A device and method for gas measurements in body cavities are provided. These may be any body cavity containing a free gas, where there is an interest in detecting and/or measuring the concentration of said free gas by non-invasive or minimally invasive method. According to an exemplary embodiment measurement of free oxygen in cranium cavities is performed by scattering media absorption spectroscopy, and in particular variations of such oxygen. This is particularly useful for diagnostic purposes based on the measurements, for instance for detecting sinusitis or the like.
