Abstract: An apparatus and method embodying the invention include utilizing a device intended to be inserted into a patient's body to determine a characteristic of a target tissue. In one apparatus and method, a device illuminates the target tissue with amplitude modulated excitation electromagnetic radiation, and the device senses a returned electromagnetic radiation. A phase shift between the excitation and return electromagnetic radiation is determined, and the phase shift is used to determine characteristics of the target tissue. A demodulation factor, representing ratios of the AC and DC components of the excitation and return electromagnetic radiation may also be calculated and used to determine characteristics of the target tissue. In another apparatus and method embodying the invention, a device illuminates a target tissue with polarized electromagnetic radiation, and a return electromagnetic radiation is sensed.

Abstract: A combined infection shield and calibration or reference target for use with a measuring instrument includes a removable calibration/reference layer. The removable calibration/reference layer has predetermined optical characteristics that can be utilized to calibrate or reference the instrument. The calibration/reference layer may have predetermined reflectance or scattering properties, a predetermined transmissivity to light, or it may have predetermined fluorescence properties. When the calibration/reference layer is removed from the remaining portions of the device, the portion of the calibration/reference layer having the predetermined optical characteristics is irrevocably altered such that the calibration/reference layer cannot be reused. The combined infection shield and target may be attached to a shield holder, which in turn is attached to an instrument. Alternatively, the infection shield and target may be attached directly to an instrument.