Figure 1
From: In Vivo Flow Mapping in Complex Vessel Networks by Single Image Correlation
Cross-correlation on raster-scanned xy-images.
(a)–(e) Confocal xy-images acquired by detecting the signal of 1-μm fluorescent beads undergoing laminar flow in a square borosilicate capillary (inner section, 720 μm); λexc = 514 nm, detection bandwidth = 530–600 nm, fline = 1000 Hz, δx = 0.04 μm; scale bar, 3 μm. The angle γ between the flow velocity vector v and the scan path (pointing as the positive x-axis) was varied in the four quadrants of the Cartesian xy-plane. In (a), (b) and (c) v (in green) points in the positive x-direction: the diagonal lines due to the beads motion keep the same orientation irrespectively of the angle γ, which affects their length and slope. In (d) and (e) v points in the negative x-direction (i.e., opposite to the scan path) and the orientation of the diagonal lines is reversed. In each image γ is reported according to the definition of panel (h). (f) A raster-scanned image (or a region of interest) is a matrix of NxxNy pixels, representing a series of intensity measurements from many adjacent confocal excitation volumes (sampled along the red pattern). The sketch highlights (dark green) two arbitrary pixels involved in the computation of the forth cross-correlation between two columns (light green) l = J-I pixels apart. (g) Exemplary CCF computed on panel (a) for (J–I)δx = 7.4 μm. (h) Definition of the angle γ between the vector v and the scan axis (positive x-axis); the range of its possible values and four arbitrarily-directed vectors for the flow velocity are shown.
