Discriminative imaging of maternal and fetal blood flow within the placenta using ultrafast ultrasound

Abstract

Being able to map accurately placental blood flow in clinics could have major implications in the diagnosis and follow-up of pregnancy complications such as intrauterine growth restriction (IUGR). Moreover, the impact of such an imaging modality for a better diagnosis of placental dysfunction would require to solve the unsolved problem of discriminating the strongly intricated maternal and fetal vascular networks. However, no current imaging modality allows both to achieve sufficient sensitivity and selectivity to tell these entangled flows apart. Although ultrasound imaging would be the clinical modality of choice for such a problem, conventional Doppler echography both lacks of sensibility to detect and map the placenta microvascularization and a concept to discriminate both entangled flows. In this work, we propose to use an ultrafast Doppler imaging approach both to map with an enhanced sensitivity the small vessels of the placenta (~100 μm) and to assess the variation of the Doppler frequency simultaneously in all pixels of the image within a cardiac cycle. This approach is evaluated in vivo in the placenta of pregnant rabbits: By studying the local flow pulsatility pixel per pixel, it becomes possible to separate maternal and fetal blood in 2D from their pulsatile behavior. Significance Statement: The in vivo ability to image and discriminate maternal and fetal blood flow within the placenta is an unsolved problem which could improve the diagnosis of pregnancy complications such as intrauterine growth restriction or preeclampsia. To date, no imaging modality has both sufficient sensitivity and selectivity to discriminate these intimately entangled flows. We demonstrate that Ultrafast Doppler ultrasound method with a frame rate 100x faster than conventional imaging solves this issue. It permits the mapping of small vessels of the placenta (~100 μm) in 2D with an enhanced sensitivity. By assessing pixel-per-pixel pulsatility within single cardiac cycles, it achieves maternal and fetal blood flow discrimination.

Adaptive Spatiotemporal SVD Clutter Filtering for Ultrafast Doppler Imaging Using Similarity of Spatial Singular Vectors

“…In order to challenge the estimators in strong clutter conditions, only the 3 highest tissue speeds were considered. This corresponds to probe motion speeds in the range [8][9][10][11][12] mm/s or [22][23][24][25][26]°/s. The 6 blood flow speeds available were clustered into 3 subgroups: small flows (2-4 cm/s), medium flows (9-15 cm/s), and high flows (19-37 cm/s).…”

“…The primary effect is the substantial increase in sensitivity to blood flow in Doppler imaging after clutter filtering, by a factor up to 30 [2]. This increased sensitivity lead to numerous clinical application, for example in cardiac imaging [3] or liver vascular imaging [4], but also opened a whole new playground in fundamental research with functional imaging [5]- [7] and preclinical applications [8], [9]. In all these examples, clutter filtering, which discriminates between blood flow and tissue signal, is critical: when targeting quantitative measurements, tissue motion can be a major source of artefacts and corrupt the measured level of blood volume or blood flow.…”

Models of Intrauterine growth restriction and fetal programming in rabbits

“…Due to their size, serial blood collections of the rabbit doe can be performed to inform of the endocrine and metabolic changes during pregnancy (Haneda et al, 2010;López-Tello, Arias-Álvarez, Jiménez-Martínez, Barbero-Fernández et al, 2017). Moreover, ultrasound imaging of the developing conceptus can be undertaken to assess longitudinal changes with subsequent follow up of the offspring (Chavatte-Palmer et al, 2008;López-Tello et al, 2015;López-Tello, Arias-Álvarez, Jiménez-Martínez, Barbero-Fernández et al, 2017;Osmanski et al, 2015;Polisca, Scotti, Orlandi, Brecchia, & Boiti, 2010). Hemodynamic changes in the rabbit placenta are similar to the human (Fischer et al, 2012;Lecarpentier et al, 2012;Polisca et al, 2010).…”

Visualization of Small-Diameter Vessels by Reduction of Incoherent Reverberation With Coherent Flow Power Doppler

“…Direct visualization of spiral artery remodeling could be used to assess the relation between preeclampsia and IUGR and the spiral arteries, but PD has been limited in its ability to detect the small-diameter vessels in the placental vasculature [12], [13]. Although effects have been made to detect the blood flow withing the placenta of rabbits [14], it is challenging to translate scientific discovery from lower order organisms, including rabbits, to humans, because the placenta is strikingly distinct in humans when compared with other animals. Three-dimensional (3D) ultrasound power Doppler has been demonstrated to provide more information than 2D power Doppler, but can only detect the ends of spiral arteries rather than the entire spiral arteries [15], which limits its diagnostic value.…”