Spatial Frequency Domain Imaging (SFDI) is a non-contact wide-field spectroscopy technique that employs sinusoidal patterns of spatially modulated light as the excitation source. By obtaining the effective modulation transfer function of the diffusively reflected light from a turbid medium, it considers the contribution of reduced scattering and absorption coefficient to this function allowing for decoupling of the optical properties. The extracted optical properties at several wavelengths can provide quantitative information on concentration of tissue chromophores such as hemoglobin, fat, and water. It also delivers information on the arrangement of tissue structural components, mainly cells and extracellular matrix proteins. The technique has been utilized to investigate many phenomena in brain, kidney, and skin tissues.
Enhancing spatial, temporal, and spectral information content in SFDI can give insight to tissue constituents, their dynamics, and distribution. In this work, we developed and validated three variations of SFDI instruments with design considerations to match specific applications:
1. High Speed SFDI instrument that detects rat cortex dynamic optical and physiological properties at 17 frames per second following cardiac arrest and resuscitation.
2. Hyperspectral SFDI instrument which measures tissue optical properties at 1000 spectral bins over a broad range, 580-950 nm, and can spatially resolve concentrations of oxy- deoxy- and met- hemoglobin as well as water and fat fractions. It utilizes principles of spatial scanning of the spectrally dispersed output of a supercontinuum laser.
3. Single pixel SFDI instrument which takes advantage of high bandwidth available for spectral encoding using a single-element detector and sparse sampling based on compressed sensing to characterize tissue optical properties over a wide field of view, 35 mm × 35 mm.