Air-pulse optical coherence elastography: how excitation angle affects mechanical wave propagation.

Area of Science:

• Biomedical Optics
• Mechanical Engineering
• Materials Science

Background:

• Optical coherence tomography elastography (OCE) infers tissue mechanical properties from dynamic responses to stimuli.
• Air-pulse stimulation is a common dynamic excitation method in OCE.
• Understanding how excitation parameters influence OCE measurements is crucial for accuracy and clinical translation.

Purpose of the Study:

• To investigate the effect of varying excitation angles on surface wave propagation in optical coherence tomography elastography.
• To assess the impact of excitation angles on mechanical wave features (velocity, amplitude, attenuation) and displacement.
• To evaluate the robustness of OCE-based elasticity estimations across different sample types and conditions.

Main Methods:

• Air-pulse stimulation was applied at various angles (0°, 45°, 70°) to isotropic (agar), anisotropic (chicken breast), and complex (porcine cornea) samples.
• Radial optical coherence tomography (OCT) scanning captured 360° en face mechanical wave propagation.
• Wave features were analyzed in spatiotemporal and wavenumber-frequency domains; intraocular pressure (IOP) was varied for cornea samples.

Main Results:

• Mechanical wave velocities showed less sensitivity to excitation angles than displacement features, indicating robustness for elasticity estimation.
• Agar and chicken breast measurements revealed consistent metrics (especially wave velocities) for excitation angles < 45°.
• Porcine cornea measurements exhibited significant disparities in wave features and elasticity with different excitation angles, particularly at high IOP (20 mmHg).

Conclusions:

• Mechanical wave velocities are a reliable metric for elasticity in dynamic OCE, less affected by excitation angle variations.
• Complex biological tissues like the cornea show greater sensitivity to excitation angle, especially under stress (high IOP).
• Optimizing excitation angle is vital for accurate biomechanical assessment in air-pulse OCE, aiding clinical translation.