<title>Physical modeling of optical characteristics of blood-containing tissue</title>

Abstract

In the course of search for systems and media that could simulate optical characteristics of bio-objects we developed a method of preparation of tissue phantoms on a gel base. Examination of fluorescence spectra of agar and gelatin gel revealed that agar gel may be used in phantom preparation as a matrix free of reabsorption effect and with low intrinsic fluorescence. But in subsequent experiments we used 10% gelatin gel in order to reproduce native fluorescence of biotissue. Phantom samples were prepared as 2.2 or 3.2 mm thick 25 mm diameter gel 'tablets' with controlled content of blood and scatterer (polystyrene latex). In phantoms without scatterer we studied the dependence of the shape of fluorescence spectrum on blood content (excitation wavelength 350 - 380 nm, observation of emission spectra within 400 - 650 nm range). We obtained an agreement of fluorescence intensity and spectrum shape transformation, as the blood concentration in phantom increases, with the changes of in vivo tissue autofluorescence spectra (literature data) when going from normal tissue to the abnormal region. Using measurements of collimated transmittance we evaluated scattering coefficient for polystyrene latex embedded in 10% gelatin gel. When blood was added, the linear dependence of extinction in phantom on latex concentration was distorted within absorption band.