Optimal processing of non-linearity in swept-source and spectral-domain optical coherence tomography

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Optimal processing of non-linearity in swept-source and spectral-domain optical coherence tomography

Vergnole, Sébastien; Lévesque, Daniel; Bizheva, Kostadinka; Lamouche, Guy

Optimal processing of non-linearity in

swept-source and spectral-domain optical

coherence tomography

Sébastien Vergnole1_{, Daniel Lévesque}1_{, Kostadinka Bizheva}2_{, and}

Guy Lamouche1

1_{Industrial Materials Institute, National Research Council Canada, Boucherville (QC), J4B 6Y4, Canada} 2_{Dept. of Physics and Astronomy University of Waterloo, Waterloo (ON), N2L3G1, Canada}

1

Outline

• Methods

• The SS-OCT case

• The SD-OCT case

• Conclusion

Motivation: Find the optimal method to process the unequally spaced

data in k-space that we measure in Fourier-domain OCT.

Hidden goal: Convince you that resampling the data through a

convolution with an optimized Kaiser-Bessel window is the optimal

method.

3

Methods

• Vandermonde:

– discrete Fourier transform for unequally spaced data; – allows to process FD-OCT data without resampling; – provides the most accurate results;

– computation time is prohibitive;

– used as the reference method to assess the image quality. • Linear or spline interpolation + FFT:

• commonly used in FD-OCT;

• oversampling by a factor is often used to increase precision at the expense of computing time;

• Identified as LIFFT and SIFFT ;

4

Methods

• Vandermonde:

– discrete Fourier transform for unequally spaced data; – allows to process FD-OCT data without resampling; – provides the most accurate results;

– computation time is prohibitive;

– used as the reference method to assess the image quality. • Linear or spline interpolation + FFT:

• commonly used in FD-OCT;

• oversampling by a factor is often used to increase precision at the expense of computing time;

• Identified as LIFFT and SIFFT ;

5

Methods

• Convolution with an optimized Kaiser Bessel window + FFT

– Introduction of convolution with a Kaiser-Bessel window + FFT in OCT:

• D. Hillmann, G. Huttmann, and P. Koch, “Using nonequispaced fast Fourier transformation to process optical coherence

tomography signals,” Proc. SPIE 7372, 73720R (2009). – We propose the use of an optimal window based on:

• P. J. Beatty, D. G. Nishimura, and J. M. Pauly, “Rapid gridding reconstruction with a minimal oversampling ratio,” IEEE Trans. Med. Imaging 24(6), 799–808 (2005).

• allows the use of a small fractional oversampling factor .

– We thus propose to resample by convolution with an

optimized Kaiser Bessel window. For details, see:

• S. Vergnole et al., Opt. Express 18, 10446-10461 (2010).

– Noted KBFFT_M where M relates to the width of the Kaiser-Bessel window.

7

Experimental setup

• Custom-built

• Santec wavelength swept source with a 30 kHz sweep rate

• 110 nm bandwidth around 1.31 m

• Mach-Zehnder configuration with balanced detection

Point spread functions

Time in ms for 1000 A-scans, evaluated on a PC with an Intel Core2 Duo CPU T7700 @ 2.4 GHz and 3.5 GB RAM and running of one processor. t = 3052 ms t = 199 ms t = 328 ms t = 129 ms t = 80 ms t = 230 ms t = 117 ms

LIFFT

SIFFT

KBFFT

LIFFT

SIFFT

KBFFT

Vandermonde

PSFs are averaged

9

Error evaluation

10

Phantom imaging

LIFFT

SIFFT

KBFFT

LIFFT

SIFFT

12

SD-OCT - PSF

SIFFT

KBFFT

SD-OCT experimental provided by Pr.

_SIFFT

Time for 1000 A-scans of 1024 points each:

Bizheva’s laboratory

13

SD-OCT - Retina

SIFFT

KBFFT

Time for 1000 A-scans of 1024 points each:

14

Conclusion

• Please try resampling using a convolution with an

optimized Kaiser-Bessel window!

Recipe in

: S. Vergnole et al., Opt. Express 18, 10446-10461 (2010).

"Experimental validation of an optimized signal processing method

to handle non-linearity in swept-source optical coherence

tomography"

Research Associate position available for the development of biomedical and industrial applications of OCT

(Canadian government laboratory, near Montreal, QC) • Ph.D. obtained within the last 5 years

• Especially gifted for laboratory work (optics)

• Fluent in French or willing to learn a new language...