2.1. Optical Phantom Preparation

Nonturbid (i.e., clear) phantoms were prepared to characterize the fluorescence emission of PpIX in an aqueous solution in the presence of various amounts of surfactant. For this set, 15 phantoms (10 mL each) were prepared with PpIX (Sigma-Aldrich, St. Louis, Missouri) solubilized in dimethyl sulfoxide (DMSO) to yield concentrations of (0.1, 1, 10) μg/mL, Tween 20 (Sigma-Aldrich) in volume fractions (TVF) of (0, 0.1, 0.5, 1, 5)%, and the balance completed with phosphate-buffered saline (PBS). An additional phantom set was also measured using egg yolk (more specifically the amphipathic phospholipid contents of egg yolk^33,34) as a surfactant, with egg yolk volume fractions of (0, 0.1, 0.5, 1, 5)%.

Two phantom sets were constructed to characterize PpIX fluorescence in turbid phantoms in the presence of surfactant: one set containing Intralipid 20% (Fresenius Kabi, Uppsala, Sweden) as the scattering agent with no background absorber, and a second set containing both Intralipid and bovine whole blood (Lampire, Ottsville, Pennsylvania) as a background absorber. Each phantom in this set contained 1.5% lipid volume fraction (LVF), while the absorbing set of phantoms also contained 2% blood volume fraction (BVF). PpIX was solubilized using DMSO at a stock concentration of 1mg/mL; dilutions from this stock were used to achieve the desired PpIX concentration in each phantom. In total, 50 phantoms (20 mL each) were constructed to include a range of five PpIX concentrations [(0.1, 0.3, 1, 3, 10) μg/mL], each prepared with five different TVF [(0, 0.1, 0.5, 1, 5)%]. Additionally, a phantom set with 1.5% LVF, 2% BVF, and 1 μg/mL PpIX was sampled with a more granular set of TVF values [(0, 0.1, 0.5, 1, 2, 3, 4, 5)%]. To confirm the stability and reliability of Intralipid as a scatterer and blood as an absorber for fluorescence measurements, two additional sets of phantoms were made varying LVF and BVF at a TVF of 0.1% for a range of PpIX concentrations [(0.1, 0.3, 1, 3 10) μg/mL]. This included variation of BVF [(0.5, 1, 2, 3)%] with a fixed LVF of 1.5%, and also variation of LVF [(1, 1.5, 2)%] with a fixed BVF of 2%. Table 1 provides a detailed overview of the combinations of constituents used within each of the phantom sets.

Detailed list of components used in the phantom sets.