This webinar considered a new class of targeted, liposomal-gadolinium MRI contrast agents that do not cross the placental barrier for preclinical studies of placental vascular architecture and placental accreta, or invasive placentation. These studies are conducted on a 1T permanent magnet MRI instrument which has high sensitivity for this gadolinium-based contrast agent.
Contrast‐enhanced magnetic resonance imaging (CE‐MRI) is a dynamic technique for imaging vasculature. However, currently available agents have small windows for image acquisition due to their rapid elimination from blood. Work from the Translational Imaging Group (TIGr) has led to the development of a new class of liposomal-gadolinium contrast agents with long circulating properties that make them an ideal tool for blood pool imaging at field strengths of 1T. TIGr has published multiple studies on the utilization of this agent for applications in imaging of cancer, neurodegenerative diseases, and placental disorders.
In this webinar, Dr. Badachhape discussed two placental studies using this agent: 1) characterization of placental vasculature through estimation of placental fractional blood volume (FBV) and 2) visualization of the retroplacental clear space, a junctional zone between the placenta and endometrium, to improve early diagnosis of placental accreta, or invasive placentation. Of crucial importance to these studies is the fact that this novel agent does not permeate the placental barrier in rodents and thus spares the fetus from gadolinium exposure.
In the first study, CE-MRI with liposomal-gadolinium is used to calculate placental fractional blood volume (FBV), which is indicative of perfusion and may enable identification of local ischemia. Using a variable flip angle method to perform T1 mapping before and after administration of liposomal-gadolinium, placental FBV was calculated at 14, 16, and 18 days of gestation in a mouse model of pregnancy. Placental FBV estimates calculated from CE-MRI were validated with contrast-enhanced computed tomography (CE-CT) where the signal is linearly proportional to the concentration of iodine contrast agent.
In the second study, the murine placenta is monitored through the second half of gestation using CE-MRI with liposomal-gadolinium in order to characterize the appearance and volume of the retroplacental clear space. In placental accreta, the placenta invades the uterine wall, thus complicating delivery. Noninvasive methods for visualizing and assessing the retroplacental clear space would greatly improve diagnosis of placental accreta. This study demonstrated that clear visualization of the murine retroplacental clear space started at day 12 of gestation.
Topics discussed in this webinar included:
- Requirements for high resolution, blood pool MR imaging at 1T
- Placental fractional blood volume estimates yielded from contrast-enhanced T1 mapping
- High-resolution imaging of the junctional zone between the placenta and endometrium
- Additional imaging applications of liposomal-gadolinium including longitudinal monitoring of neuroblastoma progression and characterization of the tumor microenvironment
Dr. Andrew Badachhape is an Instructor at Baylor College of Medicine and a senior member of the Translational Imaging Group (TIGr). He leads multiple preclinical research projects encompassing pathologies such as placental accreta, neuroblastoma, and Alzheimer’s disease. These projects feature the deployment of a new class of nanoparticle-based MRI contrast agents for blood pool imaging. In addition to novel contrast mechanisms, Dr. Badachhape has a deep interest in translating advances in machine learning and compressed sensing into clinical practice.