INTRAVENOUS MR LYMPHOGRAPHY WITH SUPERPARAMAGNETIC IRON-OXIDE PARTICLES - EXPERIMENTAL STUDIES IN RATS AND RABBITS

The inter- and intralymphonodal distribution of IV-administered superp aramagnetic iron oxide (SPIO) particles as a lymphographic contrast ag ent for MRI was studied in various animal models in rats and rabbits. In all animals a dosage of 200 mu mol Fe/kg was tested. Imaging was do ne at 1.5 Tesla using proton-density-weighted spin-echo (PD-SE) and T2 -weighted gradient-echo (T2*-GRE) sequences. The time course of signa l loss in popliteal lymph nodes of 21 rats was studied before and up t o 72 h after IV injection of SPIO. Another 6 rats were dissected 24 h after IV injection of SPIO, all lymph nodes were embedded in agar gel and imaged ex vivo. Time course and pattern of lymph node metastases w as studied in 4 VX2 tumor-bearing rabbits. Most pronounced signal loss in lymph nodes was found 24 h after IV injection of SPIO with a decre ase of signal in popliteal lymph nodes to 37 +/- 15% (9 +/- 5%) for ra ts and 56 +/- 10% (16 +/- 9%) for rabbits with the PD-SE (T2-GRE) seq uence. Ex vivo examinations of rat lymph nodes and in vivo examination s in rabbits with lymph node hyperplasia demonstrated marked variation s in contrast agent accumulation between different lymph node groups. In VX2 tumor-bearing rabbits lymph node metastases could be well delin eated in postcontrast MRI if a sufficient amount of contrast agent rea ched the lymph modes (2 rabbits). Inhomogeneous signal loss as well as supersaturation impeded correct lymph node assessment (2 rabbits). We conclude that IV MR lymphography using SPIO may be an approach for no n invasive tumor staging, but this new technique could be limited by v ariations in contrast agent distribution between different lymph node groups.