Objective: To 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.
Methods: A 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.
Results: Twenty-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.
Conclusions: Lymph 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.