In one aspect, the invention relates to a computer-implemented method of triggering optical coherence tomography data collection. The method includes collecting optical coherence tomography data with respect to a vessel using an optical coherence tomography probe disposed in the vessel; determining a clearing radius and a quality value for each frame of optical coherence tomography data collected for the vessel using a computer; determining if a blood clearing state has occurred using at least one clearing radius and at least one quality value; and generating a trigger signal in response to the blood clearing state.