One or more devices, systems, methods, and storage mediums for optical imaging medical devices, such as, but not limited to, Optical Coherence Tomography (OCT), single mode OCT, and/or multi-modal OCT apparatuses and systems, and methods and storage mediums for use with same, for calculating lumen distance(s), including based on real-time A-line signal(s), are provided herein. Examples of applications include imaging, evaluating and diagnosing biological objects, such as, but not limited to, for Gastro-intestinal, cardio and/or ophthalmic applications, and being obtained via one or more optical instruments, such as, but not limited to, optical probes, catheters, capsules and needles (e.g., a biopsy needle). Fast A-line lumen segmentation methods, which can be applied real-time to a whole arterial pullback, and devices, systems, and storage mediums for use with same, are provided herein. Techniques provided herein also improve processing efficiency and decrease calculations while achieving measurements that are more precise.