Patent ID: 8190240

Claim:
A device configured to measure concentration of a free gas in a body cavity, comprising: a light emitter arranged to emit an emitted light towards said body cavity from outside said body cavity; a light receiver arranged to collect a collected light, said collected light comprising said emitted light that has been scattered from the tissue surrounding said body cavity, a portion of said collected light having passed through said body cavity at least once, wherein said light receiver is configured to observe at least one wavelength window specific for said free gas in the body cavity; and a processor configured to assess a concentration of said free gas in said body cavity from said collected scattered light, based on optical absorption spectroscopy; wherein said assessing of said concentration of said free gas is a ratio between a measurement signal from said collected light associated with said free gas in said body cavity and a measurement signal from said collected light associated with a known concentration of a reference gas and said reference gas is water vapor.