The schematic setup of the high-speed OCT system is shown in Fig. 1. An FDML swept laser (FDML-1310-4B-APC, Optores GmbH) was used as the OCT light source, which was tuned at a central wavelength of 1308 nm with a 3 dB spectral scanning range of 110 nm, giving an A-line scanning rate of 1.6217 MHz. Output power of 30 mW from the FDML source was fiber-coupled into an OCT system engine. In the engine, the light was first split by a 90:10 fiber coupler with 10% power going to the reference arm. The remaining 90% power was further divided by a 99:1 fiber coupler into a sample arm and a recalibration arm, respectively. The reference arm and the sample arm formed a master interferometer to provide the spectral interference signal to enable the imaging of sample. The recalibration arm together with the reference arm formed a slave interferometer that was used to resample the interference signal from the master interferometer so that the spectral interference signal emerging from the sample is represented in linear k-space.12 In the sample arm, a OCT scan lens (LSM03, Thorlabs Inc.) focused the light beam into the sample with a theoretical beam size of at the focal point. To achieve a high B-frame rate, a MEMS scanner (PicoP, MicroVision Inc.)13 was used to scan the beam spot. The MEMS scanner was driven by an 18 kHz sinusoid wave generated from an arbitrary waveform generator (AWG520, Tektronix) synchronized with the light source. Considering the bidirectional movement of the scanner, the effective frame rate was therefore (fps). The configuration of the scanning system in the sample arm was so designed that it provided a B-scan size of 1 mm along the fast scanning direction, that is, the -direction (consisting of A-scans). A galvanometer scanner (6215H, Cambridge Technology) was used to provide the slow axis, that is, scanning, driven by a continuous ramp waveform at 200 Hz. There were 180 B-frames (considering the bidirectional fast scan), covering 2 mm, in the slow axis. This scanning protocol [as shown in Fig. 2(a)] provided a sampling interval of in both the - and -directions, which is enough to resolve small vessels at . Reflected light from the reference arm and the sample arm interfered at a coupler and was then detected by a 1.6 GHz dual balanced photodetector (PDB480C-AC, Thorlabs Inc.). The inference signal was sampled and digitized at by a 12 bits A/D acquisition card (ATS9360, Alazartech). The incident light power on the sample was measured at , providing a measured system sensitivity of at the focus depth position. The acquired signal (raw data) was further processed through third-order Hermite kernel resampling, fast Fourier transform, and logarithmic compression,12 and then piled into final 3-D structure datasets.