Comparison of depth dependence of light fluence rate in intralipid for wavelengths between 532-730 nm

Light penetration of laser in tissue is important for dosimetry of photodynamic therapy (PDT). In this report, depth dependence of laser under uniform light irradiation with λ (532, 630, 730 nm) was measured in intralipid, a relatively pure scattering medium. A 0.3-mm diameter isotropic detector with scattering tip was used to measure the light fluence rate. The optical penetration depth δ for the uniform light irradiation is defined as the depth where light fluence rate drops to 1/e of that at surface. Various concentrations between 1-15% were used to change effective absorption coefficient μ_eff . Measurement was made of the radial light fluence rate around a point source with known radiant power P. The result is then fitted to a diffusion model to determine μ_eff. For the uniform light irradiation, δ are 1.06, 1.24 and 0.88 cm for 532, 630 and 730 nm, respectively, in 10% intralipid. They increase with decreasing concentration of intralipid. For 15% intralipid the optical penetration for 730 nm light is longer than that for 532 nm. This trend follows that 1/μ_eff which are 0.66, 0.93 and 0.55 cm for 532, 630 and 730 nm. The authors did not observe any buildup in the surface region. The most interesting finding is that the optical penetration for 730 nm laser light is shorter than that of 532 and 630 nm laser in intralipid. This is not true in tissue where the optical penetration for 730 nm light is longer