Intensity-modulated wide-field imaging for characterizing intensity dynamics

Quantifying temporal intensity fluctuations is crucial yet challenging in many biomedical applications, e.g., assessing blood flow, tissue perfusion, and particle sizing. These fluctuations arise from dynamic scattering processes within biological tissues and are commonly characterized in the time domain by the intensity autocorrelation function g₂(τ). However, measuring g₂(τ) across a wide field of view often requires short exposures (high frame rates) or specialized high-speed cameras to capture rapid dynamics. In this work, we propose two wide-field speckle-based approaches for quantifying temporal intensity fluctuations using only standard cameras. Different from the existing laser speckle contrast imaging approaches which keep the laser intensity a constant within camera exposures, we modulate the laser intensity (temporal modulation) within camera exposures. With the temporal intensity modulations, we show that the speckle contrast can be taken as a sampling of g₂(τ) or the power spectrum density functions of the temporal intensity fluctuations. We validated the performance of the proposed approaches on blood flow imaging using both microfluidics phantom and mouse cranial windows. Experimental results demonstrate the effectiveness of both approaches in accurately quantifying temporal intensity dynamics. The proposed laser intensity modulation speckle imaging enables 2D wide-field quantification of fast temporal intensity fluctuations with significantly reduced instrumental costs associated with high-speed cameras.