Abstract
We developed a universal, real-time uniform K-space sampling (Rt-UKSS) method for high-speed swept-source optical coherence tomography (SS-OCT). An external clock uniform in K-space was generated. The clock was synchronized with the zero-crossing time of an interferometric calibration signal and used as triggers for a high-speed data acquisition system in a point-by-point fashion, hence enabling uniform data sampling in K-space. Different from the numerical calibration algorithm commonly used in an SS-OCT system, the method reported here does not require over-sampling, thus greatly reducing the demand for digitization, data processing and storage speed. The Rt-UKSS method is adaptive and applicable to a generic SS-OCT system of a wide range of A-scan rates without special adjustment. We successfully implemented the Rt-UKSS method in an SS-OCT system based on a Fourier-domain mode-locked laser (FDML) of a 40-kHz scanning rate. Real-time imaging of biological tissues using such a system was demonstrated with a measured axial resolution of 9.3 μm and detection sensitivity greater than 120dB.
Highlights
The recently developed Fourier-domain OCT technology (FD-OCT) has led to substantial improvements on A-scan rate and detection sensitivity over the conventional time-domain technologies [1,2,3]
There are several challenges associated with the numerical calibration procedure: (1) It slows down the overall data processing speed; (2) The OCT fringe signal needs to be digitized with sufficient density in order to perform accurate calibration, which increases the load of signal digitization, data transfer and storage; and (3) Since the calibration data is generally digitized only at a few time points during imaging, the numerical calibration methods can be sensitive to errors associated with any fluctuation in wavelength sweeping
We present a new hardware-based real-time uniform K-space sampling (Rt-UKSS) method, which is implemented by designing and generating an external clock to provide point-by-point triggers with uniform spatial frequency spacing for the digitizer
Summary
The recently developed Fourier-domain OCT technology (FD-OCT) has led to substantial improvements on A-scan rate and detection sensitivity over the conventional time-domain technologies [1,2,3]. We present a new hardware-based Rt-UKSS method, which is implemented by designing and generating an external clock to provide point-by-point triggers with uniform spatial frequency spacing (in K-space) for the digitizer This method relaxes the demands for data digitization, transfer, processing and storage speed by at least 2.5 folds, and it affords to handle an ~2.5 times higher A-scan rate for a given data acquisition system. This method is robust, adaptive, and applicable to a generic SS-OCT system as long as the scanning rate is within the frequency range of the external clock circuitry This method is insensitive to the instability of the swept source such as the drift of the laser spectrum or wavelength sweeping drive waveform, and avoids any potential misalignment of the calibration signal with the real-time OCT fringe signal. The performance of the new method was demonstrated by real-time imaging of biological tissues
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