New insights into uteroplacental perfusion: quantitative analysis using Doppler and contrast-enhanced ultrasound imaging

Value of contrast-enhanced ultrasound for vascular diseases of the liver - current indications and open questions

Contrast-enhanced ultrasonography (CEUS) is a widely available and well-tolerated technique that can expand the diagnosis of a variety of vascular liver diseases. This paper presents an overview of the current possibilities of the use of CEUS in vascular liver diseases. Particularly where Doppler sonography has technical limitations, CEUS provides additional opportunities to visualize vascular thrombosis and other obstructions restricting blood flow. When CT or MRI contrast agents cannot be used because of severe allergy or renal insufficiency, CEUS can be a valuable diagnostic alternative and has demonstrated comparable diagnostic performance in at least some vascular liver diseases, such as portal vein thrombosis. In addition, CEUS works without radiation and, therefore, might be particularly suitable for young patients and children. This may be useful, for example, in congenital disorders such as persistent umbilical vein or preduodenal portal vein. Vascular liver disease is rare and comprehensive data are still lacking, but the available literature provides promising insights into potential new ways to study vascular liver disease. Although most studies are based on small sample sizes or even case reports, the high diagnostic utility is undisputed.

Ferritin light chain deficiency-induced ferroptosis is involved in preeclampsia pathophysiology by disturbing uterine spiral artery remodelling

The proteomic analysis from samples of patients with preeclampsia (PE) displayed a low level of ferritin light chains (FTL), but we do not know what the significance of reduced FTL in PE pathophysiology is. To address this question, we first demonstrated that FTL was expressed in first- and third-trimester cytotrophoblasts, including extravillous trophoblasts (EVTs), of the human placenta. Furthermore, a pregnant rat model of FTL knockdown was successfully established by intravenously injecting adenoviruses expressing shRNA targeting FTL. In pregnant rats with downregulated FTL, we observed PE-like phenotypes and impaired spiral arterial remodelling, implying a causal relationship between FTL downregulation and PE. Blocking ferroptosis with ferrostatin-1 (Fer-1) significantly rescued the above PE-like phenotypes in pregnant rats with FTL knockdown. Furthermore, using trophoblast cell line and chorionic villous explant culture assays, we showed that FTL downregulation induced cell death, especially ferroptosis, resulting in defective uterine spiral artery remodelling. Eventually, this conclusion from the animal model was verified in PE patients' placental tissues. Taken together, this study revealed for the first time that FTL reduction during pregnancy triggered ferroptosis and then caused defective uterine spiral artery remodelling, thereby leading to PE.

Contrast-enhanced ultrasound evaluation of placental perfusion in brachicephalic bitches

The present study aimed to investigate placental hemodynamics to determine quantitative and qualitative parameters for pregnant brachycephalic bitches as well as describe placental vascularization and perfusion in females with fetal abnormalities close to delivery. Forty-four healthy fetuses from 22 brachycephalic bitches and 9 fetuses with gestational abnormalities (anasarca and hydrocephalus) from 8 brachycephalic bitches were evaluated. All female dogs were artificially inseminated intravaginally and underwent cesarean section at the end of gestation. Pregnancy diagnosis was made on the 25th day and experimental evaluations were performed on Days 25 (M1), 45 (M2), and 58 (M3) of gestation in normal pregnancies. Fetuses with gestational abnormalities were evaluated at the last time point. Biometric values of the fetuses were determined by B-mode and vascular indices by Doppler fluxometry of the umbilical artery, whereas qualitative assessment of contrast filling and quantitative parameters of placental perfusion were performed using CEUS. Parameter comparisons among the examined fetuses (normal and abnormal) and between the moments (M1, M2, and M3) were performed by Student's t-test and ANOVA tests, and then correlated using the Spearman test. In healthy fetuses, systolic and diastolic velocities as well as the time averages of minimum and maximum velocities increased significantly from M2 to M3 (P < 0.05), whereas the pulsatility index (P < 0.043) and vascular resistance (P < 0.001) decreased. Contrast distribution was always homogeneous in placental tissues and CEUS filling parameters remained constant during the evaluated periods (P < 0.05). In fetuses with hydrops, Doppler values were similar to those obtained in healthy subjects (P > 0.05), but CEUS evaluation demonstrated a heterogeneous distribution with lower intensity of placental tissue filling and a delay in perfusion time (P < 0.05) with a diagnostic accuracy of 75%. The association of dopplerfluxometry and CEUS allowed evaluation of qualitative and quantitative parameters of physiological pregnancy hemodynamics in all gestational thirds without evidence of significant changes in the physiology of the maternal-fetal binomial, and CEUS was shown to be applicable in the detection of failures in placental vascular filling (tissue dysfunction) in fetuses with anasarca and hydrocephaly.

