Intravoxel incoherent motion MRI to assess feto-placental diffusion and perfusion properties in small fetuses

To investigate the use of intravoxel incoherent motion (IVIM) to study microperfusion and microstructural characteristics of lungs, brain, and placenta in normal and small fetuses.

We retrospectively enrolled 30 small fetuses and 82 normal pregnancies who underwent a 1.5-T MRI examination using an IVIM-DWI. Small fetuses were distinguished in small for gestational age (SGA) and "true" fetal growth restriction (FGR). ROIs were placed on the brain parenchyma, lungs, and fetal/maternal placental sides. Differences in perfusion fraction f, diffusion coefficient D, and pseudo-diffusion coefficient D* and their correlation with gestational age (GA) and birth weight (BW) were investigated.

LUNG: f showed significantly lower values (p = 2·10^-7) in small fetuses (SGA + FGR); f discriminates SGA and FGR from normal (p = 0.001; p = 1·10^-6). f increases with GA (p < 0.0001) in the control group; a positive correlation was also obtained in small fetuses, although less significant.

FGR showed lower f values than normal ones, in both the fetal (p = 1.4·10^-7) and maternal side (p = 0.001); f discriminates between SGA and FGR (p = 0.03). In small fetuses (SGA + FGR), f correlates positively with BW.

D values in supratentorial white matter (WM) were significantly higher compared to other regions, in both normal and small fetuses. Small fetuses showed higher D values in occipital WM and pons (p = 0.041; p = 0.027) than in normal. D correlates negatively with GA in the healthy group. No correlation between D and GA was found in SGA + FGR group.

In our study, IVIM-MRI allowed us to detect microstructural and microperfusion changes in the placenta, brain, and lung of small fetuses, noninvasively.