Repeatability of129Xe MR methods for quantification of interstitial thickness

Introduction:129Xe chemical shift saturation recovery (CSSR) MR enables quantification of pulmonary gas exchange (e.g. interstitial thickening in idiopathic pulmonary fibrosis (IPF)). The repeatability of this technique is yet to be assessed and is critical for future application of the method as a quantitative outcome measure for IPF treatments. Objective: To assess the intra-subject repeatability of the 129Xe CSSR method. Methods: Five healthy volunteers (24-63 yrs) were scanned on three separate dates using 129Xe CSSR MR. Data were fitted with diffusion models to estimate alveolar septal thickness (ST), surface-area-to-volume ratio (S/V) and capillary transit time (CTT). The intra-subject standard deviation (SD) and “repeatability coefficient”, R = 1.96 x 21/2 x SD, between scans were calculated for each parameter. Results: The mean intra-subject SD of CSSR-derived ST values (0.45 µm) and associated R coefficient (1.24 µm) were considerably less than the ST difference between normals and IPF patients (∼ 7 µm [Stewart et al., MRM, 2014]). However, R coefficients of derived S/V and CTT values were of similar order to the parameters themselves. Conclusions:129Xe CSSR is a repeatable method for quantification of alveolar septal thickness and may be sufficiently sensitive to assess early changes in interstitial thickness in IPF or as an outcome measure in response to anti-fibrotic treatment.