Abstract: A sample (1) is irradiated by a pulse from a laser (2), creating fluorescence radiation, which is brought, in imaging relation or otherwise, to a detector (6) sensing from the same sample (1) in a plurality of spectral intervals (6A-6D), for obtaining intensity values. The radiation may be sensed in imaging relation, creating a multiplicity of said pluralities. The spectral intervals may be wavelength defined by passband filters (5A-5D) or time interval defined time spectral intervals controlled by a computer (7), which makes a numerical evaluation comprising a division. The tissue character may then be evaluated from the evaluation.