Safe and pivotal approaches using contrast-enhanced ultrasound for the diagnostic workup of non-obstetric conditions during pregnancy, a single-center experience

PURPOSE

Conventional ultrasound is the main imaging modality in obstetrics for assessing the maternal and fetal status. Up to date, contrast-enhanced ultrasound (CEUS) has not found widespread use in gynecology and obstetrics, but recent studies demonstrate promising results. The aim of the present study is to assess safe and valuable application of CEUS during pregnancy to investigate non-obstetric conditions.

METHODS

Five pregnant patients on whom CEUS was performed between 2019 and 2020 were included in this retrospective single-center study. A total of six CEUS examinations were performed including one CEUS-guided biopsy (mean age: 31 years, mean weeks of pregnancy: 18 weeks). CEUS examinations were performed by a consultant radiologist (EFSUMB level 3).

RESULTS

All included pregnant women safely underwent CEUS. Neither maternal nor fetal adverse effects were detected. CEUS critically helped in the diagnostic workup of a desmoid tumor of the abdominal wall, hepatic hemangioma, amebic hepatic abscess, uncomplicated renal cyst and post-inflammatory alteration of the renal cortex and for excluding active abdominal bleeding. In addition, CEUS-guided biopsy was performed to prevent intratumoral hemorrhage. Findings from CEUS prompted immediate treatment in two women, whereas in three women regular obstetric monitoring of the women could be conducted.

CONCLUSION

Our results demonstrate safe and crucial application of off-label CEUS in pregnant women to assess different non-obstetric conditions allowing to prevent additional ionizing CT or application of (gadolinium-based) contrast agent in MRI. Hence, CEUS might add pivotal value for evaluating obstetric and non-obstetric conditions and thereby directing clinical management of pregnant women in the future.

Contrast-Enhanced Ultrasound for Assessing Abdominal Conditions in Pregnancy

Background and objectives: Native ultrasound is the most common imaging modality in obstetrics. The use of contrast-enhanced ultrasound (CEUS) during pregnancy has not been officially approved by leading societies for obstetrics and ultrasound. The present study aims to monitor the safety and diagnostic performance of CEUS for assessing abdominal issues in five pregnant women. Materials and Methods: Five pregnant patients who underwent a total of 11 CEUS examinations between June 2020 and October 2020 were included (mean age: 34 years; mean time of pregnancy: 21 weeks). All CEUS scans were interpreted by one experienced consultant radiologist (EFSUMB Level 3). Results: Upon contrast application, no maternal nor fetal adverse effects were observed. Moreover, no fetal contrast enhancement was observed in any patient. CEUS helped to diagnose renal angiomyolipoma, pyelonephritis, necrotic uterine fibroid, gallbladder polyp, and superior mesenteric vein thrombosis. Conclusions: In our study, off-label use of CEUS showed an excellent safety profile allowing the avoidance of ionizing radiation exposure as well as contrast agents in case of CT or use of gadolinium-based contrast agents in case of MRI. CEUS is a promising diagnostic instrument for facilitating clinical decision-making and improving the management of pregnant women.

Contrast-enhanced ultrasound for the assessment of placental development and function

The use of contrast agents as signal enhancers during ultrasound improves visualization and the diagnostic utility of this technology in medical imaging. Although widely used in many disciplines, contrast ultrasound is not routinely implemented in obstetrics, largely due to safety concerns of administered agents for pregnant women and the limited number of studies that address this issue. Here the microbubble characteristics that make them beneficial for enhancement of the blood pool and the quantification of real-time imaging are reviewed. Literature from pregnant animal model studies and safety assessments are detailed, and the potential for contrast-enhanced ultrasound to provide clinically relevant data and benefit our understanding of early placental development and detection of placental dysfunction is discussed.

Contrast-Enhanced Ultrasound Quantification: From Kinetic Modeling to Machine Learning

Ultrasound contrast agents (UCAs) have opened up immense diagnostic possibilities by combined use of indicator dilution principles and dynamic contrast-enhanced ultrasound (DCE-US) imaging. UCAs are microbubbles encapsulated in a biocompatible shell. With a rheology comparable to that of red blood cells, UCAs provide an intravascular indicator for functional imaging of the (micro)vasculature by quantitative DCE-US. Several models of the UCA intravascular kinetics have been proposed to provide functional quantitative maps, aiding diagnosis of different pathological conditions. This article is a comprehensive review of the available methods for quantitative DCE-US imaging based on temporal, spatial and spatiotemporal analysis of the UCA kinetics. The recent introduction of novel UCAs that are targeted to specific vascular receptors has advanced DCE-US to a molecular imaging modality. In parallel, new kinetic models of increased complexity have been developed. The extraction of multiple quantitative maps, reflecting complementary variables of the underlying physiological processes, requires an integrative approach to their interpretation. A probabilistic framework based on emerging machine-learning methods represents nowadays the ultimate approach, improving the diagnostic accuracy of DCE-US imaging by optimal combination of the extracted complementary information. The current value and future perspective of all these advances are critically discussed.

