Imaging of xenofluorescent objects in strongly scattering media: first results

This paper presents an ongoing investigation of laser induced xenofluorescence using a fluorescent marker to detect objects in turbid media. The aim is the development and validation of a method for imaging vessels using near infrared fluorescence angiography techniques in strongly scattering media. The main purpose is to show the course of blood and lymph vessels in the head and neck region of tumor patients. The first step was the selection of the best method and a suitable fluorescence dye to image these vessels. Using a phantom with the optical parameters similar to skin and fat tissue different methods of fluorescence excitation and detection were investigated. The following experiments were performed: whole area two-dimensional excitation and detection (CCD camera) as well as a focused excitation with scanned detection (photo diode). Furthermore investigations of the improvement of the vessel detection using a phase demodulation technique were performed. The measurements were simultaneously accompanied by analytic calculations using diffusion approximation. The photophysical investigations of several dyes have led to the use of tsAlClPc as fluorescence dye for the technical comparison of the investigated methods. Since this phthalocyanine is phototoxic a clinical certified dye (probably Indocyanine green) will be used for future experiments. The methods with focused excitation and scanned detection have shown the best resolution, but they are slow and expensive in comparison to the CCD camera technique. Further experiments should give more information about the application dependent decision which method is best suited.