| Summary: | The<b> </b>application of the Three-Dimensional Ultra-Short Echo Time (3D UTE) pulse sequence at a high magnetic field for visualization of the distribution of <sup>19</sup>F loaded theranostic core-shell nanocapsules with Nafion® (1,1,2,2-tetrafluoroethene; 1,1,2,2-tetrafluoro-2- [1,1,1,2,3,3-hexafluoro-3-(1,2,2-trifluoroethenoxy)propan-2-yl] oxyethanesulfonic acid) incorporated into the shell is presented. The nanocarriers were formed via the layer-by-layer technique with biodegradable polyelectrolytes: PLL (Poly-L-lysine), and with Nafion®: polymer with high <sup>19</sup>F content. Before imaging, an MR (magnetic resonance) spectroscopy and T<sub>1</sub> and T<sub>2</sub> measurements were performed, resulting in values of T<sub>2</sub> between 1.3 ms and 3.0 ms, depending on the spectral line. To overcome limitations due to such short T<sub>2</sub>, the 3D UTE pulse sequence was applied for <sup>19</sup>F MR imaging. First Nafion® solutions of various concentrations were measured to check the detection limit of our system for the investigated molecule. Next, the imaging of a phantom containing core-shell nanocapsules was performed to assess the possibility of visualizing their distribution in the samples. Images of Nafion® containing samples with SNR ≥ 5 with acquisition time below 30 minutes for <sup>19</sup>F concentration as low as 1.53·10<sup>−2 </sup>mmol <sup>19</sup>F/g of sample, were obtained. This is comparable with the results obtained for molecules, which exhibit more preferable MR characteristics.
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