Advances in detection techniques enables dramatic increases in OCT imaging speeds. An alternative to time domain detection for OCT is a technique known as Fourier or frequency domain detection (Fercher et al., 1995, Golubovic et al., 1997, Häusler et al., 1998, Lexer et al., 1997). These techniques are somewhat analogous to Fourier transform spectroscopy and have a significant sensitivity and speed advantage because they measure the entire optical echo signal or A-scan is detected simultaneously rather than sequentially.
Fourier domain detection can be accomplished either by detecting the interferometric information needed for the depth resolved reflectivity profile using a spectrometer and high speed CCD camera (also referred to as “spectral / Fourier domain OCT” in the literature) or by using a frequency swept light source and detecting interferometric information with a photodetector (also referred to as “swept source OCT” or “optical frequency domain imaging” in the literature).
The acquisition speed for both approaches - using a spectrometer as a detector or using a tuneable light source - is governed by the read out rate of the CCD camera or the sweep speed of the light source, respectively. Because both approaches detect all of the echoes of light simultaneously, they offer a significant sensitivity advantage, allowing a dramatic increase in line rate (A-scan rate) in comparison to OCT with time domain detection. For ophthalmic imaging, in theory a ~400 times faster imaging speed should be possible, while preserving sensitivity. However, in practice, a factor of ~50 is achieved because of limitations in CCD cameras.
It may be interesting to note that although the basic principle of Fourier domain detection has been known since 1995 (Fercher et al., 1995), limitations in CCD technology and lack of recognition of the performance advantages delayed the use of this technique for nearly a decade. Three groups, working independently, simultaneously described the sensitivity advantage of this technique (Leitgeb, Hitzenberger and Fercher et al. from Vienna, 2003; Choma et al. 2003 and de Boer et al, 2003). The first demonstration of retinal imaging using spectral / Fourier domain OCT was performed in 2002 (Wojtkowski and Leitgeb et al., 2002). First clinical 3D retinal OCT was demonstrated in 2005 by Schmidt-Erfurth and Leitgeb et al. in Vienna.
Fercher, A.F., Hitzenberger, C.K., Kamp, G., & El-Zaiat, S.Y. (1995). Measurement of intraocular distances by backscattering spectral interferometry. Optics Communications, 117, 43-48
Leitgeb, R., Hitzenberger, C.K., & Fercher, A.F. (2003). Performance of fourier domain vs. time domain optical coherence tomography. Optics Express, 11 (8), 889-894
Lexer, F., Hitzenberger, C.K., Fercher, A.F., & Kulhavy, M. (1997). Wavelength-tuning interferometry of intraocular distances. Applied Optics, 36 (25), 6548-6562
Schmidt-Erfurth U., Leitgeb R.A., Michels S., Povazay B., Sacu S., Hermann B., Ahlers C., Sattmann H., Scholda C., Fercher A.F., Drexler W. (2005), Three-dimensional ultrahigh resolution optical cpherence tomography of macular pathologies, Investigative Ophthalmology & Visual Science, 46 (9), 3393-3402
Drexler W, Fuijmoto JG, “Optical Coherence Tomography: Technology and Applications”, Springer Publishing, 2008. 978-3-540-77549-2, 1400 pages
Häusler, G., & Lindner, M.W. (1998). Coherence Radar and Spectral Radar - new tools for dermatological diagnosis. Journal of Biomedical Optics, 3, 21-31
Wojtkowski, M., Leitgeb, R., Kowalczyk, A., Bajraszewski, T., & Fercher, A.F. (2002). In vivo human retinal imaging by Fourier domain optical coherence tomography. Journal of Biomedical Optics, 7 (3), 457-463
Choma, M.A., Sarunic, M.V., Yang, C.H., & Izatt, J.A. (2003). Sensitivity advantage of swept source and Fourier domain optical coherence tomography. Optics Express, 11 (18), 2183-2189.
de Boer, J.F., Cense, B., Park, B.H., Pierce, M.C., Tearney, G.J., & Bouma, B.E. (2003). Improved signal-to-noise ratio in spectral-domain compared with time-domain optical coherence tomography. Optics Letters, 28 (21), 2067-2069
Golubovic, B., Bouma, B.E., Tearney, G.J., & Fujimoto, J.G. (1997). Optical frequency-domain reflectometry using rapid wavelength tuning of a Cr/sup 4+/:forsterite laser. Optics Letters, 22 (22), 1704-1706