In vivo MRI of hyperpolarized silicon-29 nanoparticles

Purpose: The objective of the present work was to test the feasibility of in vivo imaging of hyperpolarized 50-nm silicon-29 (²⁹Si) nanoparticles.

Methods: Commercially available, crystalline 50-nm nanoparticles were hyperpolarized using dynamic polarization transfer via the endogenous silicon oxide-silicon defects without the addition of exogenous radicals. Phantom experiments were used to quantify the effect of sample dissolution and various surface coating on T₁ and T₂ relaxation. The in vivo feasibility of detecting hyperpolarized silicon-29 was tested following intraperitoneal, intragastric, or intratumoral injection in mice and compared with the results obtained with previously reported, large, micrometer-size particles. The tissue clearance of SiNPs was quantified in various organs using inductively coupled plasma optical emission spectroscopy.

Results: In vivo images obtained after intragastric, intraperitoneal, and intratumoral injection compare favorably between small and large SiNPs. Improved distribution of small SiNPs was observed after intraperitoneal and intragastric injection as compared with micrometer-size SiNPs. Sufficient clearance of nanometer-size SiNPs using ex vivo tissue sample analysis was observed after 14 days following injection, indicating their safe use.

Conclusion: In vivo MRI of hyperpolarized small 50-nm SiNPs is feasible with polarization levels and room-temperature relaxation times comparable to large micrometer-size particles.