Tissue of a patient is tested for dangerous characteristics by using a laser that stimulates fluorescence in the tissue. The laser energy is applied to the tissue by from an opening in a catheter, which catheter supplies clear flushing solution out the same opening. The clear solution therefore provides a clear path for the laser energy and for the fluorescent light from the tissue. An optical fiber carries the laser energy to a distal end of the catheter and carries back fluorescent light to a proximal end of the catheter. The fluorescent light is checked for fluorescent peaks by a detection subsystem by the proximal end. The detection subsystem may include an optical channel analyzer (OMA). The distal end of the catheter has a dual hood design to best provide for the passage of light and clear flushing solution through the same opening. A balloon is used in some embodiments to maintain the clear path for the light for a longer time period than otherwise possible or appropriate.