For each of the nine patients, four cross-sections according to the preservation protocols (“native”, “formalin”, “in paraffin”, “dewaxed”) were investigated. Three tumor and three salivary gland tissue regions were selected for each cross-section (Figure 2 ). Ten randomly chosen spectra were collected per tissue region resulting in 60 measurements of each tumor cross-section. In total, 2160 single FTIR spectra were recorded in reflectance mode with an infrared microscope (Autoimage, Perkin Elmer, Waltham, MA, USA) coupled to an FTIR spectrometer (FTIR System 2000, Perkin Elmer, Waltham, MA, USA) shown in Figure 1 .
Following sample illumination, the reflected light was collected with a thermoelectric cooled mercury cadmium telluride (MCT) detector. The system was referenced against air and 256 accumulations for each measurement with a gain of 4 were acquired. The spectral resolution was 4 cm−1 and the optical path difference velocity was 2 cm/s. The wavenumbers range from 4000 cm−1 to 700 cm−1. An aperture size of 50 μm × 50 μm was used, which represents the measured area integrated for each single FTIR spectrum.
Following sample illumination, the reflected light was collected with a thermoelectric cooled mercury cadmium telluride (MCT) detector. The system was referenced against air and 256 accumulations for each measurement with a gain of 4 were acquired. The spectral resolution was 4 cm−1 and the optical path difference velocity was 2 cm/s. The wavenumbers range from 4000 cm−1 to 700 cm−1. An aperture size of 50 μm × 50 μm was used, which represents the measured area integrated for each single FTIR spectrum.