A new fluorescence microscopy for tomographic observation of microcirculation by using dual-beam slit laser illumination

By designing a new epi-illumination system with dual slit laser beams, we have developed a fluorescence microscope for tomographic observations of in vivo microcirculation. Two beams of an Argon ion laser were converted into thin slit beams of thickness 28 to 60 μm by optical lenses and were illuminated onto tissue to intersect at the focal plane of the objective. The fluorescent light emitted from a FITC tracer by this cross-illumination was picked up by the microscope through a filter, with no “out of focus” noise from the tracer above and below the crossing zone. The results of in vitro experiments by using glass micropipettes (20-80 μm i.d.) filled with FITC-dextran and skeletal muscle tissue certified uniform tracer excitation in the crossing zone and the augmentation of the beam thickness due to light scattering in the tissue to be 1.7 and 2.5 times at depths of 100 and 200 μm from the surface, respectively. In vivo tests in the rabbit tenuissimus muscle revealed that this system can realize microvasculature tomography, with adequate vertical zone selectivity and spatial resolution to reconstruct its three-dimensional mapping, and long-term monitoring of tracer leakage from a single capillary to the surrounding tissue, with sufficient quantitative reliability to determine the capillary permeability and its heterogeneity along the channel.