Differentiation between nerve and adipose tissue using wide‐band spectroscopy Material Diffuse reflectance spectra were acquired using custom developed sterile disposable optical fibre probes (TNO, Eindhoven the Netherlands & Light Guide Optics, Rheinbach Germany), a modified Xenon light source (D‐light C, Karl Storz, Tuttlingen Germany), and a spectrometer (Analytical Spectral Devices, Inc., Colorado USA) equipped with two sensor technologies: a silicon (Si) based sensor and an indium gallium arsenide (InGaAs) based sensor (cross‐over point at 1000 nm). The fibre probe transports the light from the light source to the tissue and from the tissue to the spectrometer. The spectrometer acquires the spectral data in the range of 350 – 1830 nm with 1 nm spectral resolution. The system was installed on a compact trolley to facilitate in vivo tissue measurements during routine surgery. The setup was tested and approved according to the essential requirements of IEC 60601‐1 to assure patient safety. The equipment previously has been described in more detail24. Figure 9.1 shows the fibre probe tip composed of eight small optical fibres: One central receiving fibre (400 um diameter, NA 0.22 ±0.02) and seven illuminating fibres (300 um diameter, NA 0.22 ±0.02). The rigid stainless steel probe tip has a 2 mm diameter and a length of 10 mm. The remaining length of the sterile fibre probe is flexible. In vivo data acquisition During respectively thyroid and parathyroid surgery and carpal tunnel release surgery, in vivo wide‐band diffuse reflectance spectra were collected. For each tissue type, we recorded five spectra per site (taking 30 seconds per site) covering at least one site per tissue type (see also Table 9.1). The sterile fibre probe was handled by the surgeon and gently brought into direct contact with one of the designated tissues (see Figure 9.1). If blood was visibly present on the tissue surface, it was dapped away using a sterile gauze. Between the measurements on different locations, the probe tip was swiped with a clean sterile gauze wetted with saline. Acquired data was labeled according to the tissue type description of the attending surgeon. To correct for dark current8, the spectrometer was calibrated prior to in vivo data acquisition. After the completion of in vivo spectroscopy, a reference spectrum was acquired, for calibration purposes, by direct contact measurement on a white reference phantom (Optical‐grade spectralon reference; Labsphere, Inc., North Sutton, New Hampshire USA). The integration times of the Silicon and InGaAs sensor were individually optimized during the Spectralon calibration. No correction for ambient light was performed. 131
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