The present invention relates to an apparatus 100 and, a method and a computer program for determining a parameter indicative of a tissue type of an associated tissue 116. In particular, the invention relates to an apparatus 100 comprising a spectrometer 102, which spectrometer comprises a light source 104 and a detector 106, 108 arranged to measure an optical spectrum. This enables determination of a first parameter being indicative of a bile concentration. As the inventors of the present invention have made the insight that bile concentration may serve as a discriminative feature for different tissue types, the apparatus is arranged to determine a second parameter indicative of a tissue type based on a concentration of bile. According to a specific embodiment, the apparatus further comprises an interventional device 112.
