Abstract

Visible light optical coherence tomography (OCT) has recently emerged in retinal imaging, with claims of micrometer-scale axial resolution and multi-color (sub-band) imaging. Here, we show that the large dispersion of optical glass and aqueous media, together with broad optical bandwidths often used in visible light OCT, compromises both of these claims. To rectify this, we introduce the notion of spatially dependent (i.e., depth and transverse position-dependent) dispersion. We use a novel sub-band, sub-image correlation algorithm to estimate spatially dependent dispersion in our 109 nm bandwidth visible light OCT mouse retinal imaging system centered at 587 nm. After carefully compensating spatially dependent dispersion, we achieve delineation of fine outer retinal bands in mouse strains of varying pigmentation. Spatially dependent dispersion correction is critical for broader bandwidths and shorter visible wavelengths.

© 2019 Optical Society of America

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References

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2018 (2)

2015 (1)

2014 (1)

2013 (1)

2012 (2)

J. J. Hunter, J. I. Morgan, W. H. Merigan, D. H. Sliney, J. R. Sparrow, and D. R. Williams, Prog. Retinal Eye Res. 31, 28 (2012).
[Crossref]

W. Choi, B. Baumann, E. A. Swanson, and J. G. Fujimoto, Opt. Express 20, 25357 (2012).
[Crossref]

2011 (1)

F. E. Robles, C. Wilson, G. Grant, and A. Wax, Nat. Photonics 5, 744 (2011).
[Crossref]

2004 (2)

2003 (1)

1998 (1)

Augustin, M.

Backman, V.

Baumann, B.

Bernucci, M. T.

Boppart, S. A.

Bouma, B. E.

Brown, W. J.

Cense, B.

Chen, T. C.

Choi, W.

Chong, S. P.

Clement, T. S.

de Boer, J. F.

Diddams, S. A.

Dubra, A.

Duker, J.

Eugui, P.

Fujimoto, J.

Fujimoto, J. G.

Glösmann, M.

Grant, G.

F. E. Robles, C. Wilson, G. Grant, and A. Wax, Nat. Photonics 5, 744 (2011).
[Crossref]

Harper, D. J.

Hitzenberger, C. K.

Hunter, J. J.

J. J. Hunter, J. I. Morgan, W. H. Merigan, D. H. Sliney, J. R. Sparrow, and D. R. Williams, Prog. Retinal Eye Res. 31, 28 (2012).
[Crossref]

Kho, A.

Kim, S.

Ko, T.

Kowalczyk, A.

Leahy, C.

Lichtenegger, A.

Liu, W.

Marks, D. L.

Merigan, W. H.

J. J. Hunter, J. I. Morgan, W. H. Merigan, D. H. Sliney, J. R. Sparrow, and D. R. Williams, Prog. Retinal Eye Res. 31, 28 (2012).
[Crossref]

Merkle, C. W.

Morgan, J. I.

J. J. Hunter, J. I. Morgan, W. H. Merigan, D. H. Sliney, J. R. Sparrow, and D. R. Williams, Prog. Retinal Eye Res. 31, 28 (2012).
[Crossref]

Nassif, N. A.

Oldenburg, A. L.

Park, B. H.

Pierce, M. C.

Radhakrishnan, H.

Reyes, C.

Reynolds, J. J.

Robles, F. E.

F. E. Robles, C. Wilson, G. Grant, and A. Wax, Nat. Photonics 5, 744 (2011).
[Crossref]

Sliney, D. H.

J. J. Hunter, J. I. Morgan, W. H. Merigan, D. H. Sliney, J. R. Sparrow, and D. R. Williams, Prog. Retinal Eye Res. 31, 28 (2012).
[Crossref]

Sparrow, J. R.

J. J. Hunter, J. I. Morgan, W. H. Merigan, D. H. Sliney, J. R. Sparrow, and D. R. Williams, Prog. Retinal Eye Res. 31, 28 (2012).
[Crossref]

Srinivasan, V.

Srinivasan, V. J.

Swanson, E. A.

Tearney, G. J.

Van Engen, A. G.

Wax, A.

W. J. Brown, S. Kim, and A. Wax, J. Opt. Soc. Am. A 31, 2703 (2014).
[Crossref]

F. E. Robles, C. Wilson, G. Grant, and A. Wax, Nat. Photonics 5, 744 (2011).
[Crossref]

Wei, Q.

Williams, D. R.

J. J. Hunter, J. I. Morgan, W. H. Merigan, D. H. Sliney, J. R. Sparrow, and D. R. Williams, Prog. Retinal Eye Res. 31, 28 (2012).
[Crossref]

Wilson, C.

F. E. Robles, C. Wilson, G. Grant, and A. Wax, Nat. Photonics 5, 744 (2011).
[Crossref]

Wojtkowski, M.

Yi, J.

Yun, S.-H.

Zhang, H. F.

Zhang, T.

