Biomedical Applications of Emission Tomography - Correction Techniques in Emission Tomography - page 18

automated synthesis procedures at the site of the application or within short
distance to it.
The molecular imaging with SPECT and PET has successfully entered
clinical algorithms in various fields of oncological, cardiovascular, neurologi-
cal and other types of diseases. Applications range from pathophysiological
studies to clinical diagnostics, therapy control and prevention.
While clinical SPECT imaging relies on a broad variety of radiopharmaceu-
ticals (perfusion agents, metabolism tracers, receptor ligands, etc.) the success
of PET is based on the use of [ 18 F]FDG which can be used quite universally in
various conditions since it reflects glucose metabolism, a key metabolic path-
ways in organisms. However, the glucose signal is relatively unspecific for a
single disease entity; for example, macrophages accumulate [ 18 F]FDG in in-
flammatory lesions while growing tumors do the same. The development of
more specific tracers therefore remains a huge challenge for radiochemistry.

2.4.3 Examples of biomedical applications of emission
tomography
Since the field of biomedical applications is broad and quickly expanding,
this chapter aims at showing relevant areas of applying emission tomography
from recent work of our group rather than giving a complete overview. For
further reading current reviews are suggested. A special emphasis is put on
challenges for quantification of emission tomography [12, 23, 1, 24, 4, 25, 28,
8, 18, 3].

2.4.3.1 Bioluminescence imaging of tumor growth

Bioluminescence imaging (BLI) is a non-invasive, sensitive, rapid and cost-
effective means to investigate cellular behavior in a living organism. Although
the typical image acquisition is planar resulting in 2D images, the technique
can be used to quantify signals from species such as zebra fish or mice. Signals
within cells are typically generated by the use of reporter genes. A prominent
reporter gene is the rey luciferase of Photinus pyralis. This enzyme cat-
alyzes the oxidation of D-luciferin in an ATP-dependent manner resulting in
the emission of light (emission maximum 560 nm). To follow the fate of
cells in organisms, specific cell populations are transfected with the rey lu-
ciferase gene. One example is the follow-up of cancer growth and response to
therapy by the use of transduced cells expressing luciferase. Upon injection
into animals the transduced tumor cells proliferate and divide but still carry
the luciferase gene. Bioluminescence imaging makes use of the intravenous in-
jection of luciferin, which is taken up by cells and only in the case of luciferase
expression is oxidized in a chemical reaction that results in the emission of
light. The emitted bioluminescence allows non-invasive following of the in vivo
growth or regression of the genetically modified tumor cells reflecting viable
tumor cell mass. Although the image acquisition is planar, a direct correla-