An optical phantom with tissue-like properties in the visible for use in PDT and fluorescence spectroscopy

The design and characterization of optical phantoms which have the same absorption and scattering characteristics as biological tissues in a broad spectral window (between 400 and 650 nm) are presented. These low-cost phantoms use agarose dissolved in water as the transparent matrix. The latter is loaded with various amounts of silicon dioxide, Intralipid, ink, blood, azide, penicillin, bovine serum, and fluorochromes. The silicon dioxide and Intralipid particles are responsible for the light scattering whereas the ink and blood are the absorbers. The penicillin and the azide are used to ensure the conservation of such phantoms when stored at 4 degrees C. The serum and fluorochromes, such as Coumarin 30, produce an autofluorescence similar to human tissues. Various fluorochromes or photosensitizers can be added to these phantoms to simulate a cancer photodetection procedure. The absorption and fluorescence spectroscopy of the porphyrin-type fluorescent markers used clinically for such photodetection procedures is similar in these phantoms and in live tissues. The mechanical properties of these gelatinous phantoms are also of interest as they can easily be moulded and reshaped with a conventional cutter, so that complex structures and shapes, with different optical properties, can be designed. The optical properties of these phantoms were determined between 400 and 650 nm by measuring their effective attenuation coefficient (mu eff) and total reflectance (Rd). The microscopic absorption and reduced scattering coefficients (mu a, mu s') were deduced from mu eff and Rd using a Monte Carlo simulation.