Diffusion tensor MR imaging of the normal fetal lung: a preliminary report

Background Fetal lung development is a complex and continuous process involving the progressive maturation of multiple structural and functional aspects. From early embryonic stages to birth, the fetal lung transforms primitive alveoli into mature lung tissue, encompassing four main stages: the canalicular, saccular, canalicular, and alveolar stages. Accurate assessment of fetal lung development stages is essential for the health management of the fetus. Objective this study aims to evaluate the feasibility of magnetic resonance imaging (MRI)-based diffusion tensor imaging (DTI) to assess the normal fetal lung and prospectively determine whether DTI measurements can be used as markers of fetal lung development. Materials and methods Diffusion tensor imaging of normal fetal lungs was performed on 84 pregnant women at a gestational age (GA) of 18–36 weeks. Regions of interest (ROI) for both liver and lung were drawn on the b = 0 images to obtain the lung-to-liver signal intensity ratio (LLSIR), and the 3D segmentation measured the fetal lung volume (FLV). At the same time, DTI-related indices, fractional anisotropy (FA), and mean diffusivity (MD) were derived. Using regression analysis,DTI measurements, LLSIR, and FLV were correlated with gestational age. Results Thirty-two patients were excluded due to fetal motion artifacts during DTI imaging. The remaining 52 patients (61.9%) were analyzed for DTI indices. FA (r = -0.697; r = -0.711; r = -0.711; all P  < 0.001), MD (r = 0.582; r = 0.492; r = 0.567, all P  < 0.001), LLSIR (r = 0.608; r = 0.634; r = 0.637, all P  < 0.001) and FLV (r = 0.838, r = 0.888, r = 0.874, all P  < 0.001) were significantly correlated with gestational age. FA decreased dramatically before 29 weeks (slope = -0.020; -0.023; -0.022) but remained stable after 29 weeks (slope = 0.003; 0.003; 0.002). Conclusions DTI measurements coincided with the microstructural changes of the developing fetal lung. In particular, a dramatic decrease in the FA value may correspond to development from the canalicular to the saccular stage.