Magnetic resonance imaging diagnosis of metastatic lymph nodes in a rabbit model : efficacy of PJY10, the new ultrasmall superparamagnetic iron oxide agent, with monodisperse iron oxide core and multiple-interaction ligands

Abstract

Objectives: To evaluate the feasibility of detecting lymph node metastasis using the new ultrasmall superparamagnetic iron oxide particle, PJY10, in a rabbit model. Materials and Methods: To make metastatic and benign lymph nodes, either VX2 carcinoma or fecal material suspension was inoculated into thighs of 56 rabbits three weeks or three days before magnetic resonance(MR) imaging, respectively. T2*-weighted 3T MR imaging was performed before and 24 hours after PJY10 injection(5.2[n=15], 7.8[n=17], and 10.4[n=24] mg Fe/kg). MR images were correlated with pathologic results to calculate sensitivity and specificity. Quantitative analysis of the signal intensity(SI)–number of voxels[low] (the fraction of the number of voxels with the normalized SI on the postcontrast image lower than that on the precontrast image) and mean SI ratio–was also performed for each lymph node, using Students t-test, Pearson correlation and receiver operating characteristic(ROC) curve analyses. Results: Sensitivities were 100% at all three dosages, whereas specificity increased with increasing dosage(89% at 10.4mg Fe/kg). The benign nodes had a significantly higher number of voxels[low] and a lower mean SI ratio than the metastatic nodes at the dosage of 10.4mg Fe/kg(P <.001). Az values were 0.905 for the number of voxels[low] and 0.952 for the mean SI ratio. The number of voxels[low](P =.019) and the mean SI ratio(P=.034) had significant positive correlations with the histopathologic area ratio of metastatic foci in the metastatic nodes at 10.4mg Fe/kg. Conclusion: PJY10 enabled clear demonstration of lymph node metastasis with high sensitivity and specificity at its optimal dosage of 10.4mg Fe/kg.