Browsing by Subject "Blood flow measurement"

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    Quantifying and interpreting intensity fluctuations in laser speckle contrast imaging
    (2024-05) Fang, Qingwei ; Dunn, Andrew Kenneth, 1970-; Parekh, Sapun; Tunnell, James
    Intensity fluctuations contain important information about the blood flow in laser speckle contrast imaging (LSCI). The dynamic scattering of photons by red blood cells in motion is the main source of intensity fluctuations and the detected intensity fluctuation is the entangled result of blood flow, vascular network and optics. However, such entanglement is complicated and still not fully understood. Elucidating the underlying mechanism is significant in excluding the confounding factors' effect, such as vascular network and optics, and obtaining quantitative blood flow metrics, for example the blood flow speed. In addition, the direct quantification of intensity fluctuations by measuring g₂(τ ), the intensity autocorrelation function, has been proved more accurate in detecting changes in blood flow dynamics compared with the traditional LSCI. But the measurement of g₂(τ ), is hindered by expensive high-speed cameras, high requirement of data storage and processing capacity, and limited field of view in achieving sufficient sampling rates. Breaking through the camera frame rate limit would be significant for directly quantifying intensity fluctuations in wide field with higher accuracy and lower cost. Considering those gaps in the current LSCI field, we first establish a unified theoretical framework for interpreting intensity fluctuations and demonstrate its utility through analyzing two factors' impact, one in vascular network and the other in optics, i.e. the vessels' orientation and the azimuthal incident angle of laser illumination beam. We also develop methodologies to quantify intensity fluctuations in wide field independent of camera's frame rate. The 2-pulse modulated multi-exposure speckle imaging (2PM-MESI) is proposed and demonstrated. Apart from capable of directly quantifying intensity fluctuations, it is also shown robust in counteracting shot noise without pixel intensity calibration, which leads to simplified imaging protocol compared with the traditional MESI. Those efforts increase the potential of LSCI in clinical applications as a robust, quantitative, and interpretable blood flow imaging technique.