A system is provided for probing a body lumen that includes a flexible conduit that is elongated along a longitudinal axis, the flexible conduit having a proximal end and a distal end, at least one delivery waveguide and at least one collection waveguide extending along the flexible conduit, a transmission output of the at least one delivery waveguide and a transmission input of the at least one collection waveguide located along a distal portion of the conduit. A spectrometer is connected to the at least one delivery waveguide and the at least one collection waveguide, the spectrometer configured to perform spectroscopy. A controller system is configured to calculate a distance between the flexible conduit and the wall of the body lumen based on a spectroscopic measurement of the at least one primary radiation signal that traveled between the flexible conduit and body lumen.
