Abstract
Laser Speckle Contrast Imaging (LSCI) is an optical technique used to generate blood flow maps with high spatial and temporal resolution. It is well known that in LSCI, the speckle size must exceed the Nyquist criterion to maximize the speckle's pattern contrast. In this work, we study experimentally the effect of speckle-pixel size ratio not only in dynamic speckle contrast, but also on the calculation of the relative flow speed for temporal and spatial analysis. Our data suggest that the temporal LSCI algorithm is more accurate at assessing the relative changes in flow speed than the spatial algorithm.
Highlights
When coherent light is used to illuminate a rough or optically inhomogeneous object, the scattered light forms a random interference pattern called speckle [1]
We focus on continuing the discussion related to the proper spatial sampling of speckle patterns, Fig. 1 shows several pixels which are sampling a speckle, the ratio speckle area/pixel area defines the parameter N employed in the following plots
For predominantly dynamic speckle, the speckle contrast depends on the spatial sampling of the speckle pattern, for both temporal and spatial specklecontrast analysis
Summary
When coherent light is used to illuminate a rough or optically inhomogeneous object, the scattered light forms a random interference pattern called speckle [1]. In 1981, Fercher and Briers [2] demonstrated that analysis of the speckle contrast in a time-integrated speckle pattern enables visualization of blood flow in the retina. With subsequent advances in chargecoupled device (CCD) technology and an associated reduction in cost, LSCI method has been implemented in real time [3] and employed in numerous preclinical [4,5] and clinical [6] research studies as a simple method to quantify blood-flow dynamics [7]. The dynamic range of LSCI is closely related to the range of measurable speckle contrast values. This range itself is linked to several experimental parameters, including source coherence length, analysis algorithm approach (i.e., temporal vs spatial analysis), and the spatial sampling (Fig. 1) of the speckle pattern [8, 9].
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