Imaging methods providing quantitative structural, functional, and more recently also cellular and molecular information in a noninvasive manner have become valuable tools for the preclinical and clinical evaluation of drug candidates.

The field of noninvasive imaging is in rapid development: established modality such as CT, MRI, and PET are being optimized with respect to efficiency of data acquisition, data analysis, and operating comfort. For all these modalities small animal versions are currently available aimed at facilitating translational application. Novel modalities such as bioluminescence and fluorescence imaging have emerged and are rapidly becoming an attractive tool for the biologist. These techniques are attractive as they are cheap, use stable reporter systems, and are characterized by high sensitivity. They exploit readouts widely used in molecular biology, which can be further developed for in vivo application. However, translation to the clinics is not straightforward due to biophysical limitations (penetration of light) and due to the fact that many of the reporter systems are difficult or virtually impossible to apply in humans. Yet, for experimental research, optical imaging methods will become highly relevant.

A combination of the various imaging techniques currently available either by postprocessing (image fusion) or by simultaneous recording will allow a comprehensive characterization of a biological problem. Disease processes might be studied at the receptor level, by monitoring individual signaling cascades, and finally the morphological, physiological, and metabolic consequences of these molecular events. As such, multimodal imaging might become an interesting tool for system biology. For the drug developer, on the other hand, multimodality imaging should become an important instrument to understand drug effects in the intact individual.

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