Skin topography measurement by interference fringe projection: a technicalvalidation

Background/aims: The quantitative analysis of skin topography is frequently used in cosmetology to evaluate the efficacy of hydrating or anti-wrinkle creams (micro-topography studies) or creams for slimming or to alleviate st retch marks (macro-topography studies). Numerous methods involving the thre e-dimensional (3-D) reconstruction of the topography from silicone replicas have been developed. Some of the main techniques applied include optical p rofilometry based on the reflection of oblique lighting or on transparency, and profilometry by laser focusing or triangulation. Methods: We chose to test the Dermatop system developed by Eotech Co., whic h is based on interference fringe projection profilometry associated with t he Toposurf surface processing software. Owing to the system's principle of operation, we first ran three experiments to evaluate the influence of amb ient lighting on the 3-D reconstruction and the surface roughness parameter s, the influence of the calibration device built into the acquisition syste m and the influence of calibration in terms of ambient lighting correction. We then evaluated the accuracy, the repeatability and the reproducibility of the measurements provided by the system from known metal topographic sta ndards and skin replicas. Results: It was seen that external lighting can cause variations in the cal culation of parameters SPa, SPt and SPtm which can reach error levels of ab out 5% if the operator does not almost systematically calibrate the apparat us between each measurement. These three experiments enabled us to standard ise the protocol for the acquisition of 3-D information, in order to minimi se the lighting problems and yet respect the requirements for routine studi es. The correlation coefficient between the theoretical values and the mean of experimental values was 0.9955 for parameter SPa and 0.9983 for paramet er SPtm. Repeatability presented variations of under 4%, irrespective of th e parameters, and reproducibility of under 6%. Conclusions: The technique provides very satisfactory results from the poin t of view of accuracy, repeatability and reproducibility. It is an excellen t compromise between cost, accuracy and the time required.