Biological samples, imaging

Noise can be also introduced by biochemical heterogeneity of the specimen. This can be a major cause of uncertainty in biological imaging. The high (three-dimensional) spatial resolution of fluorescence microscopy results in low numbers of fluorophores in the detection volume. In a typical biological sample, the number of fluorophores in the detection volume can be as low as 2-3 fluorophores for a confocal microscope equipped with a high NA objective at a fluorescent dye concentration of 100 nM. This introduces another source of noise for imaging applications, chemical or molecular noise, related to the inherent randomness of diffusion and the interaction of molecules. 

R. M. Caprioli, T.B. Farmer and J. Gile, Molecular imaging of biological samples localization of peptides and proteins using MALDI TOF MS, Anal. Chem., 69, 4751 4760 (1997). 

Marshall AT, Xu W. Quantitative elemental x-ray imaging of frozen-hydrated biological samples. J Microsc 1998 190 305-316. 

---