Longitudinal characterization of local perfusion of the rat placenta using contrast-enhanced ultrasound imaging

The placenta performs many physiological functions critical for development. Insufficient placental perfusion, due to improper vascular remodelling, has been linked to many pregnancy-related diseases. To study longitudinal in vivo placental perfusion, we have implemented a pixel-wise time-intensity curve (TIC) analysis of contrast-enhanced ultrasound (CEUS) images. CEUS images were acquired of pregnant Sprague Dawley rats after bolus injections of gas-filled microbubble contrast agents. Conventionally, perfusion can be quantified using a TIC of contrast enhancement in an averaged region of interest. However, the placenta has a complex structure and flow profile, which is insufficiently described using the conventional technique. In this work, we apply curve fitting in each pixel of the CEUS image series in order to quantify haemodynamic parameters in the placenta and surrounding tissue. The methods quantified an increase in mean placental blood volume and relative blood flow from gestational day (GD) 14 to GD18, while the mean transit time of the microbubbles decreased, demonstrating an overall rise in placental perfusion during gestation. The variance of all three parameters increased during gestation, showing that regional differences in perfusion are observable using the pixel-wise TIC approach. Additionally, the high-resolution parametric images show distinct regions of high blood flow developing during late gestation. The developed methods could be applied to assess placental vascular remodelling during the treatment of the pathologies of pregnancy.

Maternal High-Fat Diet Consumption and Chronic Hyperandrogenemia Are Associated With Placental Dysfunction in Female Rhesus Macaques

The risk of adverse perinatal outcomes with maternal polycystic ovary syndrome may differ among hyperandrogenic and nonhyperandrogenic phenotypes and is likely modulated by maternal obesity and diet. The relative contribution of maternal hyperandrogenism and nutritional status to placental dysfunction is unknown. Female rhesus macaques (N = 39) were assigned at puberty to one of four treatment groups: subcutaneous cholesterol implants and a standard chow diet (controls); testosterone (T) implants and a normal diet; cholesterol implants and a high-fat, Western-style diet (WSD); and testosterone implants in combination with a high-fat diet. After 3.5 years of treatment, contrast-enhanced and Doppler ultrasound analyses of placental blood flow were performed for a representative subset of animals from each treatment group during pregnancy, and placental architecture assessed with stereological analysis. Placental growth factors, cellular nutrient sensors, and angiogenic markers were measured with ELISA and Western blotting. WSD consumption was associated with a 30% increase in placental flux rate relative to that in animals receiving a normal diet. T and WSD treatments were each independently associated with increased villous volume, and T also was associated with an ∼ 40% decrease fetal capillary volume on stereological analysis. T treatment was associated with significantly increased mTOR and SOCS3 expression. WSD consumption was associated with decreased GLUT1 expression and microvillous membrane localization. Hyperandrogenemic and nonhyperandrogenemic phenotypes are associated with altered placental angiogenesis, nutrient sensing, and glucose transport. WSD and T appear to have distinct effects on vascular impedance and capillary angiogenesis.

Vascular Endothelial Growth Factor Delivery to Placental Basal Plate Promotes Uterine Artery Remodeling in the Primate

Extravillous trophoblast (EVT) uterine artery remodeling (UAR) promotes placental blood flow, but UAR regulation is unproven. Elevating estradiol (E2) in early baboon pregnancy suppressed UAR and EVT vascular endothelial growth factor (VEGF) expression, but this did not prove that VEGF mediated this process. Therefore, our primate model of prematurely elevating E2 and contrast-enhanced ultrasound cavitation of microbubble (MB) carriers was used to deliver VEGF DNA to the placental basal plate (PBP) to establish the role of VEGF in UAR. Baboons were treated on days 25 to 59 of gestation (term, 184 days) with E2 alone or with E2 plus VEGF DNA-conjugated MBs briefly infused via a maternal peripheral vein on days 25, 35, 45, and 55. At each of these times an ultrasound beam was directed to the PBP to collapse the MBs and release VEGF DNA. VEGF DNA-labeled MBs per contrast agent was localized in the PBP but not the fetus. Remodeling of uterine arteries >25 µm in diameter on day 60 was 75% lower (P < 0.001) in E2-treated (7% ± 2%) than in untreated baboons (30% ± 4%) and was restored to normal by E2/VEGF. VEGF protein levels (signals/nuclear area) within the PBP were twofold lower (P < 0.01) in E2-treated (4.2 ± 0.9) than in untreated (9.8 ± 2.8) baboons and restored to normal by E2/VEGF (11.9 ± 1.6), substantiating VEGF transfection. Thus, VEGF gene delivery selectively to the PBP prevented the decrease in UAR elicited by prematurely elevating E2 levels, establishing the role of VEGF in regulating UAR in vivo during primate pregnancy.

