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All organisms carry out metabolic processes to produce chemical energy, but these biochemical pathways are not perfectly efficient and energetic waste is lost as heat. The interplay of heat production/retention/loss in endotherms has been well studied via thermal imaging. However, there is a striking absence of literature on the thermal output of ectotherms, especially invertebrate animals. We have developed a new thermal imaging technique to investigate waste heat production in the nematode worm C. elegans. No direct measurement of this metabolic waste heat has been made in C. elegans or any other mesoinvertebrate using IR imaging techniques.
In this study, thermal IR imaging was used to examine the difference in heat output between living and dead C. elegans. Living and dead C. elegans were imaged simultaneously providing a way to directly compare the temperatures of the worms. Temperature difference was used as a marker of difference in waste heat production, not absolute temperature. A cold object was used in reflectance mode to suppress the thermal background of the imaging substrate. Several different substrates with differing thermal properties were tested to minimize thermal background. The tendency for C. elegans to desiccate necessitated the development of sample preparation techniques that ensured the survival of the animals during imaging. Imaging revealed that there is a clear, repeatable difference in the thermal output of living C. elegans compared to dead animals (whose metaobolic processes have ceased). This is exciting as it points to IR imaging as being a novel investigative tool to be applied to the study of metabolism in C. elegans. In the future this opens the door to screening genetic mutants with known metabolic defects, thus providing useful data for the study of genes that impact metabolism.
Inadequate tissue perfusion is a fundamental cause of early complications following a range of procedures including the creations of skin flaps/grafts during reconstructive microsurgery and complex closures during amputation. Clinical examination remains the primary means of evaluating tissue perfusion intraoperatively. Recently, indocyanine green (ICG) angiography has been used as an adjunt to physical examination. However, ICG angiography is an invasive procedure that requires the intravenous application of a fluorescent dye.
Enhanced thermal imaging (ETI) is a non-invasive, real-time infrared imaging technique that can detect blood vessels embedded in soft tissue. ETI uses selective heating of blood via illumination with a green (532 nm) LED to produce a thermal contrast (≥ 0.5 ◦C) between blood vessels and surrounding water-rich tissue. Vessel-rich regions appear brighter in the thermal image. ETI does not require the use of dyes and recent improvements to the acquisition software have enabled real-time imaging. The compact footprint of the system could allow for use both intraoperatively and at the bedside.
In this study we evaluate the ability of ETI to assess tissue perfusion of skin flaps in a murine model. The healing and perfusion of these flaps was monitored via the density of capillary beds and vascular networks using visual inspection, fluorescent imaging, and ETI over a 12-day study period. We compare the ability of these techniques to detect early indications of necrosis and re-vascularization in grafts.
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