Segmentation of beating embryonic heart structures from 4-D OCT images using deep learning.

Optical coherence tomography (OCT) has been used to investigate heart development because of its capability to image both structure and function of beating embryonic hearts. Cardiac structure segmentation is a prerequisite for the quantification of embryonic heart motion and function using OCT. Since manual segmentation is time-consuming and labor-intensive, an automatic method is needed to facilitate high-throughput studies. The purpose of this study is to develop an image-processing pipeline to facilitate the segmentation of beating embryonic heart structures from a 4-D OCT dataset. Sequential OCT images were obtained at multiple planes of a beating quail embryonic heart and reassembled to a 4-D dataset using image-based retrospective gating. Multiple image volumes at different time points were selected as key-volumes, and their cardiac structures including myocardium, cardiac jelly, and lumen, were manually labeled. Registration-based data augmentation was used to synthesize additional labeled image volumes by learning transformations between key-volumes and other unlabeled volumes. The synthesized labeled images were then used to train a fully convolutional network (U-Net) for heart structure segmentation. The proposed deep learning-based pipeline achieved high segmentation accuracy with only two labeled image volumes and reduced the time cost of segmenting one 4-D OCT dataset from a week to two hours. Using this method, one could carry out cohort studies that quantify complex cardiac motion and function in developing hearts.