In plastic surgery, free tissue graft procedures are an essential part of fixing tissue-lack injuries or diseases. However, tissue necrosis caused by vascular occlusions or poor vascular anastomosis is a severe problem for prognosis. Follow-up surgery in the early-stage of necrosis caused by congestion or ischemia is essential to salvage the tissue, but making a diagnosis is difficult because of the slight features of these states. Therefore, a diagnosis support system that can capture the features of blood circulation of the skin flap is required to improve prognosis. We focused on system design and analysis by using spectral characteristics of blood circulation of a skin flap for this purpose. The system to be constructed is composed of a two-channel narrow-band illuminant and a color camera and can capture six-channel spectral signals. The narrow-band illuminant is designed by combining 13 kinds of light-emitting diode (LED) spectra. In this study, we first measured reflectance spectra of the early-stage skin flap necrosis of the rat model to design the narrow-band illuminant spectra. We blocked the flow of the target vessel and observed necrosis progression. A prototyped skin flap chamber was used for stable observation of spectral reflectance measurements. An evaluation experiment was conducted using a color camera and the spectrally tunable light source. Skin flap images were captured under the designedilluminants and a conventional illuminant reproduced by the spectrally tunable light source. We confirmed the effectiveness of the designed system by improvements in necrosis region detection.
In open surgery, observing organ blood circulation and distinguishing artery and vein are important to improve precision of surgery. However, there are some difficulties in this judgement and distinction because there are only slight color differences in the color of ischemic or healthy organs. Peripheral vessels between artery and vein also have subtle difference in their color. The difference in absorption coefficients between oxygenated and deoxygenated hemoglobin mainly affects these characteristics. Therefore, if the illuminant spectrum can be optimized based on the optical properties, there is a possibility to enhance the difference between the two types of vessels and blood-oxygenation levels. To achieve these purposes, we conducted a spectroscopic design of a surgical illuminant combining 14 kinds of commercially available light-emitting diode (LED) spectra by maximizing color differences between blood samples. Spectral reflectance of the blood samples whose oxygen saturation (SO2) measured in advance were employed for computer simulation. In this study, we prototyped a spectrally tunable light source which contains the same LED sets used in the simulation of the surgical illuminant. A conventional illuminant and the designed illuminant spectrum were spectrally adjusted by the spectrally tunable light source to evaluate the effectiveness of the optimal illuminant. Two kinds of cattle blood samples that have different SO2 were enclosed in glass cells and covered with cattle artery for subjective evaluation. Research participants were instructed to compare the color of samples and to sort these blood samples in a SO2 order under the two illuminant conditions. The percentage of correct answers under the designed illuminant was superior to that under the conventional illuminant. This results showed the effectiveness of the designed illuminant.