Chronic exposure to e-cig aerosols during early development causes vascular dysfunction and offspring growth deficits

Increasing popularity of electronic cigarettes (e-cigs), including among women of reproductive age, is attributed to its perceived safety compared to conventional tobacco. However, there is a major knowledge gap surrounding the effects of e-cig aerosols on pregnancy and fetal development. We aimed to evaluate the effects of vaping e-cigs during gestation on offspring growth and to asses if growth deficits are accompanied by altered maternal and fetal vascular hemodynamics. Sprague-Dawley dams were assigned to Pair-Fed Control, Pair-Fed Juice, or Juice+Nicotine groups, and then underwent either a prenatal or prenatal+postnatal exposure paradigm in a custom-engineered vaping system. Mass spectrometry identified major aerosolized constituents from e-cig vaping. The Juice+Nicotine group exhibited significantly decreased fetal weight and crown-rump length (↓46.56%, and ↓23.83%, respectively). Pre- and postnatal exposure to Juice+Nicotine resulted in decreased pup weight at postnatal day (PND) 4-10. Crown-rump length was decreased by 24.71% on PND 10. Blood flow in the Juice+Nicotine group was decreased in the maternal uterine and fetal umbilical circuits by 49.50% and 65.33%, respectively. We conclude that chronic exposure to e-cig aerosols containing nicotine during early development can have deleterious health effects on the exposed offspring. Vaping e-cigs containing nicotine during pregnancy lead to a reduction in offspring weight and crown-rump length, associated with a marked decrease in blood flow in both the maternal uterine and fetal umbilical circulation (a strong indicator of growth restriction). Thus, chronic exposure to e-cig aerosols containing nicotine can lead to potentially harmful developmental effects in early life.

Comparative determination of placental perfusion by magnetic resonance imaging and contrast-enhanced ultrasound in a murine model of intrauterine growth restriction

INTRODUCTION

Exploration of placental perfusion is essential in screening for dysfunctions impairing fetal growth. The objective of this study was to assess the potential value of contrast-enhanced ultrasonography (CEUS) and magnetic resonance imaging (MRI) for examining placental perfusion in a murine model of intrauterine growth restriction (IUGR). We also studied the reproducibility of perfusion quantification by CEUS.

METHODS

Pregnant Sprague Dawley rat models of IUGR were studied during the third trimester. Unilateral uterine artery ligation induced IUGR. Placental perfusion was evaluated by CEUS and perfusion MRI with gadolinium for both ligated and control fetoplacental units. The kinetic parameters of the two imaging modalities were then compared.

RESULTS

The analysis included 20 rats. The study showed good reproducibility of the CEUS indicators. The CEUS perfusion index approximated the blood flow rate and was halved in the ligation group (27.9 [u.a] (±14.8)) versus 61 [u.a] (±22.3) on the control side (P = 0.0003). MRI with gadolinium injection showed a clear reduction in the blood flow rate to 51.2 mL/min/100 mL (IQR 34.9-54.9) in the ligated horn, compared with 90.9 mL/min/100 mL (IQR 85.1-95.7) for the control side (P < 0.0001). The semiquantitative indicators obtained from the kinetic curves for both CEUS and MRI showed similar trends. Nonetheless, values were more widely dispersed with CEUS than MRI.

DISCUSSION

The similar results for the quantification of placental perfusion by MRI and CEUS reinforce the likelihood that CEUS can be used to identify IUGR in a murine model induced by uterine vessel ligation.

