Figure 1.

Experimental set-up for broad beam measurements. The optical properties of the Liposyn and ink used for the optical phantom were characterized independently using a broad parallel beam incident on the phantom. We used a 1 mm scattering tip isotropic detector to measure the fluence rate at different depths in the phantom using a step motor that has an accuracy of 0.1 mm. The measurements were made under five different conditions: one for Liposyn solution, three for Liposyn solution plus three ink concentrations with known optical properties, and one for pure water. The ratio between Liposyn (or Liposyn with ink) and water was fit to an exponential function: ϕ = k exp(−μ_effd), where μeff is the effective attenuation coefficient. This ratio eliminates the effect of inverse-square law and the detector sensitivity variation between water and air for the isotropic detector.