Dual-channel air-pulse optical coherence elastography for frequency response analysis

Abstract

Microliter air-pulse stimulated optical coherence elastography (OCE) was recently proposed for tissue biomechanical characterization using natural frequency oscillations. However, previous studies have not quantified actual stimulation parameters (e.g. time-frequency analysis), obscuring the actual stimulation-response function, leading to potential errors in natural frequency measurement. We propose a dual-channel air-pulse OCE method with one channel stimulating the sample and the other simultaneously measured with a pressure sensor. While pressure amplitude differences were ~10%, the frequency profiles were identical (duration: 3–35 ms; pressure: 20 Pa to 2 kPa) for both channels. The frequency response function was used to characterize the resonant features of agar phantoms (concentrations: 1–2%) and a silicone cornea phantom in an artificial anterior chamber eye model (intraocular pressure, IOP: 5–40 mmHg) under a 200 Pa stimulation pressure. The measured dominant natural frequencies increased with agar concentrations (181 Hz to 359 Hz, maximum displacements: 0.14–0.47 µm) and IOPs for the silicone cornea (333 Hz to 412 Hz, maximum displacements: 0.41–0.52 µm). These frequencies were consistent across different air–pulse durations, though coefficient variation increased as stimulus duration increased. The dual-channel OCE approach, using low-pressure stimulation and small-amplitude oscillation features, can advance our understanding of sample frequency responses when accessing delicate tissues, such as the human cornea in vivo.