Rotationally acquired 4D-optical coherence tomography of embryonic chick hearts using retrospective gating on the common central A-scan

In vivo analysis of cardiac physiology and non-invasive imaging of the beating early embryonic heart in 2 and 3D remain a challenge in cardiovascular development research. 3D-imaging of the beating heart relies on gating of the acquired images according to the cardiac cycle. Mostly ECG triggering is used for this purpose, e.g. in MRT or CT of human hearts. For visualization of embryonic chick hearts with high-resolution optical coherence tomography (OCT), a gating trigger generated by laser Doppler velocimetry has been successfully demonstrated (1). But this takes time and adds to system complexity. More recently, retrospective gating technologies were described (2; 3). In these studies, a time series of 2D images at several positions along the heart volume was used to produce a time sequence of 3D volumes of the beating heart. Rearrangement and validation of the asynchronously acquired input data are based on image similarity of adjacent pictures and a perpendicularly recorded B-scan or a repetitive low-resolution 3D-volume-scan. In our study, we introduce a novel technique that uses a rotational scan mode of a swept-source OCT system (Thorlabs) for imaging the beating embryonic heart. The central A-scan is identical with the rotational axis. Thus, the heart phase can be synchronized in every rotated image plane from the central A-scan. A rotation of 180° allows to create a complete 4D dataset of the beating embryonic chick heart.