To measure tissue optical properties of the bulk tissues, a fiberoptic reflectance probe with multiple source-collector separations was used. The optical properties and were extracted using the established technique of spatially resolved, steady-state diffuse reflectance (based on diffusion theory) as outlined by Farrell et al.23,24 Briefly, a multifiber probe with source-collector distances, , of 0.8, 1.5, 2.4, 4.0, and 5.3 mm was connected to an optical control system that consisted of a diode laser (Thorlabs, Newton, NJ) at 635 nm, an optical multiplexer (MPM-2000, Ocean Optics, Dunedin, FL), and a visible-light spectrometer (S2000, Ocean Optics). The collector fiber was connected to the spectrometer. The multiplexer was used to index the laser beam from fiber-to-fiber so as to achieve the various source-collector distances required for the spatially resolved diffuse reflectance algorithm. The well-known diffuse reflectance equations were employed to model the reflectance at each .23,24 The probe was calibrated against a diluted Intralipid (Fresenius Kabi, Sweden) solution with known optical properties and validated against a series of Intralipid-dye phantoms with and . The two optical property coefficients, and , were computed from the five reflectance measurements by solving an inverse problem. It is worth noting that the algorithm did not utilize some of the reflectance measurements in the case of low because the diffusion theory reflectance equation breaks down at low for low , as outlined in Kim et al.25 Hence, the algorithm would omit the reflectance value at, say, for , and use only four reflectance measurements to solve in the inverse problem in this scattering range. With this probe, we measured the optical properties of the six different tissues, periodically examining a well-characterized scattering solution of Intralipid as a calibration/system validation control phantom.