Table 1.

Signal, Background and Noise Sources in a Fluorescence Image.

Signal Sources	Background Sources	Noise Sources
Number tumor cells	Dark current	Electronic (shot noise)
Molecular labeling specificity	Nonspecific binding	Cell-to-cell variability
Molecular label concentration	Healthy cell antigen expression	Diffusion
Illumination intensity	Optical bleed through	Tissue heterogeneity
Fluorophore quantum efficiency	Autofluorescence	Tissue surface heterogeneity
Electronic responsivity		Illumination heterogeneity
Pixel size