Microvascular perfusion of the placenta, developing fetal liver, and lungs assessed with intravoxel incoherent motion imaging.

BACKGROUND: In utero intravoxel incoherent motion magnetic resonance imaging (IVIM-MRI) provides a novel method for examining microvascular perfusion fraction and diffusion in the developing human fetus.

PURPOSE: To characterize gestational changes in the microvascular perfusion fraction of the placenta, fetal liver, and lungs using IVIM-MRI.

STUDY TYPE: Retrospective, cross-sectional study.

SUBJECTS: Fifty-five datasets from 33 singleton pregnancies were acquired (17-36 gestational weeks).

FIELD STRENGTH/SEQUENCE: In utero diffusion-weighted echo-planar imaging at 1.5T and 3.0T with b-factors ranging from 0 to 900 s/mm2 in 16 steps.

ASSESSMENT: Using the IVIM principle, microvascular perfusion fraction (f), pseudodiffusion (D*), and diffusion coefficients (d) were estimated for the placenta, liver, and lungs with a biexponential model. A free-form nonlinear deformation algorithm was used to correct for the frame-by-frame motion of the fetal organs and the placenta. The IVIM parameters were then compared to a Doppler ultrasound-based assessment of the umbilical artery resistance index.

STATISTICAL TESTS: Pearson product-moment correlation coefficient (PMCC) to reveal outlier corrected correlations between Doppler and IVIM parameters. Gestational age-related changes were assessed using linear regression analysis (LR).

RESULTS: Placental f (0.29 ± 0.08) indicates high blood volume in the microvascular compartment, moderately increased during gestation (LR, R = 0.338), and correlated negatively with the umbilical artery resistance index (PMCC, R = -0.457). The f of the liver decreased sharply during gestation (LR, R = -0.436). Lung maturation was characterized by increasing perfusion fraction (LR, R = 0.547), and we found no gestational changes in d and D* values (LR, R = -0.013 and R = 0.051, respectively). The Doppler measurements of the umbilical artery and middle cerebral artery did not correlate with the IVIM parameters of the lungs and liver.

DATA CONCLUSION: Gestational age-associated changes of the placental, liver, and lung IVIM parameters likely reflect changes in placental and fetal circulation, and characterize the trajectory of microstructural and functional maturation of the fetal vasculature.

LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2017.