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

Area of Science:

• Biomedical Optics
• Medical Imaging
• Optical Engineering

Background:

• Spatial Frequency Domain Imaging (SFDI) is a diffuse optical technique for pixel-by-pixel quantification of tissue optical absorption (μa) and reduced scattering (μs').
• SFDI enables label-free assessment of tissue viability, oxygenation, and molecular content by extracting chromophore concentrations.
• Existing SFDI systems can be costly and large, limiting accessibility for some research groups.

Purpose of the Study:

• To present openSFDI, an open-source guide for constructing a low-cost, small-footprint, three-wavelength SFDI system.
• To detail the system's capability in quantifying μa, μs', and hemoglobin concentrations in biological tissues.
• To validate the accuracy and precision of optical property extractions from the openSFDI system.

Main Methods:

• Designed and built three openSFDI systems based on the open-source guide.
• Assessed accuracy by comparing openSFDI measurements of tissue-simulating phantoms against a commercial SFDI device.
• Evaluated precision through repeated measurements of the same phantom over one hour.

Main Results:

• The openSFDI systems demonstrated high accuracy, with errors of 0 ± 6% in μa and -2 ± 3% in μs' compared to a commercial system.
• Bland-Altman analysis showed good agreement, with limits of agreement of ±0.004 mm⁻¹ for μa and -0.06 to 0.1 mm⁻¹ for μs'.
• The system exhibited low drift, with average standard deviations of 0.0007 mm⁻¹ for μa and 0.05 mm⁻¹ for μs'.

Conclusions:

• The openSFDI system provides a reliable and accurate method for quantitative diffuse optical imaging.
• This open-source platform is customizable and accessible for research groups aiming to employ SFDI.
• The system effectively quantifies key optical properties and chromophore concentrations in biological tissues.