Evaluation of a fiber-optic-based system for optical property measurement in highly attenuating turbid media

Abstract

Fluorescence- and reflectance-based imaging techniques have a strong potential to improve clinical detection of pathologies such as cervical neoplasia. However, quantitative understanding of data collected by these approaches necessitates information on tissue optical properties <i>in vivo</i>. At present, there is minimal <i>in vivo</i> data on the optical properties of many tissues in the wavelength range that is most relevant -- the ultraviolet A to visible. We report here on the development and evaluation of a second-generation diffuse reflectance system for measurement of tissue optical properties using a linear-array fiber optic probe with maximum separation distance of 2.5 mm. Improvements over the prior system include the implementation of an imaging spectrograph, a high sensitivity CCD camera and in-line neutral density filters to maximize dynamic range and signal to noise ratio. Absolute measurements of tissue reflectance were enabled through calibration of the reflectance system. Multivariate calibration models for optical property prediction were generated using a neural network algorithm and reflectance distributions calculated by a Monte Carlo model. Spatially-resolved reflectance data sets were measured in well--characterized tissue phantoms at 405 nm for absorption coefficients (&#956;_a) from 1 to 25 cm^-1 and reduced scattering coefficients (&#956;_s') from 5 to 25 cm^-1. These models were used to estimate the optical properties of tissue phantoms from reflectance measurements. By comparing predicted and known optical properties, the average percent error for &#956;_a and &#956;_s' was found to be ± 3.2% and ±5.6%, respectively. These results indicate a level of accuracy that is more than twice that of our prior approach.