The role of the IVIM model in the study of placental microstructural characteristics in IUGR and normal placentae

The human placenta is a highly perfused tissue with complex microstructure and crucial physiological functions for foetal growth. Foetoplacental circulation impairment affects the capacity of the villous trophoblast to ensure nutrient and oxygen supply to the foetus, restricting intrauterine growth. IntraUterine Growth Restriction (IUGR) is associated with lower perinatal and postnatal outcome, and during in utero maturation, placental vascular dysfunction is the most frequent cause of IUGR. A proper in vivo assessment of placental perfusion and microarchitectural characteristics is crucial in the pregnancy management of IUGR. Currently, the macroscopic vascularisation of the placenta is monitored by ultrasonography (US) with Doppler examination. Nevertheless, ultrasound imaging and flowmetry are not able to quantify microperfusive and microstructural placental qualities.

The role of prenatal MRI in the study of placental tissue and perfusion has recently improved. However, the in vivo assessment of placental perfusion with MRI may be challenging, since the use of gadolinium still represents a controversial matter due to a lack of sufficient safety evidence for its use during pregnancy. Therefore, it is highly desirable to develop new non-invasive techniques for the in vivo quantification of placental microperfusion.

Diffusion-weighted imaging (DWI) with IntraVoxel Incoherent Motion imaging (IVIM) could be an appropriate method to study both microperfusion and placental microstructural features. IVIM parameters quantify the perfusion compartment and the diffusion compartment of biological tissue separately, with the measurement of the perfusion fraction f, the pseudo-diffusion coefficient D*, and the diffusion coefficient D.

Our study aimed to investigate the potential of the IVIM model in the in vivo quantification of placental microperfusion characteristics of healthy and IUGR placentae. Sixty-three singleton pregnancies (49 normal and 14 IUGR subjects) were enrolled. Diffusion-weighted EPI with 10 b-values (0, 10, 30, 50, 75, 100, 150, 400, 700, and 1,000s/mm2) was performed at 1.5T, and f, D* and D maps were obtained. For each subject, ROIs were manually placed in whole foetal and whole maternal placenta and in three parenchymal areas – umbilical (U), central (C), and peripheral (P) – on both the foetal and maternal sides. Differences between f, D, and D* measurements and their correlation with gestational age (GA) were investigated in both the normal and IUGR group.

Fraction of perfusion (fp) and Diffusion Coefficient (D) maps (A & B) at 31 GA with Umbilical-ROIs (ROI1 foetal, ROI2 maternal), Central ROIs (ROI3 foetal, ROI4 maternal) and Peripheral ROIs (ROI5 foetal, ROI6 maternal). Examples of fp maps of a normal (C) and an IUGR placenta (D), both at 26 GA. Umbilical cord (black arrow); foetal body (white arrowhead); maternal aorta (white asterisk); maternal kidneys (white dots). IVIM maps were obtained with the prototype software ‘MR Body Diffusion Toolbox’ (Siemens Healthcare, Erlangen, Germany).

Results showed that the perfusion fraction f was significantly lower (p=10-9) in IUGR compared to the normal group in the majority of maternal and foetal ROIs. D was higher in IUGR compared to healthy pregnancies (p=0.01) in the majority of foetal ROIs, also showing a significant negative correlation with a progressive decline of D values with gestational aging. D* was significantly lower (p=0.02) in IUGR than in the healthy group in the whole maternal ROI and the foetal P-ROI.

In conclusion, the quantification of the IVIM parameters showed great potential to study the in vivo microstructural changes occurring in normal and IUGR placentae. Although further studies are needed to confirm and validate our findings, they suggest the potential of IVIM to provide information about early placental microvascular impairment, helping to improve understanding of the pathophysiology of placental dysfunction causing a reduction of foetal growth.

Dr. Amanda Antonelli is a 4th year radiology resident in the Foetal Imaging Group of Prof. Lucia Manganaro at the Department of Radiology, ‘La Sapienza’ University of Rome, Italy.

Research Presentation Session
RPS 212 New insights in paediatric body imaging

Intravoxel incoherent motion imaging for the study of placental microstructure in intrauterine growth restriction: a prenatal in vivo MR study
A. Antonelli1, S. Capuani1, G. Ercolani1, S. Bernardo1, B. Kuehn2, R. Grimm2, A. de Rinaldis2, L. Manganaro1, C. Catalano1; 1Rome/IT, 2Erlangen/DE

Read the full abstract in the ECR 2020 Book of Abstracts
Antonelli A, et al. (2020) Intravoxel incoherent motion imaging for the study of placental microstructure in intrauterine growth restriction: a prenatal in vivo MR study. Abstract RPS 212-1 in: ECR 2020 Book of Abstracts. Insights Imaging 11, 34 (2020). DOI 10.1186/s13244-020-00851-0