Two‐Compartment Perfusion MR IVIM Model to Investigate Normal and Pathological Placental Tissue

Abstract

BackgroundPerfusion 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.PurposeInvestigate the potential of the two‐perfusion IVIM model in differentiating between normal and abnormal placentas.Study‐TypeRetrospective, case–control.Population43 normal pregnancy, 9 fetal‐growth‐restriction (FGR), 6 small‐for‐gestational‐age (SGA), 4 accreta, 1 increta and 2 percreta placentas.Field Strength/SequenceDiffusion‐weighted‐echo planar imaging sequence at 1.5 T.AssessmentVoxel‐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‐TestsANOVA 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.ResultsThere 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.ConclusionThe two‐perfusion model provides complementary information to IVIM parameters that may be useful in identifying placenta impairment.Level of Evidence2Technical Efficacy Stage1