Two-compartment perfusion MR IVIM model to investigate normal and pathological placental tissue

Background: Perfusion and diffusion coexist in the placenta and can be altered by pathologies. The two-perfusion model, where f1 and, f2 are the perfusion-fraction of the fastest and slowest perfusion compartment, respectively, and D is the diffusion coefficient, may help differentiate between normal and impaired placentas. Purpose: Investigate the potential of the two-perfusion IVIM model in differentiating between normal and abnormal placentas. Study-Type: Retrospective, case–control. Population: 43 normal pregnancy, 9 fetal-growth-restriction (FGR), 6 small-for-gestational-age (SGA), 4 accreta, 1 increta and 2 percreta placentas. Field Strength/Sequence: Diffusion-weighted-echo planar imaging sequence at 1.5 T. Assessment: Voxel-wise signal-correction and fitting-controls were used to avoid overfitting obtaining that two-perfusion model fitted the observed data better than the IVIM model (Akaike weight: 0.94). The two-perfusion parametric-maps were quantified from ROIs in the fetal and maternal placenta and in the accretion zone of accreta placentas. The diffusion coefficient D was evaluated using a b ≥ 200 sec/mm2-mono-exponential decay fit. IVIM metrics were quantified to fix f1 + f2 = fIVIM. Statistical-Tests: ANOVA with Dunn-Sidák's post-hoc correction and Cohen's d test were used to compare parameters between groups. Spearman's coefficient was evaluated to study the correlation between variables. A P-value<0.05 indicated a statistically significant difference. Results: There was a significant difference in f1 between FGR and SGA, and significant differences in f2 and fIVIM between normal and FGR. The percreta + increta group showed the highest f1 values (Cohen's d = −2.66). The f2 between normal and percreta + increta groups showed Cohen's d = 1.12. Conversely, fIVIM had a small effective size (Cohen's d = 0.32). In the accretion zone, a significant correlation was found between f2 and GA (ρ = 0.90) whereas a significant negative correlation was found between fIVIM and D (ρ = −0.37 in fetal and ρ = −0.56 in maternal side) and f2 and D (ρ = −0.38 in fetal and ρ = −0.51 in maternal side) in normal placentas. Conclusion: The two-perfusion model provides complementary information to IVIM parameters that may be useful in identifying placenta impairment. Level of Evidence: 2. Technical Efficacy Stage: 1.