(with the attenuation coefficient for the excitation energy), the intersection length
with all intersecting pixel/voxel needs to be calculated. The reconstructed images
with included attenuation correction show even tracer distributions of uniformly
distributed contrast agents, while uncorrected images would depict a decreased
contrast agent concentration in the image center.
5 Contrast Agents
In XFCT imaging, three different classes of contrast agents provide a broad palette of
opportunities for medical applications. While exogenous contrast agents are modified functional molecules with a bound signal carrier, metal-based therapeutic agents
and endogenous contrast agents contain the XF signal carrier already in their native
form. The latter two agents are ideal contrast agents as their unbiased
bio-functionality can be imaged. For XLCT imaging, only exogenous contrast
agents are available.
5.1 Exogenous Contrast Agents
Molecular probes for XFCT can be synthesized by labeling a chemical compound of
interest with a high-Z element or nanoparticle (NP). The addition of a single atom to
a molecule preserves the affinity of that molecule for biological processes; hence, its
modified behavior is very similar to the original molecule of interest. This feature
enables quantitative and unbiased measurements of biological processes. XFCT will
also be able to image NPs made from high-Z elements, such as gold [23], silver [24],
gadolinium oxide [25], zinc oxide [26], and so forth. Intensive research is ongoing in
the biomedical community to use these NPs as molecular imaging probes, as
vehicles for therapeutic drug delivery to target sites, or as sensitizers to enhance
the delivery of photothermal ablation therapy or radiation therapy [27–34]. Hence,
the ability to image the distribution of such NPs fulfills a critical need and can aid
substantially in the design and evaluation of novel imaging and therapeutic
strategies.
For the imaging with X-ray excitation energies (<30 keV), the use of silver and
gold nanoparticle agents are recommendable because they are relatively inert biological elements. Furthermore, the surface chemistry of these nanoparticles can be
modified to make them less reactive. The use of the K-shell X-rays from silver
nanoparticles (22.2 keV) and L-shell X-rays from gold nanoparticles (9.7 and
11.4 keV) provides an energy range suitable for X-ray focusing optics (see chapter
“Imaging and Instrumental Specifications”).
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with all intersecting pixel/voxel needs to be calculated. The reconstructed images
with included attenuation correction show even tracer distributions of uniformly
distributed contrast agents, while uncorrected images would depict a decreased
contrast agent concentration in the image center.
5 Contrast Agents
In XFCT imaging, three different classes of contrast agents provide a broad palette of
opportunities for medical applications. While exogenous contrast agents are modified functional molecules with a bound signal carrier, metal-based therapeutic agents
and endogenous contrast agents contain the XF signal carrier already in their native
form. The latter two agents are ideal contrast agents as their unbiased
bio-functionality can be imaged. For XLCT imaging, only exogenous contrast
agents are available.
5.1 Exogenous Contrast Agents
Molecular probes for XFCT can be synthesized by labeling a chemical compound of
interest with a high-Z element or nanoparticle (NP). The addition of a single atom to
a molecule preserves the affinity of that molecule for biological processes; hence, its
modified behavior is very similar to the original molecule of interest. This feature
enables quantitative and unbiased measurements of biological processes. XFCT will
also be able to image NPs made from high-Z elements, such as gold [23], silver [24],
gadolinium oxide [25], zinc oxide [26], and so forth. Intensive research is ongoing in
the biomedical community to use these NPs as molecular imaging probes, as
vehicles for therapeutic drug delivery to target sites, or as sensitizers to enhance
the delivery of photothermal ablation therapy or radiation therapy [27–34]. Hence,
the ability to image the distribution of such NPs fulfills a critical need and can aid
substantially in the design and evaluation of novel imaging and therapeutic
strategies.
For the imaging with X-ray excitation energies (<30 keV), the use of silver and
gold nanoparticle agents are recommendable because they are relatively inert biological elements. Furthermore, the surface chemistry of these nanoparticles can be
modified to make them less reactive. The use of the K-shell X-rays from silver
nanoparticles (22.2 keV) and L-shell X-rays from gold nanoparticles (9.7 and
11.4 keV) provides an energy range suitable for X-ray focusing optics (see chapter
“Imaging and Instrumental Specifications”).
134
D. Vernekohl and L. Xing