Feasibility of fast MR‐thermometry during cardiac radiofrequency ablation

Abstract

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.

Magnetic resonance thermometry: Methodology, pitfalls and practical solutions

“…within the tumor. Typically microwave or RF antennas, US transducers or laser fibers are utilized (91,92). While laser fibers are relatively artefact free, RF ablative devices disturb the static magnetic field B0 and cause susceptibility artefacts along with transmission and reception field perturbations making accurate thermal dose assessment in close vicinity to the device elusive.…”

Adaptive rejection of outliers for robust motion compensation in cardiac MR-thermometry

“…The heart motion magnitude is up to 16 pixels for the more extreme case of our MRI sequences set. Moreover, the blood signal has been cancelled using saturation bands [2] parallel to the imaging plane. As a consequence, the potential signal flickering introduced by the blood circulation in the left ventricular does not disturb the algorithm, although some residual partial blood intensities were detected in other cavities.…”

“…Rapid MR imaging sequences exploiting fast acquisition methods (Echo Planar Imaging combined with parallel acquisition methods) and motion compensation algorithms can be combined to provide realtime (several slices/cardiac cycle) monitoring of temperature distribution in cardiac muscle during heat deposition [2]. Temperature evolution in each pixel, calculated from the temporal changes in the phase of the MR images, provides access to the accumulated thermal dose that accounts for the effectiveness of the ablation.…”

“…Optical flow methods have already been proposed for robust compensation of motion observed in MR images [2][3][4], based on the optical flow equation (OFE in Eq. 1):…”

Real-time atrial wall imaging during radiofrequency ablation in a porcine model

“…Several attempts have been made to provide additional information on functional and morphological RF-induced changes [11][12][13][14][15][16] . Photoacoustic imaging has been used in vitro with encouraging results 13 .…”