ENABLING ULTRASOUND IMAGING FOR 4D IMAGING OF EMBRYONIC HEART
Sheldon Ho, Germaine Xin Yi Tan, Toon Jin Foo, Phan Thien Nhan, Choon Hwai Yap
National University of Singapore, Singapore
Understanding of embryonic cardiovascular fluid mechanics is important to understand the role of mechanics in congenital heart diseases. Detailed investigation can be performed if high resolution imaging on small animal embryos can be used to support computational fluid dynamics analysis. However, most methods of imaging are invasive and do not allow for repeated scans. Previously, older chick embryo cannot be analysed quantitatively due to poor imaging tehcnique. Ultrasound allows for good visualisation of chick embryos but suffer from excessive noise and poor contrast between tissue and blood. We present a novel technique to perform 4D imaging of chick embryos using an algorithm for spatial and temporal correlation, and show that this technique can be used for detailed quantification of geometry and various moving cardiovascular structures.
High-frequency 2D B-mode cine-ultrasound imaging was performed at multiple planes for a chick embryo at Hamburger-Hamilton (HH) stage 25. Images from 2025 cardiac cycles within each plane were averaged into one ensemble-averaged cardiac cycle, using quadratic mean which resulted in good contrast between blood and tissue spaces. Spatial and temporal correlation was used to determine matching phases in the cardiac cycle between neighboring imaging planes, and heart beats within the same imaging plane thus creating a 4D image of the blood space within the embryonic cardiovascular system. Vascular Modeling Toolkit (VMTK), was used for 3D segmentation over 2030 time points. Next, cardiac chamber volumes and vascular cross-sectional area over time were obtained and reported.
Processing of image using quadratic ensemble averaging allows for distinction to be obtained clearly. 4D image could be obtained through matching of the time points and allow quantification of peristaltic motion. This technique can be a powerful tool to use in studying older embryonic cardiovascular function, and could be used for future computational fluid dynamics analysis of embryonic cardiovascular system.