Development, production quality control and calibration of optical tissue-mimicking phantoms require a convenient and robust characterization method with known absolute accuracy. We present a solid phantom characterization technique based on time resolved transmittance measurement of light through a relatively small phantom sample. The small size of the sample enables characterization of every material batch produced in a routine phantoms production. Time resolved transmittance data are pre-processed to correct for dark noise, sample thickness and instrument response function. Pre-processed data are then compared to a forward model based on the radiative transfer equation solved through Monte Carlo simulations accurately taking into account the finite geometry of the sample. The computational burden of the Monte-Carlo technique was alleviated by building a lookup table of pre-computed results and using interpolation to obtain modeled transmittance traces at intermediate values of the optical properties. Near perfect fit residuals are obtained with a fit window using all data above 1% of the maximum value of the time resolved transmittance trace. Absolute accuracy of the method is estimated through a thorough error analysis which takes into account the following contributions: measurement noise, system repeatability, instrument response function stability, sample thickness variation refractive index inaccuracy, time correlated single photon counting system time based inaccuracy and forward model inaccuracy. Two sigma absolute error estimates of 0.01 cm(-1) (11.3%) and 0.67 cm(-1) (6.8%) are obtained for the absorption coefficient and reduced scattering coefficient respectively.
Solid tissue phantom are the preferred tool for the development, validation, testing and calibration of photon migration instrument. Accuracy, or trueness, of the optical properties of reference phantoms is of the utmost importance as they will be used as the conventional true value against which instrument errors will be evaluated. A detailed quantitative analysis of the uncertainty of time-resolved transmittance characterization of solid optical tissue phantom is presented. Random error sources taken into account are Poisson noise of the photon counting process, additive dark count noise and instrument response function stability. Systematic error sources taken into account are: phantom thickness uncertainty, refractive index uncertainty, time correlated single photon counting system time base calibration uncertainty. Correction procedures for these systematic errors are presented whenever a correction is possible.
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