Effective Detection of Nafion^®-Based Theranostic Nanocapsules Through ¹⁹F Ultra-Short Echo Time MRI

Abstract

The application of the Three-Dimensional Ultra-Short Echo Time (3D UTE)pulse sequence at a high magnetic field for visualization of the distribution of 19F 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 19F content. Before imaging, an MR (magnetic resonance) spectroscopy and T1 and T2 measurements were performed, resulting in values of T2 between 1.3 ms and 3.0 ms, depending on the spectral line. To overcome limitations due to such short T2, the 3D UTE pulse sequence was applied for 19F 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 min for 19F concentration as low as 1.53 × 10−2 mmol 19F/g of sample, were obtained. This is comparable with the results obtained for molecules, which exhibit more preferable MR characteristics.

Keywords

• theranostic nanocarriers
• polyelectrolites nanocapsules
• imaging
• ¹⁹F MRI
• ultra short echo time
• UTE