Reproducibility of identical solid phantoms.

Fangzhou Zhao,Pranav Lanka,Hong Qi,Rinaldo Cubeddu,Michele Lacerenza,Alessandro Torricelli,Lorenzo Spinelli,Lorenzo Frabasile,Pietro Levoni,Antonio Pifferi

doi:10.1117/1.jbo.27.7.074713

Abstract

.SignificanceTissue-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.AimThe reproducibility in fabrication of homogeneous solid phantoms is focused based on spectra measurements by instrument comparisons grounded on the time-resolved diffuse optics.ApproachEpoxy-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.ResultsWe 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%.ConclusionsResults 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.

Highlights

The possibility to probe human tissue in depth and non-invasively by visible and near-infrared light[1,2] pushed scientists and technologists to develop physics, methodologies, and instrumentation to study photon propagation in highly scattering media
From the first pioneering basic studies on photon migration[3–6] to the more recent near-infrared diffuse spectroscopy (NIRS) instrumentation involved in clinical trials,[7–12] it was clear that the availability of phantoms mimicking the optical properties and the structures of biological tissues was required for reliability of the results attained
Whatever approach is exploited for NIRS—continuous wave, time domain, or frequency domain; the geometry adopted—transmittance or reflectance; the reconstruction modality utilized—tomography or topography; the instrument configuration employed—a multichannel imaging system or a single-channel monitor; the clinical application aimed for—brain, breast, or muscle, diffuse samples with reliable and invariable properties are fundamental and important tools for (1) the development of novel approaches in basic research; (2) the instrumentation assessment in laboratory environment[13,14]; (3) interlaboratory comparison studies[15–17]; and (4) quality check in clinics.[18]

Summary

Introduction

The possibility to probe human tissue in depth and non-invasively by visible and near-infrared light[1,2] pushed scientists and technologists to develop physics, methodologies, and instrumentation to study photon propagation in highly scattering media. Whatever approach is exploited for NIRS—continuous wave, time domain, or frequency domain; the geometry adopted—transmittance or reflectance; the reconstruction modality utilized—tomography or topography; the instrument configuration employed—a multichannel imaging system or a single-channel monitor; the clinical application aimed for—brain, breast, or muscle, diffuse samples with reliable and invariable properties are fundamental and important tools for (1) the development of novel approaches in basic research; (2) the instrumentation assessment in laboratory environment[13,14]; (3) interlaboratory comparison studies[15–17]; and (4) quality check in clinics.[18] In this framework, the possibility to have phantoms with optical properties known with few percent of uncertainty is highly advisable. Though it has been fundamentally solved for liquid phantoms,[19] it remains an open issue for solid phantoms, where an accurate estimation of the optical properties is not straightforward to obtain, neither a priori—starting from properties of raw materials—nor a posteriori—from a direct measurement on diffusive phantoms

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