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

Objectives: 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.

Methods: 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.

Results: 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.

Placenta: 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.

Brain: 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.

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