Directionally dependent elasticity assessment using acoustic radiation force optical coherence elastography

Optical coherence elastography (OCE) is an imaging technique for measuring elastic properties based on optical coherence tomography (OCT). Benefitting from the high-resolution imaging and sensitive motion detection of OCT, OCE has been used to assess the elasticity distribution of ocular tissue, skin tissue, etc. The biological tissues consist of multiple layers with various biomechanical properties and, thus, show directionally dependent elasticity. In previous OCE measurements, the tissues were regarded as isotropic materials, and the elasticity was measured in one direction, which may cause the bias of elasticity assessment. In this study, we developed the OCE method for directionally dependent elasticity assessment. Acoustic radiation force (ARF) generated by a ring ultrasonic transducer was applied to induce vibration in an axial direction and an elastic wave propagating in the lateral direction. The OCT beam, parallel to the ARF, scanned the sample through the central hole of the ring ultrasonic transducer. Then, phase-resolved OCT analysis was used to detect the vibration and visualize wave propagation. The vibration amplitude depends on the axial elasticity, and the lateral elasticity determines the elastic wave velocity. Therefore, the measurements of the vibration amplitude and the wave velocity using ARF-OCE can assess the elasticity of the sample in orthogonal directions. The results from the phantom measurements show that the OCE method can reliably evaluate the directionally dependent elasticity for the anisotropic samples.