Fundamental Evaluation of Thermophysical Properties of Lipiodol Associated with Cryoablation: Freezing Experiments Using Lipiodol Phantom

Purpose To elucidate the basic thermophysical properties at low temperatures of lipiodol, which is used as a marker by transarterial injection before CT-guided cryoablation for solid tumors, by fundamental experiments with pure lipiodol phantom. Materials and Methods The freezing point of lipiodol was measured using differential scanning calorimeter (DSC) by detecting differences in the heating rate during heating from − 30 °C. Freezing experiments were conducted using pure lipiodol and a tissue phantom, which were prepared in an acrylic container at 37 °C. The growth of the frozen region was observed for 10 min. Temperatures were monitored at the cryoprobe surface and designated positions around the cryoprobe. Results The DSC experiment showed that freezing was observed between − 5 and − 30 °C, which indicated that the freezing point was approximately − 5 °C. Freezing experiments revealed that the diameter of frozen region in the lipiodol was smaller than that in the tissue phantom (5 mm vs 24 mm) after 10-min freezing. The temperature at the probe surface was − 130 °C in lipiodol, which was 25 °C lower than that in the tissue phantom. There was a larger temperature gradient near the cryoprobe in lipiodol due to lower thermal conductivity. Conclusions The present results suggest that an extremely high concentration of lipiodol (close to pure lipiodol) potentially reduces frozen region because of its lower freezing point and smaller thermal conductivity. However, since lipiodol concentrations in clinical cases differ from the current model, further studies using models that are close to clinical conditions are required. Level of Evidence No level of evidence, laboratory investigation.