The extensive development of frequency-domain optical coherence tomography (OCT) for more than a decade has enabled A-scan rates in the MHz range. Furthermore, frequency-domain OCT gives access to the amplitude and phase of the OCT signal. These characteristics have opened the possibilities of doing different kinds of averaging in order to improve OCT imaging. It is well known that multiple scattering in OCT reduces image contrast and resolution especially at greater depths within the tissue. Here, we demonstrate that complex averaging can decrease the effect of multiple scattering and improve OCT imaging contrast, in addition to increasing the dynamic range due to reducing the noise floor as previously demonstrated. We take advantage of the fact that complex averaging, in contrast to conventional magnitude averaging, is sensitive to phase changes, as one averages the complex-valued Fourier-transformed spectral fringe signals before calculating the magnitude. Any motion that leads to higher phase variance will lead to lower magnitude when performing complex averaging. Also, motion preferentially increases the phase variance of multiply scattered photons when compared to singly scattered photons with each scattering event spreading the phase. This indicates that we may reduce multiple scattering by implementing complex averaging to preferentially reduce the magnitude of the multiply scattered light signal in OCT images. We have performed several experiments on liquid phantoms that give experimental evidence for this hypothesis.
Lars Thrane, Shi Gu, Brecken J. Blackburn, Kishore V. Damodaran, Andrew M. Rollins, and Michael W. Jenkins, "Complex decorrelation averaging in optical coherence tomography: a way to reduce the effect of multiple scattering and improve image contrast (Conference Presentation)," Proc. SPIE 10053, Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXI, 100532B (Presented at SPIE BiOS: February 02, 2017; Published: 19 April 2017); https://doi.org/10.1117/12.2254916.5371868826001.
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