Fluorescence images were obtained in reflection geometry. NIR dye fluorescence was excited with an optical parametric oscillator (OPO) (GWU-Lasertechnik, Erftstadt, Germany) based on an optically nonlinear -crystal, pumped by the third harmonic (,) of a Q-switched laser (GCR–10, Spectra-Physics Inc., USA). The OPO provides laser radiation tuneable between 415 nm and 2.2 μm and was set to in our experiments to excite NIR fluorescence of the dye under investigation. Two long-pass interference filters () and a long-pass edge filter (, 3 mm) were used to cut off scattered excitation light from emitted fluorescence light. The cut-off wavelength at results from a sensitivity drop of the detector. The fluorescence was imaged onto the photocathode of a water/Peltier-cooled, intensified CCD camera (Model ICCD-576, Princeton Instruments Inc, Trenton, USA) with the help of a standard object lens of 50 mm focal length (). In order to suppress background signals caused by ambient light, the intensifier of the CCD camera was gated applying an electrical pulse () of about 10 ns duration derived from a HV pulse generator. The HV pulse generator was synchronized with an advanced trigger pulse provided by the power supply of the laser system and appropriately delayed by means of a digital delay generator. The delay of the gating pulse was adjusted to image the fluorescence of the cyanine dye (decay time ) and to suppress long-living autofluorescence components with typical decay times of 3 ns. Fluorescence was recorded using a short exposure time (0.2 s) and 4 times accumulation to avoid motion artifacts. For close monitoring of dye uptake immediately after injection, 180 images were recorded within 660 s (i.e., one image every 3.65 s), followed by time points at 30, 60, and 120 min post injection.