Multispectral characterization of tissues encountered during laparoscopic colorectal surgery A QualitySpec® Pro (Analytical Spectral Devices, Inc., Colorado USA) spectrometer was used. This is a transportable VIS/NIR spectrometer covering a wavelength range between 350 and 1830 nm, equipped with two detector technologies: Silicon from 350‐1100 nm and InGaAs from 900‐1830 nm and controlled by a spectral acquisition package called IndicoTM Pro (Version 5.6, Analytical Spectral Devices, Inc., Colorado USA). The spectrometer software facilitated optimized choice of cross‐over wavelength between the “silicon” and “beyond silicon” range. The applied light source was a modified xenon lamp (D‐light C, Karl Storz, Tuttlingen Germany). The IR‐filter was removed in order to produce wavelengths in both the visible (VIS) and near‐infrared (NIR) as well as part of the short wave infrared (SWIR) ranges of the electromagnetic spectrum. A custom fiber coupler was applied to prevent burn‐in of the light guide fibers. In addition to some narrow NIR peaks, this lamp also emits a continuum within the deeper infrared (IR) region, but with a lower intensity than the continuum in the VIS‐region. The fiber probe was designed by TNO and custom built. The fiber probe is the medium through which light is transported from light source towards tissue, and back from the tissue to the spectrometer. Scatter diffused reflection and absorption within the tissue form the tissue interactions. In Figure 7.2 the fiber probe tip is shown in detail. The fiber probe (bandwidth 350 nm – 2400 nm) is composed of eight small optical fibers: one central receiving fiber tip (illuminated yellow) which has a core diameter of 0.44 mm and seven illuminating fibers (illuminated white) which have core diameters of 0.33 mm. The total external tip measures 2 mm in diameter. Numerical aperture of both fiber types is 0.22. The stainless steel tip has a length of 10 mm. The rest of the sterile fiber is highly flexible. A custom built SMA‐adapter was used to connect the fiber probe to the cold light guide connector of the medical light source. For ex vivo tissue measurements a non‐sterile fiber probe was used on the specimens immediately after surgical extirpation. Human colonic specimen Approval from the local medical ethical review board was granted before ex vivo human tissue measurements were performed. These measurements were intended to collect the spectra of different tissue types in freshly extirpated human colon tissue. Colonic, sigmoid and rectum specimens of patients who underwent open or laparoscopic colorectal surgery during the time of this study were included. 93
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