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Abstract

The present invention provides a method for measurement of concentration of fluorophores in turbid media. The method uses a fluorescence plus reflectance technique to measure quantitatively the in vivo concentration of a fluorescent drug independent of the tissue optical properties. The method involves using the reflectance measurement as a means of correcting for tissue scattering and absorption in the fluorescence measurement. Light directed to the tissue by means of an optical fiber to excite the fluorophores. Fluorescence from the fluorophores is measured by another fiber at a distance (D1) from the source in the turbid medium, while the excitation light is simultaneously collected at a distance (D2) from the source. The ratio fluorescence/reflectance will be approximately constant for a fixed concentration of the fluorophore and a judicious choice of D1 and D2, regardless of the optical properties of the tissue. The ratio of fluorescence to reflectance on a tissue sample is compared to a calibration curve for a range of fluorophore concentrations, in order to estimate the in vivo concentration in the turbid medium. The optimum distances D1 and D2 are obtained by constructing several sample turbid mediums with known optical properties mimicking the optical properties of the samples on which the measurements are to be made. Fluorescence and reflectance measurements are performed at several distances from the excitation point for all turbid samples and a best fit obtained for each pair of distances with pairs exhibiting the lowest values of sum of squares of residuals lower than a threshold being used.

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