Feasibility of fast MR-thermometry during cardiac radiofrequency ablation

Online MR temperature monitoring during radiofrequency (RF) ablation of cardiac arrhythmias may improve the efficacy and safety of the treatment. MR thermometry at 1.5 T using the proton resonance frequency (PRF) method was assessed in 10 healthy volunteers under normal breathing conditions, using a multi-slice, ECG-gated, echo planar imaging (EPI) sequence in combination with slice tracking. Temperature images were post-processed to remove residual motion-related artifacts. Using an MR-compatible steerable catheter and electromagnetic noise filter, RF ablation was performed in the ventricles of two sheep in vivo. The standard deviation of the temperature evolution in time (TSD) was computed. Temperature mapping of the left ventricle was achieved at an update rate of approximately 1 Hz with a mean TSD of 3.6 ± 0.9 °C. TSD measurements at the septum showed a higher precision (2.8 ± 0.9 °C) than at the myocardial regions at the heart-lung and heart-liver interfaces (4.1 ± 0.9 °C). Temperature rose maximally by 9 °C and 16 °C during 5 W and 10 W RF applications, respectively, for 60 s each. Tissue temperature can be monitored at an update rate of approximately 1 Hz in five slices. Typical temperature changes observed during clinical RF application can be monitored with an acceptable level of precision.