MAGNETIC-RESONANCE LYMPHOGRAPHY IN RATS - EFFECTS OF MUSCULAR-ACTIVITY AND HYPERTHERMIA ON THE LYMPH-NODE UPTAKE OF INTRAVENOUSLY INJECTED SUPERPARAMAGNETIC IRON-OXIDE PARTICLES

Rationale and Objectives. We investigated the influence of muscular ac tivity and regional body temperature changes on the accumulation of in travenously (IV) administered, dextran-coated superparamagnetic iron o xide (SPIO) particles in the lymph nodes of rats. Methods. Four groups of rats (N = 21) were used. Five rats were allowed to move freely aft er IV contrast administration (group 1), In another five rats, muscula r inactivity (group 2) was induced during IV injection of SPIO particl es and for up to 2 hr thereafter by anesthesia. In seven rats (likewis e anesthetized), the contrast agent was administered while the extremi ties of one side of the body were warmed in a water bath for 2 hr (gro up 3). The rats in groups 1-3 received 100 mu mol Fe/kg of the contras t agent, Four rats not given SPIO particles served as the control grou p (group 4). The lymph nodes of all animals were removed 24 hr after S PIO administration and were embedded in an agar matrix for magnetic re sonance imaging at 1.5 T using a proton-density-weighted spin-echo (PD -SE) sequence and a T2-weighted gradient-recalled echo (T2* GRE) sequ ence. Results. Signal loss varied widely among the different lymph nod es in group 1. A pronounced signal reduction was observed in the mesen teric (PD-SE = 20 +/- 6%, T2 GRE = 55 +/- 19%), iliac (PD-SE = 13 +/- 13%, T2 GRE = 44 +/- 24%), and popliteal (PD-SE = 24 +/- 7%, T2* GRE = 70 +/- 11%) lymph nodes and only a moderate reduction in the mandib ular (PD-SE = 4 +/- 7%, T2 GRE = 42 +/- 15%), axillary (PD-SE = 0 +/- 4%, T2 GRE = 8 +/- 7%), and inguinal (PD-SE = 5 +/- 5%, T2* GRE = 34 +/- 18%) lymph nodes. The least pronounced signal loss occurred in th e peripheral lymph nodes of group 2, ranging from 0 +/- 3% for PD-SE s equences and 10 +/- 11% for T2 GRE sequences to 13 +/- 15% for PD-SE sequences and 41 +/- 19% for T2 GRE sequences. In group 3, the uptake of contrast material in the peripheral lymph nodes of the hypertherma l side was significantly more pronounced than on the contralateral sid e (p < .01), and the contrast agent was distributed more evenly to the different lymph node groups than in group 1. Conclusion. Muscular act ivity and regional hyperthermia markedly influence the accumulation of SPIO particles in different lymph node groups in rats. These findings must be considered in preclinical studies and in tile clinical admini stration of MR lymphography.