Appl. Opt. (2)

Biomed. Opt. Express (3)

J. Opt. Soc. Am. A (1)

Nat. Photonics (1)

F. E. Robles, C. Wilson, G. Grant, and A. Wax, Nat. Photonics 5, 744 (2011).
[Crossref]

Opt. Express (3)

Opt. Lett. (1)

Prog. Retinal Eye Res. (1)

J. J. Hunter, J. I. Morgan, W. H. Merigan, D. H. Sliney, J. R. Sparrow, and D. R. Williams, Prog. Retinal Eye Res. 31, 28 (2012).
[Crossref]

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Figures (4)

Fig. 1.
Fig. 1. Simulations based on Eqs. (1)–(6) show the severity of depth-dependent (DD) dispersion in our visible light OCT system (λ0=587nm, δλ=109nm). A: water refractive index and Gaussian spectrum versus wavelength. B: simulated axial point spread function (PSF) broadens with increasing axial depth (Δz). The PSF phase slope is encoded as the visible color of the corresponding wavelength. C: the magnitude of the PSF (dotted lines) is well-predicted by group velocity dispersion (GVD) alone (solid lines), while higher dispersion orders induce PSF asymmetry. D: PSF broadening with depth [Eq. (7)] due to GVD (colored solid lines) increases as the transform limited resolution (solid black line) is improved. For our system parameters, water dispersion severely degrades resolution (dotted black line).
Fig. 2.
Fig. 2. Visible light OCT ophthalmoscope schematic. Differences in material traversed by the beam when scanning off axis (green) lead to transverse dependence of dispersion. (L, lens; SPF, short pass filter; LPF, long pass filter; NDF, neutral density filter; M, mirror; LSC, line scan camera; C, collimator; RC, reflective collimator; SMF, single mode fiber; BS, beam splitter; PCF, photonic crystal fiber; LPF-610, 610 nm long pass filter for alignment purposes.)
Fig. 3.
Fig. 3. Correcting SDD using a sub-band, sub-image correlation algorithm. A: via short time Fourier transform (STFT), the original image is split into spectral sub-band images, which are further partitioned into sub-images. B: for each sub-image, each sub-band is correlated to a reference sub-band, resulting in a relative depth shift for each sub-band versus image depth. For each transverse position (ximg=x1 shown) and sub-band, the shift with depth is fit by a first-order polynomial with the y intercept (constant) and first-order (slope) terms relating to depth-independent (DI) and DD dispersion, respectively. Assigning parameters to the center frequency for each sub-band and center transverse position for each sub-image, we can interpolate to find the constants and slopes for every frequency (ω) and transverse position. Integration of the slopes and constants yields the cumulative sampling deviation and phase correction. To avoid depth scaling or shifting of the image, a re-centering procedure is included. Correction is achieved by complex phase correction and resampling based on the sampling deviation.
Fig. 4.
Fig. 4. A–D: zooms of visible light OCT images of the ILM and BM in a BALB/c mouse with SID (A, B) and SDD (C, D) correction. E–H: axial intensity profiles of ILM and BM in different transverse regions denoted by the corresponding colored arrows (A–D): averaged across 100 images, with SID (E, F) and SDD (G, H) correction. Table I: the full width at half-maximum (mean ± std. dev.) of the axial profiles of the ILM and BM in E–H reduce with SDD correction. J–M, Zooms of spectroscopic red–green–blue (RGB) images (λ0,blue=580nm,λ0,green=610nm,λ0,red=643nm) of the ILM (J, L) and BM (K, M) with SID and SDD correction. With SID correction, note the blue “halo” (arrows) above the ILM and below the BM due to non-overlapping sub-bands (J, K). N, P: averaged SDD corrected, spectrally shaped retinal images of C57BL/6 and BALB/c mice with outer retinal image zooms (O, Q). (ILM, inner limiting membrane; ELM, external limiting membrane; IS/OS, inner segment/outer segment junction; OST, outer segment tips; RPE, retinal pigment epithelium; BM, Bruch’s membrane; CC, choriocapillaris; SID, spatially independent dispersion; SDD, spatially dependent dispersion.)

Equations (7)

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ϕ(ω,z)=2k(ω)×z=2ωn(ω)c×z,
k(ω)=k0+kL(ω)+kNL(ω)=k0+dkdω|ω0(ωω0)+m=21m!dmkdωm|ω0(ωω0)m.
Δϕ(ω,Δz)=Δϕ0(Δz)+ΔϕL(ω,Δz)+ΔϕNL(ω,Δz).
ΔϕNL(ω,Δz)=ΔϕNL(ω)+2kNL(ω)Δz
s(τ,Δz)=F1{I(ωω0)exp[iΔϕ(ω,Δz)]}=eiΔϕ0(Δz)γ(τ2Δz/vg,0)*F1{eiΔϕNL(ω,Δz)},
psf(zimg,Δz)=s(τ,Δz)|τ=2zimg/vg,img.
δzimg,GVD=δzimg1+(2log2)2vg,img4GDD2δzimg4,

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