MRI Angiography of Physiological and Pathological Pregnancy Placentas Ex-Vivo (MAPLE): protocol for a prospective pilot study. (Preprint)

BACKGROUND Preeclampsia (PE) and intra-uterine growth restriction (IUGR) are two major pregnancy complications due to abnormal placental vasculogenesis. Data on whole fetoplacental vasculature are still missing to better understand these pathologies. Ex-vivo magnetic resonance imaging (MRI) angiography has been developed to characterize the human placental vasculature by injecting contrast within the umbilical cord. OBJECTIVE The primary objective is to compare the vascular architecture of placenta between physiological and pathological pregnancies. Secondary objectives are (i) to analyse vascularization indices and texture features according to the group and within comparable gestational age (ii) to compare de vascularization indices to histological analysis. METHODS This is a prospective controlled study. We expect to include 100 placentas: 40 from normal pregnancies and 60 from pathological pregnancies with 30 for IUGR and 30 for PE. Ex-vivo MRI acquisition will be performed shortly after delivery and with preparation by injection within the umbilical cord. The vascular architecture will be quantitatively described by vascularization indices measured from ex-vivo MRI angiography data. Comparisons of vascularization indices and texture features according to the group and within comparable gestational age will be also performed. After MR acquisition, placental histopathological analysis will be performed. RESULTS The enrolment of women began in November 2019. In view of the recruitment capacity of our institution and the availability of the MRI, the recruitment should be completed by March 2022. As of November 2021, we enrolled 70% of the population. CONCLUSIONS This study protocol aims to provide information about the fetal side of placental vascular architecture in normal and pathological placenta with MRI. CLINICALTRIAL NCT 04389099 (Clinical Trial)

Analysis of vascular architecture and parenchymal damage generated by reduced blood perfusion in decellularized porcine kidneys using a gray level co-occurrence matrix

There is no cure for kidney failure, but a bioartificial kidney may help address this global problem. Decellularization provides a promising platform to generate transplantable organs. However, maintaining a viable vasculature is a significant challenge to this technology. Even though angiography offers a valuable way to assess scaffold structure/function, subtle changes are overlooked by specialists. In recent years, innovative image analysis methods in radiology have been suggested to detect and identify subtle changes in tissue architecture. The aim of our research was to apply one of these methods based on a gray level co-occurrence matrix (GLCM) computational algorithm in the analysis of vascular architecture and parenchymal damage generated by hypoperfusion in decellularized porcine. Perfusion decellularization of the whole porcine kidneys was performed using previously established protocols. We analyzed and compared angiograms of kidneys subjected to pathophysiological arterial perfusion of whole blood. For regions of interest (ROIs) covering kidney medulla and the main elements of the vascular network, five major GLCM features were calculated: angular second moment as an indicator of textural uniformity, inverse difference moment as an indicator of textural homogeneity, GLCM contrast, GLCM correlation, and sum variance of the co-occurrence matrix. In addition to GLCM, we also performed discrete wavelet transform analysis of angiogram ROIs by calculating the respective wavelet coefficient energies using high and low-pass filtering. We report statistically significant changes in GLCM and wavelet features, including the reduction of the angular second moment and inverse difference moment, indicating a substantial rise in angiogram textural heterogeneity. Our findings suggest that the GLCM method can be successfully used as an addition to conventional fluoroscopic angiography analyses of micro/macrovascular integrity following in vitro blood perfusion to investigate scaffold integrity. This approach is the first step toward developing an automated network that can detect changes in the decellularized vasculature.

Adaptation of peristaltic pumps for laminar flow experiments

Endothelial cells (ECs) are the primary cellular constituent of blood vessels that are in direct contact with hemodynamic forces over the course of a lifetime. Throughout the body, vessels experience different types of blood flow patterns and rates that alter vascular architecture and cellular behavior. Because of the complexities of studying blood flow in an intact organism, particularly during development, modeling of blood flow in vitro has become a powerful technique for studying hemodynamic dependent signaling mechanisms in ECs. While commercial flow systems that recirculate fluids exist, many commercially available pumps are peristaltic and best model pulsatile flow conditions. However, there are many important in vivo situations in which ECs experience laminar flow conditions, such as along long, straight stretches of the vasculature. To understand EC function under these situations, it is important to be able to consistently model laminar flow conditions in vitro. Here, we outline a method to reliably adapt commercially available peristaltic pumps to reproducibly study laminar flow conditions. Our proof of concept study focuses on 2-dimensional (2D) models but could be further adapted to 3-dimensional (3D) environments to better model in vivo scenarios such as organ development. Our studies make significant inroads into solving technical challenges associated with flow modeling, and allow us to conduct functional studies towards understanding the mechanistic role of flow forces on vascular architecture, cellular behavior, and remodeling during a variety of physiological contexts.

In vitro investigation of the impact of pulsatile blood flow on the vascular architecture of decellularized porcine kidneys

A method was established using a scaffold-bioreactor system to examine the impact pulsatile blood flow has on the decellularized porcine kidney vascular architecture and functionality. These scaffolds were subjected to continuous arterial perfusion of whole blood at normal physiological (650 ml/min and 500 ml/min) and pathophysiological (200 ml/min) rates to examine dynamic changes in venous outflow and micro-/macrovascular structure and patency. Scaffolds subjected to normal arterial perfusion rates observed drops in venous outflow over 24 h. These reductions rose from roughly 40% after 12 h to 60% after 24 h. There were no apparent signs of clotting at the renal artery, renal vein, and ureter. In comparison, venous flow rates decreased by 80% to 100% across the 24 h in acellular scaffolds hypoperfused at a rate of 200 ml/min. These kidneys also appeared intact on the surface after perfusion. However, they presented several arterial, venous, and ureteral clots. Fluoroscopic angiography confirmed substantial alterations to normal arterial branching patterns and patency, as well as parenchymal damage. Scanning electron microscopy revealed that pulsatile blood perfusion significantly disrupted glomerular microarchitecture. This study provides new insight into circumstances that limit scaffold viability and a simplified model to analyze conditions needed to prepare more durable scaffolds for long-term transplantation.