In this work, the system implementation and characterization of a Phase-Resolved Doppler Optical Coherence Tomography (PR-DOCT) is presented. The phase-resolved Doppler technique was implemented on a custom built Frequency Domain OCT (FD-OCT) that was recently developed at Suranaree University of Technology. Utilizing Doppler phase changed relation in a complex interference signal caused by moving samples, PR-DOCT can produce visualization and characterization of flow activity such as blood flow in biological samples. Here we report the performance of the implemented PR-DOCT system in term of the Velocity Dynamic Range (VDR), which is defined by the range from the minimum to the maximum detectable axial velocity. The minimum detectable velocity was quantified from a histogram distribution of phase difference between consecutive depth-scan signals when performing Doppler imaging of a stationary mirror. By applying a Gaussian curve fitting to the histogram, the Full Width at Half Maximum (FWHM) of the fitted curve was measured to represent the detectable minimum flow velocity of the system. The maximum detectable velocity was limited by the phase wrapping of the Doppler signal, which is governed by the acquisition speed of the system. We demonstrate the 3D Doppler imaging and velocity measurement of feed flow phantom using 100% milk pumped through a microfluidic chip by using a syringe pump system.
We report the implementation of a high speed and high resolution spectrometer-based spectral domain optical coherence tomography (SD-OCT) system. A high speed near-infrared spectrometer was designed and built, utilizing a high speed line-array CMOS detector and all off-the-shelf optical components. The acquisition speed of more than 100,000 spectra per second was achieved, enabling a high speed 3D imaging of the implemented SD-OCT system. Here, we report the performance characterization, i.e. resolution, imaging depth, and sensitivity of the implemented system. The penetration depth and depth resolution of the system are currently 2 mm and 14.1 μm, respectively. The lateral resolution of the system was quantified by the Modulation transfer function (MTF) measurement to be about 15.5 μm. over the lateral field-of-view (x-y axes) of 30 mm × 30 mm. The acquisition speed of the system was 20 frames per second.
In this work, we report simple optical design of a high speed and high spectral resolution spectrometer based on the first order calculation. The spectrometer was design and optimized for high speed detection of spectral interference signal to be used as a detection unit of our developed Frequency Domain Optical Coherence Tomography (FD-OCT). We then detailed the hardware implementation of both the spectrometer and the FD-OCT system in our laboratory at Suranaree University of Technology, Thailand, by utilizing only off-the-shelf optical components. The spectrometer is capable of capturing of the spectral interference fringes at up to the camera limit of 130,000 spectra per second, enabling cross-sectional microscopic imaging of biological sample of more than 100 frames per second (for a 1000 depth scans per frame). In addition, we reported several simple yet robust techniques for characterization of the system performance in the context of FD-OCT 3D imaging, such as an effective lateral resolution, depth scale calibration, and depth penetration limit. The development of this high speed and high resolution spectrometer is part of our ultimate goal to develop a prototype of a research-grade FD-OCT system that provides better imaging speed and resolution in comparing to available commercial OCT systems at relatively lower cost. The design of low-cost, high performance FD-OCT system would make the technology widely accessible to other researchers in the field of biomedical research and related areas in Thailand in the next few years.