Biomedical Engineering Reference
In-Depth Information
Fig. 4.1 Dispersion effect as
it was described by Newton in
his book Opticks in 1704
(Image is courtesy of Octavo
Corp and the Warnock
Library)
distribution, has a standard d ev iation of p n. The signal-to-noise ratio (SNR) is
therefore proportional to n= p n and can be improved only by increasing the signal
in some way. At best, an imaging system is “shot-noise limited,” which means that
the quality of the detector is high enough so that the sensitivity of the system is
limited by the shot noise.
In addition, there are other disturbances that originate from the nature of the
sample and its environment, such as scattering, auto-fluorescence, and bleaching
that increase the background level and decrease the real signal. The quality of the
signal is therefore reduced, and these disturbances have to be taken into account in
setting up the system for each specific application. Post-processing can also be used
by applying various filtering methods.
4.2.2
Spectroscopy
We are all familiar with the diverse colors of a rainbow which is probably one of
the most ancient examples of a spectrum. In optics, a spectrum is a collection of
light intensities at different wavelengths. Spectroscopy is the science of acquiring,
analyzing, and explaining the spectral characteristics of matter. It is a broad and
well-established science. The dispersion of white light to its colors was initially
described by Newton in his topic Opticks published in 1704 [ 2 , 3 ], and it has been
used with increased interest ever since, see Fig. 4.1 . Spectroscopy is an important
research tool that is used in every possible science. It is interesting to note that even
quantum mechanics developed by Schrodinger in 1926 was initially based on the
experimental discovery of the hydrogen emission spectral lines as discovered by
Balmer in 1885 and formulated to a general equation by Rydberg.
What makes the spectrum so important in different sciences is the fact that
the spectrum, which is a collection of different wavelengths of electromagnetic
 
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