Proton relaxation studies and particle size analysis of suspensions of magnetic and radioactive metal colloids

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Molecular imaging allows modern medicine to examine the functions of molecules and cells in living organisms. The aim of this proposal is to increase our knowledge regarding the use of metal colloids providing positive contrast in magnetic resonance imaging. Synthesized with gadolinium and manganese, these colloids display huge potential for cell labelling and tracking. The development of contrast agents and tracers (biomarkers) providing high and specific signal in magnetic resonance imaging (MRI) and positron emission tomography (PET) could be advantageously used with a next generation of scanners combining MRI and PET, that will soon become a reality in the clinic. MRI is a non-invasive imaging technique providing high resolution pictures in low density tissues. Magnetic molecules or nanoparticles are often necessary to finely delineate the vasculature, to precisely identify disease artefacts, and to track cells. PET is also a non-invasive imaging technique, based on the detection at very high sensitivity, of radioactive tracers. Magnetic metal colloids in the form of nanoparticles can be used to improve the specificity of the MRI signal. By doping these crystalline "nanomaterials" with carefully selected radioactive atoms, a next generation of biomarkers could become available for dual PET/MRI procedures. The physico-chemical characterization of magnetic metal colloids for MRI requires the use of a fast and accurate technique for measuring the hydrodynamic radius of the nanoparticles suspended in fluids. Then, by measuring the zeta potential, it is possible to evaluate the tendency of the particles to aggregate. Finally, the potential of the contrast agent to generate strong contrast effects in MRI pictures, can be precisely measured at varying temperatures with a dedicated relaxometer (measurement of proton relaxation times). NMR proton relaxation analyzers can also be used to measure the contrast generated by suspensions of cells marked with magnetic tracers. The combined use of these technologies are crucial for the  development of magnetic and radioactive tracers for dual PET/MRI.