New understanding of phase-sensitive optical coherence tomography displacement measurement

Phase-sensitive optical coherence tomography (OCT) is fundamental to a range of label-free and functional imaging modalities, such as dynamic OCT, Doppler OCT and optical coherence elastography (OCE). These methods determine axial displacement by computing the phase difference between consecutive OCT acquisitions. Recent numerical and experimental studies have demonstrated that, even in ideal noise-free conditions, the accuracy of phase-difference-based displacement estimation declines in regions of dark speckles. This study introduces a novel physics-based deterministic model that analytically describes how speckle characteristics influence the measured phase difference, revealing the limitations of conventional displacement estimation approaches. To address these challenges, we propose a new displacement estimation technique that maps unloaded A-scans to loaded ones, enhancing accuracy and robustness in strain measurement. Simulations and experimental results confirm that this method outperforms existing approaches in both precision and reliability.