Objectives:

We sought to compare the ability of 3 ultrasmall superparamagnetic iron oxides (USPIOs) to detect and characterize antigen-induced arthritis with MR imaging.

Materials and Methods:

A monoarthritis was induced in the right knee of 18 rats. The left knee served as a normal control. Knees underwent magnetic resonance (MR) imaging before, up to 2 hours, and 24 hours after injection (pi) of 200 μmol Fe/kg SHU 555 C (n= 6), ferumoxtran-10 (n= 6), or ferumoxytol (n= 6), using T2-2D-SE 100/20, 40, 60, 80/90 (TR/TE/flipangle), T2*-3D-spoiled gradient recalled (SPGR) 100/15/38, and T1-3D-SPGR 50/1, 7/60 sequences.

Results:

Quantitative signal to noise ratio and ΔSI data of arthritic knees on T1-and T2*-weighted MR images showed no significant differences between the 3 USPIOs (P> 0.05). At 2 hours pi, SNR and ΔSI data were significantly increased from baseline on T1-weighted images and significantly decreased on T2*-weighted images (P< 0.001). At 24 hours pi, the T1-enhancement returned to baseline, whereas the T2*-enhancement remained significantly elevated (P< 0.001). Immunostains demonstrated an USPIO compartmentalization in macrophages in the arthritic synovium.

Conclusions:

Based on the relatively small number of animals in our study group, inflammation in antigen-induced arthritis can be equally detected and characterized with any of the three USPIOs evaluated.