Monte Carlo-based inverse model for calculating tissue optical properties Part I: Theory and validation on synthetic phantoms

Abstract

A flexible and fast Monte Carlo-based model of diffuse reflectance has been developed for the extraction of the absorption and scattering properties of turbid media, such as human tissues. This method is valid for a wide range of optical properties and is easily adaptable to existing probe geometries, provided a single phantom calibration measurement is made. A condensed Monte Carlo method was used to speed up the forward simulations. This model was validated by use of two sets of liquid-tissue phantoms containing Nigrosin or hemoglobin as absorbers and polystyrene spheres as scatterers. The phantoms had a wide range of absorption (0-20 cm(-1)) and reduced scattering coefficients (7-33 cm(-1)). Mie theory and a spectrophotometer were used to determine the absorption and reduced scattering coefficients of the phantoms. The diffuse reflectance spectra of the phantoms were measured over a wavelength range of 350-850 nm. It was found that optical properties could be extracted from the experimentally measured diffuse reflectance spectra with an average error of 3% or less for phantoms containing hemoglobin and 12% or less for phantoms containing Nigrosin.

Diagnosis of breast cancer using fluorescence and diffuse reflectance spectroscopy: a Monte-Carlo-model-based approach

“…Details about the Monte-Carlo-based inverse model of diffuse reflectance can be found in previous publications. 17,18,27 The accuracy of the inverse model was verified using experimental tissue phantom studies. The results indicated that for phantoms with a wide range of absorption coefficients (0 to 20 cm −1 ) and reduced scattering coefficients (7 to 33 cm −1 ), optical properties could be extracted within an average error of 3% for phantoms containing hemoglobin and within 12% for phantoms containing nigrosin.…”

“…The results indicated that for phantoms with a wide range of absorption coefficients (0 to 20 cm −1 ) and reduced scattering coefficients (7 to 33 cm −1 ), optical properties could be extracted within an average error of 3% for phantoms containing hemoglobin and within 12% for phantoms containing nigrosin. 27 The diffuse reflectance spectra were fit to the Monte Carlo model in the wavelength range of 350 to 600 nm. The primary intrinsic absorbers in the model over this wavelength range were assumed to be oxygenated and deoxygenated hemoglobin and beta-carotene.…”

“…The Monte Carlo inverse model of diffuse reflectance takes into account the specific probe geometry and incorporates a phantom calibration to account for the difference in system throughput thus allowing for a direct comparison of the absorption and scattering properties extracted from the two data sets. 27 …”

Harnessing the Power of Light to See and Treat Breast Cancer

“…Briefly, spectra were corrected for daily variations in optical throughput using a Spectralon reflectance standard, and were normalized by the CCD integration time. An inverse Monte Carlo model [11,15,16] was used to obtain values for THb concentration, β-carotene concentration and the wavelength-averaged reduced scattering coefficient from 450-600 nm (<µ s '>), for each measured site (or pixel) on the specimen surface. Upon completion of the measurements, the measured sites were inked for histological correlation.…”

“…Since each of the absorption spectra are known, the only assumption necessary to make about the tissue is the form of wavelength-dependent scattering. To date, we have assumed that scatterers in tissue can be modeled as spherical particles of a single size using Mie theory [11,15,16]. Clearly, however, cellular scatterers are neither spherical, nor of a single size.…”