Photonics Technology for Molecular Imaging

Recent progress in photonics technologies contributing to the advancements of molecular imaging are reviewed from an industrial point of view. Many imaging modalities have been developed for molecular imaging, and many of these methods rely on the detection of "photons" as a basis for image formation. These include positron emission tomography (PET), near-infrared spectroscopy (NIRS), and fluorescence microscopy. A PET system dedicated to studies of monkeys and a planar imaging system for imaging of plants and small animals have been developed. PET studies on age-related impairment of the serotonin neural functions revealed the mechanism in aged monkeys. The planar imaging system demonstrated the dynamic changes in fluoro-deoxy-glucose distribution in a rat with the time interval of 10 s. Using NIRS, quantitative temporal measurement of an absorber such as hemoglobin in tissues was achieved. The NIRS study on the human brain function suggested the relation between the applied task and the activated area. Diffusion optical tomography is also discussed. A fluorescence microscope has been developed for imaging of molecules in living cells, which is equipped with two image-intensified cooled charge-coupled device cameras having a time-gate function. Preliminary results on mRNA expressions showed the usefulness of the fluorescence resonance energy transfer imaging based on the fluorescence decay time, compared to the conventional intensity imaging method. In the near future, the application of a spatial light modulator and holography, to control the wave front of the light, will produce clearer and more precise images of molecules under microscope. Photonics technologies will provide exciting opportunities for various industries to participate in and contribute to the field of molecular imaging.