Measurement of lung water content and pleural pressure gradient with magnetic resonance imaging

The aim of this study was to develop a magnetic resonance (MR) sequence capable of measuring water content and the gravity-dependent gradient in lung density in normal lung. First, the MR signal from excised normal pig lung was characterized using a 2.1 T nuclear magnetic resonance (NMR) spectrometer. A multiecho sequence was then developed on a 0.15 T Picker MR scanner. This sequence was validated in excised normal pig lung by comparison with gravimetric lung water content. Finally, this sequence was used in five normal volunteers in the prone and supine positions during quiet breathing and in the supine position at total lung capacity (TLC). The ratio of lung water measured by MR and gravimetric techniques was 0.95 +/- 0.03. There was no significant difference in average lung density in the prone (0.21 +/- 0.03 g/ml) and in the supine (0.20 +/- 0.03 g/ml) positions. Lung density decreased at TLC (0.12 +/- 0.01 g/ml) (p < 0.01). Gradients in lung density were visible in all prone and supine scans at functional residual capacity (FRC), and on average the gradients were decreased by 90% at TLC. The average estimated pleural pressure gradient in the prone position was 0.13 +/- 0.08 cm H2O/cm lung and in the supine position was 0.38 +/- 0.23 cm H2O/cm lung. MRI allows measurement of lung water content and pleural pressure gradient.