Ultrahigh-sensitive optical coherence elastography

Abstract

The phase stability of an optical coherence elastography (OCE) system is the key determining factor for achieving a precise elasticity measurement, and it can be affected by the signal-to-noise ratio (SNR), timing jitters in the signal acquisition process, and fluctuations in the optical path difference (OPD) between the sample and reference arms. In this study, we developed an OCE system based on swept-source optical coherence tomography (SS-OCT) with a common-path configuration (SS-OCE_CP). Our system has a phase stability of 4.2 mrad without external stabilization or extensive post-processing, such as averaging. This phase stability allows us to detect a displacement as small as ~300 pm. A common-path interferometer was incorporated by integrating a 3-mm wedged window into the SS-OCT system to provide intrinsic compensation for polarization and dispersion mismatch, as well as to minimize phase fluctuations caused by the OPD variation. The wedged window generates two reference signals that produce two OCT images, allowing for averaging to improve the SNR. Furthermore, the electrical components are optimized to minimize the timing jitters and prevent edge collisions by adjusting the delays between the trigger, k-clock, and signal, utilizing a high-speed waveform digitizer, and incorporating a high-bandwidth balanced photodetector. We validated the SS-OCE_CP performance in a tissue-mimicking phantom and an in vivo rabbit model, and the results demonstrated a significantly improved phase stability compared to that of the conventional SS-OCE. To the best of our knowledge, we demonstrated the first SS-OCE_CP system, which possesses high-phase stability and can be utilized to significantly improve the sensitivity of elastography.

Keywords: Biophotonics; Optical techniques.

Fig. 1. Phase stability quantification.

Overlay of 5000 interference fringes obtained using (a) SS-OCE_COV and (b) SS-OCE_CP. c Timing consistency at zero crossings

Fig. 2. SNR quantification.

a, b Original and averaged OCT images, respectively. c, d Original and averaged Doppler OCT images, respectively

Fig. 3. Elastic wave in the silicone phantom.

Time-lapse Doppler OCT B-scans obtained using (a–d) SS-OCE_COV and (e–h) SS-OCE_CP. i, j Spatiotemporal Doppler OCT at a depth indicated by the white arrows in (a) and (e), respectively

Fig. 4. Elastic wave in rabbit cornea.

a–d Time-lapse Doppler OCT B-scans from the SS-OCE_COV system. e–h Time-lapse Doppler OCT B-scans from the common-path OCE system. i, j Spatiotemporal Doppler OCT at a depth indicated by the white arrows in (a) and (e), respectively

Fig. 5. Time-lapse Doppler OCT B-scans from SS-OCE_COV and SS-OCE_CP systems with different ARFs.

a, c, e Time-lapse Doppler OCT B-scans from the SS-OCE_COV system with large, medium, and small ARFs, respectively. b, d, f Time-lapse Doppler OCT B-scans from the SS-OCE_CP system with large, medium, and small ARFs, respectively

Fig. 6. Spatiotemporal Doppler OCT of the cornea for different ARFs.

a, c, e B-scans from the SS-OCE_COV system excited with large, medium, and small ARFs, respectively. (b), (d), and (f): B-scans from the SS-OCE_CP system excited with large, medium, and small ARFs, respectively

Fig. 7

Schematics of the SS-OCE_CP system

Fig. 8

Schematics of the 30-arcmin wedged window