Abstract

We describe a methodology for quantitative image correction in OCT which includes procedures for correction of nonlinear axial scanning and non-telecentric scan patterns, as well as a novel approach for refraction correction in layered media based on Fermat’s principle. The residual spatial error obtained in layered media with a fan-beam hand-held probe was reduced from several hundred micrometers to near the diffraction and coherence-length limits.

© 2002 Optical Society of America

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References

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Arch. Ophthalmol. (1)

S. Radhakrishnan, A. M. Rollins, J. E. Roth, S. Yazdanfar, V. Westphal, D. S. Bardenstein, and J. A. Izatt, "Real-time optical coherence tomography of the anterior segment at 1310 nm," Arch. Ophthalmol. 119, 1179-1185 (2001).
[PubMed]

Cvgip-Image Understanding (1)

D. J. Williams and M. Shah, "A fast algorithm for active contours and curvature estimation," Cvgip-Image Understanding 55, 14-26 (1992).
[CrossRef]

Int. J. Imaging Syst. Technol. (1)

P. Mattson, D. Kim, and Y. Kim, "Generalized image warping using enhanced lookup tables," Int. J. Imaging Syst. Technol. 9, 475-483 (1998).
[CrossRef]

Jpn. J. Ophthalmol. (1)

H. Ishikawa, K. Esaki, J. M. Liebmann, Y. Uji, and R. Ritch, "Ultrasound biomicroscopy dark room provocative testing: A quantitative method for estimating anterior chamber angle width," Jpn. J. Ophthalmol. 43, 526-534 (1999).
[CrossRef]

Nat. Med. (1)

W. Drexler, U. Morgner, R. K. Ghanta, F. X. Kartner, J. S. Schuman, and J. G. Fujimoto, "Ultrahighresolution ophthalmic optical coherence tomography," Nat. Med. 7, 502-507 (2001).
[CrossRef] [PubMed]

Opt. Express (1)

Opt. Lett. (4)

Skin Res. Technol. (1)

J. Welzel, "Optical coherence tomography in dermatology: a review," Skin Res. Technol. 7, 1-9 (2001).
[CrossRef] [PubMed]

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Figures (5)

Fig. 1.
Fig. 1.

A) Correction of nonlinear axial scanning B) Coordinate system of the data acquired (raw image). C) Target coordinate system in a homogeneous medium; D) Refractive interfaces in the sample alter ray paths. Abbreviations: A: full amplitude of depth scan, η: axial duty cycle of acquisition, D: distance on axis to image of scanning pivot (ISP), w: width, d: depth of acquired image, primed coordinates in raw data, unprimed in target image, P and P’: corresponding points in target and source image, φ: scan angle, φmax : extreme scan angle in the vertical center of the image, Lh : distance from P or P1 to the ISP, L1 , L2 : partial distances in inhomogeneous sample with the indices of refraction n1 and n2 , L = Lh +L1 +L2 .

Fig. 2.
Fig. 2.

Versatile lateral scanning hand held probe with a divergent scan used in these experiments. Abbreviations: CL: collimation lens, SM: scanning mirror, RL: relay lens, OL: objective lens, CG: calibration grid with a line spacing of 317 μm, translated stepwise axially, fxx: focal length of lens XX.

Fig. 3.
Fig. 3.

A) Distortion correction of nonlinear axial scanning. B) Overlay of calibration images acquired at different axial positions, each image averaged over 50 frames, corrected for nonlinear axial scanning. C) Residual error vectors in air (thin line), without correction (thick line), and with aberration correction (length x10).

Fig. 4.
Fig. 4.

A) Uncorrected image of an Intralipid© drop on a coverslip, B) corrected image

Fig. 5.
Fig. 5.

OCT images of the temporal anterior chamber angle of a human eye, imaged in vivo at 8 fps, A) raw image, B) corrected for nonlinear axial scanning (duty cycle 66.7 %) C) additionally corrected for divergent scan geometry and D) final image, corrected for refraction at the air-cornea interface (ncornea = 1.38) and at the endothelium-aqueous boundary (naqueous = 1.33)

Equations (12)

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y = f res , y ( x ' , y ' ) = A sin ( πη y ' d )
f res , y ( x ' , d 2 ) = d 2
A = d 2 sin 1 ( πη 2 ) .
x ' = F res , x x y = x
y ' = F res , y x y = d πη arcsin ( y A ) ,
φ h x y = arctan ( x / ( D y ) ) ,
L h x y = D x 2 + ( D y ) 2 .
x ' = F x h x y = arctan ( x D y ) D
y ' = F y h x y = D x 2 + ( D y ) 2
L ( P 1 , . . , P k , P ) = L h ( P 1 ) + i = 1 k 1 n i P i P i + 1 + n k P k P .
x ' = F x ( P 1 , . . . , P k , P ) = F xh ( P 1 ) ,
y' = F y ( P 1 , . . . , P k , P ) = D L ( P 1 , . . . , P k , P ) .

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