| Summary: | 碩士 === 國立中山大學 === 化學系研究所 === 103 === Magnetic resonance imaging (MRI) is one of the mostly useful non-invasive techniques in medical diagnosis, food science and materials research. The conventional theory of MRI contrast agents, assuming that they are located in a dilute, small molecular solution, gives good approximation in many situations but may fail in real biological systems because it is well-known that a typical organism is a highly crowded environment full of large and small molecules and ions. The performance of MRI contrast agent may be significantly altered by crowders and ions.
In previous work, we have studied the influence of macromolecular crowders on relaxivity of MRI contrast agents. The present study offers the first study on the influence of ions on macromolecular crowding effect on MRI contrast agents by measuring the longitudinal relaxation rate (R1), transverse relaxation rate (R2) and chemical shift (CS) of water and ion as a function of the concentration of ions in the solution system comprising commercial MRI contrast agent Dotarem (the mostly used MRI contrast agent in medical diagnosis), polyethylene glycol (PEG) as crowder and KCl, NaCl, LiCl, MgCl2 CaCl2, KI as ion source (these ions are most common in organisms). Through LSNMR 200 MHz, 500 MHz, NMRD, SSNMR 500 MHz to explore different kinds of interactions between molecules and ions in the solution systems.
From the results, it is found that the ion effect not only affects the dynamics of water molecules, but also the structures of the water-water, water-ion and water-PEG clusters. From the relaxation rates, we find that these ions affect the dynamics of the water molecule, especially Mg2+, Ca2+. The influence of both these two ions is higher than the rest. Through the measurement of chemical shift, we find that when the crowding agent is added in the ion solution, it increases the tendency of change of chemical shift. It is worth to note that the tendency of MgCl2 is opposite to other salt ions. Increasing nonlinearly with the concentration of MgCl2, water proton chemical shift and relaxation rates show that at least two or more factors affecting the changes in the systems. The results of 23Na NMR and NMRD provide us supplementary information on the dynamics and structure of clusters involving water molecules. These results demonstrate the significant effect of the ions under crowding environment on the relaxivity of MRI contrast agent and indicate that a molecular level understanding of the relaxation mechanism of MRI contrast agent in such system helps build the microscopic picture of MRI contrast generation and increases the accuracy of the MRI contrast determination of the image.
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