Localization and characterization of tissue changes by laser backscattering imaging and Monte Carlo simulation.

Laser backscattering from biological tissues depends on their composition and blood flow. The onset of the tissue abnormalities is associated with the change in composition at a specific location which may affect laser backscattering. The objective of the present work is to detect the compositional changes in tissue-equivalent phantom of fat, prepared by mixing paraffin wax with wax colors, and to characterize these in terms of their optical parameters. For this purpose these phantoms are scanned by a multi-probe non-contact automatic laser scanning system and images of the normalized backscattered intensity (NBI) are constructed. By scanning the background subtracted image of the phantom the location of the abnormality and its size from the full width at half maximum (FWHM) are determined. The data obtained by ultrasonic technique for localization of the abnormalities are in agreement with that as obtained by the present method. The optical parameters of the abnormality are obtained by matching the measured surface profiles of the abnormality with that of the profile obtained by Monte Carlo simulation. This analysis shows the possibility of detection of changes at the onset stage in tissues as required for planning of the photodynamic therapy.