Reflectance spectra were acquired using a portable spectroscopic system as illustrated in Fig. 1. For illumination of the tissue, a white light halogen broadband light source (360 to 2500 nm) with an internal shutter was used. The tissue was probed using a clinical-grade disposable 16 G fiber-embedded needle (INVIVO, Schwerin, Germany). The probe had one fiber (200 μm) connected to the light source and another fiber () connected to a spectrometer (silicon detector; Andor Technology, Belfast, United Kingdom, DU420A-BRDD), optimized for wavelengths between 400 and 1050 nm with a spectral resolution of . The center-to-center distance between the emitting and collecting fibers was 0.34 mm. The probe had a polished angle tip of 72 deg to minimize tissue damage during insertion, while the fiber ends were cut straight. The spectroscopy needle was made from materials that are heat-resistant in the temperature range that was investigated. DR spectra were acquired with a 0.3 to 1.0 s integration time, depending on the signal intensity at the start of each experiment. The integration time was kept constant during each experiment. The system was controlled by a custom-made LabView software user interface (National Instruments, Austin, Texas, USA).