Impaired reperfusion of blood vessels is a fundamental cause of complications like tissue ischemia following reconstructive microsurgery or skin grafting. Clinicians have historically relied on visual and tactile assessment to evaluate perfusion intra- and postoperatively. Recently, indocyanine green angiography (ICGA) has been implemented during procedures to map the body’s vasculature in real time. However, ICGA requires the IV administration of a fluorescent dye that can be expensive and poorly tolerated by some patients. There is a need for a cheaper, more versatile tool that can image microvessels intraoperatively and help monitor healing at the bedside. Enhanced thermal imaging (ETI) is an infrared imaging technique that uses green LEDs to induce a natural thermal contrast between blood and surrounding water-rich tissue. ETI has proven capable of delineating millimeter-scale vessels ex vivo and the venous margins of cancerous tumors. Most recently, the potential of ETI to detect capillary growth as an indicator of early wound healing within skin flaps in a murine model was evaluated. In this study, MCmatlab—a MATLAB-interfaced, Monte Carlo light transport and heat diffusion solver—was used to simulate photon deposition and heat diffusion in a mouse-scale model of perfused skin tissue under ETI operating parameters. The relationship between capillary density and the thermal signal observed at the tissue surface suggests the response captured by ETI was related to fluctuations in blood flow intrinsic to the healing process. ETI offers a promising solution for intraoperative guidance and point-of-care diagnosis of tissue perfusion.
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.
Enhanced Thermal Imaging (ETI) is a new thermal infrared (8-10 μm) imaging technique that delineates blood vessels embedded in water-rich tissue in real time. 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. The warmer blood vessels appear brighter in the thermal image. In a previous study, the growth of breast cancer tumors in an 4T1 murine orthotopic model was successfully monitored in vivo using ETI. The images highlighted regions that are routinely targeted for surgical excision around solid mass tumors. Recently, improvements to the acquisition software have enabled real-time imaging with this technique, highlighting ETI’s potential use as an intraoperative imaging tool. In this study, simulations of direct illumination and heating of the blood vessels embedded in tissue were conducted to understand the effects of LED power and vessel depth on the ability of ETI to detect vascular structures. The simulations were performed with an open-source MATLAB integrated solver, MCmatlab.
Cold-chain storage can be challenging and expensive for the transportation and storage of biologics, especially in low-resource settings. Recent research has demonstrated that anhydrous preservation in a trehalose amorphous solid matrix offers an alternative to freeze drying for the preservation of biologics. We have previously described a new processing technique, light assisted drying (LAD), to create trehalose preservation matrices of small volume (40 μL) samples. LAD uses illumination by near-infrared laser light to selectively heat water and speed dehydration. In this study we apply the LAD technique to large volume samples (250 μL) that are more comparable to therapeutic doses.
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