Effects of superparamagnetic iron oxide on radio-frequency-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 distribution in acrylamide phantoms and in an in vivo model. MATERIALS AND METHODS: In nine acrylamide phantoms with increasing SPIO content, RF was applied with simultaneous measurement of temperature profile along the probe track. Additionally, magnetic resonance imaging-guided RF ablation was performed in the liver of six rabbits after the intravenous administration of SPIO (0.05 mL per kilogram of body weight) 40 minutes prior to ablation (SPIO group) and in another six rabbits without prior SPIO administration (control group). Coagulation diameter was evaluated on the basis of postprocedural imaging and subsequent gross pathologic findings. Statistical 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 increase the diameter of coagulation on the basis of either postprocedural imaging or subsequent gross pathologic findings. Additionally, no significant 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 extent of induced coagulation can be expected.