Enhancement of fluorescence contrast using two wavelength excitation and two wavelength detection

A clear contrast in fluorescence signals from malignant and normal tissue is of great importance in the research for early cancer detection methods that make use of tumour-selective photosensitizers. Contrast is blurred by spatial variations in optical properties of the tissue, its intrinsic fluorescence and geometrical parameters of the fluorescence measurement setup. A method using two wavelength excitation and two wavelength detection that corrects the measured fluorescence signal for these artefacts has been developed. Evaluation of this method was done by in vitro and in vivo measurements using a optical fibre setup. The method corrected the measured signals for the influence of variations in absorption, scattering and setup geometry, leaving a result depending only on the photosensitizer concentration. In the imaging system using this method movement artefacts that occur during measurements are corrected for by simultaneous projection of the four resulting fluorescence images on a CCD-chip