Biomedical Applications of Emission Tomography - Correction Techniques in Emission Tomography - page 17

stem cell therapy). Again, serial non-invasive imaging studies enable as-
sessment of intra-individual changes in a few animals.

• Development. Since the majority of clinical imaging devices are now

available in a \miniaturized" fashion for small animal imaging with sim-
ilar imaging characteristics, it seems straightforward to use small animal
imaging in validation studies to characterize new imaging approaches in
animal models first and then translate into clinical imaging by using
the analogous clinical imaging modality. This is especially useful when
testing new imaging probes for molecular imaging (contrast agents, ra-
diopharmaceutical, optical dyes, etc.).

2.4.2 Clinical applications
In current medicine, much of the medical practice is based on standards of
care that are determined by averaging responses across large cohorts. Based
on clinical trials every patient receives the same treatment, biological vari-
ability within diseases and between individuals is only sparsely considered.
On the contrary, biomedical imaging can assess the individual patient's spe-
cific characteristics on the level of individual molecular signatures locally and
quantitatively in patients' whole body. This is expected to be superior to sys-
temic analyses such as blood tests when looking for the clinically important
local burden of diseases. Biomedical imaging uniquely allows doctors to detect
hidden or early disease, to select and tailor appropriate therapies, and to mon-
itor therapy eciency in individuals. In this respect|given its large potential
for studying physiology and pathophysiology non-invasively in humans and
patients|emission tomography has seen widespread application over the last
20 years in clinical research and diagnostics. With the advent and expansion
of the eld \molecular imaging" emission tomography per se was pushed to
higher levels with optical imaging most frequently used in preclinical and basic
research studies. The reasons are the low costs of the technique, easy labeling
strategies of fluorescent dyes, the long half-life and the link to microscopy.
However, optical imaging in humans is still and will most likely always be
restricted to applications where the imaging object is close to the surface
(skin, endoscopy, etc.) due to light scattering and absorption when light trav-
els through deep tissues. On the contrary, SPECT and PET have been es-
tablished for many years for clinical diagnostics and research and founded
the success of clinical nuclear medicine. SPECT and PET are not limited to
surface applications and can quantitatively sense radioactive signals in the
whole body. A huge library of clinical and experimental radiopharmaceuticals
is available. While SPECT tracers are mainly produced in-house by apply-
ing the gamma emitter 99m Tc (6 h half-life) eluted from 99 Mo generators to
commercial kits, PET relies on the cyclotron-based production of short-living
(typical range from 2 min to 2 h half-life) isotopes coupled to precursors in