Polyacrylamide-based fluorescence phantom for calibration measurements of the FAD content in human skin
In order to correctly interpret the experimental data obtained by fluorescence methods, it is necessary to determine the contribution of each component to the total signal. In this regard, new optical phantoms with known parameters of absorption, scattering and fluorescence are a matter of particular interest. The concept of a thin solid form is used to create optical phantoms of the required geometric shape, thickness and heterogeneity similar to multilayer fabrics. These phantoms are developed using a variety of polymer-based materials such as epoxy, polyester or polyurethane to provide stability of optical and mechanical properties during a extended period of time. Gelatin can be used to mimic the fluorescent properties of collagen since this protein is the main structural component of connective tissue.
The aim of this work was to create a solid optical phantom that reproduces FAD fluorescence in human skin for the calibration of a hyperspectral fluorescence imaging system.
The phantom was made of a polyacrylamide matrix with collagen and FAD at various concentrations for modelling the endogenous fluorescence of skin. The compound of the phantom matrix was produced by homogenizing acrylamide (6 g) and gelatin (0.2 g) with the addition of bisacrylamide (0.16 g) as a cross-linking agent to polymerize the structure. To mimic the skin scattering zinc oxide (0.03 g) was added to the polymer structure. Five variants of optical phantoms with different FAD concentrations were prepared: 0, 5, 10, 15, and 20 μM.
The optical characteristics of the phantom were studied using an experimental setup. It included a SPECIM hyperspectral camera (Spectral Imaging Ltd, Finland) for recording fluorescence spectra, a 450 nm laser M450LP1 (Thorlabs, USA) for fluorescence excitation and 500 nm filters (Thorlabs, USA) to separate fluorescence from the source radiation. The parameters of the phantom’s fluorescence were analyzed at different concentrations of fluorophores and their combinations.
The analysis of the fluorescence spectra of optical phantoms with different FAD concentrations shows that all spectra had their maxima corresponding to the FAD fluorescence peak (about 530 nm) upon excitation with 450 nm laser. The changes in the signal intensity corresponded to the FAD concentration changes in the phantom produced.
The use of the developed optical phantom will allow one to test and calibrate imaging systems and improve the overall quality of the diagnostic technology.
The work has been funded by the RFBR according to the research project 18-02-00669.
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Research and Development Center of Biomedical Photonics, Orel State University named after I.S. Turgenev, Orel, Russia
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