Abstract: An optical body cavity probe (110, 310, 1200, 1300) is provided with a disposable flexible comformable sheath (120) having an optical window (220), or a disposable rigid sheath (320, 1210, 1310) having an optical window (420). The electronic system includes optical sources for generating the illuminating electromagnetic energy, filters or spectrum analyzers for isolating returned wavelengths of interest, and a computer for processing the returned wavelengths of interest to determine the tissue properties of interest as well as to calibrate the system. For calibration purposes, a removable calibration body (510, 910, 1010, 1220, 1330, 1430) bearing a fluorescence pattern resides on the outside of the optical window (500, 900, 1000, 1210, 1310, 1420) so as to be in the field of view of the probe when the sheath is installed over the probe.