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

Fetal lung development is a complex and continuous process involving the progressive maturation of multiple structural and functional aspects. From early embryonic stages through birth, the fetal lung transforms primitive alveoli into mature lung tissue, progressing through four main stages: pseudoglandular, canalicular, saccular, and alveolar. Accurate assessment of fetal lung developmental stages is essential for fetal health management.

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 assess whether DTI measurements can be used as markers of fetal lung development.

DTI of normal fetal lungs was performed on Eighty-four pregnant women at a gestational age of 18-36 weeks. Regions of interest for both liver and lung were drawn on the b=0 images to obtain the lung-to-liver signal intensity ratio, and 3D segmentation was used to measure fetal lung volume. At the same time, DTI-related indices, fractional anisotropy (FA), and mean diffusivity were derived. Using regression analysis, DTI measurements, lung-to-liver signal intensity ratio, and fetal lung volume were correlated with gestational age.

Thirty-two patients were excluded due to fetal motion artifacts during DTI imaging. The remaining 52 patients (61.9%) were analyzed for DTI indices. For the left, right, and both lungs, respectively, FA (r=-0.70; r=-0.71; r=-0.71; all P<0.01), mean diffusivity (r=0.58; r=0.49; r=0.57, all P<0.01), lung-to-liver signal intensity ratio (r=0.61; r=0.63; r=0.64, all P<0.01) and fetal lung volume (r=0.84; r=0.89; r=0.87, all P<0.01) were significantly correlated with gestational age. FA decreased dramatically before 29 weeks (slope=-0.02; -0.02; -0.02, for the left, right, and both lungs, respectively) but remained stable after 29 weeks (slope=0.003; 0.003; 0.002).

DTI measurements were consistent with microstructural changes in the developing fetal lung. In particular, a dramatic decrease in the FA value may reflect the development from the canalicular to the saccular stage.