In Vivo Molecular Fluorescence Imaging - Nanotechnology for Biomedical Imaging and Diagnostics - page 274

turbid medium, its weight changes due to absorption. The remaining weight scatters
with the photon to other parts of the medium. local rules for photon transport in
scattering media are expressed as probability distributions that describe the step size
of photon movement and the angles of its deflection in each scattering event. each
photon will undergo many steps in the turbid media until it is absorbed by the media
(its weight becomes zero) or exits the boundary.

9.6 IMagIng algorIthMs

Fluorescence imaging is usually performed based on fluorescence projection (planar
imaging) or fluorescence tomography. This section briefly introduces each of these
imaging algorithms. In general, the quality of any image reconstruction depends
upon parameters such as signal-to-noise ratio, background fluorescence signal,
optical properties of the media, and depth of the target from the optical probe.

9.6.1 planar Imaging

Planar imaging or topography is based on projection of the detected fluorescence
signal on the tissue boundary. It does not consider the effect of depth and optical prop-
erties of the tissue in a reconstructed image. This method is good for fluorescence
targets that are located superficially under the skin whose depth and tissue scattering
and absorption properties do not have a significant effect on fluorescence signal.

9.6.1.1 Intensity In this mode, a camera usually captures two images, one with
and one without an emission filter. These two images are superimposed to obtain the
fluorescence image on an anatomical (white-field) image of the tissue (Fig. 9.12).
even though this method can show the location corresponding to the fluorophores'
accumulation, the fluorescence intensity cannot be used alone to quantify the

Tumor

FIgure 9.12 Superimpose of planar white-field and fluorescence images after injection of
Her2-targeted fluorescence probe in a mouse with high Her2-expressed tumor. ( See insert
for color representation of the figure.)