Improving detection specificity of iron oxide nanoparticles (IONPs) using the SWIFT sequence with long T2 suppression

In order to improve the detection specificity of iron oxide nanoparticles (IONPs) delivered to tumors, we embedded saturation pulses into the sweep imaging using Fourier transformation (SWIFT) sequence to suppress long T2 tissues and fat. Simulation of the Bloch equation was first conducted to study behavior of the saturation pulses of various lengths under different T2 and off-resonance conditions. MR experiments were then conducted using in vivo mouse xenografts and a phantom consisting of IONPs, vegetable oil, and explanted tumor specimen, without and with long T2 suppression under a 7 T magnetic field. For the in vivo study, arginine-glycine-aspartate (RGD) coated 10 nm IONPs (RGD-IONPs) were delivered to tumors implanted in nude mice through both intra-tumor and intravenous injections. Histological studies confirmed that RGD-IONPs efficiently homed to tumors through RGD-integrin interaction. Compared to conventional SWIFT, the proposed method resulted in sufficient suppression on long T2 species but less influence on short T2 species. For both the in vivo and ex vivo studies, significantly improved contrast-to-noise ratio (CNR) was achieved between the IONPs and the long T2 species.