Optimization of Ultrasmall Superparamagnetic Iron Oxide (P904)-enhanced Magnetic Resonance Imaging of Lymph Nodes: Initial Experience in a MouseModel

Abstract

Background: P904 is a novel ultra-small superparamagnetic iron oxide (USPIO) contrast agent. This study was conducted to investigate the optimal dose of P904 for magnetic resonance imaging (MRI) of lymph nodes. Materials and Methods: T2*-weighted 3T MRI was performed in 14 normal mice before and 24 h after P904 injection at varying doses. Normalized signal intensity (nSI), signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and contrast ratio (CR) were calculated to determine the optimal dose. MRI of the metastatic lymph node models (n=5) was acquired using the optimal dose and correlated with pathological results to calculate sensitivity and specificity. The mean SI ratio between pre- and postcontrast MRI was also calculated for each lymph node. Results: The mean nSI and SNR values on postcontrast images were significantly lower at 300 μmol Fe/kg than at 75 μmol Fe/kg (p<0.001). The mean CNR and CR values were significantly higher at 300 μmol Fe/kg than at the other two doses (p<0.05). At the optimal dose of 300 μmol Fe/kg, the mean SI ratio of benign lymph nodes was significantly lower than that of metastatic lymph nodes (p<0.001). The Az (areas under the receiver operating characteristic curves) value for diagnosing lymph node metastasis at the optimal dose was 0.97. Conclusion: The optimal dose for P904-enhanced MRI of the lymph nodes was 300 μmol Fe/kg, which could be used for the diagnosis of lymph node metastasis.