Abstract
One major goal in medical imaging is the elaboration of more efficient contrast agents (CAs). Those agents need to be optimized for the detection of affected tissues such as cancers or tumors while decreasing the injected quantity of agents. The paramagnetic contrast agents containing fluorine atoms can be used for both proton and fluorine magnetic resonance imaging (MRI), and they open the possibility of simultaneously mapping the anatomy using 1H MRI and accurately locating the agents using 19F MRI. One of the challenges in this domain is to synthesize molecules containing several chemically equivalent fluorine atoms with relatively short relaxation times to allow the recording of 19F MR images in good conditions. With that aim, we propose to prepare a CA containing a paramagnetic center and nine chemically equivalent fluorine atoms using a cycloaddition reaction between two building blocks. These fluorinated contrast agents are characterized by 19F NMR, showing differences in the fluorine relaxation times T1 and T2 depending on the lanthanide ion. To complement the experimental results, molecular dynamics simulations are performed to shed light on the 3D-structure of the molecules in order to estimate the distance between the lanthanide ion and the fluorine atoms.
Highlights
Magnetic resonance imaging (MRI) has become one of the most used imaging techniques in the medical field with tens of millions MRI examinations performed annually around the world [1]
The synthesis can be divided in three parts: (i) the synthesis of the DOTA-GA derivative lanthanide complexes bearing an azide function, (ii) the synthesis of the fluorinated diamagnetic compound and (iii) the combination of these two building blocks through a cycloaddition reaction
The effect of several lanthanide ions on fluorine relaxation times has been studied in order to optimize the numerous advantages of fluorine imaging while excluding its drawback such as long relaxation times and low solubility in aqueous media
Summary
Magnetic resonance imaging (MRI) has become one of the most used imaging techniques in the medical field with tens of millions MRI examinations performed annually around the world [1]. These images can be affected by the concentration of protons in the tissues as well as their longitudinal and transversal relaxation times, T1 and T2 These medical examinations can be performed thanks to endogenous local contrast from the body, but in numerous cases, this natural signal is not sufficient and the use of exogenous contrast agents (CAs) is required. The most common ones rely on the indirect detection of their effect on the bulk water signal, which is convenient because of the high-water concentration in tissues Those agents are known to affect and shorten both the longitudinal (T1) and transverse (T2) relaxation times of surrounding water proton nuclei, enhancing the contrast between tissues. T1 agents (mostly lanthanide complexes) are called positive agents because of the hyperintense signal they engender in the accumulation areas, whereas T2 agents (usually iron oxide nanoparticles) are “negative” contrast agents since they induce darker contrast in accumulation areas
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