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Chen S, Lin K, Chen X et al. Spectrally extended line field optical coherence tomography angiography. Opto-Electron Adv 8, 240293 (2025). doi: 10.29026/oea.2025.240293
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Spectrally extended line field optical coherence tomography angiography
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Abstract
Optical coherence tomography angiography (OCTA) is a powerful tool for non-invasive, label-free, three-dimensional visualization of blood vessels down to the capillary level in vivo. However, its widespread usage is hindered by the trade-off between transverse sampling rate and signal-to-noise ratio (SNR). This trade-off results in either a limited field of view (FOV) to maintain sampling density or loss of capillary details to fulfil FOV requirement. It also restricts microvascular quantifications, including flow velocimetry, which typically demand higher transverse sampling rate and SNR compared with standard qualitative OCTA. We introduce spectrally extended line field OCTA (SELF-OCTA), a cost-effective imaging modality that improves transverse sampling rate and SNR through spectrally encoded parallel sampling and increased signal acquired over longer periods, respectively. In the human skin and retina in vivo, we demonstrate its advantages in achieving significantly extended FOV without sacrificing microvascular resolution, high sensitivity to slower flow without compromising FOV, and flow velocity quantification with the highest dynamic range, emphasizing that these features can be achieved with readily available and standard OCTA hardware settings. SELF-OCTA has the potential to make wide-field, high-resolution, quantitative angiographic imaging accessible to a wider population, thereby facilitating the early detection and follow-up of vascular-related diseases. -
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References
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Chen S, Lin K, Chen X et al. Spectrally extended line field optical coherence tomography angiography. Opto-Electron Adv 8, 240293 (2025). doi: 10.29026/oea.2025.240293
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Figure 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).
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Figure 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.
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Figure 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.
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Figure 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/L Y-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 (SNRTotal, orange line) was obtained when SNRel = SNRex (cyan and blue line). Black diamond and dot indicate measured total SNR at 80384 Hz and 22000 Hz A-scan rates, respectively. SNRreceiver: signal to receiver noise ratio, SNRexcess: signal to excess noise ratio, SNRshot: signal to shot noise ratio. Scale bars: 1 mm.
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Figure 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
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Figure 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 (
$ \sqrt{D} $ $ \sqrt{v} $ $ {I}_{{\rm{\Delta}} t1}^{\mathrm{*}} $ $ {I}_{{\rm{\Delta}} t2}^{\mathrm{*}} $ $ {I}_{{\rm{\Delta}} t3} $