Development of a Fluid Dynamic Model for Quantitative Contrast-Enhanced Ultrasound Imaging

Contrast-enhanced ultrasound (CEUS) is a non-invasive imaging technique extensively used for blood perfusion imaging of various organs. This modality is based on the acoustic detection of gas-filled microbubble contrast agents used as intravascular flow tracers. Recent efforts aim at quantifying parameters related to the enhancement in the vascular compartment using time-intensity curve (TIC), and at using these latter as indicators for several pathological conditions. However, this quantification is mainly hampered by two reasons: first, the quantification intrinsically solely relies on temporal intensity variation, the explicit spatial transport of the contrast agent being left out. Second, the exact relationship between the acquired US-signal and the local microbubble concentration is hardly accessible. This paper introduces the use of a fluid dynamic model for the analysis of dynamic CEUS (DCEUS), in order to circumvent the two above-mentioned limitations. A new kinetic analysis is proposed in order to quantify the velocity amplitude of the bolus arrival. The efficiency of proposed methodology is evaluated both in-vitro, for the quantitative estimation of microbubble flow rates, and in-vivo, for the classification of placental insufficiency (control versus ligature) of pregnant rats from DCEUS. Besides, for the in-vivo experimental setup, we demonstrated that the proposed approach outperforms the performance of existing TIC-based methods.

Mechanical and Biological Effects of Ultrasound: A Review of Present Knowledge

Ultrasound is widely used for medical diagnosis and increasingly for therapeutic purposes. An understanding of the bio-effects of sonography is important for clinicians and scientists working in the field because permanent damage to biological tissues can occur at high levels of exposure. Here the underlying principles of thermal mechanisms and the physical interactions of ultrasound with biological tissues are reviewed. Adverse health effects derived from cellular studies, animal studies and clinical reports are reviewed to provide insight into the in vitro and in vivo bio-effects of ultrasound.

Real-Time Monitoring of Placental Oxygenation during Maternal Hypoxia and Hyperoxygenation Using Photoacoustic Imaging

Purpose

This preclinical study aimed to evaluate placental oxygenation in pregnant rats by real-time photoacoustic (PA) imaging on different days of gestation and to specify variations in placental oxygen saturation under conditions of maternal hypoxia and hyperoxygenation.

Material and methods

Placentas of fifteen Sprague-Dawley rats were examined on days 14, 17, and 20 of pregnancy with a PA imaging system coupled to high-resolution ultrasound imaging. Pregnant rats were successively exposed to hyperoxygenated and hypoxic conditions by changing the oxygen concentration in inhaled gas. Tissue oxygen saturation was quantitatively analyzed by real-time PA imaging in the skin and 3 regions of the placenta. All procedures were performed in accordance with applicable ethical guidelines and approved by the animal care committee.

Results

Maternal hypoxia was associated with significantly greater decrease in blood oxygen saturation (ΔO₂ Saturation) in the skin (70.74% ±7.65) than in the mesometrial triangle (32.66% ±5.75) or other placental areas (labyrinth: 18.58% ± 6.61; basal zone: 13.13% ±5.72) on different days of pregnancy (P<0.001). ΔO₂ Saturation did not differ significantly between the labyrinth, the basal zone, and the decidua. After the period of hypoxia, maternal hyperoxygenation led to a significant rise in oxygen saturation, which returned to its initial values in the different placental regions (P<0.001).

Conclusions

PA imaging enables the variation of blood oxygen saturation to be monitored in the placenta during maternal hypoxia or hyperoxygenation. This first preclinical study suggests that the placenta plays an important role in protecting the fetus against maternal hypoxia.

Non-invasive evaluation of placental blood flow: lessons from animal models

In human obstetrics, placental vascularisation impairment is frequent as well as linked to severe pathological events (preeclampsia and intrauterine growth restriction), and there is a need for reliable methods allowing non-invasive evaluation of placental blood flow. Uteroplacental vascularisation is complex, and animal models are essential for the technical development and safety assessment of these imaging tools for human clinical use; however, these techniques can also be applied in the veterinary context. This paper reviews how ultrasound-based imaging methods such as 2D and 3D Doppler can provide valuable insight for the exploration of placental blood flow both in humans and animals and how new approaches such as the use of ultrasound contrast agents or ultrafast Doppler may allow to discriminate between maternal (non-pulsatile) and foetal (pulsatile) blood flow in the placenta. Finally, functional magnetic resonance imaging could also be used to evaluate placental blood flow, as indicated by studies in animal models, but its safety in human pregnancy still requires to be confirmed.

