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

Quantifying Molecular Changes in the Preeclamptic Rat Placenta with Targeted Contrast-Enhanced Ultrasound Imaging

PURPOSE

Abnormal placental remodeling is linked to various pregnancy-related diseases, including preeclampsia (PE). This study applies a bicompartmental (BCM) model to quantify molecular expression changes in the placenta, indicative of abnormal placental remodeling, and evaluates the effectiveness of targeted contrast-enhanced ultrasound (T-CEUS) in detecting the abnormal placental vasculature. The BCM model provides high temporal resolution and differentiation of anatomical artery structures within the placenta by analyzing the distribution of contrast agents.

METHODS

A targeted contrast agent (TCA) composed of gas-filled microbubbles (MB), with a surface-conjugated peptide to target ανβ3 integrin, a biomarker for angiogenesis, was used for quantifying placental vascular development. CEUS images were acquired from timed pregnant Sprague Dawley rats with experimentally-induced reduced uterine perfusion pressure (RUPP) placental insufficiency. On gestational day (GD) 18 of a 21-day gestation, CEUS images were acquired from both Normal pregnant (NP; n = 6) and RUPP (n = 6) dams after injection of the TCA. The BCM model was used to estimate the binding dynamics of the TCA, providing a parametric map of the binding constant ( K b ) of the placenta.

RESULTS

The RUPP group showed a significant reduction in the value of K b compared to the NP group (p < 0.05). A histogram of the placental K b was compared to alternative analyses (differential target enhancement, dTE and late enhancement, LE) to demonstrate that it can differentiate between anatomical artery structures with a higher contrast-to-background ratio.

CONCLUSIONS

The BCM method differentiates molecular changes associated with the abnormal placental development associated with PE. It also reveals more intricate internal anatomical structures of the placenta in comparison to dTE and LE, suggesting that the BCM could enhance early detection and monitoring of PE.

Development and Characterization of Hemoglobin Microbubbles for Acoustic Blood Oxygen Level Dependent Imaging

Oxygen levels in tissues and organs are crucial for their normal functioning, and approaches to monitor them non-invasively have wide biological and clinical applications. In this study, we developed a method of acoustically detecting oxygenation using contrast-enhanced ultrasound (CEUS) imaging. Our approach involved the use of specially designed hemoglobin-based microbubbles (HbMBs) that reversibly bind to oxygen and alter the state-dependent acoustic response. We confirmed that the bioactivity of hemoglobin remained intact after the microbubble shell was formed, and we did not observe any significant loss of heme. We conducted passive cavitation detection (PCD) experiments to confirm whether the acoustic properties of HbMBs vary based on the level of oxygen present. The experiments involved driving the HbMBs with a 1.1 MHz focused ultrasound transducer. Through the PCD data collected, we observed significant differences in the subharmonic and harmonic responses of the HbMBs when exposed to an oxygen-rich environment versus an oxygen-depleted one. We used a programmable ultrasound system to capture high-frame rate B mode videos of HbMBs in both oxy and deoxy conditions at the same time in a two-chambered flow phantom and observed that the mean pixel intensity of deoxygenated HbMB was greater than in the oxygenated state using B-mode imaging. Finally, we demonstrated that HbMBs can circulate in vivo and are detectable by a clinical ultrasound scanner. To summarize, our results indicate that CEUS imaging with HbMB has the potential to detect changes in tissue oxygenation and could be a valuable tool for clinical purposes in monitoring regional blood oxygen levels.

New insights into human functional ultrasound imaging

Ultrasound imaging is a vital tool for exploring in vivo the placental function which is essential to understand pathological phenomena such as preeclampsia or intrauterine growth restriction. As technology advances including ready availability of three-dimensional (3D) probes and novel software, new markers of placental function become possible. The objective of this review was to provide an overview of the new ultrasound markers of placental function with a focus on the potential clinical application of three-dimensional power Doppler (3DPD). A broad-free text literature search was undertaken based on human placental studies and sixty full-text studies were included in this review. Three-dimensional power Doppler is a promising technique to predict preeclampsia in the first trimester. However, the influence of external factors such as body mass index, parameter standardisation and machine settings still need to be addressed. Contrast-enhanced ultrasound is currently reserved for research, because the required injected contrast mediums are not currently approved for use in pregnancy, although the safety data is reassuring.

Advances in imaging feto-placental vasculature: new tools to elucidate the early life origins of health and disease

Optimal placental function is critical for fetal development, and therefore a crucial consideration for understanding the developmental origins of health and disease (DOHaD). The structure of the fetal side of the placental vasculature is an important determinant of fetal growth and cardiovascular development. There are several imaging modalities for assessing feto-placental structure including stereology, electron microscopy, confocal microscopy, micro-computed tomography, light-sheet microscopy, ultrasonography and magnetic resonance imaging. In this review, we present current methodologies for imaging feto-placental vasculature morphology ex vivo and in vivo in human and experimental models, their advantages and limitations and how these provide insight into placental function and fetal outcomes. These imaging approaches add important perspective to our understanding of placental biology and have potential to be new tools to elucidate a deeper understanding of DOHaD.

Bioengineering in women's health, volume 2: pregnancy—from implantation to parturition

This special issue of Interface Focus is the second of two sets of articles on the topic of bioengineering in women's health. This second issue in the series focuses on pregnancy, a dynamic time in a women's life that involves dramatic physiologic changes within a relatively small timeframe. Pregnancy demands endurance and resilience of one's body and represents a critical component of women's health research. The health of an individual leading up to, during and after pregnancy is paramount for reproductive health and the lifelong health of offspring. The articles in this issue explore physiological events that support reproduction spanning from embryo implantation, through gestation, to delivery and parturition. Specifically, the articles highlight essential developments in placenta, fetal membranes, cervix, pelvic floor and anthropometry research. The featured bioengineering disciplines deployed to study such complex biological processes are diverse, with articles detailing the latest advancements in computational modelling at various biological length-scales, biomaterial design, material modelling, non-invasive diagnostic techniques, microfluidic devices and experimental mechanics. This second issue continues the first in this series, on the physiology of the non-pregnant woman.