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Recently we presented novel methods for acousto-optic (AO) imaging of biological tissues, taking (1) the mean square difference of speckle patterns (subtraction method) or (2) the contrast of the summation of speckle patterns (summation method) acquired from nanosecond pulses of coherent light, fired at different ultrasound phases. In this study we relate the two methods both analytically and experimentally. We experimentally show that these two methods are nearly identical provided that the maximum achievable speckle contrast is determined correctly. We show with simulations that after correction the outcome is independent of experimental detection parameters. This makes the AO methods in this study reliable, allowing quantifying speckle observations in terms of the ultrasonically tagged fractions of light. The use of tandem nanosecond pulses in one burst of ultrasound overcomes the challenge of tissue dynamics. [ABSTRACT FROM AUTHOR]

Recently we presented acousto-optic (AO) probing of scattering media using addition or subtraction of speckle patterns due to tandem nanosecond pulses. Here we present a theoretical framework for ideal (polarized, noise-free) speckle patterns with unity contrast that links ultrasound-induced optical phase modulation, the fraction of light that is tagged by ultrasound, speckle contrast, mean square difference of speckle patterns and the contrast of the summation of speckle patterns acquired at different ultrasound phases. We derive the important relations from basic assumptions and definitions, and then validate them with simulations. For ultrasound-generated phase modulation angles below 0.7 rad (assuming uniform modulation), we are now able to relate speckle pattern statistics to the acousto-optic phase modulation. Hence our theory allows quantifying speckle observations in terms of ultrasonically tagged fractions of light for near-unity-contrast speckle patterns. [ABSTRACT FROM AUTHOR]

Objective: A major challenge for treating diabetic foot ulcers is estimating the severity of ischemia, as the currently used non-invasive diagnostic techniques provide relatively poor prognostic values. Laser speckle contrast imaging (LSCI) is a promising non-invasive technique to assess microcirculation. Our aim was to investigate the stability and reproducibility of LSCI for the assessment of microcirculation in the diabetic foot, the relation of LSCI results to currently used non-invasive blood pressure measurements, and the ability of LSCI to discriminate between the degrees of ischemia. Approach: Thirty-three participants with diabetic foot ulcers were included in this prospective, single centre, observational cohort study that was conducted in the Netherlands. They were classified as non-ischemic, ischemic or critical-ischemic based on criteria formulated in the international guidelines. Two clinicians performed LSCI scans of the foot, consisting of baseline measurements, followed by two stress tests (post-occlusion peak and elevation test). With three measurement conditions and five regions of interest of the foot per patient, a total of 15 measurements were available for analyses. Main results: The intra-observer agreement of LSCI was high (interclass correlation coefficient (ICC)  =  0.711–0.950; p   <  0.001) for all 15 measurements. The inter-observer agreement was high (ICC  =  0.728–0.861; p   ⩽  0.001) for 10 measurements and moderate (ICC  =  0.476–0.570; p   ⩽  0.005) for the remaining five measurements. The inter-assessor agreement was high and significant (ICC  =  0.857–0.996; p   ⩽  0.001) for all measurements. Correlation between LSCI and non-invasive blood pressure measurements was low (ICC  =  −0.272–0.582). During both stress tests, microcirculation was significantly lower in critical-ischemic feet compared to non-ischemic feet (67.5 perfusion units (PU) versus 96.3 PU and 41.0 PU versus 63.9 PU; p   <  0.05). Significance: LSCI is a stable and reproducible technique for assessment of microcirculation in people with diabetic foot ulcers and shows significant differences between non-ischemic, ischemic and critical-ischemic patient populations. [ABSTRACT FROM AUTHOR]