High Resolution Ultrasound Superharmonic Perfusion Imaging: In Vivo Feasibility and Quantification of Dynamic Contrast-Enhanced Acoustic Angiography

Mapping blood perfusion quantitatively allows localization of abnormal physiology and can improve understanding of disease progression. Dynamic contrast-enhanced ultrasound is a low-cost, real-time technique for imaging perfusion dynamics with microbubble contrast agents. Previously, we have demonstrated another contrast agent-specific ultrasound imaging technique, acoustic angiography, which forms static anatomical images of the superharmonic signal produced by microbubbles. In this work, we seek to determine whether acoustic angiography can be utilized for high resolution perfusion imaging in vivo by examining the effect of acquisition rate on superharmonic imaging at low flow rates and demonstrating the feasibility of dynamic contrast-enhanced superharmonic perfusion imaging for the first time. Results in the chorioallantoic membrane model indicate that frame rate and frame averaging do not affect the measured diameter of individual vessels observed, but that frame rate does influence the detection of vessels near and below the resolution limit. The highest number of resolvable vessels was observed at an intermediate frame rate of 3 Hz using a mechanically-steered prototype transducer. We also demonstrate the feasibility of quantitatively mapping perfusion rate in 2D in a mouse model with spatial resolution of ~100 μm. This type of imaging could provide non-invasive, high resolution quantification of microvascular function at penetration depths of several centimeters.

Quantitative contrast-enhanced ultrasonography for the differential diagnosis of endometrial hyperplasia and endometrial neoplasms

The present study aimed to investigate the feasibility of applying contrast-enhanced ultrasonography (CEUS) imaging technology for distinguishing between benign and malignant endometrial lesions, and to screen markers that could be correlated with the pathological results. In this study, endometrial diseases were diagnosed by biopsy under hysteroscopy and CEUS examinations. The intensity and time parameters of the time-intensity curve (TIC) were analyzed. The mean arrival time (AT), time-to-peak (TTP), rise time (RT), washout half-time and clearance half-time of malignant lesions were shorter than those of benign lesions (P<0.05), whereas the average peak intensity (PI) and enhancement intensity (EI) of malignant lesions were higher than those of benign lesions (P<0.05). The receiver operating characteristic curve showed the following cut-off values: PI, 29.2 dB; EI, 21.35 dB; AT, 12.75 sec; TTP, 26.75 sec; RT, 13.2 sec; clearance half-time, 89.3 sec; and washout half-time, 75.45 sec. The lesions with PI, an EI higher than that of the cut-off and lesions with an AT, TTP, RT, half clearing time and washout half-time shorter than the cut-off were considered malignant. The TTP, RT and half clearing time were negatively correlated with microvessel density (MVD), i.e., MVD was higher when the TTP, RT and half clearing time were shorter. Overall, changes in the enhancement and clearing of lesions could be quantitatively analyzed by CEUS TIC and further discriminate benign from malignant lesions. In the present study, CEUS appeared to indirectly reflect blood vessel changes inside the lesions and provided a pre-operative non-invasive fast imaging method for the diagnosis of endometrial disease.

A longitudinal study of placental perfusion using dynamic contrast enhanced magnetic resonance imaging in murine pregnancy

INTRODUCTION

To evaluate changes in placental perfusion with advancing gestation in normal murine pregnancy using dynamic contrast enhanced magnetic resonance imaging (DCE-MRI).

METHODS

Seven timed-pregnant CD-1 mice underwent DCE-MRI scanning longitudinally on gestational days (GD) 13, 15 and 17. Placentas were segmented into high (HPZ) and low perfusion zones (LPZ) using tissue similarity mapping. Blood perfusion of the respective regions and the whole placenta was quantified using the steepest slope method. The diameter of the maternal central canal (CC) was also measured.

RESULTS

An increase in perfusion was observed between GD13 and GD17 in the overall placenta (p = 0.04) and in the HPZ (p = 0.02). Although perfusion in the LPZ showed a slight increasing trend, it was not significant (p = 0.07). Perfusion, in units of ml/min/100 ml, in the overall placenta and the HPZ was respectively 61.2 ± 31.2 and 106.2 ± 56.3 at GD13 (n = 19 placentas); 90.3 ± 43.7 and 139 ± 55.4 at GD15 (n = 20); and 104.9 ± 76.1 and 172.2 ± 85.6 at GD17 (n = 14). The size of the CC increased with advancing gestation (p < 0.05).

DISCUSSION

Using longitudinal DCE-MRI, the gestational age-dependent perfusion change in the normal murine placenta and in its regional compartments was quantified. In mid and late gestations, placental constituent regions differ significantly in their perfusion rates. The CC diameter also showed increase with advancing gestation, which may be playing an important role toward the gestational age-dependent increase in placental perfusion.

