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

A simulation study compared estimating blood flow from speckle contrast at a single camera exposure (as standard SCOS and SPG do) with fitting a curve over many exposures (multi-exposure speckle imaging). Multi-exposure kept errors under 1 % even when calibration and noise were off, while single-exposure methods could be off by up to 90 % and misjudge pulsatile flow by 22 % or more.

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SignificanceSpeckle 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 (β), and noise.AimThe 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 β mismatch, noise, and pulsatile flow.ApproachSpeckle visibility was simulated at 10,000 logarithmically spaced exposure durations (0.01 to 10 ms), incorporating ±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 β.ResultsMulti-exposure speckle imaging (MESI) maintained <1% mean error despite β mismatch or noise while maintaining ≤12% pulsatile-flow error at ±5% noise. Single-exposure methods showed errors up to 90% for β mismatch/noise and ≥22% pulsatile-flow errors.ConclusionsMESI outperformed single-exposure approaches in estimating blood flow changes by reducing β bias, minimizing noise sensitivity, and accurately tracking pulsatile dynamics.

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Wavelengths

n/a (simulation)