Abstract
We demonstrate the use of OCT-based elastography for soft-tissue characterization using natural frequency oscillations. Sub-micrometer to sub-nanometer oscillations were induced in tissue phantoms and human cornea in vivo by perpendicular air-pulse stimulation and observed by common-path OCT imaging (sensitivity: 0.24 nm). Natural frequency and damping ratio were acquired in temporal and frequency domains using a single degree of freedom method. The dominant natural frequency was constant for different stimulation pressures (4-32 Pa) and measured distances (0.3-5.3 mm), and decreased as the sample thickness increased. The dominant natural frequencies of 0.75-2% agar phantoms were 127-774 Hz (mean coefficient of variation [CV]: 0.9%), and correlated with the square root of Young's moduli (16.5-117.8 kPa, mean CV: 5.8%). These preliminary studies show repeatable in vivo corneal natural frequency measurements (259 Hz, CV: 1.9%). This novel OCE approach can distinguish tissues and materials with different mechanical properties using the small-amplitude tissue oscillation features, and is suitable for characterizing delicate tissues in vivo such as the eye.
Highlights
Soft tissue biomechanical properties are related to tissue health, and disease progression often changes the biomechanical properties of the affected tissues [1,2]
We have recently introduced an Optical coherence elastography (OCE) approach based on a higher resolution optical coherence tomography (OCT) technique and a perpendicular air-pulse stimulation method [42]
Small-amplitude damped oscillations were induced by perpendicular air-pulse stimulation, and were directly observed using the common-path OCT with displacement resolution of 0.24
Summary
Soft tissue biomechanical properties (e.g. stiffness or Young’s modulus) are related to tissue health, and disease progression often changes the biomechanical properties of the affected tissues [1,2]. In tissues with complex geometries and multiple layers, such as cornea and skin, mechanical waves traveling along the surface contain multiple highly dispersive Rayleigh-Lamb components and become very complex compared to simple Rayleigh waves [29,30]. In this case, translation of the measured wave propagation speed into the shear wave model could lead to inaccurate estimation of tissue Young’s modulus [28]. We recently proposed a modified Rayleigh-Lamb wave model to quantitatively assess the corneal viscoelasticity [30,31] This method is limited in a first-order assumption that the cornea is isotropic, homogenous, and has a flat curvature. The development of robust computational methods and tissue modeling techniques is important to provide more robust tissue elasticity estimation from dynamic OCE [21]
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