Noninvasive Methods for Determining Lesion Depth From Vesicant Exposure

Before sulfur mustard (HD) injuries can be effectively treated, assessment of lesion depth must occur. Accurate depth assessment is important because it dictates how aggressive treatment needs to be to minimize or prevent cosmetic and functional deficits. Depth of injury typically is assessed by physical examination. Diagnosing very superficial and very deep lesions is relatively easy for the experienced burn surgeon. Lesions of intermediate depth, however, are often problematic in determining the need for grafting. This study was a preliminary evaluation of two noninvasive bioengineering methodologies, laser Doppler perfusion imaging (LDPI) and indocyanine green fluorescence imaging (ICGFI), to determine their ability to accurately diagnose depth of sulfur mustard lesions in a weanling swine model. Histological evaluation was used to assess the accuracy of the imaging techniques in determining burn depth. Six female weanling swine (8-12 kg) were exposed to 400 microl of neat sulfur mustard on six ventral sites for 2, 8, 30, or 60 minutes. This exposure regimen produced lesions of varying depths from superficial to deep dermal. Evaluations of lesion depth using the bioengineering techniques were conducted at 24, 48, and 72 hours after exposure. After euthanasia at 72 hours after exposure, skin biopsies were taken from each site and processed for routine hematoxylin and eosin histological evaluation to determine the true depth of the lesion. Results demonstrated that LDPI and ICGFI were useful tools to characterize skin perfusion and provided a good estimate of HD lesion depth. Traditional LDPI and the novel prototype ICGFI instrumentation used in this study produced images of blood flow through skin lesions, which provided a useful assessment of burn depth. LDPI and ICGFI accurately predicted the need for aggressive treatment (30- and 60-minute HD lesions) and nonaggressive treatment (2- and 8-minute HD lesions) for the lesions generated in this study. Histological evaluation confirmed the accuracy of the assessment. The ICGFI instrument offers several advantages over LDPI including real-time blood flow imaging, low cost, small size, portability, and not requiring the patient to be repositioned. A negative, however, is the need for intravenous dye injection. Although this would not be an issue in a hospital, it may be problematic in a mass casualty field setting. Additional experiments are required to determine the exposure time necessary to produce a graded series of partial-thickness HD lesions and to optimize instrumental parameters. The data generated in this follow-on study will allow for a full assessment of the potential LDPI and ICGFI hold for predicting the need for aggressive treatment after HD exposure. The lasting message is that objective imaging techniques can augment the visual judgment of burn depth.