State-of-the-Art Imaging of the Placenta

"Unraveling the Clot-Miscarriage Nexus: Mechanisms, Management, and Future Directions in Thrombosis-Related Recurrent Pregnancy Loss"

Recurrent spontaneous abortion (RSA) is a multifactorial condition influenced by genetic, hormonal, immunological, and anatomical factors. Thrombophilia, characterized by a heightened propensity for blood clotting, is a significant contributor to RSA. This review examines the mechanisms connecting thrombosis and RSA, focusing on hypercoagulable states, placental thrombosis, inflammation, and endothelial dysfunction. Genetic and acquired thrombophilic factors, such as factor V Leiden mutation, prothrombin gene mutation, protein C and S deficiencies, antithrombin III deficiency, antiphospholipid syndrome, and hyperhomocysteinemia, are discussed in detail. The diagnosis of thrombophilia in RSA entails a comprehensive clinical evaluation, including the assessment of physical examination, medical history and laboratory investigations, although there is still debate over the need for universal screening. Therapeutic strategies, including anticoagulant and antiplatelet therapies, as well as lifestyle modifications, are tailored to individual risk factors and disease severity. Although anticoagulant therapy demonstrates potential in lowering the risk of miscarriage, additional research is necessary to refine treatment protocols and assess long-term outcomes. This review highlights the need for a nuanced approach to managing thrombophilia-associated RSA, balancing diagnostic precision with therapeutic efficacy to improve reproductive outcomes.

Perfusion of the placenta assessed using arterial spin labeling and ferumoxytol dynamic contrast enhanced magnetic resonance imaging in the rhesus macaque

PURPOSE

To investigate the correspondence between arterial spin labeling (ASL) flow-sensitive alternating inversion recovery (FAIR) and ferumoxytol DCE MRI for the assessment of placental intervillous perfusion.

METHODS

Ten pregnant macaques in late second trimester were imaged at 3 T using a 2D ASL FAIR, with and without outer-volume saturation pulses used to control the bolus width, and a 3D ferumoxytol DCE-MRI acquisition. The ASL tagged/control pairs were averaged, subtracted, and normalized to create perfusion ratio maps. Contrast arrival time and uptake slope were estimated by fitting the DCE data to a sigmoid function. Macaques (N = 4) received interleukin-1β to induce inflammation and disrupt perfusion.

RESULTS

The FAIR tag modification with outer-volume saturation reduced the median ASL ratio percentage compared with conventional FAIR (0.64% ± 1.42% versus 0.71% ± 2.00%; P < .05). Extended ferumoxytol arrival times (34 ± 25 seconds) were observed across the placenta. No significant DCE signal change was measured in fetal tissue ( - 0.6% ± 3.0%; P = .52) or amniotic fluid (1.9% ± 8.8%; P = .59). High ASL ratio was significantly correlated with early arrival time and high uptake slope (P < .05), but ASL signal was not above noise in late-DCE-enhancing regions. No significant differences were observed in perfusion measurements between the interleukin-1β and controls (P > .05).

CONCLUSION

The ASL-FAIR and ferumoxytol DCE-MRI methods are feasible to detect early blood delivery to the macaque placenta. Outer volume saturation reduced the high macrovascular ASL signal. Interleukin-1β exposure did not alter placental intervillous perfusion. An endogenous-labeling perfusion technique is limited due to extended transit times for flow within the placenta beyond the immediate vicinity of the maternal spiral arteries.

SWAVE Imaging of Placental Elasticity and Viscosity: Proof of Concept

The placenta is the interface between the fetus and the mother and is vital for fetal development. Ultrasound elastography provides a non-invasive way to examine in vivo the stiffness of the placenta; increased stiffness has previously been linked to fetal growth restriction. This study used a previously developed dynamic elastography method, called shear wave absolute vibro-elastography, to study 61 post-delivery clinically normal placentas. The shear wave speeds in the placenta were recorded under five different low-frequency mechanical excitations. The elasticity and viscosity were estimated through rheological modeling. The shear wave speeds at excitation frequencies of 60, 80, 90, 100 and 120 Hz were measured to be 1.23 ± 0.44, 1.67 ± 0.76, 1.74 ± 0.72, 1.80 ± 0.78 and 2.25 ± 0.80 m/s. The shear wave speed values we obtained are consistent with previous studies. In addition, our multi-frequency acquisition approach enables us to provide viscosity estimates that have not been previously reported.