Optimization of Spatial Frequency Domain Imaging Technique for Estimating Optical Properties of Food and Biological Materials

摘要

Spatial frequency domain imaging technique has recently been developed for determination of the optical properties of food and biological materials. However, accurate estimation of the optical property parameters by the technique is challenging due tomeasurement errors associated with signal acquisitions and the complex inverse parameter estimation algorithm for the diffusion model. This research was therefore aimed at optimizing the inverse algorithm for estimating the optical absorption (/Mi) andreduced scattering (mua) coefficients from spatial frequency domain diffuse reflectance generated by Monte Carlo simulation. Sensitivity analysis was first conducted, and it showed that fls'could be estimated more accurately than mua. Six data smoothingmethods were then compared, with the results indicating that the 'moving' method with a span of 5 data points was the most effective in improving the parameter estimation. Further studies were conducted to determine the optimal frequency resolution and start and end frequencies in terms of the reciprocal of mean free path (1/mfp'). The results showed that the optimal frequency resolution increased with mus' and remained stable when /iswas larger than 2 mm~(-1). The optimal end frequency decreased from 0.3/mfp' to 0.16/mfp' with mus' ranging from 0.4 mm~(-1) to 3 mm~(-1), while the optimal start frequency remained at 0 mm~(-1). A two-step method was proposed based on the optimizedfrequency parameters, which improved estimation accuracies by 37.5% and 9.8% for /h and /is', respectively, compared with the conventional method. Experimental validation with seven liquid optical phantoms showed that the optimized technique resulted in the mean absolute errors of 15.4%, 7.6%, 5.0% for /la and 16.4%, 18.0%, 18.3% for /is at the wavelengths of675 nm, 700 nm, and 715 nm, respectively. Hence, implementation of the optimized technique can result in better measurement of optical properties offood and agricultural products.