Evaluating visual perception for assessing reconstructed flap health

Abstract

Background Detecting failing tissue flaps before they are clinically apparent has the potential to improve post-operative flap management and salvage rates. This study demonstrates a model to quantitatively compare clinical appearance, as recorded via digital camera, with spatial frequency domain imaging (SFDI), a non-invasive imaging technique utilizing patterned illumination to generate images of total hemoglobin and tissue oxygen saturation. Methods Using a swine pedicle model where blood flow was carefully controlled with occlusion cuffs and monitored with ultrasound probes, throughput was reduced by 25%, 50%, 75%, and 100% of baseline values in either the artery or the vein of each of the flaps. The color changes recorded by a digital camera were quantified in order to predict which occlusion levels were visible to the human eye. SFDI was also used to quantify the changes in physiological parameters including total hemoglobin and oxygen saturation associated with each occlusion. Results There were no statistically significant changes in color above the noticeable perception levels associated with human vision during any of the occlusion levels. However there were statistically significant changes in total hemoglobin and tissue oxygen saturation levels detected at the 50%, 75%, and 100% occlusion levels for arterial and venous occlusions. Conclusion As demonstrated by the color imaging data, visual flap changes are difficult to detect until significant occlusion has occurred. SFDI is capable of detecting changes in total hemoglobin and tissue oxygen saturation as a result of partial occlusions before they are perceivable, thereby potentially improving response times and salvage rates.

Characterisation of impaired wound healing in a preclinical model of induced diabetes using wide‐field imaging and conventional immunohistochemistry assays

“…Similarly, hyperspectral imaging uses wavelengths between 500 and 700 nm to provide information on oxygenated haemoglobin (HbO 2 ) and deoxygenated haemoglobin (Hb) in burn and diabetic wounds, creating anatomical tissue StO 2 maps that may predict the risk of ulceration in the diabetic foot before it occurs . In our case, we use spatial frequency domain imaging (SFDI), which has been used to examine reconstructive surgery, port wine stain response to therapy, and burn wound severity assessment . In this study, SFDI was used to evaluate the macroscopic changes in HbO 2 , Hb, and StO 2 within wounds in normal versus streptozotocin (STZ) diabetic animals and then combining this observation with NF‐κB and iNOS expression analysis.…”

Spatial frequency domain imaging in 2019: principles, applications, and perspectives

“…14 Following this work, further studies demonstrated that SFDI could detect partial changes in flap circulation (50% blockage) prior to measurable changes in visual color. 104 Confirming the diagnostic potential of SFDI, additional work demonstrated that severe ischemic conditions measured by SFDI in a cutaneous pedicle flaps was predictive of necrosis. 101 Beyond the diagnostic potential of oxygenation imaging, it was also demonstrated that the source of the occlusion (arterial versus venous) could be identified as early as 2 min after blockage in a hemifacial composite flap transplants.…”

Review of structured light in diffuse optical imaging

“…Similar models have since been studied in animals to validate the utility of SFDI evaluation of flap profusion and viability 105 – 107 While skin flap viability is classically assessed by visual inspection, SFDI has shown promise in detecting profusion changes before they are perceptible to the eye by tracking vascular parameters such as total hemoglobin concentration and oxygen saturation 108 …”