Fig. 1. Schematic of the optical setup for LSH-DSI. (a) LD, laser diode; BE, beam expander; CL, cylindrical lens (f=50mm). The dashed box after CL includes the beam view in the orthogonal plane; IO, illumination objective; TL, tube lens (f=100mm); DO, detection objective; DM, dichroic mirror. (b) Anisotropic scattering in tissue and detected signal intensity versus scattering angle. (c) Layer-by-layer scanning enabled by sample translation. (d) Example LSH-DSI images. The first row: raw speckle images; The second row: corresponding blood flow velocity maps. S1, S2, S3, and S4 denote four different slices separated by 100μm. RS indicates raw speckle images while V represents velocity maps. Scale bars: 200μm.

Fig. 2. Quantitative comparison of blood flow velocities measured with LSH-DSI and PIV. (a) Imaging geometry. (b) Flow mapping with PIV. 1, wide-field transmission image covering both DA and PCV; 2 and 3, PIV analysis results showing blood flow in opposite directions along the DA (up) and PCV (bottom). (c) A sample raw LSH-DSI image. (d) Representative light-intensity signal picked up from a pixel in the DA. (e) Short-time power spectrum of the signal in (d). (f) Comparison of DA blood flow velocities obtained from LSH-DSI (blue) and PIV (red). (g) Comparison of PCV blood flow velocities obtained from LSH-DSI (blue) and PIV (red). Scale bar: 50μm.

Fig. 3. Head vascular imaging. (a) A transmission image of the sample. (b) A 2D flow map generated with the PIV analysis of transmission images. (c) Simple projection of 15 LSH-DSI angiograph slices. (d) Combo LSH-DSI velocity map including three consecutive slices, which were coded in red, green, and blue colors to distinguish them. (e) Representative en face angiographs from the reconstructed image stack [Video 1 (AVI, 2.85 MB) [URL: https://doi.org/10.1117/1.APN.4.1.016002.s1]. The layer depths from the bottom were 118, 149, 188, and 228μm, respectively. (f) Four test points were selected (marked by blue squares) on a single slice (No. 4) angiograph to estimate local blood flow velocities. (g) Blood velocity waveforms measured with LSH-DSI. The line colors matched those of testing point indices in (f). Scale bars: 200μm.

Fig. 4. Time-frequency analysis of speckle signals. (a) A segment of representative raw speckle signal that lasted for 2 s and was sampled at 3000 Hz. (b) The time-dependent power spectra of the signal in (a), displayed as a 2D function of time and frequency. (c) The family of time-dependent power spectra for all time points plotted as one-dimensional functions of frequency. (d) The same 2D spectra as in (b) displayed between 50 and 90 dB in power. (e) A sample power spectrum at one of the time points. Red line, a typical threshold at 60 dB for noise suppression and peak identification. The data tip indicates an identified spectral peak with a corresponding peak frequency shift (184.751 Hz) and peak power (68.8377 dB). Orange dashed-dotted line, a too-low threshold; blue dashed line, a too-high threshold. Dark red triangles, spurious peaks. Yellow arrow, low-frequency intensity fluctuation peak. (f) The peak frequency shifts for all time points in the 2-s window.