Threshold-based prediction of the coagulation zone in sequential temperature mapping in MR-guided radiofrequency ablation of liver tumours.

OBJECTIVE

To evaluate different cut-off temperature levels for a threshold-based prediction of the coagulation zone in magnetic resonance (MR)-guided radiofrequency (RF) ablation of liver tumours.

METHODS

Temperature-sensitive measurements were acquired during RF ablation of 24 patients with primary (6) and secondary liver lesions (18) using a wide-bore 1.5 T MR sytem and compared with the post-interventional coagulation zone. Temperature measurements using the proton resonance frequency shift method were performed directly subsequent to energy application. The temperature maps were registered on the contrast-enhanced follow-up MR images acquired 4 weeks after treatment. Areas with temperatures above 50°, 55° and 60°C were segmented and compared with the coagulation zones. Sensitivity and positive predictive value were calculated.

RESULTS

No major complications occurred and all tumours were completely treated. No tumour recurrence was observed at the follow-up examination after 4 weeks. Two patients with secondary liver lesions showed local tumour recurrence after 4 and 7 months. The 60°C threshold level achieved the highest positive predictive value (87.7 ± 9.9) and the best prediction of the coagulation zone.

CONCLUSIONS

For a threshold-based prediction of the coagulation zone, the 60°C cut-off level achieved the best prediction of the coagulation zone among the tested levels.

KEY POINTS: • Temperature monitoring can be used to survey MR-guided radiofrequency ablation • The developing ablation zone can be estimated based on post-interventional temperature measurements • A 60°C threshold level can be used to predict the ablation zone • The 50°C and 55°C temperature zones tend to overestimate the ablation zone.