Biomedical Engineering Reference
In-Depth Information
(a)
(b)
0.9
Tumor
Controlateral
0.9
0.85
0.85
Tumor
Control
0.8
0.8
0.75
0.75
0.7
0.7
0.65
0.65
0.6
0.6
0.55
0.55
0.5
0.5
0
2
4
6
0
2
4
6
Hours after injection
Hours after injection
FIgure 9.14
Difference between fluorescence lifetime of tumor and contralateral sites for
(a) targeted fluorescence probe and (b) nontargeted fluorescence probe to Her2 receptors in
tumors with high Her2 expression (BT474) (From ref. [67].)
tumors, the effect of the photon migration on the observed time-resolved fluores-
cence intensities should be taken into account, using other reconstruction algorithms
such as fluorescence diffuse tomography.
Fluorescence lifetime can also be used as an alternative method to diagnose
tumors with specific biomarkers. Figure 9.14 shows the difference between fluores-
cence lifetime of tumor and contralateral site for (i) bound fluorescence probe and
(ii) unbound fluorescence probe to Her2 receptors in tumors with high Her2
expression (BT474).
9.6.2
diffuse Fluorescence optical tomography
Fluorescence diffuse optical tomography (FDoT) uses an approach similar to X-ray
CT to localize and reconstruct 3D images of concentration and lifetime of the fluoro-
phores inside the tissue based on the measurements collected on the tissue boundary.
The principal difference between FDoT and X-ray tomography algorithms is the
character of light propagation through the tissue. While in X-ray tomography photons
propagate through the tissue along the straight line, in the diffuse optical regime, the
photon undergoes multiple scattering events between the source and detector, result-
ing in random changes of the propagation direction. As a result, the latter case should
be modeled by the radiative transfer equation or diffusion approximation [68, 69].
The common optical tomography algorithm is based on perturbation approxima-
tion. To generate a recursive formula for image reconstruction, photon density
(eqs. 9.16-9.23) can be written as a Taylor series of the unknown optical properties
of the media, for example, the fluorescence yield and lifetime:
+
∂
∂
ϕ
α
(9.28)
ϕα ϕα
(
%
) =
(
)
∆
α
+
L
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