Effects of superparamagnetic iron oxide on radiofrequency-induced temperature distribution: In vitro measurements in polyacrylamide phantoms and in vivo results in a rabbit liver model

PURPOSE: To determine whether contrast medium containing superparamagnetic iron oxide (SPIO) alters radio-frequency (RF)-related temperature distribut ion in acrylamide phantoms and in an in vivo model. MATERIALS AND METHODS: In nine acrylamide phantoms with increasing SPIO con tent, RF was applied with simultaneous measurement of temperature profile a long the probe track. Additionally, magnetic resonance imaging-guided RF ab lation was performed in the liver of six rabbits after the intravenous admi nistration of SPIO (0.05 mL per kilogram of body weight) 40 minutes prior t o ablation (SPIO group) and in another six rabbits without prior SPIO admin istration (control group). Coagulation diameter was evaluated on the basis of postprocedural imaging and subsequent gross pathologic findings. Statist ical analysis was performed with the Student t test. RESULTS: In the phantoms, progressive increases in iron content resulted in higher temperatures along the RF electrode track (P < .05). In the in vivo model, however, SPIO at physiologic concentrations did not significantly i ncrease the diameter of coagulation on the basis of either postprocedural i maging or subsequent gross pathologic findings. Additionally, no significan t differences were seen in other RF-related parameters including impedance, voltage, current, and grounding pad temperature. CONCLUSION: Administration of SPIO in conjunction with RF ablation of focal liver lesions is feasible and safe, but no significant difference in the e xtent of induced coagulation can be expected.