Chemistry Reference
In-Depth Information
Fluorescence-mediated tomography (FMT) is a subset of optical imaging that
plays a prominent role in the preclinical settings for the investigation of molecular
processes in intact animals [
18
]. A major drawback of older optical reflectance
imaging is the lack of quantification in the fluorescent light from the source.
Fluorescence-mediated tomography is an alternative modality which allows for
quantization of signals. This is accomplished because fluorescence tomography
enlists multiple light sources, which are paired with multiple detector pairings to
generate numerous experimental data to assist the effort to pinpoint and quantify
the fluorescence reporter within the tissue. Another benefit of fluorescence tomo-
graphic imaging is the ability to reconstruct three-dimensional images, something
that traditional reflectance imaging cannot do. Tomographic images have been
overlaid with high-resolution datasets generated from MRI, thereby leading to
two very complimentary imaging modalities resulting in superior imaging infor-
mation. In proof of principle study, mouse brain implanted with human glioma
tumor cells was examined using MRI-FMT co-registration and led to an improve-
ment in tumor localization [
19
,
20
].
The idea behind creating dual-function or multifunctional compounds lies in the
fact that no imaging technique is perfect and all have some drawbacks. Simply, if
one technique has a disadvantage and another modality can compensate for this,
then the two modalities could be complementary to each other. In case of MRI, the
aforementioned cost, sensitivity, and acquisition times are major hindrances, but it
excels in resolution and depth of penetration and provides physiological informa-
tion. Optical imaging on the other hand uses inexpensive probes and has excellent
sensitivity, requires small doses, can be used for image-guided therapy, but yields
very poor spatial resolution and has limited clinical usage due to depth of penetra-
tion. Therefore, it becomes necessary to develop long-wavelength optical imaging
agents and combine its use with other imaging techniques.
1.2
Image-Guided Therapy
Real-time imaging of the entire tumor is the goal of image-guided therapy
[
21
]. Conventionally, imaging is done preoperatively, then surgical resection of
the tumor is performed, and possibly postsurgical imaging is performed to ensure
that the entire tumor has been removed. However, imaging modalities such as
fluorescence optical imaging, due to its very short acquisition time and cancer
specific probes, offer the ability to imaging during the surgical resection process,
thereby ensuring that the entire tumor is removed. Van Dam et al. [
22
] illustrated
the importance of image-guided therapy in their work with intraoperative fluores-
cence imaging of ovarian cancer in which they used folate-FITC to determine what
areas of the patients' ovaries contain cancer which needed to surgically be removed
and which areas were normal tissue. In addition to surgery, other methods for tumor
ablation can work well with image-guided therapy. One such method is photody-
namic therapy (PDT) which currently serves as either a primary or adjunctive
