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

Significance : Spatial frequency domain imaging (SFDI) is a diffuse optical measurement technique that can quantify tissue optical absorption (μa) and reduced scattering ( μ s ′ ) on a pixel-by-pixel basis. Measurements of μa 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 μa and μ s ′ 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. 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. Approach : Accuracy was assessed by measuring nine tissue-simulating optical phantoms with a physiologically relevant range of μa and μ s ′ with the openSFDI systems and a commercial SFDI device. Precision was assessed by repeatedly measuring the same phantom over 1 h. Results : The openSFDI systems had an error of 0  ±  6  %   in μa and −2  ±  3  %   in μ s ′ , 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 μa and −0.06 to 0.1  mm  −  1 for μ s ′ . The openSFDI system had low drift with an average standard deviation of 0.0007  mm  −  1 and 0.05  mm  −  1 in μa and μ s ′ , respectively. Conclusion : The openSFDI provides a customizable hardware platform for research groups seeking to utilize SFDI for quantitative diffuse optical imaging.