Characterization of reactive versus tumor-bearing lymph nodes with interstitial magnetic resonance lymphography in an animal model

Abstract

Rationale and objectives: To determine if magnetic resonance lymphography performed with subcutaneously administered AMI-227, a nanoparticulate iron oxide contrast agent, can distinguish reactive from tumor-bearing lymph nodes.

Materials and methods: Mature male Copenhagen rats were inoculated with cell suspensions of R3327-MAT-LyLu rat prostate carcinoma (n = 21) or Freund's complete adjuvant (n = 15) in the left footpad to generate ipsilateral popliteal lymph node metastases or lymphadenitis. At 12 to 14 days after inoculation, T1-and T2-weighted magnetic resonance images of bilateral popliteal areas were obtained before and 24 hours after subcutaneous administration of AMI-227. Contrast-to-noise ratios were calculated in precontrast and postcontrast images. Bilateral popliteal nodes were excised for pathologic assessment.

Results: AMI-227 resulted in decreased contrast-to-noise ratios in reactive (T1-W = -7.01 +/- 1.13, T2- W = -31.64 +/- 5.35) and normal (T1 - W = -13.56 +/- 1.97, T2 - W = -21.62 +/- 2.51) nodes. Contrast-to-noise ratios were unchanged (T1 - W = -0.22 +/- 1.71, T2 - W = -2.20 +/- 4.19) in tumor-containing nodes. These differences in contrast-to-noise ratio changes between tumor-bearing versus nontumor-bearing nodes were statistically significant (P < 0.05). Histologic analysis showed similar distribution of AMI-227 within normal and reactive nodes, but not in tumor-bearing nodes.

Conclusions: Differences in AMI-227-uptake between tumor- and nontumor-bearing nodes detected with magnetic resonance imaging are helpful for distinguishing the two entities.