A liposomal Gd contrast agent does not cross the mouse placental barrier

The trans-placental permeability of liposomal Gadolinium (Gd) nanoparticle contrast agents was evaluated in a pregnant mouse model. Pregnant Balb/c mice at 16.5 (±1) days of gestation were imaged using a 3D Spoiled Gradient Echo method at 9.4 T using two contrast agents: a clinically approved Gd chelate, Multihance^® (gadobenate dimeglumine), and a novel experimental liposomal Gd agent. A Dynamic Contrast Enhancement (DCE) protocol was used to capture the dynamics of contrast entry and distribution in the placenta, and clearance from circulation. A blinded clinical radiologist evaluated both sets of images. A reference region model was used to measure the placental flow and physiological parameters; volume transfer constant (K^trans), efflux rate constant (K^ep). The Gd content of excised placentae and fetuses was measured, using inductively coupled plasma mass spectrometry (ICP-MS). MRI images of pregnant mice and ICP-MS analyses of placental and fetal tissue demonstrated undetectably low transplacental permeation of the liposomal Gd agent, while the clinical agent (Multihance) avidly permeated the placental barrier. Image interpretation and diagnostic quality was equivalent between the two contrast agents. Additional testing to determine both maternal and fetal safety of liposomal Gd is suggested.

Quantitative assessment of placental perfusion by contrast-enhanced ultrasound in macaques and human subjects

BACKGROUND

The uteroplacental vascular supply is a critical determinant of placental function and fetal growth. Current methods for the in vivo assessment of placental blood flow are limited.

OBJECTIVE

We demonstrate the feasibility of the use of contrast-enhanced ultrasound imaging to visualize and quantify perfusion kinetics in the intervillous space of the primate placenta.

STUDY DESIGN

Pregnant Japanese macaques were studied at mid second trimester and in the early third trimester. Markers of injury were assessed in placenta samples from animals with or without contrast-enhanced ultrasound exposure (n = 6/group). Human subjects were recruited immediately before scheduled first-trimester pregnancy termination. All studies were performed with maternal intravenous infusion of lipid-shelled octofluoropropane microbubbles with image acquisition with a multipulse contrast-specific algorithm with destruction-replenishment analysis of signal intensity for assessment of perfusion.

RESULTS

In macaques, the rate of perfusion in the intervillous space was increased with advancing gestation. No evidence of microvascular hemorrhage or acute inflammation was found in placental villous tissue and expression levels of caspase-3, nitrotyrosine and heat shock protein 70 as markers of apoptosis, nitrative, and oxidative stress, respectively, were unchanged by contrast-enhanced ultrasound exposure. In humans, placental perfusion was visualized at 11 weeks gestation, and preliminary data reveal regional differences in intervillous space perfusion within an individual placenta. By electron microscopy, we demonstrate no evidence of ultrastructure damage to the microvilli on the syncytiotrophoblast after first-trimester ultrasound studies.

CONCLUSIONS

Use of contrast-enhanced ultrasound did not result in placental structural damage and was able to identify intervillous space perfusion rate differences within a placenta. Contrast-enhanced ultrasound imaging may offer a safe clinical tool for the identification of pregnancies that are at risk for vascular insufficiency; early recognition may facilitate intervention and improved pregnancy outcomes.

Animal Models to Study Placental Development and Function throughout Normal and Dysfunctional Human Pregnancy

Abnormalities of placental development and function are known to underlie many pathologies of pregnancy, including spontaneous preterm birth, fetal growth restriction, and preeclampsia. A growing body of evidence also underscores the importance of placental dysfunction in the lifelong health of both mother and offspring. However, our knowledge regarding placental structure and function throughout pregnancy remains limited. Understanding the temporal growth and functionality of the human placenta throughout the entirety of gestation is important if we are to gain a better understanding of placental dysfunction. The utilization of new technologies and imaging techniques that could enable safe monitoring of placental growth and function in vivo has become a major focus area for the National Institutes of Child Health and Human Development, as evident by the establishment of the "Human Placenta Project." Many of the objectives of the Human Placenta Project will necessitate preclinical studies and testing in appropriately designed animal models that can be readily translated to the clinical setting. This review will describe the advantages and limitations of relevant animals such as the guinea pig, sheep, and nonhuman primate models that have been used to study the role of the placenta in fetal growth disorders, preeclampsia, or other maternal diseases during pregnancy.

Unfractionated heparin and placental pathology in high-risk pregnancies: secondary analysis of a pilot randomized controlled trial

INTRODUCTION

Heparin is often prescribed during pregnancy with the intention of improving perinatal outcomes on the basis that it exerts an anticoagulant action in the inter-villous space. Accumulating in-vitro and in-vivo evidence indicates that heparin's beneficial effects in pregnancy may result from 'non-anticoagulant' effects including the promotion of angiogenesis.

METHODS

To study the effect of heparin within the placenta, we performed secondary analyses on a pilot trial where 32 women with negative thrombophilia screens and second-trimester evidence of placental insufficiency were randomized to standard care or antenatal self-administration of unfractionated heparin (UFH) 7500 IU twice-daily. Serial placental ultrasound images were reviewed and compared with histo-pathologic findings following delivery.

