Biomedical Engineering Reference
In-Depth Information
FIGURE 12.1: Absorption spectra of tissue and spectral emission range of
common fluorescent probes and proteins. (From [58].)
of light that can be used to form images. Optical imaging technologies are
well suited for experimentation, as most of the components required can be
assembled on the laboratory bench and are modular in design. In addition,
high quality images can be obtained at moderate cost, and the systems can
be made portable or compact.
Insights on the functional and molecular levels can be obtained by vi-
sualization of endogenous tissue contrast, such as absorption and scattering
properties. The observation of molecular events and processes can be facili-
tated by exogenous contrast using fluorescence or bioluminescence approaches.
The recent increase in availability of fluorescent proteins, dyes and probes
[27, 53, 10, 59, 33] has sparked interest in the combination of optical imaging
with fluorescence. Fluorescence imaging can be divided into two main strate-
gies, (a) direct imaging, in which an engineered fluorescent probe that localizes
a specific target is introduced in the imaging subject, and (b) indirect imaging,
where transgenic methods are used for intrinsic expression of fluorescence [31].
Tissue of several centimeters thickness can be imaged when near-infrared
light is used, due to the low attenuation of light by tissue in this range; see
Figure 12.1. Several different techniques have been developed for the macro-
scopic imaging of fluorescence in vivo. In epi-illumination (reflectance) imag-
ing, the tissue surface is illuminated with an expanded light beam and im-
ages are collected from the same side of the tissue; see Figure 12.2. When
the light propagates through the tissue, it excites superficial and subsurface
 
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