Chapter 9 Figure 9.1 Fibre probe data acquisition during thyroid surgery 132 Intraoperative spectral fibre probe measurement performed during a left hemithyroidectomy procedure. The sterile optical fibre probe is gently brought into contact with the recurrent laryngeal nerve (average diameter 2 mm13). Right lower corner: close‐up of the fibre probe tip. A ring light of seven fibres (illuminated white) injects light into the tissue, one central fibre (here for illustration purposes illuminated yellow) collects the diffusely reflected light. 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 fat25‐27. Gradients are “slopes” between two predefined points in the tissue spectra, i.e.: (DR2 – DR1)/(2 – 1). Amplitude differences are “intensity differences” between two predefined spectral points, i.e. (DR2‐DR1). DR = diffuse reflectance; = wavelength. Figure 9.2 illustrates the characteristic wavelengths and features in a mean spectrum for adipose tissue data. All data processing was performed by in‐house developed software (using MATLAB environment Version 7.7.0, MathWorks Inc., Natick, Massachussetts, USA).
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