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Background: Tissue Viability Imaging (TiVi) is a new bioengineering technology intended for remote two-dimensional mapping of skin red blood cell concentration (RBC(conc)). Before use in the laboratory, work-site and dermatology clinic, critical performance parameters of this emerging technology require careful evaluation., Objective: To assess short- and long-term stability, image uniformity, distance and image size dependence, ambient light and curvature influence in a production batch of Tissue Viability Imagers., Methods: Four Tissue Viability Imagers from the same production batch were evaluated at two laboratories (one industrial and one dermatological) with respect to critical parameter performance., Results: The average systematic drift in sensitivity over time was 0.27% and <1.02% for all four units tested. Difference in sensitivity between units was limited to 4.1% and was due to offset rather than gain deviation. Spatial variation in image uniformity was below 3.08% and 1.93% in the corners and centre of an individual image, respectively. This spatial variation could be further reduced to 0.25% and 0.13%, respectively by image normalization. Ambient light from a 40 W bulb or a 11 W fluorescent light source at a distance of 50-60 cm above the object, reduced the recorded values by about 10%, while the camera to object distance and image size had no detectable influence on sensitivity. Curved objects, such as human forearm, demonstrated an edge effect limited to below 10%., Conclusion: The critical TiVi performance parameters evaluated proved stable in relation to expected variations in skin RBC(conc) over time. Calibration by way of a two-point method may reduce differences in sensitivity between instruments to further facilitate inter-laboratory comparison of results.

Background: Tissue Viability Imaging (TiVi) is an emerging bioengineering technology intended for two-dimensional mapping of skin erythema and blanching. Before TiVi can be effectively used in studies of diseased or damaged skin, the variability in normal skin red blood cell concentration (RBC(conc)) requires evaluation., Objective: To demonstrate how TiVi maps spatial and temporal variations in normal skin RBC(conc) at the dorsal side of the hand at rest and during post-occlusive hyperemia., Methods: Short-term and day-to-day variations in skin RBC(conc) were quantified at the dorsal side of the hand in four healthy volunteers at rest. In a separate study, the increase in skin RBC(conc) was recorded during post-occlusive hyperemia., Results: A lower skin RBC(conc) (179-184 TiVi units) was observed at the back of the hand and base of the thumb compared with areas adjacent to the nailfoldfold region of the fingers (190-213 TiVi units). The short-term variation (within 70 s) was <2% in all areas of the dorsal side of the hand, while day-to-day variations were in the range 5-7% in the back of the hand and up to 10% in areas adjacent to the nailfold region. In the post-occlusive hyperemia phase, up to a 60% increase in skin RBC(conc) was observed in the early part of the reactive hyperemia phase. This increase in skin RBC(conc) successively decreased but remained about 18% above the pre-occlusion level after 30 min., Conclusion: Establishment of healthy skin RBC(conc) reference values is important for the design of versatile test procedures for assessment of skin damage caused by vibration tools, chemical exposure or peripheral vascular disease.