Spatial frequency domain imaging (SFDI) exploits properties of light diffused through a scattering medium to estimate the optical properties of the tissue under consideration. This non-invasive imaging modality provides full-field, quantitative and potentially real-time measurement of absorption and reduced scattering coefficient of tissues at low cost. Given the optical properties of the tissue at various wavelengths the concentration of the tissue constituents can be quantitatively estimated which can aide in medical diagnosis and health monitoring.
In SFDI method, sinusoidally pattered light is projected onto the tissue/phantom and the diffuse reflectances are recorded at multiple spatial frequencies. This allows estimation of the modulation transfer function of the diffuse light propagation through the tissues. A least-square fit of the modulation transfer function with an analytical transport model or a Monte-carlo (MC) based forward model is used to estimate the optical properties of the tissues.
For faster acquisition and processing, the state of the art uses a frequency-pair method where the diffuse reflectance at only two spatial frequencies [0 /mm, f /mm] are recorded and a pre-computed look-up table (computed from MC based forward model) is used for the inverse mapping to optical properties. However, the accuracy of estimation may vary with the choice of the frequency pair. In this study, the bias and variance in estimation of optical properties obtained from the frequency-pair method will be compared to values obtained from multi-frequency fits. This study aims at identifying the optimal spatial frequency that may be used to increase the accuracy of estimation of optical parameters.
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