In vivo imaging, whether at the cellular or whole-animal
level, promised to revolutionize preclinical and clinical
biological and bioengineering research. By conducting
longitudinal studies, the natural course of a disease or the
experimental model can be monitored. Imaging modalities
(such as X-ray, CT, MRI, optical, and ultrasound imaging)
yield valuable information about changes in the anatomy
and physiology of the specimen. In order to gain molecular
information, animals were sacrificed, dissected, and studied
via techniques such as immunoblotting (Western),
immunofluorescence, immunohistochemistry, quantitative
RT-PCR, microarray, HT sequencing, or FACS analysis.
However, these techniques provide only information at the
time of measurement, and because subjects of these
techniques were often euthanized, longitudinal studies
could not be completed. In addition, where and when to
sample must be known beforehand, or a very large number
of animals must be uti
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