and AUC 0.835, p =< 0.001, respectively, as was MRI diastolic PA area, AUC 0.897, p =< 0.001, and AUC 0.857, p =< 0.001, respectively Significant correlations were identified between mean pulmonary arterial pressure (mPAP) and PA diameter in ILD (r = 0.608, p < 0.001), and non-ILD cohort (r = 0.426, p < 0.001). PA size was independently associated with mPAP (p < 0.001) and BSA (p = 0.001), but not with forced vital capacity % predicted (p = 0.597), Transfer factor of the lungs for carbon monoxide (TLCO) % predicted (p = 0.321) or the presence of ILD on CT (p = 0.905). The severity of ILD was not associated with pulmonary artery dilatation (r = 0.071, p = 0.459).\ud Conclusions: Pulmonary arterial pressure elevation leads to pulmonary arterial dilation, which is not independently influenced by the presence or severity of ILD measured by FVC, TLCO, or disease severity on CT. Pulmonary arterial diameter has diagnostic value in patients with or without ILD and suspected PH.