Fig. 1. (a) Imaging schematic of an OCT structural cross section; (b) OCT signal of an individual pixel is equivalent to a linear sum of some random sub-phasors; (c) OCT dynamic of static resultant phasors have different probability distributions; (d) OCTA signals, the averaging further suppresses the variances of the distributions (filled areas) [17]

Fig. 2. Flow chart of OCTA imaging algorithm based on complex cross-correlation[16]

Fig. 3. A mouse cortex microangiography via complex cross- correlation-based OCTA. (a) Three-dimensional rendering image; (b) corresponding en face angiogram; (c) OCT structural cross section overlaid with blood flow signals at the position marked by the yellow dashed line in Fig. (b)[16]

Fig. 4. (a) Schematic of a typical sample arm in an OCT system; (b) B-scan modulation frequency fm induced by off-pivot offset δ; (c) overlap between the negative and positive B-scan modulation frequencies[18]

Fig. 5. Flow chart of angular compounded OCTA method. (a)-(c) Complex-valued spectrum S˙(k,x) is reconstructed by removing one of the two conjugate terms in the depth space; (d)-(e) B-scan modulation spectrum is split into halves using a Gaussian filter bank in the spatial frequency domain; (f)-(h) angle-resolved independent sub-angiograms are generated and compounded for a new angiogram[18]

Fig. 6. Three-dimensional angiograms of the conventional method and proposed angular compounded OCT method in mouse cortex in vivo. (a) Three-dimensional perspective drawing of vasculature; section view at a superficial depth by using (b) conventional method and (c) proposed method; section view at a deeper depth (~100 μm) by using (d) conventional method and (e) proposed method[18]

Fig. 7. (a) Schematic of the sample arm in swept source OCT (SSOCT); (b) stepwise raster-scanning mode and collection of a hybrid set of sub-angiograms G(t,w,a)[17]

Fig. 8. (a) Correlation coefficients between the sub-angiograms generated by different methods; (b) CER as a function of the number of sub-angiograms[17]

Fig. 9. Representative projection angiograms using hybrid averaging method in mouse cortex in vivo. (a) No averaging; (b) averaging of 3 sub-angiograms of angular resolution; (c) hybrid averaging of 9 sub-angiograms; (d) hybrid averaging of 18 sub-angiograms[17]

Fig. 10. OCTA imaging of local ischemia stroke model of a rat cerebral vessels. (a) Before stroke; (b) the first day after the formation of stroke; (c) the tenth day after the formation of stroke[26]