Infrared Thermal Imaging as a Method of Improving Skin Graft Qualification Procedure and Skin Graft Survivability

Postoperative Time and Anatomic Location Influence Skin Graft Reperfusion Assessed With Laser Speckle Contrast Imaging

OBJECTIVES

Under optimal conditions, afferent and efferent human skin graft microcirculation can be restored 8-12 days postgrafting. Still, the evidence about the reperfusion dynamics beyond this period in a dermato-oncologic setting is scant. We aimed to characterise the reperfusion of human skin grafts over 4 weeks according to the necrosis extension (less than 20%, or 20%-50%) and anatomic location using laser speckle contrast imaging (LSCI).

METHODS

Over 16 months, all eligible adults undergoing skin grafts following skin cancer removal on the scalp, face and lower limb were enroled. Perfusion was assessed with LSCI on the wound margin (control skin) on day 0 and on the graft surface on days 7, 14, 21 and 28. Graft necrosis extension was determined on day 28.

RESULTS

Forty-seven grafts of 47 participants were analysed. Regardless of necrosis extension, graft perfusion equalled the control skin by day 7, surpassed it by day 21, and stabilised onwards. Grafts with less than 20% necrosis on the scalp and lower limb shared this reperfusion pattern and had a consistently better-perfused centre than the periphery for the first 21 days. On the face, the graft perfusion did not differ from the control skin from day 7 onwards, and there were no differences in reperfusion within the graft during the study.

CONCLUSION

Skin graft reperfusion is a protracted process that evolves differently in the graft centre and periphery, influenced by postoperative time and anatomic location. A better knowledge of this process can potentially enhance the development of strategies to induce vessel ingrowth into tissue-engineered skin substitutes.

Thermal Imaging as a Method to Indirectly Assess Peripheral Vascular Integrity and Tissue Viability in Veterinary Medicine: Animal Models and Clinical Applications

Infrared thermography (IRT) is a technique that indirectly assesses peripheral blood circulation and its resulting amount of radiated heat. Due to these properties, thermal imaging is currently applied in human medicine to noninvasively evaluate peripheral vascular disorders such as thrombosis, thromboembolisms, and other ischemic processes. Moreover, tissular damage (e.g., burn injuries) also causes microvasculature compromise. Therefore, thermography can be applied to determine the degree of damage according to the viability of tissues and blood vessels, and it can also be used as a technique to monitor skin transplant procedures such as grafting and free flaps. The present review aims to summarize and analyze the application of IRT in veterinary medicine as a method to indirectly assess peripheral vascular integrity and its relation to the amount of radiated heat and as a diagnostic technique for tissue viability, degree of damage, and wound care.

Cutaneous and local radiation injuries

The threat of a large-scale radiological or nuclear (R/N) incident looms in the present-day climate, as noted most recently in an editorial in Scientific American (March 2021). These large-scale incidents are infrequent but affect large numbers of people. Smaller-scale R/N incidents occur more often, affecting smaller numbers of people. There is more awareness of acute radiation syndrome (ARS) in the medical community; however, ionising radiation-induced injuries to the skin are much less understood. This article will provide an overview of radiation-induced injuries to the skin, deeper tissues, and organs. The history and nomenclature; types and causes of injuries; pathophysiology; evaluation and diagnosis; current medical management; and current research of the evaluation and management are presented. Cutaneous radiation injuries (CRI) or local radiation injuries (LRI) may lead to cutaneous radiation syndrome, a sub-syndrome of ARS. These injuries may occur from exposure to radioactive particles suspended in the environment (air, soil, water) after a nuclear detonation or an improvised nuclear detonation (IND), a nuclear power plant incident, or an encounter with a radioactive dispersal or exposure device. These incidents may also result in a radiation-combined injury; a chemical, thermal, or traumatic injury, with radiation exposure. Skin injuries from medical diagnostic and therapeutic imaging, medical misadministration of nuclear medicine or radiotherapy, occupational exposures (including research) to radioactive sources are more common but are not the focus of this manuscript. Diagnosis and evaluation of injuries are based on the scenario, clinical picture, and dosimetry, and may be assisted through advanced imaging techniques. Research-based multidisciplinary therapies, both in the laboratory and clinical trial environments, hold promise for future medical management. Great progress is being made in recognising the extent of injuries, understanding their pathophysiology, as well as diagnosis and management; however, research gaps still exist.

Preoperative design of flap based on computer-aided design technology: morphological flattening and analysis of three-dimensional wound

The shape of skin flaps is only described by swatches for preoperative design because of the irregular shape of skin wounds caused by trauma in the clinic. The method is rough, and the flaps cut often cannot match the wounds and affect their appearance. Computer-aided design technology helps to attain precise results in less time. This study proposes a skin wound morphological flattening algorithm based on hierarchical values. First, the skin wound is scanned by three-dimensional (3D) scanning technology to obtain a spatial mesh model consisting of triangular cells, and the mesh model is layered with a hierarchical value. Then, the layered mesh is topologically mapped to the plane. Subsequently, the stress and strain of the skin are simulated using a mechanical method, and the shape of the flattened skin wound is optimized layer by layer. Finally, the multiresolution smoothing technique is used to smooth the developed boundary contour and fit the curve to obtain a guidance plan for preoperative flap design. The results of the study showed that this method can accurately determine the shape of the skin wounds and quantitatively analyze the preoperative design results of the skin flaps. The average error of the area and edge length after flattening was reduced to less than 10%. The work is designed to realize the precise and individualized design of flap schemes before operation and to help standardize the preoperative design process.

Analysis of biomonitoring data after full-thickness skin grafting

Skin graft vascularization is investigated mainly by histological evaluation. Immunohistochemical analysis has been conducted only in mice. Transcutaneous oxygen tension (TcPO₂ ), which is an index of blood flow, has not been evaluated in skin grafts and only a few studies have reported biologic monitoring data using color tone evaluation and surface temperature. In humans, these tests can be performed non-invasively. To evaluate human skin graft vascularization, we analyzed biomonitoring data after skin grafting. We evaluated 14 patients who underwent skin grafting surgery at Nagoya City University Hospital. The TcPO₂ , color tone, surface temperature, and dermoscopic observations at recipient sites were measured at postoperative day (POD) 4, 6, and 11. Mean TcPO₂ levels at POD4, 6, and 11 were 12.7, 15.2, and 33.5 mmHg, respectively, and significantly higher at POD11 than at POD4 (p = 0.003, Steel-Dwass test). Dermoscopic observation revealed gradually increasing redness and yellowness. Color tone evaluation measured by spectrophotometry supported the appearance. The a*(redness) value at POD4, 6, and 11 was 6.19, 9.20, and 11.27, respectively, and significantly higher at POD11 than at POD4 (p < 0.001, Steel-Dwass test). The b*(yellowness) value at POD4, 6, and 11 was 8.83, 9.24, and 13.02, respectively, and significantly higher at POD11 than at POD4 (p = 0.020, Steel-Dwass test). The surface temperature did not significantly differ between graft and control sites. These findings suggest that skin graft vascularization started by POD6 and stabilized by POD11. Because TcPO₂ increases after POD4, skin grafts should remain undisturbed until at least POD11.