Fig. 1.

Conceptual plots to illustrate the advantage of pulsed imaging and gated acquisition for low level fluorescence detection in the presence of high background lighting. A, Detected signal versus acquisition time for a standard CCD where excitation light remains constant (dashed blue), for an ICCD where excitation light increases proportionally as acquisition time decreases (red), and for ambient room light only with no excitation (pink). B, Background subtracted signal versus acquisition time for CCD (dashed blue) and ICCD (red) in the context of nonspecific background signal and noise for both fixed radiant exposure, H (red shading outlined in solid red) and fixed irra-diance, E (blue shading outlined in dashed blue). Note that signal differences have been exaggerated to enable easy visualization.