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Investigations on fluorescence guided stereotactic biopsy

PpIX-concentrations in glioblastoma tissue showed a high variability. A PpIX-concentration exceeding 2.4 μmol/l is detectable by state-of-the-art fiberoptic fluorescence spectroscopy and imaging. Such an imaging fluoroscope with 30,000 pixels resolution could be introduced through a position controlled stereotactic needle. Furthermore ICG-fluorescence from vessels with diameters ≥ 0.1 mm can be detected. If one demands that destruction of normal brain tissue must be excluded by limiting the tissue heating to 42 °C, then the radiant flux at the distal fiber end must be limited to 5.3 mW (33 mW) for excitation at 405 nm (785 nm). For 785 nm excitation, incorporating extra blood vessels of 0.1 mm diameter into homogeneously perfused brain tissue reduces the tolerable radiant flux to 22 mW. According to legal laser safety regulations for human skin tissue, threshold values of 19.2 mW (28.5 mW) would be obtained.