MR imaging enables measurement of therapeutic nanoparticle uptake in rat N1-S1 liver tumors after nanoablation

Purpose To test the hypothesis that magnetic resonance (MR) imaging can quantify intratumoral superparamagnetic iron oxide (SPIO) nanoparticle uptake after nanoablation. Materials and Methods SPIO nanoparticles functionalized with doxorubicin were synthesized. N1-S1 hepatomas were successfully induced in 17 Sprague-Dawley rats distributed into three dosage groups. Baseline tumor R2* values (the reciprocal of T2*) were determined using 7-tesla (T) MR imaging. After intravenous injection of SPIO nanoparticles, reversible electroporation (1,300 V/cm, 8 pulses, 100-μs pulse duration) was applied. Imaging of rats was performed to determine tumor R2* values after the procedure, and change in R2* (ΔR2*) was calculated. Inductively coupled plasma mass spectrometry was used to determine intratumoral iron (Fe) concentration after the procedure, which served as a proxy for SPIO nanoparticle uptake. Mean tumor Fe concentration [Fe] and ΔR2* for each subject were assessed for correlation with linear regression, and mean [Fe] for each dosage group was compared with analysis of variance. Results ΔR2* significantly correlated with tumor SPIO nanoparticle uptake after nanoablation (r = 0.50, P =.039). On average, each 0.1-ms^-1 increase in R2* corresponded to a 0.1394-mM increase in [Fe]. There was no significant difference in mean SPIO nanoparticle uptake among dosage groups (P =.57). Conclusions Intratumoral SPIO nanoparticle uptake after nanoablation can be successfully quantified noninvasively with 7-T MR imaging. Imaging can be used as a method to estimate localized drug delivery after nanoablation.