OpenSFDI: an open-source guide for constructing a spatial frequency domain imaging system

Abstract

Significance: Spatial frequency domain imaging (SFDI) is a diffuse optical measurement technique that can quantify tissue optical absorption (μ_a) and reduced scattering (<inline-formula>${\mu }_s^{\text{'}}$</inline-formula>) on a pixel-by-pixel basis. Measurements of μ_a at different wavelengths enable the extraction of molar concentrations of tissue chromophores over a wide field, providing a noncontact and label-free means to assess tissue viability, oxygenation, microarchitecture, and molecular content. We present here openSFDI: an open-source guide for building a low-cost, small-footprint, three-wavelength SFDI system capable of quantifying μ_a and <inline-formula>${\mu }_s^{\text{'}}$</inline-formula> as well as oxyhemoglobin and deoxyhemoglobin concentrations in biological tissue. The companion website provides a complete parts list along with detailed instructions for assembling the openSFDI system.<p> Aim: We describe the design of openSFDI and report on the accuracy and precision of optical property extractions for three different systems fabricated according to the instructions on the openSFDI website.</p> <p> Approach: Accuracy was assessed by measuring nine tissue-simulating optical phantoms with a physiologically relevant range of μ_a and <inline-formula>${\mu }_s^{\text{'}}$</inline-formula> with the openSFDI systems and a commercial SFDI device. Precision was assessed by repeatedly measuring the same phantom over 1 h.</p> <p> Results: The openSFDI systems had an error of 0 ± 6 % in μ_a and -2 ± 3 % in <inline-formula>${\mu }_s^{\text{'}}$</inline-formula>, compared to a commercial SFDI system. Bland-Altman analysis revealed the limits of agreement between the two systems to be ± 0.004 mm ^{- 1} for μ_a and -0.06 to 0.1 mm ^{- 1} for <inline-formula>${\mu }_s^{\text{'}}$</inline-formula>. The openSFDI system had low drift with an average standard deviation of 0.0007 mm ^{- 1} and 0.05 mm ^{- 1} in μ_a and <inline-formula>${\mu }_s^{\text{'}}$</inline-formula>, respectively.</p>,<p> Conclusion: The openSFDI provides a customizable hardware platform for research groups seeking to utilize SFDI for quantitative diffuse optical imaging.</p>

Keywords: diffuse optics; frequency domain; modulated imaging; open source; optical properties; spatial frequency domain imaging.