Noncontact depth-resolved micro-scale optical coherence elastography of the cornea

Abstract

High-resolution elastographic assessment of the cornea can greatly assist clinical diagnosis and treatment of various ocular diseases. Here, we report on the first noncontact depth-resolved micro-scale optical coherence elastography of the cornea achieved using shear wave imaging optical coherence tomography (SWI-OCT) combined with the spectral analysis of the corneal Lamb wave propagation. This imaging method relies on a focused air-puff device to load the cornea with highly-localized lowpressure short-duration air stream and applies phase-resolved OCT detection to capture the low-amplitude deformation with nano-scale sensitivity. The SWI-OCT system is used here to image the corneal Lamb wave propagation with the frame rate the same as the OCT A-line acquisition speed. Based on the spectral analysis of the corneal temporal deformation profiles, the phase velocity of the Lamb wave is obtained at different depths for the major frequency components, which shows the depthwise distribution of the corneal stiffness related to its structural features. Our pilot experiments on ex vivo rabbit eyes demonstrate the feasibility of this method in depth-resolved micro-scale elastography of the cornea. The assessment of the Lamb wave dispersion is also presented, suggesting the potential for the quantitative measurement of corneal viscoelasticity. 3026-3031 (2007). 3. L. T. Nordan, "Keratoconus: diagnosis and treatment," Int. Ophthalmol. Clin. 37(1), 51-63 (1997). 4. C. Edmund, "Corneal elasticity and ocular rigidity in normal and keratoconic eyes," Acta Ophthalmol. (Copenh.) 66(2), 134-140 (1988 Biol. 93(1-3), 176-191 (2007). 17. G. Scarcelli and S. H. Yun, "Confocal Brillouin microscopy for three-dimensional mechanical imaging," Nat. ©2014 Optical Society of AmericaPhotonics 2(1), 39-43 (2008). 18. J. Schmitt, "OCT elastography: imaging microscopic deformation and strain of tissue," Opt. Express 3(6), 199-211 (1998). 19. G. Scarcelli and S. H. Yun, "In vivo Brillouin optical microscopy of the human eye," Opt. Express 20(8), 9197-9202 (2012). 20. G. Scarcelli, R. Pineda, and S. H. Yun, "Brillouin optical microscopy for corneal biomechanics," Invest.Ophthalmol. Vis. Sci. 53(1), 185-190 (2012). 21. G. Scarcelli, S. Kling, E. Quijano, R. Pineda, S. Marcos, and S. H. Yun, "Brillouin microscopy of collagen crosslinking: noncontact depth-dependent analysis of corneal elastic modulus," Invest. Ophthalmol. Vis. Sci.

Assessing mechanical properties of tissue phantoms with non-contact optical coherence elastography and Michelson interferometric vibrometry

“…However, the LMIV can only measure the wave propagation at the surface of the sample since internal scattering is dominated by the specular reflection from the surface. In contrast, OCE can provide depth-resolved elasticity measurements [46]. To further demonstrate the depth-resolved elasticity characterization by OCE, a sandwich-type agar phantom was constructed with a 2% agar layer between two layers of 1% agar (Fig.…”

“…6). Because the airpulse induced elastic wave wavelength is large, spectral analysis was utilized to provide depth-resolved elasticity assessment [46], and all three layers were differentiated successfully. Figure 6 shows the phase velocity of the air-pulse induced elastic wave at 180 Hz.…”

Non-contact single shot elastography using line field low coherence holography

“…We have previously reported a non-contact elastic wave imaging optical coherence elastography (EWI-OCE) technique [4], which utilizes point-by-point scanning and allows for two and three dimensional visualization of the low amplitude elastic wave propagation in tissue [8]. This technique has been successfully applied to assess the biomechanical properties of nephritic kidneys [9], cardiac muscle [10], and the cornea [11] among others. The typical EWI-OCE procedure involves acquisition of multiple M-mode images across various spatial positions, usually a line, of the tissue (M-B mode imaging).…”

“…Although that technique was capable of quantifying the depth-wise elasticity in tissues, it required prior knowledge of the surface wave frequency and was restricted to wave displacements within -π/2 to π/2. These limitation may not be suitable for air-pulse based applications [11,19], since the displacement amplitude and frequency cannot be known beforehand. In addition, the acquisition frame rate may not be sufficient to capture the airpulse induced elastic wave, which attenuates within a few millimeters [20].…”

Wide-field optical coherence micro-elastography for intraoperative assessment of human breast cancer margins

“…OCE utilizes OCT to measure tissue deformation induced by a mechanical load, and maps this information into an image (elastogram) of a mechanical property or parameter of the tissue [18]. Various OCE techniques have been developed with different loading and detection methods for various applications [19], including in ophthalmology [20], cardiology [21] and dermatology [22]. In our technique, termed optical coherence micro-elastography (OCME), a variant of compression, phase-sensitive OCE, a quasi-static deformation is introduced to the tissue between the acquisition of OCT B-scans [23].…”