page_title: Preclinical imaging
section_title: Combined PET-optical imaging, fluorescence
hierarchical_section_title: Preclinical imaging / Combined PET-optical imaging, fluorescence
caption_attribution_description: English: Confocal image (cLSM) of living HeLa cells. Mitochondria are stained in red (Mitotracker red), the nucleus is seen in blue (DAPI). icrotubules are stained in green (Tubulintracker green). Mitochondria form dense and dynamic networks in the cells soma and colocalize with the tubulin network.Deutsch: Konfokales Bild (cLSM) lebender Hela Zellen. Mitochondrien sind rot gefärbt (Mitotracker red), der Zellkern ist blau (DAPI). Das Mikrotubulinetzwerk ist in grün gefärbt (Tubulintracker green). Mitochondrien bilden Netzwerke und werden mittlels Motorproteinen entlang Mikrotubuli transportiert.English: Mitochondria and cytoskeleton in HeLa cells
context_page_description: Preclinical imaging is the visualization of living animals for research purposes, such as drug development. Imaging modalities have long been crucial to the researcher in observing changes, either at the organ, tissue, cell, or molecular level, in animals responding to physiological or environmental changes. Imaging modalities that are non-invasive and in vivo have become especially important to study animal models longitudinally. Broadly speaking, these imaging systems can be categorized into primarily morphological/anatomical and primarily molecular imaging techniques. Techniques such as high-frequency micro-ultrasound, magnetic resonance imaging and computed tomography are usually used for anatomical imaging, while optical imaging, positron emission tomography, and single photon emission computed tomography are usually used for molecular visualizations.
  These days, many manufacturers provide multi-modal systems combining the advantages of anatomical modalities such as CT and MR with the functional imaging of PET and SPECT. As in the clinical market, common combinations are SPECT/CT, PET/CT and PET/MR.
context_section_description: Principle: Dioxaborolane chemistry enables radioactive fluoride (¹⁸F) labeling of antibodies or red blood cells, which allows for positron emission tomography (PET) and fluorescence imaging of cancer and hemorrhages, respectively. A Human-Derived, Genetic, Positron-emitting and Fluorescent (HD-GPF) reporter system uses a human protein, PSMA and non-immunogenic, and a small molecule that is positron-emitting (boron bound F) and fluorescent for dual modality PET and fluorescence imaging of genome modified cells, e.g. cancer, CRISPR/Cas9, or CAR T-cells, in an entire mouse. The combining of these imaging modalities was predicted by 2008 Nobel Laureate, Roger Y. Tsien, to compensate for the weaknesses of single imaging techniques.
  Strengths: Combines the strengths of PET and optical Imaging, fluorescence. PET allows for anatomical imaging for location of labelled cells in entire animals or humans because the radiolabel, ¹⁸F, is within the animal or human for nearly unlimited depth of penetration. ¹⁸F has a half-life of 110 min and limits the radioactive exposure to the animal or human. Optical imaging allows for higher resolution with sub-cellular resolution of ~270 nm, or the diffraction limit of light, to allow for imaging of single cells and localizing cellular location on the cell membrane, endosomes, cytoplasm, or nuclei (see FIgure of multicolor HeLa cellls). The technique can label small molecules, antibodies, cells (cancer and red blood cells), cerebrospinal fluid, hemorrhages, prostate cancer removal, and genome edited cells expressing a genetically encoded human protein, PSMA, for imaging CRISPR/Cas9 edited and CAR T-cells.
  Weaknesses: Combining PET and optical imaging allows for two imaging agents that compensate for the weakness of the others. ¹⁸F has a half-life of 110 min and the PET signal is not permanent. Fluorescent small molecules allow for permanent signal when stored in the dark and not photobleached. Currently, there is not a single instrument that can image the PET signal and image fluorescence with subcellular resolution (see Figure of multicolor HeLa cells).  Multiple instruments are required to image PET, whole organ fluorescence, and single cell fluorescence with sub-cellular resolution.
caption: Multi-color fluorescence imaging of living HeLa cells with labelled mitochondria (red), actin (green), and nuclei (bue). Each cell is ~10 um and images show optical imaging allows for resolution ≤1 um.
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