Second generation video imaging technique for assessing dermal exposure (VITAE system)

Development of a second-generation video imaging technique for assessing occupational skin exposure (VITAE) is described, its performance evaluated, and new procedures for exposure quantification are presented. The current VITAE system has higher resolution in regard to both its picture element array and gray scale when compared with the prototype system. System performance was evaluated during extended field deployment: variability was 3-4% during data acquisition for individual worker evaluation sessions, and 10% over a 22-day study period. Variabilities attributable to subject positioning and image outlining procedures were 2.7 and 1.2%, respectively. Visual observations of fluorescent tracer deposition on skin were used to classify specific body regions as either exposed or unexposed, and two computer-based classification criteria were tested against the visual classifications. These criteria were generally better at minimizing false negative than false positive classification; sensitivity and predictive value reached 95 and 99%, respectively, when analysis was preceded by presampling of a subset of images. Variability in skin pigmentation was found to have a substantial effect on fluorescent tracer quantification, leading to development of new calibration procedures. Standard curves were generated by spotting a range of tracer concentrations on volunteer subjects and quantifying fluorescence with the VITAE system. These data were then grouped either by subject or by the magnitude of the background signal of the unexposed skin. The ability to control for the effects of skin pigmentation was found to be comparable for these two grouping methods, indicating that calibration curves can be developed without the creation of a unique curve for each subject.