[Introduction] Although magnetic resonance angiography (MRA) has the potential to visualize microvessel structure with high resolution theoretically, it is hard to visualize the structure due to low signals from microvessel. In our previous work, we succeeded in visualizing the superfine imaging of cerebrovasculature using fluorescein and Gd conjugated 8-arm polyethylene glycol (F-8-arm PEG-Gd) as the MR contrast agents (Fig. 1). Interestingly, the image was not acquired when Gd-conjugated 8-arm PEG (8-arm PEG-Gd) was used. We found that the conjugation of fluorescein to the contrast agent played an important role in visualizing the cerebrovasculature. In this presentation, we discuss that the superfine imaging is realized by the self-assembled formation of F-8arm PEG-Gd. [Results and Discussion] The hydrodynamic radius of the F-8-arm PEG-Gd was increased from 4 to 1000 nm with increasing the concentration from 0.1 to 100 mg/ml, although the radius of 8-arm PEG-Gd was constant regardless of the concentration increases. As the results of 1H-NMR measurements, the proton signals of the fluorescein in F-8arm PEG-Gd were low when D2O was used as the solvent. When absorption and emission spectra of F-8-arm PEG-Gd were measured, the peak top around 480 nm was shifted on the side of long wavelength as compared with a fluorescein monomer. These results suggested that the self-assembled structure of F-8-arm PEG-Gd was formed by stabilizing by the stacking interaction of the fluorescein. When the contrast agents were injected to stroke model rats, collateral circulation around the stroke area was clearly visualized on MRI scan. [Conclusion] The self-assembled structure of the F-8-arm PEG-Gd was formed through the fluorescein, and cerebrovasculature could be visualized by temporary circulation of the contrast agents.

Transient self-assembled polymeric contrast agents for superfine cerebrovasculature MR imaging

2019 Fall National Meeting

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