A three-wavelength frequency-domain photon migration spectroscopy instrument using in-phase and quadrature (I&Q) demodulation technique in a 140-MHz homodyne system was described here. A calibration procedure was employed to qualify absorption coefficient and reduced scattering coefficient with single source-detector separation. The performance of the frequency-domain NIRS to quantify blood oxygen saturation and the concentration of oxy-and deoxy-hemoglobin is examined with experimental measurements on a yeast-blood model. The results of the forarm arterial occlusion experiment was in good agreement with those measured