MR lymphography with iron oxide compound AMI-227: Studies in ferrets with filariasis

OBJECTIVE. The purpose of this study was to assess the MR lymphographic potential of AMI-227 to reduce the signal intensity of hyperplastic inflammatory lymph nodes by using ferrets with filariasis as the animal model. Both interstitial and IV modes of administration were studied. MATERIALS AND METHODS. Twelve ferrets were infected with the filaria Brugia malayi and six control ferrets were injected with superparamagnetic iron oxide AMI-227, either interstitially or IV. Signal intensities of the left popliteal lymph node, left hamstring muscle, and left inguinal fat were measured before, 48 hr after, and up to 138 days after contrast injection with the use of both spin-echo and gradient-echo techniques. The signal intensity data were statistically analyzed. The lymph nodes, liver, spleen, and lungs were studied with light and electron microscopy. RESULTS. Forty- eight hours after the interstitial injection of AMI-227, the signal intensities of the ipsilateral popliteal nodes of the infected and control ferrets were significantly reduced (p < .0005) without significant changes in the signal intensities of the surrounding tissues on both spin-echo and gradient-echo MR images. No nodal signal reduction occurred with the IV route of injection in ferrets. Light microscopy revealed iron to be localized within nodal marginal zones exclusively. Lymphatic trunks were visualized after interstitial injection. Signal reduction persisted to our end point of 138 days. CONCLUSION. AMI-227 shows regional specificity with significant enhancement of nodal structures and demonstrates potential as an interstitial MR lymphographic agent.