OBJECTIVETo study magnetic resonance enhancement features of inflammatory lymph nodes using different doses of ultrasmall superparamagnetic iron oxide (USPIO) particles in order to establish a standardized protocol for USPIO enhanced magnetic resonance imaging of lymph nodes.

METHODSA total of 12 healthy New Zealand rabbits were injected complete Freund's adjuvant in foot pad to establish popliteal inflammatory lymph node model. Different doses (45, 90, 135 micromol Fe/kg) of USPIO were injected intravenously. Magnetic resonance scans were performed before and after USPIO injection to observe the enhancement features of different groups. T2 signal intensity, T1 signal intensity, T2 x value, and T2 value were measured and T2 enhancement ratio was calculated at different time points.

RESULTSTwenty-four hours after USPIO injection, there was no statistical difference in T2 signal intensity and T2 enhancement ratio between 90 and 135 micromol Fe/kg dose groups, but both were superior to 45 micromol Fe/kg group (P < 0.05). There were no statistical differences in T2 signal intensity, T1 signal intensity, T2 value, and T2 enhance ratio among different postcontrast time delays from 6 to 24 hours in 90 micromol Fe/kg group (P > 0.05), and signal reduction of lymph nodes peaked 18 hours after USPIO injection. Better images were acquired with a postcontrast delay of 18-24 hours.

CONCLUSIONSLymph nodes can be enhanced well with a dose of 90 micromol Fe/kg. Postcontrast delay of 18-24 hours is appropriate for acquiring satisfactory enhancement images.