Fig. 1. Three main steps of the classical OCE technique^[45]

Fig. 2. Elastography of human breast cancer tissues obtained from elastography across different spatial scales^[68-71]

Fig. 3. Different excitation methods for OCE technology^[72]

Fig. 4. OCT-based OCE system setup. (a) SD-OCE system; (b) SS-OCE system

Fig. 5. M-scan mode with temporal repetitive scanning at a particular transverse position x0 to obtain vibration information at that position over time

Fig. 6. M-B scanning mode. (a) M-B scanning optical path setup with the OCT probe beam completing the B-scan in the x-z plane; (b) M-B scanning timing control program; (c) 3D dataset acquired in the M-B scanning mode (x, z, t)

Fig. 7. Tissue model in the 3D Cartesian coordinate system (x,y,z)

Fig. 8. Types of mechanical waves in biological tissues

Fig. 9. Imaging results of LSW with AC-ARF non-contact excitation in the agar model^[63]. (a) M-scan mode results of LSW, while white arrows indicate the different detection moments; (b) vibrational displacement curves of LSW along the depth direction at different detection moments

Fig. 10. OCE results for SAW and SRW in agar^[127]. (a) 2D vibrational displacement propagation images of SAW and SRW within agar at different moments, with yellow arrows at the top of the image indicating excitation points; (b) 3D surfaces (x, z, t) reconstructed for SAW and SRW, with white arrows indicating SAW wavefronts and black arrows indicating SRW wavefronts; (c) 2D OCT images of the agar; (d) the displacement profiles of SRW and SAW at 2.7 ms at the depths shown by the blue line in Fig. 10 (a); (e) the spatiotemporal displacement of SRW and SAW at the depths shown by the blue line in Fig. 10(a)

Fig. 11. Lamb wave propagation modes in thin plates. (a) Symmetric mode; (b) antisymmetric mode

Fig. 12. Application areas of optical coherent elastography

Fig. 13. OCE results after corneal-3D refractive surgery^[136]. (a) 2D structural image of the cornea, with red arrows indicating the boundary between the corneal cap and residual stromal bed; (b) corneal depth resolved elastography results, with red arrows indicating the boundary between the Young's modulus of the corneal cap and residual stromal bed after surgery

Fig. 14. Results of OCE experiments after keratoconus cross-linking surgery^[78]. (a) 2D structural image of the keratoconus after 15J-CXL treatment; (b) propagation process of the vibrational displacements at different times after the 15J-CXL treatment; (c) 2D structural image of the keratoconus in vivo after 30J-CXL treatment; (d) propagation process of the vibrational displacements at different times after the 30J-CXL treatment; (e) 15J-CXL depth-resolved image of the internal phase velocity of the keratoconus after treatment; (f) depth-resolved image of the internal phase velocity of the conical cornea after 30J-CXL treatment; (g) comparison of the average velocity values

Fig. 15. Mechanical stiffness of breast cancer tissue based on QEM. (a) Histopathological section of breast cancer; (b) enface diagram of OCT; (c) mechanical stiffness results of breast cancer tissue obtained by QEM technology to the OCT structure diagram

Fig. 16. OCE experimental results of non-contact LSW in isolated porcine brain tissue. (a) In vitro pig brain tissue experimental samples; (b) two-dimensional OCT structural images of cerebral vascular regions; (c) three-dimensional OCT structural images of cerebral vascular regions; (d) M-scan mode image of the LSW propagation process in the left cerebral vascular region; (e) vibration displacement curves of LSW at different times; (f) M-scan mode image of the LSW propagation process in the right cerebral vascular region; (g) vibration displacement curves of LSW at different times

Fig. 17. Results of OCE experiments based on SRW and SAW models for isolated porcine brain tissue. (a) The three regions of isolated porcine brain tissue selected in the experiments; (b) the propagation process of SRW and SAW at different moments in the FL region; (c) the results of the 3D reconstruction of the wave front surface of the propagation process at different moments of SRW and SAW; (d) the spatio-temporal displacement map of SRW and SAW

Fig. 18. Characterization of the scar tissue in vivo with four different OCT modalities^[196]. (a) Photograph of the scar area in a 28-year-old male volunteer; (b) its enlarged area with the direction of the mechanical wave propagation in the scar and adjacent skin site; (c) group velocity of the Rayleigh wave in the scar and in the normal skin tissue in two orthogonal directions; (d)‒(e) Structural OCT and OCT angiography images; (f) optic axis orientation map obtained with the PS-OCT system; (g) image of Rayleigh wave group velocity measured in the direction perpendicular to the scar within the area covered by a white dashed rectangle

Table 1. Comparison of different elastography technical parameters

Table 2. Elastic modulus results of the corneal tissue obtained from different OCE experiments

Table 3. Elastic modulus results of the crystalline lens obtained from different OCE experiments

Table 4. Elastic modulus results of sclera tissue obtained from different OCE experiments

Table 5. Elastic modulus results of retinal tissue obtained from different OCE experiments