Lung Volume Correction Increases Repeatability of 129Xe Gas Exchange MRI in IPF
Mchorse, A; Swaminathan, AC; Tighe, RM; Driehuys, B; Mummy, D
Published in: American Journal of Respiratory and Critical Care Medicine
RATIONALE:A range of hyperpolarized 129Xe gas exchange MRI markers have been proposed to assess disease progression and therapy response in diverse cardiopulmonary conditions, including COPD and types of ILD. However, variation in the breath hold maneuver is known to affect these markers. In particular, reduced lung inflation volume during the breath hold leads to higher signal from the membrane tissue as found by Garrison (2023). This variability complicates the ability to differentiate between measurement variability and true disease progression. Here, we implement a volume correction method for 129Xe membrane signal in patients with idiopathic pulmonary fibrosis (IPF). METHODS: Subjects (N=29) diagnosed with IPF who had not begun treatment underwent repeated hyperpolarized 129Xe gas exchange MRI. Images were acquired during a single breath-hold decomposed using the 1-point Dixon method into 3D isotropic images of the ventilation, interstitial membrane, and red blood cell compartments. Using the methods outlined by Garrison, the membrane to gas ratio (M:Gas) from the second scan was corrected to the lung inflation of the first. Agreement between repeated measurements was assessed using Bland-Altman analysis, calculating mean differences, 95% limits of agreement, and repeatability coefficients. RESULTS: Example images from repeated scans of a single subject are shown in Figure 1. Bland-Altman analysis showed that the inter-scan difference in mean M:Gas was reduced by 35% after applying the correction. The repeatability coefficient improved from 0.0055 to 0.0036 with volume correction, suggesting that, after lung volume correction, a M:Gas difference exceeding 0.0036 represents true physiological changes rather than measurement variability. Prior to correction, ten subjects showed M:Gas differences exceeding 25% between scans (mean difference 42%). After correction, only five subjects exhibited differences of that magnitude (mean difference 33%). CONCLUSION:Volume-based correction of membrane signal improved measurement repeatability of 129Xe gas exchange MRI in IPF patients. While overall improvement in repeatability metrics was modest, the method was particularly useful in reducing variability in cases with large lung volume differences between scans as shown in Figure 1. These findings underscore the importance of lung volume correction in longitudinal 129Xe MRI studies to enhance measurement reliability. Ongoing research in our laboratory aims to validate these findings in a broader patient population and develop strategies to distinguish volume-related variations from true therapeutic responses.
