Comparing multi- and single-exposure speckle contrast optical spectroscopy methods as estimators of blood flow in the...

Speckle contrast optical spectroscopy (SCOS) and speckle plethysmography (SPG) are increasingly used to measure deep tissue blood flow from tissues. However these methods derive flow from measurements at a single exposure duration, which could introduce errors due to inefficient choice of a single integration time, changes in speckle averaging factors ( $\beta$ ), and noise.

The aims are to compare and evaluate the robustness of single- and multi-exposure speckle contrast methods in estimating blood flow changes under experimental conditions such as $\beta$ mismatch, noise, and pulsatile flow.

Speckle visibility was simulated at 10,000 logarithmically spaced exposure durations (0.01 to 10 ms), incorporating $\pm 5$ to 15% noise, using a semi-infinite diffusion model at different physiologically relevant steady state and pulsatile flow rates. Speckle visibility was used to estimate blood flow changes using both the multi-exposure approach (non-linear fitting of the full curve) and conventional single exposure approach at 0.1, 1, and 5 ms durations (SCOS, SPG, and look-up-table), under different noise conditions and mismatches in $\beta$ .

Multi-exposure speckle imaging (MESI) maintained $<1\%$ mean error despite $\beta$ mismatch or noise while maintaining $\le 12\%$ pulsatile-flow error at $\pm 5\%$ noise. Single-exposure methods showed errors up to 90% for $\beta$ mismatch/noise and $\ge 22\%$ pulsatile-flow errors.

MESI outperformed single-exposure approaches in estimating blood flow changes by reducing $\beta$ bias, minimizing noise sensitivity, and accurately tracking pulsatile dynamics.