Novel optical techniques for imaging microcirculation in the diabetic foot

Background: The most severe diabetic foot ulcers are those related with critical ischemia, which is primarily diagnosed with non-invasive diagnostics. However, these diagnostics have several disadvantages. For example, they only provide global indications of the (macro)level of ischemia. A potential solution can be found in novel optical imaging techniques for local assessment of the microcirculation in diabetic foot ulcers. This review provides an overview of these imaging techniques (Laser Doppler Perfusion Imaging, Laser Speckle Contrast Imaging, Photoacoustic Imaging and Hyperspectral Imaging) and their applicability for the diagnostic assessment of microcirculation in diabetic foot ulcers. Method: For each technique, the following parts are described: a) their technical background; b) general clinical applications; and, c) its application for microcirculation assessment in diabetic foot ulcers. Parts a-b are based on a narrative review of the literature, part c on a systematic review that was performed in the database Scopus, covering the period from January 1, 2000 to November 31, 2017. Results: Each of these techniques has specific advantages and disadvantages for imaging microcirculation. Potential clinical use depends on measurement aims, and clinical relevance. However, none of the techniques has a strongly established clinical relevance yet: we found a limited number of publications describing clinical outcomes. Future research is needed to determine which technique is the most clinically relevant for the assessment of microcirculation in diabetic foot ulcers. Conclusion: Although promising, the currently available novel optical techniques need to be further improved technically and prospective trials are necessary to evaluate their clinical value.