Fetal sheep with tracheal occlusion: monitoring lung development with MR imaging and B-mode US

PURPOSE: To assess the accuracy of magnetic resonance (MR) imaging in determining fetal lung volume (FLV) and to observe fetal lung development with B-mode ultrasonography (US) and MR imaging. MATERIALS AND METHODS: Seven sheep fetuses between 92 and 141 gestational days (term, 145 days) with and without tracheal occlusion (controls) underwent serial MR imaging and US. FLV at MR imaging was measured with true fast imaging with steady-state precession in coronal and transverse planes. The combined cross-sectional left- and right-lung area was measured with US at three transverse levels. FLV was measured at autopsy. Statistical evaluations included linear regression analysis and calculation of the mean and 95% CI. RESULTS: No differences in FLV were observed on coronal or transverse MR images (r2 = 0.98; slope = 0.91; 95% CI: 0.82, 1.01). FLV at MR imaging at termination of the experiment was significantly related to FLV at autopsy (r2 = 0.96; slope = 1.27; 95% CI: 0.97, 1.57; n = 6). FLV at MR imaging increased more rapidly with gestational age in fetuses with tracheal occlusion (21.0 mL/d; 95% CI: 10.7, 31.3) than in controls (4.7 mL/d; 95% CI: 1.7, 7.7). Increase in left- and right-lung area at US was accelerated in fetuses with tracheal occlusion (1.60 cm2/d; 95% CI: 1.3, 1.9) compared with controls (0.38 cm2/d; 95% CI: 0.23, 0.53). Left- and right-lung area at US and FLV at MR imaging were significantly correlated (r2 = 0.82). CONCLUSION: FLV can be measured with moderate accuracy at MR imaging on both coronal and transverse images. MR imaging and B-mode US are useful tools for monitoring and quantifying tracheal occlusion-stimulated fetal lung growth in sheep fetuses.