Quantification and biodistribution of iron oxide nanoparticles in the primary clearance organs of mice using T1 contrast for heating

PurposeTo use contrast based on longitudinal relaxation times (T-1) or rates (R-1) to quantify the biodistribution of iron oxide nanoparticles (IONPs), which are of interest for hyperthermia therapy, cell targeting, and drug delivery, within primary clearance organs. MethodsMesoporous silica-coated IONPs (msIONPs) were intravenously injected into 15 naive mice. Imaging and mapping of the longitudinal relaxation rate constant at 24h or 1 week postinjection were performed with an echoless pulse sequence (SWIFT). Alternating magnetic field heating measurements were also performed on ex vivo tissues. ResultsSignal enhancement from positive T-1 contrast caused by IONPs was observed and quantified in vivo in liver, spleen, and kidney at concentrations up to 3.2mg Fe/(g tissue wt.) (61mM Fe). In most cases, each organ had a linear correlation between the R-1 and the tissue iron concentration despite variations in intra-organ distribution, degradation, and IONP surface charge. Linear correlation between R-1 and volumetric SAR in hyperthermia therapy was observed. ConclusionThe linear dependence between R-1 and tissue iron concentration in major organs allows quantitative monitoring of IONP biodistribution in a dosage range relevant to magnetic hyperthermia applications, which falls into the concentration gap between CT and conventional MRI techniques. Magn Reson Med 78:702-712, 2017. (c) 2016 International Society for Magnetic Resonance in Medicine