Prediction of cell necrosis with sequential temperature mapping after radiofrequency ablation

Abstract

Purpose: To assess the feasibility of magnetic resonance (MR) thermometry after thermoablative therapy and to quantitatively evaluate the ability of two sequence types to predict cell necrosis. Methods: Twenty patients with hepatic tumors were treated by MR-guided radiofrequency ablation. For each 10 patients, postinterventionally performed gradient echo and segmented echo planar imaging sequences were used to calculate temperature maps based on the proton resonance frequency shift method. Contrast-enhanced images acquired 1 month after therapy were registered on the temperature maps and the necrotic, nonenhanced area was segmented and compared to the area with a displayed temperature above 60° C. Sensitivity and positive predictive value of the temperature map was calculated, using the follow-up imaging as the gold standard. Results: Temperature mapping reached acceptable image quality in 45/47 cases. Sensitivity, ie, the rate of correctly detected coagulated tissue was 0.82 ± 0.08 for the gradient echo imaging (GRE) sequence and 0.81 ± 0.14 for the echo planar imaging (EPI) sequence. Positive predictive value, ie, the rate of voxel in the temperature map over 60° C that actually developed necrosis, was 0.90 ± 0.07 for the GRE sequence and 0.84 ± 0.11 for the EPI sequence. Conclusion: Sequential MR temperature mapping allows for the prediction of the coagulation zone with an acceptable sensitivity and positive predictive value using EPI and GRE sequences. © 2009 Wiley-Liss, Inc.