Abstract
We present a new signal processing method that extracts the reference spectrum information from an acquired optical coherence tomography (OCT) image without a separate calibration step of reference spectrum measurement. The reference spectrum is used to remove the fixed-pattern noise that is a characteristic artifact of Fourier-domain OCT schemes. It was found that the conventional approach based on an averaged spectrum, or mean spectrum, is prone to be influenced by the high-amplitude data points whose statistical distribution is hardly randomized. Thus, the conventional mean-spectrum subtraction method cannot completely eliminate the artifact but may leave residual horizontal lines in the final image. This problem was avoided by utilizing an advanced statistical analysis tool of the median A-line. The reference A-line was obtained by taking a complex median of each horizontal-line data. As an optional method of high-speed calculation, we also propose a minimum-variance mean A-line that can be calculated from an image by a collection of mean A-line values taken from a horizontal segment whose complex variance of the data points is the minimum. By comparing the images processed by those methods, it was found that our new processing schemes of the median-line subtraction and the minimum-variance mean-line subtraction successfully suppressed the fixed-pattern noise. The inverse Fourier transform of the obtained reference A-line well matched the reference spectrum obtained by a physical measurement as well.
Highlights
Fourier-domain schemes of optical coherence tomography (OCT) provide various attractive features over time-domain OCT (TD-OCT) [1,2,3,4]
We present a new signal processing method that extracts the reference spectrum information from an acquired optical coherence tomography (OCT) image without a separate calibration step of reference spectrum measurement
The reference spectrum is used to remove the fixedpattern noise that is a characteristic artifact of Fourier-domain OCT schemes
Summary
Fourier-domain schemes of optical coherence tomography (OCT) provide various attractive features over time-domain OCT (TD-OCT) [1,2,3,4]. This artifact is especially severe for an OCT endoscope catheter imaging since some reflection points are embodied by the fiber end, surfaces of the micro-lens, etc Those reflections may contribute to generation of fixed horizontal lines which are not related with the actual sample under imaging. Some fixed patterns are associated with fixed real reflections from the end of the sample arm as in the case of the OCT endoscope catheter This type of fixed patterns cannot be rejected by the balanced detection that only suppresses common-mode signal components. The demands for frequent calibrations may make the system very inconvenient to use for practical applications To avoid those issues, one can take advantage of a signal processing method that extracts the reference information to remove the fixed-pattern artifact. It is expected that our methods can be used for suppressing the fixed-pattern noise and for additional signal processing schemes that need the accurate information of the reference spectrum under a possible variation of the spectrum
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