Chapter 8 Figure 8.1 Intraoperative fiber probe measurement 112 Intraoperative spectral fibre probe measurement performed during a transverse colon resection (resection of a tumor in the transverse colon). The sterile optical fibre probe is gently brought into contact with one of the designated tissues. Right lower corner: close‐up of the fiber probe tip. A ring light of seven fibers (illuminated white) injects light into the tissue, one central fiber (here for illustration purposes illuminated yellow) collects the diffusely reflected light and transports it towards the spectrometer. Data processing For inter‐patient comparability, all raw in vivo spectra were corrected using the dark current and reference reflectance spectrum. Since both reflectance intensity and spectral shape are related to the composition of the tissue, no further normalization steps were performed. To identify possible distinctive features for tissue‐specific enhancement, 36 features (i.e. 18 gradients and 18 amplitude differences at predefined points in the tissue spectra) were extracted based on known wavelengths related to characteristic absorption features for blood, water and fat28‐30. We described these features in more detail in a previous publication27. Figure 8.2 illustrates the characteristic wavelengths and features in a mean spectrum for human mesenteric adipose tissue. All data processing was performed by in‐house developed software (using MATLAB environment Version 7.7.0, MathWorks Inc., Natick, Massachussetts, USA). Further analysis of the in vivo spectra was divided into two detector ranges: Si‐detector (≤1000 nm) and InGaAs‐detector (≥900 nm).
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