Diagnosis of peripheral artery disease in people with diabetes and a foot ulcer using current non-invasive blood pressure measurements is challenging. Laser speckle contrast imaging (LSCI) is a promising non-invasive technique to measure cutaneous microcirculation. This study investigated the association between microcirculation (measured with both LSCI and non-invasive blood pressure measurement) and healing of diabetic foot ulcers 12 and 26 weeks after measurement. We included sixty-one patients with a diabetic foot ulcer in this prospective, single-center, observational cohort-study. LSCI scans of the foot, ulcer, and ulcer edge were conducted, during baseline and post-occlusion hyperemia. Non-invasive blood pressure measurement included arm, foot, and toe pressures and associated indices. Healing was defined as complete re-epithelialization and scored at 12 and 26 weeks. We found no significant difference between patients with healed or non-healed foot ulcers for both types of measurements (p = 0.135–0.989). ROC curves demonstrated moderate sensitivity (range of 0.636–0.971) and specificity (range of 0.464–0.889), for LSCI and non-invasive blood pressure measurements. Therefore, no association between diabetic foot ulcer healing and LSCI-measured microcirculation or non-invasive blood pressure measurements was found. The healing tendency of diabetic foot ulcers is difficult to predict based on single measurements using current blood pressure measurements or LSCI.

A major challenge for treating diabetic foot ulcers is estimating the severity of ischemia, as 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. ApproachThirty-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 3 measurement conditions and 5 regions of interest of the foot per patient, a total of 15 measurements were available for analyses. Main resultsThe 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 5 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) vs. 96.3PU and 41.0PU vs. 63.9PU; 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.Acknowledgements: This work is supported by NWO-TTW (project number 14538), Stichting Diavasc and Ziekenhuisgroep Twente.

Although promising, the currently available novel optical techniques need to be further improved technically and prospective trials are necessary to evaluate their clinical value.