AN INNOVATIVE PHOTOGRAPHER
      Charlie showed great interest and staying power for developing new photographic techniques. In the 1950s, he helped Dr. Cone with the use of the Knebel 35-mm strobe-light camera, which gave the surgeons convenient play by play records of their operations.

     But his best known innovation was the invention in the mid-1960s of the highly specialised photographic technique for recording in the Cone laboratory and in the operating room the blood flow in the surface vessels of the brain. This procedure, which we called fluorescein angiography of the brain (FAB), could only have been created with Charlie's energy and persistence in grappling with formidable technical problems.

     Although the fluorescence of the dye flushing through the brain looked brilliant, the amount of light to expose the film was actually quite low. With ingenious originality, he processed Kodak 35mm colour film with ASA of 160, the fastest at that time, to obtain the equivalent of 1500 and eventually up to 4000. He also cleverly worked out in immense detail the use of complex colour filters.

Fluorescein angiography of the dog brain. After cold application at minus 65 degrees C for one minute, the brain
 would appear under normal light to be only moderately suffused. But on FAB a striking change shows leakage of
 dye from the damaged microvessels. These studies illuminated the mechanism of cold-induced cerebral edema.