Fig. 1. SELF-OCTA working principle. (a, b) Schematics of the 1300 nm system for skin imaging (a) and the sample arm of the system (b). SLD: superluminescent diode source; FC: fiber coupler; PC: polarization controller; CIR: circulator; L1–5: achromatic lenses; L6: camera lens; RM: reflective mirror; G: transmission grating; IMAQ: image acquisition card. (c) Process of splitting spectrum and generating partial-spectrum OCTA frame. K: wavenumber; M: the number of spectral bands, r: the transverse distance between two adjacent scan positions. DFT: discrete Fourier transform. (d) Schematics of signal mapping from partial-spectrum frames acquired over M/L consecutive Y-scan cycles to their Y image positions with M = 16 and L = 2. (e) Comparison of beam scanning between the point-scanning configuration where scanning step size along Y axis ∆y = r (left) and the SELF configuration with ∆y = L*r where L = 2 (right).

Fig. 2. Comparison of field of view in the human skin using 1300 nm system. (a–c) En face projections of vasculatures obtained with the point-scanning configuration (a), SELF configuration with M = 16 and L = 2 before (b) and after Y-deconvolution (c). From left to right: full-thickness projection (first column), capillary loops (second column), subpapillary plexus (third column), and deep vascular plexus (fourth column). Skin slabs are coded with green, yellow, and red in the full-thickness projection, respectively. (d) A schematic of skin vasculatures at different depth. (e–g) OCTA blood flow signal (red) superimposed on the OCT structural images (gray) with the point-scanning configuration (e), SELF configuration before (f) and after Y-deconvolution (g). Scale bars: 1 mm.

Fig. 3. Comparison of field of view in the human retina using 850 nm system at 68 kHz. (a–f) Images obtained from a female subject using 850 nm system with 90 nm spectral bandwidth: (a, b) OCTA en face projection with the point-scanning configuration over 12 mm × 4 mm (a) and the SELF-scanning configuration with M = 9 and L = 3 over 12 mm × 12 mm (b), respectively; (c, d) Corresponding zoom-in views of the fovea region acquired with the point (c) and SELF configuration (d), respectively; (e, f) Corresponding OCT structural image acquired with the point configuration (e) and SELF configuration after spectrum reconstruction (f). (g–k) Images obtained from a male subject using 850 nm system with 175 nm spectral bandwidth: (j) A partial-spectrum SELF-OCT cross-sectional image; (h, i) OCTA en face projections obtained with SELF configuration over 12 mm × 12 mm (h) and point configuration over 12 mm × 4 mm (i), respectively; (j, k) Corresponding zoom-in views of the fovea region acquired with the point (i) and SELF configuration (h), respectively. All OCT cross-sectional images are averaged over 2 consecutive images. Scale bars: 1 mm.

Fig. 4. Comparison of sensitivity to slow flow in the human skin. (a) OCTA images with the point configuration at an A-scan rate of 80384 Hz giving a flyback of 14% FOV. (b) OCTA images with the SELF configuration at an A-scan rate of 22000 Hz with M = 16 and L = 4 having a flyback of 4.7% FOV. From left to right: en face OCTA projections of skin vasculatures of capillary loop (first column), subpapillary plexus (second column) and deep vascular plexus (third column). (c) Schematics of SELF-OCTA signal mapping from partial-spectrum frames acquired over M/LY-scan cycles to their Y image position with M = 16, L = 4 and ∆y = 4r. (d) Signal-to-noise ratio (SNR) as a function of exposure time. Optimal theoretical SNR (SNR_Total, orange line) was obtained when SNR_el = SNR_ex (cyan and blue line). Black diamond and dot indicate measured total SNR at 80384 Hz and 22000 Hz A-scan rates, respectively. SNR_receiver: signal to receiver noise ratio, SNR_excess: signal to excess noise ratio, SNR_shot: signal to shot noise ratio. Scale bars: 1 mm.

Fig. 5. Multiple interscan time OCTA in the human skin using the SELF scanning configuration. (a) Schematics of customized interlaced scanning protocol. Blue and green dot lines represent A-scan points in the first and second scan repetitions, respectively. From top to bottom: interscan time intervals are shortened by reducing the A-scan points in a fast-axis run. (b) Schematics of SELF-OCTA signal mapping from partial-spectrum frames acquired over M/LY-scan cycles to their Y image position with M = 16, L = 2, and ∆y = 2r. By alternating between ∆t₁ and ∆t₂ along slow axis, M/L = 8 partial-spectrum OCTA frames at each Y image positions consisting of 4 frames with ∆t₁ and 4 frames with ∆t₂. (c) en face OCTA projections reconstructed from a single volume scan of 2 (N) × 384 (X) × 384 (Y) A-lines. Red arrows indicate differences in vascular visibility. Scale bars: 1 mm.

Fig. 6. Multiple interscan time OCTA and relative flow velocity with high dynamic range in the human retina using the SELF configuration at 100 kHz. (a) En face projections of retinal vasculatures with 4 different interscan time intervals reconstructed from a single volume scan of 3 (N) × 200 (X) × 400 (Y) A-lines. (b) Corresponding pseudo color-coded relative flow velocity map with dynamic ranges contributed by ∆t₁, ∆t₂ and ∆t₃. (c) Workflow for blood flow velocity map generation. (d, e) Corresponding fundus photograph (d) and OCTA image (e, adapted from Fig. 3(b)) from the same subject over 12 mm × 12 mm area (a 45-degree angle). Dashed box in (e) corresponding to imaging area in (a, b). (f) Schematics of SELF-OCTA signal mapping with M = 9, L = 1, and ∆y = r. Each Y image position has partial-spectrum frames encoding 4 different interscan time intervals. (g) Numerical simulations of OCTA signal and flow velocity: square root of amplitude decorrelation (D) as a function of square root of flow velocity (v) with I_Δt1, I_Δt2 and I_Δt3 represent OCTA signal for ∆t₁, ∆t₂, and ∆t₃, respectively. Solid lines refer to the linear range in-between the sensitivity threshold (δ) and the saturation threshold (1−δ) for ∆t₁ (orang line), ∆t₂ (green line) and ∆t₃ (blue line), respectively. Dashed lines represent scaled and intercept-nulled decorrelation functions for ∆t₁ (IΔt1*, orange dash line) and ∆t₂ (IΔt2*, green dash line) with respect to ∆t₃ (IΔt3, blue solid line). Signals beyond the linear range are represented with dotted lines. HDR: high dynamic range. DR_Δt1, DR_Δt2 and DR_Δt3: the corresponding flow velocity dynamic range. FAZ: foveal avascular zone, A: arterioles, V: venules.