Asynchronous optical coherence elastography and directional phase gradient analysis.

Significance: The stiffness and compliance of biological tissues are key properties that often change in the presence of pathology, yet current shear wave elastography approaches using optical coherence tomography (OCT) face limitations due to slow image acquisition, sensitivity to motion artifacts, and reliance on advanced hardware, hindering clinical translation.

Aim: The aim is to develop and validate a practical, high-speed method for three-dimensional shear wave imaging compatible with standard OCT systems and wave propagation variability.

Approach: We introduce a technique for the rapid, asynchronous acquisition of three-dimensional shear wave fields. Our technique operates at conventional acquisition rates and utilizes pairs of B-scans, similar to angiography scanning protocols. This approach significantly reduces motion sensitivity and enhances acquisition speed, even with much denser lateral sampling. In addition, we present a technique for estimating the shear wave number, termed directional phase gradient analysis. This method computes the phase gradient of the autocorrelation of the directionally-filtered, complex-valued shear wave and is robust across unidirectional, partially diffuse, and fully diffuse shear wave conditions.

Results: We validated the accuracy of our techniques through direct comparison with phase-locked, synchronous-mode imaging in benchtop experiments using tissue-mimicking phantoms. Furthermore, we demonstrated their robustness to variations in wave orientation, excitation amplitude, and diffusivity, as confirmed by repeated measurements on the same sample under diverse conditions.

Conclusions: Together, these methods may offer a more practical approach for shear wave imaging without requiring modifications to existing clinical phase-stable OCT systems.