Assessment of Regional Ventilation by Hyperpolarized 129Xe MRI in Patients With Idiopathic Pulmonary Fibrosis and Asthma

Rationale: Pulmonary ventilation distribution is heterogeneous in health individuals, and it may worsen in lung diseases. Hyperpolarized 129Xe MRI is a novel technique that can be used to quantify ventilation heterogeneity. In this study, we compared ventilation distributions between healthy individuals and patients with idiopathic pulmonary fibrosis (IPF) and asthma. Ventilation distribution was assessed by differences in ventilation (ΔV̇) between basal and apical compartments (ΔV̇B-A) and between posterior and anterior compartments (ΔV̇P-A). We tested the hypothesis that ventilation distribution in these patients would be worse than that in healthy controls. Methods: Participants inhaled hyperpolarized 129Xe from functional residual capacity in the supine position, and 3D MRI ventilation images were obtained during a 10-second breath hold. The imaging data were analyzed with the N4ITK bias correction method to calculate ventilation defect percentage (VDP) (Acad Radiol.2016;23:1521). Because the N4ITK method corrects intensity inhomogeneity, we also analyzed the imaging data using the radiofrequency (RF) bias-field correction method that better preserves such inhomogeneity. We divided the lung regions in the apical-basal and the anterior-posterior directions into tertiles (apical/middle/basal compartments and anterior/middle/posterior compartments respectively) and averaged the ventilation signals within the compartment. We calculated ΔV̇B-A and ΔV̇P-A). We compared ΔV̇B-A and ΔV̇P-A between the groups using an unpaired t-test. Results: We included 20 healthy controls (age:42.4±20.5 years), 30 IPF (age:74.4±5.5 years) and 10 asthma patients (age:40.4±10.0 years). VDP in controls, IPF and asthma patients were 2.22±1.82%, 7.33±6.74% and 2.59±2.90% respectively. As expected, healthy controls had greater ventilation in the basal compartment (ΔV̇B-A=0.16±0.16) and the posterior compartment (ΔV̇P-A=0.10±0.12). In IPF patients, 25 had apical-basal and anterior-posterior ventilation distributions like the controls (ΔV̇B-A=0.17±0.08; ΔV̇P-A=0.11±0.07 respectively). Five patients had less ventilation in the posterior compartment (ΔV̇P-A=-0.17±0.09, p<0.0001 vs. controls). Of these, three also had less ventilation in the basal compartment (ΔV̇B-A=-0.04±0.01, p=0.049 vs. healthy controls). In asthma patients, 6 had anterior-posterior ventilation distributions (ΔV̇P-A=0.13±0.08) like the controls. Four patients showed less ventilation in the posterior compartment (ΔV̇P-A=-0.11±0.15, p=0.0003 vs. controls). Of these, 2 also had less ventilation in the basal compartment (ΔV̇B-A= -0.17 and -0.09). MRI images from an IPF patient and an asthma patient who had abnormal ΔV̇P-A are shown in the Figure. Conclusions. With hyperpolarized 129Xe MRI, we identified a subgroup of patients with IPF and asthma with abnormal apical-posterior and/or anterior-posterior ventilation distribution patterns, despite low VDP. These abnormal ventilation patterns may represent different phenotypes, or severities, and deserve further studies.

Duke Scholars

Author Yuh-Chin Tony Huang Medicine, Pulmonary, Allergy, and Critical Care Medicine

Author Robert Matthew Tighe Medicine, Pulmonary, Allergy, and Critical Care Medicine