Reproducibility of identical solid phantoms.

Tissue-like solid phantoms with identical optical properties, known within tolerant uncertainty, are of crucial importance in diffuse optics for instrumentation assessment, interlaboratory comparison studies, industrial standards, and multicentric clinical trials. The reproducibility in fabrication of homogeneous solid phantoms is focused based on spectra measurements by instrument comparisons grounded on the time-resolved diffuse optics. Epoxy-resin and silicone phantoms are considered as matrices and both employ three different instruments for time-resolved diffuse spectroscopy within the spectral range of 540 to 1100 nm. In particular, we fabricated two batches of five phantoms each in epoxy resin and silicone. Then, we evaluated the intra- and interbatch variability with respect to the instrument precision, by considering the coefficient of variation (CV) of absorption and reduced scattering coefficients. We observed a similar precision for the three instruments, within 2% for repeated measurements on the same phantom. For epoxy-resin phantoms, the intra- and the interbatch variability reached the instrument precision limit, demonstrating a very good phantom reproducibility. For the silicone phantoms, we observed larger values for intra- and interbatch variability. In particular, at worst, for reduced scattering coefficient interbatch CV was about 5%. Results suggest that the fabrication of solid phantoms, especially considering epoxy-resin matrix, is highly reproducible, even if they come from different batch fabrications and are measured using different instruments.