Digital image analysis (DIA) of colour changes in human skin exposed to standardized thermal injury and comparison with laser Doppler measurements

Clinical macrophotography followed by digitization and computer-assisted image analysis was performed on volunteers exposed to a mild experimental thermal injury. The aim was to elaborate a non-invasive technique allowing repetitive and quantitative monitoring of induced erythema and to evaluate a possible relationship with laser Doppler measurement of skin perfusion. A standardized 1 x 1 cm large thermal trauma was induced in the skin of the ventral forearm of 12 volunteers. Photographic recordings and skin blood flow measurements were made preburn and at 30-min, 1-h, 2-h, 4-h and 12-h postburn. Image analysis was performed with two colour systems, normalized rgb-values (rgb) and Hue-Saturation-Intensity (HSI). Erythema measured by rgb and HSI was most pronounced during the first hour postburn, after which it gradually decreased in order to increase again at 12 h postburn. Skin perfusion peaked at 30 min postburn and then continuously decreased during the course of the experiments. Degree of erythema could be quantified using both colour systems and a linear relationship was obtained between the observed colour changes of both systems and changes in skin perfusion. Results may also indicate that erythema can be present without a concomitant increase in skin perfusion, probably representing postburn venous stasis. The present study showed that digital image analysis is a non-invasive technique allowing repetitive and quantitative analysis of skin erythema which can be used to monitor pathophysiological changes in the body as well as the result of their treatment.