Magentic Resonance Imaging Evaluation of Regional Lung VTS in Severe Neonatal Bronchopulmonary Dysplasia

Rationale: Bronchopulmonary dysplasia is a heterogeneous lung disease characterized by regions of cysts and fibrosis, but methods for evaluating lung function are limited to whole lung rather than specific regions of interest. Objectives: Respiratory-gated, ultrashort echo time magnetic resonance imaging was used to test the hypothesis that cystic regions of the lung will exhibit a quantifiable V-T that will correlate with ventilator settings and clinical outcomes. Methods: Magnetic resonance images of 17 nonsedated, quiet-breathing infants with severe bronchopulmonary dysplasia were reconstructed into end-inspiration and end-expiration images. Cysts were identified and measured by using density threshold combined with manual identification and segmentation. Regional V-TS were calculated by subtracting end-expiration from end-inspiration volumes in total lung, noncystic lung, total-cystic lung, and individual large cysts. Measurements and Main Results: Cystic lung areas averaged larger V-TS than noncystic lung when normalized by volume (0.8 ml V-T/ml lung vs. 0.1 ml V-T/ml lung, P<0.002). Cyst V-T correlates with cyst size (P = 0.012 for total lung cyst and P<0.002 for large cysts), although there was variability between individual cyst V-T, with 22% of cysts demonstrating negative V-T. Peak inspiratory pressure positively correlated with total lung V-T (P = 0.027) and noncystic V-T (P = 0.015) but not total lung cyst V-T (P = 0.8). Inspiratory time and respiratory rate did not improve V-T of any analyzed lung region. Conclusions: Cystic lung has greater normalized V-T when compared with noncystic lung. Ventilator pressure increases noncystic lung V-T, but inspiratory time does not correlate with V-T of normal or cystic lung.