OPS imaging is a relatively inexpensive technique and has the advantage of being portable [73]. It provides optimal image

resolution on organs covered by a thin epithelial layer and does not require the injection of fluorescein to obtain an excellent level of contrast [73]. OPS and SDF have been used during surgery to assess see more the microcirculation of several organs, including the brain [108,109], the kidney [122], or the liver [110]. The most studied site, however, is the sublingual region, where the density of perfused capillaries can be non-invasively assessed [33]. Semi-quantitative analysis of the microcirculation has been proposed with OPS, based on a scoring including both the measurement of perfused capillary density and the flow heterogeneity between the different areas [32]. The main applications of OPS and SDF concern critical care medicine. De Backer et al. showed that microcirculation assessed with OPS on the sublingual mucosa was impaired in severe sepsis [31]. In the same way, BGJ398 nmr SDF allowed identifying significant

abnormalities in microvascular density during early post-resuscitation phase, which returned to baseline within 48 hours after cardiac arrest [36]. Although the image quality is not as good as on mucosa, OPS has also been used on lower limb skin to evaluate microcirculation in chronic venous insufficiency [141]. Other applications of skin OPS imaging include the assessment of microcirculation in burn wounds [55,99]. Nonetheless, OPS use in burn wound severity is still predominantly used for research [73]. Application of pressure with OPS or SDF probes during examination modifies the flow velocity in vessels under investigation [87] and therefore induces artifacts. Moreover,

motion-induced image blurring is another limitation of OPS, attenuated in SDF imaging. Finally, they cannot be used in individuals with phototypes IV, V, and VI according to Fitzpatrick classification because melanin absorbs light at a similar wavelength to hemoglobin [137]. In conclusion, OPS and SDF imaging Uroporphyrinogen III synthase are semi-quantitative techniques implemented in small devices that can be used at the bedside. They provide good quality images of microvessels on thin epithelial layers. The most studied site is the sublingual region, and has been used mainly in critically ill patients. The main limitations of OPS and SDF imaging are the artifacts induced by movement and pressure. Finally, quantitative assessment of skin blood flow is not fully automatized yet, although this could be achieved by the development of new software [33]. Laser Doppler is based on the backscattering of a beam of laser light. The light undergoes changes in wavelength (Doppler shift) when it hits moving blood cells. The magnitude and frequency distribution of these changes in wavelength are related to the number and velocity of red blood cells [126].