Oximetry with phase modulation NIR spectroscopy based on phase measurement only

Near infrared spectroscopy, based on frequency domain methods, has been successfully applied to study turbid media^1-3, using amplitude and phase measurements. Oximetry based on phase measurements only may prove advantageous over amplitude phase measurements due to relative simplicity of use and calibration of systems with phase output only. Suggestions for hemoglobin saturation calculation, based on the diffusion approximation and phase information only, have been proposed in the past^4,5. There exist many factors though that may introduce inaccuracies in the data analysis and in the measurements, besides the inherent inability of such systems to account for absorption of water and chromophores besides oxy- and deoxy- hemoglobin. Such factors, as theoretical approximations, voltage to phase conversion and initial phase calibration, have to be carefully considered in order to produce consistent and reliable calculations. In the present work, simulation models, based on the solution of the diffusion equation in the frequency domain have been developed, to study the performance of different approximations used for the calculation of hemoglobin saturation. A new approach for data analysis is presented and investigated. Methods for instrument calibration are discussed and an example, based on experimental measurements, is demonstrated.