RESULTS

There were no differences between the two arms in either the evolution of abnormal placental lesions on ultrasound (p = 0.75) or evidence of maternal vascular under-perfusion on histopathology (p = 0.89). In pregnancies considered at increased risk for adverse pregnancy outcomes based on previous history or abnormal serum marker screen, early (second-trimester) placental ultrasound, reflecting developmental pathology had better test characteristics (sensitivity 77.8%; positive predictive value 80.8%) for predicting adverse pregnancy outcomes than third-trimester ultrasound that is reflective of placental thrombotic injury.

CONCLUSIONS

Administration of UFH did not prevent the development or evolution of abnormal placental lesions on placental ultrasound or evidence of maternal vascular underperfusion on placental histo-pathology. Second-trimester placental ultrasound may be of value in predicting those at greatest risk of adverse outcomes.

Using dynamic contrast-enhanced MRI to quantitatively characterize maternal vascular organization in the primate placenta

PURPOSE

The maternal microvasculature of the primate placenta is organized into 10-20 perfusion domains that are functionally optimized to facilitate nutrient exchange to support fetal growth. This study describes a dynamic contrast-enhanced magnetic resonance imaging method for identifying vascular domains and quantifying maternal blood flow in them.

METHODS

A rhesus macaque on the 133rd day of pregnancy (G133, term = 165 days) underwent Doppler ultrasound procedures, dynamic contrast-enhanced magnetic resonance imaging and Cesarean-section delivery. Serial T1 -weighted images acquired throughout intravenous injection of a contrast reagent bolus were analyzed to obtain contrast reagent arrival time maps of the placenta.

RESULTS

Watershed segmentation of the arrival time map identified 16 perfusion domains. The number and location of these domains corresponded to anatomical cotyledonary units observed following delivery. Analysis of the contrast reagent wave front through each perfusion domain enabled determination of volumetric flow, which ranged from 9.03 to 44.9 mL/s (25.2 ± 10.3 mL/s). These estimates are supported by Doppler ultrasound results.

CONCLUSIONS

The dynamic contrast-enhanced magnetic resonance imaging analysis described here provides quantitative estimates of the number of maternal perfusion domains in a primate placenta and estimates flow within each domain. Anticipated extensions of this technique are to the study placental function in non-human primate models of obstetric complications.

Assessment of therapeutic efficacy of miR-126 with contrast-enhanced ultrasound in preeclampsia rats

Preeclampsia is a pregnancy-specific syndrome characterized by high blood pressure and proteinuria, which has a pathophysiology of insufficient placental blood perfusion. MicroRNA-126 (miR-126), an angiogenesis-related miRNA, has been proved to play a significant role in endothelial cells response to ischemia in vitro and in vivo. However, whether miR-126 has therapeutic potential in vasculogenesis of preeclampsia placenta remains uncertain. In this study, we focused our attention on this unsolved problem. First, we established the preeclampsia animal model and over-expressed miR-126 in vivo using a specific agomir. Then we described the effects of miR-126 on placental vasculogenesis in preeclampsia rats, including the evaluation of placental blood perfusion using microbubbles-assisted contrast-enhanced ultrasonography (CEUS), placental histology, immunohistochemistry and pregnancy outcome. Finally, we investigated the possible target gene and pathway that miR-126 modulates. Together, our results showed that preeclampsia animal with over-expressed miR-126 had higher pup weight, placenta weight and proportion of live pups. Quantification of uteroplacental perfusion by CEUS and CD34 staining of placental tissue revealed that blood volume and microvessel density increased in miR-126 treated group. MiR-126 was related to PIK3R2 down-regulation and Akt activation within placenta, which had impacts on vascularization of placenta. Therefore, miR-126 may be an efficient gene therapy to promote angiogenesis and blood perfusion in preeclampsia placenta.

Decrease of uteroplacental blood flow after feticide during second-trimester pregnancy termination with complete placenta previa: quantitative analysis using contrast-enhanced ultrasound imaging

Contrast enhanced ultrasound (CEUS) was used to quantify the dynamic changes in uteroplacental blood flow before and after the interruption of fetal villus circulation resulting from feticide during a second trimester pregnancy termination in a patient with complete placenta previa. Quantitative analysis was performed on time-intensity curves acquired 24 h before and 48 h and 120 h after feticide and demonstrated the persistence of utero-placental blood flow with a progressive and two-step reduction in intervillous space and uteroplacental blood flow. Our results suggest that placental blood flow reduction after interruption of fetal circulation is a progressive and delayed mechanism.