Multispectral and Photoplethysmography Optical Imaging Techniques Identify Important Tissue Characteristics in an Animal Model of Tangential Burn Excision

Abstract

Burn excision, a difficult technique owing to the training required to identify the extent and depth of injury, will benefit from a tool that can cue the surgeon as to where and how much to resect. We explored two rapid and noninvasive optical imaging techniques in their ability to identify burn tissue from the viable wound bed using an animal model of tangential burn excision. Photoplethysmography (PPG) imaging and multispectral imaging (MSI) were used to image the initial, intermediate, and final stages of burn excision of a deep partial-thickness burn. PPG imaging maps blood flow in the skin's microcirculation, and MSI collects the tissue reflectance spectrum in visible and infrared wavelengths of light to classify tissue based on a reference library. A porcine deep partial-thickness burn model was generated and serial tangential excision accomplished with an electric dermatome set to 1.0 mm depth. Excised eschar was stained with hematoxylin and eosin to determine the extent of burn remaining at each excision depth. We confirmed that the PPG imaging device showed significantly less blood flow where burn tissue was present, and the MSI method could delineate burn tissue in the wound bed from the viable wound bed. These results were confirmed independently by a histological analysis. We found these devices can identify the proper depth of excision, and their images could cue a surgeon as to the preparedness of the wound bed for grafting. These image outputs are expected to facilitate clinical judgment in the operating room.

Improving the histologic characterization of burn depth

“…Given that 75% of dermis is composed of collagen, others have targeted the dermis for evaluation, but have been unable to consistently characterize thermally injured collagen. Some authors insist that collagen can be evaluated with H&E alone; however, characteristics of collagen in H&E‐stained tissue that correlate with denaturation have been variously described as glass‐like or as a separation of collagen . In other cases, authors do not provide detailed descriptions of collagen changes, other than identifying the entire section as necrotic, despite the presence of epithelial lined appendages with a normal appearance .…”

“…Some authors insist that collagen can be evaluated with H&E alone; however, characteristics of collagen in H&E-stained tissue that correlate with denaturation have been variously described as glass-like 9 or as a separation of collagen. 10 In other cases, authors do not provide detailed descriptions of collagen changes, other than identifying the entire section as necrotic, despite the presence of epithelial lined appendages with a normal appearance. 8 Furthermore, studies that advocate more complex staining methods such as Masson's Trichrome or polarization light evaluation of Picrosirius red-stained tissue may mislead interpretation of collagen health, as these techniques mainly identify changes in collagen fiber alignment and can be dependent on the timing of the burn injury.…”

Imaging Techniques for Clinical Burn Assessment with a Focus on Multispectral Imaging

“…In one of our recent studies using a pig model of burn excision, we demonstrated that burn-injured tissue was detec-tible with *85% accuracy and the viable wound bed to which a skin graft could be applied is detectible by MSI with 87% accuracy. 82 Analysis of the spectral difference between burn-injured tissue and wound bed tissue revealed that reflectance spectra vary most significantly at wavelengths of 515, 669, 750, and 972 nm, suggesting that burn tissues' blood, extracellular matrix, and water components makeup are quite different from healthy skin. 92 …”

“…The result has been favorable in validation testing where we found an average of 87% accuracy in the classification of tissues relevant to diagnose the preparedness of a wound bed in a burn surgery animal model. 82 …”

“…82 The progression of data collection began with a measurement of PPG signals in the region of interest before introduction of a burn wound. As expected, the PPG signal across the uninjured skin uniformly indicated healthy tissue.…”